Gold particles, catalyst supports influenced

The extent of the reduction may depend on many parameters, including the nature of the support. The size of the gold particles is also influenced by the thermal treatment, the flow rate and composition of gas through the catalyst (sometimes hydrogen is a component of the gas), and the size of the catalyst sample [1,2], It is recommended that as prepared samples are stored in a refrigerator at <273 K and that calcined catalysts should also be kept cold, and that after drying samples should be kept in a vacuum desiccator in the dark, reduction being performed immediately before use. 

In many catalytic systems, nanoscopic metallic particles are dispersed on ceramic supports and exhibit different stmctures and properties from bulk due to size effect and metal support interaction etc. For very small metal particles, particle size may influence both geometric and electronic structures. For example, gold particles may undergo a metal-semiconductor transition at the size of about 3.5 nm and become active in CO oxidation [10]. Lattice contractions have been observed in metals such as Pt and Pd, when the particle size is smaller than 2-3 nm [11, 12]. Metal support interaction may have drastic effects on the chemisorptive properties of the metal phase [13-15]. Therefore the stmctural features such as particles size and shape, surface stmcture and configuration of metal-substrate interface are of great importance since these features influence the electronic stmctures and hence the catalytic activities. Particle shapes and size distributions of supported metal catalysts were extensively studied by TEM [16-19]. Surface stmctures such as facets and steps were observed by high-resolution surface profile imaging [20-23]. Metal support interaction and other behaviours under various environments were discussed at atomic scale based on the relevant stmctural information accessible by means of TEM [24-29]. 

The objectives of this work are to study the influence of gold particles on the properties of typical catalyst supports, namely MgO and TiO. Gold has been chosen because of its relatively low catalytic activity except for oxygen transfer reactions (4). MgO, an insulator, and TiO, a semiconducting material, are widely used as catalyst supports, and for both of them metal-support interactions have been reported in the literature. Our study places main emphasis on the role of gold on thermal stability, phase transformations, solid-phase oxygen exchange activity, and adsorption characteristics of the oxides. 

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