WO2012075074A1

WO2012075074A1 - Layer-by-layer deposed multimetallic catalysts on a support

Info

Publication number: WO2012075074A1
Application number: PCT/US2011/062525
Authority: WO
Inventors: Philippe J Barthe; Steven Vanzutphen
Original assignee: Corning Incorporated
Priority date: 2010-11-30
Filing date: 2011-11-30
Publication date: 2012-06-07
Also published as: FR2967923A1

Abstract

This disclosure relates to a new metallic structure. This structure comprises a substrate (10) to which is bonded at least one first metallic layer (30) comprising at least one first metal, and is characterized in that the first metallic layer (30) comprises at least said first metal in the oxidized state bonded chemically to said substrate, a bifunctional organic layer (40) being bonded chemically via a first function suitable for bonding chemically to said first metal of the first metallic layer (30), and a second metallic layer (50), comprising at least one second metal in the oxidized state bonded chemically to said organic layer (40) via a second function suitable for bonding chemically to said second metal of the second metallic layer. This disclosure enables improvements in chemical synthesis by heterogeneous catalysis.

Description

LAYER-BY-LAYER DEPOSED MULTIMETALLIC

CATALYSTS ON A SUPPORT

[0001] This application claims the benefit of priority under 35 USC § 119 to French Patent Application Serial No. 1059920, filed November 30, 2010, the content of which is relied upon and incorporated herein by reference in its entirety.

[0002] The present disclosure relates essentially to an organometallic structure which can be used, in particular, as a catalyst, and to its method of production.

[0003] Document US 7, 189,433 discloses a film having alternating monolayers of a metal- metal bonded complex monolayer and an organic monolayer by layer-by-layer growth, said film being preparable by a preparation process comprising

- applying onto a surface of a substrate a first linker compound represented by the formula Gl-linker-G2, to produce a primer layer of the first linker compound;

in which formula Gl is selected from the group consisting of: CI₃S1 and SH; G2 is selected from the group consisting of: 4-pyridyl and 4-cyanophenyl; the linker is selected from the group consisting of: C1-C8 alkylene, C1-C8 alkenediyl, C1 -C8 alkynediyl and 1,4- arylene;

- applying onto this primer layer a metal-metal bonded complex, to produce a metal-metal bonded complex monolayer on the first primer layer, wherein the metal-metal bonded complex is selected from the group consisting of various compounds, represented by the chemical formulae set out, in particular, in claim 1 of that document, in which there are various axial ligands and equatorial ligands; M is a transition metal, and dicarboxylate bridging groups are also envisaged;

- that process also envisages applying onto the metal-metal bonded complex monolayer a second linker compound represented by the formula G3-linker-G4, to produce on the metal-metal bonded complex monolayer an organic monolayer;

in which formula G3 and G4 may be the same functional groups or different groups from those above for Gl and G2;

- optionally repeating these sequences to produce a layer-by- layer growth thin film having alternating monolayers of metal-metal bonded complex monolayers and an organic monolayer. [0004] The preferred transition metal of the metal-metal bonded complex is selected from the group consisting of: Cr₂ ⁴⁺, Μθ2⁴⁺, Re2⁴⁺, Re2⁵⁺, Ru2⁴⁺, Ru2⁵⁺, Ru2⁶⁺, Rh₂ ⁴⁺ and combinations thereof (see claim 2).

[0005] According to one particular embodiment, the first linker compound is selected from the group consisting of a compound represented by Cl₃-Si-dialkylene-pyridine for oxide surfaces, and a compound represented by the formula HS-dialkylene-pyridine for gold surfaces.

[0006] That document describes application in the solid state.

Summary

[0007] According to a first aspect, the present disclosure provides an organometallic structure comprising a substrate to which is bonded at least one first metallic layer comprising at least one first metal, characterized in that the first metallic layer comprises at least said first metal in the oxidized state bonded chemically to said substrate, a bifunctional organic layer being bonded chemically via a first function suitable for bonding chemically to said first metal of the first metallic layer, and a second metallic layer comprising at least one second metal in the oxidized state bonded chemically to said organic layer via a second function suitable for bonding chemically to said second metal of the second metallic layer.

[0008] According to one particular embodiment of this disclosure, the structure is characterized in that the first metallic layer is bonded chemically to a tie layer for bonding to the substrate.

[0009] According to one particular variant embodiment of this disclosure, the structure is characterized in that the tie layer for bonding to the substrate comprises a tie compound of formula:

Al— L-A2, in which:

Al is selected from a functional group for chemical bonding to the substrate, comprising at least one function selected from CI₃-S1, SH, or a combination of the two;

L is a linker selected from the group consisting of C1-C8 alkylene, C1 -C8 alkenediyl, C1-C8 alkynediyl and 1,4-arylene; A2 is selected from a functional group for chemical attachment to said second metallic layer, comprising at least one function selected from 4-pyridyl, 4-cyanophenyl or a combination of the two.

[0010] According to one particular embodiment of this disclosure, the structure is characterized in that the substrate comprises a surface layer comprising or consisting essentially of a metal oxide, more particularly selected from an aluminium oxide, a silicon oxide and a titanium oxide, advantageously a titanium oxide.

[0011] According to another particular embodiment of this disclosure, the structure is characterized in that the substrate has a facing surface that allows bonding, more particularly selected from a substantially planar surface - formed, for example, by a plate - and a non- planar surface - formed, for example, by a powder.

[0012] According to another particular embodiment of this disclosure, the structure is characterized in that the substrate has at least one bonding surface made of a material selected from a metal, an insulating material, a semiconductor, more particularly glass, quartz, aluminium, gold, platinum, a gold/palladium alloy, silicon, silicon on which a surface layer of silicon dioxide has been formed, and glass coated with a layer of indium tin oxide.

[0013] According to one particular variant embodiment, the structure is characterized in that the tie compound for attachment or tying to the substrate comprises a Ci₃-Si-alkylene-4- pyridine compound in which the alkylene group is CI to C8.

[0014] According to another particular variant embodiment, the structure is characterized in that the bifunctional ligand comprises a ligand of formula:

A3— L1-A4,

in which:

A3 is selected from a functional group for chemical bonding to the first metal or to the second metal, comprising at least one function selected from 4-pyridyl, 4-cyanophenyl, or a combination of the two;

LI is a linker selected from the group consisting of C1-C8 alkylene, C1 -C8 alkenediyl, C1-C8 alkynediyl and 1,4-arylene;

A4 is selected from a functional group for chemical bonding to the second metal or to the first metal, respectively, comprising at least one function selected from 4-pyridyl, 4- cyanophenyl, or a combination of the two. [0015] According to another particular feature, the structure is characterized in that the bifunctional ligand comprises a symmetrical ligand selected from:

a) 4-pyridyl-(Cl-C8)alkylene-4-pyridyl, more particularly trans-l,2-bis(4- pyridyl)ethylene

b) 4-cyanophenyl-(Cl-C8)alkylene-4-cyanophenyl, more particularly trans- l ,2-bis(4- cyanophenyl) ethylene.

[0016] According to another particular variant embodiment, the structure is characterized in that the first metal or the second metal or both are selected from the group comprising gold, palladium and an alloy of gold and palladium.

[0017] According to one particular feature, the structure is characterized in that the gold is in the form of a hydrogen tetrachloroaurate(III) compound.

[0018] According to another particular feature, the structure is characterized in that the palladium is in the form of a palladium(II) acetate compound, more particularly trimeric.

[0019] According to one particular embodiment of the organometallic structure according to this disclosure this structure comprises, on the second metallic layer, a second bifunctional organic layer bonded chemically via a first function suitable for bonding chemically to the second metal of the second metallic layer, and a third metallic layer, comprising at least one third metal in the oxidized state bonded chemically to said second organic layer via a second function suitable for bonding chemically to said third metal of the third metallic layer, so as to produce more complex structures.

[0020] According to a second aspect, the present disclosure relates to a method of producing the structure as defined above or as it results from the following description, said method being characterized in that:

a) a substrate is provided, comprising at least one bonding surface;

b) the substrate is bonded chemically to at least one first metallic layer comprising at least one first metal in the oxidized state;

c) at least one bifunctional organic layer is bonded chemically to said first metallic layer; and

d) lastly, at least one second metallic layer comprising at least one second metal in the oxidized state is bonded chemically to said bifunctional organic layer. [0021] According to one particular embodiment of the method according to this disclosure, steps b) and c) above can be carried out sequentially and repeatedly, in order to produce more complex structures.

[0022] According to one particular variant embodiment, the method is characterized in that the chemical bonding of the metal takes place by immersion of the substrate or of an intermediate structure of the substrate in a solution comprising the metal in the oxidized state.

[0023] According to another particular embodiment of this disclosure, said metallic layer, referred to as substantially a monolayer or "monoatomic layer", is formed, for example, according to the layer-by-layer formation technique, of the type described in US 7,189,433, to which a person skilled in the art may refer.

[0024] In particular, the duration of immersion of the substrate or of an intermediate structure of the substrate in a solution comprising the metal to be deposited, in the oxidized state, is selected so as to produce, the formation,substantially, of said monolayer or monoatomic layer.

[0025] In the context of the present description and of the claims, the expression "monolayer or monoatomic layer" is intended to denote the formation of a layer of metal in which the metal atoms are deposited adjacently to one another in such a way as to form a single, substantially monoatomic layer, and in which there are substantially no metal atoms stacked atop one another.

[0026] Other particular variant embodiments of the method will be apparent from the description of the structure described above, or from the description below, including the examples, which form an integral part of the present disclosure.

[0027] According to a third aspect, the present disclosure relates to the use of the structure as defined above, or as resulting from the following description, as a catalyst, particularly for producing a reactor or a microreactor, especially for carrying out chemical reactions.

[0028] In the context of the present description and of the claims, the expression "microreactor" is intended to denote microreactors also known as micro structured reactors, and the like, which are devices having enclosed fluid channels for fluid processing, the channels having cross-sectional dimensions in the several millimeter to sub-millimeter range. Multiple independent sets of fluid channels may be provided within a given microreactor, and may be used for various purposes, such as for parallel processing, or for feeding process fluid and heat exchange fluid and so forth. A microreactor of variable capacity can also be obtained by stacking-up units of individual microrector as is known to one Skilled in the microreactor art, notably from US2003/0192,587 Al of Corning Inc. The substrate of the microreactor can be made in a material selecte from glass, glass-ceramic and ceramic.

[0029] According to one particular embodiment, this use of the structure is intended for carrying out a chemical oxidation reaction, selected for example from an oxidation reaction of an alcohol to an aldehyde or to an acid, an oxidation reaction of an aldehyde to an acid, an oxidation reaction of an amine to an amide or of an amide to a nitro; or a chemical reduction reaction, selected for example from a reduction reaction of an acid or an aldehyde to an alcohol, a reduction reaction of an acid to an aldehyde, a reduction reaction of a nitro or of an amide to an amine, or a reduction reaction of an amide to an amine.

[0030] According to a fourth aspect, the present disclosure likewise encompasses a catalyst characterized in that it comprises an organometallic structure as defined above or as resulting from the following description, including the examples, which form an integral part of the present disclosure.

[0031] It will be appreciated that this disclosure allows infinite combinations of chemical reactions to be carried out by catalysis.

[0032] It will also be appreciated that this disclosure solves all of the technical problems set out above, in a way which is simple, safe, reproducible and reliable, and can be used on an industrial scale.

[0033] The present disclosure will now be described with the aid of a number of exemplary embodiments and with reference to the attached figures, which show currently preferred embodiments of this disclosure, which are given simply by way of illustration and which do not in any way limit the scope of this disclosure.

[0034] In the examples, unless otherwise stated, the percentages are given in weight, the temperature is given in °C or is room temperature, namely 22°C plus or minus 3°C, and the pressure is atmospheric pressure. Description of the Drawings

[0035] Figure 1 relates to a first currently preferred embodiment of a structure according to the present disclosure, which comprises first forming, on at least one facing surface of a clean substrate, such as a glass, ceramic or glass-ceramic substrate, a tie layer for attachment to the substrate, for example a silane-pyridine layer, in a first step; then, in a second step, depositing a metal in the oxidized state at least on one facing surface, by immersion in a solution of the metal in oxidized form, thus forming substantially a first layer, in particular a monolayer, which is metallic and is bonded chemically to the tie layer; and then, in a third step, forming an organic layer comprising a bifunctional ligand, as schematized, which is bonded chemically to the first metallic layer; and then, in a fourth step, depositing, by chemical bonding, a second metal, in the form of a layer, in particular a monolayer of the second metal, by immersion in a second solution containing the second metal in oxidized form;

[0036] Figure 2 represents a type of chemical reaction which can be implemented, for example, for the selective oxidation of benzyl alcohol to benzaldehyde with the aid of the organo metallic structure described in Figure 1 ;

[0037] Figure 3 shows a curve of conversion of benzyl alcohol in per cent by weight, on the ordinate, in relation to the reaction time, expressed in hours, on the abscissa, respectively, for: a) a single layer of gold (Au) on a substrate coated with a layer of metal oxide, in this case titanium dioxide, a structure denoted TSA;

b) a single layer of palladium on the same substrate, a structure denoted TSP;

c) a combined layer of a first metallic layer of gold (Au), followed by an organic layer of bifunctional ligand of Figure 1, and by the deposition of a second metal, palladium (Pd), a structure denoted TSNAP; and

d) an inverse combination first of a first metal, palladium (Pd), followed by a layer of the same bifunctional ligand shown in Figure 1, then by the deposit of a layer of a second metal, gold (Au), a structure denoted TSPNA;

[0038] Figure 4 shows, for the same structures as implemented for Figure 3, the selectivity curve for the same reaction of conversion of benzyl alcohol to benzaldehyde, the selectivity with respect to benzaldehyde being shown as a percentage on the ordinate, relative to the reaction time, expressed in hours, on the abscissa; and

[0039] Figure 5 also shows, for the same structures as implemented for Figure 3, the yield of benzaldehyde, as a percentage by weight, on the ordinate, relative to the reaction time, expressed in hours, on the abscissa. [0040] This disclosure will now be described in greater detail with the following examples of production of various structures, and also of catalytic reactions, particularly for the selective oxidation of benzyl alcohol to benzaldehyde, as shown in Figure 2, these examples being given solely by way of illustration, and thus not in any way limiting the scope of this disclosure. In the examples, the percentages are given by weight, the temperature is in degrees C, and the pressure is atmospheric pressure, unless indicated otherwise.

Example 1

[0041] Formation of a simple intermediate structure using a glass substrate (10) with a silane- pyridine tie layer (20) and a single metal layer (30) comprising gold, referred to as GSA (Glass-Silane-Au) structure

[0042] With reference to Figure 1, a substrate (10), here in the form of a glass plate, for example of type Eagle XG®, sold by Corning® Inc., is coated on at least one face, in practice on the two visible faces, with a tie layer (20), in this case a silane-pyridine layer of formula Ci₃Si-dialkylene-pyridine, by immersing the glass plate in a silane solution S, using 1 ml of 4-[2-(trichlorosilyl)ethyl]pyridine, at 25% in toluene, which is subsequently dissolved in 50 ml of dry toluene. It is noted that, on Figure 1, the deposit on the second face is not shown, for simplification, although the process of complete immersion of the substrate necessarily leads to the formation of a deposit on each face.

[0043] This is followed by rinsing, for example, with isopropanol, and by drying in a stream of air, and then the glass plate (10), comprising the silane tie layer (20) on its two faces, is placed in a solution of a first metal, here comprising gold in oxidized form, this solution comprising 100 mg of hydrogen tetrachloroaurate(III),which is available commercially, in solution in 50 ml of tetrahydrofuran (THF), and nitrogen is bubbled through for 5 minutes, to form a layer (30) of the first, oxidized metal, again on both faces, in this case of gold (Au). Owing to the controlled duration of the immersion, a metal monolayer is substantially formed.

[0044] This gives a first structure referred to as GSA.

Example 2

[0045] Preparation of a simple intermediate structure similar to Example 1 but comprising palladium as the metal, referred to as GSP (Glass-Silane-Palladium). [0046] The procedure described in Example 1 is repeated, but the gold solution is replaced by a palladium solution P comprising 100 mg of trimeric palladium(II) acetate in solution in 50 ml of tetrahydrofuran, or THF.

[0047] The resultant structure is abbreviatedly termed GSP.

Example 3

[0048] Preparation of a structure comprising, on a glass substrate (10), denoted G, a silane attachment layer (20), denoted S, a first layer (30) of a first metal, gold, denoted A, a bifunctional organic ligand layer (40), denoted N, and, lastly, a layer of a second metal (50), in this case palladium, denoted P, the structure being referred to abbreviatedly as GSANP.

[0049] The GSA structure obtained in Example 1 is first placed in a solution of bifunctional organic ligand, of symmetrical type, for example, comprising 200 mg of trans- l,2-bis-4- (pyridyl)ethylene, 97% grade, available commercially, for example, from Sigma Aldrich, in solution in 50 ml of THF, and is then rinsed with isopropanol and dried. Here a ligand layer, referenced 40 and also denoted N, is obtained.

[0050] The substrate, now of GSAN structure, is then placed in a solution of a second metal, in this case palladium (P), which is identical to the palladium solution described in Example 2, for 1-2 minutes.

[0051] Then a final rinsing with THF and isopropanol is carried out, and the resulting plate structure is dried and stored.

[0052] This produces the title structure, of type GSANP in abbreviation.

Example 4

[0053] Production of a glass structure with silane attachment layer S, a monolayer of a first metal, palladium, a bifunctional organic ligand layer, denoted N, and then a layer of a second metal, gold, the structure being referred to as of GSPNA type.

[0054] The procedure as described in Example 3 is repeated, but the order in which the metallic layers are deposited is reversed, starting first with the layer of palladium P and then, following the application of the bifunctional organic ligand, the layer of a second metal, gold. This produces a structure of GSPNA type. Exam le 5

[0055] Production of an intermediate structure comprising, on the substrate, a metal oxide layer, in this case, for example, titanium oxide, denoted T, with a single metal, in this case gold.

[0056] The procedure as described in Example 1 is repeated, but first of all a dense titanium dioxide layer, denoted T, is attached to the glass (G) substrate (10).

[0057] The procedure of attachment of a dense titanium dioxide layer, denoted T, is the following:

The raw materials, which are used, are:

- isopropanol, titanium tetra-n-propoxide, pentanedione-2,4 and acetic acid.

[0058] Titanium tetra n-propoxide precursor was prepared according to an esterification reaction by complexation via chelating ligand, such as 2,4-pentanedione.

[0059] 10.26 g of titanium precursor are added to 48.25 ml of isopropanol in a 120 ml glass bottle, and mixed with a stirring plate during 50 minutes resulting in a homogeneous solution.

[0060] Still with stirring solution, 7.01 g of pentadione is added and mixed during one hour.

[0061] Finally, 4.2 g of acetic acid is added and mixed during 30 minutes.

[0062] The bottle is closed with a cap and introduced in an oven at 160°C overnight (about 17 hours). Then, substrate (10) of glass G of example 1 , commercially available by CORNING, Eagle XG® is used cut into slides of 0.7 mm x 2.5 cm x 7 cm. These slides are cleaned manually by blowing nitrogen, then washed with lab soap and rinsed with distilled water and dried under infrared heating.

[0063] Then, thin films precursor solutions were deposited by dip coating, at withdrawal speeds between 3 and 15 cm/minute. The obtained films were heated in a furnace at 60°C for two hours and at 550°c for one hour, thereby providing a thin dense titanium dioxide layer, denoted T, attached on the glass substrate (10).

[0064] This substrate (10) comprising the dense layer of titanium dioxide T is first of all cleaned with a detergent, washed with ethanol or acetone and then placed for 2 minutes in a silane solution S as described in Example 1, to form the silane tie layer (20). [0065] Subsequently, the support comprising the silane tie layer (20) is rinsed with isopropanol and dried, and the structure is then placed in the solution of a first metal, in this case gold, for 1-2 minutes. This gives the layer of the first metal (30), denoted A.

[0066] A final rinse with THF and isopropanol is carried out, and the resulting structure is dried and stored. This structure, which comprises on the substrate a titanium dioxide layer T, is denoted of TSA type, containing only a single metal, in this case gold (Au), denoted A.

Example 6

Preparation of an intermediate structure of TSP type

[0067] The procedure as described in Example 5 is repeated, but the only metal deposited is palladium, denoted P, in place of gold, under the deposition conditions described in Example 2.

[0068] This gives a structure of TSP type.

Example 7

[0069] Preparation of a structure with a chemical composition TSANP, according to this disclosure

[0070] The procedure as described in Example 5 is repeated to give the structure of type TSA, which is immersed, after cleaning, in a bifunctional ligand solution, as described in Example 3, to form an organic functional ligand layer (40), N, on the layer of gold, A, and then a layer (50) of a second metal, in this case palladium, denoted P, is deposited, as described in Example 3.

[0071] This gives a structure of TSANP type- Example 8

[0072] Production of a structure with a chemical composition TSPNA, according to this disclosure

[0073] To obtain a structure with a chemical composition of TSPNA type, the procedure as described in Example 7 is repeated, but first the layer (30) of palladium (P) is deposited, after which the bifunctional ligand layer (40) (N) is formed, and, finally, the gold layer (50), denoted A, is deposited, this taking place under the same deposition conditions as those described in the preceding examples for each of the layers.

Example 9

[0074] Analytical assay of the amount of metal deposited on the structure with the different structures produced in Examples 1 to 4 and then in Examples 5 to 8

[0075] Reported in Table 1 below are the results of ICP-MS analysis, which analysis is well known to a person skilled in the art, on the structures of Examples 1 to 4, identified as indicated manually in Examples 1 to 4, by immersing the structure mid-way, for example manually, into 25 ml of an acid solution, to dissolve the metal on a single face.

[0076] From Table 1 below it is apparent that, in the successive deposition of two metallic layers, referred to as GSANP and GSPNA, in Examples 3 and 4 according to the present disclosure, the deposition first of palladium, followed by the deposition of gold, or vice versa, allows a significant quantity of gold and of palladium to be bonded.

[0077] Reported in Table 2 below are the same analytical results with the structures obtained in Examples 5 to 8, in which the substrate, in this case of Eagle XG® glass from Corning, is used with a surface layer of metal oxide, in this case of titanium dioxide, denoted T.

As Table 2 indicates, it is observed that, in the case of deposition of two metallic layers, A followed by P, or P followed by A, there is a significant bonding of the second metal.

[0078] It is also observed that, when deposition takes place directly on a substrate (10) such as glass, a deposition of gold (Example 1) of between 50 and 100 μg is obtained, and substantially the same result is obtained for deposition with palladium (Example 2).

[0079] Conversely, when gold is deposited before palladium, as described in Example 3, there is very little palladium deposited (3 μg/25 ml). This may be explained by the fact that the gold(III) in solution is reduced to gold(I) on the surface, which is therefore virtually unable to accommodate a second pyridine ligand, such that the layer of palladium is not actually able to form.

[0080] Conversely, and surprisingly, as shown in Table 2, when the substrate is coated with a layer of metal oxide, such as T1O2, denoted T, the order in which the metals are deposited is less important, except that the deposition of palladium is lower than the deposition of gold in the case of the first metallic layer, with the amount of the second metal deposited being substantially the same.

Table 1 :

Table 2 :

Example 10

[0081] Catalytic performance of the metallic bilayer structures according to this disclosure, in comparison with monolayer structures

[0082] Structures of Examples 5 to 8 were tested for their catalytic performance in selective oxidation of benzyl alcohol to benzaldehyde, as follows:

[0083] The structures as described, respectively, in Examples 5 to 8 are tested in an autoclave for the selective oxidation of benzyl alcohol, in air, to benzaldehyde, at 130°C, under an air pressure of 20 bar, in accordance with the reaction scheme shown in Figure 2.

[0084] To accomplish this, two structures made of Eagle XG®

glass from Corning, with dimensions of 7.5 x 2.5 cm, coated on both sides with the layers indicated, were used for each test.

[0085] The results are summarized in attached Figures 3 to 5. as a function of the reaction time at 130°C in the autoclave. [0086] These results clearly show that the monometallic systems such as TSA and TSP of Examples 5 and 6 have a much lower catalytic activity by comparison with the multilayer thin- film catalysts of types TSANP and TSPNA, according to this disclosure, of Examples 7 and 8; see Figure 3.

[0087] With regard to the selectivity with respect to benzaldehyde, as shown in Figure 4, the same tendency is reproduced, with both the monometallic systems being largely inferior to the multilayer systems containing at least two metals. Interestingly, the multilayer structure according to this disclosure of type TSPNA exhibits a very selective behaviour with a low residence time, in other words 100% selectivity for benzaldehyde after a reaction time of 1 hour, signifying 5.5% conversion of benzyl alcohol, and the selectivity remains high (72%) up to 10% conversion.

[0088] Looking at the yield of benzaldehyde, as shown in Figure 5, the multilayer catalysts according to this disclosure comprising at least two metal layers exhibit, surprisingly, much better performance than the corresponding metals alone.

[0089] In the first 5 hours of reaction, the benzaldehyde yield is between 5% and 10% for the metallic multilayer systems according to this disclosure, and less than 1% for the monometallic systems.

[0090] These experiments constitute striking proof that multimetallic systems according to this disclosure, produced in particular by a layer-by- layer deposition approach, represent high-performance catalysts.

[0091] In these tests, a factor of up to 6 with regard to the conversion of benzyl alcohol, a factor of up to 10 with regard to the selectivity for benzaldehyde, and a factor of up to 10 with regard to the yield of benzaldehyde, were observed between the monometallic system and the bimetallic system.

[0092] Accordingly, this disclosure produces results which are particularly unexpected to a person skilled in the art.

[0093] It will be appreciated that this structure according to this disclosure does indeed allow the technical advantages to be obtained that were set out earlier in the introductory part of the present description. [0094] Moreover, the procedure for producing the structure according to this disclosure is simplified and rationalized, and the procedure is not only rapid but also safe, reproducible and reliable, while ensuring a high catalytic yield.

[0095] It will therefore be appreciated that this disclosure allows a solution to all of the technical problems set out earlier, in a way which is simple, reproducible, reliable and can be used on an industrial scale.

[0096] The methods of use and/or the devices described herein are used generally in the implementation of any catalytic process which comprises mixing, separating, extracting, crystallizing, precipitating or treating, in any way, fluids or mixtures of fluids, including multiphase mixtures of fluids, and including fluids or mixtures of fluids, including multiphase mixtures of fluids, which also contain solids, in a micro structure. The process may include a physical process, a chemical reaction, defined as being a process which leads to the interconversion of organic, inorganic or organic and inorganic species, a biochemical process, or any form of treatment. The following, non-limiting list of reactions may be carried out with the processes and/or devices described: oxidation; reduction; substitution; removal; addition; ligand exchange; metal exchange; and ion exchange. More specifically, the reactions in the following, non-limiting list may be conducted with the processes and/or devices described: polymerization; alkylation; dealkylation; nitration; peroxidation; sulphoxidation; epoxidation; ammoxydation; hydrogenation; dehydrogenation; organometallic reactions; chemistry of precious metals/homogeneous catalysis reactions; carbonylation; thiocarbonylation; alkoxylation; halogenation; dehydrohalogenation; dehalogenation; hydroformylation; carboxylation; decarboxylation; amination; arylation; peptide coupling; aldol condensation; cyclocondensation; dehydrocyclisation; esterification; amidation; heterocyclic synthesis; dehydration; alcoholysis; hydrolysis; ammonolysis; etherification; enzymatic synthesis; ketalisation; saponification; isomerisation; quaternisation; formylation; phase transfer reactions; silylations; synthesis of nitriles; phosphorylation; ozonolysis; chemistry of azides; metathesis; hydrosilylation; coupling reactions; and enzymatic reactions.

[0097] The embodiments shown in Figures 1 to 5 form an integral part of this disclosure and should be considered only as examples. Various changes in form, in conception or in disposition may be made to this disclosure without departing from the spirit or from the scope of this disclosure, which is defined by the claims which follow.

Claims

1. A structure comprising a substrate (10) to which is bonded at least one first metallic layer (30) comprising at least one first metal, characterized in that the first metallic layer (30) comprises at least said first metal in the oxidized state bonded chemically to said substrate, a bifunctional organic layer (40) being bonded chemically via a first function suitable for bonding chemically to said first metal of the first metallic layer (30), and a second metallic layer (50), comprising at least one second metal in the oxidized state bonded chemically to said organic layer (40) via a second function suitable for bonding chemically to said second metal of the second metallic layer.

2. Structure according to Claim 1, characterized in that the first metallic layer (30) is bonded chemically to a tie layer(20) for attachment to the substrate (10).

3. Structure according to Claim 2, characterized in that the tie layer(20) for attachment to the substrate (10) comprises a tie compound of formula Al— L-A2, in which:

L is a linker selected from the group consisting of C1-C8 alkylene, C1 -C8 alkenediyl, C1-C8 alkynediyl and 1,4-arylene;

A2 is selected from a functional group for chemical bonding to said second metallic layer, comprising at least one function selected from 4-pyridyl, 4-cyanophenyl, or a combination of the two.

4. Structure according to any of Claims 1 to 3, characterized in that the substrate (10) comprises a surface layer comprising or consisting essentially of a metal oxide, more particularly selected from an aluminium oxide, a silicon oxide and a titanium oxide, advantageously a titanium oxide.

5. Structure according to any of Claims 1 to 4, characterized in that the substrate (10) has a facing surface that allows bonding, more particularly selected from a substantially planar surface - formed, for example, by a plate - and a non-planar surface - formed, for example, by a powder.

6. Structure according to any of the preceding claims, characterized in that the substrate (10) has at least one bonding surface made of a material selected from a metal, an insulating material, a semiconductor, more particularly glass, quartz, aluminium, gold, platinum, a gold/ palladium alloy, silicon, silicon on which a surface layer of silicon dioxide has been formed, and glass coated with a layer of indium tin oxide.

7. Structure according to any of Claims 2 to 6, characterized in that the compound of the tie layer (20) for attachment to the substrate (10) comprises a Cl₃-Si-alkylene-4-pyridine compound in which the alkylene group is CI to C8.

8. Structure according to any of Claims 1 to 7, characterized in that the bifunctional ligand layer (40) comprises a ligand of formula A3— L1 -A4, in which:

A4 is selected from a functional group for chemical bonding to the second metal or to the first metal, respectively, comprising at least one function selected from 4-pyridyl, 4- cyanophenyl, or a combination of the two.

9. Structure according to Claim 7, characterized in that the bifunctional ligand layer (40) comprises a symmetrical ligand selected from:

a) 4-pyridyl-(Cl -C8)alkylene-4-pyridyl, more particularly trans- l,2-bis(4- pyridyl)ethylene

b) 4-cyanophenyl-(Cl-C8)alkylene-4-cyanophenyl, more particularly trans- l,2-bis(4- cyanophenyl) ethylene.

10. Structure according to any of the preceding claims, characterized in that the first metal or the second metal or both are selected from the group containing gold, palladium and an alloy of gold and palladium.

1 1. Structure according to Claim 10, characterized in that the gold is in the form of a hydrogen tetrachloroaurate(III) compound.

12. Structure according to Claim 10, characterized in that the palladium is in the form of a palladium(II) acetate compound, more particularly trimeric.

13. Method of producing the structure as defined in any one of the preceding claims, characterized in that:

a) a substrate (10) is provided, comprising at least one bonding surface; b) the substrate (10) is bonded chemically to at least one first metallic layer (30) comprising at least one first metal in the oxidized state;

c) at least one bifunctional organic layer (40) is bonded chemically to said first metallic layer; and

d) lastly, at least one second metallic layer (50) comprising at least one second metal in the oxidized state is bonded chemically to said bifunctional organic layer.

14. Method according to Claim 13, characterized in that the chemical bonding of the metal takes place by immersion in a solution comprising the metal in the oxidized state.

15. Use of the structure according to any one of Claims 1 to 14 as a catalyst, particularly for producing a reactor or a microreactor.

16. Use of the structure, according to Claim 15, for carrying out a chemical oxidation reaction, selected for example from an oxidation reaction of an alcohol to an aldehyde or to an acid, an oxidation reaction of an aldehyde to an acid, an oxidation reaction of an amine to an amide or of an amide to a nitro; or a chemical reduction reaction, selected for example from a reduction reaction of an acid or an aldehyde to an alcohol, a reduction reaction of an acid to an aldehyde, a reduction reaction of a nitro or of an amide to an amine, or a reduction reaction of an amide to an amine.

17. Catalyst characterized in that it comprises a structure as defined in any one of Claims 1 to 12.