Preparation of supported gold catalysts for low-temperature CO oxidation via ``size-controlled`` gold colloids
- Swiss Federal Inst. of Tech., Zuerich (Switzerland). Lab. of Technical Chemistry
Catalytically active gold model catalysts have been designed via size-controlled gold colloids of 2-nm mean particle size. They were prepared by reduction of chloroauric acid with tetrakis(hydroxymethyl)phosphonium chloride in an alkaline solution, followed by adsorption of gold colloids on TiO{sub 2} and ZrO{sub 2} at a pH lower than the isoelectric point of the metal oxides. Investigation of the size of the gold particles in solution by UV-vis spectrophotometry in combination with HRTEM indicated that the gold colloids are rather stable in alkaline solution, during pH-change and purification with dialysis. Aging of the solutions showed that the particle size slowly increased over a time scale of 4 months. Analysis of the dried catalysts by XRD and HRTEM corroborated that the particle size was nearly preserved during the immobilization process. Only in the case of high loadings (16.6 wt%, compared to the calculated nominal monolayer coverage of 45--55 wt%), incomplete adsorption occurred, affording more inhomogeneous dispersion and some aggregation. After calcination at 673 K, both zirconia- and titania-based catalysts containing 1.7 wt% Au exhibited high activity in low temperature CO oxidation. Although the particle size on both supports was comparable, the Au/TiO{sub 2} catalyst showed significantly higher activity than the Au/ZrO{sub 2} catalyst. The uncalcined Au/TiO{sub 2} also exhibited high activity, whereas the uncalcined Au/ZrO{sub 2} was inactive under the same conditions, corroborating that not only the gold particle size but also the support plays a key role in CO oxidation.
- OSTI ID:
- 316346
- Journal Information:
- Journal of Catalysis, Vol. 181, Issue 2; Other Information: PBD: 25 Jan 1999
- Country of Publication:
- United States
- Language:
- English
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