# US 2009/0260349 A1 · Air-injection system to improve effectiveness of selective catalytic reduction catalyst for gasoline engines > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2009/0260349 A1 - Document ID: US20090260349A1 - Status: Published application - Kind: A1 - Application number: 12/103,805 - Filed: 2008-04-16 - Published: 2009-10-22 - Earliest claimed: 2008-04-16 - Assignees: Ford Global Technologies, LLC - Inventors: Harendra S. Gandhi; Robert Walter McCabe; Joseph Robert Theis - Web page: https://patentgrep.com/patent/US20090260349A1 ## CPC - F01N 3/206: {Adding periodically or continuously substances to exhaust gases for promoting purification, e.g. catalytic material in liquid form, NOx reducing agents} - B01D 53/9418: {for removing nitrogen oxides by selective catalytic reduction [SCR] using a reducing agent in a lean exhaust gas} - B01D 53/945: {characterised by a specific catalyst} - B01D 53/9477: {with catalysts positioned on separate bricks, e.g. exhaust systems} - F01N 3/0807: {by using absorbents or adsorbents} - F01N 3/0842: {Nitrogen oxides} - F01N 3/101: {Three-way catalysts} - F01N 3/106: {Auxiliary oxidation catalysts} - F01N 3/2053: {By-passing catalytic reactors, e.g. to prevent overheating} - F01N 3/2066: {Selective catalytic reduction [SCR]} - F01N 3/30: Arrangements for supply of additional air (control, e.g. using by-passes or variable air pump drives, F01N3/22) - F01N 13/009: {having two or more separate purifying devices arranged in series} - B01D 53/9422: {for removing nitrogen oxides by NOx storage or reduction by cyclic switching between lean and rich exhaust gases (LNT, NSC, NSR)} - B01D 2251/11: Air - B01D 2251/2062: Ammonia - B01D 2251/2067: Urea - B01D 2255/1021: Platinum - B01D 2255/1023: Palladium - B01D 2255/1025: Rhodium - B01D 2255/206: Rare earth metals - B01D 2255/20738: Iron - B01D 2255/20746: Cobalt - B01D 2255/2092: Aluminium - B01D 2255/50: Zeolites - B01D 2255/908: O2-storage component incorporated in the catalyst - B01D 2255/91: NOx-storage component incorporated in the catalyst - B01D 2258/012: Diesel engines and lean burn gasoline engines - F01N 2370/02: used in catalytic reactors - F01N 2610/02: the substance being ammonia or urea - Y02T 10/12: Improving ICE efficiencies - F01N: GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL-COMBUSTION ENGINES (arrangements in connection with gas exhaust of propulsion units in vehicles B60K13/00; combustion-air intake silencers specially adapted for, or arranged on, internal-combustion engines F02M35/00; protecting against, or damping, noise in general G10K11/16) - B01D: SEPARATION (separating solids from solids by wet methods B03B, B03D; by pneumatic jigs or tables B03B; by other dry methods B07; magnetic or electrostatic separation of solid materials from solid materials or fluids, separation by high-voltage electric fields B03C; centrifuges, vortex apparatus B04; presses per se for squeezing-out liquid from liquid-containing material B30B9/02; treatment of water C02F, e.g. softening by ion-exchange C02F1/42; {arrangements of air intake cleaners in gas turbine plants F02C7/05} ; arrangements or mounting of filters in air-conditioning, air-humidification or ventilation F24F13/28) - Y02T: CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION ## Abstract Embodiments are described to improve the durability of a lean NOx aftertreatment system. According to one embodiment of the present invention an air injection system is used to inject air continuously into the exhaust system between the upstream three-way catalyst and the downstream selective catalytic reduction (SCR) catalyst when the engine is operating at stoichiometric or rich air/fuel ratios and the exhaust temperatures are above a calibratible level (e.g., 700° C.). In another embodiment, an oxidation catalyst is positioned downstream of the air injection point to prevent exothermic reactions from occurring on the SCR. In another embodiment, the reductant for the SCR is generated in-situ. In yet another embodiment, a diverter valve with a reduction catalyst in a bypass arm is utilized to bypass the SCR during high load conditions. ## Claims ### Claim 1 A durable catalyst system for the reduction of emissions from a gasoline engine exhaust stream, comprising: a light-off catalyst closely coupled to the engine; a selective catalytic reduction catalyst positioned downstream of the light-off catalyst; a reductant injection system positioned between the light-off catalyst and the selective catalytic reduction catalyst; and an air injection system positioned between the light-off catalyst and the location for reductant injection to inject air into the exhaust stream at designated engine conditions to improve the durability of the selective catalytic reduction catalyst. ### Claim 2 (depends on 1) The system of claim 1, wherein engine controls are provided that operate in conjunction with the air injection system to inject air into the exhaust stream under designated conditions to improve the durability of the selective catalytic reduction catalyst. ### Claim 3 (depends on 1) The system of claim 1, wherein the air injection system is a pump that provides a continuous stream of air under the designated conditions. ### Claim 4 (depends on 1) The system of claim 1, wherein the air injection system provides pulsed air under the designated conditions. ### Claim 5 (depends on 1) The system of claim 1, wherein the light-off catalyst is a three-way catalyst. ### Claim 6 (depends on 1) The system of claim 1, wherein an oxidation catalyst is positioned between the location for air injection and the location for reductant injection to prevent exothermic reactions from occurring on the selective reduction catalyst and impairing durability. ### Claim 7 (depends on 1) The system of claim 1, wherein the oxidation catalyst is a Pd-based three-way catalyst having a Pd loading between 2 and 10 pgcf. ### Claim 8 (depends on 1) The system of claim 1, wherein the reductant that is injected is ammonia. ### Claim 9 (depends on 1) The system of claim 1, wherein the reductant that is injected is urea. ### Claim 10 A method of improving the durability of a catalyst system for reducing emissions from lean-burn gasoline engine exhaust emissions, comprising the following steps: providing a catalyst system that includes a light-off catalyst closely coupled to the engine and a selective catalytic reduction catalyst positioned downstream from the light-off catalyst; injecting air between the light-off catalyst and the selective catalytic reduction catalyst at certain designated conditions that could harm the durability of the selective catalytic reduction catalyst; and injecting a reductant upstream of the selective catalytic reduction catalyst. ### Claim 11 (depends on 10) The system of claim 10, wherein an oxidation catalyst is positioned between the location for air injection and the location for reductant injection to prevent exothermic reactions from occurring on the selective reduction catalyst and impairing durability. ### Claim 12 (depends on 10) The system of claim 10, wherein the oxidation catalyst is a Pd-based three-way catalyst having a Pd loading between 2 and 10 pgcf. ### Claim 13 (depends on 10) The system of claim 10, wherein the reductant that is injected is ammonia. ### Claim 14 (depends on 10) The system of claim 10, wherein the reductant that is injected is urea. ### Claim 15 A durable catalyst system for the reduction of emissions from a gasoline engine exhaust stream, comprising: a light-off catalyst closely coupled to the engine; a selective catalytic reduction catalyst positioned downstream of the light-off catalyst; a reductant injection system positioned between the light-off catalyst and the selective catalytic reduction catalyst; and a diverter valve positioned downstream of the location for reductant injection and upstream of the SCR, the diverter valve being connected to a bypass arm that includes a reduction catalyst, which can be utilized to bypass the SCR and improve NOx conversion under high load conditions. ### Claim 16 A method of improving the durability of a catalyst system for reducing emissions from lean-burn gasoline engine exhaust emissions, comprising the following steps: providing a catalyst system that includes a light-off catalyst closely coupled to the engine and a selective catalytic reduction catalyst positioned downstream from the light-off catalyst; injecting a reductant upstream of the selective catalytic reduction catalyst; and providing a diverter valve positioned between the location for reductant injection and the selective catalytic reduction catalyst, wherein the diverter valve is connected to a bypass arm that includes a reduction catalyst, to allow the exhaust emissions to bypass the selective catalytic reduction catalyst during high load conditions, so that the exhaust emissions are directed through the reduction catalyst in the bypass arm to improve NOx conversion during high load conditions. ### Claim 17 A durable catalyst system for the reduction of emissions from a gasoline engine exhaust stream, comprising: a light-off catalyst closely coupled to the engine; a selective catalytic reduction catalyst positioned downstream of the light-off catalyst; a lean NOx trap positioned between the light-off catalyst and the selective catalytic reduction catalyst, wherein the lean NOx trap has a low oxygen storage capacity to stimulate ammonia production for use by the selective catalytic reduction catalyst; and an air injection system positioned between the lean NOx trap and the selective catalytic reduction catalyst to inject air into the exhaust stream at designated engine conditions to improve the durability of the selective catalytic reduction catalyst. ### Claim 18 (depends on 17) The catalyst of claim 17, wherein a low oxygen storage capacity three-way catalyst is included between the location of air injection and the selective catalytic reduction catalyst to protect the selective catalytic reduction catalyst from exothermic reactions.