Nanosized gold catalysts

I 3 Preparation of Nanosized Gold Catalysts and Oxidation at Room Temperature... 

The selectivity of the catalyst is of major importance in the case of chlorinated VOCs the oxidation products should not contain even more harmful compounds than the parent-molecule, for example, formation of dioxins should be avoided. In addition, the minimization of CI2 and maximization of HCl in a product gas should be achieved [61]. These are just a few examples of why researchers are continuing the search for VOC oxidation catalysts as well as new reactor concepts. The new possibilities include, for example, utilization of nanosized gold catalysts in the oxidation of sulfur-containing VOCs and microwave-assisted processes where combination of adsorption and oxidation is used in low-concentration VOC oxidation [62, 63]. 

The search for better catalysts has been facilitated in recent years by molecular modeling. We are seeing here a step change. This is the subject of Chapter 1 (Molecular Catalytic Kinetics Concepts). New types of catalysts appeared to be more selective and active than conventional ones. Tuned mesoporous catalysts, gold catalysts, and metal organic frameworks (MOFs) that are discussed in Chapter 2 (Hierarchical Porous Zeolites by Demetallation, 3 (Preparation of Nanosized Gold Catalysts and Oxidation at Room Temperature), and 4 (The Fascinating Structure... 

The Haruta s discovery that nanosized gold particales adsorbed on metal-oxide powders facilitate a wide class of reactions under near-ambient conditions has attracted a worldwide interest [1]. It is known that gold is very inert in bulk phase. However, small gold clusters possess high reactivity in selective methane and alkenes oxidation and hydrogenation of linear alkenes [2]. So, gold nanoparticles have been found to be active catalysts for many reactions of industrial and environmental interest. 

Z.-Y. Yuan, V. Idakiev, A. Vantomme, T. Tabakova, T.-Z. Ren, B.-L. Su, Mesoporous and nanostructured Ce02 as supports of nanosized gold catalysts for low-temperature water-gas shift reaction, Catal. Today 131 (2008) 203-210. 

Andreeva, D., Nedyalkova, R., Ilieva, L., et al. (2003). Nanosize Gold-ceria Catalysts Promoted by Vanadia for Complete Benzene Oxidation, Appl. Catal. A Gen., 246, pp. 29-38. 

Catalysts were prepared by deposition-precipitation (DP) and deposition from suspension (DS). Deposition-precipitation of nanosize gold particles was performed by precipitation onto a support from a HAuCU solution with ammoiua at pH 9. Suspension of gold nanoparticles with average size 11 nm was synthesized by Turkevich method [3], starting from gold precursor (HAuCC) and sodium citrate. Then gold particles were deposited on support. 

Bard and co-workers have reported on the attainment of equilibrium between the nanosized particles and an electrode in the presence of a redox mediator [25a]. The study refers to the production of a mediator (methyl viologen radical cation) that reduces water in the presence of colloidal gold and platinum metal catalyst. An electrochemical model based on the assumption that the kinetic properties are controlled by the half-cell reactions is proposed to understand the catalytic properties of the colloidal metals. The same authors have used 15 nm electrodes to detect single molecules using scanning electrochemical microscopy (SECM) [25b]. A Pt-Ir tip of nm size diameter is used along with a ferrocene derivative in a positive feedback mode of SECM. The response has been found to be stochastic and Ear-adaic currents of the order of pA are observed. 

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