Insight into the Reaction Mechanism and Deactivation during CO2-Assisted Propane ODH over VOx/TiO2 Catalysts: An Operando Spectroscopic Study

The CO2-assisted oxidative dehydrogenation (ODH) of propane is of great interest for technical applications, enabling the use of the greenhouse gas CO2 in a value-adding process. Supported vanadium oxide (VOx) catalysts are a promising alternative to more active but toxic chromium oxide catalysts. Despite its common use, TiO2 has not been investigated as support material for VOx in the CO2-assisted ODH of propane. In this study, we address the interaction between titania (P25) and vanadia within the reaction mechanism using XRD, multi-wavelength Raman, UV-Vis and DRIFT spectroscopy. Besides direct and indirect ODH reaction pathways, propane dry-reforming (PDR) is identified as a side reaction, which is more prominent on bare titania. The presence of VOx enhances the stability and selectivity by participating in the redox cycle, activating CO2 and leading to a higher rate of regeneration. As main deactivation mechanisms of the catalyst system we propose the reduction of the titania lattice and the consumption of vanadium, while carbon formation appears to be less relevant. Our results highlight the importance of analysing the CO2-ODH reaction network and applying combined steady-state spectroscopies as a first step towards a detailed mechanistic understanding of CO2-assisted propane ODH over supported VOx catalysts.