JP2012066238A - Scr catalyst, exhaust gas cleaning filter, and exhaust gas cleaning apparatus - Google Patents

Abstract

An SCR catalyst, an exhaust gas purification filter, and an exhaust gas purification device that improve the NOx removal rate in a low temperature region and suppress the decrease in the NOx removal rate when exposed to a high-temperature hydrothermal atmosphere for a long time.
An SCR catalyst coated with DPF4 is obtained by supporting a third component on a carrier composed of a first component and a second component. Here, the first component is composed of at least one of Sn compounds such as Sn or SnO ₂ . The second component consists Ce, Ce compounds such CeO _2, Fe, Fe compounds such as _Fe 2 _{O 3,} Cu, from at least one of Cu compound such as CuO. The third component, W, W compound, such as WO _3, Mo, Mo compounds such as MoO _{3, V,} V compounds such as V 2 _{O 5,} Nb, Nb compound such as _{Nb 2 O 5, Ta, Ta} 2 O _It consists of at least one of Ta compounds such as ₅ .
[Selection] Figure 1

Description

  The present invention relates to an SCR (Selective Catalytic Reduction) catalyst using ammonia as a reducing agent, an exhaust gas purification filter, and an exhaust gas purification device.

Since the lean combustion engine has a lean atmosphere in which exhaust gas also contains excess oxygen, it is difficult to reduce and purify nitrogen oxides (NOx) with an oxidation catalyst or a three-way catalyst. Thus, an SCR catalyst has been developed that selectively reduces NOx under a lean atmosphere using ammonia as a reducing agent. Examples of the SCR catalyst include V ₂ O ₅ —WO ₃ / TiO ₂ catalyst disclosed in Non-Patent Document 1, zeolite-based catalysts disclosed in Non-Patent Documents 2 and 3, tungsten oxide and oxidation disclosed in Patent Document 1. Catalyst containing composite metal oxide comprising cerium, titanium oxide and zirconium oxide, catalyst containing titania-zirconia type composite oxide and metal disclosed in Patent Document 2, oxidation disclosed in Patent Document 2 Catalyst containing tungsten-zirconia type composite oxide and metal, WO ₃ / CeO ₂ —ZrO ₂ catalyst disclosed in Non-Patent Document 4, TiO ₂ disclosed in Non-Patent Document 5 with V, Cr, Ni, A catalyst carrying an oxide such as Cu has been proposed.

However, zeolitic catalysts have a problem of severe deterioration at high temperatures in the presence of water (for example, 750 ° C. or higher), and non-zeolitic oxide catalysts have higher hydrothermal resistance than zeolitic catalysts. There is a problem that the rate is not enough. On the other hand, in order to improve heat resistance and activity, a solid acid (eg WO ₃ etc.) and / or a support containing a sulfur-resistant refractory catalyst (eg SnO ₂ etc.) and a catalytic metal (eg Pt etc.) and / or An exhaust gas purifying catalyst carrying sulfuric acid is disclosed in Patent Document 3, and a carrier (for example, SnO ₂ ) and a basic metal (for example, Mg) or an oxide thereof and an acid metal or an oxide (for example, W) And the like, and a catalyst for reducing nitrogen oxide using a hydrocarbon as a reducing agent is disclosed in Patent Document 4. Although the catalyst of Patent Document 3 has heat resistance, it is a catalyst for effectively removing NOx at a low temperature (200 ° C. to 240 ° C.). The optimum temperature for NOx purification of the catalyst of Patent Document 4 is 550 ° C. to 700 ° C.

JP 2010-481 A JP 2005-238196 A JP-T-2004-513771 JP-A-6-190276

C. Ciardelli et al. Applied Catalysis B: Environmental 70 (2007) 80-90 Gongshin Qi and Ralph T. Yang: Catalysis Letters Vol. 100, Nos. 3-4, April 2005 Akatsuki / Supervised by Yoichi Nishimura New development of zeolite catalyst, 260 pages, 2004 issue, CM Publishing Chem. Commun., 2008, 1470-1472 Smirniotis PG, Pena DA, Uphade BS: ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Vol.40, No.13, p.2479, 2001

  However, the catalyst described in Patent Document 4 has a problem that the NOx removal rate is low in a low temperature range (for example, about 250 ° C.). In addition, when the SCR catalyst and the diesel particulate filter (DPF) are separately provided, the heat resistant temperature required for the SCR catalyst is about 650 ° C., so there is no problem with the catalyst of Patent Document 4, but the exhaust gas purification device When the SCR catalyst is coated and integrated on the DPF for the purpose of compacting, the heat resistance temperature required for the SCR catalyst is about 750 ° C., and thus further heat resistance needs to be improved.

  The present invention was made to solve such problems, and improved the NOx removal rate in a low temperature region and suppressed the decrease in the NOx removal rate when exposed to a high temperature hydrothermal atmosphere for a long time. It aims at providing the SCR catalyst which uses ammonia as a reducing agent, an exhaust gas purification filter, and an exhaust gas purification apparatus. In the present invention, ammonia as the reducing agent includes urea-derived ammonia.

  In the SCR catalyst according to the present invention, the amount per 1 mol of metal of the Gibbs energy change in the oxidation-reduction reaction of the first component composed of at least one of Sn or Sn compound is 40 (kcal / Metal mol) or less. A second component composed of an element or a compound thereof, and a third component composed of at least one of a Group 5 element, a Group 5 element compound, a Group 6 element, and a Group 6 element compound in the periodic table. Become.

Here, “amount of Gibbs energy change per 1 mol of metal in oxidation-reduction reaction” refers to the case where the oxide of an element is converted to a monovalent reduced state from an oxide state stable at 250 ° C. in an air atmosphere. The amount of Gibbs energy change was assigned per mole of metal. For example, with respect to Ce, Fe, and Cu, the reduction reaction is as follows.
4CeO ₂ = 2Ce ₂ O ₃ + O ₂ (g) Ce (IV → III)
2Fe ₂ O ₃ = 4FeO + O ₂ (g) Fe (III → II)
_{4CuO = 2Cu2O + O 2 (g} ) Cu (II → I)
Since the Gibbs energy change (kcal) of each reduction reaction is Ce: 144.2, Fe: 102.1, Cu: 42.7, the amount per mole (ΔG (kcal / Metal mol)) is Ce: 144.2 / 4 = 36.1, Fe: 102.1 / 4 = 25.5, Cu: 42.7 / 4 = 10.7. The Gibbs energy change can be calculated using HSC Chemistry (Outotec Research Oy.).
Ammonia SCR reaction, the ratio of NO and NO ₂ in NOx is NO: _NO 2 = 1: when high purification rate of 1 (so-called Fast reaction) but is obtained, if NO is more than NO _2, part of the NO Is required to be oxidized to NO ₂ , and the reaction is rate-limiting and the purification rate is known to decrease (so-called Standard reaction).
In an actual exhaust gas of a lean combustion engine, NO ₂ is less than NO, and an oxidation catalyst using an expensive noble metal or the like is disposed in front of the SCR catalyst, and the Fast reaction may be advanced as much as possible. However, originally, it is preferable that the SCR catalyst itself has high activity even when NO ₂ is low or not at all. One purpose of the second component, by monkey promote the oxidation of NO to NO _2, it is to increase the activity of Standard reactions. Therefore, as a result of intensive studies, it has been found that the amount of Gibbs energy change in the oxidation-reduction reaction of oxide is preferably 40 (kcal / Metal mol) or less. That is, when the amount of change in Gibbs energy is small, NO can be easily oxidized to NO _2, and the activity of the Standard reaction can be increased.

The second component is made of at least one of Ce, Ce compound, Fe, Fe compound, Cu, and Cu compound.
The third component is composed of at least one of W, W compound, Mo, Mo compound, V, V compound, Nb, Nb compound, Ta, and Ta compound.
The ratio of the mass of the second component to the total mass of the first component and the second component is preferably 7 to 90% by mass.
The second component includes Ce or a Ce compound, and the ratio of the mass of the Ce or Ce compound to the total mass in the first component and the second component may be 7 to 90% by mass.
The second component includes Fe or an Fe compound, and the ratio of the mass of the Fe or Fe compound to the total mass of the first component and the second component may be 7.5 to 80% by mass.
The first component and the second component may constitute a carrier, and the third component may be supported on the carrier.
It is preferable that the average primary particle diameter of the SCR catalyst after hydrothermal treatment at 750 ° C. for 30 hours is 20 nm or less.
The SCR catalyst can be coated on the exhaust gas purification filter.
The SCR catalyst coated on the exhaust gas purification filter preferably has a median diameter of 1.0 μm or less.
The exhaust gas purification device can be provided with the exhaust gas purification filter.

  According to the present invention, the SCR catalyst has a first component composed of at least one of Sn or an Sn compound, and the amount of Gibbs energy change in the oxidation-reduction reaction of the oxide is 40 (kcal / Metal mol) per mole of metal. A second component comprising the following element or a compound thereof and a third component comprising at least one of a Group 5 element, a Group 5 element compound, a Group 6 element, and a Group 6 element compound in the periodic table By comprising the components, it is possible to improve the NOx removal rate in a low temperature region and to suppress a decrease in the NOx removal rate when exposed to a high-temperature hydrothermal atmosphere for a long time.

1 is a schematic configuration diagram of an exhaust gas purification apparatus including an exhaust gas purification filter coated with an SCR catalyst according to an embodiment of the present invention. It is a structure schematic diagram of the modification of the exhaust gas purification apparatus provided with the exhaust gas purification filter coated with the SCR catalyst which concerns on this embodiment. The catalyst for after the hydrothermal treatment is a diagram showing the relationship between the content and the NOx removal rate of CeO ₂ in the carrier. The catalyst for after the hydrothermal treatment is a diagram showing the relationship between the content and the NOx removal rate of Fe ₂ O ₃ in the carrier. Is a graph showing the relationship between the content and the activity retention of CeO ₂ in the carrier. It is a graph showing the relationship between the content and the activity retention rate of Fe ₂ O ₃ in the carrier. It is a TEM photograph of the catalyst concerning Example 3 and comparative example 7 before and after hydrothermal treatment. It is a figure which shows the X-ray-diffraction (XRD) measurement result (XRD spectrum) before and behind hydrothermal processing about each of the catalyst which concerns on Example 3 and 22 and the comparative example 10. FIG.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
As shown in FIG. 1, an exhaust pipe 2 through which exhaust gas discharged from a diesel engine 1 flows is provided with an oxidation catalyst 3, a DPF 4 that is an exhaust gas purification filter coated with an SCR catalyst, and an oxidation catalyst 5. ing. An injection nozzle 7 for injecting urea water is provided between the oxidation catalyst 3 and the DPF 4, and the injection nozzle 7 communicates with a urea water tank 9 for storing urea water through a pipe 8. . The pipe 8 is provided with a urea water addition system 10 for supplying urea water in the urea water tank 9 to the injection nozzle 7. The urea water addition system 10 is electrically connected to an ECU 14 that is a control device.

The SCR catalyst coated with DPF 4 is obtained by supporting a third component on a carrier composed of a first component and a second component. Here, the first component is composed of at least one of Sn or a Sn compound, and the Sn compound is, for example, SnO ₂ . The second component is an element in which the amount of Gibbs energy change in the oxidation-reduction reaction of the oxide is 40 (kcal / Metal mol) or less, or a compound thereof, in particular, Ce, Ce compound, Fe, Fe compound The Ce compound is, for example, CeO ₂ , the Fe compound is, for example, Fe ₂ O ₃ , and the Cu compound is, for example, CuO. The third component is at least one of Group 5 element, Group 5 element compound, Group 6 element, Group 6 element compound in the periodic table, in particular, W, W compound, Mo, Mo compound, V , V compound, Nb, Nb compound, Ta, Ta compound, W compound is, for example, WO ₃ , Mo compound is, for example, MoO ₃ , and V compound is, for example, V ₂ O ₅ , the Nb compound is, for example, Nb ₂ O ₅ , and the Ta compound is, for example, Ta ₂ O ₅ .

  The coating of SCR catalyst onto DPF4 is performed according to the following procedure. First, the prepared SCR catalyst is pulverized using a ball mill apparatus. At this time, it is preferable to pulverize so that the median diameter measured by the laser diffraction / confusion method is 1.0 μm or less. Next, a catalyst slurry is prepared from the pulverized SCR catalyst, a binder, and ion-exchanged water. The catalyst slurry is coated on the DPF carrier constituting the DPF 4 to produce a monolith catalyst.

  As the binder, any commercially available binder can be used. For example, colloidal silica, colloidal alumina, titanium oxide sol, cerium oxide sol, tin oxide sol, and other metal oxide sols can be used. The selection of the binder may be selected in consideration of the viscosity and adhesion when the catalyst is slurried, or may be selected according to the catalyst composition. In the latter case, tin oxide sol or cerium oxide sol is suitable as the binder.

  The composition of the catalyst slurry is appropriately determined in consideration of the pore distribution of DPF4, the type of binder, workability, and the like. In particular, (mass of binder solids + mass of catalyst) / (mass of binder solids + mass of catalyst + mass of water) is preferably 50% or less, and more preferably 20% or less. Further, (mass of binder solid content) / (mass of binder solid content + mass of catalyst) is preferably 2 to 20%.

Next, the operation of the exhaust gas purification apparatus according to this embodiment will be described.
As shown in FIG. 1, after the diesel engine 1 is started, the exhaust gas discharged passes through the exhaust pipe 2. As the exhaust gas flows through the oxidation catalyst 3, a part of the nitrogen monoxide (NO) in the exhaust gas is oxidized to nitrogen dioxide (NO ₂ ). Subsequently, the exhaust gas flows through the DPF 4, whereby particulate matter (PM) in the exhaust gas is captured by the DPF 4. Further, the ECU 14 operates the urea water addition system 10 at an appropriate timing to supply the urea water in the urea water tank 9 to the injection nozzle 7 through the pipe 8, and the urea water is intermittently supplied from the injection nozzle 7 to the DPF 4. To be supplied. The urea water added to the DPF 4 is hydrolyzed by the SCR catalyst coated on the DPF 4 to become ammonia and carbon dioxide (CO ₂ ), and the generated ammonia reacts with NOx in the exhaust gas to react with nitrogen (N ₂ ). And water (H ₂ O). Ammonia remaining without being consumed in the DPF 4 is oxidized in the oxidation catalyst 5. The exhaust gas from which NOx has been purified in this way flows through the exhaust pipe 2 and is exhausted to the atmosphere.

In this embodiment, the SCR catalyst is coated on DPF4, but this is not a limitation. As shown in FIG. 2, a selective reduction type NOx catalyst 6 coated with an SCR catalyst is provided between the DPF 4 and the oxidation catalyst 5, and urea water is added to the selective reduction type NOx catalyst 6 from the injection nozzle 7. May be. Moreover, the oxidation catalyst 5 of FIGS. 1 and 2 can be omitted by controlling the amount of urea water to be added.
In this embodiment, urea water is supplied as a reducing agent, but ammonia may be supplied directly.

Next, the effect of the SCR catalyst of the present invention will be described with reference to examples.
1. Consideration about a composition of a catalyst Tables 1-3 show the composition of Examples 1-21, which are SCR catalysts according to the present invention, and Table 4 shows compositions of catalysts according to Comparative Examples 1-9.

[Catalyst preparation method]
Examples 1-6
Dissolve tin chloride (IV) pentahydrate and cerium (III) nitrate hexahydrate in the masses listed in Table 1 in 1.4 liters of ion-exchanged water, and gradually add an aqueous ammonia solution (25%) while stirring. Dropped to pH 7 or higher to obtain a precipitate. In order to remove chloride ions from the precipitate, the precipitate was washed with water, dried at 100 ° C. or more for 24 hours, then weighed 20 g, and 0.2 g of an aqueous solution of ammonium tungstate (WO ₃ content 1). .84 g). Thereafter, it was evaporated to dryness and baked at 550 ° C. for 5 hours in an atmospheric pressure atmosphere to support tungsten.

Example 7
It was prepared in the same manner as in Example 3 except that 0.2 liter of ammonium molybdate aqueous solution (MoO ₃ content 1.14 g) was used instead of the ammonium tungstate aqueous solution.

Example 8
It was prepared in the same manner as in Example 3 except that 0.2 liter of vanadium (V) ammonium aqueous solution (V ₂ O ₅ content 1.44 g) was used instead of the ammonium tungstate aqueous solution.

Example 9
It was prepared in the same manner as in Example 3 except that 0.2 liter of niobium oxalate aqueous solution (Nb ₂ O ₅ content 2.11 g) was used instead of the ammonium tungstate aqueous solution.

Example 10
It was prepared in the same manner as in Example 3 except that 0.2 liter of ethanol solution of tantalum ethoxide (Ta ₂ O ₅ content 3.50 g) was used instead of the ammonium tungstate aqueous solution.

Examples 11-13
In the same manner as in Examples 1 to 6, except that the tin (IV) chloride pentahydrate and iron (III) nitrate nonahydrate having the masses shown in Table 2 were dissolved in 1.4 liters of ion-exchanged water. Prepared.

Example 14
It was prepared in the same manner as in Example 11 except that 0.2 liter of vanadate (V) ammonium aqueous solution (V ₂ O ₅ content 1.44 g) was used instead of the ammonium tungstate aqueous solution.

Example 15
It was prepared in the same manner as in Example 11 except that 0.2 liter of niobium oxalate aqueous solution (Nb ₂ O ₅ content 2.11 g) was used instead of the ammonium tungstate aqueous solution.

Example 16
It was prepared in the same manner as in Example 11 except that 0.2 liter of ethanol solution of tantalum ethoxide (Ta ₂ O ₅ content 3.50 g) was used instead of the ammonium tungstate aqueous solution.

Examples 17 and 18
In the same manner as in Examples 1 to 6, except that the tin (IV) chloride pentahydrate and copper (II) acetate monohydrate having the masses shown in Table 3 were dissolved in 1.4 liters of ion-exchanged water. Prepared.

Example 19
It was prepared in the same manner as in Example 17 except that 0.2 liter of vanadate (V) ammonium aqueous solution (V ₂ O ₅ content 1.44 g) was used instead of the ammonium tungstate aqueous solution.

Example 20
It was prepared in the same manner as in Example 17 except that 0.2 liter of niobium oxalate aqueous solution (Nb ₂ O ₅ content 2.11 g) was used instead of the ammonium tungstate aqueous solution.

Example 21
It was prepared in the same manner as in Example 17, except that 0.2 liter of ethanol solution of tantalum ethoxide (Ta ₂ O ₅ content 3.50 g) was used instead of the ammonium tungstate aqueous solution.

Comparative Example 1
It was prepared in the same manner as in Examples 1 to 6, except that 60 g of tin (IV) chloride pentahydrate was dissolved in 1.4 liters of ion exchange water.

Comparative Examples 2-7
20 g of alumina having a BET specific surface area of 170 m ² / g, 20 g of 110 m ² / g zirconia, 20 g of 130 m ² / g titania, 20 g of 220 m ² / g silica, 22.3 g of 85 m ² / g α-FeO (OH) (20 g in terms of Fe ₂ O ₃ ) and 20 g of 130 m ² / g of cerium oxide were each immersed in 0.2 liter of an aqueous solution of ammonium tungstate (WO ₃ content 1.84 g), and evaporated to dryness to support tungsten. did. This was calcined at 550 ° C. for 5 hours in an atmospheric pressure atmosphere.

Comparative Example 8
The proton-type ZSM5 having a silica / alumina ratio of 40 was subjected to ion exchange of Fe by the CVD method, washed with water, and calcined at 550 ° C. for 5 hours.

Comparative Example 9
A V ₂ O ₅ —WO ₃ / TiO ₂ catalyst (model number: NRU-5) manufactured by Catalyst Kasei Co., Ltd. (currently JGC Catalysts & Chemicals Co., Ltd.) was used.

[Preparation method of pellet catalyst]
Each of the catalyst powders according to Examples 1 to 21 and Comparative Examples 1 to 9 was compacted at a pressure of about 1000 kgf / cm ² , crushed and sized, and pellets having a particle size of 0.5 to 1.0 nm A catalyst was prepared.

[Production method of DPF coated with catalyst]
Each of the catalyst powders according to Example 3 and Comparative Example 8 was atomized using a ball mill apparatus so that the median diameter measured by the laser diffraction / confusion method was 1.0 μm or less. 45 g of the atomized catalyst and 33 g (corresponding to about 5 g of solid content) of a binder (ceramic oxide sol U15 (Taki Chemical Co., Ltd.) for the catalyst according to Example 3) and colloidal for the catalyst according to Comparative Example 8 Silica Snow Tech N (Nissan Chemical Industry Co., Ltd.) 25g (equivalent to about 5g solid content) and 300g ion-exchanged water, the catalyst slurry (the solid content of the catalyst slurry according to Example 3 is about 13%, The solid content of the catalyst slurry according to Comparative Example 8 was about 14%. The catalyst slurry was coated on a cordierite DPF carrier (manufactured by NGK Co., Ltd., 12 mil / 300 cpsi, 35 cc) to prepare a monolith catalyst. The coating operation was performed in multiple steps, and the coating amount was adjusted so that the pressure loss of the monolith catalyst after coating increased by about 30 ± 3% relative to the pressure loss of the monolith catalyst before coating (actual pressure loss The rate of increase is described in Table 7 below).

[Method of hydrothermal treatment of catalyst]
A pellet catalyst of the catalysts according to Examples 1 to 21 and Comparative Examples 1 to 9, and a monolith catalyst prepared by coating each of the catalyst powders according to Example 3 and Comparative Example 8 on a cordierite DPF carrier, As a model for studying the effects when exposed to a high-temperature hydrothermal atmosphere for a long time, hydrothermal treatment was performed at 750 ° C. for 30 hours in a nitrogen atmosphere containing 10 vol% oxygen and 10 vol% water.

[Method for measuring NOx removal rate of pellet catalyst]
2.1 cc of each pellet catalyst before and after the hydrothermal treatment was placed in an atmospheric pressure fixed bed flow reactor, 430 ppm NO, 530 ppm ammonia, 10 vol% oxygen, 10 vol% CO ₂ , 10 vol% A 250 ° C catalyst evaluation gas consisting of water and the balance nitrogen is circulated through an atmospheric pressure fixed bed flow type reactor at 5.0 liters / minute, and flows out from the catalyst evaluation gas and pellet catalyst flowing into the pellet catalyst. The concentration of each component of the catalyst evaluation gas to be measured was measured, and the NOx removal rate was calculated from the change in the NO concentration before and after the pellet catalyst. In addition, the activity retention rate was calculated by dividing the NOx removal rate after hydrothermal treatment by the NOx removal rate before hydrothermal treatment.

[Method for measuring NOx removal rate of catalyst coated on DPF]
A monolith catalyst prepared by coating each of the catalyst powders according to Example 3 and Comparative Example 8 on a cordierite DPF carrier was placed in an atmospheric pressure fixed bed flow type reactor, and before and after the hydrothermal treatment, 430 ppm A catalyst evaluation gas at 250 ° C. consisting of NO, 530 ppm ammonia, 10 vol% oxygen, 10 vol% CO ₂ , 10 vol% water, and the balance nitrogen is supplied to an atmospheric pressure fixed bed flow reactor. The concentration of each component of the catalyst evaluation gas flowing into the monolith catalyst and the catalyst evaluation gas flowing out of the monolith catalyst is measured at a rate of 20 liters / minute, and the NOx removal rate is determined from the change in the NO concentration before and after the monolith catalyst. Calculated. In addition, the activity retention rate was calculated by dividing the NOx removal rate after hydrothermal treatment by the NOx removal rate before hydrothermal treatment.
The measurement results of the NOx removal rates for the pellet catalysts according to Examples 1 to 21 are shown in Table 5, and the measurement results of the NOx removal rates for the pellet catalysts according to Comparative Examples 1 to 9 are shown in Table 6. Table 7 shows the measurement results of the NOx removal rate for the monolith catalyst prepared by coating each of the catalyst powders according to Examples 3 and 9 and Comparative Example 8 on the cordierite DPF carrier.

Based on the results for Examples 1 to 6 and Comparative Examples 1 and 7 shown in Tables 5 and 6, for the hydrothermally treated catalyst having the composition of WO ₃ / SnO ₂ —CeO ₂ , CeO in the support The relationship between the content of ₂ and the NOx removal rate is shown in FIG. Further, based on the results of Examples 11 to 13 and Comparative Examples 1 and 6, the catalyst after hydrothermal treatment having the composition of WO ₃ / SnO ₂ —Fe ₂ O ₃ was used for Fe ₂ O _{3 in} the support. The relationship between the content and the NOx removal rate is shown in FIG. Furthermore, based on the results for Examples 1 to 6 and Comparative Examples 1 and 7 shown in Tables 5 and 6, the relationship between the content of CeO _{2 in} the carrier and the activity retention rate is shown in FIG. Based on the results of Examples 11 to 13 and Comparative Examples 1 and 6, the relationship between the content of Fe ₂ O _{3 in} the support and the activity retention is shown in FIG.

From Figure 3, if the content of CeO ₂ in the carrier is 7-90 wt%, even after hydrothermal treatment exceeds 50% NOx removal rate is obtained, more preferably, of CeO ₂ in the carrier If the content is 15 to 80% by mass, a NOx removal rate of 65% or more is obtained even after hydrothermal treatment, and the support does not contain CeO ₂ (including only SnO ₂ ) and Comparative Example 1 It was found that a higher NOx removal rate can be obtained in a low temperature range of about 250 ° C. compared to the catalyst according to Comparative Example 7 that does not contain SnO ₂ in the support (including only CeO ₂ ). Further, from FIG. 4, when the content of Fe ₂ O _{3 in} the support is 7.5 to 80% by mass, a NOx removal rate of 27% or more is obtained even after hydrothermal treatment. Compared with the catalyst according to Comparative Example 1 not containing Fe ₂ O ₃ (including only SnO ₂ ) and Comparative Example 6 not including SnO ₂ in the support (including only Fe ₂ O ₃ ), the NOx removal is higher in a low temperature range It turns out that rate is obtained. Furthermore, from FIG. 5, when the content of CeO _{2 in} the carrier is 7 to 90% by mass, an activity retention rate exceeding 0.6 is shown, and the activity retention rate is higher than that of Comparative Example 7. I understood. In addition, from FIG. 6, when the content of Fe ₂ O _{3 in} the carrier is 7.5 to 80% by mass, an activity retention rate exceeding 0.7 is shown, and the activity retention is higher than that of Comparative Example 6. It turns out that the rate is high. Therefore, it was found that the catalysts according to Examples 1 to 6 and 11 to 13 have a high NOx removal rate in a low temperature range and a small decrease in the NOx removal rate when exposed to a high temperature hydrothermal atmosphere for a long time.

  Further, from Table 5, the catalyst according to Example 7 has a NOx removal rate after hydrothermal treatment of 55% and a calculated activity retention rate of 0.66. It turned out that there exists an effect similar to the catalyst which concerns on 11-13. Since the catalyst according to Example 8 has a NOx removal rate after hydrothermal treatment of 42% and the calculated activity retention rate is 0.88, the catalysts according to Examples 1 to 6 and 11 to 13 It turned out that there is the same effect. Since the catalyst according to Example 9 has a NOx removal rate after hydrothermal treatment of 68% and the calculated activity retention rate is 0.79, the catalyst according to Examples 1 to 6 and 11 to 13 It turned out that there is the same effect. Since the catalyst according to Example 10 has a NOx removal rate after hydrothermal treatment of 38% and the calculated activity retention rate is 0.90, the catalysts according to Examples 1 to 6 and 11 to 13 It turned out that there is the same effect. The catalysts according to Examples 14 to 16 also have the same effects as the catalysts according to Examples 11 to 13 because the NOx removal rate and the activity retention rate after the hot water treatment are almost the same as those of Examples 11 to 13. I understood that. Furthermore, according to Table 7, since the same result was obtained even when the cordierite DPF carrier was coated, it was found that it was useful as a DPF integrated SCR monolith. Moreover, although the catalyst which concerns on Examples 17-21 has a low activity retention compared with the catalyst which concerns on Examples 1-16, compared with Comparative Examples 2-5, it may have a high NOx removal rate in a low temperature range. I understood.

  Further, each of the catalyst powders according to Example 3 and Comparative Example 7 was observed with a transmission electron microscope (TEM) before and after hydrothermal treatment. FIGS. 7C and 7D show TEM photographs of the catalyst according to Example 3, and FIGS. 7A and 7B show TEM photographs of the catalyst according to Comparative Example 7, respectively. In each photograph of FIGS. 7A to 7D, 30 primary particle images were arbitrarily selected to measure the diameter, and an average value thereof was calculated. As a result, the average primary particle diameter of the catalyst according to Example 3 was only increased from about 10 nm to about 15 nm by hydrothermal treatment, whereas the average primary particle diameter of the catalyst according to Comparative Example 7 was As a result of the hydrothermal treatment, it grew from about 10 nm to about 20 to 30 nm, and it was found that the degree of growth of the average primary particle diameter by the hydrothermal treatment was larger than that in Example 3. The difference in the growth of the average primary particle diameter due to such hydrothermal treatment is considered to affect the NOx removal rate and the activity retention after hydrothermal treatment. From the viewpoint of the average primary particle diameter of the catalyst, The catalysts according to Examples 1 to 16 have a fine shape with an average primary particle diameter of 20 nm or less after hydrothermal treatment at 750 ° C. for 30 hours, so that the NOx removal rate and activity retention rate after hydrothermal treatment are It is expected that an excellent effect will be obtained.

2. Consideration of catalyst preparation method [Catalyst preparation method]
Example 22
A mixed aqueous solution of tin chloride (IV) pentahydrate and cerium nitrate (III) hexahydrate was added dropwise to a stirred aqueous ammonia solution (25%) to obtain a precipitate (reverse coprecipitation method). Except for the above, it was prepared in the same manner as in Example 3 (coprecipitation method).

Comparative Example 10
17.5 g of tin oxide having a BET specific surface area of 30 m ² / g and 7.5 g of cerium oxide having a BET specific surface area of 130 m ² / g were mixed using an alumina mortar and physically mixed. This was immersed in 0.4 liter of an aqueous solution of ammonium tungstate (WO ₃ content 2.56 g), evaporated to dryness, and calcined at 550 ° C. for 5 hours in an atmospheric pressure atmosphere.

[Evaluation of NOx removal rate and activity retention rate of catalyst]
For each of the catalysts according to Example 22 and Comparative Example 10, a pellet catalyst was prepared in the same manner as the catalysts according to Examples 1 to 21 and Comparative Examples 1 to 9, and in the same manner, These pellet catalysts were hydrothermally treated, and the NOx removal rate before and after hydrothermal treatment was measured and the activity retention rate was calculated by the same method. The results are shown in Table 8.

From Table 8, it was found that the catalyst according to Example 22 had a higher NOx removal rate in the low temperature region after the hydrothermal treatment and higher activity retention than the catalyst according to Comparative Example 10. The same applies to the catalyst according to Example 3 shown in Table 3. Therefore, even with the same catalyst composition (WO ₃ / SnO ₂ —CeO ₂ (30%)), the NOx removal rate and the activity retention rate in the low temperature range differ depending on the preparation method, and in particular, in Examples 3 and 22 It has been found that such catalyst preparation methods (coprecipitation method and reverse coprecipitation method) are advantageous in terms of NOx removal rate and activity retention rate at low temperatures. This is thought to be because the composite of SnO ₂ and CeO ₂ proceeds more finely than physical mixing.

Further, for each of the catalysts according to Examples 3 and 22 and Comparative Example 10, XRD measurement was performed before and after hydrothermal treatment. The XRD measurement result (XRD spectrum) is shown in FIG. As shown in FIG. 8 (a), the catalysts according to Examples 3 and 22 prepared by the coprecipitation method and the reverse coprecipitation method before the hydrothermal treatment were more SnO ₂ than the catalyst according to Comparative Example 10. In addition, since the peak of CeO ₂ has a wide shape, it was found that the size of particles detected by XRD measurement is extremely small. As shown in FIG. 8 (b), the catalysts according to Examples 3 and 22 have a broader relationship of SnO ₂ and CeO ₂ peaks than the catalyst according to Comparative Example 10 even after hydrothermal treatment. It was found that the size of particles detected by XRD measurement is still small.

  4 DPF (exhaust gas purification filter).

Claims (12)

A first component comprising at least one of Sn or a Sn compound;
An element whose amount of Gibbs energy change in the oxidation-reduction reaction of the oxide is 40 (kcal / Metal mol) or less, or a second component made of a compound thereof;
An SCR catalyst comprising a third component comprising at least one of Group 5 element, Group 5 element compound, Group 6 element, and Group 6 element compound in the periodic table.   The SCR catalyst according to claim 1, wherein the second component is made of at least one of Ce, Ce compound, Fe, Fe compound, Cu, and Cu compound.   The SCR catalyst according to claim 1 or 2, wherein the third component comprises at least one of W, W compound, Mo, Mo compound, V, V compound, Nb, Nb compound, Ta, Ta compound.   The SCR catalyst according to any one of claims 1 to 3, wherein a ratio of a mass of the second component to a total mass of the first component and the second component is 7 to 90% by mass.   The SCR according to claim 4, wherein the second component includes Ce or a Ce compound, and a ratio of the mass of the Ce or Ce compound to the total mass in the first component and the second component is 7 to 90% by mass. catalyst.   The said 2nd component contains Fe or a Fe compound, The ratio of the mass of Fe or the Fe compound with respect to the total mass in the said 1st component and the said 2nd component is 7.5-80 mass%. SCR catalyst.   The SCR catalyst according to any one of claims 1 to 6, wherein the first component and the second component constitute a carrier, and the third component is supported on the carrier.   The SCR catalyst according to any one of claims 1 to 7, wherein an average primary particle diameter of the SCR catalyst after hydrothermal treatment at 750 ° C for 30 hours is 20 nm or less.   An exhaust gas purification filter coated with the SCR catalyst according to any one of claims 1 to 8.   The exhaust gas purification filter according to claim 9, wherein the SCR catalyst has a median diameter of 1.0 μm or less.   An exhaust gas purification device comprising the SCR catalyst according to any one of claims 1 to 8.   An exhaust gas purification device comprising the exhaust gas purification filter according to claim 9 or 10.

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