Abstract
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.
Highlights
Ethylene is, probably, the most important raw material used in petrochemistry
In the oxidative dehydrogenation (ODH) of ethane over supported vanadium oxide catalysts, ethylene, CO and CO2 have been the main reaction products the catalytic performance highly varies depending on the catalyst chosen
Alumina-supported vanadia catalysts are more selective to ethylene in the ODH of ethane than the corresponding catalysts supported on Zr-containing metal oxides
Summary
The most important raw material used in petrochemistry. the crisis of the last decade did not affect the ethane demand and the global capacity has been continuously increasing. More than 95% of the ethylene produced around the world proceeds from the steam cracking process, an easy, but inefficient, non-catalytic process. The most promising alternative is the oxidative dehydrogenation of ethane (ODH of ethane), an exothermic reaction in which ethane is fed together with oxygen. In this reaction, using standard catalytic systems the catalysts hardly deactivates as a continuous re-activation of the active sites by the oxygen fed takes place. The oxidative dehydrogenation of ethane has not been implemented yet in industry. There are promising results at the laboratory scale that make this reaction very interesting to study
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