Solid state NMR investigation of silica aerogel supported Fischer-Tropsch catalysts

The Fischer-Tropsch (F-T) catalyst is the critical component for the F-T synthesis of a variety of hydrocarbons from syngas. Fischer-Tropsch cobalt, iron and ruthenium catalysts supported on silica aerogel have been prepared using a combination of sol-gel chemistry and vapor phase deposition methods. Solid state NMR spectroscopy, a very powerful technique for analyzing the structure and dynamics of various materials, was employed in the study of these F-T catalyst systems. The silica aerogel supported F-T catalysts have been investigated using both solid state (29)si and C-13 NMR methods. T he silica aerogel's tetrahedral sub-unit structure and the influence of the loaded metal compounds have been observed. Three types of Si(O-1/2)(4) tetrahedral unit structure (Q(2), Q(3) and Q(4)) are clearly resolved in the silica aerogel samples. The calcining process and the loading of metal compounds produce line broadening in the Si-29 spectra sufficient to prevent clear resolution of the three distinct Q(n) spectral lines, but the broadened spectra indicate that the three Q sub-unit structures are still present. The ferrocene and ruthenocene molecules used in the vapor phase deposition method exhibit a rapid exchange within the silica aerogel support similar to what one would expect in the gas or liquid state. (C) 2006 Elsevier B.V. All rights reserved.