Molybdenum Carbide Nanoparticles in Silicalite-1 Zeolite for CO2-Assisted Propane Dehydrogenation

Molybdenum carbides (MoCx) have been shown to be effective catalysts in a number of challenging industrial-relevant reactions. Their promising performance combined with their natural abundance and low cost make them valuable alternatives to the use of noble metals. However, an often too limited exposure of active sites in micrometer-sized MoCx particles combined with their strong acid features depletes the ultimate catalytic performance for C–H bond activation in alkane dehydrogenation. In this work, we have synthesized highly dispersed molybdenum carbide nanoparticles (NPs) embedded into the framework of silicalite-1 zeolite (MoCx/Si-1) to be employed in direct and/or CO2-assisted propane dehydrogenation reaction. The as-synthesized MoCx/Si-1 exhibits enhanced CO2-assisted oxidative propane dehydrogenation (CO2-ODHP) performance with rates up to 172.8 μmol gcat–1 min–1 with C3H6 selectivity > 94% (61.5% C3H6 selectivity for bulk β-Mo2C), which is attributed to the moderate catalyst acidity, better H-spillover property, and the appropriate propane adsorption or propylene desorption mechanisms on such micropore systems. Extensive characterization data prove that a high concentration of exposed molybdenum oxycarbide (MoCxOy) sites was crucial for CO2-ODHP. Propane is converted on MoCxOy active sites to propylene and H2O, while the MoCxOy are reduced into MoCx sites. Subsequently, the reduced MoCx sites are reoxidized by CO2 into MoCxOy active sites and CO gas. This work designs molybdenum carbide nanoparticles embedded in Si-1 zeolite, demonstrates high activity and propylene selectivity in CO2-assisted propane dehydrogenation, and provides guidance for the application of carbides in alkane dehydrogenation.