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 the species deposited on Co-ZSM5 during the decomposition of nitromethane. At 553 K deactivation commences after 60 min, This is accompanied by the formation of bands due to NCO species between 2150 and 2300 cm(-1) and the sudden 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, which cause deactivation by blocking zeolite channels. The most likely chemistry is an initial dehydration of nitromethane to isocyanic acid (HNCO) which forms melamine by reaction with ammonia derived by hydrolysis of HNCO. Cyanuric acid, the cyclic trimer of HNCO, may be an intermediate in the process. (C) 1999 Academic Press.