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

Abstract Substoichiometric magnesium vanadate catalysts, (Mg–V i with i = 1, 2, and 3) with different V/Mg atomic ratios and stoichiometric (Mg 3 V 2 O 8 , Mg 2 V 2 O 7 and MgV 2 O 6 ), were prepared by citric acid technique. Characterization showed that substoichiometric samples correspond to well-dispersed VO 4 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 Mg 3 V 2 O 8 sample was more active for the oxidative dehydrogenation of n -butane, but less selective to C 4 alkenes than the Mg 2 V 2 O 7 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 VO 4 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.