POTENTIAL OF MIXED HALIDES AND VANADATES AS CATALYSTS FOR SOOT COMBUSTION

Several soot combustion catalysts, based on a single halide and potass ium vanadate supported on alpha-Al2O3, have been prepared, characteriz ed, and tested. Three catalysts were selected on the basis of their pr evalent activity and thermal stability: KCl + KVO3, RbCl + KVO3, and C sCl + KVO3. These compositions are more environmentally acceptable tha n previously studied Cu-based catalysts. The CsCl + KVO3 catalyst show ed the highest catalytic activity and appreciable resistance to therma l degradation. The catalyst based on RbCl + KVO3 showed the best therm al stability (comparatively low loss of chlorides at high temperatures ). The KCl + KVO3 catalyst, despite its slightly lower activity and th ermal stability, is to be particularly appreciated for its low cost. T he reaction mechanism of the catalysts is primarily linked to the form ation of eutectic liquids between halides and metavanadates. Such liqu ids wet the carbon and promote its combustion according to redox proce sses in which metavanadates should play a major role.