THERMAL-STABILITY OF CU-K-V CATALYST FOR DIESEL SOOT COMBUSTION

This paper reports a study on the thermal stability of a Cu-K-V cataly st, which showed particular promise for low temperature combustion of diesel particulate. Prolonged treatments were performed at high temper atures (400-1000 degrees C) for periods up to 15 days under different gaseous atmospheres. The effect of such treatments on the catalyst com position was investigated by means of weight-decrease measurements and composition analysis (atomic absorption, X-ray diffraction, etc.), wh ereas the catalyst activity towards soot combustion was determined via thermogravimetric analysis (TGA) and differential thermal analysis (D TA). The apparent activation energy of the soot combustion process was calculated for a collection of catalyst samples, thermally treated ac cording to several different representative conditions, by the Ozawa m ethod on the basis of the DTA results. Some of the thermal treatments (especially those performed at high temperatures: 900-1000 degrees C) resulted in a reduction of the catalyst activity as shown by the incre ase of both the activation energy and the soot ignition temperature, a s a consequence of the volatilisation of at least some of the active c ompounds of the catalyst itself (KCl, CuCl2, etc.). Any periodic therm al regeneration of a catalytically-activated trap for diesel emissions (leading to such high temperatures) performed to eliminate any accumu lated soot, has thus to be avoided by designing a trap capable of burn ing out all the soot produced at the diesel exhaust temperatures (< 40 0 degrees C).