Catalysis in General Energy Research

For the storage of hydrogen in the form of synthetic liquid fuels, the reversible catalytic hydrogenation of toluene, and the catalytic hydrogenation of CO2 yielding MeOH, are investigated. Catalytic processes are important in electrochemistry and, in particular, in the realization of electrodes with high power densities for low-temperature polymer electrolyte fuel cells. As a third area where catalysis is assigned a crucial role within General Energy Research, the treatment of exhaust gases from combustion processes will be discussed

Kinetics and Mechanism of Metal Nanoparticle Growth via Optical Extinction Spectroscopy and Computational Modeling: The Curious Case of Colloidal Gold

An overarching computational framework unifying several optical theories to describe the temporal evolution of gold nanoparticles (GNPs) during a seeded growth process is presented. To achieve this, we used the inexpensive and widely available optical extinction spectroscopy, to obtain quantitative kinetic data. In situ spectra collected over a wide set of experimental conditions were regressed using the physical model, calculating light extinction by ensembles of GNPs during the growth process. This model provides temporal information on the size, shape, and concentration of the particles and any electromagnetic interactions between them. Consequently, we were able to describe the mechanism of GNP growth and divide the process into distinct genesis periods. We provide explanations for several longstanding mysteries, for example, the phenomena responsible for the purple-greyish hue during the early stages of GNP growth, the complex interactions between nucleation, growth, and aggregation events, and a clear distinction between agglomeration and electromagnetic interactions. The presented theoretical formalism has been developed in a generic fashion so that it can readily be adapted to other nanoparticulate formation scenarios such as the genesis of various metal nanoparticles.Comment: Main text and supplementary information (accompanying MATLAB codes available on the journal webpage

Influence of Potassium Doping on the Activity and the Sulfur Poisoning Resistance of Soot Oxidation Catalysts

Soot oxidation on potassium nitrate impregnated cerium oxide and manganese cerium mixed oxide was investigated using TG-FTIR. It was found, that potassium nitrate promotes the soot oxidation by enhancing the contact between the soot and the catalyst, as soot ignition temperature corresponds to the melting point of potassium nitrate for both the individual and the mixed oxide. Since potassium nitrate is easier sulfatized than cerium or manganese, the susceptibility of the catalyst to sulfur poisoning is considerably decrease

Catalytic investigation of Fe-ZSM5 in the selective catalytic reduction of NOxwith NH3

Summary: Fe-ZSM5 coated on a cordierite monolith was characterized and tested in the selective reduction of nitrogen oxides (NOx) with ammonia. More than 70 % of the NOxwere converted at T>350 °C if only NO was present in the feed. For equimolar amounts of NO and NO2in the feed, NOxconversions of over 90 % were reached for T = 200-450 °C. Hydrothermal ageing of Fe-ZSM5 resulted in a small loss in NOxconversion and enhanced N2O formatio

Nanosecond surface interferometry measurements on designed and commercial polymers

The effect of the ablation mechanism on surface morphology changes during an ablation process was studied by comparing three different polymers: a triazene polymer, a polyimide and poly(methylmethacrylate) (PMMA) with nanosecond surface interferometry. The triazene polymer, for which only indications for a photochemical ablation mechanism had been detected in previous studies, revealed no surface swelling, which could be attributed to a thermal ablation mechanism. For polyimide, a photothermal ablation mechanism is usually used to describe the ablation process at irradiation wavelengths ≥248nm. However, the interferometric measurements do not show any surface swelling, which would be a clear indication for a thermal ablation mechanism. A surface swelling was only detected for PMMA with irradiation at 248nm and fluences below the threshold of permanent surface modification. The detected phase shift, which is proportional to the change of the film thickness and the refractive index, can be explained by the opposite signs of the thermal expansion coefficient and the thermal refractive-index coefficien

Rh-doped Ceria: Solar Organics From H2O, CO2 and Sunlight?

AbstractThe depleting supply of fossil fuels and rapidly increasing emissions of anthropogenic greenhouse gases demand sustainable solutions to the unfolding energy and environmental crises. One solution is to store concentrated solar energy in the form of chemical fuels via thermochemical cycles, which produce synthesis gas, a gas mixture of H2 and CO that is the precursor of liquid fuels in the Fischer-Tropsch (FT) processes. To date, research efforts in this field have been devoted exclusively to the improvement of synthesis gas production, and no reports are available in direct generation of organic fuels such as methane and ethanol from H2O and CO2 by solar thermochemical cycles. With the aim to generate higher grade fuels directly from H2O and CO2 via thermochemical processes, we incorporate FT catalysts into the ceria lattice. In this study, we have synthesized rhodium doped ceria by coprecipitation. X-ray powder diffraction (XRD) indicates that the as-synthesized Rh-doped ceria is single-phased. High temperature XRD reveals that the Rh-doped ceria sustains its fluorite structure even at elevated temperatures up to 1400˚C, indicating excellent structural stability highly desired for thermochemical cycles. The formation of oxygen vacancies in ceria due to the substitution of cerium by the lower valent rhodium cations is evidenced by Raman spectra. Rh-doped ceria exhibits an enhanced oxygen storage capacity (OSC) and superior activities in the conversion of H2 and CO2 into methane. These demonstrate great potential of Rh-doped ceria for the production of methane and other chemicals during the reoxidation in a thermochemical cycle, when H2O, instead of H2, is co-fed with CO2. In fact, evidence strongly indicates that the H2 produced from the splitting of H2O is partly consumed when both H2O and CO2 are used for the reoxidation of thermally reduced Rh-doped ceria. Therefore the formation of higher grade fuels seems highly likely

Mass and kinetic energy distribution of the species generated bylaser ablation of La0.6Ca0.4MnO3

The mass distributions of the species generated by laser ablation from a La0.6Ca0.4MnO3 target using laser irradiation wavelengths of 193nm, 266nm and 308nm have been investigated with and without a synchronized gas pulse of N2O. The kinetic energies of the species are measured using an electrostatic deflection energy analyzer, while the mass distributions of the species were analyzed with a quadrupole mass filter. In vacuum (pressure 10−7mbar), the ablation plume consists of metal atoms and ions such as La, Ca, Mn, O, LaO, as well as multiatomic species, e.g. LaMnO+. The LaO+ diatomic species are by far the most intense diatomic species in the plume, while CaO and MnO are only detected in small amounts. The interaction of a reactive N2O gas pulse with the ablation plume leads to an increase in plume reactivity, which is desired when thin manganite films are grown, in order to incorporate the necessary amount of oxygen into the film. The N2O gas pulse appears to have a significant influence on the oxidation of the Mn species in the plume, and on the creation of negative ions, such as LaO−,O− and O 2

Microstructure and electrical conductivity of YSZ thin films prepared by pulsed laser deposition

Yttria-stabilized zirconia (YSZ) is the most common solid electrolyte material used e.g. in ceramic fuel cells. Thin films of YSZ were deposited on c-cut sapphire single crystals by pulsed laser deposition using a KrF excimer laser focused on a polycrystalline 8 mol% Y2O3-stabilized ZrO2 target. Depending on the substrate temperature and the oxygen background pressure during deposition, different microstructures are obtained. XRD and high-resolution SEM revealed the formation of dense amorphous films at room temperature. At 600°C preferentially (111) oriented polycrystalline films consisting of densely agglomerated nm-sized grains of the cubic phase resulted. Grain size and surface roughness could be controlled by varying the oxygen background pressure. RBS and PIXE evidenced congruent transfer only for a low number of pulses, indicating a dynamical change of the target stoichiometry during laser irradiation. The in-plane ionic conductivity of the as-deposited crystalline films was comparable to bulk YSZ. The conductivity of initially amorphous YSZ passes a maximum during the crystallization process. However, the relative changes remain small, i.e. no significant enhancement of ionic conductivity related to the formation of a nanocrystalline microstructure is foun