Abstract
Gold nanoparticles used in most experiments (1–10 nm) in gold catalysis show varying degrees of reactivity, with particles below 5 nm generally being more reactive. The origin of this activity is a subject of a number of model experiments and theoretical studies on either clusters of a few atoms in size or extended surfaces (smooth or stepped). In the work described here, a classical theory for the variation of the metal workfunction with cluster size, Extended Hückel Theory (EHT) calculations combined with DFT calculations, as well as a carbon monoxide (CO) chemisorption model are combined to develop a relationship between metal particle size and the particle's reactivity towards CO. For gold, it is shown that while the contribution of the d-band hybridization energy to the total CO chemisorption energy is unfavourable for bulk gold, this is not true for gold particles below 5–6 nm. That is, the d-band hybridization energy is negative for small gold particles. This is believed to be explanation of the onset of high reactivity for small gold particles.
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Dr Noko Phala is a Lead Research Scientist at Anglo Research, a division of Anglo Operations Limited. He obtained a PhD in Chemical Engineering at the University of Cape Town in 2004, for a thesis entitled ‘a theoretical investigation in heterogeneous gold catalysis’. His areas of research include (i) search for novel metal mining/extraction technologies, and (ii) application of metals as catalysts in chemical processing. In both these fields a significant portion of his time is spent seeking to understand, rationalize, and predict surfacemolecule interactions by applying theoretical methods.
Prof Eric van Steen is the Head of the Department of Chemical Engineering at the University of Cape Town and is part of the Centre for Catalysis Research. His research interest is in heterogeneous catalysis and his current focus is on the catalytic activity of nano-sized metal particles.
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Phala, N.S., van Steen, E. Intrinsic reactivity of gold nanoparticles: Classical, semi-empirical and DFT studies. Gold Bull 40, 150–153 (2007). https://doi.org/10.1007/BF03215572
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DOI: https://doi.org/10.1007/BF03215572