焙烧与预处理条件对 Co3O4 催化氧化 CO 性能的影响

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, 150~400 ^oC 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 (150~250 ^oC) 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.

Influence of calcination and pretreatment conditions on the activity of Co3O4 for CO oxidation

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 N₂ 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.