XAFS Study of Silica-supported Chromium-based Catalyst

Silica-supported sodium-modified chromium catalyst Na-7.5%Cr/SiO2is found to be active for simultaneous activation of methane and carbon dioxide to aromatics(SAMCA). The best result shows the methane conversion of 4.0% and the selectivity of 48.7% to aromatics (benzene+toluene). X-ray absorption Cr K-edge fine structure analyses (XANES and EXAFS) and XPS are employed to study the surface structure of the catalyst. Both Cr6+and Cr3+are present on the surface, while the prosperous of Cr6+on the surface is observed. The results demonstrate that the dual-center(mixed oxidation state)/mixed site-symmetric structure—Td-Cr(VI)/Oh-Cr(III) is the catalytic active sites of Na-7.5%Cr/SiO2in SAMCA. A possible catalyst model of double-sites activation mechanism in SAMCA has been tentatively proposed.