Synthesis and catalytic performance of CeOCl in Deacon reaction

Surface chlorinated CeO2 is an efficient material for HCl oxidation, which raises the question whether an oxychloride phase could be also active in the same reaction. CeOCl was synthesized by solid state reaction of cerium oxide with anhydrous cerium chloride and tested in HCl oxidation using various feed compositions at 703 K. X-ray diffraction of post-reaction samples revealed that CeOCl is unstable, in both oxygen-rich and -lean conditions. Applying oxygen over-stoichiometric feeds led to complete transformation of CeOCl into CeO2. Considerable HCl conversions were obtained only after this transformation, which confirms the essential role of bulk cerium oxide in this catalytic system

On the structural relations of malachite. II. The brochantite MDO polytypes

The structural relation between malachite and the brochantite MDO (maximum degree of order) polytypes is discussed. It is demonstrated that the same building blocks which form the basis of brochantite polytypism also occur in malachite. The different arrangements of these building blocks in the two mineral structures are rationalized as a result of the different coordination geometries required by the respective non-metal atoms acting as linkers. The compound stoichiometries are discussed in light of a common structured formula scheme, in which pairs of H atoms can play a similar role as single non-H atoms. An overview on the occurrence of malachite-like building blocks in several other crystal structures is given

Insights into Chemical Dynamics and Their Impact on the Reactivity of Pt Nanoparticles during CO Oxidation by Operando TEM

The functionality of heterogeneous catalysts is influenced by a delicate interplay of multiple parameters, including morphology and structure, chemical potential gradients and related dynamics. Here, we report on how these factors are interconnected. Combining time-resolved transmission electron microscopy imaging and selected area electron diffraction with online conversion detection, CO oxidation over Pt nanoparticles was studied at a pressure of 700 mbar and temperatures up to 500 °C. The different interactions between reactants and catalysts over the entire range of catalytic conversion were investigated. Chemical dynamics in this reaction were found to consist of both morphological transformations and fluctuating structural dynamics. Morphological transformations were observed mostly in low activity regimes, leading to nanoparticles with increased stable surface facets. Meanwhile structural changes were observed during high activity regimes where the partial pressures remained constant. Furthermore, the observed changes were found to occur in both the bulk and the surface of the catalyst. Catalytic cycling revealed that morphological transformations and structural dynamics have different implications on the reactivity and are mostly irreversible

Oscillatory behavior in the CO-oxidation over bulk ruthenium dioxide – the effect of the CO/O₂ ratio

CO oxidation over polycrystalline ruthenium dioxide was monitored in an in-situ XRD setup. The evolution of the bulk state of the catalyst was followed by in-situ XRD during reaction, while the surface morphology and chemical state before and after reaction were investigated by HRSEM and EDX. The commercial RuO2 powder was calcined prior reaction to ensure the formation of completely oxidized RuO2. This pre-calcined RuO2 is initially inactive in CO oxidation regardless of the CO/O2 feed ratio and requires an induction period, the length of which strongly depends whether the catalyst is diluted with boron nitride or not. After this induction period oscillations in the CO2 yield occur under O2-rich conditions only. These oscillations exhibit two time constants for the diluted catalyst, while the low frequency oscillations were not observed in the case of undiluted RuO2. Furthermore, the state of the catalyst after activation in O2-rich feed conditions differs dramatically from the state after activation in CO-rich feed conditions. Firstly, the catalyst activated in an O2-rich atmosphere remains inactive under CO-rich conditions in contrast to the catalyst activated in CO-rich conditions which is afterwards active under all feed ratios examined. Secondly, the surface morphology of the catalyst is quite different. While the apical surfaces of the RuO2 crystals become roughened upon activation in the CO-rich feed, they become facetted under O2 rich activation conditions. Therefore, we conclude that at least two different active surface states on the bulk RuO2 catalyst exist