Mo-V-Nb oxide catalysts for the partial oxidation of ethane - II. Chemical and catalytic properties and structure function relationships

A mixed oxide catalyst of the composition Mo(73)V(1.8)Nb(9)O(x) and crystalline phases prepared in pure form were analysed for their acidity and reducibility. The results were used to find possible relationships between these properties and the catalytic activity of the samples, determined under a reaction pressure of 2 MPa, for the selective oxidation of ethane to ethene and acetic acid and for the formation of acetic acid from ethene. Effects of the morphology and elemental distribution of these samples, as described elsewhere, have also been considered. While all samples catalysed the oxidative dehydrogenation of ethane to ethene, only the Mo6V9O40 phase and the multiphase catalyst, the two most easily reduced samples, led to the formation of acetic acid. This suggests that the oxygenation to acetic acid is favoured over an easily reducible catalyst. The selectivities and ethane conversion obtained with the multiphase catalyst were found to be higher than with any of its crystalline components. Therefore, the amorphous part of the multiphase catalyst seems to be particularly important. For the oxidation of ethene, the acetic acid yield was highest when catalysed by the Mo6V9O40 phase. It is proposed that this result is related to the higher acidity relative to the multiphase catalyst, thereby supporting the view that the activation of the hydrocarbon occurs by heterolytic splitting of the C-H bond. (C) 1998 Academic Press.