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Reductant Generation for Solid Zeolite SCR/DPF Catalyst

IP.com Disclosure Number: IPCOM000082821D
Publication Date: 2005-Feb-28
Document File: 1 page(s) / 29K

Publishing Venue

The IP.com Prior Art Database

Abstract

Aftertreatment systems for diesel engines to meet future emission standards must reduce the emissions of nitrogen oxide (NOx) and particulate matter (PM) into the atmosphere. A combined SCR/DPF (Selective Catalytic Reduction / Diesel Particulate Filter) can reduce NOx to N2 and oxidize particulate matter (PM). The DPF is composed of an extruded base metal/zeolite SCR catalyst that is preferred for high NOx conversion at low temperatures (150-550 degrees). The SCR catalyst must have ammonia (NH3) present on its surface to reduce NOx. Ammonia may be added to the exhaust gas via external means, such as a pressurized cylinder of ammonia gas or a chemical that decomposes to ammonia in the exhaust gas, such as urea. The use of a reductant that is not already present in diesel or other lean-burn exhaust and must be externally added has many disadvantages: 1) the customer may not replenish the supply of reductant resulting in very poor NOx conversion, 2) use of pressurized ammonia gas is unsafe and may harm the customer and the environment in the case of a vehicle crash, and 3) an injection system for a chemical that decomposes to ammonia adds additional cost and complexity to the vehicle. A method is described to provide ammonia to the SCR/DPF in lieu of externally added reductant.

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Reductant Generation for Solid Zeolite SCR/DPF Catalyst

Aftertreatment systems for diesel engines to meet future emission standards must reduce the emissions of nitrogen oxide (NOx) and particulate matter (PM) into the atmosphere.  A combined SCR/DPF (Selective Catalytic Reduction / Diesel Particulate Filter) can reduce NOx to N2 and oxidize particulate matter (PM).  The DPF is composed of an extruded base metal/zeolite SCR catalyst that is preferred for high NOx conversion at low temperatures (150-550°).  The SCR catalyst must have ammonia (NH3) present on its surface to reduce NOx.  Ammonia may be added to the exhaust gas via external means, such as a pressurized cylinder of ammonia gas or a chemical that decomposes to ammonia in the exhaust gas, such as urea.  The use of a reductant that is not already present in diesel or other lean-burn exhaust and must be externally added has many disadvantages: 1) the customer may not replenish the supply of reductant resulting in very poor NOx conversion, 2) use of pressurized ammonia gas is unsafe and may harm the customer and the environment in the case of a vehicle crash, and 3) an injection system for a chemical that decomposes to ammonia adds additional cost and complexity to the vehicle.  A method is described to provide ammonia to the SCR/DPF in lieu of externally added reductant.

Method

It is advantageous to generate onboard the ammonia needed for NOx conversion by the SCR catalyst.  One way to accomplish this is to install a Lean NOx Trap (LNT) u...