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Combined small- and wide-angle X-ray scattering studies on oxide-supported Pt nanoparticles prepared by a CVS and CVD process

Guo, Xiaoai, Gao, Kun, Gutsche, Alexander, Seipenbusch, Martin, Nirschl, Hermann
Powder technology 2015 v.272 pp. 23-33
X-ray diffraction, aluminum oxide, atmospheric pressure, catalysts, crystallites, databases, fractal dimensions, mixing, models, nanoparticles, powders, quantitative analysis, silica, surface roughness, titanium dioxide, transmission electron microscopy, wide-angle X-ray scattering
Various model oxide-supported metal catalyst particles (Pt nanodots supported on silica, titania and alumina) prepared by a CVS/CVD process at atmospheric pressure have been studied by using a self-developed SAXS and WAXS laboratory system. It has been shown that simultaneous SAXS and WAXS analyses offer a structural insight into the complexity of the supported metal catalysts, allowing quantitative study on the morphological characteristics of the synthesized oxide-supported catalyst particles and fine structures, including primary particles, internal subunits, mass fractal dimension of the aggregates, surface roughness, and crystallite properties as well as the Pt nanodots. The oxide support particles under study cover a size range of 55–150nm and the Pt nanodots are in the size range of 1.8–15.8nm. The SAXS and WAXS results were compared with those by TEM and the XRD reference database, and a good agreement has been found. Experimental findings indicated that SAXS appears to be more effective than WAXS for determining the Pt dot size, especially for Pt dots smaller than 2–4nm due to the overlapping effect of the scattering signals at wide angles and the resultant difficulty in discerning the broad WAXS peaks of small Pt dots from the support background. The morphological modification of the support particle surface by mixing a certain amount of alumina into the other oxide support particles during the synthesis process has been observed through quantitative determination of the surface fractal dimension describing the surface roughness using SAXS. Simultaneous quantitative characterization of support particle structures and metal catalyst nanoparticles helped to better understand how synthesis conditions influence the resulting structures of the support particles and how this in turn affects the catalyst properties like the agglomeration or sintering of metal nanoparticles on the supports, to further optimize the synthesis process and prepare better supported metal catalyst nanoparticles.