JP5620799B2 - Catalyst production method and combustion exhaust gas purification catalyst - Google Patents

Description

The present invention relates to a method for producing a catalyst in which a noble metal is supported while forming a magnetoplumbite type composite oxide (LaMnAl ₁₁ O ₁₉ ), and a combustion exhaust gas purification catalyst.

  In general, it is considered that the exhaust gas purification catalyst is deteriorated in performance due to particle growth of noble metal fine particles which are catalytic active components. These noble metal fine particles are generally used by being dispersed on the surface of a heat-resistant alumina carrier (catalyst carrier). However, as the environmental temperature rises, the alumina surface diffuses and moves to grow repeatedly by agglomeration. Therefore, technical development has been advanced in order to suppress the performance deterioration of the noble metal catalyst by suppressing the diffusion / migration of the noble metal fine particles on the surface of the support.

  For example, Patent Document 1 discloses a method of confining noble metal fine particles in the pores of an alumina support and suppressing the movement / diffusion thereof. In such a method, when confining the noble metal fine particles in the alumina pores, an idea is made to simultaneously confine oxide particles such as cerium oxide, zirconium oxide or magnesium oxide together with the noble metal fine particles to prevent aggregation of the noble metal fine particles in the pores. ing.

However, in recent years, perovskite complex oxide catalysts having excellent heat resistance have attracted attention. Such a perovskite complex oxide is expressed as ABO _3, and in many cases, lanthanum (La) is used for A and iron (Fe), cobalt (Co), or manganese (Mn) is used for B. It has been pointed out that such a perovskite complex oxide (LaFeO ₃ , LaCoO ₃ , LaMnO ₃ ) alone has an exhaust gas purification activity, but has a small amount of processing gas and inferior NO purification performance. In order to overcome this drawback, LaFe _(1-x) Pd _x O _{3 in} which a part of LaFeO ₃ is substituted with a noble metal (Pd) has been proposed (for example, see Patent Document 2).

By the way, it has been proposed to use a magnetoplumbite type complex oxide containing alumina as a main component and lanthanum (La) as an alkaline earth metal as a catalyst. In this case, manganese or iron is used as a substituted metal atom. It has also been proposed to choose. A magnetoplumbite type complex oxide (abbreviated as MPB) is considered to be a complex oxide having better heat resistance than the above-described perovskite type complex oxide, and is composed of alumina (Al ₂ O ₃ ) and iron oxide (Fe ₂ O). ₃ ) The crystal lattice is formed with the main component, and alkali metal ions or alkaline earth metal ions are contained in the crystal lattice.

Thus, conventionally, MPB represented as AMn _x Al _12-x O ₁₉ (where A is an alkali metal, alkaline earth metal or rare earth metal) is immersed in an aqueous solution of a noble metal salt, and dried and fired. Has been proposed (see Patent Document 3). According to such prior art, 1 mol of La ₂ O ₃ , 1 mol of Mn ₂ O ₃ , 11 mol of Al ₂ O are used to synthesize Mn-substituted MPB ((La · Mn) Al ₁₁ O _19-x ). _{The three} precursors were accurately weighed and calcined at 1300 ° C. or higher, preferably 1450 ° C. for 5 hours or longer to obtain an exhaust gas catalyst.

JP 2003-135963 A JP-A-5-3136 JP-A-9-271672

However, the conventional catalyst has the following problems.
That is, the conventional one using a perovskite type complex oxide catalyst has not been deteriorated in HC, CO, NO purification performance even after heat treatment at 900 ° C. for 100 hours, and has already been installed in an actual vehicle. However, recently, combustion technology at higher temperatures has been developed from the viewpoint of improving the thermal efficiency of the combustion apparatus, and the temperature of the combustion exhaust gas has risen accordingly. The catalyst installed directly under the engine may be in a high temperature environment exceeding 900 ° C., and the conventional catalyst has a problem that it is not sufficient in heat resistance and durability when applied to the high performance combustion apparatus. .

In addition, the conventional one using the magnetoplumbite type complex oxide is considered to be able to improve the heat resistance because MPB itself is a material having excellent heat resistance, but Mn substituted MPB ((La · Mn ) Al ₁₁ O _19-x ) In order to synthesize 1 mol of La ₂ O ₃ , 1 mol of Mn ₂ O ₃ , 11 mol of Al ₂ O ₃ precursor, weighed accurately 1300 ° C. or higher, preferably 1450 Since it is necessary to calcinate at 5 ° C. for 5 hours or more, the manufacturing process is many and complicated, and the specific surface area of the obtained Mn-substituted MPB is very small, for example, 10 m ² / g or less. It is not possible.

  However, the present applicant has earnestly researched a catalyst using a magnetoplumbite type composite oxide, and in the catalyst using the magnetoplumbite type composite oxide, in particular, further improving the purifying ability of NO. In addition, there is room for improvement in maintaining a highly dispersed state of noble metals in high-temperature atmospheres (suppression of growth due to movement and aggregation of noble metals), and there is room for study on simplification of the manufacturing process in catalyst production methods. I found out.

The present invention has been made in view of such circumstances, and aims to further improve the NO purification ability and maintain high dispersion of the noble metal in a high-temperature atmosphere, and can further simplify the manufacturing process. An object of the present invention is to provide a production method and a combustion exhaust gas purification catalyst.

The invention described in claim 1 is a method for producing a catalyst in which a noble metal is supported while forming a magnetoplumbite type complex oxide (LaMnAl ₁₁ O ₁₉ ), wherein the noble metal ion is added in addition to lanthanum ion and manganese ion. An aqueous solution preparation step for preparing a mixed aqueous solution, and an aqueous solution for filling the mixed aqueous solution obtained in the aqueous solution preparation step into the pores by a pore filling method using a capillary phenomenon generated in the pores of the porous alumina. a filling step, a drying step of the mixed aqueous solution in the pores to dry the porous alumina is filled with aqueous solution filling step, by firing the porous alumina obtained in the drying step, the pores And a firing step for generating a magnetoplumbite type composite oxide containing the noble metal therein.

  According to a second aspect of the present invention, in the method for producing a catalyst according to the first aspect, the noble metal is palladium.

According to the third aspect of the present invention, at least a part of manganese in the magnetoplumbite type complex oxide (LaMnAl ₁₁ O ₁₉ ) structure is replaced with a noble metal, and La (Mn _1-x M _x ) Al ₁₁ O ₁₉ (however, A combustion exhaust gas purifying catalyst characterized in that M is composed of a noble metal).

According to a fourth aspect of the present invention, in the purification catalyst for combustion exhaust gas according to the third aspect, the noble metal is palladium and is composed of a composition formula of La (Mn _1-x Pd _x ) Al ₁₁ O _19. It is characterized by.

The invention according to claim 5 is characterized in that, in the combustion exhaust gas purifying catalyst according to claim 3 or claim 4, 0 <x <0.25 in the composition formula.

  According to the present invention, a mixed aqueous solution containing noble metal ions in addition to lanthanum ions and manganese ions is prepared, and the mixed aqueous solution is filled in the pores of porous alumina by a pore filling method, and dried and fired. A separate process for supporting the noble metal on the catalyst carrier is not required, and the manufacturing process can be simplified. Further, in the obtained catalyst, the NO purification ability can be further improved and the noble metal in the high temperature atmosphere can be improved. High dispersion can be maintained.

Further, at least a part of manganese in the structure of the magnetoplumbite type complex oxide (LaMnAl ₁₁ O ₁₉ ) is substituted with a noble metal, and the composition is La (Mn _1−x M _x ) Al ₁₁ O ₁₉ (where M is a noble metal). Since it is a combustion exhaust gas purification catalyst having the formula, it is possible to further improve the NO purification performance and maintain a high dispersion of the noble metal in a high temperature atmosphere.

The flowchart which shows the manufacturing method of the catalyst which concerns on embodiment of this invention. The graph which shows the XRD diffraction pattern of the catalyst which concerns on Examples 1-4 and Comparative Example 1 The graph which shows the activity evaluation of the catalyst which concerns on Examples 1-4 and Comparative Example 1 The graph which shows the activity evaluation of the catalyst which concerns on Examples 1-4 and Comparative Example 1 The graph which shows the activity evaluation (change of the purification rate in 450 degreeC) of the catalyst which concerns on Example 4 and Comparative Example 1 The graph which shows the activity evaluation (change of T (50)) of the catalyst which concerns on Example 1 and Comparative Example 1

Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings.
The catalyst according to the present embodiment is formed by forming magnetoplumbite-type composite oxide (LaMnAl ₁₁ O ₁₉ ) (MPB) in the pores of porous alumina, and a noble metal such as palladium (Pd) is supported thereon. As shown in FIG. 1, an exhaust gas purification catalyst can be obtained through an aqueous solution preparation step S1, an aqueous solution filling step S2, a drying step S3, a calcination step S4, and a calcination step S5. it can. In the present embodiment, a noble metal supporting step for supporting the noble metal on the catalyst carrier is unnecessary.

  The aqueous solution preparation step S1 is a mixed aqueous solution containing palladium (Pd) ions (noble metal ions) in addition to lanthanum (La) ions and manganese (Mn) ions (that is, La ions for constituting a magnetoplumbite type complex oxide). And Mn ions and palladium (Pd) ions as precious metals for causing a catalytic reaction to be essential and mixed in an aqueous solution). Other ions may be mixed as an additive.

  The aqueous solution filling step S2 is a step of filling the pores in the pores of the porous alumina with the mixed aqueous solution obtained in the aqueous solution preparation step S1 by the pore filling method using the capillary phenomenon. In this pore filling method, the pore volume of the alumina support (catalyst support) is measured, and the same volume of the aqueous solution (in this embodiment, the mixed aqueous solution obtained in the aqueous solution preparation step S1) is added and mixed. It refers to a method of filling the pores of the alumina support (catalyst support) by utilizing capillary action by stirring.

  The drying step S3 is a step of drying the porous alumina in which the mixed aqueous solution is filled in the pores in the aqueous solution filling step S2. Thus, the walls of the catalyst support pores are magnetoplumbite type composites. It will be in the state coat | covered (coating) with the component (composition) for oxide (MPB) production | generation. In the drying step S3, it is preferable to dry at 110 ° C. for about 12 hours, for example.

  The calcination step S4 is a step of baking the material dried in the drying step S3, for example, at about 600 ° C. for about 4 hours. In the firing step S5, the porous alumina obtained in the drying step S3 and subjected to the calcination step S4 is further fired in air at about 1000 ° C., and a magnetoplumbite type composite oxide is generated in the pores. It is a process. The firing time is 60 hours or more.

  Through the above steps S1 to S5, the catalyst according to the present embodiment is manufactured. That is, according to the present embodiment, magnetoplumbite type complex oxide (MPB) generation and catalytic reaction are performed in a single step (aqueous solution filling step S2) in which the mixed aqueous solution is filled into the pores of the catalyst carrier. The noble metal supporting step for supporting the noble metal on the catalyst carrier is unnecessary as described above.

  According to the above embodiment, a mixed aqueous solution containing noble metal ions (palladium ions) in addition to lanthanum (La) ions and manganese (Mn) ions is prepared, and the mixed aqueous solution is pore-filled into the pores of porous alumina. In this case, it is possible to simplify the manufacturing process without using a separate process for supporting the noble metal (palladium) on the catalyst support, and in the obtained catalyst, NO is also required. It is possible to further improve the purifying ability and maintain high dispersion of the noble metal in a high temperature atmosphere.

However, after the mixed aqueous solution is filled in the pores of the catalyst support in the aqueous solution filling step S2 as in the present embodiment, it is dried and fired, so that the magnetoplumbite type complex oxide (LaMnAl ₁₁ O ₁₉ ) structure is formed. In this embodiment, at least a part of manganese is substituted with a noble metal (the remaining palladium ions (noble metal ions) coexist as PdO fine particles), and La (Mn _1-x M _x ) Al ₁₁ O ₁₉ (where M is a noble metal; Is composed of the composition formula "Pd"). In particular, in such a composition formula, a catalyst in which 0 <x <0.25 is preferable.

In this way, at least part of manganese in the structure of magnetoplumbite type complex oxide (LaMnAl ₁₁ O ₁₉ ) is substituted with noble metal, and La (Mn _1-x M _x ) Al ₁₁ O ₁₉ (where M is a noble metal). Therefore, it is possible to further improve the NO purification ability and maintain high dispersion of the noble metal in a high temperature atmosphere. The noble metal in this embodiment is palladium (Pd), but other noble metals that undergo catalytic reaction may be used.

  According to the above catalyst carrier and catalyst production method, the pores of the porous alumina are filled with the aqueous solution obtained in the aqueous solution preparation step by the pore filling method, and the porous alumina is dried to dry the porous alumina. Since the magnetoplumbite-type composite oxide is deposited at a low temperature, the catalyst carrier and the catalyst that can maintain the purification performance of HC, CO, and NO even after being exposed to a high temperature atmosphere of, for example, about 1000 ° C for a long time are simplified. Can get to.

Furthermore, (La (Mn _x M _1-x ) Al ₁₁ O in which any of Co (cobalt), Cu (copper) or Nb (niobium) is added to (La · Mn) Al ₁₁ O ₁₉ as another metal. ₁₉ (where M is Co, Cu or Nb)). In this case, a catalyst carrier and a catalyst that can improve the low-temperature combustion activity of HC and CO and the NO purification ability under lean conditions can be obtained more easily.

Next, experimental results for showing specific characteristics and the like in the present invention will be described using examples.
Example 1
4.66 g (0.02 mol) of lanthanum nitrate (La (NO ₃ ) ₃ .6H ₂ O) and 4.31 g (0.015 mol) of manganese nitrate (Mn (NO ₃ ) ₂ .4H ₂ O) Of Pd concentration of 8.304 wt. % Dinitrodiamine Pd solution 5.80 g was mixed (aqueous solution preparation step). This mixed solution contains 0.482 g (0.005 mol) of Pd ions. In addition, since lanthanum nitrate and manganese nitrate have crystal water, the volume of the mixed aqueous solution is about 11 ml.

This mixed aqueous solution was filled in pores of 11.22 g (0.11 mol) of commercially available alumina (specific surface area: 247 m ² / g, pore volume: 1.0 ml / g) by a pore filling method (aqueous solution filling step). Then, after drying (drying process) for 12 hours in a drier kept at 110 ° C., pre-baking at 600 ° C. for 4 hours and further baking at 1000 ° C. for 60 hours (baking process), La (Mn _0.75 Pd _0.25 ) Al ₁₁ O ₁₉ catalyst powder (Example 1) was prepared. This catalyst contains 3.0 wt. % Pd (noble metal) is supported. In this example, in order to evaluate the thermal durability of the catalyst, a heat treatment was further performed at 1000 ° C. for 60 hours (total of 120 hours).

(Example 2)
4 ml of 8.66 g (0.02 mol) of lanthanum nitrate (La (NO ₃ ) ₃ .6H ₂ O) and 4.70 g (0.0164 mol) of manganese nitrate (Mn (NO ₃ ) ₂ .4H ₂ O) Of Pd concentration of 8.304 wt. % Of dinitrodiamine Pd solution (4.617 g) was mixed (aqueous solution preparation step). This mixed solution contains 0.383 g (0.0036 mol) of Pd ions. The other production steps and conditions were the same as in Example 1, and a La (Mn _0.82 Pd _0.18 ) Al ₁₁ O ₁₉ catalyst powder (Example 2) was prepared. This catalyst contains 2.37 wt. % Pd (noble metal) is supported.

Example 3
4.66 g (0.02 mol) of lanthanum nitrate (La (NO ₃ ) ₃ .6H ₂ O) and 4.88 g (0.0170 mol) of manganese nitrate (Mn (NO ₃ ) ₂ .4H ₂ O) Of Pd concentration of 8.304 wt. % Of dinitrodiamine Pd solution 3.844 g was mixed (aqueous solution preparation step). This mixed solution contains 0.319 g (0.0030 mol) of Pd ions. The other production steps and conditions were the same as in Example 1, and a La (Mn _0.85 Pd _0.15 ) Al ₁₁ O ₁₉ catalyst powder (Example 3) was prepared. This catalyst contains 1.98 wt. % Pd (noble metal) is supported.

Example 4
4.66 g (0.02 mol) of lanthanum nitrate (La (NO ₃ ) ₃ .6H ₂ O) and 5.00 g (0.0175 mol) of manganese nitrate (Mn (NO ₃ ) ₂ .4H ₂ O) Of Pd concentration of 8.304 wt. 3.191 g of% dinitrodiamine Pd solution was mixed (aqueous solution preparation step). This mixed solution contains 0.265 g (0.0025 mol) of Pd ions. The other production steps and conditions were the same as in Example 1, and a La (Mn _0.88 Pd _0.12 ) Al ₁₁ O ₁₉ catalyst powder (Example 4) was prepared. This catalyst contains 1.50 wt. % Pd (noble metal) is supported.

(Comparative Example 1)
5.66 g (0.02 mol) of lanthanum nitrate (La (NO ₃ ) ₃ .6H ₂ O) and 5.74 g (0.02 mol) of manganese nitrate (Mn (NO ₃ ) ₂ .4H ₂ O) In distilled water. Since lanthanum nitrate and manganese nitrate have crystal water, the volume of the aqueous solution is about 11 ml. This aqueous solution was filled in pores of 11.22 g (0.11 mol) of commercially available alumina (specific surface area: 247 m ² / g, pore volume: 1.0 ml / g) by the pore filling method and maintained at 110 ° C. After drying for 12 hours in the dryer, calcined at 600 ° C. for 4 hours and further calcined at 1000 ° C. for 60 hours to obtain LaMnAl ₁₁ O ₁₉ (MPB) powder, 16.1 g.

  This powder has pores of 0.3 ml / g, and Pd concentration of 8.304 wt. 3% dinitrodiamine Pd solution 5.80 g (containing 0.482 g of Pd ions), dried in a drier kept at 110 ° C. for 12 hours, and then calcined at 600 ° C. for 4 hours. % Pd / MPB catalyst (Comparative Example 1) was prepared. In order to evaluate the thermal durability of this catalyst, heat treatment was performed at 1000 ° C. for 60 hours or 120 hours.

(Comparative Example 2)
LaMnAl ₁₁ O ₁₉ (MPB) powder (5 g) prepared in Comparative Example 1 was mixed with 1.0 g of alumina sol (fibrous alumina content 10 wt.%) Diluted with 2.0 ml of distilled water and heated to 110 ° C. After drying for 12 hours in the held drier, the alumina sol-coated MPB powder was obtained by calcining at 600 ° C. for 4 hours and further calcining at 1000 ° C. for 5 hours. The surface of the MPB powder is coated with fibrous alumina having a function as a barrier (partition) material.

  The alumina sol-coated MPB powder thus obtained has a Pd concentration of 8.304 wt. 1% dinitrodiamine Pd solution 1.08 g (containing 0.09 g of Pd ions) was charged in a drier kept at 110 ° C. for 12 hours, and then calcined at 600 ° C. for 4 hours to obtain 3 % Pd / alumina sol-coated MPB catalyst (Comparative Example 2) was prepared. In order to evaluate the thermal durability of this catalyst, heat treatment was performed at 1000 ° C. for 60 hours or 120 hours.

(Experiment 1)
For the catalysts according to Examples 1 to 4 and Comparative Example 1, XRD was measured for the purpose of confirming MPB generation and PdO presence state. The measurement results are shown in FIG. According to this measurement result, it was possible to confirm the generation of MPB for all the measured samples. In addition, as for PdO, since many diffraction lines overlap with the peak of MPB, it was difficult to confirm the existence thereof, but 2θ = 29.3 (the peak indicated by symbol α in FIG. 2) and 2θ = 54.7 (the peak indicated by the symbol β in the figure) is identified as PdO.

  These two peaks are clearly present in Comparative Example 1 (3% Pd / MPB catalyst) (although the peak intensity is weak), but cannot be confirmed in Examples 1 to 4. That is, in Comparative Example 1, Pd ions exist as PdO particles, but in Examples 1 to 4, a part of Pd ions is replaced with Mn ions in the MPB structure (MPB lattice), and the MPB structure ( It can be inferred that it is incorporated in the (MPB lattice). In addition, it is considered that Pd ions that have not been incorporated into the MPB structure (MPB lattice) coexist in the catalyst as PdO particles.

(Experiment 2)
The particle diameters of the Pd particles in the catalysts according to Examples 1 to 4 and Comparative Examples 1 and 2 were measured. For the measurement of the particle diameter, the CO pulse adsorption method was used. Since Pd is an oxide (PdO), 10 vol. After reducing with% H ₂ / N ₂ at 150 ° C. for 30 minutes, the specific surface area and particle diameter of Pd particles were calculated by observing the amount of CO adsorbed at room temperature. The results are shown in Table 1 below. Here, it was assumed that Pd ions in the catalysts according to Examples 1 to 4 also exist as PdO, and the specific surface area and particle diameter of the Pd particles were calculated.

  According to Table 1 above, Example 1 and Comparative Examples 1 and 2 both carry 3% Pd, but Example 1 has 120 hours of heat treatment at 1000 ° C. for 60 hours. It can be seen that the particle size of the Pd particles is reduced even by heat treatment. From this, as in the present invention, “magnetoplumbite type complex oxide (MPB) generation and catalytic reaction are performed in a single step (aqueous solution filling step S2) in which the mixed aqueous solution is filled into the pores of the catalyst carrier. The catalyst obtained by “supporting the precious metal for carrying out the simultaneous formation” is a particle growth of precious metal particles (Pd particles) as compared with the catalyst prepared by a conventional general method in which the support is impregnated with an aqueous Pd salt solution. It was found that can be suppressed. Therefore, Example 1 (same as in Examples 2 to 4) can maintain high dispersion of the noble metal in a high temperature atmosphere.

  Moreover, the thing of Example 1 compared with the thing which apply | coated the fibrous alumina as a growth suppression material which suppresses the growth of a noble metal particle on the MPB support | carrier surface (comparative example 2), in the heat processing of 1000 degreeC-120 hours, Pd Although the particle size is slightly larger, it can be seen that the Pd particle size is almost the same in the heat treatment for 60 hours. That is, as in the present invention, “in order to cause magnetoplumbite type complex oxide (MPB) generation and catalytic reaction in a single step (aqueous solution filling step S2) of filling the mixed aqueous solution into the pores of the catalyst carrier. It can be determined that the catalyst obtained by “supporting the noble metal simultaneously” has almost the same particle size suppression effect as the catalyst obtained by coating the surface of the carrier with a barrier (partition) material.

(Experiment 3)
The catalysts according to Examples 1 to 4 and Comparative Example 1 were formed into pellets and then pulverized to obtain a powder of 0.25 to 1.0 mm, and the purification activity was evaluated using this. However, since the amount of Pd supported by La (Mn _1-x Pd _x ) Al ₁₁ O ₁₉ in Examples 1 to 4 differs from 1.5 to 3.0% depending on the value of x, the amount of sample powder used for activity evaluation To adjust the amount of Pd to 10 mg. That is, Example 1 (Pd carrying amount 3%) is 0.338 g (0.5 ml), Example 2 (Pd carrying amount 2.37%) is 0.427 g (0.63 ml), Example 3 ( A catalyst of 0.514 g (0.76 ml) was used for the Pd loading amount of 1.98%, and 0.667 g (1.0 ml) of the catalyst for Example 4 (Pd loading amount of 1.98%) was used.

The composition of the simulated gas used in the experiment is NO: 1500 ppm, CO: 0.65%, HC: 360 ppm (breakdown is C ₃ H ₈ ; 180 ppm, C ₃ H ₆ ; 180 ppm), O ₂ : 0.50% Nitrogen was used as the balance gas, and the gas flow rate was set to 1 l / min. The temperature of the catalyst layer is raised from room temperature to 600 ° C. at 45 ° C./min, and the simulated gas is allowed to pass through the catalyst layer, and the gas composition at the catalyst layer inlet and outlet at each temperature is determined by infrared spectroscopy and magnetic properties. The catalytic activity was evaluated by measuring with a formula oxygen analysis method.

  In the catalyst activity evaluation, two indices are used, one is observation of the temperature (T50) at which the concentration of HC, CO, NO is reduced by half, and the other is HC, CO, NO at 450 ° C. The purification rate was observed. These observation results are shown in Table 2 below. In Table 2, the results obtained for the catalyst heat-treated at 1000 ° C. for 60 hours are shown, and in these results, in order to facilitate mutual comparison of Examples 1 to 4 having different values of x, FIG. The experimental results are also shown in 3 and 4.

  As can be seen from the above Table 2 and FIG. 3, in Example 4 and Comparative Example 1 in which the amount of Pd supported is the same as 3%, the CO purification rate is equivalent when the activity at 450 ° C. is compared, but HC The purification rate of NO and NO is higher in Example 4, and it can be determined that the Example is superior in terms of the purification rate of HC and NO. As can be seen from Table 2 and FIG. 4, the temperature T (50) at which the concentrations of HC, CO, and NO are halved is lower in Example 4 than in Comparative Example 1, and these HC, CO, and NO are reduced. It can be judged that the embodiment is superior in purifying the water.

That is, as in the present invention, “in order to cause magnetoplumbite type complex oxide (MPB) generation and catalytic reaction in a single step (aqueous solution filling step S2) of filling the mixed aqueous solution into the pores of the catalyst carrier. It can be seen that the catalyst obtained by carrying out the loading of the noble metal at the same time is superior in exhaust gas purification performance to Comparative Example 1. This seems to be due to the fact that the dispersibility of Pd in the catalyst according to the present invention (particularly Example 4) is superior to that of Comparative Example 1. Further, when comparing La (Mn _1-x Pd _x ) Al ₁₁ O ₁₉ in Examples 1 to 4, purification of HC, CO, and NO at 450 ° C. is smaller when the value of x is smaller and the amount of Pd supported in the catalyst is smaller. Both activity and temperature T (50) at which the concentration is halved have been found to be advantageous.

However, for La (Mn _1-x Pd _x ) Al ₁₁ O ₁₉ in Examples 1 to 4, when the value of x exceeds 0.25, the amount of Pd ions that are not incorporated into the MPB structure (MPB lattice) increases. However, when the value of x is smaller than 0.1, the amount of catalyst powder applied to a catalyst body such as a vehicle is required more. Therefore, there is a risk of peeling during traveling. Therefore, 0.1 <x <0.25 is preferable in the composition formula La (Mn _1-x Pd _x ) Al ₁₁ O ₁₉ . In the composition formula La (Mn _1-x Pd _x ) Al ₁₁ O ₁₉ by eliminating problems such as peeling during running, 0 <x <0.25 is preferable.

(Experiment 4)
The catalysts according to Examples 1 to 4 and Comparative Example 1 used in Experiment 3 were further heat-treated at 1000 ° C. for 60 hours (120 hours in total), and then the purification activity was measured by the same method as in Experiment 1 to determine the catalyst activity. Thermal durability was evaluated. The results are shown in Table 3 below. In addition, the change in the purification rate at 450 ° C. and the change in T (50) in the 1000 ° C.-60 hour heat treatment words of Example 4 and Comparative Example 1 are shown in FIGS.

  As can be seen from Table 3 and FIG. 5, the HC purification rate was slightly decreased in both Example 4 and Comparative Example 1 by the heat treatment at 1000 ° C. for 120 hours. Maintained a high purification rate as compared with the catalyst of Comparative Example 1, and no decrease in activity was observed. Further, as can be seen from Table 3 and FIG. 6, the T (50) of the catalyst according to Example 4 is substantially constant not only for T (50) HC and T (50) CO but also for T (50) NO. It can be seen that the thermal durability is very good.

In addition, by comparing Table 2 with Table 3, the thermal durability is improved as the value of x of the composition of La (Mn _1-x Pd _x ) Al ₁₁ O ₁₉ in Examples 1 to 4 is reduced. It turned out that the tendency is remarkable about purification. This is considered due to the effect of suppressing the growth of Pd particles by lowering the concentration of noble metal in the catalyst. That is, the catalyst having a composition of La (Mn _1-x Pd _x ) Al ₁₁ O ₁₉ according to the present invention can reduce the concentration of noble metal in the catalyst, and also modifies the carrier to modify noble metal (oxide) particles. The noble metal particles can be stably fixed on the surface of the carrier.

An aqueous solution preparation step of preparing a mixed aqueous solution containing the noble metal ion in addition to lanthanum ions and manganese ions, and an aqueous solution preparation step in the pores by a pore filling method using a capillary phenomenon generated in the pores of porous alumina An aqueous solution filling step for filling the obtained mixed aqueous solution, a drying step for drying the porous alumina filled with the mixed aqueous solution in the pores in the aqueous solution filling step, and firing the porous alumina obtained in the drying step As a catalyst manufacturing method and a combustion exhaust gas purification catalyst having a calcining step for producing a magnetoplumbite type composite oxide containing a noble metal in the pores, it is also possible to add various steps, etc. Can be applied.

S1 aqueous solution preparation step S2 aqueous solution filling step S3 drying step S4 calcination step S5 baking step

Claims (5)

A method for producing a catalyst in which a noble metal is supported while forming a magnetoplumbite type composite oxide (LaMnAl ₁₁ O ₁₉ ),
An aqueous solution preparation step of preparing a mixed aqueous solution containing the noble metal ions in addition to lanthanum ions and manganese ions;
An aqueous solution filling step of filling the mixed aqueous solution obtained in the aqueous solution preparation step into the pores by a pore filling method utilizing a capillary phenomenon generated in the pores of the porous alumina;
A drying step of drying the porous alumina in which the mixed aqueous solution is filled in the pores in the aqueous solution filling step;
By firing the porous alumina obtained in the drying step, a firing step of generating a magnetoplumbite type composite oxide containing the noble metal in the pores ;
A method for producing a catalyst, comprising:   The method for producing a catalyst according to claim 1, wherein the noble metal is palladium. From the composition formula of La (Mn _1-x M _x ) Al ₁₁ O ₁₉ (where M is a noble metal) by substituting at least part of manganese in the magnetoplumbite type complex oxide (LaMnAl ₁₁ O ₁₉ ) structure with a noble metal. Combustion exhaust gas purification catalyst characterized by comprising The noble metal is _{palladium, La (Mn 1-x Pd} x) Al 11 O 19 becomes that which is assumed to consist of the composition formula, characterized in claims 3 purifying catalyst of the combustion exhaust gas as claimed. 5. The combustion exhaust gas purifying catalyst according to claim 3, wherein 0 <x <0.25 in the composition formula.

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