Stages of Growth

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Science  09 Nov 2007:
Vol. 318, Issue 5852, pp. 889
DOI: 10.1126/science.318.5852.889c

Many important catalysts are composed of supported metal nanoparticles. Although x-ray absorption spectroscopy has been used to probe the impact of particle size and shape on chemical reactivity, it is difficult to extract information beyond the first few coordination shells, and there is a risk with this technique of radiation damage to the samples. Chupas et al. show that by monitoring the change in pair distribution functions from the scattering of weakly absorbed (and thus minimally damaging) high-energy x-rays, they can track the growth of Pt0 nanoparticles with time. They studied the reduction of PtCl62−, supported on titanium dioxide, at temperatures from 100° to 200°C. The Pt-Cl correlations decreased linearly with time without an induction period, suggesting that the reduction is not autocatalytic, as has been seen for Pt4+ species in solution. Data collected during the heating period revealed a shift in the dominant process from reduction of the Pt ions (to make isolated metal atoms or small clusters), to rapid growth or sintering, and finally ripening of the larger clusters. — MSL

J. Am. Chem. Soc. 129, 10.1021/ja076437p (2007).

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