Redox behavior of high Si/Al ratio Cu-ZSM5 in NO decomposition

Commercial H-ZSM5 zeolites with a Si/Al ratio equal to 25 and 75 have been exchanged using copper acetate aqueous solutions with different concentrations. Copper saturation is reached at the 130 and 230% level of Cu exchange for Si/Al equal to 25 and 75, respectively, although FTIR spectra showed that a fraction of Al-OH exchange positions is still available. Catalytic activity experiments of NO decomposition have been carried out at 450 degrees C in a fixed bed reactor. Catalysts have been characterized with H-2 TPR and NO adsorption experiments at 120 degrees C. All samples are partially reduced upon thermal treatment under inert flow (He) leading to the formation of Cu+-containing sites in addition to a fraction of differently reduced copper species. The Cu+-containing sites, also responsible for NO adsorption and subsequent production of N2O at 120 degrees C, have been proposed to be the active centers. A quantitative estimation of these species, likely having multi-ionic structure, has been provided.