Direct dehydrogenation of propane over Co@silicalite-1 zeolite: Steaming-induced restructuring of Co²⁺ active sites

The chemical state of the Co-relevant active site determines the catalytic performance of the Co-containing zeolite catalysts in non-oxidative propane dehydrogenation (PDH) reaction. Herein, we demonstrate that the moderate steaming pre-treatment is an available strategy to enhance catalytic activity of silicalite-1 zeolite-supported Co catalyst through tuning the Co state. The steaming-treated Co@S-1-steam catalyst exhibits sevenfold increased specific reaction rate (0.44 s⁻¹) than the untreated Co@S-1 catalyst and maintains 95 % propylene selectivity in the PDH reaction at 590 °C. By comprehensive characterizations on the structural properties of the catalysts, multiple roles of steaming treatment are discovered. Steaming treatment can induce the reductive restructuring of the Co catalytic sites in zeolite micropores to form tetrahedral Co²⁺ species with enhanced dispersion and unsaturation degree, and significantly accelerate the selective activation of propane C[sbnd]H bonds. Furthermore, it also reduces the surface acidity and consequently promotes the desorption of propylene intermediates for enhancing the catalytic reaction rate and anti-coke stability.