(623d) Dehydrogenation of Ethylbenzene to Styrene with CO2 Over V2O5/Al2O3-ZrO2 Catalyst

Styrene has been producing by ethylbenzene dehydrogenation over iron oxide catalyst with a large excess of superheated steam. Over 70 years improvement, both material and energy consumption of this technique have well developed, but the present commercial process still has several drawbacks, such as equilibrium-limited and energy intensive. To improve ethylbenzene conversion and enhance thermal efficiency, the oxidative dehydrogenation of ethylbenzene is developed. The original attempt is using oxygen. Unfortunately, it has a number of safety issues and suffers from a significant loss of styrene selectivity by producing substantial oxidation products. As a result, it does not industrialize up to now. Carbon dioxide, as a mild oxidant, can substitute for oxygen in this process. Compared to use H₂O, using CO₂ is an obvious energy-saving process. The utilization of CO₂, which is one of main contributors to the greenhouse effect, is conformed with the trend of green chemistry. However, the present commercial catalyst is ineffective in the presence of CO₂. The indispensable requirement is the selection of a catalyst system which can activate CO₂.

Recently, several attempts are carried out in the process of dehydrogenation of ethylbenzene to produce styrene with CO₂ (DESC).Various catalyst systems based on mostly Fe-, V-containing are found to be active and selective in the course of DESC. This reaction proceeds via Mars and Van Kerevelen mechanism. Researchers have explored that catalyst’s lattice oxygen involves this redox reaction, what’s more, the catalyst activity is mainly relied on lattice oxygen activity. Compared to FeO_x, VO_x has more O active sites, therefore, it will be modified easily and then, decreased its deactivation speed. In this aspect, VO_x has greater advantage. Carrier selection is also important for a proper catalyst system. ZrO₂ has received considerable attention in catalysis and material science. Its bifunctional properties of acid and base, reducing and oxidizing ability, and high thermal stability, are suit for the process of DESC. In general, ZrO₂ has low surface area, more expensive price than many traditional oxide materials. Therefore, prepared a mixed oxide will be a good way. In addition, mixing the pure oxides is favorable to modulate the properties of each component and create new active sites. In this work, we synthesis Al₂O₃-ZrO₂ multiple oxide support, and then impregnate VO_x to prepare V₂O₅/Al₂O₃-ZrO₂ catalysts. Based on the same VO_x loading, the optimal loading amount of ZrO₂ in Al₂O₃-ZrO₂ support is also explored. The result shows that V₂O₅/Al₂O₃-ZrO₂ catalyst with ZrO₂ loading of 10 wt% demonstrates the best catalytic activity. The ethylbenzene conversion is 43% and styrene selectivity is above 97%.