Selective Oxidative Dehydrogenation of Light Alkanes over Vanadate Catalysts
It has been observed that a mixed oxide of magnesium and vanadium is a rather selective oxidative dehydrogenation catalyst for light alkanes. Selectivities of 50% and higher could be obtained at an alkane conversion of about 50%. Spectroscopic analyses of the catalysts showed that the active component was magnesium orthovanadate. Other orthovanadates were equally selective. However, magnesium pyrovanadate and magnesium metavanadate were nonselective. This was explained by the different bonding of oxygen ions in these compounds.
The reaction mechanism was consistent with the assumption that the first step of the reaction was the breaking of a C-H bond to form an alkyl radical. At lower reaction temperatures, hexane oxidation yielded a substantial amount of hexanone. At higher temperatures, butane and propane yielded only dehydrogenation products but no oxygenates. It was confirmed that some of the alkyl radicals were desorbed into the gas phase for further reaction in the postcatalytic volume.