阅读说明：本技术 含有磷化合物的废气净化用催化剂 (Catalyst for purifying exhaust gas containing phosphorus compound ) 是由 久野弘尊 中岛优 中间公博 于 2018-12-26 设计创作，主要内容包括：本发明涉及含有磷化合物的废气净化用催化剂,其具有：耐火性三维结构体(其沿着从气体流入侧端面至气体流出侧端面延伸地设置,并且具有划分形成从气体流入侧端面到气体流出侧端面贯通的多个气体流路的分隔壁),在分隔壁上从气体流入侧端面连续地形成的含Pd的下催化剂层,位于分隔壁上的最外表面、从气体流入侧端面连续地形成的含Rh的气体流入侧上催化剂层,以及,位于分隔壁上的最外表面、从气体流出侧端面连续地形成的含Rh的气体流出侧上催化剂层；其中,气体流入侧上催化剂层和气体流出侧上催化剂层以沿着气体流路方向相互间隔的方式配置,沿着气体流路方向的下催化剂层的长度为15mm以上,相对于气体流路的总长,该长度的比例为18％以上且小于100％。(The present invention relates to a catalyst for exhaust gas purification containing a phosphorus compound, which comprises: a refractory three-dimensional structure (which is provided so as to extend along a surface from a gas-inflow-side end to a gas-outflow-side end, and which has a partition wall defining a plurality of gas flow paths that penetrate from the gas-inflow-side end to the gas-outflow-side end, a Pd-containing lower catalyst layer formed continuously on the partition wall from the gas-inflow-side end, an Rh-containing gas-inflow-side upper catalyst layer formed continuously from the gas-inflow-side end on an outermost surface of the partition wall, and an Rh-containing gas-outflow-side upper catalyst layer formed continuously from the gas-outflow-side end on an outermost surface of the partition wall; wherein the gas inflow side upper catalyst layer and the gas outflow side upper catalyst layer are arranged so as to be spaced apart from each other along the gas flow path direction, the length of the lower catalyst layer along the gas flow path direction is 15mm or more, and the ratio of the length to the total length of the gas flow path is 18% or more and less than 100%.)

1. A catalyst for purifying exhaust gas containing a phosphorus compound, comprising:

a fire-resistant three-dimensional structure which is provided so as to extend along a direction from a gas inflow end surface to a gas outflow end surface, and which has a partition wall that partitions and forms a plurality of gas flow paths that penetrate from the gas inflow end surface to the gas outflow end surface,

a Pd-containing lower catalyst layer formed continuously from the gas-inflow-side end face on the partition wall,

an Rh-containing gas inflow side upper catalyst layer located on an outermost surface of the partition wall and formed continuously from the gas inflow side end face, and

an Rh-containing gas outflow side upper catalyst layer located on an outermost surface of the partition wall and formed continuously from the gas outflow side end face;

wherein the content of the first and second substances,

the gas inflow side upper catalyst layer and the gas outflow side upper catalyst layer are arranged at intervals from each other along a gas flow path direction,

the length of the lower catalyst layer along the gas flow path direction is 15mm or more, and the ratio of the length to the total length of the gas flow path is 18% or more and less than 100%.

2. The catalyst for purification of exhaust gas containing a phosphorus compound according to claim 1, wherein the sum of the thicknesses of the catalyst layers at the gas-inflow-side end portion of the catalyst layer on the gas-outflow-side is larger than the sum of the thicknesses of the catalyst layers at the gas-outflow-side end portion of the catalyst layer on the gas-outflow-side.

3. The exhaust gas purifying catalyst containing a phosphorus compound according to claim 1 or 2, wherein a distance between the catalyst layer on the gas inflow side and the catalyst layer on the gas outflow side is 5mm or more and 30mm or less.

4. The catalyst for purification of exhaust gas containing a phosphorus compound according to any one of claims 1 to 3, wherein the length of the catalyst layer on the gas inflow side in the gas flow path direction is 10mm or more, and the ratio of the length to the total length of the gas flow path is 12% or more and 57% or less.

5. The catalyst for purification of exhaust gas containing a phosphorus compound according to any one of claims 1 to 4, wherein the length of the catalyst layer on the gas outflow side in the gas flow path direction is 25mm or more, and the ratio of the length to the total length of the gas flow path is 31% or more and less than 88%.

6. The catalyst for purifying exhaust gas containing a phosphorus compound according to any one of claims 1 to 5, wherein the length of the catalyst layer on the gas inflow side in the gas flow path direction is equal to or less than the length of the lower catalyst layer.

7. The exhaust gas purifying catalyst containing a phosphorus compound according to any one of claims 1 to 6, wherein the Rh concentration of the catalyst layer on the gas inflow side is higher than the Rh concentration of the catalyst layer on the gas outflow side.

8. The exhaust gas purifying catalyst containing a phosphorus compound according to any one of claims 1 to 7, wherein the lower catalyst layer has a lower Rh concentration than that of the upper catalyst layer on the gas outflow side.

9. The exhaust gas purifying catalyst containing a phosphorus compound according to any one of claims 1 to 8, wherein at least one of the lower catalyst layer, the catalyst layer on the gas inflow side, and the catalyst layer on the gas outflow side contains CeO₂And ZrO₂The composite oxide of (3).

10. The exhaust gas-purifying catalyst containing a phosphorus compound according to any one of claims 1 to 9, wherein the refractory three-dimensional structure has a length in the gas flow path direction of more than 15mm and 1000mm or less.

11. The method for producing the catalyst for purification of exhaust gas containing a phosphorus compound according to any one of claims 1 to 10, comprising the steps of:

a step of forming the lower catalyst layer by applying a lower catalyst layer slurry containing Pd continuously from the gas-inflow-side end surface to the partition wall of the refractory three-dimensional structure, the partition wall being provided so as to extend along the gas-inflow-side end surface and the gas-outflow-side end surface and having partition walls defining a plurality of gas flow channels that penetrate from the gas-inflow-side end surface to the gas-outflow-side end surface, and drying and calcining the slurry; and

and a step of forming the gas inflow side upper catalyst layer and the gas outflow side upper catalyst layer by applying a gas inflow side upper catalyst layer slurry containing Rh continuously from the gas inflow side end surface to the partition wall, applying a gas outflow side catalyst layer slurry containing Rh continuously from the gas outflow side end surface so that the slurries do not contact each other, and then drying and calcining the slurry.

12. A method for purifying an exhaust gas containing a phosphorus compound, comprising the step of bringing the catalyst for purifying an exhaust gas containing a phosphorus compound according to any one of claims 1 to 10 into contact with an exhaust gas containing a phosphorus compound.

Technical Field

The present invention relates to a catalyst suitable for purification of an exhaust gas containing a phosphorus compound (also simply referred to as "an exhaust gas containing a phosphorus compound"). More specifically, the present invention relates to a technique for improving exhaust gas purification performance in a catalyst after exposure to exhaust gas containing a phosphorus compound at high temperature for a long period of time.

Background

With the enhancement of regulations for automobile exhaust gas (exhaust gas), the maintenance of exhaust gas purification performance for a long period of time has been increasingly demanded. This means that a long life of the catalyst, that is, improvement in long-term durability of the catalyst, is required as an exhaust gas purification post-treatment device.

Poisoning by phosphorus compounds contained in exhaust gas (also simply referred to as "phosphorus poisoning") is known to have a large influence on the reduction of the exhaust gas purification performance. Phosphorus poisoning is caused by the deposition and penetration of a phosphorus compound derived from a lubricating oil additive, such as zinc dialkyldithiophosphate contained in exhaust gas, in a catalyst layer (non-patent document 1).

It is known that the cause of the decrease in the exhaust gas purification performance due to phosphorus poisoning is the occurrence of such a phenomenon as follows. The diffusion of the exhaust gas in the catalyst layer is hindered by the phosphorus compound accumulated and permeated in the catalyst layer. In addition, an oxygen storage material (oxygen storage/release substance) cerium oxide (CeO) which has been widely used in three-way catalysts₂) Reacts with the phosphorus compound to form cerium phosphate. If phosphoric acid is formedCerium, oxygen absorption/release performance is lowered, and therefore, relaxation when the exhaust gas atmosphere becomes lean or rich becomes difficult to occur. Since this phenomenon occurs, the exhaust gas purification rate decreases.

As a technique for suppressing the reduction of the exhaust gas purification performance due to phosphorus poisoning, the following techniques are disclosed: cerium oxide and zirconium oxide (ZrO) in a catalyst using palladium (Pd)₂) A technique in which the composite oxide of (1) is used as an oxygen occluding/releasing substance (patent document 1); a technique of providing a region not coated with a catalyst layer as a phosphorus trapping region at a front end portion of a catalyst structure (patent document 2); a technique for shortening the length of an upper catalyst layer in a gas flow direction with respect to a catalyst having the upper catalyst layer on which rhodium (Rh) is supported and a lower catalyst layer on which Pd or/and platinum (Pt) is supported (patent document 3).

Disclosure of Invention

Problems to be solved by the invention

In recent years, there has been a growing demand for longer catalyst life, and there has been a demand for a catalyst that can sufficiently exhibit exhaust gas purification performance even after being exposed to exhaust gas containing a phosphorus compound at high temperature for a long period of time.

However, the present inventors have found, according to their studies, that: the catalysts disclosed in patent documents 1 to 3 cannot obtain sufficient exhaust gas purification performance after severe durability treatment by phosphorus poisoning at high temperatures.

Accordingly, an object of the present invention is to provide a catalyst which can exhibit sufficient exhaust gas purification performance even after being exposed to an exhaust gas containing a phosphorus compound at a high temperature for a long period of time.

Means for solving the problems

The present inventors have conducted intensive studies to solve the above problems. As a result, it was found that: the present invention has been completed in view of the above-described problems, and has an object to provide a refractory three-dimensional structure in which at least three catalyst layers, i.e., a lower catalyst layer, a gas inlet side upper catalyst layer, and a gas outlet side lower catalyst layer, are disposed on partition walls of the refractory three-dimensional structure, and a region where the lower catalyst layer is not formed and a region where the upper catalyst layer is not formed (the gas inlet side upper catalyst layer or the gas outlet side upper catalyst layer) are provided within predetermined ranges along the exhaust gas flow direction.

That is, an exhaust gas purifying catalyst containing a phosphorus compound according to an embodiment of the present invention includes:

a fire-resistant three-dimensional structure which is provided so as to extend along the gas inlet-side end surface to the gas outlet-side end surface, and which has a partition wall that partitions and forms a plurality of gas flow paths that penetrate from the gas inlet-side end surface to the gas outlet-side end surface,

a Pd-containing lower catalyst layer formed continuously from the end surface of the gas-inflow side on the partition wall,

an Rh-containing gas inflow-side upper catalyst layer located on the outermost surface of the partition wall and formed continuously from the gas inflow-side end face, and

an Rh-containing gas outflow side upper catalyst layer located on an outermost surface of the partition wall and formed continuously from a gas outflow side end face;

furthermore, it is characterized in that the material is,

the catalyst layer on the gas inflow side and the catalyst layer on the gas outflow side are arranged at intervals from each other in the direction of the gas flow path,

the length of the lower catalyst layer along the gas flow path direction is 15mm or more, and the ratio of the length to the total length of the gas flow path is 18% or more and less than 100%.

Drawings

Fig. 1 is a front cross-sectional view showing an exhaust gas purifying catalyst containing a phosphorus compound according to embodiment 1 of the present invention.

Fig. 2 is a front cross-sectional view showing an exhaust gas purifying catalyst containing a phosphorus compound according to embodiment 2 of the present invention.

Fig. 3 is a front cross-sectional view showing a modified example of the exhaust gas purifying catalyst containing a phosphorus compound according to embodiment 2 of the present invention.

FIG. 4 is a front cross-sectional view showing an exhaust gas-purifying catalyst containing a phosphorus compound of comparative example 1.

FIG. 5 is a front cross-sectional view showing a catalyst for purification of exhaust gas containing a phosphorus compound of comparative example 2.

FIG. 6 is a front cross-sectional view showing a catalyst for purification of exhaust gas containing a phosphorus compound of comparative example 3.

Fig. 7A is a graph showing the temperature at which the CO purification rate of the catalysts of the example of the present invention and the comparative example reaches 50%.

Fig. 7B is a graph showing the temperature at which the HC purification rates of the catalysts of the example of the present invention and the comparative example reach 50%.

Fig. 7C is a graph showing the temperature at which the NOx purification rates of the catalysts of the example of the present invention and the comparative example reach 50%.

Fig. 8A is a graph showing the time until the CO purification rate of the catalysts of the example of the present invention and the comparative example reaches 20%.

Fig. 8B is a graph showing the time at which the HC purification rates of the catalysts of the example of the present invention and the comparative example reached 20%.

Fig. 8C is a graph showing the time until the NOx purification rates of the catalysts of the example of the present invention and the comparative example reach 20%.

Fig. 9A is a graph showing the time until the CO purification rate of the catalysts of the example of the present invention and the comparative example reaches 50%.

Fig. 9B is a graph showing the time at which the HC purification rates of the catalysts of the example of the present invention and the comparative example reached 50%.

Fig. 9C is a graph showing the time at which the NOx purification rates of the catalysts of the example of the present invention and the comparative example reached 50%.

Detailed Description

Embodiments of the present invention will be described below, and the technical scope of the present invention should be determined based on the description of the claims, but is not limited to the following embodiments. In the present specification, the numerical range "a to B" means "a to B inclusive". Further, "a and/or B" means "either a or B" or "both a and B". Unless otherwise specified, the various physical properties in the present specification are values measured by the methods described in the examples below.

< catalyst for purification of exhaust gas containing phosphorus Compound >

An exhaust gas purifying catalyst containing a phosphorus compound according to one embodiment of the present invention (hereinafter, also simply referred to as "catalyst") includes:

a fire-resistant three-dimensional structure which is provided so as to extend along the gas inlet-side end surface to the gas outlet-side end surface, and which has a partition wall that partitions and forms a plurality of gas flow paths that penetrate from the gas inlet-side end surface to the gas outlet-side end surface,

a Pd-containing lower catalyst layer formed continuously on the partition wall from the end surface on the gas inflow side,

an Rh-containing gas inflow side upper catalyst layer located on an outermost surface on the partition wall, formed continuously from the gas inflow side end face, and,

an Rh-containing gas outflow side upper catalyst layer located on an outermost surface of the partition wall and formed continuously from a gas outflow side end face;

furthermore, it is characterized in that the material is,

the catalyst layer on the gas inflow side and the catalyst layer on the gas outflow side are arranged at intervals from each other in the direction of the gas flow path,

the length of the lower catalyst layer along the gas flow path direction is 15mm or more, and 18% or more and less than 100% of the total length of the gas flow path.

The catalyst of the present embodiment can exhibit sufficient exhaust gas purification performance even after being exposed to an exhaust gas containing a phosphorus compound at a high temperature for a long period of time by having the above-described configuration.

Hereinafter, the overall structure of the exhaust gas purifying catalyst containing a phosphorus compound according to the present embodiment will be described first, and then each constituent member will be described.

[ embodiment 1]

Embodiment 1 of the present invention is explained with reference to the drawings. Fig. 1 is a front cross-sectional view showing an exhaust gas purifying catalyst 1 containing a phosphorus compound according to embodiment 1. Specific examples of embodiment 1 include catalyst C of example 3 described later.

The exhaust gas purifying catalyst 1 containing a phosphorus compound according to embodiment 1 has: a refractory three-dimensional structure 10, a lower catalyst layer 20, a gas inflow side upper catalyst layer 30, and a gas outflow side upper catalyst layer 40.

As shown in fig. 1, the fire-resistant three-dimensional structure 10 extends along a direction from the gas inlet end face 10A to the gas outlet end face 10B. The fire-resistant three-dimensional structure 10 has partition walls that define a plurality of gas flow paths that penetrate from the gas inflow end surface 10A to the gas outflow end surface 10B. In fig. 1, the length of the refractory three-dimensional structure in the gas flow path direction was 80 mm.

The lower catalyst layer 20 is formed continuously from the gas inflow-side end face 10A on the partition wall. The length of the lower catalyst layer 20 along the gas flow path direction (the left-right direction in fig. 1) was 50mm, and 62.5% with respect to the total length of the gas flow path. That is, the lower catalyst layer 20 is formed from the gas inflow side end face 10A to the middle of the surface of the fire-resistant three-dimensional structure 10.

The gas-inflow-side upper catalyst layer 30 is located on the outermost surface on the partition wall, is formed continuously from the gas-inflow-side end face 10A, and is disposed on the upper face of the lower catalyst layer 20. The length of the catalyst layer 30 on the gas inflow side in the gas flow path direction was 30mm, and the proportion of the length was 37.5% with respect to the total length of the gas flow path.

The catalyst layer 40 on the gas outflow side is located on the outermost surface on the partition wall, and is formed continuously from the gas outflow side end face 10B. As shown in fig. 1, the gas outflow-side upper catalyst layer 40 has a left portion formed on the surface of the lower catalyst layer 20 and a right portion formed on the surface of the refractory three-dimensional structure 10. In other words, the gas outflow side upper catalyst layer 40 is formed in a step shape such that the total thickness of the catalyst layers at the gas inflow side end portion of the gas outflow side upper catalyst layer 40 is larger than the total thickness of the catalyst layers at the gas outflow side end portion of the gas outflow side upper catalyst layer 40. Thereby, the stepped portion 41 is formed on the gas outflow side of the catalyst layer 40 on the gas outflow side, and at the same time, the surface area of the catalyst layer 40 on the gas outflow side is increased. Further, since the step portion 41 on the gas outflow side is not provided with a wall on the gas outflow side, phosphorus poisoning is less likely to occur, and a large number of catalyst layer surfaces on the gas outflow side maintaining the catalytic activity exist, and the exhaust gas purification performance can be further improved. In fig. 1, the gas outflow side upper catalyst layer is formed in a step shape, but the gas outflow side upper catalyst layer may be formed such that the total thickness of the catalyst layers gradually decreases from the gas inflow side end portion to the gas outflow side end portion of the gas outflow side upper catalyst layer. Therefore, the catalyst for purifying exhaust gas containing a phosphorus compound according to a preferred embodiment of the present invention is characterized in that the total thickness of the catalyst layers at the gas-inflow-side end portion of the catalyst layer on the gas outflow side is larger than the total thickness of the catalyst layers at the gas-outflow-side end portion of the catalyst layer on the gas outflow side.

The length of the catalyst layer 40 on the gas outflow side in the gas flow path direction was 40mm, and the proportion of the length was 50% with respect to the total length of the gas flow path.

The gas inflow side upper catalyst layer 30 and the gas outflow side upper catalyst layer 40 are disposed so as to be spaced apart from each other in the gas flow path direction as shown in fig. 1, and the distance L separating the gas inflow side upper catalyst layer 30 and the gas outflow side upper catalyst layer 40 is 10 mm.

In the embodiment shown in fig. 1, the recess 50 is formed between the gas inflow side upper catalyst layer 30 and the gas outflow side upper catalyst layer 40 by disposing the gas inflow side upper catalyst layer 30 and the gas outflow side upper catalyst layer 40 at an interval. By forming the concave portion 50 in this way, the phosphorus compound collides with the wall of the concave portion 50 on the gas outflow side and accumulates in the concave portion 50, and the poisoning of the phosphorus compound to the catalyst layer 40 on the gas outflow side can be suppressed. As a result, the catalyst layer 40 on the gas outflow side maintains catalytic activity even after long-term exposure to the exhaust gas containing a phosphorus compound, and therefore the exhaust gas purification performance of the entire catalyst is improved as compared with the case where no recess is provided. Therefore, the catalyst of the present embodiment is suitable for purifying an exhaust gas containing a phosphorus-containing compound in an exhaust gas of an internal combustion engine, and particularly has an excellent effect of purifying nitrogen oxides, carbon monoxide, and hydrocarbons contained in an exhaust gas from an internal combustion engine such as a gasoline engine.

[ 2 nd embodiment ]

Next, the constitution of the exhaust gas purifying catalyst 2 containing a phosphorus compound according to embodiment 2 of the present invention will be described with reference to fig. 2. Fig. 2 is a front cross-sectional view showing an exhaust gas purifying catalyst 2 containing a phosphorus compound according to embodiment 2. Specific examples of embodiment 2 include catalyst a in example 1 described later. Descriptions of portions common to embodiment 1 are omitted, and only those portions having features in embodiment 2 will be described. Note that the same portions as those in embodiment 1 are denoted by the same reference numerals, and redundant description thereof is omitted. Embodiment 2 is different from embodiment 1 in the configuration of the lower catalyst layer and the gas outflow side upper catalyst layer.

As shown in fig. 2, the exhaust gas-purifying catalyst 2 containing a phosphorus compound according to embodiment 2 has a refractory three-dimensional structure 10, a lower catalyst layer 120, a gas-inflow-side upper catalyst layer 30, and a gas-outflow-side upper catalyst layer 140.

The length of the lower catalyst layer 120 along the gas flow path direction is 30mm, and the lower catalyst layer is disposed so that the length along the gas flow path direction is shorter than that of the lower catalyst layer 20 of embodiment 1.

As shown in fig. 2, the gas outflow side upper catalyst layer 140 is disposed on the surface of the refractory three-dimensional structure 10 so as to be spaced apart from the lower catalyst layer 120. At this time, the length of the gas inflow side upper catalyst layer 30 along the gas flow path direction is 30mm, which is the same as the length of the lower catalyst layer 120 along the gas flow path direction, and therefore, the gas outflow side upper catalyst layer 140 is disposed at a distance of 10mm from the lower catalyst layer 120.

As shown in fig. 3, the gas outflow upper catalyst layer 140 may be disposed so as to contact the right end of the lower catalyst layer 120. At this time, the length of the gas inflow side upper catalyst layer 30 in the gas flow path direction is shorter than the length of the lower catalyst layer 120 in the gas flow path direction, and therefore the gas outflow side upper catalyst layer 140 is disposed at a distance from the gas inflow side upper catalyst layer 30. Specific examples of the catalyst shown in FIG. 3 include catalyst B of example 2 described later.

As described in embodiment 1 and embodiment 2, the exhaust gas purifying catalyst containing a phosphorus compound of the present embodiment is characterized in that (i) a catalyst layer on a gas inflow side and a catalyst layer on a gas outflow side are disposed so as to be spaced from each other along a gas flow path direction; (ii) the length of the lower catalyst layer along the gas flow path direction is 15mm or more, and the ratio of the length to the total length of the gas flow path is 18% or more and less than 100%.

In the above feature (i), the length of the separation distance between the catalyst layer on the gas inflow side and the catalyst layer on the gas outflow side is greater than 0mm, preferably 5mm or more, more preferably 8mm or more, and further preferably 10mm or more; preferably 30mm or less, more preferably 20mm or less, and still more preferably 15mm or less. The length of the separation distance is preferably 5mm or more and 30mm or less, more preferably 8mm or more and 20mm or less, and still more preferably 10mm or more and 15mm or less. If the length of the separation distance is 0mm, that is, if there is no space between the catalyst layer on the gas inflow side and the catalyst layer on the gas outflow side, there is a possibility that the exhaust gas may not be effectively purified when poisoned by phosphorus. On the other hand, if the spacing distance is 30mm or less, it is preferable from the viewpoint that a catalyst layer on the gas outflow side having a sufficient length for purification of exhaust gas can be produced, and poisoning of phosphorus can be reduced. The length of the upper catalyst layer on the gas inflow side in the gas flow path direction is preferably equal to or less than the length of the lower catalyst layer. Although the reason is not clear, the spacing distance is preferably the above length regardless of the length of the fire-resistant three-dimensional structure.

In the above feature (ii), the length of the lower catalyst layer in the gas flow path direction is 15mm or more, preferably 20mm or more, and more preferably 30mm or more; preferably less than 100 mm. The ratio of the length is 18% or more, preferably 25% or more, and more preferably 37% or more, with respect to the total length of the gas flow path; it is necessary to be less than 100%, preferably 88% or less, more preferably 75% or less. The numerical range of the ratio of the length is necessarily 18% or more and less than 100%, preferably 25% or more and 88% or less, and more preferably 37% or more and 75% or less. If the proportion of the length of the lower catalyst layer is less than 18%, exhaust gas cannot be effectively purified under high space velocity conditions, which is not preferable from the viewpoint. On the other hand, if the ratio of the length of the lower catalyst layer is 100%, the points of change in the thickness of the catalyst layer between the gas inflow side end face and the gas outflow side end face are small, and therefore, turbulent flow and constricted flow are less likely to occur. If the turbulent flow or the contracted flow is hard to occur, the exhaust gas is hard to diffuse into the catalyst layer, and therefore, sufficient exhaust gas purification performance may not be exhibited, which is not preferable.

The length of the catalyst layer on the gas inflow side in the gas flow path direction is preferably 10mm or more, more preferably 15mm or more, further preferably 20mm or more, particularly preferably 25mm or more; preferably 40mm or less, more preferably 35mm or less, and still more preferably 30mm or less. The length is preferably 10mm to 40mm, more preferably 15mm to 35mm, still more preferably 20mm to 30mm, and particularly preferably 25mm to 30 mm. It is preferable from the viewpoint that the length of the catalyst layer on the gas inflow side is 10mm or more, since NOx can be effectively purified even under conditions of low temperature (150 to 600 ℃) and high space velocity. On the other hand, if the length of the catalyst layer on the gas inflow side is 40mm or less, a large amount of expensive Rh is not necessary, which is preferable from the viewpoint. The ratio of the length to the total length of the gas flow path is preferably 12% or more, more preferably 18% or more, further preferably 25% or more, and particularly preferably 31% or more; preferably 57% or less, more preferably 50% or less, still more preferably 44% or less, and particularly preferably 38% or less. The numerical range of the ratio of the length is preferably 12% to 57%, more preferably 18% to 50%, further preferably 25% to 44%, and particularly preferably 31% to 38%.

The length of the catalyst layer on the gas outflow side in the gas flow path direction is preferably 25mm or more, more preferably 30mm or more, further preferably 40mm or more; preferably less than 100 mm. In addition, as for the length of the catalyst layer on the gas outflow side in the gas flow path direction, the proportion of the length is preferably 31% or more, more preferably 43% or more, and further preferably 50% or more, with respect to the total length of the gas flow path; preferably less than 88%, more preferably 75% or less. The numerical range of the ratio of the length is preferably 31% or more and less than 88%, more preferably 43% or more and 75% or less, and further preferably 50% or more and 75% or less. If the ratio of the length of the catalyst layer on the gas outflow side is 31% or more, the exhaust gas purification performance at low temperatures after phosphorus poisoning is less likely to be degraded. On the other hand, if the proportion of the length of the catalyst layer on the gas outflow side is less than 88%, the length of the catalyst layer on the gas inflow side, and the spacing distance can be ensured.

The length of the catalyst layer on the gas outflow side along the gas flow path direction is a length obtained by subtracting the length of the catalyst layer on the gas inflow side and the length of the spacing distance from the total length of the gas flow path (the length of the refractory three-dimensional structure).

The above-mentioned separation distance and the length of each catalyst layer are obtained by observing a cross section obtained by cutting the catalyst in the gas flow direction. In the measurement of the predetermined position, length, and thickness, the catalyst is destroyed, and a microscope such as a slide caliper or a microscope can be used. In addition, the length can be measured using an X-ray CT apparatus without damaging the catalyst. Any method can be used as long as it can measure the length, without damaging the catalyst.

In the above description, only the lower catalyst layer, the gas inflow side upper catalyst layer, and the gas outflow side upper catalyst layer, which are essential in the present invention as catalyst layers, have been described, but the catalyst of the present embodiment may have other catalyst layers. For example, another catalyst layer may be included between the refractory three-dimensional structure and the lower catalyst layer, between the lower catalyst layer and the upper catalyst layer on the gas inflow side, or between the lower catalyst layer and the upper catalyst layer on the gas outflow side. However, in view of simplification of the manufacturing process of the catalyst, the catalyst of the present embodiment preferably has only the lower catalyst layer, the gas inflow side upper catalyst layer, and the gas outflow side upper catalyst layer as the catalyst layers.

Next, each component included in the exhaust gas purifying catalyst containing a phosphorus compound according to the present embodiment will be described.

[ fire-resistant three-dimensional Structure ]

The refractory three-dimensional structure is not particularly limited, and a refractory three-dimensional structure generally used in the field of exhaust gas purifying catalysts, preferably a honeycomb carrier, can be suitably used. Examples of the honeycomb carrier include a monolith honeycomb carrier, a metal honeycomb carrier, and a plug honeycomb carrier such as a particulate filter. As the material, heat-resistant metals such as cordierite, silicon carbide, silicon nitride, stainless steel, Fe-Cr-Al alloy, and the like can be used.

These honeycomb carriers are manufactured by extrusion molding, a method of winding and fixing a sheet-like member, or the like. The shape of the gas passing port (shape of the hole) may be hexagonal, quadrangular, triangular or corrugated. The hole density (number of holes/unit cross-sectional area) is preferably from 100 to 1200 holes/square inch (15.5 to 186 holes/square centimeter), and more preferably from 200 to 900 holes/square inch (31 to 139.5 holes/square centimeter).

The length of the fire-resistant three-dimensional structure along the gas flow path direction is preferably more than 15mm, more preferably 30mm or more, further preferably 40mm or more, particularly preferably 58mm or more, and most preferably 78mm or more; preferably 1000mm or less, more preferably 300mm or less, further preferably 200mm or less, still more preferably 100mm or less, particularly preferably 90mm or less, and most preferably 85mm or less. The length range is preferably more than 15mm and 1000mm or less, more preferably 30mm or more and 300mm or less, further preferably 40mm or more and 200mm or less, further preferably 58mm or more and 100mm or less, particularly preferably 78mm or more and 90mm or less, and most preferably 78mm or more and 85mm or less.

[ catalyst layer ]

The lower catalyst layer, the gas-inflow-side upper catalyst layer, and the gas-outflow-side upper catalyst layer each independently contain a catalyst component such as a noble metal, an oxygen storage material, a refractory inorganic oxide, and/or a promoter.

(noble metal)

The noble metal may be any noble metal used in the exhaust gas purifying catalyst, and is preferably selected from rhodium (Rh), palladium (Pd), and platinum (Pt). In each catalyst layer, 1 kind of noble metal may be used alone, or 2 or more kinds may be used in combination. In addition, the same noble metal may be used for each catalyst layer, or a plurality of noble metals may be combined for the entire catalyst by using different noble metals.

In the catalyst of this embodiment, the lower catalyst layer contains Pd, and the gas-inflow-side upper catalyst layer and the gas-outflow-side upper catalyst layer contain Rh. However, it is needless to say that the lower catalyst layer may contain a noble metal other than Pd, and the gas inflow side upper catalyst layer and the gas outflow side upper catalyst layer may contain a noble metal other than Rh. The lower catalyst layer may contain a noble metal other than Pd, preferably Rh and/or Pt, preferably any one of Rh or Pt, preferably Pt. On the other hand, the noble metal other than Rh that the catalyst layer on the gas-inflow side or the catalyst layer on the gas-outflow side may contain is each independently preferably either Pd or Pt, preferably Pd.

The Rh concentration of the catalyst layer on the gas inflow side is preferably higher than the Rh concentration of the catalyst layer on the gas outflow side. Specifically, the Rh concentration of the catalyst layer on the gas inflow side is preferably 1.1 to 5 times, more preferably 1.1 to 4 times, further preferably 1.1 to 2 times, and particularly preferably 1.1 to 1.35 times, relative to the Rh concentration of the catalyst layer on the gas outflow side. The Rh concentration in each layer is set to a percentage obtained by dividing the mass of Rh contained in the layer by the amount of the supported (total mass of solid components contained in the layer) of the layer. If the ratio is 1.1 times or more, sufficient heating performance is exhibited, and therefore, it is preferable, and if the ratio is 5 times or less, deterioration of exhaust gas purification performance due to phosphorus poisoning is suppressed, and therefore, it is preferable.

In the case where the gas inflow side upper catalyst layer contains Pd, the mass ratio of Pd to Rh (Pd/Rh) in the gas inflow side upper catalyst layer is preferably 0.05 to 5.0, more preferably 0.1 to 2.0, and further preferably 0.3 to 0.8. If Pd/Rh is 0.05 or more, Rh is less likely to be poisoned by phosphorus due to Pd in the gas inflow side catalyst layer, and therefore, it is preferable, and on the other hand, if Pd/Rh is 5.0 or less, reaction lowering of Rh due to Pd covering Rh can be suppressed, and therefore, it is preferable.

In addition, the Rh concentration of the lower catalyst layer is preferably lower than the Rh concentration of the upper catalyst layer on the gas outflow side. Specifically, the Rh concentration of the lower catalyst layer is preferably 0 to 0.5 times, more preferably 0 to 0.3 times, and further preferably 0 to 0.1 times the Rh concentration of the upper catalyst layer on the gas outflow side. Rh of the lower catalyst layer is not essential, but it is preferable that the ratio is 0.5 times or less because the performance of the lower catalyst layer is not greatly impaired.

The amount of the noble metal contained in the catalyst of the present embodiment is preferably 0.01 to 10g, more preferably 0.05 to 8g, and still more preferably 0.1 to 5g of Rh relative to a 1L fire-resistant three-dimensional structure, and preferably 0.05 to 20g, more preferably 0.5 to 15g, and still more preferably 1 to 10g of Pd relative to a 1L fire-resistant three-dimensional structure, and preferably 0.01 to 15g, more preferably 0.1 to 10g, and still more preferably 0.5 to 5g of Pt relative to a 1L fire-resistant three-dimensional structure.

The rhodium (Rh) source as the starting material is not particularly limited, and a material used in the field of purification of exhaust gas can be used. Specifically, rhodium; halides such as rhodium chloride; inorganic salts such as rhodium, nitrate, sulfate, acetate, ammonium salt, amine salt, hexamine salt, carbonate, bicarbonate, nitrite, oxalate and the like; carboxylates such as formate; and hydroxides, alkoxides, oxides, and the like. Preferred examples thereof include nitrate, ammonium salt, amine salt and carbonate. The amount of the rhodium source added is such that the rhodium source can be supported on the refractory three-dimensional structure in the above-described amount. In the present invention, the rhodium source may be used alone or as a mixture of 2 or more species.

Further, the source of palladium (Pd) as a starting material is not particularly limited, and a raw material used in the field of purification of exhaust gas can be used. Specifically, palladium; halides such as palladium chloride; inorganic salts such as palladium, nitrate, sulfate, acetate, ammonium salt, amine salt, tetraamine salt, carbonate, bicarbonate, nitrite, oxalate and the like; carboxylates such as formate; and hydroxides, alkoxides, oxides, and the like. Preferred examples thereof include nitrate, acetate, ammonium salt, amine salt, tetraamine salt and carbonate. The amount of the palladium source added is such that the palladium source can be supported on the refractory three-dimensional structure in the above amount. In the present invention, the palladium source may be used alone or as a mixture of 2 or more species.

In addition, a platinum (Pt) source as a starting material when platinum is contained as a catalytically active component is not particularly limited, and a material used in the field of purification of exhaust gas can be used. Specifically, platinum; halides such as platinum bromide and platinum chloride; inorganic salts such as platinum, nitrate, dinitrodiamine salt, tetraamine salt, sulfate, ammonium salt, amine salt, diethanolamine salt, diacetone salt, carbonate, hydrogencarbonate, nitrite and oxalate; carboxylates such as formate; and hydroxides, alkoxides, oxides, and the like. Among them, nitrate (platinum nitrate), dinitrodiammine salt (dinitrodiammine platinum), chloride (platinum chloride), tetraamine salt (tetraamine platinum), diethanolamine salt (diethanolamineplatinum), and diacetone salt (bis (acetylacetonato) platinum) are preferable. The amount of the platinum source added is such that the platinum source can be supported on the refractory three-dimensional structure in the above-described amount. In the present invention, the platinum source may be used alone or in combination of 2 or more.

(oxygen storage Material)

The oxygen storage material is a material capable of absorbing or discharging oxygen in accordance with the oxygen concentration in the exhaust gas, and examples thereof include cerium oxide, oxides composed of cerium and other elements, such as cerium-zirconium composite oxide, cerium-zirconium-lanthanum-neodymium composite oxide, and cerium-zirconium-lanthanum-yttrium composite oxide.

The crystal structure of the oxygen storage material includes cubic, tetragonal, monoclinic, orthorhombic, and the like, and preferably cubic, tetragonal, or monoclinic, and more preferably cubic or tetragonal.

The cerium source such as a cerium-zirconium composite oxide used as the oxygen storage material is not particularly limited, and a raw material used in the field of purification of exhaust gas can be used. Specifically, nitrate such as cerium nitrate, carbonate, sulfate and the like can be mentioned. Among them, nitrate is preferably used. The cerium source may be used alone or in combination of 2 or more species. The cerium source is added in an amount corresponding to cerium oxide (CeO)₂) In terms of conversion, the amount of the flame-resistant three-dimensional structure is preferably 5 to 200g, more preferably 10 to 100g, still more preferably 15 to 70g, and particularly preferably 20 to 50g, based on 1L.

The zirconium source is not particularly limited, and a raw material used in the field of purification of exhaust gas can be used. Specifically, zirconyl nitrate, zirconyl chloride, zirconium nitrate, basic zirconium sulfate, and the like can be mentioned. Among them, zirconyl nitrate and zirconium nitrate are preferably used. The zirconium source may be used alone or in a mixture of 2 or more. The amount of the zirconium source added is based on the amount of zirconium oxide (ZrO)₂) In terms of conversion, the amount of the flame-resistant three-dimensional structure is preferably 5 to 200g, more preferably 10 to 150g, and still more preferably 20 to 100g, based on 1L.

The lanthanum source is not particularly limited, can be used in the exhaust gas purification field used in the raw material, specific, can be cited lanthanum hydroxide, lanthanum nitrate, lanthanum acetate, lanthanum oxide, and so on, wherein, preferably using lanthanum nitrate, lanthanum hydroxide, the lanthanum source can be single or more than 2 kinds of mixtures, lanthanum source addition according to lanthanum oxide (L a)₂O₃) In terms of conversion, 1 to 50g, more preferably 1 to 35g, and still more preferably 1 to 20g of the flame-resistant three-dimensional structure 1L is used.

The yttrium source is not particularly limited, and a raw material used in the field of purification of exhaust gas can be used. Specifically, yttrium hydroxide, yttrium nitrate, yttrium oxalate, yttrium sulfate, and the like can be given. Among them, yttrium hydroxide and yttrium nitrate are preferably used. Incidentally, the above yttrium source may be singly or in a mixture of 2 or more. The yttrium source is added in an amount of yttrium oxide (Y)₂O₃) In terms of conversion, the amount of the flame-resistant three-dimensional structure is preferably 0 to 50g, more preferably 0 to 35g, and still more preferably 0 to 20g, based on 1L.

The neodymium source is not particularly limited, and a raw material used in the field of purification of exhaust gas can be used. Specific examples thereof include neodymium hydroxide, neodymium nitrate, neodymium oxalate, and neodymium sulfate. Among them, neodymium hydroxide and neodymium nitrate are preferably used. Note that the neodymium source may be used alone or as a mixture of 2 or more. The neodymium source is added in an amount corresponding to neodymium oxide (Nd)₂O₅) In terms of conversion, the amount of the flame-resistant three-dimensional structure is preferably 0 to 50g, more preferably 0 to 35g, and still more preferably 0 to 20g, based on 1L.

In the catalyst of the present embodiment, it is preferable that at least 1 layer of the lower catalyst layer, the gas-inflow-side upper catalyst layer, and the gas-outflow-side upper catalyst layer contains CeO₂And ZrO₂More preferably at least 2 layers comprise CeO₂And ZrO₂More preferably, all of the 3 layers of the composite oxide (C) contain CeO₂And ZrO₂The composite oxide of (3).

Containing CeO in the lower catalyst layer₂And ZrO₂In the case of the composite oxide of (3), CeO in the composite oxide₂The content of (b) is preferably 20% by mass or more, more preferably 30% by mass or more, further preferably 40% by mass or more, and particularly preferably 45% by mass or more; preferably 80% by mass or less, more preferably 60% by mass or less, still more preferably 50% by mass or less, and particularly preferably 45% by mass or less. As the CeO₂The numerical range of the content of (b) is preferably 20 to 80 mass%, more preferably 30 to 60 mass%, and still more preferably 40 to 50 mass%Particularly preferably 45% by mass or more and 50% by mass or less, or 40% by mass or more and 45% by mass or less. If CeO is present₂When the content of (b) is 20% by mass or more, since sufficient oxygen storage capacity is exhibited even when the vehicle is traveling at high speed or is suffering from phosphorus poisoning, hydrocarbon can be efficiently purified. On the other hand, if CeO₂When the content of (b) is 80% by mass or less, the heat resistance is not easily lowered, and therefore, the catalyst performance can be maintained even when the catalyst is exposed to high-temperature exhaust gas.

The catalyst layer on the gas inflow side and/or the catalyst layer on the gas outflow side contains CeO₂And ZrO₂In the case of the composite oxide of (3), CeO in the composite oxide₂The content of (b) is preferably 5% by mass or more, more preferably 10% by mass or more, further preferably 15% by mass or more, and particularly preferably 20% by mass or more; preferably 60% by mass or less, more preferably 50% by mass or less, still more preferably 40% by mass or less, and particularly preferably 30% by mass or less. As the CeO₂The numerical range of the content of (b) is preferably 5 to 60 mass%, more preferably 10 to 50 mass%, further preferably 15 to 40 mass%, and particularly preferably 20 to 30 mass%. If CeO is present₂When the content of (3) is 5% by mass or more, the amount of the phosphorus compound attached to Rh decreases, and thus the decrease in catalyst performance can be suppressed. On the other hand, if CeO₂When the content of (B) is 60% by mass or less, the phosphorus compound is less likely to adhere to CeO₂In this way, the decrease in the catalyst performance can be suppressed.

(refractory inorganic oxide)

As the refractory inorganic oxide, alumina, lanthanum-containing alumina, zirconia, silica-alumina, titania, zeolite, and the like are used, either singly or as a mixture of 2 or more kinds. The refractory inorganic oxide preferably has a small change in specific surface area at 700 ℃ or higher, preferably 1000 ℃ or higher. The BET specific surface area of the refractory inorganic oxide is not particularly limited, and is considered from the viewpoint of supporting a catalytically active component such as a noble metalPreferably 50 to 750m²A concentration of 150 to 750m²(ii) in terms of/g. The average primary particle diameter of the refractory inorganic oxide is not particularly limited, but is preferably in the range of 5nm to 20nm, more preferably 5nm to 10 nm. Within such a range, the noble metal can be supported on the refractory inorganic oxide. In the present specification, the shape or average primary particle diameter of the refractory inorganic oxide is measured by a Transmission Electron Microscope (TEM).

The content of the refractory inorganic oxide is preferably 10 to 300g, more preferably 20 to 200g, and still more preferably 50 to 100g based on 1L of the refractory three-dimensional structure, and as long as the content of the refractory inorganic oxide is within the above range, a catalyst component such as a noble metal can be dispersed and supported.

(Co-catalyst)

As the promoter, a group 1 element, a group 2 element, and/or a rare earth element may be added, potassium, magnesium, calcium, strontium, barium, lanthanum and the like may be used as the group 1 element, the group 2 element and the rare earth element, and they may be used alone or in the form of a mixture of 2 or more₂O₃) Barium oxide (BaO), barium sulfate (BaSO)₄) The amount of the flame-resistant three-dimensional structure 1L is preferably 0 to 50g, more preferably 0.5 to 30g, and still more preferably 1 to 20 g.

The catalyst of the present invention can exhibit sufficient exhaust gas purification performance even after being exposed to exhaust gas containing a phosphorus compound at high temperatures for a long period of time. In a catalyst exposed to an exhaust gas containing a phosphorus compound as phosphorus oxide (P)₂O₅) According to the present invention, even in a state where a phosphorus compound is accumulated in an amount of preferably 1 to 50g, more preferably 1 to 30g, further preferably 1 to 15g, and particularly preferably 1 to 10g, based on a fire-resistant three-dimensional structure of 1L, excellent exhaust gas cleaning performance can be exhibited, and the phosphorus compound is generally accumulated in a large amount on the gas inflow side and flows out toward the gas outflow sideThe sides gradually decrease. The phosphorus compound is present at a high concentration in the vicinity of the surface of the catalyst layer, and the concentration decreases as the concentration approaches the inside of the catalyst layer (the direction of the refractory three-dimensional structure).

The amount of the phosphorus compound accumulated in the catalyst can be analyzed using XRF (fluorescent X-ray analysis), EPMA (Electron Probe microanalyzer), SEM-EDX, or the like. When the distribution of the catalyst in the exhaust gas flow direction is examined, the amount of the phosphorus compound can be analyzed for each cleavage site by the above-mentioned XRF or the like after cleaving the catalyst by a predetermined length. The distribution can be studied by comparing the analysis results of the respective cleavage sites.

Method for producing catalyst for exhaust gas purification containing phosphorus compound

The exhaust gas purifying catalyst containing a phosphorus compound can be easily produced by those skilled in the art by appropriately referring to a known method. A preferred production method includes the following steps. That is, a method for producing an exhaust gas purifying catalyst containing a phosphorus compound according to another embodiment of the present invention includes:

a step (I) in which a slurry for a lower catalyst layer containing Pd is continuously applied from the gas-inflow-side end surface to a partition wall of a refractory three-dimensional structure that is provided so as to extend along the gas-inflow-side end surface and the gas-outflow-side end surface and that has partition walls defining a plurality of gas flow paths that penetrate from the gas-inflow-side end surface to the gas-outflow-side end surface, and the slurry is dried and fired to form a lower catalyst layer; and

and (II) a step (II) in which, after the lower catalyst layer is formed, a slurry for a gas-inflow-side upper catalyst layer containing Rh is continuously applied to the partition wall from the gas-inflow-side end surface, and a slurry for a gas-outflow-side catalyst layer containing Rh is continuously applied to the gas-outflow-side end surface so that the slurries do not contact each other, and then drying and firing are performed to form the gas-inflow-side upper catalyst layer and the gas-outflow-side upper catalyst layer.

The slurry is prepared by mixing raw materials of a noble metal, an oxygen storage material, a refractory inorganic oxide, and a co-catalyst with an aqueous medium and wet-pulverizing the mixture. Note that the slurry may be prepared using an oxygen storage material or a refractory inorganic oxide on which a noble metal or a promoter is supported in advance. Examples of the aqueous medium include water, lower alcohols such as ethanol and 2-propanol, and organic alkaline aqueous solutions. Water and/or lower alcohols are preferably used, and water is particularly preferably used. The solid matter concentration in the slurry is preferably 5 to 60 mass%, more preferably 10 to 50 mass%. As the wet grinding method, a known method can be suitably used, and for example, a method using a ball mill can be mentioned.

The method of applying the slurry to the refractory three-dimensional structure is not particularly limited, and examples thereof include a method of immersing the refractory three-dimensional structure in a vessel containing the slurry from the gas inflow side end surface or the gas outflow side end surface. At this time, the region to which the slurry is applied is controlled so that each catalyst layer has a desired length. In the step (I), the lower catalyst layer slurry is applied, dried and calcined, and then, in the step (II), the gas inflow side upper catalyst layer slurry and the gas outflow side upper catalyst layer slurry are applied, dried and calcined. In the step (II), after both the slurry for the catalyst layer on the gas inflow side and the slurry for the catalyst layer on the gas outflow side are coated (in this case, the order of coating the slurries is not particularly limited), the coated slurries may be dried and calcined together; the slurry for the catalyst layer on the gas inflow side or the slurry for the catalyst layer on the gas outflow side may be applied and dried and calcined to form one catalyst layer, and then the slurry for the other catalyst layer may be applied and dried and calcined to form the other catalyst layer.

The conditions for drying and calcining are not particularly limited as long as the catalyst component can be attached to the refractory three-dimensional structure. The drying is preferably carried out in air at a temperature of 50 to 300 ℃ and more preferably 80 to 200 ℃ for 5 minutes to 10 hours, and more preferably 30 minutes to 8 hours. Next, the calcination is preferably carried out at a temperature of 300 to 1200 ℃ and more preferably 400 to 700 ℃ for preferably 10 minutes to 10 hours and more preferably 30 minutes to 5 hours.

< method for purifying exhaust gas >

According to another aspect of the present invention, there is provided a method for purifying an exhaust gas containing a phosphorus compound, comprising the step of bringing the catalyst for purifying an exhaust gas containing a phosphorus compound into contact with an exhaust gas containing a phosphorus compound.

The exhaust gas containing phosphorus compounds is preferably an exhaust gas discharged from an internal combustion engine. As the internal combustion engine, for example, a gasoline engine, a hybrid engine, an engine using natural gas, ethanol, dimethyl ether, or the like as fuel, or the like can be used. Among them, a gasoline engine is preferable.

The temperature of the exhaust gas containing the phosphorus compound is preferably 0 to 800 ℃, i.e., the temperature range of the exhaust gas in normal operation. The air-fuel ratio (A/F) of the exhaust gas of an internal combustion engine having a temperature of 0 to 800 ℃ is preferably 10 or more and less than 30, more preferably 11 to 14.7.

The catalyst of the present invention can exhibit sufficient exhaust gas purification performance even after being exposed to high temperatures for a long period of time. Here, the high temperature exposure means exposure to exhaust gas at preferably 800 to 1200 ℃. The air-fuel ratio (A/F) of exhaust gas of an internal combustion engine having a temperature of 800 to 1200 ℃ is preferably 10 to 18.6. The time for exposing to the exhaust gas at 800 to 1200 ℃ is preferably 5 to 500 hours.

When evaluating the exhaust gas purification performance after exposure to an exhaust gas containing a phosphorus compound at a high temperature and for a long time, an effective method is: as the heat and phosphorus poisoning treatment, the catalyst is exposed to the exhaust gas containing a phosphorus compound at 800 to 1200 ℃ for 5 to 500 hours, and then the exhaust gas purification performance is examined.

In addition, the space velocity of the catalyst of the present invention is preferably 80000h even in the exhaust gas (exhaust gas)^-1Above, more preferably 100000h^-1Above, more preferably 120000h^-1In the above case, the exhaust gas (exhaust gas) can be effectively purified. The upper limit of the spatial velocity of the exhaust gas depends on the amount of exhaust gas of an internal combustion engine such as an engine, but is preferably 500000h^-1The following.