Vanadium Supported on Alumina and/or Zirconia Catalysts for the Selective Transformation of Ethane and Methanol

Vanadium supported on pure (Al2O3, ZrO2) or mixed zirconia-alumina (with Al/(Al + Zr) ratio of 0.75 or 0.25) catalysts have been prepared by wet impregnation, using homemade prepared supports. The catalysts have been characterized and tested in the oxidative dehydrogenation (ODH) of ethane and in the methanol aerobic transformation. The catalytic performance strongly depends on the nature of the metal oxide support. Thus, activity decreases in the order: VOx/ZrO2 > VOx/(Al,Zr-oxides) > VOx/Al2O3. On the other hand, at low and medium ethane conversions, the selectivity to ethylene presents an opposite trend: VOx/Al2O3 > VOx/(Al,Zr-oxides) > VOx/ZrO2. The different selectivity to ethylene at high conversion is due to the lower/higher initial ethylene formation and to the extent of the ethylene decomposition. Interestingly, VOx/(Al,Zr-oxides) with low Zr-loading present the lowest ethylene decomposition. The catalytic results obtained mainly depend on the nature of the supports whereas the role of the dispersion of vanadium species is unclear. In methanol oxidation, the catalysts tested present similar catalytic activity regardless of the support (Al2O3, ZrO2 or mixed Al2O3-ZrO2) but strong differences in the selectivity to the reaction products. Thus, dimethyl ether was mainly observed on alumina-supported vanadium oxide catalysts (which is associated to the presence of acidic sites on the surface of the catalyst, as determined by TPD-NH3). Formaldehyde was the main reaction product on catalysts supported on Zr-containing oxides (which can be related to a low presence of acid sites). In this article, the importance of the presence of acid sites in ethane ODH, which can be estimated using the methanol transformation reaction, is also discussed.