焙烧与预处理条件对Co_3O_4催化氧化CO性能的影响

Influence of calcination and pretreatment conditions on the activity of Co_3O_4 for CO oxidation

采用沉淀法制备了Co3O4,考察了焙烧和预处理条件对其结构、低温催化氧化CO性能的影响.热重分析表明,未经焙烧的样品以Co(OH)2CO3的形式存在,150~400oC空气气氛中焙烧后,样品以立方相Co3O4的形式存在.N2吸附-脱附法、X射线衍射、透射电镜及活性测试结果表明,以纳米颗粒物存在的Co3O4的比表面积、颗粒尺寸、催化氧化CO活性与焙烧温度密切相关.正电子湮没寿命谱、O2-程序升温脱附与定温条件下CO氧化测试结果表明,合适温度(150~250oC)下N2预处理有利于Co3O4表面氧空穴团的形成,它在吸附活化分子氧以及CO催化氧化反应中起到关键作用.同时讨论了预处理作用下Co3O4表面氧空穴的再构机制.

The influence of calcination and pretreatment conditions on the structure of Co3O4 and its activity for CO oxidation were studied.TG analysis indicated that the precursor of Co3O4 prepared by a precipitation method was present in the form of cobalt hydroxide carbonate,calcination of which within the temperature range of 150-400 oC in air resulted in the formation of cubic phase Co3O4.N2 adsorption-desorption,powder X-ray diffraction,transmission electron microscopy,and activity test results showed that the prepared Co3O4 samples were comprised of nanoparticles, with the specific surface area and size distribution closely related to the calcination temperature. Over these samples,a size dependence of the catalytic activity for CO oxidation was clearly observed.As identified by positron annihilation lifetime spectrum, low temperature oxygen temperature-programmed desorption,and durability testing for CO oxidation, pretreatment of Co3O4 in N 2 within the temperature range 150-250 oC favors the formation of surface oxygen vacancy clusters,the occurrence of which would be beneficial for the adsorption and activation of O2,and also for the catalytic oxidation of CO. Meanwhile, the reconstruction of oxygen vacancies on the surface of Co3O4,induced by the pretreatment process,was also discussed.