US20150337709A1

US20150337709A1 - Exhaust gas processing apparatus and method

Info

Publication number: US20150337709A1
Application number: US14/569,742
Authority: US
Inventors: Sung Mu Choi
Original assignee: Hyundai Motor Co
Current assignee: Hyundai Motor Co
Priority date: 2014-05-20
Filing date: 2014-12-14
Publication date: 2015-11-26
Also published as: KR20150133407A; CN105089746A; DE102014119503A1

Abstract

An apparatus and a method for processing exhaust gas are provided. The apparatus includes a lean NOx trap (LNT), a selective catalytic reduction (SCR) catalyst, and an oxygen storage catalyst containing an oxygen storage material and a precious metal sequentially disposed along an exhaust gas flow direction. The apparatus also includes a front lambda sensor disposed upstream of the LNT, a rear lambda sensor disposed downstream of the oxygen storage catalyst, and a temperature sensor configured to measure a temperature of exhaust gas.

Description

CROSS-REFERENCE TO RELATED APPLICATION

Pursuant to 35 U.S.C. §119(a), this application claims priority to Korean Patent Application No. 10-2014-0060050 filed on May 20, 2014, the entire contents of which are incorporated herein by reference.

BACKGROUND

1. Field of the Invention
The present invention relates to an apparatus and a method for processing exhaust gas of a vehicle. More particularly, to an apparatus and a method for processing exhaust gas, that maximizes nitrogen oxide (NOx) reduction performance using a lambda sensor and a temperature sensor without using a NOx sensor.
2. Discussion of the Related Art
As regulations of exhaust gas of vehicles are being reinforced, DeNOx catalyst technologies such as lean NOx trap (LNT) and selective catalytic reduction (SCR) are being applied in post-processing apparatuses for reducing NOx in exhaust gas. A DeNOx catalyst is a type of catalytic converter configured to eliminate NOx contained in exhaust gas, and when a reducing agent such as urea, ammonia (NH3), carbon monoxide (CO), or hydrocarbon (HC) is transferred to exhaust gas, nitrogen oxide (NOx) is reduced through an oxidation-reduction reaction with a reducing agent in the DeNOx catalyst.
In recent years, an LNT has been used as a post-processing apparatus to eliminate NOx in exhaust gas generated when a lean bum engine is operated, and the LNT adsorbs or occludes NOx contained in exhaust gas in a lean atmosphere and detaches the adsorbed or occluded NOx in a rich atmosphere.
The SCR system is adapted to effectively reduce NOx by supplying a reducing agent to the SCR catalyst, and employs a method of reducing NOx by supplying a reducing agent to exhaust gas unlike an exhaust gas recirculation (EGR) system for reducing NOx by decreasing a combustion temperature of a combustion chamber by recirculating exhaust gas. The SCR system is referred to as a selective catalyst reduction system, meaning that a reducing agent such as urea, ammonia, carbon monoxide, or hydrocarbon is brought into a reaction with NOx among oxygen and NOx more easily.
In addition, technologies such as a diesel oxidation catalyst (DOC), a diesel particulate filter (DPF), or a catalyzed particulate filter (CPF) have been developed for post-processing reduction of particulate matters (PMs) in vehicle exhaust. Further, in recent years, an SCR on diesel particulate filter (SDPF) which both collects particulate matters and reduces NOx, has been developed and used. The SDPF brings NH₃and NOx in exhaust gas into a reaction on an SCR catalyst to purify such molecules into water and N2 by coating the SCR catalyst on a porous DPF, and collects particulate matters in the exhaust gas via a filtering function,(e.g., a DPF function).
In a method of determining aging of the SCR catalyst and the SDPF catalyst, NOx sensors are mounted upstream and downstream of the SCR or the SDPF and NOx is measured by the NOx sensor to determine whether the SCR catalyst or the SDPF catalyst is aged when the purification performance of the SCR or the SDPF is substantially low. Aging may be measured directly using such a method, however, since the price of a single NOx sensor is many times as high as that of a temperature sensor, the cost for implementing a method that requires NOx sensors, disposed upstream and downstream of the catalyst, increases.

SUMMARY

Accordingly, the present invention provides an apparatus and a method for processing exhaust gas, which may improve or maximize nitrogen oxide (NOx) reduction performance using a lambda sensor and a temperature sensor without using a NOx sensor. It should be understood that NOx may include any or all of nitric oxide (NO), nitric dioxide (NO₂) and nitrous oxide (N₂O).
In accordance with an aspect of the present invention, an exhaust gas processing apparatus, may include a lean NOx trap (LNT), a selective catalytic reduction (SCR) catalyst, and an oxygen storage catalyst that contains an oxygen storage material and a precious metal and which may be sequentially disposed along an exhaust gas flow direction. Further, a front lambda sensor may be disposed on an upstream side of the LNT, a rear lambda sensor may be disposed on a downstream side of the oxygen storage catalyst, and a temperature sensor may be configured to measure a temperature of exhaust gas may also be provided.
In accordance with an aspect of the present invention, in an exhaust gas processing method, a lean NOx trap (LNT), a selective catalytic reduction (SCR) catalyst, and an oxygen storage catalyst containing an oxygen storage material and a precious metal may be sequentially disposed along an exhaust gas flow direction, and a front lambda sensor may be disposed on an upstream side of the LNT, and a rear lambda sensor may be disposed on a downstream side of the oxygen storage catalyst. The method may include measuring, by a temperature sensor, a temperature of exhaust gas. Additionally, during a rich operation of the vehicle engine, NOx may be eliminated by the SCR catalyst when NH₃generated by the LNT and NOx in the exhaust gas reacts with each other in the SCR catalyst.
Accordingly, the exhaust processing apparatus and the method of controlling the same according to the present invention may improve or maximize NOx reduction performance using a lambda sensor and a temperature sensor without using a NOx sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings are provided for reference in describing exemplary embodiments of the present invention, and the spirit of the present invention should not be construed only by the accompanying drawings. The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description when taken in conjunction with the accompanying drawings, in which:

The above and other features of the present invention will now be described in detail with reference to certain exemplary embodiments thereof illustrated the accompanying drawings which are given hereinbelow by way of illustration only, and thus are not limitative of the present invention, and wherein:

FIG. 1 is an exemplary view showing a configuration of an exhaust gas processing apparatus according to an exemplary embodiment of the present invention;

FIG. 2 is an exemplary sectional view showing a configuration of an integral SDPF/ceria catalyst in the configuration of the exemplary embodiment shown in FIG. 1;

FIG. 3 is an exemplary view schematically showing a configuration of an exhaust gas processing apparatus according to an exemplary embodiment of the present invention;

FIG. 4 is an exemplary view showing a zone coating type SCR catalyst and a ceria catalyst in the exemplary embodiment shown in FIG. 3;

FIG. 5 is an exemplary view for explaining a NH3 generation mechanism in an LNT in the present invention; and

FIG. 6 is an exemplary view depicting an NH3 generation temperature area in the present invention.

It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various features illustrative of the basic principles of the invention. The specific design features of the present invention as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particular intended application and use environment. In the figures, reference numbers refer to the same or equivalent parts of the present invention throughout the several figures of the drawing.

DETAILED DESCRIPTION

It is understood that the term “vehicle” or “vehicular” or other similar term as used herein is inclusive of motor vehicles in general such as passenger automobiles including sports utility vehicles (SUV), buses, trucks, various commercial vehicles, watercraft including a variety of boats and ships, aircraft, and the like, and includes hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles and other alternative fuel vehicles (e.g. fuels derived from resources other than petroleum). As referred to herein, a hybrid vehicle is a vehicle that has two or more sources of power, for example both gasoline-powered and electric-powered vehicles.
Although exemplary embodiments are described as using a plurality of units to perform the exemplary process, it is understood that the exemplary processes may also be performed by one or plurality of modules. Additionally, it is understood that the term controller/control unit refers to a hardware device that includes a memory and a processor. The memory is configured to store the modules and the processor is specifically configured to execute said modules to perform one or more processes which are described further below.
Furthermore, control logic of the present invention may be embodied as non-transitory computer readable media on a computer readable medium containing executable program instructions executed by a processor, controller/control unit or the like. Examples of the computer readable mediums include, but are not limited to, ROM, RAM, compact disc (CD)-ROMs, magnetic tapes, floppy disks, flash drives, smart cards and optical data storage devices. The computer readable recording medium can also be distributed in network coupled computer systems so that the computer readable media is stored and executed in a distributed fashion, e.g., by a telematics server or a Controller Area Network (CAN).
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
Unless specifically stated or obvious from context, as used herein, the term “about” is understood as within a range of normal tolerance in the art, for example within 2 standard deviations of the mean. “About” can be understood as within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value. Unless otherwise clear from the context, all numerical values provided herein are modified by the term “about.”
Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art to which the present invention pertains can easily carry out the present invention. The present invention relates to an exhaust gas processing apparatus and a method of processing exhaust gas through which a reinforced EU6 exhaust gas regulation can be dealt with, and basically includes an LNT, an SCR catalyst, and an oxygen storage catalyst.
FIG. 1 is an exemplary view showing a configuration of an exhaust gas processing apparatus according to an exemplary embodiment of the present invention. A lean NOx trap (LNT), a selective catalytic reduction (SCR) catalyst, and an oxygen storage catalyst may be sequentially disposed with reference to an exhaust gas flow direction such to allow exhaust gas discharged from an engine to sequentially pass through the LNT, the SCR, and the oxygen storage catalyst. The LNT may be a catalyst coated with a high temperature occlusion material such as Ba, and may be configured to adsorb or occlude NOx contained in exhaust gas in a lean atmosphere (e.g., during lean operation) and produce NH3 as a by-product when NOx is converted in a rich atmosphere (e.g., during rich operation). In the present invention, the SCR catalyst may be SCR on diesel particulate filter (SDPF) configured to collect particulate matter (PM) and reduce NOx.
The SDPF may be configured by coating an SCR catalyst material on a diesel particulate filter (DPF) configured to collect particulate material in diesel exhaust gas. NH3 and NOx in exhaust gas may react with each other on the SCR catalyst to be converted into water and N₂and particulate materials in the exhaust gas may be collected through a filter function, (e.g., a DPF function). The combination of the LNT and the SDPF may be included in a passive SCR catalyst system, to produce NH₃as a by-product when NOx occluded by the LNT is converted in a rich atmosphere and NH₃produced by the LNT and NOx in exhaust gas react with each other in the SDPF, to be purified (e.g., converted into ammonia and water). The oxygen storage catalyst may include a ceria catalyst in which cerium oxide (CeO₂) (i.e., an oxide of cerium also called ceria) acts as an oxygen storage material. In an exemplary embodiment of the present invention, the SDPF and the ceria catalyst may be integrally configured using one porous filter.
FIG. 2 is an exemplary sectional view showing a configuration of an integral SDPF/ceria catalyst in the configuration of the exemplary embodiment shown in FIG. 1. The integral SDPF/ceria catalyst may include a porous filter configured to collect particulate materials in diesel exhaust gas, a selective catalytic reduction (SCR) catalyst layer 12 coated on an exhaust gas inlet of the filter, and a ceria catalyst layer 13 coated on an exhaust gas outlet of the filter and containing ceria and a precious metal. The SCR catalyst layer 12 may include a coating layer that contains a zeolite catalyst, and the ceria catalyst layer 13 may be formed by immersing a precious metal (e.g., the precious material may include, but is not limited to platinum, palladium and rhodium) in ceria.
The filter may include a plurality of layered filter walls 11, and facing surfaces of the plurality of filter walls 11 may form alternating exhaust gas inlets and outlets. In particular, the SCR catalyst layer (zeolite type) 12 may be coated on one surface of the porous filter, and the ceria catalyst layer 13 containing ceria (oxygen storage material) and a precious metal may be coated on an opposite surface of the porous filter. The catalyst may be formed by coating the SCR catalyst layer 12 on a surface of the inlet of the DPF filter and coating the ceria catalyst layer 13, in which a precious metal is supported by ceria, is coated on a surface of an outlet of the DPF filter. The ceria may first be coated on a surface of the outlet of the DPF filter and a ceria catalyst layer, in which a precious metal may be supported, may be additionally coated before the ceria catalyst layer 13, in which the precious metal is supported by ceria, is coated.
The integral SDPF/ceria catalyst may be configured by providing the porous filter for collecting particulate materials of diesel exhaust gas as a basic body and coating the SCR catalyst layer 12 on an exhaust gas inlet of the filter and coating the ceria catalyst layer 13 on an exhaust gas outlet of the filter. The filter may include a plurality of layered filter walls 11 which may be spaced apart from each other by a predetermined distance. Facing surfaces of the plurality of filter walls 11 may form alternating exhaust gas inlets and outlets.
Further, plugs 14 configured to block rear ends of the inlets and front ends of the outlets may be disposed between the filter walls 11 to allow only the front ends of the inlets to be opened while the rear ends of the inlets may be blocked by the plugs 14 and only the rear ends of the outlets may be opened while the front ends of the outlets are blocked by the plugs 14. Lambda sensors L1 and L2, configured to detect a concentration of oxygen in exhaust gas, may be disposed at an upstream side of the LNT and a downstream side of the oxygen storage catalyst in the exemplary embodiment of FIG. 1 The upstream side lambda sensor (hereinafter, referred to as ‘a front lambda sensor’) L1 may be disposed upstream side of the LNT and the downstream side of Lambda sensor (hereinafter, referred to as ‘a rear lambda sensor’) L2 may be disposed downstream of the ceria catalyst (which BE an oxygen storage catalyst). That is, downstream side of the SDPF/ceria catalyst in which the SDPF and the ceria catalyst are integrally formed by using one porous filter.
Temperature sensors T1 and T2 may be disposed upstream of the SDPF (downstream of the LNT) and downstream of the ceria catalyst, and the temperature sensors T1 and T2 may be disposed upstream and downstream of the integral SDPF/ceria catalyst in an exemplary embodiment of the present invention.
FIG. 3 is an exemplary view showing a configuration of an exhaust gas processing apparatus according to another exemplary embodiment of the present invention. The LNT, the DPF (for reduction of H₂S), the SCR catalyst, and the oxygen storage catalyst may be sequentially disposed with reference to the exhaust gas flow direction to allow the exhaust gas discharged from an engine to sequentially pass therethrough. In the exemplary embodiment of FIG. 3, a separate DPF configured to reduce H₂S may be disposed between the LNT and the SCR catalyst, that is, downstream of the LNT and upstream of the SCR catalyst, and the SCR catalyst and the oxygen storage catalyst may be sequentially disposed downstream of the DPF. The oxygen storage catalyst may include a ceria catalyst.
The SCR catalyst and the ceria catalyst may be formed by coating an SCR catalyst material and a ceria catalyst, containing a precious metal and ceria, on a surface of the support through which exhaust gas passes. The SCR catalyst and the ceria catalyst may therefore be an integral catalyst which uses one support, and the support may be divided into two sections such that an SCR catalyst material may be coated on one section and a ceria catalyst material containing a precious metal and ceria (e.g., an oxygen storage material) may be coated on the other section to form a zone coating type catalyst (i.e., an integral SCR catalyst/ceria catalyst). In other words, the SCR catalyst material and the ceria catalyst material may be coated on a front area and a rear area of the support in the zone coating method, as shown in FIG. 4. The front side may be used as an SCR catalyst (e.g., zeolite type) and the rear side may be used as a ceria catalyst having a catalytic layer in which a precious metal is supported by ceria. In addition, a catalyst configuration having two bricks may be created by coating an SCR catalyst material and a ceria catalyst material on a support. In other words, a configuration of two bricks in which an SCR catalyst and a ceria catalyst are separately combined may be applied to the support.
Lambda sensors L1 and L2 may be installed upstream of the LNT and downstream of the oxygen storage catalyst in the exemplary embodiment of FIG. 3. In such an exemplary embodiment, the upstream lambda sensor (hereinafter, referred to as a front lambda sensor) L1 may be disposed upstream of the LNT and the downstream lambda sensor (hereinafter, referred to as a rear lambda sensor) L2 may be disposed downstream of the ceria catalyst (which is an oxygen storage catalyst on the downstream side of the LNT). Temperature sensors T1, T2, and T3 may be disposed upstream (downstream of the LNT) and downstream of the DPF, and downstream of the ceria catalyst.
Although configurations of exhaust gas processing apparatuses according to the exemplary embodiments of the present invention have been described with reference to FIGS. 1 to 3, such an exhaust gas processing apparatus may effectively reduce or eliminate NOx from the SCR catalyst using NH₃generated from the LNT when rich atmospheres are periodically formed through an engine air/fuel ratio control (e.g., via lambda control) to reduce the NOx stored in the LNT. In other words, NOx may be stored in the LNT in a lean atmosphere (lean operation) and NH₂may be generated by a reaction in the LNT when rich atmospheres are periodically formed. In particular NH₃and NOx may react with each other in the SCR catalyst to eliminate NOx and the ceria catalyst supporting a minimal amount of precious metal may purify CO and HC excessively generated in a rich atmosphere. Then, to effectively generate a sufficient amount of NH₃, a rich atmosphere should be maintained for several seconds after the oxygen in the LNT is completely exhausted by the rich atmosphere.
An additional rich atmosphere may be maintained using a signal of the rear lambda sensor, by locating the SCR catalyst downstream of the LNT, adding the oxygen storage catalyst (ceria catalyst) downstream of the SCR catalyst, and mounting the rear lambda sensor L2 downstream of the oxygen storage catalyst. A time period of time that a rich atmosphere may exist may be extended in response to determining that oxygen is not exhausted upstream of the rear lambda sensor L2 using a signal of the rear lambda sensor L2 since oxygen in the oxygen storage catalyst may not be exhausted even though the oxygen in the LNT is exhausted in the rich atmosphere. Accordingly, an additional rich atmosphere may be maintained, and thus an amount of NH₃generated from the LNT may increase, thereby improving the entire NOx purification performance. Of course, NH₃generated from the LNT may react with NOx in the SCR catalyst, and NH₃may be used to purify NOx in the SCR catalyst. According to the present invention, a period of time a rich atmosphere may exist may be artificially increased by disposing a ceria catalyst having an oxygen storage material and a substantially small amount of precious metal downstream of the SCR catalyst. When the lambda sensor L2 is installed downstream of the ceria catalyst such that an additional rich atmosphere maybe maintained, (i.e., the period of time the rich atmosphere may exist may be increased), a sufficient amount of NH₃may be effectively generated, and a purification of NH₃and NOx may be performed in the SCR catalyst and CO and HC may be eliminated from the ceria catalyst supporting the precious metal.
FIG. 5 is an exemplary view for explaining a NH3 generation mechanism in an LNT in the present invention. In FIG. 5, the horizontal axis denotes time and the vertical axis denotes (a) lambda value (b) temperature, and (c) concentrations of NH₃and CO in exhaust gas. Referring to FIG. 5A, a lambda breakthrough generation time point is denoted by a breakthrough point. The breakthrough point may be a time when lambda values of the lambda sensor (front lambda sensor) upstream of the LNT and the lambda sensor downstream of the LNT coincide with each other in a rich atmosphere.
It should be noted that the lambda sensor downstream of the LNT may be different from the rear lambda sensor L2 suggested in the present invention. In other words, the lambda sensor L2 disposed downstream of the ceria catalyst (which is an oxygen storage catalyst), may be a downstream lambda sensor on a rear side of the LNT (which is disposed upstream of the SCR catalyst (SDPF) of FIG. 1 and upstream of the DPF of FIG. 3). Hereinafter, the lambda sensor downstream of the LNT may be different from the rear lambda sensor, and the lambda sensor downstream of the LNT may be a lambda sensor disposed downstream of the rear end of the LNT where the rear lambda sensor refers to a lambda sensor disposed at a rear end of the ceria catalyst (which is an oxygen storage catalyst). According to the related art, a rich operating control is finished at a lambda breakthrough generation time point (defined as a time when lambda values of the upstream and downstream lambda sensors coincide), as illustrated as a breakthrough point in FIG. 5.
Further, FIG. 5B shows an exemplary temperature of exhaust gas (e.g., a temperature value sensed by the temperature sensor T1 downstream of the LNT). FIG. 5C illustrates a breakthrough point (tbt). A breakthrough point may be defined as a time during rich operation when the lambda values of the lambda sensor L1 upstream of the LNT and the lambda sensor downstream of the LNT coincide. When a rich atmosphere (e.g., having lambda value (λ) <1) is generate through engine operation, a reduction chemical reaction formula (e.g., a NOx chemical reaction performed through storage of NOx in a rich atmosphere) before generation of a breakthrough point may be as follows.
Ba(NO₃)₂+3CO→2NO+2CO₂+BaCO₃
2NO+2CO→N₂+2CO₂
When a concentration of oxygen in exhaust gas in a rich atmosphere is reduced and the content of a reducing agent such as CO or HC is increased, a nitrate occluded in a substantially high temperature occlusion material such as Ba may be separated to be converted to nitrogen N₂while being reduced by the reducing agent such as CO or HC. The reaction formula after the generation of the breakthrough point may be as follows.
CO+H₂O→CO₂+H2 (Water/Gas-Shift)
HC3+3H₂O→3CO+6H₂(Steam Reforming)
5H2+2NO→2NH₃+2H2O
Generation of NH₃in the LNT from a time when oxygen stored in the oxygen storage material of the LNT and NOx stored in the NOx occlusion material are exhausted and eliminated, and H₂and NO (detached from the LNT or supplied from the exhaust gas) react with each other to generate NH₃after NOx and 0 ₂are exhausted in the rich atmosphere condition. NH₃may be generated most, as illustrated in FIG. 5C during a time period α, after tbt (the breakthrough point). Additionally, when the rich atmosphere is maintained for the time period α a after tbt, an amount of NH₃may be increased.
Although the rich control may be completed at a breakthrough point when the lambda values of the upstream and downstream lambda sensor values coincide with each other according to the related art, a rich control may be completed when the lambda values of the front lambda sensor (the lambda sensor on the upstream side of the LNT) L1 and the rear lambda sensor L2 coincide with each other according to the present invention, whereby an additional rich control for the time period of a may be further maintained after the tbt of the related art. Since generation of NH₃may decrease when a is set to be too short and generation of NH₃may increase while generation of CO may increase excessively which may adversely influence a fuel ratio when α is set to be too long, properly adjusting or optimizing α according to an engine condition is desirable.
The additional rich operating time α (e.g., within about 5 seconds) may be increased according to the downstream oxygen storage catalyst, that is, an amount of ceria of the ceria catalyst or an amount of stored oxygen, however an excessive amount of NH₃may be generated by such continuation of the rich operation condition.
Increased NH₃generated during the additional rich operation time may react with NOx through an SCR catalyst downstream of the LNT to reduce NOx, and increased CO and HC generated during the additional rich operation time may be additionally reduced by using a precious metal contained in the ceria catalyst. Main factors, engine/catalyst conditions, which influence generation of NH₃may include a temperature of exhaust gas, a flow rate of exhaust gas, a degree of catalyst aging (e.g. degradation), and tbt, and α time may be decreased as tbt is decreased. Although the rich atmosphere for DeNox may be eliminated immediately after tbt according to the related art, a substantial amount of NH₃may be effectively generated by maintaining the rich atmosphere for an additional time period, α (as illustrated in FIG. 5) after tbt for DeNOx, whereby an amount of NOx in exhaust gas may be additionally reduced in the SCR catalyst according to exemplary embodiments of the present invention.
FIG. 6 is an exemplary view depicting a NH₃generation temperature range; generation of NH₃starts at a substantially low temperature of about 200° C., and a maximum amount of NH₃may be generated at around 300° C. NH₃may also be generated at about 350° C. or greater. The amount of NH₃generated depends on: lambda values, a flow rate of exhaust gas, and concentration.
Although exemplary embodiments of the present invention have been described in detail, the scope of the present invention is not limited thereto but various modifications and improvements made by those skilled in the art using the basic concept of the present invention defined in the claims also fall within the scope of the present invention.

Claims

What is claimed is:

1. An exhaust gas processing apparatus, comprising:

a lean NOx trap (LNT);

a temperature sensor configured to measure a temperature of an exhaust gas;

a selective catalytic reduction (SCR) catalyst; and

an oxygen storage catalyst containing an oxygen storage material and a precious metal, wherein the LNT, the SCR and the oxygen storage catalyst are sequentially disposed along an exhaust gas flow direction, and wherein a front lambda sensor is disposed upstream of the LNT, a rear lambda sensor is disposed downstream of the oxygen storage catalyst.

2. The exhaust gas processing apparatus of claim 1, wherein the oxygen storage catalyst includes a ceria catalyst containing ceria as an oxygen storage material.

3. The exhaust gas processing apparatus of claim 1, wherein the SCR catalyst is formed by coating an SCR catalyst layer on a porous filter configured to collect a particulate material in diesel exhaust gas.

4. The exhaust gas processing apparatus of claim 1, wherein the SCR catalyst and the oxygen storage catalyst form an integral catalyst which uses one porous filter, and wherein the integral catalyst comprises:

a porous filter;

an SCR catalyst layer coated on an exhaust inlet of the filter; and

an oxygen storage material catalyst layer coated on an exhaust gas outlet of the filter and containing an oxygen storage material and a precious material.

5. The exhaust gas processing apparatus of claim 4, wherein the filter is a porous filter configured to collect a particulate material in diesel exhaust gas.

6. The exhaust gas processing apparatus of claim 4, wherein the filter includes a plurality of multi-layered filter walls, and wherein facing surfaces of the plurality of filter walls form alternating exhaust inlets and outlets.

7. The exhaust gas processing apparatus of claim 1, wherein a diesel particulate filter is disposed between the LNT and the SCR catalyst.

8. The exhaust gas processing apparatus of claim 7, wherein the SCR catalyst and the oxygen storage catalyst form an integral catalyst which uses one support, and the integral catalyst is formed by coating the SCR catalyst layer and the oxygen storage material containing an oxygen storage material and a precious metal on a front area and a rear area of the support through a zone coating method.

9. The exhaust gas processing apparatus of claim 4, wherein the oxygen storage material includes ceria.

10. The exhaust gas processing apparatus of claim 1, wherein the SCR catalyst layer of the SCR catalyst contains a zeolite catalyst.

11. The exhaust gas processing apparatus of claim 1, wherein a rich operation for eliminating NOx occluded in the LNT is maintained until lambda values of the front lambda sensor and the rear lambda sensor coincide with each other during rich operation.

12. A method of controlling an exhaust gas processing apparatus, wherein a lean NOx trap (LNT), a selective catalytic reduction (SCR) catalyst, and an oxygen storage catalyst containing an oxygen storage material and a precious metal are sequentially disposed along an exhaust gas flow direction, and wherein a front lambda sensor is disposed upstream of the LNT, and a rear lambda sensor is disposed downstream of the oxygen storage catalyst, the method comprising:

measuring a temperature, by a temperature sensor, of exhaust gas disposed within the exhaust path, and

eliminating NOx, by the SCR catalyst during a rich operation when NH₃generated by the LNT and NOx in the exhaust gas react with each other in the SCR catalyst.

13. The exhaust gas processing method of claim 12, further comprising:

eliminating, by a precious metal contained in the oxygen storage catalyst, carbon monoxide (CO) and hydrocarbon (HC) in the exhaust gas.

14. The exhaust gas processing method of claim 12, further comprising:

maintaining a rich operation for eliminating NOx occluded in the LNT until the lambda values of the front lambda sensor and the rear lambda sensor coincide.

15. The exhaust gas processing method of claim 14, wherein the α is a time period (tbt) from a rich operation starting time until a time that lambda values of the front lambda sensor and the rear lambda sensor coincide, the method further comprising:

measuring, by a temperature sensor, a temperature of the exhaust gas.

16. The exhaust gas processing method of claim 12, wherein the oxygen storage catalyst is a ceria catalyst containing ceria as an oxygen storage material.

17. The exhaust gas processing method of claim 12, wherein the SCR catalyst is formed by coating an SCR catalyst layer on a porous filter configured to collect a particulate material in diesel exhaust gas.

18. The exhaust gas processing method of claim 12, wherein a diesel particulate filter is disposed between the LNT and the SCR catalyst.

19. The exhaust gas processing method of claim 12, wherein the SCR catalyst layer of the SCR catalyst contains a zeolite catalyst.

20. The exhaust gas processing method of claim 17, wherein the SCR catalyst layer of the SCR catalyst contains a zeolite catalyst.