Chemical Structural Analysis of Y-Zeolites and Mordenites by High-Resolution Solid-State NMR

Abstract

The high-resolution magic-angle-spinning (HRMAS) solid-state 29Si- and 27AI-NMR have been used in the chemical structural analysis of the synthetic zeolites. Y-zeolites (JRC-ZY 4.8 and -Y 5.6), proton-exchanged Y-zeolites (JRC-Z-HY 4.8 and -HY 5.6), mordenites (JRC-Z-M 10, -M 15 and -M 20) and proton-exchanged mordenites (JRC-Z-HM 10, -HM 15and -HM 20) given by the Catalysis Society of Japan have been investigated in this study.²⁹Si-MASNMR has permitted an identification of five distinct Si/Al orderings and the oretical Si/Al ratios on zeolitic frameworks by the computer-deconvolution of ²⁹Si-MASNMR spectra (eg. Fig.1). On the other hand the isotropic chemical shifts from ²⁷Al-MASNMR have revealed the Al-O coordinations in a zeolitic complete framework or in a noncomplete framework.
It was considered that the Si/Al ratios on zeolitic frameworks of Y-zeolites (JRC-Z-Y 4.8and -Y 5.6) have increased during the proton exchange. Especially the chemical ordering of Y-zeolite with low Si/Al ratio (JRC-Z-Y 4.8) by chemical analysis has markedly changed (Fig.2, Tables 1 and 2). This behavior has been more appreciably observed in the "AlMASNMR spectra (Fig.3, Table 3). These results have suggested that the dealumination from the zeolitic frameworks of Y-zeolites has taken place though the -Si-O- bondings have been remained.
On the other hand, with regard to the mordenites (JRC-Z-M 10, -M 15 and -M 20), no appreciable change in the Si/Al configurations on zeolitic frameworks have been spectrally observed during the proton exchange (Figs.5 and 6, Tables 4, 5 and 6). In addition, the crystallinities and some distinct tetrahedral locati ons in the Si(OAl)_n(OSi)_4-n environments of Y-zeolities and mordenites have been discussed. t Characterization of Zeolites. I.