| Abstract |
Substoichiometric magnesium vanadate catalysts, (Mg-Vi 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. (C) 2010 Elsevier B.V. All rights reserved. |
