Oxidative dehydrogenation of butane over substoichiometric magnesium vanadate catalysts prepared by citrate route

Substoichiometric magnesium vanadate catalysts, (Mg-Vi with i = 1, 2, and 3) with different V/Mg atomic ratios and stoichiometric (Mg3V2O8, Mg2V2O7 and MgV2O6), were prepared by citric acid technique. Characterization showed that substoichiometric samples correspond to well-dispersed VO4 units in the MgO matrix. Moreover, taking into account the Raman data, the coexistence of ortho, pyro and meta vanadate phases cannot be discarded. The Mg3V2O8 sample was more active for the oxidative dehydrogenation of n-butane, but less selective to C4 alkenes than the Mg2V2O7 sample. Stoichiometric samples produce mainly 1-butene, whereas for substoichiometric samples butadiene was the major reaction product for reaction temperatures higher than 748 K. The easily reducible VO4 species, and eventually the coexistence of different vanadates phases, appear to be responsible for the catalytic behaviour displayed by the substoichiometric catalysts prepared by citrate technique.