A four-way catalytic system for control of emissions from diesel engine

Abstract

The pollution caused by diesel-fuelled vehicles has become a subject of global concern. Presently, various separate technologies such as diesel oxidation catalyst, diesel particulate filter, selective catalytic reduction and ammonia selective catalytic reduction are used to control these pollutants. The four-way catalytic (FWC) system integrates all the separate control systems into a single compact unit. FWC technique using a combination of oxidation-reduction catalysts under various strategies has been investigated to simultaneously remove CO, HC, PM and NOx emitted from diesel engines. An oxidation catalyst (La 0.6 K 0.4 CoO 3) was prepared by two different methods (sol-gel and co-precipitation). The reduction catalysts: Ag/Al 2 O 3 and Cu-ZSM5 were synthesized by impregnation and ion-exchange method, respectively. The FWC was characterized by N 2sorption, X-ray diffraction, Fourier transform spectroscopy and scanning electron microscopy. The catalytic activities of FWC containing double-layer of catalysts were evaluated in a fixed-bed-tubular-reactor. The highest catalytic activity resulted by the two-layered system of La 0.6 K 0.4 CoO 3 (sol-gel) ? Cu-ZSM5 showing 100% NO conversion to N 2 at 415°C, maximum-temperature of soot-combustion at 410°C, complete C 3 H 8 conversion at 450°C and 100% CO conversion at 388°C. Maximum NO conversion was maintained up to 427°C; conversion started decreasing with further increase in temperature and 75.4% conversion remained up to 450°C. The performance of double-layered-catalytic-system was as follows: La 0.6 K 0.4 CoO 3 (sol-gel) ? Cu-ZSM5 [ La 0.6-K 0.4 CoO 3 (sol-gel) ? Ag/Al 2 O 3 [ La 0.6 K 0.4 CoO 3 (co-ppt) ? Ag/Al 2 O 3 [ La 0.6 K 0.4 CoO 3 (co-ppt) ? Cu-ZSM5.