JP2013031849A - Exhaust gas cleaning catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust gas cleaning catalyst which has high oxidation performance and NOx storage/reduction performance.SOLUTION: The exhaust gas cleaning catalyst has: a filter catalyst carrier having wall-flow gas circulation cells; an oxidation catalyst part having a first carried layer part comprising a first inorganic oxide carried on the carrier and a first catalytic metal carried on the first carried layer part; and a NOx storage/reduction part having a second carried layer part comprising a second inorganic oxide provided on the carrier, a second catalytic metal carried on the second carried layer part, and a NOx storage/reduction material carried on the second carried layer part. That the exhaust gas cleaning catalyst has the oxidation catalyst part and the NOx storage/reduction part on a three-dimensional structure makes a catalyst having high oxidation performance and NOx storage/reduction performance.

Description

  The present invention relates to an exhaust gas purification catalyst, and more particularly to an exhaust gas purification catalyst having high NOx storage reduction performance.

  Exhaust gas discharged from an internal combustion engine such as an automobile engine contains harmful components such as hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxide (NOx). If the exhaust gas containing this harmful component is discharged into the atmosphere as it is, the occurrence of pollution and environmental degradation will occur. For this reason, the exhaust gas containing these components is discharged into the atmosphere after the harmful components are purified by purification means such as an exhaust gas purification catalyst.

  In addition, with increasing interest in the global environment, particularly in automobiles, low fuel consumption and low pollution are required. As a vehicle engine that satisfies this requirement, a lean burn engine or a diesel engine is being used.

  Since lean burn engines and diesel engines burn in an oxygen-excess atmosphere, they emit a large amount of NOx. For this reason, the exhaust gas purification catalyst for purifying the exhaust gas of these engines is an occlusion reduction type catalyst in which a NOx occlusion reduction material made of an element of alkali metal or alkaline earth metal is added to an ordinary exhaust gas purification catalyst. It is used.

  However, it is known that alkali metal and alkaline earth metal elements have an action of significantly reducing the oxidation function of catalytic metal having catalytic action. For this reason, by adding the NOx occlusion reduction material, the occlusion reduction type catalyst has a problem that the oxidation performance of the catalyst metal is lowered.

  This invention is made | formed in view of the said situation, and makes it a subject to provide the catalyst for exhaust gas purification | cleaning which has high oxidation performance and NOx occlusion reduction performance.

  That is, the exhaust gas purifying catalyst of the present invention includes a filter catalyst carrier having a wall flow gas flow cell, a first carrier layer portion made of a first inorganic oxide provided on the carrier, and a first carrier layer portion. A first catalyst metal supported on the substrate, an oxidation catalyst portion having a second support layer portion made of a second inorganic oxide provided on the support, and a second catalyst metal supported on the second support layer portion. And a NOx occlusion / reduction part having a NOx occlusion / reduction material carried on the second carrying layer part.

  The exhaust gas purifying catalyst of the present invention has the oxidation catalyst part and the NOx occlusion reduction part on the carrier, so that the first catalyst metal of the oxidation catalyst part and the NOx occlusion reduction material of the NOx occlusion reduction part are not in contact with each other, The first catalytic metal no longer deteriorates the oxidation function. That is, in the exhaust gas purifying catalyst of the present invention, the oxidation catalyst part oxidizes and purifies the exhaust gas, and the NOx occlusion reduction part purifies NOx by occlusion reduction. As a result, the exhaust gas purifying catalyst of the present invention is a catalyst having high oxidation performance and NOx storage reduction performance.

  The exhaust gas purifying catalyst of the present invention has a carrier, an oxidation catalyst part, and a NOx occlusion reduction part.

  The carrier is a carrier of a filter catalyst having a wall flow gas flow cell. This carrier has fire resistance and is a member on which an oxidation catalyst portion and a NOx occlusion reduction portion are formed. That is, the support retains the catalyst component on the surface. Moreover, since the carrier has fire resistance, high-temperature exhaust gas can be purified.

  The oxidation catalyst part has a first support layer part made of a first inorganic oxide provided on a support and a first catalyst metal supported on the first support layer part. That is, since the oxidation catalyst part has the first support layer part and the first catalyst metal, the exhaust gas purifying catalyst of the present invention can oxidize and purify the exhaust gas.

  The NOx occlusion reduction part is supported on the second support layer part made of the second inorganic oxide provided on the carrier, the second catalyst metal supported on the second support layer part, and the second support layer part. NOx occlusion reduction material. That is, the NOx occlusion reduction part has the second support layer part, the second catalyst metal, and the NOx occlusion reduction material, so that the exhaust gas purification catalyst of the present invention occludes and reduces NOx in the exhaust gas. Can do.

  The exhaust gas purifying catalyst of the present invention is an exhaust gas purifying catalyst having a high NOx occlusion reduction performance without impairing the oxidation function by having an oxidation catalyst part and a NOx occlusion reduction part. Specifically, since the oxidation catalyst unit oxidizes and purifies harmful components in the exhaust gas, and the NOx storage and reduction unit reduces and purifies the NOx component, the exhaust gas purification catalyst of the present invention has a high NOx occlusion without impairing the oxidation performance It is an exhaust gas purifying catalyst having reducing performance.

  It is preferable that the oxidation catalyst portion and the NOx occlusion reduction portion are provided in a state where they are aligned in the flow direction of the exhaust gas on the carrier. That is, since the oxidation catalyst part and the NOx occlusion reduction part are arranged side by side, the oxidation catalyst part and the NOx occlusion reduction part are not mixed, so the catalytic performance of the first catalyst metal by the NOx occlusion reduction material is improved. The decline is suppressed.

  In addition, since the oxidation catalyst unit and the NOx occlusion reduction unit are provided in a state where they are aligned along the flow direction of the exhaust gas, the exhaust gas purified by the NOx occlusion reduction unit or the oxidation catalyst unit is stored in the oxidation catalyst unit or the NOx occlusion unit. Purified by the reduction unit. For this reason, high NOx occlusion reduction performance can be exhibited without impairing oxidation performance.

  The oxidation catalyst part and the NOx occlusion reduction part may be in a state where they are aligned in the flow direction of the exhaust gas, and the relative positions are not particularly limited. Specifically, when the oxidation catalyst part and the NOx occlusion reduction part are provided on the carrier in a state where they are aligned in the exhaust gas flow direction, either the oxidation catalyst part or the NOx occlusion reduction part is provided upstream. Also good.

  It is preferable that the oxidation catalyst part is provided on the upstream side in the flow direction of the exhaust gas. That is, it is preferable that the oxidation catalyst unit and the NOx occlusion reduction unit are arranged along the flow direction of the exhaust gas.

  Furthermore, the oxidation catalyst part and the NOx occlusion reduction part arranged in a state of being aligned along the flow direction of the exhaust gas may each be a plurality of parts. That is, the oxidation catalyst part and the NOx storage reduction part may be provided alternately.

  In the exhaust gas purifying catalyst of the present invention, the oxidation catalyst part and the NOx occlusion / reduction part may be provided on the same carrier or on different carriers.

  It is preferable that the oxidation catalyst part and the NOx occlusion / reduction part are provided on the carrier. That is, since the oxidation catalyst part and the NOx occlusion reduction part are provided in a stacked manner, the oxidation catalyst part and the NOx occlusion reduction part do not coexist. It has been.

  Further, since the oxidation catalyst unit and the NOx occlusion reduction unit are provided on the carrier, the exhaust gas purified by the NOx occlusion reduction unit or the oxidation catalyst unit is purified by the oxidation catalyst unit or the NOx occlusion reduction unit. The For this reason, high NOx occlusion reduction performance can be exhibited without impairing oxidation performance.

  The oxidation catalyst part and the NOx occlusion / reduction part are only required to be laminated on the carrier, and the relative positions are not particularly limited. Specifically, when the oxidation catalyst part and the NOx occlusion reduction part are provided on the carrier, either the oxidation catalyst part or the NOx occlusion reduction part may be provided in the upper layer.

Furthermore, the oxidation catalyst part and the NOx occlusion / reduction part provided by stacking on the carrier may each be a plurality of parts. That is, the oxidation catalyst part and the NOx occlusion reduction part may be alternately stacked on the carrier.
As described above, in the exhaust gas purifying catalyst of the present invention, the oxidation catalyst part and the NOx occlusion reduction part may be stacked while being aligned in the flow direction of the exhaust gas.

  The first inorganic oxide and the first catalyst metal constituting the oxidation catalyst part are not particularly limited, and materials used for conventional exhaust gas purification catalysts can be used.

  The first inorganic oxide is preferably made of at least one of alumina, silica, titania, zirconia, ceria, and zeolite. When the first inorganic oxide is composed of at least one of these, a support layer having excellent heat resistance and a large specific surface area is formed.

  The first catalytic metal is preferably made of at least one of Pt, Pd, Rh, Ag, Au, and Ir. That is, when the first catalyst metal is made of at least one of these, the oxidation catalyst part can purify the exhaust gas.

  The second inorganic oxide, the NOx occlusion reduction material, and the second catalyst metal constituting the NOx occlusion reduction part are not particularly limited, and the materials used in the conventional NOx occlusion reduction exhaust gas purification catalyst are used. be able to.

  The second inorganic oxide is preferably made of at least one of alumina, silica, titania, zirconia, ceria, and zeolite. When the second inorganic oxide is composed of at least one of these, a support layer having excellent heat resistance and a large specific surface area is formed.

  The second catalytic metal is preferably made of at least one of Pt, Pd, Rh, Ag, Au, and Ir. That is, when the second catalyst metal is made of at least one of these, the NOx occlusion reduction unit can purify the exhaust gas.

  The NOx occlusion / reduction material is preferably made of at least one selected from alkali metals and alkaline earth metals. That is, the NOx occlusion reduction material is made of at least one of these, so that the NOx occlusion reduction unit can occlude NOx.

  The first inorganic oxide and the second inorganic oxide may be either the same kind of inorganic oxide or different kinds of inorganic oxides. Since the kind of material does not increase, it is preferable that it is the same kind of inorganic oxide. Furthermore, when the same kind of inorganic oxide is used, depending on the arrangement of the oxidation catalyst part and the NOx occlusion reduction part, the first support layer and the second support layer can be formed at the same time, thereby suppressing an increase in manufacturing cost. Can do.

  The first catalyst metal and the second catalyst metal may be either the same metal or different metals. Since the kind of material does not increase, the same kind of catalyst metal is preferable. Furthermore, if the same type of catalyst metal is used, depending on the arrangement of the oxidation catalyst part and the NOx occlusion reduction part, the first catalyst metal and the second catalyst metal can be supported simultaneously, thereby suppressing an increase in manufacturing cost. Can do.

  The support may be an open flow honeycomb or a wall flow DPF, but in the present invention, it is a filter catalyst support having a wall flow gas flow cell.

  The carrier can be made of ceramics or metal, but is preferably made of ceramics in the present invention. Examples of the ceramic or metal that can form the carrier include cordierite, silicon carbide (SiC), stainless steel, and ceramic fibers.

  The amounts of the first and second inorganic oxides supported on the first support layer and the second support layer provided on the support are not particularly limited. That is, it suffices if the catalyst metal and the occlusion reduction component to be supported on each support layer can be supported.

  The amount of the first catalyst metal supported on the first support layer is preferably 0.01 to 10 wt% when the entire first support layer is 100 wt%. That is, the exhaust gas is sufficiently purified by the first support layer portion having the first catalyst metal at 0.01 to 10 wt%. If the first catalyst metal is less than 0.01 wt%, the amount of the first catalyst metal is small and the exhaust gas purification is insufficient. Moreover, when the first catalyst metal exceeds 10 wt%, the improvement in the effect of exhaust gas purification with respect to an increase in the amount of catalyst metal supported becomes small. More preferably, it is the range of 0.1-5 wt%.

  It is preferable that the amount of the NOx occlusion / reduction material supported on the second supporting layer portion is 0.5 to 30 wt% when the entire second supporting layer portion is 100 wt%. That is, the NOx occlusion reduction part can reduce and purify NOx because the second support layer part has the NOx occlusion reduction material at 0.5 to 30 wt%. If the NOx storage / reduction material is less than 0.5 wt%, the amount of NOx storage / reduction material is small, and the purification of NOx in the exhaust gas becomes insufficient. Further, when the NOx storage / reduction material exceeds 30 wt%, the improvement in the effect of NOx purification with respect to the increase in the amount of the NOx storage / reduction material carried becomes small. More preferably, it is the range of 1-20 wt%.

  Moreover, it is preferable that the load of the 2nd catalyst metal to the 2nd support layer part is 0.1-10 wt%, when the 2nd support layer part whole is 100 wt%. That is, the NOx purification is sufficiently performed when the second supporting layer portion has the second catalytic metal at 0.1 to 10 wt%. If the second catalyst metal is less than 0.1 wt%, the amount of the second catalyst metal is small and the purification of NOx in the exhaust gas is insufficient. On the other hand, when the amount of the second catalyst metal exceeds 10 wt%, the improvement in the NOx purification effect with respect to an increase in the amount of the catalyst metal supported becomes small. More preferably, it is the range of 1-5 wt%.

The ratio of the oxidation catalyst part and the NOx occlusion reduction part is not particularly limited, and can be appropriately determined depending on the components of the exhaust gas to be purified. Further, it can be determined appropriately depending on the amount of catalyst metal and NOx occlusion / reduction material supported on each.
The exhaust gas purifying catalyst of the present invention is not particularly limited as long as it has a carrier, an oxidation catalyst part, and a NOx occlusion reduction part.

  The exhaust gas purifying catalyst of the present invention has the oxidation catalyst part and the NOx occlusion reduction part on the carrier, so that the first catalyst metal of the oxidation catalyst part and the NOx occlusion reduction material of the NOx occlusion reduction part are not in contact with each other, The first catalytic metal no longer deteriorates the oxidation function. That is, in the exhaust gas purifying catalyst of the present invention, the oxidation catalyst part oxidizes and purifies the exhaust gas, and the NOx occlusion reduction part purifies NOx by occlusion reduction. As a result, the exhaust gas purifying catalyst of the present invention is a catalyst having high oxidation performance and NOx storage reduction performance.

Hereinafter, the present invention will be described using examples.
As an example, an exhaust gas purification catalyst was manufactured.

Example 1
First, 100 parts by weight of alumina powder was dispersed in 140 parts by weight of deionized water, then 3 parts by weight of alumina sol in terms of alumina was added, and wet pulverized to prepare an alumina slurry.

The prepared alumina slurry has a cylindrical shape of 12.9 cm in diameter and 15.0 cm in length in the axial direction having a wall flow gas flow cell having 47 cells / cm ² (about 300 cells / inch ² ). And then dried at 250 ° C. for 1 hour, and then fired at 500 ° C. for 1 hour to obtain an alumina-coated cordierite DPF.
The amount of alumina in the obtained alumina-coated cordierite DPF was 100 g per liter of the refractory three-dimensional structure.

  The obtained alumina-coated cordierite DPF is impregnated with a platinum nitrate aqueous solution, dried at 250 ° C. for 1 hour, then impregnated with an aqueous rhodium nitrate solution, and dried at 250 ° C. for 1 hour. Obtained. The amount of catalyst noble metal supported on the catalyst precious metal-supported alumina-coated cordierite DPF was 5 g of platinum and 0.1 g of rhodium per liter of the DPF carrier.

  After the catalytic noble metal-supported alumina-coated cordierite DPF was immersed in deionized water, suction was performed to determine the amount of water absorption per catalyst noble metal-supporting alumina-coated cordierite DPF. Note that the catalyst noble metal supported on the catalyst noble metal-supported alumina coated cordierite DPF is not dissolved in the deionized water because it is fired even when immersed in the deionized water. In addition, the amount of water absorption is measured in advance by measuring the weight of the catalyst-noble metal-supported alumina-coated cordierite DPF, and measuring the weight after soaking in deionized water, and the difference in weight between the two. The amount of water absorption was obtained.

Barium acetate and lithium nitrate were dissolved in deionized water that was half the amount of water absorption obtained, and the catalyst-noble metal-supported alumina-coated cordierite DPF was immersed in the solution only from one end face. At this time, the solution was immersed in a portion from one end face to ½ of the axial length of the DPF carrier. Then, the catalyst for gas purification of Example 1 was obtained by drying at 250 degreeC for 1 hour, and baking at 500 degreeC for 1 hour. The amount of NOx occlusion material in the exhaust gas purifying catalyst of Example 1 was 13.5 g of barium and 1.4 g of lithium per three-dimensional structure.
In the exhaust gas purifying catalyst of this example, the part where barium and lithium are supported is the NOx occlusion reduction part, and the part not supported is the oxidation catalyst part.

  Specifically, the exhaust gas purifying catalyst of the present example is a cordierite DPF carrier, an alumina coat layer portion provided on the DPF carrier, and an oxidation catalyst portion supported on platinum and rhodium supported on the alumina coat layer portion. And an alumina coat layer portion provided on the DPF carrier, platinum and rhodium supported on the alumina coat layer portion, and a NOx occlusion reduction portion having barium and lithium supported on the alumina coat layer portion. It is a catalyst.

(Example 2)
The exhaust gas purifying catalyst of Example 2 is the same exhaust gas purifying catalyst as that of Example 1 except that the supporting layer is formed of titania and the NOx occlusion reduction unit further supports potassium.
First, 100 parts by weight of titania was dispersed in 67 parts by weight of deionized water, and further 83 parts by weight of titania sol was added and wet pulverized to prepare a titania slurry.

The prepared titania slurry was applied to the same cordierite DPF carrier as in Example 1, dried at 250 ° C. for 1 hour, and then fired at 500 ° C. for 1 hour to obtain a titania-coated cordierite DPF.
The titania amount of the obtained titania-coated cordierite DPF was 100 g per liter of the fire-resistant three-dimensional structure.

  The obtained titania-coated cordierite DPF was impregnated with an aqueous platinum nitrate solution, dried at 250 ° C. for 1 hour, then impregnated with an aqueous rhodium nitrate solution, and dried at 250 ° C. for 1 hour. Obtained.

  The amount of catalyst noble metal supported on the obtained catalyst noble metal-supported titania-coated cordierite DPF was 5 g of platinum and 0.1 g of rhodium per liter of DPF carrier.

  The obtained catalyst noble metal-supported titania-coated cordierite DPF was immersed in deionized water and then suctioned to determine the amount of water absorbed per catalyst noble metal-supported titania-coated cordierite DPF.

Barium acetate, lithium nitrate, and potassium acetate were dissolved in deionized water that was half the water absorption obtained, and the catalyst noble metal-supported titania-coated cordierite DPF was immersed in the solution only from one end face. At this time, the solution was immersed in a portion from one end face to ½ of the axial length of the DPF carrier. Then, it was dried at 250 ° C. for 1 hour and then calcined at 500 ° C. for 1 hour to obtain an exhaust gas purifying catalyst of this example.
The amount of NOx occlusion material in the exhaust gas purifying catalyst of this example was 13.5 g of barium, 1.4 g of lithium, and 3.8 g of potassium per one three-dimensional structure.

(Example 3)
The exhaust gas purifying catalyst of Example 3 is the same exhaust gas purifying catalyst as that of Example 2 except that the support layer is formed of zeolite made of H-type mordenite.

  In this example, 100 parts by weight of zeolite made of H-type mordenite is dispersed in 87 parts by weight of deionized water, 63 parts by weight of silica sol is further added, and wet pulverization is performed to change the zeolite slurry to titania slurry. The exhaust gas purifying catalyst.

  In the exhaust gas purifying catalyst of this example, the amount of zeolite was 100 g per liter of DPF carrier, and the amount of catalyst noble metal was 5 g of platinum and 0.1 g of rhodium per liter of DPF carrier. The amount of NOx occlusion material was 13.5 g of barium, 1.4 g of lithium, and 3.8 g of potassium per DPF carrier.

(Reference Example 1)
The exhaust gas purifying catalyst of Reference Example 1 has a 12.9 cm diameter × 15.0 cm length having an open-flow gas flow cell with 62 cells / cm ² (400 cells / inch ² ) instead of the DPF carrier. The same exhaust gas purifying catalyst as that of Example 1 except that a cylindrical cordierite honeycomb carrier was used and potassium was further supported on the NOx occlusion reduction unit.
Further, the exhaust gas-purifying catalyst of this example was produced in the same manner as in the production methods of Examples 1 and 2.

  The amount of alumina in the exhaust gas purifying catalyst of this example was 100 g per liter of the honeycomb carrier, and the amount of catalyst noble metal was 5 g of platinum and 0.1 g of rhodium per liter of the honeycomb carrier. Further, the amount of NOx occlusion material was 13.5 g of barium, 1.4 g of lithium, and 3.8 g of potassium per honeycomb carrier.

Example 4
First, 29.5 parts by weight of barium acetate was dissolved in 200 parts by weight of deionized water, 100 parts by weight of alumina powder was added to this solution, stirred for 1 hour, dried at 250 ° C. for 12 hours, and 1 at 500 ° C. Barium-supported alumina powder was prepared by firing for a period of time.

  100 parts by weight of this barium-supported alumina powder is dispersed in 140 parts by weight of deionized water, then 19 parts by weight of aluminum nitrate nonahydrate and 3 parts by weight of alumina hydrate made of Condia are added, and wet milled to produce barium alumina. A slurry was prepared.

The obtained barium alumina slurry was formed into a cylindrical cordierite having a wall flow diameter of 12.9 cm and an axial length of 15.0 cm with 47 cells / cm ² (about 300 cells / inch ² ). It was applied to a DPF carrier, dried at 250 ° C. for 1 hour, and then fired at 500 ° C. for 1 hour to obtain a barium alumina coated cordierite DPF.
The amount of barium alumina in the obtained barium alumina coated cordierite DPF was 50 g per liter of DPF carrier.

  Subsequently, 100 parts by weight of alumina powder was dispersed in 140 parts by weight of deionized water, then 3 parts by weight of alumina sol in terms of alumina was added, and wet pulverized to prepare an alumina slurry.

  The prepared alumina slurry was applied to a barium alumina coated cordierite DPF to obtain a multilayer alumina coated cordierite DPF. Here, the amount of alumina provided in the upper layer was 50 g per liter of DPF carrier.

  Thereafter, a multilayer alumina-coated cordierite DPF is impregnated with an aqueous platinum nitrate solution, dried at 250 ° C. for 1 hour, then impregnated with an aqueous rhodium nitrate solution, and dried at 250 ° C. for 1 hour to obtain an exhaust gas purifying catalyst of Example 5. It was. The amount of catalyst noble metal in the exhaust gas purifying catalyst of this example was 5 g of platinum and 0.1 g of rhodium per liter of DPF carrier.

(Reference Example 2)
The exhaust gas purifying catalyst of Reference Example 2 is an exhaust gas purifying catalyst in which the oxidation catalyst portion and the NOx occlusion reduction portion are provided on different carriers.

Specifically, the exhaust gas purifying catalyst of Example 6 has a cylindrical shape with a cell count of 62 cells / cm ² (about 400 cells / inch ² ), a diameter of 12.9 cm, and an axial length of 7.5 cm. An oxidation catalyst in which only the oxidation catalyst portion is formed on the honeycomb structure, a cell number of 47 cells / cm ² (about 300 cells / inch ² ), a diameter of 12.9 cm, and an axial length of 7.5 cm NOx storage-reduction catalyst, in which only the NOx storage-reduction part is formed on the cylindrical honeycomb structure, and the oxidation catalyst part and the NOx storage-reduction part are respectively the oxidation catalyst part and the NOx storage-reduction part of Example 1. It is the same catalyst.

More specifically, the exhaust gas purifying catalyst of this example has an alumina catalyst coated on the surface of a honeycomb structure having 62 cells / cm ² , and an oxidation catalyst in which a catalyst noble metal is supported on the alumina, and the number of cells. The surface of a 62 / cm ² honeycomb structure is coated with alumina, and this alumina comprises a NOx occlusion reduction catalyst in which a catalytic noble metal, barium, and lithium are supported.
This oxidation catalyst and NOx occlusion reduction catalyst were produced by the same method as the production method of the oxidation catalyst part and NOx occlusion reduction part of Example 1.
The exhaust gas purifying catalyst of this example is used by being held in the same container in a state where the oxidation catalyst is arranged in the front stage and the NOx storage reduction catalyst is arranged in the vicinity of the rear stage.

  In the exhaust gas purifying catalyst of this example, the oxidation reaction is formed on a high-density carrier, so that the catalytic reaction in the NOx occlusion reduction catalyst disposed in the latter stage is promoted. That is, since the catalytic reaction in the oxidation catalyst is an exothermic reaction, heat is generated when the exhaust gas is purified by the high-density oxidation catalyst. The heat generated in the oxidation catalyst is conducted to the NOx storage reduction catalyst located in the subsequent stage, and this heat promotes the catalytic reaction in the NOx storage reduction catalyst.

(Comparative example)
The comparative example is an exhaust gas purifying catalyst that is supported in a state where a conventional NOx occlusion reduction material is mixed with a catalyst metal.

  First, 100 parts by weight of alumina powder was dispersed in 140 parts by weight of deionized water, then 19 parts by weight of aluminum nitrate nonahydrate and 3 parts by weight of alumina hydrate were added and wet pulverized to prepare an alumina slurry.

The obtained alumina slurry was formed into a cylindrical cordierite having a wall flow diameter of 12.9 cm and an axial length of 15.0 cm with a cell number of 47 cells / cm ² (about 300 cells / inch ² ). This was coated on a DPF carrier, dried at 250 ° C. for 1 hour, and then fired at 500 ° C. for 1 hour to obtain an alumina-coated cordierite DPF. Here, the amount of alumina supported on the alumina-coated cordierite DPF was 50 g per liter of the DPF carrier.

  Alumina-coated cordierite DPF was impregnated with an aqueous platinum nitrate solution, dried at 250 ° C. for 1 hour, then impregnated with an aqueous rhodium nitrate solution, and dried at 250 ° C. for 1 hour to obtain an alumina-coated cordierite DPF carrying a catalyst noble metal. . The catalyst noble metal amount of the noble metal-supported alumina-coated cordierite DPF was 5 g of platinum and 0.1 g of rhodium per liter of the DPF carrier.

  After the catalyst noble metal-supported alumina-coated cordierite DPF was immersed in deionized water, suction was performed to determine the amount of water absorption per noble metal-supported alumina-coated cordierite DPF.

  Barium acetate, lithium nitrate, and potassium nitrate were dissolved in deionized water having the obtained water absorption amount, and noble metal-supported alumina-coated cordierite DPF was immersed in the solution. This immersion was performed by immersing the solution from the both end faces of the noble metal-supported alumina-coated cordierite DPF. Then, it was dried at 250 ° C. for 1 hour and then calcined at 500 ° C. for 1 hour to obtain an exhaust gas purifying catalyst of a comparative example. The amount of NOx occlusion material of the exhaust gas purifying catalyst of the comparative example was 26.9 g of barium, 2.7 g of lithium, and 7.7 g of potassium per DPF carrier.

(Evaluation)
As an evaluation of the catalyst of each example, each reference example and comparative example, the purification performance was measured by actually purifying exhaust gas from a diesel engine.

  The purification performance was evaluated in a state where each catalyst was made durable (deteriorated). This durability (deterioration) was achieved by baking at 650 ° C. for 50 hours using an oven.

When a direct injection type diesel engine with a supercharger (4 cylinders, 2000 cc) is used, the diesel engine is operated under an operating condition in which the catalyst bed temperature is raised from 100 ° C. to 450 ° C., and the catalyst bed temperature is 300 ° C. The concentration of hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxide (NOx) was measured to determine the purification rate. In the multistage exhaust gas purification catalysts of Examples 1 to 4 (and Reference Examples 1 and 2), the exhaust gas was purified with the oxidation catalyst portion positioned upstream of the exhaust gas flow. Moreover, the measurement of the density | concentration of each component was performed using the Horiba Seisakusho gas analyzer (MEXA9100). The diesel engine was operated by keeping the rotation speed constant at 2100 rpm and changing the load (torque) so that the catalyst temperature rises to 100 to 450 ° C. Here, since the catalyst of Reference Example 1 has a structure in which two honeycomb carriers are arranged close to each other in the same container, the catalyst bed temperatures of the two catalyst portions are almost the same. From this, the catalyst bed temperature of one honeycomb carrier catalyst was used as the catalyst bed temperature of Example 6.
The purification rate was measured by measuring the gas concentration at both ends of the inlet and outlet of the catalyst and calculating the purification rate from the gas concentration based on the gas concentration.

  In addition, the particulate matter (PM) concentration discharged in this test was measured by a small tunnel dilution sampling method. Moreover, the purification rate of the particulate matter was calculated from this measured value. Table 1 shows the measurement results of the respective purification rates.

In Table 1, the purification rates of HC, CO and NOx are
Purification rate (%) = {(Enter gas component concentration (%)) − (Outlet gas component concentration (%))} × 100 / (Enter gas component concentration (%))
The PM purification rate is
Purification rate (%) = {(Entering gas PM mass (mg)) − (Outgoing gas PM mass (mg))} × 100 / (Entering gas PM mass (mg))
Respectively.

  From Table 1, the exhaust gas purification catalysts of Examples 1 to 4 (and Reference Examples 1 to 2) have higher purification rates of HC, CO, and NOx than the exhaust gas purification catalysts of Comparative Examples. Yes. That is, in the exhaust gas purifying catalysts of Examples 1 to 4, since the oxidation catalyst part and the NOx occlusion reduction part are separated, the catalytic noble metal supported on the oxidation catalyst part is oxidized by the NOx occlusion reduction material. Therefore, the exhaust gas purification catalyst has a high NOx occlusion reduction performance without impairing the oxidation performance.

Claims (9)

A filter catalyst carrier having a wall flow gas flow cell;
An oxidation catalyst portion having a first support layer portion made of a first inorganic oxide provided on the support, and a first catalyst metal supported on the first support layer portion;
A second supported layer portion made of a second inorganic oxide provided on the carrier; a second catalyst metal supported on the second supported layer portion; and NOx occlusion reduction supported on the second supported layer portion. A NOx occlusion reduction part having a material,
An exhaust gas purifying catalyst characterized by comprising:   The exhaust gas purifying catalyst according to claim 1, wherein the oxidation catalyst part and the NOx occlusion reduction part are provided in a state where the oxidation catalyst part and the NOx occlusion reduction part are arranged in a flow direction of the exhaust gas on the carrier.   The exhaust gas purifying catalyst according to any one of claims 1 and 2, wherein the oxidation catalyst part is provided upstream in a flow direction of the exhaust gas.   The exhaust gas purifying catalyst according to any one of claims 1 to 3, wherein the first inorganic oxide comprises at least one of alumina, silica, titania, zirconia, ceria, and zeolite.   The exhaust gas purifying catalyst according to any one of claims 1 to 4, wherein the first catalyst metal is made of at least one of Pt, Pd, Rh, Ag, Au, and Ir.   The exhaust gas purifying catalyst according to any one of claims 1 to 5, wherein the second inorganic oxide comprises at least one of alumina, silica, titania, zirconia, ceria, and zeolite.   The exhaust gas purifying catalyst according to any one of claims 1 to 6, wherein the second catalytic metal is made of at least one of Pt, Pd, Rh, Ag, Au, and Ir.   The exhaust gas purification catalyst according to any one of claims 1 to 7, wherein the NOx occlusion reduction material is made of at least one selected from alkali metals and alkaline earth metals.   The exhaust gas purifying catalyst according to any one of claims 1 to 8, wherein the carrier is made of ceramics.