Stability of Ba,K/CeO2 catalyst during diesel soot combustion: effect of temperature, water and sulfur dioxide

M. A. PERALTA, V. G. MILT, L. M. CORNAGLIA, C. A. QUERINI

JOURNAL OF CATALYSIS

ELSEVIER

Año: 2006 vol. 242 p. 118 - 130

0021-9517

In this work we study the stability of Ba,K/CeO2 catalysts which in previous works have shown to be very active for soot combustion. The effects of high-temperature treatments and the presence of water or sulfur dioxide on the catalytic properties for soot oxidation are studied. Fresh and deactivated catalysts are characterized by XPS, FTIR, XRD and High-Frequency CO2 pulses, and the activity is measured by TPO. Barium has only a minor effect on the activity for soot combustion while potassium has a pronounced effect in decreasing the temperature needed to burn soot. In the case of Ba,K/Ce2O, an optimum in activity as a function of  potassium content around 7 wt% is found. The optimum, which is very smooth, is due to the synergistic effect between K and CeO2. This catalyst is thermally stable up to 830°C and does not deactivate even after 30 h at 800°C. At higher temperatures, a decrease in the K/Ce surface ratio and the formation of the BaCeO3 perovskite, indicated by the XPS analyses, are the reasons for an activity loss. In these cases, there is a decrease in the level of interaction with CO2. The presence of water at 400°C does not lead to any significant modification of catalytic activity. However, the presence of water at 800°C leads to both a drastic decrease in activity and a change in surface composition as indicated by XPS, with a high degree of hydroxilation and probably to a spreading of BaO on the ceria surface. The presence of SO2 (1000 ppm in air) at 400°C deactivates the catalyst for soot oxidation, even after rather short times (32h). Under these conditions, FTIR, and XPS analyses show that barium, potassium and cerium sulfates are formed. Consequently, the activity for soot oxidation is lost, and there is no interaction between the catalyst and the CO2.  This type of catalysts has a good thermal stability and a very good tolerance to water at low temperature (e.g. 400°C). However, the presence of high concentrations of SO2 leads to a fast deactivation. This should not be a major drawback since in the near future a much lower level of sulfur in the diesel fuel is expected.