Elucidating the\nReaction Mechanism and Deactivation\nof CO<sub>2</sub>‑Assisted Propane Oxidative Dehydrogenation\nover VO<sub><i>x</i></sub>/TiO<sub>2</sub> Catalysts: A\nMultiple Operando Spectroscop

The CO<sub>2</sub>-assisted oxidative dehydrogenation\n(ODH) of\npropane is of great technical importance and enables the use (and\nthus removal from the atmosphere) of CO<sub>2</sub>, a greenhouse\ngas, in a value-adding process. Supported vanadium oxide (VO<sub><i>x</i></sub>) catalysts are a promising alternative to more active\nbut toxic chromium oxide catalysts. Despite its common use, TiO<sub>2</sub> has not been investigated as a support material for VO<sub><i>x</i></sub> in the CO<sub>2</sub>–ODH of propane.\nIn this study, we elucidate the interaction between titania (P25)\nand vanadia in the reaction mechanism by analyzing the reaction network\nand investigating the catalyst using X-ray diffraction (XRD), multiwavelength\nRaman, UV–vis and diffuse reflectance IR Fourier transform\n(DRIFT) spectroscopy. Besides direct and indirect ODH reaction pathways,\npropane dry reforming (PDR) is identified as a side reaction, which\nis more prominent on bare titania. The presence of VO<sub><i>x</i></sub> enhances the stability and the selectivity toward\npropylene by participating in the redox cycle, activating CO<sub>2</sub> and leading to a higher rate of regeneration. Additionally, VO<sub><i>x</i></sub> catalyzes the conversion of anatase to rutile,\nwhich facilitates CO<sub>2</sub> activation, thereby leading to an\nencapsulation of vanadium. At higher loadings, reducible VO<sub><i>x</i></sub> oligomers are present on the surface, facilitating\nsome PDR, but less than on bare P25. As the main deactivation mechanisms\nof the catalyst system, we propose the reduction of the titania lattice\nand the consumption of vanadium, while carbon formation appears to\nbe less relevant. Our results highlight the importance of analyzing\nthe CO<sub>2</sub>–ODH reaction network and applying a multispectroscopic\napproach to obtain a detailed mechanistic understanding of CO<sub>2</sub>-assisted propane ODH over supported VO<sub><i>x</i></sub> catalysts.