Removal of olefinic impurities from H-containing chlorofluorocarbons: R.M. Jansen Hoechst A.G. Eur. Pat. Appl. 511,612, Nov. 4, 1992; Ger. Appl. Apr. 27, 1991

Abstract

New and powerful solid-state NMR techniques have been developed in the last 10–15 years. This paper reports on some applications on the location and structure of acid sites in zeolites. The distribution and location of acid sites is one of the fundamental questions. By means of the 13C-11B and 13C-27Al heteronuclear dipole interaction, an analysis of the spatial orientation of structure-directing agents towards the B and Al atoms in the framework of a variety of zeolites (CIT-1, SSZ-24, Beta, SSZ-13, SSZ-16, ITQ-3, ITQ-4, ZSM-12, Octadecasil) has been studied. This, leads to interesting information about the mechanism of structure-direction and the location of heteroatoms, implanted into the zeolite structure. Charge ordering between the negative framework charge (B or Al sites) and quaternary ammonium cations was a general result observed by these dipolar NMR methods. 11B and 27Al quadrupolar interactions in the activated acid forms of boron or aluminum zeolites are generally large due to a strong bond distortion around the heteroatom. These quadrupolar interactions are correlated with coordination symmetries and structural distortions. The dipolar interaction is also a useful probe to characterize the proton sites associated with distorted B or Al framework atoms, and to investigate the nature of adsorbed species and their distances to the framework. A crucial advantage of the dipolar interaction compared to other NMR interactions is that it can be analyzed directly without the need of model assumptions.