JP6061406B2 - PM oxidation catalyst, exhaust gas purification filter and exhaust gas purification method using the same - Google Patents

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, ash composed 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. Since PM collected by the DPF causes an increase in pressure loss, the DPF is regenerated by periodically raising the temperature to a high temperature and burning the PM. At this time, it is desirable to regenerate at a lower temperature in order to improve fuel consumption and durability of the material, and a PM oxidation catalyst is supported on the DPF.

As such a PM oxidation catalyst, Japanese Unexamined Patent Application Publication No. 2009-45584 (Patent Document 1) discloses an exhaust gas purification catalyst for purifying particulate matter in exhaust gas discharged from an internal combustion engine. A complex oxide having an oxygen releasing ability (LaMnO ₃ , CeZrO ₂ , CoTa ₂ O ₆₎ containing at least two elements selected from the group consisting of group metal elements, transition metal elements, group 12 elements, and group 13 elements Etc.), and an exhaust gas purification catalyst having Ag and noble metals (Ru, Pd, Pt, etc.) co-supported on the composite oxide, and an exhaust gas purification device using the same. However, the exhaust gas purifying catalyst disclosed in Patent Document 1 has a problem that the Ag catalyst is poisoned by a sulfur component contained in the fuel or oil, and the activity is significantly reduced. In particular, the catalyst using a highly basic carrier such as ceria shows very high activity at the beginning, but the activity is significantly reduced by the sulfur component. For example, the PM oxidation activity when exposed to sulfur-containing gas is high. It was not enough.

  Japanese Patent Laid-Open No. 2011-218295 (Patent Document 2) discloses an exhaust gas that is disposed in an exhaust gas passage of an internal combustion engine and collects particulates in the exhaust gas discharged from the internal combustion engine to purify the exhaust gas. The purification filter includes an outer peripheral wall, a porous cell wall disposed in a polygonal lattice shape in the outer peripheral wall, and a plurality of cells partitioned in the cell wall, A plug portion closes the downstream end of the incoming gas side cell that serves as the inflow side passage through which the exhaust gas flows and the upstream end of the outgas side cell that serves as the discharge side passage that discharges the exhaust gas that has passed through the cell wall. The cell wall includes a PM combustion catalyst made of a catalyst material in which Ag is dispersed in layered alumina containing Ag, and an oxidation catalyst that oxidizes at least CO in the exhaust gas. Cage The exhaust gas characterized in that the PM combustion catalyst is supported on the wall surface of the inlet gas side cell without supporting the oxidation catalyst, and at least the oxidation catalyst is supported on the wall surface of the outlet gas side cell. A purification filter is disclosed. However, even in the exhaust gas purification filter disclosed in Patent Document 2, the Ag catalyst supported on alumina has low dispersibility and the Ag particles become coarse, so that the contact property with PM becomes low. For this reason, the PM oxidation activity when exposed to a gas containing sulfur is not sufficient, for example, the activity decreases when it is changed to silver sulfate by sulfur poisoning.

  Furthermore, Japanese Patent Laid-Open No. 06-55075 (Patent Document 3) describes at least one metal selected from platinum, palladium, rhodium, gold, silver, ruthenium, iridium, nickel, cerium, cobalt, copper, and strontium. In addition, an exhaust gas purifying catalyst having a salt or oxide supported on a phosphate is disclosed. However, even in the exhaust gas purifying catalyst disclosed in Patent Document 3, a metal having catalytic activity such as silver supported on a phosphate carrier such as aluminum phosphate has low dispersibility, such as silver particles. Since the active metal particles become coarse, the contact property with PM becomes low. For this reason, PM oxidation activity when exposed to a gas containing sulfur was not sufficient.

  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, so that there is a need for exhaust gas purification catalysts that can exhibit sufficiently higher PM oxidation activity even when exposed to sulfur-containing gas. It has become.

JP 2009-45584 A JP 2011-218295 A Japanese Patent Laid-Open No. 06-55075 JP 2012-219715 A

  The present invention has been made in view of the above-described problems of the prior art, and uses an exhaust gas purifying catalyst capable of exhibiting sufficiently high PM oxidation activity even when exposed to a gas containing sulfur, and the same. An object is to provide an exhaust gas purification filter and an exhaust gas purification method.

  As a result of intensive studies to achieve the above object, the inventors of the present invention surprisingly obtain exhaust gas purification by supporting a silver-containing substance and a phosphoric acid-containing substance on a support mainly composed of alumina. It has been found that even if the catalyst is exposed to sulfur-containing gas, it can exhibit high PM oxidation activity, and the present invention has been completed.

That is, the PM oxidation catalyst of the present invention is characterized by comprising a carrier mainly composed of alumina, and a silver-containing substance and a phosphoric acid-containing substance supported on the carrier.

In the PM oxidation catalyst of the present invention, it is preferable that silver phosphate is supported on the carrier as the silver-containing substance and the phosphoric acid-containing substance.

In the PM oxidation catalyst of the present invention, the atomic ratio (P / Ag) of phosphorus (P) to silver (Ag) in the PM oxidation catalyst is preferably 0.2 to 4.

Furthermore, in the PM oxidation catalyst of the present invention, the supported amount of the silver-containing material is 3 to 50% by mass in terms of metallic silver with respect to the total amount of the carrier, the silver-containing material, and the phosphoric acid-containing material. It is preferable.

In the PM oxidation catalyst of the present invention, the atomic ratio (P / Al) of phosphorus (P) to aluminum (Al) in the PM oxidation catalyst is 0.15 to 0.5, and the phosphoric acid It is preferable that the contained material contains an aluminum phosphate crystal phase.

The exhaust gas purification filter of the present invention is characterized in that the PM oxidation catalyst of the present invention is supported on a gas permeable substrate.

Moreover, the exhaust gas purification method of the present invention is a method characterized in that particulate matter (PM) is oxidized and removed by bringing the exhaust gas from the internal combustion engine into contact with the PM oxidation catalyst of the present invention.

  The reason why 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 can exhibit sufficiently high PM oxidation activity even when exposed to a gas containing sulfur is not necessarily determined. However, the present inventors speculate as follows.

  That is, in the present invention, the phosphoric acid-containing substance used by being supported on a carrier mainly composed of alumina is less susceptible to sulfur poisoning because sulfur adsorption is suppressed and sulfur poisoning is mitigated. Further, when the silver-containing substance and the phosphoric acid-containing substance used as active species coexist, high PM oxidation activity can be achieved, and sufficiently high PM oxidation activity is exhibited. In this way, by using a carrier mainly composed of alumina as a carrier and a catalyst comprising a silver-containing substance and a phosphoric acid-containing substance as active species, high PM oxidation activity is maintained even when exposed to a gas containing sulfur. It becomes possible to do. As a result, the present inventors speculate that a sufficiently high PM oxidation activity can be achieved even when exposed to a gas containing sulfur.

  According to the present invention, it is possible to provide an exhaust gas purification catalyst capable of exhibiting sufficiently high PM oxidation activity even when exposed to a gas containing sulfur, an exhaust gas purification filter and an exhaust gas purification method using the same. It becomes.

It is a graph which shows the 50% PM oxidation temperature of the catalyst for exhaust gas purification after the sulfur poisoning regeneration process obtained in Examples 1-3 and Comparative Examples 1-2. It is a graph which shows the 50% PM oxidation temperature of the catalyst for exhaust gas purification after the sulfur poisoning regeneration process obtained in Examples 4 to 6 and Comparative Examples 1 and 3. 2 is a graph showing XRD spectra of exhaust gas purifying catalysts obtained in Examples 1, 5, 6 and Comparative Example 1. FIG.

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

  First, the exhaust gas purifying catalyst of the present invention will be described. The exhaust gas purifying catalyst of the present invention comprises a support mainly composed of alumina, and a silver-containing substance and a phosphoric acid-containing substance supported on the support. By making such a support mainly composed of alumina carry a silver-containing substance and a phosphoric acid-containing substance as active species, the exhaust gas purifying catalyst of the present invention is exposed to a gas containing sulfur. It is also possible to exhibit 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 needs to be a carrier mainly composed of alumina (Al ₂ O ₃ ). Such a carrier containing alumina as a main component is not particularly limited except that it contains alumina as a main component. Here, “mainly composed of alumina” means that the carrier is composed only of alumina, or is composed mainly of alumina and includes other components. As other components, other compounds used as a carrier for an exhaust gas purifying catalyst for this type of application can be used. In the latter case, the content of alumina in the carrier is preferably 90% by mass or more, more preferably 95% by mass or more, and 98% by mass or more with respect to 100% by mass of the total mass of the carrier. Is particularly preferred. If the content of alumina in such a carrier is less than the lower limit, the additive component and silver phosphate react and the activity tends to decrease.

  The alumina in such a carrier is selected from the group consisting of boehmite type, pseudo boehmite type, χ type, κ type, ρ type, η type, γ type, pseudo γ type, δ type, θ type and α type. However, from the viewpoint of heat resistance, α-alumina and γ-alumina are preferably used, and γ-alumina having high activity is particularly preferable.

  In addition, other components other than alumina contained in the support mainly composed of alumina include, for example, yttrium (Y), lanthanum (La), praseodymium (from the viewpoint of thermal stability and catalytic activity of the support. Pr), cerium (Ce), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium ( Rare earths such as Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), scandium (Sc), vanadium (V) Metal oxides such as alkali metals, alkaline earth metals and transition metals can be used .

  Moreover, as a support | carrier which has such an alumina as a main component, from a heat resistant viewpoint, 90 mass% or more of alumina with respect to the total mass of 100 mass% of a support | carrier, yttrium (Y), lanthanum (La), Praseodymium (Pr), cerium (Ce), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), From erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), scandium (Sc) and vanadium (V) More preferred is a support comprising at least one metal oxide selected from the group consisting of

Further, the specific surface area of such a carrier mainly composed of alumina is not particularly limited, but is preferably 5 to 300 m ² / g, more preferably 10 to 200 m ² / g. When the specific surface area exceeds the upper limit, the heat resistance of the support itself decreases, and therefore the heat resistance of the catalyst tends to decrease. On the other hand, when the specific surface area is lower than the lower limit, active species (silver-containing substance and phosphoric acid-containing substance) The dispersibility tends 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.

In addition, the shape of such a carrier containing alumina as a main component is not particularly limited, and a conventionally known shape such as a ring shape, a spherical shape, a cylindrical shape, or a pellet shape can be used. In addition, it is preferable to use a particulate thing from a viewpoint that many active species (a silver containing material and phosphoric acid containing material) can be contained in a highly dispersible state. 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. . Further, the average particle size of such a carrier mainly composed of alumina can be appropriately changed by a conventional method (for example, a method of pulverizing with a mortar or a cold isostatic pressing method (CIP)). Further, after the exhaust gas purifying catalyst is manufactured, the average particle diameter of the carrier powder containing alumina as a main component in the catalyst may be changed by changing the average particle diameter of the catalyst by a usual method.

Furthermore, a method for producing such a carrier is not particularly limited, and a known method capable of producing a carrier containing alumina as a main component can be appropriately used. In addition, as such a carrier, commercially available alumina or a composite oxide containing alumina as a main component may be used, and the size may be appropriately adjusted by milling with a ball mill or the like.

(Silver-containing material)
The silver-containing material according to the present invention is an active species supported on a carrier mainly composed of alumina and needs to be a material containing silver and / or a silver compound. Such a silver-containing material is not particularly limited except that it is a material containing silver and / or a compound containing silver. Specific examples of such a silver-containing substance include silver (metal simple substance, Ag, metal silver), silver oxide, silver halide, silver carbonate, silver sulfate, silver phosphate, silver nitrate, silver chromate, Examples thereof include silver oxalate and silver ferrite. Among these, from the viewpoint of reactivity with phosphoric acid , it is preferably at least one selected from the group consisting of silver, silver oxide, silver halide, silver sulfate and silver phosphate, and the dispersibility of silver particles From the viewpoint, it is more preferably at least one selected from the group consisting of silver, silver sulfate, silver phosphate and silver nitrate.

In addition, it is preferable that the silver phosphate is carry | supported by the said support | carrier as what serves as the said silver containing substance and the said phosphoric acid containing substance. Specific examples of such silver phosphate include silver orthophosphate (Ag ₃ PO ₄ ), silver pyrophosphate (Ag ₄ P ₂ O ₇ ), silver triphosphate (Ag ₅ P ₃ O ₁₀ ), and metaphosphate. silver (AgPO _3), and the like.

The amount of the silver-containing material used in the present invention is not particularly limited, but is 3 to 50 in terms of metallic silver (Ag) with respect to the total amount of the carrier, the silver-containing material, and the phosphoric acid-containing material. The mass is preferably 5% by mass , more preferably 5-30% by mass, and particularly preferably 7-15% by mass. If the amount of such a silver-containing substance 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 upper limit is exceeded, the oxidation performance is saturated. Therefore, the cost tends to increase.

  Further, the average crystallite size (average primary particle size) of such a silver-containing substance is not particularly limited, but is preferably 0.1 to 300 nm, and more preferably 1 to 200 nm. If the average crystallite size of such a silver-containing substance is less than the lower limit, it strongly binds to the support and the activity tends to decrease. On the other hand, if it exceeds the upper limit, the number of particles contributing to the reaction decreases and the activity decreases. There is a tendency. Note that the average crystallite size (average primary particle size) of such a silver-containing substance is calculated using, for example, Scherrer's equation from the line width of the powder X-ray diffraction peak using an X-ray diffractometer. It can be measured by calculating.

(Phosphoric acid-containing substance)
The phosphoric acid-containing substance according to the present invention is an active species supported on a carrier mainly composed of alumina and needs to be a substance containing phosphoric acid and / or phosphate. Such a phosphoric acid-containing substance is not particularly limited except that it is a substance containing phosphoric acid and / or phosphate. As such a phosphoric acid-containing substance, specifically, as phosphoric acid, orthophosphoric acid (H ₃ PO ₄ ), pyrophosphoric acid (H ₄ P ₂ O ₇ ), triphosphoric acid (H ₅ P ₃ O ₁₀ ), metaphosphoric acid (HPO _3), and the like. In addition, as phosphates, orthophosphates, pyrophosphates, triphosphates, polyphosphates, metaphosphates, ultraphosphates, etc., these alkali metal salts, other metal salts, ammonium salts, etc. Can be mentioned. Among these, from the viewpoint of dispersibility of active species, at least one selected from the group consisting of orthophosphates, pyrophosphates, triphosphates and alkali metal salts thereof is preferable. Orthophosphates, pyrophosphates And at least one selected from the group consisting of these alkali metal salts.

The amount of the phosphoric acid-containing substance used in the present invention is not particularly limited, but the atomic ratio (P / Ag) of phosphorus (P) to silver (Ag) in the exhaust gas purification catalyst is 0.2. The supported amount is preferably ˜6 , more preferably 0.3˜5.5, and particularly preferably 0.4˜3. If the amount of the phosphoric acid-containing substance supported is less than the lower limit as the atomic ratio (P / Ag), the oxidation performance of the particulate matter tends to be insufficient, while If the upper limit is exceeded, the oxidation performance will be saturated and the cost tends to increase.

Further, the amount of the phosphoric acid-containing substance used in the present invention is not particularly limited, but the atomic ratio (P / Al) of phosphorus (P) to aluminum (Al) in the exhaust gas purification catalyst is 0. The loading amount is preferably 15 to 0.5 , more preferably 0.2 to 0.45, and particularly preferably 0.3 to 0.4. preferable. If the amount of the phosphoric acid-containing material supported is less than the lower limit as the atomic ratio (P / Al), the oxidation performance of the particulate material tends not to be sufficiently advanced, When the upper limit is exceeded, the specific surface area tends to decrease and the activity tends to decrease.

Furthermore, it is preferable that the phosphoric acid-containing substance as the active species supported on the carrier mainly composed of alumina according to the present invention contains a crystalline phase of aluminum phosphate (AlPO ₄ ). By including such a crystalline phase of aluminum phosphate (AlPO ₄ ), it is possible to suppress sulfur poisoning of the catalyst by suppressing sulfur components adsorbed on the carrier even when exposed to sulfur-containing gas. Become.

  In the exhaust gas purifying catalyst of the present invention, the atomic ratio (P / Al) of phosphorus (P) to aluminum (Al) in the exhaust gas purifying catalyst is 0.15 to 0.5, and More preferably, the phosphoric acid-containing substance contains an aluminum phosphate crystal phase. By using such a phosphoric acid-containing substance-supporting exhaust gas-purifying catalyst, a sufficiently higher PM oxidation activity can be exhibited even when exposed to sulfur-containing gas.

  Further, many of such phosphoric acid-containing substances are water-soluble, but the average crystallite diameter (average primary particle diameter) in the case of insoluble substances is not particularly limited, but is 0.1 to 300 nm. Is preferable, and it is more preferable that it is 1-200 nm. When the average crystallite diameter of such a phosphoric acid-containing substance exceeds the upper limit, the dispersibility tends to be lowered. Note that the average crystallite size (average primary particle size) of such a phosphoric acid-containing substance is obtained by, for example, the Scherrer's equation from the line width of the powder X-ray diffraction peak using an X-ray diffractometer. It can measure by calculating using.

  In the present invention, by using such a silver-containing substance and phosphoric acid-containing substance as active species, the phosphoric acid-containing substance used by being supported on a carrier mainly composed of alumina suppresses sulfur adsorption and sulfur poisoning. It is less susceptible to sulfur poisoning. In addition, the coexistence of the silver-containing substance and the phosphoric acid-containing substance used as active species can exhibit high PM oxidation activity and can exhibit sufficiently high PM oxidation activity. In this way, by using a carrier mainly composed of alumina as a carrier and a catalyst comprising a silver-containing substance and a phosphoric acid-containing substance as active species, high PM oxidation activity is maintained even when exposed to a gas containing sulfur. And a sufficiently high PM oxidation activity can be exhibited.

  The type of the carrier, the silver-containing substance and the phosphoric acid-containing substance supported on the carrier, etc. are determined by X-ray diffraction measurement to obtain an X-ray diffraction pattern, and the type of crystal present from the peak position. It can be confirmed by seeking.

  Further, a method for supporting such a silver-containing substance and a phosphoric acid-containing substance on a carrier mainly composed of alumina is not particularly limited, but a known method can be used as appropriate, for example, a silver-containing substance or The precursor dispersion or sol, and the phosphoric acid-containing substance or the precursor dispersion or sol are used to coat the alumina-based carrier sequentially or simultaneously (and then fired as necessary). Or a method of supporting alumina on a carrier as a main component by using a vapor deposition method (for example, chemical vapor deposition method, physical vapor deposition method, sputter vapor deposition method) or the like can be appropriately employed.

(Exhaust gas purification catalyst)
The exhaust gas-purifying catalyst in the present invention is not particularly limited as long as it comprises a carrier mainly composed of the alumina, and a silver-containing substance and a phosphoric acid-containing substance supported on the carrier. However, it may be in the form of a pellet-shaped pellet catalyst or the like, or may be supported on a filter.

(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 containing alumina as a main component has ions of silver-containing substance and phosphoric acid-containing substance. It is produced by a step of impregnating with an aqueous solution containing, etc., a step of heating and baking. The impregnation may be impregnated with an aqueous solution containing silver-containing substance and phosphoric acid-containing substance ions, or an aqueous solution containing silver-containing substance ions and an aqueous solution containing phosphoric acid-containing substance ions. May be prepared and impregnated individually or sequentially. Specifically, a solution containing a silver-containing substance and a phosphoric acid-containing substance at a predetermined concentration is brought into contact with the carrier mainly composed of alumina, thereby containing a predetermined amount of the silver-containing substance and the phosphoric acid-containing substance. It is possible to employ a method of impregnating (supporting) the solution on the carrier and then heating and baking the solution. Furthermore, as a method for producing such an exhaust gas purifying catalyst, first, an aqueous solution containing ions of a phosphoric acid-containing substance is impregnated into a carrier mainly composed of alumina as a carrier and then calcined and then phosphoric acid-containing substance. Then, the resulting phosphoric acid-containing material-supported carrier is impregnated with an aqueous solution containing silver-containing material ions, etc., and then baked to prepare a carrier containing mainly alumina as a silver-containing material and phosphoric acid. A method of supporting the contained substance can be employed.

  Moreover, you may implement the heat baking (baking process) after impregnating such a silver containing material and a phosphoric acid containing material in air | atmosphere. Moreover, as a baking temperature in such a baking process, 200-700 degreeC is preferable. When such a calcination temperature is less than the lower limit, it becomes difficult to support the silver-containing substance and the phosphoric acid-containing substance on the carrier, and there is a tendency that sufficient PM oxidation activity of the exhaust gas purifying catalyst cannot be obtained, When the upper limit is exceeded, the specific surface area of the support mainly composed of alumina tends to decrease, and the oxidation activity tends to decrease. 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-containing material and the phosphoric acid-containing material, and the oxidation activity of the obtained exhaust gas purifying catalyst (PM oxidation catalyst) tends to decrease, Even if the upper limit is exceeded, no further effect is obtained, and the cost for preparing the catalyst tends to increase.

(Exhaust gas purification equipment)
Since the exhaust gas purifying catalyst of the present invention can exhibit high PM oxidation activity against particulate matter contained in gas (exhaust gas) discharged from an internal combustion engine and oxidize and remove PM, the exhaust gas The exhaust gas purification device can be configured by arranging the exhaust gas purification catalyst so that the exhaust gas can come into contact with the purification catalyst.

  Such an exhaust gas purifying device is an exhaust gas purifying device for oxidizing and purifying particulate matter (PM) contained in the exhaust gas as long as it includes the exhaust gas purifying catalyst of the present invention. Good. In such an exhaust gas purification device, particulate matter contained in the gas (exhaust gas) discharged from the internal combustion engine is oxidized and purified (removed), so that the exhaust gas can contact the exhaust gas purification device. For example, the exhaust gas purification device may be arranged in a gas flow path in an exhaust gas pipe through which exhaust gas from an internal combustion engine flows. In addition, it does not restrict | limit especially as such an internal combustion engine, A well-known internal combustion engine can be used suitably, For example, the engine (a gasoline engine, a diesel engine, etc.) of a motor vehicle may be sufficient.

[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.

  Further, 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 035-10 micrometers. If the thickness of the coating layer is less than the lower limit, the surface of the filter cannot be sufficiently covered with a catalyst comprising a carrier mainly composed of the alumina and a silver-containing substance and a phosphoric acid-containing substance supported on the carrier, and particles However, when the upper limit is exceeded, the carrier mainly composed of alumina and the carrier are supported on the carrier. The catalyst containing the silver-containing material and the phosphoric acid-containing material is clogged with the pores of the filter, and the pressure loss of the 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 the 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 10-100g. If the amount is less than the lower limit, it tends to be difficult to exhibit sufficiently high catalyst performance. On the other hand, if the amount exceeds the upper limit, the aeration is performed by a catalyst including the support and the silver-containing substance. The pores of the conductive base material are blocked, and the pressure loss of the exhaust gas increases and the engine efficiency tends to decrease.

  Moreover, as such an exhaust gas purification filter, what has a porosity of 30 to 70% (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.

  Furthermore, 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 carrier mainly composed of the alumina and the carrier in advance. Preparation of a catalyst comprising a supported silver-containing material and phosphoric acid-containing material, a method of supporting the catalyst on a breathable substrate, a step of supporting a carrier on the breathable substrate, and the breathability And carrying the step of supporting the silver-containing substance and the phosphoric acid-containing substance on the carrier supported on the base material, and the silver-containing substance and phosphoric acid supported on the carrier. For example, a method of supporting a catalyst having a contained substance on a filter can be appropriately employed. In addition, the method for supporting the catalyst, the carrier, the silver-containing material and the phosphoric acid-containing material on the air-permeable substrate is not particularly limited, and a known method can be appropriately employed. For example, a method of coating the slurry on a breathable base material (after that, firing if necessary) can be used as appropriate. 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.

  Note that the exhaust gas purifying catalyst of the present invention used in the exhaust gas purifying method of the present invention can maintain high PM oxidation activity even when exposed to a gas containing sulfur. However, it is possible to exhibit sufficiently high PM oxidation activity. By contacting exhaust gas from an internal combustion engine such as a diesel engine with the exhaust gas purifying catalyst of the present invention, Particulate matter (PM) in the exhaust gas can be oxidized and removed to purify the exhaust gas. Furthermore, the particulate matter (PM) in the exhaust gas can be oxidized and removed sufficiently even when exposed to sulfur-containing gas. It becomes possible to purify. From such a viewpoint, the exhaust gas purification method of the present invention is preferably 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
First, an aqueous phosphate solution was prepared by dissolving 0.61 g of sodium orthophosphate (Alfa Aesar) in ion-exchanged water (200 g). Subsequently, 1.57 g of silver nitrate (manufactured by Wako Pure Chemical Industries) was dissolved in ion-exchanged water (100 g) to prepare a silver nitrate aqueous solution.

Next, 8.7 g of alumina powder (JGC Universal Co., Ltd., γ-Al ₂ O ₃ powder, TN4, specific surface area 150 m ^{2 /} g) as a carrier is impregnated with the obtained phosphate aqueous solution, While stirring this, the obtained silver nitrate aqueous solution was added to form a precipitate. Next, the obtained precipitate (precipitate) is filtered, dried at 110 ° C. overnight, and then calcined at 500 ° C. for 3 hours to carry silver phosphate (Ag ₃ PO ₄ ) on the alumina carrier. A catalyst powder was obtained. Next, this powder was mixed in a mortar and formed into a pellet shape having a particle diameter of 0.3 to 0.5 mm by a conventional method (cold isostatic pressing (CIP)), and a pellet-shaped catalyst (Ag ₃ PO ₄ / Al ₂ O ₃ ). The atomic ratio (P / Ag) of phosphorus (P) to silver (Ag) in the catalyst was 0.33 from the charged amount. Further, the supported amount of the silver-containing material was 10% by mass in terms of metallic silver (Ag) with respect to the total amount of the catalyst.

(Example 2)
In the same manner as in Example 1, except that 0.63 g of sodium pyrophosphate (Alfa Aesar) was used instead of sodium orthophosphate as the phosphate source, and the amount of alumina powder added was 8.6 g. A catalyst (Ag ₄ P ₂ O ₇ / Al ₂ O ₃ ) was obtained. The atomic ratio (P / Ag) of phosphorus (P) to silver (Ag) in the catalyst was 0.5 from the charged amount. Further, the supported amount of the silver-containing material was 10% by mass in terms of metallic silver (Ag) with respect to the total amount of the catalyst.

Example 3
Pellet shape in the same manner as in Example 1 except that 1.11 g of sodium metaphosphate (manufactured by Wako Pure Chemical Industries, Ltd.) was used instead of sodium orthophosphate as the phosphate source, and the amount of alumina powder added was 8.3 g. Catalyst (AgPO ₃ / Al ₂ O ₃ ) was obtained. The atomic ratio (P / Ag) of phosphorus (P) to silver (Ag) in the catalyst was 1.0 from the charged amount. Further, the supported amount of the silver-containing material was 10% by mass in terms of metallic silver (Ag) with respect to the total amount of the catalyst.

Example 4
First, 6.28 g of silver nitrate (manufactured by Wako Pure Chemical Industries) was dissolved in ion-exchanged water (250 g) to prepare a silver nitrate aqueous solution.

Next, the obtained silver nitrate aqueous solution is impregnated in 36.0 g of alumina powder (manufactured by JGC Universal Co., Ltd., γ-Al ₂ O ₃ powder, TN4, specific surface area 150 m ^{2 /} g) as a carrier and evaporated to dryness. And dried at 110 ° C. overnight and then calcined at 500 ° C. for 3 hours to obtain a powder carrying silver on the alumina carrier.

Next, 1.07 g of 85% phosphoric acid (manufactured by Alfa Aesar) was dissolved in ion-exchanged water (200 g) to prepare a phosphoric acid aqueous solution, which was impregnated with 10.0 g of the obtained powder and evaporated to dryness. Then, after drying at 110 ° C. overnight, firing was performed at 500 ° C. for 3 hours, and silver and phosphoric acid were supported on the alumina support to obtain catalyst powder. Next, this powder is mixed in a mortar and formed into a pellet shape with a particle diameter of 0.3 to 0.5 mm by a conventional method (cold isostatic pressing (CIP)), and a pellet-shaped catalyst (Ag + H ₃ PO ₄ / Al ₂ O ₃ ). The atomic ratio (P / Ag) of phosphorus (P) to silver (Ag) in the catalyst was 1.0 from the charged amount. Further, the supported amount of the silver-containing material was 9.4% by mass in terms of metallic silver (Ag) with respect to the total amount of the catalyst.

(Example 5)
A pellet-shaped catalyst in the same manner as in Example 4 except that the addition amount of phosphoric acid was changed so that the atomic ratio (P / Ag) of phosphorus (P) to silver (Ag) in the catalyst was 2.0. (Ag + H ₃ PO ₄ / Al ₂ O ₃ ) was obtained. The atomic ratio (P / Ag) of phosphorus (P) to silver (Ag) in the catalyst was 2.0 from the charged amount. Further, the supported amount of the silver-containing material was 8.8% by mass in terms of metallic silver (Ag) with respect to the total amount of the catalyst.

(Example 6)
First, 5.36 g of 85% phosphoric acid (manufactured by Alfa Aesar) was dissolved in ion exchange water (200 g) to prepare a phosphoric acid aqueous solution.

Next, 9.04 g of the obtained phosphoric acid aqueous solution was impregnated into alumina powder (JGC Universal Co., Ltd., γ-Al ₂ O ₃ powder, TN4, specific surface area 150 m ^{2 /} g) as a carrier, and evaporated to dryness. And dried at 110 ° C. overnight and then calcined at 500 ° C. for 3 hours to obtain a powder having phosphoric acid supported on the alumina carrier.

Next, 1.48 g of silver nitrate (manufactured by Wako Pure Chemical Industries) is dissolved in ion-exchanged water (250 g) to prepare an aqueous silver nitrate solution, which is impregnated with 11.56 g of the obtained powder and evaporated to dryness. After drying overnight at 50 ° C., it was calcined at 500 ° C. for 3 hours, and silver and phosphoric acid were supported on the alumina carrier to obtain a catalyst powder. Next, this powder was mixed in a mortar and formed into a pellet shape having a particle diameter of 0.3 to 0.5 mm by a conventional method (cold isostatic pressing (CIP)), and a pellet-shaped catalyst (Ag / ( H ₃ PO ₄ + Al ₂ O ₃ ) or Ag / H ₃ PO ₄ / Al ₂ O ₃ ). The atomic ratio (P / Ag) of phosphorus (P) to silver (Ag) in the catalyst was 5.0 from the amount charged. Further, the supported amount of the silver-containing material was 7.5% by mass in terms of metallic silver (Ag) with respect to the total amount of the catalyst.

(Comparative Example 1)
A silver nitrate aqueous solution was prepared by dissolving 6.28 g of silver nitrate (manufactured by Wako Pure Chemical Industries) in ion-exchanged water (250 g). Next, the obtained silver nitrate aqueous solution was impregnated in 36.00 g of alumina powder (manufactured by JGC Universal, γ-Al ₂ O ₃ powder, TN4, specific surface area 150 m ^{2 /} g) and evaporated to dryness. After drying overnight, it was calcined at 500 ° C. for 3 hours, and silver (Ag) was supported on the alumina powder to obtain a comparative catalyst powder. Next, this powder was mixed in a mortar and formed into a pellet shape having a particle diameter of 0.3 to 0.5 mm by a conventional method (cold isostatic pressing (CIP)), and a pellet-shaped comparative catalyst (Ag / Al ₂ O ₃ ). The atomic ratio (P / Ag) of phosphorus (P) to silver (Ag) in the catalyst was 0.0 from the charged amount. In addition, the supported amount of the silver-containing material was 10.0% by mass in terms of metallic silver (Ag) with respect to the total amount of the catalyst.

(Comparative Example 2)
Except for using 8.7 g of calcium phosphate (Ca ₃ (PO ₄ ) ₂ ) powder (made by Wako Pure Chemical Industries, specific surface area 10 m ^{2 /} g) instead of alumina powder (γ-Al ₂ O ₃ powder) as a carrier. In the same manner as in Example 1, a pellet-shaped comparative catalyst (Ag ₃ PO ₄ / Ca ₃ (PO ₄ ) ₂ ) was obtained. The atomic ratio (P / Ag) of phosphorus (P) to silver (Ag) in the catalyst was 6.5 based on the amount charged. In addition, the supported amount of the silver-containing material was 10.0% by mass in terms of metallic silver (Ag) with respect to the total amount of the catalyst.

(Comparative Example 3)
A silver nitrate aqueous solution was prepared by dissolving 1.57 g of silver nitrate (manufactured by Wako Pure Chemical Industries) in ion-exchanged water (250 g). Next, the obtained silver nitrate aqueous solution was impregnated in 9.00 g of aluminum phosphate powder (Alfa Aesar, AlPO ₄ powder, specific surface area 2.3 m ^{2 /} g), evaporated to dryness, and then at 110 ° C. overnight. After drying, firing was performed at 500 ° C. for 3 hours, and silver (Ag) was supported on the aluminum phosphate powder to obtain a comparative catalyst powder. Next, this powder was mixed in a mortar and formed into a pellet shape having a particle diameter of 0.3 to 0.5 mm by a conventional method (cold isostatic pressing (CIP)), and a pellet-shaped comparative catalyst (Ag / AlPO ₄ ). The atomic ratio (P / Ag) of phosphorus (P) to silver (Ag) in the catalyst was 8.0 from the amount charged. In addition, the supported amount of the silver-containing material was 10.0% by mass in terms of metallic silver (Ag) with respect to the total amount of the catalyst.

[Evaluation of characteristics of catalysts obtained in Examples 1 to 6 and Comparative Examples 1 to 3]
<ICP emission analysis>
The atomic ratio (P / Ag) of phosphorus (P) to silver (Ag) in the catalysts obtained in Examples 1 to 6 and Comparative Examples 1 to 3 and phosphorus (P) to aluminum (Al) in the catalyst The atomic ratio (P / Al ) was measured by ICP (Inductively Coupled Plasma) emission analysis.

  That is, first, an ICP emission analysis was performed on each of the obtained catalyst powders using an inductively coupled plasma (ICP) light-emitting device (CIROS 120EOP, manufactured by Rigaku Corporation), and silver atoms ( The mass content of Ag (Ag) and phosphorus atom (P) was quantified, and the atomic ratio (P / Ag) of phosphorus (P) to silver (Ag) was calculated. Moreover, the content mass of the aluminum atom (Al) and phosphorus atom (P) which exist on a catalyst powder was quantified, and it calculated | required by calculating the atomic ratio (P / Al) of phosphorus (P) with respect to aluminum (Al). . The obtained results are shown in Table 1.

  As is clear from the results of Examples 1 to 6 and Comparative Examples 1 to 3 shown in Table 1, it was confirmed that any catalyst was prepared with a P / Ag atomic ratio almost as prepared.

<PM oxidation activity evaluation test>
Using the catalysts obtained in Examples 1 to 6 and Comparative Examples 1 to 3 in the initial state, PM oxidation activity was measured as follows. Here, the “initial state” refers to a state in which neither a heat test or a sulfur poisoning test, which will be described later, has been performed after the production of the catalyst.

(Sulfur poisoning treatment)
That is, first, using a fixed bed flow reactor, a quartz reaction tube having an inner diameter of 15 mm was charged with 1.1 g of the pellet-shaped catalyst sample in the initial state obtained in Examples 1 to 6 and Comparative Examples 1 to 3, and Further, Pt / Al ₂ O ₃ (0.5 g) sufficiently poisoned with S was placed in front of the catalyst sample in order to sufficiently oxidize the supplied SO ₂ . _{Then, O 2 (10%) +} CO 2 (10%) + H 2 O (10%) / N 2 was passed through a mixed gas consisting of (balance), it was heated to 400 ° C.. Next, a mixed gas (filled gas) composed of SO ₂ (66 ppm), O ₂ (10%), CO ₂ (10%), H ₂ O (10%) and N ₂ (remainder) is put into the apparatus. , 400 ° C. (entering gas temperature), 55.5 minutes, and gas flow rate of 7 L / min (sulfur poisoning treatment). In addition, the total supply amount of the sulfur component supplied in such a sulfur poisoning process is 1.0 g / 30 g-cat.

(PM mixing process I)
Next, using a rotating frame for testing and research, a catalyst sample after sulfur poisoning treatment and a simulated particulate (simulated PM) on a cylindrical sample tube with an inner diameter of 20 mm are used as carbon powder (made by Tokai Carbon Co., Ltd. 9 (SAF) ", average particle size 19 nm), and mixed by rotating for 1 hour on a rotating frame for test research to prepare a catalyst sample. It should be noted that the amount of the simulated PM mixed with the catalyst by such a PM mixing process was an amount of 49: 1 by weight ratio of the catalyst to the simulated PM.

(Sulfur poisoning regeneration treatment)
Next, a mixed gas (filled gas) composed of O ₂ (10%) + H ₂ O (10%) / N ₂ (remainder) is applied to the catalyst sample after the sulfur poisoning treatment-PM mixing treatment I. While the temperature of the gas entering was increased from 120 ° C. to 720 ° C. at a rate of temperature increase of 20 ° C./min, the gas was supplied at a gas flow rate of 10 L / min to perform sulfur poisoning regeneration treatment.

(PM mixing treatment II)
Next, the catalyst sample after the sulfur poisoning regeneration treatment and the carbon powder (simulated PM) were mixed in the same manner as in the PM mixing treatment I to prepare an evaluation sample. It should be noted that the amount of the simulated PM mixed with the catalyst by such a PM mixing process was an amount of 49: 1 by weight ratio of the catalyst to the simulated PM.

(Measurement of PM oxidation activity of catalyst after sulfur poisoning regeneration treatment: PM purification treatment)
Next, a mixed gas composed of O ₂ (10%) + H ₂ O (10%) / N ₂ (remainder) with respect to the sample for evaluation after the PM mixing treatment II of Examples 1 to 3 and Comparative Examples 1 to ₂ (Enter gas) was supplied under the condition of a gas flow rate of 10 L / min while increasing the temperature of the gas entering the catalyst from 120 ° C. to 720 ° C. at a rate of temperature increase of 20 ° C./min. Then, until the end of the supply from the start of the supply of the mixed gas to determine the concentration of CO ₂ contained in the output gas discharged from the device. Then, based on the concentration of CO _{2 in} the output gas and the temperature of the input gas, the temperature of the mixed gas necessary for oxidizing 50% of the carbon adhering to each evaluation sample (PM 50%) The oxidation temperature was calculated and used as an index of the PM oxidation activity of the catalyst after the sulfur poisoning regeneration treatment.

  The obtained results are shown in Table 2. In addition, it can be said that the PM oxidation activity of the catalyst after the sulfur poisoning regeneration treatment is higher as the PM 50% oxidation temperature is lower. Further, as the PM oxidation activity of the catalyst after the sulfur poisoning regeneration treatment, the 50% PM oxidation temperature of the exhaust gas purification catalyst after the sulfur poisoning regeneration treatment obtained in Examples 1-3 and Comparative Examples 1-2 is shown. The graph is shown in FIG.

Furthermore, in order to evaluate the PM purification treatment (PM oxidation activity) after the sulfur poisoning regeneration treatment of the catalysts obtained in Examples 4 to 6 and Comparative Example 3, Examples 4 to 6 and Comparative Examples were conducted in the sulfur poisoning treatment. 3 except that the catalyst sample prepared in such a manner that the silver amount of the catalyst sample of No. 3 is the same as the silver amount of the catalyst sample of Example 1 and the gas flow rate in the PM purification treatment was 7 L / min. The sulfur poisoning process, the PM mixing process I, the sulfur poisoning regeneration process, the PM mixing process II and the PM purification process are performed, and the exhaust gas purification catalyst CO ₂ after the sulfur poisoning regeneration process is processed in the same manner as described above. The concentration was measured, the PM 50% oxidation temperature was calculated, and used as an index of PM oxidation activity. For comparison with Examples 4 to 6, the concentration of CO ₂ was measured in the same manner as described above except that the gas flow rate in the PM purification treatment was set to 7 L / min for the evaluation sample of Comparative Example 1. The PM 50% oxidation temperature was calculated and used as an index of PM oxidation activity.

  The obtained results are shown in Table 3. Further, as the PM oxidation activity of the catalyst after the sulfur poisoning regeneration treatment, the 50% PM oxidation temperature of the exhaust gas purification catalyst after the sulfur poisoning regeneration treatment obtained in Examples 4 to 6 and Comparative Examples 1 and 3 is shown. A graph is shown in FIG.

<Evaluation results>
As is apparent from the results described in Tables 2 and 3 and FIGS. 1 and 2, the exhaust gas purifying catalysts of Examples 1 to 6 of the present invention are sufficiently high in PM oxidation even when exposed to a gas containing sulfur. It was confirmed that it is an exhaust gas purifying catalyst capable of exhibiting activity.

  As is clear from the results shown in FIG. 1, the exhaust gas purifying catalyst in which the silver phosphate compounds of Examples 1 to 3 of the present invention are supported on alumina is compared with Comparative Example 1 in which silver is supported on alumina. Thus, it was confirmed that PM oxidation activity was high and resistance to sulfur poisoning was high. As is clear from the results shown in FIG. 2, the exhaust gas purifying catalyst in which silver and phosphoric acid of Examples 4 to 6 of the present invention were added and coexisted on alumina was also compared with Comparative Example 1. Thus, it was confirmed that the PM oxidation activity is high and the resistance to sulfur poisoning is high as in the case of carrying a silver phosphate compound. In addition, it was confirmed that the exhaust gas purifying catalyst of Example 6 has higher PM oxidation activity than Examples 4 to 5, and further resistance to sulfur poisoning. This is because, in Example 6, crystals of aluminum phosphate were observed, so the phosphoric acid-containing material of the exhaust gas purifying catalyst of Example 6 contained a crystalline phase of aluminum phosphate, and the sulfur component adsorbed on the carrier This is thought to be due to the suppression of poisoning and the reduction of poisoning. On the other hand, it was confirmed that the comparative catalyst in which silver was supported on the aluminum phosphate support of Comparative Example 3 had considerably low PM oxidation activity. It can be considered that the comparative catalyst of Comparative Example 3 had a low activity due to the low dispersibility of silver on the aluminum phosphate as the carrier.

<X-ray diffraction (XRD) measurement>
Using each catalyst obtained in Examples 1, 5, 6 and Comparative Example 1 as a measurement sample, a powder X-ray diffractometer (manufactured by Rigaku Corporation, trade name “sample horizontal X-ray diffractometer Ultima IV”) is used. Powder X-ray diffraction (XRD) measurement under the conditions of radiation source: CuKα ray (λ = 0.15406 nm), scan step: 0.02 °, holding time: 0.12 seconds, acceleration voltage: 40 kV, acceleration current: 40 mA I did it. FIG. 3 shows XRD spectra of the exhaust gas purifying catalysts obtained in Examples 1, 5, 6 and Comparative Example 1.

As is clear from the results shown in FIG. 3 (XRD spectrum), in the exhaust gas purification catalyst of Example 6, the peak of aluminum phosphate (AlPO ₄ ) was added in addition to the peak of silver phosphate (Ag ₃ PO ₄ ). Observed and confirmed that the added phosphoric acid also reacted with the support alumina. In the exhaust gas purifying catalysts of Examples 1 and 5, Ag ₃ PO ₄ peak was observed, and no signal derived from silver (Ag) was observed. Thus, in Examples 1 and 5, the supported silver (Ag) is considered to be Ag ₃ PO ₄ by the added phosphoric acid and phosphate.

  From the above results, by using an exhaust gas purifying catalyst in which a silver-containing substance and a phosphoric acid-containing substance are supported on a support mainly composed of alumina, a sufficiently high PM oxidation activity can be obtained even when exposed to sulfur-containing gas. It has been confirmed that it works. In addition, it was confirmed that the catalyst of the present invention can maintain high oxidation activity even at low temperatures even after being subjected to sulfur poisoning and is useful as a catalyst for oxidizing PM.

As described above, according to the present invention, an exhaust gas purifying catalyst capable of exhibiting sufficiently high PM oxidation activity even when exposed to sulfur-containing gas, an exhaust gas purifying filter and an exhaust gas purifying method using the same. Can be provided.
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 (7)

A PM oxidation catalyst comprising: a carrier mainly composed of alumina; and a silver-containing material and a phosphoric acid-containing material supported on the carrier. 2. The PM oxidation catalyst according to claim 1, wherein silver phosphate is supported on the carrier as the silver-containing material and the phosphoric acid-containing material. PM oxidation catalyst according to claim 1 or 2, wherein the PM atomic ratio of phosphorus (P) with respect to silver in the oxidation catalyst (Ag) (P / Ag) is characterized in that 0.2 to 6. The amount of the silver-containing material supported is 3 to 50% by mass in terms of metallic silver with respect to the total amount of the carrier, the silver-containing material, and the phosphoric acid-containing material. PM oxidation catalyst as described in any one of them. The atomic ratio (P / Al) of phosphorus (P) to aluminum (Al) in the PM oxidation catalyst is 0.15 to 0.5, and the phosphoric acid-containing substance contains a crystalline phase of aluminum phosphate PM oxidation catalyst as described in any one of Claims 1-4 characterized by the above-mentioned. An exhaust gas purification filter comprising the PM oxidation catalyst according to any one of claims 1 to 5 supported on a breathable base material. An exhaust gas purification method comprising oxidizing and removing particulate matter (PM) by bringing exhaust gas from an internal combustion engine into contact with the PM oxidation catalyst according to any one of claims 1 to 5.