JP2013072334A - Exhaust gas purifying device and exhaust gas purifying catalyst unit - Google Patents

Abstract

An exhaust gas purification apparatus and an exhaust gas purification catalyst unit that effectively suppress H ₂ S emissions in an exhaust gas purification process of an internal combustion engine using a three-way catalyst.
An exhaust gas purifying apparatus provided in an exhaust system of an internal combustion engine disclosed herein includes an H ₂ S trap catalyst unit disposed on a downstream side of an exhaust pipe from a three-way catalyst unit, H ₂ and an S-trapping catalyst 30 oxygen supply means 50 for supplying an oxygen-containing gas into, the _{H 2} S-trapping catalyst 30, the amount of released CO ₂ per catalyst 1L by CO ₂ temperature-programmed desorption measurement The base point amount per 1 L of the catalyst based on the above is at least 0.01 mol / L.
[Selection] Figure 1

Description

The present invention relates to a technique for purifying exhaust gas discharged from an internal combustion engine. More specifically, the present invention relates to an exhaust gas purification device provided in an exhaust system of an internal combustion engine, focusing on suppression of hydrogen sulfide (H ₂ S) emission, and an exhaust gas purification catalyst unit used in the device.

  It is a noble metal as an exhaust gas purification catalyst for simultaneously and efficiently purifying harmful components such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) emitted from internal combustion engines such as automobiles. A three-way catalyst having platinum (Pt), palladium (Pd), and rhodium (Rh) as main active species (catalyst metal) is widely used. In order to meet exhaust gas regulations that have been strengthened in recent years, or to minimize the use of the above-mentioned precious metals with high resource risks, further improvement in performance is desired for exhaust gas purification catalysts including the above three-way catalyst. Yes.

By the way, processing of a sulfur (S) component is mentioned as one of the problems which should be solved when processing the exhaust gas of an internal combustion engine using a three-way catalyst.
The S component contained in the exhaust gas covers the surface of the noble metal (for example, Pd) of the exhaust gas purification catalyst, thereby reducing the active point of the catalyst, resulting in a decrease in the purification performance of the catalyst called sulfur poisoning. There is a risk of inviting. Conventionally, in order to suppress such sulfur poisoning, improvements have been made from various aspects such as the configuration, material, and control of the exhaust gas purification catalyst.
For example, in order to recover the catalyst performance from sulfur poisoning, the sulfur component (typically coated on the catalyst) (typically by controlling the air-fuel ratio of the gas mixture, ie, the fuel gas air-fuel ratio and the temperature of the exhaust gas after combustion of the fuel gas). Is known to reduce sulfur oxide (SOx), vaporize it as hydrogen sulfide (H ₂ S), and desorb it from the catalyst.

However, releasing the desorbed H ₂ S directly from the exhaust pipe into the atmosphere at a high concentration is not preferable in terms of environmental hygiene because an unpleasant odor peculiar to H ₂ S is generated in the exhaust gas. Therefore, a device has been devised to suppress the discharge of H ₂ S that causes unpleasant odors.
For example, Patent Document 1 proposes an exhaust gas purification device in which a second catalyst part capable of adsorbing a sulfur compound in exhaust gas is disposed downstream of a three-way catalyst (first catalyst part) in an exhaust system (patent) Reference 1). Further, Patent Document 2 discloses an exhaust gas purification device in which an SOx absorbent is disposed upstream of a main exhaust gas purification catalyst (for example, NOx occlusion reduction type catalyst) on the exhaust system. Further, Patent Document 3 discloses an exhaust gas purification catalyst that can suppress the adsorption of SO ₃ or SO ₄ in a lean atmosphere and, as a result, suppress the generation and emission of H ₂ S in a stoichiometric or rich atmosphere. . Patent Document 4 also discloses an exhaust gas purification device that can suppress the discharge of H ₂ S in a reducing atmosphere (low-temperature stoichiometric or rich atmosphere).

Japanese Patent No. 4341196 JP 2006-305524 A JP 2008-279319 A JP 2009-178625 A

Exhaust gas purifying catalyst described in the patent documents mentioned above (exhaust gas purification apparatus), which has raised a certain effect on the emissions of H 2 _S, room for still improved in achieving further H _{2 S} emissions There is.
The present invention has been created to solve such a problem, and in an exhaust gas purification process of an internal combustion engine using a three-way catalyst, an exhaust gas purification device that can more effectively suppress the emission of H ₂ S, and An object is to provide an exhaust gas purification catalyst unit.

The present inventor has studied from various angles and has come up with the present invention capable of realizing the above object.
In other words, the exhaust gas purification device disclosed herein is an exhaust gas purification device provided in an exhaust system of an internal combustion engine, and includes a three-way catalyst portion disposed in an exhaust pipe, and a downstream of the exhaust pipe from the three-way catalyst portion. H ₂ S trap catalyst section arranged on the side, oxygen supply means for supplying oxygen-containing gas toward the H ₂ S trap catalyst section, and control section for controlling supply of oxygen-containing gas from the oxygen supply means And.
Here, the H ₂ S trap catalyst part includes a base material, a support supported on the base material, a catalyst metal supported on the support and capable of oxidizing H ₂ S in an oxidizing atmosphere. including. The base point amount per 1 L of the catalyst based on the CO ₂ desorption amount per 1 L of the catalyst measured by CO ₂ temperature programmed desorption measurement is at least 0.01 mol / L.

In such an exhaust gas purification apparatus, an H ₂ S trap catalyst part is provided downstream of the three-way catalyst part in the exhaust system of an internal combustion engine (for example, an automobile engine), and the H ₂ S trap catalyst part is CO ₂ temperature-programmed desorption. The base point amount per 1 L of the catalyst is configured to be at least 0.01 mol / L based on the amount of CO ₂ desorbed per 1 L of the catalyst by measurement (that is, CO ₂ -TPD measurement). The base point amount of the catalyst part can be specifically measured by adsorbing carbon dioxide as an acid probe molecule on a test sample and measuring the amount of carbon dioxide desorbed with an increase in temperature and the desorption temperature (CO _2- TPD).
According to the exhaust gas purification apparatus disclosed here, the H ₂ S trap catalyst portion having a strong basicity (that is, a high basic point amount) H ₂ S trap catalyst portion provides H contained in the exhaust gas passing through the three-way catalyst portion. ₂ S can be efficiently adsorbed in the H ₂ S trap catalyst part installed downstream of the three-way catalyst part. Then, H _{2 S} adsorbed in H 2 _S-trapping catalyst unit is oxidized in the H _{2 S-trapping} catalyst unit became oxidizing atmosphere by the oxygen supply means oxygen-containing gas supplied from the (typically air) And discharged as nitrogen oxides such as SO ₂ .
For this reason, according to the exhaust gas purification apparatus of this configuration, it is possible to prevent high-concentration H ₂ S from being released from the exhaust pipe, and to prevent generation of unpleasant odor peculiar to H ₂ S. Also, a process for recovering the catalyst performance from sulfur poisoning in the three-way catalyst part while preventing a large amount of H ₂ S discharge (specifically, a sulfur component coated on the catalyst by controlling the oxygen concentration and temperature of the exhaust gas) (Typically, SOx) reduction treatment) can be performed to maintain the performance of the three-way catalyst unit.

In order to achieve the above object, the present invention provides an exhaust gas purification catalyst unit provided in an exhaust system of an internal combustion engine, an exhaust pipe constituting a part of the exhaust system of the internal combustion engine, and an upstream side of the exhaust pipe And a H ₂ S trap catalyst part arranged downstream of the exhaust pipe from the three-way catalyst part, wherein the H ₂ S trap catalyst part is a base material Per 1 L of catalyst measured by CO ₂ temperature-programmed desorption measurement, comprising: a support supported on the substrate; and a catalyst metal supported on the support and capable of oxidizing H ₂ S in an oxidizing atmosphere. An exhaust gas purifying catalyst unit having a base point amount per liter of catalyst of at least 0.01 mol / L based on the amount of desorbed CO ₂ is provided.
By providing the exhaust gas purification catalyst unit having such a configuration in the exhaust system of the internal combustion engine, an exhaust gas purification device having the above-described effects can be constructed.

In a preferred aspect of the exhaust gas purifying apparatus disclosed herein, the control unit is configured to detect exhaust gas generated by combustion of an air-fuel mixture (fuel gas) in which the exhaust gas introduced from the internal combustion engine to the three-way catalyst unit is in an air-fuel ratio rich region. (Hereinafter, the exhaust gas is sometimes referred to as “rich gas”.) The oxygen-containing gas is supplied from the oxygen supply means to the H ₂ S trap catalyst section.
According to the exhaust gas purifying apparatus having such a configuration, when the exhaust gas is the rich gas (for example, when the air-fuel ratio is less than 14.7), the H ₂ S sent from the three-way catalyst unit is converted into the H ₂ S trap catalyst unit. In addition, the adsorbed H ₂ S can be efficiently oxidized with an oxidation catalyst metal in an H ₂ S trap catalyst part in which an oxygen-containing gas is introduced to form an oxidizing atmosphere, and a nitrogen oxide such as SO ₂ Can be efficiently converted and discharged to the outside (in other words, the emission of H ₂ S can be effectively suppressed).

In a preferred embodiment of the exhaust gas purifying apparatus and exhaust gas purifying catalyst unit disclosed herein, the carrier of the H ₂ S trap catalyst part is mainly composed of ceria / zirconia composite oxide and alumina.
Here, “consisting mainly of” means that the carrier is composed only of ceria-zirconia composite oxide and alumina, or a portion exceeding 50 mass% (or 50 vol%) of the whole carrier (typically Is 70% by mass and / or 70% by volume or more) is a term indicating that it is composed of ceria-zirconia composite oxide and alumina.
In the exhaust gas purification apparatus and exhaust gas purification catalyst unit having such a configuration, since the carrier of the H ₂ S catalyst is mainly composed of ceria / zirconia composite oxide and alumina, the composition and mixing ratio of these oxides are adjusted. Thus, a desired level of basic point (basic) can be easily realized. Moreover, sufficient mechanical strength and oxygen absorption / release capability can be imparted to the carrier of the H ₂ S trap catalyst part. The concentration ratio (molar ratio) of ceria and zirconia in the ceria / zirconia composite oxide is preferably rich in zirconia.

In a preferred embodiment of the exhaust gas purification device and the exhaust gas purification catalyst unit disclosed herein, the carrier of the H ₂ S trap catalyst part is selected from a rare earth element, an alkali metal element, and an alkaline earth metal element. It is configured to include at least one element.
By including this kind of element as a constituent component, a preferable basic point (basic) can be easily realized.
For example, ceria / zirconia composite oxide and / or alumina is included as a support for the H ₂ S trap catalyst part, and the ceria / zirconia composite oxide and / or alumina is at least one rare earth element (for example, yttrium (Y ), Scandium (Sc), or lanthanum (La), praseodymium (Pr), or light rare earth elements such as neodymium (Nd). For example, a ceria / zirconia composite oxide and / or alumina doped with an oxide of these rare earth elements is preferably used.

Moreover, in another preferable aspect of the exhaust gas purification device and the exhaust gas purification catalyst unit disclosed herein, the H ₂ S trap catalyst part does not substantially contain nickel (Ni).
Here, “substantially not contained” means not intentionally contained, and is a term that allows inevitable mixing of extremely small amounts.
In the exhaust gas purification device and the exhaust gas purification unit of this aspect, the environmental load can be further reduced.

It is a figure which shows typically the structure of the exhaust gas purification apparatus which concerns on one Embodiment. The structure of the honeycomb base material used to construct the three-way catalyst unit and H _{2 S-trapping} catalyst of the exhaust gas purifying catalyst unit according to an embodiment is an overall view schematically showing. Is a schematic diagram for explaining the configuration of the H _{2 S-trapping} catalyst of the exhaust gas purifying catalyst unit according to an embodiment (a sectional view). _{H 2} S H ₂ S emission maximum concentration _{when H 2} S emission maximum concentration of the case without the trap catalyst part (ppm) provided _{H 2} S-trapping catalyst portion of each sample is 100 in (ppm) It is a graph which shows a ratio (%). Is a graph showing the relationship between the basic sites of the H ₂ S-trapping catalyst unit and _{H 2} S emission maximum concentration (ppm). It is a graph showing the relationship between A / F value for operating the air injection and H _{2 S} emission maximum concentration (ppm).

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

As shown in FIG. 1, an exhaust gas purification apparatus 1 according to this embodiment is an apparatus 1 provided in an exhaust system of an internal combustion engine, for example, an automobile engine (for example, a gasoline engine) 2. The exhaust gas purifying catalyst unit 10 to be configured, a control unit 40, and an air injection (air injection device) 50 as an oxygen supply means are provided.
The exhaust gas purification catalyst unit 10 includes an exhaust pipe 12 that constitutes a part of an exhaust system of an automobile engine 2 that is an internal combustion engine, a three-way catalyst unit 20 that is disposed upstream in the exhaust gas flow from the engine 2, An H ₂ S trap catalyst unit 30 disposed downstream of the three-way catalyst unit 20 in the exhaust pipe.
The control unit 40 is configured by an ECU (an electronic control unit, that is, an engine control unit). That is, the control unit (ECU) 40 is a unit that performs control between the engine 2 and the exhaust gas purification device 1 and includes a digital computer and other electronic devices as components, as in a general control device. Typically, the control unit (ECU) 40 includes a ROM (read only memory), a RAM (random access memory), a CPU (microprocessor), an input port, an output port, and the like connected to each other by a bidirectional bus. . The device configuration of the control unit (ECU) 40 itself does not characterize the present invention, and may be conventionally employed in this type of internal combustion engine (automobile engine), and further detailed description thereof is omitted.

The air injection (AI) 50 is installed in the exhaust pipe 12 between the three-way catalyst unit 20 and the H ₂ S trap catalyst unit 30. The air injection 50 is electrically connected to the control unit 40 and operates based on a control signal output from the control unit 40. Air (that is, oxygen-containing gas) is discharged into the exhaust pipe 12 at a predetermined timing. To the H ₂ S trap catalyst unit 30. That is, the oxygen supplied from the air injection 50 can improve the oxygen concentration of the gas supplied to the H ₂ S trap catalyst unit 30 on the downstream side of the exhaust gas flow. Therefore, it is possible to convert exhaust gas of a reducing atmosphere also H _{2 S-trapping} catalyst unit 30 such that rich gas to an oxidizing atmosphere. The structure itself of the air injection 50 may be the same as that of a conventional air injection device (for example, an air pump type or a suction type) installed in an exhaust system of an automobile engine, and does not characterize the present invention. Description of is omitted.

In the exhaust gas purification apparatus 1 according to the present embodiment, a predetermined air-fuel ratio sensor (also referred to as an A / F sensor or an O ₂ sensor) 60 is provided in the exhaust pipe 12 between the engine 2 and the three-way catalyst unit 20. is set up. The air-fuel ratio sensor 60 is electrically connected to the control unit (ECU) 40, and the control unit 40 obtains information on the air-fuel ratio of the exhaust gas flowing through the exhaust pipe 12 between the engine 2 and the three-way catalyst unit 20. Input from the sensor 60 is possible. It should be noted that this type of conventional sensor may be used as the air-fuel ratio sensor 60, and it is not necessary to use a sensor having a special structure or performance in carrying out the present invention.
The control unit (ECU) 40 is also electrically connected to a fuel injection device (not shown) of the engine 2, a three-way catalyst unit 20, an H ₂ S trap catalyst unit 30, and the like. Internal temperature monitoring and operation control of the fuel injection device can be performed.

Next, the exhaust gas purification catalyst unit 10 that is a main part of the exhaust gas purification apparatus 1 according to the present embodiment will be described in detail.
In the exhaust gas purification catalyst unit 10 according to this embodiment, a three-way catalyst unit 20 is disposed on the upstream side of an exhaust pipe 12 of an automobile engine 2 that is an internal combustion engine, and H ₂ S is disposed on the downstream side of the three-way catalyst unit 20. The trap catalyst portion 30 is formed to be disposed.
The three-way catalyst unit 20 may be the same as the conventional one provided in the exhaust system of the automobile engine, and is not particularly limited.
When provided in an exhaust system of an internal combustion engine such as an automobile engine, typically a suitable base material is provided. As such a base material, various materials and forms used for conventional applications of this type can be used. For example, a cordierite having high heat resistance, a honeycomb substrate having a honeycomb structure formed from a heat resistant material such as ceramics or alloys (stainless steel, etc.) such as silicon carbide (SiC), and the like can be suitably employed. .
As an example, the honeycomb base material 70 having a cylindrical outer shape shown in FIG. 2 is suitable as a base material constituting the three-way catalyst unit 20 and the H ₂ S trap catalyst unit 30 of the exhaust gas purification catalyst unit 10 disclosed herein. is there. The honeycomb substrate 70 is provided with a plurality of regularly arranged through holes (cells) 72 as exhaust gas passages in the cylinder axis direction (arrow direction in the drawing) along the exhaust gas flow, and partition walls (cells) partitioning the cells 72 ( Rib wall) 74 is configured to be able to contact exhaust gas. In addition, according to the shape of the exhaust system (exhaust pipe) to be installed, a substrate such as a foam shape or a pellet shape may be used in addition to the illustrated honeycomb shape. Moreover, about the external shape of the whole base material, it may replace with a cylindrical shape and an elliptical cylindrical shape and a polygonal cylindrical shape may be employ | adopted.

And the catalyst coat layer which comprises a three way catalyst is formed on a base material (for example, the said honeycomb base material 70). Such a catalyst coat layer is, for example, alumina (Al ₂ O ₃ ), ceria (CeO ₂ ), zirconia (ZrO ₂ ), silica (SiO ₂ ), titania (TiO ₂ ), ceria zirconia (CeO ₂ —ZrO ₂ ). A catalyst carrier capable of oxidizing hydrocarbon (HC) and carbon monoxide (CO) and a catalyst metal capable of reducing nitrogen oxide (NOx) are supported on a porous carrier such as a composite oxide. It is constituted by.
Examples of this type of catalytic metal include platinum (Pt), rhodium (Rh), palladium (Pd), and the like, and it is preferable to use Pt having excellent oxidation activity and Rh having excellent reduction activity.
A catalyst coat layer comprising a porous carrier and a catalyst metal can be prepared by a conventionally known method. Typically, it can be prepared by a wash coat method. For example, a slurry containing porous carrier particles (powder) may be wash-coated on a substrate, and catalytic metal particles may be supported thereon, or porous carrier particles (powder) in which predetermined catalyst metal particles are previously supported. The base material may be wash-coated with a slurry. Subsequently, the target catalyst coat layer can be formed by firing under appropriate conditions.
The amount of catalyst metal supported is not particularly limited as it may be the same as that of the conventional three-way catalyst part. For example, about 0.1 to 10 g per liter of porous carrier is preferable. The formation of the catalyst coat layer based on the washcoat method may be the same as the method employed in the production of the conventional exhaust gas purification catalyst, and does not characterize the present invention.

Next, the H ₂ S trap catalyst unit 30 that characterizes the exhaust gas purification catalyst unit 10 disclosed herein will be described in detail. FIG. 3 is a diagram schematically illustrating the configuration and operational effects (functions) of the H ₂ S trap catalyst unit 30.
The basic structure of the H ₂ S trap catalyst unit 30 may be the same as that of the above-described three-way catalyst unit 20, and is typically a base material 32 made of a heat-resistant material (such as cordierite) having the above-described honeycomb structure or other structure. Further, an H ₂ S trap catalyst coat layer 36 composed of a porous carrier 34 and a catalyst metal (particle) 38 supported on the carrier 34 is provided.
The porous carrier 34 constituting the H ₂ S trap catalyst coat layer 36 disclosed herein has a base point per 1 L of catalyst based on the desorption amount of CO ₂ per 1 L of catalyst by CO ₂ temperature-programmed desorption measurement. The amount is at least 0.01 mol / L (for example, 0.01 to 0.05 mol / L). Preferably, the amount of base points per liter of catalyst is at least 0.012 mol / L (for example, 0.012-0.05 mol / L).
The material is not particularly limited as long as it has such characteristics and is suitable for this kind of application, but a ceramic porous carrier having a relatively high basicity (that is, a high basic point) is preferable. Examples include ceria, zirconia, ceria-zirconia composite oxide, alumina, and various types of zeolite (for example, zeolites of A type, ferrilite type, ZSM-5 type, mordenite type, β type, X type, and Y type). Of these, a porous carrier mainly composed of ceria / zirconia composite oxide and alumina is preferable. By adjusting the blending ratio of these two kinds of oxides, the amount of base points of the porous carrier can be increased or decreased. Further, mechanical strength and oxygen absorption / release capability can be imparted to the carrier.
Further, from the viewpoint of increasing the amount of base sites, the concentration ratio (molar ratio) of ceria and zirconia in the ceria / zirconia composite oxide is preferably rich in zirconia. For example, a molar ratio of ceria: zirconia = 1: 2 to 1: 5 is preferable.

Alternatively, the basic point amount of the porous carrier can be adjusted by introducing a highly basic substance. Examples of such substances include alkaline earth metal elements, alkali metal elements, rare earth element compounds (for example, oxides) or salts (for example, carbonates, acetates, sulfates). For example, it is particularly preferable that light rare earths (oxides) such as Y, Sc, La, Pr, and Nd are included. Use of ceria, zirconia, ceria / zirconia composite oxide, alumina, and various zeolites (particularly, ceria / zirconia composite oxide and / or alumina) containing these rare earth element oxides is preferable.
Alternatively, oxides, hydroxides, carbonates, acetates, etc. of alkaline earth metal elements (Group 2 elements) such as barium (Ba), strontium (Sr), calcium (Ca), magnesium (Mg), etc. It is preferable to use ceria, zirconia, ceria / zirconia composite oxide, alumina, and various zeolites (particularly ceria / zirconia composite oxide and / or alumina) containing the above salt.
Alternatively, ceria, zirconia, ceria / zirconia composite oxide, alumina, various oxides containing oxides, hydroxides, carbonates, acetates, etc. of alkali metal elements such as sodium (Na) and potassium (K) Of these, it is preferable to use zeolite (particularly, ceria-zirconia composite oxide and / or alumina).

These components can be contained in the porous carrier by a conventionally known method. For example, a raw material compound having a rare earth element (for example, Y, La, Pr, Nd) and a raw material compound for an element constituting the porous carrier (for example, Al, Zr, Ce) are mixed at a desired molar ratio, followed by firing. By doing so, it is possible to obtain a porous carrier made of ceramics containing the target rare earth element oxide. Alternatively, a porous carrier having a predetermined composition is dipped in a solution containing ions of an alkali metal element or an alkaline earth metal element, dried, and fired to obtain a target alkali metal element or alkaline earth metal element (second A porous carrier made of a ceramic containing a compound of a group element) or a salt can be obtained.
The content of these components (rare earth component, alkali metal component, alkaline earth metal component) contained in the porous carrier is not particularly limited as long as they are blended so as to achieve a predetermined base point amount. For example, the rare earth component may be contained so that about 1 to 20% by mass of the entire porous carrier in terms of oxide is an oxide of the rare earth element.

Although not particularly limited, a powdery (particulate) porous carrier for the H ₂ S trap is preferably used. The average particle diameter of the particles constituting the carrier (average particle diameter measured by laser diffraction / scattering method or average particle diameter based on SEM or TEM observation) is suitably from 1 nm to 1000 nm, and from 5 nm to 500 nm. Is preferable, and 20 nm or more and 250 nm or less are more preferable. The specific surface area of the particles constituting the carrier (specific surface area as measured by BET method. Hereinafter the same.) Is preferably ^{50~700m 2 / g, 100~300m 2 /} g is more preferable. When the average particle size of the particles constituting the support is too large than 1000 nm or the specific surface area is too small than 50 m ² / g, the dispersibility of the catalyst metal supported on the support tends to be reduced. This is not preferable because the purification performance deteriorates. In addition, when the particle size of the particles constituting the carrier is too smaller than 1 nm or the specific surface area is more than 700 m ² / g, the heat resistance of the carrier itself is lowered, so that the heat resistance characteristics of the catalyst are lowered. It is not preferable.

The catalyst metal (particles) 38 included in the H ₂ S trap catalyst coat layer 36 is not particularly limited as long as it is a catalyst metal capable of oxidizing H ₂ S in an oxidizing atmosphere. However, it is preferable not to include Ni in consideration of environmental load. Preferable examples include particles of platinum group metals such as Pt and Pd or alloys thereof.
The method for supporting the catalyst metal on the porous carrier 34 as described above may be a conventionally known method and does not require any special treatment in the practice of the present invention. For example, the method for supporting Pt particles or Pd particles on a carrier is not particularly limited, and for example, an impregnation method or an adsorption method can be used. In a typical impregnation method, the carrier can be prepared by impregnating an aqueous solution containing an appropriate platinum salt or palladium salt, followed by drying and baking. Although it does not specifically limit, about 300-700 degreeC is suitable for a calcination temperature. If the calcination temperature is too high, there is a possibility that the growth of the noble metal particles supported on the carrier may proceed, which is not preferable. Further, if the firing temperature is too low, the firing time tends to be prolonged, which is not preferable. The amount of catalyst metal supported is not particularly limited. For example, about 0.1 to 10 g per liter of porous carrier is preferable.

The method of forming the H ₂ S trap catalyst coat layer 36 on the substrate 32 using the porous carrier 34 on which the catalyst metal particles 38 thus prepared are supported is the above three-way catalyst unit 20. The H ₂ S trap catalyst coat layer 36 can be formed on the surface of the substrate 32 by a general wash coat method. That is, the slurry containing the porous carrier 34 on which the catalyst metal particles 38 are supported may be wash-coated on the base material 32, or the slurry containing the porous carrier 34 may be wash-coated on the base material 32 first. In addition, catalytic metal particles 38 may be supported. Next, the H ₂ S trap catalyst coat layer 36 can be formed by firing under appropriate conditions (for example, firing at about 400 to 1000 ° C. for 6 hours or less). The thickness (average thickness) of the H ₂ S trap catalyst coat layer 36 is not particularly limited, and is preferably about 10 μm to 200 μm, for example, and preferably about 30 μm to 100 μm.

  According to the exhaust gas purification apparatus 1 according to the present embodiment having the above-described configuration, information (for example, a data signal based on the oxygen concentration) from the air-fuel ratio sensor 60 is transmitted to the control unit (ECU) 40. The controller 40 calculates the air-fuel ratio of the air-fuel mixture supplied to the engine based on the input information. Further, based on the air-fuel ratio, the exhaust gas introduced into the three-way catalyst unit 20 is exhaust gas (rich gas) generated by combustion of the air-fuel mixture in the air-fuel ratio rich region, or the air-fuel mixture in the air-fuel ratio stoichiometric or lean region It is determined whether the exhaust gas generated by the combustion of the gas (hereinafter, the exhaust gas may be referred to as “lean / stoichiometric gas”), and if it is rich gas (or if the air-fuel ratio value belongs to the rich region), air injection An operation signal is output to 50.

For example, when the air-fuel ratio calculated based on the data from the air-fuel ratio sensor 60 is a rich region, for example, a gasoline engine, typically, the control unit 40 has an A / F value of 14. When it is less than 7 (stoichiometric), air (oxygen-containing gas) is injected from the air injection 50 into the exhaust pipe 12, and the injected air (oxygen-containing gas) is supplied to the H ₂ S trap catalyst unit 30. On the other hand, when the A / F value is in the stoichiometric or lean region of 14.7 or more, the control unit 40 stops air ejection from the air injection 50. By performing such an operation, the sulfur (S) component in the exhaust gas can be treated as follows.
That is, when the exhaust gas from the engine 2 is lean / stoichiometric gas, the sulfur component (eg, SO ₂ ) in the exhaust gas is supported in various forms (eg, sulfate: SO ₄ ²⁻ ) in the three-way catalyst unit 20 or a metal catalyst. Adsorbed and retained by When the exhaust gas from the engine 2 becomes rich gas and the three-way catalyst unit 20 is changed to a reducing atmosphere by the introduction of the rich gas, the adsorbed and held S is reduced to H ₂ S, and the three-way catalyst unit 20 It is discharged and introduced into the downstream H ₂ S trap catalyst section 30 through the exhaust pipe 12. Then, it is possible to reversibly adsorb _{H 2} S by the _{H 2} S adsorption component in the _{H 2} S-trapping catalyst 30.

At this time, from the control unit 40 on condition that the exhaust gas introduced into the three-way catalyst unit 20 is rich gas (in other words, the air-fuel ratio calculated based on the data from the air-fuel ratio sensor 60 is a rich region). In response to the operation signal, air is supplied from the air injection 50 toward the H ₂ S trap catalyst unit 30 through the exhaust pipe 12, and the inside of the H ₂ S trap catalyst unit 30 is changed to an oxidizing atmosphere by air (oxygen).
And Thus, as shown schematically in Figure 3, by the action of the air catalytic metal 38 in H _{2 S-trapping} catalyst 30 that (oxygen) is introduced (oxidation catalyst), introduced into the H 2 _S-trapping catalyst 30 The H ₂ S in the rich gas and the previously trapped H ₂ S are oxidized, and are typically discharged to the outside as SO ₂ and H ₂ O. Therefore, according to the exhaust gas purifying apparatus 1 according to this embodiment, it is possible to H _{2 S} of the high concentration from the exhaust pipe 12 is prevented from being released, to prevent the occurrence of H 2 _S-specific offensive odor. Further, a process for recovering the catalyst performance from sulfur poisoning in the three-way catalyst unit 20 by introducing a rich gas (reducing gas) into the three-way catalyst unit 20 at an appropriate timing while preventing a large amount of H ₂ S from being discharged. (SOx reduction treatment) can be performed to maintain the performance of the three-way catalyst unit.

  Several examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in the specific examples.

<Example 1 of production of H ₂ S trap catalyst portion>
Ceria / zirconia composite oxide (ceria / zirconia molar ratio = 1/4) powder (specific surface area: about 100 m ² / g) and θ-alumina powder (specific surface area: about 100 m ² / g) were prepared. . Using these powders and alumina hydrate (product of Nissan Chemical Industries, Ltd.) as a binder, a slurry for forming an H ₂ S trap catalyst part was prepared. The mixing ratio of the two kinds of oxide powders is adjusted so that the base point amount per 1 L of the catalyst is 0.009 mol / L based on the CO ₂ desorption amount per 1 L of the catalyst according to the CO ₂ -TPD measurement. did.
The obtained slurry was applied to a cordierite honeycomb substrate having a total length of 105 mm, a diameter of 103 mm, and a cell structure of 4.5 mil / 400 cpsi (where mil is 1/1000 inch and cpsi is the number of cells per square inch). Wash-coating was performed, followed by baking at 500 ° C. for 2 hours. The catalyst coating amount was about 120 g per 1 L of honeycomb substrate. Subsequently, Pt particles were supported as catalytic metal particles using a dinitrodiammine platinum nitrate aqueous solution, dried at 250 ° C. for 1 hour, and then calcined at 500 ° C. for 1 hour. The amount of Pt particles supported was about 2 g per liter of honeycomb substrate.
According to the above process, an H ₂ S trap catalyst portion of “Sample 1” having a base point amount per 1 L of catalyst of 0.009 mol / L based on the above CO ₂ -TPD measurement standard was produced.

<Example 2 of production of H ₂ S trap catalyst portion>
Instead of the ceria / zirconia composite oxide used in Production Example 1 above, a ceria / zirconia composite oxide containing 3% by mass of La ₂ O ₃ and 7% by mass of Pr ₂ O ₃ with the whole oxide as 100 is used. Except for the above, by using the same material as in Production Example 1 and performing the same process, H _{2 of} “Sample 2” having a base point amount of 0.015 mol / L of the catalyst based on the CO ₂ -TPD measurement standard was 0.015 mol / L. An S trap catalyst part was prepared.

<Example 3 of production of H ₂ S trap catalyst portion>
In place of the ceria / zirconia composite oxide used in Production Example 1, a ceria / zirconia composite oxide containing 5% by mass of Nd ₂ O ₃ and 5% by mass of Y ₂ O ₃ was used. H ₂ S trap of “Sample 3” using the same material as in Production Example 1 and the same process and having a base point amount of 0.015 mol / L per 1 L of catalyst based on the above CO ₂ -TPD measurement standard A catalyst part was prepared.

<Example 4 of production of H ₂ S trap catalyst portion>
Instead of the alumina used in Production Example 1, the same material as in Production Example 1 was used, except that θ-alumina containing 5% by mass of La ₂ O ₃ of the whole oxide was used. Then, an H ₂ S trap catalyst part of “Sample 4” having a base point amount of 0.013 mol / L per 1 L of catalyst based on the above CO ₂ -TPD measurement standard was prepared.

<Example 5 of production of H ₂ S trap catalyst part>
The H ₂ S trap catalyst part (that is, the catalyst-supporting honeycomb substrate) of Sample 1 prepared in Production Example 1 was subjected to alkali metal salt treatment. Specifically, the H ₂ S trap catalyst part (catalyst-supporting honeycomb substrate) of Sample 1 is immersed in a predetermined concentration of sodium carbonate aqueous solution (or an aqueous solution containing other sodium ions), and the sodium carbonate aqueous solution is absorbed by the substrate. I let you. Next, by drying at 250 ° C. and calcining at 500 ° C., the H ₂ S trap catalyst part of “Sample 5” having a base point amount of 0.012 mol / L per 1 L of catalyst based on the above CO ₂ -TPD measurement standard Was made.

<Example 6 of production of H ₂ S trap catalyst portion>
The alkaline earth metal salt treatment was performed on the H ₂ S trap catalyst portion (that is, the catalyst-supporting honeycomb substrate) of Sample 1 prepared in Production Example 1 above. Specifically, the H ₂ S trap catalyst part (catalyst-supporting honeycomb substrate) of Sample 1 is immersed in a barium carbonate aqueous solution (or an aqueous solution containing other barium ions) having a predetermined concentration, and the barium carbonate aqueous solution is absorbed by the substrate. I let you. Next, by drying at 250 ° C. and calcining at 500 ° C., the H ₂ S trap catalyst part of “Sample 6” having a base point amount of 0.014 mol / L per 1 L of catalyst based on the above CO ₂ -TPD measurement standard Was made.

<Measurement test 1 of H ₂ S emission amount>
The following tests were conducted using the H ₂ S trap catalyst parts (catalyst-supported honeycomb base materials) of Samples 1 to 6 obtained in the above production examples.
That is, in order to construct the exhaust gas purification catalyst unit 10 schematically shown in FIG. 1 described above, the sample is placed downstream of the three-way catalyst unit 20 in the exhaust system of an actual in-line four-cylinder gasoline engine (displacement amount: about 2 L). The H ₂ S trap catalyst unit 30 and the air injection 50 of any one of 1 to 6 were arranged, and the actual engine was operated using S-containing gasoline.
Specifically, an exhaust system as shown in FIG. 1 is constructed, and after operating the engine under stoichiometric conditions until S is saturated and adsorbed in the three-way catalyst unit 20 on the upstream side in the exhaust gas flow, a WOT (wide open throttle) ) The engine was operated by switching to the state, and the exhaust gas introduced into the three-way catalyst unit 20 was changed to rich gas. At this time, on the condition that the A / F value calculated based on the data from the air-fuel ratio sensor 60 is 14.0 or less, the air from the air injection 50 is exhausted to the upstream side of the H ₂ S trap catalyst unit 30. 12 and the inside of the H ₂ S trap catalyst portion 30 was made an oxidizing atmosphere. Under such conditions, the H ₂ S concentration (H ₂ S emission amount: ppm) in the exhaust gas discharged to the outside from the exhaust pipe 12 was continuously measured.

As a comparative control (control section), the H ₂ S concentration (ppm) was measured under the same conditions even in an exhaust system in which no H ₂ S trap catalyst part was installed on the downstream side of the three-way catalyst part 20. Then, the ratio (%) of the maximum concentration of H ₂ S emission in the exhaust system in which the H ₂ S trap catalyst portion of each sample was installed was calculated with the maximum concentration of H ₂ S emission in the control section being 100. The results are shown in FIG.
As shown in FIG. 4, H ₂ S is discharged even in Sample 1 in which the base point amount of the catalyst constituting the H ₂ S trap catalyst unit 30 is 0.009 mol / L per 1 L of the catalyst based on the CO ₂ -TPD measurement standard. However, in Samples 2 to 6 in which the amount of base points was 0.01 mol / L or more, significant suppression of H ₂ S discharge was observed.

<H ₂ S emission measurement test 2>
The mixing ratio of the ceria / zirconia composite oxide powder and the θ-alumina powder used in Production Example 1 above, or the alkali metal salt treatment carried out in Production Example 5 or the alkaline earth metal salt carried out in Production Example 6 The treatment was carried out by varying the degree of treatment (salt concentration treatment time, treatment frequency, etc.), and the base point amount was 0, 0.005, 0.01, 0.015, 0.02, 0.03, 0.05, and to produce a _{H 2} S-trapping catalyst section is 0.08 mol / L. And Thus, the same test as the measurement test 1, H _{2 S} concentration in the case of using the H _{2 S-trapping} catalyst of the basic sites of (H 2 _S emissions: ppm) was continuously measured . Then, the base point amount of H _{2 S} emissions maximum concentration in the exhaust system which established the H _{2 S-trapping} catalyst of the basic sites of the 100 H _{2 S} emission maximum density when using the catalyst of 0 mol / L The ratio (%) was calculated. The results are shown in FIG.
As shown in FIG. 5, it was recognized that the degree of suppression of H ₂ S emission increases as the value of the base point amount of the catalyst constituting the H ₂ S trap catalyst unit 30 increases. In particular, when the base point amount was 0.01 mol / L or more (more preferably 0.015 mol / L or more, further 0.02 mol / L or more), significant suppression of H ₂ S emission was observed.

<Measurement test 3 of H ₂ S emission amount>
The H ₂ S trap catalyst part having a base point amount of 0.02 mol / L prepared and used in the measurement test 2 is used, and air is exhausted from the air injection (AI) upstream of the H ₂ S trap catalyst part. The timing of spraying into the tube was varied.
Specifically, as in the above measurement test 1, an exhaust system as shown in FIG. 1 is constructed, and stoichiometric conditions until S is saturated and adsorbed in the three-way catalyst unit 20 upstream of the H ₂ S trap catalyst unit 30. After operating the engine below, the engine was operated by switching to the WOT state, and the exhaust gas introduced into the three-way catalyst unit 20 was changed to rich gas. The timing (condition) at which the air is injected from the air injection (AI) 50 into the exhaust pipe 12 upstream of the H ₂ S trap catalyst unit 30 is calculated based on the data from the air-fuel ratio sensor 60. When the F value is 13 or less, when it is 13.2 or less, when it is 13.4 or less, when it is 13.6 or less, when it is 13.8 or less, when it is 14.0 or less, when it is 14.2 or less, The difference was 9 cases in total: 14.4 or less and 14.6 or less.
Under these nine conditions, as in measurement test 1, the H ₂ S concentration (H ₂ S emission amount: ppm) in the exhaust gas discharged from the exhaust pipe 12 to the outside was continuously measured. Then, calculate the ratio of the H _{2 S} emission maximum concentration of each of the other conditions H _{2 S} emission maximum density under the conditions air is injected only if the A / F value is 13 or less as 100 (%) did. The results are shown in FIG.
As shown in FIG. 6, the suppression of H ₂ S emission was recognized as the A / F value at the start of air injection became closer to the stoichiometry. As is apparent from this graph, when the exhaust gas introduced into the three-way catalyst unit 20 is a rich gas, that is, when the A / F value is in a rich region from the stoichiometric range, air (oxygen-containing gas) is converted into H ₂ S. It was confirmed that it is preferable to supply the trap catalyst portion.

1 exhaust gas purifying device 2 engine 10 exhaust gas purifying catalyst unit 12 exhaust pipe 20 three-way catalyst unit 30 _{H 2} S-trapping catalyst 32 Substrate 34 carrier 36 _{H 2} S-trapping catalyst coat layer 38 catalytic metal (particles)
40 Control unit (ECU)
50 Air injection 60 Air-fuel ratio sensor 70 Honeycomb substrate

Claims (9)

An exhaust gas purification device provided in an exhaust system of an internal combustion engine,
A three-way catalyst unit disposed in the exhaust pipe;
An H ₂ S trap catalyst portion disposed downstream of the exhaust pipe from the three-way catalyst portion;
Oxygen supply means for supplying an oxygen-containing gas toward the H ₂ S trap catalyst part;
A control unit for controlling the supply of the oxygen-containing gas from the oxygen supply means;
With
The H ₂ S trap catalyst part is
A base material, a support supported on the base material, and a catalyst metal supported on the support and capable of oxidizing H ₂ S in an oxidizing atmosphere,
An exhaust gas purifying apparatus, wherein the base point amount per 1 L of catalyst is at least 0.01 mol / L based on the amount of CO ₂ desorbed per 1 L of catalyst measured by CO ₂ temperature-programmed desorption. The exhaust gas purifying apparatus according to claim 1, wherein a carrier of the H ₂ S trap catalyst part is mainly composed of a ceria / zirconia composite oxide and alumina. The support of the H ₂ S trap catalyst part is configured to include at least one element selected from a rare earth element, an alkali metal element, and an alkaline earth metal element. Exhaust gas purification equipment. The exhaust gas purifying apparatus according to any one of claims 1 to 3, wherein the H ₂ S trap catalyst part substantially does not contain nickel (Ni). When the exhaust gas introduced from the internal combustion engine into the three-way catalyst unit is exhaust gas generated by combustion of an air-fuel mixture in an air-fuel ratio rich region, the control unit supplies oxygen-containing gas from the oxygen supply unit to the H _{2 S} is configured to supply the trapping catalyst unit, an exhaust gas purifying apparatus according to any one of claims 1-4. An exhaust gas purification catalyst unit provided in an exhaust system of an internal combustion engine,
An exhaust pipe constituting a part of the exhaust system of the internal combustion engine;
A three-way catalyst portion disposed upstream of the exhaust pipe;
An H ₂ S trap catalyst portion disposed downstream of the exhaust pipe from the three-way catalyst portion;
With
The H ₂ S trap catalyst part is
A base material, a support supported on the base material, and a catalyst metal supported on the support and capable of oxidizing H ₂ S in an oxidizing atmosphere,
An exhaust gas purification catalyst unit having a base point amount per liter of catalyst of at least 0.01 mol / L based on the desorption amount of CO ₂ per liter of catalyst measured by CO ₂ temperature-programmed desorption. The exhaust gas purification catalyst unit according to claim 6, wherein the carrier of the H ₂ S trap catalyst part is mainly composed of a ceria / zirconia composite oxide and alumina. The support of the H ₂ S trap catalyst part is configured to include at least one element selected from a rare earth element, an alkali metal element, and an alkaline earth metal element. Exhaust gas purification catalyst unit. Wherein the H _{2 S-trapping} catalyst unit, nickel (Ni) is substantially free, exhaust gas purification catalyst unit according to any one of claims 6-8.

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