Mn-CaO催化剂上甲烷-二氧化碳共活化制C_2烃研究II.催化剂表征及反应机理研究

Selective Conversion of CH_4 and CO_2 to C_2 Hydrocarbons over Mn-CaO catalysts II.Catalysts Characterization and Mechanism Deduce

在Mn-CaO催化剂开展了一系列的表征,包括XRD,XPS,CO2-TPD.结合催化剂评价、表征结果,对催化反应机理进行了推测,指出Mn组分与催化剂的活性相关联而Ca组分的主要作用是提供吸附型的CO2(a)*,反应过程中形成的Mn3+/Mn2+离子对在CO2和CH4的活化过程中扮演了重要角色.

XRD, XPS, CO2-TPD were employed for characterization of Mn-CaO catalysts. Combine the results of catalyst characterization and catalyst evaluation, the following conclusions were drawn： Mn component is the active phase of Mn-CaO catalysts while the role of the Ca component is to provide adsorbed CO2; The possible mechanism for CH4 and CO2 to produce C2 hydrocarbons over Mn-CaO catalysts were deduced as follows： CO2 may first be adsorbed on CaO sites and then may be dissociated at high reaction temperature to produce CO2（a）^＊, CO2（a）^＊ was activated by Mn^2＋, CO and O^- was formed, the surface reactive oxygen species O^- abstract hydrogen from methane to give methyl radicals, which in turn are converted to C2 hydrocarbons. At the same time, Mn^3＋ was reduced to Mn^2＋.