Spinel Formation Mechanism Of ZnO/Al₂O₃ And Its Effect On Catalytic Performance Of Propane Dehydrogenation

With the increasing global demand for propylene,the oxygen-free dehydrogenation of propane has gradually become one of the important topics in the chemical industry.The development of efficient propane dehydrogenation catalysts has gradually become a hot spot of basic research and industrial application at home and abroad.Due to the high catalytic activity,low cost and low toxicity of ZnO,Zn-based catalysts are one of the important components of propane dehydrogenation catalysts.However,in practical application,ZnO/Al₂O₃will form stable ZnAl₂O₄spinel phase at high temperature,resulting in serious deactivation of the catalyst.In order to solve this problem,this paper mainly focuses on two aspects.On the one hand,conditions and mechanism of ZnAl₂O₄ spinel formation by ZnO/Al₂O₃ at high temperature should be explored.On the other hand,the formation of ZnAl₂O₄ spinel is avoided in the preparation of ZnO/Al₂O₃ catalyst,which provides theoretical guidance for the preparation of high-performance Zn-based propane dehydrogenation catalyst.（1）ZnO/R-Al₂O₃ catalyst was prepared by hydrothermal method.By changing the calcination atmosphere of the catalyst,the catalyst with different ZnAl₂O₄ spinel content was obtained.Analysis shows that the formation of ZnAl₂O₄ spinel requires the participation of water in the catalyst.Moreover,if there is reducing H in the calcination atmosphere,the O on the catalyst surface will combine with it to form compound water and promote the formation of ZnAl₂O₄ spinel,which is unfavorable to propane dehydrogenation.（2）By changing the preparation method of Al₂O₃,the generation of combined water in catalyst can be avoided.A-Al₂O₃ synthesized by sol-gel method does not contain combined water,and its surface is hydrophobic.Therefore,ZnAl₂O₄spinel is not produced during high temperature calcination process,thus higher propane dehydrogenation activity and stability are obtained.（3）In the propane dehydrogenation activity test of ZnO/X-Al₂O₃ catalyst,it is proved that the active center of propane dehydrogenation is ZnO.ZnO/A-Al₂O₃ catalyst has better catalytic performance for propane dehydrogenation due to the high content of ZnO in the catalyst because ZnAl₂O₄ spinel is not produced.