锂在甲烷氧化偶联多元氧化物催化剂中的作用

Role of Lithium in Multicomponent Oxide Catalysts for Oxidative Coupling of Methane

考察了不同Li含量对LixLa0．5Ti0．5系氧化物催化剂的甲烷氧化偶联催化性能的影响；比较了水洗前后LiLa0．5Ti0．5氧化物催化剂的催化活性，并通过XRD、IR、XPS和BET等方法时催化剂进行表征。确认了Li在含稀土、过渡金属多元氧化物中的作用。其中，表面Li的作用是缩小催化剂的比表面积，覆盖表面深度氧化活性位，提高C2选择性；体相Li的作用是部分取代Ti3+进入LaTiO3晶格形成LaTi1-yLiyO3-λ活性相，产生甲烷氧化偶联Li+－O-－Ti3+缺陷簇。（注：LixLa0．5Ti0．5和LiLa0．5Ti0．5表示该系列氧化物催化剂制备时的各金属元素的配比。用来表示催化剂的名称，并不表示实际存在的物相，以下类同，下面出现时，不再加以说明。）

The effect of Li content in a series of multicomponent oxides LixLa0.5Ti0.5 for methane oxidative coupling has been studied. The catalytic activities of LiLa0.5Ti0.5 catalyst befroe and after washing with boiling water have been compared. The surface and bulk structure of the catalysts were characterized by means of XRD、 XPS、 IR 、BET and so on. The results clearly indicated that the role of Li on the surface is to decrease the sruface area of the catalysts and to cover the deep oxidative active sites thus increasing the C2 selectivity. However, the role of lithium in the bulk is to produce active phase LaTi1-yLiyO3-λ in which the defect clusters Li+-O--Ti3+ act as the active sites for methane oxidative coupling.