Selective hydrogenation is an important class of chemical reactions for the production of speciality chemicals, pharmaceuticals and petrochemicals. The challenges in this type of reactions are to control selectivity in hydrogenation of poly-functional molecules, and avoid the possible risk of reaction runaway due to the high exothermisity. In this project the fundamentals of liquid-phase hydrogenation reactions in a structured compact multifunctional reactor were investigated. This technology represents an advance over the existing hydrogenation technologies because it exploits the effects of reduced characteristic paths of mass and heat transfer, attained in compact reactor architecture with mm-scale reaction channels and integrated static mixers and micro-heat exchangers. Catalysts based on mesoporous synthetic carbons were developed especially for preparing micro-packed beds in the compact reactor. The investigation resulted in fundamental information on reactor performance for selected model reactions, heat transfer efficiency of the integrated micro-heat exchangers, development of continuous tandem reaction, and evaluation of developed catalysts for hydrogenation and hydrodehalogenation reactions under the continuous flow conditions being used. The results demonstrate that the structured compact multifunctional reactor might be a promising technology to transfer conventional heterogeneous catalysis to flow regime.

The separation of the expensive catalysts from the solvent and reaction products remains one of the major disadvantages of homogeneous catalytic reactions, which are otherwise advantageous because of their high activity, tuneable selectivity and ease of study. Ideally, the homogeneous reactions would be carried out in continuous flow mode with the catalyst remaining in the reactor at all times, whilst the substrates and products flow over the catalyst. The system we have been studying is one where the catalyst is dissolved in a thin film of an ionic liquid, and this is supported within the pores of a microporous silica. This supported ionic liquid phase (SILP) catalyst is then placed in a tubular flow reactor, similar to that used for heterogeneous reactions. The raw materials are then injected into the rig, pass through the reactor and the products and the raw materials that have not reacted are collected at the other end of the rig. Supercritical CO₂ is used to transport the raw materials and products along the catalyst bed, allowing a continuous flow mode with low leaching for both the catalyst and the ionic liquid. We have applied this procedure first to alkene metathesis catalysed by a ruthenium complex that has been especially designed to dissolve in 1-butyl-3-methyimidazolium triflamide (BMIM NTf₂), which was used as ionic liquid. Activity is observed for the ring closing metathesis of diethyl 2,2-diallylmalonate, but the catalyst is not stable, only allowing about 300 turnovers. This instability is attributed to the formation of Ru=CH₂ moieties, which dimerise to an inactive species. More success is achieved with internal alkenes such as 2-octene and especially methyl oleate. Self metathesis of methyl oleate continues for >10.000 turnovers over 10 h, with only small decreases in activity. The cross metathesis of methyl oleate with dimethyl maleate has also been studied. Cross metathesis dominates in the early stages of the reaction but the cross metathesis products diminish with time. Surprisingly, the catalyst does not deactivate since self metathesis of methyl oleate continues. The phase behaviour of the reaction was monitored and gave us an insight into the reasons for this change in selectivity. Methoxycarbonylation reactions in continuous flow proved to be a much more difficult process than the previous metathesis reactions. Higher catalyst loading was needed to reduce the reaction times. The first continuous flow reactions showed conversion predominantly, if not exclusive, of 1-octene isomerised products. The presence of ionic liquid (IL) in the SILP system was essential, otherwise the catalyst leached out of the reactor very quickly. Batch reactions showed that none of the studied parameters (absence of presence of either BMIM NTf₂, OMIM NTf₂, silica or CO₂) had any influence on the reaction, but when observing the results it was noticed that the reactions that gave the best results were performed in a close range of pressures between 55 and 70 bar, indicating that the reaction might be pressure dependent. Further continuous flow reactions in that range of pressures gave the best conversions to methoxycarbonylation products. Unfortunately, at these pressures and without CO₂ the reaction took place in a liquid phase and thus substantial IL and catalyst leaching was observed, causing a decrease in conversion and making the reaction not feasible under continuous flow conditions. Nevertheless, the catalyst system composed of Pd, 1,2-bis(di-tert-butylphosphinomethyl)benzene (DTBPMB) ligand and acid showed an excellent linear selectivity, usually higher than 90%, both in batch and continuous flow reactions. Hydrogenation reactions of dimethyl itaconate (DMI) and dibutyl itaconate (DBI) using Rh-MeDuPhos showed excellent activity and enantioselestivity in a batch mode. In a continuous flow mode IL leaching caused a decrease of the enantioselectivity. The best results were obtained when CO₂ was not present. On the other hand, the absence of CO₂ implied that the reaction was performed in a liquid phase and therefore abundant IL leaching was observed along with a decrease in the enantioselectivity. A study of the reaction behaviour when using CO₂ in its different phases (liquid, gas and supercritical) was carried out. Under supercritical conditions IL leaching was avoided but conversion was not observed. When using CO₂ in its liquid phase some conversion was observed and full conversion occurred in its gas phase, but abundant IL leaching caused a decrease in the enantioselectivity. Better results were obtained by immobilising a Rh-MeDuPhos catalyst onto alumina via heteropoly acids. The effect of pressure, H₂ flow and substrate flow were studied and the stability of the reaction in the long term was examined under optimal conditions. More than 12,900 TONs were achieved after 4 days of continuous reaction, with conversions higher than 90% during the 3 first days and e.e. higher than 99% during the 2 first days.

L'objectif de ce travail est la synthèse et la fonctionnalisation de monolithes siliciques à porosité hiérarchique et leur utilisation en tant que microréacteur en catalyse sous flux. Une synthèse reproductible de monolithes siliciques a été mise à point. La fonctionnalisation avec une variété de fonctions a été réalisée, telle que la fonctionnalisation avec des groupements aminopropyle, avec de l'oxyde d'aluminium, par incorporation des MOFs (CuBTC) et par dépôt de nanoparticules de palladium. Les monolithes fonctionnalisés ont été testés en tant que microréacteurs catalytiques sous flux pour les réactions de Knoevenagel, de Diels-Alder et de Friedländer et montrent dans plusieurs cas une augmentation de la productivité des réactions par rapport aux réacteurs batch ou à lit fixe ainsi qu'une automatisation des procédés. La transformation pseudomorphique de monolithes siliciques en monolithes zéolithiques en phase SOD et LTA a été mise a point. Nous avons ainsi montré la première utilisation d'un monolithe macroporeux à base de zéolithes en tant que microréacteur pour la synthèse de produits de chimie fine en continu. Les monolithes zéolithiques ont aussi été analysés pour l'échange d'ions en dynamique et sont prometteurs pour une application en tant que matériaux pour la décontamination d'effluents radioactifs. / The aim of this work is the synthesis and the functionalization of silica monoliths with hierarchical porosity and their use as catalytic microreactors for flow-through chemistry. A reproducible synthesis of the silica monoliths was elaborated. The functionalization with a variety of functions has been performed, such as aminopropyl groups, aluminium oxide, MOFs (CuBTC), and palladium nanoparticles. These functionalized silica monoliths have been used for the Knoevenagel condensation, Diels-Alder reaction and Fiedländer reaction, where they show increasing productivities compared to classically used reactors (batch, packed-bed) and enable process automation. The pseudomorphic transformation of silica monoliths in zeolite monoliths in the SOD and LTA phase has been elaborated. We have preformed the first implementation of a macroporous zeolite monolith as microreactor for the fine chemical production in flow continuous conditions. The zeolite monoliths have been tested for dynamic ion exchange and are promising materials for the use as decontaminants of radioactive discharges.