Pre-converted nitric oxide gas in catalytic reduction system

• US 5,891,409 A
• Filed: 04/18/1997
• Issued: 04/06/1999
• Est. Priority Date: 08/19/1996
• Status: Expired due to Fees

• Current Assignee: Lawrence Livermore National Security LLC (Government of the United States of America)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: Hsiao, Mark C., Penetrante, Bernardino M., Merritt, Bernard T., Vogtlin, George E.
• Primary Examiner(s): Tran, Hien
• Application Number:
  US08/839,895
• Time in Patent Office: 718 Days
• Field of Search: 422/168-172, 422/174, 422/177, 423/213.7, 423/239.1, 423/213.2, 60/274, 60/275, 60/297, 60/301, 60/303
• US Class Current: 423/239.1
• CPC Class Codes: B01D 53/323 by electrostatic effects or by high-voltage electric fields
• CPC Class Codes: B01D 53/92 of engine exhaust gases exhaust or silencing apparatus for internal combustion engines, machines or engines in general, having means for purifying, rendering innocuous or otherwise treating exhaust gases F01N3/00
• CPC Class Codes: B01D 53/9431 Processes characterised by a specific device
• CPC Class Codes: B01D 53/9454 characterised by a specific device
• CPC Class Codes: F01N 13/0097 the purifying devices are arranged in a single housing
• CPC Class Codes: F01N 2240/28 a plasma reactor
• CPC Class Codes: F01N 2570/14 Nitrogen oxides
• CPC Class Codes: F01N 2610/02 the substance being ammonia or urea
• CPC Class Codes: F01N 2610/03 the substance being hydrocarbons, e.g. engine fuel
• CPC Class Codes: F01N 3/01 by means of electric or electrostatic separators
• CPC Class Codes: F01N 3/0231 using special exhaust apparatus upstream of the filter for producing nitrogen dioxide, e.g. for continuous filter regeneration systems [CRT]
• CPC Class Codes: F01N 3/035 with catalytic reactors , e.g. catalysed diesel particulate filters
• CPC Class Codes: F01N 3/0892 Electric or magnetic treatment, e.g. dissociation of noxious components electric filters F01N3/01; regeneration of exhaust filters F01N3/023; heating catalytic converters F01N3/2006
• CPC Class Codes: F01N 3/2066 Selective catalytic reduction [SCR]
• CPC Class Codes: Y02A 50/20 Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
• CPC Class Codes: Y02C 20/10 of nitrous oxide (N2O)
• CPC Class Codes: Y02T 10/12 Improving ICE efficiencies

Abstract

A two-stage catalyst comprises an oxidative first stage and a reductive second stage. The first stage is intended to convert NO to NO₂ in the presence of O₂. The second stage serves to convert NO₂ to environmentally benign gases that include N2, CO2, and H₂ O. By preconverting NO to NO₂ in the first stage, the efficiency of the second stage for NO_x reduction is enhanced. For example, an internal combustion engine exhaust is connected by a pipe to a first chamber. An oxidizing first catalyst converts NO to NO₂ in the presence of O₂ and includes platinum/alumina, e.g., Pt/Al₂ O₃ catalyst. A flow of hydrocarbons (C_x H_y) is input from a pipe into a second chamber. For example, propene can be used as a source of hydrocarbons. The NO₂ from the first catalyst mixes with the hydrocarbons in the second chamber. The mixture proceeds to a second reduction catalyst that converts NO₂ to N2, CO2, and H₂ O, and includes a gamma-alumina γ-Al₂ O₃. The hydrocarbons and NO_x are simultaneously reduced while passing through the second catalyst.

Claims

1. A method for reducing nitrogen oxides (NO_x) in engine exhausts from oxygen-rich, high-temperature combustion, the method comprising the steps of:

converting substantially all NO in an oxygen-rich engine exhaust with a first stage oxidizing catalyst to an intermediate gas flow including NO₂ ;

adding hydrocarbons into the intermediate gas flow; and

converting substantially all of said intermediate gas flow including NO₂ in the presence of hydrocarbons with a second-stage selective catalytic reduction (SCR) catalyst to an output gas flow comprising NO₂ conversion products of N₂, CO₂ and H₂ O and substantially little NO and NO₂ (NO_x);

wherein, the first stage oxidizing catalyst is used to convert NO to NO₂ and then the second-stage selective catalytic reduction (SCR) catalyst is used to convert NO₂ and the hydrocarbons to N₂, CO₂, and H₂ O.

2. A two-stage catalytic converter, comprising:

an oxygen-rich engine-exhaust gas inlet;

an oxidative first stage including a first catalyst that serves to convert NO to NO₂ in the presence of excess O₂ and is connected to the oxygen-rich exhaust gas inlet;

a hydrocarbon inlet; and

a reductive second stage including a second catalyst connected to the oxidative first stage and the hydrocarbon inlet to receive a mixture of NO₂ from the oxidative first stage and hydrocarbons from the hydrocarbon inlet, and that further serves to convert NO₂ to gases that include N₂, CO₂, and H₂ O;

wherein by preconverting NO to NO₂ in the first stage, the efficiency of the second stage for NO_x reduction is enhanced.

3. The converter of claim 2, wherein:

the first catalyst of the oxidizing first stage includes a platinum/alumina catalyst (Pt/Al₂ O₃).

4. The converter of claim 2, wherein:

the second catalyst of the reductive second stage includes a gamma-alumina catalyst (γ

-Al₂ O₃);

wherein hydrocarbons and NO_x are simultaneously reduced while passing through the second stage.