Zr-Doped TiO2–x Nano-Oxide with Coordinatively Unsaturated Ti(Zr)–O Acid–Base Pairs for Efficient Propane Dehydrogenation

Recently, some traditional oxide supports, such as nano TiO₂ and ZrO₂ with high surface energy, have been found to be partially reduced to generate oxygen vacancies and coordinatively unsaturated metal (M_cu) cations as efficient active sites for nonoxidative propane dehydrogenation (PDH). However, the primary challenge in their industrial applications is rapid deactivation because of coke, over-reduction, and aggregation under the reaction conditions of high temperature and reducible atmosphere. Herein, we reported that cost-effective and environmentally friendly Zr-doped TiO₂ (Ti_xZr₁) prepared by a simple coprecipitation method can be used as a highly efficient and stable catalyst for PDH. Ti₃Zr₁ exhibited the C₃H₆ formation rate [r(C₃H₆)] of 0.6 mmol g^–1 min^–1 at 550 °C, which was 17 times that of pure TiO₂, and a deactivation constant (K_d) 2.8 times lower than that of commercial TiO₂. Moderate Zr doping promotes the generation of surface active lattice oxygen, which can be reduced at a relatively low temperature to form oxygen vacancies and Ti(Zr)_cu–O acid–base pairs as the active sites for PDH, and their number is in line with r(C₃H₆) of Ti_xZr₁ catalysts. With the increase of the Zr doping amount, the bulk crystal phase of Ti_xZr gradually transforms from Zr-doped anatase TiO₂ to TiZrO₄ via Ti₂ZrO₆ with enhanced thermostability, which can inhibit over-reduction and aggregation of the nano-oxide.