Uncovering the 3 D Structure of Combustion‐Synthesized Noble Metal‐Ceria Nanocatalysts

Abstract

AbstractWith its unique redox properties, ceria is an oxide with a range of applications, including automotive catalytic converters, which consist of platinum‐group metal nanoparticles on ceria‐containing supports. In this work, the 3 D architecture of a ceria‐based material synthesized by the widely employed glycine‐nitrate solution combustion method is revealed for the first time. Together with N2 adsorption volumetry, scanning transmission electron microscopy (STEM) and scanning electron microscopy (SEM), STEM tomography provides a comprehensive picture of the multimodal porous network of a pre‐reduced Pt‐CeO2 catalyst, from the nanometer to the micrometer scale. This material consists of ceria nanocrystallites forming 3 D aggregates and puzzle‐like 2 D walls separating large roundish mesopores and macropores. The small voids between imperfectly assembled crystallites give rise to some microporosity. In addition, it is demonstrated that a significant proportion of platinum nanoparticles (3–4 nm) are not located at the ceria surface following the one‐step synthesis process, about half of them are buried within ceria. This result is valid for another metal (Rh) and another fuel (oxalyl dihydrazide), and has important implications for heterogeneous catalysis.