摘要
采用等体积浸渍法制备Ag/SiO2催化剂,并运用XRD、TEM和BET等多种手段对催化剂的结构进行表征;考察了Ag负载量和不同预处理条件（O2/H2）对银催化剂结构及CO催化氧化活性的影响,并初步讨论了Ag/SiO2催化剂对CO低温氧化的活性组分。实验结果表明,用O2 500℃处理后的Ag的质量分数为8%的Ag/SiO2催化剂表现出较好的氧化活性（T98=65℃）,进一步用H2在200℃处理,T98降至50℃,然而CO氧化活性随着H2处理温度（〉200℃）的进一步升高反而下降。XRD及TEM表征结果表明,经过O2 500℃处理后,催化剂中存在金属银及氧化银物种,随着H2的低温还原（50-200℃）氧化银被还原,且粒径明显降低,而H2的高温（200-500℃）还原引起银粒子的团聚,粒子大小增大。具有一定粒子大小的金属纳米Ag是低温CO催化氧化反应的活性组分。
Ag/SiO2 catalysts for CO oxidation were prepared by an incipient wetness impregnation method,and characterized by XRD and TEM.The effects of Ag loading and the different pre-treatments with O2/H2 on the crystallite structure of silver catalysts and the activity of CO oxidation over Ag/SiO2 were also studied.It was found that w（Ag）=8% Ag/SiO2 catalyst pretreated with oxygen at 500 ℃ exhibited better catalytic performance（T98=65 ℃）,and the activity was further increased after following hydrogen treatment at 200 ℃.However,the activity decreased when the treatment temperature increased to 300 ℃.Crystallite Ag and Ag2O species were observed from XRD after oxygen pretreatment at 500 ℃,and the following hydrogen treatment at 50-200 ℃ led to the reduction of the Ag2O species and the dispersion of crystallite silver.However,prolonged hydrogen treatment at high temperatures（〉200 ℃） induced the aggregation of silver particles,which may be one of reason resulting in the decrease of the activity for CO oxidation.It could therefore be concluded that nano-crystallite silver with certain particle sizes would be favor of the low-temperature CO oxidation.
基金
高等学校博士学科点专项科研基金(200801411111)
国家自然科学基金青年基金(20807010)
