Combined removal of diesel soot particulates and NOx over CeO2-ZrO2 mixed oxides

CeO2 and Ce-Zr mixed oxides with different Ce:Zr ratios were prepared: characterised by Raman spectroscopy, XRD, TEM. N-2 adsorption at -196 degrees C, and H-2-TPR; and tested for soot oxidation under NOx/O-2. Among the different mixed oxides, Ce0.76Zr0.24O2 provided the best results. Ce0.76Zr0.24O2 presented greater activity than pure CeO2 for soot oxidation by NOx/O-2 when both catalysts were calcined at 500 degrees C (soot oxidation rates at 500 degrees C are 14.9 and 11.4 mu g(soot)/s, respectively), and the catalytic activity of CeO2 decayed significantly with calcination temperature (from 500 to 1000 degrees C), whereas Ce0.76Zr0.24O2 presented enhanced thermal stability at temperatures as high as 1000 degrees C. In addition, Ce0.76Zr0.24O2 catalysed the reduction of NO, by soot at around 500 degrees C more efficiently than CeO2, thereby contributing to the decreased NOx emission level. The catalytic activity of CeO2 and Ce0.76Zr0.24O2 for soot oxidation by NOx/O-2 depended on the textural properties (BET area; crystallite size), but other properties of the oxides, such as redox behaviour and/or enhanced lattice oxygen mobility, also played a significant role. (c) 2008 Elsevier Inc. All rights reserved.