Kumar, Arun (2013) Industrially important organic transformations over modified solid catalysts. Phd. Thesis thesis, Manipal Institute of Technology, Manipal.

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Abstract

The research on solid catalysts is of immense interest due to several applications in many areas of the chemical industry. An estimated 95 % of the products of chemical industry are based on catalytic processes. Almost all the processes involved in crude oil processing and petrochemical industry such as purification, refining and chemical transformations involve catalysts. Further, organic intermediate products required for plastics, pharmaceuticals, dyes, resins, pigments and crop protection agents are produced by several catalytic technologies. Environmental protection measures such as automobile exhaust control and purification of gases released from power stations and industrial plants would be inconceivable without the use of catalysts. Reasons for widespread use of catalysis are economically and environmentally compelling, as catalytic processes can be carried out under industrially feasible conditions of pressure and temperature. This leads to lower operating costs and yield higher products with fewer by-products compared to non-catalytic processes. In this thesis, an attempt has been made to systematically study of the effect a few selected solid acid and base catalysts in alkylation and catalytic hydride transfer reactions. The thesis has been organized into six individual chapters. Chapter 1 includes introduction and significance of solid catalysts in various domains of chemical industry, importance of solid acid and base metal oxide catalysts and characterization of these materials. The importance of solid acid and base catalysts such as anion modified zirconia and magnesia are outlined. The aims and objectives of the present investigation are also described at the end of this chapter. Chapter 2 deals with the preparation and intensive characterization of tungstate promoted zirconia solid acid catalysts and their application in organic synthesis. To investigate the structural and textural properties, the synthesized catalysts were characterized by various physico-chemical characterization techniques. In this study, tungstate promoted zirconia catalysts were evaluated for selective tert-butylation of catechol. This chapter also describes the effect of variation of different experimental conditions on the selectivity of products and conversion of reactants respectively.Chapter 3 incorporates the investigation of tungstate promoted zirconia catalysts for iso-propylation of m-cresol. Based on the product distribution, a reaction mechanism has been proposed and a kinetic model tested. The results of the theoretical model were found to fit with the experimentally observed data reasonably well. The activation energies for various steps were determined from the estimated kinetic and adsorption parameters. Chapter 4 includes the structure and catalytic activity correlation of different magnesium oxide catalysts obtained from various precursors. In this chapter, a systematic preparation and characterization of magnesium oxide catalysts are described. Dehydrogenation selectivity in the benzyl alcohol reaction was used for investigating the acid-base properties of catalysts at the selected vapor phase reaction conditions. Effort has been made to correlate physico-chemical properties with vapor phase alkylation of aniline with various alcohols on MgO catalysts. Chapter 5 presents an in-house designed and fabricated vapor phase pulse reactor coupled on-line to a GC-MS and its application as a screening tool for rapid testing of small amounts of heterogeneous catalysts for activity towards selected vapor phase organic synthesis. We have employed this system to study the vapor phase catalytic hydride transfer reduction of nitrobenzene with methanol as hydrogen donor on MgO catalyst as a model reaction. Structural information of all the by-products that are formed consistently was useful to understand the reaction mechanism. Response Surface Methodology (RSM) was used to optimise the conversion of reactants and selectivity of products. Chapter 6 describes the details of the experimental work, results and discussion concerning vapor phase catalytic hydrogen transfer reduction of nitrobenzene on an inexpensive catalyst such as MgO, using abundantly available methanol as hydrogen donor. The effect of ZrO2 and ZnO as dopants on the catalytic activity of MgO has been studied. All the three catalysts were characterized by various physico-chemical techniques. Catalytic activity studies have been performed using pulse reactor coupled to a GC-MS as an on-line catalyst testing technique. The feed composition of nitrobenzene, methanol, flow rate and the reaction temperature were optimized to obtain maximum aniline selectivity. Chapter 7 includes summary of the research outcome and future prospects in this area of catalysis.

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