Sebastian Kunz

The polyol synthesis is a well-established method to form so-called “surfactant-free” nanoparticles (NPs). In the present study, the NP size resulting from the thermal reduction of the precursors H₂PtCl₆, H₂Pt(OH)₆, or Pt(acac)₂ in presence of the bases NaOH or Na(acac) at different concentrations is studied. It is shown that the size control depends more strongly on the nature of the precursor (metal salt) than on the anion present in the base. The latter is surprising as the concentration of the base anion is often an important factor to achieve a size control. The reduction of H₂PtCl₆ or H₂Pt(OH)₆ in presence of NaOH and Na(acac) confirm the observation that the NP size is determined by the OH⁻/Pt molar ratio and expands it to the base anion/Pt molar ratio. In contrast, the reduction of Pt(acac)₂ in presence of the bases NaOH (previous reports) or Na(acac) (shown in the present work) leads to larger NPs of ca. 3 nm, independent of the concentration of the base anions. Hence, the anion effect observed here seems to originate predominantly from the nature of the precursor (precursor anion dependence) and only for certain precursors as H₂PtCl₆ or H₂Pt(OH)₆ the size control depends on the base anion/Pt molar ratio.

Due to the long history of the Südzucker Group in sugar production, the company owns key know‐how in processing biomass. In the last decades, the product portfolio was extended from sugar to various products such as ethanol, starch, proteins, or glucose syrups. This article presents Zeitz as the largest production site of the Südzucker Group today. The historical development is described and the synergies between the different units from which the location benefits today as a highly integrated site. Recent R&D activities are presented, and existing technologies are discussed as future perspectives to further develop Zeitz.

The conversion of C6 sugar alcohols (hexitols) and other polyols over Ru catalysts was investigated regarding structure–activity and structure–selectivity relationships by testing various structurally different polyol reactants. In line with earlier studies, we find that hydrogenolysis reactions over supported Ru lead to CH₄ at 160 to 220 °C and 150 bar H₂. The main reaction is metal-catalyzed and preferably cleaves terminal –C–C– bonds, following a decarbonylation mechanism. While the preferential degradation pathway causes CO formation, no CO has been observed experimentally. Only CO₂ and CH₄ were found which suggests that CO is rapidly hydrogenated to CH₄ and/or converted to CO₂ by the water gas shift reaction (WGS).As a side reaction, the cleavage of terminal OH-groups (–C–O– hydrogenolysis) has been identified. Consecutive –C–O– cleavage reactions lead to reaction products that have thus far not been identified (e.g. 2,3,4,5-hexanetetrol or 2,3-butanediol). While terminal –C–OH groups are readily converted due to fast decarbonylation, intermediates without terminal OH groups are converted via a ketone intermediate which is a rather slow reaction.

Understanding the formation of nanoparticles (NPs) is key to develop materials by sustainable routes. The Co4Cat^TM process is a new synthesis of precious metal NPs in alkaline mono‐alcohols well‐suited to develop active nanocatalysts. The synthesis is ‘facile’, surfactant‐free and performed under mild conditions like low temperature. The reducing properties of the solvent are here shown to strongly influence the formation of Pt NPs. Based on the in situ formation of CO adsorbed on the NP surface by solvent oxidation, a model is proposed that accounts for the different growth and stabilization mechanisms as well as re‐dispersion properties of the surfactant‐free NPs in different solvents. Using in situ and ex situ characterizations, it is established that in methanol, a slow nucleation with a limited NP growth is achieved. In ethanol, a fast nucleation followed by continuous and pronounced particle sintering occurs.

The two-dimensional p-type semiconductor WSe₂ is a promising candidate for photoelectrochemical (PEC) H₂ generation. Despite its high absorption coefficient, the PEC hydrogen evolution reaction (HER) efficiency is low and neccesitates a catalyst to achieve higher photocurrents. Here we investigate monodisperse spherical alloy FePt and pure Pt nanocrystals (NCs) as catalysts for PEC HER on p-WSe₂ single-crystal photocathodes. After deposition of Pt or FePt, photocurrents of – 0.27 and – 4.0 mA cm⁻² at 0 V vs reversible hydrogen electrode (RHE) were achieved for the HER, which were 7.4 and 15 times higher compared to pristine WSe₂ single crystals, respectively. Calculations at the density-functional-theory (DFT) level show that the water adsorption, and thus enhanced H₂O dissociation, is preferential on FePt in comparison to Pt. The edge site of both Pt and FePt have a more negative adsorption energy than the (111) and (100) facets, indicating that the edges are the preferential sites for hydrogen production. The computational results show that the size of the Pt NC, within the range of Pt₅₅ (1.1 nm) and Pt₁₄₇ (1.6 nm), does not significantly influence the catalytic properties for HER.

This paper presents a highly sensitive thermoelectric sensor for catalytic combustible gas detection. The sensor contains two low-stress (+176 MPa) membranes of a combination of stoichiometric and silicon-rich silicon nitride that makes them chemically and thermally stable. The complete fabrication process with details, especially the challenges and their solutions, is discussed elaborately. In addition, a comprehensive evaluation of design criteria and a comparative analysis of different sensor designs are performed with respect to the homogeneity of the temperature field on the membrane, power consumption, and thermal sensitivity. Evaluating the respective tradeoffs, the best design is selected. The selected sensor has a linear thermal characteristic with a sensitivity of 6.54 mV/K. Additionally, the temperature profile on the membrane is quite homogeneous (20% root mean standard deviation), which is important for the stability of the catalytic layer. Most importantly, the sensor with a ligand (p-Phenylenediamine (PDA))-linked platinum nanoparticles catalyst shows exceptionally high response to hydrogen gas, i.e., 752 mV at 2% concentration.