WO2007029339A1

WO2007029339A1 - Exhaust gas purifying apparatus for internal combustion engine and method for exhaust gas purification

Info

Publication number: WO2007029339A1
Application number: PCT/JP2005/016683
Authority: WO
Inventors: Masayuki Kamikawa; Hidehiro Iizuka; Toshiaki Nagayama; Yuichi Kitahara; Osamu Kuroda; Masato Kaneeda
Original assignee: Hitachi, Ltd.
Priority date: 2005-09-05
Filing date: 2005-09-05
Publication date: 2007-03-15
Also published as: JPWO2007029339A1

Abstract

This invention provides an exhaust gas purifying apparatus for purifying hydrocarbons, carbon monoxide and nitrogen oxide discharged during the operation of a diesel engine. The exhaust gas purifying apparatus for a diesel engine comprises a diesel engine exhaust gas flow passage (2). A catalyst (3) having both an NOx selective reduction capability and a hydrogen production function and a lean NOx catalyst (4) are provided in that order along the diesel engine exhaust gas flow passage (2) from the upstream of the exhaust gas flow passage. The exhaust gas purifying apparatus can efficiently purify an exhaust gas discharged from diesel engines.

Description

Technical field of exhaust gas purification apparatus and exhaust gas purification method for internal combustion engine

The present invention relates to an exhaust gas purification method and apparatus for an internal combustion engine, and more particularly, to an exhaust gas purification method and apparatus for purifying hydrocarbons, carbon monoxide, and nitrogen oxides contained in exhaust gas. Background art

In recent years, awareness of global warming has increased, and co _{2 in} exhaust gas emitted from internal combustion engines such as automobiles has become a problem, and the solution is to burn fuel lean in an oxygen-rich atmosphere. Diesel engines are promising. In these engines, since the amount of fuel used is reduced, the generation of CO ₂ as combustion exhaust gas can be suppressed.

For this reason, a NOx selective reduction type catalyst has been developed that can efficiently reduce and purify NOx under the exhaust gas flow of diesel engine, which has an excess of oxygen. However, this catalyst has a problem that its temperature dependency is small, but its N O X purification ability is low, and sufficient N O X cannot be purified.

In addition, a NOx catalyst that captures NOX in a lean atmosphere and reduces and purifies the captured NOX in a lean or rich atmosphere for a gasoline engine (lean burn engine) that operates in a lean atmosphere. Has been developed. For lean NO x catalysts, NOX is oxidized to NO ₂ in a lean atmosphere and stored in a NO _X storage material, and stored in a stoichiometric or rich atmosphere. NOx storage-reduction catalyst that can reduce and purify NO x, in a lean atmosphere

There are NOX adsorption reduction catalysts that can oxidize NOX to NO ₂ and adsorb it on NOX adsorbents, and reduce and purify adsorbed NOX in a stiff or rich atmosphere. Therefore, by operating the engine in a lean atmosphere, which is most suitable for lean NO X catalyst, and operating the engine in a stoichiometric or rich atmosphere temporarily when NO X is sufficiently trapped by the NOX purification catalyst. A system that reduces and purifies NO x using exhaust gas as a reducing atmosphere has also been developed.

However, the diesel engine has a lower exhaust temperature than the gasoline engine, and it is as low as about 200 ° C. Since the lean NO x catalyst is highly temperature dependent and the catalyst temperature at which it performs sufficiently is 300 ° C or higher, placing the lean NO X catalyst under the floor of a vehicle equipped with a diesel engine will There is a problem that it is not “warm enough” and NO x cannot be sufficiently captured, reduced or purified. Although is a NOX reducing agent than C_〇及Pi HC 'H _9. Is closed criminal investigation, during diesel exhaust hardly contains.

In order to solve this problem, Japanese Patent Laid-Open No. 2 0 3 -3 3 1 4 3 2 8 describes that H ₂ , which is a reducing agent with high NOX reduction performance at low temperatures, has a stoichiometric or rejuvenating atmosphere. In order to supply the NOx occlusion reduction type catalyst to the NOx occlusion reduction type catalyst, an exhaust gas purifying device is disclosed, in which the hydrogen production catalyst is arranged upstream of the NOx occlusion reduction type catalyst. Japanese Patent Laid-Open No. 2 00 0-2 7 6 2 5 is characterized in that a NOX selective reduction catalyst is arranged upstream of the lean NO X catalyst in order to improve the performance during leaning. An exhaust gas purification device for an internal combustion engine is disclosed. Disclosure of the invention According to Patent Document 1, although the NOX reduction ability at the time of latching is improved, the NOX trapping ability at the time of leaning has not been improved, so if a large amount of NOX enters the NOX storage reduction type catalyst at the time of leaning, purification is performed. There is a fear that it cannot be exhausted. Also, in Patent Document 2, an Ir-based catalyst is used as the NOX selective reduction catalyst, but the NOX selective reduction ability at 300 ° C or lower is low, and at low temperatures of about 200 ° C. It is difficult to reduce and purify N 0 .X sufficiently.

The subject of the present invention is to provide an exhaust gas purification method and apparatus that eliminates the above-mentioned problems and that effectively purifies hydrocarbons, carbon monoxide, and nitrogen dioxide discharged during operation of an internal combustion engine.

The feature of the present invention that solves the above-mentioned problems is that the NOx selective reduction ability capable of reducing NOX during leaning from the upstream of the exhaust gas passage to the diesel engine exhaust gas passage and the CO shift reaction at the time of latching. This is an exhaust gas purification system in which a catalyst having a hydrogen production function for generating hydrogen and a 'lean NOX catalyst' are arranged in the above order.

Figure 1 shows a schematic diagram. Exhaust gas discharged from engine 1 passes through exhaust gas flow path 2 and is purified from upstream of the exhaust gas flow path by catalyst 3 having both NO 3 selective reduction ability and hydrogen production function, and lean NOX catalyst 4. According to the above configuration, since the catalyst having both NOX selective reduction ability and hydrogen production function is arranged upstream of the lean NOX catalyst with respect to the exhaust gas flow, when the exhaust gas is in an oxidizing atmosphere, NOX Increase the amount of NOX purification by selective reduction. When exhaust gas is in a reducing atmosphere, CO is emitted from the engine; hydrogen is generated from HC and H ₂ O by the CO shift reaction and steam reforming reaction, and the oxidizing atmosphere is switched to the reducing atmosphere. In particular, the NOX trapped on the lean NOX catalyst can be sufficiently purified. And because it uses a catalyst with both Nx selective reduction ability and hydrogen production function, it can improve NOx purification performance when lean. With this catalyst, it is possible to efficiently reduce and purify NOx trapped in the lean by generating hydrogen during the latching. In addition, the NO X selective reduction ability of a catalyst having both NO X selective reduction ability and hydrogen production function is sufficiently exhibited even at 200 ° C.

The component of the catalyst having both the NO X selective reduction ability and the hydrogen production function in the present invention contains a 'CO reforming component that produces hydrogen by steam reforming CO. In concrete terms, the above-mentioned 0 O reforming component is composed of at least one kind of precious metal selected from R h, P t, and P d force, and Z r 0 ₂ , C e O ₂ , T i O ₂ or, characterized that you containing composite oxide carrier containing a Z r O ₂ throat C e O _2.

As the lean NO X catalyst in the present invention, a NO X storage reduction catalyst or a NOX adsorption reduction catalyst can be used. The NO x adsorption and reduction type catalyst is chemically adsorbed after oxidizing the NO to NO ₂ in the lean operation, a reducing atmosphere exhaust gas before the NO ₂ adsorbed reach NO ₂ equilibrium adsorption amount of NOX adsorption and reduction catalyst An exhaust gas purifying catalyst that reduces and purifies the adsorbed N 0 ₂ to nitrogen (N ₂ ), and the oxide carrier is at least one selected from alkaline metals, alkaline earth metals, and rare earth elements. The NOx adsorbent is supported on at least one kind of noble metal selected from Rh, Pt, and Pd.

In order to make the exhaust gas into a reducing atmosphere, the fuel for the second time in the engine cylinder in the expansion stroke or exhaust stroke in addition to the normal fuel injection in diesel engines, without special reducing agent addition device. This can be achieved by using secondary fuel injection. In the present invention, in order to reduce and purify NO x, the exhaust gas or lean NO X catalyst is used so that the temperature of the lean NO X catalyst is sufficiently high while creating a state where there is more reducing agent compared to lean operation. The timing for heating can be determined by the following methods.

(1) Air-fuel ratio setting signal determined by E CU (Electric Control Unit), engine speed signal, intake air amount signal, 'intake pipe pressure chi no., Speed signal, throttle opening, exhaust gas temperature, etc. ^ When the NO x output during operation is estimated and the accumulated value exceeds the preset value.

(2) When the cumulative oxygen amount detected by the signal of the AZF sensor (or oxygen sensor) placed upstream or downstream of the NO X purification catalyst in the exhaust passage exceeds a predetermined amount, or only during lean operation When the cumulative amount of oxygen exceeds the specified amount.

(3) When the accumulated NO x amount is calculated based on the NO X sensor signal placed upstream of the lean NO X catalyst in the exhaust flow path and the accumulated NO x amount exceeds the predetermined amount during lean operation.

(4) When the NOx concentration during lean operation is detected by the signal from the NOx sensor placed downstream of the NOx adsorption / reduction catalyst in the exhaust passage, and the NOx concentration exceeds the specified concentration.

As described above, the time for maintaining a state where the amount of reducing agent is higher than that during lean operation and the amount of reducing agent to be charged to maintain the state are as follows. Although it can be determined in consideration of the origin and characteristics, it can be realized by adjusting the stroke, injection time, and injection interval of the fuel injection valve. Brief Description of Drawings FIG. 1 is a schematic view showing an embodiment of a diesel engine exhaust gas purification apparatus of the present invention.

FIG. 2 is a schematic view showing an embodiment of the diesel engine exhaust gas purification apparatus of the present invention. '

FIG. 3 is a schematic view showing an embodiment of the diesel engine exhaust gas purification apparatus of the present invention. '

FIG. 4 is a schematic view showing an embodiment of the diesel engine exhaust gas purification apparatus of the present invention. '

FIG. 5 is a schematic view showing an embodiment of the diesel engine exhaust gas purification apparatus of the present invention.

FIG. 6 is a block diagram showing an air-fuel ratio control method.

Fig. 7 is a flowchart of air-fuel ratio control.

Fig. 8 shows the N O X amount estimation part in the flowchart of Fig. 6. Fig. 9 shows the N O X amount estimation part in the flowchart of Fig. 6. FIG. 10 shows the NOx amount estimation part in the flowchart of FIG. Fig. 11 shows the NOx estimation part in the flowchart of Fig. 6. Figure 12 shows the NOx amount estimation part of the flow chart in Figure 6. FIG. 13 is a schematic view showing an embodiment of the diesel engine exhaust gas purification apparatus of the present invention. -Best mode for carrying out the invention

Hereinafter, embodiments of the present invention will be described with reference to the drawings and tables.

In the diesel engine exhaust gas purification apparatus of the present invention, a catalyst having both NOX selective reduction ability and hydrogen production function, lean NO x catalyst, is arranged in the above order in the middle of the exhaust path of the diesel engine. It is made up.

The catalyst that has both NO x selective reduction ability and hydrogen production function has the function of generating H ₂ by an aqueous gas shift reaction between CO and H ₂ O, which are abundant in the exhaust gas, when the exhaust gas is in a reducing atmosphere. Have And this good UNA catalyst, precious metal (P t, P d, R h , etc.) and, Z r O ₂ as a carrier, C e O _2, T i 0 ₂ Moshiku is Z r 〇 ₂ and C e various catalysts containing a composite oxide containing 0 _2, for example, P t ZC e 〇 _2, P t / ceria one zirconate - § composite oxide, and the like P t ZT i O _2. The carrier preferably has a high oxygen storage capacity, a large surface area and a large pore volume.

In the catalyst of the present invention, it has been confirmed separately (described later) that hydrogen generation occurs in the rich and that the lean has selective reduction performance.

As a lean NO X catalyst placed on the downstream side of the catalyst having both the NO X selective reduction ability and the hydrogen production function, a high-specific surface area refractory inorganic material such as alumina supporting a noble metal is used. , Alkali metals such as N a, alkaline earth metals such as C a and B a, transition metals such as T i, Mn, F e, .C u, L a, Z r.,. It is possible to use a rare earth metal, or a combination of these, a combination of these, a two-cam monolith type catalyst.

Fig. 2 shows (1) NO X adsorption reduction catalyst only, (2) NO x selective reduction catalyst and NOX adsorption reduction catalyst, (3) NOx selective reduction catalyst and hydrogen production function. In combination with NO X adsorption-reduction catalyst, shows the NO x purification rate at 2 ° C and lean of the three types of catalysts (1) Lean performance with NO X adsorption-reduction catalyst alone 51%, Rich performance 43%, Lean / Ritch total performance 47%. (2) NOX selection When combined with a reduction catalyst, lean performance is 76%, rich performance 60%, Lean / Litch total performance was 68%, and the Lean performance was improved by 25 points, but the “Litch performance” was only improved by 1.7 points. On the other hand,

(3) When combined with a catalyst having both NO X selective reduction ability and hydrogen production function, the lean performance was 82%, the richness performance was 78%, and the lean-notch total performance was 80%. The lean performance improved by 29 points, and the Rich performance improved by 35 points. Compared with the combination with N. OX selective reduction catalyst, the Rich performance was 18 points higher than the point. It depends on the hydrogen production function.

From the above, it has been found that the NOx purification method of the present invention can greatly improve the lean Z-litch performance. Especially in the present invention, by deepening the richness (increasing air-fuel ratio fuel), CO production proceeds at low temperatures, sometimes reducing and purifying NOX inside at high temperatures, and purifying exhaust gas. Advances. 'On the other hand, fuel consumption increases by deepening the ridge.

'In the above example, lean NO' X catalyst and hydrogen. A production function catalyst was created separately and placed in series, but a catalyst having both NOX selective reduction ability and hydrogen production function was supported on the lean NOX catalyst, A two-layer catalyst can also be used.

Further, a diesel particulate filter (D PF) that oxidizes and removes PM in exhaust gas may be disposed upstream of a catalyst having both N O X selective reduction ability and hydrogen production function. The filter means has a function of capturing a light.

As the filter, for example, various materials such as a ceramic sintered body, a ceramic fiber, and a metal can be used. Specifically, a filter in which a ceramic fiber is coiled and formed into a cylindrical shape, a filter in which a fiber weave is formed into an appropriate shape, and made of ceramic, the upstream end is closed and the downstream side is closed Exhaust gas passage with open end and upstream end open Various types and sizes, such as wall-flow type filters, in which exhaust gas passages with closed downstream ends are alternately arranged and porous saddle surfaces are formed between adjacent exhaust gas passages This filter can be selected appropriately according to the space used.

Example 1

An embodiment of the diesel engine exhaust gas purification apparatus of the present invention is shown in FIG.

The diesel engine exhaust gas purifying apparatus of the present embodiment includes an intake system having a diesel engine 1, an air flow sensor '6, a throttle valve 7', etc., a NOx adsorption reduction type catalyst 5, and an exhaust gas passage 2 catalyst. 5 Exhaust system with NOx selective reduction ability and hydrogen production function installed upstream from 5 AZF sensor (or oxygen concentration sensor) 8 and 10; Exhaust temperature sensor 9 and 11 And control unit (ECU) 1 2 etc. The ECU consists of an I / O L S I as an input / output interface, an arithmetic processing unit MPU, a storage device RAM and R0Μ that stores many control programs, and a timer counter.

In the diesel engine exhaust gas purification apparatus of the present embodiment, exhaust gas discharged from the diesel engine 1 first flows into the catalyst 3 having both NO X selective reduction ability and hydrogen production functions. Catalyst 3, which has both NO X selective reduction ability and hydrogen production function, reduces and purifies NOX by NO x selective reduction reaction with NOx and CO in the presence of high concentration of O ₂ during lean operation, and at the time of rich operation H ₂ is generated by the water gas shift reaction between CO and H ₂ O, and the generated H ₂ promotes the NO X reduction reaction of the NO X adsorption reduction catalyst 5.

The NO x adsorption and reduction type catalyst 5 is chemisorbed after oxidizing 'NO to NO ₂ in the lean operation, NO ₂ flat衡吸of NO ₂ adsorbed NO X adsorption and reduction catalyst 5 0

Previously exhaust gas reaching the wear amount and a reducing atmosphere, reducing the adsorbed N_〇 ₂ nitrogen (N _2), to purify. ,

In addition, as means for making the exhaust gas into a reducing atmosphere, means for increasing the hydrocarbon concentration (such as engine secondary fuel injection), means for reducing the oxygen concentration, etc.

(Intake throttling, etc.) etc. In addition, during the treatment for increasing the hydrocarbon concentration and the treatment for reducing the oxygen concentration, the catalyst temperature of the NOx adsorption reduction catalyst 5 was controlled from 25 ° C. to 500 ° C. This is because the NOx purification capacity of the NOx adsorption reduction catalyst is good at temperatures in the above range.

Example 2

FIG. 4 shows an embodiment of the diesel engine exhaust gas purification device of the present invention. FIG. 4 is a view of the NOx adsorption reduction catalyst 5 shown in FIG. 3 replaced with an absorption reduction catalyst.

NOX storage-reduction catalyst 1 3 oxidizes NO to NO ₂ during lean operation and then reacts with the storage material to generate nitrate in the storage material. The stored NOX is the NOX of NOX storage-reduction catalyst 1 3 Before reaching the equilibrium storage amount, the exhaust gas is made a reducing atmosphere, and the stored nitrate is reduced to nitrogen (N ₂ ) and purified. As in the case of the adsorptive reduction catalyst 5, when the catalyst temperature is controlled from 2550 ° C. to 500 ° C., the NOX purification ability of the NOX storage reduction catalyst 13 is good. '(Example 3)

FIG. 5 shows an embodiment of the diesel engine exhaust gas purification apparatus of the present invention. FIG. 5 shows an example in which the catalyst 3 and the catalyst 5 in FIG.

The two-layer catalyst 14 is a catalyst in which a catalyst having both NOX selective reduction ability and hydrogen production function is supported on a NOX adsorption reduction catalyst. Exhaust gas flow path 4 1

From the upstream side, the catalyst is arranged in the order of N O x selective reduction ability and hydrogen production function and N O x adsorption reduction catalyst.

Example 4

(Air-fuel ratio control method)

In Examples 1 to 3, the fuel concentration (hereinafter referred to as the air-fuel ratio) of the air-fuel mixture supplied to the engine can be controlled as follows.

Fig. 6 shows a block diagram of the air-fuel ratio control method. Load sensor output that outputs a signal according to the depression of the accelerator pedal, output signal of intake air measured by the airflow sensor, engine speed signal detected by the crank angle sensor, exhaust gas temperature signal, throttle opening ECU 14 determines the air-fuel ratio (AZF) from the information on the throttle position sensor signal, engine coolant temperature signal, starter signal, etc., and this signal is fed back from the AZF sensor (or oxygen sensor). The fuel injection amount is determined based on the corrected signal. Note that feedback control is stopped by signals from each sensor and switch at low temperatures, at idle, and at high loads. In addition, the air / fuel ratio correction learning function can be used to accurately cope with subtle or sudden changes in the air / fuel ratio.

When the determined air-fuel ratio is a reducing atmosphere, the injection condition of the injector is determined by the instruction of ECU and the rich operation is performed. On the other hand, when the lean operation is determined, it is determined whether or not the lean NOX catalyst has NOX trapping ability, and the trapping ability is determined to be equal to or higher than a predetermined specified value (for example, 50% of the equilibrium trap amount). If the fuel injection amount is determined to perform the lean operation as instructed and the adsorption capacity is determined to be less than the predetermined specified value, the air-fuel ratio is shifted for a predetermined period to activate the lean NOX catalyst. Reproduce.

Fig. 7 shows the flowchart of air-fuel ratio control. In steps 1 0 0 2 Reads signals for instructing various operating conditions or detecting operating conditions. Based on these signals, the air-fuel ratio is determined in step 1003, and the determined air-fuel ratio is detected in step 1004. Compare the air-fuel ratio determined in Step 1 0 0 5 with the theoretical air-fuel ratio. The theoretical air-fuel ratio to be compared here is precisely the air-fuel ratio at which the NOX catalytic reduction reaction rate exceeds the capture rate in the lean NO X catalyst, and the characteristics of the lean NOX catalyst are evaluated in advance. The air / fuel ratio near the stoichiometric air / fuel ratio is selected. Here, if the set air-fuel ratio ≤ the stoichiometric air-fuel ratio, the routine proceeds to step 106, and the air-fuel ratio operation is performed as instructed without performing the regeneration operation of the lean NOX catalyst. If set air / fuel ratio> stoichiometric air / fuel ratio, go to step 1 0 7 In step 1007, the estimated amount of Nx is estimated. The estimation calculation method will be described later. Subsequently, in step 1 0 0 8, it is determined whether or not the estimated NO X trapping amount is equal to or less than a predetermined limit amount. The limit trapping amount is set to a value that can sufficiently purify NX in the exhaust gas by evaluating the NOx trapping characteristics of the lean NOx catalyst by experiments in advance and considering the exhaust gas temperature and lean NOX catalyst temperature, etc. Is set. If NO x trapping capability exists, proceed to step 106, and perform the air-fuel ratio operation as instructed without regenerating the lean NO X catalyst. If NO X trapping ability is not available, proceed to step 1 0 9 and shift the air-fuel ratio to the latch side. In steps 1 0 1 0, the latch shift time is counted, and when the elapsed time T r exceeds a predetermined time (T r) c, the latch shift is terminated.

(Determination of NO x capture ability)

The determination of the NO x trapping capacity in the above steps 1 0 0 8 can be performed as follows.

'Fig. 8 shows a method for accumulating NO x emissions from various operating conditions during lean operation. Step 1 0 0 7—E 0 1 reads the signals related to the operating conditions of the lean NOX catalyst, such as the exhaust gas temperature, and signals related to various engine operating conditions that affect the NOX concentration in the exhaust gas. to estimate the amount of NO X E _N to. Step 1 0 0 7- E monument 2 integrates the E _N, compares the magnitude of the step 1 0 0 8- E 0 1 integrated value sigma E _N and holding amount upper limit value at (E _N) c. If ∑ E _N ≤ (E _N ) c, continue to accumulate, if ∑ E _N > (E _N ) c, step 1 0 0 8 — cancel accumulation at E 0 2 and proceed to step 1 0 0 9 .

■ Fig. 9 shows the method for judging from the accumulated lean operation time. Step 1 0 0 7 — Accumulate the lean operation time _HL at H 0 1, and compare the magnitude of the accumulated value ∑ and the upper limit value of accumulated time (H _r .) C at Step 1 0 0 8 — H 0 1 . If ∑ H _L ≤ (H _L ) c, continue integration. If ∑ H _L > (H _L ) c, cancel integration at step 1 0 0 8-H 0 2 and proceed to step 1 0 0 9.

Fig. 10 · is a method of judging from the AZF sensor (or oxygen sensor) signal during lean operation. Step 1 0 0 7-O 0 1 The amount of oxygen Q in lean operation. 'Step 1 0 0 8 — O 0 1 is the integrated value! : Q. And the upper limit (Q.) c of the accumulated oxygen amount. ∑ Q. ≤ (Q.) In case of c, continue integration and 積算 Q. > (Q.) In the case of c, the integration is canceled at step 1 0 0 8—O 0 2 and the process proceeds to steps 1 0 0, 9.

Fig. 11 shows the determination method based on the NO X concentration sensor signal detected at the lean NO X catalyst inlet during the line operation. Step 1 0 0 7—N 0 1 Based on the NO X concentration sensor signal, add the NOX amount Q _N at the lean NOX catalyst inlet. Step 1 0 0 8— Compare the accumulated value ∑ Q _N with the accumulated NO X upper limit value (Q _N ) c at NO 1. ∑ If Q _N ≤ (Q _N ) c, continue the integration. If ∑ Q _N > (Q _N ) c, cancel the integration at step 1 0 0 8—N 0 2 and proceed to step 1 0 0 9 Four

Fig. 12 shows the method of judgment based on the NO X concentration sensor signal detected at the lean NOO catalyst outlet during lean operation. Step 1 0 0 7 — C 0 1 detects the NO x concentration C _N at the lean NO x catalyst inlet based on the NOx dark sensor signal. Step 1 0 0 8—Compare the size of C _N and the upper limit of C _N (Q _N ) c at CO 1. If C _N ≤ (Q _N ) c, continue detection, and if C _N > (Q _N ) c, go to step 1 0 0 9.

Example 5

One embodiment of the diesel engine exhaust gas purification apparatus of the present invention is shown in FIG.

In this embodiment, a three-way catalyst 15 from the upstream side into the exhaust gas passage 4, a diesel particulate filter that oxidizes and removes particulate matter in the exhaust gas.

1 6, catalyst that has NO X selective reduction ability and hydrogen production function 3, NO x adsorption reduction type catalyst 5 are arranged, and AZ corresponding to each catalyst

In this example, F sensors (or oxygen concentration sensors) 8, 10 and 17, exhaust temperature sensors, 11, 18 and 20, pressure sensors 19 and 21, etc. are installed.

In the diesel engine exhaust gas purification apparatus of the present embodiment, the exhaust gas discharged from the diesel engine 1 is first heated by the three-way catalyst 15 to decompose HC in the exhaust gas. Since hydrocarbons in diesel engine exhaust gas are relatively high in higher hydrocarbons with 7 or more carbon atoms, they are decomposed by the three-way catalyst 15 to increase the proportion of lower hydrocarbons with 6 or less carbon atoms. The NO X reduction reaction at the NOX adsorption reduction catalyst 5 on the downstream side of the flow path can be efficiently advanced. The three-way catalyst 15 can slightly purify NOx, HC, and C0.

DPF 16 is a ceramic honeycomb filter. Within DPF 1 6 The exhaust gas flow path with the upstream end closed and the downstream end open, and the exhaust gas flow path with the upstream end open and the downstream end closed are alternately Porous wall surfaces are formed between adjacent exhaust gas flow paths (wall flow filter). Exhaust gas flowing into DPF 16 flows into an exhaust gas passage whose upstream side end is open and downstream end is closed, and is then placed between adjacent exhaust gas passages. From the porous wall surface, the upstream end is blocked, the downstream end is opened, and the gas flows into the downstream, and flows out downstream. In this process, PM in diesel exhaust gas is collected by collision and adsorption on the wall.

Note that PM collected in DPF 16 is removed by burning by raising the exhaust gas temperature after a certain amount of deposition. The method of raising the exhaust gas temperature can be engine control, electric heater, or the reaction heat of the catalyst placed upstream. Part of the combusted PM becomes' CO due to incomplete combustion, and unburned HC is also emitted, but these are adsorbed on the catalyst 3 and N 3 X that have both NOX selective reduction ability and hydrogen production function on the downstream side. It will be purified by the reduced catalyst 5. .

While the present invention has been described with reference to the embodiments, the present invention is not limited to the above embodiments, and various modifications can be made within the scope of the disclosure of the present invention.

For example, with a force not shown, a hydrogen sensor can be installed in front of the NOX catalyst to switch between lean and rich when a predetermined amount of H ₂ is detected.

Example 6

(Example catalyst 1)

Coating slurry to Kojerai bets made Ha second cam includes a C E_〇 ₂ Was coated, and drying and firing, was coated C E_〇 ₂ volumes 1 Li Tsu Torr per 1 9 0 g of the honeycomb apparent. To the C E_〇 ₂ Kotoha second cam, dried and impregnated with Jiniro Torojianmi emissions P t nitric acid solution 2 0 0 ° C, and calcined followed by 6 0 0 ° C. Thus, Example Catalyst 1 containing Pt: 2.8 g in terms of metal with respect to an apparent volume of 1 L of the honeycomb was obtained. (Test example)

Using Example Catalyst 1, a test was performed assuming that the engine was stopped by purging the residual exhaust gas after operation below the stoichiometric air-fuel ratio. The gas used in the test was a lean model gas that simulated lean lean exhaust gas and a rich model gas that simulated combustion below the stoichiometric air-fuel ratio.

The lean model gas is composed of NOX: 100 ppm, C ₃ H ₈ : 500 ppm C 1, CO: 0.1%, O ₂ : 5%, H ₂ O: 10%, N ₂ : Remaining.

Yarn且成of Li Tutsi model gas, NOX: 1 0 0 ppm, C 3 H 8: 5 0 0 ppm C 1, CO: 2%, O 2: 0%, H 2 O: 1 0%, N 2 : Remaining. The following procedure was used for testing.

① Rich model gas was circulated at 400 ° C for 3 minutes.

② After cooling to 200 ° C, the flow of lean model gas was started.

The N O X purification rate is the N O X concentration supplied as the lean model gas of Equation 1.

The rate of decrease in N O X concentration before and after circulation of the catalyst layer relative to (100 ppm). The definition is shown in Equation 1.

(160 ppm—NO X concentration after catalyst bed)

N〇x purification rate = X I 00 (Equation 1)

(N O X concentration before catalyst layer distribution)

Also,. 'C 2 O purification rate was defined as Equation 2.

(0.1% —CO concentration after distribution in the catalyst layer)

CO purification rate = X 100… (Formula 2)

(CO concentration before catalyst layer distribution) (Test results)

Table 1 shows the steady value of the NOx purification rate in the lean of Example catalyst 1 and the CO purification rate in the rich. It is clear that NOx is selectively reduced in lean because the steady NOx purification rate in lean is 25 ° / ₀ . It was also calculated from the C0 purification rate in the Rich. The amount of hydrogen produced and the hydrogen concentration in the Rich gas after the Example Catalyst 1 flowed were almost identical. From the above, it is clear that Example Catalyst 1 has hydrogen generation in the rich and has selective reduction performance in lean.

丄 ^

Example 7

(Example catalyst 2)

The slurry one adjusted to the precursor value Nari nitric acidic alumina powder and alumina M g O (average particle size: specific surface ^{area: lm 2 / g) M g} O- alumina mixed slurry prepared by adding the Kojerai bets made ha - cam After coating with (400 cell Zinc ² ), drying and firing, M was coated with 190 g of alumina and 10 g of MgO per 1 liter of Herck's apparent volume. g O-alumina coat hammer was obtained. The MgO-alumina-coated honeycomb was impregnated with Ni nitrate / Ce aqueous solution, dried at 200 ° C., and then fired at 60 ° C.

Next, impregnated with a mixture of di-rotrodiamin pt nitric acid solution, nitric acid Rh, nitric acid d, nitric acid Mn, acetic acid K and nitric acid Mn, dried at 200 ° C, followed by 60 ° C. Baked. Finally, acetic acid K, nitric acid Na, nitric acid Li, and titaure The mixture was impregnated with a sol mixture, dried at 200 ° C., and then calcined at 60 ° C. From the above, for the apparent volume of 1 L of the honeycomb, in terms of metal, C e: 41 g, R h: 0.14 g, P t: 1.2 g, P d: 3 '. 0 g, Example catalyst 2 containing K: 5.2 g, Na: 4.1 g, Li: 0.05 g, Ti: 4.3 g, Mn: 1 3.7 g was obtained. . Table 2 shows the catalyst composition.

(Example catalyst 3)

A slurry made of alumina powder and an alumina precursor and adjusted to nitric acid acidity was coated on cordierite hercum (400 Senore Zinc ² ), then dried and fired, and the apparent volume of fly cam was 1 liter. An alumina-coated hard coat coated with 190 g of alumina was obtained. The alumina coated honeycomb was impregnated with titania sol, dried at 20'0 ° C, and then fired at 60 ° C.

Next, it was impregnated with a mixed solution of durodilodiamin Pt nitric acid solution and nitric acid R h, dried at 200 ° C., and then calcined at 60 ° C.

Thus, Example Catalyst 3 containing Ti: 0.1 g, Rh: 0.14 g, Pt: 2.8 g in metal conversion with respect to the apparent volume of 1 L of the honeycomb was obtained. It was.

(Test example)

Example Catalysts 1 to 3 were used to carry out a test assuming that the engine was stopped by purging residual exhaust gas after operation below the stoichiometric air-fuel ratio. The gas used in the test was a lean model simulating lean burn exhaust gas. A gas and a rich model gas that simulates combustion below the stoichiometric air-fuel ratio. Lean modenolegus yarn is composed of NO x: 100 ppm, C ₃ H ₈ : 500 ppm

C 1, C_〇: 0. 1%, O 2: 5%, H 2 O: 1 0%, N 2: was the remainder.

Yarn且成of Li Tsuchimodenorega is, NO x: 1 0 0 ppm , C 3 H 8: 5 0 0 ppm

C 1, CO: 2%, O 2: 0%, H 2 O: 1 0%, N 2: was the remainder. ■ Tested by the following procedure.

① Rich model gas was circulated at 4.0 0 ° C.

② After cooling to 200 ° C, the Rich model gas was allowed to flow for 3 minutes, and then the lean model gas was allowed to flow for 3 minutes. This rich model gas and lean

'The operation of circulating the model gas alternately was repeated for 18 minutes.

(Test results).

Figure 2 shows the results of the three combinations. The catalyst volume used for each combination was 6 _CC .

(1) Example catalyst 2 (NO x adsorption reduction catalyst) only.

(2) Example catalyst 2 (NO x adsorption reduction catalyst) was placed downstream of Example catalyst 3 (NO x selective reduction catalyst).

(3) Example catalyst 1 (catalyst having hydrogen production function) in the downstream of Example catalyst 3 (NO x selective reduction type catalyst), and Example catalyst 2 (NO _X adsorption reduction type catalyst) in the subsequent stream Was placed.

The N 2 purification rates of the above three types of catalysts at 200 ° C and at the lean and rich are shown.

(1) The NOx adsorption reduction catalyst alone had a lean performance of 51%, a rich performance of 43%, and a total lean / rich performance of 47%.

(2) In combination with NOX selective reduction catalyst, lean performance 76%, rich performance 60%, lean norich total performance 68%. (1) Lean performance improved by 25 points, but rich performance improved by 17 points.

(3) In combination with a catalyst having both N 0 X selective reduction ability and hydrogen production function, it had a lean performance of 82%, a rich performance of 78%, and a lean norich totality of 80%. Compared to (1), the lean performance improved by 29 points and the rich performance improved by 35 points. In contrast to (2), the Litch performance is 18 points higher, which is due to the hydrogen production function. Industrial applicability

According to the present invention, the NOX purification performance at low temperatures is greatly improved. 'Furthermore, since the catalyst with hydrogen production function also has the ability to selectively reduce NOx, it also improves the NOx purification ability during lean. As a result, it is possible to reduce the frequency of switching the engine operating state to the rich operation, and to improve fuel efficiency. Compared with the case where the NOx selective reduction catalyst and the hydrogen production catalyst are arranged in series, it is possible to reduce the amount of precious metal used, reduce the heat content, and improve the space efficiency. '

Further, according to the present invention, a diesel engine exhaust gas purification catalyst capable of sufficiently reducing and purifying NOx in exhaust gas even in diesel engine having a low exhaust temperature, and an exhaust using the same A gas purification device can be provided.

Claims

The scope of the claims '

1. An internal combustion engine exhaust gas purification apparatus using a lean NO X catalyst, in which a catalyst having a hydrogen production function and NOX selective reduction ability is disposed upstream of the lean NOX catalyst in the exhaust gas flow path. Exhaust gas purification device characterized by that.

2. An exhaust gas purification apparatus for an internal combustion engine using a lean NO X catalyst, wherein the lean NOx catalyst has a catalyst component having a hydrogen production function and NOX selective reduction ability on the phosphorus NO X catalyst component. An exhaust gas purifier characterized by being a supported two-layer catalyst.

3. The exhaust gas purifying apparatus according to claim 1 or 2, wherein the lean NO X type catalyst is a NOx adsorption catalyst or an NOx occlusion reduction type catalyst.

4. An exhaust gas purifying device according to claim 1 or 2,

An exhaust gas purifying device characterized in that a diesel particulate filter is disposed upstream of the catalyst having the hydrogen production function and NO X selective reduction ability of the exhaust gas flow path.

5. The exhaust gas purifying device according to claim 4,

An exhaust gas purification apparatus, wherein a three-way catalyst is disposed upstream of the diesel particulate filter in an exhaust gas flow path.

6. A catalyst having a hydrogen production function and NO X selective reduction ability under lean conditions,

Z r 〇 ₂ as support component, C e 〇 _2, T i 〇 _2, Z r 〇 ₂ and C E_〇 ₂ including composite oxides, used either, as the catalyst component R h, P t An exhaust gas purifying catalyst characterized by using at least one kind of noble metal selected from Pd.

7. Purify the exhaust gas with the hydrogen production functional catalyst, purify the exhaust gas purified with the hydrogen production functional catalyst with the lean NOX catalyst, and flow into the NOX catalyst with the hydrogen 'sensor installed in the preceding stage of the NOX catalyst Detect the amount of hydrogen,

An exhaust gas purification system that switches lean operation to rich operation when the 'integration of the hydrogen amount exceeds a predetermined value.