Supported Molybdenum Carbide Nanoparticles as an Excellent Catalyst for CO<sub>2</sub> Hydrogenation
Marc Figueras, Ramón A. Gutiérrez, Francesc Viñes, Pedro J. Ramírez, José A. Rodríguez, Francesc Illas
Abstract
Experiments under controlled conditions show that MoC<sub>x</sub> nanoclusters supported on an inert Au(111) support are efficient catalysts for CO<sub>2</sub> conversion although with a prominent role of stoichiometry. In particular, C-deficient nanoparticles directly dissociate CO<sub>2</sub> and rapidly become deactivated. On the contrary, nearly stoichiometric nanoparticles reversibly adsorb/desorb CO<sub>2</sub> and, after exposure to hydrogen, CO<sub>2</sub> 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 MoC<sub>1.1</sub>/Au(111) to bind and dissociate C<sub>2</sub>. Model calculations carried out in the framework of density functional theory provide insight into the underlying mechanism suggesting that CO<sub>2</sub> hydrogenation on the hydrogen-covered stoichiometric MoC<sub>x</sub> nanoparticles supported on Au(111) proceeds mostly under an Eley-Rideal mechanism. Finally, 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.