Evaluation of the Au size effect: CO oxidation catalyzed by Au/TiO₂.

Journal Article · Sun Jan 01 04:00:00 EST 2006 · Journal of Catalysis

DOI:https://doi.org/10.1016/j.jcat.2006.04.018· OSTI ID:1003376

Schwartz, Viviane ^[1]; Mullins, David R ^[1]; Yan, Wenfu ^[1]; Dai, Sheng ^[1]

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1. ORNL

The size dependence of activity in gold catalysts was examined. Extended X-ray absorption fine structure was used to determine mean particle size, and a flow reactor was used to assess activity of the catalysts for CO oxidation as a function of temperature. A sequence of calcination steps was used to systematically increase the mean Au particle size while repeated measurements of the activity were conducted. In this way the size dependence could be obtained in a single catalyst to avoid differences due to variations in support, synthesis conditions, Au loading, or incidental impurities. Two Au catalysts with different Au loadings were prepared on TiO{sub 2} by deposition precipitation and used for the measurements. For Au particles with mean particle size, d, in the range of 2-10 nm, the measured TOF at 298 K varies as d{sup -1.7{+-}0.2} and d{sup -0.9{+-}0.2} for the 7.2 and 4.5 wt% Au/TiO{sub 2} (P25) catalysts, respectively. Variation between samples emphasizes the conclusion that the activity is sensitive to many factors that may mask the true structure dependence. It is concluded that the observed decrease in activity with increasing particle size beyond 2 nm is controlled by the population of low-coordinate sites, rather than by size-dependent changes in overall electronic structure of the nanoparticle. No evidence was found for maximum activity for small particle sizes, although arguments are offered for why such a maximum was expected but was not observed.

• Research Organization: Oak Ridge National Laboratory (ORNL)
• Sponsoring Organization: SC USDOE - Office of Science (SC)
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 1003376
• Journal Information: Journal of Catalysis, Journal Name: Journal of Catalysis Journal Issue: 1 Vol. 24; ISSN 0021-9517
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
77 NANOSCIENCE AND NANOTECHNOLOGY
CARBON MONOXIDE
CATALYST SUPPORTS
CATALYTIC EFFECTS
CHEMICAL PREPARATION
GOLD
NANOSTRUCTURES
OXIDATION
PARTICLE SIZE
TITANIUM OXIDES