DE112015001661T5 - Catalyst for purifying exhaust gas, and filter and method for purifying exhaust gas using same - Google Patents

Abstract

A catalyst for purifying exhaust gas includes a carrier containing alumina as a main component and a silver-containing substance and a phosphoric acid-containing substance supported on the carrier.

Description

[Technical area]

The present invention relates to a catalyst for purifying exhaust gas, a filter for purifying exhaust gas using the catalyst, and a method for purifying exhaust gas using the catalyst.

[Prior Art]

Gas discharged from an internal combustion engine contains harmful substances such as particulate matter (PM) formed by combustion and ashes of additives in oil and the like. Of these harmful substances, particulate matter is known to be an air pollutant which adversely affects plants and animals. For this reason, a filter for purifying (DPF: diesel particulate filter) is used for trapping particulate matter contained in exhaust gas from an internal combustion engine. Since PM trapped in a DPF results in increased pressure drop, the DPF is regenerated by periodically heating to a high temperature to burn the PM. It is desirable to regenerate the DPF at a lower temperature to improve fuel efficiency and durability of materials. Accordingly, a PM oxidation catalyst is supported on a DPF.

As such a PM oxidation catalyst, the unexamined discloses Japanese Patent Application Publication No. 2009-45584 (PTL 1) an exhaust gas purifying catalyst for removing particulate matter in exhaust gas discharged from an internal combustion engine, the exhaust gas purifying catalyst comprising: a composite oxide (LaMnO ₃ , CeZrO ₂ , CoTa ₂ O ₆ or the like) having oxygen releasability, and Ag and a Noble metal (Ru, Pd, Pt or the like) co-charged on the composite oxide, wherein the composite oxide includes at least two members selected from the group consisting of an alkaline earth metal element, a transition metal element, a 12th group element and a 13th group element and an exhaust gas purification device using the exhaust gas purifying catalyst. However, the exhaust gas purifying catalyst disclosed in PTL 1 has a problem that the Ag catalyst is poisoned by a sulfur component contained in fuel or oil and undergoes a significant decrease in activity. Specifically, a catalyst using a strong base carrier such as ceria is insufficient in PM oxidation activity when exposed to a sulfur-containing gas, as evidenced by, for example, the catalyst having a very high activity in the initial phase. but due to a sulfur component undergoes a significant decrease in activity and the like.

However, the unaudited revealed Japanese Patent Application Publication No. 2011-218295 (PTL 2) a filter for purifying exhaust gas disposed in an exhaust passage of an internal combustion engine and trapping particulates in exhaust gas from the internal combustion engine to perform exhaust purification, the exhaust gas purification filter comprising: a honeycomb structure having an outer peripheral wall; a porous cell wall arranged in a polygonal lattice pattern within the outer circumferential wall and a plurality of cells partitioned by the cell wall, wherein downstream ends of inlet gas cells of the cells serve as inflow side passages into which exhaust gas flows, and upstream ends of outlet gas cells of the cells serve as outflow passages; by which the exhaust gas which has passed through the cell wall is discharged blocked by plug portions, wherein an Ag-containing PM combustion catalyst comprising a catalyst material in which Ag is dispersed in a layered alumina, and an oxidation catalyst The catalyst for oxidizing at least CO in the exhaust gas is supported on the cell wall and the oxidation catalyst is not supported on wall surfaces of the inlet gas cells, but the PM combustion catalyst is supported on the wall surfaces of the inlet gas cells, whereas at least the oxidation catalyst is supported on wall surfaces of the exhaust gas cells. However, even in the case of the exhaust gas purification filter disclosed in PTL 2, the dispersibility of the Ag catalyst supported on the alumina is low, and the Ag particles are coarse. Therefore, contact properties of the Ag catalyst with PM are poor. For this reason, the filter for purifying exhaust gas disclosed in PTL 2 is insufficient in terms of PM oxidation activity when exposed to a sulfur-containing gas, as shown, for example, by an increase in activity when the Ag catalyst increases due to sulfur poisoning Silver sulfate is reacted, and the like.

Moreover, the unexamined discloses Japanese Patent Application Publication No. Hei 06-55075 (PTL 3) a catalyst for purifying exhaust gas comprising: a phosphoric acid salt; and at least one metal selected from platinum, palladium, rhodium, gold, silver, ruthenium, iridium, nickel, cerium, cobalt, copper and strontium, a salt thereof or an oxide thereof supported on the phosphoric acid salt. However, even in the case of the exhaust gas purification catalyst disclosed in PTL 3, the dispersibility of the metal having a catalytic activity such as silver supported on the phosphoric acid salt carrier such as aluminum phosphate is poor and active metal particles such as silver particles are coarse. Consequently, contact properties of the metal with PM are poor. For this reason, the catalyst is insufficient in PM oxidation activity when exposed to a sulfur-containing gas.

In addition, the unaudited revealed Japanese Patent Application Publication No. 2012-219715 (PTL 4) an exhaust gas purifying apparatus comprising an oxidation catalyst provided with a carrier formed by at least one metal salt selected from a group consisting of Ca sulfate and phosphate, and a silver-containing substance carried on the carrier, wherein the silver-containing Substance is at least one selected from a group consisting of silver, silver oxide, silver carbonate, silver sulfate and silver phosphate. According to the description in PTL 4, it is possible to provide an exhaust gas purification device in which the decrease of the particulate matter oxidation performance caused by the deposition of ash can be sufficiently inhibited and even after the deposition of ash, excellent particulate material oxidation performance can be obtained. However, a catalyst for purifying exhaust gas has recently demanded increasingly better properties, and there is a need for a catalyst for purifying exhaust gas which can have sufficiently high PM oxidation activity even when exposed to a sulfur-containing gas.

[List of citations]

[Patent Literature]

• [PTL 1] Untested Japanese Patent Application Publication No. 2009-45584
• [PTL 2] Unchecked Japanese Patent Application Publication No. 2011-218295
• [PTL 3] Untested Japanese Patent Application Publication No. Hei 06-55075
• [PTL 4] Untested Japanese Patent Application Publication No. 2012-219715

[Summary of the Invention]

[Technical problem]

The present invention has been made in view of the above-described problems of the conventional technologies, and an object of the present invention is to provide a catalyst for purifying exhaust gas which can have a sufficiently high PM oxidation activity even when exposed to a sulfur-containing gas , and a filter for purifying exhaust gas using the catalyst and a method for purifying exhaust gas using the catalyst.

[The solution of the problem]

The present inventors have intensively studied to solve the above-described problem, and thus found that when a silver-containing substance and a phosphoric acid-containing substance are supported on a carrier containing alumina as a main component, the obtained catalyst for purification Of exhaust gas may surprisingly have a high PM oxidation activity, even if it is exposed to a sulfur-containing gas. This finding has led to the completion of the present invention.

A catalyst for purifying exhaust gas of the present invention comprises:
a support containing alumina as a main component; and
a silver-containing substance and a phosphoric acid-containing substance, which are supported on the carrier.

In the exhaust gas purification catalyst of the present invention, preferably, a silver phosphate serving as both the silver-containing substance and the phosphoric acid-containing substance is supported on the support.

Moreover, in the catalyst for purifying exhaust gas of the present invention, an atomic ratio (P / Ag) of phosphorus (P) to silver (Ag) is preferably 0.2 to 4 in the catalyst for purifying exhaust gas.

Moreover, in the catalyst for purifying exhaust gas of the present invention, an amount of the supported silver-containing substance is preferably 3 to 50 mass% based on metallic silver in relation to a total amount of the carrier, the silver-containing substance and the phosphoric acid-containing substance.

Moreover, in the catalyst for purifying exhaust gas of the present invention, it is preferable that an atomic ratio (P / Al) of phosphorus (P) to aluminum (Al) is 0.15 to 0.5 in the catalyst for purifying exhaust gas and the phosphoric acid-containing substance preferably contains a crystal phase of aluminum phosphate.

An exhaust gas purification filter of the present invention comprises:
a gas-permeable substrate; and
the exhaust gas purification catalyst of the present invention supported on the gas permeable substrate.

In addition, a method of purifying exhaust gas of the present invention comprises contacting exhaust gas from an internal combustion engine with the exhaust gas purifying catalyst of the present invention to oxidatively remove particulate matter (PM).

Note that while it is not entirely clear why the exhaust gas purification catalyst, the exhaust gas purification filter using the catalyst, and the exhaust gas purification method using the catalyst of the present invention, the presence of a sufficiently high PM Oxidation activity even when the catalyst is exposed to a sulfur-containing gas, but the present inventors speculate as follows.

Specifically, the catalyst is less susceptible to sulfur poisoning because the phosphoric acid-containing substance used in the present invention, supported on the carrier containing alumina as a main component, inhibits sulfur adsorption and reduces sulfur poisoning. In addition, when the silver-containing substance and the phosphoric acid-containing substance used as the active species coexist, high PM oxidation activity can be attained and sufficiently high PM oxidation activity is present. By preparing a catalyst comprising a carrier containing alumina as a main component and a silver-containing substance and a phosphoric acid-containing active species as described above, the catalyst can maintain high PM oxidation activity even when exposed to a sulfur-containing gas. For this reason, the present inventors speculate that sufficiently high PM oxidation activity can be achieved even when the catalyst is exposed to a sulfur-containing gas.

[Advantageous Effects of Invention]

According to the present invention, it is possible to have a catalyst for purifying exhaust gas which can have a sufficiently high PM oxidation activity even when exposed to a sulfur-containing gas, a filter for purifying exhaust gas using the catalyst, and a method of To provide purification of exhaust gas using the catalyst.

[Brief Description of the Drawings]

1 FIG. 12 is a graph showing temperatures of 50% PM oxidation of exhaust gas purification catalysts obtained in Examples 1 to 3 and Comparative Examples 1 and 2 and subjected to a sulfur decontamination treatment.

2 FIG. 12 is a graph showing temperatures of 50% PM oxidation of exhaust gas purification catalysts obtained in Examples 4 to 6 and Comparative Examples 1 and 3 and subjected to a sulfur decontamination treatment.

3 FIG. 12 is a graph showing XRD spectra of the exhaust gas purification catalysts obtained in Examples 1, 5, and 6 and Comparative Example 1. FIG.

[Description of Embodiments]

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

First, a catalyst for purifying exhaust gas of the present invention will be described. The exhaust gas purification catalyst of the present invention comprises: a support containing alumina as a main component; and a silver-containing substance and a phosphoric acid-containing substance, which are supported on the carrier. Since the silver-containing substance and the phosphoric acid-containing substance serving as active species are supported on the carrier containing alumina as a main component as described above, the exhaust gas purification catalyst of the present invention can have sufficiently high PM oxidation activity even then when exposed to a sulfur-containing gas. Accordingly, the exhaust gas purification catalyst of the present invention can be suitably used, for example, as a PM oxidation catalyst for purifying exhaust gas by oxidatively removing particulate matter (PM) in exhaust gas from an internal combustion engine such as a diesel engine. The exhaust gas purification catalyst of the present invention may be more preferably used as a PM oxidation catalyst for a diesel engine.

[Carrier]

The carrier according to the present invention has to be a carrier containing alumina (Al ₂ O ₃ ) as a main component. The support containing alumina as a main component is not particularly limited as far as alumina is contained as a main component. Here, the phrase "containing alumina as a main component" means that the carrier is made exclusively of alumina or that the carrier is mainly made of alumina and contains other components. As the other components, other compounds usable as carriers of exhaust gas purification catalysts which are used for such an application are usable. In the latter case, a content of alumina in the carrier is preferably 90 mass% or more, more preferably 95 mass% or more, and particularly preferably 98 mass% or more based on 100 mass% of the carrier. If the content of alumina in the carrier is lower than the lower limit, the activity tends to decrease because the added components react with silver phosphate.

It should be noted that the alumina of the support may be at least one type of alumina selected from the group consisting of boehmite-type alumina, pseudoboehmite-type, χ-type, κ-type, ρ-type, η-type, γ-type, pseudo-γ-type, δ-type, θ-type and α-type is selected. From the viewpoint of heat resistance, it is preferable to use α-alumina or γ-alumina, and it is particularly preferable to use γ-alumina which has high activity.

Moreover, from the viewpoint of the thermal stability of the carrier and the catalytic activity, it is possible that the components other than alumina contained in the carrier containing alumina as a main component, for example, an oxide of a metal such as rare earths, alkali metals, Alkaline earth metals and transition metals, including yttrium (Y), lanthanum (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), Strontium (Sr), Barium (Ba), scandium (Sc), vanadium (V), and the like.

Moreover, the support containing alumina as a main component is more preferably a support from the viewpoint of heat resistance, which comprises: alumina in an amount of 90 mass% or more based on 100 mass% of the carrier; and an oxide of at least one metal selected from the group consisting of yttrium (Y), lanthanum (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), strontium (Sr), barium (Ba), scandium (Sc) and vanadium (V).

Moreover, a specific surface area of the support containing alumina as a main component is not particularly limited, and is preferably 5 to 300 m ² / g, and more preferably 10 to 200 m ² / g. When the specific surface area exceeds the upper limit, the heat resistance of the catalyst tends to decrease because the heat resistance of the support itself decreases. Meanwhile, when the specific surface area is lower than the lower limit, the dispersibility of the active species (the silver-containing substance and the phosphoric acid-containing substance) tends to decrease. The specific surface area can be calculated as a BET specific surface area from an adsorption isotherm by using the BET adsorption isotherm equation.

In addition, a shape of the support containing alumina as a main component is not particularly limited, and it is possible to use the support having an already known shape such as a ring shape, a spherical shape, a cylindrical shape or a pellet shape , It should be noted that, from the viewpoint that the active species (the silver-containing substance and the phosphoric acid-containing substance) may be contained in large amounts in a highly dispersed state, a particulate carrier is preferably used. When the carrier is particulate, particles of the carrier have an average primary particle diameter of preferably 1 to 1000 nm, and more preferably 5 to 500 nm. It should be noted that the average primary particle diameter of the carrier is calculated by using the Scherrer equation from the linewidth of a powder X-ray diffraction peak , which is measured by using an X-ray diffraction device, can be determined. In addition, the average particle diameter of the support containing alumina as a main component may be optionally changed by a usual method (for example, a method of crushing the support in a mortar, a cold isostatic press (CIP) or the like). Moreover, the average particle diameter of a powder of the carrier containing alumina as a main component in the catalyst can be changed by changing the average particle diameter of a catalyst for purifying exhaust gas by a usual method after the preparation of the catalyst.

Moreover, a method for producing the carrier is not particularly limited, and it is possible to optionally use a known method by which the carrier containing alumina as a main component can be produced. In addition, commercially available alumina, a commercial composite oxide containing alumina as a main component or the like may be used as the carrier. The size of the carrier may optionally be adjusted by grinding the carrier with a ball mill or the like.

(Silver-containing substance)

The silver-containing substance according to the present invention is an active species supported on the carrier containing alumina as a main component, and has a substance containing silver and / or a silver compound. The silver-containing substance is not particularly limited insofar as the silver-containing substance is a substance containing silver and / or a silver-containing compound. Concrete examples of the silver-containing substance include silver (simple substance of the metal, Ag, metal silver), silver oxides, silver halides, silver carbonates, silver sulfates, silver phosphates, silver nitrates, silver chromates, silver oxalates, silver ferrites and the like. Of these examples, the silver-containing substance is preferably at least one selected from the group consisting of silver, silver oxides, silver halides, silver sulfates and silver phosphates from the viewpoint of reactivity with phosphoric acid. From the viewpoint of dispersibility of silver particles, more preferably, the silver-containing substance is at least one selected from the group consisting of silver, silver sulfates, silver phosphates and silver nitrates.

It should be noted that preferably a silver phosphate serving as both the silver-containing substance and the phosphoric acid-containing substance is supported on the carrier. Concrete examples of the 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 ), silver metaphosphate (AgPO ₃ ), and the like.

An amount of the silver-containing substance to be supported and used in the present invention is not particularly limited, and is preferably 3 to 50 mass%, more preferably 5 to 30 mass%, and particularly preferably 7 to 15 mass%, based on metallic silver ( Ag), relative to a total amount of the carrier, the silver-containing substance and the phosphoric acid-containing substance. When the amount of the supported silver-containing substance is less than the lower limit, it tends to be impossible to obtain a sufficiently high particulate matter oxidation performance. However, if the amount exceeds the upper limit, the cost tends to be high because the oxidation performance is saturated.

In addition, an average crystallite diameter (average primary particle diameter) of the silver-containing substance is not particularly limited and is preferably 0.1 to 300 nm, and more preferably 1 to 200 nm. When the average crystallite diameter of the silver-containing substance is less than the lower limit, the activity tends to decrease because the silver-containing substance is firmly bound to the carrier. However, if the average crystallite diameter exceeds the upper limit, the activity tends to decrease as the number of particles contributing to the reaction decreases. It should be noted that the average crystallite diameter (average primary particle diameter) of the silver-containing substance can be computationally determined, for example, by using the Scherrer equation from the line width of a powder X-ray diffraction peak measured by using an X-ray diffraction device.

(Phosphoric acid substance)

The phosphoric acid-containing substance according to the present invention is an active species supported on the carrier containing alumina as a main component, and has a substance containing phosphoric acid and / or a phosphoric acid salt. The phosphoric acid-containing substance is not particularly limited, as long as the phosphoric acid-containing substance is a substance containing phosphoric acid and / or a phosphoric acid salt. Concrete examples of the phosphoric acid-containing substance include phosphoric acids such as 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. Concrete examples of the phosphoric acid-containing substance also include phosphoric acid salts such as orthophosphoric acid salts, pyrophosphoric acid salts, triphosphoric acid salts, polyphosphoric acid salts, metaphosphoric salts and ultraphosphoric acid salts, and further include alkali metal salts thereof, other metal salts thereof, and ammonium salts thereof and the like. Of these examples, from the viewpoint of the dispersibility of the active species, the phosphoric acid-containing substance is preferably at least one selected from the group consisting of orthophosphoric acid salts, pyrophosphoric acid salts, triphosphoric acid salts and alkali metal salts thereof, and more preferably at least one selected from the group consisting of Orthophosphoric acid salts, pyrophosphoric acid salts and alkali metal salts thereof.

An amount of the phosphoric acid-containing substance to be supported and used in the present invention is not particularly limited, and is preferably a supported amount such that an atomic ratio (P / Ag) of phosphorus (P) to silver (Ag) in the catalyst Purification of exhaust gas may be 0.2 to 6, more preferably a supported amount such that the atomic ratio (P / Ag) can be 0.3 to 5.5, and particularly preferably a supported amount such that the atomic ratio (P / Ag) can be from 0.4 to 3. If the amount of the phosphoric acid-containing substance supported is less than the lower limit of the atomic ratio (P / Ag), it tends to be impossible to obtain a sufficiently high particulate matter oxidation performance. However, if the amount exceeds the upper limit of the atomic ratio (P / Ag), the cost tends to be high because the oxidation performance is saturated.

Moreover, the amount of the phosphoric acid-containing substance supported and used in the present invention is not particularly limited and is preferably a supported amount such that an atomic ratio (P / Al) of phosphorus (P) to aluminum (Al) in the catalyst for purifying Exhaust gas may be 0.15 to 0.5, more preferably a supported amount such that the atomic ratio (P / Al) may be 0.2 to 0.45, and particularly preferably a supported amount such that the atomic ratio (P / Al) can be 0.3 to 0.4. If the amount of the phosphoric acid-containing substance supported is less than the lower limit in terms of the atomic ratio (P / Al), it tends to be impossible to obtain a sufficiently high particulate matter oxidation performance. However, if the amount exceeds the upper limit of the atomic ratio (P / Al), the activity tends to decrease as the specific surface area decreases.

Moreover, the phosphoric acid-containing substance serving as the active species supported on the carrier containing alumina as a main component according to the present invention preferably contains a crystal phase of aluminum phosphate (AlPO ₄ ). When such a crystal phase of aluminum phosphate (AlPO ₄ ) is contained, it is possible to prevent adsorption of a sulfur component to the carrier and to reduce sulfur poisoning of the catalyst even if the catalyst is exposed to a sulfur-containing gas.

Moreover, in the catalyst for purifying exhaust gas of the present invention, it is more preferable that the atomic ratio (P / Al) of phosphorus (P) to aluminum (Al) in the catalyst for purifying exhaust gas is 0.15 to 0.5 is, and that the phosphoric acid-containing substance contains a crystal phase of aluminum phosphate. The catalyst for the purification of exhaust gas, in which the phosphoric acid-containing Substance is supported, may have a higher enough PM oxidation activity when exposed to a sulfur-containing gas.

Moreover, most of the phosphoric acid-containing substances are water-soluble. However, when the phosphoric acid-containing substance is not water-soluble, the average crystallite diameter (average primary particle diameter) is not particularly limited and is preferably 0.1 to 300 nm, and more preferably 1 to 200 nm. When the average crystallite diameter of the phosphoric acid-containing substance exceeds the upper limit, decreases the dispersibility tends to decrease. It should be noted that the average crystallite diameter (average primary particle diameter) of the phosphoric acid-containing substance can be computationally determined, for example, by using the Scherrer equation from the linewidth of a powder X-ray diffraction peak measured by using an X-ray diffraction device.

In the present invention, the silver-containing substance and the phosphoric acid-containing substance are used as the active species, and the phosphoric acid-containing substance used by being supported on the carrier containing alumina as a main component inhibits sulfur adsorption and reduces sulfur poisoning. Consequently, the catalyst is less susceptible to sulfur poisoning. Moreover, since the silver-containing substance and the phosphoric acid-containing substance used as the active species coexist, a high PM oxidation activity can be obtained, and a sufficiently high PM oxidation activity can be present. As described above, by preparing the catalyst comprising the carrier containing alumina as a main component and the silver-containing substance and the phosphoric acid-containing substance as the active species, high PM oxidation activity can be maintained and sufficiently high PM oxidation activity can be obtained even if the catalyst is exposed to a sulfur-containing gas.

It should be noted that each type of the carrier, the silver-containing substance and the phosphoric acid-containing substance supported on the carrier and the like can be identified by obtaining an X-ray diffraction pattern by X-ray diffraction measurement and the type of crystals present based on the positions is determined by peaks.

Moreover, methods for supporting the silver-containing substance and the phosphoric acid-containing substance on the support containing alumina as a main component are not particularly limited, and known methods may be used, if necessary. Optionally, for example, a method using a dispersion or a sol of the silver-containing substance or a precursor thereof and a dispersion or a sol of the phosphoric acid-containing substance or a precursor thereof, and the support containing alumina as a main component may be used sequentially or coated simultaneously with the dispersions or sols (followed, if necessary, by calcination); a method in which the silver-containing substance and the phosphoric acid-containing substance are supported by using a vapor deposition method (such as a chemical vapor deposition method, a physical vapor deposition method, or a sputtering method) on the support containing alumina as a main component; or similar.

(Catalyst for purifying exhaust gas)

An exhaust gas purification catalyst of the present invention may be any one as far as the catalyst contains the support containing alumina as a main component; the silver-containing substance and the phosphoric acid-containing substance supported on the carrier. A form of the catalyst is not particularly limited and may be a pellet catalyst form having pellet shapes or the like, or may be a form supported on a filter.

(Method for producing a catalyst for purifying exhaust gas)

A method for producing a catalyst for purifying exhaust gas of the present invention is not particularly limited, and if necessary, a known method may be used. For example, the catalyst is prepared by the steps of: impregnating the carrier containing alumina as a main component with an aqueous solution containing ions or the like of the silver-containing substance and the phosphoric acid-containing substance; and performing calcination by heating. It should be noted that as for the impregnation, an aqueous solution containing ions or the like of the silver-containing substance and the phosphoric acid-containing substance may be used for the impregnation, or both an aqueous solution, the ions or the like contains the silver-containing substance, as well as an aqueous solution containing ions or the like of the phosphoric acid-containing substance, prepared separately and can be used individually and sequentially or simultaneously for the impregnation. Concretely, a method may be employed in which a solution containing the silver-containing substance and the phosphoric acid-containing substance in predetermined concentrations is contacted with the carrier containing alumina as a main component to the carrier with the solution, the predetermined amounts the silver-containing substance and the phosphoric acid-containing substance, to impregnate (to support the solution on the support), and this support is then calcined by heating. Moreover, as the method for producing a catalyst for purifying exhaust gas, there can be employed a method in which first the carrier containing alumina as a main component is impregnated with an aqueous solution containing ions or the like of the phosphoric acid-containing substance, followed by calcination to obtain a carrier on which the phosphoric acid-containing substance is carried, and the resulting carrier carrying the phosphoric acid-containing substance is then impregnated with an aqueous solution containing ions or the like of the silver-containing substance, followed by calcination to support the silver-containing substance Substance and the phosphoric acid-containing substance on the support containing alumina as a main component.

Moreover, after impregnation with the silver-containing substance and the phosphoric acid-containing substance, calcination can be carried out by heating (calcination step) in the air. Moreover, a calcination temperature in the calcination step is preferably 200 to 700 ° C. If the calcining temperature is lower than the lower limit, it is difficult to support the silver-containing substance and the phosphoric acid-containing substance on the support, so that it is tantamount to imparting the catalyst for purifying exhaust gas with a sufficient PM oxidation activity. Meanwhile, if the calcination temperature exceeds the upper limit, the specific surface area of the support containing alumina as a main component is likely to decrease, so that the oxidation activity tends to decrease. Meanwhile, a calcination time is preferably 0.1 to 100 hours. If the calcination time is lower than the lower limit, it is difficult to support the silver-containing substance and the phosphoric acid-containing substance, so that the oxidation activity of the obtained exhaust gas purifying catalyst (PM oxidation catalyst) tends to decrease. However, even if the calcination time exceeds the upper limit, no further increase in the effect can be obtained, so that the cost for preparing the catalyst tends to increase.

(Device for purifying exhaust gas)

The exhaust gas purification catalyst of the present invention may have a high PM oxidation activity to particulate matter contained in gas (exhaust gas) discharged from an internal combustion engine to oxidatively remove the PM. Thus, an exhaust gas purifying apparatus can be formed by disposing the exhaust gas purifying catalyst so that the exhaust gas can come into contact with the exhaust gas purifying catalyst.

The exhaust gas purifying apparatus may be any one as far as the apparatus is an exhaust gas purifying apparatus used for removing particulate matter (PM) contained in exhaust gas by the oxidation thereof, and which includes the exhaust gas purifying catalyst of the present invention. In the exhaust gas purification apparatus, the cleaning (removal) is performed by oxidizing particulate matter contained in gas (exhaust gas) discharged from an internal combustion engine. Consequently, the exhaust gas purifying apparatus can be arranged so that the exhaust gas can come into contact with the exhaust gas purifying apparatus. For example, it is possible to adopt a configuration in which the exhaust gas purifying apparatus is disposed in a gas flow passage in an exhaust pipe through which exhaust gas from an internal combustion engine flows. It should be noted that the internal combustion engine is not particularly limited and, if necessary, a known internal combustion engine can be used. For example, the internal combustion engine may be an automotive internal combustion engine (a gasoline engine, a diesel engine, or the like).

(Filter for cleaning exhaust gas)

Next, a filter for purifying exhaust gas of the present invention will be described. The exhaust gas purification filter of the present invention comprises: a gas-permeable substrate (filter); and the exhaust gas purifying catalyst of the present invention supported on the gas permeable substrate.

The exhaust gas purification filter of the present invention is not particularly limited as far as the exhaust gas purification catalyst of the present invention is supported on a gas-permeable substrate. As the gas-permeable substrate of the exhaust gas purification filter, a known gas-permeable substrate (filter) may optionally be used, and examples thereof include particulate filters, monolithic filters, honeycomb filters, pellet-shaped filters, plate-shaped filters, foamed ceramic filters, and the like. It should be noted that, when the embodiment in which the catalyst for purifying exhaust gas of the present invention is carried on the gas-permeable substrate (filter), it is more preferable to adopt a configuration in which the catalyst for purifying exhaust gas of the present invention is supported on a particulate filter since a higher particulate matter (PM) oxidation performance can be obtained.

Moreover, a material of the gas-permeable substrate of the exhaust gas purification filter is not particularly limited, and a known material may optionally be used. Examples of the material of the gas-permeable substrate include ceramics such as cordierite, silicon carbide, mullite and aluminum titanate; Metals such as stainless steel containing chromium and aluminum; and the same.

Moreover, it is preferable to use as the filter for purifying exhaust gas one having pores with an average pore diameter of 1 to 300 μm. The use of a substrate having such an average pore diameter allows more efficient removal of particulate material by its oxidation.

Moreover, in the exhaust gas purifying filter, preferably, a coating layer of the exhaust gas purifying catalyst of the present invention is formed. The coating layer has a thickness of preferably 0.025 to 25 μm, and more preferably 0.035 to 10 μm. If the thickness of the coating layer is lower than the lower limit, it is apt to provide a sufficiently high oxidation performance because a surface of the filter can not be sufficiently coated with the catalyst containing the carrier containing alumina as a main component and the catalyst silver-containing substance and the phosphoric acid-containing substance carried on the carrier, and contact points with particulate matter decrease. Meanwhile, if the thickness of the coating layer exceeds the upper limit, the engine efficiency tends to decrease because the pores of the filter are clogged by the catalyst containing the carrier containing alumina as a main component and the silver-containing substance and the phosphoric acid-containing one Substance, which are supported on the carrier comprises, and the pressure drop of the exhaust gas increases.

Moreover, in the filter for purifying exhaust gas, the amount of the catalyst carried on the gas-permeable substrate is not particularly limited, and the amount may be adjusted according to the internal combustion engine and the like, if necessary. The amount of the supported catalyst is preferably 1 to 300 g, and more preferably 10 to 100 g, per liter of the volume of the gas-permeable substrate. If the supported amount is less than the lower limit, the presence of sufficiently high catalytic performance tends to be difficult. Meanwhile, if the supported amount exceeds the upper limit, the engine efficiency tends to decrease because the pores of the gas permeable substrate are clogged by the catalyst comprising the carrier and the silver-containing substance, and the pressure loss of the exhaust gas increases.

Moreover, the exhaust gas purification filter preferably has a porosity of 30 to 70% (more preferably 40 to 65%). The "porosity" in the present case refers to a volume ratio of void fractions within the gas-permeable substrate. In addition, if the porosity is less than the lower limit, there is a higher possibility that the pores may be clogged with particulate matter in exhaust gas. However, if the porosity exceeds the upper limit, it tends to be difficult to trap particulate matter in exhaust gas, and the strength of the filter tends to decrease.

Moreover, a method for supporting the catalyst for purifying exhaust gas of the present invention on the gas-permeable substrate in the filter for purifying exhaust gas is not particularly limited, and it may be possible to use any of a method in which the catalyst containing the exhaust gas is used Support comprising alumina as a main component, and containing the silver-containing substance and the phosphoric acid-containing substance supported on the support, is prepared in advance, and this catalyst is supported on the gas-permeable substrate; a method in which the catalyst containing the carrier containing alumina as a main component and the silver-containing substance and the phosphoric acid-containing substance supported on the carrier are supported on the filter by carrying out the steps of supporting the support on the gas-permeable substrate and supporting the silver-containing substance and the phosphoric acid-containing substance on the support supported on the gas-permeable substrate; and the same. In addition, methods for supporting the catalyst, the carrier, the silver-containing substance, or the phosphoric acid-containing substance on the gas-permeable substrate are not particularly limited, and known methods may optionally be used. For example, it is possible to optionally employ a method in which a slurry of the catalyst, the carrier or the like is prepared and the gas-permeable substrate is coated with the slurry (followed, if necessary, by calcination) or the like. It should be noted that, as the catalyst for purifying exhaust gas, other known components which are useful for catalyst for oxidation of particulate material may be used as appropriate, as far as no effect of the present invention is impaired.

(Process for purifying exhaust gas)

Next, a method of purifying exhaust gas of the present invention will be described. The method of purifying exhaust gas of the present invention is a method comprising contacting exhaust gas from an internal combustion engine with the exhaust gas purifying catalyst of the present invention for oxidative particulate matter removal (PM).

In the exhaust gas purification method of the present invention, a method for contacting exhaust gas with the catalyst for purifying exhaust gas is not particularly limited, and a known method may be optionally used. For example, a method may be adopted in which exhaust gas from an internal combustion engine is contacted with the exhaust gas purifying catalyst by disposing the above-described exhaust gas purifying catalyst of the present invention in an exhaust pipe through which exhaust gas is exhausted the exhaust gas emitted from the internal combustion engine flows.

It should be noted that the exhaust gas purification catalyst of the present invention used in the exhaust gas purification method of the present invention can maintain a high PM oxidation activity even when exposed to a sulfur-containing gas. Thus, the catalyst can exhibit sufficiently high PM oxidation activity even when exposed to a sulfur-containing gas. By bringing exhaust gas from, for example, an internal combustion engine such as a diesel engine into contact with the exhaust gas purifying catalyst of the present invention, particulate matter (PM) in the exhaust gas can be sufficiently oxidatively removed and the exhaust gas can be purified. Moreover, particulate matter (PM) in the exhaust gas can be sufficiently oxidatively removed and the exhaust gas purified even when the catalyst is exposed to a sulfur-containing gas. From such a viewpoint, the exhaust gas purification method of the present invention may be suitably employed, for example, as a method for removing particulate matter (PM) into exhaust gas discharged from an internal combustion engine such as a diesel engine, or the like.

[Examples]

Hereinafter, the present invention will be described more concretely based on Examples and Comparative Examples. However, the present invention is not limited to the following examples.

(Example 1)

First, an aqueous solution of phosphoric acid salt was prepared by dissolving 0.61 g of sodium orthophosphate (manufactured by Alfa Aesar) in ion-exchanged water (200 g). Then, an aqueous silver nitrate solution was prepared by dissolving 1.57 g of silver nitrate (manufactured by Wako Pure Chemical Industries, Ltd.) in ion-exchanged water (100 g).

Next, 8.7 g of a supported alumina powder (manufactured by Nikki-Universal Co., Ltd., γ-Al ₂ O ₃ powder, TN 4, specific surface area: 150 m ² / g) was obtained with that obtained above aqueous phosphoric acid salt solution impregnated. Further, to the alumina powder, the aqueous silver nitrate solution as obtained above was added while stirring the alumina powder to form a deposit. Subsequently, the obtained deposit (deposited product) was filtered, dried overnight at 110 ° C, and then calcined at 500 ° C for 3 hours. Thus, silver phosphate (Ag ₃ PO ₄ ) was deposited on the Supported alumina carrier to obtain a catalyst powder. Then, this powder was mixed in a mortar and formed by a usual method (cold isostatic press (CIP)) in pellet form having particle diameters of 0.3 to 0.5 mm. Thus, a pellet-shaped catalyst (Ag ₃ PO ₄ / Al ₂ O ₃ ) was prepared. It should be noted that the atomic ratio (P / Ag) of phosphorus (P) to silver (Ag) in the catalyst was 0.33 based on the amounts of the starting materials. In addition, the amount of the supported silver-containing substance was 10 mass% based on metallic silver (Ag) in proportion to the total amount of the catalyst.

(Example 2)

A pellet-shaped catalyst (Ag ₄ P ₂ O ₇ / Al ₂ O ₃ ) was obtained in the same manner as in Example 1 except that 0.63 g of sodium pyrophosphate (manufactured by Alfa Aesar) was used as a phosphoric acid salt source in place of the sodium orthophosphate the amount of the alumina powder added was changed to 8.6 g. It should be noted that the atomic ratio (P / Ag) of phosphorus (P) to silver (Ag) in the catalyst was 0.5 based on the amounts of the starting materials. In addition, the amount of the supported silver-containing substance was 10 mass% based on metallic silver (Ag) in proportion to the total amount of the catalyst.

(Example 3)

A pellet-shaped catalyst (AgPO ₃ / Al ₂ O ₃ ) was obtained in the same manner as in Example 1 except that instead of the sodium orthophosphate, 1.11 g of sodium metaphosphate (manufactured by Wako Pure Chemical Industries, Ltd.) was used as a phosphoric acid salt source were used and the amount of the alumina powder added was changed to 8.3 g. It should be noted that the atomic ratio (P / Ag) of phosphorus (P) to silver (Ag) in the catalyst was 1.0 based on the amounts of the starting materials. In addition, the amount of the supported silver-containing substance was 10 mass% based on metallic silver (Ag) in proportion to the total amount of the catalyst.

(Example 4)

First, an aqueous silver nitrate solution was prepared by dissolving 6.28 g of silver nitrate (manufactured by Wako Pure Chemical Industries, Ltd.) in ion-exchanged water (250 g).

Next, 36.0 g of a supported alumina powder (manufactured by Nikki-Universal Co., Ltd., γ-Al ₂ O ₃ powder, TN 4, specific surface area: 150 m ² / g) was mixed with the obtained aqueous silver nitrate solution impregnated, followed by concentration to dryness, drying overnight at 110 ° C and then calcining for 3 hours at 500 ° C. Thus, a powder was obtained in which silver was supported on the alumina carrier.

Subsequently, by dissolving 1.07 g of 85% phosphoric acid (manufactured by Alfa Aesar) in ion-exchanged water (200 g), an aqueous phosphoric acid solution was prepared, and 10.0 g of the powder obtained above was impregnated with this aqueous phosphoric acid solution, followed by concentration to dryness, dry at 110 ° C overnight and then calcine at 500 ° C for 3 hours. Thus, silver and phosphoric acid were supported on the alumina carrier to obtain a catalyst powder. Then, this powder was mixed in a mortar and formed by a usual method (cold isostatic press (CIP)) in pellet form having particle diameters of 0.3 to 0.5 mm. Thus, a pellet-shaped catalyst (Ag + H ₃ PO ₄ / Al ₂ O ₃ ) was obtained. It should be noted that the atomic ratio (P / Ag) of phosphorus (P) to silver (Ag) in the catalyst was 1.0 based on the amounts of the starting materials. In addition, the amount of the supported silver-containing substance was 9.4 mass% based on metallic silver (Ag) in proportion to the total amount of the catalyst.

(Example 5)

A pellet-shaped catalyst (Ag + H ₃ PO ₄ / Al ₂ O ₃ ) was obtained in the same manner as in Example 4 except that the amount of phosphoric acid added was changed so that an atomic ratio (P / Ag) of Phosphorus (P) to silver (Ag) of 2.0 in the catalyst was achieved. It should be noted that the atomic ratio (P / Ag) of phosphorus (P) to silver (Ag) in the catalyst was 2.0 based on the amounts of the starting materials. In addition, the amount of the supported silver-containing substance was 8.8 mass% based on metallic silver (Ag) in proportion to the total amount of the catalyst.

(Example 6)

First, by dissolving 5.36 g of 85% phosphoric acid (manufactured by Alfa Aesar) in ion-exchanged water (200 g), an aqueous phosphoric acid solution was prepared.

Next, 9.04 g of a supported alumina powder (manufactured by Nikki-Universal Co., Ltd., γ-Al ₂ O ₃ powder, TN 4, specific surface area: 150 m ² / g) was mixed with the obtained aqueous phosphoric acid solution impregnated, followed by concentration to dryness, drying overnight at 110 ° C and then calcining for 3 hours at 500 ° C. Thus, a powder was obtained in which phosphoric acid was supported on the alumina support.

Subsequently, by dissolving 1.48 g of silver nitrate (manufactured by Wako Pure Chemical Industries, Ltd.) in ion-exchanged water (250 g), an aqueous silver nitrate solution was prepared. Then, 11.56 g of the powder obtained above was impregnated with this aqueous silver nitrate solution, followed by concentration to dryness, overnight drying at 110 ° C, and then calcination at 500 ° C for 3 hours. Thus, silver and phosphoric acid were supported on the alumina carrier to obtain a catalyst powder. Then, this powder was mixed in a mortar and formed by a usual method (cold isostatic press (CIP)) in pellet form having particle diameters of 0.3 to 0.5 mm. Thus, a pellet-shaped catalyst (Ag / (H ₃ PO ₄ / Al ₂ O ₃ ) or Ag / H ₃ PO ₄ / Al ₂ O ₃ ) was obtained. It should be noted that the atomic ratio (P / Ag) of phosphorus (P) to silver (Ag) in the catalyst was 5.0 based on the amounts of the starting materials. In addition, the amount of the supported silver-containing substance was 7.5 mass% based on metallic silver (Ag) in proportion to the total amount of the catalyst.

Comparative Example 1

An aqueous silver nitrate solution was prepared by dissolving 6.28 g of silver nitrate (manufactured by Wako Pure Chemical Industries, Ltd.) in ion-exchanged water (250 g). Next, 36.00 g of an alumina powder (manufactured by Nikki-Universal Co., Ltd., γ-Al ₂ O ₃ powder, TN 4, specific surface area: 150 m ² / g) was impregnated with the obtained aqueous silver nitrate solution, followed by Concentrate to dryness, dry overnight at 110 ° C, and then calcine at 500 ° C for 3 hours. Thus, silver (Ag) was supported on the alumina powder to obtain a catalyst powder for comparison. Then, this powder was mixed in a mortar and formed by a usual method (cold isostatic press (CIP)) in pellet form having particle diameters of 0.3 to 0.5 mm. Thus, a pellet-shaped comparative catalyst (Ag / Al ₂ O ₃ ) was obtained. It should be noted that the atomic ratio (P / Ag) of phosphorus (P) to silver (Ag) in the catalyst was 0.0, based on the amounts of the starting materials. In addition, the amount of the supported silver-containing substance was 10.0 mass% based on metallic silver (Ag) in proportion to the total amount of the catalyst.

(Comparative Example 2)

A pellet-shaped comparative catalyst (Ag ₃ PO ₄ / Ca ₃ (PO ₄ ) ₂ ) was obtained in the same manner as in Example 1 except that (γ-Al ₂ O ₃ powder) was used in place of the alumina powder serving as the carrier. 8.7 g of a calcium phosphate (Ca ₃ (PO ₄ ) ₂ ) powder (manufactured by Wako Pure Chemical Industries, Ltd., specific surface area: 10 m ² / g) were used. It should be noted that the atomic ratio (P / Ag) of phosphorus (P) to silver (Ag) in the catalyst was 6.5 based on the amounts of the starting materials. About that In addition, the amount of the supported silver-containing substance was 10.0 mass% based on metallic silver (Ag) in proportion to the total amount of the catalyst.

(Comparative Example 3)

An aqueous silver nitrate solution was prepared by dissolving 1.57 g of silver nitrate (manufactured by Wako Pure Chemical Industries, Ltd.) in ion-exchanged water (250 g). Next, 9.00 g of an aluminum phosphate powder (made by Alfa Aesar, AlPO ₄ powder, specific surface area: 2.3 m ² / g) was impregnated with the obtained aqueous silver nitrate solution, followed by concentration to dryness, overnight drying at 110 ° C and then calcining for 3 hours at 500 ° C. Thus, silver (Ag) was supported on the aluminum phosphate powder to obtain a catalyst powder for comparison. Then, this powder was mixed in a mortar and formed by a usual method (cold isostatic press (CIP)) in pellet form having particle diameters of 0.3 to 0.5 mm. Thus, a pellet-shaped comparative catalyst (Ag / AlPO ₄ ) was obtained. It should be noted that the atomic ratio (P / Ag) of phosphorus (P) to silver (Ag) in the catalyst was 8.0 based on the amounts of the starting materials. In addition, the amount of the supported silver-containing substance was 10.0 mass% based on metallic silver (Ag) in proportion to the total amount of the catalyst.

[Evaluation of properties of catalysts obtained in Examples 1 to 6 and Comparative Examples 1 to 3]

<ICP emission spectroscopy>

The atomic ratio (P / Ag) of phosphorus (P) to silver (Ag) and the atomic ratio (P / Al) of phosphorus (P) to aluminum (Al) in each of the catalysts obtained in Examples 1 to 6 and Comparative Examples 1 to 3 was measured by ICP (inductively coupled plasma) emission spectroscopy.

Specifically, first, a powder of each of the obtained catalysts was subjected to ICP emission spectroscopy using an inductively coupled plasma (ICP) emission spectrometer (manufactured by Rigaku Corporation, CIROS 120EOP), and the mass fractions of silver atoms (Ag) and phosphorus atoms (P ) were quantified and the atomic ratio (P / Ag) of phosphorus (P) to silver (Ag) was calculated. In addition, the mass fractions of aluminum atoms (Al) and phosphorus atoms (P) present on the catalyst powder were quantified and the atomic ratio (P / Al) of phosphorus (P) to aluminum (Al) was calculated. Table 1 shows the results obtained. [Table 1] catalyst Atomic ratio (P / Ag) Atomic ratio (P / Al) carrier Supported material Based on quantities of starting materials Based on results of ICR emission spectroscopy Based on results of ICP emission spectroscopy example 1 Al ₂ O ₃ Ag ₃ PO ₄ 0.33 0.36 0.02 Example 2 Al ₂ O ₃ Ag ₄ P ₂ O ₇ 0.5 0.54 0.03 Example 3 Al ₂ O ₃ (AgPO ₃ ) 1.0 1.1 0.06 Example 4 Al ₂ O ₃ Ag + H ₃ PO ₄ 1.0 1.0 0.05 Example 5 Al ₂ O ₃ Ag + H ₃ PO ₄ 2.0 2.1 0.11 Example 6 Al ₂ O ₃ H ₃ PO ₄ / Ag 5.0 5.5 0.36 Vergl.bsp. 1 Al ₂ O ₃ Ag 0.0 0.0 0.00 Vergl.bsp. 2 Ca ₃ (PO ₄ ) ₂ Ag ₃ PO ₄ 6.5 - - Vergl.bsp. 3 AlPO ₄ Ag 8.0 8.6 1.00

As apparent from the results of Examples 1 to 6 and Comparative Examples 1 to 3 shown in Table 1, it was found that each of the prepared catalysts had a P / Ag atomic ratio approximately equal to that based on the amounts of the starting materials ,

<PM oxidation activity evaluation test>

The PM oxidation activity was measured by using each of the above-described catalysts obtained in Examples 1 to 6 and Comparative Examples 1 to 3 in an initial state as follows. It should be noted that the "initial state" herein refers to a state in which the catalyst after its preparation has not been subjected to any of a heat resistance test, a sulfur poisoning test and the like which will be described later.

(Sulfur poisoning treatment)

Concretely, first, in a flow-type fixed bed reaction apparatus, 1.1 g of a sample of the pellet-shaped catalyst in an initial state obtained in each of Examples 1 to 6 and Comparative Examples 1 to 3 was packed in a quartz glass reaction tube having an inner diameter of 15 mm. Moreover, to adequately oxidize SO ₂ to be supplied, a Pt / Al ₂ O ₃ (0.5 g) sufficiently poisoned with sulfur (S) was placed upstream of the catalyst sample. Subsequently, a mixed gas consisting of O ₂ (10%) + CO ₂ (10%) + H ₂ O (10%) / N ₂ (balance) was passed, and the temperature was raised to 400 ° C. Next, a mixed gas (inlet gas) consisting of SO ₂ (66 ppm), O ₂ (10%), CO ₂ (10%), H ₂ O (10%) and N ₂ (balance) under the conditions of 400 ° C (inlet gas temperature), 55.5 minutes and a gas flow rate of 7 l / minute fed into the device (sulfur poisoning treatment). It should be noted that the total amount of the sulfur component supplied in the sulfur poisoning treatment was 1.0 g / 30 g cat.

(PM mixing treatment I)

Next, by using a rotating device for experiment and research, a catalyst sample was prepared as follows. Concretely, the catalyst sample subjected to the sulfur poisoning treatment and, as a model particle (Model PM), a carbon powder (manufactured by TOKAI CARBON CO., LTD., Product name: "SEAST 9 (SAF)", average particle diameter: 19 nm) were placed in a cylindrical sample tube placed with an inner diameter of 20 mm and mixed by rotation for 1 hour on the rotating device for experiment and research. It should be noted that the amount of the model PM mixed in this PM mixing treatment with the catalyst was such an amount that a catalyst weight ratio to the model PM of 49: 1 resulted.

(Sulfur detoxification)

Subsequently, the catalyst sample subjected to the sulfur poisoning treatment and the PM mixing treatment I became a mixed gas (inlet gas) consisting of O ₂ (10%) + H ₂ O (10%) / N ₂ (balance) under the condition of a gas flow rate of 10 l / minute while raising the temperature of the catalyst inlet gas from 120 ° C to 720 ° C at a temperature increase rate of 20 ° C / minute. Thus, a sulfur decontamination treatment was performed.

(PM mixing treatment II)

Next, a sample for evaluation was prepared by mixing the sulfur-poisoning-treated catalyst sample and the carbon powder (Model-PM) with each other in the same manner as in the above described PM-mixing treatment I. It should be noted that the amount of the model -PM mixed with the catalyst in this PM mixing treatment was such an amount as to result in a catalyst weight ratio of 49: 1 to the model PM.

(Measurement of PM Oxidizing Activity of Sulfur Decontamination Treated Catalysts: PM Removal Treatment)

Then, each of the evaluation samples of Examples 1 to 3 and Comparative Examples 1 and 2 subjected to the PM mixing treatment II was mixed gas consisting of O ₂ (10%) + H ₂ O (10%) / N ₂ (balance) ( Inlet gas) under the condition of a gas flow rate of 10 l / minute while raising the temperature of the catalyst inlet gas from 120 ° C to 720 ° C at a temperature increasing rate of 20 ° C / minute. Then, the CO ₂ concentration contained in the exhaust gas discharged from the apparatus was measured in a period from the start to the end of the supply of the mixed gas. Then, based on the CO ₂ concentration in the outlet gas and the temperature of the inlet gas, the temperature (temperature of a 50% PM oxidation) of the mixed gas necessary for 50% oxidation of the carbon attached to each evaluation sample was calculated and expressed as used an index of PM oxidation activity of the sulfur decontamination treatment catalyst.

Table 2 shows the results obtained. It should be noted that the lower the temperature of 50% PM oxidation, the higher the PM oxidation activity of the sulfur decontamination treatment catalyst was. In addition, shows 1 As the PM oxidation activities of the catalysts subjected to the sulfur decontamination treatment, a graph showing the temperatures of a 50% PM oxidation of the exhaust gas purification catalysts described in Examples 1 to 3 and Comparative Examples 1 and 2 were obtained and subjected to the sulfur decontamination treatment. [Table 2] Temperature of a 50% PM oxidation [° C] example 1 547.0 Example 2 532.5 Example 3 572.8 Comp. 1 577.7 Comp. 2 579.6

Moreover, a PM removal treatment (PM oxidation activity) of each of the catalysts obtained in Examples 4 to 6 and Comparative Example 3 and subjected to the sulfur decontamination treatment was evaluated as follows. Concretely, the sulfur poisoning treatment, PM mixing treatment I, sulfur decontamination treatment, PM mixing treatment II and PM removal treatment were carried out in the same manner as in Example 1 described above, except that the catalyst sample was any of Examples 4 to 6 and Comparative Example 3 was used in a silver amount equal to that of the catalyst sample of Example 1 in the sulfur poisoning treatment, and that the gas flow rate in the PM removal treatment was changed to 7 liters / minute. The CO ₂ concentration in the exhaust gas purification catalyst subjected to the sulfur decontamination treatment was measured in the same manner as described above. The temperature of the 50% PM oxidation was calculated in the same manner as described above and used as an index of PM oxidation activity. It should be noted that, for comparison with Examples 4 to 6, the CO ₂ concentration in the evaluation sample of Comparative Example 1 was measured in the same manner as described above, except that the gas flow rate in the PM removal treatment was 7 l / Minute was changed. The temperature of the 50% PM oxidation was calculated in the same manner as described above and used as an index of PM oxidation activity.

Table 3 shows the results obtained. In addition, shows 2 as PM oxidation activities of the catalysts subjected to the sulfur detoxification treatment, a graph showing the temperatures of a 50% PM oxidation of the exhaust gas purification catalysts obtained in Examples 4 to 6 and Comparative Examples 1 and 3 and the sulfur decontamination treatment have been subjected shows. [Table 3] Temperature of a 50% PM oxidation [° C] Example 4 542.8 Example 5 536.4 Example 6 527.4 Comp. 1 553.6 Comp. 3 671.7

<Evaluation results>

As can be seen from the in Table 2 and 3 as well 1 and 2 As shown in the results, it was found that each of the exhaust gas purification catalysts of Examples 1 to 6 of the present invention was capable of exhibiting a sufficiently high PM oxidation activity even when exposed to a sulfur-containing gas.

It should be noted that, as from the in 1 It has been found that each of the exhaust gas purification catalysts of Examples 1 to 3 of the present invention, in which a silver phosphate compound was supported on alumina, had a higher PM oxidation activity and a higher resistance to sulfur poisoning than that of Comparative Example 1 in which silver was supported on alumina. In addition, as from the in 2 According to the results shown, each of the exhaust gas purification catalysts of Examples 4 to 6 of the present invention, in which silver and a phosphoric acid were added and coextrusively supported on the alumina, was found to have a higher PM oxidation activity than that of Comparative Example 1 and, as in the cases where a silver phosphate compound was supported, had high resistance to sulfur poisoning. It should be noted that the catalyst for purifying exhaust gas of Example 6 was found to have a higher PM oxidation activity and a higher resistance to sulfur poisoning than the catalysts of Examples 4 and 5. Presumably, this is because In fact, it can be seen that in Example 6, aluminum phosphate crystals were observed - the phosphoric acid-containing substance of the exhaust gas purification catalyst of Example 6 contained a crystal phase of the aluminum phosphate and prevented the sulfur component from adsorptively attaching to the carrier and reduced the poisoning. On the other hand, it was found that the comparative catalyst of Comparative Example 3 in which silver was supported on the aluminum phosphate support had a very low PM oxidation activity. The activity of the comparative catalyst of Comparative Example 3 was low, presumably because the dispersibility of silver on the supported aluminum phosphate was low.

<X-ray diffraction (XRD) measurement>

By using each of the catalysts obtained in Examples 1, 5 and 6 and Comparative Example 1 as a measurement sample, powder X-ray diffraction (XRD) measurement under the conditions was performed with a powder X-ray diffraction apparatus (manufactured by Rigaku Corporation, product name "Horizontal Sample Holder Type Ultima IV X-ray diffraction apparatus") X-ray source: Cu Kα radiation (λ = 0.15406 nm), scanning step: 0.02 °, retention time: 0.12 seconds, acceleration voltage: 40 kV and accelerating current: 40 mA. 3 shows XRD spectra of the catalysts obtained in Examples 1, 5 and 6 and Comparative Example 1 for purifying exhaust gas.

As from the in 3 As shown in the results (XRD spectra) shown, for the catalyst for purifying the exhaust gas of Example 6, in addition to a peak of silver phosphate (Ag ₃ PO ₄ ), peaks of aluminum phosphate (AlPO ₄ ) were observed, indicating that the added phosphoric acid was also reacted with alumina, which served as the carrier. Moreover, for the exhaust gas purification catalysts of Examples 1 and 5, peaks of Ag ₃ PO _{4 were} observed, and no signal attributable to silver (Ag) was observed. In view of these observations, the supported silver (Ag) in Examples 1 and 5 was apparently reacted with the phosphoric acid added or the phosphoric acid salt added to Ag ₃ PO ₄ .

In view of the results described above, it has been shown that when a catalyst for purifying exhaust gas is prepared by supporting a silver-containing substance and a phosphoric acid-containing substance on a carrier containing alumina as a main component, the catalyst will have a sufficiently high PM even then Oxidation activity when exposed to a sulfur-containing gas. In addition, it has been demonstrated that the catalyst of the present invention can maintain high oxidation activity from a low temperature even after sulfur poisoning and is useful as a catalyst for oxidation of PM.

[Industrial Applicability]

As described above, according to the present invention, it is possible to use a catalyst for purifying exhaust gas which can have a sufficiently high PM oxidation activity even when exposed to a sulfur-containing gas, and a filter for purifying exhaust gas using the catalyst and to provide a method for purifying exhaust gas using the catalyst.

Accordingly, the catalyst for purifying exhaust gas, the exhaust gas purifying filter using the catalyst, and the exhaust gas purifying method using the catalyst of the present invention are particularly useful as a PM oxidation catalyst for removing particulate matter from exhaust gas Incident combustion engine such as a diesel engine is included, as a filter for purifying exhaust gas using the PM oxidation catalyst, as a method for purifying exhaust gas using the PM oxidation catalyst, and the like.

Claims (7)

Catalyst for purifying exhaust gas, comprising: a support containing alumina as a main component; and a silver-containing substance and a phosphoric acid-containing substance, which are supported on the carrier. A catalyst for purifying exhaust gas according to claim 1, wherein a silver phosphate serving as both the silver-containing substance and the phosphoric acid-containing substance is supported on the carrier. A catalyst for purifying exhaust gas according to claim 1 or 2, wherein an atomic ratio (P / Ag) of phosphorus (P) to silver (Ag) in the catalyst for purifying exhaust gas is 0.2 to 6. A catalyst for purifying exhaust gas according to any one of claims 1 to 3, wherein an amount of the supported silver-containing substance is 3 to 50 mass% based on metallic silver in relation to a total amount of the carrier, the silver-containing substance and the phosphoric acid-containing substance. A catalyst for purifying exhaust gas according to any one of claims 1 to 4, wherein an atomic ratio (P / Al) of phosphorus (P) to aluminum (Al) in the catalyst for purifying exhaust gas is 0.15 to 0.5, and the phosphoric acid-containing substance contains a crystal phase of aluminum phosphate. A filter for purifying exhaust gas, comprising: a gas-permeable substrate; and The catalyst for purifying exhaust gas according to any one of claims 1 to 5, which is supported on the gas-permeable substrate. A method of purifying exhaust gas comprising: Contacting gas from an internal combustion engine with the exhaust gas purification catalyst according to any one of claims 1 to 5 to oxidatively remove particulate matter (PM).

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