Authors: Michael Bowker Richard Holroyd Matthew House R Bracey Chanut Bamroongwongdee Mervyn Shannon Albert Carley
Publish Date: 2008/03/27
Volume: 48, Issue: 1-4, Pages: 158-165
Abstract
The role of Mo in the selective oxidation reaction is considered in some detail focusing on the selective oxidation of methanol to formaldehyde The reaction mechanism and kinetics will be described It is notable that Mo tends to segregate to the surface of iron molybdate catalysts proven by scanning transmission electron microscopy and XPS and so it dominates the surface even at very low loadings This is manifest in reaction data too for instance the selectivity to formaldehyde for a catalyst with only 20 Mo present is 50 at 50 conversion whereas for pure iron oxide it is close to zero at all conversions The active site for the reaction is MoVI which cycles through MoIV during the reaction MoIV itself is shown to be unselective for the reaction Lattice oxygen in the material can readily reoxidise the surface at temperatures above 300 °C Some of the mechanistic behaviour is analogous to the role of Mo in enzymatic processes such as xanthine oxidation and the two areas of catalysis by molybdenum are compared and contrasted The role of different types of oxygen such as ‘lattice’ oxygen ‘surface’ oxygen bridging and terminal oxygen species will be defined and clarified and the modified Mars–van Krevelen description of the heterogeneous reaction will be given
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