Tesis sobre el tema "Nanocatalysts for Hydrogenation reactions"

This thesis reports a computational discovery and design of highly efficient electrocatalysts for various of electrochemical reactions. The method is based on the Density Functional Theory (DFT) by using Vienna ab initio simulation package (VASP). This project is a step forward in developing the low-cost, high activity, selectivity, stability and scalability for the electrochemical reactions, which could make a contribution to the global-scale green energy system for a clean and sustainable energy future.

In this research, SMFs panels were applied for further deposition of CNFs, ZnO and Al2O3 to hydro-genate selectively acetylene to ethylene. To understand the role of different structures of the examined supports, the characterization methods of SEM, ASAP, NH3-TPD and N2 adsorption-desorption isotherms were used. Following the characterization of green oil by FTIR, the presence of more unsaturated constitu-ents and then, more branched hydrocarbons formed upon the reaction over alumina-supported catalyst in comparison with the ones supported on CNFs and ZnO was confirmed, which in turn, could block the pores mouths. Besides the limited hydrogen transfer, the lowest pore diameters of Al2O3 / SMFs close to the sur-face, supported by N2 adsorption-desorption isotherms could explain the fast deactivation of this catalyst, compared to the other ones. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35216

This thesis centres on the development of colloidal nanoparticles for the hydrogenation of carbon dioxide to methanol. Chapter two focusses on the synthesis of zinc oxide (ZnO) nanoparticles through the hydrolysis of diethylzinc in the presence of sub-stoichiometric quantities of organic ligands. Characterisation of the product, through a range of spectroscopic, diffraction and electron microscopy techniques, reveals small (3-4 nm), equiaxial, mono-disperse ZnO nanoparticles coordinated to alkyl-carboxylate, phosphinate and sulfinate ligands. Detailed investigation of the dioctyl-phosphinate capped-zinc oxide nanoparticles reveals that increasing the loading of ligand into the reaction (from 0.05-0.33 equivalents of ligand to zinc) does not affect the size or morphology of the nanoparticles, rather influencing the ligand density and coverage of the nanoparticle surface. In chapter three, these partially capped ZnO nanoparticles, mixed with copper nanoparticles, demonstrate catalytic activity for CO2 hydrogenation. Post-reaction analysis showed significant nanoparticle rearrangement, with an interface forming between the copper and the ZnO. In some cases, a self-assembled nanostructure is observed, consisting of a copper nanoparticle sandwiched between two pyramidal zinc oxide nanoparticles. The ligand has a significant effect on the activity of the catalyst; more reductively stable di-alkyl phosphinate ligands show superior activity to carboxylates. Decreasing the ligand loading on the zinc oxide nanoparticles, results in a higher peak activity due to the decreased ligand density exposing more of the catalyst surface, however the stability of the catalyst is also reduced. In chapter four, the interface between nanoparticles is targeted, with the goal of depositing copper onto the ZnO colloids through reduction and thermolysis reactions to form hybrid Cu/ZnO nanostructures. The most effective route entails the hydrogenolysis of mesitylcopper(I) on to the ZnO nanoparticles, the resulting nanocatalyst displays superior peak activity to both the mixed nanoparticle catalyst described above and a suspension of the commercial catalyst run under the same conditions.

The work described in this thesis is focused on the development of new bidentate iridium complexes and their applications in the asymmetric reduction of olefins, ketones and imines. Three new types of iridium complexes were synthesized, which included pyridine derived chiral N,P-iridium complexes, achiral NHC complexes and chiral NHC-phosphine complexes. A study of their catalytic applications demonstrated a high efficiency of the N,P-iridium complexes for asymmetric hydrogenation of olefins, with good enantioselectivity. The carbene complexes were found to be very efficient hydrogen transfer mediators capable of abstracting hydrogen from alcohols and subsequently transfer it to other unsaturated bonds. This hydrogen transferring property of the carbene complexes was used in the development of C–C and C–N bond formation reactions via the hydrogen borrowing process. The complexes displayed high catalytic reactivity using 0.5–1.0 mol% of the catalyst and mild reaction conditions. Finally chiral carbene complexes were found to be activated by hydrogen gas. Their corresponding iridium hydride species were able to reduce ketones and imines with high efficiency and enantioselectivity without any additives, base or acid.

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 5: Submitted. Paper 6: Manuscript.

 

In this thesis we have computationally studied two types of reduction processes which can be classified as asymmetric hydrogenation of ketones and reduction of imines. Density functional theory has been applied throughout the thesis. The reduction of acetophenone to phenylethanol catalysed by the trans- Ru(II)H2(diphosphine)(diamine) has been studied with an emphasis on the effect of the structure of the diphosphine and diamine ligands. The computed reaction pathways of the Ru(II)H2(diphosphine)[(S,S)-DPEN] catalysed reactions with different (S)-diphosphine ligands (XylBINAP, TolBINAP and BINAP) shows that the presence of two methyl groups in the meta position is critical to obtaining a high difference in activation energy for the reaction pathways associated with the (R)- and (S)-alcohols, and consequently high enantioselectivity. The effect of the diamine structure, while keeping the TolBINAP and XylBINAP fixed, has also been analysed. To enhance the enantioselectivity of the TolBINAP system, the addition of two methyl groups and the removal of a phenyl group on the diamine (DMAPEN) create the necessary steric interactions. We conclude this section by reporting a correlation between the enantiomeric excess and the difference in the computed activation energies along the two most favourable (S)- and (R)-reaction pathways, which shows that the computational procedure adopted could be used to predict the enantiomeric excess of ketone hydrogenation reactions catalysed by Noyori-type catalysts, and assist in the choice of ligands when optimising the enantiomeric excess. Calculations yield new insights into the structural, electronic and catalytic properties of the hydrogenation of ketones catalysed by the simplified Fe(II)H2(PH3)2(en) and real Fe(II)H2(diphosphine)(diamine) complexes. Calculations conducted using several different functionals on the trans- and cis-isomers of Fe(II)H2[(S)-XylBINAP][(S,S)-DPEN] complexes show that, as with the Ru(II)H2(diphosphine)(diamine) complexes, the trans- [Fe(II)H2(diphosphine)(diamine)] complex is the more stable isomer. Analysis of the spin states of the trans-[Fe(II)H2(diphosphine)(diamine)] complexes also shows that the singlet state is significantly more stable than the triplet and quintet states, as with the Ru(II)H2(diphosphine)(diamine) complexes. Calculations on the catalytic cycle for the hydrogenation of ketones using the two simplified trans-[M(II)H2(PH3)2(en)] catalysts, where M is either Ru or Fe, show that the mechanism of reactions as well as the activation energies are very similar, in particular: (a) the ketone/alcohol hydrogen transfer reaction occurs through the metal–ligand bifunctional mechanism, with energy barriers of 3.4 kcal/mol and 3.2 kcal/mol for the ruthenium- and iron-catalysed reactions respectively; (b) the heterolytic splitting reactions of H2 across the M=N bond for the regeneration of the ruthenium and iron catalysts have activation barriers of 13.8 kcal/mol and 12.8 kcal/mol respectively, and the heterolytic splitting steps are expected to be the rate-determining steps for both catalytic systems. The reduction of acetophenone by the trans- [Fe(II)H2{(S)-XylBINAP}{(S,S)-DPEN}] complexes along the two competitive reaction pathways shows that the intermediates for the iron catalytic system are similar to those responsible for a high enantioselectivity of (R)-alcohol in the trans-[Ru(II)H2{(S)- XylBINAP}{(S,S)-DPEN}] catalysed acetophenone hydrogenation reaction. Thus, the high enantiomeric excess in the hydrogenation of acetophenone could, in principle, be achieved using iron catalysts. In experimental work, Xiao and co-workers discovered cyclometalated iridium complexes in imine reduction with an unusually broad substrate scope, which shows that the more positive hydricity of iridium hydride affords a higher activity. To study these systems computationally, we initially tested parameters, including exchange-correlation functionals, basis sets and pseudopotentials, subsequently studying the charge and molecular orbital properties of isolated iridium(III) catalysts with different electrondonating and withdrawing functional groups, and investigating their mechanistic details. Three possible reaction pathways in the hydride formation step and six possible reaction pathways in the hydride transfer step have been suggested to locate transition states in both the gas phase and methanol solution. Our results show that hydride formation is the rate-determining step and with explicit methanol included in the reaction, the activation energies in the hydride formation and hydride transfer steps drop by ca. 10 and 4 kcal/mol respectively, compared with those computed in the gas phase.

Hydrogenation and hydrofunctionalisation reactions provide efficient, sustainable methodologies for the manipulation of synthetic handles and the formation of carbon-heteroatom bonds from readily available starting materials. Traditional hydrogenation methods typically require precious or semi-precious transition metal complexes or finely divided powders. Iron-based catalysts offer several advantages over more traditional ‘noble’ metal systems due to the high abundance, long-term availability, low cost and low toxicity of iron. To date, the most powerful iron-catalysed hydrogenation and hydrofunctionalisation reactions have required either highly air-sensitive iron(0) complexes or iron(II) complexes activated with an extremely reactive, pyrophoric organometallic reagent. An operationally simple and environmentally benign formal hydrogenation protocol has been developed using a simple iron(III) salt and NaBH4; an inexpensive, bench stable, stoichiometric reductant. This reaction has been applied to the reduction of terminal alkenes (22 examples, up to 95% yield) and nitro groups (26 examples, up to 95% yield) in ethanol, under ambient conditions (Scheme A1). Two novel series of structurally related alkoxy-tethered N-heterocyclic carbene (NHC) iron(II) complexes have been developed as catalysts for the regioselective hydroboration of alkenes. Significantly, Markovnikov selective alkene hydroboration with pinacolborane (HBpin) has been controllably achieved for the first time using an iron catalyst (11 examples, 35-90% isolated yield) with up to 37:1 branched:linear selectivity (Scheme A2). anti-Markovnikov selective alkene hydroboration was also achieved using catecholborane (HBcat) and modification of the ligand backbone (6 examples, 44-71% yield). In both cases, ligand design has enabled activator-free iron catalysis.

Iron oxide supported gold catalysts were tested for the room temperature oxidation of carbon monoxide. The effect of heat treatment on the activity of the catalysts was investigated the catalysts being heated to 75, 120, 200, 300 and 400°C. The most active catalysts were obtained by using a calcination temperature of 120°C. Gold catalysts supported on zinc oxide were also tested for activity in the oxidation of carbon monoxide at room temperature. These catalysts were found to be less active than the Au/FejCh catalysts. The effect of heat treatment was also investigated, and the uncalcined catalysts were found to be the most active. Characterisation of both types of catalyst by XPS revealed a clear difference between catalysts of high and low conversion. Further investigation of the catalysts by XANES, TEM, and the XPS of gold colloids revealed that this difference was due to a change in the ratio of metallic and ionic gold, with the former being more abundant in catalysts with lower activities. The XANES analysis revealed the ionic gold to be in the form of Au1. XPS analysis of the samples also revealed the presence of a surface hydroxyl species in the catalysts with high activity constant with the Bond-Thompson mechanistic model for CO oxidation The iron oxide supported gold catalysts were also used in the hydrogenation of crotonaldehyde. The catalysts were tested for selectivity towards crotyl alcohol and total conversion at a variety of different heat treatments and reaction temperatures, and the highest conversions were obtained at a reaction temperature of 150°C. The best overall conversions were obtained with catalysts that had been heated at 75°C. The highest selectivity towards crotyl alcohol was obtained with catalysts which were calcined at 300°C. The affect of reduction on the activity of the catalysts for crotonaldehyde hydrogenation was also explored. It was found that catalysts that were not reduced prior to reaction had a higher activity and were less prone to deactivation during the reaction. The correlation between the oxidation state of the gold and the activity of the catalyst for the hydrogenation reaction was very similar to that found in the carbon monoxide oxidation catalysts. "High pressure" XPS studies were carried out on polycrystalline gold foil, an iron oxide film, and a thick gold film to test the contributions that part makes to the activity iron oxide supported gold catalysts. Both the gold foil and the iron oxide and thick gold films proved to be unreacrive towards carbon monoxide and oxygen.

Catalytic nanoreactors, prepared by the Layer-by-Layer encapsulation of zeolite H-Beta, were used in the dynamic kinetic resolution (DKR) of 1-phenylethanol and 1-indanol. Yields for both alcohols were clearly above 50%, with ee’s over 85%, indicating successful protection of the pH-sensitive enzyme, candida antarctica lipase B, from the acidic zeolite. Attention proceeded to the DKR of amines, which can involve the undesired hydrogenolysis reaction during the racemisation step. Thus, the phenomenon of hydrogenolysis was investigated. The hydrogenolysis of various amines, imines, and nitriles with an aromatic ring adjacent to the a-carbon was achieved under relatively mild conditions over Pd/C in high yield. The relationship between the various reactions involved in hydrogenolysis and thus hydrogenation of nitriles was clarified, which lead to the proposal of a mechanism based on homogeneous analogues. The mechanism provided an explanation for the ease of hydrogenolysis of substrates with an aromatic ring adjacent to the (it-carbon: the carbometallated intermediate is more stable when the aromatic ring is in that position. DFT calculations not only supported this explanation, but also indicated that the affinity of the aromatic ring to the Pd/C surface is also responsible for the ease of hydrogenolysis. A kinetic model was then proposed to explain why the relatively mild conditions enabled continual hydrogenolysis to occur. The high catalyst loadings, combined with a limited rate of H2 dissolution into the solvent, were responsible, as the hydrogenation reaction (unlike the hydrogenolysis) remained diffusion limited. Furthermore, at very low catalyst loadings, benzylamine was found to poison the catalyst and prevent continued hydrogenolysis. The knowledge gained on hydrogenolysis was then applied to the hydrogenolysis of secondary amines. It was found that the larger the difference between the relative rates of hydrogenolysis of the secondary amine’s constituent primary amines, the more selective the cleavage of the faster C-N bond in the secondary amine. Furthermore, the hydrogenolysis of a secondary amine is faster than either of its constituent primary amines, while steric hindrance when the amine is substituted at the (it-carbon similarly decreases the rate of hydrogenolysis. Both factors are consistent with the necessary formation of a Schiff base for the hydrogenolysis of a primary amine. However, an important exception was found. When one of the constituent primary amines prevents favourable access to the catalyst surface, the secondary amine is unable to undergo hydrogenolysis.

Heterogeneous catalysis is a key industrial process involved in the synthesis of nearly all chemicals currently produced. The environmental impact of these processes is huge so improvements must be made to current catalysts. Should a new material provide better yields at lower energy cost the benefits to both the industry and the planet are significant. There are many ways to change the behaviour of a catalyst, the addition of dopants, the selective blocking of active sites, and changing the strength of the support interaction to name a few. One technique that has become increasingly investigated is interstitial modification, the insertion of a light element into a metal lattice to change the metal's catalytic properties. The work presented in this thesis devises greener synthetic routes to the known Pd-^interstitialB/C catalyst and investigates potential routes to a novel interstitial material, Pd-^interstitialLi/C. Initially, successful verification of interstitial modification comes from the characteristic increase in palladium lattice parameter from 3.89 to 4.00 Å and the blocking of the β-hydride formation. Initial catalytic screening determines the synthetic route which yields the most active catalyst which subsequently undergoes thorough characterisation. The wealth of evidence generated confirms the interstitial location of lithium within the palladium lattice, as well as adding to the current understanding of the Pd-^interstitialB/C material. EELS analysis on Pd-^interstitialB is the closest to direct observation of boron within the palladium lattice to date. PDF on Pd-^interstitialLi shows 13.7 % of the palladium octahedral interstitial sites are occupied by lithium. This is the first report of interstitial lithium within palladium to date. The effect of the interstitial modification on catalytic hydrogenation by two elements that have opposite effects on the surface electronics of the host palladium gives intriguing results. The effect on catalysis varies depending on the conditions investigated. This bank of hydrogenation data allows an informed choice as to which interstitial material would be best suited to the gas or liquid phase catalytic hydrogenation under investigation.

Surface catalysed reactions play an important role in chemical productions. Developments of catalyst requiring high activity whilst improving on product selectivity can potentially have a profound effect in the chemical industry. Traditional catalyst modifications were focused on tuning the size, shape and foreign metal doping to form well defined metal nanoparticles of unique functionalities. Here, we show new approach to engineering of metal nanocatalysts via a subsurface approach can modify the chemisorption strength of adsorbates on the surface. Carbon modified nanoparticles were synthesised using glucose to stabilise Pd nanoparticles at a molecular level. Upon heat treatment, the carbonised glucose encapsulated the Pd nanoparticles with carbon atoms take residence in the octahedral holes (15 at.%). These materials were tested in liquid phase stereoselective hydrogenations of 3-hexyn-1-ol and 4-octyne. The former has importance in the fragrance industry towards the production of leaf fragrance alcohol. It was shown for the first time that the geometrically and electronically modified Pd with interstitial carbon atoms reduced the adsorption energy of alkenes, ultimately leading to higher reaction selectivity. Boron modified Pd nanoparticles was synthesised using BH₃.THF in the liquid phase. The material possess high B interstitial saturation (20 at.%), which can be synthesised for the first time below 100°C. These materials were tested in the liquid phase selective hydrogenation of various alkynes and 2-chloronitrobenzene, of which the latter has importance in the pesticides industry. Kinetic modelling on the hydrogenation of 4-octyne suggests these subsurface occupied B does play a pivotal role on increasing the reaction selectivity, as removal of these species lead to decreased selectivity. Au nanoparticles were synthesised and characterised using H¹³COOH NMR. The new liquid NMR characterisation method is successfully applied to examine the chemisorption strength of metal nanoparticles. An attempt to synthesise PVP capped B modified Pd nanoparticles with the above NMR characterisation was investigated. It is believed the examples of subsurface atom modifications as shown here may offer future catalyst developments in this area.

The application of heterogeneous catalysts to industrial processes is a key factor in the synthesis of nearly all chemicals currently produced, however billions of pounds are lost every year due to unplanned reactor shutdowns and catalyst replacement as a result of catalytic deactivation processes. Poisoning of heterogeneous catalysts by sulfur compounds is a particularly prominent class of deactivation processes, affecting a wide range of catalytic materials and catalytic reactions, including the industrially-prominent Haber-Bosch process for the synthesis of ammonia and steam reforming of methane for the synthesis of hydrogen. However, while the effects of sulfur adsorption on catalytic behaviour are often unmistakably apparent, the fundamental interactions leading to these effects are not yet well understood. The work presented in this thesis uses a combination of models systems, novel and traditional characterization techniques, and methods of modifying catalyst geometric and electronic structure to approach the topic of sulfur poisoning from a fundamental perspective. Particular focus is placed on using selective decoration of active sites to develop a system of model hydrogenation reactions to relate changes in catalytic behaviour to changes in geometric and electronic structure. Application of these model reactions to investigate the sensitivities of palladium- and ruthenium-based catalytic systems to modification by sulfur shows contrasting effects for the two metals. While both systems exhibit similar geometric effects of modification, the palladium-based catalysts are far more sensitive than the ruthenium-based catalysts to modification of electronic structure. Additionally, controlled variation in particle size for the palladium-based catalysts demonstrates that catalytic behaviour is dominated by electronic structure for small nanoparticles and geometric structure for large nanoparticles. This leads small nanoparticles to show increased sensitivity to electronic modification effects resulting from sulfur adsorption. Ultimately, the research presented within this thesis provides a basis for the intelligent design of heterogeneous catalysts for improving tolerance for sulfur poisoning, and for utilizing the effects of sulfur modification to optimize catalytic activity and selectivity for the synthesis of fine chemicals.

L’objectif de ce travail doctoral a été de développer de nouvelles méthodes éco-compatibles pour réaliser efficacement des réactions de (dé)hydrogénation et d’hydroélémentation catalysées par des catalyseurs bien définis de fer, de manganèse et également de rhénium. La première partie de ce travail porte sur le développement des premiers exemples de réaction de borylation de dérivés styrènes et acétyléniques terminaux avec le pinacolborane via une réaction d’activation de liaison C-H catalysée par des systèmes à base de Fe(PMe3)4 ou de Fe(OTf)2/ DABCO. Dans une seconde partie, des complexes de fer à base de ligands carbènes N-hétérocycliques (NHC) tels que Fe(CO)4(IMes) et [CpFe(CO)2(IMes)][I] ont été efficacement utilisés pour la synthèse d’une grande variété d’amines cycliques (pyrrolidines, pipéridines et azépanes) via une réaction d’amination réductrice catalytique en présence d’hydrosilanes. De façon très intéressante, les catalyseurs commerciaux Mn2(CO)10 et Re2(CO)10 en présence de triéthylsilane, ont permis de réduire sélectivement les esters, acides carboxyliques et amides en acétals, alcools et amines correspondants. En complément de l’hydrosilylation, l’hydrogénation d’aldéhydes, cétones et aldimines a pu être efficacement menée grâce à l’utilisation de nouveaux précatalyseurs bien définis de manganèse à base de ligands bidentes facilement accessibles tels que la pyridinyl-phosphine et la 2-picolylamine. Dans la continuité de notre intérêt pour le développement de nouveaux catalyseurs à base de métaux du groupe 7, une série de complexes de rhénium coordinés à des ligands amino-bisphosphino a montré une excellente aptitude à promouvoir l’hydrogénation de composés carbonylés (aldéhydes, cétones), la mono-méthylation sélective d’amines avec le méthanol comme agent de méthylant durable et la synthèse quinolines substituées. La dernière partie de se travail décrit le développement d’oxydations aérobies d’amines pour préparer des aldimines, des composés N-hétéroaromatiques et des dérivés de type benzoimidazole via une catalyse au manganèse en l’absence de ligands ou d’additifs
This research work is aimed at developing advanced eco-friendly methodologies in the area of iron, manganese and rhenium-catalyzed (de)hydrogenation and hydroelementation reactions. Initially, we reported the first examples of highly selective catalytic direct C-H borylation of styrene derivatives and terminal alkynes with pinacolborane using Fe(PMe3)4 and Fe(OTf)2/DABCO as catalyst systems, respectively. Afterwards, N-heterocyclic carbene (NHC) based iron complexes Fe(CO)4(IMes) and [CpFe(CO)2(IMes)][I] were efficiently employed in the catalytic reductive amination reactions with hydrosilanes to access a large variety of cyclic amines (pyrrolidines, piperidines and azepanes). Interestingly, with the commercially available Mn2(CO)10 or Re2(CO)10 as catalyst and Et3SiH as an inexpensive hydrosilane source, carboxylic esters, acids and amides can be chemospecifically reduced to the corresponding acetals, alcohols and amines. Besides hydrosilylation, we also explored the application of a series of well-defined manganese pre-catalysts featuring readily available bidendate pyridinyl-phosphine and 2-picolylamine ligands in hydrogenation reactions of aldehydes, ketones and aldimines. In line with our interest in developing group 7 metals based catalysts, we have also demonstrated that a series of amino-bisphosphino ligands coordinated rhenium catalysts can efficiently promote the hydrogenation of carbonyl derivatives, the mono N-methylation of anilines with methanol and the dehydrogenative synthesis of substituted quinolines. Lastly we also developed the Mn-catalysed ligand- and additive-free aerobic oxidation of amines to prepare aldimines, N-heteroaromatics and benzoimidazole derivatives

The area of methanol synthesis and utilization has been attracting research interests due to its positive impact on the environment and also from energy perspectives. Methanol synthesis from CO₂ hydrogenation not only produces methanol which is a key platform chemical and a clean fuel, but can also recycle CO₂ which is one of the major greenhouse gases causing global warming. As a mobile energy carrier (particularly as a hydrogen carrier), methanol is a versatile molecule which is able to generate H₂ via its decomposition. Catalysis plays a decisive role in the success of both methanol synthesis from CO₂ hydrogenation and its reverse decomposition reaction. Pd/Ga₂O₃ binary catalyst has recently been identified as an active catalyst for the methanol synthesis reaction. In this thesis, it is reported the shape effect of Pd promoted Ga₂O₃ for this reaction. The catalytic H₂ evolution from methanol photodecomposition has also been studied over these catalysts. Three shapes of Ga₂O3 nanomaterials (i.e. rod and plate β-Ga₂O3, and particle γ-Ga₂O₃) have been synthesized, followed by doping with Pd metal to form corresponding Pd/Ga₂O₃ nanocatalysts. It was found that a (002) polar Ga2O3 surface which was dominantly presented on the plate form was unstable, giving a higher degree of oxygen defects and mobile electrons in the conduction band than the other non-polar (111) and (110) surfaces of the rod form. It was shown that a significantly stronger metal support interaction was found between the (002) polar Ga₂O₃ on the plate form and Pd, which gave higher methanol yield and selectivity. For methanol photodecomposition, it was found that, for pure Ga₂O₃ catalysts of different shapes, the plate form with a highest degree of defects (unstable polar surface) could encourage a non-radiative catalytic recombination of electron and hole pairs upon irradiation, hence giving a highest photocatalytic activity for H₂ production. Once Pd was introduced onto these oxide surfaces, it was noted that there was a fast and readily electron transfer from the conduction band of Ga₂O₃ to Pd due to the formation of a Schottky junction between the two materials. This produces metal sites for hydrogen production and further enhances the rate of the photocatalytic reaction over the radiative recombination of excitons. However, it was also found that at higher Pd content (>1%), the significantly shortened exciton lifetimes reduce the catalytic rate hence giving an overall volcanic response of activity to increasing Pd content for each shape of Ga₂O₃. At the higher Pd content, the plate form appeared to sustain a longer lifetime for photocatalysis compared to the other forms at the equivalent Pd loading.

Processes for chemical conversions often either involve one of two divergent catalyst types. Heterogeneous catalysts (bulk material) represent a simple system, which can easily be removed from the reaction mixture after use. Homogeneous catalysts (soluble species) on the other hand, are often much more difficult to separate, but generally provide excellent improved catalytic performance in part because of their equal homogeneous distribution within the reaction media. Moreover, they allow for more tuneability through the use of various ligands. The emerging use of nanoparticle catalysts effectively bridges the gap between homogeneous and heterogeneous catalysis. Often, the smaller the particles become, the more they offer catalytic properties similar to homogeneous catalyst systems. Unfortunately, the reduction in size also makes separation increasingly difficult—again, similar to homogeneous systems. To address the issue of separation, the field of magnetic nanoparticle catalysis emerged. By simple application of an external magnet, magnetic nanoparticle catalysts can be recovered and easily reused. Most examples of magnetic nanoparticle catalysis employ the particle only as a vehicle for magnetic recovery, rather than the catalyst itself. Complex strategies of this kind include coating with a polymer or silica, to which a metal-binding ligand can be anchored. By such a system, one could envision anchoring of nearly any pseudo-homogeneous metal, enabling a broad catalytic scope. The focus of this work is instead on the use of simple magnetic nanoparticles where the particles themselves act not only as the means for magnetic recovery, but also as catalysts. This thesis covers three general types of simple magnetic nanoparticle catalysts. First, this work demonstrated that reduced iron nanoparticles with a shell of iron oxide can efficiently catalyze the hydrogenation of unsaturated hydrocarbons. This scheme can also be adapted to a flow system by growing the nanoparticles in the presence of amphiphillic polymers. Second, in order to address the limited catalytic offering of iron, the scope of reactions can be expanded by decorating these same iron/iron oxide nanoparticles with a more catalytically active metal. Copper- and ruthenium- decorated nanoparticles have been synthesized and used for the azide-alkyne click reaction and transfer hydrogenation, respectively. Third, work presented in this thesis shows that other metals can also be incorporated directly into the magnetic nanoparticle lattice. For example, CuFe2O4 nanoparticles have been used to catalyze the Biginilli condensation and cross-dehydrogenative coupling reactions. By the use of these three general types of bare particles, we have expanded the scope of simple magnetic nanoparticle catalyzed reactions.
Les procédés chimiques impliquent souvent des catalyseurs de l'un des deux types suivants. Les catalyseurs hétérogènes (matériaux) constituent un système simple, qui peut généralement être aisément retiré du mélange réactionnel après usage. D'autre part, les catalyseurs homogènes (espèces solubles) sont souvent beaucoup plus difficiles à séparer ; en revanche, ils offrent en general une excellente performance catalytique étant donnée leur répartition homogène dans le milieu réactionnel. De plus, ces derniers peuvent être facilement modifiés par l'usage de divers ligands pour ainsi améliorer leur performance. L'utilisation croissante de nanoparticules en catalyse offre une alternative entre la catalyse homogène et hétérogène. De façon générale, plus leur taille est petite, plus les particules possèdent des propriétés catalytiques similaires à celles des systèmes homogènes. Malheureusement, la réduction de leur taille rend d'autant plus difficile leur séparation, comme dans le cas des systèmes homogènes. Pour résourdre ce problème de séparation, le domaine de la catalyse à base de nanoparticules magnétiques a vu le jour. Grâce à l'utilisation d'un aimant externe, les catalyseurs de nanoparticules magnétiques peuvent être récupérés et réutilisés facilement. Dans la plupart des exemples de catalyse faisant usage de nanoparticules magnétiques, les particules sont uniquement utilisées comme ancre pour la récupération magnétique, et non comme catalyseurs. Les stratégies complexes de ce type comprennent l'enrobage des nanoparticules avec un polymère ou bien avec de la silice, auquel un ligand de coordination peut être ancré. Par un tel système, on peut envisager l'ancrage de presque n'importe quel métal pseudo-homogène, ce qui permet un large éventail catalytique. L'objectif de ce travail est plutôt axé sur l'utilisation de nanoparticules magnétiques simples où les particules agissent non seulement comme moyen de récupération magnétique, mais également en tant que catalyseurs. Cette thèse porte sur trois types généraux de catalyseurs simples de nanoparticules magnétiques. Tout d'abord, il est démontré que des nanoparticules de fer réduit, dotés d'une coquille d'oxyde de fer, peuvent catalyser efficacement l'hydrogénation d'hydrocarbures insaturés. Cette réaction peut également être adaptée à un système "in flow", en préparant les nanoparticules en présence de polymères amphiphiles. Deuxièmement, considérant le potentiel catalytique limité du fer, la portée de ces réactions peut être étendue par la décoration de ces mêmes nanoparticules de fer / oxyde de fer à l'aide d'un second métal possédant un potentiel catalytique plus élevé. Des nanoparticules décorées de cuivre et de ruthénium ont été synthétisées et utilisées pour effectuer des réactions de couplage azoture-alcyne (click) et d'hydrogénation de transfert, respectivement. Troisièmement, il est démontré que d'autres métaux peuvent également directement être incorporés dans un réseau de nanoparticules magnétiques. Par exemple, des nanoparticules de CuFe2O4 peuvent être utilisées pour catalyser des réactions de condensation de Biginilli ainsi que des réactions de couplage inter-déshydrogénation. Par l'utilisation de ces trois types généraux de particules nues, nous avons élargi la portée des réactions catalysées par des nanoparticules magnétiques simples.

Magnetic separation has received a lot of attention as a robust, highly efficient and rapid catalyst separation technology. Many studies have focused on developing methodologies for the immobilization of catalytic active species, but the development of magnetic supports has been mainly limited to silica, polymer or carbon-coated magnetic nanoparticles (NPs). The design of magnetic nanocomposites and the incorporation of other oxides are highly welcome to broaden the application of this separation technology in the field of catalysis. In this context, studies of the thermal stability of silica-coated magnetite (Fe3O4@SiO2) were performed to evaluate the possibility of calcining it without losing the magnetic properties of the support. The calcination would permit the deposition of different oxides on the silica surface, such as ceria and titania. The calcined Fe3O4@SiO2 material preserved the core-shell morphology and magnetic properties, but increased its surface area six times. New magnetic supports were developed by using post-coating process for the deposition of ceria and titania onto silica-coated magnetite. Magnetically recoverable Rh, Pd and Ru nanocatalysts were prepared. The catalysts were employed in hydrogenation of cyclohexene, benzene or phenol and the study of the influence of each support on the catalytic activity was a main objective of this thesis. The catalysts were prepared by two different approaches: the impregnation and the sol-immobilization of pre-formed metal NPs. The colloidal metal NPs were prepared by reduction of metal salts and also by decomposition of organometallic complexes. Rhodium catalysts prepared by impregnation of rhodium(III) chloride and reduction with H2 showed some reproducibility issues that were surpassed by using NaBH4 or hydrazine as reducing agents. The preparation of catalysts by the immobilization of colloidal NPs is an interesting alternative to obtain reproducible and very active catalysts. Nanoparticles of Pd, Rh and Ru were prepared by an organometallic approach and immobilized on calcined Fe3O4@SiO2, Fe3O4@SiO2CeO2 and Fe3O4@SiO2TiO2. The elimination of the stabilizing agent leads to more active catalysts upon recycling. Rhodium catalysts supported on ceria support was the most active catalyst in the hydrogenation of cyclohexene (TOF 125,000 h-1). Palladium catalysts were the most selective catalyst for the hydrogenation of phenol to cyclohexanone, no matter the support used. The formation of cyclohexanol is enhanced with titania and the hydrodeoxygenation to produce cyclohexane occurred mainly with silica.
A separação magnética tem recebido muita atenção como uma tecnologia robusta, altamente eficiente e rápida para recuperar catalisadores sólidos após uso em reações em fase líquida. Muitos estudos têm focado nas metodologias para a imobilização de espécies cataliticamente ativas, mas o desenvolvimento de suportes magnéticos tem se limitado a nanopartículas magnéticas revestidas com sílica, polímeros ou carbono. O desenvolvimento de nanocompósitos magnéticos com a incorporação de outros óxidos é muito desejável para ampliar a aplicação dessa tecnologia de separação em catálise. Nesse contexto, estudos da estabilidade térmica de magnetita revestida com sílica (Fe3O4@SiO2) foram realizados para avaliar a possibilidade de calcina-la sem perder as propriedades magnéticas do suporte. Uma etapa de calcinação é necessária para a deposição de diferentes óxidos na superfície da sílica, tais como céria e titânia. O Fe3O4@SiO2 calcinado preservou a morfologia \"core-shell\" e as propriedades magnéticas, porém apresentou um aumentou de seis vezes na área superficial. Novos suportes magnéticos foram desenvolvidos pela deposição de céria e titânia sobre magnetita previamente revestida com sílica. Nanocatalisadores magneticamente recuperáveis de Rh, Pd e Ru foram preparados. Os catalisadores foram utilizados na hidrogenação de ciclo-hexano, benzeno ou fenol e o principal objetivo dessa tese foi o estudo da influência de cada suporte na atividade catalítica. Os catalisadores foram preparados de duas formas diferentes: impregnação-redução e imobilização de nanopartículas (NPs) metálicas pré-formadas. As NPs coloidais foram preparadas pela redução de sais metálicos e, também, pela decomposição de complexos organometálicos. Catalisadores de ródio preparados pela impregnação de cloreto de ródio(III) e redução com H2 mostraram alguns problemas de reprodutibilidade, que foram superados utilizando NaBH4 ou hidrazina como agentes redutores. A preparação de catalisadores pela imobilização de NPs coloidais é uma alternativa interessante para obter catalisadores reprodutíveis e muito ativos. Nanopartículas de Pd, Rh e Ru foram preparadas a partir de organometálicos e imobilizadas em Fe3O4@SiO2 calcinada, Fe3O4@SiO2CeO2 e Fe3O4@SiO2TiO2. A eliminação do agente estabilizante torna os catalisadores mais ativos durante os reusos. O catalisador de Rh sobre o suporte de céria foi o catalisador mais ativo na hidrogenação de ciclohexeno (TOF 125000 h-1). O catalisador de Pd foi o catalisador mais seletivo para a hidrogenação de fenol em ciclo-hexanona, independente do suporte usado. A formação de ciclo-hexanol é favorecida pelo suporte de titânia e a hidrodesoxigenação para produzir ciclo-hexano ocorreu principalmente no suporte de sílica.

This thesis investigates the catalytic properties of tartaric acid‐nickel supported catalysts, obtained from hydrotalcite‐like compound precursors, in the enantioselective hydrogenation of methyl acetoacetate to methyl 3‐hydroxybutyrate. Variables of reaction during modification such as pH and tartaric acid concentration, as well as Ni particle size above a minimum threshold of ca. 20 nm, proved not to have a major effect on enantioselectivity. However, the nature of the cations constituting the catalyst support was found to influence the enantioselectivity observed. Specifically, when iron or chromium were constituents of the supporting oxide matrix, enantioselectivities were found to be much higher. For systems containing nickel, magnesium (or zinc) and aluminium as the cations present in the parent hydrotalcite phase, when a series of materials of the same composition obtained from different synthetic methods, the urea hydrolysis method leads to catalysts with enantiodifferentiation ability, whereas materials prepared by the coprecipitation method does not. Also, this thesis researches the use of different types of ordered mesoporous silicas as supports of tartaric‐acid nickel in the aforementioned reaction. Even though the techniques of metal deposition explored did not allow incorporation of Ni in the internal surface of the materials, it was found that the morphology of the support plays an important role in enantioselectivity. In addition, for a given material, the incorporation of Ni via solid state reaction resulted in a catalyst with improved catalytic properties compared to one prepared by wet impregnation techniques.

Thesis (PhD)--Stellenbosch University, 2015.
ENGLISH ABSTRACT: The synthesis of a range of siloxane functionalized Ru(arene)Cl(N,N) complexes allowing for the synthesis of novel MCM-41 and SBA-15 immobilized ruthenium(II) catalysts, is described in this thesis. Two distinctly different approaches were envisaged to achieve successful heterogenization of these siloxane functionalized complexes. Condensation of the siloxane functionalized complexes, C2.4-C2.6 (siloxane tether attached to imine nitrogen) and C3.5-C3.7 (siloxane tether via the arene ring), with the surface silanols of the synthesized silica support materials MCM-41 and SBA-15, afforded immobilized catalysts IC4.1-IC4.6 (siloxane tether attached to imine nitrogen) and IC4.7-IC4.12 (siloxane tether via the arene ring). Model and siloxane functionalized complexes C2.1-C2.6 were prepared by the reaction of diimine Schiff base ligands L2.1-L2.6 with the [Ru(p-cymene)2Cl2]2 dimer. A second, novel, approach involved the introduction of the siloxane tether on the arene ligand of the complex. Cationic arene functionalized Ru(arene)Cl(N,N) complexes, C3.1-C3.4, were prepared with varying N,N ligands including bipyridine and a range of diimine ligands, with either propyl or diisopropyl(phenyl) substituents at the imine nitrogen (greater steric bulk around the metal center). The reaction of these propanol functionalized complexes with 3-(triethoxysilyl)propyl isocyanate, afforded urethane linked siloxane functionalized complexes C3.5-C3.8, where the siloxane tether is attached to the arene ring of the complex. The complexes were fully characterized by FT-IR spectroscopy, NMR (1H and 13C) spectroscopy, ESI-MS analysis and microanalysis. Suitable crystals for the alcohol functionalized complex C3.1 were obtained and the resultant orange crystals were analyzed by single crystal XRD. The heterogenized catalysts, IC4.1-IC4.12, were characterized by smallangle powder X-ray diffraction, scanning and transmission electron microscopy (SEM and TEM), thermal gravimetric analysis (TGA), inductively coupled plasma optical emission spectroscopy (ICP-OES) and nitrogen adsorption/desorption (BET) surface analysis to name but a few. ICP-OES allowed for direct comparison of the model and immobilized systems during catalysis ensuring that the ruthenium loadings were kept constant. The application of the model complexes C2.1-C2.3 and C3.1-C3.3, as well as their immobilized counterparts, IC4.1-IC4.12, as catalyst precursors in the oxidative cleavage of alkenes (1-octene and styrene), were investigated. The proposed active species for the cleavage reactions was confirmed to be RuO4 (UV-Vis spectroscopy). In general it was observed that at lower conversions, aldehyde was formed as the major product. Increased reaction times resulted in the conversion of the formed aldehyde to the corresponding carboxylic acid. For the oxidative cleavage of 1-octene using the systems with the siloxane tether attached to the imine nitrogen, the immobilized systems outperformed the model systems in all regards. Higher conversions and selectivities of 1-octene towards heptaldehyde were obtained when using immobilized catalysts IC4.1-IC4.6, as compared to their non-immobilized model counterparts (C2.1-C2.3) at similar times. It was found that the immobilized catalysts could be used at ruthenium loadings as low as 0.05 mol %, compared to the model systems where 0.5 mol % ruthenium was required to give favorable results. Complete conversion of 1-octene could be achieved at almost half the time needed when using the model systems as catalyst precursors. The activity of the model systems seems to increase with the increase in steric bulk around the metal center. These model and immobilized systems were also found to cleave styrene affording benzaldehyde in almost quantitative yield in some case (shorter reaction times). The systems, with the siloxane tether via the arene ring, were found to be less active for the cleavage of 1-octene when compared to the above mentioned systems (siloxane tether attached to the imine nitrogen). The immobilized systems IC4.7-IC4.12 performed well compared to their model counterparts, but could not achieve the same conversions at the shorter reaction times as were the case for IC4.1-IC4.6. This lower activity was ascribed to the decreased stability of these systems in solution compared to the above mentioned systems with the tether attached to the imine nitrogen. This was confirmed by monitoring the conversion of the complex (catalyst precursor) to the active species in the absence of substrate (monitored by UV-Vis spectroscopy). It was observed that model complex C3.1 could not be detected in solution after 1 hour, compared to complex C2.2 which was detected in solution even after 24 hours. Experiments were carried out where MCM-41 was added to a solution of model complex C2.2 under typical cleavage reaction conditions. A dramatic increase in the conversion was achieved when compared to a reaction in the absence of MCM-41. An investigation into the effect of the support material on the formation of the expected active species was carried out using UV-Vis spectroscopy. The presence of the active species, RuO4, could be observed at shorter reaction times in the presence of MCM-41. This suggested that the silica support facilitates the formation of the active species from the complex during the reaction, therefore resulting in an increased activity. It was also observed that RuO4 is present in solution in reactions where the immobilized catalyst systems are used after very short reaction times, compared to the prolonged times required for this to occur as is the case for the model systems. Model and immobilized catalysts, C2.1-C2.3 and IC4.1-IC4.6, were also applied as catalysts for the transfer hydrogenation of various ketones. The immobilized systems could be recovered and reused for three consecutive runs before the catalysts became inactive (transfer hydrogenation of acetophenone). Moderate to good conversion were obtained using the immobilized systems, but were found to be less active their model counterparts C2.1-C2.3.
AFRIKAANSE OPSOMMING: Die sintese van `n reeks siloksaan gefunksioneerde Ru(areen)Cl(N,N) komplekse, wat die sintese van nuwe MCM-41 en SBA-15 geimmobiliseerede rutenium(II) katalisatore toelaat, word in hierdie tesis beskryf. Twee ooglopend verskillende metodes is voorgestel om die suksesvolle immobilisering van die siloksaan gefunksioneerde komplekse te bereik. Die kondensasie van die siloksaan gefunksioneerde komplekse, C2.4-C2.6 (siloksaan ketting geheg aan die imien stikstof) en C3.5-C3.7 (siloksaan ketting geheg aan die areen ligand), met die oppervlak silanol groepe van die silika materiale MCM-41 en SBA-15, laat die sintese van geimmobiliseerde katalisatore IC4.1-IC4.6 (siloksaan ketting geheg aan die imien stikstof) en IC4.7-IC4.12 (siloksaan ketting geheg aan die areen ligand) toe. Model en siloksaan gefunksioneerde komplekse C2.6-C2.6 is berei deur die reaksie tussen Schiff basis ligande, L2.1-L2.6, en die [Ru(p-simeen)2Cl2]2 dimeer. `n Tweede, nuwe benadering wat die sintese van komplekse met die siloksaan ketting geheg aan die areen ligand behels, is ook gevolg. Kationiese areen gefunksioneerde Ru(areen)Cl(N,N) komplekse, C3.1-C3.4, is berei deur die N,N ligande rondom die metaal sentrum te wissel vanaf bipiridien tot `n reeks diimien ligande met propiel of diisopropielfeniel substituente by die imien stikstof. Hierdie propanol gefunksioneerde komplekse is met 3-(triëtoksiesiliel)propiel-isosianaat gereageer om sodoende die uretaan gekoppelde siloksaan gefunksioneerde komplekse C3.5-C3.8 op te lewer. Al die komplekse is ten volle gekaraktariseer deur van FT-IR spektroskopie, KMR (1H and 13C) spektroskopie, ESI-MS analise en mikroanalise gebruik te maak. In die geval van model kompleks C3.1, is `n kristalstruktuurbepaling ook uitgevoer. Die heterogene katalisatore, IC4.1- IC4.12, is gekaraktariseer deur poeier X-straaldiffraksie, skandeer- en transmissieelektronmikroskopie, termogravimetriese analise (TGA), induktief gekoppelde plasma optiese emissie spektroskopie (IKP-OES) en BET oppervlak analises, om net `n paar te noem. IKP-OES het ons toegelaat om `n direkte vergelyking te tref tussen die model en geimmobiliseerde sisteme tydens die katalise reaksies. Model komplekse C2.1-C2.3 en C3.1-C3.3, sowel as hul geimmobiliseerde eweknieë IC4.1- IC4.12, is vir die oksidatiewe splyting van alkene (1-okteen en stireen) getoets. Die voorgestelde aktiewe spesie wat tydens hierdie reaksie gevorm word, RuO4, is bevestig deur van UV-Vis spektroskopie gebruik te maak. Oor die algemeen is dit gevind dat aldehied oorheersend gevorm word by laer omsetting. Wanneer die reaksietyd verleng is, is daar gevind dat die aldehied na die ooreenstemmende karboksielsuur omgeskakel is. Wanneer die geimmobiliseerde katalisatore gebruik is tydens die oksidatiewe splitsing van 1-okteen, het die sisteme, met die ketting geheg aan die imien stikstof, deurgangs beter as die model sisteme gevaar. Hoër omskakelings van 1-okteen en hoë selektiwiteite vir heptaldehied is behaal wanneer die geimobiliseerded katalisatore IC4.1-IC4.6 met die nie-geimmobiliseerde model sisteme (C2.1- C2.3) vergelyk is by dieselfde reaksietye. Die geimobiliseerde sisteme kon by rutenium beladings van so laag as 0.05 mol % gebruik word. Dit is in teenstelling met die model sisteme waar 0.5 mol % rutenium nodig was om die reaksie suksesvol te laat plaasvind. Die totale omskakeling van 1-okteen is bereik in die helfte van die tyd wat nodig was wanneer die model sisteme gebruik is. Dit is gevind dat die aktiwiteit van die model sisteme toeneem met `n toename in die steriese grootte van die ligand rondom die metaal. Beide die model en geimmobilseerde sisteme kon ook gebruik word vir die oksidatiewe splyting van stireen. Bensaldehied kon in kwantitiewe opbrengs gevorm word in sommige gevalle. `n Laer aktiwiteit vir die oksidatiewe splyting van 1-okteen is vir die sisteme waar die siloksaan ketting aan die areen ligand geheg is, waargeneem. Hoewel die geimmobiliseerde sisteme IC4.7-IC4.12 beter as hul model eweknieë gevaar het, kon die aktiwiteite wat met IC4.1-IC4.6 bereik is nie geewenaar word nie. Hierdie laer aktiwiteit is toegeskryf aan die verlaagde stabiliteit van dié sisteme in oplossing in vergelyking met IC4.1-IC4.6 (ketting geheg aan die imine stikstof). Die stabiliteit van beide sisteme is getoets deur die omskakeling van die model komplekse (C2.2 en C3.1; katalise voorgangers) na die aktiewe spesie te monitor (UV-Vis spektroskopie). Na 1 uur kon die model kompleks C3.1 nie meer in die oplossing waargeneem word nie. In teenstelling kon model kompleks C2.2 nog selfs na 24 uur in die oplossing bespeur word. Om die rol van die silika materiale tydens die reaksie te ondersoek, is `n eksperiment uitgevoer waar MCM-41 by `n oplossing van kompleks C2.2 gevoeg is. `n Toename in die omskakeling van 1-okteen is waargeneem in vergelyking met `n reaksie waar geen silika teenwoordig was nie. UV-Vis spektroskopie is gebruik om die invloed van die silika op die vorming van die aktiewe spesie te ondersoek. In eksperimente waar MCM-41 teenwoordig was, kon die aktiewe spesie, RuO4, by baie korter reaksietye waargeneem word. Dit wil blyk of die silika materiaal die vorming van die aktiewe spesie vanaf die kompleks aanhelp en sodoende `n toename in die spoed van die reaksie bewerkstellig. RuO4 kon ook by baie korter reaksietye waargeneem word wanneer die geimmobiliseerde sisteme gebruik is. Beide model en geimmobiliseerde sisteme, C2.1-C2.3 en IC4.1-IC4.6, is getoets vir die oordrag hidrogenering van verskilende ketone. Dit was moontlik om die geimmobiliseerde sisteme drie keer te herwin en vir daaropvolgende reaksies te gebruik. Vir die geimmobiliseerde sisteme kon egter slegs gemiddelde omskakelings verkryg word en het swakker gevaar as hul model ekwivalente sisteme, C2.1-C2.3.

In this study various microbial and enzymatic methods developed for enantioselective acyloin synthesis for preparation of some pharmaceutically important intermediates. By performing Aspergillus flavus (MAM 200120) mediated biotransformation, enantioselective bio-oxidation of meso-hydrobenzoin was achieved with a high ee value (76%). Racemic form of hydrobenzoin was also employed for the same bio-oxidation process and this bioconversion was resulted in accumulation of meso form (>
90% yield) confirming the suggested mechanism of oxidation-reduction sequence of hydrobenzoin. Wieland-Miescher ketone (3,4,8,8a-tetrahydro-8a-methylnaphthalene-1,6(2H,7H)-dione) is an important starting material for bioactive compounds like steroids and terpenoids. Many synthetic approaches include enantioselective reduction of this compound. In this study Aspergillus niger (MAM 200909) mediated reduction of Wieland-Miescher ketone was achieved with a high yield (80%), de (79%) and ee (94%) value and these results were found much more superior than previously reported studies. Carboligating enzymes benzaldehyde lyase (BAL) (EC 4.1.2.38) and benzoiyl formate decarboxilase (BFD) (E.C. 4.1.1.7) are used for biocatalytic acyloin synthesis. These enzymes are immobilized to surface modified superparamagnetic silica coated nanoparticles by using metal ion affinity technique. With this system recombinant histidine tagged BAL and BFD purified and immobilized to magnetic particles by one-pot purification-immobilization procedure. SDS page analysis showed that our surface modified magnetic particles were eligible for specific binding of histidine tagged proteins. Conventional BAL and BFD catalyzed benzoin condenzation reactions and some representative acyloin reactions were performed with this system with a high enantioselectivity (99-92%) and yield. Results obtained with magnetic particle-enzyme system were also found comparable with that of free enzyme catalyzed reactions.

The major part of this thesis concerns the development of catalytic methodologies based on palladium nanoparticles immobilized on aminopropyl-functionalized siliceous mesocellular foam (Pd0-AmP-MCF). The catalytic activity of the precursor to the nanocatalyst, PdII-AmP-MCF is also covered by this work. In the first part the application of Pd0-AmP-MCF in Suzuki-Miyaura cross-coupling reactions and transfer hydrogenation of alkenes under microwave irradiation is described. Excellent reactivity was observed and a broad range of substrates were tolerated for both transformations. The Pd0-AmP-MCF exhibited high recyclability as well as low metal leaching in both cases. The aim of the second part was to evaluate the catalytic efficiency of the closely related PdII-AmP-MCF for cycloisomerization of various acetylenic acids. The catalyst was able to promote formation of lactones under mild conditions using catalyst loadings of 0.3 - 0.5 mol% at temperatures of up to 50 oC in the presence of Et3N. By adding 1,4-benzoquinone to the reaction, the catalyst could be recycled four times without any observable decrease in the activity. The selective arylation of indoles at the C-2 position using Pd-AmP-MCF and symmetric diaryliodonium salts is presented in the third part. These studies revealed that Pd0-AmP-MCF was more effective than PdII-AmP-MCF for this transformation. Variously substituted indoles as well as diaryliodonium salts were tolerated, giving arylated indoles in high yields within 15 h at 20 - 50 oC in H2O. Only very small amounts of Pd leaching were observed and in this case the catalyst exhibited moderate recyclability. The final part of the thesis describes the selective hydrogenation of the C=C in different α,β-unsaturated systems. The double bond was efficiently hydrogenated in high yields both under batch and continuous-flow conditions. High recyclability and low metal leaching were observed in both cases.

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: Submitted. Paper 5: Submitted.

 

Il a été démontré que le catalyseur ZnO/Pt(111) présente des performances catalytiques remarquables dans l'oxydation du CO à basse température. L'identification des sites actifs dans l'oxydation du CO est importante pour une compréhension mécaniste de la relation structure-réactivité. Nous avons d'abord établi une recette pour fabriquer des films minces de ZnO sur Pt(111) par évaporation par faisceau électronique, caractérisée par STM et LEED. Le film se développe en mode couche par couche, à parti rd'une monocouche de type grapheme jusqu'à la surface ZnO(0001)-Zn terminée. Le rôle des limites ZnO/Pt a été révélé par la STM ex situ après exposition à l'O2:CO. Pour mettre en lumière le rôle des limites, une étude comparative systématique du catalyseur ZnO/Pt(111) avec la surface Pt(111) a été entreprise. La spectroscopie de masse et l'analyse NAP-XPS en phase gazeuse étaient pertinentes pour déterminer les régimes dans lesquels la limitation du transfert de masse commence à se produire, ce qui a permis de discuter de la relation entre les fractions molaires à l'état stable des réactifs/produit et la réactivité de surface, et pour étalonner la densité de surface des adsorbats. Les spectres XPS en phase solide nous ont donné accès à la dynamique du film monocouche ZnO ne couvrant que partiellement la surface Pt(111). Le rôle des hydroxyls liés au ZnO a été mis en évidence par l'observation de la signature chimique des produits de réaction associative CO+OH. Le carboxyle formé à basse temperature peut être l'espèce intermédiaire qui conduit à l'évolution du CO2, les OHs à la limite Pt/ZnO étant le co-catalyseur, ce qui explique l'effet synergique du ZnO et du Pt
The ZnO/Pt(111) catalyst has been shown to exhibit remarkable catalytic performances in the low temperature CO oxidation. The identification of the active sites in CO oxidation is important for a mechanistic understanding of the structure-reactivity relationship. We first established a recipe to fabricate ZnO thin films on Pt(111) using e-beam evaporation, characterized by STM and LEED. The film grows in layer-by-layer mode, starting from a graphene-like monolayer tothe ZnO(0001)-Zn terminated surface. The role of the ZnO/Pt boundaries was revealed by STM ex situ after exposure to the O2: CO mixture. To shedlight on the role of the boundaries, a systematic comparative study of the ZnO/Pt(111) catalyst with the Pt(111) surface was under taken. The mass spectroscopy and gas phase NAP-XPS analysis were relevant, to determine the regimes where mass transfer limitation starts to occur, allowing a discussion on the relation between steady-state molar fractions of reactants/product and surface reactivity, and to calibrate the surface density of the adsorbates.Solid phase XPS spectra gave us access to the dynamics of the ZnO monolayer film covering only partially the Pt(111) surface. The role of ZnO-bound hydroxyls was highlighted by the observation of the chemical signature of the CO+OH associative reaction products. The carboxyl formed at the low temperature can be the intermediate species that leads to the evolution of CO2, the OHs at the Pt/ZnO boundary being the co-catalyst, which explains the synergistic effect of ZnO and Pt

In this thesis the synthesis of vicinal stereocenters is investigated in two distinct contexts, namely the construction of 3,3-disubstituted oxindoles and the synthesis of b-hydroxy-a-amino acids. Both scaffolds are prevalent in a range of natural products and biologically relevant compounds and, therefore, methods for their synthesis are of great import. First, the construction of 3,3-disubstituted oxindoles using palladium-catalyzed domino reactions is described.  This covers two stereospecific methods for the construction of the desired oxindoles based on domino carbopalladation sequences.  The termination events for these domino reactions are carbonylation or cross-coupling.  In the carbopalladation-carbonylation reaction, we studied the possibilty of suppressing b-hydride elimination for substrates possessing pendant b-hydrogens.  In the carbopalladation-cross-coupling sequence, we examined the role of the boron source and substrate scaffold in the outcome of the reaction.  In both of these methods, an intricate balance of rates needs to be attained in order to achieve the desired domino sequences.  Thus, these investigations offer insight into the rates of the competing reactions, and the factors that influence these processes. Secondly, the stereoselective synthesis of b-hydroxy-a-amino acids is explored.  This has lead to two separate methods for the construction of this scaffold.  We first examined a 1,3-dipolar cycloaddition of azomethine ylides to aldehydes for the construction of syn-b-hydroxy-a-amino esters.  It was found that one set of azomethine ylides reacted through a 1,3-dipolar cycloaddition, while the other set reacted via a direct aldol reaction.  Finally, we studied an asymmetric transfer hydrogenation reaction to provide anti-b-hydroxy-a-amido esters from the corresponding a-amido-b-ketoesters.  Two protocols were developed for the reduction of these substrates, one using triethylammonium formate and the other using sodium formate in an emulsion.  The latter method gives high yields, diastereoselectivities and enantioselectivities for a broad range of substrates.
QC 20120605

Process development of new complex reactions in the pharmaceutical and fine chemicals industries is challenging, and expensive. The field is beginning to see a bridging between fundamental first-principles investigations, and utilisation of data-driven statistical methods, such as machine learning. Nonetheless, process development and optimisation in these industries is mostly driven by trial-and-error, and experience. Approaches that move beyond these are limited to the well-developed optimisation of continuous variables, and often do not yield physical insights. This thesis describes several new methods developed to address research questions related to this challenge. First, we investigated whether utilising physical knowledge could aid statistics-guided self-optimisation of a C-H activation reaction, in which the optimisation variables were continuous. We then considered algorithmic treatment of the more challenging discrete variables, focussing on solvents. We parametrised a library of 459 solvents with physically meaningful molecular descriptors. Our case study was a homogeneous Rh-catalysed asymmetric hydrogenation to produce a chiral γ-lactam, with conversion and diastereoselectivity as objectives. We adapted a state-of-the-art multi-objective machine learning algorithm, based on Gaussian processes, to utilise the descriptors as inputs, and to create a surrogate model for each objective. The aim of the algorithm was to determine a set of Pareto solutions with a minimum experimental budget, whilst simultaneously addressing model uncertainty. We found that descriptors are a valuable tool for Design of Experiments, and can produce predictive and interpretable surrogate models. Subsequently, a physical investigation of this reaction led to the discovery of an efficient catalyst-ligand system, which we studied by operando NMR, and identified a parametrised kinetic model. Turning the focus then to ligands for asymmetric hydrogenation, we calculated versatile empirical descriptors based on the similarity of atomic environments, for 102 chiral ligands, to predict diastereoselectivity. Whilst the model fit was good, it failed to accurately predict the performance of an unseen ligand family, due to analogue bias. Physical knowledge has then guided the selection of symmetrised physico-chemical descriptors. This produced more accurate predictive models for diastereoselectivity, including for an unseen ligand family. The contribution of this thesis is a development of novel and effective workflows and methodologies for process development. These open the door for process chemists to save time and resources, freeing them up from routine work, to focus instead on creatively designing new chemistry for future real-world applications.

The bidentate ligand 1,2-bis(ditertbutylphosphinomethyl)benzene has been shown to be a very efficient catalyst for operating the alkoxycarbonylation of alkenes and unsaturated esters and carboxylic acids giving a very high selectivity to the linear product with very few exceptions to this general rule. Due to the increasing prices of petroleum feedstock and petroleum-derived chemicals, the preparation of chemicals starting from renewable resources and waste products from the industry becomes an interesting alternative. Fatty acids and fatty esters, due to the existence of one or more unsaturation in their alkyl chain are subjected to the alkoxycarbonylation reactions in presence of 1,2-bis(ditertbutylphosphinomethyl)benzene, palladium, methane sulfonic acid, carbon monoxide and methanol, yielding diesters with a long carbon chain (up to 19 carbon atoms). The diesters are shown to be readily prepared from unpurified olive, rapeseed or sunflower oils as well as from tall oil. In the last case triesters are also formed. The diesters are subjected to hydrogenation in the presence of 1,1,1-tris(diphenylphosphinomethyl)ethane, ruthenium and hydrogen, in a mixture of dioxane and water at high temperature, yielding the corresponding diols. The resulting products of the reactions are monomers for preparing polyesters having the potential to replace some existing petroleum-based polymers (for instance polyethylene). The aminocarboxylation reaction in the presence of the same palladium/1,2-bis(ditertbutylphosphinomethyl) benzene catalyst, in the presence of aniline, 2{naphthol and potassium iodide in diethylether, is employed for preparing esteramides, which are subjected to hydrogenation. Aromatic polyamides are prepared by melting together an aromatic diamine and diacids obtained from methoxycarbonylation. Finally, N-Heterocyclic Carbene (NHC) ligands are employed for preparing new palladium complexes which are used in the Suzuki-Miyaura cross-coupling reaction in a water/isopropanol mixture. Other complexes based on copper are employed for developing an inexpensive transmetallation reaction for transferring a NHC ligand from copper to palladium and gold.

Cette thèse portait sur l’utilisation des complexes de cobalt de basse valence bien définis tel HCo(PMe3)4/HCoN2(PPh3)3 ainsi que les complexes haute valence de la famille des Cp*Co(III) stables à l’air, et leurs applications en activation de liaisons R–H (R = B, C, Si). Premièrement, nous avons utilisé avec succès le complexe HCo(PMe3)4 pour catalyser l'hydroboration et la diboration régio- et setéréosélective d’alcynes. De plus, nous avons étendu cela à la silaboration d'alcyne. Ensuite, nous avons démontré que les complexes HCo(PMe3)4 et HCoN2(PPh3)3 permettaient l’ hydrogénation stéréo-divergente d’alcynes and fonction du complexe utilisé . Enfin, nous avons exploré l'application des complexes de type Cp*Co(III) stables avec des additifs de type acides chiraux en fonctionnalisation asymétrique de liaisons C–H. De plus, nous avons commencé la synthèse du complexe chiraux de type Cp*Co(III), ou le Cp est cette fois chiral
This thesis was focused on well-defined low-valent cobalt complexes HCo(PMe3)4/HCoN2(PPh3)3, the bench stable family Cp*Co(III) of complexes and their applications in R–H activation (R = B, C, Si). First, we successfully used the HCo(PMe3)4 complex to catalyze regio- and stereo-selective hydroboration and diboration of alkynes. In addition, we exploited the HCo(PMe3)4 complex to catalyze silaboration of alkyne. Then, we demonstrated that the HCo(PMe3)4 complex and HCoN2(PPh3)3 complex were useful in the stereo-divergent hydrogenation of alkynes. Finally, we explored the application of the bench- stable Cp*Co(III) together with chiral additives in asymmetrical C–H bond functionalization. In addition, we conducted the elementary exploitation in synthesis of chiral Cp*Co(III) complexes

La producció d’hidrogen, a gran escala, a partir d’aigua ha esdevingut un repte des de fa uns quants any enrere. Així, una via ecològica i eficient per a la generació d’hidrogen ha de ser establerta. Entre totes les possibilitats, la electròlisis mitjançant la tecnologia de membranes bescanviadores de protons (PEM) és la tècnica més prometedora per a aconseguir tal propòsit. A més a més, aquesta aproximació també pot ser considerada per a dur a terme reaccions electroquímiques per altres propòsits més enllà de la generació d’hidrogen, com per exemple, la reducció de contaminants d’origen químic. A la llum d’aquests antecedents, reactors electro-catalítics multi-funció basats en membranes de bescanvi protòniques, integrats en un sistema en flux, per a (1) producció d’hidrogen i (2) reducció de nitrats (contaminant estudiat) a nitrogen, van ser dissenyats, construïts i finalment avaluats, satisfactòriament. Catalitzadors heterogenis basats en metalls van ser utilitzats com a materials d’elèctrode per a realitzar les reaccions electroquímiques desitjades. El MoS2, així com, el Co3O4 van ser descoberts com a materials prometedors per a la producció d’hidrogen en sistemes d’electròlisis PEM degut al seu rendiment, preu i abundància en l’escorça terrestre. Utilitzant la mateixa estratègia, catalitzadors suportats en SnO2 van ser emprats per a la reducció en continu de nitrats, en fase aquosa, sota condicions electroquímiques. Aquesta aproximació va ser anomenada reducció de nitrats assistida mitjançant electròlisis. El catalitzador de SnO2 modificat amb PdCu va destacar com el material d’elèctrode amb millor rendiment en termes de conversió i selectivitat. Mitjançant la modificació dels paràmetres de treball, així com, la configuració del reactor, la versatilitat i flexibilitat d’aquesta estratègia van ser avaluades per a poder afinar la formació de productes durant la reacció.
La producción de hidrógeno, a gran escala, a partir de agua se ha convertido en un reto desde ya hace unos cuantos años. Así, una vía ecológica y eficiente para la generación de hidrógeno tiene que establecerse. Entre todas las posibilidades, electrólisis mediante la tecnología de membranas de intercambio de protones (PEM) es la técnica más prometedora para conseguir dicho propósito. Además, dicha aproximación también puede ser considerada para llevar a cabo otras reacciones electroquímicas con propósitos totalmente distintos a la producción de hidrógeno, como por ejemplo, la reducción de contaminantes de origen químico. A la luz de estos antecedentes, reactores electroquímicos multifuncionales basados en membranas de intercambio protónicas, integrados en un sistema en flujo, para (1) producción de hidrógeno y (2) reducción de nitratos (contaminante estudiado) a nitrógeno, fueron diseñados, construidos y evaluados, satisfactoriamente. Catalizadores heterogéneos basados en metales fueron utilizados como materiales de electrodo para realizar las reacciones electroquímicas deseadas. MoS2, así como, Co3O4 fueron descubiertos como materiales prometedores para la producción de hidrógeno en sistemas de electrólisis PEM, debido a su rendimiento, precio y abundancia en la corteza terrestre. Empleando la misma estrategia, catalizadores soportados en SnO2 fueron utilizados para la reducción en continuo de nitratos, en fase acuosa, bajo condiciones electroquímicas. Esta aproximación fue llamada reducción de nitratos asistida mediante electrolisis. Catalizador de SnO2 modificado con PdCu destacó como el material de electrodo con mejor rendimiento en términos de conversión y selectividad. Mediante la modificación de los parámetros de trabajo, así como, la configuración del reactor, la versatilidad y flexibilidad de esta estrategia fueron evaluadas para poder ajustar la formación de productos durante la reacción.
Large-scale hydrogen production from water has become a challenge since several years ago. Thus, a clean and efficient way for hydrogen generation has to be stablished; among all possibilities, electrolysis by means of proton exchange membrane (PEM) technology is the most promising technique to achieve such goal. Furthermore, this approach can be also considered as potential strategy to perform electrochemical reactions for other purposes rather than only hydrogen production, like chemical pollutants reduction. In the light of this backgrounds, a multipurpose proton exchange membrane (PEM) electrocatalytic reactors, integrated in a flow system, for (1) hydrogen production and (2) nitrate reduction (target pollutant) towards nitrogen, were successfully designed, constructed and lately evaluated. Metal-based heterogeneous catalysts were employed as electrode material to carry out desired electrochemical reactions. MoS2 as well as Co3O4 were found as promising materials for hydrogen production in PEM electrolysis system due to its performance, price and abundance on Earth’s crust. Using same strategy, SnO2 supported catalysts were employed for continuous aqueous phase nitrate reduction under electrochemical conditions. This approach was called electrolysis-assisted nitrate reduction. PdCu dopped SnO2 catalyst stood up as the best performing electrode material in terms of conversion and selectivity. By modifying working parameters as well as reactor configuration, versatility and flexibility of this strategy were evaluated in order to fine tune products formation during reaction.

Doctor of Philosophy
Department of Chemical Engineering
Mary E. Rezac
Catalytic membrane reactors are a class of reactors that utilize a membrane to selectively deliver reactants to catalysts integrated in the membrane. The focus of this research has been on developing and characterizing polymeric catalytic membranes for three-phase hydrogenation reactions, where the membrane functions as a gas/liquid phase contactor allowing selective delivery of hydrogen through the membrane to reach catalytic sites located on the liquid side of the membrane. The benefit of conducting three-phase reactions in this manner is that delivering hydrogen through the membrane to reach catalytic sites avoids the necessity of hydrogen dissolution and diffusion in the liquid phase, which are both inherently low and often described as causing mass-transfer and reaction rate limitations for the reactive system. This work examines two types of membrane reactor systems, porous polytetrafluoroethylene and asymmetric Matrimid membranes, respectively, for the ruthenium catalyzed aqueous phase hydrogenation of levulinic acid. The highly hydrophobic PTFE material provides an almost impermeable barrier to the liquid phase while allowing hydrogen gas to freely transport through the pores to reach catalytic sites located at the liquid/membrane interface. Catalytic rates as a function of hydrogen pressure over the range 0.07 to 5.6 bar are presented and shown to be higher than those of a packed bed reactor under similar reaction conditions. An increasing catalytic benefit was obtained operating at temperatures up to 90 °C, which is attributed to increased hydrogen permeability and avoidance of the decreasing solubility of hydrogen in water with increasing temperature. The membrane reactor was shown to be stable with no decrease in catalytic activity over 200 hours of operation. The Matrimid membrane reactor work demonstrates the feasibility of applying an integrally-skinned asymmetric membrane for an aqueous phase hydrogenation reaction and focuses on the impact that membrane hydrogen permeance and catalyst loading have on catalytic activity. The non-porous nature of the separating layer in the Matrimid membrane allowed successful operation up to 150 °C. The overall catalytic rates were approximately an order of magnitude lower than those achieved in the PTFE membrane reactor system due primarily to significantly lower hydrogen permeances, nevertheless rates were still higher than control experiments. This work also focuses on characterizing Matrimid/solvent thermodynamic relationships for a variety of organic solvents, looking at sorption, diffusion, and polymer relaxation behavior in thin films ranging from 0.1 to 2.0 µm in thickness using quartz crystal microbalance techniques. Diffusion coefficients at infinite dilution for water and C1-C6 alcohols are given as a function of van der Waals molar volume and a clear dependency is shown ranging from 2E-11 to 6.5E-13 cm²/s for water and hexanol, respectively, for 0.26 µm thick films. Diffusion coefficients for all studied vapor penetrants displayed a marked dependence on thickness spanning approximately two orders of magnitude for each respective vapor penetrant over the range 0.1 to 1.0 µm. Chemically cross-linking Matrimid is a method to mitigate some of the relatively high sorption and swelling behavior exhibited in the presence of sorbing species. An in-depth analysis on the vapor phase ethylenediamine cross-linking of Matrimid films and its impact on diffusion, sorption, and relaxation is also described.

Il existe un grand nombre de ligands très efficaces actuellement employés pour la catalyse d’hydrogénation (BINAP, MeO-BIPHEP) et de couplage (S-PHOS, ligands PAP). La plupart d’entre eux possède une symétrie C2. Au cours de la thèse, nous avons étudié l’influence de la symétrie C1 sur les performances catalytiques de mono- et de diphosphines possédant une structure biaryle ou hétéro aromatique/ aromatique. Nous avons également étudié l’influence de leurs propriétés stériques et électroniques. Ces structures ont, pour la plupart, été obtenues par couplage aryne suivi par des réactions d’échange halogène/lithium régiosélectives permettant d’introduire de nombreux types de phosphines sur le noyau biaryle. Le profil électronique i. E. Les propriétés s-donneuses et p-accepteuses de ces nouveaux ligands originaux a été déterminé par les méthodes classiques. Par ailleurs, des tests d’hydrogénation des doubles liaisons C-C et C-O ainsi que des couplages C-C de type Suzuki-Miyaura ont été effectués. Nous avons ainsi montré que pour chaque type de réactions, au moins une de nos phosphines est aussi efficaces que les ligands classiques
Transition metal enantioselective catalysis is certainly among the most challenging and widely investigated area in modern organometallic chemistry. Chiral compounds qualifying as ligands for asymmetric catalysis continue to be designed and synthesized at a frenetic pace and competitors keep on emerging. In the field of atropisomeric biaryl diphosphine ligands, BINAP and MeO-BIPHEP are one of the most efficient one. On the other hand, the literature only shows very few C1-symmetric examples in this ligand class, none of them having a high structural or electronic diversity. In this context, we disclosed the access to the following C1-symmetric mono- and diphosphine ligands and we studied the influence of their steric and electronic properties. Most of them were obtained via aryne coupling, regioselective halogen/lithium exchange, phosphination sequence. Their electronic profile i. E. Their s-donor properties and their p-acidic character were determined according to the classical methods. Finally, we used them in catalytic hydrogenations of C-C and C-O double bonds and C-C Suzuki-Miyaura coupling reactions and we proved that whatever the reaction, at least one of our ligands was as efficient as the classical ones

Abstract In this Ph.D. project, the effective parameters in the sol-immobilization method which can affect catalytic reactivity including: capping agent, solvent of synthesis, and support were studied. The synthesized catalysts were employed in the liquid phase hydrogenation reactions of two biomass derived molecules namely furfural and vanillin. In this regard, the role of protective agents, which are used to stabilize colloidal nanoparticles (NPs) in solutions, for Pd NPs supported on carbon support in the liquid phase hydrogenation of furfural was explored. The use of Pd as a hydrogenation catalyst is well documented, as hydrogenation reactions can only be performed by metals that can easily chemisorb hydrogen. Pd is one of such metals capable of dissociate hydrogen even at room temperature. The capping agent adsorbed on the surface of the NPs can alter their activity and selectivity, by modifying the particle size, size distribution, morphology, and stability against leaching and agglomeration. Besides, the effect of the amount of protective agent and the synthesis solvents have been investigated, allowing better insight into the metal-support interaction in Pd/TiO2 catalysts for the hydrogenation of furfural. Then, the effect of using different carbonaceous supports with various chemical-physical properties on the activity and selectivity towards the hydrodeoxygenation of vanillin as a lignin model compound was explored. To better understand the role of the capping agents in controlling the activity and the selectivity of the furfural hydrogenation, a series of carbon-supported Pd nanoparticles were prepared through controlled sol-immobilization method using different capping agents, including polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), and poly(diallyldimethylammonium) chloride (PDDA) containing oxygen and/or nitrogen groups. The catalysts were characterized by different techniques. UV-Vis and Fourier-transform infrared (FTIR) spectroscopy were used to evaluate the interaction between capping agents and Pd precursor, while transmission electron microscopy (TEM) was performed to study the final morphology of the catalyst. Finally, X-ray photoelectron spectroscopy (XPS) was employed to investigate the surface chemistry of the carbon support, the chemical state, and the exposure of supported palladium species. The UV-Vis spectra of the system composed of Pd precursor plus capping agent demonstrated the interaction of the metal with PVA and PVP. In the case of PDDA, changes to the precursor salt complex were noticed through shifts in [PdCl4]2- absorbance bands. The disappearance of the peaks associated with Pd2+ and the observed scattering indicated a complete reduction to Pd0 and the formation of metal nanoparticles. The interaction of the capping agents with the Pd precursor was studied by FTIR spectroscopy. For PVA, the peaks corresponding to the stretching vibrations of C–O–C linkage were observed, which suggested the presence of cross-linked PVA molecules, and the slight modification observed for the peaks in the spectrum of PVA + Na2PdCl4 suggested a weak interaction between the metal precursor and the –OH groups present in PVA. In the case of PVP, a decrease in the intensity of the peak after the addition of Pd was observed which confirmed that both O and N groups are present in PVP interaction with the metal precursor. For PDDA, after the addition of Pd, the intensity of the peaks decreased, which indicated that the activity of the vibrational modes is modified in the mixture, probably due to PDDA–Pd interaction. The morphological characteristics of the synthesized catalysts were evaluated by HRTEM. We noticed that the capping agent has a major effect on the size and distribution of Pd NPs when using activated carbon as the support. All catalysts had an average particle size of 3–4 nm, with the presence of isolated larger particles in the case of PdPDDA/C. The XPS survey data revealed that only Pd, C, N, and O species were present on the surface of the catalysts. Depending on the capping agent used, substantial differences were observed in the relative amount of Pd on the surface: PdPVA/C (1.30 %) > PdPDDA/C (0.76 %) > PdPVP/C (0.50 %). The data also showed a different oxygen content in the samples. PdPVA/C displayed the highest relative amount of O (14.7 % compared to PdPDDA/C (9.70 %) and PdPVP/C (9.10 %)), respectively. The highest oxygen content on the surface of PdPVA/C catalyst is probably due to the presence of –OH groups in PVA. PdPVP/C exhibited the highest N content (2.95 %), higher than PdPDDA/C (1.86 %) due to the presence of a pyrrole-type N species in PVP and dimethyl-ammonium groups in PDDA, while in the PdPVA/C N was not detected on the surface, as expected. The performance of the prepared catalysts was examined for the liquid-phase hydrogenation of furfural (furfural 0.3 M; furfural/metal ratio 500 mol/mol, 5 bar H2, temperature range of 25–75 °C) with 2-propanol as solvent. The catalytic results revealed that the activity of catalysts is correlated to the relative amount of Pd at the surface: PdPVA/C (1.3%) > PdPDDA/C (0.76%) > PdPVP/C (0.50%). At 75 °C the catalysts exhibit similar reactivity. We ascribed this effect to the partial removal of a capping agent during the reaction, thereby exposing a higher number of active sites to the reactant. In the next step, since the best results were obtained using PVA, this latter was chosen as the protective agent, focusing on the effects that its amount and the change of the solvent of synthesis to methanol-water mixtures might have on the preparation of Pd/TiO2 catalysts. This new approach indicates the necessity of using the capping agent, and results also show that the acidification step, which lowers the isoelectric point (IEP) to afford anchoring of the NPs to the surface of the support, can be eliminated while still maintaining the same degree of Pd immobilization (≥ 96%) and particle size control (< 2 nm). These samples were evaluated for furfural hydrogenation; there was an improvement in selectivity towards furfuryl alcohol and tetrahydrofurfuryl alcohol, whereas ether by-products were suppressed. Supported Pd NPs were prepared in accordance with the standard sol-immobilization method, in which the temperature of the chemical reduction was maintained at 1 °C. This temperature was chosen as earlier research in our workgroup reviled the formation of smaller nanoparticles when lower temperatures were used. UV-Vis spectroscopy was performed to characterize the precursor salt and colloidal solutions during NPs preparation. Changes to the precursor salt complex were noticed through shifts in [PdCl4]2- absorbance bands. Catalysts prepared with increasing volumes of MeOH showed shifts in the distinctive ligand to metal charge transfer (LMCT) and d-d transitions. This confirms a change to the Pd metal precursor complex when it is solvated in either the MeOH/H2O mixture or in pure MeOH. One reason for this is the exchange of ligands between the Pd salt complex and the solvent synthesis. The Pd % loading of each catalyst was measured using microwave plasma – atomic emission spectroscopy (MP-AES). All catalysts were characterized using TEM, in order to get information of their average NP sizes and particle size distributions/dispersions. An initial comparison of catalysts, showed that an acidified immobilization step increases the average NP size. The bigger NP size and dispersion was found for the sample prepared by H2O as the solvent, PVA, and acidification step, which it can be ascribed to the interaction of the stabilizer agent (PVA) with acid during the immobilization step. XAFS was performed to investigate both changes to Pd oxidation state (XANES) and the local structural environment with respect to Pd (EXAFS). The results confirmed that by using PVA in the solvent system, the Pd oxidation state contains a greater quantity of Pd2+. Interestingly, by removing the acidification step during the synthesis, an increase in the oxidized Pd state was observed. This was consistent with the TEM data indicating this increase in Pd2+ is related to the observed particle sizes. Pd surfaces are known to form passivating oxide layers when exposed to air with an increase in the temperature needed to form a bulk oxide structure. Therefore, the Pd2+ fraction refers to the quantity of the available Pd surface and hence the particle size. Fitting of the 1st shell Pd K edge EXAFS data was consistent with the trends observed through TEM and XANES characterization. The presence of small Pd NPs is confirmed by the decreased magnitude of Pd-Pd scattering, signified by smaller CNPd-Pd. All catalysts were tested for the hydrogenation of furfural at 50°C. Although the XANES, EXAFS, and TEM data have all confirmed that sample prepared by the pure MeOH contains smaller NPs than the sample prepared by pure H2O, the initial catalytic activity showed that the sample synthesized by H2O has a significant increase in initial TOF h-1. In addition, furfural hydrogenation performed over the bare TiO2 support displayed 98.4 % selectivity to the acetal product (2-(diisopropoxymethyl) furan), at isoconversion, while sample prepared by H2O revealed less selectivity to the acetal (18.8%). To understand these differences in activity/selectivity we performed further HRTEM investigations of the fresh samples. These studies have identified a 'halo' of PVA around NPs produced using MeOH (e.g. PdMeP) and at the interface between NPs and support. We suggest that the poor solubility of PVA in methanol is responsible for this increase in PVA clustering on the catalytic surface/support interface identified with HRTEM. We also propose that the active sites on TiO2 are formed through the spillover of hydrogen onto the support and accounts for the superior yield of acid catalysed products for Pd/TiO2 compared to TiO2 alone. In the case of Pd/TiO2, the catalysts prepared using MeOH result in aggregation of PVA at the Pd-TiO2 interface, which restrict spillover effects and decreases the amount of acid catalysed products. For the catalysts prepared without the addition of PVA, we observed a higher proportion of ethers than for the analogous catalysts prepared with PVA. This further supports our hypothesis that PVA at the metal-support interface limits the spillover of hydrogen. Catalyst recycle tests were carried out over six consecutive hydrogenation cycles. The catalysts prepared without PVA quickly deactivated with almost negligible performance by the sixth consecutive run. The TEM analysis of the spent sample confirmed that when PVA is not present the samples quickly agglomerate and effective surface area of Pd rapidly diminishes. Finally, the effect of support on both activity and selectivity of the catalyst in the hydrogenation of vanillin to vanillyl alcohol and the subsequent hydrodeoxygenation (HDO) to creosol was studied. Four types of carbonaceous materials (three activated carbon: Norit, KB, G60, and a carbon nanofiber: HHT) were used as support for Pd nanoparticles. Catalysts were synthesized with sol immobilisation method using PVA as the capping agent, and tested in the hydrodeoxygenation reaction of vanillin under mild reaction conditions (50 °C, 5 bar H2 and isopropanol as solvent). Catalysts have been extensively characterized by TEM, XPS and BET in order to correlate the surface properties with the catalytic behaviour and selectivity to the target products. In the end, recycle tests were carried out on the most active catalyst to determine the reusability of the material used. BET analysis was conducted on Pd-supported catalysts. Pd/Norit catalyst has the highest surface area (2000 m2/g), whereas Pd/HHT has the lowest surface area (40 m2/g). The average pore radius of all samples was in the range of 2 nm for Pd/KB to 25,4 nm for Pd/HHT. XPS analysis were performed on the synthesized catalysts to determine the oxidation state of the Pd, the graphitization order and the presence and abundance of oxygen functionality. Pd/Norit, Pd/KB and Pd/G60 had a similar amount of C1s species (84.4 %, 87.3 % and 91.1 %, respectively), while Pd/HHT had the highest number of C 1s (98.8 %). Evaluation of O1s species revealed that the Pd/HHT catalyst has the lowest amount of functionalisation (0.9 %), while Pd/Norit the highest one (14.3 %). The results showed that the Pd/HHT catalyst has the highest amount of C=C (82.1 %), therefore the support can be considered highly graphitised. TEM analysis were performed to determine the mean particle size and size distribution. In all samples, the nanoparticles are homogeneously distributed on the support. Pd/Norit and Pd/KB had similar mean Pd particle sizes (2.5 and 2.7 nm respectively). Whereas, Pd/G60 and Pd/HHT displayed higher mean Pd nanoparticle diameters (3.5 and 3.9 nm, respectively). The catalysts were tested in the vanillin HDO reaction. The reaction profile shows the features of a typical consecutive reaction, with vanillyl alcohol as the intermediate product, and creosol as the final product. Interesting, an additional product was detected in the reaction mixture, namely vanillyl isopropyl ether. The ether is produced by reaction of vanillyl alcohol with a molecule of solvent (isopropanol) and it is consumed with time since it is in equilibrium with the alcohol. The results revealed that the rate of conversion of vanillin enhances with increasing degree of graphitisation. These results can be explained by the strong interaction between the graphitic plane of the support and the aromatic ring of the substrate that allows a better interaction with the active metal nanoparticles. At the same time, the activity in the vanillin hydrogenation reaction decreases with an increase in oxygen content at the carbon surface. The support-substrate interaction is responsible for the change in activity; the increase in oxygen functionality actually disrupts the graphical plane structure of the support. The support affected the selectivity at the lower conversion. In fact, at 50 % of conversion, vanillyl alcohol was the main product of Pd/Norit, Pd/HHT and Pd/KB (selectivity in the 73-82 %), while Pd/G60 provided high levels of both vanillyl isopropyl ether and creosol (23 and 21 %, respectively). The formation of ether was associated with the amount of carboxylic support functionality (COOH groups). The recycling tests were carried out on the most active catalyst: Pd/HHT. After five consecutive reactions, the conversion did not significantly decrease, demonstrating the high stability of the catalyst. Comparably, the selectivity of vanillyl alcohol remained almost unchanged.