甲烷氧化偶联Mn_2O_3-Na_2WO_4/SiO_2催化剂——Ⅱ.表面氧种和结构

Mn-Na2WO4/SiO2 Catalyst for Oxidative Coupling of Methane Ⅱ. Surface Oxygen Species and Structure

本文用XPS详细考察了Mn_2O_3-Na_2WO_4/SiO-2催化剂的表面氧种,提出了该催化剂表面活性相在SiO_2表面分散的一种可能的表面结构模型。 实验部分详见另文,这里需要指出。所有催化剂样品在XPS分析前,均经在能谱仪预处理室(～10^(-3)Pa)和超高真空测试室(基础真空6.7×10^(-8)Pa)递次的450C和700C原位加热处理,以使在大气中吸附的水分和气体脱附。各元素的特征谱峰由联机计算机以多道模式同时录取(通能50eV),并累加1 h以获取高信噪比数据。

The surface oxygen species and surface structure of Mn -Na2WO4/SiO2 catalyst was investigated at 300 K with XPS. The results show that, in addition to the Mn2O3 free crystallites and dispersed Na2WO4, a new surface compound is formed in this system via strong interaction between Na2WO4 and SiO2 support. It is suggested that the W=O tetrahedra in Na2WO4occupy 3- fold sites on cristobalite and the formula of the surface compound is Si3WO8.5, in which there are three W-O-Si bonds and one W = O bond . A possible redox mechanism for the oxidative coupling of methane on the catalyst was discussed preliminarily.