Effect of Ce Content on the Chemical Looping Oxidative Dehydrogenation of Propane to Propylene over a VO[sub.x]-CeO[sub.2]/γ-Al[sub.2]O[sub.3] Oxygen Carrier

The chemical looping oxidative dehydrogenation of propane to propylene (CL-ODHP) replaces molecular oxygen with lattice oxygen (O[sub.latt]) in oxygen carriers. This method boosts propylene selectivity by avoiding the deep oxidation of propane. Herein, a series of 10V-XCe/Al oxygen carriers with different Ce contents were prepared to realize different VO[sub.x]-CeO[sub.y] interactions. The effect of the Ce content in 10V-XCe/Al oxygen carriers on the CL-ODHP reaction was studied and the optimal Ce content was determined. CeO[sub.2] prevents the outward diffusion and evolution of O[sub.latt] in VO[sub.x] carriers to the adsorbed electrophilic oxygen species (O[sub.elec]), effectively inhibiting the loss of O[sub.latt], improving the selectivity of propylene, and extending the lifetime and activity of the oxygen carriers. After characterizing and analyzing the oxygen carriers, it was found that 10V-3Ce/Al has the highest specific surface area, highest oxygen capacity, and lowest reducibility. The 10V-3Ce/Al also delivers the highest oxidative dehydrogenation performance. At 550 °C, the average propylene and CO[sub.x] selectivity values of 10V-3Ce/Al were 81.87% and 7.28%, respectively (vs. 62.79% and 25.64% respectively, for 10V/Al). It is demonstrated that 10V-3Ce/Al exhibits good cycle stability with no significant decrease in catalytic performance after 15 cycles. In situ diffuse-reflectance infrared Fourier-transform spectroscopy indicates that CL-ODHP on 10V-3Ce/Al undergoes the Mars-van Krevelen mechanism. The migration and evolution of O[sub.latt] in oxygen carriers is controlled by reasonably modifying the metal oxide interactions to improve propylene yield. This work will thus guide the subsequent development of novel and efficient CL-ODHP oxygen carriers.