Simultaneous abatement of diesel soot and NOx by perovskite-type catalysts

The major pollutants present in diesel exhaust gases are soot particulate and nitrogen oxides (NO{sub x}). A potential solution to the related environmental problems could be the use of soot traps, on which suitable catalysts are deposited for contemporary soot combustion and NO{sub x} reduction. Some perovskite-type catalysts (simple, A{sub 1-x}A{prime}{sub x}B{sub 1-y}B{prime}{sub y}O{sub 3{+-}{delta}}, or layered, A{sub 2-x}A{prime}{sub x}B{sub 1-y}B{prime}{sub y}O{sub 4{+-}{delta}}, where A, A{prime} = La, Sr, K...; B, B{prime} = Mn, Co, Cu, Cr, Mg, V,...) proved to promote effectively the above simultaneous reactions, showing, moreover, a fair stability at temperature (above 800{degrees}C) higher than those typical of diesel exhaust gases seldom exceeding 500{degrees}C. Several perovskite catalysts were prepared (citrates method), characterized (XRD, BET,...) and tested using a temperature-programmed-reaction technique. A He flow containing fixed amounts of NO{sub x} (1850 ppmv) and O{sub 2} (4 vol-%) was fed to a fixed bed of a catalyst-soot mixture; NO{sub x} and soot conversion were monitored as a function of the temperature. The results obtained show that La-K-Cu-V-based perovskite solids (e.g. La{sub 2-x}K{sub x}Cu{sub 1-y}V{sub y}O{sub 4}) give the best compromise between soot oxidation and NO{sub x} reduction rates. The role of each single constituting element of these catalysts andmore » their thermal stability are discussed.« less