透射电子显微镜原位观察Cu/ZnO甲醇催化剂前驱体的分解过程

本文通过透射电子显微镜原位研究了甲醇催化剂前驱体锌孔雀石的分解过程。HRTEM、电子衍射及STEM面扫元素分析结果显示锌孔雀石分解过程可大致分为四个阶段。分解首先同时引发于锌孔雀石晶体内部的随机区域和晶体外表面,导致局域结构塌陷形成内部孔洞和非晶表面扩散层；随后孔洞逐渐增多增大,表面扩散层进一步增厚,同时CuO在孔洞区域和表面扩散层区域逐步结晶形成小晶粒；最后锌孔雀石结构完全分解,形成相互交织的CuO和ZnO,其中CuO小晶粒被非晶态ZnO相互隔离；此后进一步加热,ZnO方逐步结晶得到相互交织的CuO晶粒和ZnO晶粒,即焙烧后催化剂的结构。本研究通过TEM直观观察了整个分解过程的结构变化,增进了对甲醇催化剂前驱体焙烧过程的理解,也将有助于优化催化剂焙烧条件。

Decomposition process of Cu/ZnO methanol catalyst precursor: An in situ observation by TEM

The decomposition process of one of the best methanol catalyst precursors, zincian malachite, was studied, and the structural change during the decomposition was in situ observed by TEM. Combined HRTEM, ED and STEM mapping analysis suggest mainly four decomposition stages exist. The zincian malachite crystal firstly decomposed at random zones and outer surface, causing local structural collapse with holes formation in the bulk and amorphous diffused layer formation on the surface; then the holes grew larger and more holes appeared, and the collapsed layer on surface diffused further, meanwhile, CuO crystallized gradually at both hole sites and diffused layer regions; finally the structure of zincian malachite completely collapsed to afford intersected CuO and ZnO in the form of crystalline CuO separated by amorphous ZnO; after that, ZnO began to crystallize under further heating to give the final calcined catalyst with interdispersed CuO crystallites and ZnO crystallites. The direct observation of structural change during decomposition furthers our understanding on the calcination process of methanol catalyst precursors, and could give clues for optimizing calcination condition.