Cu-ZSM-5 and Cu-AITS-1 catalysts were prepared by solid state ion exchange and studied in DeNO(x) reactions. A NO3 type surface complex was found to be an active intermediate in the decomposition of NO and N2O. Copper was oxidized to Cu2+ in the decomposition reactions. Oscillations at full N2O conversion were observed in the gas phase O-2 concentration, without any change in the N-2 concentration. The oscillation was synchronized by gas phase NO formed from the NO3 complex. The same complex seems to be an active intermediate also in NO selective catalytic reduction (SCR) by methane, whereas carbonaceous deposits play a role in NO SCR by propane. TPD reveals that only 10-20% of the total copper in the zeolites participates in the catalytic cycles.