Formation of copper nanoparticles in mordenites with variable SiO₂/Al₂O₃ molar ratios under redox treatments

A series of protonated copper-containing mordenites with different SiO₂/Al₂O₃ molar ratios (MR) in the range of 10.MR.206 was prepared by ion exchange in copper nitrate aqueous solution. The electron paramagnetic resonance of hydrated copper Mordenites series testifies of several Cu²⁺ ions sites. Hydrogen reduction of copper ions incorporated into the mordenites was shown to lead to different reduced copper species including small metallic particles inter alia. The structural properties and acidity of mordenites were characterized. The optical appearance of the copper particles showed strong but nonmonotonic dependence on the MR value, in line with the variation in acidity of this series of mordenites. Correlations between mordenite properties and the formation of different reduced copper species are discussed.