甲烷氧化偶联Mn_2O_3-Na_2WO_4/SiO_2催化剂——Ⅰ.表面分散状态和氧化物/担体相互作用

Mn-Na2WO4/SiO2 Catalyst for Oxidative Coupling of Methane Ⅰ. Surface Dispersion State and Oxide /Support Interaction

担载型Mn_2O_3-Na_2WO_4/SiO_2催化剂具有优异的甲烷氧化偶联制乙烯催化活性。在最佳反应条件下,甲烷转化率和C_2烃收率分别达到37.1％和23.9％;在1000 h连续操作后性能基本维持不变;并且由于它适于流化床操作,对这类强放热反应的工业化较为有利,本文报导用XRD、XPS和PASCA(化学分析正电子湮没谱)方法研究该催化剂活性组分Na_2WO_4和Mn_2O_3在SiO_2载体上的分散状态和氧化物/担体相互作用的结果。 催化剂由混浆法和浸渍法制备,并经750—850℃焙烧。系列配比的催化剂均经AAS分析证实体相组成。催化剂比表面积用Sorptmaeic—1822型比表面积测定仪测定(N_2吸附,

Mn exists as Mn2O3 free crystallites in Mn - Na2WO4/SiO2 system. Na2WO4 exists in three different states- well-dispersed phase (when content less than 4 wt%), among which about 1. 5 wt% occupy the strong - interaction sites, the remainder occupy the weak - interaction sites on the silica surface, and an excess of 4 wt % appears as free crystallites. With the participation of the strong interaction between Na2WO4 and silica support, reconstruction of the support from original silica gel to a-cubic quartz (cristobalite) is observed.