Suitability of some promising soot combustion catalysts for application in diesel exhaust treatment

In this work, the effect of thermal treatment at 380°C and 600°C, under gaseous atmospheres containing some typical components of diesel emissions (SO2 and water), was studied on some promising catalysts for diesel particulate combustion. In particular, the ageing behaviour of two novel catalysts (based on CsVO3+KCl and KVO3+KCl, respectively) and of a more widely studied Cu–K–V–Cl catalyst was investigated. The catalytic activities of these novel catalysts were lower than that of the Cu–K–V–Cl one, but, contrary to this last counterpart, they almost completely maintained their activity during ageing treatments in dry or humid air at 380°C and 600°C, respectively. Moreover, after prolonged thermal exposure in wet air, the activity of the Cu–K–V–Cl catalyst became comparable with that of the CsVO3+KCl one, while remaining still slightly higher than that of the KVO3+KCl catalyst. The thermal treatments of all the catalysts under investigation in an atmosphere containing SO2 did not cause an activity decrease. X-ray diffraction analyses showed the formation of new phases (sulphates and vanadates with a K/V ratio different from that of metavanadates) which could also improve the catalytic activity, counterbalancing the loss of active components due to evaporation at high temperatures. Furthermore, the catalyst activity was evaluated after employing repeatedly these catalysts in carbon combustion. The catalytic activities were generally slightly lowered by the repeated use, even though, from this viewpoint, that of Cu–K–V–Cl was more affected than those of the other catalysts. On the basis of the obtained results the CsVO3+KCl catalyst was found to allow the best compromise between satisfactory catalyst activity and stability.