On the Structure Dependence of CO Oxidation over CeO2 Nanocrystals with Well-Defined Surface Planes

Journal Article · Sun Jan 01 04:00:00 EST 2012 · Journal of Catalysis

DOI:https://doi.org/10.1016/j.jcat.2011.09.011· OSTI ID:1038790

Wu, Zili ^[1]; Li, Meijun ^[1]

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1. ORNL

CO oxidation is a model reaction for probing the redox property of ceria-based catalysts. In this study, CO oxidation was investigated over ceria nanocrystals with defined surface planes (nanoshapes) including rods ({110} + {100}), cubes ({100}), and octahedra ({111}). To understand the strong dependence of CO oxidation observed on these different ceria nanoshapes, in situ techniques including infrared and Raman spectroscopy coupled with online mass spectrometer, and temperature-programmed reduction (TPR) were employed to reveal how CO interacts with the different ceria surfaces, while the mobility of ceria lattice oxygen was investigated via oxygen isotopic exchange experiment. CO adsorption at room temperature leads to strongly bonded carbonate species on the more reactive surfaces of rods and cubes but weakly bonded ones on the rather inert octahedra surface. CO-TPR, proceeding via several channels including CO removal of lattice oxygen, surface water-gas shift reaction and CO disproportionation reaction, reveals that the reducibility of these ceria nanoshapes is in line with their CO oxidation activity, i.e., rods > cubes > octahedra. The mobility of lattice oxygen also shows similar dependence. It is suggested that defect sites and coordinatively unsaturated sites on ceria play a direct role in facilitating both CO interaction with ceria surface and the reactivity and mobility of lattice oxygen. The nature and amount of the defect and low coordination sites are intrinsically affected by the surface planes of the ceria nanoshapes. Several reaction pathways for CO oxidation over the ceria nanoshapes are proposed and certain types of carbonates, especially those associated with reduced ceria surface, are considered among the reaction intermediates to form CO2, while the majority of carbonate species observed under CO oxidation condition are believed to be spectators.

• Research Organization: Oak Ridge National Laboratory (ORNL); Center for Nanophase Materials Sciences
• Sponsoring Organization: SC USDOE - Office of Science (SC)
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 1038790
• Journal Information: Journal of Catalysis, Journal Name: Journal of Catalysis Journal Issue: 1 Vol. 285; ISSN 0021-9517; ISSN JCTLA5
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
ADSORPTION
CARBON MONOXIDE
CARBONATES
CATALYSTS
CERIUM OXIDES
CO oxidation
DEFECTS
ISOTOPIC EXCHANGE
MASS SPECTROMETERS
OXIDATION
OXYGEN
RAMAN SPECTROSCOPY
REACTION INTERMEDIATES
REDUCTION
REMOVAL
WATER GAS
ceria nanoshapes
cubes
in situ spectroscopy
octahedra
reaction mechanism
rods
structure dependence