Catalytic activity of H- and FeH-ferrierite (FER) zeolites with iron content from 50 to 4000 ppm in NO-NO2 equilibration and SCR of NOx by propane was measured, both in NO2-poor and NO2-rich streams. The activity of FeH-FER in SCR in NO2-poor streams depends strongly on the Fe content; this relationship is valid down to traces of iron, while no such correlation was indicated in NO2-rich streams. This was rationalized by realizing the negligible activity of zeolite protons for NO-NO2 equilibration. Accordingly the SCR activity of H-FER in NO2-poor streams necessitates presence of iron traces. In the NO2-O-2-propane mixtures a process in absence of zeolite catalyst initiating propane oxidation and NO2 --> NO conversion, but without N-2 formation, was evidenced at temperatures over 350 C. It is suggested that such a radical process participate in characteristic narrow temperature window for NOx reduction by propane.