A carefully designed in situ XRD experiment when guided by atomistic simulations can provide data on the atomistic structure of a surface layer of platinum nanoclusters. Even the adsorption process for a strongly bonded adsorbate can be monitored and interpreted, providing data that are not available from other techniques. The data reported here present the first observation of surface reconstruction of nanocrystals by X-ray diffraction known to the authors. We were able to observe repeatable in situ evolution of Pt nanocrystal diffraction peak positions on exchange of gas atmosphere from hydrogen to helium. Experiments at room temperature and at 373 K shows various hydrogen desorption rate in He atmosphere but a very similar rate of an average lattice constant change with clearly separated desorption and reconstruction phases. The hydrogen desorption rate has been shown to be controlled by a slower process-hydrogen spillover and its activation energy was estimated. Diffraction peaks of Pt on exposition to O(2) shift at various degree to lower angles due to surface relaxation-the effect being particle-size-dependent and illustrating elongation of surface Pt-Pt bonds caused by adsorption. The results show the possibility for XRD to become a nanosurface science tool enabling the combination of structure analysis with adsorption/desorption measurements within the pressure gap and material gap.

Atoms at the surface of nanocrystals contribute appreciably to the X‐ray diffraction pattern. Phenomena like chemisorption, affecting the displacement of surface atoms with respect to their positions in the perfect crystallographic structure, cause diffraction peak shifts and intensity changes. These effects are easily measurable for small nanocrystals up to 10 nm size. This article reports diffraction effects of chemisorption of adsorbing gases H2, O2, CO and NO for a series of in situ powder diffraction experiments on nanocrystalline Pt supported on silica. On the basis of previous diffraction observation of Pt surface reconstruction during hydrogen desorption, it was possible to quantify this effect versus crystallite size and rationalize the observed diffraction peak shift for the other adsorbing species. This enabled the surface reconstruction to be distinguished from the surface relaxation effect, the latter depending monotonically on the adsorption energy. Even if no phase transition occurs, monitoring of a peak's position, intensity, width and gas composition (via mass spectrometry) during a carefully designed physicochemical process (including surface chemical reaction) enables insight into and understanding of the surface structure evolution (e.g. amorphization, relaxation, reconstruction or changes in the overall morphology). The proposed technique can be used as a surface science tool, allowing studies of nanocrystals under high pressure.

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We report an operando XRD/MS experiment on nanocrystalline Pt supported on silica, monitoring quick, low temperature coalescence of Pt in an NO atmosphere accompanied by surface reconstruction deduced from an apparent lattice parameter (ALP) evolution.