Synergizing Mo<sub><i>n</i></sub> Clusters and Mo<sub>2</sub>C Nanoparticles on Oxidized Carbon Nanotubes Boosting the CO<sub>2</sub> Reduction Activity
Shuo Cao, Zun Guan, Ying Ma, Bing Xu, Jun Ma, Wei Chu, Riguang Zhang, Giuliano Giambastiani, Yuefeng Liu
Abstract
The design and synthesis of highly efficient and selective catalysts for CO 2 thermal reduction remain a challenging issue of modern catalysis. Molybdenum carbide has attracted great interest in CO 2 -to-CO conversion (Reverse Water Gas Shift process, RWGS) because of its ability to dissociate CO 2 and H 2 . However, single dominant Mo- or C-terminated facets of molybdenum carbide are unlikely to activate CO 2 and H 2 molecules simultaneously. Herein, we demonstrate how structural diversity of cogenerated molybdenum species (i.e., Mo n nanoclusters and Mo 2 C nanoparticles) on the surface of an oxygen-enriched C-carrier boosts synergistically the chemoselective RWGS process with rates up to 581 μmol CO2 ·g Mo –1 ·s –1 with CO selectivity > 99% already at 400 °C under an H 2 -rich environment. This catalytic outcome ranks among the highest reported so far for molybdenum carbide- or noble metal-based catalysts in the process, and it is up to 1.8 times higher than that measured on Mo 2 C-based nanoparticles. The enhanced reactivity of the structurally mixed catalyst has been ascribed to a synergistic modulation of the geometrical and electronic structure of different Mo sites that reduces the temperature at which CO production starts and facilitates the chemoselective CO desorption pathway. Experimental and in silico studies have also unveiled the existence of a linear correlation between the percentage of high-valence molybdenum species in the metal active-phase composition (Mo δ+ %) and the increase in the RWGS rate.