SUITABILITY OF SOME PROMISING SOOT COMBUSTION CATALYSTS FOR APPLICATION IN DIESEL EXHAUST TREATMENT

In this work, the effect of thermal treatment at 380 degrees C and 600 degrees C, under gaseous atmospheres containing some typical componen ts 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, re spectively) and of a more widely studied Cu-K-V-Cl catalyst was invest igated. The catalytic activities of these novel catalysts were lower t han that of the Cu-K-V-CI one, but, contrary to this last counterpart, they almost completely maintained their activity during ageing treatm ents in dry or humid air at 380 degrees C and 600 degrees C, respectiv ely. Moreover, after prolonged thermal exposure in wet air, the activi ty of the Cu-K-V-CI catalyst became comparable with that of the CsVO3KCl one, while remaining still slightly higher than that of the KVO3+K Cl catalyst. The thermal treatments of all the catalysts under investi gation in an atmosphere containing SO2 did not cause an activity decre ase. X-ray diffraction analyses showed the formation of new phases (su lphates and vanadates with a K/V ratio different from that of metavana dates) which could also improve the catalytic activity, counterbalanci ng the loss of active components due to evaporation at high temperatur es. Furthermore, the catalyst activity was evaluated after employing r epeatedly these catalysts in carbon combustion. The catalytic activiti es were generally slightly lowered by the repeated use, even though, f rom this viewpoint, that of Cu-K-V-CI was more affected than those of the other catalysts. On the basis of the obtained results the CsVO3+KC l catalyst was found to allow the best compromise between satisfactory catalyst activity and stability. (C) 1998 Elsevier Science B.V. All r ights reserved.