Oxidative dehydrogenation of ethane over chromium-vanadium mixed oxide and chromium oxide catalysts

Oxidative dehydrogenation of ethane to ethylene was investigated at temperatures below 500 degrees C over Cr-O and Cr-V-0 oxide'catalysts prepared by the complexation method. The catalysts were characterized by XRD, H-2 TPR, and XPS techniques. The Cr-O catalyst was more active than Cr-V-0 mixed oxide in the selective oxidation of ethane using 02 or CO2 as the oxidant. Cr-O showed activity at temperatures as low as 250 degrees C. TPR results showing easier reduction of Cr-O at much lower temperatures than Cr-V-0 support a correlation between the reducibility and the activity of the catalysts in this reaction. XPS results indicating the reduction of chromium and vanadium species from Cr (6+) to Cr3+ and from V5+ to V4+ (and V3+) support a redox mechanism for this oxidative dehydrogenation reaction. Over Cr-O catalyst, total conversion and ethylene selectivity values of 0. 11 and 0.91 were obtained, respectively, at 250 degrees C for an O-2/C2H6 feed ratio of about 0.33 and at a space time of 0.24 g s/cm(3). With this catalyst, the ethane conversion increased to 0.3, and the ethylene selectivity decreased to about 0.75 when the temperature was increased to 400 degrees C. For both catalysts, higher selectivity values, i.e., above 0.95, were observed when CO2 was used as a mild oxidant instead Of O-2