Study On The Oxidative Dehydrogenation Of Ethylbenzene Over Potassium-Modified Ceria Catalys

Styrene is an important organic feedstock for the production of plastics and synthetic rubber.Currently,the ethylbenzene direct dehydrogenation process accounts for about 83.3%of global styrene production,but this process still faces problems such as high feed ratios of steam to ethylbenzene,limited thermodynamic equilibrium conversions,and complex product separation.The advantage of ethylbenzene oxidative dehydrogenation over direct dehydrogenation of ethylbenzene is that the oxidant can be used to completely oxidize the hydrogen produced during the reaction to water simultaneously,avoiding the equilibrium conversion rate limitation in conventional dehydrogenation,making full use of the heat generated in the combustion of hydrogen,and thus reducing the process energy consumption.CO₂ethylbenzene oxidative dehydrogenation can convert CO₂to CO at the same time as ethylbenzene dehydrogenation,inhibiting the deep oxidation of hydrocarbons,and providing an opportunity for styrene preparation and CO₂resource recovery.It provides a new way for styrene preparation and resource utilization of CO₂.In this paper,we proposed the use of K/Ce O₂as an ethylbenzene oxidative dehydrogenation catalyst and the innovative use of CO₂-O₂mixed oxidation atmosphere to increased the catalyst lattice oxygen supplementation for the efficient conversion of ethylbenzene to styrene.It was confirmed by HSC software simulation that the oxidative dehydrogenation reaction of ethylbenzene could be achieved under the mixed CO₂-O₂atmosphere to reach the thermoneutral condition.The alkali metal Li/Na/K oxide-loaded Ce O₂was successfully prepared by precipitation and over-impregnation methods,and the XRD,H₂-TPR and TEM characterization and performance tests under Ar atmosphere showed that the surface loading of alkali metal could significantly improve the oxygen storage capacity of the catalyst,and the catalytic performance was highly dependent on the type of alkali metal,with the best performance of 10%K/Ce O₂catalyst and the ethylbenzene conversion reached 71.9%and styrene selectivity reached 94.6%.The optimal experimental conditions for the oxidative dehydrogenation of ethylbenzene were obtained after atmosphere optimization,reaction temperature optimization and space velocity optimization.Under the optimal conditions of CO₂-4O₂oxidation atmosphere,temperature 500℃and space velocity 5.0 h^-1,the 10%K/Ce O₂catalyst achieved 96.1%average conversion of ethylbenzene,94.2%average selectivity of styrene and 90.5%yield of styrene after 50 hours of long-term stability test.Despite the small amount of K₂CO₃and carbon formation,the 10%K/Ce O₂catalytic performance remained excellent and showed good structural stability.CO₂and O₂play an important role in the mixed atmosphere,with CO₂mainly suppressing the by-product generation and ensuring high styrene selectivity;O₂plays a decisive role in enhancing the conversion of ethylbenzene.The catalyst surface reaction in ethylbenzene atmosphere shows that both CO₂and O₂can individually participate in oxygen intertransport and supplement lattice oxygen,but in the mixed atmosphere CO₂-O₂,O₂is the main force for lattice oxygen supplementation,while oxygen vacancies are the driving force for oxygen exchange during oxidative dehydrogenation,and CO₂induces Ce O₂to form oxygen vacancies and promotes oxygen exchange between gaseous oxygen and Ce O₂.The dehydrogenation of ethylbenzene in CO₂-O₂follows the Mars-van Krevelen（Mv K）reaction mechanism of redox via Ce³⁺/Ce⁴⁺pairs.The oxidative dehydrogenation strategy of ethylbenzene by using oxygen-rich vacancy catalysts and based on the CO₂-O₂mixed atmosphere proposed in this paper provides important insights into the efficient dehydrogenation of ethylbenzene under mild conditions.