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Schlagwörter:
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Zusammenfassung:
The analysis of the microstructure of materials, typically of the size and the crystal defects,
is widely conducted in heterogeneous catalysis to understand the correlation of the
microstructure with the catalytic performance. The active catalysts are reported to be
supported components, materials with nanosized particles, high crystal defect density or
high porosity. However, such factors make the microstructure analysis difficult. Although
High Resolution (Scanning) Transmission
Electron Microscopy (HR-(S)TEM) and X-ray
Diffraction (XRD) as individual tools are commonly used for microstructure analysis, the
techniques are limited in statistics (TEM) and average out local structural fluctuations
(XRD).
To provide accurate microstructure information using stated techniques for nanosized
materials the methods of microstructure analysis have been systematically studied. A
methodological development for a comprehensive and quantitative description of the microstructure of inorganic catalysts is presented based on a beneficial interplay of complementary local HR-(S)TEM and integral XRD techniques. The extension of the local
information, including size distribution and type of defects obtained from HR-(S)TEM to an integral one, resampling the whole sample was achieved by a simulation of XRD data with Whole Powder Pattern Mode
lling (WPPM) approach.
In this study, five materials are selected for
tackling the issues. The modelling strategies for
WPPM were firstly studied in two sections: (A) Nanosized ZnO is chosen as an example for the discussion on how to select the appropriate parameters including crystallite shape and
the type of distribution function for a size analysis. (B) Nanosized Au@Carbon and CuO are studied as examples for understanding the accuracy of microstructure analysis if both size
and defects are incorporated during modelling. Secondly, a physical mixture of ZnO, CuO
and carbon was studied for addressing the detection limits of XRD regarding the low
loading complex on amorphous support. Accordingly, a real CuO/ZnO@Carbon adsorbent
used for NOx
removal was analyzed. Finally, in addition to the microstructure analysis, the
crystal structure analysis was also incorporated by using Rietveld method for CoFe2O4, a
precursor for the ammonia decomposition reaction. Since the microstructure and the crystal
structure of such catalysts undergo changes during the reaction, in-situ
XRD characterization was highlighted to monitor the corresponding variation. The correlation
with catalytic performance can then be proposed.
