Oxidative dehydrogenation of ethane with carbon dioxide over silica molecular sieves supported chromium oxides: Pore size effect

Abstract

SBA-15 with varied pore size from 4 to 8 nm were synthesized by tuning the temperature of hydrothermal treatment, the supports were then used to load the active phase CrO x through a conventional impregnation method. The resulting catalysts were characterized by small/wide angle XRD, N 2 adsorption/desorption, FT-IR, TEM-EDX, XPS, TPR and CO 2 -TPD to study the feature of structure, surface chemical state, redox and basicity. It was found from these results that the metal species could be well dispersed on catalysts with larger pore size. Cr 6+ species could enter into the framework by substituting the Si atoms of SBA-15, and Cr 3+ mainly exist on extra framework. Pore size had profound effects on reducibility, surface composition and basicity. Cr 6+ species were necessary to activate the C-H bonds of alkanes, while the basicity played an important role in activating C-O bonds of CO 2 . The best performances were achieved over the sample Cr supported on SBA-15 with a pore diameter of 7 nm in oxidative dehydrogenation of ethane in the presence of CO 2 . • Pore size of SBA-15 was tuned by changing hydrothermal temperature. • Cr 6+ could enter the framework of SBA-15 by partially replacing Si atoms. • Cr 6+ and Cr 3+ species co-existed on extra framework of SBA-15. • Cr 6+ species were important for activating alkane. • Activation of CO 2 was related to basicity of catalysts.