Noble metal salts

Electroless plating on metal substrates can be improved by addition of pentaerythritol, either to a photosensitive composition of a noble metal salt (99), or with glycerine to nickel plating solutions (100). Both resolution and covering power of the electrolyte are improved. 

Principles The reduction reaction is controlled essentially by the usual kinetic factors such as concentration of reactants, temperature, agitation, catalysts, etc. Where the reaction is vigorous, as, for example, when a powerful reducing agent like hydrazine is used, wasteful precipitation of A/, may occur throughout the whole plating solution followed by deposition on all exposed metallic and non-metallic surfaces which can provide favourable nucleation sites. In order to restrict deposition and aid adhesion, the selected areas are pre-sensitised after cleaning the sensitisers used are often based on noble metal salts. 

Oxidation of alkenes with noble metal salts... 

In some cases shape-control has also been achieved tetra( -octyl)ammonium glycolate transforms Pd(N03)2 predominantly into trigonal Pd particles [186]. Recent work has confirmed that the colloidal protective agents not only prevent particle agglomeration but even provide control of the crystal growth during particle synthesis (see e.g., Ref. [187-191]). The drawbacks of this route are the restriction to noble metal salts and the limited industrial availability of A-(octyl)j RC02. 

PVP, a water soluble amine-based pol5mer, was found to be an optimum protective agent because the reduction of noble metal salts by polyols in the presence of other surfactants often resulted in non-homogenous colloidal dispersions. PVP was the first material to be used for generating silver and silver-palladium stabilized particles by the polyol method [231-233]. By reducing the precur-sor/PVP ratio, it is even possible to reduce the size of the metal particles to few nanometers. These colloidal particles are isolable but surface contaminations are easily recognized because samples washed with the solvent and dried in the air are subsquently not any more pyrophoric [231,234 236]. 

Ammonium formate is used in chemical analysis to separate base metals from noble metal salts. 

The conversion rates, and the selectivities of the various catalysts used, are listed in Table 7.2. Among these, CuCl was seen to be the most efficient, but no carbonate was produced however, the substrate was very effectively converted when noble metal salts such as Pd(II), Rh(III), Ru(III), and Au(III) were used as catalysts. This behavior may be explained only if a polymerization reaction were to occur when the noble metal salts/[BMIm][PhS03] systems had been used, as confirmed by the presence of some black tar on the inner wall of the reactor when the reaction had been completed. In the absence of a metal salt as catalyst, the reaction did not yield any product, even after a long reaction time. 

Noble metal salts of heteropolyacids function in novel ways as catalysts. Pd. sPW12O40 supported on... 

An example of the use of direct redox reactions in the preparation of bimetallic catalysts is the modification of copper catalysts by the addition of ruthenium, platinum, gold, or palladium [11-14], Assuming the metallic state for copper atoms on the surface, the redox reaction with the noble metal salts is... 

There exists a huge number of synthetic procedures for metal nanoparticles, especially those consisting of noble metals because of the easy reducibUity of noble metal salts. To discuss all the syntheses in detail wonld exceed the scope of this article by far. Rather, synthetic strategies, elucidated with the help of examples, will be discussed in the following. 

It is possible that the bands at 250 and 243 cm.", observed in the arsenic salt, represent vibrations of the [Xe2F3] cation but they were not detected in the spectra of the Ru, Os, and Ir salts. Since the noble-metal salt spectra were so much weaker than the spectrum of the arsenic salt it is probable that in the former these bands were not distinguishable from the background. 

A slight deficiency of CsF mixed with [Xe,F,i]+ -AuF,]-was heated under dry N, to 110 °C, at which temperature XeF, evolved. The XeF, displacement CsF -)- [Xe,F ]- [AuF,] ->- 2XeF, + CsAuF, was completed under vacuum, (the slight excess of xenon complex sublimed out of the reactor) and a pale yellow solid remained. X-Ray powder photographs established that CsAuF, is isomorphous with the other CsMF, noble metal salts. Crystal data CsAuF,i M = 443-9 rhombohedral, a — 5-24 i 0-01 A a = 96-5 0-3°, V = 141 A, 2=1, Z c = 5-22 g cm-. Space... 

The oxidation of sulfoxides to sulfones is accomplished with air in the presence of noble metal salts [10 or with sodium permanganate [837] (equations 578 and 579). 

These catalysts are prepared by adding a suspension of a supporting colloid in an appropriate solvent to a solution of a noble metal salt dissolved in the same solvent. The resulting mixture is then reduced with hydrogen at room temperature and atmospheric pressure to convert the metal salt to the metal. Frequently (5,6) it has been found necessary, in order to obtain reduction, to convert the noble metal salt to the corresponding hydroxide prior to the reduction. 

Table IV. Ethylene-Noble Metal Salts Interactions...

A typical procedure for Au deposition is shown in scheme 1. By adjusting pH, temperature, and concentration of noble metal salts, hydroxide precipitates can be deposited exclusively on the surfaces of the supports without forming precipitates in solution. Then the precursor is washed several times to remove Na and Cl ions and is finally calcined in air at temperatures above 250 °C after drying overnight. 

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