Manganese-based oxides promoted lean NO_xtrap (LNT) catalyst

摘要

MnOx-containing, base-metal oxide mixtures (e.g., MnOx—CeO2) are useful NOx oxidation catalyst materials and NOx storage materials in lean-burn engine exhaust gas treatments using Lean NOx Trap (LNT) systems. These oxidation catalyst materials are used in combination with a NOx storage material and a NOx reduction material. MnOx-containing oxide mixtures can replace platinum (Pt) in LNT systems where the exhaust of the engine is repeatedly varied between a relatively long fuel-lean mode of operation and a relatively short fuel-rich mode of operation. The combination of the MnOx oxidation catalyst, NOx storage material, and NOx reduction catalyst material serves to complete the oxidation of unburned hydrocarbons and carbon monoxide, and to convert NOx to nitrogen.

主权项

1. A method for converting a mixture of nitrogen oxides (NOx), comprising nitrogen oxide (NO) and nitrogen dioxide (NO2), to nitrogen (N2) in an exhaust gas of an internal combustion engine, the engine operating by burning a mixture of air and fuel that is controllable between (i) a mixture in which the content of fuel is lean with respect to the stoichiometric air-to-fuel mass ratio, and (ii) a mixture in which the content of fuel is rich with respect to the stoichiometric air-to-fuel mass ratio; the method comprising:
passing the exhaust gas from the engine in contact with each of: an oxidation catalyst material for oxidation of NO to NO2 in the exhaust gas, the oxidation catalyst material comprising particles of co-precipitated mixed oxides of two or more base metals including manganese, the co-precipitated mixed oxides consisting of one or more mixed oxides selected from the group consisting of MnOx—CeO2, MnOx—ZrO2 and MnOx—Y2O3, and a storage material for temporarily removing NOx from the exhaust gas when the engine operates in a fuel-lean mode, and a reduction catalyst material to reduce NO and NO2 to N2 when the engine operates in a fuel-rich mode; and managing the operation of the engine by cycling the air-to-fuel mass ratio between time periods of fuel-lean mode and time periods of fuel-rich mode, the duration of the time periods being such that (i) oxygen in the exhaust during a cycle's fuel-lean mode promotes the oxidation of NO to NO2, and NOx is temporarily removed from the exhaust gas, and (ii) fuel constituents in the exhaust during the cycle's fuel-rich mode are available for the reduction of NOx to N2 before the exhaust is discharged to the ambient atmosphere.