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The aim of this work is to investigate homogeneous and heterogeneous catalysis by HPAs for the conversion of renewable feedstocks. This includes the preparation, characterisation and testing of a range of acidic solid materials such as bulk HPAs, CS2.sHo.sPW12040and the acidic composites comprising H3PW12040 (HPW) supported on Nb20s, Zr02 and Ti02. The HPW supported on Ti02, Zr02 and Nb20s were prepared by impregnation method and then characterised regarding their acid properties and the chemical structure of HPA on the catalyst surface, compared to "standard" HPA catalysts such as bulk and silica-supported H3PW12040 and CS2.5HO.SPW12040In. contrast to the parent acid H3PW12040 and CS2.sHo.sPWI2040, possessing strong Brensted acid sites, the catalysts supported on Ti02, Zr02 and Nb20s possess both Brensted and Lewis acid sites, with the latter mainly originating from the oxide support. These catalysts possess weaker acid sites than H3PW 12040and CS2.sHo.sPW12040,with their acid strength being similar to that of acidic zeolites. The catalytic activity (turnover frequency) in gasphase isopropanol dehydration decreases in the order: H3PW12040> CS2.sHo.sPW12040> 15%H3PW12040/Si02 > 15%H3PW120401Ti02 » 15%H3PW120401Nb20S > 15%H3PWI2040/Zr02, which is in line with the acid strength determined by NH3 adsorption calorimetry. 31p MAS NMR and FTIR indicate an increasing interaction between support and HPA in the following order: Si02 < Ti02 < Nb20s, Zr02, whilst the strength of acid sites decreases in that order. Esterification of hexanoic acid and transesterification of ethyl propanoate and ethyl hexanoate with excess methanol (1:20 molar ratio) were tested at 60 QC and ambient pressure with a range of HPA catalysts in homogeneous and heterogeneous systems in comparison with conventional homogeneous and solid acid catalysts such as H2S04, Amberlyst-15 and zeolites HY and H-Beta. In these reactions, the intrinsic catalytic activity (turnover frequency, TOF) of HPA catalysts is significantly higher than that of the conventional acid catalysts. The TOF values decrease with decreasing catalyst acid strength in the order: H3PW12040~ CS2.sHo.5PW12040> ~SiW 12040> 15%H3PW12040INb205, 15%H3PWI2040/Zr02, 15%H3PWI2040/Ti02> H2S04> HY, H-Beta> Amberlyst-15. Supported HPA catalysts suffer from leaching and exhibit significant contribution of homogeneous catalysis by the leached HPA. The isomerisation of a-pinene is studied in the gas phase over solid HPA catalysts in a fixed bed continuous flow reactor at 200°C and ambient pressure. The reaction yields camphene as the main product in a mixture with monoterpene byproducts such as limonene, terpinolenes, terpinenes, p-pinene, p-cymene and others. The strong Brensted solid acids exhibit high initial activities, but suffer from catalyst deactivation, resulting in low camphene yields. Conversely, the HPA catalysts supported on Nb20S, Zr02 and Ti02, although weaker acids, show more stable performance in a-pinene isomerisation.

Published work on the cleavage of carbon-silicon bonds has boon reviewed, with particular reference to cleavage by alkaline and other nucleophilic reagents. Tho apparent dissociation constants of several acids of the type -R3SiCH2C6H4CO2H (where R is alkyl or aryl) p have been determined opectrophotometrically in aqueous methanol, and the results are discussed. Tho alkaline cleavage of trobenzyltrimethylsilane has been examined in aqueous dioxane. At high water concentrations increases in solvent polarity retard the cleavago, as required by a mechanism involving charge dispersion in the transition state. At high dioxano concentrations, increases in solvent polarity are accompanied by increases in the rate of reaction, and this is suggested to result from association between the solvent components. In cleavage of o-nitrobenzy1trimothylsilane by aqueous methanol it has been shown that there is no appreciable salt effect. Addition of various nucleophilic reagents has shown that nucleophilic power towards carbon is not an indication of nucleophilic power towards silicon. A kinetic study of the effect of 3ubstituent3, X, on the ease of alkaline cleavage of the bonzyl-silicon bond in (C113)3SiCH2C6H4X, has, conßirnted that electron-withdrawal in X accelerates the reaction, In cleavage of anions ofthe type n-R3SiCH2C6H4CO (where R iss alkyl or aryl) , the reaction is retarded by electron-release in R, and accelerated by electron-withdrawal in R. Bulky groups attached to silicon slow the reaction by storically hindering; hydroxide ion attack on i. licon. Similar conclusions were reached with cilanou of the typo p-R3SiCIi2C6H4C1 (where R is alkyl or aryl), and furthermore, in- compounds of the type p-XC6H4(Cii3) 2S'CH2C6H4Cl, electron-supply in X rotardD, and electron-withdrawal in X accelerates the reaction. All the experimental results are consistent with a mechanism involving nucleophilic attack on cilicon, either by a synchronous bimolecular (Sn2) process, or equally well, by one involving initial formation of a pontacovalent silicon inteztcdiat©.

Density Functional Theory (DFT) calculations have been carried out to study the factors that affect the cyclometallation reactions of the model system [Ir(-Cp)(dmba−H)(2- RCO2)]+ (R= CH3, CF3, CCl3, OH and Ph), as well as the triflate analogue. The limiting step is, in all cases, the dissociation of one arm of the chelating base and in most cases a 1-intermediate was located. The transition state for the subsequent C−H activation exhibits short MC−H and OH interactions which combine to allow an easy hydrogen transfer. The combination of these two factors leads to a new term Ambiphilic Metal Ligand Activation (AMLA) to describe these C−H activation processes. The above study was extended to [M(ring)(dmba−H)(2-OAc)] systems, (where M(ring) = {Rh(-Cp)}+, {Ru(-C6H6)}+ and {Ru(-Cp)}). Cationic systems have very similar activation energies (E‡), although small variations in the overall energy were computed. These effects were rationalized in terms of the strengths of the M−C and M−O bonds formed and broken in the reaction. The neutral systems gave a lower E‡ although the products were less stable. In addition, the substitution of the dmba−H ligand for related imine or amide substrates shows that these species also readily undergo facile cyclometallation. Finally, the intermolecular C−H activation of benzene by [Ir(-Cp)(PH3)(2-OAc)]+ and the incorporation of this step into a catalytic cycle for the hydroarylation of ethene was assessed. The rate-limiting step is associated with the alkene insertion step (E‡ = 16.7 kcal/mol), while the C−H activation is slightly more accessible. Therefore, this model appears to be a promising target for catalysis.

An alternative cleaner route for the production of aromatic amino-compounds under mild reaction conditions (P = 1 atm; 393 K ≤ T ≤ 573 K) via the continuous gas phase reduction of aromatic nitro derivates has been investigated over (oxide and/or carbon) supported Au, Ag, Pd, Ni, Ni-Pd, Au-Pd and Au-Ni catalysts. Taking the hydrogenation of p-chloronitrobenzene as a model reaction, Pd/Al2O3 promoted the exclusive production of nitrobenzene and aniline, i.e. hydrodechlorination with subsequent -NO2 group reduction prevailed. In contrast, p-chloroaniline was the only product detected over a series of supported Ni catalysts. This is the first time that such product exclusivity has been achieved in gas phase operation. The synthesis of bimetallic Pd-Ni/Al2O3 (prepared via co-impregnation) proved effective to enhance catalytic activity while maintaining 100% selective -NO2 reduction, a result ascribed to bimetallic particle formation as established by TPR, H2 chemisorption and XRD analyses. Nevertheless, the three systems (supported Pd, Ni and Pd-Ni) suffered a loss of activity with time-on-stream. Monometallic Au catalysts promoted the exclusive and time invariant formation of p-chloroaniline. The incorporation of Au (as a modifier) with Pd via reductive deposition to form Au-Pd/Al2O3 (Pd/Au=10 mol/mol) did not influence catalytic performance, which was equivalent to that delivered by Pd/Al2O3, i.e. aniline was the predominant product. On the other hand, the inclusion of Pd (as a promoter) with Au (at Au/Pd≥20) via co-impregnation and/or co-deposition precipitation resulted in increased hydrogenation rate while retaining exclusivity to pchloroaniline, an effect resulting from a surface Pd-Au synergism demonstrated by DRIFTS analysis. With the goal of elevating the catalytic activity of Au, the possible role of the oxide (Al2O3 vs. TiO2) support to modify catalytic response was considered. Au/TiO2 delivered a higher specific rate that was attributed to a combination of smaller Au particle size (with higher number of defects) and possible p-chloronitrobenzene activation via interaction(s) with TiO2 surface oxygen vacancies. This work was extended to decouple the individual contribution of each factor by (i) considering a series of oxide supports that exhibited a range of acid-base and redox surface properties, i.e. Al2O3, TiO2, Fe2O3 and CeO2 and (ii) controlling the Au particle size using two synthesis methods (deposition-precipitation and impregnation). The results demonstrated that specific activity increased with decreasing particle size (from 9 to 3 nm), regardless of the nature of the support. Furthermore, in the case of Au/Fe2O3, XRD and TPR analyses have established that Au can promote the partial reduction of the iii support (from α-Fe2O3 to Fe3O4), an effect more pronounced for smaller Au particles (< 5 nm) where H2-TPD suggests the participation of spillover hydrogen in this reduction step. A similar effect was also found for the TiO2 allotropic phase transition (from anatase to rutile), which can occur at lower temperatures due to the presence of Au, as demonstrated by DRS UV-vis, XRD and BET measurements. Having established that supported Au is effective in promoting the exclusive reduction of p-chloronitrobenzene to p-chloroaniline, hydrogenation selectivity was proved further by considering the reduction of m-dinitrobenzene. The reaction products, i.e. m-nitroanline (partial -NO2 reduction) and m-phenylenediamine (complete -NO2 reduction) are both high value intermediates in the fine chemical industry but existing routes can not achieve high selectivity to either product. It is shown that the nature of the oxide support (for TiO2-rutile, TiO2-anatase, Al2O3, CeO2, Fe2O3) does not have a direct effect on the rate of nitro-group reduction, which is controlled by Au particle size where a mean size of 5 nm was found to be critical in that with larger particles, nitrogroup reduction rate was structure insensitive. In contrast, the nature of the support has a direct effect on the selectivity response. Au/TiO2 and Au/Fe2O3 promoted the exclusive hydrogenation of m-dinitrobenzene to m-nitroaniline, Au/CeO2 delivered mphenylenediamine as the sole product and Au/Al2O3 generated a mixture of both products. This response can be accounted for on the basis of a modification to the electronic character of the Au nanoclusters induced by the acid-base Lewis properties of the support that impacts on the adsorption/activation of m-dinitrobenzene. A similar alteration of the electronic nature of Au can also be induced by alteration of the Au particle size or the introduction of a second metal (Ni). Taking the same reaction over Au/Al2O3, Ni/Al2O3 and Au-Ni/Al2O3, it is established that it is possible to control product composition in terms of partial (over Au) or complete nitro-group reduction (over Ni) or a combination of both (over Au-Ni), which can be attributed to a surface Au-Ni synergism as suggested by XPS and EDX mapping measurements. In order to assess the impact of annealing treatment on catalytic response, the analysis was extended to the preparation and application of an Au-Ni/Al2O3 alloy, formation of which is demonstrated by XRD, DRS UV-Vis and HRTEM. While alumina supported bimetallic and alloy both promoted the formation of both m-nitroaniline and mphenylenediamine via a predominantly stepwise reduction mechanism, the annealed (alloy) system delivered rate constants up to two orders of magnitude lower. In the final section of this thesis, the catalytic behaviour of supported (TiO2) Au and Ag is iv compared in the selective hydrogenation of a series of para-substituted nitroarenes. While both catalysts promoted the exclusive nitro-group reduction, Ag/TiO2 delivered lower reaction rates. The reaction mechanism has been probed by adopting the Hammett approach, where the linear correlation and positive slopes (higher for Au than Ag) associated with the Hammett plots are consistent with an electron withdrawing substituent activation effect, i.e. nucleophilic attack and a more effective reactant activation over Au/TiO2. The results presented in this thesis demonstrate, for the first time, that catalytic hydrogenation over gold-based catalysts in continuous flow gas operation is a viable, clean high throughput route to aromatic amines. The findings of this thesis show that Au on reducible supports with dAu < 5 nm is the optimum monometallic formulation while -NO2 group reduction rate and/or selectivity can be controlled (or tuned) by (i) changing the acid-base Lewis character of the support, (ii) modifying Au dispersion or (iii) incorporation of Pd or Ni as promotors. This work represents a critical advancement in the sustainable production of high value fine chemicals.

Hollow finite cylindrical catalysts are becoming of more interest as catalyst support not only because they produce lower pressure drops than with conventional solid pellets but also because they provide the associated extra external surface area which enhances diffusion-limited reactions. Dynamic simulation of diffusion, conduction and reactions in this type of catalyst has been studied. The numerical method, Alternating Direction Implicit Method (ADIM), has been used for solving the coupled elliptic governing equations. The simulation applied to methane-steam reforming involves multiple (parallel) reactions and multicomponent mixtures of products and reactants within the catalyst. The numerical method proposed is expected to be capable of following steep gradient of methane concentration across the cylindrical catalyst during methane-steam reforming. From a critical literature evaluation of kinetics of methane-steam reforming, it was found that the data of Bodrov et al. (1967a) and that of Kopsel and Meyer (1980) were obtained from experiments in the temperature range of industrial application. The ADIM was able to follow, successfully, the steep gradient of methane concentration during methane-steam reforming by employing kinetic expressions derived by Kopsel and Meyer (1980) within hollow, finite cylindrical catalyst. The numerical method has been used for comparative study of temperature and concentration profile across the catalyst by employing several kinetic expressions for methane-steam reforming. The kinetic expressions of Bodrov et al (1967a), modified by comprehensively reinterpreting their data, also produce diffusion-controlled profiles across the hollow finite cylindrical catalyst. The comparative study found that the kinetic expressions of De Deken et al (1982) and the more elaborate kinetics of Xu and Froment (1989) do not produce diffusion-controlled profile across the catalyst at high temperature.

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