CO2-Oxidative Dehydrogenation of Ethane to Ethylene over Cr/MCM-41 Nanocatalyst Synthesized via Hydrothermal/Impregnation Methods: Influence of Chromium Content on Catalytic Properties and Performance

A series of mesoporous Cr(x)/MCM-41 nanocatalysts with 0, 2, 5, 8 and 11 wt.% content of chromium were synthesized by hydrothermal/impregnation method. The effect of chromium loading on the structure and catalytic performance of Cr/MCM-41 nanocatalysts in the oxidative dehydrogenation of ethane with CO2 was investigated. The catalysts were characterized by XRD, FESEM, EDX, DRS, BET and FTIR analysis. Various chromium species including Cr6+, Cr3+ and crystalline Cr2O3 were found in the calcined Cr(x)/MCM-41 samples. Particles of crystalline alpha-Cr2O3 were detected in the catalyst with Cr total content above 2 wt.%. The variation of Cr content indicates that the Cr6+/Cr3+ ratio of samples increased with the Cr loading up to 8 wt.%. However, a decreasing trend was observed with further increase of Cr content. This can be justified by Cr surface density. It was found that there is an optimum Cr content in Cr(8%)/MCM-41 for the best catalytic activity, attributable to higher active Cr6+ species, and more uniform dispersion of chromium species with monolayer coverage on MCM-41 and also, homogeneous surface morphology with smallest particle size. It was found that this catalyst effectively dehydrogenated ethane to ethylene in the presence of CO2 at 700 degrees C, giving 53% ethylene yield. (C) 2016 Elsevier B.V. All rights reserved.