Determination of Acidity Functions of Liquid Acids by C-13 NMR and Development of a Theoretically Justified Calibration of Solid Acidity

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ABSTRACT CTS-9528412 This is an extension of the earlier development of a nuclear magnetic resonance (NMR) spectroscopic method for determining Hammett acidity functions for real catalysts. The main thrust is the application of the method to solid "acids", a class of materials to which the Hammett acidity concept does not apply. A parameter named "relative protonating ability" is defined and used for acid "strength" comparisons; it is determined by protonation of indicators at stoichiometric ratios to the acid sites or molecules. Both traditional solid acids as well as materials formed by surface treatment of solids are studied, including heteropolymetallates, sulfated metal oxides, and zeolites. To expand the measureable acidity range, fluorinated alkenones and aromatic hydrocarbons are studied as possible indicators. The dependence of protonation on temperature is studied from -80( C to 200( C. The acid strengths are correlated with catalytic activity for well-studied reactions such as isomerizations of olefins or paraffins. Solid acids are being used with increasing frequency in industrial processes because of their perceived environmental advantages. However, adequate objective measures of their acid strength are not available. In addition, there is controversy about how acidity in solids should be defined. These issues are addressed in this project. This project is supported jointly by the Divisions of Chemical and Transport Systems and of Chemistry. ***