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

An exploratory study has been carried out to determine the potential of ope n-pore ceramic foam as support for molten-salt diesel soot oxidation cataly sts. These catalysts are based on eutectic mixtures of Cs2O, V2O5, MoO3, an d Cs2SO4 Open-pore ceramic foams are very interesting, since they can act a s supports and as soot filters. 50 ppi alpha-alumina foam has been tested a s 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 sal t deposited on the foam. Stable rates in the range from 5 to 25 mu g(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 'deactiv ation' that occurs after the thermal treatment up to 100 h at 725 K probabl y has a physical explanation. During the treatment, the molten salt redistr ibutes to a configuration that has less catalyst available for accelerating the soot oxidation. (C) 1999 Elsevier Science B.V. All rights reserved.