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利用XPS及氩离子溅射等技术对CO偶联和临氢反应中所用催化剂表面活性组分和助剂的含量及其化学状态进行了分析 ,并通过测定氢在催化剂表面的化学吸附 ,以及氢浓度对催化剂活性的影响 ,探讨了CO偶联反应中催化剂临氢失活的主要原因 .XPS表征结果表明 ,CO偶联反应中催化剂活性组分以Pd0 和Pd2 + 形式共存 ;而临氢反应后仅以Pd0 形式存在 ,助剂FeO从催化剂的内部向表面迁移且有少量Fe2 + 转变为Fe3 + .催化剂临氢失活的主要原因是H2 在活性组分Pd及助剂Fe(主要是FeO)表面均可形成解离吸附 ,形成的金属氢化物可在低活化能条件下发生迁移 .这种迁移有利于副产物乙醇的生成 ,从而削弱了CO偶联主反应 ,催化剂表面活性组分Pd的相对含量减少 ,并几乎处于钝化状态 ,导致临氢反应中CO转化率、草酸二乙酯选择性及空时收率均下降 .停止通入H2 后 ,催化剂的活性可恢复至正常状态
The content and chemical state of the surface active components and additives used in the CO coupling and hydrogenation reactions were analyzed by XPS and argon ion sputtering. The chemical adsorption of hydrogen on the surface of the catalyst was also measured. Concentration on the activity of the catalyst to discuss CO coupling reaction of hydrogen deactivation of the catalyst main reason.XPS characterization results show that CO coupling reaction of the catalyst active components Pd0 and Pd2 + form coexistence; and after the hydrogen reaction Only in the form of PdO, the promoter FeO migrates from the interior of the catalyst to the surface and a small amount of Fe2 + changes to Fe3 + .The main reason of the catalyst inactivation of hydrogen is that the active hydrogen component is Pd and Fe (mainly FeO) The surface can be formed dissociative adsorption, the formation of metal hydride can migrate at low activation energy conditions.This migration is conducive to the formation of ethanol by-product, thus weakening the CO coupling reaction, the catalyst surface active component Pd The relative content decreased and almost passivated, which led to the decrease of CO conversion, diethyl oxalate selectivity and the time-space yield in the hydrogen reaction.After stopping the introduction of H2, the activity of the catalyst could be restored normal status