Catalytic combustion of gasoline particulate soot over CeO2-ZrO2 catalysts

A series of CeO2-ZrO2 mixed oxide catalysts having different mass ratios (wCeO2-(1–w)ZrO2) were prepared using a co-precipitation method and subsequently applied to the combustion of soot in gasoline engine exhaust. The soot combustion activities of the catalysts were assessed via the temperature-programmed oxidation of powder mixtures, applying steps of 10 °C·min–1 from room temperature to 850 °C. These catalysts were also characterized by X-ray diffraction (XRD), Raman spectroscopy, N2 adsorption-desorption, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), oxygen storage capacity (OSC), and H2 temperature-programmed reduction (H2-TPR). After being calcined at 800 °C, 70%CeO2-30%ZrO2 exhibited the highest soot combustion activity, such that the maximum product concentration temperature (Tm) was decreased from 719 to 625 °C when employing this catalyst. The 70%CeO2-30%ZrO2 also showed excellent thermal stability, indicating that this could be an appropriate catalyst for soot combustion in gasoline direct injection engines. The differences in the soot combustion activities of the catalysts were closely related to their structures, surface compositions, and redox properties. XRD and Raman data demonstrated that the ceriumrich samples presented a typical cubic phase, while a tetragonal phase was observed in the case of the zirconium-rich samples. XPS showed that the molar fraction of Ce3+ in total Ce and the molar fraction of surfaceadsorbed oxygen to lattice oxygen on the surfaces of various samples differed, and these variations induced their different catalytic activities. The 70%CeO2-30%ZrO2 sample showed the largest OSC value and the most pronounced reduction properties. This same material was also found to have excellent thermal stability with regard to structure, surface composition, and redox properties, as reflected in the minimal degradation of the soot combustion activity of this catalyst with increasing calcination temperature.

Duke Scholars

Author Li Lan Molecular Genetics and Microbiology