Parent, Michelle Antoinette2006-07-282006-07-2819971997http://hdl.handle.net/10012/182Heteropoly oxemetalates are ionic solids with discrete cations and anions. Although a wide variety of these exist, those with the Keggin anion, XM12O40^n-(X = P, Si; M = W, Mo), are among those which are most thermally stable. When protons serve as the cations, superacids with an overall chemical formula of HnXM12O40 result. Heteropoly acids (HPA's) are multifunctional, being capable of acting catalytically in oxidation processes or, alternatively as acid catalysts, depending on their elemental composition. Salts of 12-tungstophosphoric, 12-tungstosilicic and 12-molybdophosphoric acids were prepared with stoichiometric and nonstoichiometric quantities of silver(I) and thallium(I) cations. All of the salts except silver 12-molybdophosphate have high surface areas (with at least a 10-fold increase over that observed with the pure HPA) and microporous structures, as shown by analysis of nitrogen adsorption-desorption isotherms, obtained at 77 K. A microporous structure could not be obtained for silver(I) 12-molybdophosphate. Powder X-ray diffraction and infrared spectroscopy confirm that the Keggin anions retain their structure and the substituted cations reside in positions previously occupied by the protons in the heteropoly acid. In contrast, attempts to prepare salts containing the divalent copper(II) cation proved unsuccessful in forming solids with a microporous structure. Studies of the surface and bulk properties revealed that the isolated solids were a mixture of the copper cation and the 12-heteropoly acid. Solid state ion exchange with the monovalent copper(I) cation and the 12-tungstophosphoric acid was also unsuccessful in forming a high surface area solid, although powder XRD patterns indicated that there may be favourable orientation of the anions to facilitate a microporous structure. Solid state ion exchange of the copper(I) ion and the ammonium 12-tungstophosphate salt indicated that migration of the copper)I_ cation into the bulk had occurred although this resulted in a lower surface area and smaller microporous structure than present in the ammonium salt. The Brunauer/Emmett/Teller (BET), MP, Dubinin-Radushkevich (DR) and Horvath-Kawazoe-Satio-Foley (HKSF) methods were used in the analysis of the N2 adsorption-desorption isotherms of the stoichiometric thallium salts of 12-tungstosilicic and 12-molybdophosphoric acids. A comparative study regarding the advantages and disadvantages of each methods is discussed with respect to obtaining information on the surface areas, micropore volumes and pore size distributions. Solid-state 1H NMR studies showed that protons remained in the stoichiometric and nonstoichiometric cesium(I), silver(I) and thallium(I) 12-heteropoly salts, although the numbers decreased as the preparative cation to proton ratio increased. As shown from NH3 TPD studies the distribution of acid strengths shifts as the nature of the cation and stoichiometry of the salt are altered. The cesium(I), silver(I) and thallium(I) 12-heteropoly salts of various stoichiometries were examined as heterogeneous catalysts in the acid catalyzed processes of the isomerization of 1-butene and the dehydration of primary, secondary, and tertiary butanols. In comparison to HPA's, the creation of a microporous structure in the salts increases the accessibility to the protons in the solid lattice; however there is a decrease in the number of available acid sites as the amount of cation substituted into the salt is increased. In addition, the incorporation of a nonprotonic cation causes a shift in the distribution of acidic strengths of the salt, with the disappearance of the strongest acid sites as the cation:proton ratio is increased. Further analysis of the catalytic data indicated that the acidic strength may be the result of a perturbation in the chemical environment by interaction of the nonprotonic cations with the oxygen atoms of the Keggin anions.application/pdf11973668 bytesapplication/pdfenCopyright: 1997, Parent, Michelle Antoinette. All rights reserved.Harvested from Collections CanadaDoctoral Thesis