This project consists of a set of studies addressing the issue of acidity in zeolites and related materials. Intermediates in H-ZSM-5 are studied spectroscopically - nuclear magnetic resonance being the prime tool - to characterize species whose stoichiometry and reactivity have been established separately; the objectives are the determination of the structure of the intermediates, the nature of their interactions with the zeolite lattice, and the barrier heights for them to undergo further transformations. The effect of various dealumination procedures and the roles of framework and nonframework aluminum concentrations are examined by preparation of and investigation of the acidity of a series of well-characterized H-Y zeolites; acidity surrogates used include temperature- programmed desorption and thermal gravimetric analysis of amines, alkane cracking, and alkali-metal poisoning. A series of metal-substituted ZSM-5 and ALPO-5 molecular series are prepared and examined to determine the relative acid strengths of these materials and to determine the necessary conditions for maintaining the metal ions in the framework. Zeolites are already widely used in the petroleum and chemicals industries both as catalysts and separations media. Despite this, factors influencing their performance are poorly understood. This work promises an approach to more rational design for applications of zeolites and related framework materials, better quality control over synthetic zeolites, and possible new applications of known or new framework materials in chemical processing, environmental control, and other areas.
