The relationship between the local structure of copper(I) ions on Cu+/zeolite catalysts and their photocatalytic reactivities for the decomposition of NOx into N2 and O2 at 275 K

Cu+/zeolite catalysts were prepared by a combination of ion-exchange and thermovacuum treatments. In situ characterization of these catalysts and their photocatalytic reactivities for the decomposition of NOx (NO and N2O) have been investigated by means of in situ photoluminescence, XAFS, ESR, UV, and FT-IR techniques along with an analysis of the reaction products. It was found that Cu(I) ions included within the nanopores of ZSM-5 and mordenite zeolites exist as isolated Cu(I) monomers with planar three-coordinate or two-coordinate geometry, while in the Y-zeolite cavities they exist as the [Cu(I)-Cu(I)] dimer species as well as the isolated Cu(I) monomer species. UV irradiation of these Cu+/zeolite catalysts in the presence of NOx led to the photocatalytic decomposition of NOx into N-2 and O-2 at temperatures as low as 275 K. A local charge separation involving an electron transfer from the electronically excited state of a Cu(I) ion (3d(9)4s(1) state) to the anti-pi-bonding orbital of an NO molecule was found to play a vital role in initiating the photocatalytic decomposition of NO,. Furthermore, the photocatalytic reactivity of these Cu+/zeolite catalysts was found to be strongly affected by the local structure of the Cu(I) ions which could easily be modified by changing the type of zeolites and loading of the copper ion. Special attention has, therefore, been focused an the relationship between the local structure of copper ions on the catalysts and their photocatalytic reactivities. (C) 1998 Elsevier Science S.A.