The peaks for silanol protons in the high resolution 1H NMR spectrum obtained on mesoporous silica materials may be broadened and shifted downfield by hydrogen bonding with absorbed water molecules. The spectrum may be further complicated by overlapping of the resonance for hydrogen-bonded silanol with the corresponding broad peak due to hydrogen-bonded water. These complications hamper a quantitative analysis of the spectra for these and similar materials. It is demonstrated in this paper that absorbed water can be removed by exposing the sample to dry N2 during magic angle spinning. This results in significantly enhanced spectral resolution for the silanol protons in the 1H 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.
Revised: April 1, 2008 |
Published: May 1, 2005
Citation
Hu J., J. Kwak, J.E. Herrera, Y. Wang, and C.H. Peden. 2005.Line narrowing in H-1 MAS spectrum of mesoporous silica by removing adsorbed H2O using N-2.Solid State Nuclear Magnetic Resonance 27, no. 3:200-205.PNNL-SA-42819.