WO2020048852A1

WO2020048852A1 - Process for the preparation of alpha, beta unsaturated aldehydes by oxidation of alcohols in the presence of a liquid phase

Info

Publication number: WO2020048852A1
Application number: PCT/EP2019/073033
Authority: WO
Inventors: Michaela FENYN; Joseph John ZAKZESKI; Nicolas VAUTRAVERS; Joaquim Henrique Teles
Original assignee: Basf Se
Priority date: 2018-09-07
Filing date: 2019-08-29
Publication date: 2020-03-12

Abstract

Process for the preparation of alpha, beta unsaturated aldehydes by oxidation of alcohols in the presence of a liquid phase

Description

The present invention relates to a process for preparing alpha, beta unsaturated aldehydes, such as in particular, prenal (3-methyl-2-butenal) by oxidation of alcohols in the presence of a liquid phase. More specifically, the invention relates to a process for preparing alpha, beta unsaturated aldehydes, such as, in particular prenal (3-methyl-2-butenal) by oxidation of alcohols in the pres- ence of a liquid phase and a catalyst, wherein the liquid phase contains at least 25 weight-% water based on the total weight of the liquid phase and the oxidant is oxygen and/or hydrogen peroxide, and wherein the catalyst comprises at least one intermetallic compound.

Technical Background:

Prenal is an important chemical intermediate especially for the preparation of terpene-based fra- grances, such as citral, and for the preparation of vitamins, such as vitamin E, and therefore is of great technical and economic importance.

The most common procedures for preparing prenal use prenol (3-methyl-2-buten-1 -ol) or iso- prenol (3-methyl-3-buten-1 -ol) as starting compounds. Thus, EP 0 881 206 describes the oxida- tion of these starting compounds with oxygen in the gas phase using a silver catalyst. The selec- tivity of this approach could be improved by further developing the catalytic system, as disclosed e.g. in WO 2008/037693. However, in order to obtain sufficient conversion rates and selectivity it is necessary to carry out the gas phase procedure at temperatures of about 360°C while main- taining short contact times. This is required, on the one hand, to ensure adequate reactivity and, on the other hand, to prevent decomposition reactions of the sensitive reactants and products. These conditions can only be accomplished by using expensive equipment.

Processes for preparing alpha, beta unsaturated aldehydes by oxidation in the liquid phase using organic solvents are disclosed in Tetrahedron, Vol 9 (1960), 67-75, Adv. Synth. Catal. 345 (2003), 517-523 as well as in Green Chemistry, 2 (2000), 279-282.

Chem. Commun. (2008), 3181 -3183, describes the oxidation of benzylalcohol and cinnamylalco- hol with oxygen in water. Catalysis Today 121 (2007), 13-21 describes the oxidation of substituted benzyl alcohols with oxygen. Chem. Commun. (2007), 4375-4377 discloses the oxidation of cin- namyl alcohol to cinnamic acid as well as the oxidation of benzyl alcohol to benzoic acid in the presence of water and oxygen. Catalysis Today 57 (2000) 127-141 describes the oxidation of 5- hydroxymethylfurfural as well as the oxidation of cinnamyl alcohol. JP 2010-202555A describes the oxidation of 3 groups of alcohols to the corresponding aldehydes in a liquid phase with oxygen as oxidant. None of these references discloses a process for the preparation of the alpha, beta unsaturated aldehydes according to the present invention.

WO 99/18058 discloses a process for the aerobic oxidation of primary alcohols, such as hexanol in the absence of solvents. Chem. Commun. (2007) 4399-4400 describes the formation of alpha, beta unsaturated aldehydes in high yields with aqueous hydrogen peroxide as the oxidant in the presence of Pt black catalyst under organic solvent free conditions. Table 1 discloses this reaction for a list of alcohols: Entry 7 discloses the oxidation of 3-methyl-2-butenol to 3-methyl-2-butenal with 5% hydrogen peroxide as oxidant and Pt black as catalyst. 3-methyl-2-butenal is obtained with a yield of 91 %. Entry 4 discloses this reaction for cinnamyl alcohol. On page 4399, left column this document expressly states the necessity of using hydrogen peroxide as oxidant:“Without the use of H2O2 (under an air atmosphere), cinnamaldeyde was obtained in only < 10% yield.” In footnote 12, this reference summarizes previous work:“Although the oxidation of cinnamyl alcohol to cinnamaldehyde with O2 (or air) has been reported, organic solvents and/or base are necessary to achieve high yield and selectivity.”

Chem. Commun. (2007) 4399-4400 is considered the closest prior art, as it discloses a process for the preparation of prenal from prenol by oxidation with aqueous hydrogen peroxide as oxidant in an aqueous liquid phase in the presence of a catalyst with a yield of 91 %.

It was an objective of the invention to provide a simple and efficient process for preparing alpha, beta unsaturated aldehydes of formula (I), in particular prenal, which is suitable for industrial scale preparations. The process should be easy to handle, asure high yields and high selectivity of the aldehyde to be prepared, thus avoiding over-oxidation to the corresponding acid. Moreover, the use of toxic or expensive reagents should be avoided. Moreover, the process should allow high space-time-yields (STY), which are of major importance for the economic suitability in industrial scale processes. The space-time-yield (STY) is defined as the amount of product obtained per reaction volume per hour of reaction, expressed as g/l/h. The reaction volume is the volume of the reactor in which the reaction takes place. In case the reaction is conducted in a cylindrical reactor, the reaction volume is the volume of the cylindrical reactor in which the reaction takes place. Of special interest are processes which allow high space-time-yields in a reaction time, in which at least 40%, preferably at least 50% conversion is achieved. Furthermore, it was desired to provide a process which enables easy recovery of the aldehyde.

Moreover, the process should allow a high specific activity (SA), which is of major importance for the economic suitability in industrial scale processes. The specific activity (SA) is defined as the amount of product obtained per amount of catalytically active metal per hour of reaction, ex- pressed as g/g/h. Of special interest are processes which allow high specific activities in a reaction time, in which at least 40%, preferably at least 50% conversion is achieved.

Summary of the Invention:

It has now been found that this objective is achieved by an oxidation in the presence of a catalyst and in the presence of a liquid phase, wherein the liquid phase contains at least 25 weight-% of water based on the total weight of the liquid phase, determined at 20 °C and 1 bar, and wherein oxygen and/or hydrogen peroxide is used as the oxidant, and wherein the catalyst comprises at least one intermetallic compound. It has surprisingly been found that the alpha, beta unsaturated aldehydes of formula (I) can be obtained with excellent yield and selectivity with the process according to the invention. The process according to the invention is further associated with a series of advantages. The pro- cess according to the invention enables the preparation of alpha, beta unsaturated aldehydes of formula (I) with high yield under mild conditions, both of temperature and pressure, while requir- ing only moderate to low amounts of catalyst. The process can be conducted with no or low amounts of organic solvent, thus avoiding or minimizing environmentally problematic waste streams. The process also allows a simple isolation of the desired aldehyde. With the process according to the invention specific activities can be achieved, which are higher than the specific activities that are possible with processes according to the prior art.

Therefore, the present invention relates to a process for the preparation of alpha, beta unsatu- rated aldehydes of general formula (I)

wherein Ri, R₂ and R₃, independently of one another, are selected from hydrogen; Ci-C₆-alkyl, which optionally carry 1 , 2, 3, or 4 identical or different substitu- ents which are selected from N0₂, CN, halogen, C₁-C₆ alkoxy, (Ci-C₆-alkoxy)carbonyl, C₁-C₆ acyl, C₁-C₆ acyloxy and aryl; and C₂-C₆-alkenyl, which optionally carry 1 , 2, 3, or 4 identical or different substituents which are selected from N0₂, CN, halogen, C₁-C₆ alkoxy, (Ci-C₆-alkoxy)carbonyl, C₁-C₆ acyl, C₁-C₆ acyloxy and aryl; by oxidation of alcohols of general formula (II)

wherein R₁, R₂ and R₃ have the meaning as given above

in the presence of a catalyst and in the presence of a liquid phase,

• wherein the liquid phase contains at least 25 weight-% water based on the total weight of the liquid phase, determined at a temperature of 20 °C and a pressure of 1 bar and

• wherein the oxidant is oxygen and/or hydrogen peroxide, and

• wherein the catalyst comprises at least one intermetallic compound. General definitions:

In the context of the present invention, the terms used generically are, unless otherwise stated, defined as follows:

The prefix C_x-C_y denotes the number of possible carbon atoms in the particular case.

Alkyl and also all alkyl moieties in radicals derived therefrom, such as e.g. alkoxy, acyl, acyloxy, refers to saturated, straight-chain or branched hydrocarbon radicals having x to y carbon atoms, as denoted in C_x-C_y.

Thus, the term Ci-C₄-alkyl denotes a linear or branched alkyl radical comprising from 1 to 4 carbon atoms, such as methyl, ethyl, propyl, 1 -methylethyl (isopropyl), butyl, 1 -methylpropyl (sec-butyl),

2-methylpropyl (isobutyl) or 1 , 1 -dimethylethyl (tert-butyl).

The term Ci-C₆-alkyl denotes a linear or branched alkyl radical comprising 1 to 6 carbon atoms, such as methyl, ethyl, propyl, 1 -methylethyl, butyl, 1 -methylpropyl, 2-methylpropyl, 1 ,1 -di- methylethyl, pentyl, 1 -methylbutyl, 2-methylbutyl, 3-methylbutyl, 2,2-dimethylpropyl, 1 -ethylpro- pyl, hexyl, 1 ,1 -dimethylpropyl, 1 ,2-dimethylpropyl, 1 -methylpentyl, 2-methylpentyl, 3-methylpen- tyl, 4-methylpentyl, 1 ,1 -dimethylbutyl, 1 ,2-dimethylbutyl, 1 ,3-dimethylbutyl, 2,2-dimethylbutyl, 2,3- dimethylbutyl, 3,3-dimethylbutyl, 1 -ethylbutyl, 2-ethylbutyl, 1 ,1 ,2-trimethylpropyl, 1 ,2,2-trime- thylpropyl, 1 -ethyl-1 -methylpropyl and 1 -ethyl-2-methylpropyl.

The term alkenyl denotes mono- or poly-, in particular monounsaturated, straight-chain or branched hydrocarbon radicals having x to y carbon atoms, as denoted in C_x-C_y and a double bond in any desired position, e.g. Ci-C₆-alkenyl, preferably C2-C6-alkenyl such as ethenyl, 1 -pro- penyl, 2-propenyl, 1 -methylethenyl, 1 -butenyl, 2-butenyl, 3-butenyl, 1 -methyl-1 -propenyl, 2-me- thyl-1 -propenyl, 1 -methyl-2-propenyl, 2-methyl-2-propenyl, 1 -pentenyl, 2-pentenyl, 3-pentenyl, 4- pentenyl, 1 -methyl-1 -butenyl, 2-methyl-1 -butenyl, 3-methyl-1 -butenyl, 1 -methyl-2-butenyl, 2-me- thyl-2-butenyl, 3-methyl-2-butenyl, 1 -methyl-3-butenyl, 2-methyl-3-butenyl, 3-methyl-3-butenyl, 1 ,1 -dimethyl-2-propenyl, 1 ,2-dimethyl-1 -propenyl, 1 ,2-dimethyl-2-propenyl, 1 -ethyl-1 -propenyl, 1 - ethyl-2-propenyl, 1 -hexenyl, 2-hexenyl, 3-hexenyl, 4-hexenyl, 5-hexenyl, 1 -methyl-1 -pentenyl, 2- methyl-1 -pentenyl, 3-methyl-1 -pentenyl, 4-methyl-1 -pentenyl, 1 -methyl-2-pentenyl, 2-methyl-2- pentenyl, 3-methyl-2-pentenyl, 4-methyl-2-pentenyl, 1 -methyl-3-pentenyl, 2-methyl-3-pentenyl,

3-methyl-3-pentenyl, 4-methyl-3-pentenyl, 1 -methyl-4-pentenyl, 2-methyl-4-pentenyl, 3-methyl-4- pentenyl, 4-methyl-4-pentenyl, 1 ,1 -dimethyl-2-butenyl, 1 ,1 -dimethyl-3-butenyl, 1 ,2-dimethyl-1 -bu- tenyl, 1 ,2-dimethyl-2-butenyl, 1 ,2-dimethyl-3-butenyl, 1 ,3-dimethyl-1 -butenyl, 1 ,3-dimethyl-2-bu- tenyl, 1 ,3-dimethyl-3-butenyl, 2,2-dimethyl-3-butenyl, 2, 3-dimethyl-1 -butenyl, 2,3-dimethyl-2-bu- tenyl, 2,3-dimethyl-3-butenyl, 3, 3-dimethyl-1 -butenyl, 3,3-dimethyl-2-butenyl, 1 -ethyl-1 -butenyl, 1 -ethyl-2-butenyl, 1 -ethyl-3-butenyl, 2-ethyl-1 -butenyl, 2-ethyl-2-butenyl, 2-ethyl-3-butenyl, 1 ,1 ,2- trimethyl-2-propenyl, 1 -ethyl-1 -methyl-2-propenyl, 1 -ethyl-2-methyl-1 -propenyl and 1 -ethyl-2-me- thyl-2-propenyl;

The term substituents denotes radicals selected from the group consisting of NO₂, CN, halogen, C1-C6 alkoxy, (Ci-C₆-alkoxy)carbonyl, C1-C6 acyl, C1-C6 acyloxy and aryl.

The term halogen denotes in each case fluorine, bromine, chlorine or iodine, especially fluorine, chlorine or bromine.

The term alkoxy denotes straight-chain or branched saturated alkyl radicals comprising from 1 to 6 (Ci-C₆-alkoxy) or 1 to 4 (Ci-C₄-alkoxy) carbon atoms, which are bound via an oxygen atom to the remainder of the molecule, such as methoxy, ethoxy, n-propoxy, 1 -methylethoxy (isopropoxy), n-butyloxy, 1 -methylpropoxy (sec-butyloxy), 2-methylpropoxy (isobutyloxy) and 1 ,1 -dimethyleth- oxy (tert-butyloxy).

The term (Ci-C₆-alkoxy)carbonyl denotes alkoxy radicals having from 1 to 6 carbon atoms which are bound via a carbonyl group to the remainder of the molecule. Examples thereof are methox- ycarbonyl, ethoxycarbonyl, propoxycarbonyl, isopropoxycarbonyl, n-butoxycarbonyl, sec- butoxycarbonyl, isobutoxycarbonyl and tert-butoxycarbonyl, n-pentyloxycarbonyl and n-hex- yloxycarbonyl.

The term C1-C6 acyl denotes straight-chain or branched saturated alkyl radicals comprising from 1 to 6 carbon atoms, which are bound via a carbonyl group to the remainder of the molecule. Examples thereof are formyl, acetyl, propionyl, 2-methylpropionyl, 3-methylbutanoyl, butanoyl, pentanoyl, hexanoyl.

The term C1-C6 acyloxy denotes C1-C6 acyl radicals, which are bound via an oxygen atom to the remainder of the molecule. Examples thereof are acetoxy, propionyloxy, butanoyloxy, penta- noyloxy, hexanoyloxy.

The term aryl denotes carbocyclic aromatic radicals having from 6 to 14 carbon atoms. Examples thereof comprise phenyl, naphthyl, fluorenyl, azulenyl, anthracenyl and phenanthrenyl. Aryl is preferably phenyl or naphthyl, and especially phenyl.

Selectivity is defined as the number of moles of the alpha, beta unsaturated aldehyde of the gen- eral formula (I) formed divided by the number of moles of the alcohol of the general formula (II) that were consumed. The amounts of alpha, beta unsaturated aldehyde of the general formula (I) formed and of alcohol of the general formula (II) consumed can easily be determined by a GC analysis as defined in the experimental section.

The terms“conducted” and“performed” are used synonymously. Preferred embodiment of the invention

The remarks made below regarding preferred embodiments of the reactant(s) and product(s) and the process according to the invention, especially regarding preferred meanings of the variables of the different reactant(s) and product(s) and of the reaction conditions of the process, apply either taken alone or, more particularly, in any conceivable combination with one another.

Alcohol(s) of general formula (II)

Reactant(s) of the process of the invention are alcohol(s) of general formula (II)

wherein Ri, R₂ and R₃, independently of one another, are selected from

• hydrogen;

• Ci-C₆-alkyl, which optionally carry 1 , 2, 3, or 4 identical or different substituents which are selected from NO₂, CN, halogen, C₁-C₆ alkoxy, (Ci-C₆-alkoxy)carbonyl, C₁-C₆ acyl, C₁-C₆ acyloxy and aryl; and

• C₂-C₆-alkenyl, which optionally carry 1 , 2, 3, or 4 identical or different substituents which are selected from NO₂, CN, halogen, C₁-C₆ alkoxy, (Ci-C₆-alkoxy)carbonyl, C₁-C₆ acyl, C₁- C₆ acyloxy and aryl;

The terms“reactant(s)” and“alcohol(s) of general formula (II)” are used synonymously. The term alcohol(s) encompasses one alcohol as well as a mixture of more than one alcohol according to formula (II).

In one embodiment of the invention alcohol(s) of general formula (II) are used, wherein R₃ is H.

In one embodiment of the invention alcohol(s) of general formula (II) are used, wherein Ri, R₂ and R₃, independently of one another, are selected from the group consisting of H, Ci-C₆-alkyl and C₂-C₆-alkenyl.

In one embodiment of the invention alcohol(s) of general formula (II) are used, wherein Ri, R₂ and R₃, independently of one another, are selected from the group consisting of H, Ci-C₆-alkyl and C₂-C₄-alkenyl.

In one embodiment of the invention alcohol(s) of general formula (II) are used, wherein Ri, R₂ and R₃, independently of one another, are selected from the group consisting of H, Ci-C₄-alkyl and C₂-C₆-alkenyl. In one embodiment of the invention alcohol(s) of general formula (II) are used, wherein Ri, R₂ and R3, independently of one another, are selected from the group consisting of H, Ci-C4-alkyl and C2-C₄-alkenyl.

In one embodiment of the invention alcohol(s) of general formula (II) are used, wherein R₁, R₂ and R₃, independently of one another, are selected from the group consisting of H, CH₃ and C₂H₅.

In one embodiment of the invention alcohol(s) of general formula (II) are used, wherein R₁, R₂ and R₃, independently of one another, are selected from the group consisting of H and CH₃.

In one embodiment of the invention an alcohol of the general formula (II) is used, wherein R1 is H and R₂ and R3 are CH3.

In one embodiment of the invention an alcohol of the general formula (II) is used, wherein R3 is H and R1 and R₂ are CH₃ (= 3-Methyl-2-buten-1 -ol, prenol).

In one embodiment of the invention an alcohol of the general formula (II) is used, wherein R1 is CH₃, R₃ is H and R₂ is C₆-Alkenyl, preferably 1 -methyl-1 -pentenyl, 2-methyl-1 -pentenyl, 3-methyl- 1 -pentenyl, 4-methyl-1 -pentenyl, 1 -methyl-2-pentenyl, 2-methyl-2-pentenyl, 3-methyl-2-pentenyl, 4-methyl-2-pentenyl, 1 -methyl-3-pentenyl, 2-methyl-3-pentenyl, 3-methyl-3-pentenyl, 4-methyl-3- pentenyl, 1 -methyl-4-pentenyl, 2-methyl-4-pentenyl, 3-methyl-4-pentenyl, 4-methyl-4-pentenyl,

1 .1 -dimethyl-2-butenyl, 1 ,1 -dimethyl-3-butenyl, 1 ,2-dimethyl-1 -butenyl, 1 ,2-dimethyl-2-butenyl,

1 .2-dimethyl-3-butenyl, 1 ,3-dimethyl-1 -butenyl, 1 ,3-dimethyl-2-butenyl, 1 ,3-dimethyl-3-butenyl,

2.2-dimethyl-3-butenyl, 2,3-dimethyl-1 -butenyl, 2,3-dimethyl-2-butenyl, 2,3-dimethyl-3-butenyl,

3.3-dimethyl-1 -butenyl, 3,3-dimethyl-2-butenyl, 1 -ethyl-1 -butenyl, 1 -ethyl-2-butenyl, 1 -ethyl-3-bu- tenyl, 2-ethyl-1 -butenyl, 2-ethyl-2-butenyl, 2-ethyl-3-butenyl, 1 ,1 ,2-trimethyl-2-propenyl, 1 -ethyl- 1 -methyl-2-propenyl, 1 -ethyl-2-methyl-1 -propenyl and 1 -ethyl-2-methyl-2-propenyl; Each double bond in the alkenyl moiety can independently of each other be present in the E- as or the Z- configuration.

In one embodiment of the invention an alcohol of the general formula (II) is used, wherein R₂ is CH₃, R₃ is H and R₁ is C₆-Alkenyl, preferably 1 -methyl-1 -pentenyl, 2-methyl-1 -pentenyl, 3-methyl- 1 -pentenyl, 4-methyl-1 -pentenyl, 1 -methyl-2-pentenyl, 2-methyl-2-pentenyl, 3-methyl-2-pentenyl, 4-methyl-2-pentenyl, 1 -methyl-3-pentenyl, 2-methyl-3-pentenyl, 3-methyl-3-pentenyl, 4-methyl-3- pentenyl, 1 -methyl-4-pentenyl, 2-methyl-4-pentenyl, 3-methyl-4-pentenyl, 4-methyl-4-pentenyl,

3.3-dimethyl-1 -butenyl, 3,3-dimethyl-2-butenyl, 1 -ethyl-1 -butenyl, 1 -ethyl-2-butenyl, 1 -ethyl-3-bu- tenyl, 2-ethyl-1 -butenyl, 2-ethyl-2-butenyl, 2-ethyl-3-butenyl, 1 ,1 ,2-trimethyl-2-propenyl, 1 -ethyl- 1 -methyl-2-propenyl, 1 -ethyl-2-methyl-1 -propenyl and 1 -ethyl-2-methyl-2-propenyl; Each double bond in the alkenyl moiety can independently of each other be present in the E- as or the Z- configuration. In one embodiment of the invention the alcohol of the general formula (II) is selected from the group consisting of (2E)-3,7-dimethylocta-2,6-dien-1 -ol, (2Z)-3,7-dimethylocta-2,6-dien-1 -ol, 3- methylbut-2-en-1 -ol, (E)-2-methylbut-2-en-1 -ol and (Z)-2-methylbut-2-en-1 -ol.

In one embodiment of the invention the alcohol of the general formula (II) is 3-methylbut-2-en-1 - ol. In case the alcohol of general formula (II) is 3-methylbut-2-en-1 -ol, the invention also encom- passes the embodiment that 2-methyl-3-buten-2-ol (dimethylvinylcarbinol, DMVC) is added to the reaction and subsequently isomerized to 3-methylbut-2-en-1 -ol.

In one embodiment of the invention the alcohol of the general formula (II) is a mixture of (2E)-3,7- dimethylocta-2,6-dien-1 -ol and (2Z)-3,7-dimethylocta-2,6-dien-1 -ol.

Alpha, beta unsaturated aldehvde(s) of general formula (I)

Product(s) of the process of the invention are alpha, beta unsaturated aldehyde(s) of general formula (I)

wherein Ri, R₂ and R3, independently of one another, are selected from hydrogen; Ci-C₆-alkyl, which optionally carry 1 , 2, 3, or 4 identical or different substituents which are selected from NO2, CN, halogen, C1-C6 alkoxy, (Ci-C₆-alkoxy)carbonyl, C1-C6 acyl, C1-C6 acyloxy and aryl; and C2-C6-alkenyl, which optionally carry 1 , 2, 3, or 4 identical or different sub- stituents which are selected from NO2, CN, halogen, C1-C6 alkoxy, (Ci-C₆-alkoxy)carbonyl, C1-C6 acyl, C1-C6 acyloxy and aryl.

The terms“product(s)” and“alpha, beta unsaturated aldehyde(s) of general formula (I)” are used synonymously. The term“aldehyde(s)” encompasses one aldehyde as well as a mixture of more than one aldehyde according to formula (I).

Liquid Phase

It has surprisingly been found that the process according to the invention can be performed in the presence of a liquid phase, wherein the liquid phase contains at least 25 weight-% water based on the total weight of the liquid phase, determined at a temperature of 20 °C and a pressure of 1 bar.

The process according to the invention is conducted in the presence of a liquid phase. The liquid phase consists of all components of the reaction which are liquid at 20 °C and a pressure of 1 bar. All weight-% of the liquid phase referred to in the process according to the invention are based on the total weight of the liquid phase, determined at a temperature of 20 °C and a pressure of 1 bar.

The process according to the invention is conducted at the interphase between liquid phase and the solid catalyst (heterogeneous catalyzed process).

The solid catalyst is not liquid at a temperature of 20°C and a pressure of 1 bar and is therefore by definition not included in the weight-% of the liquid phase.

The liquid phase can consist of one or more, e.g. two or three distinct liquid phases. The number of liquid phases can be chosen by a man skilled in the art, dependent for example on the choice and concentration of the alcohol(s) of general formula (II) or on optional solvent(s).

The process according to the invention can be conducted in the presence of a liquid phase, which consists of one liquid phase (mono-phase system). The process according to the invention can be conducted in the presence of a liquid phase, which consists of more than one, e.g. two, three or more distinct liquid phases (multi-phase system).

In case the process according to the invention is conducted in the presence of a liquid phase which consists of one liquid phase, the liquid phase contains at least 25 weight-% water, deter- mined at a temperature of 20 °C and a pressure of 1 bar.

In case the process according to the invention is conducted in the presence of a liquid phase which consists of more than one liquid phase, at least one distinct liquid phase contains at least 25 weight-% water, determined at a temperature of 20 °C and a pressure of 1 bar.

In one embodiment of the invention the process according to the invention can be performed in the presence of a liquid phase, which consists of two or three distinct liquid phases, wherein each distinct liquid phase contains at least 25 weight-% of water based on the total weight of this distinct liquid phase, determined at a temperature of 20 °C and a pressure of 1 bar.

The water content of a liquid phase can for example be adjusted by adding water (e.g. if a liquid phase is an aqueous phase) or by adding water and/or solvents and/or solubilizers (e.g. if a liquid phase is a non-aqueous phase, e.g. comprising reactant(s) and/or product(s) not dissolved in the aqueous phase).

The following preferred ranges for the water content of a liquid phase apply for the at least one or each distinct liquid phase accordingly.

In a preferred embodiment of the invention the process is performed in a liquid phase, which contains at least 30 weight-%, preferably at least 40 weight-%, more preferably at least 50 weight- % of water. In a further embodiment the process can be performed in a liquid phase, which con- tains at least 60 weight-%, preferably at least 70 weight-%, more preferably at least 80 weight-%, more preferably at least 90 weight-%, more preferably at least 95 weight-% of water. According to one embodiment of the invention, the process can be performed in a liquid phase which con- tains 99,5 weight-% of water. All weight-% of water are based on the total weight of the liquid phase (or the at least one or each distinct liquid phase in case more than one liquid phase is present).

In one embodiment of the invention each distinct liquid phase contains at least 25 weight-% of water based on the total weight of this distinct liquid phase. The weight-% of water are determined at a temperature of 20 °C and a pressure of 1 bar.

Solvent(s)

The process according to the invention can be carried out in the presence of a liquid phase which essentially consist of reactant(s), product(s), water and oxidant.

The process according to the invention can be carried out as a heterogeneous catalyzed process in the presence of a liquid phase which essentially consist of reactant(s), product(s), water and oxidant(s).

In these embodiments, the liquid phase contains no solvent.

The term“solvent” encompasses any component other than reactant(s), product(s), water and possibly oxidant(s) or possibly catalyst(s) which is liquid at a temperature of 20 °C and a pressure of 1 bar and which is thus part of the liquid phase.

It is therefore one of the advantages of the present invention, that the process can be performed in the presence of a liquid phase, which comprises less than 75 weight-%, preferably less than 70 weight-% solvent based on the total weight of the liquid phase.

In case a solvent is employed, a suitable solvent can be selected depending on the reactant(s), product(s), catalyst(s), oxidant and reaction conditions. The term“solvent” encompasses one or more than one solvents.

The following preferred ranges for the solvent content of a liquid phase apply for the liquid phase (for mono-phase systems) or for the at least one distinct liquid phase (for multi-phase systems).

In a preferred embodiment of the invention the process is performed in a liquid phase, which contains less than 70 weight-%, preferably less than 60 weight-%, preferably less than 50 weight- %, preferably less than 40 weight-%, preferably less than 30 weight-%, more preferably less than 20 weight-%, more preferably less than 10 weight-% solvent based on the total weight of the liquid phase (for mono-phase systems) or the at least one distinct liquid phase (for multi-phase sys- tems). Advantageously the process according to the invention can be performed in the presence of a liquid phase, which contains less than 5 weight-% solvent based on the total weight of the liquid phase (for mono-phase systems) or the at least one distinct liquid phase (for multi-phase sys- tems). In one embodiment of the invention the process is performed in the presence of a liquid phase which contains less than 3 weight-%, preferably less than 1 weight-% of solvent. In one embodiment of the invention the process is performed in the presence of a liquid phase which contains no solvent.

In case a solvent is employed, suitable solvents are for example protic or aprotic solvents.

In case a solvent is employed, it has been found to be advantageous to use an aprotic organic solvent for the reaction of the alcohol(s) of general formula (II).

In case a solvent is employed, solvents are preferred that have a boiling point above 50°C, for instance in the range of 50 to 200°C, in particular above 65°C, for instance in the range of 65 to 180°C, and specifically above 80°C, for instance in the range of 80 to 160°C.

Useful aprotic organic solvents here include, for example, aliphatic hydrocarbons, such as hex- ane, heptane, octane, nonane, decane and also petroleum ether, aromatic hydrocarbons, such as benzene, toluene, the xylenes and mesitylene, aliphatic C3-Cs-ethers, such as 1 ,2-dimethoxy- ethane (DME), diethylene glycol dimethyl ether (diglyme), diethyl ether, dipropyl ether, methyl isobutyl ether, tert-butyl methyl ether and tert-butyl ethyl ether, dimethoxymethane, diethox- ymethane, dimethylene glycol dimethyl ether, dimethylene glycol diethyl ether, trimethylene glycol dimethyl ether, trimethylene glycol diethyl ether, tetramethylene glycol dimethyl ether, cycloali- phatic hydrocarbons, such as cyclohexane and cycloheptane, alicyclic C3-C6-ethers, such as tet- rahydrofuran (THF), tetrahydropyran, 2-methyltetrahydrofuran, 3-methyltetrahydrofuran, 1 ,3-di- oxolane, and 1 ,4-dioxane, 1 ,3,5-trioxane, short-chain ketones, such as acetone, ethyl methyl ketone and isobutyl methyl ketone, C3-C6-esters such as methyl acetate, ethyl acetate, methyl propionate, dimethyloxalate, methoxyacetic acid methyl ester, ethylene carbonate, propylene car- bonate, ethylene glycol diacetate and diethylene glycol diacetate, C3-C6-amides such as dime- thylformamide (DMF) and dimethylacetamide and N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), C3-C6-nitriles such as acetonitrile, propionitrile or mixtures of these solvents with one another.

According to an embodiment of the present invention those of the aforementioned aprotic sol- vents are preferred that have a boiling point above 50°C, for instance in the range of 50 to 200°C, in particular above 65°C, for instance in the range of 65 to 180°C, and specifically above 80°C, for instance in the range of 80 to 160°C.

More preferably the solvent, if employed, is selected from the group consisting of 1 ,2-dimethoxy- ethane (DME), diethylene glycol dimethyl ether (diglyme), diethoxymethane, dimethylene glycol dimethyl ether, tri-methylene glycol dimethyl ether, tetramethylene glycol dimethyl ether, 1 ,3-di- oxolane, 1 ,4-dioxane, 1 ,3,5-trioxane, dimethylacetamide, methyl acetate, dimethyloxalate, meth- oxyacetic acid methyl ester, ethylene carbonate, propylene carbonate, ethylene glycol diacetate and diethylene glycol diacetate, toluene, the xylenes, mesitylene, Cz-Cio-alkanes, such as octane or nonane, THF, 1 ,4-dioxane and mixtures thereof, and specifically selected from toluene, ortho- xylene, meta-xylene, para-xylene and mesitylene.

In a preferred embodiment, the solvent, if employed, is selected from solvents which have a water solubility of greater 150 g/l at 20 °C. In a preferred embodiment the solvent, if employed, is se- lected from solvents which have a vapour pressure of below 100 mbar at 20°C.

In a preferred embodiment the solvent, if employed, is selected from the group consisting of di- ethylene glycol dimethyl ether, triethylene glycol dimethylether and dimethylacetamide, polyox- ymethylene dimethylether of general formula (III) H₃C-0-(CH₂0)_n-CH₃ wherein n = 3 to 8, dime- thyloxalate, methoxyacetic acid methyl ester, ethylene carbonate, propylene carbonate, ethylene glycol diacetate and diethylene glycol diacetate.

In a preferred embodiment of the process according to the invention, the reactant(s) and prod- uct(s) are present from 1 to less than 75 weight-%, preferably 1 to 70 weight-%, preferably 1 to 50 weight-% based on the total weight of the liquid phase, preferably from 2 to 45 weight-% based on the total weight of the liquid phase, more preferably from 3 to 40 weight-% based on the total weight of the liquid phase.

In case the liquid phase consists of more than one distinct phase, the reactant(s) and product(s) are preferably present in at least one distinct liquid phase from 1 to less than 75 weight-%, pref- erably from 1 to 70 weight-%, preferably 1 to 50 weight-%, preferably from 2 to 45 weight-%, more preferably from 3 to 40 weight-% based on the total weight of the at least one distinct liquid phase.

In case the liquid phase consists of more than one distinct phase, the reactant(s) and product(s) are preferably present in each distinct liquid phase from 1 to less than 75 weight-%, preferably 1 to 70 weight-%, preferably 1 to 50 weight-% , preferably from 2 to 45 weight-%, more preferably from 3 to 40 weight-% based on the total weight of each distinct liquid phase,

Oxidant(s)

The process according to the invention is performed with oxygen and/or hydrogen peroxide as oxidant. Oxygen can be used undiluted or diluted. The oxygen can be diluted with other inert gases like N₂, Ar or C0₂, e.g in the form of air. In a preferred embodiment of the invention oxy- gen is used undiluted. Hydrogen peroxide can be used as an aqueous solution. In a preferred embodiment of the invention oxygen is used as oxidant.

Catalyst

The process according to the invention can be performed as a heterogeneous catalyzed pro- cess or as a homogeneous catalyzed process. In a preferred embodiment of the invention the process is conducted as a heterogeneous cata- lysed process. In such a heterogeneous catalyzed process the catalyst and reactant(s)/prod- uct(s) are in different phases, which are in contact with each other. The reactant(s)/product(s) are in the liquid phase, whereas the catalyst will be, at least partially in a solid phase. The reac- tion will take place at the interphase between liquid phase and solid phase.

The process according to the invention is carried out in the presence of a catalyst, wherein the catalyst comprises at least one intermetallic compound (IMC).

An intermetallic compound (IMC) in terms of this invention is a compound made from at least two different metals in an ordered or partially ordered structure with defined stoichiometry. The structure can be similar or different to the structure of the pure constituent metals. Examples for intermetallic compounds are ordered, partially ordered and eutectic alloys, Laves-phases, Zintl- phases, Heussler-phases, Hume-Rothary-phases, and other intermetallic compounds known to the skilled in the art. Also included are compounds comprising elements belonging to the group of semimetals, like selenides, tellurides, arsenides, antimonides, silizides, germanides and bo- rides.

In one embodiment the intermetallic compound comprises at least one catalytically active metal and at least one promotor.

In one embodiment of the invention at least 50 wt.-%, at least 60 wt.-%, at least 70 wt.-%, pref- erably the at least 85 wt.-%, preferably at least 90 wt.-% and more preferably at least 95 wt.-% of the at least one catalytically active metal and the at least one promotor are in the structure of an intermetallic compound.

The catalytically active metal can be selected from the elements selected from the groups 8,

9, 10 and 1 1 of the periodic table (according to IUPAC nomenclature). The elements of group 8, 9, 10 and 11 of the periodic table comprise iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium, platinum, copper, silver and gold.

In a preferred embodiment, the catalytically active metal is selected from elements from the groups 10 and 1 1 of the periodic table (according to IUPAC nomenclature).

In a preferred embodiment, the catalytically active metal is selected from elements selected from the group consisting of platinum, palladium and gold.

In a preferred embodiment of the invention the catalytically active metal is platinum.

The intermetallic compound preferably comprises at least one promotor, which enhances the activity of the catalytically active metal. Examples for promotors are bismuth (Bi), antimony (Sb), lead (Pb), cadmium (Cd), tin (Sn), tellurium (Te), cerium (Ce), selenium (Se) or thallium (Tl). In a preferred embodiment, the intermetallic compound comprises at least one promotor se- lected from the group consisting of bismuth (Bi), antimony (Sb), lead (Pb), cadmium (Cd), tin (Sn) and tellurium (Te). In a preferred embodiment, the intermetallic compound comprises at least one promotor selected from the group consisting of bismuth (Bi), lead (Pb) and cadmium (Cd). In a preferred embodiment, the catalyst comprises bismuth (Bi).

In a preferred embodiment, the intermetallic compound comprises as catalytically active metal platinum and as promotor bismuth.

Suitable molar ratios of the catalytically active metal and the promotor are in the range from 1 : 0.01 to 1 : 10, preferably 1 : 0.67 to 1 : 5, preferably 1 : 0.5 to 1 : 3, more preferably from 1 : 0.1 to 1 : 2.

In one embodiment of the invention the catalyst comprises at least one intermetallic compound of the general formula A_xB_y, wherein

A is the at least one catalytically active metal and B is the at least one promotor,

x in A_xBy is in the range 0,05 - 10, preferably from 0,1 to 5, preferably from 0,2 to 4, more pref- erably 0,25 to 3, more preferably from 0,5 to 2, more preferably from 0,67 to 1.

y in A_xBy is in the range 0,05 - 10, preferably from 0,1 to 5, preferably from 0,2 to 4, more pref- erably 0,25 to 3, more preferably from 0,5 to 2, more preferably from 0,67 to 1.

A is one or more elements selected from Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu, Ag and Au,

B is one or more elements selected from Bi, Sb, Pb, Cd, Sn, Te, Ce, Se and Tl

More preferred are intermetallic compounds of general formula A_xB_y wherein

A is one or more elements selected from Pd, Pt and Au,

B is one or more elements selected from Bi, Pb and Cd,

Even more preferred are intermetallic compounds of the general formula A_xB_y wherein

A is Pt,

B is one or more elements selected from Bi, Pb and Cd, x in A_xBy is in the range 0,05 - 10, preferably from 0,1 to 5, preferably from 0,2 to 4, more pref- erably 0,25 to 3, more preferably from 0,5 to 2, more preferably from 0,67 to 1.

A is Pt, B is Bi,

The term intermetallic compound (IMC) also encompasses mixtures of different intermetallic compounds of general formula A_xB_y as specified hereinbefore.

Examples for intermetallic compounds according to this invention are RhPb, RhPb₂, Rh₄Pbs, Rh₂Sn, RhSn, RhSn₂, RhSn₄, Rh₂Sb, RhSb, RhSb₂, RhSb₃, IrPb, IrSn, lr₅Sn₇, lrSn₂, lr₃Sn₇, lrSn₄, IrSn, lr₅Sn₇, lrSn₂, lr₃Sn₇, lrSn₄, PdsPb, PdisPbg, Pd₅Pb₃, PdPb, PdsSn, Pd_2oSni₃, Pd₂Sn, PdSn, PdsSn₇, PdSn₂, PdSn3, PdSn₄, PdsSb, Pd_2oSb7, PdsSb₂, PdsSb3, Pd₂Sb, PdSb, PdSb₂, Ru₂Sn₃, RuSn₂, Ru₃Sn₇, RuSb, RuSb₂, RuSb₃, NiPb, Ni₃Sn₄, Ni₃Sn₂, Ni₃Sn, NiSn, Ni₅Sb₂, Ni₃Sb, NiSb₂, NiSb_3, PtBi, PtBi₂, Pt₂B _, PtPb, PtsPb, PtPb₂, PtPb₄, PtSb, PtSb₂, Pto_.3Sbo_.7, PtsSb, PtsSb₂, Pt₇Sb, PtSn, Pto_.gSno_.i , Pto_.94Sno_.06, PtSn₂, PtSn₄, Pt₂Sn3, and PtsSn.

Preferred intermetallic compounds are selected from the group consisting of PtBi, PtBi₂, Pt₂Bi3_, PtPb, PtsPb, PtPb₂, PtPb₄, PtSb, PtSb₂, Pto.3Sbo.7, PtsSb, Pt3Sb₂, Pt7Sb, PtSn, Pto.gSno.i, Pto.94Sno.06, PtSn₂, PtSn₄, Pt₂Sn₃, and Pt₃Sn

Preferred intermetallic compounds are selected from the group consisting of PtBi, PtBi₂ and Pt₂Bi3.

The presence of intermetallic compounds can be detected by standard methods for charac- terizing solids, like for example electron microscopy, solid state NMR, XPS (X-ray photoelectron spectroscopy) or Powder X-Ray Diffraction (PXRD). PXRD-analysis can preferably be employed for unsupported intermetallic compounds, whereas XPS analysis is preferred for the analysis of supported intermetallic compounds. PXRD-analysis can for example be performed as described in Zhang et al., J. Am. Chem. Soc. (2015) 137, p 6264“Characterization of Pt-Bi intermetallic NPs” or as described in Cui et al., J Am. Chem. Soc. (2014), 136, 10206-10209 and the Sup- porting Information thereto. XPS can for example be performed as described in the examples below.

Preparation of intermetallic compounds (IMCs)

IMCs can be prepared by standard methods, for example as described in Zhang et al., J. Am. Chem. Soc. (2015) 137, 6263-6269; Zhang et. al., Electrochemistry Communications (2012) 25, 105-108 or Furukawa et al., RSC Adv. (2013), 3, 23269-23277. IMCs can also be prepared by the so called“DiSalvo” Method, as described in Cui et al., J. Am. Chem. Soc. (2014), 136, 10206-10209 or Chen et al. (2012), J. Am. Chem. Soc. 134, 18453-18459. IMCs can also for example be prepared as described in WO 2018073367.

Step g) Preparation of IMCs

In one embodiment the intermetallic compounds (IMCs) are obtainable by g-1) providing a composition comprising the at least one metal compound and the at least one promotor compound

g-2) reducing the composition

g-3) performing an annealing step

g-4) optionally recovering the IMCs.

It is within the scope of the invention, that IMCs are obtainable in a reaction, which combines steps g-1 ) and g-2) or steps g-2) and g-3).

Step g-1 )

The metal compound and the promotor compound can be provided for example as described in step-b) herein. In a preferred embodiment the metal compound and the promotor compound are provided in a solvent, preferably in an aprotic solvent as describe above.

In one embodiment of the invention, the metal compound and the promotor compound are pro- vided as chlorides.

The reducing of the composition is preferably performed as described in step e) herein for the reduction of the catalyst precursor.

In case the reducing agent in step g-2) is provided in a solvent, it is preferred that the solvent is identical to the solvent of composition provided in step g-1 ).

It is within the scope of the invention to employ a stabilizer and/or a solvent which also serve(s) as a reducing agent.

In one embodiment of the invention the reducing agent is selected from the group consisting of potassium triethyl borohydride (K(C H₅) BH) and lithium triethyl borohydride (Li(C H₅) BH).

In one embodiment of the invention, step g-1 ) and step g-2) are performed in a one pot reaction.

In one embodiment of the invention, step g-1 ) and step g-2) are performed in a one pot reaction, the metal compound and the promotor compound are provided as chlorides and the reducing agent is selected from potassium triethyl borohydride (K((C H₅) BH) and lithium triethyl borohy- dride (Li(C H₅) BH). In this embodiment the generated insoluble by-product KCI or LiCI then serves as a matrix that stabilizes the IMCs generated and minimizes agglomeration. Typically, such a one pot reaction is performed in an aprotic solvent, for example in THF.

To control the size of the IMCs and/or to prevent agglomeration, a stabilizer, preferably an inor- ganic stabilizer can be added to the composition in step g-2) or a reducing agent, which also serves as stabilizer can be employed. Likewise, a solvent, which also serves as a stabilizer can be employed in step g-4 (for example ethylene glycol).

Step g-3) Annealing step

The annealing step is preferably performed by treatment of the composition obtained in step g- 2) at temperatures between 200 to 700 °C.

In a further embodiment, steps g-2) and g-3) can be combined into a single step by thermal treatment of the composition obtained in step g-1 ) in the presence of a reducing agent or at a temperature where reduction occurs.

Step g-4) Recovering of IMCs

In one embodiment the IMCs can be employed directly as obtained after the annealing step. In an alternative embodiment the IMCs can be recovered, for example by suitable separation means such as filtration and/or centrifugation. The recovery step can preferably be performed in the presence of a stabilizer, such as for example PVP or ethylene glycol.

The so obtainable IMCs can be of various sizes, for example in the range of 1 to 50 nm, prefer- ably 5 to 30 nm, but can also be in the size of pm (agglomerates). The size of the IMC can be adjusted by means known to a person skilled in the art, for example by choice of solvent and/or stabilizer and/or time of the annealing step. The structure of the IMCs is generally adjusted by varying the temperature of the annealing step.

The intermetallic compound can be used in any form, e.g. unsupported or on a support. The intermetallic compound can be used in an unsupported form, for example as a powder, a mesh, a sponge, a foam or a net. In a preferred embodiment, the intermetallic compound is on a sup- port.

On a support

The term“on a support” encompasses that the intermetallic compound can be located on the outer surface of a support and/or on the inner surface of a support. In most cases, the interme- tallic compound will be located on the outer surface of a support and on the inner surface of a support.

In case the intermetallic compound is on a support, the catalyst comprises the catalytically ac- tive metal(s), the promotor(s) and the support. In case the intermetallic compound is on a support, the support can for example be a powder, a shaped body or a mesh, for example a mesh of iron-chromium-aluminium (FeCrAI), that was tempered in the presence of oxygen (commercially available under the trademark Kanthal^®).

In a preferred embodiment of the invention the intermetallic compound is on a support. In a pre- ferred embodiment, the intermetallic compound is on a support and the support is selected from the group consisting of powders and shaped bodies. In case a support in the form of a powder is employed, such powders usually have a particle size in the range of 1 to 200 pm, preferably 1 to 100 pm. The shaped bodies can for example be obtained by extrusion, pressing or tableting and can be of any shape such as for example strands, hollow strands, cylinders, tablets, rings, spherical particles, trilobes, stars or spheres. Typical dimensions of shaped bodies range from 0.5 mm to 250 mm.

In a preferred embodiment, the support has a diameter from 0.5 to 20 mm, preferably from 0.5 to 10 mm, more preferably from 0.7 to 5 mm, more preferably from 1 to 2.5 mm, preferably 1 .5 to 2.0 mm.

In a preferred embodiment, the support is obtained by extrusion and is in the form of a strand or hollow strand. In one embodiment, a support is employed with strand diameters from 1 to 10 mm, preferably 1.5 to 5 mm. In one embodiment, a support is employed with strand lengths from 2 to 250 mm, preferably 2 to 100 mm, preferably 2 to 25 mm, more preferably 5 to 10 mm. In one embodiment, a support is employed with a strand diameter of 1 to 2 mm and strand lengths of 2 to 10 mm.

In a preferred embodiment, the intermetallic compound is on a support, wherein the support is selected from the group consisting of carbonaceous and oxidic materials.

Suitable support materials are for example carbonaceous or oxidic materials. A preferred carbonaceous support is activated carbon. The surface area of carbonaceous support materi- als preferably is at least 200 m²/g, preferably at least 300 m²/g. In case a carbonaceous support is used an activated carbon with a surface area of at least 300 m²/g is preferred. In a preferred embodiment, the intermetallic compound is on an activated carbon support, preferably with an activated carbon support with a surface area of at least 300 m²/g.

In case an oxidic support is used, the oxides of the following elements can be used: Al, Si, Ce, Zr, Ti, V, Cr, Zn, Mg. The invention also encompasses the use of mixed oxides comprising two or more elements. In one embodiment of the invention mixed oxides are used as support se- lected from the group consisting of (Al/Si), (Mg/Si) and (Zn/Si) mixed oxides. In a preferred em- bodiment, an oxidic support is used, selected from the group consisting of aluminum oxide and silcium dioxide. Aluminium oxide can be employed in any phase, such as alpha aluminium oxide (0AI2O3), beta aluminium oxide (b-Aΐ2q3), gamma aluminium oxide (Y-AI2O3,), delta aluminium oxide (b-AhCh), eta aluminium oxide (g-A Os), theta aluminium oxide (Q-AI2O3), chi aluminium oxide (X-AI2O3), kappa aluminium oxide (K-AI2O3) and mixtures thereof. The term beta aluminium oxide (b-AI₂0₃) describes the compound Na20 HAI2O3.

In a preferred embodiment, the oxidic support is selected from the group consisting of alpha alu- minium oxide (0AI2O3), beta aluminium oxide (b-Aΐ2q3), gamma aluminium oxide (Y-AI2O3), delta aluminium oxide (b-AhCh), and theta aluminium oxide (Q-AI2O3).

In a preferred embodiment, the oxidic support is selected from the group consisting of alpha alu- minium oxide (0AI2O3), beta aluminium oxide (b-Aΐ2q3) and gamma aluminium oxide (Y-AI2O3). In one embodiment, the oxidic support is gamma aluminium oxide (Y-AI2O3).

Commercially available gamma aluminium oxide (Y-AI2O3), can be treated at temperatures from 500 to 700°C, preferably at temperatures from 550°C to 600°C to ensure that the complete AI2O3 is in the gamma-phase.

In one embodiment the oxidic supports can have a BET-surface area (BET, Brunnauer-Emmet- Teller determined according to DIN 66131 by N2 adsorption at 77 K) from 0.1 to 500 m²/g. Pref- erably the oxidic supports have a BET-surface area of at least 0.1 m²/g, preferably at least 1 m²/g, preferably at least 10 m²/g, more preferably of at least 30 m²/g, more preferably of at least 50 m²/g, more preferably of at least 75 m²/g, preferably of at least 100 m²/g, preferably of at least 150 m²/g especially preferred of at least 200 m²/g.

In a further embodiment, the oxidic support has a BET-surface area of 1 m²/g to 50 m²/g. In a further embodiment, the oxidic support has a BET-surface area of 10 m²/g to 300 m²/g, prefera- bly of 20 to 100 m²/g. In a further embodiment, the oxidic support has a BET-surface area of 100 m²/g to 300 m²/g, preferably 150 to 300 m²/g.

In a preferred embodiment, the support is AI2O3 with a BET-surface area of 100 to 300 m²/g.

In one embodiment, the intermetallic compound comprises platinum and bismuth and is on a support.

In one embodiment, the intermetallic compound comprises platinum and bismuth and is on a support, wherein the support is selected from carbonaceous and oxidic materials.

In one embodiment, the intermetallic compound comprises platinum and bismuth and is on a support, wherein the support is selected from carbonaceous and oxidic materials, and wherein the oxidic material is selected from the group consisting of oxides of the elements selected from the group consisting of Al, Ce, Zr, Ti, V, Cr, Zn and Mg.

In one embodiment, the catalyst intermetallic compound comprises platinum and bismuth and is on a support, wherein the support is selected from carbonaceous materials and oxidic materials, and wherein the oxide is selected from the group consisting of oxides of the elements selected from the group consisting of Al, Ce, Zr and Ti.

In a preferred embodiment, the intermetallic compound on a support is selected from the group consisting of platinum-bismuth intermetallic compounds on carbon and platinum-bismuth inter- metallic compounds on aluminium oxide.

In a preferred embodiment, the intermetallic compound on a support is selected from the group consisting of PtBi/C, PtBh/C, Pt2Bi3/C, PtBi/AhCh, PtBh/AhCh, and Pt2Bi3/Al2C>3.

In a preferred embodiment, the intermetallic compound comprises platinum and bismuth and is on an aluminium oxide support, wherein the aluminium oxide is selected from the group consist- ing of alpha aluminium oxide (0AI2O3), beta aluminium oxide (b-Aΐ2q3), gamma aluminium ox- ide (Y-AI2O3,), delta aluminium oxide (b-AhCh), eta aluminium oxide (g-A Os), theta aluminium oxide (Q-AI2O3), chi aluminium oxide (X-AI2O3) and kappa aluminium oxide (K-AI2O3).

In case the catalytically active metal is on a support, the content of the catalytically active metal of the catalyst usually is in the range of 0.1 to 20 weight-%, preferably 0.1 to 15 weight-%, pref- erably in the range of 0.5 to 10 weight-%.

The catalyst can for example be prepared by

- providing a support as described in step a),

- providing the intermetallic compound (IMC), preferably prepared as described in step g)

- depositing the IMC on the support as described in step c)

optionally performing a drying step

In one embodiment of the invention, the catalyst is obtainable by, preferably obtained by

- providing a support,

providing the intermetallic compound (IMC),

depositing the IMC on the support,

optionally performing a drying step

- providing a support as described in step a),

providing the intermetallic compound (IMC), prepared as described in step g)

- depositing the IMC on the support as described in step c)

optionally performing a drying step

In an alternative embodiment the catalyst can be prepared by

a) providing a support b) providing a composition comprising the at least one metal compound and the at least one promotor compound

c) depositing the composition on a support

d) optionally performing a drying and/or calcination step

e) reducing the so obtained catalyst precursor and

f) performing an annealing step, preferably at temperatures of 200 to 700 °C.

In a preferred embodiment of the invention, the catalyst is obtainable by, preferably obtained by a) providing a support

b) providing a composition comprising the at least one metal compound and the at least one promotor compound

c) depositing the composition on a support

d) optionally performing a drying and/or calcination step

e) reducing the so obtained catalyst precursor and

f) performing an annealing step, preferably at temperatures of 200 to 700 °C.

Step a) Providing a support

A suitable support is provided, for example by adding the support in form of a powder or a shaped body directly to a reactor vessel or by providing the support as a slurry (in case the sup- port is in form of a powder).

Step b) Providing a composition comprising the at least one metal compound and the at least one promotor compound

The metal compound is a precursor of the catalytically active metal. The catalytically active metal is obtained by reduction of the metal compound.

The promotor compound is a precursor of the promotor. The promotor is obtained conversion (by oxidation and/or reduction) of the promotor compound to the promotor.

The metal compound and the promotor compound can be employed as solution, for example as an aqueous solution of a water-soluble salt of the at least one metal compound and the at least one promotor or as a non-aqueous solution. They can also be employed as a colloid in which the non-dissolved metal compound and/or promotor compound are dispersed in a liquid phase.

In a preferred embodiment, the metal compound is employed as a salt. Depending on the solu- bility of the salt, aqueous or non-aqueous solutions can be employed.

Suitable salts of the metal compound include nitrates, acetates, sulphates, citrates, oxides, hy- droxides and chlorides and combinations thereof. Preferably water-soluble salts are used. In a preferred embodiment, the metal compound is selected from the group consisting of plati num salts. Depending on the solubility of the platinum salt, aqueous or non-aqueous solutions of the platinum salt can be employed. Examples for suitable platinum salts are H₂PtCl₆, PtCU, Pt(NH₃)₂(N0₃)₂, Pt(N0₂)₂(NH₃)₂/NH₄0H, Pt(N0₃)₂, platinum hydroxides such as Pt(OH)₂, Pt(OH)₄, or H₂Pt(OH)₆, all of which can be stabilized in amines, for example in monoethanola- mine Pt0₂, bis(2,4-pentanedionato)Platinum (II) = Pt(C₅H₇0₂)₂, K₂PtCI₄, NaPtCU, (NH₄)₂PtCI₄.

In a preferred embodiment, the platinum salt is selected from the group consisting of H₂PtCl₆, Pt(NH₃)₂(N0₃)₂, Pt(N0₂)₂(NH₃)₂/NH₄0H and Pt(N0₃)₂.

Suitable salts of the promotor compound include nitrates, acetates, sulphates, citrates, oxides, hydroxides and chlorides and combinations thereof. Preferably water-soluble salts are used.

In a preferred embodiment, the promotor compound is selected from the group consisting of Bi salts, Cd salts and Pb salts.

In an alternative embodiment to step-b), the metal compound and the promotor compound can be provided as separate compositions and deposited separately on the support.

The deposition of the composition obtained in step b) on the support can be performed with any known method, for example by chemical or physical vapour deposition or by contacting and mixing the support with the composition (= immersion) or by spraying the composition on the support.

In a preferred embodiment, the deposition is performed by immersion and/or spraying.

In case the deposition is performed by immersion or by spraying, the composition obtained in step b) can be employed as solution or as colloid or as a colloid which is generated in situ dur- ing the immersion or spraying. The deposition by immersion or spraying can be performed at a temperature of 1 to 100 °C. The pH value at which the deposition step is performed can be cho- sen depending on the metal compound and or promotor compound used. The deposition can be performed from 0.1 to 24 hours, usually from 0.5 to 2 hours. The deposition can be performed at different pressures, for example at pressures from 1 to 1000 mbar (atmospheric pressure), suit- able pressures are for example 50 mbar, 70 mbar, 100 mbar, 250 mbar, 500 mbar or atmos- pheric pressure. The so obtained catalyst precursor can optionally be dried and/or calcined prior to the reduction step.

In case the deposition step is performed by immersion or by spraying, the volume of the solution or colloid of the composition obtained in step b) is ideally chosen, so that at least 90%, prefera- bly 100% of the pore volume of the support will be filled with the solution or colloid (so called“in- cipient-wetness” method). The concentration of the metal compound in the composition ob- tained in step b) is ideally chosen so that, after deposition and reduction, a catalyst with the de- sired content of catalytically active metal is obtained.

The deposition step can be conducted in one step or in multiple, consecutive steps. The deposi- tion step can also be performed as a combination of spraying and immersion.

The catalyst precursor can then be recovered by suitable separation means such as filtration and/or centrifugation. The catalyst precursor can then be washed with water, preferably until a conductivity of less than 400 pS/cm, preferably less than 200 pS/cm is obtained.

In one embodiment, a drying step and/or a calcination step d) can be performed subsequent to the deposition step c).

The calcination step d) can be performed in customary furnaces, for example in rotary furnaces, in chamber furnaces, in tunnel furnaces or in belt calciners.

The calcination step d) can be performed at temperatures from above 200°C to 1 150°C, prefer- ably from 250 to 900°C, preferably from 280°C to 800°C and more preferably from 500 to 800 °C, preferably from 300°C to 700°C. The calcination is suitably conducted for 0.5 to 20 hours, preferably from 0.5 to 10 hours, preferably from 0.5 to 5 hours.

The calcination of the catalyst precursor in step d) mainly serves the purpose to stabilize the metal compound and the promotor compound deposited on the support and to remove unde- sired components.

Step e) Reduction step

The so obtained catalyst precursor can then be reduced, for example by treatment with a gas (gas phase reduction) or by treatment of the catalyst precursor with a solution of a reducing agent (liquid phase reduction).

The gas phase reduction of the catalyst precursor can be performed by treating the catalyst precursor with hydrogen and/or CO. The hydrogen and/or CO can further comprise at least one inert gas, such as for example helium, neon or argon, N₂, C0₂ and/or lower alkanes, such as methane, ethane, propane and/or butane. Preferably N₂ is employed as the inert gas. The gas phase reduction can be performed at temperatures from 30°C to 200 °C, preferably from 50°C to 180°C, more preferably from 60 to 130°C. Usually the gas phase reduction is performed over a period from 1 to 24 hours, preferably 3 to 20 hours, more preferably 6 to 14 hours.

The liquid phase reduction of the catalyst precursor is performed by treating the catalyst pre- cursor with a solution of a reducing agent. Suitable reducing agents are quaternary alkyl ammo- nium salts; formic acid; salts of formic acid, such as sodium formate, potassium formate, lithium formate or ammonium formate; citric acid; salts of citric acid such as sodium citrate, potassium citrate, lithium citrate, ammonium citrate; ascorbic acid; salts of ascorbic acid such as sodium ascorbate, potassium ascorbate, lithium ascorbate and ammonium ascorbate; tartaric acid; salts of tartaric acid, such as sodium tartrate, potassium tartrate, lithium tartrate and ammonium tar- trate; oxalic acid; salt of oxalic acid, such as potassium oxalate, sodium oxalate, lithium oxalate and ammonium oxalate; ammonium hydrogen carbonate (NH4HCO3); hydroxylamine; hypo- phosphoric acid; hyposphoshites, such as for example sodium hypophosphite (NahhPC^); so dium sulfite (Na2SC>3); hydrazine; phenylhydrazine; C1 to C₄ alcohols such methanol, ethanol, 1 - propanol, 2-propanol, 1 -butanol, iso-butanol (2-methyl-1 -propanol), 2-butanol; diols; polyols; re- ducing sugars, such as glucose, fructose; borohydrides, such as LiBH₄, NaBH₄, NaBI-hCN, KBH₄, LiBH(C2H₅)3; KBH(C2H₅)3_, diboran (B2H6); lithium aluminium hydride (LiAIH₄); formalde- hyde; N-vinyl pyrrolidone (NVP), polyvinyl-pyrrolidone (PVP); phenol; sodium thiocyanate;

iron(ll) sulfate; sodium amalgam; zinc mercury amalgam.

The liquid phase reduction can be performed at a temperature from 10 to 95°C, preferably from 50 to 90°C. The pH of the reduction step can be chosen depending on the reducing agent used.

In a preferred embodiment, the reduction step is performed by treatment of the catalyst precur- sor with a solution of a reducing agent.

In a preferred embodiment, the reduction step is performed by treatment of the catalyst precur- sor with a solution of a reducing agent, wherein the reducing agent is selected from the group consisting of quaternary alkyl ammonium salts; formic acid; salts of formic acid, such as sodium formate, potassium formate, lithium formate or ammonium formate; citric acid; salts of citric acid such as sodium citrate, potassium citrate, lithium citrate, ammonium citrate; ascorbic acid; salts of ascorbic acid such as sodium ascorbate, potassium ascorbate, lithium ascorbate and ammo- nium ascorbate; tartaric acid; salts of tartaric acid, such as sodium tartrate, potassium tartrate, lithium tartrate and ammonium tartrate; oxalic acid; salt of oxalic acid, such as potassium oxa- late, sodium oxalate, lithium oxalate and ammonium oxalate; ammonium hydrogen carbonate (NH₄HC0₃); hydroxylamine; hypophosphoric acid; hyposphoshites, such as for example sodium hypophosphite (NaH2PC>2); sodium sulfite (Na2SC>3); hydrazine; phenylhydrazine; C1 to C₄ alco- hols such methanol, ethanol, 1 -propanol, 2-propanol, 1 -butanol, iso-butanol (2-methyl-1 -propa- nol), 2-butanol; diols; polyols; reducing sugars, such as glucose, fructose; borohydrides, such as LiBH₄, NaBH₄, NaBH₃CN, KBH₄, LiBH(C₂H₅)₃; KBH(C₂H₅)_3, diboran (B₂H₆); lithium aluminium hydride (LiAIH₄); formaldehyde; N-vinyl pyrrolidone (NVP), polyvinyl-pyrrolidone (PVP); phenol; sodium thiocyanate; iron(ll) sulfate; sodium amalgam; zinc mercury amalgam.

In a preferred embodiment, the reduction step is performed by treatment of the catalyst precur- sor with a solution of a reducing agent, wherein the reducing agent is selected from the group consisting of sodium formate, sodium citrate, sodium ascorbate, polyols, reducing sugars, for- maldehyde, methanol, ethanol, 2-propanol, potassium triethyl borohydride (K(C2H₅)3BH) and lithium triethyl borohydride (Li(C2H₅)3BH). The catalyst can then be recovered by suitable separation means such as filtration and/or cen- trifugation. Typically, the catalyst is then washed with water, preferably until a conductivity of less than 400 pS/cm, preferably less than 200 pS/cm is obtained.

Drying steps can be performed for example subsequent to step c) and/or subsequent to step e). The drying of the catalyst precursor obtained in step c) or of the catalyst obtained in step e) can generally be performed at temperatures above 60°C, preferably above 80°C, more prefera- bly above 100°C. The drying can for example be performed at temperatures from 120 °C up to 200 °C. The drying will normally be performed until substantially all the water is evaporated. Common drying times range from one to up to 30 hours and depend on the drying temperature. The drying step can be accelerated by the use of vacuum.

Annealing step f)

The annealing step is preferably performed by treatment of the catalyst obtained in step e) at temperatures between 200 to 700 °C.

In a further embodiment, steps e) and f) can be combined into a single step by thermal treat- ment of the precursor obtained in step c) in the presence of a reducing agent or at a tempera- ture where reduction occurs.

Annealing step q-3) or f)

The annealing step is preferably performed at temperatures between 200 to 700 °C, preferably under chemically inert conditions.

The annealing step is the step in which the IMC structure is mainly generated. The extend of the IMC structure can be adjusted for example by varying the temperature or the duration of the an- nealing step.

The extent to which the IMCs structure is obtained can be monitored for example by PXRD analysis. If needed, the temperature and/or time of thermal treatment can be adapted, to achieve the desired extend of IMC structure.

Generally, the annealing steps g-3) or f) are performed by heating the composition obtained in step g-2) or the catalyst obtained in step c) to the desired temperature under chemically inert conditions wherein the gas mixture present does not contain any reactive components that can undergo chemical reaction with the composite material. Particularly the mixture should not corn- prise oxidizing agents like for example oxygen, water, NO_x, halides or there like. The heating can be performed by any method suited to heat solids or wet solids like heating in muffle fur- naces, microwaves, rotary kilns, tube furnaces, fluidized bed and other heating devices known to the person skilled in the art.

Distribution on the support In case the intermetallic compound is on a support, it can be evenly distributed on the support or can be unevenly distributed on the support. It can for example be concentrated in the core or in defined layers of the support. The intermetallic compound can be located partially or com- pletely on the inner surface of the support or can be located partially or completely on the outer surface of the support. In case the intermetallic compound is located completely on the inner surface of the support, the outer surface of the catalyst is identical to the outer surface of the support.

The distribution of the intermetallic compound, the catalytically active metal and the promotor can be determined with Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray Spectroscopy (EDXS). The distribution can for example be determined by preparing a cross section of the catalyst. In case the catalyst is a sphere the cross section can be prepared through the center of the sphere. In case the catalyst is a strand, the cross section can be pre- pared by cutting the strand at a right angle to the axis of the strand. Via backscattered elec- trons (BSE) the distribution of the catalytically active metal in the catalyst can be visualized. The amount of intermetallic compound, the catalytically active metal and the promotor can then be quantified via EDXS whereby an acceleration voltage of 20 kV is usually used.

In a preferred embodiment of the invention a catalyst is employed, wherein the intermetallic compound is located in the outer shell of the catalyst. In this embodiment, the intermetallic corn- pound is mainly located in the outer shell of the catalyst.

In one embodiment, the outer shell of the catalyst is the space from the outer surface of the cat- alyst to a depth of X from the outer surface of the catalyst, wherein X is 15% of the distance from the outer surface of the catalyst to the center of the catalyst. For example, in case a cata- lyst is employed which is a sphere and has a diameter of 1.5 mm, the outer shell is the space from the outer surface to a depth of 1 12.5 pm from the outer surface.

In one embodiment, the outer shell of the catalyst is the space from the outer surface of the cat- alyst to a depth of X from the outer surface of the catalyst, wherein X is 30% of the distance from the outer surface of the catalyst to the center of the catalyst. For example, in case a cata- lyst is employed which is a sphere and has a diameter of 1.5 mm, the outer shell is the space from the outer surface to a depth of 225 pm from the outer surface.

In one embodiment, the outer shell of the catalyst is the space from the outer surface of the cat- alyst to a depth of 100 pm from the outer surface of the catalyst. In one embodiment, the outer shell is the space from the outer surface of the catalyst to a depth of 400 pm, preferably 300 pm, preferably 200 pm from the outer surface of the catalyst.

In a preferred embodiment, at least 50 weight-%, preferably at least 70 weight-%, preferably at least 80 weight-%, preferably at least 90 weight-%, preferably at least 95 weight-% of the inter- metallic compound is located in the outer shell of the catalyst, wherein the outer shell of the cat- alyst is the space from the outer surface of the catalyst to a depth of X from the outer surface of the catalyst, wherein X is 15% of the distance from the outer surface of the catalyst to the center of the catalyst.

In a preferred embodiment, at least 70 weight-%, preferably at least 80 weight-%, preferably at least 90 weight-%, preferably at least 95 weight-% of the intermetallic compound is located in the outer shell of the catalyst, wherein the outer shell of the catalyst is the space from the outer surface of the catalyst to a depth of X from the outer surface of the catalyst, wherein X is 30% of the distance from the outer surface of the catalyst to the center of the catalyst.

In a further embodiment of the invention, at least 50 weight-%, preferably at least 70 weight-%, preferably at least 80 weight-%, preferably at least 90 weight-%, preferably at least 95 weight-% of the intermetallic compound is located in the outer shell of the catalyst, wherein the outer shell of the catalyst is the space from the outer surface of the catalyst to a depth of 100 pm from the outer surface of the catalyst.

In a further embodiment of the invention, at least 70 weight-%, preferably at least 80 weight-%, preferably at least 90 weight-%, preferably at least 95 weight-% of the intermetallic compound is located in the outer shell of the catalyst, wherein the outer shell of the catalyst is the space from the outer surface of the catalyst to a depth of 400 pm, preferably to a depth of 300 pm, prefera- bly to a depth of 200 pm from the outer surface of the catalyst.

In a further embodiment of the invention, a catalyst is employed, wherein the dispersity of the intermetallic compound is on average in the range of 10% to 100%, preferably 30% to 95% (de- termined with CO-sorption according to DIN 66136-3). Catalysts in which the intermetallic corn- pound is located in the outer shell of the catalyst can for example be obtained by the deposition- reduction method as described above. The distribution of the intermetallic compound in the outer shell of the catalyst can be effected for example by the choice of the deposition method and/or the choice of the deposition parameters such as temperature, pH and time and the com- bination of these parameters. A description of the different methods of preparation can for ex- ample be found in ..Handbook of Heterogeneous Catalysis", edited by G. Ertl, H. Knozinger, J. Weitkamp, Vol 1. Wiley-VCH, 1997. Chapter 2, part 2.2.1.1. Impregnation and Ion Exchange, authors M. Che, O. Clause, and Ch. Marcilly, p. 315-340.

One embodiment of the invention is directed to a process for the preparation of alpha, beta un- saturated aldehydes of general formula (I)

wherein Ri, R₂ and R₃, independently of one another, are selected from hydrogen; Ci-C₆-alkyl, which optionally carry 1 , 2, 3, or 4 identical or different substitu- ents which are selected from NO2, CN, halogen, C1-C6 alkoxy, (Ci-C₆-alkoxy)carbonyl, C1-C6 acyl, C1-C6 acyloxy and aryl; and C2-C6-alkenyl, which optionally carry 1 , 2, 3, or 4 identical or different substituents which are selected from NO2, CN, halogen, C1-C6 alkoxy, (Ci-C₆-alkoxy)carbonyl, C1-C6 acyl, C1-C6 acyloxy and aryl; by oxidation of alcohols of general formula (II)

wherein R1, R2 and R3 have the meaning as given above

in the presence of a catalyst and in the presence of a liquid phase,

• wherein the oxidant is oxygen and/or hydrogen peroxide, and

• wherein the catalyst comprises at least one intermetallic compound, wherein a catalyst is used which is obtainable by, preferably obtained by a) providing a support

c) depositing the composition on a support

d) optionally performing a drying and/or calcination step

e) reducing the so obtained catalyst precursor and

f) performing an annealing step, preferably at temperatures of 200 to 700 °C.

wherein R1, R₂ and R₃, independently of one another, are selected from hydrogen; Ci-C₆-alkyl, which optionally carry 1 , 2, 3, or 4 identical or different substitu- ents which are selected from NO2, CN, halogen, C1-C6 alkoxy, (Ci-C₆-alkoxy)carbonyl, C1-C6 acyl, C1-C6 acyloxy and aryl; and C2-C6-alkenyl, which optionally carry 1 , 2, 3, or 4 identical or different substituents which are selected from NO2, CN, halogen, C1-C6 alkoxy, (Ci-C₆-alkoxy)carbonyl, C1-C6 acyl, C1-C6 acyloxy and aryl; by oxidation of alcohols of general formula (II)

wherein Ri, R₂ and R₃ have the meaning as given above in the presence of a catalyst and in the presence of a liquid phase,

• wherein the oxidant is oxygen and/or hydrogen peroxide, and

• wherein the catalyst comprises at least one intermetallic compound, wherein a catalyst is used which is obtainable by, preferably obtained by o providing a support,

o providing the at least one intermetallic compound (IMC),

o depositing the IMC on the support,

o optionally performing a drying step

wherein R₁, R₂ and R₃, independently of one another, are selected from hydrogen; Ci-C₆-alkyl, which optionally carry 1 , 2, 3, or 4 identical or different substitu- ents which are selected from NO₂, CN, halogen, C₁-C₆ alkoxy, (Ci-C₆-alkoxy)carbonyl, C₁-C₆ acyl, C₁-C₆ acyloxy and aryl; and C₂-C₆-alkenyl, which optionally carry 1 , 2, 3, or 4 identical or different substituents which are selected from NO₂, CN, halogen, C₁-C₆ alkoxy, (Ci-C₆-alkoxy)carbonyl, C₁-C₆ acyl, C₁-C₆ acyloxy and aryl; by oxidation of alcohols of general formula (II)

(II) wherein Ri, R₂ and R₃ have the meaning as given above in the presence of a catalyst and in the presence of a liquid phase,

• wherein the oxidant is oxygen and/or hydrogen peroxide, and

• wherein the catalyst comprises at least one intermetallic compound on a support, and

• wherein the intermetallic compound is located mainly in the outer shell of the cat- alyst.

wherein R₁, R₂ and R₃, independently of one another, are selected from hydrogen; Ci-C₆-alkyl, which optionally carry 1 , 2, 3, or 4 identical or different substitu- ents which are selected from N0₂, CN, halogen, C₁-C₆ alkoxy, (Ci-C₆-alkoxy)carbonyl, C₁-C₆ acyl, C₁-C₆ acyloxy and aryl; and C₂-C₆-alkenyl, which optionally carry 1 , 2, 3, or 4 identical or different substituents which are selected from N0₂, CN, halogen, C₁-C₆ alkoxy, (Ci-C₆-alkoxy)carbonyl, C₁-C₆ acyl, C₁-C₆ acyloxy and aryl; by oxidation of alcohols of general formula (II)

• wherein the oxidant is oxygen and/or hydrogen peroxide, and

• wherein the catalyst comprises at least one intermetallic compound, and • wherein the catalyst comprises the intermetallic compound on a support and

• wherein at least 50 weight-%, preferably at least 70 weight-%, preferably at least 80 weight-%, preferably at least 90 weight-%, preferably at least 95 weight-% of the intermetallic compound is located in the outer shell of the catalyst, wherein the outer shell of the catalyst is the space from the outer surface of the catalyst to a depth of X from the outer surface of the catalyst, wherein X is 15% of the dis tance from the outer surface of the catalyst to the center of the catalyst.

wherein Ri, R₂ and R3, independently of one another, are selected from hydrogen; Ci-C6-alkyl, which optionally carry 1 , 2, 3, or 4 identical or different substitu- ents which are selected from NO2, CN, halogen, C1-C6 alkoxy, (Ci-C₆-alkoxy)carbonyl, C1-C6 acyl, C1-C6 acyloxy and aryl; and C2-C6-alkenyl, which optionally carry 1 , 2, 3, or 4 identical or different substituents which are selected from NO2, CN, halogen, C1-C6 alkoxy, (Ci-C₆-alkoxy)carbonyl, C1-C6 acyl, C1-C6 acyloxy and aryl; by oxidation of alcohols of general formula (II)

wherein Ri, R₂ and R3 have the meaning as given above in the presence of a catalyst and in the presence of a liquid phase,

• wherein the oxidant is oxygen and/or hydrogen peroxide, and

• wherein the catalyst comprises at least one intermetallic compound

• wherein the catalyst comprises the intermetallic compound on a support and

• wherein at least 70 weight-%, preferably at least 80 weight-%, preferably at least 90 weight-%, preferably at least 95 weight-% of the intermetallic compound is located in the outer shell of the catalyst, wherein the outer shell of the catalyst is the space from the outer surface of the catalyst to a depth of X from the outer surface of the catalyst, wherein X is 30% of the distance from the outer surface of the catalyst to the center of the catalyst.

wherein Ri, R₂ and R3, independently of one another, are selected from hydrogen; Ci-C₆-alkyl, which optionally carry 1 , 2, 3, or 4 identical or different substitu- ents which are selected from NO2, CN, halogen, C1-C6 alkoxy, (Ci-C₆-alkoxy)carbonyl, C1-C6 acyl, C1-C6 acyloxy and aryl; and C2-C6-alkenyl, which optionally carry 1 , 2, 3, or 4 identical or different substituents which are selected from NO2, CN, halogen, C1-C6 alkoxy, (Ci-C₆-alkoxy)carbonyl, C1-C6 acyl, C1-C6 acyloxy and aryl; by oxidation of alcohols of general formula (II)

• wherein the oxidant is oxygen and/or hydrogen peroxide, and

• wherein the catalyst comprises at least one intermetallic compound

• wherein the catalyst comprises the intermetallic compound on a support and

• wherein at least 50 weight-%, preferably at least 70 weight-%, preferably at least 80 weight-%, preferably at least 90 weight-%, preferably at least 95 weight-% of the intermetallic compound is located in the outer shell of the catalyst, wherein the outer shell of the catalyst is the space from the outer surface of the catalyst to a depth of 100 pm from the outer surface of the catalyst. One embodiment of the invention is directed to a process for the preparation of alpha, beta un- saturated aldehydes of general formula (I)

wherein R₁, R₂ and R₃ have the meaning as given above in the presence of a catalyst and in the presence of a liquid phase,

• wherein the oxidant is oxygen and/or hydrogen peroxide, and

• wherein the catalyst comprises at least one intermetallic compound, and

• wherein the catalyst comprises the intermetallic compound on a support and

• wherein at least 70 weight-%, preferably at least 80 weight-%, preferably at least 90 weight-%, preferably at least 95 weight-% of the intermetallic compound is located in the outer shell of the catalyst, wherein the outer shell of the catalyst is the space from the outer surface of the catalyst to a depth of 400 pm, preferably to a depth of 300 pm, preferably to a depth of 200 pm from the outer surface of the catalyst. Process mode

The embodiments of the process mode described hereinafter can suitably be applied in all pro- cesses described above.

In one embodiment of the invention, the process is conducted as a batch process and the molar ratio of the catalytically active metal to the alcohol(s) of general formula (II) is in the range 0.0001 : 1 to 1 : 1 , more preferably in the range 0.001 : 1 to 0.1 : 1 and even more preferably in the range 0.001 : 1 to 0.01 : 1.

In one embodiment of the invention, the process is conducted as a continuous process and the catalyst load (defined as total amount of alcohol of general formula (II)/ total amount of catalytically active metal in the reactor/time unit) is in the range 0.01 to 100 g of alcohol(s) of general formula (II) per g of catalytically active metal per hour, more preferably in the range 0.1 to 20 g of alcohol(s) of general formula (II) per g of catalytically active metal per hour.

In one embodiment of the invention, the process is conducted as a continuous process and the catalyst load (defined as total amount of alcohol of general formula (II)/ total amount of catalytically active metal in the reactor/time unit) is in the range 30 to 40000 g of alcohol(s) of general formula (II) per g of catalytically active metal per hour, more preferably in the range 1000 to 9000, more preferably in the range 1200 to 5000, preferably 1500 to 4000, preferably in the range of 1650 to 3500 g of alcohol(s) of general formula (II) per g of catalytically active metal per hour.

The process according to the invention can be performed in reaction vessels customary for such reactions, the reaction being configurable in a continuous, semi-batch or batch-wise mode. In general, the particular reactions will be performed under atmospheric pressure. The process may, however, also be performed under reduced or increased pressure.

The process according to the invention can be performed under pressure, preferably under a pressure between above 1 bar and 15 bar (absolute), preferably between above 1 bar and 10 bar (absolute).

The process according to the invention can be performed at a partial pressure of oxygen from 0.1 to 15 bar, preferably from 0.2 to 10 bar, preferably from 0.2 to 8 bar, more preferably from 0.2 to 5 bar, more preferably from 1 to 3, preferably from 1 to 2.5, more preferably from 1.2 to 2 bar.

In a preferred embodiment of the invention the process is conducted as a batch process. In a preferred embodiment of the invention the process is conducted as a semi-batch process. In a preferred embodiment of the invention the process is conducted as a continuous process.

In a preferred embodiment of the invention the process is conducted with a fixed-bed catalyst. In case the process according to the invention is conducted with a fixed-bed catalyst, suitable fixed- bed reactors can be selected from the group consisting of trickle-bed reactors, bubble-packed reactors, multi-tubular reactors and plate reactors.

The process according to the invention can be conducted in one fixed-bed reactor or can prefer- ably be conducted in more than one, preferably more than two, more preferably more than three, preferably three to five fixed-bed reactors. The one or more fixed-bed reactors can be arranged in series or in parallel.

The process according to the invention can be conducted at common values of weight hourly space velocity (WHSV), defined as the hourly mass flow of the process feed (in kg/h) per catalyst (in kg). The process can for example be performed at WHSV values of 1 to 20000, preferably 10 to 10000, preferably 20 to 5000, preferably 20 to 500, more preferably from 50 to 100 kg/kg/h.

The process according to the invention can be conducted in one or more fixed-bed reactor(s) with or without heat exchange. In one embodiment of the invention, the fixed-bed reactor(s) can be operated so that a constant temperature is held over one, some or all fixed-bed reactors. In one embodiment of the invention, the fixed-bed reactor(s) can be operated so that a defined temper- ature gradient is maintained over one, some or all fixed-bed reactors without heat addition or removal. In one embodiment of the invention, the fixed-bed reactor(s) can be operated with a temperature-controlled profile, wherein a defined temperature profile is maintained over one, some or all fixed-bed reactors with internal or external heat addition or removal.

In a preferred embodiment of the invention the process is conducted in a trickle-bed reactor with a fixed-bed catalyst. In one embodiment of the invention, the process is conducted with more than one, preferably more than two, more preferably more than three trickle-bed reactors, which are arranged in series or in parallel, preferably in series. In one embodiment, the process is conducted with three to five trickle-bed reactors, which are arranged in series. In one embodiment, one or more, preferably each of the trickle-bed reactors can be provided with a liquid recycle stream.

In a preferred embodiment of the trickle-bed reactor, the components of the reaction can be in- serted to the reactor concurrently, meaning that the liquid phase(s) and the gas phase comprising the oxidant oxygen, are inserted to the reactor at the same side, preferably at the top of the reactor.

In one embodiment of the invention the process is conducted in a bubble-packed reactor with a fixed-bed catalyst. In one embodiment of the invention, the process is conducted with more than one, preferably more than two, more preferably more than three bubble-packed reactors, which are arranged in series or in parallel, preferably in series. In one embodiment, the process is con- ducted with three to five bubble-packed reactors, which are arranged in series.

In one embodiment of the bubble-packed reactor, the components of the reaction can be inserted in the reactor concurrently, meaning that the liquid phase(s) and the gas phase comprising the oxidant oxygen, are inserted to the reactor at the same side, preferably at the bottom of the reac- tor. In one embodiment of the bubble-packed reactor, the components of the reaction can be inserted in the reactor countercurrently, meaning that the liquid phase(s) and the gas phase corn- prising the oxidant oxygen, are inserted to the reactor at opposite sides. In one embodiment, the liquid phase(s) are inserted to the reactor at the bottom of the reactor, whereas the gas phase comprising oxygen as oxidant is inserted at the top of the reactor. In one embodiment, the liquid phase(s) are inserted to the reactor at the top of the reactor, whereas the gas phase comprising oxygen as oxidant is inserted at the bottom of the reactor.

In a preferred embodiment of the invention the process is conducted as a slurry process. The process can be conducted in a slurry-based system as stirred tank reactor or slurry bubble col- umn.

The reaction is carried out by contacting alcohol(s) of general formula (II), water, catalyst, the oxidant and optional components, such as for example one or more solvent(s), under suitable reaction conditions.

These components can in principle be contacted with one another in any desired sequence. For example, the alcohol(s) of general formula (II), if appropriate dissolved in water or a solvent or in dispersed form, can be initially charged and admixed with the catalyst or, conversely, the catalytic system can be initially charged and admixed with the alcohol(s) of general formula (II) and water. Alternatively, these components can also be added simultaneously to the reaction vessel.

As an example for a batch-wise slurry process a stirred tank reactor can be used where the cat- alyst, the reactant, water, and optionally solvent are loaded, the reactor is then pressurized with oxygen. The reaction is then performed until the desired conversion is achieved.

As an example for a batch-wise slurry process a stirred tank reactor can be used where the cat- alyst, the reactant(s), if appropriate dissolved in water or solvent or in dispersed form, water and optionally one or more solvent(s) are loaded, the reactor is then pressurized with oxygen. The reaction is then performed until the desired conversion is achieved.

As an example for a semi-batch process a stirred tank reactor can be used where the catalyst, the reactant(s), water, and optionally solvent are loaded, the oxygen is then continuously fed to the reactor until the desired conversion is achieved. As another example for a semi-batch process a fixed bed catalyst in a trickle-bed reactor can be used. The solution of reactant(s), water, op- tionally comprising solvent, are then pumped in a loop over the catalyst, oxygen is passed as a continuous stream through the reactor. In one embodiment of the invention the oxygen can be added in excess, the excess being released to the off gas, alternatively the oxygen can be added in an amount required to replenish the consumed oxygen.

As an example for a continuous slurry process, a continuous stirred tank reactor can be used in which the catalyst is present. The solution of the reactant(s), water, optionally comprising solvent and the oxidant are added continuously. Oxygen can be added in excess, off-gas can then be taken out continuously. In an alternative embodiment, oxygen can be added in an amount to replenish the consumed oxygen. The liquid reaction product can be taken off continuously through a filter in order to keep the catalyst in the reactor.

In a further example for a continuous fixed bed process, both the solution of reactant(s) and the oxidant are continuously fed to a trickle bed reactor containing the catalyst. In this case, it is possible to partly or fully recycle the gas and/or the liquid back to the reactor in order to achieve the desired conversion of reactant(s) and/or oxygen.

In a preferred embodiment, the process according to the invention is carried out in a continuous mode.

It has surprisingly been found that the process of the invention leads to selectivities of the alpha, beta unsaturated aldehyde (based on the alcohol of general formula (II)) in the range of over 90%, preferably over 93%, preferably over 95%, preferably over 97% more preferably over 99%.

Preferably the process according to the invention is conducted until a conversion of the alcohol of general formula (II) in the range of 10 to 99.99%, preferably in the range of 30 to 95%, and most preferably in the range of 50 to 80 % is obtained.

Preferably the process according to the invention is performed at a temperature in the range from 1 to 250 °C, preferably in the range from 5 to 150 °C, preferably in the range from 20 to 100 °C, more preferably in the range from 25 °C to 80 °C, preferably in the range from 30 to 70°C and more preferably in the range of 35 to 50 °C. In one embodiment of the invention, the process is performed at a temperature in the range of 40 to 80 °C.

The obtained crude product may be subjected to conventional purification measures, including distillation or chromatography or combined measures. Suitable distillation devices for the purifi cation of the compounds of formula (I) include, for example, distillation columns, such as tray columns optionally equipped with bubble cap trays, sieve plates, sieve trays, packages or filler materials, or spinning band columns, such as thin film evaporators, falling film evaporators, forced circulation evaporators, wiped-film (Sambay) evaporators, etc. and combinations thereof.

The invention is further illustrated by the following non-limiting examples: Examples - Catalyst preparation

Example C1

C1A - IMC preparation (step g) / PtBi was synthesized as follows (steps g-1 to g-3):

1 .2 mmol PtCU and 1 .2 mmol BiC were weighed out in an argon-filled glove box and dissolved in 10 ml. of THF by stirring. The reducing agent potassium triethylborohydride KBH(C2H₅)3 (1 .0 M in THF, Sigma-Aldrich) with 30 mol % excess was mixed with THF to form a 15 mL solution. Then the solution was drawn up into a syringe and injected into a solution of the reducing agent under vigorous stirring. The sample was dried under vacuum until most of the THF was gone. Hexane was then added to precipitate the PtBi-KCI powders. The sample was then washed three times with THF and hexane without contacting air. The product was then dried under vacuum for 2 h and transferred to the glove box. The product was placed into silica tubes, which were sealed under vacuum and then annealed at 400 °C for 6h. The resulting PtBi-KCI powders were analyzed with PXRD as described below. P-XRD analysis confirmed the IMC structure.

The KCI containing powders were then mixed with water and centrifuged until the solution did not contain any chloride (AgNC>3 test of the wash solution). PVP was then added and the solution was ultrasonicated.

C1 B - Preparation of a supported IMC catalyst

Step a): Support: 8,25 g of aluminium oxide (gamma-AhOs strands with a mean diameter of 1 .5 mm (commercially available from Exacer s.r.l. Italy), was heated to 550°C for 4 hours and main- tained at 550 °C for 1 hour.

Step c): 6,19 g of an aqueous suspension obtained in example C1A comprising 0,165 g of the PtBi IMC and 0,017 g PVP were ultrasonicated for 10 minutes. The suspension was then added to 8,25 g of the support and mixed with a spatula for approx.15 minutes. The catalyst was subse- quently dried at 80°C for 1 hour.

The distribution of the catalytically active metal Pt was determined with SEM-EDXS in a cross section of the strands: the majority of the Pt was located within 100 pm from the outer surface of the catalyst. The resulting catalyst was examined with XPS as described below. The XPS anal- ysis confirmed the IMC structure.

Example C2

C2A - IMC preparation (step g) / Pt₂Bi₃ was synthesized as follows (steps g-1 to g-3):

0.6 mmol PtCI₄ and 0.9 mmol BiC were weighed out in an argon-filled glove box and dissolved in 10 mL of THF by stirring. The reducing agent potassium triethylborohydride KBH(C2H₅)3 (1 .0 M in THF, Sigma-Aldrich) with 30 mol % excess was mixed with THF to form a 15 mL solution. Then the solution was drawn up into a syringe and injected into a solution of the reducing agent under vigorous stirring. The sample was dried under vacuum until most of the THF was gone. Hexane was then added to precipitate the Pt2Bi3-KCI powders. The sample was then washed three times with THF and hexane without contacting air. The product was then dried under vac- uum for 2 h and transferred to the glove box. The product was placed into silica tubes, which were sealed under vacuum and then annealed at 400 °C for 6h. The resulting Pt2Bi3-KCI powders were analyzed with PXRD as described below. P-XRD analysis confirmed the IMC structure.

The KCI containing powders were then mixed with water and centrifuged until the solution did not contain any chloride (AgNCh test of the wash solution). PVP was then added and the solution was ultrasonicated.

C2B - Preparation of a supported IMC catalyst

Step a): Support: 12,9 g of aluminium oxide (gamma-AhOs strands with a mean diameter of 1 .5 mm (commercially available from Exacer s.r.l. Italy), was heated to 550°C for 4 hours and main- tained at 550 °C for 1 hour.

Step c): 9,6 g of an aqueous suspension obtained in example C2A comprising 0,258 g of the Pt₂Bi₃ IMC and 0,026 g PVP were ultrasonicated for 10 minutes. The suspension was then added to 12,9 of the support and the support was spray impregnated at 500 mbar for 15 minutes in a rotary evaporator. The catalyst was subsequently dried at 80°C for 1 hour.

The distribution of the catalytically active metal Pt was determined with SEM-EDXS in a cross section of the strands: the majority of the Pt was located within 100 pm from the outer surface of the catalyst. The resulting catalyst was examined with XPS as described below. The XPS analysis confirmed the IMC structure.

Example C3

C3A - IMC preparation (step g) / PtBh was synthesized as follows (steps g-1 to g-3):

1 .2 mmol PtCI₄ and 2.4 mmol BiC were weighed out in an argon-filled glove box and dissolved in 10 ml. of THF by stirring. The reducing agent potassium triethylborohydride KBH(C2H₅)3 (1 .0 M in THF, Sigma-Aldrich) with 30 mol % excess was mixed with THF to form a 15 mL solution. Then the solution was drawn up into a syringe and injected into a solution of the reducing agent under vigorous stirring. The sample was dried under vacuum until most of the THF was gone. Hexane was then added to precipitate the PtBh-KCI powders. The sample was then washed three times with THF and hexane without contacting air. The product was then dried under vacuum for 2 h and transferred to the glove box. The product was placed into silica tubes, which were sealed under vacuum and then annealed at 400 °C for 6h. The resulting PtBh-KCI powders were ana- lyzed with P-XRD as described below. P-XRD analysis confirmed the IMC structure.

The KCI containing powders were then mixed with water and centrifuged until the solution did not contain any chloride (AgNCh test of the wash solution). PVP was then added and the solution was ultrasonicated. C3B - Preparation of a supported IMC catalyst

Step a): Support: 14,65 g of aluminium oxide (gamma-AhOs strands with a mean diameter of 1 .5 mm (commercially available from Exacer s.r.l. Italy), was heated to 550°C for 4 hours and main- tained at 550 °C for 1 hour.

Step c): 10,99 g of an aqueous suspension obtained in example C3A comprising 0,293 g of the PtBh IMC and 0,029 g PVP were ultrasonicated for 10 minutes. The suspension was then added to 14,65 g of the support and the support was impregnated at 500 mbar for 15 minutes in a rotary evaporator. The catalyst was subsequently dried at 80°C for 1 hour.

PXRD Analysis

The Pt-Bi materials were analyzed regarding their phase purity and structure with XRD using a Bruker D8 Advance diffractometer from Bruker AXS GmbH, Karlsruhe equipped with a Lynxeye XE 1 D-Detector, using variable slits, from 10° to 90° 2theta. The anode of the X-ray tube consisted of copper. To suppress the Cu radiation, a nickel filter was used. The following parameters were used: Voltage: 40 kV, Current: 40 mA, Step size: 0.02 ° 2theta, Scan speed 0.2 s/step, Soller slits (primary side): 2.5 °; Soller slits (secondary side): 2.5 °; Divergence slit: 0.17 °.

The phases present in each sample were identified by search and match of the data available from International Centre for Diffraction Data (ICDD, Version 2015).

XPS Analysis

XPS analysis was performed with a Phi Versa Probe 5000 spectrometer using monochromatic Al Ka radiation (50.4 W) with a spot size of 200x200 pm in standard configuration. The instrument work function was calibrated to give a binding energy (BE) of 84.00 eV for the Au 4f7/2 line of metallic gold and the spectrometer dispersion was adjusted to give a BE of 932.62 eV for the Cu 2p3/2 line of metallic copper. The built in Phi charge neutralizer system was used on all speci- mens. To minimize the effects of differential charging, all samples were mounted insulated against ground. Survey scan analyses were carried out with a pass energy of 1 17.4 eV and an energy step size of 0.5 eV. High resolution analyses were carried out on the same analysis area with a pass energy of 23.5 eV and an energy step size of 0.1 eV. Spectra have been charge corrected to the main line of the carbon 1 s spectrum set to 284.8 eV as a typical value quoted for the energy of the peak of adventitious hydrocarbon. All Spectra were analyzed using CasaXPS software version 2.3.20 using Shirley background subtraction. Relative sensitivity factors and transmission function as provided by the instrument manufacturer were used for quantification.

Claims

1 . Process for the preparation of alpha, beta unsaturated aldehydes of general formula (I)

• wherein the oxidant is oxygen and/or hydrogen peroxide, and

• wherein the catalyst comprises at least one intermetallic compound.

2. Process according to any of the preceding claims, wherein an alcohol according to formula (II) is used, wherein R₁, R₂ or R₃, independently of one another, are selected from H and CH₃.

3. Process according to any of the preceding claims, wherein an alcohol according to for- mula (II) is used, wherein R₃ is H and R₂ and R₁ are CH₃.

4. Process according to any of the preceding claims, wherein the liquid phase contains at least 50 weight-%, preferably at least 70 weight-% water based on the total weight of the liquid phase.

5. Process according to any of the preceding claims, wherein the oxidation is carried out at a temperature of 20 °C to 100 °C, preferably at a temperature of 20 °C to 70 °C.

6. Process according to any of the preceding claims, wherein the oxidation is carried out under a partial pressure of oxygen between 0.2 and 8 bar.

7. Process according to any of the preceding claims, wherein the intermetallic compound comprises at least one catalytically active metal and at least one promotor.

8. Process according to any of the preceding claims, wherein the intermetallic compound comprises a catalytically active metal selected from the group consisting of platinum, palladium and gold, preferably platinum.

9. Process according to any of the preceding claims, wherein the intermetallic compound is on a support.

10. Process according to any of the preceding claims, wherein the support is selected from the group consisting of carbonaceous materials and oxidic materials.

1 1. Process according to any of the preceding claims, wherein the support is selected from the group consisting of alpha aluminium oxide (0AI2O3), beta aluminium oxide (b-Aΐ2q3) and gamma aluminium oxide (Y-AI2O3).