CO+H_2催化剂中γ-Al_2O_3的酸碱协合作用

THE ACID BASE SYNERGISM ON γ-Al_2O_3 IN CO+H_2CATALYSTS

本文表征并分析了γ-Al_2O_3的表面性质与催化活性之间的对应关系。结果表明,CO+H_2生成的甲醇在γ-Al_2O_3表面的脱水反应与催化剂的表面孔隙分布关系不大,而和催化剂表面的酸碱浓度密切相关。TPD、IR、XPS实验征明,γ-Al_2O_3表面酸位主要是Lewis酸,还有一定量的碱性位。吸附在Lewis酸位上的甲醇分子受临近的碱中心作用解离成活化态的甲氧基团,后者是生成二甲醚所必需的活性中间体。因此,在γ-Al_2O_3表面甲醇脱水反应是一种酸碱协同的催化反应。作为催化剂的γ-Al_2O_3必须具有相适宜数量的表面酸碱浓度。

In this paper, the relations between surface properties of the γ-Al_2O_3and activities of the mixed catalysts have been studied. The results show that methanol-produced from CO+H_2-dehydration reaction was not significantly effective to the pore size distribution of γ-Al_2O_3, but it had an important bearing on the acid-base value on γ-Al_2O_3. The experimetns of TPD, IR and XPS proved that on the surface of γ-Al_2O_3there were most Lewis acid sites and some basic sites. Because of the action of adjacent basic sites the methanol molecules adsorbed on Lewis acid sites were dissociated into activated state of methyoxy groups [CH_3O-]. The groups were necessary for active intermediates to synthesize dimethyl ether. Therefore, on the surface of γ-Al_2O_3 CH_3OH, dehydration reaction was catalysed by the acid-base synergism. As a catalyst, γ-Al_2O_3 must be of matched acid-base value.