Selective oxidation of n-butane on a V-P-O catalyst: Study under fuel-richconditions

A vanadium pyrophosphate oxide (V-P-O) catalyst has been tested for n-butan e oxidation under fuel-rich conditions (O-2/C4H10 = 0.6) A rapid decrease i n maleic anhydride production was observed with time. XPS analysis showed t hat this was associated with a rapid reduction of the catalyst surface. Fro m the evolution of the distribution of products, it has been inferred that CO formation mainly occurs by the oxidation of adsorbed butane whereas CO2 is formed by the overoxidation of maleic anhydride. It has been concluded t hat the n-butane activation occurs on V4+ sites while the insertion of oxyg en in the C-4-intermediates leading to MA takes place on V5+ sites. The dea ctivation in fuel-rich conditions is not so drastic when the V-P-O catalyst has been previously oxidized at a relatively low temperature (500 degrees C). In this case oxygen is stored in the V-P-O surface region, hence favori ng the specific O-inserting role of V5+ responsible for IMA formation. (C) 2000 Academic Press.