EFFECT OF COEXISTENCE OF MAGNESIUM VANADATE PHASES IN THE SELECTIVE OXIDATION OF PROPANE TO PROPENE

The study of oxidative dehydrogenation of propane was carried out over V-Mg-0 catalysts. The citrate method was used to prepare catalysts wi th the Mg/V atomic ratio varying from 1/4 to 9/1. Three pure Mg vanada tes and the corresponding biphasic catalysts were obtained from very h omogeneous Mg-V-citrate precursors after calcination at 550-degrees-C. Among the three pure Mg vanadates, alpha-Mg2V2O7 (pyrovanadate) was f ound to be the most selective, while MgV2O6 (metavanadate) is the wors t one. Interestingly, the catalytic behavior of biphasic catalysts is quite different from that of pure Mg vanadate phases. For example, the selectivity of Mg3V2O8 (orthovanadate) can be promoted by a coexistin g pyrovanadate phase or excess magnesium oxide in intimate contact. Th ese differences are discussed in terms of the different specific activ ities of phases and possible synergy effects between the phases. (C) 1 994 Academic Press, Inc.