FTIR studies of the origin of deactivation during the decomposition of nitromethane on Co-ZSM5

In situ Fourier transform infrared spectroscopy has been used to observe th e species deposited on Co-ZSM5 during the decomposition of nitromethane. At 553 K deactivation commences after 60 min, This is accompanied by the form ation of bands due to NCO species between 2150 and 2300 cm(-1) and the sudd en development of a very strong band at 1662 cm(-1). The latter band can be assigned to the s-triazine compound, melamine, and/or derivatives of it, w hich cause deactivation by blocking zeolite channels. The most likely chemi stry is an initial dehydration of nitromethane to isocyanic acid (HNCO) whi ch forms melamine by reaction with ammonia derived by hydrolysis of HNCO. C yanuric acid, the cyclic trimer of HNCO, may be an intermediate in the proc ess. (C) 1999 Academic Press.