Relationships between basicity and reactivity of zeolite catalysts
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A wide variety of characterization methods, including UV-vis spectroscopy of adsorbed I2, microcalorimetry of CO2 adsorption, and x-ray absorption spectroscopy at the Cs LIII edge of zeolite cations, was applied to a series of alkali containing zeolites in order to elucidate the nature of the basic sites on these materials. In addition, three catalytic reactions involving basic zeolites were studied. In the first case, alkali-exchanged zeolites (L, Beta, X and Y) were used as catalysts for the side-chain alkylation of toluene with methanol to form styrene and ethylbenzene. Zeolites with low base site densities and appropriate base strengths catalyzed toluene alkylation without decomposing methanol to carbon monoxide. In the second example, ruthenium metal clusters were supported on alkali and alkaline earth exchanged X zeolites and tested as catalysts for ammonia synthesis. Zeolites containing alkaline earth ions exhibited rates greater than those containing alkali ions. Finally, zeolite X loaded with alkali metal was an active catalyst for toluene alkylation with ethylene whereas zeolite X loaded with alkali oxide was inactive for the reaction. These results suggest that exciting opportunities exist for the use of basic zeolites as catalysts and catalyst supports.
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