稀土元素对甲硫醇催化分解活性位点的调控作用

采用等体积浸渍法制备La、Ce改性的MCM-41催化剂,考察不同稀土金属元素对甲硫醇催化分解活性位点的调控作用。采用N_2吸附-脱附、XRD、XPS、H_2-TPR和NH_3/CO_2-TPD等对La、Ce改性催化剂进行物理化学性能测试,确定稀土元素La、Ce在催化剂中存在的形态和作用。研究表明,甲硫醇催化分解存在两步反应,低温条件下甲硫醇催化分解生成甲硫醚中间体,高温条件下甲硫醚进一步催化分解生成硫化氢和甲烷等小分子产物。对于10%Ce/MCM-41催化剂,表面活性氧是甲硫醇催化分解的低温活性中心,强酸性位点是甲硫醇催化分解的高温活性中心,二者在反应中起协同催化作用,而对于10%La/MCM-41催化剂,强酸性位点是甲硫醇催化分解的活性中心。

Regulation of rare earth elements on active sites for catalytic decomposition of methyl mercaptan

Rare-earth elements (La and Ce) modified MCM-41 catalysts were synthesized by the conventional incipient wetness impregnation method.The effects of different rare earth elements on controlling the active sites for catalytic decomposition of methyl mercaptan were investigated.The physical and chemical properties were characterized by N₂ adsorption-desorption,XRD,XPS,H₂-TPR,NH₃/CO₂-TPD analysis,and the morphology and effect of rare-earth elements in the catalyst were determined.Result showed that two-step reaction was occurred in the catalytic decomposition of methyl mercaptan.At low temperature,methyl mercaptan was decomposed to intermediates DMS (CH₃SCH₃).At high temperature,DMS was further decomposed to small molecular products such as CH₄ and H₂S.For the 10%Ce/MCM-41 catalyst,surface active oxygen species are the active center at low temperature while the strong acid site is the active center at high temperature.For the 10%La/MCM-41 catalyst,strong acid site is the active center for the catalytic decomposition of methyl mercaptan.