SCR and LNT catalysts for combined LNT-SCR applications

摘要

The current invention refers to the LNT and the SCR catalysts designed for combined LNT-SCR applications. LNT catalysts are based on proton- conducting oxides of fluorite structure, namely Ca (Sr)-La-Ce (Zr, Pr) mixed oxides in which up to 40 mol-% of lanthanum is replaced by calcium and/ or strontium, and up to 66 mol-% of cerium is replaced by zirconium and/or praseodymium, further combined with Pt-Pd or Pt-Pd-Rh precious metal components. SCR catalysts are Cu/ zeolite modified by citrate treatment or Cu-Ce, Mn-Ce or Co-Ce/modified zeolite. The invention also deals with a catalyst system for an exhaust gas treatment system, in particular to be used as an exhaust gas treatment system for a combustion engine, comprising the LNT-catalyst according to this invention and the SCR-catalyst of the invention, wherein the SCR-catalyst is positioned downstream of the LNT-catalyst.