JP2016215160A - Catalyst for exhaust gas purification, exhaust gas purification filter using the same, and exhaust gas purification method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To exhibit sufficiently high PM oxidation activity even after ash deposition, having sufficiently high PM oxidation activity, and sufficiently suppressing a reduction in oxidation performance of particulate matter due to ash deposition. To provide an exhaust gas purifying catalyst capable of A support comprising a barium oxoacid salt and / or a strontium oxoacid salt, and a silver oxoacid salt supported on the support, wherein the barium oxoacid salt comprises boron, phosphorus and An oxoacid salt containing at least one selected from the group consisting of sulfur, and the strontium oxoacid salt is an oxoacid salt containing at least one selected from the group consisting of boron, phosphorus and sulfur, The exhaust gas purifying catalyst, wherein the silver oxo acid salt is an oxo acid salt containing at least one selected from the group consisting of phosphorus and sulfur. [Selection figure] None

Description

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

  The gas discharged from the internal combustion engine contains harmful substances such as particulate matter (PM) generated by combustion and ash made of additives in oil. 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 as described above, the timing of the DPF regeneration process and the temperature conditions 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. Thus, in the conventional PM oxidation catalyst as described in Patent Documents 1 to 3, the purification performance could not be sufficiently exhibited due to the accumulation of ash.

  Japanese Patent Laid-Open No. 2012-219715 (Patent Document 4) discloses a support made of at least one metal salt selected from the group consisting of Ca sulfate and phosphate, and silver supported on the support. 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-mentioned object, the present inventors have surprisingly realized that a silver oxoacid salt is supported on a carrier comprising a barium oxoacid salt and / or a strontium oxoacid salt. The exhaust gas-purifying catalyst obtained in the present invention has sufficiently high PM oxidation activity, and the deterioration of particulate matter oxidation performance due to ash deposition is sufficiently suppressed, and sufficiently advanced PM oxidation even after ash deposition. It has been found that the activity can be exhibited, and the present invention has been completed.

  That is, the exhaust gas purifying catalyst of the present invention comprises a carrier comprising a barium oxoacid salt and / or a strontium oxoacid salt, and a silver oxoacid salt carried on the carrier, the barium oxoacid The salt is an oxo acid salt containing at least one selected from the group consisting of boron, phosphorus and sulfur, and the strontium oxo acid salt is at least one selected from the group consisting of boron, phosphorus and sulfur 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 oxo acid salt is 1 to 50% by mass in terms of metallic silver with respect to the total amount of the carrier and the silver oxo acid salt. Is preferred.

  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 a gas permeable substrate.

  The exhaust gas purification method of the present invention is a method characterized in that particulate matter (PM) is oxidized and removed by bringing exhaust gas from an internal combustion engine into contact 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 comprises a carrier composed of the barium oxoacid salt and / or strontium oxoacid salt, and the silver oxoacid salt 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 invention is activated by giving an electron to the silver ion (Ag ⁺ ) in the silver oxo acid salt. By receiving electrons from particulate matter (PM, mainly carbon: C), carbon dioxide (CO ₂ ) is obtained. 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 coming into 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 comprises the barium oxoacid salt and / or the strontium oxoacid salt, and the barium (Ba) or strontium (Sr) oxoacid salt of such a carrier. Since the compound has moderate basicity / acidity, the present inventors infer that the above-mentioned 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 is deposited on an exhaust gas purifying catalyst or a particulate filter. The present inventors speculate that

  As a result, a sufficiently high PM oxidation activity can be achieved, and further, a reduction in the oxidation performance of particulate matter due to ash deposition can be sufficiently suppressed, and a sufficiently high PM oxidation activity can be achieved even after ash deposition. The present inventors speculate that this can be achieved.

  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.

It is a graph which shows the initial 50% PM oxidation temperature of the catalyst for exhaust gas purification obtained in Examples 1-2 and Comparative Examples 1-6. It is a graph which shows the 50% PM oxidation temperature of the catalyst for exhaust gas purification after the ash deposition obtained in Examples 1-2 and Comparative Examples 1-6 and after the ash deposition-heat treatment.

  Hereinafter, the present invention will be described in detail with reference to 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 comprising a barium oxoacid salt and / or a strontium oxoacid salt, and a silver oxoacid salt carried on the carrier, wherein the barium oxoacid salt comprises An oxoacid salt comprising at least one selected from the group consisting of boron, phosphorus and sulfur, wherein the strontium oxoacid salt includes at least one selected from the group consisting of boron, phosphorus and sulfur The silver oxoacid salt is an oxoacid salt containing at least one selected from the group consisting of phosphorus and sulfur. The exhaust gas purifying catalyst of the present invention is obtained by supporting the silver oxo acid salt as an active species on the support composed of such barium oxo acid salt and / or strontium oxo acid salt. It is possible to exhibit 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 will be possible to demonstrate. 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 a barium oxoacid salt and / or a strontium oxoacid salt, and the barium oxoacid salt comprises at least one selected from the group consisting of boron, phosphorus and sulfur. It is necessary that the strontium oxoacid salt is an oxoacid salt containing at least one selected from the group consisting of boron, phosphorus and sulfur. The carrier composed of such barium oxoacid salt and / or strontium oxoacid salt is not particularly limited except that it is an oxoacid salt containing at least one selected from the group consisting of boron, phosphorus and sulfur. Here, “consisting of barium oxoacid salt and / or strontium oxoacid salt” means that the carrier is composed only of the barium oxoacid salt and / or strontium oxoacid salt, or mainly The barium oxoacid salt and / or the strontium oxoacid salt means that the composition contains other components within a range not impairing the effects of the present invention. 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 the barium oxoacid salt and / or the strontium oxoacid salt in the carrier is preferably 50% by mass or more, more preferably 80% by mass or more with respect to 100% by mass of the total mass of the carrier. More preferably. When the content of the barium oxoacid salt and / or the strontium oxoacid salt in the 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 ).

  Furthermore, examples of components other than the barium oxoacid salt and strontium oxoacid salt 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 ( Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), magnesium (Mg), calcium (Ca), scandium (Sc), vanadium (V) and other rare earths, alkali metals, alkalis Metal oxides such as earth metals and transition metals can be used.

In addition, 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, and those having a conventionally known shape such as a ring shape, a spherical shape, a cylindrical shape, and 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, 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.

  The method for producing such a carrier is not particularly limited, and a known method capable of producing a carrier comprising the barium oxoacid salt and / or strontium oxoacid salt may be appropriately used. it can. 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 the carrier composed of the barium oxoacid salt and / or the strontium oxoacid salt, and is selected from the group consisting of phosphorus and sulfur. It needs to be an oxo acid salt containing one species. 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 may be an oxoacid salt similar to the oxoacid salt in the carrier composed of the barium oxoacid salt and / or the strontium oxoacid acid salt. It may be an acid 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. It is preferably 0.1 to 50% by mass in terms of conversion, 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 can be calculated, for example, from the line width of the 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, as a method of supporting the silver oxoacid salt on the carrier composed of such barium oxoacid salt and / or strontium oxoacid salt, although not particularly limited, a known method can be appropriately used, For example, by using a dispersion or sol of a silver oxoacid salt or a precursor thereof, a method of coating a carrier made of barium oxoacid salt and / or strontium oxoacid salt (after that, calcining if necessary) It is possible to appropriately employ a method of supporting a carrier made of barium oxoacid salt and / or strontium oxoacid salt by using a vapor deposition method (for example, chemical vapor deposition method, physical vapor deposition method, sputter vapor deposition method) or the like. it can.

(Exhaust gas purification catalyst)
The exhaust gas purifying catalyst in the present invention comprises a carrier comprising the above-mentioned barium oxoacid salt and / or strontium oxoacid salt, and the above-mentioned silver oxoacid salt carried on the carrier. There is no particular limitation on the form, but it may be a pellet-shaped pellet catalyst or the like, or a form 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 used as appropriate. For example, the carrier composed of the barium oxoacid salt and / or the strontium oxoacid salt is used as the above-mentioned method. It is produced by a step of impregnating an aqueous solution containing silver oxo acid salt ions and the like, and a step of heating and baking. In the impregnation, specifically, a solution containing the silver oxoacid salt in a predetermined concentration is brought into contact with the carrier composed of the barium oxoacid salt and / or the strontium oxoacid salt. It is possible to employ a method in which a solution containing a predetermined amount of the silver oxoacid salt is impregnated (supported) on the carrier and then heated and fired.

  In addition, the heating and baking (baking step) after impregnating such a silver oxo acid salt may be performed in the air. Moreover, as a baking temperature in such a baking process, 200-700 degreeC is preferable. 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 composed of barium oxoacid salt and / or strontium oxoacid salt tends to decrease, and this tends to decrease the oxidation activity. The firing time is preferably 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 is characterized in that the exhaust gas purification catalyst of the present invention is supported on a gas permeable substrate (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 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.

  Moreover, as such an exhaust gas purification filter, it is preferable that the coat layer by the exhaust gas purification catalyst of the present invention is formed, and the thickness of the coat layer is preferably 0.025 to 25 μm. It is more preferable that it is 05-10 micrometers. When the thickness of the coat layer is less than the lower limit, the surface of the filter is sufficiently covered with a catalyst comprising a carrier comprising the barium oxoacid salt and / or strontium oxoacid salt and a silver oxoacid salt carried on the carrier. The contact point with the particulate matter tends to be reduced and it becomes difficult to impart sufficiently high oxidation performance. On the other hand, when the upper limit is exceeded, the barium oxoacid salt and / or Or the pores of the filter are blocked by a catalyst comprising a carrier made of strontium oxoacid salt and a silver oxoacid salt carried on the carrier, and the pressure loss of exhaust gas tends to increase and the engine efficiency tends to decrease. is there.

  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 It is preferable that it is 1-300g with respect to 1 liter of volume of a material, and it is more preferable that it is 5-100g. 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.

  Moreover, as such an exhaust gas purification filter, a filter having a porosity of 30 to 80% (more preferably 40 to 65%) is preferable. 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 purification filter, the method for supporting the exhaust gas purification catalyst of the present invention on the breathable base material is not particularly limited. For example, the barium oxoacid salt and / or the strontium oxooxide is previously used. A catalyst comprising an acid salt carrier and a silver oxoacid salt supported on the carrier is prepared, and the catalyst is supported on a breathable substrate, or the carrier is supported on the breathable substrate. And a carrier made of the barium oxoacid salt and / or the strontium oxoacid salt, and A method of supporting a catalyst comprising a silver oxoacid salt supported on a carrier on a filter can be appropriately employed. 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 particulate matter may be used as long as the effects of the present invention are not impaired.

[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 characterized in that exhaust gas from an internal combustion engine 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 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.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.

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) 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 then 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, alumina sol (Nissan Chemical Industry Co., Ltd., trade name “AS-520”, average particle size of 10 to 20 nm) corresponding to a solid content of 8% by mass was added to and mixed with the obtained calcium 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 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 of 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) ceria sol is a cordierite particulate filter (DPF) substrate (manufactured by NGK, diameter 30 mm × length 50 mm). And impregnating so as to enter inside the pores of the partition wall having a porosity of 60% and an average pore diameter of 30 μm), then removing excess slurry with a suction machine, drying at 110 ° C. for about 3 hours, By baking at a baking temperature for 5 hours, the 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. Thus, a comparative catalyst (a 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 × length 50 mm, porosity 60%, average pore diameter 30 μm) was used as a comparative particulate filter.

[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-attached particulate filter) obtained in Examples 1-2 and the comparative catalyst (catalyst-attached particulate filter or particulate filter) obtained in Comparative Examples 1-6, respectively, PM oxidation activity was measured as follows.

  That is, first, particulate matter (PM) generated using a PM adhesion test combustion particle generator (Combustion Aerosol Standard; CAST, manufactured by Matter Engineering Co., Ltd.), air (20 L / min) at room temperature (25 ° C.) The catalyst obtained in Examples 1 and 2 and Comparative Examples 1 and 2 by passing through the particulate filter with catalyst or the particulate filter obtained in Examples 1 and 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, the 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.) 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 obtained results are shown in Table 1. In addition, as the PM oxidation activity evaluation results of the initial catalyst, the initial exhaust gas purification catalyst (catalyst particulate filter) obtained in Examples 1-2 and the initial comparative catalyst obtained in Comparative Examples 1-6 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-attached particulate filter) obtained in Examples 1-2 and the comparative catalyst (catalyst-attached particulate filter or particulate filter) obtained in Comparative Examples 1-6, respectively, PM oxidation activity after ash deposition and after ash deposition-heat treatment was measured as follows.

  That is, first, calcium sulfate hemihydrate (manufactured by Wako Pure Chemical Industries, Ltd., trade name “baked gypsum”) 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 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 performed under the same conditions on 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 for 5 hours under a temperature condition of 600 ° C. 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.

  The results obtained as described above are shown in Table 1. 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) after ash deposition and after ash deposition-heat treatment obtained in Examples 1-2. 2) and a graph showing the 50% PM oxidation temperature of the comparative catalyst (catalyst-attached particulate filter or particulate filter) after ash deposition and ash deposition-heat treatment obtained in Comparative Examples 1 to 6 are shown in FIG.

<Evaluation results>
As is apparent from the results shown 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 described in FIG. 1, the particulate filters with catalysts of Examples 1 and 2 and Comparative Examples 1 to 5 have a 50% PM oxidation temperature as compared with the particulate filter of Comparative Example 7. 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 6 is almost the same as that of Comparative Example 7, and Pt—Pd / Al ₂ O ₃ exhibits almost catalytic activity for PM oxidation under the present experimental conditions. It was confirmed not to show. Moreover, 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 or SrSO ₄ support showed particularly high PM oxidation activity. Expression was confirmed.

Further, as is clear from the results shown in FIG. 2, the 50% PM oxidation temperature of the particulate filter with catalyst of Comparative Examples 2, 3 and 5 is for comparison after either ash deposition or after ash deposition-heat treatment. The catalyst was almost the same as in Comparative Example 7. 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 4, the 50% PM oxidation temperature after ash deposition was lower than that of Comparative Example 7, 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, the catalyst for exhaust gas purification in which a silver oxo acid salt is supported on a carrier made of barium oxo acid salt and / or strontium oxo acid salt has sufficiently high PM oxidation activity. In addition, it was confirmed that the decrease in the oxidation performance of the particulate matter due to the ash deposition was sufficiently suppressed, and a sufficiently high PM oxidation activity was exhibited even after the ash deposition. From this, it was confirmed that it 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.

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.

(Comparative Example 5)
Alumina sol (manufactured by Nissan Chemical Industries, trade name “AS-520”, average particle size of 10-20 nm ) is a cordierite particulate filter (DPF) substrate (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.

Then the sample in a stream of air containing 1L / min _H 2 O (3%), was heat-treated for 5 hours at a temperature of 600 ° C.. 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.

As is clear from the results shown in FIG. 1, the particulate filters with catalysts of Examples 1-2 and Comparative Examples 1-4 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, and Pt—Pd / Al ₂ O ₃ has almost catalytic activity for PM oxidation under the present experimental conditions. It was confirmed not to show. Moreover, 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 or SrSO ₄ support showed particularly high PM oxidation activity. Expression was confirmed.

Further, as is apparent from the results described in FIG. 2, 50% PM oxidation temperature of the catalyst with a particulate filter of Comparative Example 2及 beauty 4 after Ash deposition and ash deposition - catalyst for comparison or after heat treatment Was almost 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.

Claims (6)

A support comprising a barium oxoacid salt and / or a strontium oxoacid salt, and a silver oxoacid salt supported on the support,
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.
An exhaust gas purifying catalyst characterized by that. 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 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 ). Exhaust gas purification catalyst.   The amount of the silver oxoacid salt supported is 1 to 50% by mass in terms of metallic silver with respect to the total amount of the carrier and the silver oxoacid salt. The exhaust gas purifying catalyst according to any one of the above.   An exhaust gas purification filter comprising the exhaust gas purification catalyst according to any one of claims 1 to 4 supported on a breathable base material.   An exhaust gas purification method comprising contacting exhaust gas from an internal combustion engine with the exhaust gas purification catalyst according to claim 1 to oxidize and remove particulate matter (PM).