New insights into the composition and catalytic performance of VOx-Ga/γ-Al2O3 for the oxidative dehydrogenation of propane to propene

Abstract

Oxidative dehydrogenation (ODH) of propane is a promising alternative route for propene production. In this work, we developed a series of vanadium and gallium oxides supported on γ-Al₂O₃ catalysts by an incipient wetness impregnation method. Among the employed catalysts, the VGA-2 showed superior catalytic activity, and the catalyst was demonstrated for longevity in ODH of propane with a stable activity using a continuous flow fixed bed reactor at 400 °C. H₂-TPR and UV-visible spectra showed the presence of highly dispersed monomeric VO_x species with tetrahedral coordination geometry, which influences product selectivity. The characterization results also conferred that the redox nature of vanadium (V⁵⁺ and V⁴⁺) oxide and higher V⁵⁺ content on the surface of the VGA-2 catalysts are more favourable for C–H activation. In addition, the pyridine-FTIR and ⁷¹Ga solid-state NMR studies further substantiated the presence of Lewis acid sites and tetrahedrally coordinated Ga³⁺O_x species that are highly responsible for the ODHP activity, respectively. Furthermore, in situ-DRIFTS studies conferred that the propane adsorption at ambient temperature showed the formation of intermediate propoxide species with the evolution of σ-bonds and with further increase in the temperature to 325 °C; the stretching vibrations of the C–H and –C–H bonds in the propylene molecule were observed. The spent catalysts were also analyzed by thermogravimetric analysis, where the optimized catalyst (VGA-2) showed the least coke deposition.