Liquid phase heterogeneous catalysis — deeper insight: novel transient response technique with ESI-MS as a detector

Processes in the chemical industry convert readily available startingmaterials tomore valuable product molecules. Catalytic materials are used in these processes to accelerate chemical transformations so that reactions proceed in a highly efficient manner, achieving high yields of desirable products and avoiding unwanted by-products. Compared to classical stoichiometric procedures, catalysts often allowmore economical and environment-friendly production. Development of heterogeneous catalysts for liquid the phase processes requires detailed knowledge about phenomena that occur on the catalyst surface during the catalytic reaction in liquid phase. Transient response techniques with detectors that can perform continuous, rapid, multi-component and simultaneous detection are ideal for such studies. However, there are hardly any transient techniques available that allow experimental investigation of the adsorption of reactants, intermediates and probe-molecules from liquid phase on the surface of catalysts. The existing liquid phase detectors are not able to detect more than one specie simultaneously and rapidly, making the more detailed study of the catalytic reaction mechanisms impossible. The work described in this thesis focuses on development and application of a transient response technique for studies of adsorption and catalytic reactions over heterogeneous catalysts in liquid phase with Electro-Spray Ionization (ESI-MS) and Membrane Inlet Mass Spectrometry (MIMS) as detectors. Two test reactions, i.e. reduction of nitrite over Pt/SiO2 and oxidation of glucose over Pt/CNF/Ni catalysts, were used to demonstrate that it is possible to monitor reactants, intermediates and products during reaction in (semi)quantitative manner. Nitrite hydrogenation is a relevant reaction for both nitrate to nitrogen de-nitrification of drinkingwater, aswell as nitrate hydrogenation to hydroxyl-amine, an intermediate in the production of caprolactam. Oxidative conversion of glucose is important in view of the anticipated shift towards renewable feedstocks for the chemical industry. Glucose can be upgraded to more valuable compounds e.g. gluconic acid, a building block for production of chelating agents.