Abstract:
The V2O5-LnO-Al2O3 catalysts(LnO: La2O3, CeO2, Pr6O11, Nd2O3, Yb2O3) were synthesized via the route by combining the urea-hydrolysis assisted hydrothermal and evaporation-induced self-assembly methods. For all the catalysts,the V2O5 and LnO loading were fixed to 9% and 7%(mass fraction), respectively.The catalysts were characterized by the N2 adsorption/desorption, XRD, Raman, H2-TPR, XPS and TG-DSC techniques. Under the conditions of 0.1 MPa, 550 ℃, CO2/ethylbenzene (EB) of 20(molar radio)and contact time of 0.17 h, the promotional effects of rare earth oxides on the catalytic performance of V2O5-Al2O3 for the oxidative dehydrogenation of ethylbenzene with CO2 (CO2-ODEB) were investigated.Results indicate that the addition of rare earth oxide into V2O5-Al2O3 had clear impacts on the textural, structural and reduction properties of the catalysts, the extent of which is strongly dependent on the specific LnO. Among the investigated catalysts,V2O5-Pr6O11-Al2O3 catalyst showed the highest initial EB conversion, which is mainly attributed to the more ordered mesostructure, the largest specific surface area and the most abundant reducible VOx species on the surface of the catalyst. In contrast,V2O5-CeO2-Al2O3 catalyst showed the best stability for CO2-ODEB.This is well explained as the stable redox recycle of V5+/V4+ due to the highest amount of the oxygen defects, a higher amount of reducible VOx species and the higher reducibility of the catalyst. Although the coke deposition over the catalyst for CO2-ODEB was alleviated by adding LnO into V2O5-Al2O3, the catalyst deactivation caused by the irreversible reduction of V5+ was more significant,revealing the critical role of the irreversibly reduced V5+ for the deactivation of the catalyst.