Effects of molybdena on the catalytic properties of vanadia domains supported on alumina for oxidative dehydrogenation of propane

The oxidative dehydrogenation (ODH) of propane was investigated on vanadia dispersed on alumina containing a nominal polymolybdate monolayer (4.8 Mo/nm2). Dehydrogenation rates and selectivities on these catalysts were compared with those on vanadia domains dispersed on alumina. At a given vanadia surface density, ODH reaction rates per gram of catalyst were about 1.5–2 times greater on MoOx-coated Al2O3 than on pure Al2O3 supports. The higher activity of vanadia dispersed on MoOx-coated Al2O3 reflects the greater reducibility of VOx species as a result of the replacement of VOAl with VOMo bonds. The MoOx interlayer also increased the alkene selectivity by inhibiting propane and propene combustion rates relative to ODH rates. This appears to reflect a smaller number of unselective V2O5 clusters when alkoxide precursors are used to disperse vanadia on MoOx/Al2O3 as compared to the use of metavanadate precursor to disperse vanadia on pure Al2O3. At 613 K, the ratio of rate coefficients for propane combustion and propane ODH was three times smaller on MoOx/Al2O3 than on Al2O3 supports. The ratio of rate constants for propene combustion and propane ODH decreased by a similar factor.