Highly resolved proton magnetic resonance spectra of hydroxyl groups in hydrogen-zeolites

Abstract

With magic angle spinning of glass ampoules containing dehydrated hydrogen-zeolites, four different proton magnetic resonance lines at 270 MHz could be separated. The line at highest magnetic field (1.8 ppm with respect to TMS) is due to non-acid OH groups formed on zeolite crystal surfaces (terminal hydroxyl groups) and at crystal defects. The two lines at medium field (3.9–4.6 and 4.8–5.6 ppm) are caused by the acid or so-called structural OH groups giving rise to low- and high-frequency bands in infrared spectra, and the major part of the signal at the lowest magnetic field (7.0–7.5 ppm) is attributed to residual NH 4 + ions of the zeolite. An advantage of this technique compared with infrared spectroscopy is that the band areas are strictly proportional to the number of protons contributing to the signal.