Supported Molybdenum Carbide Nanoparticles as an Excellent Catalyst for CO2 Hydrogenation

Abstract

Experiments under controlled conditions show that MoCx nanoclusters supported on an inert Au(111) support are efficient catalysts for CO2 conversion, although with a prominent role of stoichiometry. In particular, C-deficient nanoparticles directly dissociate CO2 and rapidly become deactivated. On the contrary, nearly stoichiometric nanoparticles reversibly adsorb/desorb CO2 and, after exposure to hydrogen, CO2 converts predominantly to CO with a significant amount of methanol and no methane or other alkanes as reaction products. The apparent activation energy for this process (14 kcal/mol) is smaller than that corresponding to bulk δ-MoC (17 kcal/mol) or a Cu(111) benchmark system (25 kcal/mol). This trend reflects the superior ability of MoC1.1/Au(111) to bind and dissociate CO2. Model calculations carried out in the framework of density functional theory provide insights into the underlying mechanism suggesting that CO2 hydrogenation on the hydrogen-covered stoichiometric MoCx nanoparticles supported on Au(111) proceeds mostly under an Eley-Rideal mechanism. The influence of the Au(111) is also analyzed and proven to have a role on the final reaction energy but almost no effect on the activation energy and transition state structure of the analyzed reaction pathways.