Soot oxidation catalyzed by a Cu/K/Mo/Cl catalyst: evaluation of the chemistry and performance of the catalyst |
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Authors: | Guido Mul John PA Neeft Freek Kapteijn Michiel Makkee and Jacob A Moulijn |
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Affiliation: | aDelft University of Technology, Section Industrial Catalysis, Julianalaan 136, 2628 BL Delft, The Netherlands |
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Abstract: | Several non-supported oxidic compounds potentially present in a Cu/K/Mo/Cl catalyst (copper molybdates, potassium molybdates, and a mixed copper-potassium molybdate (K2Cu2(MoO4)3)) have been tested individually on their activity in the oxidation of a model soot (Printex-U, which non-catalytically oxidizes at 875 K). These oxidic compounds are active between 665 and 720 K, but only after establishment of ‘tight contact’ between the catalyst and soot in a ball mill. Without the ball mill procedure (‘loose contact’) these oxides are less active (the soot oxidation temperature is shifted to about 790 K), while a ZrO2 supported Cu/K/Mo/Cl catalyst still shows a high activity around 670 K. Hence, the ‘loose contact’ activity of the supported Cu/K/Mo/Cl catalyst is not explained by the presence of an active oxidic compound. DRIFT and XRD analyses have shown that addition of KCl to CuMoO4 (two compounds present within the Cu/K/Mo/Cl catalysts) followed by calcination at 950 K in air, eventually results in the formation of a mixed potassium-copper molybdate. Simultaneously several volatile copper, potassium and chlorine containing compounds (e.g. K2CuCl4) are formed. These copper and chlorine containing compounds possess a high ‘loose contact’ soot oxidation activity between 600 and 690 K. A catalytic cycle, involving 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 reformed by reaction of copper molybdates with KCl, which serves as a chlorine supplier. |
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Keywords: | Soot Cu/K/Mo/Cl-catalyst Oxidation Potassium molybdate Copper molybdate K2Cu2(MoO4)3 Cu2OCl2 |
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