Oxidative Dehydrogenation Of Ethylbenzene Over Ce-based Catalysts Under CO₂ Atmosphere

Dehydrogenation of ethylbenzene is one of the ten most important processes for the production of petrochemical raw materials.The current process of ethylbenzene dehydrogenation are limited by many defects,such as reaction equilibrium constrained by thermodynamics,high energy consumption,deactivation of catalyst and poor selectivity of styrene.Oxidative dehydrogenation of ethylbenzene with CO₂ as oxidant is an effective way to solve these problems.In this paper,catalytic performance of CexAl catalysts containing different amount of CeO₂ were investigated.CexAl catalysts were modified by ZrO₂?Cr₂O₃?MgO and La₂O₃.The catalysts were characterized by BET?XRD?SEM and H₂-TPR.The catalytic performance was evaluated under CO₂ atmosphere.Subsequently,the effects of reaction temperature?feed ratio of CO₂:EB?contact time?calcination temperature and nano/non-nano carrier on the catalytic performance were investigated.Finally,the deactivation mechanism of the catalyst was studied.The main results are as following:?1?CexAl catalysts with different CeO₂ loadings were prepared by impregnation method.Results showed that the catalytic performance was the best when the CeO₂ loading was 15%?w?.The conversion of ethylbenzene was 46.1%and the selectivity to styrene was 98.4%after 12 h reaction.The Ce15 Al catalyst was prepared by precipitation and impregnation respectively.It was found that the catalyst prepared by the precipitation method had good reducibility,high specific surface area,small particle size and better catalytic performance.After 12 h,the conversion of ethylbenzene was 48.1%,and its selectivity to styrene was98.2%.?2?ZrO₂ and Cr₂O₃ were used to modify the Ce15 Al catalyst.The optimum loadings of ZrO₂ and Cr₂O₃ were 10%?w?and 3%?w?,respectively.Compared with Ce15 Al catalyst,the initial activity of Ce15Cr3 Al catalyst is greatly increased,and its coke deposition rate increased,leading to its faster deactivation.Ce15Zr10 Al has good catalytic performance,and the stability of catalyst is greatly increased.MgO and La₂O₃ were used to modify the Ce15Zr10 Al catalyst.The optimum loadings of MgO and La₂O₃ were 1%?w?and 4%?w?,respectively.Compared with Ce15Zr10 Al catalyst,the catalytic performance of Ce15Zr10Mg1 Al catalyst increased,but the stability deteriorated.The catalytic performance and the stability of Ce15Zr10La4 Al catalyst were significantly improved.?3?The influences of preparation conditions and reaction conditions on the reaction were investigated.The optimized reaction conditions is as following:reaction temperature of 600?,CO₂ to ethylbenzene ratio of10:1,contact time of 163 h·g-cat·mol^-1EB,and the catalyst calcination temperature of 550?.In this case,the conversion of ethylbenzene was56.5%at 12 h,and the selectivity to styrene was 97.4%.?4?The catalytic performance of Ce15Zr10La4 Al catalyst was evaluated for 100 h on stream.After 100 h reaction,the conversion of ethylbenzene dropped to 24%and the selectivity to styrene was 98.7%.The catalyst was regenerated by CO₂ and air.After CO₂ regeneration,the amount of coke deposition decreased,but there was still significant coke deposition,and the conversion of ethylbenzene increased from 24%to27.6%.After the regeneration of air,coke completely eliminated.Besides,the reaction conversion of ethylbenzene is recovered to 40%after 12 h reaction,but it is still lower than that of the fresh catalyst.Coke deposition and catalyst sintering are both important reasons for deactivation of the catalyst,and the reduction of the active component is not the main cause of the catalyst deactivation.The experimental results show that this kind of catalyst has potential application prospects and is worthy of further study.