Selective oxidation of ethane: Developing an orthorhombic phase in Mo-V-X (X = Nb, Sb, Te) mixed oxides

Mo-V-X (X = Nb, Sb and/or Te) mixed oxides have been prepared by hydrothermal synthesis and heat-treated in N-2 at 450 degrees C or 600 degrees C for 2 h. The calcination temperature and the presence or absence of Nb determines the nature of crystalline phases in the catalyst. Nb-containing catalysts heat-treated at 450 degrees C are mostly amorphous solids, while Nb-free catalysts heat-treated at 450 degrees C and samples treated at 600 degrees C clearly contain crystalline phases. TPR-H-2 experiments show higher H-2-consumption on catalysts with amorphous phases. Catalytic results in the oxidative dehydrogenation of ethane indicate that the selective production of the olefin is strongly related to the development of the orthorhombic Te2M20O57 or (SbO)(2)M20O56 (M = Mo, V, Nb) phase (the so-called M1 phase), which is mainly formed at 600 degrees C. This active and selective crystalline phase is characterized to show moderate reducibility and active centers enough for the selective oxidative activation of ethane with the minimum quantity possible of active centers for ethylene activation. In this sense, the best yield to ethylene has been achieved on a Mo-V-Te-Nb mixed oxide. (C) 2008 Elsevier B.V. All rights reserved.