SELECTIVE REDUCTION OF NOX BY METHANE ON CO-FERRIERITES .2. CATALYST CHARACTERIZATION

Co-ferrierite, active for the selective NO reduction by CH4, was characterized by X-ray photon spectroscopy and magnetic susceptibility measurements. The adsorption of NO and NO2 was studied by diffuse-reflectance FTIR spectroscopy to discover which intermediates participate in the NO(x) reduction. The valence state of cobalt in Co-ferrierite and other Co-zeolite catalysts was found to be 2+. The dominant NO species adsorbed on Co-Y, Co-ZSM-5, and Co-ferrierite is in a dinitrosyl form appearing at 1810 and 1897 cm-1 for Co-Y and 1810 and 1890 cm-1 for Co-ZSM-5 and Co-ferrierite. The mononitrosyl form of the adsorbed NO is a minor species appearing at 1930-1935 cm-1 on all three samples. The mononitrosyl species on all samples is extremely weakly adsorbed. The dinitrosyl species adsorbed on Co-ferrierite is strongly adsorbed and needs to be heated above 300-degrees-C to desorb. Interestingly, the weakly adsorbed mononitrosyl species is enhanced in an O2 environment (100 Torr of O2) and is now stable to 200-degrees-C. However, in an oxygen environment, the dinitrosyl species is less stable, desorbing at approximately 200-degrees-C. All adsorbed NO species disappear at >200-degrees-C in 100 Torr O2, and adsorbed NO2 species were observed. NO2 adsorbed on Co-ferrierite shows a weakly adsorbed, covalent N2O5 in addition to stable species, such as nitro, nitrito, and nitrato species. Together with earlier kinetic and reaction studies, we suggest a mechanism for the selective reduction of NO(x) by CH4.