Reaction of NH3 with trichlorosilylated silica gel: a study of the reaction mechanism as a function of temperature

Abstract

Activation of the silica substrate with chlorosilanes increases the ammonia uptake by a factor of 5–10, compared with untreated silica. The reaction mechanism of ammonia with trichlorosilylated silica gel is examined in detail. Physisorbed NH₄Cl causes a shift in the Si—NH₂ stretching vibrations. Several side reactions occur during the chlorosilylation step, the ammoniation step and the thermal treatment of the reacted sample. Amine functions subsequently convert to silazanes and eventually nitrides. A novel mechanism for silazane formation is proposed. The different species on the silica surface are quantified as a function of the reaction temperature.