Function of various levels of hierarchical organization of porous Ce0.9REE0.1O1.95 mixed oxides in catalytic activity

Abstract

In this paper, the effect of the hierarchical arrangement of nanocrystallites on CO oxidation and soot combustion activity has been investigated. Hierarchically structured star-shaped particles (HS stars) were compared with microemulsion-derived, loosely arranged nanoparticles (NPs). Star-like Ce_0.9REE_0.1O_1.95 mixed oxides were synthesized by oxidative thermolysis of Ce_0.9REE_0.1(HCOO)₃ mixed formates. The study of the synthesis, structure and catalytic activity of the porous, star-like ceria-based mixed oxides was presented for the first time. It was shown that each level of the hierarchical structure of the star-like mixed oxides has its own functionality and it is vulnerable to modifications. In-depth characterization of as-synthesized ceria allowed determination of the relationship between the hierarchically structured nature of the material and its catalytic activity in CO oxidation and soot combustion. It was concluded that the presence of the 3D structure composed of ceria nanocrystals significantly improves the stability and catalytic activity of the star-like material in comparison to the nanopowder. Moreover, introduction of the trivalent RE ion into the ceria structure led to further improvement of the CO oxidation performance. Finally, the key–lock catalysis concept was applied to explain the enhanced activity of the hierarchically structured star-shaped ceria particles as a catalyst in the soot combustion process in comparison to nanocrystalline CeO₂.