Über den Einfluss von Sauerstoffdefektstellen auf die katalytische Aktivität von Zinkoxid

Drastic Events and Gradual Change Define the Structure of an Active Copper-Zinc-Alumina Catalyst for Methanol Synthesis

The copper-zinc-alumina (CZA) catalyst is one of the most important catalysts. Nevertheless, understanding of the complex CZA structure is still limited and hampers further optimization. Critical to the production of a highly active and stable catalyst are optimal start-up procedures in hydrogen. Here, by employing operando X-ray absorption spectroscopy and X-ray diffraction, we follow how the industrial CZA precursor evolves into the working catalyst. Two major events in the activation drastically alter the copper- and zinc-containing components in the CZA catalyst and define the final working catalyst structure: the reduction of the starting copper(II) oxide, and the ripening and re-oxidation of zinc oxide upon the switch to catalytic conditions. These drastic events are also accompanied by other gradual, structural changes. Understanding what happens during these events is key to develop tailored start-up protocols that are aimed at maximal longevity and activity of the catalysts.

Zn or O? An Atomic Level Comparison on Antibacterial Activities of Zinc Oxides

For the first time, the influence of different types of atoms (Zn and O) on the antibacterial activities of nanosized ZnO was quantitatively evaluated with the aid of a 3D-printing-manufactured evaluation system. Two different outermost atomic layers were manufactured separately by using an ALD (atomic layer deposition) method. Interestingly, we found that each outermost atomic layer exhibited certain differences against gram-positive or gram-negative bacterial species. Zinc atoms as outermost layer (ZnO-Zn) showed a more pronounced antibacterial effect towards gram-negative E. coli (Escherichia coli), whereas oxygen atoms (ZnO-O) showed a stronger antibacterial activity against gram-positive S. aureus (Staphylococcus aureus). A possible antibacterial mechanism has been comprehensively discussed from different perspectives, including Zn(2+) concentrations, oxygen vacancies, photocatalytic activities and the DNA structural characteristics of different bacterial species.

Indium Oxide as a Superior Catalyst for Methanol Synthesis by CO2 Hydrogenation

Methanol synthesis by CO2 hydrogenation is attractive in view of avoiding the environmental implications associated with the production of the traditional syngas feedstock and mitigating global warming. However, there still is a lack of efficient catalysts for such alternative processes. Herein, we unveil the high activity, 100 % selectivity, and remarkable stability for 1000 h on stream of In2 O3 supported on ZrO2 under industrially relevant conditions. This strongly contrasts to the benchmark Cu-ZnO-Al2 O3 catalyst, which is unselective and experiences rapid deactivation. In-depth characterization of the In2 O3 -based materials points towards a mechanism rooted in the creation and annihilation of oxygen vacancies as active sites, whose amount can be modulated in situ by co-feeding CO and boosted through electronic interactions with the zirconia carrier. These results constitute a promising basis for the design of a prospective technology for sustainable methanol production.

Role of Exposed Surfaces on Zinc Oxide Nanostructures in the Catalytic Ethanol Transformation

For a series of nanometric ZnO materials, the relationship between their morphological and surface functionalities and their catalytic properties in the selective decomposition of ethanol to yield acetaldehyde was explored. Six ZnO solids were prepared by a microemulsion-precipitation method and the thermal decomposition of different precursors and compared with a commercial sample. All these materials were characterized intensively by XRD and SEM to obtain their morphological specificities. Additionally, surface area determinations and IR spectroscopy were used to detect differences in the surface properties. The density of acid surface sites was determined quantitatively using an isopropanol dehydration test. Based on these characterization studies and on the results of the catalytic tests, it has been established that ZnO basal surfaces seem to be responsible for the production of ethylene as a minor product as well as for secondary reactions that yield acetyl acetate. Furthermore, one specific type of exposed hydroxyl groups appears to govern the surface catalytic properties.

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.

Structural isomerism and thermodynamic properties of the methylzinc alkoxide molecules (MeZnOR)n (R = Me, tBu) and cations [(MeZnOMe)n]+ (n = 3, 4) studied by B3LYP and PCM calculations

Zinc oxide is a semiconductor as well as a catalyst in important industrial processes, and alkylzinc alkoxide species of the type (RZnOR)(n) are precursors for the preparation of nanoscaled zinc oxide particles. In this work, the structures, thermodynamic properties, dipole moments, and molecular vibrations of substituted zinc oxide molecules and cations have been studied by density functional calculations at the B3LYP/6-31+G(2df,p) level. The neutral tetramers (MeZnOMe)(4) and (MeZnO(t)Bu)(4) are cubane-like species of T(d) symmetry in the gas phase, whereas the cation [(MeZnOMe)(4)](+) is approximately of C(3v) symmetry due to a Jahn-Teller distortion. For the neutral trimers (MeZnOMe)(3) and (MeZnO(t)Bu)(3) two structural isomers of almost identical energy were located on the potential energy surfaces: A closo-cluster with eight ZnO bonds is most stable both as isolated molecule and in a polarizable continuum, but a roof-shaped structure with seven ZnO bonds differs in enthalpy by less than 8 kJ mol(-1). In the case of the analogous cation [(MeZnOMe)(3)](+), the isomer with the roof-shaped Zn(3)O(3) skeleton is 31.7 kJ mol(-1) more stable in the gas phase than the cluster isomer. A particularly long Zn-C bond in the most stable cationic tri- and tetramers explains the loss of a methyl group, observed mass spectrometrically after electron impact ionization. The dissociation of the tetramers (MeZnOMe)(4) and (MeZnO(t)Bu)(4) into 4/3 trimers is endothermic and endergonic, but less so for the tert-butyl derivative compared to the all-methyl cluster. This destabilizing effect of tert-butyl substituents on the tri- and tetrameric clusters follows also from the larger internuclear distances between the non-hydrogen atoms in the structures of (MeZnO(t)Bu)(n) (n = 3 and 4) compared to the analogous all-methyl derivatives. Remarkable differences of the atomic charges of the carbon atoms of methyl or tert-butyl groups attached to oxygen have been found.

Nucleation and growth of ZnO in organic solvents--an in situ study

ZnO is a metal oxide material which possesses versatile properties and applications. Therefore, the target-oriented preparation of ZnO has become a major issue. Many preparation techniques involve bottom-up methods from precursor solutions. In the current contribution, a special precursor system is described that enables a fine-control of kinetic parameters for the nucleation and growth of ZnO in various organic solvents. A large variety of analytical techniques could be applied in an in situ fashion to probe for the ZnO formation at all times and all length scales. Among the analytical techniques are UV/vis, Raman, Fluorescence, X-ray absorption, 1H NMR-spectroscopy, dynamic light-scattering, and TEM. Three different regimes for nucleation and growth with different characteristics could be identified. Furthermore, the effect of different parameters on the resulting ZnO particle size was investigated.