Fabrication of Co/HMS catalyst by modulating the hydrothermal time for the oxidative dehydrogenation of C2H6 with CO2 to C2H4

A series of cobalt doped hexagonal mesoporous silica (Co-HMS) with the different hydrothermal time was prepared by direct hydrothermal method and applied for oxidative dehydrogenation (ODH) reaction of ethane with carbon dioxide. Structural and chemical properties of the catalysts were characterized by nitrogen adsorption, X-ray powder diffraction (XRD), transmission electron microscopy (TEM), electron dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and Raman and ultraviolet–visible (UV–vis) spectroscopy. These characterizations showed that cobalt not only entered the framework of Co-HMS catalysts but also was evenly dispersed in the bulk. The valence state and coordination mode of cobalt played an important role in the whole ODH reaction system of ethane with carbon dioxide. 1%Co-HMS (1 h) with dominant Co2+ had the highest conversion of ethane (26.0%). The formation of tetrahedral coordination Co2+(Td) is beneficial to the breaking of ethane hydrocarbon bond and the improvement of ethylene selectivity. 1%Co-HMS (1 h) with more Co2+(Td) performed the highest ethylene selectivity of 92.6%, which was stable during the 10 h reaction time.