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

Abstract

CeO2 and Ce–Zr mixed oxides with different Ce:Zr ratios were prepared; characterised by Raman spectroscopy, XRD, TEM, N2 adsorption at −196 ◦C, and H2-TPR; and tested for soot oxidation under NOx/O2. 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/O2 when both catalysts were calcined at 500 ◦C (soot oxidation rates at 500 ◦C are 14.9 and 11.4 μgsoot/s, respectively), and the catalytic activity of CeO2 decayed significantly with calcination temperature (from 500 to 1000 ◦C), whereas Ce0.76Zr0.24O2 presented enhanced thermal stability at temperatures as high as 1000 ◦C. In addition, Ce0.76Zr0.24O2 catalysed the reduction of NOx by soot at around 500 ◦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/O2 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.