How the charge transfer in high performance oxidation catalysts controls activity and selectivity: noncontact measurement of Hall charge carrier mobilities and concentrations under reaction conditions

• Applicant: Professor Dr. Maik Eichelbaum
• Subject Area: Physical Chemistry of Solids and Surfaces, Material Characterisation ; Analytical Chemistry
• Term: from 2012 to 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 224546003

We are aiming at the development of a microwave-based noncontact spectroscopic method in order to study the dynamic charge transfer in selected oxidation catalysts under reaction conditions. The microwave Hall effect is to be measured to determine the density, mobility, and type of charge carriers (electron, hole, ion) in catalysts situated in a fixed bed flow-through reactor. By the variation of reaction temperature, gas phase composition, and gas hourly space velocity (contact time) the correlation of the measured values with the catalytic activity and selectivity is to be investigated for selected catalytic systems and reactions, i.e. the selective oxidation of propane to acrylic acid and n-butane to maleic anhydride on vanadium phosphate and oxide catalysts. Our goal is to discriminate between charge transfer on the catalyst surface, sub-surface, and in the bulk and to distinguish between charge carrier concentration and mobility and to identify the impact on the catalytic performance. For this purpose our recently developed microwave cavity perturbation technique for the in situ characterization of heterogeneous catalysts is to be extended to measure the microwave Hall effect in a bimodal resonator in a static magnetic field. The setup is to be calibrated with suitable single crystals and powders. The results are to be compared and explained by in situ photoelectron spectroscopy and alternative available in situ and ex situ spectroscopic techniques, X-ray diffractometry, and thermoanalysis. Moreover, the hitherto existing microwave conductivity measurement at 9 GHz is to be extended to the frequency range between 1 and 20 GHz by the construction of adequate resonators in order to probe the effect of grain boundaries and particle contacts and to be able to compare the results with low frequency and DC measurements.

• DFG Programme: Research Grants