Ceramic foam as a potential molten salt oxidation catalyst support in the removal of soot from diesel exhaust gas

Abstract

An exploratory study has been carried out to determine the potential of open-pore ceramic foam as support for molten-salt diesel soot oxidation catalysts. These catalysts are based on eutectic mixtures of Cs 2O, V 2O 5, MoO 3, and Cs 2SO 4. Open-pore ceramic foams are very interesting, since they can act as supports and as soot filters. 50 ppi α-alumina foam has been tested as support substance. Attractive methods have been developed for depositing the molten salt on the external surface of the pore walls of the foam. The combustion of ‘loose-contact’ synthetic soot has been analysed with a micro-flow reactor. The oxidation rate is a function of the amount of molten salt deposited on the foam. Stable rates in the range from 5 to 25 μg soot/g soot,initial/s at 650 K have been observed. These rates are in the same order of magnitude as measured for the best catalytic fuel additives; and, therefore, catalytic foams are very promising. The initially minor ‘deactivation’ that occurs after the thermal treatment up to 100 h at 725 K probably has a physical explanation. During the treatment, the molten salt redistributes to a configuration that has less catalyst available for accelerating the soot oxidation.