Formation of surface-bonded methoxy groups in the sorption of methanol and methyl iodide on zeolites studied by carbon-13 MAS NMR spectroscopy

Terminal and bridging methoxyls on zeolites detected by13C magic angle spinning NMR spectroscopy

“…4) which is (owing to the theoretical value of intermediate electronegativity, S int D 2.32) well in line with the published dependence of the corresponding signal on the actual electronegativity of lattice oxygen. 20 This dependence, completed with new results, is demonstrated in Fig. 4.…”

“…In spite of this, we observe relatively strong signals in the region 48-50 ppm. (ii) It follows from recently published studies 20,21 that signals of bridging-type methoxy groups, originating from the reaction of methylium ions with non-defect structures of various zeolites, are linearly correlated with Sanderson's intermediate electronegativities of the lattice oxygen atoms. For the most basic oxygen, which is present in the structure of CsX zeolite, chemisorbed methylium ion, bonded to this most basic oxygen in a bridging configuration, exhibits a chemical shift of 54 ppm (see Fig.…”

“…The first confirmation of surface methoxy species by 13 C magic angle spinning (MAS) NMR published by Derouane et al 16 was followed by frequent further studies. 2,3,17 -22 Problems associated with the 13 C MAS NMR signals assignment in methanol-zeolite systems were discussed in some recent studies; 2,3,20 however, general agreement has not yet been reached.…”

“…It was proposed 20,21 to rationalize the behaviour of surface methoxy groups in various zeolitic structures using the equalized electronegativity concept. 13 C MAS NMR signals of chemisorbed methylium ions attached to various lattice oxygen atoms depend on their actual electronegativity in the lattice.…”

Characterization of basic guest compounds on solid catalysts by13C CP/MAS NMR spectroscopy of surface methoxy groups

“…and 16 C Ł H 3 I/u.c., respectively. The MAS central lines of both spectra consist of signals due to methoxy groups bound to guest compounds (50-52 ppm 7,20,21 ), methoxy groups bound to zeolitic framework oxygen atoms (55.3 ppm 7,16 -18,20,21 ) and dimethyl ether (61.0 ppm 16,20 ). On the sample loaded with 2 C Ł H 3 I/u.c., about 50% of the methoxy groups are bound to guest compounds (signals at 50-52 ppm).…”