Selection of optimum chromium oxide-based catalysts for propane oxidehydrogenation

Propane oxidative dehydrogenation has been studied at 350-500°C, 1.0 bar and feed flow rate of 75 cm3/min over several supported chromium oxide-based catalysts. Effects of various chromium loadings, different supports, catalyst precursors and reaction conditions were investigated in an attempt to select an optimum catalyst for the reaction. Chromium oxides of different loadings ranging from 0.1 to 20 wt.% on γ-Al2O3 were tested. At 450°C, 10 wt.% loading exhibited propane conversion of 19%. γ-Al2O3 gave the best performance when MgO, TiO2, SiO2 and γ-Al2O3 were tested as supports. As a precursor, Cr(NO3)3•9H2O exhibited the best results compared with K2Cr2O7, CaCr2O7, Na2Cr2O7, Cr2SO4•12H2O and CrO3. Effects of reaction temperatures and feed compositions were also evaluated on a 10 wt.% Cr-Al-O catalyst. The maximum selectivity to propene obtained was 61% while the yield was 18%. The 10 wt.% Cr-Al-O catalyst was characterized by X-ray diffraction patterns (XRD), temperature-programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS) which confirmed the presence of both Cr3+ and Cr6+ in the calcined catalyst and, also, the predominance of Cr3+ in the spent catalyst..