Ru-doped ceria–zirconia mixed oxides catalyze soot combustion

Abstract

We used ceria-based catalysts to reduce the soot combustion temperature from 600 °C to values included in the operation range of diesel exhausts (270–400 °C). We synthesized CeO2–ZrO2 by the sol–gel method and effectively deposited the mixed oxide on cordierite. We confirmed the structural and morphological properties of the material and the formation of mixed oxides by N2 adsorption/desorption isotherms, temperature-programmed reduction, oxygen storage capacity, and scanning and transmission electron microscopies. We investigated how the addition of Ru nanoparticles (0.5 wt%) affected the catalytic activity of Ce0.4Zr0.6O2 in terms of soot oxidation. Thermal analyses of soot oxidation in the presence of the catalyst revealed that the soot combustion temperature decreased 250 °C on average. This result indicates that oxygen species originated at low temperatures, accounting for high reactivity toward soot combustion. We assessed the catalytic activity of the fresh and recycled supported catalysts in a stationary engine motor and conducted a comparative analysis of the final soot impregnated on paper filters by diffuse reflectance spectroscopy. We were able to use the catalyst in several cycles (three times of 40 min); we did not detect activity loss after the recycling, and the material retained its structural properties. Our data demonstrated that we can reuse the catalyst to efficiently oxidize soot, as attested by the thermal analysis. Moreover, the use of this catalyst reduced soot emissions by more than 84 % according to dynamic tests in a stationary engine.