Metal-oxide semiconductors are of great interest for gas-sensing applications. We provide new insights into the mode of operation of ceria-based gas sensors during ethanol gas sensing using combined operando Raman−gas-phase FTIR spectroscopy. Visible Raman spectroscopy is employed to monitor the presence of oxygen vacancies in ceria via F 2g mode softening, while simultaneously recorded FTIR spectra capture the gas-phase composition. Such an experimental approach allowing the direct observation of oxygen vacancies in metal-oxide gas sensors has not been reported in the literature. By systematically varying the gas atmosphere and temperature, we can relate the sensor response to the spectroscopic signals, enabling us to obtain new fundamental insight into the functioning of metal-oxide semiconductor gas sensors, as well as their differences from heterogeneous catalysts.

To investigate the influence of particle size in terms of electrocatalysis for the hydrogen evolution reaction (HER), small Ptn species with $n=1,10,13$ atoms and nanoparticles are deposited onto native titanium dioxide. These species are compared to the bare support as well as to bulk platinum with respect to the catalytic activity. Photoelectron spectroscopy showed Pt4f core-level shifts to higher binding energies with decreasing cluster size. In addition, the various species contribute significant density of states into the valence band gap of TiO2, thereby with larger particle size, the resulting band gap narrows. For nanoparticles, metal-like behaviour was already observed. Electrochemical measurements in 0.1 M H2SO4 showed the highest overall catalytic activity for bulk platinum and large Pt nanoparticles. A different assertion is obtained when the activities are related to the mass of the catalyst used, indicating that clusters with a size of about ten atoms seem to be most active. In comparison with the results from photoelectron spectroscopy regarding the electronic structure, no clear correlation to the catalytic activity was found. In terms of degradation induced due to the electrochemical treatment, the cluster samples showed no sintering effects, but instead, some detachment took place.

A compact, ultrahigh vacuum, radiative heater based on pyrolytic boron nitride that efficiently directs nearly all of its radiation to the sample was designed and constructed. It is shown that the heater reaches temperatures of 1300 K experimentally at 60% of its maximum power. A COMSOL Multiphysics® simulation and an analytical model predict an ultimate temperature of up to 1500 K. Furthermore, the heater does not introduce any contamination to the sample. This is accomplished by a custom-made Nb radiation shield, which was manufactured by selective laser melting and holds a flag-style sample holder. Before manufacturing, the whole assembly was simulated with COMSOL Multiphysics to validate the design of the radiation shield.

A high-pressure reaction cell was developed to study the catalytic activity of supported subnanometer catalysts under atmospheric conditions. With the help of a capillary, the gas composition in the vicinity of the catalyst surface can be analyzed. First, the mean residence time of the gaseous components in the capillary was determined. The dependence of the partial pressures of the reactants on the vertical distance between the capillary and the catalyst was then characterized with the aid of a polycrystalline Pt sample. A Pt(111) surface was then used to validate the experimental setup concerning the CO oxidation under oxygen-rich conditions at a total pressure of 1000 mbar. The partial orders of reaction for CO and O2 agree with values from the literature. The change in the reaction mechanism, which was also described in the literature, could be observed from the temperature-dependent investigation of the CO oxidation. The obtained turn-over frequency and the activation energy at about 660 K agree well with the values obtained in the high-pressure CO oxidation studied in a batch reactor. The efficiency of the experimental setup is demonstrated by examining supported Pt10 clusters since the site density was reduced by a factor of 15 compared to the bulk samples. Taking the Pt site density into account, the sample with the decamers is approximately 5–6 times more active than the Pt(111) surface at a temperature of 673 K. Accordingly, the activation energy for the CO oxidation of 106 kJ mol−1 significantly decreased compared to the value of 132 kJ mol−1 for Pt(111). This finally proves that the high-pressure cell enables the systematic investigation of the size-dependent catalytic behavior of nanoclusters with low degrees of coverage in the future.