JP5825221B2 - Exhaust gas purification catalyst and method for producing the same - Google Patents

Description

  The present invention relates to an exhaust gas purifying catalyst and a method for producing the same, and more particularly, a platinum group metal for exhaust gas purifying and a base metal-supported aluminum phosphate catalyst, for example, harmful components contained in exhaust gas discharged from an internal combustion engine such as an automobile. The present invention relates to a platinum group metal and base metal-supported aluminum phosphate catalyst to be purified, and a method for producing the same.

In recent years, exhaust gas regulations have been strengthened worldwide year by year from the viewpoint of protecting the global environment.
As a countermeasure, an exhaust gas purifying catalyst is used in an internal combustion engine. In this exhaust gas purification catalyst, platinum such as Pt, Pd, and Rh is used as a catalyst component in order to efficiently purify hydrocarbons (hereinafter sometimes abbreviated as HC), CO, and nitrogen oxides in the exhaust gas. Various catalysts including group elements are used.

  Patent Document 1 discloses a catalyst for purifying exhaust gas in which 0.01 to 5% by weight of one or more kinds of noble metals selected from the group consisting of Pt, Pd, Rh and Ir are supported on a phosphoric acid compound (Patent Document 1). One claim 1) is described.

  Patent Document 2 is an exhaust gas purifying catalyst characterized in that it is a molded article of a phosphate carrying at least one metal selected from metals having catalytic activity, a compound thereof, or a metal oxide (Patent Document 2). Two claims 1) are described.

Patent Document 3 includes a heat-resistant AlPO ₄ compound having a tridymite crystal structure and a BET specific surface area of 50 to 150 m ² / g, and a group consisting of Pt, Pd, and Rh supported on the AlPO ₄ compound. An exhaust gas purifying catalyst (claim 1 of Patent Document 3) characterized by comprising at least one selected precious metal component is described.

JP-A-8-150339 Japanese Patent No. 6-55075 Japanese Patent No. 4,505,046

  There is a need for an exhaust gas purification catalyst that reduces the amount of noble metal contained in the exhaust gas purification catalyst, and that does not easily deteriorate due to heat exhausted from the engine, sulfur components contained in fuel, and the like. Furthermore, in order to adapt to exhaust gas purification standards, there is a need for an exhaust gas purification apparatus that can remove the above components even better even under conditions of low exhaust gas temperature, such as when starting an engine and during low-speed operation.

  As a result of diligent efforts, the present inventors can solve the above problem by supporting a platinum group metal such as Pt and a base metal such as Cu on the aluminum phosphate fired body. And found that very good results can be obtained.

Aspects of the present invention are as follows.
(1) On the aluminum phosphate fired body,
Exhaust gas purification comprising at least one platinum group metal selected from the group consisting of Ru, Rh, Pd, Os, Ir, and Pt and at least one base metal selected from the group consisting of Cu and Zn Catalyst.
(2) The exhaust gas purifying catalyst according to (1), wherein the platinum group metal is Pt and the base metal is Cu.
(3) The supported amount of the platinum group metal on the support is 0.0001 wt% to 2.0 wt%, and the supported amount of the base metal on the support is 0.0001 wt% to 2.0 wt%. Or the exhaust gas purification catalyst according to (2).
(4) The exhaust gas purification catalyst according to any one of (1) to (3), wherein the platinum group metal and the base metal are supported by a co-impregnation supporting method.
(5) The exhaust gas purification catalyst according to any one of (1) to (4), wherein the aluminum phosphate has a tridymite crystal structure.
(6) On the aluminum phosphate fired body,
And supporting at least one platinum group metal selected from the group consisting of Ru, Rh, Pd, Os, Ir, and Pt, and at least one base metal selected from the group consisting of Cu and Zn. The manufacturing method of the purification catalyst for exhaust gas.
(7) The method for producing an exhaust gas purifying catalyst according to (6), wherein the platinum group metal is Pt and the base metal is Cu.
(8) The amount of the platinum group metal supported on the support is 0.0001 wt% to 2.0 wt%, and the amount of the base metal supported on the support is 0.0001 wt% to 2.0 wt%. ) Or the method for producing an exhaust gas purification catalyst according to (7).
(9) The method for producing an exhaust gas purification catalyst according to any one of (6) to (8), wherein the step of supporting the platinum group metal and the base metal is a co-impregnation supporting method.
(10) By the step of calcining the aluminum phosphate obtained from the aqueous solution adjusted to have a pH of 3.5 to 4.5 at a temperature of 1000 ° C. to 1200 ° C. for 2 hours or more to obtain a calcined aluminum phosphate, The method for producing an exhaust gas purification catalyst according to any one of (6) to (9), further including providing the aluminum phosphate.

  The exhaust gas purifying catalyst according to the present invention reduces the amount of noble metal contained in the exhaust gas purifying catalyst, utilizes heat resistance to heat exhausted from the engine, and performance excellent in poisoning resistance such as sulfur, and particularly exhaust gas. When CO is HC or HC, it is possible to express very good catalytic activity at low temperatures.

FIG. 1 shows CO purification characteristics, that is, after production and before aging treatment (Example 1: (a), Comparative Example 1: (b), and Comparative Example 2: (c)), and after aging treatment (Example 2). : (D), Comparative Example 3: (e), and Comparative Example 4: (f)), the CO gas purification rate (% by volume) was compared with the gas temperature (° C.) at the catalyst inlet. It is the graph which measured and plotted. FIG. 2 shows C ₃ H ₆ purification characteristics, that is, after production, before aging treatment (Example 1: (a), Comparative Example 1: (b), and Comparative Example 2: (c)), and after aging treatment ( Example 2: (d), Comparative Example 3: (e), and Comparative Example 4 (f)) HC gas purification rate (% by volume), gas temperature at the catalyst inlet (° C.) It is the graph which measured and plotted with respect to.

Note that in this specification, impurities or the like may be generated even if they are generated so as to have these compositions by the name of the inorganic compound or the notation using the ratio of the contained metal (as exemplified below). Including a composition that is actually generated. Therefore, according to the notation using the name of the inorganic compound or the ratio of the contained metal, for example, in the structure of the inorganic compound, for example, elements such as oxygen, hydrogen, and nitrogen are excessive in the chemical formula within ± 1 atom number. Or an inorganic compound with an under-existing composition, that is, for example, in the case of aluminum phosphate, AlPO ₄ also contains, for example, AlPO ₂ to AlPO ₅ when the number of oxygen is ± 1, and Al / P The ratio of 1 ± about 0.3 is also included, and further, those having hydrogen not represented in the compound as an impurity are included.

The sintered body of aluminum phosphate according to the present invention includes one or more selected from the group consisting of a tridymite type crystal structure, a burrinite type crystal structure, a cristobalite type crystal structure, or an amorphous material.
Among these, from the viewpoint of heat resistance, a tridymite crystal can be included as a main component.

  As the aluminum phosphate fired body according to the present invention, an aluminum phosphate fired body obtained by a known method can be used without particular limitation.

The production method of the aluminum phosphate fired body is not particularly limited, and a known method such as a neutralization method can be employed. For example, in an aqueous solution of an Al-containing compound, an aqueous phosphoric acid solution is added so that the molar ratio of P to Al is approximately equivalent, and further, aqueous ammonia is added to adjust pH to separate and dry the precipitate obtained. Then, the method of baking at said baking temperature is mentioned. Examples of the Al-containing compound include metal salts such as hydroxide and nitrate, and specifically include Al (OH) ₃ , Al (NO ₃ ) _{3 and the} like.

  As the solvent used in the mixed solution containing the aluminum salt and phosphoric acid, any solvent that can dissolve the aluminum-containing compound and phosphoric acid, for example, an aqueous solvent such as water, an organic solvent, or the like can be used. it can.

And when the aluminum phosphate fired body according to the present invention has a tridymite type crystal structure, for example,
(A) a method of firing an aluminum phosphate obtained from an aqueous aluminum phosphate solution having a predetermined pH at a predetermined temperature for a predetermined time;
(B) a method of adding an excessive amount of phosphate ions to aluminum ions and producing unreacted phosphate ions in the product when producing an aluminum phosphate fired body,
(C) A foaming agent such as a thermoplastic resin such as an olefin resin having a diameter capable of generating a desired pore diameter, a thermoplastic resin such as a phenol resin, or the like is mixed in the raw material for producing the aluminum phosphate fired body, Those obtained by a wide range of methods such as a method of burning off the foaming agent in the firing step can be used.

  Here, the pH of the aqueous solution, the firing temperature, and the firing time during the formation of aluminum phosphate in the above (a) are not particularly limited as long as they do not adversely affect the tridymite crystal structure, and about 3.0 to about 10.0, respectively. Usually used conditions such as in the range of about 1000 ° C. to 1200 ° C., about 1 hour to about 10 hours can be used.

  The purification catalyst according to the present invention is selected from the group consisting of ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), and platinum (Pt) in the aluminum phosphate fired body. And supporting at least one platinum group metal. The form of loading is not particularly limited, and it is sufficient that the platinum group metal is supported substantially uniformly thereon.

  The particle size of the platinum group metal nanoparticles to be supported is not particularly limited, and can be, for example, about 0.5 nm or more, about 1 nm or more, about 2 nm or more, about 3 nm or more, about 4 nm or more, and about 10 nm or less. , About 9 nm or less, about 8 nm or less, about 7 nm or less, about 6 nm or less.

  The amount of platinum group metal with respect to the aluminum phosphate fired body is about 0.0001 wt% or more, about 0.001 wt% or more, about 0.01 wt% or more, about 0.1 wt% or more, about 0.2 wt% or more, about 0 .3 wt% or more, about 0.4 wt% or more, about 0.5 wt% or more, about 0.6 wt% or more, about 0.7 wt% or more, about 0.8 wt% or more, about 0.9 wt% or more, about 1 wt% About 3 wt% or less, about 2.5 wt% or less, about 2.3 wt% or less, about 2.0 wt% or less, about 1.9 wt% or less, about 1.8 wt% or less, about 1. wt% or less. 7 wt% or less, about 1.6 wt% or less, about 1.5 wt% or less, about 1.4 wt% or less, about 1.3 wt% or less, about 1.2 wt% or less, about 1.1 wt% or less. .

  The purification catalyst according to the present invention is obtained by supporting at least one base metal selected from the group consisting of copper (Cu) and zinc (Zn) on the aluminum phosphate fired body. There is no particular limitation on the form of the support, and it is sufficient that the base metal is supported substantially uniformly on the top.

  The particle size of the supported base metal nanoparticles is not particularly limited, and can be, for example, about 0.5 nm or more, about 1 nm or more, about 2 nm or more, about 3 nm or more, about 4 nm or more, about 10 nm or less, about It can be 9 nm or less, about 8 nm or less, about 7 nm or less, about 6 nm or less.

  The amount of the base metal with respect to the aluminum phosphate fired body is about 0.0001 wt% or more, about 0.001 wt% or more, about 0.01 wt% or more, about 0.1 wt% or more, about 0.2 wt% or more, about 0.3 wt%. % Or more, about 0.4 wt% or more, about 0.5 wt% or more, about 0.6 wt% or more, about 0.7 wt% or more, about 0.8 wt% or more, about 0.9 wt% or more, about 1 wt% or more About 3 wt% or less, about 2.5 wt% or less, about 2.3 wt% or less, about 2.0 wt% or less, about 1.9 wt% or less, about 1.8 wt% or less, about 1.7 wt% Hereinafter, it may be about 1.6 wt% or less, about 1.5 wt% or less, about 1.4 wt% or less, about 1.3 wt% or less, about 1.2 wt% or less, or about 1.1 wt% or less.

  As a method for supporting platinum group metal nanoparticles and / or base metal nanoparticles on an aluminum phosphate fired body, there is no particular limitation, and impregnation support method, co-impregnation support for supporting platinum group nanoparticles and base metal nanoparticles simultaneously on a support. A general method such as a method, a sequential supporting method in which any one of platinum group nanoparticles and base metal nanoparticles is sequentially supported, and a surface precipitation method can be used.

  Among these, the co-impregnation supporting method is preferable because it can promote alloying of platinum group nanoparticles and base metal nanoparticles at high temperature.

  To equalize the particle size of the platinum group metal nanoparticles and / or base metal nanoparticles, the platinum group metal and / or base metal nanoparticles of a desired particle size can be provided, such as about 1 nm, about 2 nm, about 3 nm, about 4 nm, etc. Platinum group metal colloids and base metal colloids can also be used. Other platinum group metal and / or base metal nanoparticle sources, for example, platinum acetate group metal and / or base metal compound, platinum nitrate group metal and / or base metal compound, platinum chloride group metal and / or base metal compound, platinum synthesized therefrom Group metal and / or base metal nanoparticles may be used. However, since aluminum phosphate is easily soluble in a strong acid, it is preferable not to contain nitrate ions, chloride ions, and the like.

In the catalyst according to the present invention, 0.66 wt% Pt and 1.0 wt% Cu are supported by a co-impregnation method as shown in Examples 1 and 2 below and the graphs of FIGS. 1 and 2. The T50 (° C.) of the AlPO ₄ catalyst showed a small value for both CO and HC gas types both before and after the aging treatment.

On the other hand, as shown in the following Comparative Examples 1 to 4 and the graphs of FIGS. 1 and 2, the AlPO ₄ catalyst in which 0.66 wt% Pt and 1.0 wt% Fe were supported by the co-impregnation method. The T50 (° C.) of the La—Al ₂ O ₃ catalyst loaded with T50 (° C.) and 1.33 wt% Pt by impregnation is used in the CO and HC gas species both before and after the aging treatment. The value is higher than that of the catalyst according to the present invention.

As shown in Examples 1 and 2 and Comparative Examples 1 to 4 and FIGS. 1 and 2, T50 of the catalyst (Comparative Examples 1 and 3) in which Pt and Fe are supported on AlPO ₄ is Pt The Pt-supported La—Al ₂ O ₃ catalyst supported twice the amount is approximately the same or lower before the aging treatment, but lower than (Comparative Examples 2 and 4) after the aging treatment. However, T50 of the catalyst in which Pt and Cu are supported on AlPO ₄ using Cu instead of Fe (Examples 1 and 2) is equal to the catalyst in which Pt and Fe are supported on AlPO ₄ (Comparative Example 1). 3) and a Pt-supported La—Al ₂ O ₃ catalyst (Comparative Examples 2 and 4) in which double amount of Pt is supported, lower values are obtained both before and after the aging treatment. It turned out that a wonderful result was obtained. From these facts, it has been found that not only the initial characteristics of the catalyst but also the effect of suppressing the deterioration of the catalyst after the aging treatment seems to be manifested by the combination of three kinds of Pt, Cu and AlPO ₄ .

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

(Production Example 1: Co-impregnation support method)
Aluminum nitrate nonahydrate (manufacturer: Wako Pure Chemical Industries, Ltd.) was dissolved in ion-exchanged water, and 85 wt% phosphoric acid was added to the aqueous aluminum solution. On the other hand, 28 wt% aqueous ammonia was added dropwise to adjust the pH to 3.5 to 4.5 and stirred at room temperature for 12 hours. At this point, the solution was cloudy.
This cloudy liquid was separated into a precipitate and a supernatant with a centrifuge, and the precipitate was purified twice with ion-exchanged water. This was dried at 120 ° C. for 12 hours. The dried product was crushed and fired at 1100 ° C. for 5 hours. After allowing to cool, the fired product was crushed to obtain a powder of an aluminum phosphate fired body.
On the other hand, Pt and Cu particles were supported by an impregnation method. Dinitroamine Pt was used as the Pt source, and Cu acetate was used as the Cu source. A mixed liquid was used such that the supported amount of Pt particles was 0.66 wt% with respect to the support, and the supported amount of Cu particles was 1.0 wt% with respect to the support. The powder of the aluminum phosphate fired body was dispersed in ion-exchanged water, and a liquid containing the Pt source and Cu source was added thereto. The temperature was raised to 120 to 150 ° C. while stirring to evaporate the solvent. The obtained dried product was crushed and calcined at 500 ° C. for 2 hours. After allowing to cool, the fired product was crushed to obtain catalyst powder (Example 1).

(Comparative Example 1)
A catalyst powder was obtained in the same procedure as in (Production Example 1) except that Fe was used instead of Cu.
(Comparative Example 2)
(Production Example 1) Except that the amount of Pt particles supported on the support was 1.33 wt%, and a Pt catalyst was obtained using La-added Al ₂ O ₃ (La-Al ₂ O ₃ ) instead of aluminum phosphate. ) To obtain catalyst powder.

(Catalyst evaluation method)
The catalyst powder was compression molded by applying a pressure of 2 t, and then pulverized and compression molded into pellets having a diameter of about 2.5 mm was used as an evaluation sample. If necessary, this was placed in a rich / lean switchable gas flow constant temperature furnace and subjected to heat treatment at 1000 ° C. for 5 hours while periodically changing the gas atmosphere (aging treatment).

A gas flow-type catalyst evaluation device was used for gas purification performance measurement. The amount of catalyst was 2 g. As a model gas, by volume, CO: 0.65%, C ₃ H ₆ : 3000 ppmC, NO: 1500 ppm, O ₂ : 0.7%, H ₂ O: 3%, CO ₂ : 10%, N ₂ : remaining The model gas was used and the flow rate was set to 15 liters / minute. The SV was about 300,000 hours- ¹ . The gas composition after passing through the catalyst was measured using an infrared spectrometer (manufacturer name: HORIBA, Ltd., model number: MEXA-6000FT).

(result)
When the powder of the aluminum phosphate fired body obtained in Example 1 and Comparative Example 1 was measured with an X-ray diffractometer (manufacturer name: Rigaku Corporation, model number: RINT), phosphoric acid having a tridymite crystal structure Formation of an aluminum fired body was confirmed.

In Table 1, for Examples 1 and 2 and Comparative Examples 1 to 4, the supported metal, presence or absence of aging treatment, CO T50 (° C.), and HC (C ₃ H as HC in Examples and Comparative Examples) ₆ is used.) T50 (° C.) of The T50 temperature was measured at the catalyst inlet.
T50 (° C.) refers to a temperature at which the amounts of CO and HC gas species are 50% by volume after passing through the catalyst and before passing through the catalyst.

Further, FIG. 1 and FIG. 2 show graphs of the catalyst characteristic evaluation results.
As shown in the graphs of FIGS. 1 and 2, the T50 (° C.) of the AlPO ₄ catalyst in which 0.66 wt% Pt and 1.0 wt% Cu are supported by the co-impregnation method is , CO and HC showed a small value (Example 1: (a) in FIGS. 1 and 2), and even after aging treatment, the value was not so large in either CO or HC. (Example 2: (d) in FIG. 1 and FIG. 2).

On the other hand, T50 of AlPO ₄ catalyst supporting 0.66 wt% Pt and 1.0 wt% Fe supported by the co-impregnation method and Al ₂ O ₃ catalyst supporting 1.33 wt% Pt by the impregnation method ( (° C.) shows a large value with respect to the sample of Example 1 in both CO and HC before the aging treatment (Comparative Example 1: (b) in FIGS. 1 and 2) and Comparative Example 2: In addition to (c) in FIG. 1 and FIG. 2, after aging treatment, all the gas types of CO and HC became larger values than the sample of Example 1 (Comparative Example). 3: (e) in FIGS. 1 and 2 and Comparative Example 4: (f) in FIGS. 1 and 2).

As described above, the co-supported AlPO ₄ catalyst (Example 1) of a platinum group metal such as Pt and a base metal such as Cu according to an embodiment of the present invention has a base metal other than Cu or has a base metal. Compared with a catalyst (Comparative Examples 1 and 2) whose carrier is not an AlPO ₄ catalyst, good catalytic activity can be maintained not only before the aging treatment but also after the aging treatment (Example 2, Comparative Examples 3 and 4). It has been shown. Then, it becomes clear that the performance difference between the catalyst according to the embodiment of the present invention and the conventional catalyst is greatly affected by a platinum group metal such as Pt, a base metal such as Cu, and a combination of three kinds of AlPO _4. It was.

  As described above, the exhaust gas purification catalyst according to the present invention has good performance as an exhaust gas purification catalyst even under low temperature conditions. For these reasons, the use of the oxidation catalyst according to the present invention is not limited to the exhaust gas purification catalyst, and can be used for various applications in a wide field.

Claims (2)

On the aluminum phosphate fired body,
Carrying a platinum group metal that is P t and a base metal that is Cu ;
The supported amount of the platinum group metal on the support is 0.0001 wt% to 2.0 wt%, and the supported amount of the base metal on the support is 0.0001 wt% to 2.0 wt%,
The platinum group metal and the base metal are supported by a co-impregnation supporting method,
The aluminum phosphate has a tridymite crystal structure, the exhaust gas purifying catalyst. On the aluminum phosphate fired body,
Platinum group metal is P t, and the step of supporting the base metal is a C u seen including,
The supported amount of the platinum group metal on the support is 0.0001 wt% to 2.0 wt%, and the supported amount of the base metal on the support is 0.0001 wt% to 2.0 wt%,
Step of supporting the platinum group metal and the base metal, Ru co-impregnation supporting method der, process for preparing a catalyst for flue gas purification of claim 1.

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