铼前体对乙烯环氧化银催化剂性能的影响

Effect of rhenium precursor on performance of silver catalyst for ethylene epoxidation

以无机高铼酸(HReO_4)和有机甲基三氧化铼(CH_3ReO_3)为前体,分别采用共浸渍法和二次浸渍法制备了系列负载型乙烯环氧化银催化剂,采用TG-DSC,TEM,SEM,XPS,O_2-TPD等方法对催化剂试样进行表征,研究了热处理温度及铼助剂的负载方式等制备条件对催化剂性能的影响。实验结果表明,以CH_3ReO_3为前体、采用二次浸渍法先负载铼、并在120℃下处理后再负载银和铯制得的Re*/Ag-Cs催化剂性能最优,反应温度低至218.1℃,环氧乙烷选择性可达83.16%。表征结果显示,单一铼组分在α-Al_2O_3晶片上的分布是不均匀的任意分布;不同铼前体对催化剂中银和铯的价态没有影响;对于Ag-Cs-Re催化剂,银颗粒平均粒径为110 nm,而Re*/Ag-Cs催化剂,银颗粒平均粒径为80 nm;Re*/Ag-Cs催化剂弱吸附氧的脱附温度比Ag-Cs-Re催化剂低约10℃,说明Re*/Ag-Cs催化剂活性较高。

A series of supported silver catalysts for ethylene epoxidation were prepared by co-impregnation and secondary impregnation using the precursors of inorganic perrhenic acid(HReO4)and organic methyltrioxorhenium(CH3ReO3),respectively.The effects of heating temperature and rhenium loading method on the catalyst performance were investigated.The catalysts were characterized by TG-DSC,TEM,SEM,XPS and O2-TPD.The evaluation results show that the Re*/Ag-Cs catalyst with the precursor of CH3ReO3 loaded first,and the silver and cesium loaded late after treatment at 120℃has the best performance with the reaction temperature of 218.1℃and ethylene oxide selectivity of 83.16%.The analysis results show that single rhenium component is distributed randomly on theα-Al2O3 crystal,different rhenium precursors have no effect on the valence of silver and cesium in the catalyst.The average particle size of the silver particle is 110 nm for the Ag-Cs-Re catalyst,while it is 80 nm for the Re*/Ag-Cs catalyst.The desorption temperature of weakly adsorbed oxygen on the Re*/Ag-Cs catalyst is around 10℃lower than that on the Ag-Cs-Re catalyst,which indicates higher activity of the Re*/Ag-Cs catalyst.