Study of the organic carbon content of silica gel carbonised by pyrolysis of alcohols

Silica gel partially carbonised by pyrolysis of a mixture of C, aliphatic a nd aromatic alcohols at 773 K for 6 h was studied by means of transmission electron microscopy. temperature-programmed desorption (TPD), reaction gas chromatography, and quantum chemical methods. Pyrolysis of n-heptanol and b enzyl alcohol at the silica gel surface results in formation of the carbon deposit (globules of 100-500 nm on the outer surfaces of silica gel and sma ller carbon particles distributes on the external and internal surfaces of the oxide matrix) and grafted different organic compounds, which begin to d esorb at relatively low temperatures (350-500 K) and activation energies of approximate to 70-120 kJ mol(-1). These compounds are not entirely removed from the surface on washing in solvents and subsequent drying at 470 K, as they can be packed in the pyrocarbon deposit between graphene sheets or in silica gel pores partially filled or blocked by pyrocarbon. Some of these compounds have also the second high-temperature TPD maximum at T close to t he temperature of alcohol pyrolysis. (C) 2001 Elsevier Science B.V. All rig hts reserved.