IR experiments under flow of NO and propane on H/Cu-ZSM-5 evidence at 623 K the appearance of bands at 2248, 2157 and 2047 cm(-1), tentatively assigned through the use of (NO)-N-15 to nitrile, carbonyl (CO-Cu+) and isocyano species respectively. Addition of O-2 suggests conversion of isocyano to isocyanato species (2208 cm(-1)) which by hydrolysis leads to NH3 formation, revealed by IR bands at 3366, 3290, 3192 and 1610 cm(-1).