TPR study on differently prepared copper mordenites

Abstract

Three kinds of copper mordenite such as copper ion-exchanged, impregnated and physically mixed hydrogen mordenites were prepared and TPR study was carried out. For the fresh ion-exchanged mordenite, two distinct reduction processes were observed; one for the reduction of Cu(II) ion to Cu(I) ion at 225°C and the other for the reduction of Cu(I) to copper metal at 480°C, respectively. Successive TPR/oxygen-treatment lowered the first reduction temperature to 200°C and raised the hydrogen consumption. However, the second peak at 480°C for Cu(I) to copper metal was diminished. The reduction peak at 200°C may be an indicative of the newly formed ionic compounds such as cluster of copper ions. Impregnation of cupric salts leads to the formation of similar cluster of copper ions as those appeared in ion-exchanged mordenite. The treatments of CuO-mixed mordenite also decreased the reduction temperature due to the well dispersed CuO particles on the crystal surface and also formed the same cluster copper ions as appeared in the ion-exchanged one. The cluster of copper ions on the crystal surface created the higher activity for CO oxidation.