SiO_2改性α-Al_2O_3载体对银催化剂结构与性能的影响

EFFECTS OF α-Al_2O_3 SUPPORT MODIFIED BY SiO_2 ON STRUCTURE AND PERFORMANCE OF SILVER CATALYST

采用硅溶胶浸渍方法,对已制成的-αAl2O3载体进行SiO2表面改性,以不同量SiO2改性的-αAl2O3为载体制备了一系列负载银催化剂,测定了它们的孔结构、氧化学吸附量等物化性质,用乙烯环氧化反应评价了它们的催化性能,以考察SiO2改性载体表面对载体和催化剂结构与性能的影响。结果表明,少量SiO2沉积改性没有明显改变载体的孔结构;改性对单负载银催化剂上活性组分银的分散状况影响不大,但催化活性明显降低,最高降幅达63%,选择性略有提高(提高0.5%-3.4%);改性引起载体与银之间相互作用发生变化是负载银催化剂催化性能发生明显变化的主要原因。该改性方法简单易行,且可以排除孔结构差异对催化剂性能的影响,可用于对比不同载体材料对负载型银催化剂性能的影响。

By impregnation method the prepared then a series of silver catalysts supported on α-Al2O3 supports were modified with silica sol, modified α-Al2O3 were prepared. In order to investigate the effects of SiO2 modification on the structure and properties of these supports and silver catalysts, the pore structures, oxygen chemi-adsorption amounts were determined, and the catalytic performances were evaluated by ethylene epoxidation reaction in micro-reactor. Experimental results indicated that SiO2 modification did not obviously change both the pore structure of modified supports and the Ag dispersion on the catalysts, but the catalytic activity of the silver catalysts lowered obviously, which declined significantly by 63%, and the selectivity of ethylene oxide increased slightly （0. 5%-3.4%）. The main reason for SiO2 modification to cause the change of catalytic performance is the change of interaction between the support and Ag in silver catalysts. This modification method is simple, while it can eliminate the effects of pore structure on catalytic performances of catalyst and can be used to compare the effects of various support materials on catalytic properties of silver catalyst.