A systematic study of the synthesis conditions for the preparation of highly active gold catalysts

Supported gold catalysts were prepared by a deposition-precipitation method in order to investigate the influence of the synthesis conditions on the difference in catalytic activities for CO oxidation. The optimization of the synthesis parameters resulted in highly active Au/TiO2, Au/Co3O4, Au/Al2O3 and Au/ZrO2 catalysts. SiO2 was found to bean unsuitable support material for the deposition-precipitation method. With increasing pH value during precipitation and decreasing temperature of calcination increasing catalytic activity was observed. The optimum pH was in the range of eight to nine and slightly dependent on the nature of the support. The optimum temperature of calcination was 200degreesC. According to XRD and TEM the increasing catalytic activity could be attributed to a decrease in the gold particle size. However, comparing two samples with similar gold particle sizes, Au/TiO2 is more active than Au/Al2O3, This indicates that the catalytic activity is not only a particle size effect, but the role of the metal oxide is more than just the stabilization of the gold particles. (C) 2002 Elsevier Science B.V. All rights reserved.