WO2016190294A1

WO2016190294A1 - Exhaust gas purifying catalyst, exhaust gas purifying filter using same and exhaust gas purification method

Info

Publication number: WO2016190294A1
Application number: PCT/JP2016/065268
Authority: WO
Inventors: 山崎　清; 榊原　雄二; 将嗣菊川; 祐介新名; 優一祖父江
Original assignee: トヨタ自動車株式会社
Priority date: 2015-05-25
Filing date: 2016-05-24
Publication date: 2016-12-01
Also published as: JP6392704B2; JP2016215160A

Abstract

An exhaust gas purifying catalyst which comprises: a carrier containing at least one salt selected from the group consisting of oxo acid salts of barium and oxo acid salts of strontium; and an oxo acid salt of silver supported by the carrier. The oxo acid salts of barium are oxo acid salts containing at least one substance selected from the group consisting of boron, phosphorus and sulfur; the oxo acid salts of strontium are oxo acid salts containing at least one substance selected from the group consisting of boron, phosphorus and sulfur; and the oxo acid salt of silver is an oxo acid salt containing at least one substance selected from the group consisting of phosphorus and sulfur.

Description

Exhaust gas purification catalyst, exhaust gas purification filter and exhaust gas purification method using the same

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

Gas discharged from the internal combustion engine contains particulate matter (PM) generated by combustion, toxic substances such as ash made of additives in oil, and the like. Among such harmful substances, particulate substances are known as air pollutants that adversely affect animals and plants. Therefore, a purification filter (DPF: Diesel Particulate Filter) is used to collect particulate matter contained in the exhaust gas discharged from the internal combustion engine. The PM collected by the DPF causes an increase in pressure loss and a decrease in the output of the internal combustion engine. Therefore, the PM is periodically raised to a high temperature (for example, heated to around 650 ° C.), and the PM is burned (oxidized and removed). ) To regenerate the DPF. At this time, in order to improve fuel consumption and material durability, it is desirable to regenerate at a lower temperature, and it has been studied to carry a PM oxidation catalyst on the DPF. As such a PM oxidation catalyst, it is known that a catalyst containing silver (Ag) exhibits high PM oxidation activity.

As such a PM oxidation catalyst, Japanese Patent Application Laid-Open No. 2003-170051 (Patent Document 1) discloses at least one selected from the group consisting of gold, silver, copper, iron, zinc, manganese and rare earth elements as an active component. A PM oxidation catalyst in which an element is supported on an alkaline earth metal hydroxide, oxide, carbonate or sulfate as a carrier component is disclosed. Further, International Publication No. 2007/043442 (Patent Document 2) discloses an oxidation catalyst composed of a carrier made of a complex oxide of cerium and zirconium and Ag or an oxide of Ag carried on the carrier. Yes. Furthermore, Japanese Patent Application Laid-Open No. 2007-196135 (Patent Document 3) discloses using an oxidation catalyst obtained by firing boehmite on which silver is supported.

However, in the conventional PM oxidation catalyst as described in Patent Documents 1 to 3, when the ash contained in the gas is deposited on the oxidation catalyst at the time of use, the particulate matter and the oxidation catalyst are caused by the ash. As a result, the purification performance of the particulate matter was deteriorated. In addition, in order to regenerate the oxidation catalyst with reduced particulate matter purification performance in this way, the exhaust gas must be heated to a high temperature, and a large amount of fuel was consumed in the regeneration treatment of the catalyst purification performance. Further, when the conventional PM oxidation catalyst as described in Patent Documents 1 to 3 is used, there is a problem that the fuel consumption of the internal combustion engine is reduced. Furthermore, since the PM oxidation performance of the conventional PM oxidation catalyst as described in Patent Documents 1 to 3 changes depending on the use as described above, the timing for performing the regeneration process of the DPF and the temperature condition at that time are determined. Not only was it difficult to set, but when the catalyst was supported on a base material such as DPF, the base material could be destroyed by heat due to the oxidation of a large amount of PM. As described above, the conventional PM oxidation catalysts as described in Patent Documents 1 to 3 cannot sufficiently exhibit purification performance due to ash accumulation.

Japanese Patent Application Laid-Open No. 2012-219715 (Patent Document 4) discloses a carrier made of at least one metal salt selected from the group consisting of Ca sulfate and phosphate, and silver carried on the carrier. An exhaust gas purification apparatus including an oxidation catalyst including at least one silver-containing material selected from the group consisting of silver oxide, silver carbonate, silver sulfate, and silver phosphate is disclosed. According to the description of the publication, the exhaust gas purification device capable of sufficiently suppressing the reduction in the oxidation performance of the particulate matter due to the ash deposition and exhibiting the excellent oxidation performance of the particulate matter even after the ash deposition. It is possible to provide.

However, in recent years, the required characteristics for exhaust gas purification catalysts have been increasing more and more, have sufficiently high PM oxidation activity, and the deterioration of the oxidation performance of particulate matter due to the accumulation of ash is sufficiently suppressed. An exhaust gas purifying catalyst capable of exhibiting sufficiently high PM oxidation activity even after deposition has been demanded.

JP 2003-170051 A International Publication No. 2007/043442 JP 2007-196135 A JP 2012-219715 A

The present invention has been made in view of the above-mentioned problems of the prior art, has a sufficiently high PM oxidation activity, and sufficiently suppresses a reduction in oxidation performance of particulate matter due to ash deposition. It is an object of the present invention to provide an exhaust gas purifying catalyst capable of exhibiting sufficiently high PM oxidation activity even after deposition, an exhaust gas purifying filter and an exhaust gas purifying method using the same.

As a result of intensive studies to achieve the above object, the present inventors have developed a silver oxo acid salt on a carrier containing at least one selected from the group consisting of barium oxo acid salt and strontium oxo acid salt. As a result of the loading, the exhaust gas purifying catalyst obtained surprisingly has a sufficiently high PM oxidation activity, and further the deterioration of the oxidation performance of the particulate matter due to the accumulation of ash is sufficiently suppressed. The present inventors have found that a sufficiently high PM oxidation activity can be exhibited even in the present invention, and the present invention has been completed.

That is, the exhaust gas purifying catalyst of the present invention comprises a carrier containing at least one selected from the group consisting of barium oxoacid salt and strontium oxoacid salt, and silver oxoacid salt carried on the carrier. The barium oxoacid salt is an oxoacid salt containing at least one selected from the group consisting of boron, phosphorus and sulfur, and the strontium oxoacid salt is a group consisting of boron, phosphorus and sulfur An oxoacid salt containing at least one selected from the above, wherein the silver oxoacid salt is an oxoacid salt containing at least one selected from the group consisting of phosphorus and sulfur.

In the exhaust gas purifying catalyst of the present invention, the barium oxoacid salt is at least one selected from the group consisting of barium sulfate (BaSO ₄ ) and barium sulfite (BaSO ₃ ), and the strontium oxoacid salt Is preferably at least one selected from the group consisting of strontium sulfate (SrSO ₄ ) and strontium sulfite (SrSO ₃ ).

In the exhaust gas purifying catalyst of the present invention, the silver oxoacid salt is at least one selected from the group consisting of silver sulfate (Ag ₂ SO ₄ ) and silver sulfite (Ag ₂ SO ₃ ). Is preferred.

Furthermore, in the exhaust gas purifying catalyst of the present invention, the supported amount of the silver oxoacid salt is 0.1 to 50% by mass in terms of metallic silver with respect to the total amount of the carrier and the silver oxoacid salt. Preferably there is.

The exhaust gas purification filter of the present invention comprises a breathable base material and the exhaust gas purification catalyst of the present invention supported on the breathable base material.

The exhaust gas purification method of the present invention is a method of oxidizing and removing particulate matter (PM) by contacting exhaust gas from an internal combustion engine with the exhaust gas purification catalyst of the present invention.

The exhaust gas purification catalyst of the present invention, the exhaust gas purification filter using the exhaust gas purification method, and the exhaust gas purification method have sufficiently high PM oxidation activity and sufficiently reduce the oxidation performance of particulate matter due to ash deposition. Although the reason why it is suppressed and a sufficiently high PM oxidation activity can be exhibited even after ash deposition is not necessarily clear, the present inventors speculate as follows.

That is, in the present invention, the exhaust gas-purifying catalyst is a carrier containing at least one selected from the group consisting of the barium oxoacid salt and the strontium oxoacid salt, and the silver oxoacid supported on the carrier. The oxygen ion (O ²⁻ ) in the oxo acid ion of the silver oxo acid salt contained in the exhaust gas purifying catalyst of the present invention is converted into the silver ion (Ag ⁺ ) in the silver oxo acid salt. It is activated by giving electrons to carbon dioxide, and becomes carbon dioxide (CO ₂ ) by receiving electrons from particulate matter (PM, mainly carbon: C). Alternatively, silver ions (Ag ⁺ ) in a silver oxo acid salt are reduced to contact with particulate matter (PM, mainly carbon: C) to become Ag in a metal state, and the particulate matter is oxidized and oxidized. It becomes carbon (CO ₂ ). After that, Ag (metal) is oxidized by contact with oxygen (O ₂ ) in the gas phase to become Ag ions again, and oxygen ions (O ²⁻ ) are generated from the oxygen. Such a series of reactions in the oxidation treatment of PM can be expressed by the following reaction formulas (1) to (2).

(1) 4Ag ⁺ + C + 2O ²⁻ → 4Ag + CO ₂
(2) 4Ag + O ₂ → 4Ag ⁺ + 2O ²⁻
By such a cycle, the inventors speculate that silver oxoacid salts can catalyze particulate matter (PM).

Incidentally, the carrier carrying the silver oxo acid salts of cerium oxide: the case of a basic support such as a composite oxide containing (ceria CeO ₂₎ or CeO _2, and oxoacid ions of cerium (Ce) ionic bond As a result, oxygen is not activated. Further, in the case of an acidic carrier such as titanium oxide (titania: TiO ₂ ) or tin oxide (SnO ₂ ), the reduced Ag becomes stable, and thus re-oxidation by O ₂ does not proceed.

The carrier for the exhaust gas purifying catalyst of the present invention contains at least one selected from the group consisting of the barium oxoacid salt and the strontium oxoacid salt. Such a carrier such as barium (Ba) or strontium Since the oxo acid salt of (Sr) has moderate basicity / acidity, the present inventors infer that the above cycle proceeds without delay.

In addition, the silver oxoacid salt supported on the carrier of the exhaust gas purifying catalyst of the present invention has a relatively low melting point (for example, 660 ° C. in Ag ₂ SO ₄ ) and high temperature (temperature at which PM is oxidized). In the region), it is considered that at least a part is in a molten state, and silver ions are dispersed so as to cover the entire surface of the carrier because it has melting properties on the carrier. Therefore, in the exhaust gas purifying catalyst comprising the silver oxoacid salt supported on the carrier, the contact point between Ag ions and PM is remarkably increased, and it becomes possible to obtain higher PM oxidation activity. The present inventors speculate.

Furthermore, in the exhaust gas purifying catalyst of the present invention, as described above, the silver oxo acid salt has a melting property on the carrier at a high temperature. The carrier having the oxo acid salt of barium (Ba) or strontium (Sr) of the present invention includes calcium sulfate (CaSO ₄ ), calcium phosphate (Ca ₃ (PO ₄ ) ₂ , CaHPO ₄ , CaH ₄ (PO ₄ ) _2, etc. ) And the basic / acidity of the ash particles as a main component, the silver oxo acid salt on the carrier melts and the silver oxo acid salt, silver (Ag) or silver ion (Ag ⁺ ) can migrate to the ash particles in contact with the catalyst. Then, the silver oxoacid salt, silver (Ag) or silver ion (Ag ⁺ ) that has moved to the surface of the ash particles comes into contact with particulate matter (PM, mainly carbon: C) on the surface of the ash particles. It is possible to cause the oxidation reaction as described above (reaction formulas (1) to (2)), and it is possible to catalyze PM oxidation even if ash accumulates on exhaust gas purification catalysts and particulate filters. The present inventors speculate that

As a result, in the exhaust gas purifying catalyst of the present invention, a sufficiently high PM oxidation activity can be achieved, and further, the deterioration of the oxidation performance of the particulate matter due to the ash deposition can be sufficiently suppressed. The present inventors infer that it is possible to exhibit a sufficiently high PM oxidation activity even in the case of the above.

According to the present invention, it has a sufficiently high PM oxidation activity, and the deterioration of the oxidation performance of the particulate matter due to the ash deposition is sufficiently suppressed, and a sufficiently high PM oxidation activity is achieved even after the ash deposition. It is possible to provide an exhaust gas purification catalyst that can be exerted, an exhaust gas purification filter and an exhaust gas purification method using the same.

6 is a graph showing initial 50% PM oxidation temperatures of exhaust gas purifying catalysts obtained in Examples 1 and 2 and Comparative Examples 1 to 6. 6 is a graph showing 50% PM oxidation temperature of exhaust gas purifying catalysts after ash deposition and after ash deposition-heat treatment obtained in Examples 1-2 and Comparative Examples 1-6.

Hereinafter, the present invention will be described in detail on the basis of preferred embodiments thereof.

[Exhaust gas purification catalyst]
First, the exhaust gas purifying catalyst of the present invention will be described. The exhaust gas purifying catalyst of the present invention comprises a carrier containing at least one selected from the group consisting of barium oxoacid salt and strontium oxoacid salt, and silver oxoacid salt supported on the carrier. The barium oxoacid salt is an oxoacid salt containing at least one selected from the group consisting of boron, phosphorus and sulfur, and the strontium oxoacid salt is selected from the group consisting of boron, phosphorus and sulfur Wherein the silver oxoacid salt is an oxoacid salt containing at least one selected from the group consisting of phosphorus and sulfur. By supporting the silver oxoacid salt as an active species on a carrier containing at least one selected from the group consisting of barium oxoacid salt and strontium oxoacid salt, The catalyst for exhaust gas purification of the invention can exhibit sufficiently high PM oxidation activity, and further, the deterioration of the oxidation performance of particulate matter due to ash deposition is sufficiently suppressed, and even after ash deposition. It is possible to exhibit a sufficiently high PM oxidation activity. Therefore, the exhaust gas purifying catalyst of the present invention can be suitably employed as a PM oxidation catalyst for purifying exhaust gas by oxidizing and removing particulate matter (PM) in exhaust gas from an internal combustion engine such as a diesel engine. More preferably, the exhaust gas purifying catalyst of the present invention can be employed as a PM oxidation catalyst for diesel.

(Carrier)
The carrier according to the present invention is a carrier comprising at least one selected from the group consisting of barium oxoacid salt and strontium oxoacid salt, wherein the barium oxoacid salt is composed of boron, phosphorus and sulfur. It is necessary that the strontium oxoacid salt includes at least one selected from the group consisting of boron, phosphorus, and sulfur. . The carrier containing at least one selected from the group consisting of barium oxoacid salt and strontium oxoacid salt is an oxoacid salt containing at least one selected from the group consisting of boron, phosphorus and sulfur. There are no particular restrictions except for certain. Here, “the carrier comprising at least one selected from the group consisting of barium oxoacid salt and strontium oxoacid salt” means that the carrier comprises the barium oxoacid salt and strontium oxoacid salt. Or the carrier mainly contains at least one selected from the group consisting of the barium oxoacid salt and the strontium oxoacid salt, and has the effects of the present invention. It means that it is configured to include other components within a range that does not deteriorate. As other components, other metal oxides and additives used as a carrier for this type of application can be used. In the latter case, the content of at least one selected from the group consisting of the barium oxoacid salt and the strontium oxoacid salt in the carrier is 50% by mass or more with respect to 100% by mass of the total mass of the carrier. Is preferable, and it is more preferable that it is 80 mass% or more. If the content of at least one selected from the group consisting of barium oxoacid salt and strontium oxoacid salt in such a carrier is less than the lower limit, the effects of the present invention tend not to be sufficiently obtained.

In such a carrier, the oxo acid salt containing boron is not particularly limited, and besides borate (orthoborate), metaborate, tetraborate, perborate, hypoborate, Boronate, borate and the like can be used. Among these, borate (orthoborate) and metaborate are preferable from the viewpoint of being stable at high temperatures.

In addition, the oxo acid salt containing phosphorus is not particularly limited, and specifically, phosphate (orthophosphate), diphosphate (pyrophosphate), polyphosphate (metaphosphate) , Phosphites and the like can be used. Among these, from the viewpoint of being stable at high temperatures, phosphates (orthophosphates), phosphites, and polyphosphates are preferable.

Furthermore, the oxo acid salt containing sulfur is not particularly limited. Specifically, in addition to sulfate, sulfite, peroxomonosulfate, thiosulfate, dithionate, disulfite, dithionate , Disulfate, peroxodisulfate, polythionate, and the like can be used. Among these, from the viewpoint of being stable at high temperatures, sulfates and sulfites are preferable, and barium sulfate (BaSO ₄ ) or strontium sulfate (SrSO ₄ ) is more preferable.

In the exhaust gas purifying catalyst of the present invention, the barium oxoacid salt is at least one selected from the group consisting of barium sulfate (BaSO ₄ ) and barium sulfite (BaSO ₃ ), and the strontium oxo More preferably, the acid salt is at least one selected from the group consisting of strontium sulfate (SrSO ₄ ) and strontium sulfite (SrSO ₃ ).

Further, other components other than the barium oxoacid salt and strontium oxoacid salt that can be contained in such a support include, for example, yttrium (Y) and lanthanum from the viewpoint of thermal stability and catalytic activity of the support. (La), praseodymium (Pr), cerium (Ce), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium Rare earth such as (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), magnesium (Mg), calcium (Ca), scandium (Sc), vanadium (V), alkali metals, An oxide of a metal such as an alkaline earth metal or a transition metal can be used.

Further, the specific surface area of such a carrier is not particularly limited, but is preferably 0.5 to 200 m ² / g, more preferably 1 to 100 m ² / g. If the specific surface area exceeds the upper limit, the heat resistance of the support itself decreases, so the heat resistance of the catalyst tends to decrease. On the other hand, if the specific surface area is less than the lower limit, the active species (the silver oxoacid salt) is dispersed. Tend to decrease. Such a specific surface area can be calculated as a BET specific surface area from the adsorption isotherm using the BET isotherm adsorption equation.

Furthermore, the shape of such a carrier is not particularly limited, but a conventionally known shape such as a ring shape, a spherical shape, a cylindrical shape, or a pellet shape can be used. From the viewpoint that a large amount of active species (the silver oxoacid salt) can be contained in a highly dispersible state, it is preferable to use a particulate material. When the carrier is in the form of particles, the average primary particle size of the carrier particles is preferably 1 to 1000 nm, and more preferably 5 to 500 nm. The average primary particle diameter of such a carrier can be measured by calculating from the line width of the powder X-ray diffraction peak using the Scherrer's equation using an X-ray diffractometer. . Alternatively, such an average primary particle size can be calculated by analyzing an image with an electron microscope.

Further, the method for producing such a carrier is not particularly limited, but it is known that a carrier containing at least one selected from the group consisting of the barium oxoacid salt and the strontium oxoacid salt can be produced. These methods can be used as appropriate. Further, as such a carrier, a commercially available barium oxoacid salt and / or strontium oxoacid salt may be used, and the size may be appropriately adjusted by milling with a ball mill or the like.

(Silver oxo acid salt)
The silver oxoacid salt according to the present invention is an active species supported on a carrier including at least one selected from the group consisting of the barium oxoacid salt and the strontium oxoacid salt, and includes phosphorus and sulfur. It is necessary that the oxoacid salt contains at least one selected from the group consisting of: Such a silver oxo acid salt is not particularly limited except that it is an oxo acid salt containing at least one selected from the group consisting of phosphorus and sulfur. The silver oxo acid salt is not particularly limited as an oxo acid salt containing phosphorus. Specifically, in addition to a phosphate (orthophosphate, Ag ₃ PO ₄ ), a diphosphate ( Pyrophosphate, Ag ₄ P ₂ O ₇ ), polyphosphate (metaphosphate, AgPO ₃ ), phosphite, and the like can be used. Among these, phosphate (orthophosphate), phosphite, and metaphosphate are preferable from the viewpoint of being stable at high temperatures, and silver orthophosphate (Ag ₃ PO ₄ ) is more preferable. preferable. The oxo acid salt containing sulfur is not particularly limited. Specifically, in addition to sulfate, sulfite, peroxomonosulfate, thiosulfate, dithionate, disulfite, dithionate , Disulfate, peroxodisulfate, polythionate, and the like can be used. Among these, sulfate and sulfite are preferable from the viewpoint of being stable at high temperatures. The silver oxoacid salt according to the present invention is an oxoacid similar to the oxoacid salt in the carrier containing at least one selected from the group consisting of the barium oxoacid salt and the strontium oxoacid salt. Even a salt may be a different oxoacid salt.

Furthermore, in the exhaust gas purifying catalyst of the present invention, the silver oxoacid salt is at least one selected from the group consisting of silver sulfate (Ag ₂ SO ₄ ) and silver sulfite (Ag ₂ SO ₃ ). Is more preferable.

The supported amount of the silver oxoacid salt used in the exhaust gas purifying catalyst of the present invention is not particularly limited, but metal silver (Ag) with respect to the total amount of the carrier and the silver oxoacid salt. In terms of conversion, it is preferably 0.1 to 50% by mass, and more preferably 1 to 40% by mass. If the amount of the silver oxoacid salt supported is less than the lower limit, the oxidation performance of the particulate matter tends to be not sufficiently advanced. On the other hand, if the amount exceeds the upper limit, the oxidation performance is low. The cost tends to increase because of saturation.

The average crystallite size (average primary particle size) of such a silver oxoacid salt is not particularly limited, but is preferably 1 to 500 nm, and more preferably 2 to 100 nm. If the average crystallite size of the silver oxo acid salt is less than the lower limit, it strongly binds to the support and the activity tends to decrease, whereas if it exceeds the upper limit, the number of particles contributing to the reaction decreases, and the activity It tends to decrease. The average crystallite size (average primary particle size) of such a silver oxoacid salt is, for example, from the line width of a powder X-ray diffraction peak using an X-ray diffractometer, Scherrer's equation It can measure by calculating using. Alternatively, such an average crystallite size (average primary particle size) can be calculated by analyzing an image with an electron microscope.

Further, the method of supporting the silver oxoacid salt on a carrier containing at least one selected from the group consisting of barium oxoacid salt and strontium oxoacid salt is not particularly limited, but is a known method. For example, at least one selected from the group consisting of barium oxoacid salt and strontium oxoacid salt using a dispersion or sol of silver oxoacid salt or a precursor thereof. Barium oxoacid salt and strontium oxoacid salt by using a method of coating (including firing if necessary) on a support containing oxygen and a vapor deposition method (for example, chemical vapor deposition, physical vapor deposition, sputter vapor deposition) A method of supporting on a carrier containing at least one selected from the group consisting of can be suitably employed.

(Exhaust gas purification catalyst)
The exhaust gas-purifying catalyst in the present invention includes a carrier containing at least one selected from the group consisting of the barium oxoacid salt and the strontium oxoacid salt, and the silver oxoacid supported on the carrier. Although it is provided with a salt and the form thereof is not particularly limited, it may be in the form of a pellet-shaped pellet catalyst or the like and may be supported on a filter such as DPF.

(Manufacturing method of exhaust gas purification catalyst)
The method for producing the exhaust gas purifying catalyst of the present invention is not particularly limited, and a known method can be appropriately used. For example, the catalyst is selected from the group consisting of the barium oxoacid salt and the strontium oxoacid salt. It is produced by a step of impregnating a carrier containing at least one kind with an aqueous solution containing ions of the silver oxo acid salt, a step of heating and baking. In the impregnation, specifically, the solution containing the silver oxoacid salt in a predetermined concentration is at least one selected from the group consisting of the barium oxoacid salt and the strontium oxoacid salt. It is possible to employ a method in which a solution containing a predetermined amount of the silver oxo acid salt is impregnated (supported) on the support, and then heated and fired.

Further, the heat-firing (firing step) after impregnating such a silver oxo acid salt may be carried out in the air. Further, the firing temperature in such a firing step is preferably 200 to 700 ° C. When such a calcination temperature is lower than the lower limit, it becomes difficult to support the silver oxoacid salt on the support, and there is a tendency that sufficient PM oxidation activity of the exhaust gas purifying catalyst cannot be obtained. If it exceeds, the specific surface area of the support containing at least one selected from the group consisting of barium oxoacid salt and strontium oxoacid salt tends to decrease, and this tends to decrease the oxidation activity. The firing time is preferably from 0.1 to 100 hours. When such a calcination time is less than the lower limit, it becomes difficult to support the silver oxoacid salt, and the oxidation activity of the resulting exhaust gas purification catalyst (PM oxidation catalyst) tends to decrease. Even if it exceeds, the further effect is not acquired and it exists in the tendency which leads to the increase in the cost for preparing a catalyst.

[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 comprises a breathable base material (filter) and the exhaust gas purification catalyst of the present invention carried on the breathable base material.

Such an 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 a gas permeable substrate. As the breathable substrate of such an exhaust gas purification filter, a known breathable substrate (filter) can be appropriately used. For example, a particulate filter, a monolith filter, a honeycomb filter, a pellet filter Examples thereof include a filter, a plate-like filter, and a foamed ceramic filter. When the exhaust gas purifying catalyst of the present invention is supported on a gas permeable substrate (filter), a higher level of particulate matter (PM) oxidation performance can be obtained. More preferably, the exhaust gas purifying catalyst of the present invention is supported on a particulate filter.

In addition, the material of the breathable substrate of such an exhaust gas purification filter is not particularly limited, but a known material can be used as appropriate, for example, cordierite, silicon carbide, mullite, ceramics such as aluminum titanate, Examples thereof include metals such as stainless steel including chrome and aluminum.

Further, as such an exhaust gas purification filter, it is preferable to use a filter having pores having an average pore diameter of 1 to 300 μm. By using a base material having such an average pore diameter, it becomes possible to oxidize and purify the particulate matter more efficiently.

In addition, as such an exhaust gas purification filter, a coat layer is preferably formed by the exhaust gas purification catalyst of the present invention, and the thickness of the coat layer is preferably 0.025 to 25 μm. More preferably, the thickness is from 05 to 10 μm. When the thickness of the coating layer is less than the lower limit, a carrier containing at least one selected from the group consisting of the barium oxoacid salt and the strontium oxoacid salt, and a silver oxoacid salt carried on the carrier, The surface of the filter cannot be sufficiently covered with the catalyst provided, and the contact point with the particulate matter tends to be reduced, and it tends to be difficult to provide a sufficiently high oxidation performance. The pores of the filter are blocked by a catalyst comprising a support containing at least one selected from the group consisting of the barium oxoacid salt and the strontium oxoacid salt and a silver oxoacid salt supported on the support. The pressure loss of exhaust gas increases and the engine efficiency tends to decrease.

Further, in such an exhaust gas purification filter, the amount of the catalyst supported on the breathable base material is not particularly limited, but the amount can be appropriately adjusted according to an internal combustion engine or the like, and the breathable group The amount is preferably 1 to 300 g, more preferably 5 to 100 g, per 1 liter of material volume. If the supported amount is less than the lower limit, it tends to be difficult to exhibit sufficiently high catalyst performance. On the other hand, if the upper limit is exceeded, a catalyst comprising the support and the silver oxoacid salt is used. The pores of the air-permeable base material are clogged, and the pressure loss of the exhaust gas increases, and the engine efficiency tends to decrease.

In addition, such an exhaust gas purification filter preferably has a porosity of 30 to 80% (more preferably 40 to 65%). Here, the “porosity” refers to the volume ratio of the hollow portion inside the breathable substrate. In addition, when the porosity is less than the lower limit, the pores tend to be clogged by the particulate matter in the exhaust gas. On the other hand, when the porosity exceeds the upper limit, it is difficult to collect the particulate matter in the exhaust gas. The strength of the filter tends to decrease.

Further, in such an exhaust gas purifying filter, the method for supporting the exhaust gas purifying catalyst of the present invention on the breathable base material is not particularly limited. For example, the barium oxoacid salt and the strontium oxoacid salt are previously used. A method comprising preparing a catalyst comprising a support containing at least one selected from the group consisting of: and a silver oxoacid salt supported on the support, and supporting the catalyst on a breathable substrate; The barium oxoacid salt and the strontium oxoacid are obtained by carrying out a step of supporting a carrier on a substrate and a step of supporting a silver oxoacid salt on the carrier supported on the breathable substrate. Appropriately adopted is a method of supporting a catalyst comprising a support containing at least one selected from the group consisting of salts and a silver oxoacid salt supported on the support on a filter. Rukoto can. In addition, the method for supporting the catalyst, the carrier, and the silver oxo acid salt on the breathable substrate is not particularly limited, and a known method can be appropriately employed. For example, a slurry such as a catalyst or a carrier is prepared, and the slurry is vented. For example, a method of coating (subsequent firing if necessary) on the conductive substrate can be appropriately used. In addition, as such an exhaust gas purifying catalyst, other known components that can be used as a catalyst for oxidizing a particulate material may be appropriately contained within a range not impairing the effects of the present invention.

[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 a method of oxidizing and removing particulate matter (PM) by bringing exhaust gas from an internal combustion engine into contact with the exhaust gas purification catalyst of the present invention.

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 adopted as appropriate. For example, the gas discharged from the internal combustion engine A method of bringing the exhaust gas from the internal combustion engine into contact with the exhaust gas purification catalyst by disposing the exhaust gas purification catalyst according to the present invention in a circulating exhaust gas pipe may be adopted.

The exhaust gas purifying catalyst of the present invention used in the exhaust gas purifying method of the present invention has a sufficiently high PM oxidation activity, and further, a decrease in the oxidation performance of particulate matter due to ash deposition is sufficiently suppressed, It is possible to exhibit sufficiently high PM oxidation activity even after ash deposition. By contacting exhaust gas from an internal combustion engine such as a diesel engine with such an exhaust gas purifying catalyst of the present invention, The particulate matter (PM) in the exhaust gas can be sufficiently removed by oxidation to purify the exhaust gas, and the particulate matter (PM) in the exhaust gas can be sufficiently removed by oxidation after the ash is deposited. It becomes possible to purify. From such a point of view, the exhaust gas purification method of the present invention is suitably employed as a method for purifying particulate matter (PM) in exhaust gas discharged from an internal combustion engine such as a diesel engine, for example. Can do.

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

(Example 1)
Ion-exchanged water is added to barium sulfate (BaSO ₄ , manufactured by Wako Pure Chemical Industries, Ltd.), and a small nano-superdispersion machine (manufactured by Kotobuki Kogyo Co., Ltd., trade name “Wet Disperser” Nano-Superdispersion) is used with zirconia beads (diameter 50 μm). Machine milled with an ultra apex mill “UAM015”) for about 1 hour to obtain a barium sulfate slurry. When the particle size distribution of the obtained barium sulfate slurry was measured, the center particle size was about 0.5 μm. Next, alumina sol (Nissan Chemical Industry Co., Ltd., trade name “AS-520”, average particle size 10 to 20 nm) corresponding to a solid content of 8% by mass was added to and mixed with the obtained barium sulfate slurry, and cordierite Particulate filter (DPF) base material (manufactured by NGK, diameter 30 mm x length 50 mm, porosity 60%, average pore diameter 30 μm) was impregnated so as to enter the inside of the partition pores, and then extra with a suction machine The slurry was removed, dried at 110 ° C. for about 3 hours, and then fired in the atmosphere at a firing temperature of 500 ° C. for 5 hours to obtain the base material on which the barium sulfate coating layer was formed. The supported amount (coat amount) of barium sulfate per liter of the base material (DPF) was 33 g / L.

Next, the base material on which the barium sulfate coating layer is formed is impregnated with an aqueous solution in which silver sulfate (Ag ₂ SO ₄ , manufactured by Wako Pure Chemical Industries, Ltd.) is dissolved in ion-exchanged water, and the temperature is 110 ° C. After drying for about 3 hours under conditions, the catalyst for exhaust gas purification in a form supported on DPF (silver sulfate / barium sulfate (Ag ₂ SO ₄ / BaSO ₄ )) is fired at 500 ° C. in the atmosphere for 5 hours. A particulate filter with a catalyst) was produced. The supported amount of silver sulfate per liter of the base material (DPF) was 7.5 g / L in terms of silver. The supported amount of silver sulfate was 17% by mass in terms of metallic silver with respect to the total amount of the barium sulfate (carrier) and the silver sulfate (silver oxoacid salt).

(Example 2)
Exhaust gas purification catalyst (silver sulfate / strontium sulfate (Ag)) supported by DPF in the same manner as in Example 1 except that strontium sulfate (SrSO ₄ , manufactured by Wako Pure Chemical Industries, Ltd.) was used instead of barium sulfate. ₂ SO ₄ / SrSO ₄ ) catalyzed particulate filter). When the particle size distribution of the strontium sulfate slurry obtained in the manufacturing process was measured, the center particle size was about 0.6 μm. In addition, the supported amount (coat amount) of strontium sulfate per liter of the base material (DPF) is 33 g / L, and the supported amount of silver sulfate per liter of the base material (DPF) is 7.5 g / L in terms of silver. Met. The supported amount of silver sulfate was 17% by mass in terms of metallic silver with respect to the total amount of strontium sulfate (carrier) and silver sulfate (silver oxoacid salt).

(Comparative Example 1)
Calcium sulfate hemihydrate (baked Setsukou, manufactured by Wako Pure Chemical Industries, Ltd.) is calcined in the atmosphere at 500 ° C. for 3 hours, ion-exchanged water is added to the powder, and small size using zirconia beads (diameter 50 μm) A calcium sulfate slurry was obtained by milling for about 1 hour with a nano-superdisperser (manufactured by Kotobuki Kogyo Co., Ltd., trade name “Wet Disperser“ Nano Super Disperser Ultra Apex Mill ”UAM015”). When the particle size distribution of the obtained barium sulfate slurry was measured, the center particle size was about 0.7 μm. Next, an alumina sol corresponding to a solid content of 8% by mass (manufactured by Nissan Chemical Industries, trade name “AS-520”, average particle size of 10 to 20 nm) is added to and mixed with the obtained calcium sulfate slurry. Particulate filter (DPF) base material (manufactured by NGK, diameter 30 mm x length 50 mm, porosity 60%, average pore diameter 30 μm) was impregnated so as to enter the inside of the partition pores, and then extra with a suction machine The slurry was removed, dried at 110 ° C. for about 3 hours, and then fired in the atmosphere at a firing temperature of 500 ° C. for 5 hours to obtain the base material on which the calcium sulfate coating layer was formed. The supported amount (coat amount) of calcium sulfate per liter of the base material (DPF) was 33 g / L.

Next, the base material on which the calcium sulfate coating layer is formed is impregnated with an aqueous solution in which silver sulfate (Ag ₂ SO ₄ , manufactured by Wako Pure Chemical Industries, Ltd.) is dissolved in ion-exchanged water, and the temperature is 110 ° C. After drying for about 3 hours under the conditions, the catalyst for comparison (a particulate filter with silver sulfate / calcium sulfate (Ag ₂ SO ₄ / CaSO ₄ ) catalyst) is manufactured by firing at 500 ° C. in the atmosphere for 5 hours. did. The supported amount of silver sulfate per liter of the base material (DPF) was 7.5 g / L in terms of silver. The supported amount of silver sulfate was 17% by mass in terms of metallic silver with respect to the total amount of calcium sulfate and silver sulfate.

(Comparative Example 2)
Example 1 was used except that silver nitrate (manufactured by Wako Pure Chemical Industries, Ltd.) was used instead of silver sulfate and the base material on which the barium sulfate coating layer was formed was impregnated with an aqueous solution in which the silver nitrate was dissolved. Thus, a comparative catalyst (particulate filter with silver / barium sulfate (Ag / BaSO ₄ ) catalyst) was prepared. When the particle size distribution of the barium sulfate slurry obtained in the process of preparing the comparative catalyst was measured, the center particle size was about 0.5 μm. Further, the supported amount (coat amount) of barium sulfate per liter of the base material (DPF) was 33 g / L, and the supported amount of silver per liter of the base material (DPF) was 7.5 g / L. The supported amount of silver was 19% by mass with respect to the total amount of barium sulfate and silver. In the process of preparing the comparative catalyst, it was confirmed that silver nitrate was decomposed into silver and nitrate ions were removed by firing at 500 ° C. in the atmosphere.

(Comparative Example 3)
Ceria sol (manufactured by Taki Chemical Co., Ltd., trade name “Nidoral”, model number “U-15”, CeO ₂ content 15% by mass, colloidal particle diameter of about 8 nm) and a cordierite particulate filter (DPF) substrate ( After impregnation so as to enter the inside of the partition pores having a diameter of 30 mm × length of 50 mm, porosity of 60%, average pore diameter of 30 μm, manufactured by NGK, Ltd., excess slurry was removed with a suction machine, and about 110 ° C. After drying for 3 hours, the substrate on which a coat layer of ceria (CeO ₂ ) was formed was obtained by firing at a firing temperature of 500 ° C. in the atmosphere for 5 hours. The loading amount (coating amount) of ceria per liter of the base material (DPF) was 60 g / L.

Next, the base material on which the ceria coat layer is formed is impregnated with an aqueous solution in which silver nitrate (manufactured by Wako Pure Chemical Industries, Ltd.) is dissolved in ion-exchanged water, dried at 110 ° C. for about 3 hours, A comparative catalyst (a particulate filter with silver / ceria (Ag / CeO ₂ ) catalyst) was produced by firing at a firing temperature of 500 ° C. for 5 hours. The amount of silver supported per liter of the base material (DPF) was 7.5 g / L. Further, the supported amount of silver was 11% by mass with respect to the total amount of CeO ₂ and silver. In the process of preparing the comparative catalyst, it was confirmed that silver nitrate was decomposed into silver and nitrate ions were removed by firing at 500 ° C. in the atmosphere.

(Comparative Example 4)
A comparative catalyst (silver / alumina (Ag / Ag /)) was used in the same manner as in Comparative Example 3 except that alumina sol (manufactured by Nissan Chemical Industries, trade name “AS-520”, average particle size 10 to 20 nm) was used instead of ceria sol. Al ₂ O ₃ ) catalyst particulate filter) was prepared. The amount of alumina supported (coat amount) per 1 L of the substrate (DPF) was 30 g / L, and the amount of silver supported per 1 L of the substrate (DPF) was 7.5 g / L. The amount of silver supported was 20% by mass with respect to the total amount of alumina and silver. In the process of preparing the comparative catalyst, it was confirmed that silver nitrate was decomposed into silver and nitrate ions were removed by firing at 500 ° C. in the atmosphere.

(Comparative Example 5)
Alumina sol (manufactured by Nissan Chemical Industries, trade name “AS-520”, average particle size 10-20 nm) is a cordierite particulate filter (DPF) base material (manufactured by NGK, diameter 30 mm × length 50 mm, After impregnation so as to enter the inside of the partition pores having a porosity of 60% and an average pore diameter of 30 μm, the excess slurry is removed with a suction machine, dried at 110 ° C. for about 3 hours, and then fired at 500 ° C. in the atmosphere. By firing at a temperature for 5 hours, the above-mentioned base material on which a coat layer of alumina (Al ₂ O ₃ ) was formed was obtained. The amount of alumina supported (coat amount) per liter of the base material (DPF) was 30 g / L.

Next, a platinum dinitrodiammine nitric acid (Pt (NH ₃ ) ₂ (NO ₂ ) ₂ / HNO ₃ ) aqueous solution in which platinum is dissolved and palladium are dissolved in the base material on which the alumina coat layer is formed. A predetermined amount of palladium nitrate (Pd (NO ₃ ) ₂ ) aqueous solution is impregnated, platinum and palladium are supported by a selective adsorption method, dried at 110 ° C. for about 3 hours, and then fired at a firing temperature of 500 ° C. in the atmosphere for 5 hours. As a result, a comparative catalyst (platinum / palladium / alumina (Pt—Pd / Al ₂ O ₃ ) catalyst-attached particulate filter) was produced. The supported amount of platinum and palladium per liter of the base material (DPF) was 0.6 g / L for platinum and 0.3 g / L for palladium. The supported amounts of platinum and palladium were 1.9% by mass for platinum and 0.97% by mass for palladium, respectively, with respect to the total amount of alumina, platinum and palladium.

(Comparative Example 6)
A cordierite particulate filter (DPF) base material (manufactured by NGK, diameter 30 mm x length 50 mm, porosity 60%, average pore diameter 30 μm) is directly used as a particulate filter for comparison (no catalyst supported) )Using.

[Evaluation of characteristics of catalysts obtained in Examples 1 and 2 and Comparative Examples 1 to 6]
<PM oxidation activity test>
Using the exhaust gas-purifying catalyst (catalyst filter with catalyst) obtained in Examples 1 and 2 and the catalyst for comparison (particulate filter with catalyst or particulate filter) obtained in Comparative Examples 1 to 6, respectively, PM oxidation activity was measured as follows.

That is, first, particulate matter (PM) generated by using a PM adhesion test combustion particle generator (Combustion Aerosol Standard; CAST, Matter Engineering) is used as air (20 L / min) at room temperature (25 ° C.). The catalyst obtained in Examples 1 and 2 and Comparative Examples 1 to 2 were passed through the particulate filter with catalyst or the particulate filter obtained in Examples 1 to 2 and Comparative Examples 1 to 6 together. The PM was adhered to each of the comparative catalysts obtained in 6 (PM adhesion treatment). Note that the PM adhesion amount was 2 g / L in all cases.

Next, a particulate filter with catalyst or particulate filter with PM attached is installed in a fixed bed flow type reactor (product name “CATA-5000”, manufactured by Best Sokki Co., Ltd.), and the catalyst input gas temperature is used as a pretreatment. N ₂ gas was supplied at 500 L for 15 minutes at 15 L / min, and then cooled to room temperature.

Subsequently, the supply gas was switched to 15 L / min of simulated exhaust gas composed of O ₂ (10%), H ₂ O (10%) and N ₂ (remainder), and from 200 ° C. to 720 ° C. at a rate of temperature increase at 20 ° C./min. The temperature was raised, and the amount of PM oxidation was calculated from the CO ₂ and CO concentrations in the output gas from the sample. As an index of the PM oxidation activity, the temperature at which 50% of the PM adhesion amount was oxidized, that is, the 50% PM oxidation temperature was used. It can be said that the lower the 50% PM oxidation temperature, the higher the PM oxidation activity.

The results obtained are shown in Table 1. In addition, as an evaluation result of the PM oxidation activity of the initial catalyst, the initial exhaust gas purification catalyst (catalyst particulate filter) obtained in Examples 1 and 2 and the initial comparative catalyst obtained in Comparative Examples 1 to 6 were used. A graph showing the 50% PM oxidation temperature in (a particulate filter with a catalyst or a particulate filter) is shown in FIG.

<Ash resistance test>
Using the exhaust gas-purifying catalyst (catalyst filter with catalyst) obtained in Examples 1 and 2 and the catalyst for comparison (particulate filter with catalyst or particulate filter) obtained in Comparative Examples 1 to 6, respectively, PM oxidation activity after ash deposition and after ash deposition-heat treatment was measured as follows.

That is, first, calcium sulfate 0.5 hydrate (trade name “baked gypsum” manufactured by Wako Pure Chemical Industries, Ltd.) was fired in the atmosphere at 700 ° C. for 5 hours to obtain a simulated ash powder. This powder was dispersed in 33 L / min of air using an aerosol generator (trade name “RGB-1000” manufactured by PALAS), and the gas containing simulated ash of 18 L / min was used as the above Examples 1-2 and It was passed through the particulate filter with catalyst or the particulate filter obtained in Comparative Examples 1-6. The processing time was 7 hours. The ash deposition amount was about 10.5 g / L per volume of the substrate.

Next, the PM oxidation activity test was carried out under the same conditions for the catalyst-attached particulate filters or particulate filters of Examples 1-2 and Comparative Examples 1-6 after ash deposition. The obtained result is defined as PM oxidation activity after ash deposition.

Next, this sample was heat-treated at 600 ° C. for 5 hours in an air stream containing 1 L / min of H ₂ O (3%). And said PM oxidation activity test was further implemented on the same conditions, respectively. The obtained result is defined as PM oxidation activity after ash deposition-heat treatment.

Table 1 shows the results obtained as described above. Further, as an evaluation result of the PM oxidation activity of the catalyst after ash deposition and ash deposition-heat treatment, the exhaust gas purifying catalyst (catalyst particulate filter with catalyst) obtained in Examples 1 and 2 after ash deposition and ash deposition-heat treatment was obtained. ) And Comparative Examples 1 to 6 are graphs showing the 50% PM oxidation temperature of the comparative catalyst (catalyzed particulate filter or particulate filter) after ash deposition and after ash deposition-heat treatment, as shown in FIG.

<Evaluation results>
As is clear from the results described in Table 1 and FIGS. 1 and 2, the exhaust gas purifying catalysts of Examples 1 and 2 of the present invention have sufficiently high PM oxidation activity and particles due to ash deposition. It has been confirmed that the catalyst is an exhaust gas purifying catalyst that sufficiently suppresses the deterioration of the oxidation performance of the particulate matter and can exhibit sufficiently high PM oxidation activity even after ash deposition.

As is clear from the results shown in FIG. 1, the particulate filters with catalysts of Examples 1 and 2 and Comparative Examples 1 to 4 have a 50% PM oxidation temperature as compared with the particulate filter of Comparative Example 6. The temperature was lowered. That is, it can be said that these particulate filters with catalyst catalyze PM oxidation. On the other hand, the 50% PM oxidation temperature of the particulate filter with catalyst of Comparative Example 5 is almost the same as that of Comparative Example 6. Under the present experimental conditions, Pt—Pd / Al ₂ O ₃ has almost catalytic activity for PM oxidation. It was confirmed not to show. Further, the particulate filter with catalyst of Examples 1 and 2 showed the highest PM oxidation activity among all the samples, and Ag ₂ SO ₄ supported on BaSO ₄ and SrSO ₄ supports showed particularly high PM oxidation activity. Expression was confirmed.

Further, as is apparent from the results shown in FIG. 2, the 50% PM oxidation temperature of the particulate filter with catalyst of Comparative Examples 2 and 4 is the same for both comparative catalysts after ash deposition and ash deposition-heat treatment. It became substantially the same as Comparative Example 6. That is, it was confirmed that these particulate filters with a catalyst lose catalytic activity once the ash is deposited. On the other hand, in the particulate filters with catalysts of Examples 1 and 2 and Comparative Examples 1 and 3, the 50% PM oxidation temperature after ash deposition was lower than that of Comparative Example 6, and ash was deposited on the catalyst. It can also be said that it can provide a catalytic action. After ash deposition, the catalyzed particulate filters of Examples 1 and 2 showed the highest PM oxidation activity among all samples. This is considered that during the PM oxidation activity test, part of Ag ₂ SO ₄ supported on the BaSO ₄ or SrSO ₄ carrier moved to the ash particles and expressed the PM oxidation activity on the ash. Further, the exhaust gas purifying catalyst (particulate filter with catalyst) of Examples 1 and 2 after the ash deposition-heat treatment had higher PM oxidation activity than that after the ash deposition, and almost the same activity as the initial stage. This is presumably because Ag ₂ SO ₄ further moved to the ash particles by the heat treatment, and the number of active sites that express PM oxidation activity on the ash increased. From the above, it was confirmed that Ag ₂ SO ₄ supported on BaSO ₄ or SrSO ₄ carrier has particularly high ash resistance.

From the above results, an exhaust gas purification catalyst in which a silver oxo acid salt is supported on a support containing at least one selected from the group consisting of barium oxo acid salt and strontium oxo acid salt can be sufficiently obtained. It has been confirmed that it has a high level of PM oxidation activity, and that the deterioration of the oxidation performance of the particulate matter due to ash deposition is sufficiently suppressed, and that it exhibits sufficiently high PM oxidation activity even after ash deposition. From this, it was confirmed that the exhaust gas purifying catalyst of the present invention is useful as a catalyst for oxidizing PM.

As described above, according to the present invention, the present invention has a sufficiently high PM oxidation activity, and the deterioration of the oxidation performance of the particulate matter due to the ash deposition is sufficiently suppressed, and even after the ash deposition. It is possible to provide an exhaust gas purification catalyst capable of exhibiting a high degree of PM oxidation activity, an exhaust gas purification filter using the same, and an exhaust gas purification method.

Therefore, the exhaust gas purifying catalyst of the present invention, the exhaust gas purifying filter and the exhaust gas purifying method using the same, a PM oxidation catalyst for purifying particulate matter contained in exhaust gas from an internal combustion engine such as a diesel engine, It is particularly useful as the exhaust gas purification filter or exhaust gas purification method used.

Claims

A carrier comprising at least one selected from the group consisting of barium oxoacid salt and strontium oxoacid salt, and a silver oxoacid salt supported on the carrier,
The barium oxoacid salt is an oxoacid salt containing at least one selected from the group consisting of boron, phosphorus and sulfur,
The strontium oxoacid salt is an oxoacid salt containing at least one selected from the group consisting of boron, phosphorus and sulfur,
The silver oxo acid salt is an oxo acid salt containing at least one selected from the group consisting of phosphorus and sulfur.
Exhaust gas purification catalyst.
The barium oxoacid salt is at least one selected from the group consisting of barium sulfate (BaSO 4 ) and barium sulfite (BaSO 3 );
2. The exhaust gas purifying catalyst according to claim 1, wherein the strontium oxoacid salt is at least one selected from the group consisting of strontium sulfate (SrSO 4 ) and strontium sulfite (SrSO 3 ).
The exhaust gas purifying catalyst according to claim 1 or 2, wherein the silver oxo acid salt is at least one selected from the group consisting of silver sulfate (Ag 2 SO 4 ) and silver sulfite (Ag 2 SO 3 ). .
The amount of the silver oxoacid salt supported is 0.1 to 50% by mass in terms of metallic silver based on the total amount of the carrier and the silver oxoacid salt. The exhaust gas purifying catalyst according to one item.
An exhaust gas purification filter comprising a breathable base material and the exhaust gas purification catalyst according to any one of claims 1 to 4 supported on the breathable base material.
An exhaust gas purification method in which exhaust gas from an internal combustion engine is brought into contact with the exhaust gas purification catalyst according to any one of claims 1 to 4 to oxidize and remove particulate matter (PM).