Study On Catalytic Performance Of MO_x/Al₂O₃ For Dehydrogenation Of Ethylbenzene With CO₂

Styrene is one of the most important basic chemical products and is widely used in the production of plastics,resins and synthetic rubber.Industrially,styrene is mainly produced by dehydrogenation of ethylbenzene under a large amount of high temperature?600-650°C?superheated water vapor steam,and the energy consumption is huge.Therefore,there is an urgent need to develop new processes to solve the high energy consumption problem of the traditional ethylbenzene dehydrogenation process.The use of CO₂ as a mild oxidant instead of superheated water vapor steam for oxidize ethylbenzene dehydrogenation to styrene not only reduces the reaction temperature,but also greatly reduces the energy consumption of styrene production,and also improves the dehydrogenation efficiency of ethylbenzene.To this end,this paper studies energy-saving,high-efficiency and environmentally friendly new processes for the dehydrogenation of ethylbenzene to styrene,explores the structure-activity relationship and deactivation mechanism of the catalyst,and designs and develops a catalyst system with excellent performance,which provides theoretical basis and technical support to industrial applications.At the same time,the resource utilization of CO₂ is also of great sig-nificance to promote the energy-saving emission reduction of chemical processes and the construction of a low-carbon society.The paper mainly studied the catalytic performance of CeO₂/Al₂O₃ and TiO₂/Al₂O₃ for the dehydrogenation of ethylbenzene to styrene with CO₂ and the deactivation behavior of TiO₂/Al₂O₃ catalyst.The physicochemical properties of the catalyst were characterized by nitrogen adsorption,XRD,NH₃-TPD,CO₂-TPD,H₂-TPR,Raman,XPS,TGA and other techniques.The relationship between the structure of the catalyst and its properties was de-picted.The active phase of the TiO₂/Al₂O₃ catalyst and the cause of its deactivation were re-vealed.The following conclusions are drawn:1.CeO₂/Al₂O₃ and TiO₂/Al₂O₃ are suitable for the dehydrogenation of ethylbenzene with CO₂.Compared with CeO₂/Al₂O₃,the TiO₂/Al₂O₃ catalyst has higher catalytic activity.The aluminum sec-butoxide aluminum was used as the aluminum source,and the calcination temperature was 600°C.The 40 wt%TiO₂/Al₂O₃ catalyst prepared by sol-gel method showed the best catalytic performance.Under the reaction conditions of 550°C and 0.1 MPa,the initial EB conversion and styrene selectivity were 50%and 98%,respectively,and the activity of the catalyst decreased slightly for 50 h.EB conversion of TiO₂/Al₂O₃ catalyst in CO₂ atmosphere was significantly higher than that in N₂ atmosphere,indicating that CO₂promoted the dehydrogenation of ethylbenzene.2.The performance of CeO₂/Al₂O₃ and TiO₂/Al₂O₃ catalysts is closely related to the preparation method.Compared with the hydrothermal synthesis method and the impregnation method,the catalyst prepared by the sol-gel method has a larger specific surface area and pore diameter,a stronger metal oxide-support interaction,and abundant medium-acid center,which improves the active component.The dispersibility and the adsorption capacity of ethylbenzene inhibit the reduction of titanium and the formation of graphite-like carbon dep-osition,thus exhibiting good catalytic activity and stability in the dehydrogenation of ethylbenzene in CO₂.For the TiO₂/Al₂O₃ catalyst,the highly dispersed anatase TiO₂ is the active phase for the dehydrogenation of ethylbenzene in CO₂.3.Carbon deposition and deep reduction of titanium species are the main reasons for the de-activation of TiO₂/Al₂O₃ catalysts.The amount of carbon deposition is related to the activity of the catalyst.The higher the activity of the catalyst and the larger the amount of converted ethylbenzene result in the more carbon deposits.When the reaction temperature is 550°C,the carbon deposition increases with the prolong of reaction time in the initial stage of the reaction.The deactivation of TiO₂/Al₂O₃ catalyst is mainly attributed to carbon deposition.As the reaction proceeds,the carbon deposition rate slows down and the activity decreases.The deep reduction of titanium species is an important factor in the deactivation of TiO₂/Al₂O₃catalysts.