JP2018176054A - Exhaust gas purification catalyst, and exhaust gas purification filter, and exhaust gas purification method - Google Patents

Abstract

[Problem] To provide an exhaust gas purifying catalyst capable of exhibiting high PM oxidation activity while sufficiently suppressing oxidation of NH3. [Solution] A carrier mainly composed of alumina, silver (Ag), and at least one Group 6 element (M) selected from the group consisting of chromium, molybdenum, and tungsten, supported on the carrier. , at least a part of the silver (Ag) and at least a part of the Group 6 element (M) form a composite oxide, and the silver (Ag) and the Group 6 element A catalyst for purifying exhaust gas, characterized in that the atomic ratio (Ag/M) to a group element (M) is 0.3 to 3. [Selection diagram] None

Description

  The present invention relates to an exhaust gas purification catalyst, and an exhaust gas purification filter and an exhaust gas purification method using the same.

  Gases discharged from an internal combustion engine include harmful substances such as particulate matter (PM: Particulate Matter) generated by combustion and ash (Ash) composed of additives in oil and the like. Among such harmful substances, particulate matter is known as an air pollutant which adversely affects animals and plants. Therefore, an exhaust gas purification filter such as a DPF (Diesel Particulate Filter) is used to collect particulate matter contained in exhaust gas discharged from an internal combustion engine. Since PM collected by the DPF causes an increase in pressure loss, the DPF is regenerated by periodically raising the temperature to a high temperature and burning the PM. At this time, in order to improve the fuel consumption and the durability of the material, it is desirable to regenerate at a lower temperature, and the PMF is supported on the DPF.

  As such a PM oxidation catalyst, JP-A-2012-135742 (Patent Document 1) includes a porous alumina support having a pore distribution peak value measured with a mercury porosimeter in the range of 10 to 100 nm, Particulate combustion comprising a catalyst component comprising an alloy having an alloy composition of 75 to 25 mass% of Ag and 25 to 75 mass% of Pd supported on the surface of the porous alumina carrier and / or on the inner wall surface of the pores A catalyst is disclosed.

  In addition, JP-A-2015-199061 (Patent Document 2) discloses a PM oxidation catalyst comprising a support comprising alumina as a main component, and a silver-containing substance and a phosphoric acid-containing substance supported on the support. ing.

However, according to the findings of the present inventors, although the conventional PM oxidation catalyst as disclosed in the above-mentioned patent documents has excellent PM oxidation activity, in recent years the cost reduction and the effective space are effective. From the viewpoint of utilization, etc., it was not necessarily sufficient from the viewpoint of the need for a catalyst design that gives DPF the function of NOx purification etc. using NH ₃ as a reducing agent together with the function of PM oxidation. . That is, the present inventors have found that in the conventional PM oxidation catalyst, such as disclosed in JP, utilized to cause the oxidation of NH ₃ by the oxidizing power, the NH ₃ with the function of the PM oxidation as a reducing agent It has been found that there is a problem that it is not always sufficient to have functions such as NOx purification.

JP 2012-135742 A JP, 2015-199061, A

The present invention has been made in view of the problems of the above-mentioned prior art, and an exhaust gas purification catalyst capable of exhibiting high PM oxidation activity while sufficiently suppressing the oxidation of NH ₃ , and use thereof It is an object of the present invention to provide an exhaust gas purification filter and an exhaust gas purification method.

As a result of intensive studies to achieve the above object, the present inventors have found that an alumina-based carrier contains silver and a Group 6 element in the form containing their complex oxides and that they have a specific ratio By supporting the catalyst so as to be as described above, it has been found that an exhaust gas purification catalyst capable of exhibiting high PM oxidation activity while sufficiently suppressing the oxidation of NH ₃ can be obtained, and the present invention has been completed.

That is, the exhaust gas purification catalyst of the present invention is
An alumina-based carrier,
Silver (Ag) and at least one Group 6 element (M) selected from the group consisting of chromium, molybdenum and tungsten, supported on the carrier
And at least a portion of the silver (Ag) and at least a portion of the group 6 element (M) form a composite oxide, and the silver (Ag) and the group 6 The atomic ratio (Ag / M) to the element (M) is 0.3 to 3.

  In the exhaust gas purifying catalyst of the present invention, the amount of silver (Ag) carried is preferably 2 to 30% by mass in terms of metallic silver with respect to the total amount of the catalyst. The exhaust gas purifying catalyst of the present invention is suitably used as a PM oxidation catalyst for oxidizing and removing particulate matter (PM) in exhaust gas.

  Further, the exhaust gas purification filter of the present invention is characterized in that the exhaust gas purification catalyst of the present invention is supported on an air-permeable substrate.

  The exhaust gas purification method of the present invention is characterized in that the exhaust gas is brought into contact with the exhaust gas purification catalyst of the present invention to oxidize and remove the particulate matter (PM).

In addition, according to the exhaust gas purifying catalyst of the present invention, the reason why high PM oxidation activity is exhibited in a state where oxidation of NH ₃ is sufficiently suppressed is not necessarily clear, but the present inventors are as follows: I guess like. That is, in the conventional PM oxidation catalyst as disclosed in the patent document, atomic oxygen is generated on the surface of silver particles in the catalyst, and NH ₃ is oxidized by the oxygen. On the other hand, in the exhaust gas purifying catalyst of the present invention, at least a portion of silver (Ag) in the catalyst forms a composite oxide with at least a portion of the Group 6 element (M); In the complex oxide, the formation of atomic oxygen is less likely to occur while maintaining the same high PM oxidation activity as silver (Ag), so the high PM oxidation activity is obtained in the state where the oxidation of NH ₃ is sufficiently suppressed. The present inventors speculate that it will be exhibited.

According to the present invention, it is possible to provide an exhaust gas purification catalyst capable of exhibiting high PM oxidation activity while sufficiently suppressing the oxidation of NH ₃ , and an exhaust gas purification filter and an exhaust gas purification method using the same. It becomes possible.

It is a graph which shows the XRD pattern of the catalyst for exhaust gas purification obtained in Examples 1, 2 and 4. It is a graph which shows 50% PM oxidation temperature of the catalyst for exhaust gas purification obtained in Examples 1-5 and Comparative Examples 1-5. It is a graph showing the NH ₃ conversion of the catalyst for purification of exhaust gas obtained in Examples 1 to 5 and Comparative Examples 1 to 5.

  Hereinafter, the present invention will be described in detail in line with its preferred embodiments.

(Catalyst for exhaust gas purification)
First, the exhaust gas purifying catalyst of the present invention will be described. The exhaust gas purification catalyst of the present invention is
An alumina-based carrier,
Silver (Ag) and at least one Group 6 element (M) selected from the group consisting of chromium, molybdenum and tungsten, supported on the carrier
And at least a portion of the silver (Ag) and at least a portion of the group 6 element (M) form a composite oxide, and the silver (Ag) and the group 6 The atomic ratio (Ag / M) to the element (M) is 0.3 to 3.

The carrier in the exhaust gas purification catalyst of the present invention is a carrier containing alumina (Al ₂ O ₃ ) as a main component. Such an alumina-based support is composed of only alumina, or is composed of mainly contained alumina and other components. The content of alumina in the alumina-based support is preferably 90% by mass or more, more preferably 95% by mass or more, and more preferably 98% by mass or more based on 100% by mass of the total mass of the support. Being particularly preferred. The alumina in such a carrier is selected from the group consisting of boehmite, pseudoboehmite, χ, κ, ρ, η, γ, pseudoγ, δ, θ and α. It is preferable to use α-alumina, γ-alumina, and θ-alumina from the viewpoint of heat resistance.

  In addition, as other components other than alumina contained in such an alumina-based support, other compounds used as an exhaust gas purification catalyst support of this type of application can be used, with particular limitations. (Y), lanthanum (La), praseodymium (Pr), cerium (Ce), neodymium (Nd), promethium (Pm), samarium (Sm) from the viewpoint of the thermal stability and heat resistance of the carrier. , Europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), magnesium (Mg) , Calcium (Ca), strontium (Sr), barium (Ba), scandium (Sc) and Oxide of at least one metal selected from the group consisting of um (V) are preferred.

The specific surface area of the carrier used in the present invention is not particularly limited, but is preferably 5 to 300 m ² / g, more preferably 10 to 200 m ² / g. If the specific surface area exceeds the upper limit, the heat resistance of the support itself tends to decrease, so that the heat resistance of the catalyst tends to decrease. On the other hand, if it is less than the lower limit, the dispersibility of the supported active species tends to decrease. It is in. Such a specific surface area can be calculated as an BET specific surface area from an adsorption isotherm using a BET isothermal adsorption equation.

  Further, the shape of the carrier used in the present invention is not particularly limited, and those having a conventionally known shape such as particle shape, ring shape, spherical shape, cylindrical shape, pellet shape and the like can be used. In addition, it is preferable to use a particulate thing from the viewpoint that many active species to be supported can be contained in the state of high dispersibility. When the carrier is in the form of particles, the average primary particle diameter of the carrier particles is preferably 1 to 1000 nm, and more preferably 5 to 500 nm. The average primary particle size of such a carrier can be measured by using the X-ray diffractometer from the line width of the powder X-ray diffraction peak using Scherrer's equation (Scherrer's equation). . In addition, the average particle size of such a carrier can be appropriately changed by a conventional method (for example, a method of grinding with a mortar, a cold isostatic press method (CIP) or the like). In addition, after the catalyst for exhaust gas purification is produced, the average particle size of the powder of the carrier in the catalyst may be changed by changing the average particle size of the catalyst according to a standard method.

  In the exhaust gas purifying catalyst of the present invention, it is necessary to support silver (Ag) and at least one Group 6 element (M) selected from the group consisting of chromium, molybdenum and tungsten on the carrier.

  In the exhaust gas purification catalyst of the present invention, silver (Ag) supported on the support is an active species for PM oxidation, and the presence of silver on the support sufficiently enhances the oxidation performance to PM. Is possible. The amount of silver (Ag) supported in the exhaust gas purification catalyst of the present invention is preferably 2 to 30% by mass, and more preferably 5 to 25% by mass, in terms of metallic silver, based on the total amount of the catalyst. And 5 to 15% by mass is particularly preferable. If the supported amount of such silver is less than the lower limit, the oxidation performance to PM tends not to be sufficiently high, while if the upper limit is exceeded, the oxidation performance is saturated and the cost is high. Tend to

Further, in the catalyst for exhaust gas purification of the present invention, the Group 6 element (M) supported on the carrier together with the silver (Ag) is at least one metal selected from the group consisting of chromium, molybdenum and tungsten, By forming a complex oxide with silver at least in part, it is an active species for sufficiently suppressing the oxidation of NH ₃ while maintaining the high PM oxidation activity of silver. The amount of supported Group 6 element (M) in the exhaust gas purification catalyst of the present invention is such that the atomic ratio (Ag / M) of silver (Ag) to the Group 6 element (M) is 0.3 to 3 It is necessary. If such an atomic ratio (Ag / M) is less than 0.3, the oxidation performance to PM can not be made sufficiently high, while if it exceeds ₃ , the oxidation of NH ₃ is sufficiently suppressed. become unable. Also, from the viewpoint of improving the balance between the oxidation performance for PM and the oxidation suppression performance for NH ₃ , the atomic ratio (Ag / M) is more preferably 0.4 to 2.5, and more preferably 0.5 to 0.5. Particularly preferred is 2.

In the exhaust gas purification catalyst of the present invention, it is necessary that at least a part of the silver (Ag) and at least a part of the group 6 element (M) form a composite oxide. In this manner, at least a part of silver (Ag) in the catalyst forms a complex oxide with at least a part of the Group 6 element (M), thereby maintaining the same high PM oxidation activity as silver, while maintaining the atom. As a result, it is difficult to cause the formation of oxygen and the high PM oxidation activity is exhibited in a state where the oxidation of NH ₃ is sufficiently suppressed. In the catalyst for purifying exhaust gas of the present invention, at least a part of the silver (Ag) may form a composite oxide with at least a part of the group 6 element (M), but it is preferable to NH ₃ From the viewpoint of further improving the oxidation inhibition performance, the peak corresponding to silver (Ag) in the obtained silver and tungsten-supported alumina catalyst powder is within the detection limit or less in powder X-ray diffraction (XRD) measurement described later Preferably, the complex oxide is formed.

Ag ₂ WO ₄ , Ag ₂ MoO ₄ , Ag ₂ CrO ₄ , Ag ₂ W ₂ O ₇ , Ag ₂ Mo ₂ O, for example, are composite oxides of silver (Ag) and a group 6 element (M). ₇ and Ag ₂ Cr ₂ O ₇ and AgCrO ₂ etc., among which Ag ₂ WO ₄ , Ag ₂ MoO ₄ and Ag ₂ CrO ₄ are preferable from the viewpoint that heat resistance tends to be higher.

Moreover, when the silver (Ag) which has not formed the said complex oxide is contained, it does not specifically limit as a form of such silver, Metal silver (metal silver single-piece | unit), silver oxide, silver nitrate, Silver compounds such as silver sulfate, silver carbonate, silver oxalate, silver phosphate, and silver halide are mentioned, and silver carbonate, silver phosphate, silver sulfate and the like from the viewpoint that the oxidation of NH ₃ tends to be further suppressed among them. Is preferred. Moreover, when the said 6th group element (M) which is not forming the said complex oxide is contained, it does not specifically limit as a form of such a 6th group element (M), The said 6th group Examples include elemental metals of elements (M), and oxides of the above-mentioned group 6 elements (M), ammonium salts, halogen salts (sodium salts etc.), and the like, and compounds of group 6 such as silver, among which silver and complex oxides are formed. The oxide of the Group 6 element (M) is preferable from the viewpoint that it tends to be easy to do.

  A composite oxide of silver (Ag) and the sixth group element (M) supported on the carrier, silver (Ag), the sixth group element (M), the silver compound, the sixth group The presence of an elemental compound or the like can be confirmed, for example, by X-ray diffraction (XRD) measurement described later to obtain an X-ray diffraction pattern and analyzing peaks corresponding to those components.

According to such an exhaust gas purification catalyst of the present invention, high PM oxidation activity is exhibited in a state in which the oxidation of NH ₃ is sufficiently suppressed. Therefore, the exhaust gas purification catalyst of the present invention It is suitably used as a PM oxidation catalyst for oxidizing and removing particulate matter (PM).

(Method of manufacturing catalyst for exhaust gas purification)
It does not specifically limit as a manufacturing method of the catalyst for exhaust gas purification of the present invention, For example, the following methods:
(I) After impregnating the support with a solution containing one of a silver salt and a salt of the Group 6 element, the support may be calcined if necessary, and then the support may further contain a silver salt or the Group 6 element A method of impregnating a solution containing the other of the above salts and calcining to obtain the exhaust gas purifying catalyst of the present invention.
(Ii) A method of obtaining the exhaust gas purification catalyst of the present invention by supporting the coprecipitate obtained from a solution containing a silver salt and a salt of the group 6 element on the carrier and calcining it.
(Iii) A method of impregnating a solution containing a silver salt and a salt of the Group 6 element in the carrier and calcining it to obtain the exhaust gas purifying catalyst of the present invention.
Thus, the exhaust gas purification catalyst of the present invention can be obtained, but the method (ii) is more preferable from the viewpoint of easily increasing the content of the composite oxide.

  The silver salt used herein is not particularly limited, and examples thereof include silver nitrate, silver sulfate, silver carboxylate and the like. The salt of the Group 6 element is not particularly limited, and tungstate (orthotungstate) salt, metatungstate, paratungstate, molybdate, chromate, dichromate, etc. The salt of the acid of the Group 6 element is mentioned, and in particular, from the viewpoint of high solubility in water, the salt of the acid of the Group 6 element is preferably an ammonium salt or an alkali metal salt. Further, the solvent constituting the solution is not particularly limited, and water, alcohol and the like can be mentioned, and water is preferable from the viewpoint of cost and safety.

  The method and conditions for impregnating the carrier with the solution, drying if necessary, and firing are not particularly limited, but the firing temperature in such a firing step is preferably 300 to 600 ° C., 400 -500 ° C is more preferred. If such a calcination temperature is less than the lower limit, the complex oxide tends to be difficult to be sufficiently obtained. On the other hand, if the upper limit is exceeded, the specific surface area of the carrier decreases and the PM oxidation activity decreases. It tends to end up. In addition, the firing time is not particularly limited, but about 0.1 to 100 hours is preferable. Furthermore, as such a baking atmosphere, you may implement in air | atmosphere.

  Further, the method of bringing the solution into contact with the carrier is not limited to the above-mentioned impregnation method, and may be a method of causing the carrier to carry the solution by spraying, coating or the like. Furthermore, after the firing step, the obtained exhaust gas purifying catalyst may be subjected to a pulverization treatment, a molding treatment, and the like as necessary to obtain a desired shape.

(Exhaust gas purification filter)
Next, the exhaust gas purification filter of the present invention will be described. The exhaust gas purification filter of the present invention is characterized in that the exhaust gas purification catalyst of the present invention is carried on a gas permeable base material (filter).

  The exhaust gas purification filter of the present invention is not particularly limited except that the exhaust gas purification catalyst of the present invention is supported on the air-permeable substrate. A well-known breathable base material (filter) can be suitably used as a breathable base material of such an exhaust gas purification filter, and for example, a particulate filter, a monolith filter, a honeycomb filter, a pellet form A filter, a plate-like filter, a filter made of foamed ceramic, etc. may be mentioned. When the exhaust gas purifying catalyst of the present invention is supported on a gas permeable substrate (filter), a higher degree of particulate matter (PM) oxidation performance can be obtained. More preferably, the exhaust gas purifying catalyst of the invention is supported on a particulate filter.

  Also, the material of the air-permeable substrate of such an exhaust gas purification filter is not particularly limited, but known materials can be appropriately used. For example, ceramics such as cordierite, silicon carbide, mullite, aluminum titanate, etc. Examples thereof include metals such as stainless steel containing chromium and aluminum.

  Further, as such an exhaust gas purification filter, it is preferable to use one having pores with an average pore diameter of 1 to 300 μm. By using a substrate having such an average pore diameter, it is possible to oxidize and purify the particulate matter more efficiently. Moreover, as such an exhaust gas purification filter, one having a porosity of 30 to 70% (more preferably 40 to 65%) is preferable. The "porosity" as used herein refers to the volume fraction of the hollow portion inside the air-permeable substrate.

  Further, in the exhaust gas purification filter of the present invention, it is preferable that a coat layer formed by the exhaust gas purification catalyst of the present invention is formed, and the thickness of the coat layer is not particularly limited. It is preferable that it is about 25 micrometers.

  Furthermore, in the exhaust gas purification filter of the present invention, the amount of the catalyst supported on the air-permeable substrate is also not particularly limited, and is appropriately set according to exhaust characteristics of an internal combustion engine or the like, desired purification performance, etc. For example, it is preferable that it is about 1 to 300 g with respect to 1 liter of the volume of the air-permeable substrate.

  The method for supporting the exhaust gas purifying catalyst of the present invention on the air-permeable substrate is not particularly limited. For example, a method for supporting a previously prepared catalyst on the air-permeable substrate, first for the air-permeable substrate A method of supporting the silver (Ag) and the group 6 element (M) on the carrier after supporting the carrier to form a composite oxide of these, and the like can be appropriately adopted.

(Exhaust gas purification method)
Next, the exhaust gas purification method of the present invention will be described. The exhaust gas purification method of the present invention is characterized in that the exhaust gas is brought into contact with the exhaust gas purification catalyst of the present invention to oxidize and remove particulate matter (PM).

  As described above, in the exhaust gas purification method of the present invention, the method for bringing the exhaust gas into contact with the exhaust gas purification catalyst is not particularly limited, and a known method can be suitably adopted. For example, exhaust gas is emitted from an internal combustion engine such as a diesel engine A method may be employed in which the exhaust gas from the internal combustion engine is brought into contact with the exhaust gas purification catalyst by arranging the exhaust gas purification catalyst of the present invention in the exhaust gas pipe through which the gas flows.

  The exhaust gas purification apparatus for carrying out the exhaust gas purification method of the present invention is not particularly limited as long as it has the exhaust gas purification catalyst of the present invention. In such an exhaust gas purification apparatus, the particulate matter contained in the gas (exhaust gas) discharged from the internal combustion engine is oxidized and purified (removed), so that the exhaust gas can come into contact with the exhaust gas purification catalyst. The exhaust gas purification catalyst may be disposed in a gas flow path in an exhaust gas pipe through which exhaust gas from an internal combustion engine flows, for example. In addition, it does not specifically limit as such an internal combustion engine, A well-known internal combustion engine can be used suitably, For example, an automobile engine (diesel engine etc.) may be used.

  Hereinafter, the present invention will be more specifically described based on examples and comparative examples, but the present invention is not limited to the following examples.

Example 1
4.9 g of silver nitrate (manufactured by Wako Pure Chemical Industries, Ltd.) is dissolved in 150 mL of ion-exchanged water, and the obtained solution is a γ-Al ₂ O ₃ powder (manufactured by JGC Universal, TN 4 (trade name), specific surface area: 150 m ² / G) After impregnating to 25 g and evaporating to dryness, it was dried overnight at 110 ° C. and further calcined in air at 500 ° C. for 3 hours to obtain a silver-supported alumina catalyst powder. Then, 1.6 g of ammonium metatungstate (manufactured by Japan Inorganic Chemical Industry Co., Ltd.) is dissolved in 150 mL of ion-exchanged water, and the obtained solution is impregnated with 13 g of the silver-supported alumina catalyst powder and evaporated to dryness. The slurry was dried overnight in air and then calcined at 500 ° C. for 3 hours in the air to obtain a silver and tungsten-supported alumina catalyst powder. Then, the obtained powder was mixed in a mortar and formed into a pellet shape having a particle diameter of 0.3 to 0.5 mm by a standard method (cold isostatic press (CIP)) to obtain a pellet-shaped catalyst. The atomic ratio (Ag / W) of silver to tungsten in the obtained catalyst was 2, and the supported amount of silver in the catalyst was 10% by mass in terms of metallic silver with respect to the total amount of the catalyst.

<X-ray diffraction (XRD) measurement>
Using the powder X-ray diffractometer (manufactured by RIGAKU Co., Ltd., trade name "sample horizontal X-ray diffractometer Ultima IV") using the silver and tungsten-supporting alumina catalyst powder obtained in Example 1 as a measurement sample, an X-ray source: Powder X-ray diffraction (XRD) measurement was performed under the conditions of CuKα ray (λ = 0.15406 nm), scan step: 0.02 °, retention time: 0.12 seconds, acceleration voltage: 40 kV, acceleration current: 40 mA.

As a result, it was confirmed that silver tungstate (Ag ₂ WO ₄ ), which is a composite oxide of silver and tungsten, was produced in the silver- and tungsten-supported alumina catalyst powder obtained in Example 1. The obtained XRD pattern is shown in FIG.

<Particulate matter (PM) oxidation activity evaluation>
The pellet catalyst obtained in Example 1 and simulated PM (carbon powder, manufactured by Tokai Carbon Co., Ltd., trade name “Siest 9 (SAF), average particle diameter 19 nm) become 49: 1 by weight ratio A catalyst sample was obtained by mixing the catalyst and simulated PM by placing it in a sample tube (cylindrical with an inner diameter of 20 mm) and rotating it for 1 hour on a rotating frame for test and research. Next, a mixed gas (entering gas) consisting of O ₂ (10% by volume) + H ₂ O (10% by volume) / N ₂ (remainder) is supplied to the obtained catalyst sample (7 L / min) to enter the catalyst while raising the temperature from 120 ° C. to 720 ° C. the gas temperature at a heating rate of 20 ° C. / min, the concentration of CO ₂ contained in the output gas exhausted until completion supply starting supply of the mixed gas It was measured. And, based on the concentration of CO ₂ in the output gas and the temperature of the incoming gas, the temperature of the mixed gas required to oxidize 50% of the simulated PM in the catalyst sample (50% PM oxidation temperature Asked for). The obtained results are shown in Table 1 and FIG.

<Ammonia (NH ₃ ) oxidation suppression evaluation>
The pelleted catalyst 1g obtained in Example 1 was placed into a sample tube as a catalyst sample (cylindrical inside diameter 15 mm), _NH in the catalyst sample 3 (400ppm) + NO (400ppm ) + O 2 (10 volume%) + _CO 2 ( Model gas (entering gas) consisting of 10 vol%) + H ₂ O (5 vol%) / N ₂ (remainder) is supplied (10 L / min), temperature of entering gas to catalyst is 20 ° C / min The NH ₃ conversion rate (NH ₃ oxidation rate) was determined from the NH ₃ concentration in the outlet gas at 400 ° C. while raising the temperature from 100 ° C. to 600 ° C. The obtained results are shown in Table 1 and FIG.

(Example 2)
The same as Example 1 except that the amounts of silver nitrate and ammonium metatungstate were 4.9 g and 3.1 g, respectively, and the atomic ratio of silver to tungsten (Ag / W) in the resulting catalyst was 1 Thus, a pellet-shaped catalyst comprising silver and a tungsten-supported alumina catalyst powder was obtained. The supported amount of silver in the obtained catalyst was 9% by mass in terms of metallic silver with respect to the total amount of the catalyst.

The silver and tungsten-supported alumina catalyst powder obtained in Example 2 was subjected to powder X-ray diffraction (XRD) measurement in the same manner as in Example 1. As a result, the silver and tungsten-supported alumina catalyst obtained in Example 2 were measured. It was also confirmed that silver tungstate (Ag ₂ WO ₄ ), which is a composite oxide of silver and tungsten, was produced also in the powder. The obtained XRD pattern is shown in FIG. Furthermore, the 50% PM oxidation temperature and the NH ₃ conversion rate were determined for the pelletized catalyst obtained in Example 2 in the same manner as in Example 1. The obtained results are shown in Table 1, FIG. 2 and FIG.

(Example 3)
Example 1 except that the amounts of silver nitrate and ammonium metatungstate were 4.9 g and 6.2 g, respectively, and the atomic ratio of silver to tungsten (Ag / W) in the resulting catalyst was 0.5. In the same manner as above, a pellet-shaped catalyst comprising silver and a tungsten-supported alumina catalyst powder was obtained. The supported amount of silver in the obtained catalyst was 7.7% by mass in terms of metallic silver with respect to the total amount of the catalyst.

Then, the 50% PM oxidation temperature and the NH ₃ conversion rate were determined for the pellet-like catalyst obtained in Example 3 in the same manner as in Example 1. The obtained results are shown in Table 1, FIG. 2 and FIG.

(Example 4)
A solution A was obtained by dissolving 2.5 g of sodium tungstate dihydrate (manufactured by Wako Pure Chemical Industries, Ltd.) in 200 mL of ion-exchanged water. Further, a solution B was obtained by dissolving 2.3 g of silver nitrate (manufactured by Wako Pure Chemical Industries, Ltd.) in 100 mL of ion exchanged water. Next, 12 g of γ-Al ₂ O ₃ powder (manufactured by JGC Universal Corp., TN4 (trade name), specific surface area: 150 m ² / g) is added to solution A, and solution B is further added to the dispersion obtained while stirring. In addition, the powder on which the precipitate is supported is separated by filtration from the dispersion in which a pale yellow precipitate (coprecipitate) containing silver and tungsten is formed, separated by filtration, washed with ion exchanged water, and evaporated to dryness at 110 ° C. The slurry was dried overnight in air and then calcined at 500 ° C. for 3 hours in the air to obtain a silver and tungsten-supported alumina catalyst powder. Then, the obtained powder was mixed in a mortar and formed into a pellet shape having a particle diameter of 0.3 to 0.5 mm by a standard method (cold isostatic press (CIP)) to obtain a pellet-shaped catalyst. The atomic ratio (Ag / W) of silver to tungsten in the obtained catalyst was 2, and the supported amount of silver in the catalyst was 10% by mass in terms of metallic silver with respect to the total amount of the catalyst.

The silver and tungsten-supported alumina catalyst powder obtained in Example 4 was subjected to powder X-ray diffraction (XRD) measurement in the same manner as in Example 1. As a result, the silver and tungsten-supported alumina catalyst obtained in Example 4 were measured. It was also confirmed that silver tungstate (Ag ₂ WO ₄ ), which is a composite oxide of silver and tungsten, was produced also in the powder. Moreover, in the silver and tungsten-supported alumina catalyst powder obtained in Example 4, the peak corresponding to silver (Ag) was below the detection limit. The obtained XRD pattern is shown in FIG. Furthermore, the 50% PM oxidation temperature and the NH ₃ conversion rate were determined for the pellet-like catalyst obtained in Example 4 in the same manner as in Example 1. The obtained results are shown in Table 1, FIG. 2 and FIG.

(Example 5)
A solution A was obtained by dissolving 1.9 g of sodium molybdate dihydrate (manufactured by Wako Pure Chemical Industries, Ltd.) in 200 mL of ion-exchanged water. Further, a solution B was obtained by dissolving 2.3 g of silver nitrate (manufactured by Wako Pure Chemical Industries, Ltd.) in 100 mL of ion exchanged water. Next, 12 g of γ-Al ₂ O ₃ powder (manufactured by JGC Universal Corp., TN4 (trade name), specific surface area: 150 m ² / g) is added to solution A, and solution B is further added to the dispersion obtained while stirring. In addition, the powder on which the precipitate is supported is separated by filtration from the dispersion in which a white precipitate (coprecipitate) containing silver and molybdenum is formed, separated by filtration, washed with ion exchanged water, and evaporated to dryness at 110 ° C. It was dried overnight and further calcined at 500 ° C. for 3 hours in the air to obtain a silver and molybdenum supported alumina catalyst powder. Then, the obtained powder was mixed in a mortar and formed into a pellet shape having a particle diameter of 0.3 to 0.5 mm by a standard method (cold isostatic press (CIP)) to obtain a pellet-shaped catalyst. The atomic ratio (Ag / Mo) of silver to molybdenum in the obtained catalyst was 2, and the supported amount of silver in the catalyst was 10% by mass in terms of metallic silver with respect to the total amount of the catalyst.

Then, when the powder X-ray diffraction (XRD) measurement was performed in the same manner as in Example 1 on the silver- and molybdenum-supported alumina catalyst powder obtained in Example 5, the silver- and molybdenum-supported alumina catalyst obtained in Example 5 was measured. It was confirmed that silver molybdate (Ag ₂ MoO ₄ ), which is a composite oxide of silver and molybdenum, was also formed in the powder. Furthermore, the 50% PM oxidation temperature and the NH ₃ conversion rate were determined for the pelleted catalyst obtained in Example 5 in the same manner as in Example 1. The obtained results are shown in Table 1, FIG. 2 and FIG.

(Comparative example 1)
A pellet-shaped catalyst composed of a silver-supported alumina catalyst powder was obtained in the same manner as in Example 1 except that the silver-supported alumina catalyst powder obtained in Example 1 was used as it was (without supporting tungsten). The supported amount of silver in the obtained catalyst was 11% by mass in terms of metallic silver with respect to the total amount of the catalyst. Then, the 50% PM oxidation temperature and the NH ₃ conversion rate of the pelletized catalyst obtained in Comparative Example 1 were determined in the same manner as in Example 1. The obtained results are shown in Table 1, FIG. 2 and FIG.

(Comparative example 2)
The same as Example 1, except that the amounts of silver nitrate and ammonium metatungstate were 4.9 g and 0.77 g, respectively, and the atomic ratio of silver to tungsten (Ag / W) in the resulting catalyst was 4 Thus, a pellet-shaped catalyst comprising silver and a tungsten-supported alumina catalyst powder was obtained. The supported amount of silver in the obtained catalyst was 10.4% by mass in terms of metallic silver with respect to the total amount of the catalyst.

Then, the 50% PM oxidation temperature and the NH ₃ conversion rate of the pelletized catalyst obtained in Comparative Example 2 were determined in the same manner as in Example 1. The obtained results are shown in Table 1, FIG. 2 and FIG.

(Comparative example 3)
A pellet-shaped catalyst made of alumina powder was obtained in the same manner as in Example 1 except that the γ-Al ₂ O ₃ powder used in Example 1 was used as it was (without supporting silver and tungsten). Then, the 50% PM oxidation temperature and the NH ₃ conversion rate of the pelletized catalyst obtained in Comparative Example 1 were determined in the same manner as in Example 1. The obtained results are shown in Table 1, FIG. 2 and FIG.

(Comparative example 4)
Dissolve 1.6 g of ammonium metatungstate (manufactured by Japan Inorganic Chemical Industry Co., Ltd.) in 150 mL of ion-exchanged water, and obtain the resulting solution as a γ-Al ₂ O ₃ powder (manufactured by JGC Universal Corp., TN 4 (trade name) 14 g of 150 m ² / g), evaporated to dryness, dried at 110 ° C. overnight, and further calcined at 500 ° C. in air for 3 hours to obtain a tungsten-supported alumina catalyst powder. Then, in the same manner as in Example 1 except that the obtained tungsten-supporting alumina catalyst powder was used as it was (without supporting silver), a pellet-shaped catalyst made of a tungsten-supporting alumina catalyst powder was obtained. The supported amount of tungsten in the obtained catalyst was 7.4% by mass in terms of metallic tungsten with respect to the total amount of the catalyst. Then, the 50% PM oxidation temperature and the NH ₃ conversion rate of the pelletized catalyst obtained in Comparative Example 4 were determined in the same manner as in Example 1. The obtained results are shown in Table 1, FIG. 2 and FIG.

(Comparative example 5)
1.1 g of ammonium metatungstate (manufactured by Japan Inorganic Chemical Industry Co., Ltd.) is dissolved in 150 mL of ion-exchanged water, and the obtained solution is γ-Al ₂ O ₃ powder (manufactured by JGC Universal, TN 4 (trade name), specific surface area : Impregnated into 3.9 g of 150 m ^{2 /} g), evaporated to dryness, dried at 110 ° C. overnight, and further calcined in air at 500 ° C. for 3 hours to obtain a tungsten-supported alumina catalyst powder. Further, 1.6 g of silver nitrate (manufactured by Wako Pure Chemical Industries, Ltd.) is dissolved in 150 mL of ion-exchanged water, and the obtained solution is γ-Al ₂ O ₃ powder (manufactured by JGC Universal Corp., TN4 (trade name), specific surface area: The slurry was impregnated with 4.0 g of 150 m ^{2 /} g), evaporated to dryness, dried at 110 ° C. overnight, and further calcined in air at 500 ° C. for 3 hours to obtain a silver-supported alumina catalyst powder. Then, they are formed into pellets having a particle diameter of 0.3 to 0.5 mm according to a standard method (Cold isostatic pressing (CIP)) using each of the obtained catalyst powders to form a pellet-shaped catalyst, Were mixed to obtain a mixed catalyst of a tungsten-supported alumina catalyst and a silver-supported alumina catalyst.

The atomic ratio (Ag / W) of silver to tungsten in the obtained mixed catalyst was 2, and the supported amount of silver in the catalyst was 10% by mass in terms of metallic silver with respect to the total amount of the catalyst. Then, the 50% PM oxidation temperature and the NH ₃ conversion rate were determined for the mixed catalyst obtained in Comparative Example 5 in the same manner as in Example 1. The obtained results are shown in Table 1, FIG. 2 and FIG.

<Evaluation result>
As apparent from the results shown in Table 1 and FIG. 2, the catalysts of the present invention (Examples 1 to 5) are catalysts consisting of alumina powder (Comparative Example 3) and catalysts consisting of tungsten-supporting alumina powder (Comparative Example 4) It was confirmed that the PM oxidation activity was very high as compared with. The lower the 50% PM oxidation temperature, the more the simulated PM can be oxidized at a lower temperature, indicating that the PM oxidation activity is high.

Moreover, as is clear from the results shown in Table 1 and FIG. 3, in the catalysts of the present invention (Examples 1 to 5), the NH ₃ conversion rate was low, and the oxidation of NH ₃ was sufficiently suppressed. confirmed. On the other hand, the atomic ratio (Ag / W) of silver to tungsten although the catalyst (comparative example 1) consisting of silver-supporting alumina powder and the composite oxide of silver and tungsten was out of the range of the present invention In the catalyst (comparative example 2) and the mixed catalyst of the tungsten-supported alumina catalyst and the silver-supported alumina catalyst (comparative example 5), although the PM oxidation activity was good, the NH ₃ conversion rate is almost 100% in all It was confirmed that the oxidation of NH ₃ was not suppressed at all.

From the above results, it is clear that the catalyst of the present invention (Examples 1 to 5) can sufficiently suppress the oxidation of NH ₃ while maintaining relatively high PM oxidation activity.

As described above, according to the present invention, an exhaust gas purification catalyst capable of exhibiting high PM oxidation activity while sufficiently suppressing the oxidation of NH ₃ , an exhaust gas purification filter using the same, and exhaust gas purification It becomes possible to provide a method.

Therefore, the exhaust gas purification catalyst of the present invention, the exhaust gas purification filter and exhaust gas purification method using the same comprise a PM oxidation catalyst for purifying particulate matter contained in exhaust gas from an internal combustion engine such as a diesel engine, It is useful as an exhaust gas purification filter and an exhaust gas purification method used, and in particular, very useful as a technology for a PM oxidation catalyst in the case of providing a function such as NOx purification using NH ₃ as a reducing agent together with the function of PM oxidation is there.

Claims (5)

An alumina-based carrier,
Silver (Ag) and at least one Group 6 element (M) selected from the group consisting of chromium, molybdenum and tungsten, supported on the carrier
And at least a portion of the silver (Ag) and at least a portion of the group 6 element (M) form a composite oxide, and the silver (Ag) and the group 6 An exhaust gas purification catalyst characterized in that an atomic ratio (Ag / M) to an element (M) is 0.3 to 3.   The exhaust gas purifying catalyst according to claim 1, wherein a supported amount of silver (Ag) in the catalyst is 2 to 30% by mass in terms of metallic silver with respect to a total amount of the catalyst.   The exhaust gas purification catalyst according to claim 1 or 2, wherein the catalyst is a PM oxidation catalyst for oxidizing and removing particulate matter (PM) in exhaust gas.   An exhaust gas purification filter characterized in that the exhaust gas purification catalyst according to any one of claims 1 to 3 is supported on a gas permeable base material.   A method for exhaust gas purification, comprising contacting exhaust gas with the catalyst for exhaust gas purification according to any one of claims 1 to 3 to oxidize and remove particulate matter (PM) in the exhaust gas.