JP2010046656A - Catalyst for purifying exhaust gas and exhaust gas purification method using the catalyst - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst for purifying exhaust gas which has sufficiently high exhaust gas purification performance and can sufficiently purify NOx in exhaust gas in a low temperature range even after sulfur poisoning, and an exhaust gas purification method using the catalyst. <P>SOLUTION: The catalyst for purifying exhaust gas includes a first catalyst powder comprising a first porous carrier and a first noble metal supported by the first porous carrier, wherein the first noble metal contains at least Pt, the content of the Pt in the first noble metal exceeds 50 wt.% of the total amount of the first noble metal, and the amount of a supported NOx occlusion material is 0.03 mol or less per 100 g of the first porous carrier, a second catalyst powder comprising a second porous carrier and second noble metal supported by the second porous carrier, wherein the second noble metal contains at least Rh, the content of the Rh in the second noble metal exceeds 50 wt.% of the total amount of the second noble metal, and the amount of a supported NOx occlusion material is 0.03 mol or less per 100 g of the second porous carrier, a third catalyst powder comprising a third porous carrier, third noble metal supported by the third porous carrier, and an NOx occlusion material supported by the third porous carrier, wherein the noble metal contains at least Pd, the amount of the supported Pd is 0.05 g or more per 100 g of the third porous carrier, and the amount of the supported NOx occlusion material is more than 0.03 mol per 100 g of the third porous carrier. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification catalyst and an exhaust gas purification method using the same.

Conventionally, various exhaust gas purification catalysts have been put into practical use in order to purify exhaust gas discharged from an internal combustion engine such as an automobile engine. As such an exhaust gas purification catalyst, the air-fuel ratio is controlled from the lean side so as to change from the lean side to the stoichiometric to rich side (rich spike), so that NOx is occluded in the NOx occlusion material on the lean side, and the NOx NOx occlusion reduction type exhaust gas purifying catalysts are known which purify by releasing them on the stoichiometric or rich side and reacting with reducing components such as HC and CO. Then, as such NOx storage reduction catalyst for purifying an exhaust gas, an exhaust gas purifying catalyst comprising _the NO _x storage material comprising an alkali metal or the like and a noble metal supported carrier is known.

For example, in JP-A-2003-80081 (Patent Document 1), a base material, a first inorganic oxide supported on the base material, and Pt, Pd, Rh supported on the first inorganic oxide. , An oxidation catalyst part having a first catalytic metal composed of at least one of Ag, Au and Ir, a second inorganic oxide supported on the base material, Pt supported on the second inorganic oxide, A NOx occlusion reduction part having a second catalyst metal composed of at least one of Pd, Rh, Ag, Au and Ir, and a NOx occlusion material supported on the second inorganic oxide, and the oxidation catalyst part; An exhaust gas purifying catalyst is disclosed in which the NOx occlusion reduction part is arranged in a state where the NOx occlusion reduction part is arranged in the flow direction of the exhaust gas on the base material. In JP 2007-144285 A (Patent Document 2), a first support made of CeO ₂ and a second support made of oxides of Ti, Si, W, etc. are provided. A NOx storage material that stores nitrogen oxides and a catalyst for purifying exhaust gas, in which a noble metal is supported and a noble metal is supported on the second support, are disclosed. Furthermore, in Japanese Patent Application Laid-Open No. 2006-231204 (Patent Document 3), a base material, a catalyst support layer formed on the base material, and Pt, Pd, Rh and NOx storage materials supported on the catalyst support layer. An exhaust gas purifying catalyst is disclosed, in which Rh is supported at a high concentration downstream of the exhaust gas flow, and Pt and Pd are supported at a high concentration upstream of the exhaust gas flow. However, conventional exhaust gas purifying catalysts as described in Patent Documents 1 to 3 do not necessarily have sufficient NOx purification performance in a low temperature range.

Japanese Patent Laid-Open No. 2003-80081 JP 2007-144285 A JP 2006231120 A

  The present invention has been made in view of the above-mentioned problems of the prior art, has sufficiently high exhaust gas purification performance, and can sufficiently purify NOx in exhaust gas at low temperatures even after sulfur poisoning. It is an object of the present invention to provide an exhaust gas purification catalyst and an exhaust gas purification method using the catalyst.

  As a result of intensive studies to achieve the above object, the present inventors have obtained a first catalyst powder comprising a first porous carrier and a first noble metal supported on the first porous carrier in an exhaust gas purification catalyst. A second catalyst powder comprising a second porous carrier and a second noble metal supported on the second porous carrier, a third porous carrier, a third noble metal supported on the third porous carrier, and the A third catalyst powder comprising a NOx occlusion material supported on a third porous carrier, wherein the first noble metal contains at least Pt, and the content of Pt in the first noble metal is the same as that of the first noble metal. More than 50% by mass with respect to the total amount, at least Rh is contained in the second noble metal, and the content of Rh in the second noble metal is more than 50% by mass with respect to the total amount of the second noble metal, 3 Noble metal contains at least Pd, The amount of Pd supported on the porous carrier is 0.05 g or more with respect to 100 g of the third porous carrier, and the amount of NOx occlusion material supported on each carrier in the first to second catalyst powders is set respectively. By setting the amount of the NOx occlusion material supported on the carrier in the third catalyst powder to be 0.03 mol or less with respect to 100 g of the carrier and exceeding 0.03 mol with respect to 100 g of the carrier, the exhaust gas purification catalyst is sufficiently high. The present inventors have found that it has exhaust gas purification performance and can sufficiently purify NOx in exhaust gas at low temperatures even after sulfur poisoning, and has completed the present invention.

That is, the exhaust gas purifying catalyst of the present invention comprises a first porous carrier and a first noble metal supported on the first porous carrier, the first noble metal containing at least Pt, The Pt content is more than 50% by mass with respect to the total amount of the first noble metal, and the amount of NOx occlusion material supported is 0.03 mol or less with respect to 100 g of the first porous carrier. Catalyst powder,
A second noble metal supported on the second porous carrier, wherein the second noble metal contains at least Rh, and the content of Rh in the second noble metal is that of the second noble metal. A second catalyst powder that exceeds 50% by mass with respect to the total amount, and the amount of NOx occlusion material supported is 0.03 mol or less with respect to 100 g of the second porous carrier;
A third porous support; a third noble metal supported on the third porous support; and a NOx occlusion material supported on the third porous support, wherein the third noble metal contains at least Pd, A third catalyst having a loading amount of 0.05 g or more with respect to 100 g of the third porous carrier and a loading amount of the NOx storage material exceeding 0.03 mol with respect to 100 g of the third porous carrier. Powder,
It is characterized by providing.

  In the exhaust gas purifying catalyst of the present invention, the content of the first catalyst powder is 5 to 60% by mass with respect to the total amount of the first to third catalyst powders, and the content of the second catalyst powder is 5 to 40% by mass with respect to the total amount of the first to third catalyst powders, and the content of the third catalyst powder is 30 to 90% by mass with respect to the total amount of the first to third catalyst powders. It is preferable that

In the exhaust gas purifying catalyst of the present invention, the following conditions (A) to (C):
(A) The first to third catalyst powders are arranged so that the exhaust gas contacts the second catalyst powder and the third catalyst powder after the exhaust gas contacts the first catalyst powder.
(B) The first to third catalyst powders are disposed so that the exhaust gas contacts the first catalyst powder, the second catalyst powder, and the third catalyst powder in this order,
(C) The first to third catalyst powders are arranged so that the exhaust gas contacts the first catalyst powder, the third catalyst powder, and the second catalyst powder in this order.
It is preferable to satisfy any one of the conditions.

  Furthermore, in the exhaust gas purifying catalyst of the present invention, a catalyst base, a first catalyst layer made of the first catalyst powder, and a second catalyst layer made of the second catalyst powder and the third catalyst powder, And the first to second catalyst layers are preferably arranged on the catalyst base so that the exhaust gas contacts the second catalyst layer after the exhaust gas contacts the first catalyst layer. .

  The exhaust gas purification method of the present invention is a method characterized by purifying exhaust gas by bringing the exhaust gas into contact with the exhaust gas purification catalyst of the present invention.

The reason why the above object is achieved by the exhaust gas purifying catalyst and the exhaust gas purifying method of the present invention is not necessarily clear, but the present inventors speculate as follows. That is, first, when an exhaust gas purification process using the exhaust gas purification catalyst of the present invention is examined, it is presumed that the process consists of the following four steps.
(First Step) NO in exhaust gas is oxidized to NO ₂ mainly on Pt.
NO ₂ is a (second step) acidic substance is occluded in the NOx-absorbing material is a basic substance.
(Third step) When the air-fuel ratio is introduced in the form of a short-time pulse (rich spike), the oxygen concentration decreases, and NOx is released from the NOx storage material.
(Fourth step) The released NOx mainly reacts with reducing gas such as CO or HC on Rh, and is reduced to N ₂ to be purified.

  And in this invention, it is guessed that a 1st-4th step is accelerated | stimulated as follows. First, in the first step, Pt plays an important role among noble metals. Such Pt tends to decrease its activity when a NOx occlusion material (alkali metal, alkaline earth metal, etc.) coexists in the vicinity on the same carrier. Therefore, in the present invention, the amount of the NOx occlusion material in the first catalyst powder in which Pt is supported on the carrier is 0.03 mol or less with respect to 100 g of the first porous carrier. Thus, since the 1st catalyst powder does not contain a NOx occlusion material substantially, the activity fall of Pt in the 1st catalyst powder is fully suppressed. Therefore, in the present invention, the activity of Pt in the first catalyst powder can be sufficiently exhibited, and the first step is promoted.

  Further, in order to promote the second and third steps, the noble metal existing in the vicinity of the NOx storage material needs to exhibit sufficient activity on the carrier on which the NOx storage material is supported. However, generally, when the noble metal and the NOx storage material are close to each other on the same carrier, the activity of the noble metal tends to be reduced from the metal state to the oxide state. Therefore, in the present invention, in the third catalyst powder in which the NOx occlusion material is supported on the support, Pd is supported as an essential component on the support as a noble metal. Such Pd exhibits sufficient activity even in an oxide state, and its activity decrease is less than Pt and Rh even when coexisting with the NOx storage material. Further, in the present invention, in order to sufficiently exhibit the purification activity of such Pd, the amount of Pd supported is 0.05 g or more with respect to 100 g of the carrier. As described above, in the present invention, since the predetermined amount of Pd and the NOx storage material are used in combination in the third catalyst powder, the third catalyst powder can exhibit sufficiently high activity. And the third step is fully facilitated.

  Furthermore, Rh plays an important role among the noble metals in the fourth step. Such Rh tends to decrease in activity when NOx occlusion material is present in the vicinity of the same carrier. Therefore, in the present invention, the amount of NOx occlusion material in the second catalyst powder in which Rh is supported on the carrier is 0.03 mol or less with respect to 100 g of the first porous carrier, It contains substantially no NOx storage material. Accordingly, in the present invention, the decrease in Rh activity in the second catalyst powder is sufficiently suppressed, and thereby the fourth step is sufficiently promoted.

  As described above, in the exhaust gas purifying catalyst of the present invention, the first to fourth steps can be promoted by the first to third catalyst powders. It is presumed that the NOx can be sufficiently purified even under a low temperature condition.

  According to the present invention, an exhaust gas purification catalyst having sufficiently high exhaust gas purification performance and capable of sufficiently purifying NOx in exhaust gas in a low temperature range even after sulfur poisoning, and exhaust gas purification using the catalyst It becomes possible to provide a method.

It is a graph which shows the NOx purification rate of the catalyst for exhaust gas purification obtained in Example 1 and Comparative Examples 1-4. It is a graph which shows the NOx purification rate of the catalyst for exhaust gas purification obtained in Example 2 and Comparative Examples 5-7. It is a graph which shows the relationship between entering gas temperature (300 degreeC, 350 degreeC, 400 degreeC) and the NOx purification rate after the high temperature endurance test of the catalyst for exhaust gas purification obtained in Examples 3-5 and Comparative Examples 8-12. is there. It is a graph which shows the NOx purification rate after the high temperature endurance test of the catalyst for exhaust gas purification obtained in Examples 3-5 and Comparative Examples 8-12 on 350 degreeC temperature conditions. The entered gas temperature (300 ° C., 350 ° C., 400 ° C.) and the NOx purification rate after the sulfur poisoning durability test of the exhaust gas purification catalysts obtained in Example 3, Comparative Example 8, Comparative Example 11 and Comparative Example 12 It is a graph which shows the relationship. It is a graph which shows the NOx purification rate after the sulfur poisoning endurance test of the exhaust gas purification catalyst obtained in Example 3, Comparative Example 8, Comparative Example 11 and Comparative Example 12 under the temperature condition of 350 ° C.

  Hereinafter, the present invention will be described in detail with reference to preferred embodiments thereof.

First, the exhaust gas purifying catalyst of the present invention will be described. That is, the exhaust gas purifying catalyst of the present invention comprises a first porous carrier and a first noble metal supported on the first porous carrier, the first noble metal containing at least Pt, The Pt content is more than 50% by mass with respect to the total amount of the first noble metal, and the amount of NOx occlusion material supported is 0.03 mol or less with respect to 100 g of the first porous carrier. Catalyst powder,
A second noble metal supported on the second porous carrier, wherein the second noble metal contains at least Rh, and the content of Rh in the second noble metal is that of the second noble metal. A second catalyst powder that exceeds 50% by mass with respect to the total amount, and the amount of NOx occlusion material supported is 0.03 mol or less with respect to 100 g of the second porous carrier;
A third porous support; a third noble metal supported on the third porous support; and a NOx occlusion material supported on the third porous support, wherein the third noble metal contains at least Pd, A third catalyst having a loading amount of 0.05 g or more with respect to 100 g of the third porous carrier and a loading amount of the NOx storage material exceeding 0.03 mol with respect to 100 g of the third porous carrier. Powder,
It is characterized by providing.

  First, the first catalyst powder will be described. The first catalyst powder includes a first porous carrier and a first noble metal supported on the first porous carrier. The first porous carrier is not particularly limited as long as it is a porous carrier made of a metal oxide that can be used as a carrier for an exhaust gas purification catalyst. Examples of such metal oxides include titania, magnesia, alumina, silica, zirconia, ceria, and composite oxides and solid solutions thereof. Moreover, as a metal oxide as a material of such a first porous carrier, from the viewpoint of heat resistance, sulfur poisoning resistance and compatibility with Pt, alumina, ceria-alumina composite oxide, titania-zirconia solid solution, It is preferably at least one selected from magnesia-alumina solid solutions. In addition, as such a 1st porous support | carrier, 1 type of support | carriers may be used independently, or 2 or more types of support | carriers may be mixed and used. Moreover, it does not restrict | limit especially as a manufacturing method of the 1st porous support | carrier which consists of such a metal oxide, A well-known method can be employ | adopted suitably. A commercially available porous carrier may also be used.

  Moreover, the shape of such a 1st porous support | carrier is a powder form. The average particle size of the first porous carrier is preferably 1 to 100 μm. When the average particle size is less than the lower limit, the sintering of the support tends to be promoted. On the other hand, when the upper limit is exceeded, the specific surface area tends to be small and the dispersibility of the noble metal tends to decrease. In addition, such an average particle diameter can be calculated | required by observing with a scanning electron microscope (SEM), and taking the particle size distribution of arbitrary 100 particles.

The specific surface area of such a carrier is not particularly limited, but is preferably 30 m ² / g or more (more preferably 50 to 250 m ² / g) from the viewpoint of obtaining higher catalytic activity.

  Furthermore, the average diameter of the pores of the first porous carrier is not particularly limited, but is preferably 100 nm or less, more preferably 10 nm or less, and particularly preferably 5 nm or less. The first porous carrier having such very fine pores has a sufficiently high adhesion to various substrates, and the durability stability when coated on the substrate tends to improve more reliably. is there.

  Further, the first noble metal supported on the first porous carrier needs to contain at least Pt. Such a first noble metal may be composed only of Pt, or may contain other noble metals other than Pt and Pt. By such Pt in the first noble metal, it is possible to promote the first step of the exhaust gas purification process described above. In addition, examples of other noble metals other than Pt that can be contained in the first noble metal include Rh, Pd, Os, Ir, Au, and the like. From the viewpoint of heat resistance and catalytic activity, It is preferably at least one of Rh and Pd.

  Further, the Pt content in the first noble metal needs to exceed 50% by mass with respect to the total amount of the first noble metal. The content of Pt in the first noble metal is more preferably 70% by mass or more with respect to the total amount of the first noble metal. When the Pt content in the first noble metal is less than the lower limit, the catalytic activity of the first catalyst powder is lowered, and the NOx purification efficiency of the obtained exhaust gas purification catalyst tends to be lowered.

The amount of the first noble metal supported is preferably 0.1 to 5 g, more preferably 0.5 to 3 g based on 100 g of the first porous carrier. The supported amount is less than the lower limit of the noble metal, becomes insufficient catalytic activity obtained by the noble metal tend to decrease _the NO _x purification activity of exhaust gas-purifying catalyst, while when it exceeds the upper limit, the cost As the price rises, it tends to be difficult to sufficiently suppress the noble metal grain growth. In addition, the method for supporting the first noble metal on the first porous carrier is not particularly limited, and a known method can be appropriately employed. For example, a salt of a noble metal (such as nitrate) is contained. A method may be employed in which the solution to be baked is brought into contact with the first porous carrier and calcined.

  The first catalyst powder has a NOx occlusion material loading of 0.03 mol or less with respect to 100 g of the first porous carrier. That is, the first catalyst powder is one in which the NOx storage material is not substantially supported on the first porous carrier. When the amount of the NOx occlusion material supported exceeds the upper limit, Pt in the first catalyst powder tends to be in an oxide state, and the NOx purification activity of the exhaust gas purification catalyst decreases.

  Next, the second catalyst powder will be described. Such a second catalyst powder includes a second porous carrier and a second noble metal supported on the second porous carrier. Such a second porous carrier is basically the same as the first porous carrier described above. In addition, as a metal oxide as such a material of the second porous carrier, zirconia, ceria, alumina, titania, and complex oxidation thereof are used from the viewpoint of heat resistance, sulfur poisoning resistance and compatibility with Rh. It is preferable that it is at least 1 sort (s) selected from a thing and a solid solution.

  Further, the second noble metal supported on the second porous carrier needs to contain at least Rh. Such a second noble metal may be composed of only Rh or may contain other noble metals other than Rh and Rh. By such Rh in the second noble metal, it becomes possible to promote the fourth step of the aforementioned exhaust gas purification process. In addition, examples of other noble metals other than Rh that can be contained in the second noble metal include Pt, Pd, Os, Ir, Au, and the like. From the viewpoint of heat resistance and catalytic activity, It is preferably at least one of Pt and Pd.

  The content of Rh in the second noble metal needs to exceed 50% by mass with respect to the total amount of the second noble metal. The Rh content in the second noble metal is more preferably 65% by mass or more based on the total amount of the second noble metal. When the Rh content in the second noble metal is less than the lower limit, the catalytic activity of the second catalyst powder is lowered, and the NOx purification efficiency of the obtained exhaust gas purification catalyst tends to be lowered.

The amount of the second noble metal supported is preferably 0.05 to 3 g, more preferably 0.1 to 2 g, based on 100 g of the second porous carrier. Wherein in the carrying amount of the second noble metal is below the lower limit, there is a tendency that the catalytic activity obtained by the second noble metal becomes insufficient _the NO _x purification activity of exhaust gas-purifying catalyst decreases, while when it exceeds the upper limit However, as the cost increases, it tends to be difficult to sufficiently suppress the grain growth of the noble metal. In addition, the method for supporting the second noble metal on the second porous carrier is not particularly limited, and a known method can be appropriately employed. For example, a salt of a noble metal (for example, nitrate or the like) is contained. You may employ | adopt the method of making a solution contact the said 2nd porous support | carrier, and baking.

  The second catalyst powder has a NOx occlusion material loading of 0.03 mol or less with respect to 100 g of the first porous carrier. That is, the second catalyst powder is one in which the NOx storage material is not substantially supported on the second porous carrier. When the amount of the NOx occlusion material supported exceeds the upper limit, Rh in the second catalyst powder tends to be in an oxide state, and the NOx purification activity of the exhaust gas purification catalyst is lowered.

  Next, the third catalyst powder will be described. The third catalyst powder includes a third porous carrier, a third noble metal supported on the third porous carrier, and a NOx storage material supported on the third porous carrier. Such a third porous carrier is basically the same as the third porous carrier described above. In addition, as a metal oxide as a material of such a third porous carrier, from the viewpoint of heat resistance, sulfur poisoning resistance, and compatibility with Pd and NOx storage materials, alumina, magnesia, ceria, zirconia, titania, In addition, at least one selected from these complex oxides and solid solutions is preferable.

  Further, the third noble metal supported on the third porous carrier needs to contain at least Pd. Such a third noble metal may be composed only of Pd or may contain other noble metals other than Pd and Pd. Such Pd in the third noble metal can promote the second and third steps of the exhaust gas purification process described above. In addition, examples of other noble metals other than Pd that can be contained in the third noble metal include Pt, Rh, Os, Ir, Au, and the like. From the viewpoint of heat resistance and catalytic activity, It is preferably at least one of Pt and Rh.

  Further, the amount of such Pd supported needs to be 0.05 g or more with respect to 100 g of the third porous carrier. The amount of Pd supported is preferably 0.05 to 6 g and more preferably 0.1 to 3 g with respect to 100 g of the third porous carrier. If the amount of Pd supported is less than the lower limit, the catalytic activity obtained by Pd tends to be insufficient. On the other hand, if it exceeds the upper limit, the effect obtained by Pd saturates and the economy tends to decrease. is there.

The amount of the noble metal supported other than Pd in the third noble metal is preferably 0.01 to 4 g, preferably 0.05 to 2 g with respect to 100 g of the third porous carrier. More preferred. If the loading amount of the noble metal other than Pd in the third noble metal is less than the lower limit, the catalytic activity obtained by the noble metal becomes insufficient, and the NO _x purification activity of the exhaust gas purification catalyst tends to decrease, On the other hand, when the upper limit is exceeded, the cost increases and it tends to be difficult to sufficiently suppress the noble metal grain growth. In addition, the method for supporting the third noble metal on the third porous carrier is not particularly limited, and a known method can be appropriately employed. For example, a salt of a noble metal (for example, nitrate or the like) is contained. You may employ | adopt the method of making a solution contact the said 3rd porous support | carrier, and baking.

  The NOx occlusion material supported on the third porous carrier is preferably at least one selected from the group consisting of alkali metals and alkaline earth metals. Examples of such alkali metal elements include lithium (Li), sodium (Na), potassium (K), and cesium (Cs). Examples of such alkaline earth metal elements include magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and the like. Such an alkali metal has a high NOx occlusion ability in a high temperature range, while an alkaline earth metal has a high NOx occlusion ability in a low temperature range. Therefore, you may use both together.

The amount of the NOx occlusion material supported needs to be more than 0.03 mol with respect to 100 g of the third porous carrier. In addition, the amount of such NOx occlusion material supported is preferably 0.03 to 2 mol, and more preferably 0.1 to 0.5 mol. Tend supported amount of such NOx-absorbing material is no longer provide a sufficient NOx storage performance is less than the lower limit, on the other hand, said third noble metal by exceeds the upper limit NOx-absorbing material is coated NO _X purification performance It tends to decrease.

  Further, the method for supporting the NOx occlusion material is not particularly limited. For example, salts of the above-described elements that are preferably used as the NOx occlusion material (for example, carbonate, nitrate, citrate, carboxylate, dicarboxylate) , Sulfate) or an aqueous solution containing the complex is brought into contact with the carrier, dried, and further calcined.

  Although the first to third catalyst powders have been described above, a preferred embodiment of the exhaust gas purifying catalyst of the present invention including such catalyst powders will be described below.

  In the exhaust gas purifying catalyst of the present invention, the content of each catalyst powder in the catalyst is not particularly limited as long as it includes the first to third catalyst powders described above. Is preferably in the following range. That is, first, the content of the first catalyst powder is preferably 5 to 60% by mass and more preferably 10 to 40% by mass with respect to the total amount of the first to third catalyst powders. . If the content of the first catalyst powder is less than the lower limit, the NOx oxidation performance is lowered, so that the low-temperature activity tends to be lowered. The activity tends to decrease.

  Moreover, as content of the said 2nd catalyst powder, it is preferable that it is 5-40 mass% with respect to the total amount of the said 1st-3rd catalyst powder, and it is more preferable that it is 5-30 mass%. When the content of the second catalyst powder is less than the lower limit, the NOx reduction performance decreases, and therefore the purification performance of NOx released from the NOx storage material tends to decrease. Since the amount of occlusion decreases, the high temperature activity tends to decrease.

  Furthermore, as content of the said 3rd catalyst powder, it is preferable that it is 30-90 mass% with respect to the total amount of the said 1st-3rd catalyst powder, and it is more preferable that it is 50-80 mass%. When the content of the third catalyst powder is less than the lower limit, the NOx occlusion amount decreases, and therefore, particularly high temperature activity tends to decrease. On the other hand, when the upper limit is exceeded, the NOx redox activity decreases, Low temperature activity tends to decrease.

  In addition, the form of such an exhaust gas purifying catalyst is not particularly limited, and may be in the form of a honeycomb-shaped monolith catalyst, a pellet-shaped pellet catalyst, or the like. The manufacturing method of the exhaust gas purifying catalyst having such a form is not particularly limited, and a known method can be appropriately adopted. For example, a catalyst for purifying exhaust gas is obtained by molding each catalyst powder mixture into a pellet. A method, a method of obtaining a catalyst for exhaust gas purification by coating a catalyst substrate with a slurry containing each catalyst powder, and the like may be employed. Further, such a catalyst base is not particularly limited and is appropriately selected depending on the use of the obtained exhaust gas purification catalyst, etc., but is not limited to a DPF base, a monolithic base, a pellet base, a plate base. A material or the like is preferably employed. The material of such a catalyst substrate is not particularly limited, but a substrate made of a ceramic such as cordierite, silicon carbide, mullite, or a substrate made of a metal such as stainless steel including chromium and aluminum is preferable. Adopted.

  Further, when the first to third catalyst powders are supported on the catalyst base, the total amount of the first to third catalyst powders supported on the catalyst base is 100 per liter capacity of the catalyst base. It is preferable that it is -350g / L, and it is more preferable that it is 150-300g / L. When the total amount of the first to third catalyst powders is less than the lower limit, it tends to be difficult to obtain sufficient catalytic activity. On the other hand, when the upper limit is exceeded, pores of the catalyst base material are blocked. Tend to cause pressure loss.

Furthermore, in such an exhaust gas purifying catalyst, the following conditions (A) to (C):
(A) The first to third catalyst powders are arranged so that the exhaust gas contacts the second catalyst powder and the third catalyst powder after the exhaust gas contacts the first catalyst powder.
(B) The first to third catalyst powders are disposed so that the exhaust gas contacts the first catalyst powder, the second catalyst powder, and the third catalyst powder in this order,
(C) The first to third catalyst powders are arranged so that the exhaust gas contacts the first catalyst powder, the third catalyst powder, and the second catalyst powder in this order.
It is preferable to satisfy any one of the conditions. That is, in the present invention, when the exhaust gas is brought into contact with the exhaust gas purification catalyst, it is preferable to arrange the first to third catalyst powders so that the exhaust gas first comes into contact with the first catalyst powder. Since the first catalyst powder can oxidize NO in the exhaust gas more efficiently when purifying the exhaust gas by arranging each catalyst powder so that the exhaust gas first comes into contact with the first catalyst powder in this way, NO ₂ Can be efficiently brought into contact with the second and third catalyst powders. Therefore, it is possible to more efficiently promote the first to fourth steps of the above-described exhaust gas purification process.

  Moreover, as the exhaust gas purifying catalyst satisfying such a condition (A), for example, an exhaust gas purifying catalyst having a two-layer structure, which is disposed on the catalyst base and on the upper layer side (surface side). For exhaust gas purification comprising a first catalyst layer made of the first catalyst powder and a second catalyst layer made of the second catalyst powder and the third catalyst powder disposed on the lower layer side (catalyst base side) A catalyst, a first catalyst part made of a first catalyst base on which the first catalyst powder is supported, and a second catalyst part made of a second catalyst base on which second and third catalyst powders are supported. An exhaust gas purifying catalyst in which the first catalyst part is disposed upstream of the exhaust gas flow path and the second catalyst part is disposed downstream is exemplified.

  The exhaust gas purifying catalyst satisfying the condition (B) is, for example, an exhaust gas purifying catalyst having a three-layer structure, and the first catalyst arranged as a catalyst base and an upper layer (surface side). Catalyst layer (I) made of powder, catalyst layer (II) made of the second catalyst powder arranged as an intermediate layer, and catalyst layer made of the third catalyst powder arranged as a lower layer (catalyst base side) (III), a first catalyst portion comprising a first catalyst base on which the first catalyst powder is supported, and a second catalyst base on which the second catalyst powder is supported. And a third catalyst part made of a third catalyst base on which the third catalyst powder is supported, and the first to third catalyst parts are first from the upstream side of the exhaust gas flow path. An exhaust gas purifying catalyst, etc. arranged in the order of the catalyst part, the second catalyst part, and the third catalyst part It is below.

  Furthermore, as the exhaust gas purifying catalyst that satisfies the condition (C), for example, an exhaust gas purifying catalyst having a three-layer structure, the catalyst base and the first catalyst arranged as an upper layer (surface side) Catalyst layer (I) made of powder, catalyst layer (III) made of the third catalyst powder arranged as an intermediate layer, and catalyst layer made of the second catalyst powder arranged as a lower layer (catalyst base side) (II), an exhaust gas purifying catalyst, a first catalyst portion comprising a first catalyst base on which the first catalyst powder is supported, and a second catalyst base on which the second catalyst powder is supported. And a third catalyst part made of a third catalyst base on which the third catalyst powder is supported, and the first to third catalyst parts are first from the upstream side of the exhaust gas flow path. Exhaust gas purifying catalyst in the form of a catalyst part, a third catalyst part, and a second catalyst part arranged in this order And the like.

  Further, among exhaust gas purifying catalysts satisfying any one of these conditions (A) to (C), from the viewpoint of catalyst activity and ease of catalyst preparation, from the catalyst base and the first catalyst powder. The first catalyst layer and the second catalyst layer made of the second catalyst powder and the third catalyst powder, and the first to second catalyst layers are in contact with the first catalyst layer in the exhaust gas. The exhaust gas purifying catalyst (the first catalyst layer is disposed on the upper layer side and the second catalyst layer is disposed on the lower layer side) disposed on the catalyst base so that the exhaust gas contacts the second catalyst layer later Exhaust gas purifying catalysts) are preferred. The method for producing the exhaust gas purifying catalyst in such a form is not particularly limited. For example, first, a slurry containing a mixture of the second catalyst powder and the third catalyst powder is coated on the catalyst base, and the second catalyst After forming the layer, a slurry containing the first porous carrier is coated on the second catalyst layer, and then an aqueous solution containing a Pt salt (nitrate, etc.) is brought into contact with the catalyst base material and fired. Thus, a method of obtaining the exhaust gas purifying catalyst by forming the first catalyst layer and the second catalyst layer on the catalyst base may be adopted, or a mixture of the second catalyst powder and the third catalyst powder may be used. After the slurry containing the catalyst is coated on the catalyst base to form the second catalyst layer, the slurry containing the first catalyst powder is coated on the second catalyst layer and the first catalyst layer and the second catalyst layer on the catalyst base. 2 Forming a catalyst layer for exhaust gas purification by forming a catalyst layer The may be adopted.

  Next, the exhaust gas purification method of the present invention will be described. That is, the exhaust gas purification method of the present invention is a method characterized in that exhaust gas is purified by bringing the exhaust gas into contact with the exhaust gas purification catalyst of the present invention. Such an exhaust gas purification method is not particularly limited except that the exhaust gas purification catalyst of the present invention is used and the exhaust gas is brought into contact with the exhaust gas purification catalyst of the present invention. For example, the exhaust gas purification catalyst of the present invention may be disposed in an exhaust gas pipe through which exhaust gas discharged from an internal combustion engine flows, and the exhaust gas may be contacted with the exhaust gas purification catalyst of the present invention to purify the exhaust gas. In such an exhaust gas purification method, since the exhaust gas purification catalyst of the present invention is used, CO, HC and NOx can be efficiently purified at the same time, and NOx can be removed even under relatively low temperature conditions. It can be purified sufficiently.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.

Example 1
First, TiO ₂ —ZrO ₂ composite oxide prepared by coprecipitation using 90 g of Al ₂ O ₃ (trade name “MI386” manufactured by WR Grace Co., Ltd., average particle size 22 μm) and titanium tetrachloride and zirconium oxynitrate ( A dispersion liquid was obtained by dispersing 180 g of a third porous carrier made of a mixture having an average particle size of 20 μm and a weight ratio of each component (TiO ₂ : ZrO ₂ ) of 30:70) 90 g in ion-exchanged water. Next, after adding a Pd nitrate solution to the dispersion, the solid content obtained by evaporating the solvent is baked in the atmosphere at 400 ° C., whereby Pd is added to 180 g of the third porous carrier. 0.5 g of Pd-supported powder was obtained. Next, the total amount of the obtained Pd-supported powder is added to an aqueous solution containing 0.2 mol of Ba acetate Ba, and the resulting mixture is heated to 100 ° C. to remove moisture from the mixture. The solid content was calcined in the atmosphere at a temperature of 400 ° C. to obtain 220 g of a third catalyst powder in which Ba and Pd were supported on the third porous carrier.

Next, Rh is 0.5% by mass in a second porous carrier composed of 220 g of the third catalyst powder and 50 g of ZrO ₂ (trade name “RC-100” manufactured by Daiichi Rare Element Co., Ltd., average particle diameter: 2 μm). The supported Rh supported powder (second catalyst powder) was mixed to obtain slurry (I). Thereafter, the slurry (I) is coated on a cordierite monolith substrate having a diameter of 30 mm and a length of 25 mm (capacity: 17.5 cc), and the second catalyst powder and the third catalyst are coated on the surface of the monolith substrate. A catalyst layer (A) comprising powder was produced. When forming the catalyst layer (A), the slurry was coated on the substrate so that the supported amount of the catalyst layer (A) was 270 g / L per liter of the monolith substrate.

Next, CeO ₂ —Al ₂ O ₃ composite oxide (average particle diameter 20 μm, weight ratio of each component (CeO ₂ : Al ₂ O ₃ ) prepared by coprecipitation using cerium nitrate and aluminum nitrate was 25:75. A slurry (II) of 40 g of the first porous carrier consisting of 1) was prepared. Then, the slurry (II) was coated on the catalyst layer (A) to produce an upper layer made of the first porous carrier on the catalyst layer (A). Next, after impregnating and supporting a dinitrodiammine Pt nitric acid solution on the monolith substrate on which each layer is formed such that the amount of Pt supported per liter of the monolith substrate is 1.5 g / L, Baking was performed at a temperature condition of 400 ° C., and Pt was supported on the entire upper layer and lower layer. Thus, a catalyst layer (B) made of the first catalyst powder in which Pt is supported on the first porous carrier is produced on the catalyst layer (A), and the catalyst layer (A) is formed on the monolith substrate. And an exhaust gas purifying catalyst in a form in which the catalyst layer (B) was laminated. The total coating amount of the catalyst layer (A) and the catalyst layer (B) was 310 g / L. Table 1 and Table 2 show constituent elements and the like in the exhaust gas purification catalyst thus obtained.

(Comparative Example 1)
First, TiO ₂ —ZrO ₂ composite oxide prepared by coprecipitation using 90 g of Al ₂ O ₃ (trade name “MI386” manufactured by WR Grace Co., Ltd., average particle size 22 μm) and titanium tetrachloride and zirconium oxynitrate ( CeO prepared by a coprecipitation method using 180 g of a third porous carrier composed of a mixture of 90 g having an average particle size of 20 μm and a weight ratio of each component (TiO ₂ : ZrO ₂ ) of 30:70), and cerium nitrate and aluminum nitrate. 40 g of a first porous carrier comprising _2- Al ₂ O ₃ composite oxide (average particle diameter 20 μm, weight ratio of each component (CeO ₂ : Al ₂ O ₃ ) 25:75), ZrO ₂ (first rare Rh-supported powder (second catalyst powder) in which 0.5% by mass of Rh is supported on a second porous carrier consisting of 50 g of trade name “RC-100” manufactured by Elemental Co., Ltd. The slurry was prepared combined. Next, the slurry was coated on a cordierite monolith base material having a diameter of 30 mm and a length of 25 mm (capacity: 17.5 cc) to form a catalyst layer on the surface of the monolith base material. When forming such a catalyst layer, the substrate was coated with the slurry so that the supported amount of the catalyst layer was 270 g / L per liter of the monolith substrate. Next, an aqueous solution containing Ba acetate is impregnated and supported on the monolith substrate on which the catalyst layer is formed so that the supported amount of Ba per 1 L of the monolith substrate is 0.2 mol / L. The catalyst layer was baked at a medium temperature of 400 ° C. to carry Ba over the entire area of the catalyst layer. Next, after impregnating and supporting a dinitrodiammine Pt nitric acid solution on the monolith substrate on which the catalyst layer is formed so that the amount of Pt supported per liter of the monolith substrate is 2.0 g / L, The catalyst layer was calcined at a temperature of 400 ° C. and Pt was supported on the entire area of the catalyst layer to obtain an exhaust gas purifying catalyst for comparison of the single layer structure. The total coating amount of the catalyst layer including Ba was 310 g / L. Table 1 and Table 2 show constituent elements and the like in the exhaust gas purification catalyst thus obtained.

(Comparative Example 2)
The amount of Pt supported on the catalyst layer is set to 1.5 g / L per liter of the monolith substrate, and further the Pd nitrate solution is used so that the amount of Pd supported is 0.5 g / L per liter of the monolith substrate. Exhaust gas purification catalyst for comparison of a single layer structure was obtained in the same manner as in Comparative Example 1 except that Pd was supported on the entire region. The total coating amount of the catalyst layer including Ba is 310 g / L. Tables 1 and 2 show constituent elements and the like of the exhaust gas purifying catalyst thus obtained.

(Comparative Example 3)
First, TiO ₂ —ZrO ₂ composite oxide prepared by coprecipitation using 90 g of Al ₂ O ₃ (trade name “MI386” manufactured by WR Grace Co., Ltd., average particle size 22 μm) and titanium tetrachloride and zirconium oxynitrate ( 180 g of a third porous carrier comprising a mixture of 90 g having an average particle diameter of 20 μm and a weight ratio of each component (TiO ₂ : ZrO ₂ ) of 30:70), ZrO ₂ (trade name “RC” The slurry (III) was prepared by mixing the second catalyst powder made of Rh-supported powder in which 0.5% by mass of Rh was supported on the second porous carrier composed of 50 g of −100 ”, average particle diameter 2 μm). Next, the slurry (III) was coated on a cordierite monolith base material having a diameter of 30 mm and a length of 25 mm (capacity: 17.5 cc) to form a catalyst layer on the surface of the monolith base material. When forming the catalyst layer, the substrate was coated with the slurry (III) such that the supported amount of the catalyst layer was 230 g / L per liter of the monolith substrate. Next, an aqueous solution containing Ba acetate is impregnated and supported on the monolith substrate on which the catalyst layer is formed so that the supported amount of Ba per 1 L of the monolith substrate is 0.2 mol / L. The catalyst layer (C) was manufactured on the monolith substrate by calcining at a temperature condition of 400 ° C. so that Ba was supported on the entire catalyst layer.

Next, CeO ₂ —Al ₂ O ₃ composite oxide (average particle diameter 20 μm, weight ratio of each component (CeO ₂ : Al ₂ O ₃ ) prepared by coprecipitation using cerium nitrate and aluminum nitrate was 25:75. A slurry (II) of 40 g of the first porous carrier consisting of 1) was prepared. Then, the slurry (II) was coated on the catalyst layer (C), and an upper layer made of the first porous carrier was formed on the catalyst layer (C). Next, after impregnating and supporting a dinitrodiammine Pt nitric acid solution on the monolith substrate on which each layer is formed such that the amount of Pt supported per liter of the monolith substrate is 2.0 g / L, Baking was performed at a temperature condition of 400 ° C., and Pt was supported on the entire upper layer and lower layer. As a result, a catalyst layer (D) made of the first catalyst powder in which Pt is supported on the first porous carrier is manufactured on the catalyst layer (C), and the catalyst layer (C) and the catalyst are formed on the monolith substrate. An exhaust gas purifying catalyst was obtained for comparison of the form in which the layer (D) was laminated. The total coating amount of the catalyst layer (C) and the catalyst layer (D) was 310 g / L. Table 1 and Table 2 show constituent elements and the like in the exhaust gas purification catalyst thus obtained.

(Comparative Example 4)
In the same manner as in Example 1 except that Pd was not supported on the third porous carrier and the supported amount of Pt was changed from 1.5 g / L to 2.0 g / L, Pt and Pt were formed on the monolith substrate. A catalyst layer (E) formed of a catalyst powder (no Pd) composed of a third porous carrier on which Ba is supported and the second catalyst powder (Rh-supported powder) is manufactured, and an upper layer is formed from the first catalyst powder. The catalyst layer (F) was produced, and an exhaust gas purifying catalyst for comparison of the form in which the catalyst layer (E) and the catalyst layer (F) were laminated on the monolith substrate was obtained. The total coating amount of the catalyst layer including Ba is 310 g / L. Tables 1 and 2 show constituent elements and the like of the exhaust gas purifying catalyst thus obtained.

[Evaluation of characteristics of exhaust gas purifying catalysts obtained in Example 1 and Comparative Examples 1 to 4]
<High temperature durability test (1)>
Using the exhaust gas purifying catalysts obtained in Example 1 and Comparative Examples 1 to 4, the lean gas and the rich gas having the composition shown in Table 3 were added to each catalyst under the temperature condition of 750 ° C. A high temperature endurance test (1) was conducted in which the sample was circulated for 5 hours while fluctuating at intervals of seconds / 10 seconds.

<Sulfur poisoning durability test (1)>
Using the exhaust gas purifying catalysts obtained in Example 1 and Comparative Examples 1 to 4 after the high temperature durability test (1), the sulfur poisoning treatment shown in Table 4 under the temperature condition of 380 ° C. for each catalyst. The rich gas and the lean gas for (S poisoning treatment) are circulated for 40 minutes at a flow rate of 30 L / min while changing at intervals of lean / rich = 40 seconds / 5 seconds, and 1.5 g / L of sulfur per 1 L of catalyst is equivalent to sulfur. S ₂ poisoning treatment was performed by supplying SO ₂ . Next, for each catalyst after the S poisoning treatment, under the temperature condition of 580 ° C., the rich gas and lean gas for the S regeneration treatment (S regeneration) having the composition shown in Table 4 were set to lean / rich = 5 seconds / 5 seconds. The catalyst was regenerated by desorbing the poisoned sulfur by flowing at a flow rate of 30 L / min for 10 minutes while varying the interval.

<NOx purification test (1)>
Using the exhaust gas purifying catalysts obtained in Example 1 and Comparative Examples 1 to 4 after the sulfur poisoning endurance test (1), each catalyst has the composition shown in Table 5 under a temperature condition of 300 ° C. The rich gas and lean gas were circulated at a flow rate of 30 L / min while varying the interval of lean / rich = 40 seconds / 3 seconds, and the NOx purification rate in a steady state was measured. In addition, the space velocity (SV) at the time of measurement was 51400h- ¹ . Further, NOx purification rate, for each catalyst, the concentration of the NO _x contained in each of the front and rear of the gas that contacts the catalyst was measured to determine based on the value of the concentration of NO _x. The obtained results are shown in FIG.

  As is clear from the results shown in FIG. 1, it was confirmed that the exhaust gas purifying catalyst (Example 1) of the present invention exhibits sufficiently high NOx purification performance even under a low temperature condition of 300 ° C. . On the other hand, the exhaust gas purification catalysts for comparison (Comparative Examples 1 to 4) did not have sufficient NOx purification performance. From these results, in the exhaust gas purifying catalysts obtained in Comparative Examples 1 and 2, the NOx occlusion material (Ba) was supported on the entire region (all porous supports) (supported amount: more than 0.03 mol per 100 g of support). Therefore, it is presumed that the NOx occlusion material decreased the activities of Pt and Rh in the catalyst and did not provide sufficient catalytic activity. Further, in the exhaust gas purifying catalysts obtained in Comparative Examples 3 to 4, Pd was not supported on the third porous support on which the NOx occlusion material was supported. It is presumed that the noble metal supported on the catalyst could not exhibit sufficient catalytic activity, and sufficient NOx purification performance could not be obtained.

(Example 2)
Coprecipitation method using 20 g of Al ₂ O ₃ (trade name “MI386” manufactured by WR Grace Co., Ltd., average particle diameter of 22 μm) instead of 40 g of CeO ₂ —Al ₂ O ₃ composite oxide, titanium tetrachloride and zirconium oxynitrate In the same manner as in Example 1 except that a mixture of 20 g of a TiO ₂ —ZrO ₂ composite oxide (average particle size 20 μm) prepared by the above was used as the first porous carrier, the second layer as the lower layer was formed on the monolith substrate. A catalyst layer (G) made of the catalyst powder and the third catalyst powder is produced, and a catalyst layer (H) made of the first catalyst powder is produced thereon, and the catalyst layer (G) and the catalyst are formed on the monolith substrate. An exhaust gas purifying catalyst in a form in which the layer (H) was laminated was obtained. The total coating amount of the catalyst layer including Ba is 310 g / L. Tables 6 and 7 show constituent elements and the like of the exhaust gas purifying catalyst thus obtained.

(Comparative Example 5)
The slurry (II) containing 40 g of CeO ₂ -Al ₂ O ₃ composite oxide was not coated on the catalyst layer (C), and Pt was supported directly on the catalyst layer (C) using a dinitrodiammine Pt nitric acid solution. Except that Pt was supported so that the amount was 2.0 g / L per liter of monolith substrate, the same method as in Comparative Example 3 was adopted to obtain an exhaust gas purification catalyst for comparison of one-layer structures. . The total coating amount of the catalyst layer including Ba is 270 g / L. Tables 6 and 7 show constituent elements and the like of the exhaust gas purifying catalyst thus obtained.

(Comparative Example 6)
Instead of the slurry (II) containing 40 g of CeO ₂ —Al ₂ O ₃ composite oxide, 20 g of Al ₂ O ₃ (trade name “MI386” manufactured by WR Grace Co., Ltd., average particle size 22 μm) and titanium tetrachloride and oxy Comparative Example 3 except that the slurry (IV) of 40 g of the first porous carrier made of a mixture of 20 g of a TiO ₂ —ZrO ₂ composite oxide (average particle size 20 μm) prepared by coprecipitation using zirconium nitrate was used. In the same manner as above, a catalyst layer (I) having the same structure as the catalyst layer (C) is produced as a lower layer on the monolith substrate, and a catalyst layer (J) made of the first catalyst powder is produced as an upper layer thereof An exhaust gas purifying catalyst was obtained for comparison of the form in which the catalyst layer (I) and the catalyst layer (J) were laminated on the monolith substrate. The total coating amount of the catalyst layer including Ba is 310 g / L. Tables 6 and 7 show constituent elements and the like of the exhaust gas purifying catalyst thus obtained.

(Comparative Example 7)
On the monolith substrate in the same manner as in Example 2 except that Pd was not supported on the third porous carrier and the amount of Pt supported was changed from 1.5 g / L to 2.0 g / L per liter of monolith substrate. A catalyst layer (K) consisting of a catalyst powder (no Pd) made of a third porous carrier on which Pt and Ba are supported and a second catalyst powder (Rh-supported powder) is produced, and the first catalyst is formed on the upper layer. A catalyst layer (L) made of powder was produced to obtain an exhaust gas purifying catalyst for comparison of the form in which the catalyst layer (K) and the catalyst layer (L) were laminated on the monolith substrate. The total coating amount of the catalyst layer including Ba is 310 g / L. Tables 6 and 7 show constituent elements and the like of the exhaust gas purifying catalyst thus obtained.

[Evaluation of characteristics of exhaust gas purifying catalysts obtained in Example 2 and Comparative Examples 5 to 7]
<NOx purification test (2)>
First, the same tests as the high temperature durability test (1) and the sulfur poisoning durability test (1) were sequentially performed on the exhaust gas purifying catalysts obtained in Example 2 and Comparative Examples 5 to 7, respectively. did. Then, the NOx purification test (1) described above was performed on the exhaust gas purification catalysts obtained in Example 2 and Comparative Examples 5 to 7 after the high temperature durability test (1) and the sulfur poisoning durability test (1). ) And the NOx purification rate was measured. The obtained results are shown in FIG.

  As is apparent from the results shown in FIG. 2, it was confirmed that the exhaust gas purifying catalyst (Example 2) of the present invention exhibits sufficiently high NOx purification performance even under a low temperature condition of 300 ° C. It was. On the other hand, the exhaust gas purification catalysts for comparison (Comparative Examples 5 to 7) did not have sufficient NOx purification performance. This is because, in the exhaust gas purifying catalyst obtained in Comparative Example 5, the NOx storage material (Ba) was supported on the entire region (all porous supports) (supported amount: more than 0.03 mol per 100 g of support). It is presumed that the NOx occlusion material decreased the activity of Pt and Rh in the catalyst, and sufficient catalytic activity was not obtained. Further, in the exhaust gas purifying catalysts obtained in Comparative Examples 6-7, Pd was not supported on the third porous support on which the NOx occlusion material was supported. It is presumed that the noble metal supported on the catalyst could not exhibit sufficient catalytic activity, and sufficient NOx purification performance could not be obtained.

(Preparation Example 1: Preparation of Pt / Al ₂ O ₃ powder)
A dispersion was obtained by adding 1 L of ion-exchanged water to 100 g of Al ₂ O ₃ (trade name “MI386” manufactured by WR Grace Co., Ltd., average particle size 22 μm) and stirring, and then Pt was converted into metal in the dispersion in dinitrodiammine Pt solution was added containing 1g, by removing the water, to prepare a Pt / _Al 2 _{O 3} powder of _Al 2 _{O 3} which Pt is carried.

(Preparation Example 2: Preparation of Pd / Al ₂ O ₃ powder)
A dispersion was obtained by adding 1 L of ion-exchanged water to 100 g of Al ₂ O ₃ (trade name “MI386” manufactured by WR Grace Co., Ltd., average particle diameter 22 μm) and stirring, and then Pd was converted into metal in the dispersion A Pd / Al ₂ O ₃ powder composed of Al ₂ O ₃ supporting Pd was prepared by adding a Pd nitrate solution containing 0.7 g of the solution and removing water.

(Preparation Example 3: Preparation of Rh / ZrO ₂ powder)
A dispersion was obtained by adding 1 L of ion-exchanged water to 100 g of ZrO ₂ (trade name “RC-100” manufactured by Daiichi Rare Element Co., Ltd., average particle diameter: 2 μm) and stirring, and then adding Rh into the dispersion. A Rh / ZrO ₂ powder consisting of ZrO ₂ supporting Rh was prepared by adding a Rh nitric acid solution containing 1 g in terms of metal and removing water.

(Preparation Example 4: Preparation of BaK / Pt / Al ₂ O ₃ powder)
After 100 g of Pt / Al ₂ O ₃ powder obtained in Preparation Example 1 was added to 1 L of ion-exchanged water and stirred to obtain a dispersion, the supported amount of Ba was 0 per 1 g of support (Al ₂ O ₃ ). .4 mmol and the amount of K supported is 0.8 mmol per 1 g of support (Al ₂ O ₃ ). By adding Ba acetate solution and K acetate solution to the dispersion and removing water, Pt / Al in ₂ O ₃ powder and a Ba and K was obtained BaK / Pt / _Al 2 _{O 3} powder was supported. (Preparation Example 5: Preparation of BaK / Pd / Al ₂ O ₃ powder)
In the same manner as in Preparation Example 4, except that 100 g of the Pd / Al ₂ O ₃ powder obtained in Preparation Example 2 was used instead of 100 g of the Pt / Al ₂ O ₃ powder obtained in Preparation Example 1, Pd / Al and the Ba and carrier K was obtained supported BaK / Pd / _Al 2 _{O 3} powder ₂ O ₃ powder.

(Preparation Example 6: Preparation of BaK / Rh / ZrO ₂ powder)
After 100 g of Rh / ZrO ₂ powder obtained in Preparation Example 3 was added to 1 L of ion-exchanged water and stirred to obtain a dispersion, the supported amount of Ba was 0.2 mmol per 1 g of support (ZrO ₂ ) and By adding an acetic acid Ba solution and an acetic acid K solution to the dispersion so that the amount of K supported is 0.4 mmol per 1 g of the carrier (ZrO ₂ ), and removing water, the Ba and Rh / ZrO ₂ powders are mixed with Ba. A BaK / Rh / ZrO ₂ powder carrying K was obtained.

(Example 3)
First, 50 g of Pt / Al ₂ O ₃ powder obtained in Preparation Example 1 was used as the first catalyst powder, and 50 g of Rh / ZrO ₂ powder obtained in Preparation Example 3 was used as the second catalyst powder. Since a mixture of 100 g of the obtained BaK / Pt / Al ₂ O ₃ powder and 70 g of the BaK / Pd / Al ₂ O ₃ powder obtained in Preparation Example 5 was used as the third catalyst powder, these powders were respectively used in the aforementioned weight. It measured so that it might become, and mixed powder was obtained by dry-mixing using a mortar. The weight of each powder is a value converted to the weight of the carrier (the same applies to Examples 4 to 5 and Comparative Examples 8 to 12 below). Next, the mixed powder obtained in this manner is compacted at about 1000 kgf / cm ² , crushed and sized to give 0.5 to 1.0 mm pellets, and a pellet-shaped exhaust gas purification catalyst is obtained. It was. Tables 8 and 9 show constituent elements and the like of the exhaust gas purifying catalyst thus obtained.

Example 4
First, a mixture of 38 g of the Pt / Al ₂ O ₃ powder obtained in Preparation Example 1 and 12 g of the Pd / Al ₂ O ₃ powder obtained in Preparation Example 2 was used as the first catalyst powder. In addition, 50 g of Rh / ZrO ₂ powder was used as the second catalyst powder, 112 g of BaK / Pt / Al ₂ O ₃ powder obtained in Preparation Example 4 and 58 g of BaK / Pd / Al ₂ O ₃ powder obtained in Preparation Example 5. Therefore, these powders were measured so as to have the above-mentioned weights, and were dry-mixed using a mortar to obtain mixed powders. And the pellet-shaped exhaust gas purification catalyst was obtained like Example 3 except having used such mixed powder. Tables 8 and 9 show constituent elements and the like of the exhaust gas purifying catalyst thus obtained.

(Example 5)
First, a mixture of 25 g of the Pt / Al ₂ O ₃ powder obtained in Preparation Example 1 and 25 g of the Pd / Al ₂ O ₃ powder obtained in Preparation Example 2 was used as the first catalyst powder. The Rh / ZrO ₂ powder 50 g was used as the second catalyst powder, and the BaK / Pt / Al ₂ O ₃ powder 125 g obtained in Preparation Example 4 and the BaK / Pd / Al ₂ O ₃ powder 45 g obtained in Preparation Example 5 were used. Therefore, these powders were measured so as to have the above-mentioned weights, and were dry-mixed using a mortar to obtain mixed powders. And the pellet-shaped exhaust gas purification catalyst was obtained like Example 3 except having used such mixed powder. Tables 8 and 9 show constituent elements and the like of the exhaust gas purifying catalyst thus obtained.

(Comparative Example 8)
First, 50 g of Pt / Al ₂ O ₃ powder obtained in Preparation Example 1, 100 g of BaK / Pt / Al ₂ O ₃ powder obtained in Preparation Example 4, and BaK / Pd / Al obtained in Preparation Example 5 _A mixed powder was obtained by dry-mixing 70 g of ₂ O ₃ powder and 50 g of BaK / Rh / ZrO ₂ powder obtained in Preparation Example 6 using a mortar. And the pellet-shaped exhaust gas purification catalyst for comparison was obtained like Example 3 except having used such mixed powder. Tables 8 and 9 show constituent elements and the like of the exhaust gas purifying catalyst thus obtained.

(Comparative Example 9)
First, 50 g of Pd / Al ₂ O ₃ powder obtained in Preparation Example 2, 150 g of BaK / Pt / Al ₂ O ₃ powder obtained in Preparation Example 4, and BaK / Pd / Al obtained in Preparation Example 5 20 g of ₂ O ₃ powder and 50 g of BaK / Rh / ZrO ₂ powder obtained in Preparation Example 6 were dry mixed using a mortar to obtain a mixed powder. And the pellet-shaped exhaust gas purification catalyst for comparison was obtained like Example 3 except having used such mixed powder. Tables 8 and 9 show constituent elements and the like of the exhaust gas purifying catalyst thus obtained.

(Comparative Example 10)
First, 50 g of Rh / ZrO ₂ powder obtained in Preparation Example 3, 150 g of BaK / Pt / Al ₂ O ₃ powder obtained in Preparation Example 4, and BaK / Pd / Al ₂ O obtained in Preparation Example 5. _Three powders (70 g) were dry mixed using a mortar to obtain a mixed powder. And the pellet-shaped exhaust gas purification catalyst for comparison was obtained like Example 3 except having used such mixed powder. Tables 8 and 9 show constituent elements and the like of the exhaust gas purifying catalyst thus obtained.

(Comparative Example 11)
First, 150 g of BaK / Pt / Al ₂ O ₃ powder obtained in Preparation Example 4, 70 g of BaK / Pd / Al ₂ O ₃ powder obtained in Preparation Example 5, and BaK / Rh obtained in Preparation Example 6. A mixed powder was obtained by dry-mixing 50 g of / ZrO ₂ powder using a mortar. And the pellet-shaped exhaust gas purification catalyst for comparison was obtained like Example 3 except having used such mixed powder. Tables 8 and 9 show constituent elements and the like of the exhaust gas purifying catalyst thus obtained.

(Comparative Example 12)
First, 150 g of Pt / Al ₂ O ₃ powder obtained in Preparation Example 1, 70 g of Pd / Al ₂ O ₃ powder obtained in Preparation Example 2, and 50 g of Rh / ZrO ₂ powder obtained in Preparation Example 3 Was mixed dry using a mortar to obtain a mixed powder. And the pellet-shaped exhaust gas purification catalyst for comparison was obtained like Example 3 except having used such mixed powder. Tables 8 and 9 show constituent elements and the like of the exhaust gas purifying catalyst thus obtained.

[Evaluation of characteristics of exhaust gas purification catalysts obtained in Examples 3 to 5 and Comparative Examples 8 to 12]
<High temperature durability test (2)>
2 g of each of the exhaust gas purifying catalysts obtained in Examples 3 to 5 and Comparative Examples 8 to 12 was used, and lean gases and rich gases having the compositions shown in Table 10 were leaned for each catalyst under a temperature condition of 750 ° C. / Rich = 4 minutes / 1 A high temperature durability test (2) was conducted for 5 hours at a flow rate of 1 L / min while fluctuating at intervals of 1 minute.

<NOx purification test (3)>
The exhaust gas purifying catalysts obtained in Examples 3 to 5 and Comparative Examples 8 to 12 after the high temperature endurance test (2) were each used in terms of carrier, and each catalyst was used at atmospheric pressure fixed bed flow type reactor (best Installed in Sokki CATA-5000-6), and the rich gas and the lean gas having the composition shown in Table 11 were circulated at a flow rate of 10 L / min while changing at intervals of lean / rich = 40 seconds / 6 seconds. The NOx purification rate was measured. In addition, such measurement of the NOx purification rate was performed by setting the inlet gas temperatures to 300 ° C., 350 ° C., and 400 ° C., respectively. Furthermore, NOx purification rate, for each catalyst, the concentration of the NO _x contained in each of the front and rear of the gas that contacts the catalyst was measured to determine based on the value of the concentration of NO _x. FIG. 3 shows a graph showing the relationship between the inlet gas temperature (300 ° C., 350 ° C., 400 ° C.) and the NOx purification rate of the exhaust gas purification catalysts obtained in Examples 3-5 and Comparative Examples 8-12. A graph of the NOx purification rate of the exhaust gas purification catalysts obtained in Examples 3 to 5 and Comparative Examples 8 to 12 under the temperature condition of 350 ° C. is shown in FIG.

  As is clear from the results shown in FIGS. 3 to 4, the exhaust gas-purifying catalyst of the present invention containing all of the first catalyst powder, the second catalyst powder, and the third catalyst powder (Examples 3 to 5). ) Is sufficiently sufficient under any temperature conditions as compared with the exhaust gas purifying catalysts obtained in Comparative Examples 8 to 11 comprising only one or two of the first to third catalyst powders. It was confirmed to show a high NOx purification activity. Note that the exhaust gas purifying catalyst obtained in Comparative Example 11 consisting only of the third catalyst powder showed the lowest NOx purification activity in the entire temperature range. Further, the exhaust gas-purifying catalyst obtained in Comparative Example 12 containing no third catalyst powder has high activity under the low temperature conditions of 300 ° C, but is sufficient under the temperature conditions of 350 ° C and 400 ° C. It has been found that the NOx purification activity is reduced, particularly under a temperature condition of 400 ° C., and sufficient catalytic activity cannot be obtained under a temperature condition of 350 or higher. From these results, the exhaust gas purifying catalyst (Examples 3 to 5) of the present invention is more than a certain level of NOx over the entire temperature range as compared with the exhaust gas purifying catalysts obtained in Comparative Examples 8 to 12. It was confirmed that the purification activity can be exhibited stably, and it has been found that it has a sufficiently high NOx purification activity.

<Sulfur poisoning endurance test (2)>
The exhaust gas purifying catalyst obtained in Example 3, Comparative Example 8, Comparative Example 11 and Comparative Example 12 after the high temperature durability test (2) was carried out was used in an amount of 1.1 g in terms of carrier, and the temperature was 400 ° C. Under the conditions, the rich gas and the lean gas for sulfur poisoning treatment (S poisoning) shown in Table 12 were circulated at a flow rate of 10 L / min for 15 minutes while fluctuating at intervals of lean / rich = 40 seconds / 6 seconds. S poisoning treatment was performed by supplying SO ₂ equivalent to 3 g of sulfur per 270 g. Next, for each catalyst after the S poisoning treatment, the rich gas for the S regeneration treatment (S regeneration) having the composition shown in Table 12 and the lean gas were varied at intervals of lean / rich = 6 seconds / 6 seconds, and 10 L / The catalyst was regenerated at a flow rate of min at 650 ° C. for 10 minutes and then at 680 ° C. for 10 minutes to desorb the poisoned sulfur.

<NOx purification test (4)>
The NOx purification test described above, using 1.1 g of the exhaust gas purification catalyst obtained in Example 3, Comparative Example 8, Comparative Example 11 and Comparative Example 12 after the sulfur poisoning durability test (2) in terms of carrier. The same test as in (3) was performed to measure the NOx purification rate. FIG. 5 shows the relationship between the inlet gas temperature and the NOx purification rate, and FIG. 6 shows the NOx purification rate under the temperature condition of 350 ° C.

  As is apparent from the results shown in FIGS. 5 to 6, the exhaust gas-purifying catalyst (Example 3) of the present invention containing all of the first to third catalyst powders is sufficient in any temperature range. It was confirmed that high NOx purification activity was exhibited. In contrast, the exhaust gas purifying catalyst obtained in Comparative Example 8 containing only the first and third catalyst powders did not have sufficient activity at temperatures of 300 ° C. and 350 ° C. Further, the exhaust gas purifying catalyst obtained in Comparative Example 11 consisting only of the third catalyst powder has sufficient activity in any temperature range as compared with the exhaust gas purifying catalyst of the present invention (Example 3). I couldn't. In addition, the exhaust gas purifying catalyst obtained in Comparative Example 12 containing no third catalyst powder shows high activity at temperatures of 350 ° C. and 400 ° C., although the activity is high under low temperature conditions of 300 ° C. There wasn't. From these results, the exhaust gas purifying catalyst of the present invention (Example 3) was compared with the exhaust gas purifying catalysts obtained in Comparative Example 8, Comparative Example 11 and Comparative Example 12 after the sulfur poisoning test. In addition, it was confirmed that sufficiently high NOx purification activity can be stably exhibited in all temperature ranges, and it has been found that it has sufficiently high NOx purification activity even after the sulfur poisoning test.

  As described above, according to the present invention, an exhaust gas purifying catalyst having sufficiently high exhaust gas purifying performance and capable of sufficiently purifying NOx in exhaust gas in a low temperature range even after sulfur poisoning and its It is possible to provide an exhaust gas purification method using a catalyst.

  Therefore, the exhaust gas purifying catalyst of the present invention is particularly useful as a catalyst for purifying gas discharged from an internal combustion engine of an automobile because it has excellent NOx purification performance.

Claims (5)

A first noble metal supported on the first porous carrier, wherein the first noble metal contains at least Pt, and the content of the Pt in the first noble metal is that of the first noble metal. A first catalyst powder that exceeds 50% by mass with respect to the total amount, and the amount of NOx occlusion material supported is 0.03 mol or less with respect to 100 g of the first porous carrier;
A second noble metal supported on the second porous carrier, wherein the second noble metal contains at least Rh, and the content of Rh in the second noble metal is that of the second noble metal. A second catalyst powder that exceeds 50% by mass with respect to the total amount, and the amount of NOx occlusion material supported is 0.03 mol or less with respect to 100 g of the second porous carrier;
A third porous support; a third noble metal supported on the third porous support; and a NOx occlusion material supported on the third porous support, wherein the third noble metal contains at least Pd, A third catalyst having a loading amount of 0.05 g or more with respect to 100 g of the third porous carrier and a loading amount of the NOx storage material exceeding 0.03 mol with respect to 100 g of the third porous carrier. Powder,
An exhaust gas purifying catalyst comprising:   The content of the first catalyst powder is 5 to 60% by mass with respect to the total amount of the first to third catalyst powders, and the content of the second catalyst powder is the total amount of the first to third catalyst powders. The content of the third catalyst powder is 5 to 40% by mass with respect to the total amount of the first to third catalyst powders, and is 30 to 90% by mass. The catalyst for exhaust gas purification as described. The following conditions (A) to (C):
(A) The first to third catalyst powders are arranged so that the exhaust gas contacts the second catalyst powder and the third catalyst powder after the exhaust gas contacts the first catalyst powder.
(B) The first to third catalyst powders are disposed so that the exhaust gas contacts the first catalyst powder, the second catalyst powder, and the third catalyst powder in this order,
(C) The first to third catalyst powders are arranged so that the exhaust gas contacts the first catalyst powder, the third catalyst powder, and the second catalyst powder in this order.
The exhaust gas-purifying catalyst according to claim 1 or 2, wherein any one of the conditions is satisfied.   A catalyst base; a first catalyst layer comprising the first catalyst powder; a second catalyst layer comprising the second catalyst powder and the third catalyst powder; and the first to second catalyst layers comprising: 4. It arrange | positions on the said catalyst base material so that exhaust gas may contact the said 2nd catalyst layer, after exhaust gas contacts the said 1st catalyst layer, Any one of Claims 1-3 characterized by the above-mentioned. The exhaust gas-purifying catalyst according to Item.   An exhaust gas purification method comprising purifying exhaust gas by bringing the exhaust gas into contact with the exhaust gas purification catalyst according to any one of claims 1 to 4.

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