Quick low temperature coalescence of Pt nanocrystals on silica exposed to NO – the case of reconstruction driven growth?

Kaszkur, Zbigniew; Mierzwa, Bogusław; Juszczyk, W.; Rzeszotarski, Piotr; Łomot, Dariusz

doi:10.1039/c3ra48078j

Cited by 3 publications

(2 citation statements)

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“…The procedure of data analysis was reported previously. 10 The observed structural changes are repeatablethe position, intensity and width of diffraction maxima form a regular repeatable pattern if one neglects the shortening of the CO cycle causing the changes to be not completed. The evolution of position and intensities closely resembles the one simulated theoretically (Fig.…”

Section: Resultsmentioning

confidence: 98%

“…The gas supply system and elements of the measurement control were described previously. 10 The gases used were helium of 99.999% purity, hydrogen (99.9995%) and CO (99.998% purity with CO 2 as a principal contaminant). The powder diffraction patterns were collected on a D5000 powder diffractometer (Bruker AXS) equipped with a LynxEye strip detector providing good resolution and quick data collection.…”

Section: Methodsmentioning

confidence: 99%

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Self-diffusion in nanocrystalline alloys

Kaszkur

Juszczyk

Łomot

2015

Phys. Chem. Chem. Phys.

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We report an operando XRD/MS experiment on a nanocrystalline Pd(70%)Ag(30%) alloy supported on silica (10 wt% of metal) monitoring slow reversible Pd (in CO) and subsequently Ag (in He) surface segregation at 673 K. XRD data following CO and He flow show structural changes that can be modeled and interpreted in terms of the diffusion phenomena within a typical metal nanocluster. Qualitative differences in the rate of both segregation processes suggest different diffusion mechanisms as the Pd segregation involves vacancy depletion. The experimental details suggest that this kind of experiment can provide a very sensitive response to subtle changes at the surface of nanoclusters. Segregation processes can be stopped at any time by lowering the temperature below 573 K which allows engineering of the metal surface e.g. preparing for a catalytic low temperature reaction on a well-defined surface.

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Section: Resultsmentioning

confidence: 98%

Section: Methodsmentioning

confidence: 99%

Self-diffusion in nanocrystalline alloys

Kaszkur

Juszczyk

Łomot

2015

Phys. Chem. Chem. Phys.

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Powder diffraction in studies of nanocrystal surfaces: chemisorption on Pt

2014

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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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