Smart Molecular Reveals Surface Structure and Reactivity of Ceria Nanoshapes
To gain a fundamental understanding of the interplay between surface structure and catalytic behavior, ORNL researchers used ceria nanocrystals with well-defined surface planes to provide direct insight into how the surface structure of an oxide catalyst can affect its surface chemistry. Adsorption, transformation and desorption of a ‘smart’ probe molecule, methanol, was examined on three differently faceted CeO2 nanoparticles. Methanol surface chemistry on the uniformly shaped nanoparticles was studied by in situ IR and Raman spectroscopy and by analysis of desorbed products. Three types of methoxy adsorbates sites are observed and their distribution and rates of dehydrogenation are dependent upon the shape of the nanoparticles. Speciation of the adsorbate types are only partly explained by the coordination sites exhibited by different crystallographic facets. Molecular transformations, including creation of formyl and formate intermediates, are controlled by the shape of the ceria nanocrystals. Surface and bulk defect sites, more prevalent on rod-like than octahedral particles, profoundly affect the surface chemistry altering methoxy types, product distribution and stability during ceria catalysis. This study points to a strategy for better understanding the role of surface structure of current heterogeneous catalysts and for the design of more efficient catalysts via shape control.
The adsorption, desorption and decomposition of methanol show shape-dependent chemistry on ceria cubes and octahedral nanocrystals.
Zili Wu, Meijun Li, David R. Mullins, Steven H. Overbury, “Probing the Surface Sites of CeO2 Nanocrystals with Well-Defined Surface Planes via Methanol Adsorption and Desorption”. ACS Catalysis 2012, 2, 2224-2234; DOI: 10.1021/cs300467p