JP2015208712A - Catalyst for exhaust gas purification and selective reduction method of nitrogen oxide and oxidative removal method of solid carbon ingredient using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst for exhaust gas purification which exerts a high activity to both selective reduction of nitrogen oxides and oxidative removal of solid carbon ingredients, e.g. soot.SOLUTION: A catalyst for exhaust gas purification has a structure in which an oxide showing solid acidity and a manganese oxide are supported on a complex oxide containing cerium. The content of cerium in the complex oxide is 5-45 mol%, relative to the total amount of the complex oxide and based on CeO; the carrying amount of the oxide showing solid acidity is 5-23 pts. mass, relative to the amount of the complex oxide of 100 pts. mass and based on the oxide; and the carrying amount of manganese oxide is 0.1-9 pts. mass, relative to the total amount of the complex oxide and the oxide showing solid acidity of 100 pts. mass and based on manganese.

Description

  The present invention relates to an exhaust gas purifying catalyst, a method for selectively reducing nitrogen oxides using the same, and a method for oxidizing and removing a solid carbon component.

  Conventionally, in order to purify (remove) nitrogen oxides (NOx) in exhaust gas discharged from an internal combustion engine such as a diesel engine, the nitrogen oxides are converted to Ce-Zr-R-A-O catalyst in the presence of ammonia ( A technique is known in which R and A are both brought into contact with a transition metal) and selectively reduced to render them harmless (see, for example, Patent Document 1).

  In addition, a technique is known in which nitrogen oxides in exhaust gas are rendered harmless in the presence of ammonia using a catalyst in which tungsten oxide is supported on a cerium oxide support (see, for example, Patent Document 2).

Special table 2010-506724 gazette JP 2009-291664 A

  However, in the case of the catalyst described in the above-mentioned Patent Document 1, although it exhibits activity for detoxifying nitrogen oxides, it does not necessarily have sufficient activity for oxidizing and removing solid carbon components including soot contained in exhaust gas. Not shown, it was necessary to additionally use an oxidation catalyst to oxidize the soot.

  The present invention has been made in view of the above-described problems of the prior art, and is for exhaust gas purification that exhibits high activity for both selective reduction of nitrogen oxides and oxidation removal of solid carbon components including soot. It is an object of the present invention to provide a catalyst, a selective reduction method of nitrogen oxides using the exhaust gas purification catalyst, and a method of oxidizing and removing a solid carbon component.

As a result of intensive studies to solve the above problems, the present inventors have completed the present invention. That is, the present invention has a structure in which an oxide showing solid acidity and a manganese oxide are supported on a composite oxide containing cerium, and the content of the cerium in the composite oxide is determined by the composite oxide. a 5 to 45 mol% in terms of CeO ₂ things based on the total amount of supported oxides having the solid acidity, be 5 to 23 parts by mass in terms of oxide with respect to the composite oxide 100 parts by weight An exhaust gas-purifying catalyst is provided, in which the supported amount of the manganese oxide is 0.1 to 9 parts by mass in terms of manganese with respect to 100 parts by mass in total of the composite oxide and the oxide exhibiting solid acidity. .

  According to the exhaust gas purifying catalyst, having the above-described configuration can exhibit high activity for both selective reduction of nitrogen oxides and oxidation removal of solid carbon components including soot, and nitrogen oxidation. It is possible to efficiently selectively reduce substances and to efficiently oxidize and remove the solid carbon component. In particular, the exhaust gas-purifying catalyst has a structure in which a solid acid oxide and manganese oxide are supported on a composite oxide containing cerium, and the content of cerium in the composite oxide is within the above range. Thus, when the solid carbon component is oxidized and removed by combustion, a sufficient amount of lattice oxygen can be obtained due to the change in the valence of cerium contained in the composite oxide, and the solid carbon component is efficiently oxidized and removed. It becomes possible. Furthermore, in the exhaust gas purifying catalyst, high activity for both selective reduction of nitrogen oxides and oxidative removal of solid carbon components is obtained by setting the supported amounts of oxides and manganese oxides exhibiting solid acidity within the above range. be able to.

In the exhaust gas purifying catalyst, the composite oxide further contains zirconium, and the zirconium content in the composite oxide is 55 to 95 mol% in terms of ZrO _{2 based on the} total amount of the composite oxide. Is preferred. As a result, the exhaust gas purifying catalyst has more excellent heat resistance and can obtain excellent oxidative removal performance of the solid carbon component.

  In the exhaust gas-purifying catalyst, the oxide exhibiting solid acidity preferably contains niobium. Thereby, the exhaust gas purifying catalyst can exhibit higher activity for selective reduction of nitrogen oxides and oxidation removal of solid carbon components.

  The present invention also provides a method for selective reduction of nitrogen oxides in exhaust gas, which comprises the step of bringing the exhaust gas purifying catalyst of the present invention into contact with exhaust gas containing nitrogen oxides in the presence of a reducing agent. . According to such a selective reduction method of nitrogen oxides, since the exhaust gas purifying catalyst of the present invention is used, nitrogen oxides in the exhaust gas can be efficiently selectively reduced and rendered harmless.

  The present invention further provides a method for oxidizing and removing the solid carbon component in the exhaust gas, which comprises the step of bringing the exhaust gas purifying catalyst of the present invention into contact with the exhaust gas containing the solid carbon component. According to such a solid carbon component oxidation removal method, since the exhaust gas purifying catalyst of the present invention is used, the solid carbon component in the exhaust gas can be efficiently oxidized and removed.

  According to the present invention, an exhaust gas purifying catalyst exhibiting high activity for both selective reduction of nitrogen oxides and oxidation removal of solid carbon components such as soot, and nitrogen using the exhaust gas purifying catalyst A method for selective reduction of an oxide and a method for oxidizing and removing a solid carbon component can be provided.

  Hereinafter, the present invention will be described in detail with reference to preferred embodiments thereof.

[Exhaust gas purification catalyst]
The exhaust gas purifying catalyst of the present embodiment has a structure in which a composite oxide containing cerium is used as a carrier, and an oxide showing solid acidity and manganese oxide are supported on the carrier. Hereinafter, the components of the exhaust gas purifying catalyst will be described.

(Composite oxide containing cerium)
The exhaust gas-purifying catalyst contains a composite oxide containing cerium (hereinafter, also simply referred to as “composite oxide”) as a carrier for supporting solid oxide and manganese oxide. As the composite oxide, for example, a composite oxide containing a solid solution composed of cerium and a second component can be used.

The content of cerium in the composite oxide is 5 to 45 mol% in terms of CeO _{2 based on the} total amount of the composite oxide. When the content of cerium is less than 5 mol% in terms of CeO ₂ , the amount of released lattice oxygen due to the change in the valence of cerium is reduced when oxidizing and removing solid carbon components such as soot by combustion, The combustion activity of the solid carbon component is reduced. On the other hand, when the content of cerium exceeds 45 mol% in terms of CeO ₂ , the sintering of the composite oxide proceeds at a high temperature, the combustion activity of the solid carbon component decreases, and the activity supported on the composite oxide This leads to inhibition of the functions of the seeds, and the NOx purification efficiency also decreases. Further, from the viewpoint of further improving the oxidation removal performance of the solid carbon component while maintaining good heat resistance, the cerium content (in terms of CeO ₂ ) is more preferably 10 to 40 mol%, and 15 to 30 More preferably, it is mol%.

The composite oxide may contain one or more of silicon, aluminum, yttrium, lanthanum, praseodymium, neodymium, samarium, europium, gadolinium, titanium, zirconium, and tungsten as the second component. Among these, the composite oxide preferably contains zirconium because both the heat resistance of the composite oxide and the release of lattice oxygen can be achieved at a high level. From the same viewpoint, the composite oxide is particularly preferably CeO ₂ —ZrO ₂ .

The content of the second component in the composite oxide is preferably 55 to 95 mol% in terms of oxide (for example, in terms of ZrO _{2 in} the case of zirconium) based on the total amount of the composite oxide. When the content of the second component is less than 55 mol% in terms of oxide, the sintering of the composite oxide proceeds at a high temperature, and the combustion activity of the solid carbon component decreases, and is supported on the composite oxide. This leads to inhibition of the function of the active species, and the purification efficiency of NOx also decreases. On the other hand, if the content of the second component exceeds 95 mol% in terms of oxide, since the content of cerium is less than 5 mol% in terms of CeO _2, when oxidizing and removing the solid carbon component by burning, The amount of lattice oxygen released by the change in the valence of cerium decreases, and the combustion activity of the solid carbon component decreases. Moreover, from the viewpoint of further improving the oxidation removal performance of the solid carbon component, the content of the second component (as oxide) is more preferably 60 to 90 mol%, and 70 to 85 mol%. Further preferred.

The shape of the composite oxide is not particularly limited, and examples thereof include powder, pellet, monolith, gauze, grid, and the like. Among these, the shape of the composite oxide is preferably powder or monolith from the viewpoint of increasing the specific surface area. When the composite oxide is in the form of powder, the average particle size is preferably 1 to 100 nm, more preferably 5 to 50 nm, from the viewpoint of improving the activity with respect to oxidative removal of the solid carbon component. In addition, the specific surface area of the composite oxide is preferably 3 m ² / g or more, preferably 10 m ² / g or more, from the viewpoint of selective activity reduction of nitrogen oxides and improvement in activity against oxidative removal of the solid carbon component. More preferred.

  Note that the composite oxide may have a crystal form or may be amorphous. The composite oxide may partially contain a hydroxide.

  The method for producing the composite oxide is not particularly limited, and can be produced by, for example, a method in which powder raw materials are mixed and then fired, a method in which various precursor solutions are precipitated with an alkali and then fired. Moreover, as said complex oxide, you may use a commercial item.

(Oxide showing solid acidity)
Examples of oxides that exhibit solid acidity include niobium oxide, molybdenum oxide, tungsten oxide, vanadium oxide, chromium oxide, iron oxide, zinc oxide, tin oxide, boron oxide, phosphorous oxide, alumina, titania, zirconia, and silica alumina. , Titania silica, titania zirconia, zirconia silica, magnesia silica, aluminum phosphate, zirconium phosphate, iron phosphate, hydrotalcite, viscosity mineral and the like. These can be used alone or in combination of two or more. Among these, niobium oxide, molybdenum oxide, and tungsten oxide are preferable, and niobium oxide is more preferable because of its high activity for selective reduction of nitrogen oxides and oxidation removal of solid carbon components. For example, tungsten oxide may be partially dissolved by ammonia, but niobium oxide is preferable because it does not have such a fear and has excellent stability. In addition, niobium oxide (V) (Nb ₂ O ₅ ) is specifically exemplified as niobium oxide, molybdenum oxide (VI) (MoO ₃ ) is specifically exemplified as molybdenum oxide, and tungsten oxide is specifically exemplified. Includes tungsten oxide (VI) (WO ₃ ).

  In the exhaust gas purifying catalyst, the supported amount of the oxide exhibiting solid acidity is 5 to 23 parts by mass in terms of oxide and 7 to 20 parts by mass when the composite oxide is 100 parts by mass. Preferably, it is 9-18 mass parts, More preferably, it is 10-15 mass parts. When the loading amount is less than 5 parts by mass, the activity is low with respect to the nitrogen oxide purification reaction, and when the loading amount exceeds 23 parts by mass, the activity corresponding to the loading amount cannot be obtained, resulting in an increase in cost. .

  Note that the oxide exhibiting solid acidity may have a crystal form or may be amorphous. Moreover, the oxide which shows the said solid acidity may contain the hydroxide in part.

  In the exhaust gas purifying catalyst, the oxide showing solid acidity may be directly supported on the composite oxide, or supported on the manganese oxide supported on the composite oxide (that is, manganese oxide). May be indirectly supported on the composite oxide via

(Manganese oxide)
Examples of the manganese oxide include MnO ₂ , MnO, M ₂ O ₃ , Mn ₃ O ₄ , MnO ₃ , Mn ₂ O _{7 and the} like, and a plurality of these may coexist. Among these, MnO ₂ (manganese (IV) oxide) is preferable, and MnO ₂ (manganese (IV) oxide) and other manganese oxides may coexist.

  In the exhaust gas purifying catalyst, the amount of manganese oxide supported is 0.1 in terms of manganese (Mn) when the total amount of the composite oxide and the oxide exhibiting solid acidity supported thereon is 100 parts by mass. It is preferable that it is -9 mass parts, It is more preferable that it is 0.1-6 mass parts, It is still more preferable that it is 0.1-4 mass parts. When the loading amount is less than 0.1 parts by mass, the activity is low with respect to the nitrogen oxide purification reaction. On the other hand, when the loading amount exceeds 9 parts by mass, the reduction used in the nitrogen oxide purification reaction is reduced. The manganese oxide may oxidize the agent (for example, ammonia) to generate NOx, and the purification rate of nitrogen oxides decreases.

  The manganese oxide may have a crystal form or may be amorphous. The manganese oxide may partially contain a hydroxide.

  In the exhaust gas purifying catalyst, the manganese oxide may be directly supported on the composite oxide, and may be supported on the oxide exhibiting the solid acidity supported on the composite oxide (that is, the solid acidity is increased). It may be supported indirectly on the composite oxide via the oxide shown.

(Other ingredients)
The exhaust gas purifying catalyst of the present embodiment may further contain other components other than the above-described composite oxide, oxide showing solid acidity, and manganese oxide. As other components, known components used for exhaust gas purification catalysts can be used without particular limitation, and examples thereof include Cu ion exchange zeolite, Fe ion exchange zeolite, and noble metals.

(Manufacturing method of exhaust gas purification catalyst)
The method for producing the exhaust gas purifying catalyst described above is not particularly limited, and can be produced by a known method. As an example of the production method, for example, the composite oxide is mixed in a solution containing a raw material of an oxide exhibiting solid acidity, a raw material of a manganese oxide, and a solvent capable of dissolving or dispersing them, and then dried and fired. The method of performing is mentioned. Here, as the raw material of the oxide showing solid acidity, for example, when the oxide showing solid acidity is niobium oxide, niobium chloride, niobium oxychloride, metal niobium, various niobium alkoxides, various niobate salts Etc. Similarly, when the oxide showing solid acidity is other than niobium oxide, chlorides, oxychlorides, metals, various alkoxides, various salts, etc. of the elements constituting the oxide showing solid acidity can be used as raw materials. . On the other hand, as raw materials for manganese oxide, manganese acetate / anhydride, manganese acetate / hydrate (manganese acetate / tetrahydrate, etc.), manganese metal, various manganates, manganese chloride / anhydride, manganese chloride / Examples thereof include hydrates, manganese nitrates / anhydrides, manganese nitrates / hydrates, manganese phosphates / anhydrides, manganese phosphates / hydrates, manganese carbonates / anhydrides, manganese carbonates / hydrates, and the like. Examples of the solvent include solutions containing metal chelating agents such as water, various alcohols, and citric acid. In addition, as a complex oxide, you may use what carried the oxide which shows solid acidity beforehand as a commercial item.

  The drying method is not particularly limited, and the solvent may be removed using an evaporator, or the solvent may be removed by heating. Moreover, baking can be performed by heating at 300-800 degreeC in the air for 5-180 minutes, for example.

[Immobilization of exhaust gas purification catalyst]
The exhaust gas purifying catalyst of the present embodiment can be used by being immobilized on a filter for purifying exhaust gas, for example, a diesel particulate filter (Diesel Particulate Filter). When the filter is made of porous ceramics, the exhaust gas-purifying catalyst can be immobilized on the surface or pores of the porous ceramics. As the ceramic, cordierite, alumina, silica, mullite, silicon nitride, aluminum titanate, or the like can be used.

  Immobilization of the exhaust gas purifying catalyst is, for example, by dispersing the exhaust gas purifying catalyst in a dispersion medium such as water to form a slurry, coating the slurry on the partition wall surface of the filter or inside the partition wall, and then firing the slurry. It can be carried out. Firing can be performed, for example, by heating in air at 300 to 800 ° C. for 5 to 180 minutes. In addition, a binder component can be added to the slurry as necessary for the purpose of enhancing the adhesion of the exhaust gas purifying catalyst to the filter. As the binder, alumina sol, silica sol, zirconia sol, ceria sol, or the like can be used.

[Selective reduction method of nitrogen oxide and oxidation removal method of solid carbon component]
The selective reduction method of nitrogen oxides using the exhaust gas purification catalyst of the present embodiment and the oxidation removal method of the solid carbon component use a filter or the like on which the exhaust gas purification catalyst of the present embodiment is fixed, for exhaust gas purification. It can be performed by a method including a step of bringing a catalyst into contact with an exhaust gas containing nitrogen oxides and / or a solid carbon component.

  In the method for purifying nitrogen oxides according to the present embodiment, it is necessary to add a reducing agent in order to purify nitrogen oxides. However, the amount of the reducing agent to be added is to reduce and decompose nitrogen oxides. There is no particular limitation as long as it is a necessary amount. As the reducing agent, an ammonia source such as ammonia or aqueous ammonia may be used, or an ammonia precursor capable of generating ammonia may be used. Examples of the ammonia precursor include urea and urea water that can generate ammonia by thermal decomposition. From the viewpoint of safety during handling, it is preferable to use urea or urea water.

  The amount of the reducing agent to be injected is not particularly limited as long as it is an amount necessary for reductive decomposition of nitrogen oxides, and the amount according to the characteristics such as the amount of nitrogen oxides and the purification performance of the catalyst. It is preferable to inject. Thus, nitrogen oxide can be purified with high efficiency by adjusting and adding the amount of the reducing agent.

  In the method for selective reduction of nitrogen oxides and the method for oxidizing and removing solid carbon components according to the present embodiment, the reaction temperature is preferably in the range of 100 ° C. to 500 ° C., and the efficiency of these reactions is improved. It is more preferable that the temperature is in the range of 150 ° C. to 500 ° C. in terms of further increase.

  In the present embodiment, the selective reduction of nitrogen oxides and the oxidative removal of the solid carbon component can be performed simultaneously using, for example, one filter. That is, by using the exhaust gas purifying catalyst of the present embodiment, the selective reduction of nitrogen oxides and the oxidative removal of solid carbon components can proceed simultaneously by carrying out the reaction at the reaction temperature while adding a reducing agent. it can. Therefore, when constructing an exhaust gas purification apparatus, by using a filter or the like on which the exhaust gas purification catalyst of this embodiment is fixed, an apparatus for selectively reducing nitrogen oxides and a solid carbon component for oxidizing and removing are used. It is not necessary to provide a separate device, and the exhaust gas purification device can be simplified and the installation space can be reduced.

  The exhaust gas purifying catalyst of the present embodiment exhibits high activity for selective reduction of nitrogen oxides and oxidation removal of solid carbon components, for example, exhaust gas discharged from an internal combustion engine such as a diesel engine, and It is useful for purifying solid carbon components such as nitrogen oxides and soot contained in exhaust gas generated when burning fossil fuels such as coal.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example. In addition, the performance evaluation method in each Example and a comparative example is as follows.

<Nitrogen oxide purification performance (selective reduction performance) evaluation method>
0.5 g of the catalyst obtained in each example and comparative example was dispersed in 2 g of water to prepare a catalyst slurry. A honeycomb substrate made of cordierite (diameter 12 mm, height 5 mm) was immersed in this catalyst slurry, so that the honeycomb substrate was coated with the catalyst slurry and fired in air at 500 ° C. for 50 minutes. The catalyst loading was 50 g per liter of honeycomb substrate volume. The obtained catalyst-supporting honeycomb was evaluated for nitrogen oxide purification performance with a catalyst analyzer (trade name: BELCAT, manufactured by Nippon Bell Co., Ltd.). The reaction gas, NO and ammonia are both 940 volume ppm, water vapor 10 volume%, the remainder using a gas comprising nitrogen, reaction temperature 250 ° C., under the conditions of a space velocity (SV) 23000h ^-1, nitrogen oxides The purification rate was measured. The purification rate of nitrogen oxides was calculated by the following equation from the concentration of nitrogen oxides at the inlet and outlet of the catalyst analyzer. The higher the nitrogen oxide purification rate, the higher the catalyst purification performance (selective reduction performance).
Nitrogen oxide purification rate (%) = (nitrogen oxide concentration at the inlet−nitrogen oxide concentration at the outlet) × 100 / nitrogen oxide concentration at the inlet

<Oxidation removal performance evaluation method for solid carbon component>
The catalyst obtained in each Example and Comparative Example and carbon powder (Ketjen Black, trade name: EC600J, manufactured by Lion Corporation) were mixed in an agate bowl so that the mass ratio was 100: 1. Using 10 mg of the obtained mixed powder, the exothermic peak temperature was measured with a differential thermothermal weight (TG-DTA) analyzer, which was defined as the combustion temperature. The measurement was performed under an air stream (flow rate 200 mL / min). When the combustion temperature was measured using only carbon powder (0.3 mg) without using a catalyst, the combustion temperature was 600 ° C. It is evaluated that the lower the combustion temperature of the mixed powder with respect to this temperature (600 ° C.), the higher the activity of the catalyst and the better the oxidation removal performance of the solid carbon component.

Example 1
Manganese acetate tetrahydrate 0.235 g, water 25 mL, and cerium-zirconium composite oxide supporting niobium oxide (niobium oxide: cerium oxide: zirconium oxide = 10.2: 22.3: 67.5 (mass) Ratio)) 1 g. After removing moisture from the obtained mixture while heating to 50 ° C. with an evaporator, the catalyst was calcined in air at 500 ° C. for 50 minutes, and niobium oxide and manganese oxide were supported on the cerium-zirconium composite oxide. A powder was obtained.

In the obtained catalyst, the amount of manganese oxide supported was 5.3 parts by mass in terms of manganese when the cerium-zirconium composite oxide supporting niobium oxide was 100 parts by mass. In the obtained catalyst, the supported amount of niobium oxide is 11.4 parts by mass with respect to 100 parts by mass of the cerium-zirconium composite oxide, and the cerium content in the cerium-zirconium composite oxide is CeO. It was 19.1 mol% in terms of ₂ . When the above-described performance evaluation was performed using the obtained catalyst, the purification rate of nitrogen oxides was 46%, and the combustion temperature of the solid carbon component was 393 ° C.

(Example 2)
The amount of manganese acetate tetrahydrate was reduced, and the amount of manganese oxide supported was 0.5 parts by mass in terms of manganese when the cerium-zirconium composite oxide supporting niobium oxide was 100 parts by mass. Except for the above, a catalyst was prepared in the same manner as in Example 1. When the above-described performance evaluation was performed using the obtained catalyst, the purification rate of nitrogen oxides was 50%, and the combustion temperature of the solid carbon component was 381 ° C.

(Example 3)
The amount of manganese acetate tetrahydrate was reduced, and the amount of manganese oxide supported was 1.0 parts by mass in terms of manganese when the cerium-zirconium composite oxide supporting niobium oxide was 100 parts by mass. Except for the above, a catalyst was prepared in the same manner as in Example 1. When the above-described performance evaluation was performed using the obtained catalyst, the purification rate of nitrogen oxides was 63%, and the combustion temperature of the solid carbon component was 381 ° C.

Example 4
The amount of manganese acetate tetrahydrate was reduced, and the amount of manganese oxide supported was 2.6 parts by mass in terms of manganese when the cerium-zirconium composite oxide supporting niobium oxide was 100 parts by mass. Except for the above, a catalyst was prepared in the same manner as in Example 1. When the above-described performance evaluation was performed using the obtained catalyst, the purification rate of nitrogen oxides was 65%, and the combustion temperature of the solid carbon component was 379 ° C.

(Comparative Example 1)
The compounding amount of manganese acetate tetrahydrate was increased, and the amount of manganese oxide supported was 11.1 parts by mass in terms of manganese when the cerium-zirconium composite oxide supporting niobium oxide was 100 parts by mass. Except for the above, a catalyst was prepared in the same manner as in Example 1. When the above-mentioned performance evaluation was performed using the obtained catalyst, the purification rate of nitrogen oxides was 33%, and the combustion temperature of the solid carbon component was 370 ° C.

(Comparative Example 2)
Comparative example of cerium-zirconium composite oxide supporting niobium oxide without supporting manganese oxide (niobium oxide: cerium oxide: zirconium oxide = 10.2: 22.3: 67.5 (mass ratio)) No. 2 catalyst. When the performance evaluation described above was performed using this catalyst, the purification rate of nitrogen oxides was 38%, and the combustion temperature of the solid carbon component was 368 ° C.

(Comparative Example 3)
0.235 g of manganese acetate tetrahydrate, 25 mL of water, and 1 g of cerium-zirconium composite oxide (cerium oxide: zirconium oxide = 26.2: 73.8 (mass ratio)) were mixed. After removing water from the obtained mixture with an evaporator, the mixture was calcined in air at 500 ° C. for 50 minutes to obtain a catalyst powder in which manganese oxide was supported on a cerium-zirconium composite oxide.

In the obtained catalyst, the amount of manganese oxide supported was 5.3 parts by mass in terms of manganese when the cerium-zirconium composite oxide was 100 parts by mass. Further, in the obtained catalyst, the cerium - content of cerium-zirconium composite oxide has a 20.3 mol% in terms of CeO _2. When the above-described performance evaluation was performed using the obtained catalyst, the purification rate of nitrogen oxides was 17%, and the combustion temperature of the solid carbon component was 380 ° C.

(Comparative Example 4)
Comparative Example, except that the amount of manganese acetate tetrahydrate was increased and the amount of manganese oxide supported was 11.1 parts by mass in terms of manganese when the cerium-zirconium composite oxide was 100 parts by mass A catalyst was prepared in the same manner as in 3. When the above-described performance evaluation was performed using the obtained catalyst, the purification rate of nitrogen oxides was 18%, and the combustion temperature of the solid carbon component was 370 ° C.

(Comparative Example 5)
Without supporting manganese oxide, a cerium-zirconium composite oxide (cerium oxide: zirconium oxide = 26.2: 73.8 (mass ratio)) was used as the catalyst of Comparative Example 5 as it was. When the above-described performance evaluation was performed using this catalyst, the purification rate of nitrogen oxides was 0%, and the combustion temperature of the solid carbon component was 443 ° C.

  Table 1 summarizes the compositions and performance evaluation results of the catalysts prepared in Examples 1 to 4 and Comparative Examples 1 to 5.

As shown in Table 1, when Examples 1 to 4 and Comparative Examples 1 to 5 are compared, it is higher for nitrogen oxide purification to support niobium oxide in a cerium oxide-zirconium oxide solid solution (composite oxide). It was confirmed that the compound exhibited an activity, and by supporting an optimum amount of manganese, it exhibited a higher activity for the purification of nitrogen oxides. Moreover, about the oxidation removal performance of a solid carbon component, compared with the combustion temperature (600 degreeC) when not using a catalyst, a combustion temperature can be reduced with the catalyst of Examples 1-4 and Comparative Examples 1-4, and almost, It was confirmed that the activity was comparable. In addition, the catalyst of the comparative example 5 had high combustion temperature compared with another catalyst, and activity was a little inferior.

Claims (5)

A complex oxide containing cerium has a structure in which an oxide showing solid acidity and manganese oxide are supported,
The content of the cerium in the composite oxide is 5 to 45 mol% in terms of CeO _{2 based on the} total amount of the composite oxide,
The amount of the oxide exhibiting solid acidity is 5 to 23 parts by mass in terms of oxide with respect to 100 parts by mass of the composite oxide,
The exhaust gas-purifying catalyst, wherein the supported amount of the manganese oxide is 0.1 to 9 parts by mass in terms of manganese with respect to 100 parts by mass in total of the composite oxide and the oxide exhibiting solid acidity. The composite oxide further comprises zirconium;
The exhaust gas-purifying catalyst according to claim 1, wherein a content of the zirconium in the composite oxide is 55 to 95 mol% in terms of ZrO _{2 based on the} total amount of the composite oxide.   The exhaust gas-purifying catalyst according to claim 1 or 2, wherein the oxide exhibiting solid acidity contains niobium.   Selective reduction of nitrogen oxides in exhaust gas, comprising a step of bringing the exhaust gas purifying catalyst according to any one of claims 1 to 3 into contact with exhaust gas containing nitrogen oxides in the presence of a reducing agent. Method. The oxidation removal method of the solid carbon component in waste gas including the process which the catalyst for exhaust gas purification as described in any one of Claims 1-3 and the waste gas containing a solid carbon component are made to contact.