Selective catalytic reduction of nitric oxide with ammonia on MFI-type ferrisilicate

The catalytic properties of framework Fe³⁺ in MFI-type H-ferrisilicate for the selective reduction of nitric oxide with ammonia in the presence of oxygen have been investigated and compared with those of Fe-exchanged ZSM-5, iron oxide supported on silicalite and HZSM-5. H-ferrisilicate exhibited a high activity and selectivity for the reduction of nitric oxide into nitrogen. A side reaction, i.e. the oxidation of ammonia with oxygen into nitrogen, occurred only above 773 K. The activity and selectivity of Fe-exchanged ZSM-5 for the reduction of nitric oxide were comparable to those of H-ferrisilicate, while iron oxide supported on silicalite catalysed the oxidation of ammonia with oxygen into nitric oxide preferentially under the same reaction conditions. The catalytic activity of HZSM-5 for this reaction was much lower than that of H-ferrisilicate. Therefore, the framework Fe³⁺ ions in H-ferrisilicate are the active sites for the selective catalytic reduction of nitric oxide.