JP2007007606A - Engine exhaust gas cleaning catalyst, catalytic reactor, and engine exhaust gas cleaning method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an engine exhaust gas cleaning catalyst, a catalytic reactor and an engine exhaust gas cleaning method for removing a substance to be removed such as nitrogen oxide, particulate matter, carbon monoxide and hydrocarbon from engine exhaust gas. <P>SOLUTION: The engine exhaust gas cleaning catalyst is made by covering a network foam structure with a nitrogen oxide reducing catalyst. The catalytic reactor is composed of the nitrogen oxide reducing catalyst and an oxidation catalyst which is arranged on the downstream side of an engine exhaust gas flow from the reducing catalyst. The cleaning method comprises a step of bringing the engine exhaust gas into contact with the nitrogen oxide reducing catalyst in a coexistence with a prescribed amount of hydrocarbon reductant. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to nitrogen oxide (hereinafter also referred to as NOx), particulate matter (hereinafter also referred to as PM), carbon monoxide (hereinafter also referred to as CO), and hydrocarbon (hereinafter referred to as HC) contained in engine exhaust gas. The present invention relates to an engine exhaust gas purification catalyst, a catalytic reactor, and a purification method for removing a substance to be removed. More specifically, the present invention relates to the above exhaust gas by coexisting nitrogen oxides, particulate matter, carbon monoxide, hydrocarbons and engine fuel such as light oil as a reducing agent contained in oxygen-excess engine exhaust gas. The present invention relates to a purification method for decomposing and removing components.

  (1) Nitrogen oxides, particulate matter, and carbon monoxide contained in engine exhaust gas are conventionally removed by a three-way catalyst and an engine combustion system that carry materials such as platinum, palladium, and rhodium. . However, oxygen excess exhaust gas such as gas discharged from a lean combustion engine such as a diesel engine has a drawback that the removal efficiency by the above three-way catalyst is low and it is not an effective catalyst.

(2) As an engine exhaust gas purification catalyst, a catalyst component in which platinum, palladium or the like is supported on γ-alumina and coated on a monolith substrate such as a ceramic honeycomb body or a metal honeycomb body has been put into practical use. However, in the purification catalyst, a sulfur compound (hereinafter also referred to as SO ₂ ) in the engine exhaust gas is oxidized to produce sulfates and sulfites, so that the use of the purification catalyst causes catalyst poisoning. There was a drawback.

  (3) The ammonia selective reduction method is well known as a method for purifying nitrogen oxide in exhaust gas containing excess oxygen. However, it is difficult to handle highly toxic ammonia gas at mobile sources such as cars, and the urea selective reduction method has been proposed as an alternative. However, when this urea selective reduction method is used, the infrastructure for supplying urea water is improved. However, there is a drawback that a large amount of investment is required.

  (4) Furthermore, the nitrogen oxide storage reduction method has been put into practical use mainly in small cars. However, alternating operation of lean combustion and rich combustion is required, and the current situation is that it has not been put into practical use in large engines from the viewpoint of fuel consumption and operation control.

  The above background art is a technique generally known to those skilled in the art, and does not relate to a known literature invention.

  A first object of the present invention is to provide an engine exhaust gas purification catalyst including a foamed nitrogen oxide reduction catalyst that increases the chance of contact with engine exhaust gas.

A second object of the present invention is a nitrogen oxide reduction catalyst carrying titanium added to prevent catalyst poisoning by sulfur oxide (SO ₂ ) and silver added for nitrogen oxide reduction. Another object is to provide an engine exhaust gas purification catalyst including a foam-like nitrogen oxide reduction catalyst obtained by coating a foam-like structure with a foam-like structure.

  A third object of the present invention is to provide a catalytic reactor in which the above foamed nitrogen oxide reduction catalyst and a foamed oxidation catalyst supporting platinum or palladium are combined.

  A fourth object of the present invention is to provide an engine exhaust gas purification method that efficiently removes substances to be removed such as nitrogen oxides, particulate matter, carbon monoxide, and hydrocarbons from engine exhaust gas.

  The invention according to claim 1 of the present invention is an engine exhaust gas purifying catalyst, wherein a network-like foam structure is coated with a nitrogen oxide reduction catalyst.

  The invention according to claim 2 of the present invention is characterized in that the nitrogen oxide reduction catalyst is a composite catalyst in which titanium is supported on γ-alumina as a support and silver is further supported on the titanium. To do.

  The invention according to claim 3 of the present invention is a catalytic reactor, which is disposed on the downstream side of the exhaust gas flow of the nitrogen oxide reduction catalyst and the nitrogen oxide reduction catalyst, and has a mesh-like foam structure. A γ-alumina support is formed thereon, and an oxidation catalyst formed by supporting either platinum or palladium thereon is included.

  According to a fourth aspect of the present invention, there is provided a method for purifying an engine exhaust gas, the nitrogen oxide contained in the engine exhaust gas containing oxygen in excess of the stoichiometric air-fuel ratio, and the weight of the nitrogen oxide. The method includes the step of bringing the engine exhaust gas into contact with the nitrogen oxide reduction catalyst according to claim 1 or 2 in the presence of a hydrocarbon reducing agent in a ratio of 0.5 to 3 by weight. Is.

  The invention according to claim 5 of the present invention is a method for purifying engine exhaust gas, wherein the nitrogen oxide contained in the engine exhaust gas containing oxygen in excess of the stoichiometric air-fuel ratio and the weight of the nitrogen oxide Contacting the engine exhaust gas with the nitrogen oxide reduction catalyst in the presence of a 0.5 to 3 weight ratio hydrocarbon reducing agent; and contacting the engine exhaust gas with the nitrogen oxide reduction catalyst. The method further comprises contacting the engine exhaust gas with an oxidation catalyst disposed downstream of the exhaust gas flow of the nitrogen oxide reduction catalyst.

  The invention according to claim 6 of the present invention is an engine exhaust gas purification method, wherein the hydrocarbon reducing agent is removed from the particulate matter in the engine exhaust gas when the soluble organic component (SOF) is removed from the nitrogen oxides. It is characterized by using as a part of.

  According to this invention, since it comprised so that the foam-like nitrogen oxide reduction catalyst was included, the contact opportunity of this reduction catalyst and engine exhaust gas can be raised, and nitrogen oxide, particulate matter, There is an effect that a substance to be removed such as hydrocarbon and carbon monoxide can be efficiently removed.

  According to the present invention, the nitrogen oxide reduction catalyst is configured to be a composite catalyst in which titanium is supported on γ-alumina as a support and silver is further supported on the titanium. Due to this action, the production of hardly decomposable aluminum sulfate from the sulfur oxide is suppressed, and there is an effect that catalyst poisoning can be avoided.

  According to the present invention, the catalytic reactor is disposed on the downstream side of the nitrogen oxide reduction catalyst and the exhaust gas flow of the nitrogen oxide reduction catalyst, and the γ-alumina support is placed on the network foam structure. And the catalyst is poisoned by sulfur oxides in the engine exhaust gas by a nitrogen oxide reduction catalyst. Combustion of unreacted hydrocarbon reducing agent such as light oil added to engine exhaust gas by oxidation catalyst and particulate matter (soot) in engine exhaust gas and oxidation of carbon monoxide By performing the above, there is an effect that the engine exhaust gas can be purified by decomposing both into carbon dioxide gas and water.

  According to the present invention, the engine exhaust gas purification method is performed by using a nitrogen oxide contained in an engine exhaust gas containing oxygen in excess of the stoichiometric air-fuel ratio and a weight ratio of 0.5 to 3 to the weight of the nitrogen oxide. The engine exhaust gas is contacted with the nitrogen oxide reduction catalyst in the presence of the hydrocarbon reducing agent, and after the engine exhaust gas and the nitrogen oxide reduction catalyst are contacted, the engine exhaust gas is Since it is configured to include the step of contacting the oxidation catalyst disposed downstream of the exhaust gas flow of the nitrogen oxide reduction catalyst, first, the catalyst poisoning by the sulfur oxide in the engine exhaust gas is performed by the nitrogen oxide reduction catalyst. Next, the unreacted substance of hydrocarbon reducing agent such as light oil added to the engine exhaust gas by the oxidation catalyst and particulate matter (soot) in the engine exhaust gas By performing the oxidation of the baked and carbon monoxide, there is an effect that both can be decomposed into carbon dioxide and water promote purification of engine exhaust gases.

  According to this invention, in the engine exhaust gas purification method, the soluble organic component (SOF) among the particulate matter in the engine exhaust gas is used as a part of the hydrocarbon reducing agent when removing the nitrogen oxides. As a result, combustion of this hydrocarbon reducing agent and particulate matter (soot) in engine exhaust gas and oxidation of carbon monoxide can be performed efficiently, and the catalyst temperature range is wide, and light oil as a fuel can be used. In terms of a nitrogen oxide reduction method using a hydrocarbon reducing agent, there is an effect that it can be advantageously applied to, for example, automobiles that are mobile sources.

Embodiment 1 FIG.
The engine exhaust gas purifying catalyst according to Embodiment 1 of the present invention is obtained by coating a nitrogenous oxide reduction catalyst on a network-like foam structure, and the nitrogen oxide reduction catalyst comprises titanium on γ-alumina as a carrier. The composite catalyst is formed by supporting and further supporting silver on the titanium.

(Foam-like structure)
The foam-like structure used in the first embodiment is not particularly limited. For example, a ceramic foam body or urethane formed by firing a metal foam or urethane foam base material after coating a ceramic component. A metal foam body or the like obtained by plating one or two types of iron, nickel, chromium and the like on the foam base material can be used. Such a foam-like structure is a porous material having a relatively high specific surface area due to a high porosity of 90% or more and connected pores, and has a substantially mesh shape, so that it is used as a kind of filter. It is something that can be done. In addition, the foam-like structure can form a turbulent state in the gas fluid by supplying a gas fluid to the structure, thereby increasing the contact effect between the exhaust gas component and the catalyst metal. Therefore, it is much more advantageous than the conventional purification catalyst.

(Catalyst carrier)
As the catalyst carrier, porous materials such as alumina, silica, silica / alumina, zeolite, titania and the like can be used. Among them, examples of the carrier suitably used in the present invention include γ-alumina, which has high heat resistance and high dispersibility of the catalyst metal and can be easily processed into a foam-like structure. This γ-alumina contains 70% or more of alumina, preferably 95% or more, and particularly preferably does not contain impurities such as Na ₂ O and K ₂ O. Moreover, you may use (gamma) -alumina as a support | carrier of a catalyst in the state of a primary particle or a secondary particle. Here, the alumina particles have different properties such as particle size depending on the alumina raw material or production conditions (pH, drying / calcination temperature, etc.). For example, ultrafine particles (primary particles) of 10 to 50 Å (1 Å = 10 ^-10 m) are prepared with Al alkoxide and 1 µ (1 µ = 10 ^-6 m) or more with Al salt. Moreover, the secondary particle obtained by granulating this primary particle has a particle size of 10-1000 micrometers, and this can also be used alone or in combination with the primary particle. Moreover, the said (gamma) -alumina can also be coat | covered and used for a suitable monolith base material. For example, a honeycomb carrier can be formed by coating a metal and cordierite honeycomb material with γ-alumina with an adhesive such as alumina sol, and drying and firing.

(Catalyst metal and loading method)
In obtaining the nitrogen oxide reduction catalyst in the first embodiment, 0.5-50 μm of γ-alumina support is added to the metal salt solution and stirred in order to support titanium and silver on the γ-alumina support. However, after solid-liquid separation, a method of drying at 120 ° C. for about 10 to 15 hours and firing in air at 500 to 600 ° C. for about 1 to 3 hours can be used. Here, examples of the metal compound to be used include titanium trichloride, titanium tetrachloride, titanium tetraisopropoxide (titanium alkoxides) and the like as titanium compounds, and silver compounds include silver nitrate and silver acetate. Can be mentioned. Although the density | concentration of the metal salt solution used shall be about 0.05-1 mol / L, it is not limited to this.

  By the above loading method, a titanium layer is first formed on the γ-alumina carrier, and a silver layer is formed on the titanium layer. As the titanium layer, any one of titanium trichloride, titanium tetrachloride, and titanium alkoxide is used, and the solid-liquid ratio with respect to the γ-alumina carrier is 2 (v / v) and supported while stirring. After the loading operation, titanium hydroxide is generated by neutralization with ammonia water, and after solid-liquid separation, drying is performed at a temperature of 120 ° C. for 10 hours, and baking is performed at a temperature of 550 ° C. in an air atmosphere for 2 to 3 hours. . Here, the chemical form of titanium is mainly anatase type. The amount of titanium supported on the nitrogen oxide reduction catalyst is 0.2 to 1% by weight.

  The silver layer is supported with stirring by adding the above-mentioned titanium supported to a silver nitrate or silver acetate solution. In the operation after loading, drying and firing are performed in the same manner as the titanium layer formation. In addition, the silver carrying amount with respect to a nitrogen oxide reduction catalyst shall be 0.1 to 2 weight%.

  In obtaining the foamed nitrogen oxide reduction catalyst, the nitrogen oxide reduction catalyst is added to the alumina sol solution as an adhesive while stirring, and the mixture is stirred for 8 to 10 hours by a ball mill to prepare a catalyst slurry. Next, 5-30% by weight of catalyst slurry is wash-coated on the ceramic foam or metal foam as a monolith structure, and the excess slurry is blown off with air, followed by drying at a temperature of 120 ° C. for 10 hours. A foamed nitrogen oxide reduction catalyst is obtained by performing calcination in an air atmosphere at a temperature of 550 ° C. for 2 to 3 hours.

By using the nitrogen oxide reduction catalyst thus obtained as an engine exhaust gas purification catalyst, nitrogen oxidation in engine exhaust gas in an oxygen-excess atmosphere in the presence of nitrogen oxide and an organic compound such as light oil fuel. As the product is removed, the soluble organic component (SOF) in the particulate matter (PM) also acts as a nitrogen oxide reducing agent, so the nitrogen oxide and particulate matter (PM) are simultaneously removed from the engine exhaust gas. Is done. In addition, sulfur oxide (SO ₂ ) in engine exhaust gas, which is a poison for the catalyst, is converted to sulfurous acid or sulfuric acid by the oxidation action of silver, and reacts with titanium to produce titanium sulfate. When the reduction reaction temperature of the product reaches around 450 to 550 ° C., titanium sulfate is decomposed and discharged as sulfur oxide (SO ₂ ), so that the production of difficult-to-decompose aluminum sulfate is suppressed, and catalyst poisoning is also reduced. Can be avoided. In particular, even when the catalyst temperature is 400 ° C. or lower, the catalyst activity does not decrease, and the nitrogen oxide removal activity by the catalyst is maintained.

  As described above, according to the first embodiment, since it is configured to include the foam-like nitrogen oxide reduction catalyst, the contact opportunity between the reduction catalyst and the engine exhaust gas can be increased. There is an effect that substances to be removed such as nitrogen oxides, particulate substances, hydrocarbons, and carbon monoxide can be efficiently removed.

  According to the first embodiment, the nitrogen oxide reduction catalyst is configured to be a composite catalyst in which titanium is supported on γ-alumina as a support and silver is further supported on the titanium. By the action of silver and titanium, it is possible to suppress the production of hardly decomposable aluminum sulfate from sulfur oxide, thereby avoiding catalyst poisoning.

  In the first embodiment, a net-like metal foam structure is used as the monolith structure. However, the present invention is not limited to this, and in addition, a ceramic foam structure is used. It can also be used.

Embodiment 2. FIG.
The catalytic reactor according to Embodiment 2 of the present invention is arranged on the downstream side of the exhaust gas flow of the nitrogen oxide reduction catalyst and the nitrogen oxide reduction catalyst, and on the network foam structure, the γ-alumina carrier And an oxidation catalyst formed by supporting either platinum or palladium thereon. This catalytic reactor employs a structure in which a nitrogen oxide reduction catalyst and an oxidation catalyst are arranged in this order from the engine side. Nitrogen oxides and particulate matter (soluble organic components) in the engine exhaust gas are removed with a foam-like nitrogen oxide reduction catalyst, and hydrocarbons, carbon monoxide and particulate matter (soot) are removed with an oxidation catalyst.

  After preparing a mixed sol of alumina sol (solid content of 60% or more) and cerium nitrate equivalent to 10% as the support for the oxidation catalyst, and then wash-coating 5 to 30% by weight of the mixed sol on the foam substrate. Then, drying at 120 ° C. for 12 hours and firing at 500 ° C. in an air atmosphere for about 2 to 3 hours to obtain a foam-like alumina carrier. Here, the metal compound used is supported on a foam-like alumina support using tetraammineplatinum hydrochloride or tetraamminepalladium hydroxide, dried at 120 ° C. for 10 hours, and heated at 500 ° C. for 2 hours. The fired product is used as foamed platinum or palladium oxidation catalyst. The supported amount of platinum or palladium with respect to the oxidation catalyst is 0.1 to 1% by weight.

  As described above, according to the second embodiment, the nitrogen oxide reduction catalyst and the oxidation catalyst arranged on the downstream side of the exhaust gas flow of the nitrogen oxide reduction catalyst are configured. The catalyst reduction by sulfur oxides in the engine exhaust gas can be avoided by the product reduction catalyst, and then the unreacted substances such as light oil and other hydrocarbon reducing agents added to the engine exhaust gas by the oxidation catalyst and the engine exhaust gas. Combustion with the particulate matter (soot) in the inside and oxidation of carbon monoxide have the effect that both can be decomposed into carbon dioxide gas and water to purify the engine exhaust gas.

Embodiment 3 FIG.
In the engine exhaust gas purification method according to Embodiment 3 of the present invention, a catalyst reactor in which the foam-like reduction catalyst and the foam-like oxidation catalyst are combined is installed in the middle of an exhaust pipe connected to the engine, and engine exhaust gas is obtained. It is carried out by contacting with. This engine exhaust gas is an exhaust gas containing oxygen in excess of the theoretical combustion amount of a diesel engine or the like.

  When the catalyst reactor according to the second embodiment is brought into contact with the engine exhaust gas, a fuel or an organic compound is added to the exhaust gas as a reducing agent. The reducing agent addition amount is preferably 0.5 to 3 (weight ratio) with respect to the weight of nitrogen oxides in the exhaust gas. Here, when the ratio is less than 0.5 weight ratio, the effect of adding the reducing agent is reduced, whereas when the weight ratio exceeds 3 weight ratio, the addition effect of the reducing agent reaches a peak, so the addition range is set. Yes.

  In a specific operation method of the catalytic reactor, when the exhaust gas temperature reaches 350 ° C., the addition of the reducing agent is started, and the nitrogen oxide in the exhaust gas is decomposed into nitrogen and oxygen by the foamed nitrogen oxide reduction catalyst. At this time, the particulate matter (soluble organic component) is also decomposed into carbon dioxide gas and water because it acts as a reducing agent. Next, unreacted reducing agent, carbon monoxide, and particulate matter (soot) remaining in the exhaust gas that has passed through the foamed nitrogen oxide reduction catalyst are decomposed into carbon dioxide and water by contacting the foamed catalyst. Is done.

  Thus, in the engine exhaust gas purification method according to Embodiment 3, nitrogen oxides, particulate matter, hydrocarbons, and carbon monoxide in exhaust gas in an oxygen-excess atmosphere are removed more efficiently than conventional purification catalysts. In addition, the exhaust gas can be reliably purified. In particular, nitrogen oxides and particulate matter can be efficiently and simultaneously removed.

The following examples illustrate the invention in more detail. However, the present invention is not limited to the following examples.
Example 1
(NOx reduction catalyst)
A carrier obtained by crushing γ-alumina (manufactured by Mizusawa Chemical Co., Ltd.) to a particle size of 0.5 to 30 μm was used. This carrier was added to a titanium trichloride solution (0.06 mol / L) at a solid-liquid ratio of 2 (v / v) and supported while stirring at a temperature of 50 ° C. for 1 hour. After solid-liquid separation, it is washed three times with twice the amount of ion-exchanged water of the solid (carrier), then transferred to twice the amount of water at 50 ° C., and neutralized by adding aqueous ammonia while stirring ( After pH = 7), drying at 120 ° C. for 12 hours and firing at 550 ° C. for 3 hours in air were performed to form a titanium support layer on γ-alumina. Next, this titanium-supported product is added to a silver nitrate solution (0.12 mol / L), and a supporting operation is performed at 30 ° C. for 40 minutes with stirring. After solid-liquid separation, once with twice the amount of ion-exchanged water, After washing with water, drying at 120 ° C. for 12 hours and baking at 550 ° C. for 1 hour in air were performed. The amount of metal supported on the powdered NOx reduction catalyst thus obtained was 0.17% by weight of titanium and 0.6% by weight of silver.

  The NOx reduction catalyst in the form of foam is placed in a 500 cc ball mill at a ratio of 50 parts of powdered NOx reduction catalyst, 13 parts of alumina sol, 0.5 part of methylcellulose and 170 parts of water, and mixed under conditions of a rotation speed of 80 rpm and 6 hours. A catalyst slurry was prepared. This catalyst slurry was coated (wash coated) at a rate of 120 g / L with respect to a metal (nickel) foam having a cell number of 30 / inch (pore diameter: 0.8 mm) and a volume of 40 cc, and was heated at 120 ° C. for 6 hours. Were dried and calcined in air at 500 ° C. for 90 minutes.

The NOx removal performance test uses a simulated exhaust gas with oxygen 10%, NOx concentration 600 ppm, moisture concentration 7%, SO ₂ concentration 10 ppm, balance gas nitrogen gas, and a fixed bed flow type with a space velocity (SV) of 20, 000 / h. At this time, light oil was used as a reducing agent, and 1-fold amount (light oil / NOx = 1 (w / w)) was added to the amount of NOx. The catalyst temperature in the continuous test was set to 350 ° C., 400 ° C., 450 ° C., and 500 ° C., and the NOx removal rate calculated by the atmospheric pressure chemiluminescence method from the NOx concentration ratio before and after the catalyst reactor for each temperature. It is shown in Table 1.

Comparative Example 1
The powdered NOx reduction catalyst of Example 1 was applied to a metal honeycomb substrate (diameter 36 mm, height 50 m) of 300 cells / inch ² , and the catalyst slurry similar to Example 1 was wash-coated at a weight ratio of 20%. A NOx reduction catalyst was prepared. The NOx removal performance test was conducted using a simulated exhaust gas in which oxygen is 10%, NOx concentration is 600 ppm, moisture concentration is 7%, SO ₂ concentration is 10 ppm, and the balance gas is nitrogen gas, and the space velocity (SV) is 20, 000 / h. At this time, gas oil was used as the reducing agent, and 1-fold amount (light oil / NOx = 1 (w / w)) was added to the NOx amount. The catalyst temperature in the continuous test is the same as in Example 1. Further, the NOx removal rate was calculated from the NOx concentration ratio before and after the catalytic reactor by the atmospheric pressure chemiluminescence method, and the results are shown in Table 2.

  The NOx removal rate of the foam-like NOx reduction catalyst of Table 1 according to Example 1 is about 10% higher than that of the honeycomb-like NOx reduction catalyst of Table 2 according to Comparative Example 1 by about 10%, and 350 At 20 ° C., it was about 20% higher. In addition, when the NOx removal rate after 50 hours had elapsed, no reduction in the removal rate was observed at any catalyst temperature.

  Thus, it can be seen that in the foam-like NOx reduction catalyst having a network structure, the exhaust gas in the catalyst layer forms a turbulent flow, so that the reaction efficiency is high and it is more advantageous than the honeycomb catalyst.

Example 2
(Oxidation catalyst)
A metal (nickel) foam of 50 cells / inch (pore diameter 0.5 mm) and a volume of 20 cc was wash-coated with 10% by weight of a mixture of alumina sol and 7 parts of cerium nitrate, dried at 120 ° C. for 6 hours, 500 Firing was performed in air at 2 ° C. for 2 hours to prepare a γ-alumina carrier. This support was immersed in tetraammineplatinum hydrochloride (0.1 mol / L), dried at 120 ° C. for 4 hours, and calcined at 500 ° C. for 2 hours to prepare a foam-like platinum catalyst. The platinum loading at this time was 0.5% by weight.

Example 3
(Catalytic reactor)
In a stainless steel catalyst reactor (diameter 36 mm, length 30 cm), first, 40 cc of the foam-like NOx reduction catalyst prepared in Example 1 and Example 2 was charged on the engine side, and the exhaust gas flow was more downstream than this reduction catalyst. 20cc of platinum catalyst is packed on the side, and the removal rate of each concentration of nitrogen oxide (NOx), black smoke, hydrocarbon (HC) and carbon monoxide (CO) in the engine exhaust gas with respect to the catalyst temperature is investigated, and the catalytic reaction The performance of the vessel was confirmed.

  The engine used was a direct-injection fuel pump, a diesel engine with a displacement of 2400 cc and an AC generator, and the catalytic reactor was installed at a position branched from the middle of the exhaust pipe. The composition of the engine exhaust gas was NOx: 600 to 700 ppm, oxygen: 8 to 10%, CO: 90 to 110 ppm, HC: 160 to 400 ppm, and moisture: 4 to 7%.

The performance test conditions were changed every 50 ° C. within the range of SV20,000 / h for NOx reduction catalyst, SV40,000 / h for platinum catalyst and 350 to 500 ° C. catalyst temperature. As a reducing agent, a light oil fuel was added in an amount 1 time (w / w) to the amount of NOx immediately before the catalytic reactor. In component analysis, NOx is chemiluminescence, oxygen is magnetic wind, CO is non-dispersive infrared spectroscopy (NDIR), HC is flame ionization (FID), moisture is gravimetric, and black smoke concentration is JISZ 8808 (in exhaust gas) The removal rate of each component was calculated from the concentration ratio before and after the catalytic reactor, and the results are shown in Table 3.

  From Table 3, the removal performance of the catalytic reactor in which the NOx reduction catalyst and the platinum catalyst were combined was observed. Nitrogen oxide (NOx) showed a little over 50%, which was equivalent to Example 1. It can be seen that almost all of the black smoke is burning. Similarly, almost all hydrocarbons (HC) and carbon monoxide (CO) are oxidized. From this, in the catalytic reactor according to Example 3, combustion of surplus light oil reducing agent, black smoke, hydrocarbon (HC) and carbon monoxide (CO) occurs simultaneously with the nitrogen oxide (NOx) reduction reaction, and the engine It can be seen that multiple components in the exhaust gas can be purified simultaneously.

Claims (6)

  An engine exhaust gas purification catalyst comprising a mesh-like foam structure coated with a nitrogen oxide reduction catalyst.   2. The engine exhaust gas purification catalyst according to claim 1, wherein the nitrogen oxide reduction catalyst is a composite catalyst in which titanium is supported on γ-alumina as a carrier and silver is further supported on the titanium. .   A nitrogen oxide reduction catalyst according to claim 1 or 2, and a γ-alumina support formed on a network-like foam structure while being arranged downstream of the exhaust gas flow of the nitrogen oxide reduction catalyst. And an oxidation catalyst formed by supporting either platinum or palladium thereon.   In the coexistence of nitrogen oxides contained in engine exhaust gas containing oxygen in excess of the stoichiometric air-fuel ratio and a hydrocarbon reducing agent in a weight ratio of 0.5 to 3 with respect to the weight of the nitrogen oxides, A method for purifying engine exhaust gas, comprising the step of bringing the exhaust gas into contact with the nitrogen oxide reduction catalyst according to claim 1 or 2.   In the coexistence of nitrogen oxides contained in engine exhaust gas containing oxygen in excess of the stoichiometric air-fuel ratio and a hydrocarbon reducing agent in a weight ratio of 0.5 to 3 with respect to the weight of the nitrogen oxides, The step of bringing the exhaust gas into contact with the nitrogen oxide reduction catalyst according to claim 1 or 2, and the contact between the engine exhaust gas and the nitrogen oxide reduction catalyst, the engine exhaust gas is converted into the nitrogen oxide. 5. The engine exhaust gas purification method according to claim 4, further comprising the step of contacting an oxidation catalyst disposed downstream of the exhaust gas flow of the reduction catalyst.   6. The engine exhaust gas purification method according to claim 5, wherein a soluble organic component of particulate matter in the engine exhaust gas is used as a part of the hydrocarbon reducing agent when removing nitrogen oxides.