NMR characterization, acidity and stability studies of some modified zeolites

A number of pentasil type zeolites were prepared incorporating boron or gallium. The chemical environment of boron and gallium in modified zeolites was investigated by ²⁹Si, ²⁷Al, ¹¹B, and ⁷¹Ga magic-angle spinning (MAS) NMR. The ¹¹B spectra showed a number of peaks and indicated the incorporation of boron mostly in tetrahedral environments. The framework Si/Al ratios in these zeolites have been worked out from the intensities of different peaks in the silicon spectra. Temperature-programmed desorption results showed a marked decrease in the acidity of the zeolites when boron or gallium was incorporated. Thermal analysis results indicated that both boron and gallium substitution decreased the thermal stability of the zeolites.