JP2015137583A - Exhaust emission control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control device enhancing capacity of reducing a nitrogen oxide.SOLUTION: An exhaust emission control device includes: a reduction catalyst 22B that is arranged in an exhaust passage, and reduces a nitrogen oxide contained in exhaust; an ammonia generation catalyst 22A that is arranged on the upstream side in an exhaust flow direction with respect to the reduction catalyst 22B, and supplies ammonia to exhaust; and a downstream addition valve 24 that is arranged on the upstream side in the exhaust flow direction with respect to the reduction catalyst 22B, and supplies hydrocarbon to exhaust. The reduction catalyst 22B has an ammonia reduction layer that promotes reduction reaction of a nitrogen oxide using ammonia, and a hydrocarbon reduction layer that promotes reduction reaction of a nitrogen oxide using hydrocarbon.

Description

  The technology of the present disclosure relates to an exhaust purification device that reduces nitrogen oxides contained in exhaust.

An exhaust gas purification apparatus that purifies exhaust gas by reducing nitrogen oxide (hereinafter referred to as NO _x ) contained in the exhaust gas is mounted in the exhaust passage of the vehicle. For example, as described in Patent Document 1, the exhaust purification device includes a reduction catalyst that promotes a reaction for reducing NO _x using ammonia. When the reduction catalyst promotes the reduction reaction of NO _x , the exhaust purification device reduces the amount of NO _x contained in the exhaust.

JP 2012-97729 A

By the way, the exhaust emission control device can reduce a part of NO _x contained in the exhaust gas by promoting a reduction reaction of NO _x using ammonia. However, since the remaining NO _x contained in the exhaust is not reduced by the reduction catalyst, an exhaust purification device having a higher ability to reduce is required.

  An object of the technology of the present disclosure is to provide an exhaust purification device with an increased ability to reduce nitrogen oxides.

  One aspect of the exhaust emission control device according to the technology of the present disclosure is a reduction catalyst that is disposed in an exhaust passage and that reduces nitrogen oxides contained in the exhaust, and is disposed upstream of the reduction catalyst in a direction in which the exhaust flows. An ammonia supply unit that supplies ammonia to the exhaust gas; and a hydrocarbon supply unit that is arranged upstream of the reduction catalyst in the flow direction of the exhaust gas and supplies hydrocarbons to the exhaust gas. The reduction catalyst is a laminated structure, an ammonia reduction layer that promotes a reduction reaction of the nitrogen oxide using the ammonia, and a hydrocarbon reduction layer that promotes a reduction reaction of the nitrogen oxide using the hydrocarbon; Have.

  According to one aspect of the exhaust purification device of the technology of the present disclosure, the reduction catalyst promotes the reduction reaction of nitrogen oxides using hydrocarbons in addition to the reduction reaction of nitrogen oxides using ammonia. The ability of the device to reduce nitrogen oxides is increased.

  In another aspect of the exhaust emission control device according to the technology of the present disclosure, the ammonia reduction layer includes a first catalyst carrier that is a particle of a first porous material, and the hydrocarbon reduction layer is a particle of a second porous material. A second catalyst carrier. The diameter of the holes of the first catalyst carrier is smaller than the molecular diameter of the hydrocarbon, and the diameter of the holes of the second catalyst carrier is equal to or larger than the molecular diameter of the hydrocarbon. The ammonia reduction layer forms a surface of the reduction catalyst that covers the hydrocarbon reduction layer and contacts the exhaust.

  According to another aspect of the exhaust emission control device in the technology of the present disclosure, hydrocarbons easily reach the hydrocarbon reduction layer through the ammonia reduction layer, so that the reduction reaction of nitrogen oxides in the hydrocarbon reduction layer is performed. More likely to occur.

  In another aspect of the exhaust emission control device according to the technology of the present disclosure, the ammonia reduction layer includes copper and the first catalyst carrier, and the hydrocarbon reduction layer includes copper and the second catalyst carrier. The first catalyst support is at least one selected from the group consisting of a SAPO-34 type zeolite and a SAPO-47 type zeolite, and the second catalyst support is a ZSM-5 type zeolite, and It is at least one selected from the group consisting of beta zeolite.

  According to another aspect of the exhaust emission control device according to the technology of the present disclosure, ammonia can enter the hole of the first catalyst carrier, while hydrocarbon does not enter the hole of the first catalyst carrier, and the second catalyst. It reaches the hydrocarbon reduction layer formed by the carrier. Therefore, in both the ammonia reduction layer and the hydrocarbon reduction layer, the reduction reaction of nitrogen oxides by mutually different reducing agents is surely promoted, so that the ability of the exhaust gas purification device to reduce nitrogen oxides is further increased.

  Another aspect of the exhaust gas purification apparatus according to the technology of the present disclosure is an ammonia generation catalyst in which the ammonia supply unit promotes a reduction reaction of the nitrogen oxide using the hydrocarbon to generate the ammonia.

According to another aspect of the exhaust emission control device according to the technology of the present disclosure, ammonia is generated by reduction of nitrogen oxides, so that the ability of the exhaust emission control device to reduce nitrogen oxides is further increased.
In another aspect of the exhaust purification device according to the technology of the present disclosure, the hydrocarbon supply unit includes a hydrocarbon addition valve that adds hydrocarbons to the exhaust.

  According to another aspect of the exhaust emission control device according to the technology of the present disclosure, it is possible to suppress the reduction reaction of nitrogen oxides in the hydrocarbon reduction layer from occurring due to the lack of hydrocarbons. Therefore, the ability of the exhaust purification device to reduce nitrogen oxides is enhanced.

It is a schematic block diagram which shows the whole structure of the exhaust gas purification apparatus of this indication with the engine by which an exhaust gas purification apparatus is mounted. It is sectional drawing which shows the cross-sectional structure of a reduction catalyst. FIG. 3 is a cross-sectional view showing a cross-sectional structure of the reduction catalyst along the line 3-3 in FIG. 2. It is a schematic diagram which shows typically the structure of a reduction catalyst. It is a graph showing the relationship between the purification rate and the temperature of the NO _x with hydrocarbons at each catalyst. Is a graph showing the relationship between the purification rate and the temperature of the NO _x with ammonia in the catalyst. It is a graph showing a purification rate of the NO _x in the example and the comparative example. It is a fragmentary sectional view showing a part of section structure along a cell extension direction in a reduction catalyst of a modification. It is a fragmentary sectional view showing a part of section structure along a cell extension direction in a reduction catalyst of a modification. It is a fragmentary sectional view showing a part of section structure along a cell extension direction in a reduction catalyst of a modification. It is a schematic block diagram which shows schematic structure of the exhaust gas purification apparatus of a modification. It is a schematic block diagram which shows schematic structure of the exhaust gas purification apparatus of a modification. It is a schematic block diagram which shows schematic structure of the exhaust gas purification apparatus of a modification. It is a schematic block diagram which shows schematic structure of the exhaust gas purification apparatus of a modification.

  An embodiment of an exhaust emission control device will be described with reference to FIGS. Below, the structure of the engine in which the exhaust emission control device is mounted, the structure of the reduction catalyst, and the action of each catalyst will be described in order.

[Schematic configuration of the engine]
The schematic configuration of the engine will be described with reference to FIG.
As shown in FIG. 1, the cylinder block 11 of the engine 10 has six cylinders 11a arranged in a line. A common rail 12 extending in the direction in which the cylinders 11a are arranged is disposed in the vicinity of the cylinder block 11, and the common rail 12 stores fuel with increased pressure, for example, light oil. The common rail 12 is connected to six fuel injection valves 13, and each fuel injection valve 13 injects light oil toward different cylinders 11a. The fuel injection valve 13 is an example of a hydrocarbon supply unit.

  The cylinder block 11 is connected to an intake manifold 14 that supplies intake air to the cylinder 11a, and an end of the intake manifold 14 opposite to the cylinder block 11 is connected to an intake pipe 15 through which intake air flows. In the intake pipe 15, an intercooler 16 and a compressor 17 a constituting the turbocharger 17 are arranged in order from the cylinder block 11 side in the intake pipe 15. The intake manifold 14, the intake pipe 15, the intercooler 16, and the compressor 17a constitute an intake passage, and the intake air flows from the end of the intake pipe 15 opposite to the intake manifold 14 toward the cylinder block 11. .

  The cylinder block 11 is connected to the exhaust manifold 18 at a position facing the intake manifold 14 in the cylinder block 11. An end of the exhaust manifold 18 opposite to the cylinder block 11 is connected to an exhaust pipe 19 through which exhaust discharged from the cylinder block 11 flows. Each of the exhaust manifold 18 and the exhaust pipe 19 is connected to each other by being connected to a turbine 17 b constituting the turbocharger 17.

The engine 10 is equipped with an exhaust purification device 20 that purifies exhaust by reducing nitrogen oxide (hereinafter referred to as NO _x ) contained in the exhaust. The exhaust purification device 20 includes an upstream catalyst 21, a downstream catalyst 22, an upstream addition valve 23, a downstream addition valve 24, a fuel tank 25, and a fuel addition pump 26.

  In the exhaust emission control device 20, the upstream catalyst 21 and the downstream catalyst 22 are disposed in the exhaust pipe 19, and the upstream catalyst 21 is disposed upstream of the downstream catalyst 22 in the flow direction as the exhaust flow direction. Each of the upstream catalyst 21 and the downstream catalyst 22 has a casing formed in a cylindrical shape. Note that the exhaust manifold 18, the exhaust pipe 19, the casing of the upstream catalyst 21, and the casing of the downstream catalyst 22 constitute an exhaust passage, and the exhaust is from the exhaust manifold 18 to the exhaust pipe 19 on the side opposite to the exhaust manifold 18. It flows toward the end of the.

The upstream catalyst 21 includes a casing, and a cylindrical low-temperature reduction catalyst 21A and a cylindrical filter 21B are arranged along the flow direction in the casing. The low temperature reduction catalyst 21A is disposed upstream of the filter 21B in the flow direction. Cold reduction catalyst 21A reduces the NO _x contained in the exhaust by prompting a reduction reaction of the NO _x contained in the exhaust, the filter 21B is to purify the exhaust by capturing the soot, which is an example of the fine particles contained in the exhaust .

  The low-temperature reduction catalyst 21A includes a platinum group element and a catalyst carrier that supports the platinum group element. The platinum group element is preferably at least one selected from the group consisting of platinum, palladium, rhodium, and iridium. The catalyst support is preferably at least one selected from the group consisting of zeolite and alumina.

Cold reducing catalyst 21A has, for example, in the range of temperature of 0.99 ° C. or higher 350 ° C. or less, the activity to promote the reaction of reducing NO _x with hydrocarbons, i.e., catalytic activity.
Since the filter 21B captures the fine particles contained in the exhaust, the function of the reduction catalyst 22B is less likely to be impaired by the adhesion of the fine particles. The NO _x reduction reaction promoted by the low temperature reduction catalyst 21A is an exothermic reaction. For this reason, the low temperature reduction catalyst 21A promotes the NO _x reduction reaction, whereby the temperature of the exhaust is increased. As a result, the exhaust gas whose temperature is increased by the low temperature reduction catalyst 21A is supplied to the filter 21B. When the temperature of the exhaust gas is raised above the temperature at which the soot captured by the filter 21B burns, the soot in the filter 21B burns to regenerate the filter 21B.

The downstream catalyst 22 includes a casing, and a cylindrical ammonia generation catalyst 22A and a cylindrical reduction catalyst 22B are arranged along the flow direction in the casing. The ammonia generation catalyst 22A is disposed upstream of the reduction catalyst 22B in the flow direction. The ammonia generation catalyst 22A generates ammonia by promoting the reduction reaction of NO _x contained in the exhaust gas, and the reduction catalyst 22B exhausts the exhaust gas by promoting the reduction reaction of NO _x using two mutually different reducing agents. reduce the NO _x contained in the.

The ammonia generation catalyst 22A includes silver and a catalyst carrier supporting silver, and the catalyst carrier is preferably at least one selected from the group consisting of zeolite and alumina. The catalyst support preferably supports titanium or titanium oxide in addition to silver. By supporting titanium or titanium oxide on the catalyst carrier, the activity for promoting the reaction of reducing NO _x using ammonia contained in the ammonia generating catalyst 22A, that is, the catalytic activity is enhanced. For example, the ammonia generation catalyst 22A has catalytic activity in a temperature range of 150 ° C. or higher and 650 ° C. or lower. The ammonia generation catalyst 22A is an example of an ammonia supply unit.

  The upstream addition valve 23 is disposed upstream of the upstream catalyst 21 in the flow direction, and injects light oil toward the exhaust flowing through the exhaust pipe 19. The downstream addition valve 24 is disposed between the upstream catalyst 21 and the downstream catalyst 22 in the flow direction, and injects light oil toward the exhaust flowing through the exhaust pipe 19. Each of the upstream addition valve 23 and the downstream addition valve 24 is an example of a hydrocarbon supply unit.

  The fuel tank 25 stores light oil injected from the upstream addition valve 23 and the downstream addition valve 24. The fuel tank 25 may be a fuel tank connected to the common rail 12 or may be a fuel tank different from the fuel tank connected to the common rail 12. The fuel tank 25 is connected to a fuel supply pipe 25a, and the fuel supply pipe 25a is connected to the upstream pipe 25a1 connected to the upstream addition valve 23 and the downstream addition valve 24 on the way from the fuel tank 25 toward each addition valve. It branches off to the downstream pipe 25a2 to be connected.

  The fuel supply pipe 25a is connected to the fuel addition pump 26 on the fuel tank 25 side from the position where the fuel supply pipe 25a branches into two pipes. The fuel addition pump 26 discharges light oil in the fuel tank 25 toward the upstream addition valve 23 and the downstream addition valve 24 at a predetermined discharge pressure. The fuel addition pump 26 is, for example, an electric pump.

  An upstream valve 25b for opening and closing the fuel passage formed by the upstream pipe 25a1 is attached to the upstream pipe 25a1, and a downstream valve 25c for opening and closing the fuel passage formed by the downstream pipe 25a2 is attached to the downstream pipe 25a2. Is attached.

  While the upstream valve 25b is open, the fuel passage by the upstream pipe 25a1 is opened, while the fuel passage by the upstream pipe 25a1 is closed while the upstream valve 25b is closed. While the downstream valve 25c is open, the fuel passage by the downstream pipe 25a2 is opened, while the fuel passage by the downstream pipe 25a2 is closed while the downstream valve 25c is closed.

  An air flow meter 31 is attached to the intake pipe 15 upstream of the compressor 17a in the direction in which the intake air flows. The air flow meter 31 measures the intake air amount, which is the flow rate of the intake air flowing through the intake pipe 15, and outputs the current intake air amount as a measured value.

  An upstream temperature sensor 32 is attached to the exhaust pipe 19 upstream of the low temperature reduction catalyst 21A in the upstream catalyst 21, and a downstream temperature sensor 33 is attached upstream of the ammonia generation catalyst 22A in the downstream catalyst 22. Yes. The upstream temperature sensor 32 measures the temperature of the exhaust gas supplied to the low temperature reduction catalyst 21A and outputs the current measurement value. The downstream temperature sensor 33 measures the temperature of the exhaust gas supplied to the ammonia generation catalyst 22A and outputs the current measurement value. The measurement value of the upstream temperature sensor 32 is handled as the temperature of the low temperature reduction catalyst 21A and the temperature of the filter 21B, and the measurement value of the downstream temperature sensor 33 is handled as the temperature of the ammonia generation catalyst 22A and the temperature of the reduction catalyst 22B.

  A vehicle equipped with the engine 10 includes a control device 40 that controls the engine 10. The control device 40 includes an input unit, a calculation unit, an output unit, and a drive unit. The input unit is connected to the air flow meter 31, the upstream temperature sensor 32, and the downstream temperature sensor 33, and the drive unit is connected to the upstream addition valve 23 and the downstream addition valve 24.

  The calculation unit calculates the amount of fuel injected by the upstream addition valve 23 using the intake air amount and the temperature at the upstream catalyst 21, and the downstream addition valve 24 uses the intake air amount and the temperature at the downstream catalyst 22 to calculate the amount of fuel injected. The amount of fuel to be injected is calculated.

  When the low temperature reduction catalyst 21A has a catalytic activity, the calculation unit generates a control signal based on the calculated fuel amount of the upstream addition valve 23 and outputs the control signal to the drive unit. The drive unit responds to the control signal. A drive signal for driving the upstream addition valve 23 with a drive amount is generated and output. The calculation unit generates a control signal based on the calculated fuel amount of the downstream addition valve 24 and outputs the control signal to the drive unit when the reduction catalyst 22B has a catalyst active temperature, and the drive unit drives according to the control signal. A drive signal for driving the downstream addition valve 24 in an amount is generated and output.

[Composition of reduction catalyst]
The configuration of the reduction catalyst 22B will be described with reference to FIGS. 2 shows a cross-sectional structure of the reduction catalyst 22B along a plane orthogonal to the flow direction, and FIG. 3 shows a part of the cross-sectional structure of the reduction catalyst 22B along the line 3-3 in FIG. Only the multilayer catalyst formed on one surface of the cell wall is shown.

  As shown in FIG. 2, the reduction catalyst 22B includes a monolith carrier 51 having a cylindrical shape. The monolithic carrier 51 has a cell wall 51a composed of a plurality of walls extending along the flow direction, and the cross-sectional shape in the direction orthogonal to the flow direction in the cell wall 51a is a lattice shape. The monolithic carrier 51 has a plurality of cells 51h partitioned by cell walls 51a. Each cell 51h is a hole extending along the flow direction, and the cross-sectional shape in a direction orthogonal to the flow direction in each cell 51h is substantially rectangular.

  As the material for forming the monolithic carrier 51, ceramic or metal is used. When the forming material of the monolith support 51 is ceramic, for example, cordierite, silica, silicon carbide, silicon nitride, mullite, zircon, alumina, aluminum titanate, or the like is used as the forming material. When the forming material of the monolithic carrier 51 is a metal, for example, iron, titanium, stainless steel, and other alloys mainly containing iron are used as the forming material.

The cell wall 51a has the multilayer catalyst 52 in the wall part which comprises the internal peripheral surface of each cell 51h. The multilayer catalyst 52 is in contact with the exhaust flowing in the cell 51h.
As shown in FIG. 3, the multilayer catalyst 52 includes a hydrocarbon reduction layer 61 that covers the cell wall 51 a of the monolith support 51, and an ammonia reduction layer 62 that covers the hydrocarbon reduction layer 61. The ammonia reduction layer 62 covers the hydrocarbon reduction layer 61, thereby forming a surface 22s in contact with the exhaust Ex in the reduction catalyst 22B. The reduction catalyst 22B is a laminated structure in which a hydrocarbon reduction layer 61 and an ammonia reduction layer 62 are laminated.

The hydrocarbon reduction layer 61 is a catalyst that promotes a reaction of reducing NO _x using hydrocarbons. The hydrocarbon reduction layer 61 includes copper and a particulate catalyst carrier supporting copper, and includes zeolite as the catalyst carrier. The material for forming the catalyst carrier is preferably at least one selected from the group consisting of ZSM-5 type zeolite and beta type zeolite among zeolites. The catalyst carrier included in the hydrocarbon reduction layer 61 is an example of a second catalyst carrier, and zeolite is an example of a second porous material.

The hydrocarbon reduction layer 61 includes a catalyst support on which copper is supported and an adhesive for attaching the catalyst support to the monolith support 51.
The ZSM-5 type zeolite and the beta type zeolite constituting the hydrocarbon reduction layer 61 are porous materials, and the pore size which is the diameter of the pores of the ZSM-5 type zeolite and the beta type zeolite is the carbonization contained in the light oil. It is larger than the molecular diameter of hydrogen. Note that the pore size of the ZSM-5 type zeolite and the beta type zeolite is larger than the molecular size of the hydrocarbon means that the hydrocarbon molecules can enter the pores of the ZSM-5 type zeolite and the beta type zeolite. That's it. The diameter of the pores of the ZSM-5 type zeolite and the diameter of the pores of the beta type zeolite are, for example, 7 mm.

In the hydrocarbon reduction layer 61, the hydrocarbons in the light oil used as the reducing agent for NO _x are the hydrocarbons contained in the exhaust, and at least one of the upstream addition valve 23 and the downstream addition valve 24 is added to the exhaust. Includes light oil hydrocarbons. The hydrocarbon mainly includes alkanes having 10 to 20 carbon atoms, and includes linear alkanes and branched alkanes.

The hydrocarbon reduction layer 61 promotes a reaction of reducing NO _x using NO _x and hydrocarbons. Thereby, the hydrocarbon reduction layer 61 reduces the NO _x contained in the exhaust gas by reducing the NO _x contained in the exhaust gas to nitrogen.

The ammonia reduction layer 62 is a catalyst that promotes a reaction of reducing NO _x using ammonia. The ammonia reduction layer 62 includes copper and a particulate catalyst carrier that supports copper, and includes zeolite as the catalyst carrier. The material for forming the catalyst support is preferably a zeolite having a chabasite structure, and is preferably at least one selected from the group consisting of SAPO-34 type zeolite and SAPO-47 type zeolite. SAPO is silicoaluminophosphate. The catalyst carrier included in the ammonia reduction layer 62 is an example of a first catalyst carrier, and zeolite is an example of a first porous material.

The ammonia reduction layer 62 includes a catalyst carrier on which copper is supported, and an adhesive for attaching the catalyst carrier to the hydrocarbon reduction layer 61.
The SAPO-34 type zeolite and SAPO-47 type zeolite constituting the ammonia reduction layer 62 are porous materials. The pore diameter, which is the diameter of the pores of the SAPO-34 type zeolite and the SAPO-47 type zeolite, is smaller than the molecular diameter of hydrocarbons contained in light oil and larger than the molecular diameter of ammonia. Note that the pore diameter of the SAPO-34 type zeolite and the SAPO-47 type zeolite is smaller than the molecular diameter of the hydrocarbon means that the hydrocarbon molecules cannot enter the pores of the SAPO-34 and SAPO-47. That's it. On the other hand, when the pore diameter of the SAPO-34 type zeolite and the SAPO-47 type zeolite is larger than the molecular diameter of ammonia, the ammonia molecules may enter the pores of the SAPO-34 type zeolite and the SAPO-46 type zeolite. It is a state that can be done. The pore diameter of the SAPO-34 type zeolite and the pore diameter of the SAPO-47 type zeolite are, for example, 3 mm.

The ammonia reduction layer 62 promotes a reaction of reducing NO _x using NO _x and ammonia. Thus, the ammonia reduction layer 62, by reducing the NO _x contained in the exhaust to nitrogen, reduce the NO _x contained in the exhaust.

  As shown in FIG. 4, ammonia A enters the hole 71 h of the catalyst carrier 71 constituting the ammonia reduction layer 62, while the hydrocarbon H does not enter the hole 71 h of the catalyst carrier 71. Therefore, the hydrocarbon H reaches the hydrocarbon reduction layer 61 through a plurality of gaps 62 g formed between the particles of the catalyst carrier 71. Then, the hydrocarbon H that has reached the hydrocarbon reduction layer 61 enters the hole 81 h of the catalyst carrier 81 that constitutes the hydrocarbon reduction layer 61.

Therefore, in the ammonia reduction layer 62, in addition to promoting the reduction reaction of NO _x using the ammonia A that has entered the hole 71h as a reducing agent, hydrocarbons contained in the exhaust constitute the ammonia reduction layer 62. It reaches the hydrocarbon reduction layer 61 through the plurality of gaps 62 g of the catalyst carrier 71. Therefore, also in the hydrocarbon reduction layer 61, the reduction reaction of NO _x using the hydrocarbon H that has entered the hole 81h as a reducing agent is promoted.

[Action of each catalyst]
The operation of each catalyst provided in the exhaust purification device 20 will be described with reference to FIGS. Hereinafter, the operation of the low-temperature reduction catalyst 21A, the ammonia generation catalyst 22A, and the reduction catalyst 22B will be described, and the hydrocarbon reduction layer 61 and the ammonia reduction layer 62 will be described separately for the reduction catalyst 22B.

In FIG. 5, when exhaust gas and hydrocarbons are supplied to an exhaust purification device including one of the low temperature reduction catalyst 21 </ b> A, the ammonia generation catalyst 22 </ b> A, the hydrocarbon reduction layer 61, and the ammonia reduction layer 62. The NO _x purification rate is shown. Note that the NO _x purification rate in FIG. 5 is calculated using the NO _x concentration of the exhaust gas entering each catalyst or reduction layer and the NO _x concentration of the exhaust gas exiting from each catalyst or reduction layer.

  As shown in FIG. 5, in the low temperature reduction catalyst 21A, the purification rate increases from 150 ° C. to 200 ° C., and reaches a maximum value at 200 ° C. In the low-temperature reduction catalyst 21A, the purification rate decreases from 200 ° C. to 350 ° C., and when it exceeds 350 ° C., the purification rate becomes zero. That is, the low-temperature reduction catalyst 21A has catalytic activity at 150 ° C. to 350 ° C., and maximum catalytic activity at 200 ° C.

  In the ammonia generation catalyst 22A, the purification rate increases from 150 ° C. to 200 ° C., and is kept substantially constant from 200 ° C. to 300 ° C. The purification rate decreases from 300 ° C. to 350 ° C., and reaches a minimum value at 350 ° C. The purification rate increases from 350 ° C. to 400 ° C., and above 400 ° C., the purification rate is kept substantially constant at a value smaller than the purification rate at 200 ° C. to 300 ° C. That is, the ammonia generation catalyst 22A has catalytic activity at 150 ° C. to 650 ° C., and generates ammonia over a wide temperature range of 150 ° C. to 650 ° C.

  In the hydrocarbon reduction layer 61, the purification rate increases from 250 ° C. to 400 ° C., and is kept substantially constant from 400 ° C. to 450 ° C. And a purification rate becomes small toward 450 to 650 degreeC. That is, the hydrocarbon reduction layer 61 has catalytic activity at 250 ° C. to 650 ° C., and in particular, the catalytic activity becomes maximum at 400 ° C. to 450 ° C. where the low temperature reducing catalyst 21A has no catalytic activity.

Among the catalysts using hydrocarbon as a reducing agent, the temperature at which the low-temperature reduction catalyst 21A has the highest activity is 200 ° C., and the temperature range at which the activity of the hydrocarbon reduction layer 61 is highest is 400 ° C. or more and 450 ° C. or less. That is, since the temperature ranges having the highest activity in the two catalysts do not overlap, the exhaust purification device can reduce NO _x with a high purification rate using hydrocarbons in the two temperature ranges.

  Although the ammonia generating catalyst 22A has catalytic activity over 150 ° C. to 650 ° C., the catalytic activity at 350 ° C. or higher and 650 ° C. or lower is smaller than the catalytic activity at 200 ° C. or higher and 300 ° C. or lower. On the other hand, the hydrocarbon reduction layer 61 has catalytic activity at 350 ° C. or higher and 650 ° C. or lower. Therefore, according to the ammonia generation catalyst 22A and the hydrocarbon reduction layer 61, the ammonia generation catalyst 22A has a temperature range of 200 ° C. or more and 300 ° C. or less even in the temperature range of 350 ° C. or more and 650 ° C. or less. A catalytic activity equivalent to or higher than the catalytic activity can be obtained.

On the other hand, in the ammonia reduction layer 62, the purification rate is 0 from 150 ° C. to 650 ° C. That is, the ammonia reduction layer 62 does not promote the NO _x reduction reaction using hydrocarbons.
FIG. 6 shows NO when the exhaust gas and ammonia are supplied to an exhaust purification device including one of the low temperature reduction catalyst 21A, the ammonia generation catalyst 22A, the hydrocarbon reduction layer 61, and the ammonia reduction layer 62. The purification rate of _x is shown. The NO _x purification rate in FIG. 6 is calculated by the same method as in FIG.

  As shown in FIG. 6, in the hydrocarbon reduction layer 61, the purification rate is substantially 0 from 150 ° C. to 200 ° C., and increases from 200 ° C. to 300 ° C. The purification rate decreases from 300 ° C. to 650 ° C., and becomes substantially zero at 650 ° C. That is, the hydrocarbon reduction layer 61 has catalytic activity over 150 ° C. to 650 ° C.

  In the ammonia reduction layer 62, the purification rate increases from 150 ° C. to 250 ° C., and is kept substantially constant from 250 ° C. to 350 ° C. At this time, the purification rate of the ammonia reduction layer 62 is larger than the purification rate of the hydrocarbon reduction layer 61. And a purification rate becomes small toward 350 to 650 degreeC. However, the purification rate of the ammonia reduction layer 62 is larger than the purification rate of the hydrocarbon reduction layer 61 from 350 ° C. to 650 ° C.

The hydrocarbon reduction layer 61 has both an activity of promoting NO _x reduction reaction using hydrocarbon as a reducing agent and an activity of promoting NO _x reduction reaction using ammonia as a reducing agent. When the hydrocarbon reduction layer 61 forms the surface 22s of the reduction catalyst 22B, the hydrocarbon reduction layer 61 maintains a concentration of both hydrocarbons and ammonia contained in the exhaust gas in the hydrocarbon reduction layer 61. 61 is supplied.

Thereby, hydrocarbon and ammonia compete with the hole 81 h of the catalyst carrier 81 of the hydrocarbon reduction layer 61. Therefore, compared with the case where only hydrocarbons or only ammonia is supplied, the reduction amount of NO _x using hydrocarbons and the reduction amount of NO _x using ammonia are both small. When the lower layer of the hydrocarbon reduction layer 61 is the ammonia reduction layer 62, the ammonia reduction layer 62 is supplied with exhaust gas in which ammonia is consumed in the hydrocarbon reduction layer 61. Therefore, since the amount of ammonia supplied is small, it may be difficult to promote the NO _x reduction reaction.

On the other hand, the ammonia reduction layer 62 does not promote the reduction reaction of NO _x using hydrocarbon as a reducing agent. Therefore, when the ammonia reduction layer 62 forms the surface 22s of the reduction catalyst 22B, the hydrocarbon reduction layer 61 is supplied with exhaust gas whose amount of ammonia has been reduced by passing through the ammonia reduction layer 62. On the other hand, the hydrocarbons contained in the exhaust gas reach the hydrocarbon reduction layer 61 through the plurality of gaps 62 g of the catalyst carrier 71 constituting the ammonia reduction layer 62. As a result, it becomes easy to enter the hole 81 _h of the catalyst carrier 81 of the hydrocarbon reduction layer 61, and the reaction of NO _x using hydrocarbon as a reducing agent easily proceeds in the hydrocarbon reduction layer 61.

In this way, the ammonia reduction layer 62 covers the hydrocarbon reduction layer 61 to form the surface 22s of the reduction catalyst 22B, so that the reduction of NO _x using two different reducing agents is performed in one reduction catalyst 22B. The reaction becomes easier to proceed. As a result, the ability of the exhaust purification device 20 to reduce NO _x increases.

Moreover, the NO _x purification rate using ammonia by the ammonia reduction layer 62 is larger than the NO _x purification rate using hydrocarbons by the hydrocarbon reduction layer 61. Therefore, the above-described reduction catalyst 22B is preferable in that ammonia is supplied to the ammonia reduction layer 62 rather than the hydrocarbon reduction layer 61.

On the other hand, the temperature range in which the ammonia generation catalyst 22A has catalytic activity and the temperature range in which the ammonia reduction layer 62 has catalytic activity overlap. Therefore, the ammonia generated by the ammonia generation catalyst 22 _{</ b} > A is used for the NO _x reduction reaction in the ammonia reduction layer 62 regardless of the temperature of the ammonia reduction layer 62.

On the other hand, in the low temperature reduction catalyst 21A and the ammonia generation catalyst 22A, the purification rate is 0 from 150 ° C. to 650 ° C. That is, the low temperature reduction catalyst 21A and the ammonia generation catalyst 22A promote the NO _x reduction reaction using ammonia. Absent.

[Example]
The exhaust purification device 20 shown in FIG. 1 is used as an example, and the exhaust purification device 20 in which the reduction catalyst 22B includes only the ammonia reduction layer 62 is used as a comparative example. The engine 10 includes Examples, and was measured purification rate of the NO _x when operated at the same conditions of each of the engine with a comparative example. Incidentally, the purification rate of the NO _x is calculated using the concentration of the exhaust of the NO _x entering the exhaust gas purification device 20, and a concentration of the NO _x exiting the exhaust purification device 20.

As shown in FIG. 7, in the example, it was confirmed that the NO _x purification rate was 65%. On the other hand, in the comparative example, it was confirmed that the NO _x purification rate was 60%. That is, according to the reduction catalyst 22B provided in the embodiment, the exhaust purification device has been observed that the increasing ability to reduce NO _x.

As described above, according to the exhaust gas purification apparatus of one embodiment, the effects listed below can be obtained.
(1) Since the reduction catalyst 22B promotes the NO _x reduction reaction using hydrocarbons in addition to the NO _x reduction reaction using ammonia, the ability of the exhaust purification device 20 to reduce NO _x is enhanced.

(2) Since the hydrocarbons easily reach the hydrocarbon reduction layer 61 through the ammonia reduction layer 62, the NO _x reduction reaction in the hydrocarbon reduction layer 61 is more likely to occur.
(3) While ammonia can enter the hole 71h of the catalyst carrier 71, the hydrocarbon does not enter the hole 71h of the catalyst carrier 71 and reaches the hydrocarbon reduction layer 61 formed by the catalyst carrier 81. Therefore, in both the ammonia reduction layer 62 and the hydrocarbon reduction layer 61, the reduction reaction of NO _x by mutually different reducing agents is surely promoted, so that the ability of the exhaust purification device 20 to reduce NO _x is further increased.

(4) Since the ammonia is produced by reduction of NO _x, it is increased more ability to reduce NO _x in the exhaust gas purification device 20.
(5) It is suppressed that the reduction reaction of NO _x in the hydrocarbon reduction layer 61 hardly occurs due to the lack of hydrocarbons. Therefore, the ability to reduce NO _x in the exhaust gas purifying device 20 is enhanced.

The embodiment described above can be implemented with appropriate modifications as follows.
The exhaust purification device 20 may not include the downstream addition valve 24. Even in such a configuration, the upstream addition valve 23 injects the light oil toward the exhaust, whereby the light oil is also supplied to the downstream catalyst 22.

  The exhaust purification device 20 may not include the upstream addition valve 23. Even with such a configuration, for example, the fuel may be injected from the fuel injection valve 13 toward the cylinder 11a under the condition that the fuel injected from the fuel injection valve 13 flows to the exhaust pipe 19. Thereby, the low temperature reduction catalyst 21A of the upstream catalyst 21 uses the fuel injected from the fuel injection valve 13 as a reducing agent.

The exhaust purification device 20 may not include both the upstream addition valve 23 and the downstream addition valve 24. In such a configuration, the fuel may be injected from the fuel injection valve 13 toward the cylinder 11a under the condition that the fuel injected from the fuel injection valve 13 flows to the exhaust pipe 19. Thereby, the reduction of NO _{x in} the upstream catalyst 21 and the downstream catalyst 22 is performed by the fuel injected from the fuel injection valve 13.

The metal contained in the hydrocarbon reduction layer 61 is not limited to copper, and may be other metals as long as it can promote the NO _x reduction reaction using hydrocarbon as a reducing agent. Further, the metal included in the ammonia reduction layer 62 is not limited to copper, but may be other metals as long as it can promote the reduction reaction of NO _x using ammonia as a reducing agent. However, in the structure in which the ammonia reduction layer 62 is stacked on the hydrocarbon reduction layer 61, each layer preferably contains copper in order to exhibit the function of the hydrocarbon reduction layer 61 and the function of the ammonia reduction layer 62. .

The catalyst support 81 of the hydrocarbon reduction layer 61 is not limited to at least one selected from the group consisting of ZSM-5 type zeolite and beta type zeolite. The formation material of the catalyst carrier 81 is a porous material, and other materials can be used as long as they can promote a NO _x reduction reaction using hydrocarbon as a reducing agent by supporting a metal. Good.

The catalyst support 71 of the ammonia reduction layer 62 is not limited to at least one selected from the group consisting of SAPO-34 type zeolite and SAPO-47 type zeolite. The material for forming the catalyst carrier 71 is a porous material, and may be another material as long as it can promote a NO _x reduction reaction using ammonia as a reducing agent by supporting a metal. .

-The diameter of the hole 71h which the catalyst support | carrier 71 of the ammonia reduction layer 62 has may be more than the molecular diameter of a hydrocarbon. Even with such a configuration, as long as ammonia can enter the pores of the catalyst carrier 71, the ammonia reduction layer 62 can promote the NO _x reduction reaction using ammonia as a reducing agent.

The diameter of the hole 71h of the catalyst support 71 of the ammonia reduction layer 62 may be equal to or less than the molecular diameter of ammonia. Even this structure, if a configuration in which the reduction reaction of the NO _x to a reducing agent of ammonia on the surface of the catalyst carrier 71 is promoted, it is possible to obtain not a little effect in conformity with the above (1).

-The diameter of the hole 81h which the catalyst support 81 of the hydrocarbon reduction layer 61 has may be below the molecular diameter of a hydrocarbon. Even this structure, if a configuration in which the reduction reaction of the NO _x to hydrocarbons in the surface of the catalyst carrier 81 and the reducing agent is promoted, it is possible to obtain not a little effect in conformity with the above (1).

The multilayer catalyst 52 formed on the monolith support 51 only needs to have a hydrocarbon reduction layer and an ammonia reduction layer, and the hydrocarbon reduction layer covers the ammonia reduction layer to form the surface 22s of the reduction catalyst 22B. May be. Even in such a configuration, as long as it has a hydrocarbon reduction layer that promotes a reduction reaction of NO _x using hydrocarbon as a reducing agent and an ammonia reduction layer that promotes a reduction reaction of NO _x using ammonia as a reducing agent, The effect according to (1) can be obtained. As described above, the configuration in which the ammonia reduction layer covers the hydrocarbon reduction layer to form the surface 22s of the reduction catalyst 22B is preferable.

The downstream catalyst 22 has catalytic activity that is an activity that promotes a reaction for reducing NO _x using hydrocarbons at a low temperature, for example, in a temperature range of 150 ° C. or higher and 350 ° C. or lower, downstream of the reduction catalyst 22B. You may further provide a downstream low-temperature reduction catalyst. The downstream low-temperature reduction catalyst may have the same configuration as the low-temperature reduction catalyst 21A included in the upstream catalyst 21. When the downstream catalyst 22 includes a downstream low temperature catalyst, the catalyst carrier of the downstream low temperature reduction catalyst may be the same as the catalyst carrier of the reduction catalyst 22B, or may be a catalyst carrier independent of the reduction catalyst 22B. .

  When the catalyst carrier of the downstream low-temperature reduction catalyst is the same as the catalyst carrier of the reduction catalyst 22B, the multilayer catalyst 52 having the hydrocarbon reduction layer 61 and the ammonia reduction layer 62 is located in a portion including the upstream end of the reduction catalyst 22B. What is necessary is just to locate the layer which functions as a downstream low-temperature reduction catalyst in another part. Hereinafter, the configuration of the reduction catalyst 22B will be described with reference to FIGS. 8 to 10 show a part of the cross-sectional structure along the direction in which the cell 51h of the monolith support 51 extends in the reduction catalyst 22B.

  As shown in FIG. 8, in such a reduction catalyst 22B, in the direction in which the cell 51h of the monolith support 51 extends, a multilayer catalyst having a hydrocarbon reduction layer 61 and an ammonia reduction layer 62 at a site upstream of the reduction catalyst 22B. 52 is located. A low temperature catalyst layer 63 having the same thickness as the multilayer catalyst 52 is located downstream of the multilayer catalyst 52.

  Alternatively, as shown in FIG. 9, in the direction in which the cell 51h of the monolith support 51 extends, the ammonia reduction layer 62 is located over substantially the entire direction in which the cell 51h extends. On the other hand, the hydrocarbon reduction layer 61 is located upstream in the extending direction of the cell 51 h, and the low temperature catalyst layer 63 is located downstream of the hydrocarbon reduction layer 61. As a result, the ammonia reduction layer 62 is positioned above the hydrocarbon reduction layer 61 and the low temperature catalyst layer 63 and covers the hydrocarbon reduction layer 61 and the low temperature catalyst layer 63.

  As shown in FIG. 10, in the configuration in which the hydrocarbon reduction layer 61 and the low temperature catalyst layer 63 are located below the ammonia reduction layer 62, the low temperature catalyst layer 63 extends downstream from the ammonia reduction layer 62. May be.

In the exhaust purification device 20, the temperature of the exhaust gas entering the upstream catalyst 21 is the highest, and the temperature of the exhaust gas exiting from the downstream catalyst 22 is the lowest. Therefore, in the exhaust purification device 20, the temperature at the upstream end of the upstream catalyst 21 is highest and the temperature at the downstream end of the downstream catalyst 22 tends to be lowest. Therefore, the downstream low-temperature catalyst having catalytic activity at a temperature lower than that of the reduction catalyst 22B is positioned downstream of the reduction catalyst 22B, so that the downstream low-temperature catalyst uses the reducing agent remaining in the exhaust to reduce NO _x . Reduce. As a result, the ability of the exhaust purification device 20 to reduce NO _x contained in the exhaust can be enhanced.

  As shown in FIG. 11, the upstream catalyst 21 may not include the filter 21B, and as long as the reduction catalyst 22B is the multilayer catalyst 52, the effect according to the above (1) can be obtained.

  As shown in FIG. 12, the upstream catalyst 21 may not include the low-temperature reduction catalyst 21A, and as long as the reduction catalyst 22B is the multilayer catalyst 52, the effect according to the above (1) can be obtained. In addition, in this structure, it is preferable to have the structure for raising the temperature of the filter 21B, for example, the burner arrange | positioned upstream of the filter 21B in a distribution direction, the oxidation catalyst etc. which the filter 21B carries.

  As shown in FIG. 13, the exhaust purification device 20 does not have to include the upstream catalyst 21 and the upstream addition valve 23, and as long as the reduction catalyst 22B is the multilayer catalyst 52, the effect according to the above (1) Can be obtained.

  As shown in FIG. 14, the exhaust purification device 20 may be configured not to include the ammonia catalyst 22 </ b> A of the downstream catalyst 22 in addition to the upstream catalyst 21 and the upstream addition valve 23. In such a configuration, the exhaust purification device 20 only needs to include a urea addition valve 27 that adds ammonia, for example, urea, which is a product of ammonia, to the exhaust, and a urea tank 28 that is connected to the urea addition valve 27. The urea addition valve 27 and the urea tank 28 are an example of an ammonia supply unit. Even if it is such a structure, since the reduction catalyst 22B is the multilayer catalyst 52, the effect according to said (1) can be acquired.

  The downstream catalyst 22 may not include the ammonia generation catalyst 22A. Such a configuration may include a urea addition valve and a urea tank as in the modification described with reference to FIG.

  The exhaust purification device 20 may be configured not to include the filter 21B of the upstream catalyst 21 and the ammonia generation catalyst 22A of the downstream catalyst 22. Such a configuration may include a urea addition valve and a urea tank as in the modification described with reference to FIG.

  The exhaust purification device 20 may be configured not to include the low-temperature reduction catalyst 21A of the upstream catalyst 21 and the ammonia generation catalyst 22A of the downstream catalyst 22. Such a configuration may include a urea addition valve and a urea tank as in the modification described with reference to FIG.

The cross-sectional shape of the cell 51h is not limited to a rectangular shape, and may be, for example, a trapezoidal shape, a square shape, a sinusoidal shape, a hexagonal shape, an elliptical shape, a circular shape, or the like.
The reduction catalyst 22B is not configured to include the monolith support 51, but may be configured to include a pellet-shaped support or a plate-shaped support as the support. Even if it is such a structure, if the reduction catalyst 22B is a structure provided with the hydrocarbon reduction layer 61 and the ammonia reduction layer 62, the effect according to said (1) can be acquired.

  The fuel supplied to the cylinder block 11 is not limited to light oil but may be compressed natural gas (CNG) or gasoline. Even with such a configuration, it is possible to obtain the effect (1).

The technical idea grasped from the above-described embodiment will be additionally described.
(Appendix 1)
The low-temperature reduction catalyst that further promotes the reduction reaction of the nitrogen oxide using the hydrocarbon at a temperature lower than that of the hydrocarbon reduction catalyst upstream of the ammonia supply unit in the exhaust flow direction. The exhaust emission control device according to claim 5.

According to such a configuration, the exhaust purification device further includes the low-temperature reduction catalyst in addition to the reduction catalyst, so that nitrogen oxides can be reduced in a wider temperature range.
(Appendix 2)
The hydrocarbon addition valve is a first addition valve;
The first addition valve is one of two hydrocarbon addition valves;
The two hydrocarbon addition valves include the first addition valve and the second addition valve,
The first addition valve is
Arranged between the low-temperature reduction catalyst in the direction of flow of the exhaust and the hydrocarbon reduction catalyst,
The second addition valve
The exhaust emission control device according to claim 5, wherein the exhaust gas purification device is disposed upstream of the low-temperature reduction catalyst in a direction in which the exhaust flows.

  According to such a configuration, since the hydrocarbon addition valve is arranged one by one near each of the two catalysts using hydrocarbons, since there is not enough hydrocarbon in each catalyst, the reduction reaction of nitrogen oxides is performed. Less likely to occur.

(Appendix 3)
The exhaust emission control device according to claim 1, further comprising a filter that captures particulates contained in the exhaust gas between the low-temperature reduction catalyst and the ammonia supply unit in a direction in which the exhaust gas flows.

  According to such a configuration, exhaust gas from which at least a part of the fine particles have been removed by the filter is supplied to the reduction catalyst disposed downstream of the filter. Therefore, it is suppressed that the fine particles contained in the exhaust gas adhere to the reduction catalyst, so that the reduction catalyst does not easily promote the reduction reaction of nitrogen oxides.

  DESCRIPTION OF SYMBOLS 10 ... Engine, 11 ... Cylinder block, 11a ... Cylinder, 12 ... Common rail, 13 ... Fuel injection valve, 14 ... Intake manifold, 15 ... Intake pipe, 16 ... Intercooler, 17 ... Turbocharger, 17a ... Compressor, 17b ... Turbine, DESCRIPTION OF SYMBOLS 18 ... Exhaust manifold, 19 ... Exhaust pipe, 20 ... Exhaust purification device, 21 ... Upstream catalyst, 21A ... Low temperature reduction catalyst, 21B ... Filter, 22 ... Downstream catalyst, 22A ... Ammonia production catalyst, 22B ... Reduction catalyst, 22s ... Surface 23 ... Upstream addition valve, 24 ... Downstream addition valve, 25 ... Fuel tank, 25a ... Fuel supply pipe, 25a1 ... Upstream pipe, 25a2 ... Downstream pipe, 25b ... Upstream valve, 25c ... Downstream valve, 26 ... Fuel addition pump, 27 ... Urea addition valve, 28 ... Urea tank, 31 ... Air flow meter, 32 ... First temperature sensor Sir, 33 ... second temperature sensor, 40 ... control device, 51 ... monolith support, 51a ... cell wall, 51h ... cell, 52 ... multilayer catalyst, 61 ... hydrocarbon reduction layer, 62 ... ammonia reduction layer, 62g ... gap, 63 ... low temperature catalyst layer, 71, 81 ... catalyst carrier, 71h, 81h ... hole, A ... ammonia, Ex ... exhaust, H ... hydrocarbon.

Claims (5)

A reduction catalyst disposed in the exhaust passage to reduce nitrogen oxides contained in the exhaust;
An ammonia supply unit that is arranged upstream of the reduction catalyst in the direction in which the exhaust flows, and that supplies ammonia to the exhaust;
A hydrocarbon supply unit that is arranged upstream of the reduction catalyst in a direction in which the exhaust flows, and that supplies hydrocarbons to the exhaust,
The reduction catalyst is a laminated structure,
An ammonia reduction layer that promotes a reduction reaction of the nitrogen oxide using the ammonia;
And a hydrocarbon reduction layer that promotes a reduction reaction of the nitrogen oxide using the hydrocarbon. The ammonia reduction layer includes a first catalyst carrier that is a particle of a first porous material,
The hydrocarbon reduction layer includes a second catalyst carrier that is a particle of a second porous material,
The pore diameter of the first catalyst support is smaller than the molecular diameter of the hydrocarbon,
The diameter of the pores of the second catalyst support is not less than the molecular diameter of the hydrocarbon,
The ammonia reduction layer is
The exhaust emission control device according to claim 1, wherein a surface of the reduction catalyst that covers the hydrocarbon reduction layer and contacts the exhaust is formed. The ammonia reduction layer includes copper and the first catalyst carrier,
The hydrocarbon reduction layer includes copper and the second catalyst support,
The first catalyst support is at least one selected from the group consisting of a SAPO-34 type zeolite and a SAPO-47 type zeolite,
The exhaust emission control device according to claim 2, wherein the second catalyst carrier is at least one selected from the group consisting of ZSM-5 type zeolite and beta type zeolite. The ammonia supply unit is
The exhaust emission control device according to any one of claims 1 to 3, wherein the exhaust gas purification catalyst is an ammonia generation catalyst that promotes a reduction reaction of the nitrogen oxide using the hydrocarbon to generate the ammonia. The hydrocarbon supply unit is
The exhaust emission control device according to any one of claims 1 to 4, further comprising a hydrocarbon addition valve that adds hydrocarbons to the exhaust gas.

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