A combined anomalous XRPD, EXAFS, IR, UV-Vis and photoluminescence study on isolated and clustered silver species in Y zeolite

摘要

In this contribution we report on structural (XRD and EXAFS), optical (UV-Vis DRS and photoluminescence) IR (adsorption of CO) characterization of a virtually homoionic Ag-Y zeolite (Si/Al = 2.63). Our study shows that the zeolite is a virtually 100% exchanged silver faujasite, showing almost isolated Ag~+ counterions (EXAFS estimates that clustered species represent less than 2% of the whole silver). Synchrotron radiation XRPD measurements (ESRF, BM16), performed at the Ag-K edge [λ= 0.486103(2) A], just before [λ = 0.486093(2) A] and far away [λ= 0.491153(2) A], allowed us to locate the nearly totality of the expected Ag~+ counterions: 52.0(4) out of 52.9 per unit cell, located in five different sites. Two out of the five are located in the supercage, and thus accessible to small ligand molecules, as detected by IR spectroscopy that singled out the presence of two distinct Ag~+···CO adducts. A subsequent EXAFS (ESRF, BM29), UV-Vis DRS and photoluminescence spectroscopic study on the aggregation of Ag clusters upon thermal reduction of Ag-Y zeolite will be also briefly reported.