Gold catalysts colloid structures

Duff, D.G. and Baiker, A., Preparation and structural properties of ultrafine gold colloids for oxidation catalysis, in Preparation of Catalysts VI, Poncelet, G., Martens, J., Delmon, B., Jacobs, P.A., and Grange, P., Eds., Elsevier, Amsterdam, 1995, p. 505. 

Au/ZrC>2 catalysts are less active than Au/TiC>2 catalysts, whatever method of preparation is used deposition of colloidal gold,83,91 DP12 or laser vaporisation.70 Activity depends on the method used (Table 6.12), and appears to be due only to the presence of Au°. The reason for the difference between zirconia and titania is not understood Zr4+ is more difficult to reduce than Ti4+, so anion defects may be harder to form. The lattice structures also differ in monoclinic zirconia (baddleyite) the Zr4+ ion is unusually seven coordinate, and phase transitions into tetragonal and cubic structures occur at >1370 and >2570 K, respectively. However, the... 

Bimetallic particles with layered structures have opened fascinating prospects for the design of new catalysts. Schmid et al. [10m] have applied the classical seed-growth method [20] to synthesize layered bimetallic Au/Pd and Pd/Au colloids in the size range of 20-56 nm. The sequential reduction of gold salts and palladium salts with sodium citrate allows the gold core to be coated with Pd. This layered bimetallic colloid is stabilized by trisulfonated triphenylphosphane and sodium sulfanilate. More than 90% metal can be isolated in the solid state and is redispersable in water in high concentrations. 

Recently a technique for the preparation of catalyst particles with a narrow size distribution was developed [8], yielding colloidal metal clusters stabilized by a shell of surfactants. By adsorbing these clusters on substrate surfaces, model electrodes for dispersed electrocatalysts can be prepared [9]1 Figure 2 compares two samples prepared from different colloidal solutions of such clusters adsorbed on a gold surface. It is evident that both samples differ significantly wifii respect to their mesoscopic structure. 

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