The selective catalytic reduction of NO with ethanol in the presence of oxygen excess was studied over H-ZSM-5 and Ag/H-ZSM-5 catalysts. Temperature programmed surface reaction (TPSR) studies were performed in order to: (i) assess the effect of replacing NO by NO 2 , (ii) evaluate the catalysts performance and (iii) study the formation of organic and organo-nitro compounds, as a result of nitrogen oxides and ethanol interaction.When using NO 2 instead of NO, an almost complete conversion of NO 2 is observed on zeolite acid sites, giving rise to NO and partial oxidized hydrocarbons. NO x conversion is higher on Ag/H-ZSM-5 (48% vs. 19%) but it is not greatly affected when NO is replaced by NO 2 .Steady-state NO x conversion to N 2 was evaluated at 500°C over H-ZSM-5 and Ag/H-ZSM-5 and it was found to be higher over Ag/H-ZSM-5 (48% vs. 24%). Similar NO x conversions were attained with NO or NO 2 in reactor feed.Formation of RNO x compounds (CH 3 NO 2 ), cyanides (acetonitrile) and iso-cyanates (HNCO) was shown. Ethanol reactions, such as dehydration to C 2 H 4 and partial oxidation to acetaldehyde or acetic acid, were observed on the studied temperature range.An approach to the deNO x reaction mechanism over H/ZSM-5 and Ag/H-ZSM-5 catalysts was performed based on the identification by MS of several organic and organo-nitro compounds.