沉淀剂对AU/ZnO催化剂CO氧化性能及催化剂结构的影响

在25 C和进料中含水条件下,考察了由Na2CO3,(NH4)2CO3,NaOH和NH4OH等4种沉淀剂制备的Au/ZnO催化剂上CO氧化活性和稳定性.结果表明,沉淀剂影响Au/ZnO催化剂的前体组成、金粒子和ZnO粒子大小、比表面积及CO氧化性能.由NH4OH制备的Au/ZnO催化剂活性和稳定性较差,CO转化率只有15%;由其它3种沉淀剂制备的Au/ZnO催化剂的CO氧化活性和稳定性明显改善,可至少连续反应1 100 h,且保持CO完全氧化,其中Na2CO3是最佳沉淀剂.在反应过程中反应气氛可引起金粒子的聚集及在催化剂表面生成新的碱式碳酸锌物相.催化剂的稳定性与金粒子长大速度和碳酸根累积量有关.

Effect of Precipitant on the Performances and Structures of Au/ZnO Catalysts for CO Oxidation

Various Au/ZnO catalysts were prepared by a coprecipitation method with four kinds of precipitants, Na 2CO 3, (NH 4) 2CO 3, NaOH and NH 4OH, and the catalytic performance of CO oxidation at an ambient temperature and humidity were studied. It was found that the precipitants play an important role for the Au/ZnO catalyst structure, such as the precursors, the particle size of ZnO and metallic gold and the BET surface area of Au/ZnO catalysts. The sample prepared by using NH 4OH as precipitant exhibited a lower activity and poorer stability, while the Au/ZnO catalysts prepared by other three precipitants can maintain CO completely oxidized to CO 2 for at least 1 100 h. The feed gas mixture can result in sintering of metallic gold and accumulation of carbonate like species on the surface of Au/ZnO catalysts during the CO oxidation process. The stability is related to the rate of gold sintering and the amount of hydrozincite formed on the catalyst surface.