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FTIR mechanistic studies on the selective catalytic reduction of NOx by methane and ethane over supported cobalt catalysts

The NOx species formed after NO adsorption and NO+O2 co‐adsorption on Co‐ZSM‐5, CoY, Co/SiO2 (high cobalt dispersion) and Co/SiO2 (low cobalt dispersion) were studied by means of IR spectroscopy. It was found that NO adsorption on all samples leads to the formation of Co2+(NO)2 species, which are stable on Co‐ZSM‐5 and CoY but are destroyed during evacuation on Co/SiO2. The stable species produced upon NO+O2 co‐adsorption are different kinds of surface NOx− anionic species. The principal compounds formed on Co‐ZSM‐5 and Co/SiO2 with a high cobalt dispersion are surface monodentate nitrates, characterized by an IR band at ∼1535 cm−1. These nitrates are thermally stable but easily interact with hydrocarbons which confirms that they are key species in selective catalytic reduction (SCR). No monodentane nitrates are formed on CoY and Co/SiO2 with a low cobalt dispersion, which accounts for the low SCR activity reported for such samples. Copyright © 2001 John Wiley & Sons, Ltd.