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Issue 25, 2007
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Time-resolved in situXAS study of the preparation of supported gold clusters

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Abstract

Incipient-wetness impregnation of γ-Al2O3 with HAuCl4 and subsequent removal of chlorine with NaOH, and deposition-precipitation of HAuCl4 on TiO2 at pH 7 resulted in supported Au3+ species. Time-resolved in situ XAS at the Au L3 edge showed that the Al2O3-supported oxidic or hydroxidic species were reduced in hydrogen at 440 K to yield small metallic gold clusters. The Au3+ precursor decomposed to metallic gold in inert atmosphere at 573 K and in oxidizing atmosphere above 623 K. In all atmospheres, initially small clusters were formed that gradually grew with increasing temperature. The TiO2-supported species were considerably less stable. In hydrogen and carbon monoxide, Au0 clusters of 1 to 1.5 nm were formed at room temperature, which was the lowest temperature studied. In inert and oxidizing atmosphere, the Au3+ precursor decomposed fully to metallic gold at 530 K, as shown by XAS and temperature-programmed experiments. Large clusters were obtained already in the initial stage of reduction. Residual chlorine inhibited the reduction and led to sintering of the gold clusters. Exposure of the TiO2-supported catalyst precursor to light or the X-ray beam led to partial reduction, and STEM showed that storage of the reduced gold clusters under ambient conditions led to agglomeration and bimodal cluster-size distributions.

Graphical abstract: Time-resolved in situ XAS study of the preparation of supported gold clusters

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Article information


Submitted
22 Feb 2007
Accepted
19 Apr 2007
First published
04 May 2007

Phys. Chem. Chem. Phys., 2007,9, 3312-3320
Article type
Paper

Time-resolved in situ XAS study of the preparation of supported gold clusters

E. Bus, R. Prins and J. A. van Bokhoven, Phys. Chem. Chem. Phys., 2007, 9, 3312
DOI: 10.1039/B702747H

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