Structured catalysts in layered hydroxide materials for selective CO2 electroreduction reaction – CALHYCO2
Hybrid catalysts for the selective electroreduction of CO2; molecular catalyst@ nanostructured lamellar hydroxide materials
The CO2 transformation is a major challenge (chemistry and catalysis). The need to reduce the amount of CO2 emitted into the atmosphere and the increasing energy demands, motivate the search for viable solutions to use CO2 (waste) as a carbonaceous raw material (resource) for the production of chemicals of interest and fuels. Among the various methods to reduce CO2, electrocatalysis has a promising potential for large-scale development.
Innovative catalytic materials - Selective electroreduction of CO2
The development of electrochemical CO2 reduction (CO2ERR) depends strongly on the improvement of the efficiency of the catalytic systems used, to facilitate the selective and efficient transformation of CO2 (low overpotential; high current densities) but also on the development of new heterogeneous catalysts. Molecular catalysts (MolCat) based on Ru, Re and Mn are good candidates for CO2ERR, but many advances are still needed to improve energy yields and efficiency. Most importantly, methods to immobilize the catalysts to generate catalytic materials (heterogenization) need to be developed. In addition to the practical benefits of having a solid catalyst, heterogenization of MolCat in host matrices, is an objective of modifying and controlling the local environment of the catalyst, which can be beneficial to the efficiency and durability of the catalytic reaction. The main objective of the CALHYCO2 project is: (1) to create and develop innovative materials by combining nanostructured lamellar hydroxide (LOH) host matrices, by chemical modification of LDH (lamellar double hydroxides) and LSH (lamellar single hydroxides) with molecular metal complexes ([M]MolCat) or inorganic metal oxides (MOCat) catalysts ; (2) with these materials to study the CO2 electroreduction reaction, for the production of formic acid (AF : HCOOH) or carbon monoxide (CO), on analytical and preparative scales. The host matrices (LSH and LDH) were chosen to realize the heterogenization of molecular catalysts and to control their environment, but also for their excellent CO2 adsorption properties. In the hybrid materials ([M]MolCat@LOH) both components (LOH and [M]MolCat) have their own function. The cooperative and synergistic effects within these nanostructured hybrid materials are expected to lead to a significant improvement in the performance of CO2ERR catalysis.
The synthesis of organic and inorganic catalysts, the preparation of host and hybrid materials and their characterization, the implementation of electrocatalysis reactions in heterogeneous phase using an aqueous medium and, the characterization of the products of CO2 reduction and the studies of redox mechanisms are the approaches used to achieve the objectives set by the 4 partners of this project.
[M]MolCat molecular catalysts. For each synthesis (ligand and metal complex) a preliminary work is performed in order to find and define the protocols to obtain the products on a gram scale. A series of [Re(L)(CO)3Cl] complexes (L = bpy variously functionalized) have been first synthesized. Ru and Mn carbonyl complexes are in progress.
[M]MolCat@LDH/LSH hybrid catalysts. We have shown that the insertion of [Re(bpy-4,4'-(COOH)2)(CO)3Cl] into LSH is possible; this result is promising and encouraging for the future. [M]Porphyrin@LDH/LSH type hybrid materials (e.g. ZnLSH-MTetraSulfonate PhenylPorphyrin with M = Fe and Co; ZnCrLDH-FeTSPP, MgAlLDH-FeTSPP) have been synthesized. The first step of one of the [M]MolCat@LSH synthesis strategies (insertion of a ligand in the LSH: bpy@ZnLSH), has been successfully completed. It remains to show that the complexation of the inserted bpy is possible and that it allows to obtain [M]MolCat@ZnLSH.
During the first months of the project, efforts were concentrated on the development of LDH with various metals (Cu, Mg, Al, Zn Cr) and various anionic intercalants, and their characterization (structural and redox in presence and without CO2) in view of their use as host matrices to prepare [M]MolCat@LDH and MOCat@LDH. Hybrid compound models (Cat@LOH), associating lamellar copper hydroxides and alkyl chains of various lengths functionalized by carboxylic and sulfonic acids or sulfate functions, were prepared and characterized. The synthesis of hetero-bimetallic Cu/Zn-LSH has been initiated. This work will be pursued with a focus on the structural characterization of these new materials; the properties of the latter will be compared to the same type LDH materials.
The new LOH are characterized as they are studied. For example, the intercalation of bpy or porphyrin ligands, successfully achieved in the inter lamellar space of ZnLSH ZnCr-LDH, has been proven by PXRD and FTIR; the exact chemical compositions of LSH/LDH are deduced from the analysis of EDX and XPS spectra. The morphology of the materials is studied by SEM. Later, the catalytic properties of the materials can be correlated to their structures.
The characterization of the redox properties and the catalytic activity towards CO2ERR have been implemented. We focused on HDL-based catalysts deposited on carbon conductive electrodes and on the characterization of their redox properties on an analytical scale. We performed preliminary preparative electrolysis with various catalytic materials in order to identify (qualitative and quantitative product analysis) the most promising candidates for CO2ERR but also, to know their potential as host matrix for [M]MolCat.
The research work undertaken will be consolidated and continued in accordance with the plan initially proposed in the project document
Two short-term scientific publications are planed
CALHYCO2 collaborative fundamental research project concerns the design and the development of innovative nanostructured layered hydroxide catalysts, containing metallic-organic complexes or metal oxides catalysts, for selective CO2 electroreduction. Layered Double Hydroxides and Layered Simple Hydroxides, are selected as metal-based functional host matrices (CO2 adsorbent and proton source) to structure, to modify and control the catalyst local environment. Due to their sophisticated structure, the developed catalysts should considerably improve the efficiency and durability of the catalytic CO2 electroreduction. Mechanistic studies, to decipher the factors governing the redox catalytic activity of these materials, will complete the experimental developments.
Madame Sylvie Chardon (DEPARTEMENT DE CHIMIE MOLECULAIRE)
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
IPCMS Institut de physique et chimie des matériaux de Strasbourg (UMR 7504)
Havard University / Nocera Group
DCM DEPARTEMENT DE CHIMIE MOLECULAIRE
ICCF INSTITUT DE CHIMIE DE CLERMONT-FERRAND
Help of the ANR 544,075 euros
Beginning and duration of the scientific project: September 2019 - 51 Months