Line narrowing in H-1 MAS spectrum of mesoporous silica by removing adsorbed H2O using N-2

Abstract

The peaks for silanol protons in the high-resolution H-1 NMR spectrum obtained on mesoporous silica materials may be broadened and shifted downfield by hydrogen bonding with adsorbed water molecules. Overlapping of the resonance for hydrogenbonded silanol with the corresponding broad peak due to hydrogen-bonded water may further complicate the spectrum. These complications hamper a quantitative analysis of the spectra for these and similar materials. It is demonstrated in this paper that adsorbed water can be removed by exposing the sample to dry N-2 during magic angle spinning. This results in significant line narrowing for the silanol protons in the H-1 MAS spectrum. The enhanced spectral resolution makes it possible to quantify the various hydroxyl groups in a complex metal-oxide catalyst. Results obtained on tungsten oxide supported on SBA- 15 mesoporous silica materials are reported. Additionally, the proton chemical shift of tungsten hydroxyl is identified for the first time. (C) 2004 Elsevier Inc. All rights reserved