Deposition of gold

Comparative studies for the effect of the preparation method on the WGS or PROX activity of gold-ceria catalysts clearly 

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 

One of the main drawbacks of ceria-based catalysts is deactivation with time-on-stream. In order to overcome this Cargnello et al. applied a new method to create very small Au nanoparticles (average diameter 2 nm) embedded inside the CeO support. There was good thermal stability after aging treatments at relatively high temperatures (up to 250°C). The aim of this methodology was to stabilize the Au phase by encapsulation of preformed Au nanoparticles inside a porous ceria layer. A mixture of thiolates was used to protect the gold particles and to direct the self-assembly assisted precipitation of Ce(OH)x species around 

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Kodas, T. T., Baum, T. H., andComita, P. B., Kinetics ofLaser-Induced Chemical Vapor Deposition of Gold, / Appl. Phys., 62(l) 281-286(July 1,1987)... 

A modified DP method with urea as a precipitating agent, called the DP urea method, has been developed for Ti02 support [27]. Deposition of gold NPs by this method was appHed to AI2O3 [28], Ce02 [28], and Mn203 [29] supports. Aqueous urea solution produces hydroxyl ions above 60 °C as foUows ... 

Baum, T.H. (1987) Laser chemical vapor deposition of gold. Journal of the Electrochemical Society, 134, 2616. 

Saliba, R., Mingotaud, C., Argoul, F. and Ravaine, S. (2001) Electroless deposition of gold films under organized monolayers. 

Over single crystal surfaces with defect sites, vacuum deposition of gold vapor or size-selected gold anion clusters at low temperatures can lead to relatively homogeneous... 

Selective Deposition of Gold Nanoclusters on Well-Defined Materials... 

This mechanism as a main cause for epithermal-type Au deposition is supported by sulfur isotopic data on sulfides. Shikazono and Shimazaki (1985) determined sulfur isotopic compositions of sulfide minerals from the Zn-Pb and Au-Ag veins of the Yatani deposits which occur in the Green tuff region. The values for Zn-Pb veins and Au-Ag veins are ca. +0.5%o to -f4.5%o and ca. -l-3%o to - -6%c, respectively (Fig. 1.126). This difference in of Zn-Pb veins and Au-Ag veins is difficult to explain by the equilibrium isotopic fractionation between aqueous reduced sulfur species and oxidized sulfur species at the site of ore deposition. The non-equilibrium rapid mixing of H2S-rich fluid (deep fluid) with SO -rich acid fluid (shallow fluid) is the most likely process for the cause of this difference (Fig. 1.127). This fluids mixing can also explain the higher oxidation state of Au-Ag ore fluid and lower oxidation state of Zn-Pb ore fluid. Deposition of gold occurs by this mechanism but not by oxidation of H2S-rich fluid. 

This reaction suggests that a decrease in H2S concentration, and increases in H+ concentration and (H2 fugacity) and temperature variations are important causes for the deposition of gold in electrum. 

It is also likely that the deposition of gold in electrum occurs by the following oxidation reaction. 

The Okuaizu fluid may account for the more efficient transport and deposition of gold. - = not determined. 

Pol VG, Gedanken A, Calderon-Moreno J (2003) Deposition of gold nanoparticles on silica spheres a sonochemical approach. Chem Mater 15 1111-1118... 

Zanella, R., et al., Deposition of gold nanoparticles onto thiol-functionalized multiwalled carbon nanotubes, journal of Physical Chemistry B, 2005.109(34) p. 16290-16295. 

Shahrokhian, S. and S. Rastgar, Electrochemical deposition of gold nanoparticles on carbon nanotube coated glassy carbon electrode for the improved sensing oftinidazole. Electrochimica Acta, 2012. 78(0) p. 422-429. 

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. 

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... 

Gold is recovered economically in South Africa, Russia, Canada, Australia, Mexico, China, and India and in the states of California, Utah, Alaska, Nevada, and South Dakota in the United States. Small, scattered deposits of gold are found in several other states, including Florida, Arkansas, Washington, Oregon, Texas, Georgia, and the Carolinas. All the gold that has been refined in the world would form a cube with a volume of over 8,000 cubic meters. 

Electroless Deposition of Gold. Okinaka (21) verified the mixed-potential theory for the case of electroless gold deposition. Eigure 8.6 shows that the partial cathodic... 

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