硫酸钠对Mn/SiO_2催化剂结构及其甲烷氧化偶联反应性能的影响

Abstract

采用等体积浸渍法制备了Na2SO4改性的Mn/SiO2催化剂,考察了Mn-Na2SO4/SiO2催化剂中各组分对甲烷氧化偶联合成C2产物(C2H4+C2H6)的影响,并采用X射线衍射、X射线光电子能谱、Raman光谱和程序升温还原等手段表征了催化剂中的物相结构、表面组分价态与含量以及氧化还原性能.结果表明,在Mn/SiO2催化剂中添加Na2SO4可使载体SiO2由无定形转变为α-方石英相,使催化剂表面的Mn物种由Mn3O4转变为Mn2O3,从而大大提高了甲烷转化率和目标产物C2的选择性.因此,推测Mn2O3物种在反应条件下构成了甲烷氧化偶联反应的活性中心.

The oxidative coupling of methane to C-2 hydrocarbons (C2H4 and C2H6) was examined on MnNa2SO4/SiO2. The catalysts were characterized using X-ray diffraction, X-ray photoelectron spectroscopy, laser Raman spectroscopy, and temperature-programmed reduction with H-2. The addition of Na2SO4 to Mn/SiO2 led to the exclusive transformation of amorphous SiO2 to alpha-cristobalite and the concurrent oxidation of Mn3O4 to Mn2O3. The observed effects on the structure and catalytic performance suggest that Mn2O3 species act as the active sites for the methane activation, which may provide the basis for the rational design of new efficient catalysts for the oxidative coupling of methane.