Functionnalised Copper Electrochemical Catalysts for Conversion of Co2 to Small Molecules

The present invention belongs to the field of catalytic chemistry, and more specifically to catalysed reduction chemical reactions, preferably of COinto small molecules.

The present invention relates to a new catalyst compound comprising at least a copper (Cu) layer, wherein the copper layer is functionalized with at least one aryl functional group and its use thereof in a reduction chemical reaction, preferably in reduction of COinto CO, ethylene and other small molecules such as gaseous hydrocarbons (methane, propane) or liquid molecules (ethanol, formic acid, propanol). The invention relates to the process of manufacture of said catalyst compound and to a process electrochemical conversion of COto small molecules and in particular ethylene.

In the description below, references between [1-4] refer to the list of references at the end of the examples.

The release of carbon dioxide (CO) is a major concern for the environment. Its capture and recycling into small organic bricks such as carbon monoxide (CO), formic acid (HCOOH), methane (CH) or methanol (CHOH), ethanol (CHOH) and ethylene (CH) could prove to be very advantageous.

Particularly, the electrochemical conversion of COinto small molecules such as gaseous hydrocarbons (methane, ethylene) or liquid molecules (ethanol, formic acid) is an attractive method as these molecules can be used as fuels or organic bricks to produce longer hydrocarbon molecules [1-3]. Currently only copper-based catalysts (Cu) can convert COin small organic molecules, but their efficiency is still limited—preventing its use in industrial process [4].

Therefore, there is a critical necessity to explore for an easier and cheaper way to produce small molecules such as ethylene and gaseous hydrocarbons (methane, ethylene) or liquid molecules (ethanol, formic acid) from COin a cheap and environmentally friendly procedure.

Applicant has developed a new process and a new catalyst compound that solves all of the problems listed above.

The present invention deals with a new process and a new catalyst compound, and its applications, such as a method to convert COinto small molecules, more preferably ethylene, at room temperature and atmospheric pressure. Being able to produce such small molecules at room temperature and atmospheric pressure in large quantities is, to the knowledge of Applicant, something that was not observed in the art.

Applicant surprisingly found out that using a functionalized Cu catalyst made according to process of the invention gives very good yields in conversion of COinto small molecules such as ethylene and gaseous hydrocarbons (methane, ethylene) or liquid molecules (ethanol, formic acid). Specifically, it was identified that the performance is considerably improved by grafting specific functional groups on the surface of inorganic electro-catalysts. These functional groups, substituted aryl groups, allow increasing the current density and improving the Faradaic efficiency of the reaction towards the production of ethylene up to about 83% at −3.55 V in a membrane-electrode-assembly cell (MEA).

The catalyst compound of the invention is based on copper (Cu) and optionally Ag, Bi, Zn and/or Sn crystal grown on a porous gas diffusion layer (typically a commercial carbon support such as a gas diffusion electrode or a porous polymer substrate such as PTFE, nylon or PVDF) via electrodeposition and then functionalization with various substituted aryl groups. The catalyst compound obtained by the process of the invention may present a raspberry-like morphology.

A first object of the invention is a process of manufacture of a catalyst compound comprising the steps of:

Advantageously, the process according to the invention is a process of manufacture of a catalyst compound comprising the steps of:

Advantageously, the diazonium salt may be chosen from diazonium salts of formula I, wherein Xis chosen from BF, Cland HSO.

It is meant by “aryl”, a group derived from arenes by removal of a hydrogen atom from a ring carbon atom; arenes being monoyclic and polycyclic aromatic hydrocarbons (IUPAC). According to the invention aryl groups may comprise from 4 to 10 carbon atoms, preferably 6 carbon atoms. According to the invention, aryl groups Arand Ardo not comprise, heteroatoms besides the heteroatoms comprised in R, Fand R.

Advantageously, the diazonium salt may be chosen from diazonium salts of formula I, wherein Arand/or Arare aryl groups comprising 6 carbon atoms and are phenyl groups. Preferably, Arand/or Arare phenyl groups substituted by at least one —Rgroup in ortho, meta and/or para position.

Advantageously, when Aris substituted by more than one Rgroup (i.e., a=2 or 3), the Rgroups may be identical or different from each other.

Advantageously, when Aris substituted by more than one Rgroup (i.e., b=2 or 3), the Rgroups may be identical or different from each other.

In other terms, when there is more than one Rsubstituent, the Rsubstituents may be identical or different from each other and/or when there is more than one Rsubstituent, the Rsubstituents may be identical or different from each other. Also, when there is Rand Rgroups, the Rand Rgroups may be identical or different. For example, when there are two R, they may both be R, and yet be identical or different (e.g. one may be -Me and the other may be -Et or they may both be -Me). Also, for example, when one Rsubstituent and one Rsubstituent are both R, they may be identical or different (e.g. one may be -Me and the other may be -Et or they may both be -Me).

Advantageously, the diazonium salt may be chosen from diazonium salts of formula I, wherein a=1 or 2.

Advantageously, the diazonium salt may be chosen from diazonium salts of formula I, wherein b=1 or 2, more preferably 1.

Advantageously, the diazonium salt may be chosen from diazonium salts of formula I, wherein b=0.

Advantageously, the diazonium salt may be chosen from diazonium salts of formula I, wherein at least one Ris a halo group, preferably chosen from Br, Cl and I.

Advantageously, the diazonium salt may be chosen from diazonium salts of formula I, wherein at least one Ris —NO.

Advantageously, the diazonium salt may be chosen from diazonium salts of formula I, wherein at least one Ris —R, preferably chosen from -Me, -Et and —Pr (Pr being either isopropyl or n-propyl).

Advantageously, the diazonium salt may be chosen from diazonium salts of formula I, wherein at least one Ris —OR, preferably chosen from —OMe, —OEt and —OPr (Pr being either isopropyl or n-propyl).

Advantageously, the diazonium salt may be chosen from diazonium salts of formula I, wherein at least one Ris —NRR, preferably chosen from —NEt, —NMe, —NPr, —NMeEt and —NMePr (Pr being either isopropyl or n-propyl). Advantageously, the diazonium salt may be chosen from diazonium salt of formula I, wherein at least one Rgroup is a group of formula II.

Advantageously, the diazonium salt may be chosen from diazonium salts of formula I, wherein at least one Ris a halo group, preferably chosen from Br, Cl and I.

Advantageously, the diazonium salt may be chosen from diazonium salts of formula I, wherein at least one Ris —NO.

Advantageously, the diazonium salt may be chosen from diazonium salts of formula I, wherein at least one Ris —R, preferably chosen from -Me, -Et and —Pr (Pr being either isopropyl or n-propyl).

Advantageously, the diazonium salt may be chosen from diazonium salts of formula I, wherein at least one Ris —OR, preferably chosen from —OMe, —OEt and —OPr (Pr being either isopropyl or n-propyl).

Advantageously, the diazonium salt may be chosen from diazonium salts of formula I, wherein at least one Ris —NRR, preferably chosen from —NEt, —NMe, —NPr, —NMeEt and —NMePr (Pr being either isopropyl or n-propyl).

Advantageously, the diazonium salt may be chosen from diazonium salts of formula I, wherein at least one Rgroup is a group of formula II and Arand Arare each substituted by one —Rgroup, preferably -Me. The diazonium salt may be chosen from diazonium salts of formula I, wherein at least one Rgroup is a group of formula II and Aris substituted by two —ORgroups, preferably —OMe and Aris substituted by one —NOgroup. The diazonium salt may be chosen from diazonium salts of formula I, wherein at least one Rgroup is a group of formula II and Aris substituted by one —ORgroup, preferably —OMe.

Advantageously, the diazonium salt may be chosen from the following salts:

The different anions in the table above may be used independently to the nature of the cations. For example, “2-methyl-4-[(2-methylphenyl)diazenyl]benzenediazonium”, “4-[(4-methoxyphenyl)amino]benzene-1-diazonium chloride” or “dichlorozinc;2,5-dimethoxy-4-[(4-nitrophenyl)diazenyl]benzenediazonium;dichloride” may have BFas counter anion.

Advantageously, the diazonium salt of formula I may be chosen from the following salts:

Preferably, the diazonium salt of formula I may be chosen from the following salts:

Advantageously, step a) of the process according to the invention may be depositing or coating copper on a porous gas diffusion layer, the porous gas diffusion layer being optionally pre-treated. Preferably, step a) of the process according to the invention may be electrodepositing copper on the porous gas diffusion layer, the porous gas diffusion layer being optionally pre-treated. Alternatively, step a) of the process according to the invention may be coating of copper particles on the porous gas diffusion layer, the porous gas diffusion layer being optionally pre-treated. Alternatively, step a) of the process according to the invention may be depositing of copper particles using physical vapour deposition process such as metal evaporation or sputtering. Step a) of the process according to the invention may also be a combination of previously cited deposition or coating methods.

Advantageously, step a) and/or step b) of the process according to the invention may be conducted using a potentiostat.

Advantageously, the porous gas diffusion layer may be a commercial conducting carbon-based gas diffusion electrode or a porous polymer substrate such as (PTFE, nylon, PVDF).

Advantageously, step a) and/or step b) of the process according to the invention may be conducted under a current density from 5 mA·cmto 50 mA·cm, preferably from 10 mA·cmto 20 mA·cm, and more preferably at 15 mA·cm.

Advantageously, in step a) of the process according to the invention, the quantity of deposited Cu may be from 0.5 C·cmto 50 C·cm, preferably between 15 C·cmto 35 C·cm, more preferably at 15 mA·cm.

Advantageously, step a) and/or step b) of the process according to the invention may be done under pulse deposition or galvanostatic method. Preferably, the applied current density for electrodepositing copper is 15 mA·cm, and the electrodepositing time is 5 minutes.

Advantageously, in the step a) of the process according to the invention, the source of copper (Cu) may be chosen in the group comprising CuBr, CuCland CuSO. The source of copper may be an electrolyte comprising CuBr, sodium tartrate dibasic dihydrate and KOH.