The effect of varying the metal ratio in a chromium molybdate catalysts for the oxidative dehydrogenation of n-octane

Chromium molybdate catalysts with varying Cr/Mo ratios were synthesized by co-precipitation. The catalysts were characterized using XRD, Raman spectroscopy, TPR, BET surface area measurements, ICP-OES and HR-TEM. X-ray diffraction and Raman studies revealed that the dominant phase in the catalysts was Cr-2(MoO4)(3). Furthermore, Raman spectroscopy showed that excess Mo and Cr exist as MoO3 and Cr2O3 phases, respectively. The catalytic activation of n-octane was investigated from 350 to 550 degrees C, in a continuous flow fixed-bed reactor with the GHSV fixed at 4000 h(-1). Catalytic testing revealed that the conversion of n-octane and product selectivity varied with Cr/Mo ratio. At 6% isoconversion (350 degrees C), the stoichiometric catalyst, i.e. the catalyst with a Cr/Mo ratio of 0.67, produced octenes and carbon oxides as the major products with a selectivity of 51% and 49%, respectively.