Gold catalysis: Effect of particle size on reactivity towards various substrates

In this contribution the general rules and the exceptions in the area of gold catalysis are discussed in order to establish a correlation between the size of the catalytically active element and its reactivity towards different classes of substrate molecules. The general behaviour of gold is that it is inactive in massive form while it can be used as a highly active catalyst when downsized. Throughout this paper experimental data from different sources are collected to proof that – according to this general behaviour – small molecules (CO, NO, etc.) can be activated only on small nanoparticles or roughened Au(1 1 1) surfaces, whereas Au(1 1 1) single crystals or extended metal films are active in the reaction of large molecules. This observation defines the applicability area of gold nanoparticles and the activity of large gold surfaces, films or single crystals.The above effect can be modulated by interfacial interaction between gold species and active oxide either if gold is deposited directly on them or is supported on inactive oxides (such as model SiO2/Si(1 0 0) or high surface area amorphous or mesoporous silica) with minute amounts of promoter oxide. The oxide may invoke electronic interaction and simultaneously the defect structure of oxides likely has a key issue in the formation and stabilization of Au nanoparticles.On the other hand, it turned out that in some cases – independently of the interface – the key issue is the available gold area of Au nanoparticles dictating the reaction rate of a substrate.

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► General rules and exceptions in gold catalysis are reviewed.
► General rule: downsizing of the active element is required for catalytic activity.
► General rule is often broken in connection with reactions of large molecules.
► Interfacial interaction with oxide support further modulates the activity pattern.