Britt Hvolbæk

Catalytic activity of Au nanoparticles

Au is usually viewed as an inert metal, but surprisingly it has been found that Au nanoparticles less than 3–5 nm in diameter are catalytically active for several chemical reactions. We discuss the origin of this effect, focusing on the way in which the chemical activity of Au may change with particle size. We find that the fraction of low-coordinated Au atoms scales approximately with the catalytic activity, suggesting that atoms on the corners and edges of Au nanoparticles are the active sites. This effect is explained using density functional calculations.

Trends in the Catalytic CO Oxidation Activity of Nanoparticles

Introduction While extended gold surfaces are generally considered chemically inert [1], nanosized (<5 nm) gold particles can be very effective catalysts for a number of oxidation reactions [2-5]. There are reports of similar size effects for silver catalysts [6]. The origin of the nano-effects in the catalytic properties of these metals is widely debated [5], and no consensus has been reached yet. Based on a set of density functional theory calculations we compare the catalytic activity for the CO oxidation reaction over extended surfaces and small nano-particles of a number of metals.

Search Directions for Direct H2O2 Synthesis Catalysts Starting from Au12 Nanoclusters

We present density functional theory calculations on the direct synthesis of H2O2 from H2 and O2 over an Au12 corner model of a gold nanoparticle. We first show a simple route for the direct formation of H2O2 over a gold nanocatalyst, by studying the energetics of 20 possible elementary reactions involved in the oxidation of H2 by O2. The unwanted side reaction to H2O is also considered. Next we evaluate the degree of catalyst control and address the factors controlling the activity and the selectivity. By combining well-known energy scaling relations with microkinetic modeling, we show that the rate of H2O2 and H2O formation can be determined from a single descriptor, namely, the binding energy of oxygen (EO). Our model predicts the search direction starting from an Au12 nanocluster for an optimal catalyst in terms of activity and selectivity for direct H2O2 synthesis. Taking also stability considerations into account, we find that binary Au–Pd and Au–Ag alloys are most suited for this reaction.