Selective and non-selective oxygen species determining the product selectivity in the oxidative conversion of propane over vanadium mixed oxide catalysts

The selectivity of catalytic oxidation reactions strongly depends on the availability of different oxygen species participating in the catalytic reaction. Lattice oxygen is generally assumed to act as the selective agent. However, although adsorbed, electrophilic oxygen species should lead to total oxidation, several indications have been reported that these species may also participate in selective reaction steps on the catalytic surface of several metal oxides. In the present work the role of different oxygen species on vanadium containing catalysts, V-Mg-O, V-P-O and V-Sb-O is elucidated using vacuum pulse experiments and stationary flow experiments at reduced pressure (P < 1 kPa). Isotopic labelled O-18(2) was partly used as oxidant in order to distinguish between lattice and adsorbed oxygen. On V-Mg-O and V-P-O catalysts adsorbed oxygen play a significant role in total oxidation, whereas only catalytically active lattice oxygen is available on V-Sb-oxide. However, on V-Mg-O and V-Sb-O different types of lattice oxygen exist leading either to selective or non-selective products. (C) 1999 Elsevier Science Ltd. All rights reserved.