N2O ORIGIN IN NO REDUCTION WITH NH3 OVER COPPER ZEOLITES

Ammonia oxidation has been studied between 298 to 800 K on zeolite NaY and copper-based catalysts (Cu(x)-NaY, x being the exchange degree). The main product of the reaction was N-2. The rates of NH3 conversion in selective catalytic reduction (SCR) of NO by NH3 (NH3 + O-2 + NO) a nd in NH3 oxidation (NH3 + O-2) were similar on Cu (195)-NaY, but diff ered at lower temperature on Cu(76)-NaY. On Cu(25)-NaY, the rate of NH (3 )conversion in SCR of NO was always much faster. During the SCR of NO on Cu(76)-NaY, two waves of N(2)O( )formation were observed, while on Cu(25)-NaY, no N2O was detected. The formation of N2O at low temper ature was ascribed to the decomposition of ammonium nitrate formed on CuO aggregates. The second N2O formation at a higher temperature resul ted from the ammonia oxidation which occurred either on next-neighbour isolated Cu2+ Or On [CuOCu](2+) dimers. (C) Academie des Sciences/Els evier, Paris.