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

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 Cr Oxthrough 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).