Catalytic behavior of V-containing zeolites in the transformation of propane in the presence of oxygen

The catalytic behavior in propane oxidative dehydrogenation to propylene of V-containing silicalite-1, silicalite-2, ZSM-5 and boralite, prepared either by direct hydrothermal synthesis or by consecutive impregnation with ammonium vanadate of the zeolites in the acid form is reported. Results show that selectivity to propylene depends on the V content and is comparatively higher in samples prepared by direct hydrothermal synthesis than in those prepared by impregnation, but the concentration of propane and the propane to oxygen ratio considerably affect the results. At higher reaction temperatures the presence of weak acid sites due to vanadium ions induces the formation of aromatics. The formation of the latter is enhanced in V-containing boralite and ZSM-5 samples. Maximum selectivities to propylene up to 80-85% are obtained, but only at low propane or oxygen conversion (around 5%).