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

The NO, species formed after NO adsorption and NO + O-2 co-adsorption on Co -ZSM-5,COY, Co/SiO2 (high cobalt dispersion) and CO/SiO2 (low cobalt disper sion) were studied by means of IR spectroscopy. It was found that NO adsorp tion on all samples leads to the formation of Co2+ (NO)(2) species, which a re stable on Co-ZSM-5 and COY but are destroyed during evacuation on Co/SiO 2. The stable species produced upon NO + O-2 co-adsorption are different ki nds of surface NOx- anionic species. The principal compounds formed on Co-Z SM-5 and CO/SiO2 with a high cobalt dispersion are surface monodentate nitr ates, characterized by an IR band at similar to 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 monode ntane nitrates are formed on COY and Co/SiO2 with a low cobalt dispersion, which accounts for the low SCR activity reported for such samples. Copyrigh t (C) 2001 John Wiley & Sons, Ltd.