Searching for the active sites of Co-H-MFI catalyst for the selective catalytic reduction of NO by methane: A FT-IR in situ and operando study

A Co-H-MFI sample has been studied through FT-IR spectroscopy of in situ adsorption and co-adsorption of probe molecules (o-toluonitrile, CO, NO) and has been tested in the CH4-SCR process under IR operando conditions. The o-toluonitrile (oTN) adsorption and the oTN and NO coadsorption, show that both Co2+ and Co3+ species are present on the catalyst surface. Co3+ species are located inside the zeolitic channels while Co2+ ions are distributed both at the external and at the internal surfaces. The operando study show the activity of Co3+ species in the reaction. The existence of three parallel reactions, CH4-SCR, CH4 total oxidation and NO to NO2 oxidation, has been confirmed. Isocyanate species and nitratelike species appear to be intermediates of CH4-SCR and NO oxidation, respectively. A mechanism for CH4-SCR has been proposed. Co2+ substitutional sites, very evident and predominant in the catalyst, which are very hardly reducible, seem not to play a key role in the SCR process.