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 3V 2O 8, Mg 2V 2O 7 and MgV 2O 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 3V 2O 8 sample was more active for the oxidative dehydrogenation of n-butane, but less selective to C 4 alkenes than the Mg 2V 2O 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.