The reactions of formamide and nitromethane, two possible intermediates in the selective catalytic reduction of nitrogen oxides by methane, have been studied over Co-ZSM5, H-ZSM5 and Cu-ZSM5. Formamide, a possible surrogate for nitro-somethane, reacts completely below 250°C over Co-ZSM5 with formation of NH3 and CO by one route and HCN and H2O by another. Inclusion of NO causes partial conversion of NH3 to N2 at 300°C. H-ZSM5 behaves similarly but with a higher conversion of NH3 in the presence of NO. Cu-ZSM5 gives CO2 and N2 alone, apparently because of its high oxidation activity. The reaction of nitromethane over H-ZSM5 is similar to that previously established for Co-ZSM5 with NH3 and CO2 as the initial products and subsequent N2 formation by the NH3-SCR reaction. Again N2 formation is more extensive with H-ZSM5 than Co-ZSM5 when NO is present while Cu-ZSM5 gives only CO2 and N2. Deactivation is characteristic of the reaction of nitromethane over all three zeolites at temperatures below ≈280°C with eventual breakthrough of isocyanic acid (HNCO) as a product. In situ FTIR measurements with H-ZSM5 indicate that deactivation is due to reactions of HNCO to form deposits of s-triazine compounds which can be removed by NO2. The overall conclusion is that nitromethane and formamide, and by inference nitrosomethane, react in ways which are consistent with the possibility that species of these types could be intermediates in the methane-SCR reaction over zeolite catalysts. Distinction between them is possible only with catalysts of low oxidation capability when CO formation is consistent with the involvement of nitrosomethane and CO2 formation with that of nitromethane.
|Number of pages||10|
|Publication status||Published - 17 Dec 1999|
- Hydrogen cyanide
- SCR of nitrogen oxides