Multiscale Structure-Performance Relationships in Supported Palladium Catalysis for Multiphase Hydrogenations

The performance of heterogeneous catalysts in multiphase reactions in general is governed by different types of extrinsic and intrinsic structural effects on all length scales, i.e., on the macro- (m to cm), meso- (mm to µm), and microlevel (nm). This PhD research, with a catalysis-engineering approach, focused on several of these multiscale structure-performance relationships of supported palladium (Pd) catalysts applied in, industrially important, multiphase hydrogenations. The structure-performance relationships were studied in various batch and continuous reactors of which most are related to important topics in process intensification such a monolithic reactors and flow chemistry. The performance of monolithic Pd catalysts was enhanced by combining a new type of structured highly porous monoliths with a pressure pulse generating gas-liquid flow (i.e., Taylor flow). This induced a convective flow inside the ‘open’ monolith walls thereby enhancing the mass exchange with the Pd catalyst. This favourable result opens the avenue to higher catalyst loadings without increasing internal mass transfer limitations. Furthermore, a proof of concept study showed that a cheap and readily available gas chromatography capillary, wall-coated with an alumina-supported Pd catalyst and operated in the Taylor flow regime, can be used to synthesize high-value products and to rapidly produce (visual) information about catalytic hydrogenations. This Pd capillary flow device is an excellent alternative for expensive microchip technology and bulky round-bottom flasks. Finally, the intrinsic property of Pd to absorb hydrogen into its crystal lattice was shown to have a strong influence on its performance in the hydrogenation of aromatic nitriles. The transformation into stable Pd ?-hydride above a certain threshold hydrogen pressure induced a persistent change in activity and by-product selectivity.Chemical EngineeringApplied Science