Thermal analysis and EPR study of copper species in mordenites prepared by conventional and microwave-assisted methods

Copper-exchanged mordenites prepared by different methods, conventional and microwave assisted, have been investigated by TG, DSC, temperature-programmed reduction (TPR), and EPR methods. TPR study of hydrated and annealed at 573 and 973 K samples revealed that the copper reduction occurs directly from Cu2+ to Cu0, and Cu2+ ions are in different local environments. The microwave-assisted treatment leads to formation of [Cu–O–Cu]2+ species in the main mordenite channels. The most easily recoverable copper in the fully hydrated samples corresponds to the individual Cu2+ ions coordinated by H2O molecules, and the number of these [Cu(H2O)n]2+ complexes does not depend on the preparation method and the total copper content. According to the EPR study, upon sample dehydration, [Cu(H2O)n]2+ species lose water and approach the wall of the zeolite forming a bond with reversible charge transfer from a framework oxygen to Cu2+.