V 2O 5–SiO 2 systems prepared by flame pyrolysis as catalysts for the oxidative dehydrogenation of propane

Abstract

VO x /SiO 2 catalysts were prepared through an innovative flame pyrolysis (FP) technique and tested for the oxidative dehydrogenation of propane. The samples, of different V loadings, were characterized by electron paramagnetic resonance (EPR), micro-Raman, and FT-IR spectroscopy to assess the nature of the vanadium active sites in comparison with a sample prepared by impregnation. The active sites of the FP-prepared catalysts appeared as highly dispersed V 5+O groups partly incorporated into the silica matrix and interacting poorly with one another. Lower dispersion can be achieved at the same V loading with the catalyst prepared by impregnation. EPR revealed V 4+O groups pointing out normally from the catalyst surface and sitting in the center of a surface array of oxygen atoms. These V 4+ groups helped demonstrate the difference in catalytic behavior of the various samples. Catalytic activity measured under both aerobic and anaerobic conditions revealed a promisingly high selectivity with the FP-prepared samples. The best results were obtained with a 10 wt% V loading, which provided the best propylene yield among the samples, especially under anaerobic conditions (up to 80% selectivity at 10% propane conversion). This is likely related to the much higher dispersion of the VO x species in the FP-prepared samples, which also helps reduce the coke formation triggered by exposed surface acid sites.