JP6335087B2 - Exhaust gas purification catalyst - Google Patents

Description

  The present invention relates to an exhaust gas purification catalyst, and more particularly to an exhaust gas purification catalyst for purifying exhaust gas discharged from an internal combustion engine or the like.

An exhaust gas purifying catalyst comprising a three-way catalyst capable of simultaneously purifying carbon monoxide (CO), hydrocarbon (HC) and nitrogen oxide (NO _x ) contained in exhaust gas is a precious metal such as Pt, Rh and Pd. Active substance.

  Since such noble metals, especially Pt and Rh, are expensive and the price fluctuates severely, various catalysts that can be produced at low cost without using noble metals have been studied.

  Thus, a catalyst is proposed in which, for example, Cu, which is a transition metal, is used as an active component instead of a noble metal element, and is supported on a catalyst carrier (alumina) (see, for example, Patent Document 1).

JP-A-5-329369

  On the other hand, from the viewpoint of reducing environmental burdens in recent years, it is increasingly desired to improve the purification performance of exhaust gas purification catalysts.

  Then, this invention is providing the catalyst for exhaust gas purification which can aim at the improvement of exhaust gas purification performance, being able to reduce use of platinum.

  The exhaust gas purifying catalyst of the present invention includes a first catalyst in which copper is supported on a cerium-containing oxide and a second catalyst in which platinum is supported on alumina, and the supported ratio of copper is the same as that of the first catalyst. It is 0.75 mass% or more with respect to the sum total with the said 2nd catalyst, and the loading ratio of the said platinum is less than 1 mass% with respect to the sum total with the said 1st catalyst and the said 2nd catalyst. It is characterized by.

  According to the exhaust gas purifying catalyst of the present invention, the copper loading ratio is 0.75% by mass or more with respect to the total of the first catalyst and the second catalyst. Even if it reduces so that it may become less than 1 mass% with respect to the sum total with a 2nd catalyst, the improvement of exhaust gas purification performance can be aimed at. Therefore, the exhaust gas purification performance can be improved while the use of platinum can be reduced.

FIG. 1 is a graph showing the 50% purification temperature of CO with respect to the copper loading ratio of the exhaust gas purification catalysts of each Example and each Comparative Example. FIG. 2 is a graph showing the 50% CO purification temperature of the exhaust gas purifying catalysts of each Example and each Comparative Example.

  The exhaust gas purifying catalyst of the present invention includes a first catalyst in which copper is supported on a cerium-containing oxide, and a second catalyst in which platinum is supported on alumina.

1. Regarding the first catalyst Examples of the cerium-containing oxide include cerium oxide (CeO ₂ ) and ceria-based composite oxides represented by the following general formula (1).
General formula (1)
Ce _{1- (a + b)} Zr _a L _b O _2-c (1)
(Wherein L represents a rare earth element (excluding Ce) and / or alkaline earth metal, a represents the atomic ratio of Zr, b represents the atomic ratio of L, and 1- ( a + b) indicates the atomic ratio of Ce, and c indicates the amount of oxygen defects.)
In the general formula (1), examples of the rare earth element represented by L include Sc (scandium), Y (yttrium), La (lanthanum), Pr (praseodymium), Nd (neodymium), Pm (promethium), Sm ( Samarium), Eu (europium), Gd (gadolinium), Tb (terbium), Dy (dysprosium), Ho (holmium), Er (erbium), Tm (thulium), Yb (ytterbium), Lu (lutetium) and the like It is done.

  In the general formula (1), examples of the alkaline earth metal represented by L include Be (beryllium), Mg (magnesium), Ca (calcium), Sr (strontium), Ba (barium), Ra (radium), and the like. Is mentioned.

  Among such rare earth elements and alkaline earth metals represented by L, rare earth elements are preferable, and Y (yttrium) is more preferable. These rare earth elements and alkaline earth metals can be used alone or in combination of two or more.

  In the general formula (1), the atomic ratio of Zr represented by a is in the range of 0.2 to 0.7, preferably 0.2 to 0.5 (preferably less than 0.5). Range.

  Moreover, in General formula (1), the atomic ratio of L shown by b is the range of 0-0.2, Preferably, it is the range of 0.01-0.1. That is, L is not an essential component but an optional component, and when included, has an atomic ratio of 0.2 or less. When the atomic ratio of L indicated by b exceeds 0.2, phase separation or other complex oxide phases may be generated.

  In the general formula (1), the atomic ratio of Ce represented by 1- (a + b) is preferably more than a, specifically in the range of 0.3 to 0.8, preferably It is in the range of 0.5 to 0.6.

  Further, in the general formula (1), c represents the amount of oxygen defects, and this is the ratio of vacancies that can be formed in the crystal lattice of the fluorite-type crystal lattice that is usually formed by the oxides of Ce, Zr, and L. means.

  The ceria-based composite oxide is not particularly limited. For example, according to the description of paragraph numbers [0090] to [0102] of JP-A-2004-243305, a suitable ceria-based composite oxide for preparing the composite oxide can be used. It can be produced by a method such as a coprecipitation method, a citric acid complex method, or an alkoxide method.

Among such cerium-containing oxides, a ceria-based composite oxide represented by the general formula (1) is preferable, and Ce _{1- (a + b)} Zr _a Y _b O _2-c is more preferable. The ceria-zirconia type complex oxide shown by these is mentioned.

  The method for supporting copper on the cerium-containing oxide is not particularly limited, and a known method can be used.

  More specifically, for example, first, a salt solution containing copper is prepared, the cerium-containing oxide is impregnated with the salt solution containing copper, and then dried and fired as necessary.

  Examples of the salt containing copper include copper inorganic acid salts (for example, sulfate, nitrate, chloride, phosphate, etc.), copper organic acid salts (for example, acetate, oxalate, etc.) and the like. It is done.

  Moreover, the solution of the salt containing copper can be prepared, for example, by adding the above-mentioned salt to water at a ratio that gives a predetermined stoichiometric ratio and stirring and mixing.

  Moreover, practical examples of the salt solution containing copper include an aqueous copper (II) nitrate solution (such as an aqueous solution of copper (II) nitrate trihydrate).

  And the copper loading ratio in the exhaust gas purifying catalyst can be adjusted by adjusting the copper concentration (copper content) of the salt solution containing copper.

  The firing temperature after impregnating the cerium-containing oxide with a salt solution containing copper is, for example, 350 to 1000 ° C., preferably 400 to 800 ° C., and the firing time is, for example, 0.5 -5 hours, preferably 0.5-3 hours.

  Thereby, copper (more specifically, copper oxide) is supported on the cerium-containing oxide, and the first catalyst is prepared.

  In the first catalyst, the loading ratio of copper (in metal conversion) is, for example, 0.83% by mass or more, preferably 1% by mass or more, more preferably 2% by mass or more, for example, 24% by mass or less, preferably , 21% by mass or less, more preferably 10% by mass or less, and particularly preferably 7% by mass or less.

2. Regarding the second catalyst As the alumina, for example, α-alumina, θ-alumina, γ-alumina and the like are mentioned, and preferably θ-alumina is mentioned.

  α-alumina has an α-phase as a crystal phase, and examples thereof include AKP-53 (trade name, high-purity alumina, manufactured by Sumitomo Chemical Co., Ltd.). Such α-alumina can be obtained by a method such as an alkoxide method, a sol-gel method, or a coprecipitation method.

  θ Alumina is a kind of intermediate (transition) alumina that has a θ phase as a crystal phase and transitions to α alumina. For example, activated alumina such as SPHERALITE 531P (trade name, γ alumina, manufactured by Procatalyze) (Γ-alumina) can be obtained by heat treatment at 900 to 1100 ° C. for 1 to 10 hours in the air.

  γ-alumina has a γ-phase as a crystal phase and is not particularly limited, and examples thereof include known ones used for exhaust gas purification catalysts.

  In addition, alumina containing La and / or Ba can also be used. Alumina containing La and / or Ba can be produced according to the description of paragraph number [0073] of JP-A No. 2004-243305.

  The method for supporting platinum on alumina is not particularly limited, and a known method can be used.

  More specifically, for example, first, a solution of a salt containing platinum is prepared, and after impregnating alumina with the solution of the salt containing platinum, if necessary, the solution is dried and fired.

  Examples of the salt containing platinum include dinitrodiammine platinum and platinum chloride.

  Moreover, the solution of the salt containing platinum can be prepared, for example, by adding the above-mentioned salt to the inorganic acid at a ratio that gives a predetermined stoichiometric ratio and stirring and mixing. Examples of the inorganic acid include hydrochloric acid, sulfuric acid, nitric acid and the like.

  As a salt solution containing platinum, practically, for example, a dinitrodiammine platinum nitric acid solution (so-called Pt-P salt nitric acid solution) and the like can be mentioned.

  And the carrying | support ratio of the platinum in the exhaust gas purification catalyst can be adjusted by adjusting the platinum concentration (platinum content) of such a salt solution containing platinum.

  Moreover, the calcination temperature after impregnating the salt solution containing platinum in alumina is, for example, 350 to 1000 ° C., preferably 400 to 800 ° C., and the calcination time is, for example, 0.5 to 5 hours, Preferably, it is 0.5 to 3 hours.

  As a result, platinum is supported on alumina, and the second catalyst is prepared.

In the second catalyst, the loading ratio of platinum (in metal conversion) is, for example, 0.01% by mass or more, preferably 0.025% by mass or more, more preferably 0.03% by mass or more, for example, 10% by mass. Less than, preferably 1.1% by mass or less, and more preferably 0.07% by mass or less.
3. Exhaust gas purification catalyst The exhaust gas purification catalyst is prepared by pulverizing and mixing the first catalyst and the second catalyst.

  The blending ratio of the first catalyst is, for example, 10% by mass or more, preferably 40% by mass or more, more preferably 50% by mass or more, for example, 90% by mass with respect to the sum of the first catalyst and the second catalyst. Hereinafter, it is preferably 80% by mass or less.

  The blending ratio of the second catalyst is, for example, 10% by mass or more, preferably 20% by mass or more, for example, 90% by mass or less, preferably 60% by mass or less, with respect to the total of the first catalyst and the second catalyst. More preferably, it is 50 mass% or less.

  If the blending ratio of each of the first catalyst and the second catalyst is within the above range, the exhaust gas purification performance can be reliably improved.

  Further, the loading ratio of copper (in metal conversion) is 0.75% by mass or more, preferably 1.0% by mass or more, and more preferably 1.5% by mass with respect to the total of the first catalyst and the second catalyst. % Or more, for example, 12% by mass or less, preferably 10% by mass or less, more preferably 5% by mass or less, and particularly preferably 4% by mass or less.

  When the copper loading ratio is in the above range, the exhaust gas purification performance can be reliably improved.

  In addition, the supported proportion of platinum (in metal conversion) is, for example, 0.01% by mass or more, preferably 0.02% by mass or more and less than 1% by mass, preferably with respect to the total of the first catalyst and the second catalyst. Is 0.04 mass% or less.

  If the platinum loading ratio is equal to or higher than the lower limit value, the exhaust gas purification performance can be reliably improved, and if the platinum loading ratio is less than the upper limit value, the amount of platinum used can be reduced. .

  The mass ratio of platinum to copper (platinum: copper) in the exhaust gas purification catalyst is, for example, 1:20 to 1: 500, preferably 1:30 to 1: 400, more preferably 1: 100. ~ 1: 200.

The specific surface area (BET specific surface area) of the exhaust gas purifying catalyst is, for example, 65 m ² / g or more, preferably 70 m ² / g or more, more preferably 71 m ² / g or more, for example, 80 m ² / g or less. It is preferably 75 m ² / g or less, more preferably 73 m ² / g or less.

  If the specific surface area of the exhaust gas purification catalyst is in the above range, the exhaust gas purification performance can be reliably improved and excellent processability can be obtained. Moreover, peeling when the exhaust gas purifying catalyst is formed as a coat layer as described later can be suppressed.

  The exhaust gas-purifying catalyst thus obtained can be used as it is, but for example, can be supported (coated) on a catalyst carrier.

  The catalyst carrier is not particularly limited, and examples thereof include known catalyst carriers such as a honeycomb monolith carrier made of cordierite.

  For carrying (coating) on the catalyst carrier, for example, first, water is added to the obtained exhaust gas-purifying catalyst to form a slurry, which is then coated on the catalyst carrier, dried, and then about 300-800. The heat treatment is performed at a temperature of about 300 to 600 ° C.

  In such a case, the catalyst for purification of exhaust gas of the present invention is a known heat-resistant oxidation such as alumina or complex oxide (for example, perovskite complex oxide, fluorite complex oxide) if necessary. Can be used in combination with food.

  Such an exhaust gas purifying catalyst includes a first catalyst in which copper is supported on a cerium-containing oxide, and a second catalyst in which platinum is supported on alumina.

Since the copper loading ratio is 0.75% by mass or more with respect to the total of the first catalyst and the second catalyst, the platinum loading ratio is set to the total of the first catalyst and the second catalyst. Even if the amount is reduced to less than 1% by mass, exhaust gas (carbon monoxide (CO), hydrocarbon (HC) and nitrogen oxide (NO _x ) discharged from an internal combustion engine (eg, gasoline engine, diesel engine, etc.)) In particular, CO) can be well purified. Therefore, it is possible to improve the exhaust gas purification performance while reducing the use of platinum.

  Such an exhaust gas purifying catalyst can be suitably used as a catalyst for purifying exhaust gas discharged from an engine, particularly as a catalyst for purifying exhaust gas discharged from a diesel engine.

  Next, although this invention is demonstrated based on an Example and a comparative example, this invention is not limited by the following Example. In the following description, “part” and “%” are based on mass unless otherwise specified. In addition, the numerical value of the Example shown below can be substituted to the corresponding numerical value (namely, upper limit value or lower limit value) described in embodiment.

Production Example 1
Cerium methoxypropylate [Ce (OCH (CH ₃ ) CH ₂ OCH ₃ ) ₃ ] is 0.1 mol in terms of Ce and zirconium methoxypropylate [Zr (OCH (CH ₃ ) CH ₂ OCH ₃ ) ₃ ] is in terms of Zr 0.09 mol, yttrium methoxypropylate [Y (OCH (CH ₃ ) CH ₂ OCH ₃ ) ₃ ] in 0.01 mol in terms of Y and 200 mL of toluene were mixed and stirred to dissolve, A mixed alkoxide solution was prepared.

Further, 80 mL of deionized water was added dropwise to the mixed alkoxide solution for hydrolysis. From the hydrolyzed solution, toluene and deionized water were distilled off and evaporated to obtain a dry solid. The obtained solid was air-dried at 60 ° C. for 24 hours and then heat-treated (fired) at 450 ° C. for 3 hours in an electric furnace, whereby Ce _0.50 Zr _0.45 Y _0.05 O _2. A powder of a ceria-zirconia-based composite oxide (hereinafter referred to as CZY) shown in FIG.

Example 1
To 4.98 parts by mass of CZY powder, an aqueous solution of copper (II) nitrate (specifically, 0.29 parts by mass of copper (II) nitrate trihydrate salt having a copper content of 26.04 mass% was added to 30 parts by mass of water). 30.3 parts by mass of an aqueous solution prepared by dissolving in copper, dried at 110 ° C for one day and night, and then heat-treated (fired) at 650 ° C for 1 hour in the air in an electric furnace to support copper. 5.00 parts by mass of CZY powder (first catalyst, hereinafter abbreviated as Cu-supported CZY) was obtained. In the Cu-supported CZY, the support ratio of copper (metal conversion) was 1.5% by mass.

  Dinitrodiammine platinum nitric acid solution (specifically, nitric acid prepared by dissolving 0.055 parts by mass of dinitrodiammine platinum nitric acid solution having a platinum content of 4.511% by mass in 30 parts by mass of water in 5.00 parts by mass of θ alumina. 30.1 parts by mass of an aqueous solution), dried at 110 ° C. for one day and night, and then heat-treated (fired) in the atmosphere at 650 ° C. for 1 hour in an electric furnace, thereby supporting the θ-alumina powder carrying the platinum (second Catalyst, hereinafter abbreviated as Pt-supported alumina.) 5.00 parts by mass were obtained. In the Pt-supported alumina, the support ratio of platinum (metal conversion) was 0.05% by mass.

  Then, 5.00 parts by mass of Cu-supported CZY and 5.00 parts by mass of Pt-supported alumina are pulverized and mixed in a mortar for 10 minutes, whereby an exhaust gas purification catalyst 10.00 which is a mixed powder of Cu-supported CZY and Pt-supported alumina. A mass part was obtained.

The specific surface area of the exhaust gas purification catalyst was 74.5 m ² / g. In the exhaust gas purifying catalyst, the supporting ratio of copper (metal conversion) was 0.75% by mass, and the supporting ratio of platinum (metal conversion) was 0.025% by mass.

Example 2
Exhaust gas purification catalyst in the same manner as in Example 1 except that an aqueous solution of copper nitrate (II) was prepared by dissolving 0.57 parts by mass of copper nitrate (II) trihydrate salt in 30 parts by mass of water. Was prepared. In Example 2, the specific surface area of the exhaust gas purification catalyst was 71.7 m ² / g. In the exhaust gas purifying catalyst, the supporting ratio of copper (metal conversion) was 1.50 mass%, and the supporting ratio of platinum (metal conversion) was 0.025 mass%.

Example 3
Exhaust gas purification catalyst in the same manner as in Example 1 except that an aqueous solution of copper nitrate (II) was prepared by dissolving 1.14 parts by mass of copper (II) nitrate trihydrate salt in 30 parts by mass of water. Was prepared. In Example 3, the specific surface area of the exhaust gas purification catalyst was 72.4 m ² / g. In the exhaust gas purification catalyst, the loading ratio of copper (metal conversion) was 3.00 mass%, and the loading ratio of platinum (metal conversion) was 0.025 mass%.

Example 4
Exhaust gas purifying catalyst in the same manner as in Example 1 except that an aqueous solution of copper nitrate (II) was prepared by dissolving 1.71 parts by mass of copper nitrate (II) trihydrate salt in 30 parts by mass of water. Was prepared. In Example 4, the specific surface area of the exhaust gas purifying catalyst was 70.7 m ² / g. In the exhaust gas purifying catalyst, the supporting ratio of copper (metal conversion) was 4.50% by mass, and the supporting ratio of platinum (metal conversion) was 0.025% by mass.

Example 5
Exhaust gas purification catalyst in the same manner as in Example 1 except that an aqueous solution of copper nitrate (II) was prepared by dissolving 2.28 parts by mass of copper nitrate (II) trihydrate salt in 30 parts by mass of water. Was prepared. In Example 5, the specific surface area of the exhaust gas purification catalyst was 68.2 m ² / g. In the exhaust gas purification catalyst, the loading ratio of copper (converted to metal) was 6.00% by mass, and the supporting ratio of platinum (converted to metal) was 0.025% by mass.

Example 6
Exhaust gas purification catalyst in the same manner as in Example 1 except that an aqueous solution of copper nitrate (II) was prepared by dissolving 3.80 parts by mass of copper nitrate (II) trihydrate salt in 30 parts by mass of water. Was prepared. In Example 6, the specific surface area of the exhaust gas purifying catalyst was 66.9 m ² / g. In the exhaust gas purification catalyst, the loading ratio of copper (metal conversion) was 10.00 mass%, and the loading ratio of platinum (metal conversion) was 0.025 mass%.

Comparative Example 1
Exhaust gas purification catalyst in the same manner as in Example 1 except that an aqueous solution of copper (II) nitrate was prepared by dissolving 0.10 parts by mass of copper (II) nitrate trihydrate salt in 30 parts by mass of water. Was prepared. In Comparative Example 1, the specific surface area of the exhaust gas purification catalyst was 77.6 m ² / g. In the exhaust gas purification catalyst, the supporting ratio of copper (metal conversion) was 0.25% by mass, and the supporting ratio of platinum (metal conversion) was 0.025% by mass.

Comparative Example 2
Only 5 parts by mass of the Pt-supported alumina of Example 1 was used as an exhaust gas purification catalyst. That is, Cu-supported CZY was not mixed with Pt-supported alumina.

Comparative Example 3
A dinitrodiammine platinum nitric acid solution was prepared in the same manner as in Example 1 except that 0.55 parts by mass of a dinitrodiammine platinum nitric acid solution having a platinum content of 4.511% by mass was dissolved in 30 parts by mass of water. Pt-supported alumina was prepared, and only 5 parts by mass of the Pt-supported alumina was used as an exhaust gas purification catalyst. That is, Cu-supported CZY was not mixed with Pt-supported alumina. In the exhaust gas purification catalyst, the loading ratio of platinum (in metal conversion) was 0.50% by mass.

Comparative Example 4
Only 5 parts by mass of Cu-supported CZY of Example 2 was used as an exhaust gas purification catalyst. That is, Pt-supported alumina was not mixed with Cu-supported CZY.

Evaluation 1) Endurance treatment (Air 750 ° C., 5 hours)
The exhaust gas purification catalysts obtained in each Example and each Comparative Example were subjected to high temperature durability treatment under the following conditions.

In this high-temperature endurance treatment, the exhaust gas purifying catalyst obtained in each example and each comparative example was subjected to an atmospheric condition of 10% water-containing air (O ₂ : 20%, H ₂ O: 10%, N ₂ : Balance). For 5 hours at 750 ° C. and cooled to room temperature.
2) Purification rate evaluation (T50)
The exhaust gas purifying catalysts of the respective examples and comparative examples after the durability treatment were molded into pellets having a size of 0.5 mm to 1.0 mm to prepare test pieces.

  As a model gas of exhaust gas discharged from a diesel engine, a gas having a composition shown in Table 1 below was used. And while increasing the temperature of the exhaust gas discharged by the combustion of the model gas from room temperature to 750 ° C. at a rate of 30 ° C./min, the model gas is supplied to each test piece, and the CO in the exhaust gas is The temperature at which 50% purification was performed (50% purification temperature (T50): ° C.) was measured.

  The results are shown in Table 2, FIG. 1 and FIG.

Discussion As shown in FIG. 1, the exhaust gas purifying catalysts (Examples 1 to 6) having a copper loading ratio of 0.75% by mass or more are catalysts having a copper loading ratio of less than 0.75% by mass (comparison). Compared with Example 1 and Comparative Example 2), it had an excellent exhaust gas purification rate.

  Moreover, as shown in FIG. 2, the exhaust gas purifying catalyst (Examples 1 to 6) including the first catalyst and the second catalyst is composed of only the catalyst composed of only the first catalyst (Comparative Example 4) and the second catalyst. Compared with each of the catalysts (Comparative Example 2), the exhaust gas purification rate was excellent.

Claims (1)

A first catalyst in which copper is supported on a cerium-containing oxide;
A second catalyst in which platinum is supported on alumina;
The copper loading ratio is 0.75% by mass or more with respect to the total of the first catalyst and the second catalyst,
The exhaust gas purifying catalyst, wherein the platinum loading ratio is less than 1% by mass with respect to the total of the first catalyst and the second catalyst.

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