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 av ailability of different oxygen species participating in the catalytic react ion. Lattice oxygen is generally assumed to act as the selective agent. How ever, although adsorbed, electrophilic oxygen species should lead to total oxidation, several indications have been reported that these species may al so participate in selective reaction steps on the catalytic surface of seve ral 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 us ing vacuum pulse experiments and stationary flow experiments at reduced pre ssure (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, wh ereas 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 leadi ng either to selective or non-selective products. (C) 1999 Elsevier Science Ltd. All rights reserved.