The interaction of NO with copper ions in ZSM5: and EPR and IR investigation

The interaction of nitric oxide with copper ZSM5 zeolites at room temperature has been studied by EPR and FT-IR spectroscopy in the aim of investigating the surface intermediates involved in the decomposition of NO to N2 and O2. Particular care has been devoted to obtaining a catalyst in a well-defined oxidation state, i.e., with one of the two ionic forms of copper (Cu2+ or Cu+) clearly prevailing on the other. The interaction of NO with Cu2+/ZSM5 yields a reversibly adsorbed nitrosylic adduct easily desorbed upon pumping at 333 K. The species is diamagnetic and bears a partial positive charge. Cu+ is unstable under NO pressure and undergoes oxidation at room temperature. In the early stages of the interaction a paramagnetic nitrosyl of Cu+ is formed having a partial negative charge on NO. This species evolves with time (or NO pressure) towards a diamagnetic dinitrosyl capable of eliminating N2 with simultaneous oxidation of the site to Cu2+.