Chemische Aktivität von dünnen Oxidschichten: Starke Träger- Wechselwirkungen ergeben eine neue ZnO-Dünnfilmphase

From Chain- to Graphene-like Hydroxyl-terminated (ZnO)n Clusters with n≤6 Obtained via Zinc Dimethoxide Hydrolysis and Condensation: Ab initio Structural, Electronic, Vibrational and Optical Properties Calculations

Recent reports are focusing on the structural evolution from the atomic-scale and also at the expenses of alkyl zinc alkoxide precursors towards (ZnO)_n clusters and nanostructures with different interesting motifs, but still not much is known about their electronic properties. In this manuscript, we present a theoretical study using DFT and TD-DFT methodologies on the hydrolysis and condensation of zinc dimethoxide precursor in its monomeric, dimeric and trimeric forms towards thermodynamically stable hydroxyl-terminated (ZnO)_n clusters with novel chain- and graphene-like fashions. For all cases, distinct vibrational and optical spectra features were assigned evidencing a global monotonic decrease in the opto-electronic gap with increasing oligomerization and cyclization stages. In addition, the electron-affinity of all clusters was also observed to be enhanced with increasing oligomerization and cyclization stages and the electronic charge localization in -e charged clusters was observed to be strongly related to the presence of zinc-oxo subunits and other particular structural features. Our calculations also indicate that the stabilization through hydroxyl termination of both chain- and graphene-like ZnO clusters not only could be a promising driving force to obtain larger atomic-scale 1D and 2D nanostructures but also envisage interesting properties, particularly as electronic acceptor materials for energy applications.

Chemical Batteries with CO2

Efforts to obtain raw materials from CO₂ by catalytic reduction as a means of combating greenhouse gas emissions are pushing the boundaries of the chemical industry. The dimensions of modern energy regimes, on the one hand, and the necessary transport and trade of globally produced renewable energy, on the other, will require the use of chemical batteries in conjunction with the local production of renewable electricity. The synthesis of methanol is an important option for chemical batteries and will, for that reason, be described here in detail. It is also shown that the necessary, robust, and fundamental understanding of processes and the material science of catalysts for the hydrogenation of CO₂ does not yet exist.

New Insights into the Role of Al2 O3 in the Promotion of CuZnAl Catalysts: A Model Study

The Cu/Al₂ O₃ /ZnO(0001)-Zn ternary model catalysts and their binary analogues were prepared and characterized. It was found that Al₂ O₃ grew on the ZnO(0001)-Zn surface by a layer-by-layer model, whereas Cu grew on the ZnO(0001)-Zn surface as two-dimensional clusters up to 0.2 monolayers (ML), and thereafter formed three-dimensional clusters. Because of the layer-by-layer growth of Al₂ O₃ on the ZnO(0001)-Zn, Cu/Al₂ O₃ can be considered without the effect of ZnO. Ternary model catalyst Cu/Al₂ O₃ /ZnO(0001)-Zn, which has all three parts on the surface, was prepared by deposition of Cu on the surface of Al₂ O₃ /ZnO(0001)-Zn. Low-energy ion scattering spectra showed that Cu preferred to locate at the Al₂ O₃ /ZnO interfaces. Compared with Cu/ZnO, the addition of Al₂ O₃ obviously suppressed the reduction of copper oxides and led to a higher concentration of Cu⁺ . The Cu clusters were found to be covered by thin ZnO_x overlayers after reduction of Cu/Al₂ O₃ /ZnO(0001)-Zn by using H₂ . Therefore, the high activity of industrial Cu/ZnO/Al₂ O₃ catalysts may origin from Cu⁺ -rich clusters at the Al₂ O₃ /ZnO interface that are covered by thin ZnO_x overlayers.

Heterogeneous catalysis

A heterogeneous catalyst is a functional material that continually creates active sites with its reactants under reaction conditions. These sites change the rates of chemical reactions of the reactants localized on them without changing the thermodynamic equilibrium between the materials.

Quantification of zinc atoms in a surface alloy on copper in an industrial-type methanol synthesis catalyst

Methanol has recently attracted renewed interest because of its potential importance as a solar fuel. Methanol is also an important bulk chemical that is most efficiently formed over the industrial Cu/ZnO/Al2O3 catalyst. The identity of the active site and, in particular, the role of ZnO as a promoter for this type of catalyst is still under intense debate. Structural changes that are strongly dependent on the pretreatment method have now been observed for an industrial-type methanol synthesis catalyst. A combination of chemisorption, reaction, and spectroscopic techniques provides a consistent picture of surface alloying between copper and zinc. This analysis enables a reinterpretation of the methods that have been used for the determination of the Cu surface area and provides an opportunity to independently quantify the specific Cu and Zn areas. This method may also be applied to other systems where metal-support interactions are important, and this work generally addresses the role of the carrier and the nature of the interactions between carrier and metal in heterogeneous catalysts.