ESR and TPD study of the interaction of nitromethane and ammonia with HZSM-5 and CuZSM-5 zeolites

The properties of complexes formed on HZSM-5 and CuZSM-5 zeolites in the co urse of ammonia and nitromethane adsorption are studied. Ammonia adsorbs on CuZSM-5 and forms two species, which decompose at different temperatures T -dec. One is due to the formation of the Cu2+(NH3)(4) complex (T-dec = 450 K), and the other is assigned to ammonia adsorbed on copper(II) compounds, Cu2+O- and Cu2+-O2--Cu2+, or CuO clusters (T-dec = 650-750 K). Ammonia adso rption on Cu+ and Cu-0 is negligible compared with that on the Bronsted aci d sites and copper(II). Nitromethane adsorbed on HZSM-5 and CuZSM-5 at 400- 500 K transforms into a series of products including ammonia. Ammonia also forms complexes with the Bronsted acid sites and copper(II) similar to thos e formed in the course of adsorption from the gas phase, but the Cu2+(NH3)( 4) complexes on CuZSM-5 are not observed. Possible structures of ammonia an d nitromethane complexes on Bronsted acid sites and the Cu2+ cations in zeo lite channels are discussed. The role of these complexes in selective NOx r eduction by hydrocarbons over the zeolites is considered in connection with their thermal stability.