Ion-exchanged binuclear Ca2OX clusters, X = 1-4, as active sites of selective oxidation over MOR and FAU zeolites.

A new series of calcium oxide clusters Ca(2)O(X) (X = 1-4) at cationic positions of mordenite (MOR) and faujasite (FAU) is studied via the isolated cluster approach. Active oxide framework fragments are represented via 8-membered window (8R) in MOR, and two 6R and 4R windows (6R+4R) possessing one common Si-O-Si moiety in FAU. Structural similarities between the Ca(2)O(X)(8R) and Ca(2)O(X)(6R+4R) moieties are considered up to X = 4. High oxidation possibilities of the Ca(2)O(2)(nR) and Ca(2)O(3)(nR) systems are demonstrated relative to CO, whose oxidation over the Ca-exchanged zeolite forms is well studied experimentally. Relevance of the oxide cluster models with respect to trapping and desorption of singlet dioxygen is discussed. Copyright 2009 Wiley Periodicals, Inc.