Catalytic activity of nanocrystalline porous La0.8K0.2Fe(1-x)Mn(x)O3 for simultaneous removal of soot and nitrogen oxides.

The nanocrystalline, porous, perovskite La0.8K0.2Fe(1-x)Mn(x)O3 (x = 0-0.5) catalysts were prepared by the citrate-gel process. All the perovskite catalysts can effectively catalyze the soot combustion and among them the La0.8K0.2Fe0.7Mn0.3O3 catalyst exhibits the highest catalytic activity, with a lowest T50 (366 degrees C). This optimized La0.8K0.2Fe0.7Mn0.3O3 catalyst then was coated onto a honeycomb ceramic by the citrate-gel assisted dip-coating method and its catalytic performance was evaluated by the bench test in the practical exhaust emission. It is proved that the La0.8K0.2Fe0.7Mn0.3O3-coated honeycomb ceramic device simultaneously has a effective capture of soot particulates and a good absorption of NO(x) from the exhaust emission at a low temperature and begins to efficiently catalyze oxidization reactions of the soot particulates at around 230 degrees C, and conversion of NO(x) at about 290 degrees C, with a conversion rate of 16.6% at 400 degrees C. This catalytic performance enhancement for simultaneous removal of soot and NO(x) can be largely attributed to the synergistic effect of Fe and Mn, pore structure of a large channel with various small pores connected, and microstructural characteristics of La0.8K0.2Fe0.7Mn0.3O3 catalyst. The catalytic mechanism of capture-oxidation-reduction is rationally proposed.