Carleton Author

Parker, Stephen C.

Department

Physics and Astronomy

Journal Title

Topics In Catalysis

Publication Date

2007

Month/Season

June

Volume No.

44

Issue No.

1-2

First Page

3

Last Page

13

Publisher

Springer Verlag

File Name

033_Parker-Stephen_ReactivityAndSinteringKineticsOfModelCatalysts.pdf

Keywords

Catalysis, gold, TiO2, sintering, nanoparticles, particle growth, selective oxidation

Abstract

We review here our studies of the reactivity and sintering kinetics of model catalysts consisting of gold nanoparticles dispersed on TiO2(110). First, the nucleation and growth of vapor-deposited gold on this surface was experimentally examined using x-ray photoelectron spectroscopy and low energy ion scattering. Gold initially grows as two-dimensional islands up to a critical coverage, hcr, after which 3D gold nanoparticles grow. The results at different temperatures are fitted well with a kinetic model, which includes various energetic parameters for Au adatom migration. Oxygen was dosed onto the resulting gold nanoparticles using a hot filament technique. The desorption energy of Oa was examined using temperature programmed desorption (TPD). The Oa is bonded ~40% more strongly to smaller (thinner) Au islands. Gaseous CO reacts rapidly with this Oa to make CO2, probably via adsorbed CO. The reactivity of Oa with CO increases with increasing particle size, as expected based on Brønsted relations. Propene adsorption leads to TPD peaks for three different molecularly adsorbed states on Au/TiO2(110), corresponding to propene adsorbed on gold islands, to Ti sites on the substrate, and to the perimeter of gold islands, with adsorption energies of 40, 52 and 73 kJ/mol, respectively. Thermal sintering of the gold nanoparticles was explored using temperature-programmed low-energy ion scattering. These sintering rates for a range of Au loadings at temperatures from 200 to 700 K were well fitted by a theoretical model which takes into consideration the dramatic effect of particle size on metal chemical potential using a modified bond additivity model. When extrapolated to simulate isothermal sintering at 700 K for 1 year, the resulting particle size distribution becomes very narrow. These results question claims that the shape of particle size distributions reveal their sintering mechanisms. They also suggest why the growth of colloidal nanoparticles in liquid solutions can result in very narrow particle size distributions.

Rights Management

Carleton College does not own the copyright to this work and the work is available through the Carleton College Library following the original publisher's policies regarding self-archiving. For more information on the copyright status of this work, refer to the current copyright holder.

RoMEO Color

Green

Preprint Archiving

Yes

Postprint Archiving

Yes

Publisher PDF Archiving

No

Contributing Organization

Carleton College

Type

Article

Format

application/pdf

Language

English

DOI

10.1007/s11244-007-0274-z

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