Molybdenum Carbide Nanoparticles in Silicalite-1 Zeolite for CO<sub>2</sub>-Assisted Propane Dehydrogenation
Bing Xu, Jun Ma, Shuo Cao, Ying Ma, Giuliano Giambastiani, Yuefeng Liu
Abstract
Molybdenum carbides (MoC x ) 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 MoC x 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 (MoC x /Si-1) to be employed in direct and/or CO 2 -assisted propane dehydrogenation reaction. The as-synthesized MoC x /Si-1 exhibits enhanced CO 2 -assisted oxidative propane dehydrogenation (CO 2 -ODHP) performance with rates up to 172.8 μmol g cat –1 min –1 with C 3 H 6 selectivity > 94% (61.5% C 3 H 6 selectivity for bulk β-Mo 2 C), 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 (MoC x O y ) sites was crucial for CO 2 -ODHP. Propane is converted on MoC x O y active sites to propylene and H 2 O, while the MoC x O y are reduced into MoC x sites. Subsequently, the reduced MoC x sites are reoxidized by CO 2 into MoC x O y active sites and CO gas. This work designs molybdenum carbide nanoparticles embedded in Si-1 zeolite, demonstrates high activity and propylene selectivity in CO 2 -assisted propane dehydrogenation, and provides guidance for the application of carbides in alkane dehydrogenation.