Silicon-29 cross-polarization/magic angle spinning NMR evidence for geminal silanols on vacuum-activated aerosil silica

Silicon-29 CPMAS NMR spectroscopy has been used to study aerosil silica which has been activated under vacuum up to 1000/degrees/C and where spectra have been recorded with samples still under vacuum. For all temperatures up to 800/degrees/C activation, a signal due to geminal (Si(OH)/sub 2/) silanol groups was detected, thus clearly demonstrating for the first time that these species exist on aerosil silicas which have been vacuum activated in this temperature range. Line broadening occurs for 1000/degrees/C activation, and the geminal signal cannot be distinctly resolved.