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Scientific reports 10(1), 8 (2020). doi:10.1038/s41598-019-55770-y, Published by Macmillan Publishers Limited, part of Springer Nature, [London]

Die Mikrostrukturstrukturanalyse unter Berücksichtigung von Kristallitgröße und Kristalldefekten ist in der heterogenen Katalyse weit verbreitet. Aktive Katalysatoren können auf Trägern abgeschieden sein, nanoskalig und/oder stark deformiert sein. Solche Eigenschaften erschweren die Mikrostrukturanalyse. Um dennoch die genaue Mikrostruktur solcher Materialien zu erhalten, wurde eine Methodik entwickelt, die auf einer Kombination von lokaler TEM und XRD mit integrierter Linienprofilanalyse basiert. Nanoskaliges ZnO, Au@Kohlenstoff und CuO wurden als Beispiele für die Diskussion von Modellierungsstrategien ausgewählt. Eine physikalische Mischung einer niedrigen Konzentration der aktiven Komponente auf einem amorphen Träger wurde gewählt, um die Nachweisgrenzen der Methode zu untersuchen. Als Anwendungsbeispiel wurde CoFe\(_{2}\)O\(_{4}\) als Ausgangsstoff für die Ammoniak-Zersetzung verwendet. Hierbei wurde die Mikrostruktur- und die Kristallstrukturanalyse von \(\it in-situ\) XRD Daten kombiniert. Microstructure analysis, considering size and the crystal defects, is widely conducted to heterogeneous catalysis. The active catalysts can be supported components or nanosized/heavily deformed materials. However, such factors make the microstructure analysis difficult. To obtain accurate microstructure for such materials a methodology is developed based on interplay of local TEM and integral XRD with Whole Powder Pattern Modelling approach. Nanosized ZnO, Au@Carbon and CuO are selected as examples to the discussion of modelling strategies. Next, a physical mixture of low loading complex on amorphous support was studied for the detection limits of XRD. As an application, CoFe\(_{2}\)O\(_{4}\) used as a precursor for ammonia decomposition is conducted to combine the analysis of microstructure and crystal structure by means of \(\it in-situ\) XRD. The correlation of microstructure with catalytic performance can then be proposed.

Nanoscopic gold particles have gained very high interest because of their promising catalytic activity for various chemicals reactions. Among these reactions, low-temperature CO oxidation is the most extensively studied one due to its practical relevance in environmental applications and the fundamental problems associated with its very high activity at low temperatures. Gold nanoparticles supported on manganese oxide belong to the most active gold catalysts for CO oxidation. Among a variety of manganese oxides, Mn2O3 is considered to be the most favorable support for gold nanoparticles with respect to catalytic activity. Gold on MnO2 has been shown to be significantly less active than gold on Mn2O3 in previous work. In contrast to these previous studies, in a comprehensive study of gold nanoparticles on different manganese oxides, we developed a gold catalyst on MnO2 nanostructures with extremely high activity. Nanosized gold particles (2-3 nm) were supported on α-MnO2 nanowires and mesoporous β-MnO2 nanowire arrays. The materials were extremely active at very low temperature (-80 °C) and also highly stable at 25 °C (70 h) under normal conditions for CO oxidation. The specific reaction rate of 2.8 molCO·h(-1)·gAu(-1) at a temperature as low as -85 °C is almost 30 times higher than that of the most active Au/Mn2O3 catalyst.

OA gold The reduction of NO2 in air at ambient temperatures with activated carbons can be increased by the infiltration of metal oxide nanoparticles into the sorbents. The NO2 is first adsorbed to the activated carbon and subsequently catalytically reduced to physiologically neutral substances by the metal oxides. The catalytic reduction at ambient temperatures is rather slow. In a former study concerning the application in cabin air filters, it was shown that the modification of activated carbon with 5 wt% CuO/ZnO leads to reduced breakthrough of NO2 and that the adsorbent was able to regenerate between repeated NO2 adsorption cycles. Here we show that the efficiency of the sorbent can be more than doubled by increasing the metal oxide infiltration to 20 wt% whereas a further increase in loading yields no additional improvement, due to a partial transformation of the oxidic compounds.