EFFECT OF CATION REDUCIBILITY ON OXIDATIVE DEHYDROGENATION OF BUTANE ON ORTHOVANADATES

The orthovanadates of Mg, Zn, Cr, Ni, Cu and Fe were prepared, characterized with X-ray diffraction, laser Raman spectroscopy, and temperature programmed reduction, and tested for butane oxidation at 500-degrees-C using a feed of C4/O2/He of 4/8/88. The reaction results of these orthovanadates, when taken together with those of Nd, Sm and Eu orthovanadates obtained previously, indicated a correlation between the selectivity for oxidative dehydrogenation of butane to butenes and butadiene and the aqueous reduction potential of the component cation. The more reducible cations showed lower selectivities. The correlation was interpreted with a model that in the selectivity-determining step of the reaction, the probability that the surface intermediate could form a carbon-oxygen bond depended on the ease of removal of a lattice oxygen in the M-O-V group in the orthovanadate. Other correlations for the selectivity were attempted, which included the oxygen 1s binding energy and the electronegativity of the cations, but they were less successful.