JP6741666B2 - Exhaust gas purification catalyst - Google Patents

Description

The present invention relates to an exhaust gas purification catalyst that can be used to purify exhaust gas emitted from an internal combustion engine.

Exhaust gas from an automobile that uses gasoline as a fuel contains harmful components such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NO _x ). The hydrocarbon (HC) is oxidized and converted into water and carbon dioxide, the carbon monoxide (CO) is oxidized and converted into carbon dioxide, and the nitrogen oxide (NO) is converted. With regard to _x ), it is necessary to reduce and convert it into nitrogen and purify each harmful component with a catalyst.
As a catalyst for treating such exhaust gas (hereinafter referred to as “exhaust gas purification catalyst”), three-way catalysts (TWCs) capable of oxidizing and reducing CO, HC and NO _x are used. ing. The three-way catalyst is generally attached in the form of a converter at an intermediate position between the engine and the muffler of the exhaust pipe.

Examples of such a three-way catalyst include a refractory oxide porous body having a high specific surface area, for example, an alumina porous body having a high specific surface area, and platinum (Pt), palladium (Pd), rhodium (Rh), and the like. It is known that a noble metal is supported on a substrate, for example, a monolithic substrate made of a refractory ceramic or a metal honeycomb structure, or a refractory particle. There is.

However, since precious metals such as platinum (Pt), palladium (Pd), and rhodium (Rh) are very expensive, it is required to reduce the amount of precious metal elements used in the development of exhaust gas purification catalysts. ..

Therefore, in place of these noble metals, for example, a catalyst has been proposed in which a transition metal such as copper (Cu) is supported as an active component on a catalyst carrier (alumina, zeolite, etc.) (see, for example, Patent Document 1).

Patent Document 2 discloses an exhaust gas purifying catalyst obtained by mixing a compound containing Cu and alumina to prepare a mixture, and heat-treating the mixture at 850° C. or higher and less than 1200° C. There is.

Patent Document 3 is a catalyst containing CuAl ₂ O ₄ having a spinel crystal structure to which a rare earth element is added, wherein the rare earth element is a lanthanoid, and CuO is supported on the surface of CuAl ₂ O _4. It is present and has an X-ray diffraction pattern by Cu-Kα ray, which has a diffraction peak attributed to CuO and CuAl ₂ O ₄ and does not have a diffraction peak attributed to α-Al ₂ O _3. Is disclosed.
The Patent Document 3, by supporting the Cu to alumina by calcining at a temperature to produce the _{CuAl 2 O 4 ([0030]} ), present in the form of CuO is supported on the surface of CuAl ₂ O ₄ Therefore, it is described that the promoting action of CuAl ₂ O ₄ can be utilized while ensuring the catalytic activity of CuO ([0009]).

JP-A-5-96132 JP 2012-071271 A Japanese Patent Laid-Open No. 2012-115771

The present inventor has focused on copper (Cu) as a catalytically active component and studied an exhaust gas purifying catalyst having a structure in which Cu element is present on the surface of alumina particles. It was found that the catalytic activity does not increase as expected even if it is increased. Further research on the cause has revealed that CuAl ₂ O ₄ formation inhibits the catalytic activity of Cu.

Based on this finding, the present inventor has demonstrated that an exhaust gas purifying catalyst having a structure in which Cu element is present on the surface of alumina particles exhibits excellent catalytic activity and can be effectively used as a three-way catalyst. It aims to provide a new exhaust gas purification catalyst that can be used.

In order to solve such a problem, the present invention is an exhaust gas purifying catalyst having a structure in which Cu element is present on the surface of alumina particles, which is measured by X-ray Photoelectron Spectroscopy (XPS). When the total area of the peaks corresponding to the binding energies of the Cu 2p orbital (Cu2p) and the Al 2p orbital (Al2p) is 100%, the ratio of the Cu2p peak area (also referred to as “Cu coverage”) ) Is 7 to 28%, an exhaust gas purifying catalyst is proposed.

According to the exhaust gas purifying catalyst proposed by the present invention, excellent catalytic activity can be exhibited without using a noble metal as a catalytically active component, and the catalyst can be effectively used as a three-way catalyst.

Next, the present invention will be described based on embodiments. However, the present invention is not limited to the embodiment described below.

<This exhaust gas purification catalyst>
An exhaust gas purifying catalyst according to an example of an embodiment of the present invention (hereinafter referred to as “main exhaust gas purifying catalyst”) is an exhaust gas purifying catalyst having a structure in which Cu element is present on the surface of alumina particles.

(Alumina particles)
The alumina particles may be particles of Al ₂ O _3, it may be particles containing in addition to the other components of the Al ₂ O _3.

Examples of the “other components” other than Al ₂ O ₃ that the alumina particles may contain include lanthanoids and barium (Ba) oxides.
Examples of the lanthanoid include lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), and terbium (Tb). , Dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

Regarding the content of the “other component”, from the viewpoint of preventing the Cu from reacting with the “other component” to reduce the dispersibility of Cu and reduce the catalytic activity, _It is preferably 5% by mass or less, and more preferably 3% by mass or less, based on ₂ O ₃ . On the other hand, from the viewpoint of ensuring thermal stability, the content of the “other component” is preferably 0.5% by mass or more based on Al ₂ O ₃ .

Examples of the crystal structure of Al ₂ O ₃ forming the alumina particles include δ-Al ₂ O ₃ , γ-Al ₂ O ₃ , θ-Al ₂ O ₃ and α-Al ₂ O ₃ . Among them, in the present exhaust gas purification catalyst, γ-Al ₂ O ₃ and θ-Al ₂ O ₃ are preferable from the viewpoint of the balance between heat resistance and specific surface area, and among them, the dispersibility of Cu is high while maintaining heat resistance. From the viewpoint of being able to do so, θ-Al ₂ O ₃ is particularly preferable.
The alumina particles may be alumina particles in which two or more kinds of Al ₂ O ₃ having different crystal structures are combined.

(Average particle size)
The average particle diameter (D50) of the alumina particles is preferably 1 μm to 60 μm.
When the average particle diameter (D50) of the alumina particles is 1 μm or more, heat resistance can be maintained while maintaining peel strength, which is preferable. On the other hand, if the average particle diameter (D50) of the present alumina is 60 μm or less, it is possible to improve the gas contact property while maintaining the peel strength.
From this point of view, the average particle diameter (D50) of the alumina particles is preferably 1 μm to 60 μm, more preferably more than 3 μm or 50 μm or less, and particularly preferably 5 μm or more or 40 μm or less.

(Cu element)
The Cu element existing on the surface of the alumina particles includes the case where it exists in the state of CuO _x (0≦x≦1), CuAl ₂ O ₄ or the like.
At this time, the CuAl ₂ O ₄ was presumed to exist on the surface of the alumina particles in a state where the Cu element was in solid solution with alumina, and the CuO _x (0≦x≦1) was supported on the surface of the alumina particles. Presumed to exist in the state.

In this exhaust gas purification catalyst, the Cu 2p orbital (also referred to as “Cu2p”) measured by X-ray photoelectron spectroscopy (XPS) with respect to the abundance ratio of Cu element present on the surface of alumina particles And the total area of each peak corresponding to the binding energy of the Al 2p orbital (also referred to as “Al2p”) is 100%, the ratio of the peak area of Cu2p, that is, the Cu coverage is 7 to 28%. Is preferred.
At this time, the ratio of the peak area of Cu2p to the total area of the peak areas of Cu2p and Al2p measured by X-ray photoelectron spectroscopy can be said to indicate the existence ratio of the Cu element on the surface of the alumina particles. Since Cu exposed on the surface acts as an active species, the larger the Cu coverage is, the better, but if it is too large, sintering will occur.
From this viewpoint, the Cu coverage is preferably 7 to 28%, and more preferably 20% or less from the viewpoint of preventing Cu sintering and further improving the NO _x purification performance. % Or less, and particularly preferably 15% or less.
In addition, "the presence of the Cu element on the surface of the alumina particles" includes the case where the Cu element exists in a solid solution state in the alumina, such as the Cu element being CuAl ₂ O _4, and the alumina is used as CuO. It also includes the case of existing in the state of being supported on the particle surface.
In addition, "supporting" refers to a state in which an active metal such as Cu is immobilized without reacting with an inorganic porous material such as alumina.

Further, the exhaust gas purification catalyst preferably contains Cu0 to 1 valence and Cu2 valence, and the Cu0 to 1 valence contained in the catalyst is larger than the Cu2 valence contained in the catalyst. This is because Cu0 to 1 valences are higher in catalytic activity than Cu2 valences because they are closer to metal Cu.

From such a viewpoint, with respect to the peak area of 925 eV to 940 eV (corresponding to Cu0 to divalence) obtained by measuring the binding energy of the 2p orbital of Cu by X-ray photoelectron spectroscopy (XPS), Ratio of peak area of 925 eV to 935 eV (corresponding to Cu0 to 1 valence: Cu0 valence peak is observed overlapping with shoulder portion of Cu1 valence peak, and thus Cu0 to 1 valence peak is included in this shoulder portion) (Also referred to as "Cu0 to monovalent area ratio") is preferably 50% or more.

At this time, the peak area of 925 eV to 940 eV correlates with the content of Cu of 0 to 2 valence, and the peak area of 925 eV to 935 eV correlates with the content of Cu of 0 to 1 valence. It is preferable that the “area ratio of Cu” is 50% or more. Among Cu 0 to 1 valence (Cu, Cu ₂ O, etc.) and Cu ₂ valence (CuO, CuAl ₂ O _4, etc.), Cu 0 to 1 valence It means that a higher abundance ratio is preferable. Since the catalytic activity of Cu0 to 1 valence is higher than that of Cu2 valence, the catalytic activity of the present exhaust gas purification catalyst can be enhanced by increasing the existence ratio of Cu0 to 1 valence.
From this viewpoint, the area ratio of Cu0 to monovalent Cu is more preferably 55% or more, and even more preferably 60% or more.
As will be described later, by firing in a nitrogen atmosphere, the abundance ratio of Cu0 to 1 valence can be increased rather than Cu2 valence. However, the method is not limited to such a method, and a reducing atmosphere such as hydrogen or carbon monoxide may be used.

Further, the exhaust gas purifying _{catalyst, CuO x (0 ≦ x ≦} 1) and CuAl ₂ O ₄ wherein the warm reaction method by _{H 2 (H 2} -TPR) the CuO _x and in the hydrogen consumption peak obtained by In the peak area of CuAl ₂ O ₄ , the peak area ratio of CuAl ₂ O _{4 to} the peak areas of CuO _x and CuAl ₂ O ₄ ((CuAl ₂ O ₄ /(CuO _x +CuAl ₂ O ₄ ))×100) is 50. % Or less is preferable.

From the research results of the present inventor, it has been found that even if the Cu coating amount is increased, if the content of CuAl ₂ O ₄ increases, the catalytic activity of the Cu element that is the catalytically active species is inhibited.
From such a viewpoint, the peak area ratio ((CuAl ₂ O ₄ /(CuO _x +CuAl ₂ O ₄ ))×100) is preferably 50% or less, more preferably 45% or less, and even more preferably 40% or less. Is more preferable.
As will be described later, it has been confirmed that it is possible to suppress the generation of CuAl ₂ O ₄ while increasing the Cu coating amount by firing in a nitrogen atmosphere. However, the method is not limited to such a method, and it is considered that the same effect as firing in a nitrogen atmosphere can be obtained even in a reducing atmosphere of hydrogen or carbon monoxide as described above.

Further, when the amount of CuAl ₂ O ₄ is quantified from the peak area (hydrogen consumption), the content of CuAl ₂ O ₄ is preferably 15% by mass or less in the exhaust gas purification catalyst.
In this exhaust gas purifying catalyst, by setting the content of CuAl ₂ O ₄ to be 15% by mass or less, the catalytic activity will be favorably maintained.
From this viewpoint, the content of CuAl ₂ O ₄ is more preferably 10 mass% or less, and particularly preferably 9 mass% or less.

<Method of manufacturing the exhaust gas purifying catalyst>
The exhaust gas purifying catalyst of the present invention is prepared by, for example, dissolving copper nitrate in water to prepare an aqueous solution, and impregnating alumina with this to make a slurry, and drying the slurry, and then 600 to 1000° C., preferably 600 to It can be obtained by firing at 900° C. in a nitrogen atmosphere (also referred to as “N ₂ firing”).
Further, it can be obtained by applying the above-mentioned slurry to a base material and firing at N ₂ at 600 to 1000° C., preferably 600 to 900° C.
However, the production method is not limited to this.

By firing with N _2, it is possible to suppress the generation of CuAl ₂ O ₄ while increasing the Cu coating amount. Moreover, the ratio of Cu0 to monovalent can be increased by firing N ₂ . The air annealing, while increasing the ratio of Cu2 valence than Cu0~1 valence, the _{N 2} firing, it is easy increased Cu0~1 monovalent ratio is confirmed than Cu2 valence reversed.

<Characteristics and applications of this exhaust gas purification catalyst>
The exhaust gas purifying catalyst can exhibit the exhaust gas purifying catalytic performance without supporting a noble metal as a catalytically active species. That is, hydrocarbons (HC) and carbon monoxide (CO) oxidize and have a catalytic activity for reducing and purifying nitrogen oxides (NO _x ). Among them, NO _x reducing performance and CO oxidation. Especially good performance. Therefore, CO, HC and NO _x can be effectively used as a three-way catalyst capable of redox. However, it does not prevent carrying the noble metal.

The exhaust gas purification catalyst can be molded into an appropriate shape such as pellets and used alone as a catalyst, or can be used as a form supported on a base material made of a ceramic or metal material.

The exhaust gas purifying catalyst can be produced as a three-way catalyst by forming a catalyst layer on the surface of a base material having a honeycomb shape together with, for example, a binder and an NO _X storage agent such as Ba hydroxide. The catalyst layer may have a single layer structure or a multilayer structure of two or more layers.

More specifically, the present exhaust gas purifying catalyst, the inorganic porous material as required, OSC materials, NO _X absorbent, and the like as a binder, mixing water and stirring to form a slurry and the resulting slurry For example, it can be manufactured by coating a base material such as a ceramic honeycomb body and firing the base material to form a catalyst layer on the surface of the base material.

Examples of the base material include fire resistant materials such as ceramics and metal materials.
The material of the ceramic substrate, refractory ceramic material, for example, cordierite, cordierite-alpha alumina, silicon nitride, zircon mullite, spodumene, alumina-silica magnesia, zirconium silicate, sillimanite, magnesium silicate, Mention may be made of petalite, alpha alumina and aluminosilicates.
The material of the metallic substrate may include refractory metals such as stainless steel or other suitable iron-based corrosion resistant alloys.

Examples of the shape of the base material include a honeycomb shape, a filter shape, a pellet shape, and a spherical shape.
As the honeycomb material, for example, a cordierite material such as ceramics can be used. Alternatively, a honeycomb made of a metal material such as ferritic stainless steel can be used.
When a honeycomb-shaped substrate is used, for example, a monolithic substrate having a large number of parallel fine gas flow passages, that is, channels, can be used inside the substrate so that a fluid flows through the substrate. At this time, the catalyst layer can be formed by coating the inner wall surface of each channel of the monolith-type substrate with the catalyst composition by wash coating or the like.

As the inorganic porous body, for example, silica, a porous body of a compound selected from the group consisting of alumina and titania compounds, such as alumina, silica, silica-alumina, alumino-silicates, alumina-zirconia, alumina-chromia and A porous body made of a compound selected from alumina-ceria can be mentioned.

Examples of the OSC material, that is, a cocatalyst having an oxygen storage capacity (OSC) include a cerium compound, a zirconium compound, a ceria-zirconia composite oxide, and a ceria-zirconia-alumina composite oxide. ..

Examples of the NO _X storage agent include alkaline earth metals and alkali metals. Among them, one or more metals selected from the group consisting of magnesium, barium, boron, thorium, hafnium, silicon, calcium and strontium can be selected. Among them, barium is preferable from the viewpoint of better NO adsorption property at low temperature.

As the binder component, an organic binder or an inorganic binder such as an aqueous solution of zirconia sol or alumina sol can be used.

<Explanation of terms>
In the present specification, when expressed as “X to Y” (X and Y are arbitrary numbers), “preferably larger than X” or “preferably Y” is included together with the meaning of “X or more and Y or less” unless otherwise specified. It also means "less than".
Further, when expressed as “X or more” (X is an arbitrary number) or “Y or less” (Y is an arbitrary number), it means “preferably greater than X” or “less than Y”. It also includes intent.

Hereinafter, the present invention will be described in more detail based on the following examples and comparative examples.

<Example 1>
A Cu-supported alumina slurry was obtained by adding a 1 mass% La-containing θ-Al ₂ O ₃ powder to a copper nitrate aqueous solution and stirring the mixture, and then adding a zirconia sol.
Φ40 mm×L60 mm (300 cells): 165 g/L of the slurry obtained above was applied to a Koshigiken stainless honeycomb substrate having a carrier volume of 0.0754 L, and after blowing excess slurry, hot air at 100° C. was used as a slurry. The coated surface was dried by directly contacting it.
Next, after calcining at 450° C. for 1 hour to remove nitrate radicals, calcining was performed at 600° C. for 4 hours in nitrogen to obtain a catalyst (sample) of Example 1.
Each component in the slurry was 11.3 parts by mass of copper oxide, 80.2 parts by mass of alumina containing 1% by mass of La, and 8.5 parts by mass of zirconia sol.

<Examples 2 to 7, Comparative Examples 1 to 3>
As shown in Table 1, the catalysts of Examples 2 to 7 and Comparative Examples 1 to 3 were prepared in the same procedure as in Example 1 except that the mass% of copper oxide, the type of alumina, the firing temperature, and the firing atmosphere were changed. Sample) was obtained.
In Comparative Example 3, a Cu-supported alumina slurry was prepared, applied to a stainless honeycomb substrate and dried in the same manner as in Example 1, and baked at 450° C. for 1 hour to remove nitrate radicals. However, firing was not performed in nitrogen at 600° C. for 4 hours.

<Surface analysis by XPS>
The surfaces of the catalysts (samples) obtained in Examples and Comparative Examples were analyzed by X-ray photoelectron spectroscopy (XPS).
Quantum 2000 (beam condition: 50 W, 200 μm diameter) manufactured by ULVAC-PHI, Inc. was used as an XPS analyzer, and narrow measurement for state/semi-quantification was performed using “MultiPack ver. 6.1” as analysis software. An Al-Kα ray (1486.8 eV) was used as an X-ray source, and operation was performed at 17 kV×0.023A.
Charge correction: Charge correction was performed with C1s set to 284.0 eV.

More specifically, for the catalysts (samples) obtained in Examples and Comparative Examples, the catalyst surface was analyzed under the above conditions using an X-ray photoelectron spectrometer (XPS), and the obtained X-ray photoelectron spectrum , The total area of the peak areas obtained by detecting the Cu0 to divalent photoelectrons corresponding to the binding energy of Cu2p and the peak areas obtained by detecting the photoelectrons of the Al oxide corresponding to the binding energy of Al2p is 100%. The ratio of the peak area of Cu2p (“Cu coverage” in Table 1) was calculated.
Moreover, the Cu surface is analyzed under the above conditions using an X-ray photoelectron spectrometer (XPS), the peaks of 925 eV to 940 eV and the peaks of 925 eV to 935 eV are waveform-separated, and the peak areas of 925 eV to 940 eV (Cu0 to valence 2). The ratio of the peak area (corresponding to Cu0 to 1 valence) of 925 eV to 935 eV to (corresponding to) was calculated (“Cu0 to 1 valence area ratio (%)” in Table 1).
The X-ray photoelectron spectrometer (XPS) can perform semi-quantitative analysis on elemental components having a depth of about 10 nm from the particle surface.

<Measurement of average particle size>
The average particle size (D50) of alumina was measured using a laser diffraction/scattering type particle size distribution and is shown in Table 1.
A sample (powder) was put into a water-soluble solvent using an automatic sample feeder for a laser diffraction particle size distribution measuring device (“Microtorac SDC” manufactured by Nikkiso Co., Ltd.), and 30 W ultrasonic waves were applied at a flow rate of 50%. After irradiation for a second, the particle size distribution was measured using a laser diffraction particle size distribution measuring device "MT3000II" manufactured by Nikkiso Co., Ltd., and D50 was measured from the obtained volume-based particle size distribution chart. At this time, the measurement conditions were a particle refractive index of 1.5, a spherical particle shape, a solvent refractive index of 1.3, a set zero of 30 seconds, a measurement time of 30 seconds, and an average value of two measurements.

<H ₂ -TPR>
Heating the reaction method using H ₂ by (H _2-TPR), hydrogen was measured consumption peaks of the catalyst powder obtained in Examples and Comparative Examples (samples).
Specifically, using a flow-through tubular reactor equipped with a heat conduction type detector, 2% hydrogen (argon balance) was circulated to measure H ₂ -TPR at room temperature to 800° C. went. _{Incidentally,} in the peak area of the CuO _x and CuAl ₂ O ₄ hydrogen consumption peaks appearing hydrogen consumption peak of 100 to 350 ° C. seen in H 2-TPR measurements _CuO x, 350 ° C. or more as CuAl ₂ O _4, CuO _x and CuAl ₂ O CuAl ₂ O ₄ of the peak area ratio to the peak area of _{4 ((CuAl 2 O 4 /} (CuO x + CuAl 2 O 4)) × 100, "CuAl ₂ O ₄ peak area ratio of Table 1 ( %). Also, the amount of CuAl ₂ O ₄ was quantified from the obtained peak area (hydrogen consumption), and the “amount of CuAl ₂ O ₄ in the catalyst (mass %)” in Table 1 was determined.

In addition, when CuAl ₂ O ₄ peak area ratio (%)=0 in Table 1, it means a state where all Cu is supported on alumina as CuO _x , and when larger than 0, part of Cu is CuO _x. Is supported on alumina as a part, and a part thereof exists as a solid solution in alumina like CuAl ₂ O ₄ .
In addition, in Example 6 and Comparative Example 2, the content of copper oxide in the catalyst was higher than that of the other materials, so that the hydrogen consumption peak by H ₂ -TPR behaved differently from the others, and the accurate CuAl ₂ O ₄ content was shown. The peak could not be extracted. Therefore, "CuAl ₂ peak area ratio of O _4" and "CuAl ₂ O ₄ content in the catalyst" was quantified impossible. However, it was confirmed from XRD that most of Cu was present as CuO _x in Example 6 and most of Cu was present as CuAl ₂ O ₄ in Comparative Example 2.

<Exhaust gas purification performance evaluation test>
The catalyst (purification performance evaluation sample) obtained in each of the examples and comparative examples was measured for the temperature (° C.) at which 50% purification rate of CO, HC and NO _{x in} the model gas having the following composition was reached. The three-way purification performance of each catalyst was evaluated. The evaluation conditions are as follows.

(Model gas composition)
CO: 1.25%
C ₃ H _6: 1740ppm
NO: 2450ppm
O ₂ : 0.6%
CO ₂ : 14%
H ₂ O: 10%
N ₂ : balance A/F: 14.5
Gas flow rate: 25 L/min
Temperature rising rate: 20°C/min

From the above-mentioned Examples/Comparative Examples and the test results conducted by the present inventor so far, regarding the exhaust gas purifying catalyst having the structure in which the Cu element is present on the surface of the alumina particles, the X-ray photoelectron spectroscopy (XPS) ), when the total area of each peak area of Cu2p and Al2p measured as 100%, if the ratio of the peak area of Cu2p ("Cu coverage") is 7 to 28%, the noble metal as a catalytically active component. It was found that excellent catalytic activity is exhibited even without supporting.

Further, from the above-mentioned Examples/Comparative Examples and the test results conducted by the present inventor so far, the peak energy of 925 eV to 940 eV obtained by measuring the binding energy of the 2p orbital of Cu by X-ray photoelectron spectroscopy ( If the ratio of the peak area of 925 eV to 935 eV (corresponding to Cu0 to 1 valence) to Cu0 to valence of 2 (equivalent to Cu0 to 1 valence) is 50% or more, further increase the catalytic activity. It turns out that you can do it.

Further, from the above Examples and Comparative Examples and the test results to date present inventors have carried _{out, CuO x (0 ≦ x ≦} 1) and CuAl ₂ O ₄ wherein the warm reaction method by _{H 2 (H 2} - in the peak area of the CuO _x and CuAl ₂ O ₄ in the hydrogen consumption peak obtained by TPR), the peak area ratio of CuO _x and CuAl ₂ O ₄ of CuAl ₂ O ₄ to the peak area _{((CuAl 2 O 4 / (} CuO It has been found that the catalytic activity can be further increased when _x + CuAl ₂ O ₄ ))×100) is 50% or less.

Claims (4)

An exhaust gas purifying catalyst having a structure in which Cu element is present on the surface of alumina particles, each peak area of Cu2p and Al2p measured by X-ray photoelectron spectroscopy (XPS: X-ray Photoelectron Spectroscopy). , The peak area ratio of Cu2p is 7 to 28%, and is obtained by measurement by the X-ray photoelectron spectroscopy (XPS: X-ray Photoelectron Spectroscopy), 925 eV to An exhaust gas purifying catalyst, wherein the ratio of the peak area of 925 eV to 935 eV (corresponding to Cu 0 to 1 valence) to the peak area of 940 eV (corresponding to Cu 0 to 2 valence) is 50% or more. Include _{CuO x (0 ≦ x ≦ 1} ) and CuAl ₂ O _4, in the peak area of the CuO _x and CuAl ₂ O ₄ in the hydrogen consumption peak obtained by heating the reaction method using _{H 2 (H 2 -TPR),} CuO _{claims x} and CuAl ₂ O peak area ratio of CuAl ₂ O ₄ to the peak area of _{4 ((CuAl 2 O 4 /} (CuO x + CuAl 2 O 4)) × 100) is equal to or less than 50% The exhaust gas purifying catalyst according to 1. The exhaust gas purifying catalyst according to claim 1 or 3, wherein the content of CuAl ₂ O ₄ contained in the catalyst is 15% by mass or less. The exhaust gas purifying catalyst according to claim 1, wherein the exhaust gas purifying catalyst is a three-way catalyst.