JP2005023895A - Method and device for exhaust-emission control for lean-burn-system internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently purify exhaust emission of a lean-burn-system internal combustion engine by reducing NO<SB>x</SB>in the exhaust emission by NH<SB>3</SB>. <P>SOLUTION: A NH<SB>3</SB>-adsorption NO<SB>x</SB>-reduction catalyst 3 is provided in an exhaust emission passage in a lean-burn-system internal combustion engine. On the catalyst, NH<SB>3</SB>is once adsorbed, and NO<SB>x</SB>in the exhaust emission is reduced by the adsorbed NH<SB>3</SB>. At least either one of NH<SB>3</SB>or a precursor of NH<SB>3</SB>is intermittently supplied to the upstream of the NH<SB>3</SB>-adsorption NO<SB>x</SB>-reduction catalyst 3. When NH<SB>3</SB>is supplied in the exhaust gas, the NH<SB>3</SB>is firstly adsorbed in the NH<SB>3</SB>-adsorption NO<SB>x</SB>-reduction catalyst 3, then the adsorbed NH<SB>3</SB>reacts efficiently with NO<SB>x</SB>in the exhaust emission to effect NO<SB>x</SB>-reduction purification. NH<SB>3</SB>reacts with NO<SB>x</SB>at a molar ratio of 1:1, but even if NH<SB>3</SB>is excessively supplied, the excess NH<SB>3</SB>remains in the state of being adsorbed on the NH<SB>3</SB>-adsorption NO<SB>x</SB>-reduction catalyst 3, so NH<SB>3</SB>is not discharged. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to an exhaust gas purification method and an exhaust gas purification device, and more particularly to an exhaust gas purification method and an exhaust gas purification device that reduce and purify NO _x in exhaust gas from a lean combustion internal combustion engine with excess oxygen with NH ₃ .

NO _x emitted from power plants, various chemical factories, automobile engines, etc. is considered to be the cause of photochemical smog and acid rain, and the development of effective removal means is desired. For example, exhaust gas from a lean combustion internal combustion engine often contains several volume% or more of oxygen, and therefore it is necessary to use a treatment method that can efficiently purify NO _x in the presence of oxygen.

As such a treatment method, for example, there is a method in which NO _x selective reduction catalyst in which Cu is supported on zeolite is used, and NO _x is selectively reduced and purified by HC in exhaust gas. However, none of the current NO _x selective reduction catalysts satisfy practically sufficient NO _x purification performance and durability performance. Further, since a large excess of HC is required with respect to NO _x , there is a risk that excess HC will be discharged.

Further, NH ₃ denitration method of contacting the exhaust gas with the NH ₃ is known. NH ₃ denitration method of the NH ₃ with a reducing agent, utilization efficiency for even oxygen exhaust gas coexist 1 volume% or more NH ₃ selectively reacts with NO _x, NO _x purification rate and a reducing agent This is an advantageous method.

Examples of NH ₃ denitration catalysts used in this NH ₃ denitration method include V ₂ O ₅ —TiO ₂ catalysts as described on page 248 of “Catalyst Course 7 (Basic Industrial Catalytic Reaction)” (published by Kodansha). And a VW-Ti catalyst, a catalyst described in JP-A-53-030995, and the like.

However, with such NH ₃ denitration catalyst, high activity is obtained over a wide temperature range in the purification of gas having a small space velocity of about SV = 10000 / h. However, when the space velocity exceeds this, sufficient activity is obtained. Cannot be obtained. For this reason, when it is used in automobile exhaust gas having a large space velocity, there is a drawback in that a sufficient amount of catalyst is required to obtain sufficient activity and the catalyst device is enlarged.

JP-A-10-146528 discloses an NH ₃ denitration catalyst in which at least palladium (Pd) and zinc (Zn) are supported on an alumina (Al ₂ O ₃ ) support. According to this NH ₃ denitration catalyst, high NO _x purification activity can be obtained at a low temperature of 300 to 400 ° C. even in a high space velocity region exceeding SV = 10000 / h. Therefore, even if the amount of catalyst is small, sufficient NO _x purification activity can be obtained, and the catalyst device can be miniaturized, so that it can be used as an exhaust gas purification catalyst for automobiles.

The reaction between NO _x and NH ₃ is represented by the reaction formula (1).

NO + NH ₃ + (1/4) O ₂ → N ₂ + (3/2) H ₂ O (1)
That in the case of using NH ₃ denitration catalyst, the addition of NH ₃ in an amount of commensurate to _the amount of NO _x is required, NH ₃ in excess if the NH ₃ was excessively added would be directly discharged There is a bug. Therefore, it is necessary to precisely control the addition amount of NH _{3 so} as to have a molar ratio of 1: 1 with respect to NO _x . It is difficult to control. That is, even if NO _x : NH ₃ = 1: 1 in the total amount, NO _x or NH ₃ is instantaneously discharged. Furthermore, since NH ₃ denitration catalyst contains heavy metals such as vanadium and Cu, it is not preferable as a catalyst for exhaust gas purification of automobiles.

Further, according etc. JP-A 05-317652 and JP also conceivable to use a NO _x storage-and-reduction type catalyst. According to _the NO _x storage-reduction catalyst, NO _x is occluded in the lean atmosphere, the released NO _x when it is intermittently rich atmosphere, it is possible to reduce and purify by extensive reduction component present. However, since it is necessary to intermittently have a rich atmosphere, there are restrictions on the suppression of fuel consumption.

Further using a NO _x storage-and-reduction type catalyst is also a method of reducing the NO _x occluded in _the NO _x storage material in NH _3. However, the NO _x storage material itself cannot be a catalyst for the reaction between NO _x and NH ₃ . In addition, since the NO _x storage material and the noble metal such as Pt are supported separately from each other, the storage site and the reaction site are separated from each other, and NO _x must move between them for the reaction. Don't be. Therefore, the reactivity is low, and it is difficult to reduce NO _x especially at a low temperature of 300 ° C or lower. Since the NO _x storage material is basic, NH _3, which is the same basic substance, is difficult to approach and has low reactivity with the stored NO _x . The SO _x in the exhaust gas reacts with _the NO _x storage material, there is a problem that _the NO _x storage ability is lost.
JP 53-030995 A JP 05-317652 A JP-A-10-146528 “Catalyst Course 7 (Basic Industrial Catalysis)” (published by Kodansha), page 248

The present invention has been made in view of such circumstances, and an object thereof is to efficiently purify NO _x in exhaust gas from a lean combustion internal combustion engine by reducing with NH ₃ .

To solve the above problems lean burn characteristics of the exhaust gas purifying method for an internal combustion engine of the present invention, lean burn the adsorbed NH _{3 the} NO _x reduction catalyst for reducing with NH ₃ adsorbed the NO _x in the exhaust gas temporarily adsorbs NH ₃ place in the exhaust gas line of type internal combustion engine is to intermittently supply at least one of NH ₃ and NH ₃ precursor upstream of the NH ₃ adsorbing _the NO _x reduction catalyst.

The NH ₃ precursor is desirably urea or an aqueous urea solution.

In addition, a control cylinder, which is at least one cylinder of a lean combustion internal combustion engine having a plurality of cylinders, is intermittently operated with a rich air-fuel ratio with excessive fuel, and the remaining cylinders are always operated with a lean air-fuel ratio with excessive air to control. An NH ₃ generation catalyst that generates NH ₃ from exhaust gas is placed in the exhaust gas flow path from the cylinder, and the NH ₃ adsorption NO _x flows into the combined exhaust gas flow path where exhaust gases from all cylinders flow downstream from the NH ₃ generation catalyst. the reduction catalyst is disposed, it is preferred to use the reduction of the NO _x and NH ₃ generated by the NH ₃ synthesizing catalyst by NH ₃ adsorbing _the NO _x reduction catalyst.

The feature of the exhaust gas purification apparatus of the lean combustion type internal combustion engine of the present invention is that the NH ₃ and the NH ₃ precursor arranged in the exhaust gas flow path of the lean combustion type internal combustion engine intermittently supply at least one of them into the exhaust gas. ₃ a supply means, and the adsorbed NH _{3 the} NO _x reduction catalyst for reducing with NH ₃ and NH _3, which is disposed downstream of the supply means once adsorbed NH ₃ adsorbed the NO _x in the exhaust gas, that comprise is there.

Another feature of the exhaust gas purification apparatus for a lean combustion internal combustion engine according to the present invention is that NH ₃ from exhaust gas is introduced into an exhaust gas flow path from a control cylinder, which is at least one cylinder of a lean combustion internal combustion engine having a plurality of cylinders. the resulting NH ₃ synthesizing catalyst arranged in the NH ₃ adsorbed the NO _x in the exhaust gas temporarily adsorbs NH ₃ in the confluent exhaust passage exhaust gas flows merges from all the cylinders from the NH ₃ synthesizing catalyst downstream This is because an NH ₃ adsorption NO _x reduction catalyst to be reduced is arranged.

  It is desirable that the control cylinder is intermittently operated with a rich air-fuel ratio with excess fuel, and the remaining cylinders are always operated with a lean air-fuel ratio with excess air.

The NH ₃ adsorption NO _x reduction catalyst is preferably formed by supporting iron (Fe) on at least one of β-type zeolite and ZSM-5-type zeolite.

  According to the exhaust gas purification method and the exhaust gas purification device of the present invention, exhaust gas from a lean combustion internal combustion engine can be efficiently purified, and deterioration of fuel consumption can be suppressed.

In the exhaust gas purification method and exhaust gas purification apparatus of the present invention, intermittently supplying NH ₃ upstream of the NH ₃ adsorbing _the NO _x reduction catalyst. This NH ₃ adsorption NO _x reduction catalyst is excellent in the adsorption ability of NH ₃ and has high NO _x selective reduction reaction activity shown in the formula (1). Therefore, when the NH ₃ in the exhaust gas is supplied, NH ₃ is first adsorbed to the NH ₃ adsorbing _the NO _x reduction catalyst, NH ₃ will reduce and purify the NO _x reacts well NO _x and efficiency. Further, according to the formula (1), NO _x and NH ₃ react at a molar ratio of 1: 1, but even if NH ₃ is supplied in excess, the excess is adsorbed on the NH ₃ adsorption NO _x reduction catalyst. Therefore, NH ₃ is not discharged. Therefore, NH ₃ sufficient for the reaction can be adsorbed on the NH ₃ adsorption NO _x reduction catalyst, and NO _x can be sufficiently reduced and purified.

The NH ₃ adsorption _the NO _x reduction catalyst, those are used which have the ability to reduce in NH ₃ and NO _x adsorbing NH _3, for example, β-type zeolite and at least one iron of ZSM-5 type zeolite (Fe) It is desirable to use a supported catalyst. β-type zeolite and ZSM-5 type zeolite have strong Bronsted acid properties. Further, Fe supported on β-type zeolite and ZSM-5 type zeolite easily generates empty electron orbits, and this becomes a Lewis acid point. Therefore, NH ₃ can be adsorbed at many acid sites at a temperature of about 500 ° C. or less, and a large amount of NH ₃ can be adsorbed.

It is known that an oxide catalyst containing Cu or V shows high activity in the reaction of the formula (1), and an oxide catalyst containing Fe is less active than these. However, a catalyst obtained by supporting iron (Fe) on at least one of β-type zeolite and ZSM-5-type zeolite exhibits an activity equal to or higher than that of an oxide catalyst containing Cu or V. This is because Fe ion-supported on β-type zeolite and ZSM-5-type zeolite is supported in extremely high dispersion and is not susceptible to oxygen poisoning, which is covered with oxygen atoms, so the activity of NO _x and NH ₃ This is thought to be because of its excellent chemical ability.

Therefore, by using a catalyst in which iron (Fe) is supported on at least one of β-type zeolite and ZSM-5-type zeolite, NH ₃ adsorption ability is further improved, and NO _x reduction and purification performance is further improved.

In an NH ₃ adsorption NO _x reduction catalyst in which iron (Fe) is supported on at least one of β-type zeolite and ZSM-5 type zeolite, the supported amount of Fe is in the range of 0.1 to 10% by weight as Fe ₂ O _3. It is desirable. If the supported amount is less than 0.1% by weight, the adsorption ability of NH ₃ and the reducing ability of NO _x are reduced. If the supported amount is more than 10% by weight, the separated Fe becomes an oxide of Fe having low activity without being supported on the zeolite. It is not preferable.

To supply NH ₃ into the exhaust gas, a method of adding NH ₃ gas, a method of spraying ammonia water, or a substance that generates NH ₃ by decomposition such as urea or hexamethylenetetramine (NH ₃ precursor) There is a method of spray addition as it is or as a solution. If urea or urea aqueous solution is added, it can be added at low cost without problems of odor.

NH ₃ is supplied intermittently. That is, when the supply of NH _3, can be adsorbed NH ₃ amount of NH ₃ adsorbed _the NO _x reduction catalyst to supply the NH ₃ to saturation, to stop the supply prior to reaching the point, or saturation point reached saturation point Can prevent NH ₃ emissions.

The exhaust gas purification apparatus of the present invention capable of performing the above-described exhaust gas purification method of the present invention is such that at least one of NH ₃ and NH ₃ precursor disposed in the exhaust gas flow path of a lean combustion internal combustion engine is intermittently contained in the exhaust gas. includes a NH ₃ supply means for supplying, and NH ₃ adsorbing _the NO _x reduction catalyst for reducing with NH ₃ and NH _3, which is disposed downstream of the supply means once adsorbed NH ₃ adsorbed the NO _x in the exhaust gas, to It is characterized by

As for the NH ₃ supply means, at least one of NH ₃ and the NH ₃ precursor varies depending on each of gas, liquid, and solid, but known means such as a compressed gas ejection device, a liquid spray device, and a powder supply device can be used. .

Further, by a combination of NH ₃ synthesizing catalyst with adjusting the air-fuel ratio to the fuel rich supply without using at least one of NH ₃ and NH ₃ precursors, as unnecessary NH ₃ supply means, the NH ₃ in the exhaust gas can do. That is, an NH ₃ production catalyst is disposed upstream of the NH ₃ adsorption NO _x reduction catalyst, and the fuel cell is operated for a predetermined time under a slightly fuel rich condition with respect to air. Then, in the NH ₃ production catalyst, NH ₃ is produced by the reaction between incomplete combustion products such as CO, HC, H ₂ and water vapor and NO _x, and is supplied to the NH ₃ adsorption NO _x reduction catalyst. The NH ₃ adsorption _the NO _x reduction catalyst NH ₃ adsorbed in reacts with NO _x in the exhaust gas, even NH ₃ itself as well as reduce and remove NO _x disappears is consumed.

As this NH ₃ production catalyst, a known catalyst can be used, but a catalyst in which at least one of Pt and Pd is supported on a metal oxide carrier is preferable. Examples of the metal oxide support include alumina, titania, zirconia, and ceria. The amount of noble metal supported is preferably in the range of 0.05 to 10% by weight with respect to the metal oxide support. If the amount is less than 0.05% by weight, it becomes difficult to express the activity. Even if the amount exceeds 10% by weight, the activity is saturated and the cost is increased, so that noble metal grows at a high temperature.

Such NH ₃ generation catalyst can convert NO _x to NH ₃ with high efficiency, and can oxidize and remove harmful components such as unburned HC or CO discharged during lean combustion surplus, and NH ₃ adsorption NO _x reduction Since it is disposed upstream of the catalyst, it is suitable in that it is exposed to a relatively high temperature but has excellent heat resistance.

When using an NH ₃ generation catalyst, it is necessary to perform control to intermittently adjust the air-fuel ratio to be rich in fuel. However, when the air-fuel ratio is adjusted to be rich in fuel, there arises a problem that fuel efficiency is deteriorated. This problem is verified below.

S = (Actual amount of air supplied to the engine / Amount of air required for complete combustion of fuel) If defined as S, the amount of NO _x emitted by normal lean combustion with S of 1.5 or more is approximately 1.0. against NO _x emissions, it is generally about 1 / 5-1 / 10. Even if S is less than 0.8, the amount of exhausted NO _x decreases. Therefore, in order to efficiently produce NH ₃ with the NH ₃ production catalyst, S is preferably in the range of 0.8 to 1.0.

If the fuel rich condition in which S is in the range of 0.8 to 1.0 is 10 to 20% of the total operation time, most of the exhausted NO _x is converted to NH ₃ and exhausted during lean combustion. A sufficient amount of NH ₃ is produced to reduce and remove all of the NO _x amount. Therefore, 80 to 90% of the total operation time can be made lean combustion with excess oxygen, and since it becomes combustion with excess oxygen on a time average, fuel consumption hardly deteriorates. In order to produce NH ₃ more efficiently with the NH ₃ production catalyst, S is preferably less than 1.0 and closer to 1.0, and as S is less than 1.0 and closer to 1.0, deterioration of fuel consumption can be further suppressed.

Therefore, in another exhaust gas purification method of the present invention, a control cylinder, which is at least one cylinder of a lean combustion internal combustion engine having a plurality of cylinders, is intermittently operated at a rich air-fuel ratio with excess fuel, and the remaining cylinders are always operated. An NH ₃ generation catalyst that generates NH ₃ from exhaust gas is placed in the exhaust gas flow path from the control cylinder, and the exhaust gas from all cylinders joins downstream from the NH ₃ generation catalyst. the NH ₃ adsorption _the NO _x reduction catalyst is disposed in the confluence exhaust gas flow path to flow, it is used for the reduction of the NO _x and NH ₃ generated by the NH ₃ synthesizing catalyst by NH ₃ adsorbing _the NO _x reduction catalyst.

By doing so, a sufficient amount of NH ₃ can be generated by the NH ₃ generation catalyst, and NO _x generated in all cylinders can be sufficiently purified. Since only the control cylinder is intermittently made rich, the deterioration of fuel consumption can be suppressed.

An exhaust gas purification apparatus of the present invention that performs this exhaust gas purification method is an NH ₃ generation catalyst that generates NH ₃ from exhaust gas in an exhaust gas flow path from a control cylinder that is at least one cylinder of a lean combustion internal combustion engine having a plurality of cylinders. was placed, which was arranged adsorbed NH _{3 the} NO _x reduction catalyst the exhaust gas temporarily adsorbs NH ₃ in the confluent exhaust gas passage flows merge is reduced with NH ₃ adsorbed the NO _x in the exhaust gas from all the cylinders is there.

  The number of control cylinders is not limited, but a smaller one is desirable from the viewpoint of fuel consumption, and only one cylinder is sufficient. It is desirable that this control cylinder is intermittently operated with a rich air-fuel ratio with excess fuel, and the remaining cylinders are always operated with a lean air-fuel ratio with excessive air.

For example, S of at least one cylinder of a multi-cylinder engine is intermittently controlled so as to be 0.8 to 1.0, and other cylinders are controlled so that S is 1.5 or more. In the control cylinder where S is controlled to be 0.8 to 1.0, fuel-rich oxygen-deficient combustion occurs, and NH ₃ is produced from NO _x by the NH ₃ production catalyst. NH ₃ The generated adsorbed flows into the NH ₃ adsorbing _the NO _x reduction catalyst, when the S of the control cylinder is controlled to be 1.5 or more, the NO _x in the exhaust gas by NH ₃ that is adsorbed N Reduce to ₂ and remove. The amount of NH ₃ produced and adsorbed can be adjusted by the number of control cylinders and / or the time thereof.

  Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples.

(Example 1)
FIG. 1 schematically shows an exhaust gas purifying apparatus according to this embodiment. This exhaust gas purification device is composed of an NH ₃ supply device 2 arranged in the exhaust system of the engine 1 and an NH ₃ adsorption NO _x reduction catalyst 3 arranged at a position 0.8 m downstream of the NH ₃ supply device 2. Has been.

  The engine 1 is a 2.2L, 4-cylinder turbocharged diesel engine.

The NH ₃ supply device 2 includes a tank 20 into which a 30% by weight aqueous solution of urea is charged and a compressed air introduction device 21. The compressed water introduced from the compressed air introduction device 21 exhausts urea water in the tank 20 into exhaust gas. It can be sprayed inside.

Hereinafter, a method for producing the NH ₃ adsorption NO _x reduction catalyst 3 will be described, and a detailed description of the configuration will be given.

A β-type zeolite powder having a SiO ₂ / Al ₂ O ₃ ratio of 40 is prepared, impregnated with a predetermined amount of an iron (III) nitrate nonahydrate aqueous solution having a predetermined concentration, dried at 120 ° C., and then in the atmosphere 300 A catalyst powder was prepared by calcining at 3 ° C. for 3 hours. The supported amount of Fe in the catalyst powder is 0.04 mol of Fe with respect to 100 g of β-type zeolite.

A predetermined amount of ion-exchanged water and a silica sol binder were added to the obtained catalyst powder, and the mixture was pulverized to a predetermined particle size using a ball mill to prepare a slurry. This slurry was wash coated on a cordierite cylindrical honeycomb substrate (2 L, 400 cells / in ² ) and calcined in the atmosphere at 300 ° C. for 3 hours to obtain NH ₃ adsorption NO _x reduction catalyst 3. It was. The coating amount is 200 g per liter of honeycomb substrate.

Using this exhaust gas purification device, 1.2 ml of urea water was intermittently sprayed into the exhaust gas for 0.5 seconds every 30 seconds from the NH ₃ supply device 2 while the engine 1 was operated at 1700 rpm and 68 Nm. The catalyst bed temperature of the NH ₃ adsorption NO _x reduction catalyst 3 was 270 ° C.

While operating in this state, the average concentrations of NO _x and NH _{3 in} the output gas from the NH ₃ adsorption NO _x reduction catalyst 3 were measured, and the NO _x purification rate was calculated. The results are shown in Table 1. Incidentally, NO _x average concentration in the exhaust gas from the engine 1 is 150 ppm.

(Example 2)
FIG. 2 schematically shows the exhaust gas purifying apparatus of this embodiment. This exhaust gas purifying apparatus includes an NH ₃ generation catalyst 5 disposed 50 cm downstream from the outlet of the engine 4 in an exhaust gas flow path of one control cylinder 10 of the engine 4, and all cylinders downstream of the NH ₃ generation catalyst 5. And an NH ₃ adsorption NO _x reduction catalyst 6 disposed 130 cm downstream from the outlet of the engine 4 in a combined exhaust gas flow path where exhaust gas from the exhaust gas flows. The NH ₃ adsorption NO _x reduction catalyst 6 is the same as the NH ₃ adsorption NO _x reduction catalyst 3 of Example 1.

  The engine 4 is a 2.0-liter, 4-cylinder direct-injection gasoline engine equipped with an electronic fuel injection valve.

Hereinafter, a method for producing the NH ₃ production catalyst 5 will be described, and a detailed description of the configuration will be used.

A predetermined amount of ion-exchanged water and a silica sol binder were added to the γ-alumina powder, and the slurry was pulverized to a predetermined particle size using a ball mill. The slurry cylindrical honeycomb substrate made of cordierite (0.5 L, 400 cells / in ²⁾ and washcoat and calcined 3 hours at 500 ° C. in air. The coating amount is 200 g per liter of honeycomb substrate. Thereafter, a predetermined amount of a dinitrodiammine platinum aqueous solution having a predetermined concentration was impregnated into the coat layer, dried at 120 ° C., and then calcined in the atmosphere at 300 ° C. for 3 hours to prepare NH ₃ production catalyst 5.

Using this exhaust gas purification device, only the control cylinder 10 is operated under the condition that the air-fuel ratio 14 is alternately repeated for 5 seconds and the air-fuel ratio 22 is repeated for 10 seconds, and the other three cylinders are operated under the condition that the air-fuel ratio is always 22. The average concentration of NO _x and NH _{3 in} the gas emitted from the NH ₃ adsorption NO _x reduction catalyst 6 was measured, and the NO _x purification rate was calculated. The results are shown in Table 1. The NO _x average concentration in the exhaust gas from the engine 4 was 370 ppm, and the catalyst bed temperature of the NH ₃ production catalyst 5 and the catalyst bed temperature of the NH ₃ adsorption NO _x reduction catalyst 6 were about 300 ° C., respectively.

Example 3
NH except that SiO ₂ / Al ₂ O ₃ ratio of SiO ₂ / Al ₂ O ₃ ratio instead of the β-type zeolite powder of 40 was used ZSM-5 type zeolite powder of 40 in the same manner as in Example 1 ₃ An adsorption NO _x reduction catalyst 3 was prepared, and the NO _x and NH ₃ average concentrations in the output gas of the NH ₃ adsorption NO _x reduction catalyst 3 were measured in the same manner using the same exhaust gas purifying apparatus as in Example 1. _{x The} purification rate was calculated. The results are shown in Table 1.

(Example 4)
Adsorption of NH _{3 in the same} manner as in Example 1 except that ZSM-5 type zeolite powder with SiO2 / Al ₂ O ₃ ratio of 40 was used instead of β type zeolite powder with SiO ₂ / Al ₂ O ₃ ratio of 40 The NO _x reduction catalyst 6 was prepared, and the NO _x and NH ₃ average concentrations in the output gas of the NH ₃ adsorption NO _x reduction catalyst 6 were measured in the same manner using the same exhaust gas purification device as in Example 2, and the NO _x The purification rate was calculated. The results are shown in Table 1.

(Comparative Example 1)
A predetermined amount of ion-exchanged water and a silica sol binder were added to a commercially available powder of VW-Ti oxide, and the mixture was pulverized to a predetermined particle size using a ball mill to prepare a slurry. This slurry was wash-coated on a cordierite cylindrical honeycomb substrate (2 L, 400 cells / in ² ), and calcined in the atmosphere at 500 ° C. for 3 hours to prepare a VW-Ti catalyst. The coating amount is 200 g per liter of honeycomb substrate.

An exhaust gas purification apparatus was prepared in the same manner as in Example 1 except that the VW-Ti catalyst prepared above was arranged instead of the NH ₃ adsorption NO _x reduction catalyst 3, and in the same manner as in Example 1. While intermittently spraying urea water, the average concentrations of NO _x and NH _{3 in} the gas emitted from the VW-Ti catalyst were measured, and the NO _x purification rate was calculated. The results are shown in Table 1.

(Comparative Example 2)
An exhaust gas purification apparatus was prepared in the same manner as in Example 2 except that the VW-Ti catalyst prepared in Comparative Example 1 was used in place of the NH ₃ adsorption NO _x reduction catalyst 6. Then, the average concentrations of NO _x and NH _{3 in} the gas discharged from the VW-Ti catalyst were measured, and the NO _x purification rate was calculated. The results are shown in Table 1.

(Comparative Example 3)
Except that the VW-Ti catalyst prepared in Comparative Example 1 was used in place of the NH ₃ adsorption NO _x reduction catalyst 6, the same exhaust gas purification device as in Example 2 was used, and only the control cylinder 10 was always empty. The average concentrations of NO _x and NH _{3 in} the output gas from the VW-Ti catalyst 7 when operating at a fuel ratio of 14 and the other three cylinders operating at a constant air-fuel ratio of 22 are shown. Measured and calculated NO _x purification rate. The results are shown in Table 1. The average NO _x concentration in the exhaust gas from the engine 4 was 700 ppm.

(Comparative Example 4)
A predetermined amount of ion-exchanged water and an alumina sol binder were added to a mixed powder of γ-alumina powder and TiO ₂ —ZrO ₂ solid solution powder, and a slurry was prepared by pulverizing to a predetermined particle size using a ball mill. This slurry was wash-coated on a cordierite cylindrical honeycomb substrate (2 L, 400 cells / in ² ) and fired at 500 ° C. for 3 hours in the air. The coating amount is 200 g per liter of honeycomb substrate.

Thereafter, a predetermined amount of a dinitrodiammine platinum aqueous solution having a predetermined concentration was impregnated into the coating layer, dried at 120 ° C., and then fired in the atmosphere at 300 ° C. for 3 hours to carry Pt. Next, impregnated with a predetermined amount of a mixed aqueous solution of barium acetate, potassium acetate and lithium acetate, dried at 120 ° C., calcined in the atmosphere at 300 ° C. for 3 hours to carry Ba, K and Li, and occluded NO _x A reduced catalyst was prepared. The supported amounts are 2 g of Pt, 0.2 mol of Ba, 0.1 mol of K, and 0.1 mol of Li per liter of honeycomb substrate volume.

An exhaust gas purification apparatus was prepared in the same manner as in Example 1 except that the NO _x storage reduction catalyst prepared above was arranged in place of the NH ₃ adsorption NO _x reduction catalyst 3, and NO in the same manner as in Example 1. The average concentration of NO _x and NH _{3 in} the gas emitted from the _x storage reduction catalyst was measured, and the NO _x purification rate was calculated. The results are shown in Table 1.

(Comparative Example 5)
An exhaust gas purification apparatus was prepared in the same manner as in Example 2 except that the same NO _x storage reduction catalyst as in Comparative Example 4 was disposed instead of the NH ₃ adsorption NO _x reduction catalyst 6, and the same procedure as in Example 2 was performed. The average concentration of NO _x and NH _{3 in} the output gas from the NO _x storage reduction catalyst was measured, and the NO _x purification rate was calculated. The results are shown in Table 1.

(Comparative Example 6)
An exhaust gas purification apparatus was prepared in the same manner as in Example 2 except that the same NO _x storage reduction type catalyst as in Comparative Example 4 was disposed instead of the NH ₃ adsorption NO _x reduction catalyst 6, and all cylinders were set at an air-fuel ratio of 12. The NO _x purification rate is measured by measuring the average concentration of NO _x and NH _{3 in} the gas emitted from the NO _x storage reduction catalyst when operated under conditions where the air-fuel ratio is 22 and 55 seconds alternately. Was calculated. The results are shown in Table 1. The average NO _x concentration in the exhaust gas from the engine 4 was 370 ppm.

<Evaluation>
The fuel consumption in the exhaust gas purification methods of Examples 2 and 4 using NH ₃ generation catalyst and Comparative Examples 2, 3, 5 and 6 is calculated, and the condition that the air-fuel ratio is always 22 for all the cylinders of engine 4 used The fuel consumption deterioration rate was calculated on the basis of the fuel consumption when driving with the vehicle. The results are also shown in Table 1.

尿素水を噴霧する条件で行ったものどうしの比較から、実施例１，３の方法は比較例１，４に比べてNO_x 浄化率が高く、比較例１よりNH₃ 排出量も著しく少ないことがわかる。比較例１では、NH₃ 脱硝触媒であるＶ−Ｗ−Ti系触媒がNH₃ を吸着あるいは貯蔵する能力が低い。そのため尿素水を添加していない間はNH₃ が存在しないためNO_x を還元することが困難でNO_x が放出され、尿素水を添加している間はNO_x に対して過剰なNH₃ が供給されるため過剰分のNH₃ が放出されたと考えられる。また、空燃比が制御されない常時希薄燃焼条件では、NO_x 吸蔵還元型触媒に吸蔵されたNO_x を還元することが困難であるので、比較例４ではNO_x 浄化率が低くなっている。

From the comparison between those performed under the conditions of spraying urea water, the methods of Examples 1 and 3 have a higher NO _x purification rate than Comparative Examples 1 and 4, and the NH ₃ emission amount is significantly smaller than Comparative Example 1. I understand. In Comparative Example 1, the VW-Ti catalyst that is an NH ₃ denitration catalyst has a low ability to adsorb or store NH ₃ . Therefore while not adding urea water is NO _x release is difficult to reduce the NO _x because the NH ₃ does not exist, excessive NH ₃ relative to NO _x is during the addition of the urea water It is thought that excess NH ₃ was released because of the supply. In addition, under constant lean combustion conditions in which the air-fuel ratio is not controlled, it is difficult to reduce NO _x stored in the NO _x storage-reduction catalyst. Therefore, in Comparative Example 4, the NO _x purification rate is low.

However, in Examples 1 and 3, the NO _x purification rate is high and NH ₃ emission is also suppressed, which is clearly an effect of arranging an NH ₃ adsorption NO _x reduction catalyst.

Comparing those performed under the conditions for controlling the air-fuel ratio, Examples 2 and 4 have higher NO _x purification rates than Comparative Examples 2 and 5, and less deterioration in fuel consumption than Comparative Examples 3 and 6. It can be seen that NO _x purification performance and fuel efficiency performance are compatible. In Comparative Examples 2 and 5, the NO _x purification performance is low. The VW-Ti catalyst and the NO _x storage reduction catalyst which are NH ₃ denitration catalysts have low ability to adsorb or store NH ₃ . Therefore, it is difficult to reduce NO _x while NH ₃ does not exist while the air-fuel ratio is 22, and NO _x is released, while excess NH ₃ is supplied to NO _x while the air-fuel ratio is 14. It is thought that excess NH ₃ was released.

In Comparative Example 3, the control cylinder is always operated at a rich air-fuel ratio to generate a large amount of NH ₃ , so that the NO _x purification rate is improved as compared with Comparative Example 2. In exchange for that, however, NH ₃ emissions have increased significantly. Then, in Comparative Example 6, although _the NO _x purification rate compared to Comparative Example 5 for operating at intermittent rich air-fuel ratio in all cylinders is improved, fuel efficiency is deteriorated.

It is explanatory drawing which shows the exhaust gas purification apparatus of one Example of this invention. It is explanatory drawing which shows the exhaust gas purification apparatus of the 2nd Example of this invention.

Explanation of symbols

1: Engine 2: NH ₃ supply means 3: NH ₃ adsorption NO _x reduction catalyst
20: Urea aqueous solution tank 21: Compressed air introduction device

Claims (8)

Temporarily adsorbs NH ₃ is arranged in the exhaust gas line of the NH ₃ adsorbing _the NO _x reduction catalyst to lean burn internal combustion engine reduction with NH ₃ adsorbed the NO _x in the exhaust gas, upstream of the NH ₃ adsorbing _the NO _x reduction catalyst An exhaust gas purification method for a lean combustion internal combustion engine, wherein at least one of NH ₃ and NH ₃ precursor is intermittently supplied to the side. The exhaust gas purification method for a lean combustion internal combustion engine according to claim 1, wherein the NH ₃ precursor is urea or an aqueous urea solution. A control cylinder, which is at least one cylinder of the lean combustion internal combustion engine having a plurality of cylinders, is intermittently operated with a rich air-fuel ratio with excess fuel, and the remaining cylinders are always operated with a lean air-fuel ratio with excess air, the NH ₃ synthesizing catalyst to produce a NH ₃ from the exhaust gas in the exhaust gas line from the control cylinder is arranged, the NH ₃ to the junction exhaust passage exhaust gas flows merges from all the cylinders from the NH ₃ synthesizing catalyst downstream adsorption _the NO _x reduction catalyst disposed, purification of exhaust gas lean burn internal combustion engine according to claim 1 that uses the NH ₃ generated by the NH ₃ synthesizing catalyst for the reduction of the NO _x in the NH ₃ adsorbing _the NO _x reduction catalyst Method. The exhaust gas of a lean combustion type internal combustion engine according to any one of claims 1 to 3, wherein the NH ₃ adsorption NO _x reduction catalyst comprises iron (Fe) supported on at least one of β-type zeolite and ZSM-5-type zeolite. Purification method. NH ₃ supply means for intermittently supplying at least one of NH ₃ and NH ₃ precursor arranged in the exhaust gas flow path of the lean combustion internal combustion engine into the exhaust gas, and arranged downstream of the NH ₃ supply means exhaust gas purifying device comprising the NH ₃ adsorbing _the NO _x reduction catalyst for reducing with NH ₃ which temporarily adsorbs NH ₃ adsorbed the NO _x in the exhaust gas, to comprise the. An NH ₃ generation catalyst that generates NH ₃ from exhaust gas is disposed in an exhaust gas flow path from a control cylinder, which is at least one cylinder of a lean combustion internal combustion engine having a plurality of cylinders, and all the downstream side of the NH ₃ generation catalyst is disposed downstream of the NH ₃ generation catalyst. Lean combustion, characterized in that an NH ₃ adsorption NO _x reduction catalyst that once adsorbs NH ₃ and reduces NO _x in the exhaust gas with NH ₃ adsorbed in the combined exhaust gas flow path where the exhaust gas from the cylinders merges flows Exhaust gas purification device for internal combustion engine.   The exhaust gas purification apparatus of a lean combustion type internal combustion engine according to claim 6, wherein the control cylinder is intermittently operated with a rich air-fuel ratio with excess fuel, and the remaining cylinders are always operated with a lean air-fuel ratio with excess air. The exhaust gas of a lean combustion internal combustion engine according to any one of claims 5 to 7, wherein the NH ₃ adsorption NO _x reduction catalyst comprises iron (Fe) supported on at least one of β-type zeolite and ZSM-5-type zeolite. Purification equipment.

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