JP2022144590A - Exhaust gas purification catalyst and its manufacturing method - Google Patents

Abstract

To provide a catalyst capable of reducing precious metals, while having excellent three-dimensional purification performance considering heat resistance as a three-component catalyst for simultaneously purifying CO, HC and NOx at a theoretical air fuel ratio, in a copper-containing alumina catalyst expected to be active at low cost.SOLUTION: An exhaust gas purifying catalyst contains copper and alumina, and an amount of copper contained is, when calculated by (number of moles of Cu)/[(number of moles of Al) + (number of moles of Cu) with respect to the total amount of alumina and copper )]×100, 1 to 20% relative to a total amount of alumina and copper.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to an exhaust gas purifying catalyst and a method for producing the same.

Copper catalysts have been attracting attention as catalysts for _purifying exhaust gases. (Practical technology).

In addition, the copper-supported alumina catalyst can improve the chemical and thermal instability of zeolites and their molecular sieve materials.

For example, using a catalyst in which copper is supported on aluminum by ion exchange so that the molar ratio of copper atoms to aluminum atoms (Cu/Al) is 0.01 to 0.1, carbonization from exhaust gas with excess oxygen Purification of nitrogen oxides in the presence of hydrogen has been described (see, for example, US Pat.

In addition, it is described that a highly heat-resistant copper-alumina composite oxide having two characteristic peaks in an X-ray diffraction pattern is placed in an oxygen-excess exhaust gas to purify NO _x in the exhaust gas ( For example, see Patent Document 4).

Recently, a catalyst technology has been disclosed in which a copper-containing catalyst is used as a three-way catalyst with an air-fuel ratio close to the stoichiometric air-fuel ratio instead of such excess oxygen, and it is possible to reduce the use of expensive and rare precious metals.

For example, Patent Document 5 discloses a spinel-type composite metal oxide catalyst in which the A-site element is Fe, Cr, Co, or Cu, and the B-site element is Mn, Fe, Cr, Co, or Al. , it is possible to sufficiently purify CO, _THC and NOx in the exhaust gas while preventing a decrease in activity due to oxidation.

However, when the concentration of CO, _THC , and NOx contained in the exhaust gas that has passed through this catalyst-supported substrate is 50% of that of the exhaust gas in the inflow gas, the purification temperature T50 is measured. The temperature ranges from 325°C to 600°C, and calcination is limited to relatively low temperatures up to about 600°C in order to create fine particles of the catalyst. Therefore, there is a problem that the heat resistance is poor and the heat durability is poor for use under the actual exhaust gas temperature of 600 to 800° C. and even higher temperatures.

Further, Patent Document 6 describes a catalyst comprising a first catalyst portion such as V, Cr, Fe, Mn, Ga, Zn, and a second catalyst portion such as Mn, Co, Ni, Cu, Mo. there is However, since it is necessary in principle to make fine particles in their production, firing at 500° C. is applied, and no countermeasures are taken against material changes in high-temperature exhaust gas.

Therefore, methods for more practically assisting the performance of noble metal catalysts have also been disclosed.

For example, Patent Document 7 describes a first purifying member that contains a 3d transition element such as copper but does not contain a noble metal, and also describes that it is supported on alumina. Modifications and configurations (arrangements) for replacing a portion of the precious metal catalyst are disclosed. However, the ratio of effective Rh and Pd noble metal reduction was one-fourth of the total (25% reduction), which was still insufficient in terms of cost.

Also, US Pat. No. 6,200,004 describes an oxidation catalyst composition comprising at least one platinum group metal impregnated in a porous alumina material, the porous alumina material comprising a copper-alumina spinel phase. According to Patent Document 8, it is described that the CO purifying activity after firing at 900° C. is excellent. However, it is not used for NO purification and does not have the performance of a three-way catalyst.

JP-A-1-203609 JP 2015-164729 A JP-A-5-329369 JP-A-8-059236 JP 2013-027858 A JP 2019-202269 A JP 2013-107056 A Japanese Patent Publication No. 2020-514034

From the above, although the copper-containing alumina catalyst is useful, as a three-way catalyst that simultaneously _purifies CO, HC and NOx at the stoichiometric air-fuel ratio, it has a three-way purification performance considering heat resistance and a precious metal reduction effect. However, the technology is not satisfactory.

The present invention is a copper-containing alumina catalyst that can be expected to be active at low cost, and is a three-way catalyst that simultaneously _purifies CO, HC, and NOx at a stoichiometric air-fuel ratio. An object of the present invention is to provide a catalyst that can reduce the

As a result of diligent efforts, the present inventors have determined that the amount of copper contained is (number of moles of Cu) / [(number of moles of Al) + (number of moles of Cu)] × 100 with respect to the total amount of alumina and copper. , the catalyst is 1 to 20% (preferably a catalyst in which Cu (1+) and Cu (2+) coexist as the oxidation number of copper observed in the X-ray absorption fine structure (XAFS) method ), as a three-way catalyst that simultaneously _purifies CO, HC and NOx at a stoichiometric air-fuel ratio, it is possible to reduce precious metals while having excellent three-way purification performance in consideration of heat resistance. Based on such findings, the inventors have further studied and completed the present invention. That is, the present invention includes the following configurations.

Section 1. An exhaust gas purification catalyst,
containing copper and alumina,
1 to 20% when the amount of copper contained is represented by (number of moles of Cu) / [(number of moles of Al) + (number of moles of Cu)] × 100 with respect to the total amount of alumina and copper. Exhaust gas purification catalyst.

Section 2. Item 2. The exhaust gas purifying catalyst according to item 1, wherein the copper is dissolved in the alumina crystal by substitution.

Item 3. Item 3. The exhaust gas purifying catalyst according to Item 1 or 2, wherein the copper contains copper-supported alumina supported on the alumina.

Section 4. General formula (1):
Al _1-x Cu _x O _y
[In the formula, x represents 0.01 to 0.2. y indicates 1.10 to 1.60. ]
Item 4. The exhaust gas purifying catalyst according to item 3, which has crystals having a composition represented by:

Item 5. 5. The exhaust gas purifying catalyst according to any one of items 1 to 4, wherein Cu(1+) and Cu(2+) coexist as copper oxidation numbers observed in an X-ray absorption fine structure (XAFS) method.

Item 6. 6. The exhaust gas purifying catalyst according to any one of Items 1 to 5, which has a specific surface area of 55 m ² /g or more and has a median distribution of pore volumes of 15 to 30 nm.

Item 7. 7. The exhaust gas purifying catalyst according to any one of Items 1 to 6, further comprising a noble metal supported thereon.

Item 8. Item 8. The exhaust gas purifying catalyst according to any one of items 1 to 7, which is arranged upstream and/or downstream in the passage direction of the exhaust gas as compared with the catalyst having a larger amount of noble metal supported than the exhaust gas purifying catalyst.

Item 9. A method for producing an exhaust gas purification catalyst according to any one of Items 1 to 8,
(1) impregnating the alumina with a copper precursor solution;
(2) firing at 500° C. or higher after step (1); and (3) firing at 800 to 1100° C. after step (2);
A manufacturing method comprising:

Item 10. moreover,
(4) The production method according to Item 9, comprising a step of treating with a gas corresponding to the exhaust gas composition at 500 to 700° C. after step (3).

Item 11. A method for purifying exhaust gas,
Using the exhaust gas purifying catalyst according to any one of items 1 to 8 and a catalyst having a larger amount of noble metal supported than the exhaust gas purifying catalyst, and
A purification method, wherein the exhaust gas purifying catalyst is arranged upstream and/or downstream in the passing direction of the exhaust gas compared to a catalyst having a larger amount of noble metal supported than the exhaust gas purifying catalyst.

According to the present invention, a copper-containing alumina catalyst, which can be expected to be active at low cost, is a three-way catalyst that simultaneously purifies CO, HC, and NO _x at a stoichiometric air-fuel ratio, and has excellent three-way purification performance in consideration of heat resistance. , a catalyst capable of reducing precious metals can be provided.

As used herein, "contain" is a concept that includes both "comprise," "consist essentially of," and "consist of."

Further, in this specification, when a numerical range is indicated by "A to B", it means from A to B.

The present invention is not limited to the following embodiments, and changes, modifications, and improvements can be made without departing from the scope of the invention.

1. Exhaust gas purifying catalyst The exhaust gas purifying catalyst of the present invention contains copper and alumina, and the amount of copper contained is calculated by dividing the total amount of alumina and copper by (number of moles of Cu) / [(number of moles of Al) + (number of moles of Cu)]×100, it is 1 to 20%.

(1-1) Copper In the exhaust gas purification catalyst of the present invention, the form of copper contained is not particularly limited, but the oxidation number of copper observed in the X-ray absorption fine structure (XAFS) method is Cu (1+ ) and Cu(2+) coexist. This makes it easier to improve the three-way purification performance and heat resistance.

Assuming that the total amount of copper contained in the exhaust gas purification catalyst of the present invention is 100 mol%, the content of Cu(1+) is preferably 0 to 61 mol%, and 1 to 22, from the viewpoint of three-way purification performance and heat resistance. Mole % is more preferred.

Assuming that the total amount of copper contained in the exhaust gas purification catalyst of the present invention is 100 mol%, the content of Cu(2+) is preferably 26 to 100 mol%, 77 to 99, from the viewpoint of three-way purification performance and heat resistance. Mole % is more preferred.

A part of the copper contained in the exhaust gas purifying catalyst of the present invention may be Cu(0). However, the content of Cu(0) is preferably small from the viewpoint of ternary purification performance and heat resistance. Specifically, the total amount of copper contained in the exhaust gas purification catalyst of the present invention is preferably 0 to 13 mol %, more preferably 0 to 1 mol %, based on 100 mol %. Furthermore, it is desirable that the amount of metallic copper is less than the amount of noble metal.

The Cu(1+)/Cu(2+) ratio tends to increase as the total amount of copper contained in the exhaust gas purification catalyst of the present invention increases. In other words, by using copper with mixed oxidation states, the oxidation number fluctuates as the catalytic reaction progresses, but it is easy to promote the oxidation-reduction reaction for exhaust gas purification, and the three-way purification performance and heat resistance are improved. Cheap.

In the exhaust gas purification catalyst of the present invention, from the viewpoint of ternary purification performance and heat resistance, the radial distribution function by extensive X-ray absorption fine structure (EXAFS) analysis is around 1.5 Å (1.45 to 1.55 Å, In particular, it is preferable that a peak is observed at 1.48 to 1.52 Å). On the other hand, from the viewpoint of ternary purification performance and heat resistance, the radial distribution function by extended X-ray absorption fine structure (EXAFS) analysis is around 2.1 Å (2.05 to 2.15 Å, especially 2.08 to 2.0 Å). 12 Å) and around 1.4 Å (1.35-1.45 Å, especially 1.38-1.42 Å). The peak around 1.5 Å belongs to the Cu—O bond, the peak around 2.1 Å belongs to the Cu—Cu bond, and the peak around 1.4 Å belongs to the Cu—O—Cu bond. That is, in the exhaust gas purifying catalyst of the present invention, it is preferable that the Cu species is not agglomerated.

(1-2) Alumina Examples of alumina include γ-alumina, θ-alumina, and δ-alumina. These aluminas can be used alone or in combination of two or more. Although any alumina can be used, γ-alumina is preferable from the viewpoint of ternary purification performance and heat resistance.

γ-alumina has a γ-phase as a crystal phase, and is not particularly limited, and examples thereof include known ones conventionally used in exhaust gas purifying catalysts and the like.

θ-alumina has a θ-phase as a crystal phase, and is a kind of intermediate (transition) alumina between γ-alumina and α-alumina. Such θ-alumina can be obtained, for example, by heat-treating γ-alumina in the atmosphere at 900 to 1100° C. for 1 to 10 hours.

δ-alumina can be obtained as an intermediate phase of the above two types (γ-alumina and θ-alumina) by methods such as the alkoxide method and coprecipitation method.

In addition, rare earth elements (Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, etc.), alkaline earth metals Alumina containing elements (Be, Mg, Ca, Sr, Ba, Ra, etc.) can also be used, and alumina containing these rare earth elements and alkaline earth metal elements is disclosed in, for example, JP-A-2004-243305. but is also commercially available, for example from Solvay. Furthermore, the coexistence of two or more rare earth elements does not interfere with the effect.

Furthermore, alumina can be used in the presence of other oxides and composite oxides (oxides containing two or more kinds of metals and not containing alumina), if necessary. For example, cerium oxide, cerium zirconium oxide, and zirconium oxide are particularly preferred, and they can coexist.

When other oxides, composite oxides, etc. coexist, the total amount of alumina and other oxides and composite oxides is 100% by mass, and the content of alumina is 50% by mass from the viewpoint of ternary purification performance and heat resistance. % or more is preferable, and 70% by mass or more is more preferable. In addition, the upper limit of the content rate of alumina is usually 100% by mass.

(1-3) Exhaust gas purifying catalyst In the exhaust gas purifying catalyst of the present invention, the amount of copper contained is calculated by dividing the total amount of alumina and copper by (number of moles of Cu)/[(number of moles of Al) + (number of Cu number of moles)]×100, it is 1 to 20%, preferably 3 to 10%, more preferably 5 to 8%. If the concentration of copper exceeds the above upper limit, the catalytic activity of the exhaust gas purifying catalyst is lowered. As the copper concentration increases, the content of the CuAl ₂ O ₄ spinel phase, which will be described later, tends to increase, and the CuAl ₂ O ₄ spinel phase does not have NO _x purification activity, so the copper concentration should not be too high. Further, when the concentration of copper is below the above lower limit, the catalytic activity of the exhaust gas purification catalyst is lowered. In addition, when the alumina contains a rare earth element or an alkaline earth metal element, or when the exhaust gas purification catalyst of the present invention contains other metal oxides, composite oxides, etc., the concentration of copper is such that the alumina component and copper is determined by the ratio of

As described above, the exhaust gas purifying catalyst of the present invention contains copper and alumina. is preferably

Further, in the exhaust gas purifying catalyst of the present invention, it is preferable that copper is dissolved in the alumina crystal by substitution. As a result, the copper is fixed in the alumina, and chemical and thermal stability can be expected, so that the ternary purification performance and heat resistance are particularly likely to be improved.

In this way, when copper is in a substitutional solid solution in the alumina crystal, general formula (1):
Al _1-x Cu _x O _y
[In the formula, x represents 0.01 to 0.2. y indicates 1.10 to 1.60. ]
It is preferable to have crystals with a composition represented by

In the general formula (1), x has the same meaning as the concentration of copper described above. In other words, x is preferably 0.01 to 0.2, more preferably 0.03 to 0.1, and even more preferably 0.05 to 0.08, from the viewpoint of catalytic activity of the exhaust gas purification catalyst. As x increases, the content of the CuAl ₂ O ₄ spinel phase, which will be described later, tends to increase, and the CuAl ₂ O ₄ spinel phase does not have NO _x purification activity, so x should not be too large.

In general formula (1), y is preferably 1.10 to 1.60, more preferably 1.20 to 1.60, and further 1.30 to 1.60 from the viewpoint of ternary purification performance and heat resistance. preferable. The oxygen component determines the composition of a stable composite metal oxide depending on the oxidation number of copper, and also includes the possibility that copper takes an oxidation number of 3 to 0 depending on the conditions during the reaction. can be understood as variable.

The exhaust gas purifying catalyst of the present invention is not limited to containing not only the crystals having the composition represented by the general formula (1), but also the CuAl ₂ O ₄ spinel phase. This CuAl ₂ O ₄ spinel phase tends to form more easily as the copper concentration increases.

However, although the CuAl ₂ O ₄ spinel phase has CO purification activity, its HC purification activity is low and it has no NO _x purification activity. , CuAl ₂ O ₄ spinel phase and the total amount of 100% by mass, the content of crystals having the composition represented by the above general formula (1) is preferably 50 to 100% by mass (especially 80 to 100% by mass), The content of the CuAl ₂ O ₄ spinel phase is preferably 0 to 40% by mass (especially 0 to 20% by mass).

Although the exhaust gas purifying catalyst of the present invention can reduce the amount of precious metals, it does not prevent the precious metals from being supported. Examples of such noble metals include one or more of Pt, Pd, Rh, Au, Ru, Ir, Ag, and the like. When these precious metals are supported, the supported amount is preferably 0.00001 to 20% by mass, preferably 0.0001 to 2%, based on the total amount of the exhaust gas purification catalyst of the present invention being 100% by mass, from the viewpoint of reducing the amount of noble metals. % by mass is more preferred. In this way, even if the amount of precious metal is reduced, it is possible to exhibit purification activity equal to or greater than that of the conventional catalyst.

Further, the exhaust gas purifying catalyst of the present invention can be used as a catalyst as it is, but can also be formed by coating it on a catalyst carrier, for example. The catalyst carrier is not particularly limited, and examples thereof include known catalyst substrate carriers such as honeycomb-shaped monolithic carriers made of cordierite, heat-resistant alloys, and the like.

The exhaust gas purification catalyst of the present invention as described above preferably has a specific surface area of 55 m ² /g or more, more preferably 55 to 300 m ² /g, from the viewpoint of three-way purification performance and heat resistance. More preferably 60 to 200 m ² /g. In the present invention, the specific surface area is measured by a nitrogen adsorption method.

From the viewpoint of three-way purification performance and heat resistance, the exhaust gas purifying catalyst of the present invention as described above preferably has a pore volume distribution of 10 to 30 nm, particularly 15 to 25 nm. In the present invention, the pore size distribution is measured by the nitrogen adsorption method and calculated by the BJH (Barrett-Joyner-Halenda) method.

Further, when using an exhaust gas purifying catalyst with a plurality of compartments, the exhaust gas purifying catalyst of the present invention has a larger amount of noble metal supported than the conventionally used exhaust gas purifying catalyst of the present invention. It can be installed upstream, downstream in the direction of passage of the exhaust gas, or both upstream and downstream in the direction of passage of the exhaust gas. In particular, from the viewpoint of activating a noble metal catalyst at a lower temperature, it is preferable to install the exhaust gas purifying catalyst of the present invention on the downstream side in the passage direction of the exhaust gas. It is also preferable from the viewpoint of reaction control to sandwich the exhaust gas purifying catalyst of the present invention between catalysts having a larger amount of noble metal supported than the exhaust gas purifying catalyst of the present invention.

The catalyst having a larger amount of noble metal supported than the exhaust gas purifying catalyst of the present invention is not particularly limited as long as the amount of noble metal supported is larger than that of the exhaust gas purifying catalyst of the present invention. As a noble metal (Pt, Pd, Rh, Au, Ru, Ir, Ag, etc.) 0.25 to 25.0% by mass, particularly 0.5 to 5.0% by mass. The catalyst carrier that can be used in this case includes, for example, a known catalyst substrate carrier such as a honeycomb-shaped monolithic carrier made of cordierite, a heat-resistant alloy, or the like.

In the case of using an exhaust gas purifying catalyst for a plurality of compartments, if the exhaust gas purifying catalyst of the present invention is used in some compartments, conventionally used exhaust gas purifying catalysts can be used in other compartments, and there are particular restrictions. no.

2. Method for producing exhaust gas purifying catalyst The method for producing the exhaust gas purifying catalyst of the present invention is not particularly limited,
(1) impregnating the alumina with a copper precursor solution;
(2) a step of firing at 500° C. or higher after step (1); and (3) a step of firing at 800 to 1100° C. after step (2).

Also, after step (3),
(4) After the step (3), it is preferable to include a step of treating with a gas corresponding to the exhaust gas composition at 500 to 700°C.

For adding copper to alumina, for example, first, a copper-containing salt solution (copper precursor solution) is prepared, alumina is impregnated with this salt-containing solution (step (1)), and then calcined ( Steps (2) and (3)).

In step (1), alumina and other metal oxides can be mixed, and the mixing method is not particularly limited, and examples thereof include known physical mixing methods such as dry mixing, wet mixing, and pulverization mixing. be done.

Examples of salts containing copper include inorganic salts such as sulfates, nitrates, chlorides and phosphates; and organic acid salts such as acetates and oxalates. A copper-containing salt solution can be prepared, for example, by adding the above-mentioned salt to water in a proportion that gives a predetermined stoichiometric ratio, and stirring and mixing.

Examples of practical examples of the salt solution containing copper include a copper nitrate solution, a copper chloride solution, and the like. By adjusting the copper concentration, the content concentration of copper in the exhaust gas purification catalyst can be adjusted.

Regarding the concentration of the copper-containing salt solution, the copper concentration is, for example, preferably 0.01 to 60% by mass, more preferably 5 to 50% by mass, with the total amount of the copper-containing salt solution being 100% by mass.

When the alumina is θ-alumina, δ-alumina, or γ-alumina, it is coprecipitated with a copper-containing salt solution when it is precipitated from an aqueous aluminum salt solution using ammonia or the like in the process of producing the alumina. and then sintering to obtain alumina containing copper.

The firing temperature in step (2) is 500° C. or higher, preferably 550 to 650° C. from the viewpoint of reaction between components.

The firing time in step (2) is not particularly limited, but from the viewpoint of progress of the reaction, it is preferably 30 minutes to 24 hours, more preferably 1 to 3 hours.

The firing temperature in step (3) is 800-1100° C., preferably 850-950° C., from the viewpoint of product stabilization.

The firing time in step (3) is not particularly limited, but from the viewpoint of progress of stabilization, it is preferably 30 minutes to 24 hours, more preferably 1 to 3 hours.

After the step (3), it is preferable to heat-treat with a gas corresponding to the exhaust gas composition, the temperature is preferably 500 to 700 ° C. (especially 550 to 650 ° C.), and the heating time is 10 minutes to 3 hours (especially 30 minutes to 1 hour) is preferred.

As an alternative to treatment with a gas equivalent to the exhaust gas composition, for example, heat treatment is performed in an inert gas stream containing a low concentration hydrogen gas of about 5% by mass, and then at 500 to 700 ° C. for a short time or with a small amount of oxygen. Alternatively, an oxidation treatment may be performed, that is, a treatment under oxidation-reduction conditions may be performed.

In order to produce the exhaust gas purifying catalyst of the present invention by coating it on a catalyst carrier, for example, first, the above-described exhaust gas purifying catalyst, and further, other known heat-resistant oxides and exhaust gas purifying oxides mixed as necessary. Water is added to the catalyst to form a slurry, which is coated on a catalyst substrate, dried in the air at, for example, 50 to 200° C. for 1 to 48 hours, and then calcined at 250 to 1000° C. for 1 to 12 hours. can be done.

Examples are given below to further describe the present invention, but the present invention is not limited to the examples.

[Example 1]
Activated alumina powder manufactured by Sumitomo Chemical Co., Ltd. (specific surface area: 135 m ² /g, crystal form: γ-alumina) was impregnated with an aqueous solution of copper nitrate, dried at 110°C for one day and night, and then dried in an electric furnace at 600°C in the atmosphere. It was heat-treated (calcined) for 1 hour and further calcined at 900° C. for 10 hours to obtain an exhaust gas purifying catalyst which was a copper-containing alumina powder (copper-supported alumina in which copper was supported on alumina).

When the ratio of copper is expressed as x = (number of moles of Cu) / [(number of moles of Al) + (number of moles of Cu)] x = 0.01, 0.03, 0.05, 0.08 , 0.1, 0.2, and 0.33, exhaust gas purifying catalysts with different copper contents were obtained through the above steps.

When the specific surface area was measured by a nitrogen adsorption method, it was 120 m ² /g at x = 0.01, 101 m ² /g at x = 0.03, 100 m ² /g at x = 0.05, and 100 m 2 /g at x = 0.08. 92 m ² /g, 82 m ² /g at x=0.1, 55 m ² /g at x=0.2 and 45 m ² /g at x=0.33.

Moreover, in the pore volume measurement, all the samples had a distribution center at 15 to 30 nm.

Both the specific surface area and the pore volume hardly change even when a mixed gas simulating the components in the exhaust gas of a gasoline engine is passed through later.

A powder with a high specific surface area is preferable for improving activity, suggesting that performance improvement can be expected at x=0.01 to 0.2.

[Example 2]
The three-way catalyst activity measurement of the catalyst obtained in Example 1 was carried out using a fixed bed flow reactor. 100 mg (0.1 g) of the sample was weighed and set in a straight reaction tube, and a mixed gas (Table 1, volume % display) simulating the components in the exhaust gas of a gasoline engine was passed at a flow rate of 500 mL / min to pass through the catalyst. The post gas composition was measured and a catalyst performance test was performed.

In the temperature rising process, the temperature was raised from room temperature to 700 ° C. at 10 ° C./min, held for 30 minutes, then gradually cooled to room temperature, cooled in air, and then raised to 700 ° C. at 4 ° C./min. , NO and C ₃ H ₆ conversion rates were used to evaluate the activity of the catalyst. The space velocity converted to volume is 120000/hour.

The temperature at which 50% purification is achieved (50% purification temperature (T50)) and the temperature at which 80% purification is achieved (80% purification temperature (T80)) are measured (the temperature is expressed in °C, the same shall apply hereinafter) and the table is displayed. Summarized in 2. In addition, in Table ₂ , HC shows _C3H6 .

From the above, in the exhaust gas purifying catalyst, the amount of copper and alumina is 1 to 20 when the ratio of copper is expressed as (number of moles of Cu) / [(number of moles of Al) + (number of moles of Cu)] × 100. It can be seen that % is preferred. Also, considering the NO purification rate, it is preferably 3 to 10%, more preferably 5 to 8%. Here, with the catalysts with x=0.05 and 0.08, the conversion rates of CO, NO and C ₃ H ₆ were all 100% at 600°C. That is, the copper-alumina powder is sintered at 900°C and is a single material in which copper is stably fixed, and can be used as a catalyst capable of purifying 100% of the three components at 600°C.

[Example 3]
The produced phase and crystal plane spacing were examined by X-ray diffraction method. The crystal structure of the prepared sample was evaluated by using an X-ray diffractometer (MiniFlexII manufactured by Rigaku Co., Ltd.). The (440) crystal plane spacing of alumina was measured from the XRD measurement results for samples of each composition.

In the sample with x=0.33 in Example 1, a spinel phase of CuAl ₂ O ₄ was formed. On the other hand, in the samples with x = 0.01, 0.03, 0.05, 0.08, and 0.1, the crystal plane spacing of the original alumina phase changed sequentially, and the XRD peak shifted. , a form in which Al ions are replaced by Cu ions, that is, Al _1-x Cu _x O _y , and the Cu species added in the range of x = 0 to 0.1 is substituted and dissolved in the Al ₂ O ₃ crystal. It was shown (Table 3). It is considered that there is an approximate proportional relationship between the lattice constant and the concentration of the constituent elements. Furthermore, from the relationship between the interplanar spacing and the composition, the solid solution amount of copper tends to increase in the original alumina phase (γ phase) within the range of x=0.2. In other words, in the range of x=0 to 0.2, it is suggested that all or most of the added Cu species dissolved in Al ₂ O ₃ by substitution. The ₂ O ₄ spinel phase coexists, and the ratio of the spinel phase with low activity increases. Thus, at x = 0.0 to 0.2, all or part of the copper is fixed in the original active (γ phase-derived) alumina, and chemical and thermal stability is expected. It is a catalyst that can At this time, since the spinel phase does not have NO purification activity as shown in Example 2, there is an upper limit to the optimum x.

Next, the interplanar spacing of the (440) plane was measured by XRD after evaluating the three-way catalyst activity. The composition relationships are listed in Table 3. While the interplanar spacing increased in the range of x=0 to 0.1, it was about 1.405 Å above that. The solid solubility limit of Cu species differs between the catalyst during preparation in the atmosphere and after the three-way catalytic reaction, x=0 to 0.2 or less for the former, and x=0 to 0.08 or less for the latter. As the amount of copper added increases, the activity of the three-way catalyst increases, and in the composition, it is most desirable that the Cu species remain dissolved in Al ₂ O ₃ without precipitating even after the catalytic reaction. It is suggested that the greater the number of , the better the catalytic activity. Even when x=0.08 to 0.2, it is conceivable that other phases are mixed, but since the amount of active copper as a whole is large, the purification activity can be maintained. Of course, if x is over 0.2 and there is too much copper, CuO and Cu ₂ O are formed as a solid phase in addition to the CuAl ₂ O ₄ phase, which is undesirable because it covers the surface.

XAFS measurements were performed to investigate differences in the chemical state and structure of Cu in the catalyst. The oxidation state of Cu species was analyzed by fitting XANES (X-ray absorption edge structure area) (Table 4). Cu, CuO and Cu ₂ O were used as reference samples. Cu(1+) and Cu(2+) coexist, the ratio is Cu(1+)/Cu(2+)=1-61/99-26 (mol ratio). The ratio of Cu(1+)/Cu(2+) tends to decrease with increasing x depending on the composition. In other words, it is shown that copper in mixed oxidation states is important for ternary activity in this catalyst. A small amount of Cu(0) does not affect the purification characteristics, and its presence does not hinder the use of the present catalyst.

In addition, from the EXAFS analysis results (radial distribution function), all peaks around 1.5 Å attributed to Cu—O bonds were confirmed in the composition, but 2 attributed to Cu—Cu bonds and Cu—O—Cu bonds. Few peaks near 0.1 Å and 1.4 Å were observed, indicating that the Cu species were not aggregated. Cu species are mainly present as Cu(2+) and Cu(1+) in a highly dispersed state within and on the surface of alumina. It is thought to promote oxidation-reduction reactions. It can be understood that it is preferable to coexist with the oxidation number of Cu dispersed within a certain range.

[Example 4]
Among the catalysts obtained in Example 1, catalysts with x=0, 0.05 and 0.08 were used to prepare platinum (Pt)-supported catalysts. The amount of Pt supported was set to 0.1 mass % equivalent to the catalyst weight. It was impregnated with a dinitrodiammineplatinum (II) nitric acid solution (Tanaka Kikinzoku Kogyo Co., Ltd.), dried at 90°C for about 24 hours, and heat-treated in air at 600°C for 3 hours to obtain a Pt-supported catalyst. After that, the sample was heat-treated in the atmosphere at 900° C. for 3 hours to prepare a sample. For these, the three-way catalyst activity measurement of Example 2 was performed using a fixed bed flow reactor under the same conditions as in Example 2 to perform a performance evaluation test. As a comparative example, a catalyst with x=0 (alumina carrier) supporting 0.5% by mass of Pt was prepared and evaluated in the same manner.

The temperature at 50% purification (50% purification temperature (T50)) and the temperature at 80% purification (80% purification temperature (T80)) were measured, and the results are shown in Table 5. In addition, in Table ₅ , HC shows _C3H6 .

The Al ₂ O ₃ catalyst (x=0) supporting 0.1% by mass of Pt showed only a purification rate of 30% or less even when the temperature was raised to 700°C. On the other hand, the catalyst obtained by adding 0.1% by mass of Pt to the copper-alumina catalyst had sufficient purification performance. This purification performance is almost the same as that of the 0.5% by mass Pt/Al ₂ O ₃ catalyst, and considering the amount of Pt, the present invention has the effect of being able to make a catalyst with activity equivalent to that of the conventional catalyst at 20%. rice field.

[Example 5]
Next, the performance was further evaluated with respect to the use of equivalent zone-coated catalysts. 0.010 g of 1% by mass Pd/Al ₂ O ₃ catalyst (x=0) was placed in the front, and 0.090 g of the catalyst with x=0.08 obtained in Example 1 was placed in the rear (implementation sample Z1: Pd amount 90 % reduction). Furthermore, for comparison, a 0.1% by mass Pd-supported alumina catalyst (H1) and a 0.25% by mass Pd-supported alumina catalyst (H2) were similarly produced using an alumina carrier (x=0). The three-way catalyst activity measurement of Example 2 was performed using a fixed bed flow reactor under the same conditions as the performance evaluation test. As shown in Table 6, the Z1 catalyst of the present invention exhibits purification performance at a lower temperature than the 0.1 mass % Pd catalyst of H1 and the 0.25 mass % Pd catalyst of H2 of the comparative examples. It was highly active. As an effect of reducing Pd, the present invention sample of this example showed similar or better performance with 0.1% by mass of Pd compared to the catalyst with 0.25% by mass of Pd, and the amount of Pd was reduced. The effect of maintaining the activity of the catalyst is also evident.

[Example 6]
In addition, the performance was evaluated for the utilization of another zone-coated catalyst equivalent. 0.025 g of 1% by weight Pd/Al ₂ O ₃ catalyst (x=0) in front and 0.025 g and 0.075 g of catalyst with x=0.08 obtained in Example 1 behind, respectively (mass A test was conducted for the arrangement (Z2) with a ratio of 1:3). In addition, 0.075 g of the catalyst with x = 0.08 obtained in Example 1 was placed in the front, and 0.025 g of the 1% by mass Pd/Al ₂ O ₃ catalyst (x = 0) was placed in the rear (implementation sample Z3). , so that the total amount of catalyst was 0.1 g. In other words, the same evaluation was made for the case where the catalyst arrangement was reversed. Furthermore, a 0.5% by mass Pd/Al ₂ O ₃ catalyst (H3) in which the total amount of Pd is doubled (0.5% by mass) was produced and compared. The three-way catalyst activity measurement of Example 2 was performed using a fixed bed flow reactor under the same conditions as the performance evaluation test. The results are shown in Table 7. Z2, Z3 and H3 are almost the same in terms of performance, and it is clear that they have the effect of halving the amount of Pd. Moreover, the position of placing the copper catalyst did not matter before or after the noble metal catalyst.

These results show that the use of the catalyst of the present invention in a honeycomb or other shaped converter or in a multi-reactor arrangement catalytic apparatus can significantly reduce the amount of precious metals.

Claims (11)

An exhaust gas purification catalyst,
containing copper and alumina,
1 to 20% when the amount of copper contained is represented by (number of moles of Cu) / [(number of moles of Al) + (number of moles of Cu)] × 100 with respect to the total amount of alumina and copper. Exhaust gas purification catalyst. 2. The exhaust gas purifying catalyst according to claim 1, wherein said copper is in substitution solid solution in said alumina crystals. 3. The exhaust gas purifying catalyst according to claim 1, wherein said copper contains copper-supported alumina supported on said alumina. General formula (1):
Al _1-x Cu _x O _y
[In the formula, x represents 0.01 to 0.2. y indicates 1.10 to 1.60. ]
4. The exhaust gas purifying catalyst according to claim 3, having crystals having a composition represented by: The exhaust gas purifying catalyst according to any one of claims 1 to 4, wherein Cu(1+) and Cu(2+) coexist as oxidation numbers of copper observed by an X-ray absorption fine structure (XAFS) method. The exhaust gas purifying catalyst according to any one of claims 1 to 5, which has a specific surface area of 55 m ² /g or more and has a median distribution of pore volumes of 15 to 30 nm. 7. The exhaust gas purifying catalyst according to any one of claims 1 to 6, further carrying a noble metal. The exhaust gas purifying catalyst according to any one of claims 1 to 7, which is arranged upstream and/or downstream in the passing direction of the exhaust gas, compared to the catalyst having a larger amount of noble metal supported than the exhaust gas purifying catalyst. A method for producing an exhaust gas purification catalyst according to any one of claims 1 to 8,
(1) impregnating the alumina with a copper precursor solution;
(2) a step of firing at 500° C. or higher after step (1); and (3) a step of firing at 800 to 1100° C. after step (2). moreover,
(4) The production method according to claim 9, comprising a step of treating with a gas corresponding to the exhaust gas composition at 500 to 700°C after step (3). A method for purifying exhaust gas,
Using the exhaust gas purification catalyst according to any one of claims 1 to 8 and a catalyst having a higher amount of noble metal supported than the exhaust gas purification catalyst, and
A purification method, wherein the exhaust gas purifying catalyst is arranged upstream and/or downstream in the passing direction of the exhaust gas compared to a catalyst having a larger amount of noble metal supported than the exhaust gas purifying catalyst.