Highly Active Nanosized Anatase TiO2–x Oxide Catalysts In Situ Formed through Reduction and Ostwald Ripening Processes for Propane Dehydrogenation

The research and development of abundant, non-toxic, low cost, and high-performance catalysts are urgently required for the production of propylene through propane dehydrogenation (PDH) reaction. Here, the pure TiO2 nanoparticles, obtained through in situ reduction, exhibit excellent catalytic PDH performance. At 600 °C, the initial propane conversion could reach 67%, and the one-pass yield of propylene was 45%. The propane conversion was 21% at 550 °C, and propene selectivity could reach as high as 94%. According to ex/in situ characterization results and Quantum chemical calculations, the dynamic formation and reaction mechanism of active sites were detailedly investigated. The reductive propane and its derivatives can react with surface lattice oxygen of nanosized anatase TiO2 to form oxygen vacancies and coordinatively unsaturated Ti cations (Ticus), which can catalyze PDH with high propene selectivity; the rate of C3H6 formation is in line with the surface oxygen vacancy concentration. Notably, the Ostwald ripening of nanosized TiO2 with high surface energy is crucial to the formation of oxygen vacancies. The agglomeration of nanosized TiO2 at high temperature makes the lattice oxygen atoms mobile and active, which are consumed abruptly and then form oxygen vacancies and Ticus more easily. It is denoted as “mutation reduction”. The surface oxygen vacancy concentration is also influenced by the oxygen migration rate from bulk to surface driven by thermal energy and potential energy (the differences of concentration).