New supported transition metal complexes: synthesis, characterization and application as catalysts for oxidation/hydrodesulphurization reactions

This thesis deals with the synthesis and charcterisation of some supported transition metal complexes and their catalytic properties. Two industrially important reactions were carried out: i) cyclohexanol oxidation and ii) hydrodesulphurization of diesel. Thesis is divided into nine chapters. An overview of the heterogenised homogeneous systems is given in Chapter 1. Chapter 2 deals with the materials and methods used for the preparation and characterisation. Details regarding the synthesis and characterisation of zeolite encapsulated transition metal complexes are given in Chapter 3 to Chapter 7. In Chapter 8, the results of catalytic activity studies of the cyclohexanol oxidation using the zeolite encapsulated complexes are presented. Details of preparation of hydrodesulphurization catalysts through the molecular designed dispersion method, their characterization and catalytic activity studies are presented in Chapter 9. References are given at the end of the thesis.

Studies on some supported transition metal complex and metal oxide catalysts for oxidation reactions

Zeolite encapsulated transition metal complexes have received wide attention as an effective heterogenized system that combines the tremendous activity of the metal complexes and the attractive features of the zeolite structure. Zeolite encapsulated complexes offer a bright future for attempts to replace homogeneous systems retaining its catalytic activity and minimizing the technical problems. especially for the partial oxidation of organic compounds. Studies on some zeolite encapsulated transition metal complexes are presented in this thesis. The ligands selected are technically important in a bio-mimetic or structural perspective. Attempts have been made in this study to investigate the composition, structure and stability of encapsulated complexes using available techniques. The catalytic activity of encapsulated complexes was evaluated for the oxidation of some organic compounds. The recycling ability of the catalyst as a result of the encapsulation was also studied.Our studies on Cu-Cr/Al2O3, a typical metal oxide catalyst. illustrate the use of design techniques to modify the properties of such conventional catalysts. The catalytic activity of this catalyst for the oxidation of carbon monoxide was measured. The effect of additives like Ce02 or Ti02 on the activity and stability of this system was also investigated. The additive is potent to improve the activity and stability ofthe catalyst so as to be more effective in commercial usage.

A comparative study of medium and large pore zeolites in alkylation reactions

In this thesis an attempt has been made to compare the catalytic activity of some medium and large pore zeolites in a few alkylation and acylation reactions. The work reported in the present study is basically centered around the following zeolites namely, ZSM-5, mordenite, zeolite Y and beta. The major reactions carried out were benzoylation of o-xylene, propionylation of toluene and anisole and benzylation of 0xylene.The programme involves the synthesis, modifications and characterization of the zeolite catalysts by various methods. The influence of various parameters such as non-framework cations, Si/AI ratio of zeolites, temperature of the reaction, catalyst concentration, molar ratio of the reactants and recycling of the catalysts were also examined upon the conversion of reactants and the formation of the desired products in the alkylation / acylation reactions.The general conclusions drawn by us from the results obtained are summarized in the last chapter of the thesis. Zeolite beta offers interesting opportunities as a potential catalyst in alkylation reactions and the area of catalysis by medium and large pore zeolites is very fascinating and there is plenty of scope for further research in this field. Moreover, zeolite based catalysts are effective in meeting current industrial processing and more stringent environment pollution limits.

Acetalization of ketones on K-10 clay and rare earth exchanged HFAU-Y zeolites: A mild and facile procedure for the synthesis of dimethylacetals

Dimethylacetals of ketones; cyclohexanone, acetophenone, and benzophenone have been prepared by reacting ketones with methanol under mild reaction conditions. Large pore zeolites (H-Y and its rare earth metal, Ce3+, La3+, and RE3+ modified forms), and mesoporous clay (K-10 montmorillonite and its cerium exchanged counterpart) with regular pore structure, silica and silica-alumina have been used as catalysts. Clay catalysts are found to be much more active than zeolites, thanks to slightly bigger pore size. The nature of the pores of the solid acid catalysts determine acetalization efficiency of a particular catalyst. As evidenced by the reaction time studies, the catalyst decay is greater over the zeolites than over the clays. Carrying out the reaction with ketones of different molecular sizes it is shown that K-10 clays and rare earth exchanged H-Y zeolites are promising environmentally friendly catalysts for their use in the production fine chemicals.

Effect of pore size on the catalytic activities of K-I 0 clay and H-zeolites for the acetalization of ketones with methanol

One-pot acetalizations of cyclohexanone. acetophenone and benzophenone were carried out using methanol over H-montmorillonite clay (a mesoporous material). silica, alumina, and different zeolites such as HFAU-Y.HBeta, H-ZSM-5, and H-mordenite. In all the cases a single product-the corresponding dimethylacetal-was obtained in high yields. Hemiacetal formation was not observed with any catalyst. A comparison of catalytic activity indicated that montmorillonite K-10 is the most active catalyst for the reaction. As evidenced by the reaction time studies, the catalyst decay is greater over the zeolite catalyst than over the clay.

Lewis acidity of rare earth exchanged zeolites

The Lewis acidity of yttrium and dysprosium exchanged zeolite Y and ZSM-5 has been determined by titration method using Hammett indicators. The acidity of the Y form increases with increase in concentration of the rare earth cation in the Y zeolite. It is independent of the amount of the rare earth ion for ZSM-5. The data have been correlated with the activity of these zeolites for the esterification of butanol using acetic acid.

Beckmann rearrangement of E,E-cinnamaldoxime on rare earth exchanged (Ce3+, La3+, and RE3+) HFAU-Y zeolites: An efficient green process for the synthesis of isoquinoline

In this paper, a novel application of solid acid catalysts in the Beckmann rearrangement of E,E-cinnamaldoxime in the synthesis of an important heterocyclic compound; isoquinoline is reported. E,E-Cinnamaldoxime under ambient reaction conditions on zeolite catalysts underwent Beckmann rearrangement to produce isoquinoline in yields of ca. 86–95%. Cinnamonitrile and cinnamaldehyde were formed as by-products. LaH-Y zeolite produces maximum amount of the desired product (yield 95.6%). However, the catalysts are susceptible for deactivation due to the basic nature of the reactants and products, which neutralize the active sites. H-Y zeolite is more susceptible (22% deactivation in 10 h) for deactivation compared to the cerium-exchanged counterpart (18% deactivation in 10 h). Thus, the optimal protocol allows isoquinoline to be synthesised in excellent yields through the Beckmann rearrangement of cinnamaldoxime. The reaction is simple, effective, does not involve any other additives, and environmentally benign.

Studies on some new Schiff base complexes of ruthenium and neodymium

In the present study an attempt has been made to synthesize some simple complexes of multidentate ligands. Analogous zeolite encapsulated complexes were also synthesized and characterized. Immobilization on to polymer supports through covalent attachment is expected to solve the problem of decomposition of many complexes during catalytic reaction. Hence the work is also extended to the synthesis and characterization of some polymer supported complexes of Schiff base Iigands. All the three types of synthesized complexes, simple, zeolite encapsulated and polystyrene anchored, were subjected to catalytic activity study towards catechol-oxidation reaction. A selected group of complexes were also screened for their catalytic activity towards phenol-oxidation reaction. Biological screening of the synthesized ligands and neat complexes were done with a view to establish the effect of complexation on biological systems.

Studies on Simple and Encapsulated Transition Metal Complexes of Schiff Bases Derived from Diaminonaphthalene

Schiff base complexes of transition metal ions have played a significant role in coordination chemistry.In the present study we have synthesized some new Mn(II),Co(II) and Cu(II) complexes of Schiff bases derived from 1,8-diaminonaphthalene.Even though we could not isolate theses Schiff bases (as they readily cyclise to form the perimidine compounds),we were able to characterize unequivacally the complexes synthesized from these compounds as complexes of Schiff Bases. We Synthesized three perimidine derivatives ,2-(quinoxalin-2-yl)-2,3-dihydro-1H-perimidine,2-(2,3-dihydro-1H-perimidin-2-yl)-6-methoxyphenol and 4-(2,3-dihyro-1H-perimidin-2-yl)-2-methoxyphenol by the condensation of 1,8-diaminonaphthalene with quinoxaline-2-carboxaldehyde,2- hydroxy-3-methoxybenzaldehyde or 4-hydroxy-3-methoxybenzaldehyde respectively.Theses compounds were used as precursor ligands for the preparation of Schiff base complexes.The complexes were characterized by using elemental analysis ,conductance and magnetic susceptibility measuremets ,infrared and UV-Visible spectroscopy ,thermogravimetric analysis and EPR spectroscopy .We also encapsulated the complexes in zeolite Y matrix and these encapsulated complexes were also characterized. We have also tried theses complexes as catalysts in the oxidation of cyclohexanol and decomposition of hydrogen peroxide.

Simple and Encapsulated Transition Metal Complexes of Schiff Bases Derived from Quinoxaline-2-Carboxaldehyde and Diamines: Biological and Catalytic Activity Studies

This thesis is mainly concerned with the synthesis and characterisation of new simple and zeolite encapsulated transition metal (manganese(II),nickel(II),and copper(II)complexes of quinoxaline based double Schiff base ligands.Theses ligands are N,N'-bis(quinoxaline-2-carboxalidene)hydrazine,N,N'-bis(quinoxaline-2-carboxalidene)-1,2-diaminoethane,N,N'-bis(quinoxaline-2-carboxalidene)-1,3-diamonopropane,N,N'-bis(quinoxaline-2-carboxalidene)-1,4-diaminobutane,N,N'-bis(quinoxaline-2-carboxalidene)-1,2-diaminocyclohexane and N,N'-bis(quinoxaline-2-carboxalidene)-1,2-diaminobenzene.The Schiff base ligands have been characterised by spectral and single crystal XRD studies.Theses ligands provide great structural diversity during complexation.Mn(II) and Ni(II) form octahedral with these Schiff bases,whereas Cu(II) forms both octahedral and tetrahedral complexes.Studies on the biological and Catalytic activity of the copper(ll) complexes are also presented in this thesis.

“A comparative study of medium and large pore zeolites in alkylation reactions”

Zeolites have established themselves as industrial catalysts for over two decades for a variety of hydrocarbon processing reactions where acidity and shape selectivity are important factors. As solid catalysts, zeolites may be advantageous and superior compared to their homogenous counterparts due to their characteristic properties. It is only in recent years that the utility of zeolites for organic synthesis is recognized for producing specific organic intermediates and fine chemicals in high selectivity. In this thesis an attempt has been made to compare the catalytic activity of some medium and large pore zeolites in a few alkylation and acylation reactions. The work reported in the present study is basically centered around the following zeolites namely, ZSM-5, mordenite, zeolite Y and beta. The major reactions carried out were benzoylation of o-xylene, propionylation of toluene and anisole and benzylation of oxylene. . The programme involves the synthesis, modifications and characterization of the zeolite catalysts by various methods. The influence of various parameters such as non-framework cations, Si/Al ratio of zeolites, temperature of the reaction, catalyst concentration, molar ratio of the reactants and recycling of the catalysts were also examined upon the conversion of reactants and the formation of the desired products in the alkylation/ acylation reactions. The general conclusions drawn by us from the results obtained are summarized in the last chapter of the thesis. Zeolite beta ofi'ers interesting opportunities as a potential catalyst in alkylation reactions and the area of catalysis by medium and large pore zeolites is very fascinating and there is plenty of scope for further research in this field. Moreover, zeolite based catalysts are effective in meeting current industrial processing and more stringent environment pollution limits.

Alkylation of Benzene with higher olefins over zeolites: A green route for lab synthesis.

The objective of the present work is to improve the textural and structural properties of zeolite-Y through ion exchange with rare earth metals. We meant to obtain a comparative evaluation of the physicochemical properties and catalytic activity of rare earth modified H-Y, Na-Y, K-Y, and Mg-Y zeolites. Friedel-Crafts alkylations of benzene with higher 1- olefins such as 1-octene, 1-decene, and 1dodecene for the synthesis of linear alkylbenzene (LAB) have been selected for the present study. An attempt has also been directed towards the correlation of the enhancement in 2-phenylalkane formation to the improvement in the textural and structural properties upon rare earth modification for the zeolite-Y. The present method for LAB synthesis stands as an effective Green alternative for the existing hydrofluoric acid technology