Spin-lattice (T1) relaxation studies using solid-state and solution-state :31p nuclear magnetic resonance spectroscopy have proven to be a reliable procedure for determining the onset of a "liquid-like" character of the supported phase in a supported aqueous phase catalyst. It has also been shown that the appearance of the liquid-like character, which can be determined by the length of T b occurs at the onset of maximum catalytic activity in a supported aqueous phase catalyst. Direct sulfonation of 1,2-bis(diphenylphosphino)ethane (DPPE) has yielded 1,2-(bis[di-m-sodiumsulfonato]phenylphosphino)ethane (DPPETS), a new water soluble ligand that has been characterized and used in the synthesis of several new complexes with palladium, rhodium, platinum and nickel centers. T 1 relaxation times and the magnitude of the chemical shift anisotropy of several of the complexes have been determined with solid- and solution-state 31 P NMR and several complexes have been evaluated for their potential in biphasic hydrogenation and hydroformylation catalysis. / Ph. D.

M.Sc. (Chemistry) / Please refer to full text to view abstract

The synthesis of pure tris(6-hydroxymethyl-2-pyridylmethyl)amine (H₃L₁₁) is reported for the first time. New complexes of H₃L₁₁ with copper(II), manganese(II) and iron(III) have been characterised by X-ray crystallography. Linear [Fe₃(L₁₁)₂](ClO₄)₃ reveals the tightest Fe-O-Fe angle (87.6°) and shortest Fe...Fe distance (2.834 Å) presently found for a weakly antiferromagnetically-coupled high spin alkoxide-bridged polyiron(III) system. H₃L₁₁ provides a route to various hydrophobic peralkylated TPA ligand derivatives for creating a hydrophobic pocket for the assembly of iron catalysts for the novel 1-hydroxylation of n-alkanes. New 6-py substituted TPA ligands containing methyl (L₁₅) and n-octyl (L₁₆) ether linkages were synthesised via alkylation. Two further novel 6-py substituted ligands were synthesized incorporating n-hexyl substituents on one (L₂₁) and two (L₂₂) of the py moieties. Here a urea spacer group was used to promote hydrogen–bond assisted heterolytic O-O cleavage (generation of the potent FeV=O oxidant) within the hydroxoperoxoiron(III) precursor. High spin [FeII(L)(CH₃CN)[subscript(x)]](CF₃SO₃)₂ complexes (x = 0–2, L = L₁₅,₁₆,₂₁,₂₂) were characterised in solution by ¹H NMR. The structure of [Fe(L₂₂)](CF₃SO₃)₂ reveals a distorted iron(II) centre bound to four N atoms and two urea carbonyls. Iron(II) complexes of H₃L₁₁, L₁₅,₁₆,₂₁,₂₂ and tris(6-Br)-TPA (L₂₄), were investigated for catalysis of the oxygenation of cyclohexane by H₂O₂. Reaction of the iron(II) complexes with H₂O₂ and [superscript(t)]BuOOH was followed by time-resolved EPR and UV-VIS spectrophotometry. A correlation between the observed catalytic activity and the nature of the FeIII(L)-OOR intermediates generated is apparent. A convenient ‘one-pot’ synthesis of benzene-1,3,5-triamido-tris(l-histidine methyl ester) is reported along with attempts at preparing N,N’-bis(pyridylmethyl)-1,3- diaminopropane-2-carboxylic acid (L₂₅), a new water soluble pyridine-amine ligand. The final demetallation step resulted in ligand hydrolysis to the novel amino acid; 1,3-diaminopropane- 2-carboxylic acid which was characterised as its HCl salt by X-ray crystallography.

Chemical catalysts are divided into two traditional categories: homogeneous and heterogeneous catalysts. Although homogeneous (molecular) catalysts tend to have high activity and selectivity, their wide application is hampered by the difficulties in catalyst separation. In contrast, the vast majority of industrial scale catalysts are heterogeneous catalysts based on solid materials. Immobilized catalysts, combining the advantages of homogeneous and heterogeneous catalysts, have developed into an important field in catalysis research. This dissertation presents synthesis, characterization and evaluation of several novel immobilized catalysts. In the first part, MNP supported aluminum isoproxide was developed for ROP of Є-caprolactone to achieve facile magnetic separation of catalysts from polymerization system and reduce toxic metal residues in the poly(caprolactone) product. Chapter 3 presents a silica coated MNP supported DMAP catalyst that was synthesized and displayed good activity and regio-selectivity in epoxide ring opening reactions. In Chapter 4, hybrid sulfonic acid catalysts based on polymer brush materials have been developed. The unique polymer brush architecture permits high catalyst loadings as well as easy accessibility of the active sites to be achieved in this catalytic system. In Chapter 5, aminopolymer-silica composite supported Pd catalysts with good activity and selectivity were developed for the selective hydrogenation of alkynes. In this case, the aminopolymer composite works as a stabilizer for palladium nanoparticles, as well as a modifier to tune the catalyst selectivity. All in all, the general theme of the thesis is developing new immobilized catalysts with improved activity/selectivity as well as easy separation via rational catalyst design.

In recent times, as regulations and legislations for exhaust treatment have become more stringent, a major concern in the arena of environmental catalysis is to find new efficient and economical exhaust treatment catalysts. Chapter 1 is a review of the current status of various NOx abatement techniques and understanding the role of “auto-exhaust catalysts” involved therein. Chapter 2 presents the studies on synthesis of ionically substituted precious metal ions like Pd2+, Pt2+ and Rh3+ in CeO2 matrix and their comparative three-way catalytic performances for NO reduction by CO, as well as CO and hydrocarbon oxidation. Ce0.98Pd0.02O2- showed better catalytic activity than ionically dispersed Pt or Rh in CeO2. The study in Chapter 3 aims at synthesizing 1 atom% Pd2+ ion in TiO2 in the form of Ti0.99Pd0.01O2- with oxide ion vacancy. A bi-functional reaction mechanism for CO oxidation by O2 and NO reduction by CO was proposed. For NO reduction in presence of CO, the model based on competitive adsorption of NO and CO on Pd2+, NO chemisorption and dissociation on oxide ion vacancy fits the experimental data. The rate parameters obtained from the model indicates that the reactions are much faster over this catalyst compared to other catalysts reported in the literature. In Chapter 4 we present catalytic reduction of NO by H2 over precious metal substituted TiO2 (Ti0.99M0.01O2-, where M = Ru, Rh, Pd, Pt) catalysts. The rate of NO reduction by H2 depends on the reducibility of the catalysts. Chapter 5 presents the studies on reduction of NO by NH3 in presence of excess oxygen. 10 atom % of first row transition metal ions (Ti0.9M0.1O2-, where M = Cr, Mn, Fe, Co and Cu) were substituted in anatase TiO2 and TPD study showed that the Lewis and Bronsted acid sites are adsorption sites for NH3, whereas NO is found to dissociatively chemisorbed in oxide ion vacancies. The mechanism of the low temperature catalytic activity of the SCR and the selectivity of the products were studied to understand the mechanism by studying the by-reactions like ammonia oxidation by oxygen. A new catalyst Ti0.9Mn0.05Fe0.05O2- has shown low temperature activity with a broad SCR window from 200 to 400 °C and more selectivity than commercial vanadium-oxides catalysts. We attempted NO dissociation by a photochemical route with remarkable success. In Chapter 6 we report room temperature photocatalytic activity of Ti0.99Pd0.01O2- for NO reduction and CO oxidation by creating redox adsorption sites and utilizing oxide ion vacancy in the catalyst. The reduction of NO is carried out both in the presence and in the absence of CO. Despite competitive adsorption of NO and CO on the Pd2+ sites, the rate of reduction of NO is two orders of magnitude higher than unsubstituted TiO2. High rates of photo-oxidation of CO with O2 over Ti0.99Pd0.01O2- were observed at room temperature. In Chapter 7 the results are summarized and critical issues are addressed. Novel idea in this thesis was to see if both noble metal ions and base metal ions substituted in TiO2 and CeO2 reducible supports can act as better active sites than the corresponding metal atoms in their zero valent state.