Gold hydroxide

Gold-hydroxyd, n. gold hydroxide, specif, auric hydroxide, gold(III) hydroxide, -jodid, n. gold iodide, specif, auric iodide, gold(III) iodide, -jodiir, n. aurous iodide, gold (I) iodide, -kafer, m. gold beetle. 

Figure 6. Postulated role of magnesium citrate in the deposition precipitation of gold hydroxide on Mg(OH)2.

One solution-based approach that works for gold catalysts, in that it produces highly active catalysts, is the deposition-precipitation (DP) method [8]. The DP method entails adjusting the pH, temperature, and gold concentration of an HAUCI4 solution to form a gold hydroxide species which is then deposited onto the support material [8]. This catalyst precursor is washed, dried, and annealed to form small (<5nm) catalyst particles [9]. The DP method has a number of limitations for example, DP cannot produce Au particles with diameters less than 5 nm on support materials with low-isoelectric points (lEPs) like SiOz and WO3 [5,10,11]. 

A preformed support may be impregnated with this HAuCU and then treated with a reducing agent. Alternatively, when the pH of a mixture of HAuCU and various metal ions is raised, gold hydroxide and metal hydroxide coprecipitate. Drying, calcination, and reduction of this mixture provide Au(0) supported upon a metal oxide. Suitable reducing agents include H2, BH4, citrate, and ascorbate. Permutations of... 

Gold hydroxide is made according to the procedure outlined in the next preparation and heated to constant weight at 140-150°C. 

It is important to carefully wash the samples to remove Na and Cl. This is possible by washing in water at 80°C [107, 108]. This method is valid for a limited number of supports, depending on the respective precipitation rates of support metal hydroxide and gold hydroxide, which is supposed to precipitate as such their reciprocal affinity determines the gold particle size [22,109]. 

The zinc and gold hydroxides precipitate roughly at the same pH ( 7). In the case of Au/Fe203, the iron/hydroxide precipitates at lower pH ( 3), that... 

Apart from these silver-based activation procedures, Nolan and coworkers found another way to synthesize catalytically active gold catalysts. By treatment of IPr-Au(I) chloride with potassium hydroxide, they were able to isolate a bench-stable, NHC-gold hydroxide complex (see Scheme 9.10) [26]. This rather basic com-... 

Figure 9>15. Corrosion of positively biased gold conductor in the presence of moisture. Dark deposits are gold hydroxide corrosion products, which lead to electrical shorts between conductors.

The effect of the preparation method (co-precipitation or deposition-precipitation) on the performance of PROX reactions was rationalized on the basis of sequential precipitation, which occurred due to the different solubilities of the hydroxide species formed during the CP stage. With Au/ceria, the gold hydroxide, with a much lower solubility product ( p = 5 x 10 ), should be formed before Ce(OH)3 with = 1.6 x lO , thus favoring the aggregation of gold... 

The hydrolysis of gold(III) has only been studied on a very small number of occasions. Jirsa and Jelinek (1924) studied the solubility of gold hydroxide and determined a solubility constant of log = -45.05. This is equivalent to a solubility constant of log = —3.06. Mironov (2005) determined a solubility constant for stable red gold(III) hydroxide of log = -7.62 (unstable... 

NiOl-3), and Be(0H)2 ). These gold catalysts are active in the oxidation of CO at a temperature as low as -70 C. However, coprecipitation is valid only for a selected group of metal oxides as mentioned above, because the precipitation rates of support metal hydroxide and gold hydroxides and their affinity might determine in the dispersion of gold. 

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