SOOT OXIDATION CATALYZED BY A CU K/MO/CL CATALYST - EVALUATION OF THECHEMISTRY AND PERFORMANCE OF THE CATALYST/

Several non-supported oxidic compounds potentially present in a Cu/K/M o/Cl catalyst (copper molybdates, potassium molybdates, and a mixed co pper-potassium molybdate (K2Cu2(MoO4)(3))) have been tested individual ly on their activity in the oxidation of a model soot (Printex-U, whic h non-catalytically oxidizes at 875 K). These oxidic compounds are act ive between 665 and 720 K, but only after establishment of 'tight cont act' between the catalyst and soot in a ball mill. Without the ball mi ll procedure ('loose contact') these oxides are less active (the soot oxidation temperature is shifted to about 790 K), while a ZrO2, suppor ted Cu/K/Mo/Cl catalyst still shows a high activity around 670 K. Henc e, the 'loose contact' activity of the supported Cu/K/Mo/Cl catalyst i s not explained by the presence of an active oxidic compound. DRIFT an d XRD analyses have shown that addition of KCI to CuMoO4, (two compoun ds present within the Cu/K/Mo/Cl catalysts) followed by calcination at 950 K in air, eventually results in the formation of a mixed potassiu m-copper molybdate. Simultaneously several volatile copper, potassium and chlorine containing compounds (e.g. K2CuCl4) are formed. These cop per and chlorine containing compounds possess a high 'loose contact' s oot oxidation activity between 600 and 690 K. A catalytic cycle, invol ving Cu2OCl2, is proposed to explain the high 'loose contact' activity of copper chlorides and supported Cu/K/Mo/Cl catalysts. The activity of the latter catalyst will be maintained as long as Cu2OCl2 can be re formed by reaction of copper molybdates with KCl, which serves as a ch lorine supplier.