Alcohol gold nanoparticle

Liu YC, Yu CC, Yang KH (2006) Active catalysts of electrochemically prepared gold nanoparticles for the decomposition of aldehyde in alcohol solutions. Electrochem Commun... 

Oliveira, R.L., Kiyohara, P.K. and Rossi, L.M. (2010) High performance magnetic separation of gold nanoparticles for catalytic oxidation of alcohols. Green Chemistry, 12 (1), 144-149. 

Gold nanoparticles can also be stabilized using polymers that do not have specific functional groups through physisorption. Among the possible stabilizers, the polymers used most often to stabilize Au NPs are the water soluble polymers poly(N-vinylpyrrolidone) (PVP), polyethylene glycol) (PEG), poly(vinyl pyridine), poly(vinyl alcohol) (PVA), poly(vinyl methyl ether) (PVME), and polyelectrolytes such as PAA, chitosan, polyethyleneimine (PEI) or poly(diallyl dimethylammonium) chloride (PDDA) [99]. 

The partial oxidation of alcohols, to afford carbonyl or carboxylic compounds, is another synthetic route of high industrial interest For this, scC02 was investigated as a reaction medium for the aerobic oxidation of aliphatic, unsaturated, aromatic and benzylic acids with different catalytic systems, mainly based on the use of noble metals, both in batch [58-64] and in continuous fixed-bed reactors [65-70]. In this context, very promising results have been obtained when studying the catalytic activity of supported palladium and gold nanoparticles in the oxidation of benzyl alcohol to benzaldehyde these allowed conversions and selectivities in excess of 90% to be achieved [71-73]. 

Recently, gold has emerged as one of the most active catalysts for alcohol oxidation and is especially selective for poly alcohols. In 2005, Corma [184] and Tsu-kuda [185], independently demonstrated the potential of gold nanoparticles for the oxidation of aliphatic alcohols. For example, in the case of gold nanoparticles deposited on nanocrystalline cerium oxide [184], a TOF of 12 500 h 1 was obtained for the conversion of 1-phenylethanol into acetophenone at 160 °C (Fig. 4.67). Moreover this catalyst is fully recyclable. Another example of a gold catalyst with exceptional activity is a 2.5% Au-2.5% Pd/Ti02 as catalyst [186]. In this case for 1-octanol a TOF of 2000 h-1 was observed at 160 °C (reaction without solvent, Fig. 4.67). 

For the preparation of gold nanopartides supported on insoluble solids, the most widely used procedure is the precipitation-deposition method [32-36]. Starting from an aqueous solution of HAuCh, addition of a base leads to precipitation of a mixture of Au(OH)3 and related oxy/hydroxides that adsorbs into the solid and is then reduced to metallic gold by boiling the adsorbed species in methanol or any other alcohol. In this procedure, it has been established that the pH of the precipitation and the other experimental conditions (nature of the alcohol, temperature and time of the reduction, calcination procedure, etc.) can provide a certain control of the particle size of the resulting nanoparticles [3j. Figure 12.2 illustrates the steps required in the formation of supported gold nanoparticles. 

The currently most widely accepted reaction mechanism for alcohol oxidation catalyzed by supported gold nanoparticles has been proposed by analogy with the assumed reaction mechanism for alcohol oxidation in palladium and platinum metals taking into consideration the kinetic data and mechanistic information obtained from gold-catalyzed CO oxidation [110]. Scheme 12.11 illustrates a reasonable mechanistic proposal. 

Scheme 12.12 Pictorial representation of the formation of metal-alcoholate at the surface of ceria supported gold nanoparticles.

The role of the particle size of gold specifically in the catalytic activity for the aerobic oxidation of alcohols (as opposed to CO oxidation) has been addressed by Tsukuda and coworkers, who prepared two colloidal gold nanoparticles of 1.3 0.3 and 9.5 1.0nm diameter stabilized by polyvinylpyrroHdone [112]. Particles with different sizes were obtained by rapid reduction of AuCh either with NaBH4 or Na2S03. Data of the initial reaction rate, both uncorrected and corrected by the... 

Table 12.5 Results of the gas phase air oxidation of volatile alcohols catalyzed by gold nanoparticles, 1 wt.% supported on Aerosil (200m g" ). The selectivity in all cases was 100%. (Data taken from Ref [117].)...

Aerobic oxidation of simple volatile aliphatic alcohols, including ethanol [116], can be carried out conveniently in the gas or vapor phase. Gold nanoparticles (1%) supported on silica have been found to be a convenient catalyst [117]. Volatile primary and secondary aliphatic alcohols can be oxidized to their carbonyl compounds in the gas phase using air at atmospheric pressure in a fk-bed tubular reactor (Table 12.5) [117]. 

Other diols, polyols [77], amino alcohols [77] and glucose [77, 80,120] have also been oxidized with remarkable selectivity to hydroxy- and amino- acids by oxygen in strong basic aqueous media using gold nanoparticles supported on carbon and metal oxides as catalysts (Schemes 12.14 and 12.15). 

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