US20190276941A1

US20190276941A1 - Selective Electrochemical Hydrogenation of Alkynes to Alkenes

Info

Publication number: US20190276941A1
Application number: US16/334,132
Authority: US
Inventors: Bernhard Schmid; Günter Schmid; Christian Reller
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2016-09-22
Filing date: 2017-08-16
Publication date: 2019-09-12
Also published as: CN109790631A; EP3481973A1; AU2017329370B2; WO2018054612A1; EP3481973B1; AU2017329370A1; DE102016218230A1

Abstract

Various embodiments include a method for the partial electrochemical hydrogenation of alkynes of the chemical formula (I) to alkenes,

- wherein R and R′ are selected from inorganic and/or organic radicals, the method comprising: hydrogenating the compound of the chemical formula (I) on a copper-containing electrode.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Stage Application of International Application No. PCT/EP2017/070699 filed Aug. 16, 2017, which designates the United States of America, and claims priority to DE Application No. 10 2016 218 230.7 filed Sep. 22, 2016, the contents of which are hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The present disclosure relates to electrochemistry. Various embodiments may include methods for the partial electrochemical hydrogenation of alkynes of the chemical formula (I) to alkenes,

- wherein R and R′ are selected from inorganic and/or organic radicals.

BACKGROUND

Alkenes such as ethene and propene are currently produced mainly by the catalytic cracking of crude oil (naphtha). An alternative approach is the partial hydrogenation of alkynes (e.g. ethyne). These may also be prepared from coal or carbides, for example, and are thus not dependent on crude oil. However, problems of selectivity occur in classical hydrogenation. Frequently, over-reduction to alkanes occurs. The hydrogen required for the hydrogenation is currently also obtained from coal gasification or steam reforming and is therefore also closely linked with oil production.
The catalytic hydrogenation of alkynes has been achieved to date by specifically poisoned noble metal catalysts. An example of this is the Lindlar catalyst, which is a palladium catalyst poisoned with lead and quinoline. Another possibility is the “Birch analog reduction” which is conducted with a solution of alkali metals in liquid ammonia. The latter process is very expensive but selective for E-alkenes.
Novel approaches for producing hydrocarbons from carbon dioxide or carbon monoxide for example, are apparent in the context of the electrification of the chemical industry. Here, electrification of the chemical industry means carrying out processes electrochemically which up to now are carried out by classical thermal methods or are currently not possible. For instance, the electrochemical hydrogenation of ethyne to ethene is also known from X. Song, H. Du, Z. Liang, Z. Zhu, D. Duan, S. Liu, Int. J. Electrochem. Sci., 2013, 8, 6566-6573. However, the authors here use exclusively electrodes composed of the noble metal palladium and the substrate choice is also limited to ethyne.

SUMMARY

The teachings of the present disclosure describe simple and readily accessible methods for producing alkenes from alkynes which preferably proceeds without expensive noble metals. For example, a partial reduction of alkynes can be performed by an electrochemical method using a Cu electrode in water-based electrolytes. The electrode can be constructed either as a solid electrode or as a gas diffusion electrode here. Due to the better substrate availability of alkynes, the latter is particularly suitable. The methods exhibit high selectivity and activity here, even in the case of non-activated alkynes and challenging substrates having electron donating groups and/or streric hindrance.
For example, some embodiments include a method for the partial electrochemical hydrogenation of alkynes of the chemical formula (I) to alkenes,

- wherein R and R′ are selected from inorganic and/or organic radicals,
- wherein the compound of the chemical formula (I) is hydrogenated on a copper-containing electrode.

In some embodiments, the inorganic and/or organic radical is selected from —H, -D, substituted or unsubstituted alkyl, alkenyl, alkynyl and/or aryl radicals, —OH, —OR*, —SH, —SR*, —NH₂, —NR*R*, —COOH, —COOR*, —CHO, —COR*, —PH₂, —PR*R*, —F, —Cl, —Br, —I, —NO and —NO₂, where R* and R* are organic and/or inorganic radicals.
In some embodiments, neither R nor R′ are —H or -D.
In some embodiments, the alkyne of the chemical formula (I) comprises no electron-withdrawing radicals.
In some embodiments, the electron-withdrawing radicals are selected from —COOH, —COOR* and fluorinated alkyl and/or aryl radicals.
In some embodiments, the alkyne of the chemical formula (I) comprises no further reducible functional groups apart from the triple bond.
In some embodiments, the hydrogenation is carried out with a proton donor selected from water and alcohols having 1 to 20 carbon atoms.
In some embodiments, the copper-containing electrode is configured as a gas diffusion electrode, wherein the alkyne of the chemical formula (I) is gaseous.
Some embodiments include the use of a copper-containing electrode for the partial electrochemical hydrogenation of alkynes of the chemical formula (I) to alkenes,

- wherein R and R′ are selected from inorganic and/or organic radicals.

As another example, some embodiments include a device for the partial electrochemical hydrogenation of alkynes of the chemical formula (I) to alkenes,

- wherein R and R′ are selected from inorganic and/or organic radicals, comprising: an electrolysis cell (1) comprising a copper-containing electrode, which is configured to reduce the alkyne of the chemical formula (I) to alkene; a source of the alkyne of the chemical formula (I) (3) which is configured to provide the alkyne of the chemical formula (I); and a first feeding device (2) for the alkyne of the chemical formula (I) which is configured to feed the alkyne of the chemical formula (I) from the source of the alkyne of the chemical formula (I) to the electrolysis cell.

In some embodiments, the copper-containing electrode is configured as a gas diffusion electrode, wherein the first feeding device (2) for the alkyne of the chemical formula (I) feeds the alkyne of the chemical formula (I) to the gas diffusion electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

The attached drawings are intended to elucidate embodiments of the present teachings, and to provide further understanding thereof. In combination with the description, they serve to explain concepts and principles of the teachings herein. Other embodiments and many of the advantages specified are apparent in relation to the drawings. The elements of the drawings are not necessarily drawn to scale with respect to one another. Identical, functionally identical, and equivalent elements, features, and components are each provided with the same reference symbols in the figures of the drawings, unless otherwise stated.

The FIGURE shows a schematic representation of a device incorporating teachings of the present disclosure.

DETAILED DESCRIPTION

Some embodiments include a method for the partial electrochemical hydrogenation of alkynes of the chemical formula (I) to alkenes,

- wherein R and R′ are selected from inorganic and/or organic radicals,
  wherein the compound of the chemical formula (I) is hydrogenated on a copper-containing electrode.

Some embodiments include the use of a copper-containing electrode for the partial electrochemical hydrogenation of alkynes of the chemical formula (I) to alkenes,

- wherein R and R′ are selected from inorganic and/or organic radicals.

Some embodiments include a device for the partial electrochemical hydrogenation of alkynes of the chemical formula (I) to alkenes,

All chemical compounds comprising a triple bond between 2 carbon atoms are referred to as alkynes. The teachings herein therefore are not limited to ethyne but can be applied to other alkynes. A general scheme of the electrochemical reaction of alkynes of the chemical formula I is as follows:
wherein the H⁺ ions depicted can instead also be D⁺ ions for example.
The good selectivity arises in this case due to the low reactivity of the alkenes forming to electrohydrogenation with Cu electrodes. In particular, electronically deactivated internal alkenes such as crotyl alcohol (trans-2-butenol) appeared inert to over-reduction.
The copper-containing electrode is not especially limited and may comprise copper in addition to other constituents, for example other metals and/or ceramics as substrate, but may also consist of copper. It may also be chemically treated, for example for oxide formation. It can also be configured as a solid electrode or as a gas diffusion electrode. Due to the greater substrate availability of alkynes, the latter, i.e. the gas diffusion electrode, is particularly suitable, especially for gaseous alkynes such as ethyne, propyne, 1-butyne or 2-butyne. In contrast to palladium electrodes, the present copper-containing electrodes are much more cost effective.
For example, a copper-containing electrode can be formed by depositing a layer containing a Cu⁺/Cu-comprising catalyst on a non-copper substrate, as described in DE 10 2015 203 245, or also by depositing the layer on a copper substrate. The Cu⁺/Cu-comprising catalyst is also referred to below as copper/copper ion catalyst, copper catalyst or similar and also simply as catalyst, unless it appears otherwise from the text, such that these terms are to be understood to be synonymous in the context of the present disclosure.
The non-copper substrate is also referred to simply as substrate, unless it appears otherwise from the text. It is also not excluded here that the non-copper substrate comprises copper, as long as it does not consist substantially only of copper. For instance, the substrate may also consist of brass or comprise brass for example. For instance, the non-copper substrate comprises, for example, less than 60% by weight copper, based on the total weight of the substrate, less than 50% by weight, or less than 40% by weight and even less than 20% by weight, for example no copper at all.
In some embodiments, in the production of an electrode of this kind, all conductive substrates can be used. In some embodiments, the substrate comprises at least one metal such as silver, gold, platinum, nickel, lead, titanium, nickel, iron, manganese or chromium or alloys thereof such as stainless steels and/or at least one non-metal such as carbon, Si, boron nitride (BN), boron-doped diamond, etc., and/or at least one conductive oxide such as indium tin oxide (ITO), aluminum zinc oxide (AZO) or fluorinated tin oxide (FTO), for the production of photoelectrodes for example, and/or at least one polymer based on polyacetylene, polyethoxythiophene, polyaniline, or polypyrrole for the production of polymer-based electrodes.
The Cu⁺/Cu-comprising catalyst can be produced in various ways and is not particularly limited, wherein the various production methods of the Cu⁺/Cu-comprising catalyst can also be effected on copper substrates. In some embodiments, electroreduction catalysts can be obtained if the catalyst is deposited in situ on the electrode substrate. An ex situ deposition in accordance with the invention is not excluded however. The substrate must not necessarily comprise copper or be copper in this case, but can be any conductive material, especially also including conductive oxides. Particular preference is given to porous configurations of such an electrode in order to obtain gas diffusion electrodes.
In some embodiments, a charge compensation in the Cu⁺/Cu-comprising catalyst can be effected by incorporating anions present in solution during production, for example hydroxide ions (OH⁻), O₂ ⁻, halide ions (halogen-), for example fluoride, chloride, bromide, iodide, sulfate, hydrogencarbonate, carbonate or phosphate, etc.
In some embodiments, the layer comprising copper can also be deposited on the surface of the electrode from a solution comprising copper ions. In some embodiments, dendritic structures from solution can be applied in the coating, wherein complete coating of the substrate does not have to be achieved here, i.e. parts of the substrate may still be visible. The coating of the substrate, also like the structures of the catalyst, can be analyzed in this case by scanning electron microscopy (SEM) or transmission electron microsocopy (TEM) for example.
In the electrodes, the substrate is not necessarily completely covered by the coating. In some embodiments, the coverage of the coating in terms of surface area can be, for example, 10 to 99.9%, based on the surface area of the substrate, or 50 to 95%, or even 70 to 90%. For example, the substrate is only covered such that the growth of the catalyst takes place dendritically.
Crystalline micro- to nanoporous systems for the Cu⁺/Cu-comprising catalyst can be obtained and/or those having a particularly high surface area of, for example, more than 100 m²/g, or equal to or more than 500 m²/g, or even equal to or more than 1000 m²/g, wherein addition of substances such as brighteners is not excluded. The Cu⁺/Cu-comprising catalyst may comprise pores in this case of a size from 10 nm to 100 μm, or from 50 nm to 50 μm, or even from 100 nm to 10 μm. The Cu⁺/Cu-comprising catalyst may also comprise dendritic structures having a fine structure, for example the gap between two dendrites having a dimension of 1 to 100 nm, or 2 to 20 nm, or even 3 to 10 nm. The coating may be porous for example. The Cu⁺/Cu-comprising catalyst can be crystalline to an extent of at least 40% by weight, based on the catalyst, or to an extent of at least 70% by weight, or even to an extent of at least 80% by weight, wherein the Cu⁺/Cu-comprising catalyst and/or the coating may be crystalline.
The substrate may be porous, for example to be able to produce gas diffusion electrodes. The substrate may have pore sizes from 10 nm to 100 μm, or from 50 nm to 50 μm, or even from 100 nm to 10 μm. By means of the porous configuration of the non-copper substrate, or even of a copper substrate, such as a gas diffusion electrode for example, good transport of a gaseous alkyne to the Cu⁺/Cu-comprising catalyst can be ensured and the efficiency of the electrolysis can be further improved. Especially by means of a suitable pore size, specific directing to particular sections of the catalyst can be ensured.
The concentration of Cu⁺ in the porous copper catalyst layer/the coating comprising the Cu⁺/Cu-comprising catalyst is, for example, greater than 1 mol %, or greater than 5 mol %, or more than 10 mol %, or even greater than 20 mol %, and for example up to 99.9 mol %, based on the coating.
In the copper-containing electrode the substrate may be porous. The substrate can, in this case, have pores of a size from 10 nm to 100 μm, or from 50 nm to 50 μm, or even from 100 nm to 10 μm. This may be appropriate for embodiments, for example, in which the electrode is a gas diffusion electrode.
In some embodiments, the substrate in the copper-containing electrode comprises, for example, at least one metal such as silver, platinum, nickel, lead, titanium, nickel, iron, manganese or chromium or alloys thereof such as stainless steels, and/or at least one non-metal such as carbon, Si, boron nitride (BN), boron-doped diamond etc., and/or at least one conductive oxide such as indium tin oxide (ITO), aluminum zinc oxide (AZO) or fluorinated tin oxide (FTO)—for example for the production of photoelectrodes, and/or at least one polymer based on polyacetylene, polyethoxythiophene, polyaniline, or polypyrrole, such as in polymer-based electrodes for example. Copper alloys or mixtures of the materials mentioned with copper as well as also substrates of copper or copper oxide are also possible.
In some embodiments, the coating is at least partially crystalline. In some embodiments, the Cu⁺/Cu-comprising catalyst is crystalline to an extent of at least 40% by weight, based on the catalyst, or to an extent of at least 70% by weight, or even to an extent of at least 80% by weight. In accordance with particular embodiments, the Cu⁺/Cu-comprising catalyst and/or the coating is/are crystalline.
In some embodiments, the coating of the copper-containing electrode is micro- to nanoporous and/or has a particularly high surface area of, for example, more than 500 m²/g, or equal to or more than 800 m²/g, or even equal to or more than 1000 m²/g. In some embodiments, the coating is therefore porous. The Cu⁺/Cu-comprising catalyst can have pores of a size from 10 nm to 100 μm, or from 50 nm to 50 μm, or even from 100 nm to 10 μm. The Cu⁺/Cu-comprising catalyst may also comprise dendritic structures having a fine structure, for example the gap between two dendrites having a dimension of 1 to 100 nm, or 2 to 20 nm, or even 3 to 10 nm.
In some embodiments, the concentration of Cu⁺ in the porous copper catalyst layer is, for example, greater than 1 mol %, or greater than 5 mol %, or more than 10 mol %, or even greater than 20 mol %, and up to 99.9 mol %, based on the coating.
In some embodiments, the coverage of the coating in terms of surface area in the copper-containing electrode can be, for example 10 to 99.9%, based on the surface area of the substrate, or 50 to 95%, or even 70 to 90%. In some embodiments, the substrate is covered such that the growth of the catalyst takes place dendritically.
In some embodiments, the following features are useful in forming the copper-containing electrode as a gas diffusion electrode (GDE), as for the gas diffusion electrode described in 102015215309.6. In some embodiments, a gas diffusion electrode as copper-containing electrode comprises, for example, a support, maybe containing copper, e.g. in the form of a fabric, and a first layer comprising at least copper and at least one binder, wherein the (first) layer comprises hydrophilic and hydrophobic pores and/or channels, further comprising a second layer comprising copper and at least one binder, wherein the second layer is located on the support and the first layer on the second layer, wherein the content of binder in the first layer is less than in the second layer.
In this case, hydrophobic is understood to mean water-repellent. Hydrophobic pores and/or channels are therefore those which repel water. In particular, hydrophobic properties are associated with substances or molecules having non-polar groups. In contrast thereto, hydrophilic is understood to mean the ability to interact with water and other polar substances. The second layer, exactly like the first layer, can comprise hydrophilic and/or hydrophobic pores and/or channels.
In some embodiments, there is a gas diffusion electrode comprising a support, maybe containing copper, e.g. in the form of a fabric, and a first layer comprising at least copper and at least one binder, wherein the layer comprises hydrophilic and hydrophobic pores and/or channels.
The hydrophilic and hydrophobic regions of the GDE can achieve a good triphasic relationship between liquid, solid and gas. In the electrode, for example, hydrophobic channels or regions and hydrophilic channels or regions are found on the electrolyte side wherein, in the hydrophilic regions, catalyst centers of lower activity are located. In addition, inactive catalyst centers are located on the gas sides. Particularly active catalyst centers are in the triple phase region of liquid, solid and gas. An ideal GDE therefore has maximum penetration of the bulk material with hydrophilic and hydrophobic channels in order to obtain as many triple phase regions as possible for active catalyst centers. In some embodiments, the first layer comprises hydrophilic and hydrophobic pores and/or channels. By means of suitably adjusting the first layer, it can be achieved that as many active catalyst centers as possible are present in the gas diffusion electrode.
The support is not particularly limited to the above, as long as it is suitable for a gas diffusion electrode and, in some cases, contains copper. In the extreme case, for example, parallel wires can also form a support. In some embodiments, the support is a fabric, e.g. a mesh, or even a copper mesh. As a result, both a sufficient mechanical stability and functionality as a gas diffusion electrode can be ensured, for example with respect to high electrical conductivity. By using copper in the support, suitable conductivity can be provided and the risk of infiltration by undesirable foreign metals can be prevented. In some embodiments, the support therefore consists of copper. In some embodiments, a copper-containing support is a copper mesh having a mesh size w of 0.3 mm<w<2.0 mm, or 0.5 mm<w<1.4 mm and a wire diameter x of 0.05 mm<x<0.5 mm, or 0.1 mm<x≤0.25 mm.
In some embodiments, the first layer comprises copper, also high electrical conductivity of the catalyst and also, particularly in connection with a copper mesh, a homogeneous potential distribution across the whole electrode surface (potential-dependent product selectivity) can be assured.
In some embodiments, the binder comprises a polymer, for example a hydrophilic and/or hydrophobic polymer, for example, a hydrophobic polymer, especially PTFE. As a result, a suitable adjustment of the hydrophobic pores or channels can be achieved.
In particular, to produce the first layer, PTFE particles having a particle diameter between 5 and 95 μm, preferably between 8 and 70 μm are used. Suitable PTFE powders include, for example, Dyneon® TF 9205 and Dyneon TF 1750. Suitable binder particles, PTFE particles for example, can be for example approximately spherical, for example spherical, and can be produced, for example, by emulsion polymerization. In some embodiments, the binder particles are free of surface-active substances. The particle size in this case can be determined for example in accordance with ISO 13321 or D4894-98a and can, for example, correspond to the manufacturers' specifications (e.g. TF 9205: mean particle size 8 μm according to ISO 13321; TF 1750: mean particle size 25 μm according to ASTM D4894-98a).
In some embodiments, the first layer comprises at least copper, which can be present, for example, in the form of metallic copper and/or copper oxide, and which functions as catalyst center. In this case, the first layer preferably comprises metallic copper in oxidation state 0.
In some embodiments, the first layer may also comprise, for example, copper oxide, especially Cu₂O. The oxide in this case can contribute to stabilizing the copper oxidation states of +1 and thus maintaining the long-term stability with respect to selectivity for ethylene. Under the electrolysis conditions, it can be reduced to copper. In some embodiments, the first layer comprises at least 40 atom %, or at least 50 atom %, or even at least 60 atom % copper, based on the layer.
In some embodiments, the first layer can also comprise further promoters which, in combination with the copper, improve the catalytic activity of the GDE. For example, the first layer comprises at least one metal oxide, e.g. ZrO₂, Al₂O₃, CeO₂, Ce₂O₃, ZnO₂, MgO; and/or at least one copper-rich intermetallic phase, at least one Cu-rich phase selected from the group of the binary systems comprising Cu—Al, Cu—Zr, Cu—Y, Cu—Hf, CuCe, Cu—Mg and the ternary systems comprising Cu—Y—Al, Cu—Hf—Al, Cu—Zr—Al, Cu—Al—Mg, Cu—Al—Ce having Cu contents >60 atom %; and/or copper-containing perovskite and/or defective perovskite and/or compounds related to perovskite, e.g. YBa₂Cu₃O_7−δ, wherein 0≤δ≤1 (corresponding to YBa₂Cu₃O₇₋₅X_σ), CaCu₃Ti₄O₁₂, La_1.85Sr₀₁₅CuO_3.930Cl_0.053, (La,Sr)₂CuO₄. Viable promoters in this case are the metal oxides.
In some embodiments, the metal oxide used may be insoluble in water so that aqueous electrolytes can be used in an electrolysis using the gas diffusion electrode. The metal oxides may not be inert, but may be hydrophilic reaction centers which can serve to provide protons.
The promoters, especially the metal oxide, can in this way support the function and production of electrocatalysts that are stable long-term, by stabilizing catalytically active Cu nanostructures. As a result, the structural promoters can reduce the high surface mobilities of the Cu nanostructures and therefore their tendency to sinter. The concept originates from heterogeneous catalysis and is used successfully within high temperature processes. In some embodiments, the promoters used for the electrochemical reduction can be the following metal oxides which cannot be reduced to metals in the electrochemical window: ZrO₂(E=−2.3V), Al₂O₃(E=−2.4V), CeO₂(E=−2.3V), MgO (E=−2.5V). It should be noted here that the oxides specified are not added as additives but are part of the catalyst itself. In addition to its function as promoter, the oxide also fulfils the feature of stabilizing copper in the oxidation stage of I.
In some embodiments, the gas diffusion electrodes are metal oxide-copper catalyst structures which are produced as follows. For the production of the metal oxides, the precipitation according to particular embodiments cannot be effected, as frequently described, in a pH regime between pH=5.5-6.5, but in a region between 8.0-8.5, such that hydroxide-carbonates similar to malachite (Cu₂[(OH)₂|CO₃]), azurite (Cu₃(CO₃)₂(OH)₂) or aurichalcite (Zn,Cu)₅[(OH)₆|(CO₃)₂]) are not formed as precursor, but hydrotalcite (Cu₆Al₂CO₃(OH)₁₆.4 (H₂O)), which can be obtained in greater yield. Likewise, layered double hydroxides (LDHs) are suitable, having a composition M^z _1−xM³⁺ _x(OH)₂]^q+(Xⁿ⁻)_q/n.yH₂O, where M¹⁺=Li⁺, Na⁺, K⁺, M²⁺=Ca²⁺, Mg^2+,Cu²⁺ and M³⁺=Al, Y, Ti, Hf, Ga. The corresponding precursors can be precipitated by co-addition of a metal salt solution and a basic carbonate solution in a pH-controlled manner. A particular feature of these materials is the presence of particularly fine copper crystallites having a size of 4-10 nm, which are stabilized structurally by the oxide present.
After precipitation, drying may include subsequent calcination in an O₂/Ar gas stream. The oxide precursors generated can then also be reduced directly in an H₂/Ar gas stream, in which only the Cu₂O or CuO is reduced to Cu and the oxide promoter is retained. The activation step can also be carried out electrochemically afterwards. In order to improve the electrical conductivity of the applied layer prior to electrochemical activation, some oxide precursors and activated precursors can also be mixed. In order to be able to increase the basic conductivity, 0-10% by weight copper powder of a similar particle size can also be mixed in.
In some embodiments, the finished calendered gas diffusion electrode is subjected to subsequent calcination/thermal treatment before the electrochemical activation is carried out.
A further production possibility of suitable electrocatalysts is based on the approach of producing copper-rich intermetallic phases such as CusZr, Cu₁₀Zr₇, Cu₅₁Zr₁₄, which can be produced from the melt. Corresponding ingots can be milled and fully or partially calcined retrospectively in the O₂/argon gas stream and be converted into the oxide form. Of particular interest are the Cu-rich phases of the binary systems Cu—Al, Cu—Zr, Cu—Y, Cu—Hf, CuCe, Cu—Mg and the corresponding ternary systems having Cu contents >60 atom %: CuYAl, ChHfAl, CuZrAl, CuAl Mg, CuAl Ce.
Copper-rich phases are known, for example, from E. Kneller, Y. Khan, U. Gorres, The Alloy System Copper-Zirconium, Part I. Phase Diagram and Structural Relations, Zeitschrift ftir Metallkunde [Journal of metallurgy] 77 (1), pp. 43-48, 1986 for Cu—Zr phases, from Braunovic, M.; Konchits, V. V.; Myshkin, N. K.: Electrical contacts, fundamentals, applications and technology; CRC Press 2007 for Cu—Al phases, from Petzoldt, F.; Bergmann, J. P.; Schtrer, R.; Schneider, 2013, 67 Metall, 504-507 (see Table 1 for example) for Cu—Al phases, from Landolt-Börnstein—Group IV Physical Chemistry Volume 5d, 1994, pp. 1-8 for Cu—Ga phases, and from P. R. Subramanian, D. E. Laughlin, Bulletin of Alloy Phase Diagrams, 1988, 9, 1, 51-56 for Cu—Hf phases.

TABLE 1

Copper-aluminum phases (taken from Petzoldt, F.; Bergmann,
J. P.; Schürer, R.; Schneider, 2013, 67 Metall, 504-507)

				Specific
				elec.
	Cu	Al	Hardness	resistance
Phase	[wt %]	[wt %]	[HV]	[μΩcm]

Cu	100	0	100	1.75
Γ₁	80	20	1050	14.2
Cu₉Al₄
Δ	78	22	180	13.4
Cu₃Al₂
ζ₂	75	25	624	12.2
Cu₄Al₃
η₂CuAl	70	30	648	11.4
θ CuAl₂	55	45	413	8.0
Al	0	100	60	2.9

In some embodiments, these copper-rich intermetallic phases may include a proportion of copper greater than 40 atom %, or greater than 50 atom %, or even greater than 60 atom %. However, in some embodiments, the intermetallic phases also comprise non-metallic elements such as oxygen, nitrogen, sulfur, selenium and/or phosphorus, i.e. for example oxides, sulfides, selenides, nitrides and/or phosphides are present. The intermetallic phases are partially oxidized for example.
In some embodiments, the following copper-containing perovskite structures and/or defective perovskite and/or compounds related to perovskite can be used for electrocatalysts: YBa₂Cu₃O_7−δ, wherein 0≤δ≤1, CaCu₃Ti₄O₁₂, La_1.85Sr_0.15, CuO_3.930Cl_0.053, (La,Sr)₂CuO₄. In some embodiments, mixtures of these materials can be used for electrode preparation or that subsequent calcination or activation steps are carried out as required.
In some embodiments, the catalyst particles comprise or consist of copper, for example copper particles which are used for producing the GDE, have a uniform particle size between 5 and 80 μm, or 10 to 50 μm, or even between 30 and 50 μm. Furthermore, the catalyst particles may have a high purity without traces of foreign metals.
By means of suitable structuring, optionally with the aid of promoters, high selectivity and long-term stability can be achieved.
In some embodiments, the promoters, for example the metal oxides, can also have a corresponding particle size in the production.
In order to further adjust the porosity of the electrode, Cu powder supplements having a particle diameter of 50 to 600 μm, or 100 to 450 μm, or even 100-200 μm, can be added. The particle diameter of these supplements is, for example, ⅓- 1/10 of the total layer thickness of the layer. Instead of Cu, the supplement can also be an inert material such as a metal oxide. In this manner, an improved formation of pores and channels can be achieved.
In some embodiments, the first layer comprises less than 5% by weight, or less than 1% by weight, or even no carbon- and/or carbon black-based or carbon- or carbon black-like, for example conductive, fillers, based on the layer. In some embodiments, the first layer comprises no surface-active substances. In some embodiments, the first and/or second layer also do not comprise any sacrificial material, for example a sacrificial material with a release temperature of below approximately 275° C., e.g. of below 300° C. or below 350° C., in particular no pore former which typically can remain at least partially in the electrode when using such a material in the production of electrodes. For instance, if only a (first) layer is present in the GDE, the content or proportion of binder, for example PTFE, can be for example 3-30% by weight, or 3-20% by weight, or 3-10% by weight, or even 3-7% by weight, based on the one (first) layer.
The GDE described above further comprises a second layer comprising copper and at least one binder, wherein the second layer is located on the support and the first layer on the second layer, wherein the content of binder in the first layer is less than in the second layer. In addition, the second layer may comprise coarser Cu or inert material particles, for example having particle diameters of 50 to 700 μm, or 100-450 μm, in order to provide a suitable channel or pore structure.
In some embodiments, the second layer in this case comprises 3-30% by weight binder, or 10-30% by weight binder, or 10-20% by weight binder, or >10% by weight binder, or even >10% by weight and up to 20% by weight binder, based on the second layer, and the first layer comprises 0-10% by weight binder, e.g. 0.1-10% by weight binder, or 1-10% by weight binder, or 1-7% by weight, or even 3-7% by weight binder, based on the first layer. Here, the binder can be the same as in the first layer, for example PTFE. In some embodiments, the particles for producing the second layer may correspond to those of the first layer, but may also be different therefrom. The second layer in this case is a metal particle layer (MPL), which is below the catalyst layer (CL). By means of such layering, specifically strongly hydrophobic regions can be established in the MPL and a catalyst layer having hydrophilic properties can be generated. Owing to the strongly hydrophobic character of the MPL, an undesirable penetration of the electrolyte into the gas transport channels, i.e. a stream thereof, can likewise be prevented.
In some embodiments, the second layer partially penetrates the first layer. This enables a good transfer between the layers with respect to diffusion. In addition to the second layer, the GDE may comprise further layers still, for example on the first layer and/or on the other side of the support.
To produce such a multi-layered GDE, firstly, for example, a mixture for an MPL can be sieved, based on a highly conductive Cu mixture of dendritic Cu having particle sizes between 5-100 μm, or than 50 μm and coarser Cu or inert material particles having particle sizes of 100-450 μm, or 100-200 μm, with a PTFE content of 3-30% by weight, or 20% by weight, in a layer thickness of 0.5 mm for example on a Cu mesh having a mesh size of 1 mm for example (thickness e.g. 0.2-0.6 mm, e.g. 0.4 mm) and can be drawn via a frame or doctor blade. Corresponding dendritic copper may also be present in the first layer.
Subsequently, the catalyst/PTFE mixture (CL) can be further sieved, for example with a PTFE content of 0.1-10% by weight, and can be smoothed out or drawn over a 1 mm thick frame for example, such that an overall layer thickness (Hf) of 1 mm can be obtained. The layer thus prepared can then be supplied to a calender having a gap width H₀=0.4-0.7 mm, or 0.5-0.6 mm, and be rolled out so that a multi-layered gas diffusion electrode can be obtained, as shown schematically in FIG. 3, having a copper mesh 8, an MPL 9 and a CL 10. By means of the MPL, better mechanical stability, further prevention of penetration of electrolyte and better conductivity can be achieved, especially when using meshes as supports. A stepwise production of the GDE by sieving and rolling out in each case of each individual layer can result in a lower adhesion between the layers and is therefore may be less effective.
The degree of fibrillation of the binder, PTFE for example, (structural parameter ζ) correlates directly with the applied shear rate since the binder, a polymer for example, behaves as a shear-thinning (pseudoplastic) fluid on rolling out. After extrusion, the layer obtained by fibrillation has an elastic character. This structural modification is irreversible such that this effect can no longer be subsequently strengthened by further rolling out, rather the layer is damaged by the elastic behavior on further exposure to shear forces. A particularly intense fibrillation may disadvantageously result in rolling up on the layer side of the electrode such that excessively high contents of binder should be avoided.
In some embodiments, the gas diffusion electrode may apply a copper-PTFE base layer as second layer to improve contact of nanoscale materials while simultaneously maintaining a high porosity. The base layer may be characterized by very high conductivity, for example 7 mOhm/cm or more, and may have a high porosity, for example of 50-70%, and a hydrophobic character. The binder content, for example PTFE, can be selected for example between 3-30% by weight, e.g. 10-30% by weight. The copper intermediate layer as second layer can itself be catalytically active as the first layer in the region of the overlapping zone of the catalyst layer, and particularly serves for better surface electrical connection of the electrocatalyst. With the aid of this method, the amount of catalyst required can be reduced by a factor of 20-30.
The method of two-layered construction further offers the possibility of omitting binder materials within the catalyst layer as first layer, whereby better electrical conductivity can be achieved. It also allows processing of very ductile or brittle powder particles. Subsequent electrochemical activation of the resulting electrode may optionally be carried out, by chemical or electrochemical activation for example, and is not particularly restricted. An electrochemical activation procedure may result in cations of the conducting salt of the electrolyte (e.g. KHCO₃, K₂SO₄, NaHCO₃, KBr, NaBr) penetrating the hydrophobic GDE channels and as a result hydrophilic regions are created.
The method according to the invention is suitable for the partial electrochemical hydrogenation of alkynes of the chemical formula (I) to alkenes,

- wherein R and R′ are selected from inorganic and/or organic radicals.

In this case, the inorganic and/or organic radicals are not particularly restricted, and the inorganic radicals may also comprise organic substructures, for example in adducts or complexes. According to particular embodiments, organic radicals comprise 1 to 100 carbon atoms, for example 1 to 40 carbon atoms, or 1 to 20 carbon atoms, e.g. 1-10, 1 to 6, 1 to 4, 1 to 2 carbon atoms or even only 1 carbon atom. All inorganic radicals are possible as inorganic radicals. Derivatives of inorganic radicals and/or substituted organic radicals are also useful. Feasible as inorganic and/or organic radicals are, for example, —H, -D, —OH, —OR*, —SH, —SR*, —NH₂, —NR*R*, —COOH, —COOR*, —CHO, —COR*, —PH₂, —PR*R*, —F, —Cl, —Br, —I, —NO, —NO₂, and also substituted or unsubstituted alkyl, alkenyl, alkynyl and aryl groups, where R* and R* can likewise be in this case any organic side chains, for example having 1 to 100 carbon atoms, for example 1 to 40 carbon atoms, preferably 1 to 20 carbon atoms, e.g. 1-10, 1 to 6, 1 to 4, 1 to 2 carbon atoms or even only 1 carbon atom, or inorganic side chains, such as —H, -D, —OH, —SH, —NH₂, —COOH, —CHO, —PH₂, —F, —Cl, —Br, —I, —NO, —NO₂, and also substituted or unsubstituted alkyl, alkenyl, alkynyl and aryl groups. Therefore, all alkynes are suitable as reactants of the method. As a consequence, compounds of the chemical formula (I) having two or more C—C triple bonds can also be partially hydrogenated. In accordance with particular embodiments however, the compound of the chemical formula (I) has only one C—C triple bond, namely the one depicted in the chemical formula (I).
In this context, partial hydrogenation is understood to mean the hydrogenation of an alkyne, i.e. a triple bond, to alkene, i.e. a double bond. The reaction takes place electrochemically using electricity, for example in an electrolysis cell.
In some embodiments, the inorganic and/or organic radicals R and R′ are selected from substituted or unsubstituted alkyl, alkenyl, alkynyl and/or aryl radicals, preferably alkyl and/or aryl radicals, having 1 to 40 carbon atoms, or 1 to 20 carbon atoms, e.g. 1-10, 1 to 6, 1 to 4, 1 to 2 carbon atoms or even only 1 carbon atom, —H, -D, —OH, —OR*, —SH, —SR*, —NH₂, —NR*R*, —COOH, —COOR*, —CHO, —COR*, —PH₂, —PR*R*, —F, —Cl, —Br, —I, —NO and —NO₂, where R* and R* are organic and/or inorganic radicals preferably selected from —H, -D, —OH, —SH, —NH₂, —COOH, —CHO, —PH₂, —F, —Cl, —Br, —I, —NO, —NO₂, and also substituted or unsubstituted alkyl, alkenyl, alkynyl and aryl groups, e.g. alkyl and/or aryl groups, having 1 to 40 carbon atoms, or 1 to 20 carbon atoms, e.g. 1-10, 1 to 6, 1 to 4, 1 to 2 carbon atoms or even only 1 carbon atom.
Suitable substituents for the substituted or unsubstituted alkyl, alkenyl, alkynyl and aryl groups or radicals are, for example, -D, —OH, —SH, —NH₂, —COOH, —CHO, —PH₂, —F, —Cl, —Br, —I, —NO, —NO₂. Therefore, functionalized side chains such as, for example, —CH₂—OH or fluorinated alkyl and/or aryl radicals such as —CF₃may result.
If R and R′ are in each case —H or -D, then the compound of the chemical formula (I) is the special case ethyne. If either R or R′, but not both, is —H or -D, the alkyne is referred to as a terminal alkyne. In the case of internal alkynes, neither R nor R′ is —H or -D. In the case of terminal alkenes, the amount of charge used may be precisely controlled, since over-hydrogenation is possible, albeit with lower efficiency. In accordance with particular embodiments, neither R nor R′ are —H or -D, owing to this necessary control, i.e. internal alkynes are hydrogenated.
In some embodiments, electron-poor and therefore activated alkynes are less suitable for the method since the desired alkenes are more reactive to electrohydrogenation. Therefore, poorer selectivities are achieved with electron-poor alkenes. In some embodiments, alkynes described herein may bear no electron-withdrawing radicals such as, e.g. —COOH, —COOR*, —CF₃(in which R* is as defined above). In some embodiments, the alkyne of the chemical formula (I) therefore has no electron-withdrawing radicals. In some embodiments, the electron-withdrawing radicals are selected from —COOH, —COOR* and fluorinated alkyl and/or aryl radicals, preferably perfluorinated alkyl and/or aryl radicals such as —CF₃.
In some embodiments, alkynes bear no functional groups which may in turn be converted by electroreduction. Simultaneous electroreduction of a reducible side chain or a reducible radical is possible however. Examples of such alkynes having a reducible side chain or a reducible radical are alkynes bearing functional groups such as —CHO, —COR*, —NO or —NO₂, or side chains thereof comprising these radicals. The reduction of aldehydes (—CHO), ketones (—COR*) and nitro compounds (—NO₂) could be confirmed experimentally. In this case, alcohols (—CH₂—OH) or (—CHR*—OH) were obtained from aldehydes (—CHO) and ketones (—COR*) and amines (—NH₂) from nitro compounds (—NO₂). In some embodiments, therefore, the alkyne of the chemical formula (I) comprises no further reducible functional groups apart from the triple bond.
In some embodiments, gaseous or water-soluble/water-miscible alkynes, gaseous alkynes for example, may be used as alkyne of the chemical formula (I). Examples of such suitable compounds are ethyne, propyne, 1-butyne or 2-butyne, propargyl alcohol (2-propyn-1-ol) and 2-butyn-1-ol.
Good synergy is apparent particularly in the case of using gaseous alkynes of the chemical formula (I) with a copper-containing gas diffusion electrode. In some embodiments, therefore, the copper-containing electrode is configured as a gas diffusion electrode, wherein the alkyne of the chemical formula (I) is gaseous.
In some embodiments, the hydrogenation is carried out with a proton donor selected from water and alcohols having 1 to 20 carbon atoms, e.g. water and alcohols having 1 to 12, e.g. 1 to 6 or 1 to 4 carbon atoms. The water in this case may also be fully or partially deuterated, i.e. comprise HDO or D₂O, or also tritium, for example in the production of radioactive markers.
Although an electrolyte that can be used in the method is not particularly restricted, some embodiments use an aqueous electrolyte. In addition, any conductive salts and/or ionic liquids can be used. Mixtures of water with inert organic solvents, such as 1,4-dioxane for example, can be used to improve the substrate solubility.
Some embodiments include use of a copper-containing electrode for the partial electrochemical hydrogenation of alkynes of the chemical formula (I) to alkenes,

- wherein R and R′ are selected from inorganic and/or organic radicals.

The copper-containing electrode corresponds in this case to that which has been described in connection with the methods above.
Some embodiments include a device for the partial electrochemical hydrogenation of alkynes of the chemical formula (I) to alkenes,

- wherein R and R′ are selected from inorganic and/or organic radicals, comprising
  an electrolysis cell (1) comprising a copper-containing electrode, which is configured to reduce the alkyne of the chemical formula (I) to alkene; a source of the alkyne of the chemical formula (I) (3) which is configured to provide the alkyne of the chemical formula (I); and a first feeding device (2) for the alkyne of the chemical formula (I) which is configured to feed the alkyne of the chemical formula (I) from the source of the alkyne of the chemical formula (I) to the electrolysis cell.

The electrolysis cell is not particularly restricted in this case, as long as it comprises the copper-containing electrode which can correspond to that of the methods described above. In some embodiments, using the device, the methods can be carried out. In this case, the copper-containing electrode can function as cathode. The other constituents of the electrolysis cell such as anode, optionally membrane, power source etc., are not particularly restricted, as well as the arrangement thereof.
Examples of a possible cell arrangement are as follows. A cathode chamber II can be arranged such that a catholyte is fed from below and then exits the cathode chamber II from above. In some embodiments, however, the catholyte can also be fed from above, as for example in falling film electrodes. At the anode A, which is electrically linked to the cathode K by means of a power source for providing the voltage for the electrolysis, the oxidation of a substance takes place in an anode chamber I, which substance is fed from below, for example with an anolyte, in which the anolyte then exits the anode chamber with the product of the oxidation. The anode chamber and cathode chamber can be separated by a membrane M. In such a 3-chamber design, as well as in other designs, a reaction gas, such as an alkyne of the chemical formula (I) for example, can be conveyed through a gas diffusion electrode as cathode into the cathode chamber II for the reduction. Embodiments with porous anodes are also feasible. Chambers I and II may also be separated by a membrane M as described.
In contrast thereto, in the PEM (proton or ion exchange membrane) set-up, a cathode K, a gas diffusion electrode for example, and an anode A are directly adjacent to the membrane M, whereby the anode chamber I is separated from the cathode chamber II.
Hybrid forms of these cell designs are also feasible, in which on the catholyte side for example, a set-up with a gas diffusion electrode can be provided, which is not directly adjacent to the membrane, whereas on the anolyte side the anode can be adjacent to the membrane. Obviously, other hybrid forms or other configurations of the exemplary electrode chambers depicted are also feasible.
Also feasible are embodiments without a membrane. In some embodiments, the electrolyte on the cathode side and the electrolyte on the anode side may therefore be identical, and the electrolysis cell/electrolysis unit can be operated without a membrane. In some embodiments, the electrolysis cell comprises a membrane, but this may be associated with additional inconvenience with regard to the membrane as well as the voltage applied. Catholyte and anolyte can also optionally be mixed again outside the electrolysis cell.
The membrane, if present, can also be of multi-layered design, so that separate feedings of anolyte and catholyte are enabled. Separation effects are achieved in aqueous electrolytes by the hydrophobicity of intermediate layers for example. Conductivity can nevertheless be ensured if conductive groups are integrated into such separation layers. The membrane can be an ion-conducting membrane or a separator which only effects a mechanical separation and is permeable to cations and anions.
By using a gas diffusion electrode, it is possible to construct a three-phase electrode. For example, a gas can be fed from behind to the electrically active front side of the electrode in order to carry out an electrochemical reaction there. In accordance with particular embodiments, the gas diffusion electrode can only be supplied in countercurrent, i.e. a gas such as the alkyne of the chemical formula (I) is fed past the reverse side of the gas diffusion electrode in relation to the electrolytes, wherein the gas can penetrate through the pores of the gas diffusion electrode and the product can be discharged from the rear. The gas flow may be reversed during countercurrent to the flow of the electrolyte, so that potential liquid pressed through can be transported away.
By means of adequate porosity of the gas diffusion electrode, two operating modes are thus possible: one cell variant enables a direct active perfusion of the GDE with a gas. The products formed are removed from the electrolysis cell through the catholyte outlet and can be separated from the liquid electrolyte in a downstream phase separator. The second cell variant describes an operating mode in which the gas flows in the rear region of the GDE by an applied gas pressure. The gas pressure should be selected in this case such that it is identical to the hydrostatic pressure of the electrolyte in the cell so that no electrolyte permeates through.
In order to further prevent penetration of electrolyte through the gas diffusion electrode, a film can be applied to the side of the gas diffusion electrode facing away from the electrolyte in order to prevent the electrolyte crossing over to the gas. The film can be provided so as to be suitable for this purpose, and is hydrophobic for example.
In some embodiments, the electrolysis cell comprises a membrane which separates the cathode chamber and the anode chamber of the electrolysis cell in order to prevent mixing of the electrolytes. The membrane is not particularly restricted in this case, as long as it separates the cathode chamber and the anode chamber. In particular, the membrane substantially prevents a cross-over of the gases arising at the cathode and/or anode to the anode and cathode chambers. In some embodiments, the membrane is an ion exchange membrane, for example based on polymer. In addition to polymer membranes, ceramic membranes can also be used.
The anode material is likewise not particularly restricted and primarily depends on the desired reaction. Exemplary anode materials include platinum or platinum alloys, palladium or palladium alloys, and glassy carbon. Other anode materials are also conductive oxides such as doped or non-doped TiO₂, indium tin oxide (ITO), fluorine-doped tin oxide (FTO), aluminum-doped zinc oxide (AZO), iridium oxide, etc. Optionally, these catalytically active compounds can also be applied superficially only in thin film technology, for example on a titanium support.
In addition, the source of the alkyne of the chemical formula (I) and a first feeding device (2) for the alkyne of the chemical formula (I) are not particularly restricted. The alkyne of the chemical formula (I) can for example originate as source from a reservoir or other container as well as from a separate reactor, etc. For example, tubes, hoses etc. may serve as first feeding device. In particular, the source of the alkyne of the chemical formula (I) and the first feeding device (2) for the alkyne of the chemical formula (I) are adjusted to the particular alkyne in regard to the materials used so that they are not attacked by the alkyne of the chemical formula (I).
In some embodiments, there are further feeding devices, e.g. for electrolyte, discharge devices, pumps, heating and/or cooling devices etc.
In some embodiments, the copper-containing electrode is configured as a gas diffusion electrode, wherein the first feeding device (2) for the alkyne of the chemical formula (I) feeds the alkyne of the chemical formula (I) to the gas diffusion electrode.
The aforementioned embodiments, configurations, and other developments can be combined with one another as desired, where appropriate. Further possible configurations, developments and implementations of the invention also include combinations not explicitly specified above or in the following in relation to the features of the invention described in the working examples. In particular, a person skilled in the art will also add individual aspects as improvements or supplements to the respective basic form of the present invention.
The handful of exemplary embodiments described below may illuminate the teachings of the present disclosure but do not limit the scope of the teachings thereto.

EXAMPLES

The four following working examples were carried out in an H-cell. Here, a 2 cm²large solid Cu electrode was used which had been coated with high-purity Cu from a CuSO₄solution. A constant current of 30 mA was applied. 0.1M aqueous KBr was used as electrolyte. In order to avoid influences from the anode, the anode chamber was separated off by a Nafion N 117 membrane.

Example 1: Reduction of Ethyne

After a 10 minute run-in phase, in which the cell was purged with argon, a flow of 7.7 ml/min of ethyne was passed through the cell. This resulted in a current yield of 60% for the reduction of ethyne to ethene. Over-reduction to ethane occurred at a maximum current yield of 1.5%. The current residue resulted in formation of hydrogen. The total conversion of the gas stream was around 1.5%.

Example 2: Reduction of Propargyl Alcohol

The cell was purged with argon during the whole experiment. After a 10 minute run-in phase, propargyl alcohol (32 μl, 0.55 mmol) was added to the electrolyte. On the basis of this sample weight, a charge equivalent of 3.7 F/mol (2 F/mol required) is apparent. Despite the significant charge excess, only traces of propanol occurred. Conversely, the conversion of propargyl alcohol to allyl alcohol was complete. At the starting concentration of 0.1M propargyl alcohol, also no more hydrogen evolution occurred. Electricity efficiency for the conversion of propargyl alcohol to allyl alcohol at high concentrations is therefore significantly above 90%.

Example 3: Reduction of 1-butyn-1-ol

The cell was purged with argon during the whole experiment. After a 10 minute run-in phase, butyn-1-ol (32 μl, 0.43 mmol) was added to the electrolyte. The conversion of butyn-1-ol to crotyl alcohol was complete. The initial electricity yield is over 90%. Despite a charge equivalent of 4.8 F/mol used (2 F/mol required), no over-reduction to n-butanol could be observed.

Comparative Example 1: Reduction of Allyl Alcohol

The cell was purged with argon during the whole experiment. After a 10 minute run-in phase, allyl alcohol (32 μl, 0.47 mmol) was added. In contrast to the alkynes, neither high electricity yields nor high conversion could be observed. After a charge equivalent of 4.4 F/mol, a conversion of only 34% could be observed.

Comparative Example 2: Reduction of Potassium Fumarate

The cell was purged with argon during the whole experiment. After a 10 minute run-in phase, fumaric acid (58.7 mg, 0.51 mmol) and KOH (200 μl 5M, 1 mmol) were added. The conversion to potassium succinate after a charge equivalent of 4.1 F/mol was complete. The initial electricity yield was over 90%.
Using a gas diffusion electrode, the results of electrohydrogenation of ethyne over a solid Cu electrode and 15 mA/cm²at a current density of 170 mA/cm²could be readjusted.
The reactions arising from the examples are therefore as follows:
Good selectivity, as shown here, is achieved by the low reactivity with respect to electrohydrogenation with Cu electrodes. Electronically deactivated internal alkenes such as crotyl alcohol appeared inert to over-reduction.
It has been shown in the experiments that the method according to the invention exhibits high selectivity and activity.
Ethyne, propargyl alcohol and 2-butyn-1-ol were evaluated as substrates. None of the 3 substrates is to be considered as activated, which underlines the high activity of the catalytic process. Propargyl alcohol and 2-butyn-1-ol are to be considered as difficult substrates since both bear electron donating substituents. 2-butyn-1-ol is also an internal alkyne which is also sterically hindered.
The alkyne hydrogenation described here, in addition to the high-volume compounds, can also be used for the electroorganic synthesis of specialty chemicals such as active ingredients or feedstuff additives.

Claims

What is claimed is:

1. A method for the partial electrochemical hydrogenation of alkynes of the chemical formula (I) to alkenes,

wherein R and R′ each comprise at least one inorganic or organic radicals, the method comprising:

hydrogenating the compound of the chemical formula (I) on a copper-containing electrode.

2. The method as claimed in claim 1, wherein the inorganic and organic radicals comprise at least one compound selected from the group consisting of: —H, -D, alkyl, alkenyl, alkynyl and/or aryl radicals, —OH, —OR*, —SH, —SR*, —NH₂, —NR*R*, —COOH, —COOR*, —CHO, —COR*, —PH₂, —PR*R*, —F, —Cl, —Br, —I, —NO, and —NO₂, where R* and R* are organic and/or inorganic radicals.

3. The method as claimed in claim 1, wherein neither R nor R′ are —H or -D.

4. The method as claimed in claim 1, wherein the alkyne of the chemical formula (I) comprises no electron-withdrawing radicals.

5. The method as claimed in claim 4, wherein the electron-withdrawing radicals comprise a compound selected from the group consisting of: —COOH, —COOR*, and fluorinated alkyl or aryl radicals.

6. The method as claimed in claim 1, wherein the alkyne of the chemical formula (I) comprises no further reducible functional groups apart from the triple bond.

7. The method as claimed in claim 1, wherein the hydrogenation is carried out with a proton donor selected from water and alcohols having 1 to 20 carbon atoms.

8. The method as claimed in claim 1, wherein:

the copper-containing electrode is configured as comprises a gas diffusion electrode; and

the alkyne of the chemical formula (I) is gaseous.

9. (canceled)

10. A device for the partial electrochemical hydrogenation of alkynes of the chemical formula (I) to alkenes,

wherein R and R′ are selected from inorganic and/or organic radicals, the device comprising:

an electrolysis cell with a copper-containing electrode configured to reduce the alkyne of the chemical formula (I) to an alkene;

a source of the alkyne of the chemical formula (I); and

a first feeding device configured to feed the alkyne of the chemical formula (I) from the source of the alkyne of the chemical formula (I) to the electrolysis cell.

11. The device as claimed in claim 10, wherein:

the copper-containing electrode comprises a gas diffusion electrode; and

the first feeding device for the alkyne of the chemical formula (I) feeds the alkyne of the chemical formula (I) to the gas diffusion electrode.