Niobium oxide as support material for the oxidative dehydrogenation of propane

Abstract

The ability of using niobium oxide (Nb 2O 5) as a support for preparing surface metal oxide species and testing the catalyst for the ODH of propane was done in the present study. Chromium oxide was used as the representative surface metal oxide species. To test the objective several loadings of Cr 2O 3/Nb 2O 5 were prepared by the incipient wetness impregnation technique. Surface area analysis, Raman, X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) spectroscopy and TPR studies were used to characterize the sample. It was observed that surface chromium oxide species are formed similar to those on other oxide supports and similar monolayer coverages were achieved. However, the reduction characteristic ( T max temperature) was different due to the change in the Cr–O–support bond. The ODH of propane over the Cr 2O 3/Nb 2O 5 catalysts revealed that the activity increased up to monolayer coverage and then decreased due to the presence of Cr 2O 3 crystals. Similar observations were seen for the V 2O 5/Nb 2O 5 and MoO 3/Nb 2O 5 catalysts. The turnover frequency (TOF) was independent of coverage for the surface chromium, vanadium and molybdenum oxide species on Nb 2O 5. The constant TOF suggests the structure insensitivity of this type of reaction. The propene selectivities were high and relatively constant for the Cr 2O 3/Nb 2O 5 catalysts revealing the higher yields that can be obtained on this series of catalysts compared to the Cr 2O 3/Al 2O 3 and Cr 2O 3/TiO 2 catalysts. Additional studies involving tungsten and molybdenum oxide additives on 1% Cr 2O 3/Nb 2O 5 reveal the effect of exposed support surface on the propene selectivities.