CuOx/sulphated-ZrO2, in situ sulphated CuOx/ZrO2, and CuSO4/ZrO2 as catalysts for the abatement of NO with C3H6 in the presence of excess O2.

Copper oxide supported on ZrO2 catalysts (CuOx/ZrO2) were prepared by impregnation of ZrO2 with aqueous solutions of Cu(NO3)2. Copper sulphated- zirconia catalysts were prepared by three different methods: (i) impregnation of ZrO2 with aqueous solutions of CuSO4, (ii) impregnation of sulphated-ZrO2 with toluene solutions of Cu(acetylacetonate)2, and (iii) sulphation of CuOx/ZrO2 via the gas-phase. Samples were characterized by X-ray diffraction (XRD), UV-VIS diffuse reflectance (DRS), Fourier transformed infrared (FT-IR), and redox cycles with CO and O2. The reduction of NO with C3H6 in the presence of excess O2 was studied in a flow apparatus fed by a reactant mixture of NO:C3H6:O2 = 4000:2000:20000 ppm in He. Irrespective of the preparation method, (i) catalysts with the same sulphate content had the same covalent sulphates, and (ii) catalysts with the same copper content and with the same sulphate content were equally active and selective. Sulphated samples were far more selective than the correspondent unsulphated CuOx/ZrO2, particularly sulphated samples with higher copper content. The presence of sulphates (i) made CuII less reducible than in CuOx/ZrO2 and (ii) prevented CuO segregation. The catalytic activity and selectivity of copper sulphated catalysts depends on a cooperative effect of copper and sulphate. The role of copper is to determine the activity for the NO reduction, and that of sulphate to maintain high the selectivity.