Solid-State NMR Study of Acid Sites in Zeolite Y Using Ammonia and Trimethylamine as Probe Molecules

摘要

The importance of acidic forms of zeolites in heterogeneous catalysis has prompted numerous studies to determine the nature of the acid sites. Many of the techniques have been reviewed recently by Jacobs. Of primary concern in this solid-state NMR study was the possible use of nitrogeneous bases enriched in N as probes of the number and strength of Bronsted acid sites. A similar study has been carried out on zeolite Y using trimethylphosphine as a basic probe molecule. In the pure H-Y form of the zeolite, only one phosphorus resonance was observed in the proton-decoupled mode, although variations in the chemical shift and the spinning side bands upon removal of (CH3)3P at different temperatures suggested the presence of at least two (CH3)3P-H species. One of these is an immobilized complex, attributed to coordination with hydroxyl protons, and the other is a complex which shows a high degree of motion on the NMR time scale. Reprints.