deNOx over Ag/H-ZSM-5: Study of NO2 interaction with ethanol

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 NO2, (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 NO2 instead of NO, an almost complete conversion of NO2 is observed on zeolite acid sites, giving rise to NO and partial oxidized hydrocarbons. NOx conversion is higher on Ag/H-ZSM-5 (48% vs. 19%) but it is not greatly affected when NO is replaced by NO2. Steady-state NOx conversion to N2 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 NOx conversions were attained with NO or NO2 in reactor feed. Formation of RNOx compounds (CH3NO2), cyanides (acetonitrile) and iso-cyanates (HNCO) was shown. Ethanol reactions, such as dehydration to C2H4 and partial oxidation to acetaldehyde or acetic acid, were observed on the studied temperature range. An approach to the deNOx 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.