Gold Precursors

When a nucleation has a substantially higher free energy barrier than the corresponding surface reaction, then larger nanocrystals will be obtained in contrast. 

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Hydrothermal Synthesis of Brookite. Typically, NaOH solution (2M) was added to 5 mL titanium tetrachloride with stirring to adjust the pH value of the solution to 10, producing a basic colloidal solution. The solution obtained was transferred into an autoclave and heated at 200°C for 24 h. The white precipitates were separated by centrifugation and washed three times with deionized water and once with ethanol. The product was dried at 70°C in air overnight and was ground to a fine powder before the deposition of gold precursor on its surface. 

Deposition-Precipitation (DP) of Gold Precursor on Surface-Modified Amorphous Silica. The gold nanoparticles were deposited on the above surface-modified amorphous silicas by using the same process as that given in Section 5.2.2.2. 

The key effect of oxide supports on the catalytic activities of metal particles is exerted through the interface between oxides and metal particles. The key objective of this study is to develop synthesis methodologies for tailoring this interface. Here, an SSG approach was introduced to modify the surface of mesoporous silica materials with ultrathin films of titanium oxide so that the uniform deposition of gold precursors on ordered mesoporous silica materials by DP could be achieved without the constraint of the low lEP of silica. The surface sol-gel process was originally developed by Kunitake and coworkers.This novel technology enables molecular-scale control of film thickness over a large 2-D substrate area and can be viewed as a solution-based... 

The first descriptions of heteronuclear luminescent supramolecular complexes were given by Fackler et al. in 1988 and 1989. In these studies, one gold-thallium and one gold-lead complex were reported. As in the case of the gold-silver dinuclear systems, the extended systems appeared as a result of the unidirectional polymerization of dinuclear or trinuclear units through metal-metal interactions. These were prepared by reaction of the gold precursor [PPN][Au(MTP)2] (PPN = N(PPh3)2 ... 

It is desirable to begin this chapter with some general remarks about of use of terms to describe methods of preparation, because they are sometimes used loosely and inaccurately. The methods fall into two classes (i) the support and the gold precursor are formed at the same time and (ii) the gold precursor is applied to the preformed support. The procedure for method (i) is termed coprecipitation (Section 4.2.2), and although capable of many minor variations (e.g. as in the sol-gel method, Section 4.4.1), it does not have the same wealth of alternative procedures as does the second method. These may be listed as follows. 

In impregnation the pores of the support are filled with a solution of the gold precursor. Where just the needful volume is used, the method is impregnation to incipient wetness, but sometimes an excess of solution is used and the solvent removed by evaporation, so that concentrated solution finally resides in the pores (Sections 4.2.1 and 4.3.1). In these methods, the metal dispersion ultimately obtained depends critically on the conditions of drying.1... 

Methods of Preparation using Chloride-Free Gold Precursors... 

It is very difficult and indeed perhaps impossible to derive any general conclusions as to how the method of preparation affects the structure and activity of supported gold catalysts, as so much depends on the gold precursor and the support each system needs to be considered on its own. Only a few strong correlations are apparent, and there is much speculation it is easier to list the unresolved questions than the definitive conclusions. 

Zanella, R., Delannoy, L. and Louis, C. (2005). Mechanism of deposition of gold precursors onto Ti02 during the preparation by cation adsorption and deposition-precipitation with NaOH and urea. Appl. Catal. A-Gen. 291(1-2), 62-72. 

A number of techniques may be used to synthesize nanoclusters. In this experiment, a gold precursor is transformed into nanoclusters with diameters <2nm via a two-step reaction. The first step consists of phase-transfer into an organic layer where it reacts with triphenylphosphine. In the second step, the mixture is reduced by sodium borohydride. 

To check whether the presence of gold would alter the adsorption characteristics of MgO, an infrared study of CO adsorption at room temperature was carried out. The results are shown in Figure 3. When blank MgO that had been subjected to the same pretreatment as Au/MgO except for the impregnation with the gold precursor salt was exposed to 10 Torr of CO gas at 293 K, no adsorption of CO was observed and the infrared spectrum showed no band whatsoever that could be... 

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