High activity supported gold catalysts by incipient wetness impregnation

It is generally thought that catalysts produced by incipient wetness impregnation (IW) are very poor for low temperature CO oxidation, and that it is necessary to use methods such as deposition-precipitation (DP) to make high activity materials. The former is true, indeed such IW catalysts are poor, and we present reactor data, XPS and TEM analysis which show that this is due to the very negative effect of the chloride anion involved in the preparation, which results in poisoning and excessive sintering of the Au particles. With the DP method, the chloride is largely removed during the preparation and so poisoning and sintering are avoided. However, we show here that, contrary to previous considerations, high activity catalysts can indeed be prepared by the incipient wetness method, if care is taken to remove the chloride ion during the process. This is achieved by using the double impregnation method (DIM). In this a double impregnation of chloroauric acid and a base are made to precipitate out gold hydroxide within the pores of the catalyst, followed by limited washing. This results in a much more active catalyst, which is active for CO oxidation at ambient temperature. The results for DIM and DP are compared, and it is proposed that the DIM method may represent an environmentally and economically more favorable route to high activity gold catalyst production. (C) 2007 Elsevier B.V. All rights reserved.

A study of co-precipitated bimetallic gold catalysts for water-gas shift reaction

Synthesis, testing and characterisation of bimetallic gold, Au-M on ceria as catalysts were carried out for low temperature water-gas shift reaction (WGS). Amongst the entire screened catalysts 3 wt% (AU-Pt)/CeO2 displayed the best WGS activity than the monometallic promotors, giving the light-off curve at the lowest temperature in the range 100-300 degrees C. (Au-Pd)/CeO2 also achieved the same activity but at a higher temperature. It was also found that WGS activity was strongly correlated with the surface reducibility which in turn depended on the modified local electronic band structure of promoted ceria. These results clearly suggest that the key role of bimetallic promoter may involve in facilitating the creation of defective reduced surface by exerting its local electronic effect on ceria to form the surface germinal -OH groups in water which act as active sites for enhanced WGS activity. (C) 2008 Elsevier B.V. All rights reserved.

An electrochemical study of 4-aminothiophenol/pt nanoparticle multilayers on gold electrodes

Quartz crystal microbalance (QCM) measurements of the formation of a 4-aminothiophenol (4-ATP)self-assembled monolayer (SAM) at a gold electrode showed that a surface coverage of 118 ng cm(-2) was obtained after a 3 h exposure period, indicating that good surface coverage was achieved. Cyclic voltammetry of the ferricyanide redox couple across this SAM modified surface produced similar results to those of a bare electrode; however, the electroreduction of oxygen was found to be impaired. The 4-ATP SAM layer was not stable to repeated electrochemical oxidation and reduction; it is believed that the 4-ATP SAM layer was first converted to a 4'-mercapto-N-phenylquinone diimine (NPQD) layer followed by subsequent formation of a 4'-mercapto-N-phenylquinone monoimine (NPQM) layer. We also report a quartz crystal microbalance study of the attachment of platinum nanoparticles to such SAM modified electrodes. We show that five times the amount of platinum nanoparticles can be attached to a 4-ATP modified electrode surface (observed frequency change - 187 Hz) compared with an NPQD modified electrode surface (observed frequency change -35 Hz). The presence of the platinum particles was confirmed electrochemically by their surface electrochemical properties, which were different from those of the underlying gold electrode. It is believed that this is the first time that such direct evidence of electrochemical communication between platinum nanoparticles and a SAM modified electrode surface has been obtained. It was also shown to be possible to build up multilayer SAM/nanoparticle modified surfaces while maintaining efficient electrochemical communication. Up to three SAM/nanoparticle sandwich layers were constructed.

The syntheses, structures and redox properties of phosphine-gold(I) and triruthenium-carbonyl cluster derivatives of tolans

The syntheses of several ethynyl-gold(I) phosphine substituted tolans (1,2-diaryl acetylenes) of general form [Au(C=CC6H4C=CC6H4X)(PPh3)] are described [X = Me (2a), OMe (2b), CO2Me (2c), NO2 (2d), CN (2e)]. These complexes react readily with [Ru-3(CO) 10(mu-dppm)] to give the heterometallic clusters [Ru3(mu-AuPPh3)(mu-eta(1), eta(2)-C2C6H4C, CC6H4X)(CO)(7)(mu-dppm)] (3a-e). The crystallographically determined molecular structures of 2b, 2d, 2e and 3a-e are reported here, that of 2a having been described on a previous occasion. Structural, spectroscopic and electrochemical studies were conducted and have revealed little electronic interaction between the remote substituent and the organometallic end-caps. (C) 2007 Elsevier B. V. All rights reserved.

Low temperature CO oxidation on supported and unsupported gold compounds

Several simple gold compounds and their physical mixtures with TiO2 Were tested for low temperature CO oxidation. No true catalytic activity was found for gold precursors on their own, although both Au2O3 and Au(OH)(3) react well with CO even at room temperature in a non-catalytic manner. Despite that catalytic activity was obtained by physically mixing Au(OH)(3) or Au2O3 with TiO2 and the results further emphasise the importance of a good contact between the gold and the support for good CO oxidation activity. (c) 2005 Published by Elsevier.

Multiple morphologies of gold nano-plates by high-temperature polyol syntheses

High-temperature polyol methods were used to fabricate micro- or nano-sized gold plates. 1,2propanediol served as both medium and reducing agent. Triangular plates and polygonal plate shapes derived from triangular prisms as well as pentagonal structured gold particles have been synthesized. Poly(vinylpyrrolidone) (PVP) plays an important role, but is not necessary, for the formation of these structures. These gold plates may have applications in the characterisation of adsorbed proteins or peptides. (C) 2008 Elsevier B. V. All rights reserved.

In situ formation of gold nanoparticles with a thermoresponsive block copolymer corona

Gold nanoparticles with a polymer coating exhibiting large and reversible thermoresponsiveness are prepared via a one-pot synthesis method using narrow polydispersity thermoresponsive block copolymers. (C) 2007 Elsevier B.V. All rights reserved.

‘Inherited commitments’: do changes in ownership affect corporate social responsibility (CSR) at African gold mines?

This paper critically examines the issue of ‘inherited corporate social responsibility’ in the gold mining industry, focusing specifically on the case of sub-Saharan Africa, a region plagued with excessive corruption, rampant poverty and weak governance. Whilst there appears to be little incentive to proactively engage with communities and implement cutting-edge environmental policies in the region, mine managers argue otherwise, highlighting a number of reasons for embracing corporate social responsibility (CSR). After briefly reviewing the philosophical underpinnings of CSR, the paper provides an in-depth analysis of these arguments, in the process, underscoring how tenuous the case for CSR in the extractive industries, and gold mining more specifically, is in the context of sub-Saharan Africa. Following a change in ownership, new management faces few pressures to embrace CSR in its entirety and therefore, more often than not, finds itself in a position to implement programs and policies of its choice. More research is needed that further popularizes the issue of ‘inherited CSR’ in the gold mining sector and extractive industries more generally.

Structural adjustment and subsistence industry: artisanal gold mining in Ghana

Since the implementation of Ghana's national Structural Adjustment Programme (SAP), policies associated with the programme have been criticized for perpetuating poverty within the country's subsistence economy. This article brings new evidence to bear on the contention that the SAP has both fuelled the uncontrolled growth of informal, poverty-driven artisanal gold mining and further marginalized its impoverished participants. Throughout the adjustment period, it has been a central goal of the government to promote the expansion of large-scale gold mining through foreign investment. Confronted with the challenge of resuscitating a deteriorating gold mining industry, the government introduced a number of tax breaks and policies in an effort to create an attractive investment climate for foreign multinational mining companies. The rapid rise in exploration and excavation activities that has since taken place has displaced thousands of previously-undisturbed subsistence artisanal gold miners. This, along with a laissez faire land concession allocation procedure, has exacerbated conflicts between mining parties. Despite legalizing small-scale mining in 1989, the Ghanaian government continues to implement procedurally complex and bureaucratically unwieldy regulations and policies for artisanal operators which have the effect of favouring the interests of established large-scale miners.