Effect of surface methoxy groups on the 27Al quadrupole parameters of framework aluminum atoms in calcined zeolite H–Y

Via conversion of 13C-enriched methanol and applying a new stopped-flow protocol, the Brønsted acid sites (SiOHAl groups) of a calcined zeolite H–Y were highly covered by surface methoxy groups (SiOCH3Al). These methoxy groups (δ13C=56.6 ppm) were formed at bridging OH groups in the direct vicinity of framework aluminum atoms. The methylated zeolite Y was used to perform first 27Al spin-echo NMR investigations of the influence of surface methoxy groups on zeolitic framework aluminum atoms. The formation of methoxy groups on calcined zeolite H–Y was found to decrease the 27Al quadrupole coupling constant of framework aluminum atoms from 14.8±0.2 MHz (uncovered SiOHAl groups) to 12.8±0.2 MHz (SiOCH3Al).