摘要
研究了甲烷在La_2O_3/MgO催化剂上的氧化偶联。发现制备过等对催化剂的行为有显著影响。比较了催化剂的反应性能和体相结构,表明在MgO上存在着三种La_2O_3的状态:高分散La_2O_3是最活泼的;La(OH)_3不太活泼;而呈六方晶相的La_2O_3晶粒活性最低。在催化剂中加入Na_2CO_3和K_2CO_3可以改进催化剂的活性和选择性。还考察了反应条件如温度和空速的影响。
The performance of La2O3/MgO catalysts was studied with emphasis on the relation between the catalytic activity and the structure of catalyst. It is found that three dispersion states of lanthana exist in succession on MgO surface with increasing La2O3 loading; well-dispersed La2O3, La(OH)3 and hexagonal La2O3 crystalline. The methane conversion and the selectivity for C2 products decrease in the order: well-dispersed La2O3 >La(OH)3>hexagonal La2O3 crystalline. The preparation process shows significant influence on the performance of the catalysts , the catalysts prepared by calcination in two steps give higher C2 selectivity and C2 yield. The C2 selectivity increases drastically (from 50.9% to 63.4%) and a C2 yield of 17.5% is obtained with Na2CO3 and K2CO3 doping, it is believed that the alkali doping not only modifies the basicity of the catalysts, but also improves the dispersion of La2O3 on catalyst surface. The effect of reaction conditions, such as temperature and space velocity, were also studied.
关键词
氧化镧
氧化镁
甲烷
氧化偶联
Lanthanum oxide,magnesium oxide,supported catalyst,bulk phase,methane,oxidative coupling
