Formation of copper nanospecies of de-NO x catalysts based on Cu-mordenite: role of variable silica-alumina ratio and effects of adsorbed water

Abstract

We report measurements in copper mordenites showing that silica-alumina molar ratio (MR) strongly affects conversion efficiency for NO x , and that these catalysts are among the most active available for de-NO x at moderate temperatures. Copper mordenites' rapid deactivation by water has led us to also investigate the effects of adsorbed water on framework and extra-framework ions, mainly using NMR of 27 Al and 1 H. Adsorbed water content has been monitored and controlled in mordenite samples via TGA, as well as by vacuum calcination. Several proton NMR measurements have been performed to aid in the interpretation of spectra, including variable pulse-delay spin echo and 1 H/ 27 Al TRAPDOR. A number of surface characterization techniques have been applied to both H and Cu mordenites.

Catalytic performance of commercial Cu-ZSM-5 zeolite modified by desilication in NH 3 -SCR and NH 3 -SCO processes

“…The absorption bands at about 200-300 nm can be assigned to oxygen-to-metal charge transfer related to Cu+ or Cu2+ cations (centered respectively at about 210 and 250 nm) stabilized by the zeolite framework [39][40][41]. Some works [42,43] attribute the band at about 210 nm to the zeolite structure (band originating from the charge transfer O2-Al3+) and the bands at higher wavelengths to Cu+ and Cu2+ (centered at about 250 and 300 nm, respectively). However, independently from the exact assignment (the band originated from the zeolite structure can overlap with the bands characteristic of MLCT) it can be concluded that this absorption range is related to copper introduced to ion-exchange positions.…”