JP6376532B2 - Method for producing exhaust gas purification catalyst - Google Patents

Description

The present invention relates to a method for producing a catalyst for purifying exhaust gas medium to clean carbon-based particulate matter composed mainly of soot contained in exhaust gases (PM).

  The exhaust gas from a diesel engine contains carbon-based particulate matter (hereinafter referred to as “PM”) containing soot as a main component, and this PM is easily scattered when released into the atmosphere. Adversely affect. For this reason, diesel vehicles are equipped with a filter (DPF: Diesel Particulate Filter) that collects PM before PM is released into the atmosphere, but when the amount of collected PM increases, the filter Clogging occurs. As a method for eliminating this clogging, a method is used in which fuel is injected into an electric heater, burner, or exhaust system and burned, the temperature of the filter is raised using the combustion heat, and the collected PM is burned. However, there has been a problem that the fuel consumption is deteriorated and the structure of the apparatus is complicated.

  For this reason, for example, Non-Patent Document 1 discloses a method in which an exhaust gas purifying catalyst is disposed on a filter and PM is burned at a low temperature of about 300 ° C. to regenerate DPF. This exhaust gas purifying catalyst is produced by supporting silver particles on carrier particles made of cerium oxide.

  However, the filter may be heated to about 1000 ° C. when used in a diesel vehicle, and the exhaust gas purifying catalyst of the conventional example is heated to about 1000 ° C. (about 1000 ° C. There was a problem of deactivation when receiving a thermal history.

K. Shimizu, 5 others, "Carbon oxidation with Ag / ceria prepared by self-dispersion of Ag powder into nano-particles", Catalyst Today 175, 2017. 93-99

In view of the above points, it is possible to burn PM at a low temperature, moreover, to provide a method for producing a catalyst for purifying exhaust gas medium not inactivated even when heated to about 1000 ° C. and Problems Is.

  In order to solve the above-mentioned problem, production of an exhaust gas purification catalyst according to the present invention, in which carrier particles composed of tin oxide and cerium oxide are produced, and metal fine particles are supported on the produced carrier particles to obtain an exhaust gas purification catalyst. The method comprises preparing a slurry by mixing cerium oxide powder and carbon fine particles in a precursor liquid containing at least one of tin fine particles and tin oxide fine particles, drying the prepared slurry, and firing the dried one Then, it is produced by removing carbon fine particles. The cerium oxide powder includes granules.

  According to the present invention, a case where a precursor liquid containing tin fine particles is used as an example will be described. When preparing tin oxide carrier particles, cerium oxide powder and carbon fine particles as a template are mixed in the precursor liquid. When the slurry adjusted by the above is dried, a carbon fine particle intervened between tin fine particles and cerium oxide is obtained. When the product obtained by this drying is fired, the tin fine particles are oxidized to become tin oxide, and carrier particles composed of tin oxide and cerium oxide are obtained, and the carbon fine particles are burned and removed. The part from which the carbon fine particles are removed becomes a void. For this reason, the carrier particles obtained after firing are porous and have a large surface area, and also have oxygen vacancies which are effective sites for supporting the metal fine particles. If metal fine particles such as Ag are supported on the carrier particles, a larger amount of metal fine particles are supported than in the conventional example. It was confirmed that the exhaust gas-purifying catalyst thus produced can burn PM at a low temperature and does not deactivate even when heated to about 1000 ° C.

  In the present invention, it is preferable to set the weight of the carbon fine particles contained in the slurry to 30% or more of the weight of tin. If the weight of the carbon fine particles is less than this, the tin oxide carrier particles may not be porous and have oxygen vacancies.

  In the present invention, it is preferable to use a metal tin fine particle dispersion in which metal tin fine particles are dispersed in a solvent as the precursor liquid.

The schematic diagram explaining the manufacturing method of the catalyst for exhaust gas purification of embodiment of this invention. The graph which shows the performance of the catalyst for exhaust gas purification obtained in Example 1 of this invention. The graph which shows the performance of the catalyst for exhaust gas purification obtained in Example 2 of this invention. The graph which shows the performance of the catalyst for exhaust gas purification obtained in the comparative example 1 of this invention. The graph which shows the performance of the catalyst for exhaust gas purification obtained in the comparative example 2 of this invention. The graph which shows the relationship between the tin oxide content rate of a carrier particle, and exothermic peak temperature _Tpk . Graph showing the relationship between the tin oxide content and the temperature T ₅₀ of the support particles.

  Hereinafter, an exhaust gas purifying catalyst and a manufacturing method thereof according to an embodiment of the present invention will be described with reference to the drawings. First, referring to FIG. 1, carbon fine particles are mixed in a precursor liquid containing tin fine particles or tin oxide fine particles, cerium oxide powder is further mixed and stirred to prepare a slurry.

As the precursor liquid, a metal tin fine particle dispersion or a tin oxide fine particle dispersion (colloidal solution) obtained by dispersing tin fine particles or tin oxide fine particles coated with a dispersant in a solvent can be used. Here, it is preferable to set the weight of the carbon fine particles contained in the slurry to 30% or more of the weight of tin. If the weight of the carbon fine particles is less than this, the carrier particles described later may not be porous and have oxygen vacancies. As the carbon fine particles, those having a BET specific surface area of 100 m ² / g or more are preferably used, and those having a BET specific surface area of 250 m ² / g or more are more preferably used. If the BET specific surface area is less than 100 m ² / g, the effect as a mold may be insufficient. Moreover, it is preferable to perform ultrasonic treatment when stirring.

  As the tin fine particles, those having an average particle diameter in the range of 1 nm to 50 nm can be used. When the average particle size is less than 1 nm, the specific surface area increases, the amount of the dispersant covering the surface of the tin fine particles increases, and there arises a problem that the detachment of the dispersant becomes insufficient during firing. On the other hand, when the average particle diameter exceeds 50 nm, there arises a problem that the dispersibility of the tin fine particles is lowered.

  The metal tin fine particle dispersion preferably contains a dispersant for enhancing the dispersibility of the tin fine particles, and the dispersant is at least one of a fatty acid having 6 to 18 carbon atoms and an aliphatic amine having 6 to 18 carbon atoms. One is preferably used. In the case of fatty acids or aliphatic amines having less than 6 carbon atoms, there is a problem that the dispersibility of the tin fine particles is lowered. On the other hand, in the case of fatty acids and aliphatic amines having 19 or more carbon atoms, there arises a problem that the elimination of fatty acids and aliphatic amines from the surface of tin fine particles becomes insufficient during firing. As the fatty acid, for example, carboxylic acid can be used. Specifically, C6 hexanoic acid, 2-ethylbutyric acid, neohexanoic acid (2,2-dimethylbutyric acid); C7 heptanoic acid, 2-methylhexanoic acid, cyclohexanecarboxylic acid; C8 Octanoic acid, 2-ethylhexanoic acid, neooctanoic acid (2,2-dimethylhexanoic acid); Nonanoic acid having 9 carbon atoms; Decanoic acid having 10 carbon atoms, neodecanoic acid (2,2-dimethyloctanoic acid); At least one selected from the group consisting of undecanoic acid of 12 carbons; dodecanoic acid having 12 carbon atoms; tetradecanoic acid having 14 carbon atoms; and palmitic acid having 16 carbon atoms; It is preferable to use it. Examples of aliphatic amines include hexylamine, cyclohexylamine, and aniline having 6 carbon atoms; heptylamine having 7 carbon atoms; octylamine having 8 carbon atoms; 2-ethylhexylamine; nonylamine having 9 carbon atoms; decylamine having 10 carbon atoms; At least one selected from the group consisting of dodecylamine having 12 carbon atoms; tetradodecylamine having 14 carbon atoms: palmitylamine having 16 carbon atoms; and stearylamine and oleylamine having 18 carbon atoms can be preferably used.

  As the solvent of the tin metal fine particle dispersion containing the above-mentioned dispersant, a low polarity solvent can be used. Specifically, octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, toluene, xylene, At least one liquid hydrocarbon selected from cyclododecane, cyclododecene, octylbenzene, and dodecylbenzene can be used alone or in combination.

  Moreover, as a precursor liquid containing tin oxide fine particles, a commercially available tin oxide sol solution can be preferably used. Alcohol, water, etc. are used as a solvent of a commercially available tin oxide sol solution.

  As the cerium oxide powder, one having an average particle diameter in the range of 0.1 to 1 μm can be used. The cerium oxide powder includes granules.

  Next, carrier particles are obtained by drying the slurry, firing the product obtained by drying, and grinding the product obtained by firing. Drying is preferably performed at a temperature of 65 to 110 ° C. under reduced pressure. Firing is preferably performed in an oxygen-containing atmosphere such as the air at a temperature at which the carbon fine particles completely burn, for example, a temperature of 600 to 800 ° C. By firing in this way, tin is oxidized to tin oxide, and carrier particles composed of tin oxide and cerium oxide are obtained. Moreover, since the carbon fine particles as the mold burn and desorb at the time of firing, the desorbed portions become vacancies. For this reason, the obtained carrier particles are porous and have a large surface area, and also have oxygen vacancies which are effective sites for supporting the metal fine particles.

  An exhaust gas purifying catalyst can be obtained by supporting catalytic metal fine particles on the porous carrier particles obtained in this way. Silver fine particles can be used as the catalyst metal fine particles, and a known method can be used as the supporting method. For example, it is possible to obtain a catalyst for exhaust gas purification by mixing and stirring a silver fine particle dispersion with carrier particles, obtaining a slurry, evaporating and drying the slurry, firing the evaporated dry solid, and pulverizing the slurry. it can.

Next, a more specific example of the present embodiment will be described.
Example 1
In Example 1, a tin fine particle dispersion (tin nanometal ink manufactured by ULVAC, Inc.) “Sn1T”, tin concentration: 30.6% by weight, solvent: toluene) was used as a precursor liquid, and the tin fine particle dispersion was performed in the flask. To 0.66 g of the liquid, 0.10 g of carbon fine particles (carbon black “Printex 90” manufactured by Orion Engineered Carbons, BET specific surface area: 300 m ^{2 /} g) were mixed and stirred uniformly by ultrasonic treatment. To this stirred material, 1.02 g of cerium oxide powder (“Cerium oxide (IV) powder” manufactured by High Purity Chemical Laboratory, particle size: 0.2 μm) is further mixed (immersed), and uniformized by ultrasonic treatment. A slurry was prepared by stirring (at this time, the weight of the carbon fine particles contained in the slurry is 50% of the weight of tin). The slurry was heated to 80 ° C. while reducing the pressure with a rotary evaporator, and the solvent (toluene) of the tin fine particle dispersion was distilled off to obtain an evaporated dry solid. The evaporated and dried product was recovered, dried at 110 ° C. for 8 hours, then baked in an air atmosphere at 700 ° C. for 3 hours, and the baked product was pulverized to obtain tin oxide and cerium oxide. The carrier particle comprised by these was obtained. The tin oxide content in the obtained carrier particles was 20% by weight (the cerium oxide content was 80% by weight). 1.0 g of this carrier particle is put in a flask, and 1.17 g of a silver nanoparticle dispersion (silver nanometal ink “Ag1T” manufactured by ULVAC, Inc., silver concentration: 4.5 wt%, solvent: toluene) is mixed. A slurry was prepared by stirring uniformly by sonication. The slurry was heated to 80 ° C. while reducing the pressure with a rotary evaporator, and the solvent (toluene) of the silver nanoparticle dispersion was distilled off to obtain an evaporated dry product. The evaporated and dried product was collected, dried at 110 ° C. for 8 hours, and then baked in a muffle furnace at 600 ° C. for 3 hours in an air atmosphere. The fired product was pulverized to obtain an exhaust gas purification catalyst in which silver particles were supported on carrier particles (the amount of silver supported was 5% by weight of the total weight of the exhaust gas purification catalyst). The exhaust gas-purifying catalyst thus obtained was designated as sample 1a, and a part of this exhaust gas-purifying catalyst that had been fractionated and further subjected to heat treatment at 1000 ° C. for 10 hours was designated as sample 1b. The performance of these samples 1a and 1b was evaluated by “tight contact conditions”. The “tight contact condition” is a performance evaluation method in a state in which PM to be purified and the catalyst are sufficiently mixed to improve the contact between them. Specifically, carbon black as a pseudo PM (carbon black “Printex 55” manufactured by Orion Engineered Carbons, BET specific surface area: 110 m ² / g) and the above samples 1a and 1b in a weight ratio of 1:10. The mixture was mixed for 30 minutes using a mortar, and each mixed powder was subjected to thermogravimetric-suggested thermal analysis (TG-DTA) in an atmosphere in which a mixed gas of nitrogen: oxygen = 79: 21 was flowed, and simulated PM The temperature at which the exothermic reaction associated with the combustion of NO was measured with the DTA profile, and the weight loss associated with the combustion of the pseudo PM was measured with the TG profile, thereby evaluating the performance of the samples 1a and 1b. Referring to the DTA profile in FIG. 2, the exothermic peak temperature _Tpk of sample 1a shown by a solid line in the figure is 302 ° C., and the exothermic peak temperature _Tpk of sample 1b shown by a broken line is 370 ° C. (see Table 1) ), The difference between the two was confirmed to be 68 ° C. Further, from the TG profile, the temperature T _{50 at} which the weight of the pseudo PM is reduced by half by combustion is obtained. As shown in Table 2, the sample 1a is 332 ° C., the sample 1b is 432 ° C., T ₅₀ was also 450 ° C. or lower, and it was confirmed that the difference between the two was 100 ° C. From these results, the exhaust gas purifying catalyst obtained in Example 1 can burn PM at a low temperature, and has excellent heat resistance that does not deactivate even when heated to about 1000 ° C. I found out.

(Example 2)
The amount of tin fine particle dispersion is 1.65 g, the amount of carbon fine particles is 0.25 g (at this time, the weight of carbon fine particles contained in the slurry is 50% of the weight of tin), and cerium oxide powder Except that the amount of the mixture was changed to 0.64 g, an exhaust gas purification catalyst was obtained in the same manner as in Example 1, and the obtained catalyst was designated as sample 2a (at this time, the tin oxide content in the carrier particles) Was 50% by weight (the cerium oxide content was 50% by weight). In the same manner as in Example 1, the sample 2a was further heat-treated at 1000 ° C. for 10 hours as a sample 2b, and the performance of these samples 2a and 2b was evaluated. Referring to the DTA profile of FIG. 3, the exothermic peak temperature _Tpk of sample 2a shown by a solid line in the figure is 338 ° C., and the exothermic peak temperature _Tpk of sample 2b shown by a broken line is 362 ° C. (see Table 1). The difference between the two was confirmed to be 24 ° C. Further, as shown in Table 2, the temperature _{T 50} of the sample 2a is 370 ° C., a temperature _{T 50} of the sample 2b is 414 ° C., is any of _{T 50} is also 450 ° C. or less, the difference therebetween is 44 ° C. It was confirmed that. From these results, the exhaust gas purifying catalyst obtained in Example 2 can burn PM at a low temperature, and has excellent heat resistance that does not deactivate even when heated to about 1000 ° C. I found out.

(Example 3)
The amount of tin fine particle dispersion is 2.64 g, the amount of carbon fine particles is 0.40 g (at this time, the weight of carbon fine particles contained in the slurry is 50% of the weight of tin), and cerium oxide powder Except that the mixing amount was 0.26 g, an exhaust gas purification catalyst was obtained in the same manner as in Example 1, and the obtained catalyst was designated as sample 3a (at this time, the tin oxide content in the carrier particles) Was 80% by weight (the cerium oxide content was 20% by weight). As in Example 1, the sample 3a was further heat-treated at 1000 ° C. for 10 hours as a sample 3b, and the performance of these samples 3a and 3b was evaluated. From the DTA profile not shown in the figure, the exothermic peak temperature T _pk of the sample 3a is 366 ° C., the exothermic peak temperature T _pk of the sample 3b is 374 ° C. (see Table 1), and the difference between the two is 8 ° C. confirmed. Further, as shown in Table 2, the temperature _{T 50} of the sample 3a is 410 ° C., a temperature _{T 50} in the sample 3b is 430 ° C., is any of _{T 50} is also 450 ° C. or less, the difference between 20 ° C. It was confirmed that. From these results, the exhaust gas purifying catalyst obtained in Example 3 can burn PM at a low temperature, and has excellent heat resistance that does not deactivate even when heated to about 1000 ° C. I found out.

Example 4
As a precursor solution, using tin oxide sol (Sellnax CX-S204IP manufactured by Nissan Chemical Industries, tin oxide concentration 20 wt%, isopropyl alcohol solvent), the amount of the mixture was 1.30 g (at this time included in the slurry) Except that the weight of carbon fine particles is 50% of the weight of tin), an exhaust gas purifying catalyst was obtained in the same manner as in Example 1 above, and the obtained catalyst was used as sample 4a. In the same manner as in Example 1, sample 4a was further heat-treated at 1000 ° C. for 10 hours as sample 4b, and the performance of these samples 4a and 4b was evaluated. From the DTA profile not shown, it was confirmed that the exothermic peak temperature T _pk of the sample 4a was 310 ° C., the exothermic peak temperature T _pk of the sample 4b was 380 ° C., and the difference between them was 70 ° C. Further, from the TG profile not shown, it was confirmed that the temperature T _{50 of the} sample 4a was 338 ° C., the T ₅₀ of the sample 4b was 429 ° C., and the difference between them was 91 ° C. From these results, the exhaust gas purifying catalyst obtained in Example 5 can burn PM at a low temperature and has excellent heat resistance that does not deactivate even when heated to about 1000 ° C. I found out.

(Comparative Example 1)
Next, a comparative example for the above embodiment will be described. In Comparative Example 1, when producing carrier particles, the tin fine particle dispersion and the carbon fine particles are not blended, and the cerium oxide powder is used in the same manner as in Example 1 except that 1.28 g of cerium oxide powder is used. A catalyst was obtained, and the obtained catalyst was designated as sample 5a. In the same manner as in Example 1, sample 5a was further heat-treated at 1000 ° C. for 10 hours as sample 5b, and the performance of these samples 5a and 5b was evaluated. With reference to the DTA profile of FIG. 5, the exothermic peak temperature _Tpk of the sample 5a indicated by the solid line in the figure is 297 ° C., and the exothermic peak temperature _Tpk of the sample 5b indicated by the broken line is 494 ° C. It was confirmed to be as large as 197 ° C. Further, as shown in Table 2, the temperature _{T 50} of the sample 5a is 310 ° C., a temperature _{T 50} of the sample 5b is 464 ° C., the difference between them was confirmed to be as large as 154 ° C.. From these results, it was found that the exhaust gas purifying catalyst obtained in Comparative Example 1 had low heat resistance and was deactivated when heated to about 1000 ° C.

(Comparative Example 2)
In Comparative Example 2, the above procedure was performed except that the carrier particles were not mixed with cerium oxide powder, the amount of the tin fine particle dispersion was 3.29 g, and the amount of carbon fine particles was 0.50 g. An exhaust gas purifying catalyst was obtained in the same manner as in Example 1, and the obtained catalyst was designated as Sample 6a (at this time, the weight of the carbon fine particles contained in the slurry was 50% of the weight of tin). In the same manner as in Example 1, sample 6a was further heat-treated at 1000 ° C. for 10 hours as sample 6b, and the performance of these samples 6a and 6b was evaluated. With reference to the DTA profile in FIG. 6, the exothermic peak temperature _Tpk of the sample 6a indicated by the solid line in the figure is 390 ° C., and the exothermic peak temperature _Tpk of the sample 6b indicated by the broken line is 382 ° C. It was confirmed to be 8 ° C. Further, as shown in Table 2, the temperature _{T 50} of the sample 6a is 439 ° C., a temperature _{T 50} of the sample 6b is 464 ° C., the difference between them was confirmed that 25 ° C. and less. However, T _{50 of} sample 6b was 450 ° C. or higher, and the exhaust gas purifying catalyst obtained in Comparative Example 2 was found to have insufficient activity when heated to about 1000 ° C.

Figure 6 is a graph showing the relationship between the tin oxide content of carrier particles exothermic peak temperature T _pk, FIG. 7 is a graph showing the relationship between a tin oxide content and the temperature T ₅₀ of the support particles. According to these graphs, in order to reduce both T _pk and T ₅₀ which are indicators of PM combustion temperature, it is preferable to set the tin oxide content in the range of 20 to 80 wt%, and 50 to 80 wt. % Is more preferable.

  As described above, according to the present embodiment and examples, when the carrier particles are produced, the cerium oxide powder and the carbon fine particles as the template are mixed with the precursor liquid. Then, what has carbon fine particles intervening between cerium oxide and tin fine particles is obtained. When the product obtained by this drying is fired, the tin fine particles are oxidized to become tin oxide particles, and the carbon fine particles are burned and removed, and the portions where the carbon fine particles are removed become pores. For this reason, the carrier particles obtained after firing are composed of cerium oxide and tin oxide, are porous and have a large surface area, and have oxygen vacancies that are effective sites for supporting metal fine particles. It will be a thing. If metal fine particles such as Ag are supported on the carrier particles, a larger amount of metal fine particles are supported than in the conventional example. It was confirmed that the exhaust gas-purifying catalyst thus produced can burn PM even at a low temperature and does not deactivate even when heated to about 1000 ° C.

  The present invention is not limited to the above. For example, in the above-described embodiments and examples, the cerium oxide powder is mixed after the carbon fine particles are mixed with the precursor liquid. However, the cerium oxide powder and the carbon fine particles may be mixed at the same time. Carbon fine particles may be mixed after mixing.

Moreover, although the case where the precursor liquid containing tin fine particles was used as an example has been described in the above embodiment and examples, the carrier particles may be produced using the precursor liquid containing tin oxide fine particles.

Claims (2)

A method for producing an exhaust gas purification catalyst by producing carrier particles composed of tin oxide and cerium oxide, and obtaining metal exhaust particles by carrying metal fine particles on the produced carrier particles,
The carrier particles are prepared by mixing a cerium oxide powder and carbon fine particles with a precursor liquid containing at least one of tin fine particles and tin oxide fine particles, drying the prepared slurry, and firing the dried one. Produced by removing carbon particles ,
A method for producing an exhaust gas purifying catalyst, wherein a metal tin fine particle dispersion in which metal tin fine particles are dispersed in a solvent is used as the precursor liquid . The process according to claim 1, wherein the exhaust gas purifying catalyst is characterized in that the weight of the carbon particles contained in the slurry is set more than 30% by weight of tin.

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