Hydrogen pre–reduction determined Co–silica interaction and performance of cobalt catalysts for propane dehydrogenation

Co@MCM–41 catalysts with and without hydrogen pre–reduction treatments are prepared for catalyzing non–oxidative propane dehydrogenation (PDH) to propylene. Multi–stage migration of framework Co²⁺ into extra–framework Co⁰ species can be achieved by the pre–reduction. The location and chemical states of Co species in catalysts are related to the pre–reduction temperature and time duration. The catalysts reduced at 650–700 °C are consisting of both framework Co²⁺ ions and small–size Co⁰ nanoclusters confined in the MCM–41 channels, displaying 2–3 times higher reaction rates in the selective PDH reactions in comparison with the unreduced catalyst. A higher pre–reduction temperature of 750–800 °C causes the formation of large Co particles that are responsible for significantly declined reaction rates and propylene selectivity as well as severe coke deposition. Hydrogen pre–reduction tunes the interaction between Co species and silica support, determining the performances of propane activation, propylene desorption and coke formation for the Co–catalyzed PDH reactions.