JP5545167B2 - Catalyst material and method for producing the same - Google Patents

Description

The present invention is suitable for use in the catalytic material and a manufacturing method thereof used to promote the burning of particulates de I over diesel engines.

  Conventionally, as a catalyst material for accelerating the combustion of carbon contained in particulates (PM) of diesel engines, a layered structure of alumina and silver has been proposed (for example, see Patent Document 1). According to the catalyst material described in Patent Document 1, carbon combustion can be started at a lower temperature than the conventional one such as 300 ° C to 400 ° C.

JP 2009-219970 A

  By the way, the PM combustion performance of the catalyst material depends on the number of active points, but the number of active points depends on the catalyst surface area if the catalyst amount is the same.

  Here, in the catalyst material described in Patent Document 1, metallic silver and a silver beta alumina portion serve as active sites. However, since the catalyst material has a layered structure of alumina and silver, the surface areas of the metallic silver and silver beta alumina portions are small, that is, the active sites are limited. For this reason, in order to exhibit the required catalyst performance, a considerable amount of expensive silver is required, and there is a problem that the manufacturing cost increases.

  Further, generally, when a flame retardant ash component discharged from a diesel engine is deposited on an active point of a catalyst material, there is a problem that particulate matter (PM) combustion performance cannot be exhibited.

  An object of this invention is to provide the catalyst material which can expand an active surface area, and its manufacturing method in view of the said point.

To achieve the above object, according to the invention of claim 1, comprising a layered structure of alumina and silver are alternately laminated, and the silver was dispersed calcium sulfate, and the layered structure, silver It is characterized by being in contact with dispersed calcium sulfate.

According to this, although details are unknown, for example, when oxygen contained in the exhaust gas of an internal combustion engine adheres to the metallic silver and silver beta alumina portions of the layered structure, it changes to active oxygen (O2-). It is thought that oxygen propagates in the calcium sulfate containing silver and reacts with the carbon on the calcium sulfate surface to become carbon dioxide, that is, the carbon can be burned. At this time, since the calcium sulfate portion can be an active surface, the active surface area can be increased.

The catalyst material according to 請 Motomeko 1, Ru is used for burning particulates of a diesel engine.

In this case, there is a concern that the catalyst performance may be degraded by the flame-retardant ash discharged from the diesel engine, but since the main component of the ash component is calcium sulfate, the ash component is a layered structure of metallic silver and silver. Even if it adheres to the beta alumina part and covers the active surface, silver can be dispersed in ash (calcium sulfate) by the heat treatment process. As a result, the calcium sulfate in which silver is dispersed is in contact with the layered structure. The particulates can be burned with the active surface of the metallic silver and the silver beta alumina portion or the calcium sulfate portion in which silver is dispersed.

Further, in the invention according to claim 2, in the catalyst material of claim 1, the content of silver in the calcium sulfate is, it is characterized in that at least 0.1 wt%. As described above, when the content of silver in calcium sulfate is 0.1 wt% or more, the performance as a catalyst can be sufficiently exhibited.

The invention according to claim 3 is a catalyst material used for burning particulates of a diesel engine, wherein the layered structure is formed by alternately laminating alumina and silver, and sulfuric acid in which silver is dispersed. A method for producing a catalyst material in which a layered structure and calcium sulfate in which silver is dispersed are in contact with each other, and a mixing step of mixing the layered structure and calcium sulfate. And a heat treatment step of diffusing silver into calcium sulfate by heat-treating the layered structure and calcium sulfate.

  According to this, since silver contained in the layered structure can be dispersed in calcium sulfate in the heat treatment step, it is not necessary to add silver separately in the mixing step. Therefore, it becomes possible to easily produce a catalyst material having a layered structure and calcium sulfate in which silver is dispersed.

The invention according to claim 4 is characterized in that, in the method for producing a catalyst material according to claim 3 , the temperature of the heat treatment is 600 ° C. or more and 1000 ° C. or less. Thus, it is possible to sufficiently diffuse silver into calcium sulfate by maintaining the structure of the layered structure by setting the heat treatment temperature to 1000 ° C. or less and setting the heat treatment temperature to 600 ° C. or more. Become.

The invention according to claim 5 is the method for producing the catalyst material according to claim 1 , characterized by comprising a mixing step of mixing the layered structure, silver and calcium sulfate.

According to this, in the mixing step, it is possible to disperse the silver in the calcium sulfate may provide a manufacturing method capable of properly producing a catalyst material according to claim 1.

It is a figure which shows the typical structure of the catalyst material which concerns on embodiment of this invention. It is a schematic diagram for demonstrating the effect | action of the catalyst material which concerns on embodiment of this invention. It is a graph which shows the result of having measured the amount of silver in calcium sulfate by an energy dispersive X-ray fluorescence spectrometer. It is a characteristic view which shows the relationship between the weight change about each catalyst (A, B, C) and heating temperature.

  An embodiment of the present invention will be described with reference to FIGS. The catalyst material of this embodiment is used to promote the combustion of carbon contained in the particulate (PM) of the diesel engine.

FIG. 1 is a diagram showing a schematic configuration of a catalyst material according to the present embodiment. As shown in FIG. 1, the catalyst material of the present embodiment has a layered structure in which alumina (Al 2 O 3) 1 and silver 2 are alternately laminated (hereinafter referred to as layered silver alumina catalyst 3) and silver 4 are dispersed. And calcium sulfate (CaSO 4) 5. More specifically, the catalyst material has a structure in which the layered silver alumina catalyst 3 is covered with calcium sulfate 5 in which silver 4 is dispersed.

Here, the layered silver alumina catalyst 3 has a layered structure of alumina 1 and silver 2, and in this embodiment, Ag-beta alumina in which silver enters the alumina itself is used as the alumina 1. Metal silver is adopted as the silver 2 .

Moreover, the catalyst material of this embodiment is carry | supported by the support | carrier (not shown). Here, ceramics such as alumina, silica (SiO ₂ ), cordierite (Mg ₂ Al ₃ (AlSi ₅ O ₁₈ )), silicon carbide (SiC), etc. can be used as the material of the carrier. Further, as the carrier, a honeycomb structure, a ball type, a DPF (diesel particulate collection filter), a pellet, or the like can be adopted.

  Next, the operation of the catalyst material of this embodiment will be described. FIG. 2 is a schematic diagram for explaining the operation of the catalyst material according to the present embodiment.

The exhaust gas from the internal combustion engine of the vehicle contains oxygen. Although details are unknown, when oxygen in the exhaust adheres to the metallic silver and silver beta alumina portion 2 of the layered silver alumina catalyst 3, it changes to active oxygen (O ₂ ⁻ ), and this active oxygen contains silver 4 It is thought that it propagates in the calcium sulfate 5 and reacts with PM (carbon) on the surface of the calcium sulfate 5 to become carbon dioxide, that is, carbon contained in the PM can be combusted.

At this time, the calcium sulfate 5 plays a role of providing a part where the silver 4 can be dispersed, and further a part which propagates active oxygen. As a result, not only the metal silver and silver beta alumina parts of the layered silver alumina catalyst, The silver-dispersed calcium sulfate portion in contact with the layered silver alumina catalyst can also be used as a carbon combustible region. Therefore, the state where the layered silver alumina catalyst is in contact with calcium sulfate in which silver is dispersed can be regarded as one new catalyst body, and the effective region where the contacted carbon can be combusted is the conventional metal silver and silver beta alumina. In addition to the portion, it can be expanded to the calcium sulfate region in which silver is dispersed, and the active surface area can be expanded. As a result, it is possible to reduce the amount of silver used as a result, while ensuring the performance as a catalyst, it is possible to eliminate the need for additional silver usage to achieve the required catalytic performance as the surface area increases. It becomes.

  In addition, when the layered silver alumina catalyst 3 is used as a catalyst, even when ash containing calcium sulfate as a main component is deposited and the active sites of the layered silver alumina catalyst 3 are buried, the layered silver alumina catalyst 3 is subjected to heat treatment. Silver contained in the alumina catalyst 3 can be dispersed in calcium sulfate. Thereby, since the active surface area can be expanded and active oxygen can propagate, even if ash is deposited on the catalyst, PM combustion performance can be exhibited.

  Next, a method for manufacturing the exhaust purification catalyst of the present embodiment will be described. First, a layered silver alumina catalyst and calcium sulfate are mixed (mixing step). Subsequently, the mixed layered silver alumina catalyst and calcium sulfate are heat-treated (heat treatment step). Thereby, silver contained in the layered silver alumina catalyst can be dispersed (diffused) in calcium sulfate.

  According to this manufacturing method, since silver contained in the layered silver alumina catalyst can be dispersed in calcium sulfate in the heat treatment step, it is not necessary to add silver separately in the mixing step. Therefore, the catalyst material of this embodiment can be manufactured easily.

  In the present embodiment, the silver content in the calcium sulfate is 0.1 wt% or more. This is because, according to the experiments of the present inventors, it has been found that if the silver content in calcium sulfate is less than 0.1 wt%, the performance as a catalyst cannot be exhibited sufficiently.

  In the present embodiment, the temperature of the heat treatment in the heat treatment step is 600 ° C. or higher and 1000 ° C. or lower. This is because, as shown in FIG. 3 to be described later, when the heat treatment temperature is lower than 600 ° C., silver cannot be sufficiently diffused in calcium sulfate. On the other hand, according to experiments by the present inventors, it has been found that when the heat treatment temperature is higher than 1100 ° C., the structure of the layered silver alumina catalyst cannot be maintained.

  Here, although the silver in the layered silver alumina catalyst diffuses into calcium sulfate, there is a concern that the performance of the layered silver alumina catalyst itself may be deteriorated, but according to the experiments of the present inventors, the diffusion amount of silver is heated for a long time. It was found that the amount of the treatment was as small as about 1% or less, and the influence on the performance was hardly seen.

  Next, although not limited thereto, the exhaust purification catalyst and the manufacturing method thereof according to the above embodiment will be described more specifically with reference to the following examples.

Example 1
In Example 1, a mixture of transition alumina and silver oxide or silver acetate is subjected to hydrothermal treatment at 150 ° C. or higher in an environment where acetic acid is present, and the transition alumina and silver ions are reacted to produce Ag-beta alumina. The catalyst as a laminated body formed by laminating a layer made of silver and a layer made of silver was formed. This catalyst material is capable of burning fine carbon powder from a low temperature around 400 ° C., similarly to the silver alumina ball catalyst of Example 2 (see FIG. 4) described later.

In the present embodiment, the molar ratio of silver oxide to alumina is 1 or more when silver oxide is 1, and the molar ratio of silver oxide to acetic acid is 1 or more when silver oxide is 1. To do. At this time, the dispersibility becomes higher as the amount of acetic acid is increased to some extent, but if the amount of acetic acid is too large, silver cannot enter the layered alumina layer. Specifically, 10.0 g of Al ₂ O ₃ , 23.0 g of Ag ₂ O, and 12.0 g of acetic acid were prepared and dispersed in 1000 ml of ion-exchanged water.

  Next, this dispersion was sealed in a pressure vessel equipped with an inner vessel made of Teflon (registered trademark). Then, a layered silver alumina catalyst sol having a laminated structure was obtained by hydrothermal treatment at 185 ° C. for 24 hours.

  The sol of the layered silver alumina catalyst thus obtained can be dried and calcined to obtain a catalyst powder. Moreover, when apply | coating to a support | carrier etc., it can utilize with a sol state.

  The layered silver alumina catalyst can be used by being supported on a carrier such as a ceramic honeycomb structure by dip coating or the like. The ceramic honeycomb structure includes, for example, an outer peripheral wall, partition walls provided in a honeycomb shape inside the outer peripheral wall, and a plurality of cells partitioned by the partition walls and penetrating at least partially at both end faces. Have.

  Here, the cell penetrating through both end faces means that the cell is opened at both end portions of the ceramic honeycomb structure, and the cell is configured as a hole penetrating between the both end portions. All of the plurality of cells may be open at both end faces of the structure. Moreover, about the one part cell among several cells, the part of the said both end surfaces may be obstruct | occluded with the plug material etc.

  In the ceramic honeycomb structure of the present example, the end of the cell located on the upstream end surface serving as the exhaust inlet side and the downstream end surface serving as the exhaust outlet side is disposed with the portion where the plug portion is disposed. And non-existing portions alternately. In addition, a large number of holes are formed in the partition wall so that exhaust can pass through.

  The overall size of the ceramic honeycomb structure of this example is 30 mm in diameter and 50 mm in length, and the cell size is 0.3 mm in cell thickness and 1.47 mm in cell pitch. Further, the ceramic honeycomb structure was made of cordierite, and the cell had a quadrangular cross section. In addition, various cross-sectional shapes, such as a triangle and a hexagon, can be employ | adopted for a cell.

  The layered silver alumina catalyst is supported on the partition walls as the inner surface of the cell in the ceramic honeycomb structure. In such a honeycomb structure of the present embodiment, layered alumina in which silver is dispersed is used as a catalyst material, so that soot can be burned at a low temperature. The layered silver alumina catalyst becomes a catalyst excellent in initial performance and durability when fired at a firing temperature of around 962 ° C., which is the melting point of silver.

  Subsequently, a method for coating calcium sulfate around the above-described layered silver alumina catalyst will be described.

  A mixed slurry of the layered silver alumina catalyst sol and calcium sulfate was prepared. The ceramic honeycomb structure was immersed in the catalyst dispersion and then dried. Further, by repeating immersion and drying, a mixed catalyst material of a layered silver alumina catalyst and calcium sulfate was supported on the ceramic honeycomb structure. Then, it baked at 900 degreeC for 1 hour, and diffused silver in calcium sulfate. In this manner, a ceramic honeycomb structure in which the silver-containing calcium sulfate-coated silver alumina catalyst was supported on the inner surface of the ceramic honeycomb structure of the present example, that is, the partition walls, was obtained. By using this ceramic honeycomb structure, it is possible to burn soot at a low temperature by taking advantage of the excellent characteristics of the layered silver alumina catalyst.

(Example 2)
In Example 2, α-alumina balls were used as the carrier, and a catalyst material was supported on the surface of the α-alumina balls. Hereinafter, a method for manufacturing the exhaust purification catalyst according to the second embodiment will be described.

  First, 100 g of α-alumina balls having a diameter of 2 mm were prepared as a carrier, 1.16 g of silver oxide and 1.2 g of acetic acid were prepared as a material containing silver, and about 35 ml of distilled water was added thereto and mixed. The mixture was sealed in a pressure vessel, hydrothermally treated at 185 ° C. for 24 hours, then removed from the pressure vessel, and the silver acetate adhering to the surface was washed with pure water three times. . Then, it was dried at 80 ° C. for 3 hours and baked at 1000 ° C. for 4 hours.

  As a result, a silver alumina ball catalyst (hereinafter also referred to as catalyst A) in which a layered silver alumina catalyst was formed on the surface of an α-alumina ball as a carrier was obtained.

  Next, a method for coating calcium sulfate around the silver alumina ball catalyst will be described. As calcium sulfate, a commercially available product may be used, or an ash component in which the main component contained in actual exhaust is calcium sulfate may be used.

  First, 0.5 g of silver alumina ball catalyst and 0.05 g of calcium sulfate powder were placed in a 30 cc screw tube, and treated with a rotary granulator (manufactured by ASONE Corporation, model: PZ-01R) at 25 rpm for 3 minutes. A calcium-coated silver alumina ball catalyst was obtained.

  Next, a silver-containing calcium sulfate-coated silver alumina ball catalyst (hereinafter also referred to as catalyst B) in which a calcium sulfate-coated silver alumina ball catalyst is calcined at 600 ° C. for 1 hour in the air and silver is diffused into the calcium sulfate. Obtained.

  FIG. 3 shows the result of measuring the abundance of silver in calcium sulfate by an energy dispersive X-ray fluorescence analyzer (manufactured by Shimadzu Corporation, model: EDX-800HS). From FIG. 3, it was confirmed that silver was diffused in calcium sulfate by firing at a temperature of 600 ° C. or higher. As a result, the calcium sulfate portion into which silver has been diffused can also be catalyzed, that is, exhibit a function as a catalyst for burning carbon contained in PM.

  In this way, by covering the surface of the silver alumina ball catalyst with calcium sulfate in which silver is diffused, the surface area and mode that were limited only by the silver alumina ball catalyst can be changed to various modes as long as calcium sulfate can be taken. Can be adopted. Specifically, for example, the surface area of the catalyst can be increased by providing uneven projections on the surface of calcium sulfate. Further, for example, even if a part where the catalyst is to be supported has a special shape, the catalyst can be supported on the part by changing the shape of calcium sulfate according to the shape of the part.

(Comparative example)
In contrast to Example 2, the surface of the silver alumina ball catalyst was coated with calcium sulfate, and then the calcination step was not performed, and the uncalcined calcium sulfate-coated silver alumina ball catalyst (hereinafter referred to as catalyst) in which no silver was present in the calcium sulfate. (Also referred to as C).

(Smoke burning performance evaluation)
With respect to the catalysts A, B, and C produced in Example 2 and the comparative example, the characteristics as the exhaust gas purifying catalyst were evaluated, that is, the soot combustion performance was evaluated. In this evaluation, the weight change and heat balance of the carbon fine powder when each catalyst is heated together with the carbon fine powder are measured by a differential thermothermal gravimetric simultaneous measurement device (manufactured by SII Nanotechnology, Inc., model: EXSTAR TG / DTA6000). This was done by measuring.

First, as a carbon fine powder to be burned, soot collected from a diesel engine was used, and this soot was coated on the surface of each catalyst by the following method to prepare a sample for evaluation.
That is, first, in each of the catalysts A, B, and C, the weight ratio of soot to the catalyst was adjusted to 1. Specifically, about 1 mg of the catalyst B per 6 pieces (about 0.15 g) is put in a 30 cc screw tube, and at 25 rpm, 3 times with a rotary granulator (manufactured by ASONE Corporation, model: PZ-01R). The surface of the catalyst B was coated with soot. For the catalysts A and C, soot was coated on the surface in the same manner.

Next, each catalyst A, B, C coated with soot is set in the above-mentioned differential thermothermal gravimetric simultaneous measurement apparatus, and a mixed gas composed of 10% by volume of O ₂ gas and 90% by volume of N ₂ gas, While flowing through each of the catalysts A, B, and C at 100 ml / min, heating was performed at a heating rate of 10 ° C./min.

  The result is shown in FIG. FIG. 4 is a characteristic diagram showing the relationship between the change in weight and the heating temperature for each of the catalysts A, B, and C. In FIG. 4, the weight change is shown as the burning rate [mg / sec].

  As can be seen from the data of catalyst A (silver alumina ball catalyst) shown in FIG. 4, carbon combustion starts from around 400 ° C., and there is a combustion peak around 550 ° C. Further, in the catalyst C (uncalcined calcium sulfate-coated silver alumina ball catalyst), the rising temperature was 500 ° C. or higher, which was higher than that of the catalyst A, and the carbon fine powder did not burn unless the combustion peak was not as high as 650 ° C. . From these results, it can be seen that in the catalyst C, calcium sulfate does not function as a catalyst.

  On the other hand, it can be seen that catalyst B (silver-containing calcium sulfate-coated silver alumina ball catalyst) can exhibit almost the same performance as catalyst A. Although the details are unknown, this difference appears in the same macroscopic composition, but the difference is that calcium sulfate and layered silver-alumina catalyst are mixed and calcined. As a result, the catalytic effect of the layered silver alumina ball catalyst propagates through the calcium sulfate in which silver has diffused, and the calcium sulfate portion in which silver has diffused also exerts its function as a catalyst. This is thought to be due to the fact that

(Other embodiments)
In the above embodiment, as a method for producing the catalyst material, after mixing the layered silver alumina catalyst and calcium sulfate, the mixed layered silver alumina catalyst and calcium sulfate are heat-treated to diffuse silver into the calcium sulfate. However, the present invention is not limited thereto, and silver and calcium sulfate may be mixed (mixing step) to disperse silver in calcium sulfate. After that, when mixed or contacted with the layered silver alumina catalyst, the function as a catalyst can be exhibited.

  In the second embodiment, an example in which an α-alumina ball made entirely of α-alumina is used as the carrier has been described. However, the present invention is not limited to this, and the surface portion of the carrier on which the catalyst material is carried is α-. Any alumina may be used, and the inside may be made of another material. Specifically, the carrier may be one obtained by coating α-alumina on the surface of a core material made of a material different from α-alumina such as cordierite by coating / spraying.

  In Example 2, the example in which the layered silver alumina catalyst surface is coated with calcium sulfate as the calcium sulfate-coated silver alumina ball catalyst has been described. However, the present invention is not limited thereto, and the layered silver alumina catalyst and calcium sulfate are used. A mixture of these may be used.

1 Silver beta alumina 2 Silver 3 Layered silver alumina catalyst (layered structure)
4 Silver (metal or oxide)
5 Calcium sulfate

Claims (5)

A catalyst material used for burning particulates of a diesel engine,
A layered structure in which alumina and silver are alternately laminated;
Having calcium sulfate dispersed with silver ,
The catalyst material, wherein the layered structure and the calcium sulfate in which the silver is dispersed are in contact with each other. The catalyst material according to claim 1 in which the content of silver in the prior SL calcium sulfate, characterized in that at least 0.1 wt%. A catalyst material used for burning particulates of a diesel engine, comprising: a layered structure in which alumina and silver are alternately laminated; and calcium sulfate in which silver is dispersed; and the layered structure, A method for producing a catalyst material in contact with the calcium sulfate in which the silver is dispersed,
A mixing step of mixing the layered structure and calcium sulfate;
A method for producing a catalyst material, comprising: a heat treatment step of diffusing silver into calcium sulfate by heat-treating the mixed layered structure and calcium sulfate. The method for producing a catalyst material according to claim 3 , wherein the temperature of the heat treatment is 600 ° C or higher and 1000 ° C or lower. It is a manufacturing method of the catalyst material of Claim 1 , Comprising:
A method for producing a catalyst material, comprising a mixing step of mixing the layered structure, the silver, and the calcium sulfate.

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