Role of the different copper species on the activity of Cu/zeolite catalysts for SCR of NOx with NH3

The SCR of NOx with NH3 has been studied by using different Cu zeolite catalysts, prepared both with ZSM5 and BETA zeolite supports by ionic exchange or by impregnation. The catalysts were characterized by ICP-AES, N-2 adsorption at 196 degrees C, XRD, TEM, XPS and H-2-TPR. The catalysts characterization confirmed the presence of different Cu(II) species on all catalyst (CuO and Cu(II) exchanged on tetrahedral and octahedral positions of the zeolites framework). Clear evidences of Cu(I) or Cu(0) species were not obtained. CuO was more abundant in high copper-content catalysts and in ZSM5 catalysts, due to its lower ionic exchange capacity, while isolated Cu(II) ions are more abundant in low copper-content catalysts and in BETA catalysts. It was concluded that CuO catalyzes the oxidation of NO to NO2, and this favors the reduction of NOx at lower temperature (the NH3-NO2 reaction is faster than the NH3-NO reaction because NO2 is much more oxidizing than NO), whereas isolated Cu(II) ions maintain high NOx conversion at high temperatures. (C) 2013 Elsevier B.V. All rights reserved.