Qing-Qing Hao

V2O5/Ce0.6Zr0.4O2-Al2O3 as an efficient catalyst for the oxidative dehydrogenation of ethylbenzene with carbon dioxide.

Vanadium has been widely used in catalysis because metaloxide-supported vanadia can catalyze many industrially important reactions, such as oxidation reactions. 2] The activity of the supported vanadia is highly dependent on the specific oxide support as a result of the so-called strong metal oxide–support effect. Although many researchers have attempted to gain insight into the catalytic mechanism, by using theoretic calculations and various characterization techniques, it is not yet fully understood. Thus, the design of a high-performance supported vanadia catalyst, especially one with a high degree of stability, is still a challenge. The oxidative dehydrogenation of hydrocarbons (ODH) to alkenes is industrially important for various large-volume synthetic polymers. Because ODH with molecular oxygen as oxidant is a promising solution, many efforts have been reported. Based on the concepts of dehydrogenation and selective catalytic oxidation of hydrogen, the commercial SMART process for the oxidative dehydrogenation of ethylbenzene was developed. This process co-feeds oxygen and steam in seriesreactor system. b] To overcome safety problems that result from mixing oxygen and light hydrocarbons, a novel idea to remove the dehydrogenation product of hydrogen by using reducible lattice oxygen was proposed, and a high-performance catalyst for the selective combustion of hydrogen in the presence of light hydrocarbons has been developed. Alternatively, ODH using CO2, being a soft oxidant without the problem of deep oxidation, is very attractive because it may open up new directions for oxidation reactions, and create a new route for ODH. Thus, oxidative dehydrogenation of ethylbenzene with CO2 (CO2-ODEB) has been extensively investigated as an efficient, energy-saving, and environmentally benign process. 7] Although the supported vanadia catalyst shows high activity towards CO2-ODEB, [7a–f] which proceeds via the Mars–van Krevelen redox mechanism, 2] it still suffers from severe catalyst deactivation. Being an excellent redox material, ceria stabilized with zirconia has found widespread use as catalyst or catalyst support. 8] Moreover, defect-site-enriched ceria (with the nature of the defects determined by the applied preparation method) has been reported to promote ODEB with N2O. [9] Thus, the combination of CeZrO2 with vanadia may create a unique ODH catalyst, provided that a very well dispersed oxide can be achieved. In this case, CO2-ODEB may proceed according to the redox cycle illustrated in Scheme 1. The oxidation of Ce to Ce by CO2 and the reduction of V 5+ to lower oxidation states (possibly V) by ethylbenzene are directly involved in CO2ODEB. Subsequently, V is oxidized to V with the reduction of Ce to Ce to complete the full cycle.