Gold selective oxidation

The washed slime is dried and melted to produce slag and metal. The slag is usually purified by selective reduction and smelted to produce antimonial lead. The metal is treated ia the molten state by selective oxidation for the removal of arsenic, antimony, and some of the lead. It is then transferred to a cupel furnace, where the oxidation is continued until only the silver—gold alloy (dorn) remains. The bismuth-rich cupel slags are cmshed, mixed with a small amount of sulfur, and reduced with carbon to a copper matte and impure bismuth metal the latter is transferred to the bismuth refining plant. 

This method is especially valid for the preparation of gold NPs mixed with activated carbon, which are active and stable for the selective oxidation of hydrocarbons and alcohols in water. Over activated carbon gold could not be directly deposited as NPs by using the techniques described above, such as DP and even by GG. Gold colloids with mean diameters from 2.5 to lOnm stabilized by poly vinyl alcohol or poly vinyl p5rrolidone are used. 

Selective Oxidation with Molecular Oxygen on Gold-based Catalysts 237... 

R. M. Torres Sanchez, A. Ueda, K. Tanaka and M. Hamta, Selective oxidation of CO in hydrogen over gold supported on manganese oxides, J. Catal. 168, 125—127 (1997). 

B. Qiao, and Y. Deng, Highly effective ferric hydroxide supported gold catalyst for selective oxidation of CO in the presence of H2, Chem. Commun. 17, 2192-2193 (2003). 

S. Carrettin, P. McMom, P. Johnston, K. Griffin, and G. J. Hutchings, Selective oxidation of glycerol to glyceric acid using a gold catalyst in aqueous sodium hydroxide, Chem. Commun. 7, 696-697 (2002). 

M. Haruta, B. S. Uphade, S. Tsubota, and A. Miyamoto, Selective oxidation of propylene over gold deposited on titanium-based oxides, Res. Chem. Intermed. 24(3), 329-336 (1998). 

Rossignol, C. and Arrii, S. and Morfin, F. and Piccolo, L. and Caps, V. and Roussel, J. (2005). Selective oxidation of CO over model gold-based catalysts in the presenee of H2. Journal of Catalysis, 230,476-483. 

Figure 4.1 (a) STM image of gold nanoparticles on a titania crystal surface (b) plot of the catalytic activity of gold nanoparticles versus size in the selective oxidation of carbon monoxide with oxygen to carbon dioxide (c) an artist s rendition of the raft-like shapes of the nanoparticles. 

In 2006, Beltrame et al. investigated the catalytic activity of a colloidal solution of gold in the selective oxidation of o-glucose to o-gluconic acid. This reaction was performed at 303-333 K in water, at atmospheric pressure and with different glucose and oxygen concentrations at a pH of 9.5 [122]. The results showed that the reaction rate was proportional to the oxygen concentration. 

The oxidation of propene to propene oxide is considered an essential practice in industrial chemistry [1]. Haruta et al. showed that this process can be led by heterogeneous catalysis with gold supported over titania [15, 16]. Another goal in the gold catalysis sequence is the selective oxidation of some alcohols and carbohydrates with molecular oxygen, as studied by Prati and Rossi [17]. 

In comparison to the bismuth molybdate and cuprous oxide catalyst systems, data on other catalyst systems are much more sparse. However, by the use of similar labeling techniques, the allylic species has been identified as an intermediate in the selective oxidation of propylene over uranium antimonate catalysts (20), tin oxide-antimony oxide catalysts (21), and supported rhodium, ruthenium (22), and gold (23) catalysts. A direct observation of the allylic species has been made on zinc oxide by means of infrared spectroscopy (24-26). In this system, however, only adsorbed acrolein is detected because the temperature cannot be raised sufficiently to cause desorption of acrolein without initiating reactions which yield primarily oxides of carbon and water. 

Gold-catalyzed oxidation of styrene was firstly reported by Choudhary and coworkers for Au NPs supported on metal oxides in the presence of an excess amount of radical initiator, t-butyl hydroperoxide (TBHP), to afford styrene oxide, while benzaldehyde and benzoic acid were formed in the presence of supports without Au NPs [199]. Subsequently, Hutchings and coworkers demonstrated the selective oxidation of cyclohexene over Au/C with a catalytic amount of TBHP to yield cyclohexene oxide with a selectivity of 50% and cyclohexenone (26%) as a by-product [2]. Product selectivity was significantly changed by solvents. Cyclohexene oxide was obtained as a major product with a selectivity of 50% in 1,2,3,5-tetramethylbenzene while cyclohexenone and cyclohexenol were formed with selectivities of 35 and 25%, respectively, in toluene. A promoting effect of Bi addition to Au was also reported for the epoxidation of cyclooctene under solvent-free conditions. 

Electric double layer forces between polyelectrolyte and non-polymer surfaces in aqueous media have also been studied very intensively [371,394,400-402]. The adhesion between polyelectrolyte surfaces could be reduced considerably by increasing the ionic strength of the medium [400]. Using an electrochemical cell and a gold coated tip, the adhesion between electroactive layer of p oly( vinyl-ferrocene) was controlled through the selective oxidation or reduction of the polymer films [401]. 

Gold has emerged as an effective catalyst for the selective oxidation of methane to methanol. Various possible pathways for the oxidation are discussed.29 Suitably substituted furans are transformed into phenols by the use of gold catalyst (1). It has been suggested, on the basis of kinetic isotope effect and trapping studies, that the key intermediate is an arene oxide. The postulation is also supported by DFT calculations.30... 

Bimetallic colloids containing gold and palladium or platinum have been deposited onto carbon or graphite for use as catalysts for the selective oxidation of organic compounds52 (Section 8.3), in the same way as for pure gold colloids (Section 4.6). 

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