Gaydhankar, T. R. (2012) Studies on the solid acid catalysts containing group VI elements: synthesis, characterization and screening for their catalytic activities. PhD thesis, CSIR-National Chemical Laboratory, Pune, India.

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Abstract

Zirconia has attracted considerable interest owing to its broad range of applications in various fields, ranging from catalysis to high performance transformation-toughened structural engineering ceramics, solid oxide fuel cells, gas sensors, electro-optical materials, fabrication, automotive exhaust treatment, etc., in addition to the classical application of catalyst support. But zirconia has poor thermal stability and is known to sinter at high temperatures, which leads to catalytic deactivation. Therefore, more efforts have been devoted in recent years to design a suitable porous zirconia having enhanced thermal stability, high surface area and catalytically active tetragonal phase. After, exhaustive literature survey, very few reports are found wherein tetragonal phase along with high surface area zirconia are stable at higher temperatures, however it is seen that the detailed comparative studies are not reported. As a result optimization of synthesis parameters for the preparation of high surface area tetragonal zirconia with good thermal stability using facile synthesis procedures was the primary objective of this work. The emphasis has been placed on the characterization of the structure at each stage of the route, leading to an understanding of the various possible mechanisms that play an important role in stabilizing the tetragonal zirconia. This study has also provided an opportunity to investigate broader issues concerning the solution based processing of zirconia. The redox and catalytic properties of porous zirconia and zirconia supported materials as composite oxides are dependent upon numerous factors, which include crystallite size, phase modification, acidity, oxidation state, dispersion, morphology etc. In addition, catalyst prepared with in nano-meter scale results in increasing the specific surface area, narrow pore size distribution, ordered channels, thus improving the catalytic performance. In order to enhance the thermal stability of tetragonal zirconia and its acidic nature, incorporation of the Group VI elements of the periodic table such as chromium, molybdenum and tungsten oxides which are thermally more stable than sulfated zirconia, is required. Especially, MoO3 and WO3 supported zirconia when calcined at high temperatures are found to be highly acidic and used as a powerful catalyst for vide variety of industrially important acid catalyzed reactions. Therefore, it is interesting to investigate the structural and catalytic properties of novel MoO3 and WO3 supported zirconia composite oxide materials. However the nature, number and strength of acid sites, morphology, surface area, pore size, surface density, suitable phase for high selectivity toward the desired products etc and other physicochemical properties of solid acid catalyst strongly relies on the preparation methods, precipitating agent, starting precursors, calcination temperature, pre-treatment etc. Generally, two main methods are most commonly reported in the literature for the preparation of metal oxides; the conventional precipitation method and sol-gel method. However, most of the synthesis routes to prepare high surface area of t-ZrO2 supported solid acid catalyst are complicated and require tedious procedures involving close control of synthesis parameters such as temperature, pressure, pH, and/or the use of relatively expensive zirconium alkoxides. In such context, simple and easy synthesis routes are highly desired especially for the practical applications of ZrO2 based solid acid catalyst with high surface area. Therefore in the present investigations, MoO3 and WO3 supported zirconia solid acid catalyst, possessing high specific surface area and better thermal stability are synthesized. The thermal and structural stability of the solid acid catalyst prepared during these studies are strongly influenced by the synthetic methodology. All the samples are systematically characterized by using various analytical and spectroscopic techniques; the data obtained are co-related with synthesis parameters. This requires a wide range of complementary characterization techniques, including Powder XRD, N2 adsorption-desorption, TG-DTA, TEM, SEM, UV-Vis, RAMAN, NH3-TPD, XRF, AAS, ICP, SAXS, FT-IR and TPD. In conclusion, thermally stable high surface area, pure zirconia, molybdenum and tungsten oxide supported zirconia solid acid catalyst are successfully prepared after optimization of various synthesis parameters. Physico-chemical characterization of all these materials show that they are thermally stable up to 800 oC temperature; possessing high surface area, tetragonal phase and excellent textural properties. The results of this investigations contribute not only to the understanding of a particular route for processing zirconia based materials, but also to a broader understanding the effects of various other synthesis parameters on the physical and chemical properties of the catalyst. Molybdenum oxide supported zirconia solid acid catalyst is utilized for organic synthesis involving biologically important molecules.

Item Type: Thesis (PhD)
Additional Information: Co-guide Nikalje,M.D.
Subjects: Catalysis and Surface Science
Materials Chemistry
Divisions: UNSPECIFIED
Depositing User: Tejas R Gaydhankar
Date Deposited: 04 Jan 2013 11:54
Last Modified: 26 Jul 2017 08:15
URI: http://ncl.csircentral.net/id/eprint/1055

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