Cobalt on and in zeolites and silica–alumina: Spectroscopic characterization and reactivity

The adsorption of CO at 130 K has been studied on Co-H-FER, Co-H-MFI and Co-H-MOR, as well as on Co-silica–alumina and on Co-containing mesoporous materials. Over Co-H-MFI also the adsorption of NO and of ammonia and the coadsorption of ortho-toluonitrile and CO have been investigated. The data show that on all samples Lewis acidic isolated Co2+ species are predominant. However, small amounts of oxidizing sites, possibly Co3+ and/or cobalt oxide particles also exist. This is shown by the oxidation of part of CO to CO2 and of NO to NO+ at very low temperature as well as by the formation of Co3+ mononitrosyls upon adsorption of NO. These sites, although difficult to be evidenced by direct spectroscopic measurements, are likley the active sites for CH4-SCR, where NO is activated as an adsorbed NxOy species able to react selectively with methane.