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选用不同的碱土金属氯化物为原料,采用共研磨的方法制备出了具有不同表面碱性的MCl2-TiO2-SnO2(M=Mg,Ca,Sr,Ba)催化剂,并考察了催化剂的甲烷氧化偶联反应性能.通过N2吸脱附(BET)、X-射线衍射(XRD)、X-射线光电子能谱(XPS)和CO2程序升温脱附(CO2-TPD)等技术对催化剂进行了表征.结果表明,随碱土金属元素的不同,催化剂呈现出了强弱不同的碱性吸附位.催化剂表面的碱性对活化甲烷具有促进作用,同时也带来乙烯深度氧化副反应的发生.碱量越大的弱碱性吸附位对甲烷的活化越有利,而强碱性吸附位则能导致催化剂活性降低,甚至是催化剂失活.乙烯的选择性与催化剂表面晶格氧的相对浓度密切相关.表面晶格氧的相对浓度较高的催化剂,其乙烯选择性也较大.
MCl2-TiO2-SnO2 (M = Mg, Ca, Sr, Ba) catalysts with different surface alkalis were synthesized by co-grinding method using different alkaline earth metal chlorides as raw materials. The effects of methane oxidation couple The reaction performance was characterized by means of N2 adsorption-desorption (BET), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and CO2 temperature-programmed desorption (CO2-TPD) The results showed that the catalysts exhibited different alkaline adsorption sites depending on the content of alkaline earth metals.The alkalinity of the catalyst surface promoted the activation of methane and also caused the deep oxidation of ethylene. Of the weakly basic adsorption sites are more favorable for the activation of methane, while strong basic adsorption sites can lead to a decrease in the activity of the catalyst and even deactivation of the catalyst. The selectivity of ethylene is closely related to the relative concentration of lattice oxygen on the surface of the catalyst. Surface Crystals The higher relative oxygen concentration of the catalyst, the ethylene selectivity is also greater.