The reactivity of different nitrogen-containing compounds, which may be formed as intermediates during the selective catalytic reduction of nitrogen oxides with organic compounds over alumina (HC-SCR), has been investigated in the temperature range of 60-610 degrees C in a flow reactor system equipped with an FTIR gas analyzer. Tert-butylnitrile N-oxide (t-CNO), t-butyl isocyanate (t-NCO) and t-butyl cyanide (t-CN) were used as model compounds. The reactivity tests comprised the decomposition and oxidation reactions in a stream of O-2 and Nz, and in mixtures of NO2 or NO with O-2 (HC-SCR conditions). These studies revealed that t-CNO isomerizes readily to t-NCO and then decomposes to CO2 and I-butylamine. The latter rapidly reacts with NO2 to form N-2 or further decomposes into isobutene and NH3, which may be followed by the conventional SCR with NH3 as a reducing agent. This suggests that once nitrile N-oxides are formed under HC-SCR conditions they are readily converted to N-2 through several reaction steps.