Synthesis, Characterization and Catalytic activity of Zirconia-Ceria catalysts

Title

Synthesis, Characterization and Catalytic activity of Zirconia-Ceria catalysts

Creator

S Jayashree

Description

The development of catalysts is critical for the economical and environmentally efficient generation of chemical compounds that underlie every aspect of our society. Catalysts are key players in research involving the discovery of pharmaceuticals, materials, and polymers. In addition, catalysis is especially powerful in bulk synthesis, allowing the production of compounds, polymers and commodity chemicals via routes that would otherwise be impossible. Ceria is the unique rare earth for which dioxide is the normal stable phase contrary to the others for which Ln2O3 is the normal stoichiometry. The applications of ceria based materials are related to a potential redox chemistry involving Ce(III) and Ce(IV), high affinity of the element for oxygen and sulphur and absorption/excitation energy bands associated with its electronic structure. Zirconium is one of the more abundant elements, and is widely distributed in the Earth's crust. Being very reactive chemically, it is found only in the combined state or as part of a complex of oxides as in zircon, elpidite, and eudialyte. Doping ceria with zirconia may improve the oxygen storage properties of ceria at three different levels. At the level of the microstructure, it inhibits surface diffusion and in turn the loss of surface area at high temperatures. At the microscopic level, substantial doping may result in the formation of an interface structure that facilitates the oxygen transport from bulk to the surface. At the atomic-level, it stabilizes the oxygen defective structure. The texture, structure and thermal stability of ceria-zirconia doped oxides are closely related to the ratio of cerium to zirconium in the solid solution. Chapter 1 comprises of the general introduction of catalysis, importance of solid acid catalysis, sulphated metal oxides, pure ceria, pure zirconia, modified ceria and zirconia. It gives a brief introduction about the nitration of toluene. The aim and objectives of the present investigation are also described at the end of this chapter. Chapter 2 comprises of a thorough literature survey on the significance of solid acid and super acid catalysts in various domains of chemical industry and importance of anion promoted zirconia and ceria catalysts. The definition of ??super acid and their classification vii on the basis of origin of the active sites are also outlined. Importance of modified metal oxides is also outlined. Chapter 3 deals with the experimental procedures and techniques employed in this investigation. Scientific aspects of the precipitation and impregnation methods were outlined. The experimental details of surface area measurements by BET method, application of X-ray powder diffraction studies for crystalline phase and size determination, elemental detection by EDAX, spectral details from FTIR and thermal stability by TGA have been described. Chapter 4 deals with the various characterization results and discussion of pure, doped and sulphated Zirconia-ceria solid acid catalysts. The bulk and surface properties of the catalyst was discussed by XRD, BET surface area, TGA and FTIR. All characterization results revealed that the incorporated sulphate ions has a significant influence on the surface and bulk properties of the ZrO2-CeO2 catalyst. The prepared catalysts are investigated for the liquid phase nitration of toluene under various reaction conditions. Chapter 5 gives with the summary and conclusion of the present study. It also gives the future scope of the present study. On the whole, zirconia-ceria solid acid catalysts were successfully synthesized by simple route. Physicochemical characterization of all these catalysts revealed that the loaded sulphated and doped metal oxides show a significant influence on the surface and bulk properties of the ZrO2 - CeO2. These catalysts are found to be active for the liquid phase nitration of toluene. Key words: Solid acid catalysis, Zirconia-Ceria, Sulphated zirconia-ceria, Nitration of toluene

Source

Chemistry

Date

2012