Thermal decomposition of ZSM—5 and silicalite precursors

Abstract

The combined technique of thermogravimetric analysis and mass spectrometry was used to observe the thermal decomposition of the following silicalite and zeolite precursors: tetraethylammonium-silicalite, tetrapropylammonium-silicalite, tetraethylammonium-ZSM—5, tetrapropylammonium-ZSM—5, methylamine-ZSM—5 and propylamine-ZSM—5. It was possible to distinguish the organic base molecules associated with acid sites from those not associated with acid sites by the composition of the evolved volatiles. Reaction sequences for the decomposition of the precursors have been proposed which involve a Hofmann elimination reaction followed by β-elimination reactions for tetraalkylammonium ions not associated with acid sites, and sequential Hofmann reactions for organic ions at acid sites. For the amine-ZSM—5 decompositions the physisorbed amines are evolved, unreacted, at ≈180°C while the amines at the acid sites undergo elimination reactions between 350° and 500°C.