LAUSR

Abstract This work investigates the influences of Cu content, Si/Al ratio, and sample preparation method on the active Cu species in mordenite (MOR). The Cu/MOR prepared by multiple Cu-exchange procedures showed an optimum Cu/Al ratio for the formation of the most active species for methanol formation. XANES spectra indicated that isolated Cu+ species were formed after CH4 interaction and were re-oxidized under a flow of water steam. The Cu-MOR samples obtained by an ion-exchange method presented well-dispersed CuO in the zeolite pores, while samples obtained by an impregnation method presented segregated CuO and were inactive for CH4 activation. The methodology used for in situ UV-Vis spectra analyses indicated that various Cu species were active for CH4 oxidation. Isolated Cu2+ species were not involved in CH4 activation at temperatures lower than 300 °C. The isolated Cu2+ species were partially hydrolyzed by O2 treatment and species like [CuOH]+ and [CuOx]n or polynuclear Cu2+-oxyhydroxide were formed. The formation of polynuclear species in substitution of di-copper would impact the specific activity with the Cu content and decrease the activity for methanol production.”