JP2005342554A - Catalyst support particle, method of manufacturing the particle and catalyst for purification of exhaust gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst for purification of exhaust gas controlling production of hydrogen sulfide, a support particle for the catalyst and a method of manufacturing the particle. <P>SOLUTION: The catalyst support particle 1 consists of an oxide of a mixture comprising at least one metal selected from a group of nickel and cobalt, and cerium and zirconium. A method of manufacturing the particle and a catalyst for purification of exhaust gas consisting of the particle supporting a noble metal are also provided. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an exhaust gas purifying catalyst for purifying exhaust gas from an automobile engine, etc., catalyst carrier particles therefor, and a method for producing the same.

The exhaust gas from an internal combustion engine such as an automobile engine contains nitrogen oxides (NO _x ), carbon monoxide (CO), hydrocarbons (HC), and the like. These materials are generally oxidizes CO and HC, are removed by an exhaust gas purifying catalyst for reducing NO _x. As a typical exhaust gas purification catalyst used here, a noble metal such as platinum (Pt), rhodium (Rh) and / or palladium (Pd) is supported on a porous metal oxide carrier such as γ-alumina. There is a three way catalyst.

When such an exhaust gas purification catalyst is used, the sulfur component in the fuel is generally released as sulfur dioxide. However, in an oxidizing atmosphere, sulfur components in the fuel may be adsorbed on the catalyst as sulfur trioxide (SO ₃ ). Thus, the sulfur oxide component adsorbed in the oxidizing atmosphere may be reduced in a high temperature reducing atmosphere and released as hydrogen sulfide. Since this hydrogen sulfide has a bad odor, it is desirable to suppress the release of hydrogen sulfide.

  As a method for controlling the discharge of hydrogen sulfide, it has been proposed to separately provide a catalyst for removing hydrogen sulfide and to add hydrogen or the like to the three-way catalyst to oxidize hydrogen sulfide.

In Patent Document 1, regarding the use of nickel oxide and / or cobalt oxide for suppressing the release of hydrogen sulfide, a composite oxide of ceria-zirconia and a noble metal are added to an active alumina layer containing a powder of nickel oxide or the like and an alumina powder. An exhaust gas purifying catalyst is proposed. According to this exhaust gas purification catalyst, the reaction between alumina and nickel, which forms spinel crystal type NiAl ₂ O ₄ and reduces the surface area of activated alumina, by supporting the ceria-zirconia solid solution on particles such as nickel oxide. It can be prevented.

  In Patent Document 2, by disposing a metal oxide particle selected from the group consisting of alumina, nickel oxide and iron oxide together with a noble metal on a carrier particle of a ceria-zirconia solid solution, the surface movement of the noble metal is limited, Thereby, grain growth of precious metal is suppressed.

  Patent Document 3 proposes that the carrier particles having a ceria-zirconia solid solution and a rare earth element regulate the amount of zirconia and the rare earth element to suppress sulfur poisoning of the carrier. Patent Document 4 proposes that the carrier particles having a ceria-zirconia solid solution regulate the amount of zirconia to suppress sulfur poisoning of the carrier. In Patent Document 5, a ceria-zirconia solid solution and a catalyst support made of a metal oxide such as alumina that does not dissolve in the ceria-zirconia solid solution are used to suppress sintering of the ceria-zirconia solid solution and to have a feature in pore distribution. It has disclosed a highly active and highly durable catalyst that enables high dispersion support and gas diffusion improvement of precious metals.

JP-A-1-242149 JP 2003-126694 A JP 2000-176282 A Japanese Patent Laid-Open No. 11-19514 JP 2002-160922 A

As shown in Patent Document 1, the sulfur component in the fuel is adsorbed on the catalyst as sulfur trioxide (SO ₃ ), and this sulfur component is reduced in a high-temperature reducing atmosphere and released as hydrogen sulfide. This has traditionally been a problem.

  This release of hydrogen sulfide becomes particularly remarkable when a ceria-zirconia solid solution having an oxygen storage ability (hereinafter referred to as OSC) that stores oxygen in an oxidizing atmosphere and releases oxygen in a reducing atmosphere is used. This is because ceria tends to occlude sulfur as sulfate in an oxidizing atmosphere.

  Patent Documents 1 and 2 both use ceria-zirconia solid solution and nickel oxide, but do not pay attention to the fact that ceria tends to occlude sulfur as a sulfate. Therefore, since ceria and nickel oxide are used as separate particles, the sulfur component released from ceria in a reducing atmosphere may not be sufficiently captured by nickel or the like as a sulfide. Further, if the amount of nickel oxide or the like is increased to prevent the release of hydrogen sulfide, the heat resistance of the catalyst may be lowered. In patent documents 3-5, the problem regarding discharge | release of hydrogen sulfide is not considered.

  Therefore, the present invention provides an exhaust gas purification catalyst that suppresses the release of hydrogen sulfide in a catalyst carrier catalyst containing a ceria-zirconia solid solution.

  The catalyst carrier particles of the present invention are characterized by comprising an oxide in which at least one metal selected from the group consisting of nickel and cobalt, cerium and zirconium are mixed.

  Here, “mixed oxide” means not only a case where all metal oxides form a solid solution, but also a case where each metal oxide forms a different phase, and some metals. For example, it also means a case where an oxide of cerium and zirconium forms a solid solution and an oxide of another metal forms a separate phase.

According to the catalyst support particle of the present invention, the sulfur component accumulated as sulfate in the ceria part, particularly in the ceria-zirconia solid solution part in the oxidizing atmosphere can be easily moved to the adjacent nickel part of the same particle in the reducing atmosphere. it can. Sulfur components stored in nickel as sulfides in a rich atmosphere are released as sulfur oxide (SO ₂ ) in a reducing atmosphere. Therefore, according to the present invention, release of hydrogen sulfide in a reducing atmosphere can be suppressed even in catalyst carrier particles containing ceria, particularly ceria-zirconia solid solution. Also according to the invention,

  In one embodiment, in the catalyst support particles of the present invention, an oxide of cerium and zirconium at least partially forms a solid solution. According to this aspect, catalyst carrier particles having improved OSC ability and heat resistance due to the ceria-zirconia solid solution can be obtained.

  In another embodiment, the catalyst support particles of the present invention are made of an oxide in which a rare earth element other than Ce, particularly an element selected from the group consisting of Y, La, and Pr is further mixed. According to this aspect, the oxide can be stabilized and the heat resistance and sulfur poisoning resistance of the catalyst support particles can be improved.

  In another embodiment, the catalyst support particles of the present invention have a zirconium content of 50 to 70 mol% based on the total of cerium and zirconium. According to this aspect, the OSC ability and heat resistance due to the ceria-zirconia solid solution can be further improved.

  In another embodiment, in the catalyst support particles of the present invention, at least one metal selected from the group consisting of nickel and cobalt is 2.5 to 20 mol% based on the total of cerium and zirconium. According to this aspect, it is possible to satisfactorily suppress the release of hydrogen sulfide while maintaining a high HC purification rate.

  The exhaust gas purifying catalyst of the present invention comprises a noble metal supported on the catalyst carrier particles of the present invention.

  According to the exhaust gas purification catalyst of the present invention, release of hydrogen sulfide can be suppressed even in a high-temperature reducing atmosphere.

  The method for producing catalyst support particles of the present invention generates a precipitate from a solution containing at least one metal selected from the group consisting of nickel and cobalt, cerium, and an alkoxide and / or salt of zirconium, particularly nitrate. Drying and calcining the resulting precipitate.

  According to the method for producing catalyst carrier particles of the present invention, catalyst carrier particles comprising an oxide in which at least one metal selected from the group consisting of nickel and cobalt, cerium and zirconium are mixed are produced. be able to.

  Another method for producing catalyst support particles of the present invention is to generate a precipitate from a solution containing an alkoxide and / or salt of cerium and zirconium, and an alkoxide of at least one metal selected from the group consisting of nickel and cobalt. And / or generating a precipitate from the solution containing the salt and drying and calcining the resulting precipitate together.

  According to the method for producing catalyst carrier particles of the present invention, catalyst carrier particles comprising an oxide in which at least one metal selected from the group consisting of nickel and cobalt, cerium and zirconium are mixed are produced. And can promote the cerium and zirconium oxides at least partially forming a solid solution.

  In another method for producing catalyst support particles of the present invention, a sol of at least one metal selected from the group consisting of nickel and cobalt, cerium, and zirconium is mixed to generate a precipitate, and the precipitate is dried and calcined. Including doing.

  According to the method for producing catalyst carrier particles of the present invention, catalyst carrier particles comprising an oxide in which at least one metal selected from the group consisting of nickel and cobalt, cerium and zirconium are mixed are produced. be able to.

  In the following, the present invention will be specifically described based on the embodiments shown in the drawings. However, these drawings are diagrams schematically showing an exhaust gas purification apparatus constituting the present invention, and the present invention is limited to these embodiments. Is not to be done.

  In the conventional exhaust gas purification catalyst of Patent Document 2, as schematically shown in FIG. 2, noble metal is supported on carrier particles 3 and nickel oxide particles 5 made of ceria-zirconia solid solution. On the other hand, in the exhaust gas purifying catalyst of the present invention, as schematically shown in FIG. 1, ceria, zirconia and nickel oxide are mixed to form particles containing these three types of oxides.

  The carrier of the present invention can be produced by any method, and can be produced, for example, by an alkoxide method or a coprecipitation method. In the alkoxide method, a support of the present invention can be obtained by coprecipitating a mixture of alkoxides such as cerium, zirconium and nickel by hydrolysis, followed by drying and firing. In the coprecipitation method, the carrier of the present invention can be obtained by adding an alkaline substance to a mixed solution of a salt such as cerium, zirconium and nickel to cause coprecipitation, and drying and firing the obtained coprecipitate. . Moreover, each sol of cerium, zirconium and nickel can be mixed, and the precipitate can be dried and fired. In these methods, a ceria-zirconia precursor may be precipitated in advance, and then a precursor such as nickel oxide may be precipitated, and the resulting precipitate may be dried and fired together.

  The term “sol” in the alumina sol, silica sol, and ceria sol used for the production of the metal oxide particles of the present invention is a liquid, for example, an organic dispersion medium such as water, alcohol, acetylacetone, particularly a metal oxide or metal dispersed in water. A hydrate colloid means a substance that forms an oxide of its metal by removing the dispersion medium and firing. Specific examples of the sol include substances obtained by hydrolyzing and condensing these metal alkoxides, acetylacetonates, acetates, nitrates, and the like in a solution. These sols are known materials, and commercially available ones can be obtained.

  Distillation and drying of the dispersion medium from the raw material sol or precipitate can be carried out at any method and at any temperature. it can. Moreover, baking can be performed at the temperature generally used in the synthesis | combination of a metal oxide, for example, 500 degreeC or more (for example, 500-1100 degreeC).

  The catalyst carrier particles of the present invention thus obtained preferably have a small particle size in order to obtain a large surface area, and can have a particle size of, for example, 50 μm or less, 10 μm or less, 5 μm or less, or 1 μm or less.

  Moreover, although the exhaust gas purification catalyst carrier of the present invention can be used alone, it is preferable to use it by mixing with alumina particles such as γ-alumina in terms of surface area and heat resistance.

  The exhaust gas purifying catalyst of the present invention is obtained by supporting a noble metal on the catalyst carrier particles of the present invention. Examples of the noble metal to be supported here include Pt, Rh, Pd, Ir, and Ru, but it is particularly preferable to support platinum because ceria prevents platinum sintering. The amount of noble metal supported on the metal oxide particles is generally 0.01 to 5% by mass, particularly 0.1 to 2% by mass, based on the metal oxide particles.

  The catalyst support particle of the present invention contains an oxide of at least one metal selected from the group consisting of nickel and cobalt, ceria, and zirconia, but further contains one or more metal oxides other than these. You can also. For example, the catalyst carrier particles of the present invention can be arbitrarily selected from the group consisting of s-block metals, d-block metals, p-block metals, and f-block metals as metals other than these. Are Na, K, Mg, Ca, Ba, Sr, La, Y, Pr, Nd, Sm, Eu, Gd, Ti, Zr, Sn, Mn, Fe, Co, Ni, Cr, Nb, Cu, V, Examples include Mo, W, Zn, and Ta. In particular, rare earth elements other than Ce, such as La, Y, Pr, Nd, Sm, Eu, and Gd, and more particularly one or more rare earth elements selected from La, Y, and Pr are heat resistant and sulfur poisoning of the carrier particles. It is preferable for prevention. These elements can be added to the production of catalyst support particles as metal salts, sols, alkoxides, etc., as in ceria and the like.

  The exhaust gas-purifying catalyst of the present invention can also be used by coating a monolithic carrier, such as a ceramic honeycomb.

  The catalyst support particles of the present invention can be made, for example, as follows:

Nickel nitrate hexahydrate 15.1g as Ni raw material, Ce material as calculated _as CeO ₂ in 28% strength by weight aqueous solution of cerium nitrate 159.7 g, zirconium oxynitrate of 18% strength by weight in terms of ZrO ₂ as a Zr raw material 177.7 g of the aqueous solution is dissolved in 1100 g of ion exchange water and mixed. 32.4 g of a hydrogen peroxide solution (30% aqueous solution) containing hydrogen peroxide having a molar number 1.1 times that of cerium ions contained in this mixed aqueous solution is added to the above aqueous solution and mixed with stirring. In this way, an aqueous solution mixed so that the composition ratio of NiO: CeO ₂ : ZrO ₂ is 0.2: 1: 1 by molar ratio is prepared. While stirring this aqueous solution, 114.6 g of ammonia water (25% aqueous solution) containing ammonia having a molar number of 1.2 times the cation contained in the above mixed solution was dropped and neutralized to form a precipitate. Let The obtained precipitate is dried at 120 ° C. and then calcined to obtain about 80 g of carrier particles in which NiO is mixed with CeO ₂ —ZrO ₂ at the atomic level.

  Hereinafter, the present invention will be described based on examples, but the present invention is not limited thereto.

[Example 1]
(A) Production of CeO ₂ —ZrO ₂ —NiO Support Particles Nickel nitrate hydrate as Ni raw material, cerium nitrate aqueous solution as Ce raw material, and zirconium oxynitrate aqueous solution as Zr raw material are dissolved in ion exchange water and mixed did. A hydrogen peroxide solution containing hydrogen peroxide having a mole number 1.1 times that of cerium ions in the mixed aqueous solution was added to the above aqueous solution and mixed with stirring. As a result, an aqueous solution having a composition ratio of CeO ₂ : ZrO ₂ : NiO in a molar ratio of 1: 1: 0.02 was prepared. While stirring this aqueous solution, ammonia water containing ammonia having a molar number of 1.2 times the cation contained in the above mixed solution was added dropwise, neutralized and precipitated. The obtained precipitate was dried at 120 ° C. and then fired to obtain carrier particles in which NiO was mixed with CeO ₂ —ZrO ₂ at the atomic level.

(B) a CeO ₂ -ZrO ₂ -NiO carrier particles obtained in CeO ₂ -ZrO ₂ -NiO platinum supported above the carrier particles (a), using an platinum dinitrodiamine nitric acid solution, platinum relative to the support weight 1.5% by weight was supported.

(C) the ZrO ₂ carrier particles obtained by carrying the general method of rhodium to ZrO ₂ carrier particles, using a rhodium nitrate solution, was supported 1.0 wt% rhodium relative to the support weight.

(D) Production of coating slurry 50 parts by weight of activated alumina powder, 100 parts by weight of platinum-supported CeO ₂ —ZrO ₂ —NiO support particles obtained in (b) above, and rhodium-supported ZrO ₂ support particles 40 obtained in (c) above Distilled water was added to 5.88 parts by weight of boehmite powder as a binder to prepare a coating slurry.

(E) Coating on honeycomb substrate A coating slurry obtained in (d) above is coated on a honeycomb substrate having a capacity of 1.3 liters, dried and fired, and 195 g is coated on 1 liter of honeycomb substrate. did. Accordingly, platinum and rhodium were 1.5 g and 0.4 g, respectively, for 1 liter of honeycomb substrate. The catalyst obtained here is used as the catalyst of Example 1.

[Examples 2 to 10]
In step (a) of Example 1, an aqueous solution was prepared so that the molar ratio of CeO ₂ : ZrO ₂ : NiO would be the composition ratio shown in Examples 2 to 10 in Table 2, and then ammonia required according to the composition ratio Except having used water, it carried out similarly to Example 1, and obtained the catalyst of Examples 2-10.

[Comparative Example 1]
(A) In the same manner except that no addition of nickel nitrate in Example 1 in the CeO ₂ -ZrO ₂ of Example 1 of the carrier particles step (a), the obtain a CeO ₂ -ZrO ₂ carrier particles.

(B) a CeO ₂ -ZrO ₂ carrier particles obtained by the CeO ₂ -ZrO ₂ platinum to the carrier particle bearing above (a), using an platinum dinitrodiamine nitric acid solution, a platinum 1.5 wt relative to the support weight % Was loaded.

A ZrO ₂ carrier particles obtained by carrying the general method of rhodium to (c) ZrO ₂ carrier particles, using a rhodium nitrate solution, carrying 1 wt% rhodium relative to the support weight.

(D) Production of coating slurry 50 parts by weight of activated alumina powder, 100 parts by weight of platinum-supported CeO ₂ —ZrO ₂ support particles obtained in (b) above, and 40 parts by weight of rhodium-supported ZrO ₂ support particles obtained in (c) above Then, distilled water was added to 0.5 parts by weight of nickel oxide and 5.88 parts by weight of boehmite powder as a binder to prepare a coating slurry. Here, the molar ratio of CeO ₂ : ZrO ₂ : NiO was 1: 1: 0.02 with respect to the total of platinum-supported CeO ₂ —ZrO ₂ carrier particles and nickel oxide particles.

(E) Coating on honeycomb substrate A coating material obtained in (d) above was coated on a honeycomb substrate with a capacity of 1.3 liters, dried and fired, and 195 g + 0.5 g with respect to 1 liter of honeycomb substrate. (Nickel oxide corresponding to the target composition) was coated. Accordingly, platinum and rhodium were 1.5 g and 0.4 g, respectively, for 1 liter of honeycomb substrate. The catalyst obtained here is used as the catalyst of Comparative Example 1.

[Comparative Examples 2 to 7]
In the step (d) of Comparative Example 1, the molar ratio of CeO ₂ : ZrO ₂ : NiO is shown in Comparative Examples 2 to 7 in Table 2 with respect to the total of platinum-supported CeO ₂ —ZrO ₂ carrier particles and nickel oxide particles. Comparison was made in the same manner as in Comparative Example 1 except that the coating slurry was prepared so as to have a molar ratio, and the coating amount was changed to an amount obtained by adding 195 g to the weight of nickel oxide corresponding to the target composition. The catalysts of Examples 2-7 were obtained.

[Evaluation]
The obtained catalyst was evaluated for (a) hydrogen sulfide generation amount, (b) catalytic activity, and (c) OSC ability.

(A) Hydrogen sulfide generation amount A model gas having a composition simulating the exhaust gas shown in Table 1 was passed through the catalyst, and the amount of hydrogen sulfide generated was measured. Here, the catalyst was kept at 600 ° C., the gas of composition A was allowed to flow for 10 minutes, and then the gas of composition B was allowed to flow for 5 minutes. The results are shown in Table 2.

(B) Catalytic activity The catalyst was attached to an exhaust gas system of an engine with a displacement of 3 liters, and a 200-hour durability test was performed under the conditions of an air fuel consumption (A / F) of 14.6 and an inlet gas temperature of 850 ° C. After that, using the same engine, under the conditions of A / F = 14.6 and an input gas temperature of 400 ° C., the conversion rate of HC {100% × (HC concentration in input gas−HC concentration in output gas) / input HC concentration in gas} was measured. The results are shown in Table 2.

(C) OSC ability For Examples 3 and 8 to 10, the OSC ability was measured. In these examples, the ratio of the number of moles of ceria and zirconia is changed while maintaining the number of moles of nickel oxide with respect to the sum of ceria and zirconia constant. The results are shown in Table 2.

  As is clear from Table 2 above, when compared with the comparative example in which nickel oxide is added to the coating slurry in the form of particles, all the examples in which nickel oxide, ceria, and zirconia are dispersed in a single particle are used. In this case, the amount of hydrogen sulfide generated is significantly reduced, and when the amount of nickel oxide is the same, the HC addition rate is also improved.

Moreover, from FIG. 3 which summarized the H ₂ S production amount and the HC purification rate for the catalysts of Examples 1 to 7, nickel is in the range of 2.5 to 20 mol% with respect to the total number of moles of cerium and zirconium. It can be seen that this is preferable for prevention of hydrogen sulfide release and HC purification.

Furthermore, from FIG. 4 that summarizes the OSC ability and the amount of H ₂ S produced for the catalysts of Examples 3 and 8 to 10, the zirconium is in the range of 50 to 70 mol% with respect to the total of cerium and zirconium. It can be seen that OSC capability and prevention of hydrogen sulfide release are preferable.

It is a figure which represents the catalyst support particle | grains of this invention notionally. It is a figure which represents notionally the catalyst carrier particle of the past (patent document 2). It is a figure showing the hydrogen sulfide production amount and HC purification rate with respect to Examples 1-10 with respect to the molar fraction of nickel. It is a figure showing the hydrogen sulfide production amount and OSC ability with respect to Examples 3 and 8-10 with respect to the molar fraction of zirconium.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Catalyst support particle | grains 3 of this invention containing oxide of cerium, zirconium, and nickel ... Ceria-zirconia solid solution catalyst support particle 5 ... Nickel oxide particle

Claims (9)

  Catalyst support particles comprising an oxide in which at least one metal selected from the group consisting of nickel and cobalt, cerium, and zirconium are mixed.   2. The catalyst carrier particle according to claim 1, wherein the oxide of cerium and zirconium at least partially forms a solid solution.   The catalyst carrier particle according to claim 1 or 2, wherein the catalyst carrier particle comprises an oxide in which a rare earth element other than cerium is further mixed.   The catalyst carrier particle according to any one of claims 1 to 3, wherein zirconium is 50 to 70 mol% with respect to a total of cerium and zirconium.   The at least one metal selected from the group consisting of nickel and cobalt is 2.5 to 20 mol% with respect to the total of cerium and zirconium, according to any one of claims 1 to 4. Catalyst carrier particles.   An exhaust gas purifying catalyst, wherein a noble metal is supported on the catalyst carrier particles according to any one of claims 1 to 5.   Generating a precipitate from a solution containing an alkoxide and / or salt of at least one metal selected from the group consisting of nickel and cobalt, cerium and zirconium, and drying and calcining the resulting precipitate. A method for producing catalyst carrier particles.   Generating a precipitate from a solution containing cerium and zirconium alkoxides and / or salts, and generating a precipitate from a solution containing alkoxides and / or salts of at least one metal selected from the group consisting of nickel and cobalt And drying and calcining the resulting precipitate together, a method for producing catalyst support particles.   A method for producing catalyst support particles, comprising mixing a sol of at least one metal selected from the group consisting of nickel and cobalt, cerium, and zirconium, generating a precipitate, and drying and calcining the precipitate.

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