The oxidative dehydrogenation (ODH) of ethane to ethylene is an interesting alternative to steam cracking of natural gas or oil derivatives because, in addition to allowing a lower reaction temperature, it avoids external supply of energy (due to its exothermic character), coke is not formed and the catalyst is in situ regenerated during the reaction. This paper shows the synthesis, characterization and catalytic performance for ethane ODH of MoVOx, MoVTeOx and MoVTeNbOx mixed oxide catalysts, which were activated in N2 in the 400-600 °C temperature range. The catalysts were prepared hydrothermally, and characterized by several physico-chemical techniques, i.e. N2-adsorption, XRD, TPR-H2, TPD-NH3, Raman, EPR and XPS spectroscopy. M1 presenting catalysts showed high selectivity to ethylene at low ethane conversion. However, the main difference in catalytic performance for ethane ODH of these catalysts lies on the extent of the over-oxidation of the ethylene formed at high ethane conversion. The different catalytic behavior of catalysts is compared with physico-chemical properties, including adsorption properties (of ethane, ethylene or CO2), and the nature of surface sites (determined by XPS) depending on composition and/or heat-treatment. These results indicate that the M1-containing catalysts present relatively low ability to activate ethylene, especially the MoVTeNbO sample heat-treated at 600°C, avoiding the further ethylene oxidation to COx. The XPS results of catalysts show important changes in the surface composition of catalysts depending of heat-treatment, especially the V4+/V5+ and the V/Mo ratio, which seems to have a strong influence of the selectivity to ethylene. In addition, the nature of active/selective sites for ethane oxidative dehydrogenation is also discussed.

Oxidative dehydrogenation of ethane over MoV(Te)(Nb)Ox oxides catalysts: Influence of catalyst activation procedure

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