Photocatalytic gas-phase CO2 hydrogenation over MoS2-based materials. An Operando XAS analysis.

Metal dichalcogenides are excellent catalysts in a variety of industrial-relevant processes. Specifically, the photocatalytic reduction of CO2 over molybdenum sulfide (MoS2) is under research for the production of solar fuels, since the wide-range light absorption and gas adsorption capacity of MoS2. Recently, we have developed a low-temperature synthesis methodology able to induce the formation of a molybdenum oxysulfide (MoOxSy) phase. As a result, the surface of layered nanomaterials shows defects in the sulfide sublattice and combined Mo oxidation states (Mo4+, Mo5+ and Mo6+), which enable the doping with metal cations, such as Ni2+ or Ru3+, via photoassisted precipitation. This produces mixed metal environments with a high number of sulfide vacancies and oxide insets. The photocatalytic activity tests of metal-doped MoOxSy under light irradiation at different wavelengths, from UV at 365 nm to infrared at 940 nm at 523 K shows an increase of the CO2 conversion and continuous CO and CH4 productivities about 1.5 mmol/gcat·h. Although the hydrogenation occurs through the initial CO2 chemisorption on the catalyst, there is an interest in determining the role played by surface structure in the catalytic process. The concentration of surface sulfide defects and the presence of mixed oxidation states for molybdenum appears to have an impact in the catalytic performance. In addition, the incorporation of doping metals into the surface would modify the electronic structure of the gas-solid interface to enhance the catalytic reaction rates. To determine the influence of all these factors in the surface structure of the metal-doped MoOxSy catalysts and the changes occurring upon the CO2 hydrogenation, an in-situ EXAFS experiment is planned under reaction conditions at 523K and 1.7 bar. This experiment will serve to analyze the electron environment of Mo atoms upon CO2 hydrogenation and the role played by metal nanoclusters and sulfide vacancies in the photocatalytic process.