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 ²⁹Si and ¹³C NMR methods. The 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 (Q₂, Q₃ and Q₄) are clearly resolved in the silica aerogel samples. The calcining process and the loading of metal compounds produce line broadening in the ²⁹Si 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.