Reactive oxygen in NaCuX zeolites

The amount of oxygen in NaCuX zeolites which is readily available for oxidation of CO has been determined as a function of temperature, copper concentration and catalyst pretreatment. Under fairly mild conditions this reactive oxygen is associated with reduction of part of the Cu(II) to Cu(I). Experiments with N₂O and esr measurements indicate that the reactive oxygen is an O^2- species. Prolonged reduction of the catalysts with CO can lead to reduction of zeolite Cu(I) to Cu(0) and an associated increase in reactive oxygen. Reduction of the catalysts with hydrocarbon similarly involves reduction of Cu(I) to Cu(0). However, in this case there is evidence (X-ray, esr) of agglomeration of Cu(0) leading to formation of a CuO phase on oxidation.