JP4775954B2 - Exhaust gas purification catalyst and regeneration method thereof - Google Patents

Description

  The present invention relates to an exhaust gas purifying catalyst and a regeneration method thereof.

In order to remove harmful components such as hydrocarbon gas (HC), carbon monoxide (CO), and nitrogen oxides (NO _x ) in exhaust gas from automobile engines, exhaust gas purification catalysts have been used conventionally. As such an exhaust gas purification catalyst, a three-way catalyst that simultaneously purifies HC, CO, and NOx in exhaust gas burned at a stoichiometric air-fuel ratio is known, and is generally made of cordierite, metal foil, etc. A base material (support base material) formed in a shape, a support (catalyst support layer) made of activated alumina powder, silica powder or the like formed on the surface of the base material, and a noble metal such as platinum supported on the support And a catalyst component.

  For example, JP-A-5-317652 (Patent Document 1) discloses an exhaust gas purification catalyst in which an alkaline earth metal oxide and platinum are supported on a porous carrier.

  In JP-A-6-99069 (Patent Document 2), 1 to 20 g of palladium, 50 to 250 g of alumina, and 10 to 10 of cerium oxide per 1 l of the carrier substrate on the surface of the carrier substrate. An exhaust gas purifying catalyst comprising 150 g and a catalyst component layer supporting each catalyst component of 8 to 50 g of barium oxide is disclosed.

  Further, in Japanese Patent Application Laid-Open No. 10-174866 (Patent Document 3), a first catalyst layer in which at least palladium is supported on a first porous carrier, and a second porous layer formed on the surface of the first catalyst layer. A second catalyst layer supporting at least rhodium on the support, and the supported mass of palladium per unit mass of the first porous support in the first catalyst layer is the second porous support unit in the second catalyst layer. There is disclosed an exhaust gas purifying catalyst that is larger than the supported mass of rhodium per mass.

  However, in the exhaust gas purifying catalysts as described in Patent Documents 1 to 3, when exposed to high temperature (especially 800 ° C. or higher) exhaust gas for a long time, a catalyst such as platinum, rhodium, or palladium supported on the carrier. Since noble metal particles having activity are aggregated, sintering (granular growth) occurs and the specific surface area is reduced, there is a problem that the catalytic activity is lowered.

  For this reason, various methods have been developed to regenerate the exhaust gas purifying catalyst in which noble metal particles have grown. For example, Japanese Patent Laid-Open No. 7-75737 (Patent Document 4) discloses a method for regenerating an exhaust gas purifying catalyst in which a noble metal is supported as an active species on an inorganic porous base material, in which a halogen acts on the catalyst. A method is disclosed in which a halide of a noble metal is generated on the base material and then halogen is eliminated from the halide. However, in the method of regenerating the exhaust gas purification catalyst by acting a halogen as in the method described in Patent Document 4, it is very difficult to regenerate the catalyst while it is mounted on the exhaust system of the internal combustion engine. In addition, there is a limit to shortening the time required for the regeneration treatment for redispersing the grain-grown noble metal to regenerate the catalyst activity.

JP 2000-202309 A (Patent Document 5) discloses an exhaust gas purifying catalyst comprising a support containing at least one selected from alkaline earth metal oxides and rare earth oxides and platinum supported on the support. On the other hand, a method of performing an oxidation treatment and then performing a reduction treatment is disclosed. However, even the method described in Patent Document 5 is not necessarily sufficient in terms of shortening the time required for the regeneration treatment for regenerating the catalytic activity by redispersing the grown platinum particles and reducing the temperature. .
JP-A-5-317652 JP-A-6-99069 Japanese Patent Laid-Open No. 10-174866 JP-A-7-75737 JP 2000-202309 A

  The present invention has been made in view of the above-described problems of the prior art, and even when exposed to high-temperature exhaust gas for a long time, the aggregation of the noble metal particles is sufficiently suppressed, and the generation of noble metal grain growth is sufficiently performed over a long period of time. As a result, the decrease in catalytic activity can be sufficiently suppressed, and when grain growth occurs during use, precious metal can be redispersed in a short time even in a relatively low temperature range to facilitate catalytic activity. An object of the present invention is to provide an exhaust gas purifying catalyst that can be regenerated and that can be easily regenerated even when it is mounted on an exhaust system of an internal combustion engine, and a method for regenerating the exhaust gas purifying catalyst. .

The present inventors have made intensive studies to achieve the above object, a carrier containing a composite oxide of at least one element selected from the group consisting of zirconia A and a rare earth element and 3A group elements Surprisingly, the occurrence of noble metal grain growth is sufficiently suppressed over a long period of time by a catalyst for purification of exhaust gas comprising a noble metal supported on such a carrier and a specific additive component supported on the carrier, and catalytic activity In addition, it is possible to sufficiently suppress the decrease in the temperature, and further, by performing oxidation treatment and reduction treatment on such an exhaust gas purification catalyst, the time required for the regeneration treatment and the temperature can be reduced. As a result, it was found that the catalyst activity can be efficiently regenerated, and the present invention has been completed.

That is, the precious metal catalyst for purification of exhaust gas of the present invention comprises a support containing a composite oxide of at least one element selected from the group consisting of zirconia A and a rare earth element and 3A group elements, which is supported on the support And an additive component containing at least one element selected from the group consisting of an alkaline earth metal element, a rare earth element and a group 3A element supported on the carrier,
The amount of the noble metal supported is in the range of 0.05 to 2% by mass with respect to the mass of the catalyst, and
The loading amount of the additive component is such that the molar ratio (amount of additive component / amount of noble metal) in the range of 0.5 to 10 in terms of metal relative to the amount of the noble metal,
It is characterized by.

  In the exhaust gas purifying catalyst of the present invention, iron is further supported on the carrier, and the supported amount of iron has a molar ratio (the amount of iron / the amount of noble metal) to the amount of the noble metal in terms of metal is 0. The amount is preferably in the range of 8-12.

  In addition, the composite oxide according to the present invention preferably has a value of oxygen 1s orbital bond energy of 531 eV or less.

As examples of the composite oxide according to the present invention, a zirconia, La lanthanum, cerium, neodymium, praseodymium, be a composite oxide of at least one element selected from the group consisting of yttrium and scandium preferred .

Furthermore, the element contained in the additive component according to the present invention is at least one element selected from the group consisting of magnesium, calcium, neodymium , praseodymium , barium, lanthanum, cerium, yttrium, and scandium. preferable.

  Further, the method for regenerating an exhaust gas purifying catalyst of the present invention is a method characterized by subjecting the exhaust gas purifying catalyst of the present invention to an oxidation treatment and a reduction treatment that are heated in an oxidizing atmosphere containing oxygen. It is.

  In the regeneration method of the exhaust gas purifying catalyst of the present invention, the temperature in the oxidation treatment is preferably 500 to 1000 ° C.

  In the above method for regenerating an exhaust gas purifying catalyst of the present invention, the oxygen concentration in the oxidizing atmosphere is preferably 1% by volume or more.

  Furthermore, in the method for regenerating an exhaust gas purification catalyst of the present invention, it is preferable that the oxidation treatment and the reduction treatment are performed in a state where the exhaust gas purification catalyst is mounted on an exhaust system of an internal combustion engine.

  The reason why the above object is achieved by the exhaust gas purifying catalyst and the regeneration method of the present invention is not necessarily clear, but the present inventors speculate as follows. That is, in the exhaust gas purifying catalyst of the present invention, a composite oxide of zirconia and / or alumina and at least one element selected from the group consisting of alkaline earth metal elements, rare earth elements and 3A group elements (preferably In addition, a complex oxide having a high electron density of oxygen and having a binding energy value of oxygen 1s orbital of 531 eV or less exhibits extremely strong interaction with noble metals. Since the additive containing at least one additive element selected from the group consisting of alkaline earth metal elements, rare earth elements, and Group 3A elements is supported on the carrier, the basicity of the carrier is improved. For this reason, the carrier exhibits a stronger interaction with the noble metal. Therefore, even if the exhaust gas purifying catalyst of the present invention is exposed to high temperature exhaust gas for a long time, grain growth of noble metal particles is sufficiently suppressed, and a decrease in catalytic activity can be sufficiently suppressed.

  Furthermore, when grain growth occurs using the exhaust gas purifying catalyst of the present invention for a long period of time, a strong interaction occurs at the interface between the noble metal particles supported in the grain grown state and the carrier. Therefore, when heated in an oxidizing atmosphere containing oxygen (preferably heated at 500 to 1000 ° C.), the noble metal forms a composite oxide and a metal oxide with the support and gradually spreads on the support surface. Is done. As a result, the noble metal on the support is supported in a highly dispersed state in an oxide state (redispersion) in a relatively short period of oxidation treatment, and then the noble metal in the oxide state is reduced to the metal state by performing a reduction treatment. The present inventors infer that the catalytic activity is regenerated.

  When iron (Fe) is further supported on the carrier, Fe is alloyed with a noble metal in a reducing atmosphere, and Fe is deposited on the surface of the noble metal as an oxide in an oxidizing atmosphere. Therefore, by further supporting iron (Fe) on the carrier, it is possible to more sufficiently suppress the noble metal grain growth mainly in a lean atmosphere during use, and to tend to more sufficiently suppress the decrease in catalytic activity. is there. In addition, the presence of Fe in the vicinity of the noble metal facilitates the oxidation and reduction of the noble metal, thereby improving the activity of the exhaust gas purification reaction. The speed can be improved, and the catalytic activity tends to be regenerated by making the noble metal finer.

  According to the present invention, it is possible to sufficiently suppress the occurrence of noble metal particle growth over a long period of time by sufficiently suppressing the aggregation of noble metal particles even when exposed to high temperature exhaust gas for a long time, thereby sufficiently suppressing the decrease in catalytic activity. In addition, when grain growth occurs during use, the catalytic activity can be easily regenerated by redispersing the noble metal in a short time even in a relatively low temperature range, and it can be used in the exhaust system of an internal combustion engine. It is possible to provide an exhaust gas purifying catalyst that can be easily regenerated even in a mounted state, and a method for regenerating the exhaust gas purifying catalyst.

  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. That is, the exhaust gas purifying catalyst of the present invention comprises a carrier containing a complex oxide of zirconia and / or alumina and at least one element selected from the group consisting of alkaline earth metal elements, rare earth elements and 3A group elements. A catalyst comprising a noble metal supported on the support and an additive component containing at least one element selected from the group consisting of an alkaline earth metal element, a rare earth element and a group 3A element supported on the support. And
The amount of the noble metal supported is in the range of 0.05 to 2% by mass with respect to the mass of the catalyst, and
The loading amount of the additive component is such that the molar ratio (amount of additive component / amount of noble metal) in the range of 0.5 to 20 in terms of metal with respect to the amount of the noble metal,
It is characterized by.

  The carrier according to the present invention contains a composite oxide of zirconia and / or alumina and at least one element selected from the group consisting of alkaline earth metal elements, rare earth elements and 3A group elements. Examples of such alkaline earth metal elements include magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). Among them, interaction with noble metals and oxides thereof. Mg, Ca, and Ba are preferable from the viewpoint of strong and high affinity. As rare earth elements and Group 3A elements, scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), terbium (Tb) Dysprosium (Dy), ytterbium (Yb), lutetium (Lu), etc. Among them, La, Ce, Nd, Pr from the viewpoint that the interaction with the noble metal and its oxide is strong and the affinity tends to be large. , Y and Sc are preferred, and La, Ce and Y are more preferred.

  In such a carrier, the above-described zirconia and / or alumina and at least one element selected from the group consisting of an alkaline earth metal element, a rare earth element, and a group 3A element must form a composite oxide. There is. That is, a state in which zirconia and / or alumina and at least one element selected from the group consisting of an alkaline earth metal element, a rare earth element, and a group 3A element coexist (for example, zirconia particles and / or alumina particles). And a state in which at least one oxide particle selected from the group consisting of alkaline earth metal oxide particles, rare earth oxide particles and 3A group oxide particles is uniformly dispersed) In addition, the precious metal on the support cannot be sufficiently redispersed, and the catalytic activity is not sufficiently regenerated.

  The ratio (composition ratio) of zirconia and / or alumina constituting such a composite oxide and at least one element selected from the group consisting of alkaline earth metal elements, rare earth elements and 3A group elements is not particularly limited. However, the ratio of zirconia and / or alumina in the composite oxide is preferably 5 to 90% by mass, and more preferably 10 to 70% by mass. When the ratio of zirconia and / or alumina in the composite oxide is less than the above lower limit, the specific surface area becomes small and the grain growth of the noble metal particles cannot be sufficiently suppressed. Even if it is adopted and regenerated, the precious metal particles on the support tend not to be sufficiently small. On the other hand, even if the above upper limit is exceeded, the precious metal particles on the support do not tend to be sufficiently small. .

  In addition, the composite oxide preferably has a value of bond energy of oxygen 1s orbitals of 531 eV or less, and particularly preferably a value of 531 to 529 eV. When a composite oxide having a binding energy value exceeding 531 eV is used, the interaction between the noble metal and the carrier is not sufficiently strong, and the noble metal on the carrier is not oxidized even when an oxidation treatment is performed during the regeneration treatment. There is a tendency not to redistribute sufficiently. On the other hand, when a composite oxide having a binding energy value of less than 529 eV is used, the interaction between the noble metal and the support becomes too strong, and the noble metal on the support is active even when the reduction treatment is performed during the regeneration process. It tends to be difficult to return to a new state.

Examples of the composite oxide satisfying such conditions include the following:
_{CeO 2 -ZrO 2 -Y 2 O 3} : 530.04eV
ZrO ₂ -La ₂ O _3: 530.64eV
CeO ₂ —ZrO ₂ : 530 eV
_{CeO 2 -ZrO 2 -La 2 O 3} -Pr 2 O 3: 529.79eV
Is mentioned.

  Moreover, the said support | carrier should just contain the above-mentioned complex oxide, and alumina, a zeolite, a zirconia etc. may further be contained as another component. In that case, the ratio of the composite oxide in the carrier according to the present invention is preferably 50% by mass or more.

Further, the shape of such a carrier is not particularly limited, but is preferably in the form of a powder because the specific surface area can be improved and higher catalytic activity can be obtained. The specific surface area of such a carrier is not particularly limited, but is preferably 1 m ² / g or more. Such a specific surface area can be calculated as a BET specific surface area from an adsorption isotherm using a BET isotherm adsorption equation.

  When the carrier is in powder form, the particle size (secondary particle size) of the carrier is not particularly limited and is preferably 5 to 200 μm. If the particle diameter is less than the lower limit, it tends to be costly and difficult to handle, and on the other hand, if it exceeds the upper limit, the exhaust gas purifying catalyst of the present invention is formed on a substrate as described later. It tends to be difficult to form a stable coat layer.

  In addition, the manufacturing method in particular of the said carrier concerning this invention is not restrict | limited, For example, it can obtain by the following methods. That is, in the presence of ammonia from an aqueous solution containing a salt of various metals (for example, nitrate) as a raw material of the composite oxide and, if necessary, a surfactant (for example, a nonionic surfactant). Thus, the composite oxide coprecipitate is produced, and the obtained coprecipitate is filtered, washed, dried, and further baked to obtain a support made of the composite oxide.

  In the exhaust gas purifying catalyst of the present invention, a noble metal is supported on the carrier. Examples of such noble metals include platinum, rhodium, palladium, osmium, iridium, and gold. From the viewpoint that the obtained exhaust gas purifying catalyst exhibits higher catalytic activity, platinum, rhodium, and palladium are preferable. From the viewpoint of regeneration, platinum and palladium are preferable.

  In the exhaust gas purifying catalyst of the present invention, the amount of the noble metal supported is in the range of 0.05 to 2% by mass (more preferably 0.1 to 0.5% by mass) with respect to the mass of the catalyst. If the amount of the noble metal supported is less than the lower limit, the catalytic activity obtained from the noble metal tends to be insufficient. On the other hand, if the amount exceeds the upper limit, the cost increases and grain growth tends to occur.

  In the exhaust gas purifying catalyst of the present invention, the noble metal is preferably supported on a carrier in the form of finer particles. The particle diameter of such noble metal is more preferably 3 nm or less, and more preferably 2 nm or less. When the particle diameter of the noble metal exceeds the upper limit, it tends to be difficult to obtain high catalytic activity.

  The method for supporting the noble metal on the carrier is not particularly limited. For example, after bringing an aqueous solution containing a salt of a noble metal (eg, dinitrodiamine salt) or a complex (eg, tetraammine complex) into contact with the carrier. A method of drying and further firing can be employed.

  In the exhaust gas purifying catalyst of the present invention, an additive component containing at least one element selected from the group consisting of an alkaline earth metal element, a rare earth element and a group 3A element is supported on the carrier. In the present invention, by supporting the supporting component on a carrier, the basicity of the carrier can be improved, and an extremely strong interaction can be imparted between the carrier and the noble metal supported on the carrier. It is possible to sufficiently suppress the occurrence of noble metal grain growth and sufficiently suppress the decrease in catalytic activity. In addition, since a very strong interaction acts between the support and the noble metal as described above, when grain growth occurs using the support, the regeneration process using the regeneration method for the exhaust gas purifying catalyst of the present invention described later is adopted. As a result, the precious metal can be redispersed in a short time to regenerate the catalytic activity.

In addition, as an element contained in such an additive component, the basicity of the carrier can be further improved to more sufficiently suppress the occurrence of grain growth, and even when grain growth occurs, the catalytic activity can be more easily performed. From the viewpoint that it can be regenerated, at least one element selected from the group consisting of magnesium, calcium, neodymium , praseodymium , barium, lanthanum, cerium, yttrium and scandium is preferred, and neodymium , barium, yttrium and scandium are more preferred. . Further, the additive component may be any component that contains the above element, and examples thereof include the element itself, oxides of the element, salts of the element (carbonates, nitrates, sulfates), and mixtures thereof. It is done.

  In addition, the supported amount of such an additive component is such that the molar ratio (amount of additive component / amount of noble metal) to the amount of the noble metal in terms of metal is in the range of 0.5 to 20 (more preferably 1 to 10). Amount. If such a molar ratio is less than the lower limit, the support amount of the additive component is not sufficient, so that the basicity of the support cannot be sufficiently improved, and the effect of sufficiently suppressing the noble metal grain growth cannot be obtained. When the upper limit is exceeded, the specific surface area of the carrier is lowered, and the dispersibility of the noble metal is lowered.

Furthermore, the loading amount of such an additive component is preferably an amount such that the additive component is 1.28 × 10 ⁻⁶ to 1.28 × 10 ⁻³ mol per 1 g of the carrier. The amount is more preferably 10 ^{−6 to} 2.56 × 10 ⁻⁴ mol.

  In addition, since the amount of such an additive component is small, it is preferable to reliably control the amount to be supported on the outer surface of the carrier, and from the viewpoint that the amount supported is preferably small in terms of cost. It is preferable that the carrier is supported at a high density in the vicinity of the outer surface. In such a state, when the carrier is in a powder form, 80% or more of the additive component is 30% from the outer surface of the carrier between the outer surface of the carrier and the center of the carrier. % Is preferably carried in the region.

  Further, the method for supporting the additive component on the carrier is not particularly limited, and for example, an aqueous solution containing a salt of the above element (for example, carbonate, nitrate, citrate, acetate, sulfate) or a complex is used. A method of drying after contact with the carrier and further firing can be employed. In addition, if necessary, the support may be preheated and stabilized, and then the additive may be supported. In the present invention, the order of loading the additive component and the noble metal on the carrier is not particularly limited.

  In the exhaust gas purifying catalyst of the present invention, it is preferable that iron is further supported on the carrier. By supporting Fe in this way, Fe is alloyed with a noble metal in a reducing atmosphere, and on the other hand, Fe is precipitated as an oxide on the surface of the noble metal in an oxidizing atmosphere. There is a tendency to sufficiently suppress the decrease in catalyst activity, and further, when the regeneration treatment adopting the regeneration method of the exhaust gas purification catalyst of the present invention described later is performed, the active point It tends to be possible to regenerate the catalytic activity by further miniaturizing the noble metal.

  The amount of iron supported is such that the molar ratio (the amount of iron / the amount of noble metal) to the amount of the noble metal in a metal conversion is in the range of 0.8 to 12 (more preferably 1 to 10). It is preferable. When the molar ratio is less than the lower limit, the amount of iron supported is small and the effect of suppressing the grain growth of the noble metal tends to be insufficient, and when the upper limit is exceeded, excessively supported iron is not supported by the support. Since the specific evaluation area is reduced and the surface of the noble metal is covered, the catalytic activity tends to be reduced.

Further, such as the supported amount of such iron, it is preferable that the iron per the carrier 1g is an amount to be ^{1.28 × 10 -6 ~5.13 × 10 -4} mol, 5.13 × 10 - ^The amount is more preferably ^{6 to} 1.28 × 10 ⁻⁴ mol.

  In the exhaust gas purifying catalyst of the present invention, the state of the iron supported on the carrier is not particularly limited, but it is preferable that the iron is supported closer to the noble metal. By supporting the iron in the vicinity of the noble metal, the effect of suppressing grain growth of the noble metal tends to be further improved, and a regeneration treatment employing the regeneration method of the exhaust gas purifying catalyst of the present invention described later was performed. In this case, the precious metal that is the active point tends to be redispersed faster.

  Further, the method for supporting such iron is not particularly limited, and for example, an aqueous solution containing an iron salt (for example, carbonate, nitrate, citrate, acetate, sulfate) or a complex is used as the carrier. The method of drying after making it contact and also baking can be employ | adopted. Such iron loading may be carried out simultaneously with the noble metal. For example, a method in which a mixed solution of an aqueous solution of a noble metal salt and an aqueous solution of an iron salt is brought into contact with the carrier and then dried and further fired. The method employed can be adopted.

  The form of the exhaust gas purifying catalyst of the present invention is not particularly limited, and may be a form of a honeycomb-shaped monolith catalyst, a pellet-shaped pellet catalyst, or the like. The substrate used here is not particularly limited, and is appropriately selected depending on the use of the obtained catalyst, etc., but a DPF substrate, a monolith substrate, a pellet substrate, a plate substrate, etc. are suitably employed. Is done. Also, the material of such a base material is not particularly limited, but a base material made of a ceramic such as cordierite, silicon carbide, mullite, or a base material made of a metal such as stainless steel including chromium and aluminum is suitably employed. Is done. Further, the method for producing such a catalyst is not particularly limited. For example, in the case of producing a monolithic catalyst, the honeycomb-shaped substrate formed of cordierite or metal foil is made of the above carrier powder. A method in which a coat layer is formed and a noble metal is supported thereon is preferably employed. Alternatively, the above-described carrier powder may be preliminarily supported with a noble metal, and then the noble metal-supported powder may be used to form a coating layer on the substrate.

  Further, when such an exhaust gas purifying catalyst of the present invention is used for a long time and grain growth occurs in the noble metal supported on the carrier, the exhaust gas purifying catalyst regenerating method of the present invention described later is applied. Thus, it is possible to re-disperse the noble metal and sufficiently regenerate the catalytic activity. The particle size of the noble metal supported on the carrier after such regeneration treatment is preferably 3 nm or less (more preferably 2 nm or less) from the viewpoint of obtaining high catalytic activity.

  While the exhaust gas purification catalyst of the present invention has been described above, the method for regenerating the exhaust gas purification catalyst of the present invention will be described below.

  The method for regenerating an exhaust gas purifying catalyst of the present invention is a method characterized by subjecting the exhaust gas purifying catalyst of the present invention to an oxidation treatment and a reduction treatment that are heated in an oxidizing atmosphere containing oxygen. .

  As an oxidizing atmosphere in which the oxidation treatment according to the present invention is carried out, noble metal corresponding to the number of moles can be oxidized as long as oxygen is contained, but the oxygen concentration should be 1% by volume or more. Preferably, it is 1-20 volume%, and it is more preferable. If the oxygen concentration is less than the lower limit, redispersion of the noble metal on the support tends not to proceed sufficiently. On the other hand, the higher the oxygen concentration, the better from the viewpoint of oxidation, but it exceeds the oxygen concentration in the air. In order to exceed 20% by volume, a special device such as an oxygen cylinder is required, and the cost tends to increase. Moreover, as gas other than oxygen in the oxidizing atmosphere concerning this invention, it is preferable not to contain reducing gas, and it is preferable to use nitrogen gas or an inert gas.

  The heating temperature in the oxidation treatment according to the present invention may be a temperature at which the supported noble metal is oxidized, but is preferably a temperature in the range of 500 to 1000 ° C. If the oxidation treatment temperature is less than 500 ° C., the rate of redispersion of the noble metal on the support tends to be extremely slow and does not proceed sufficiently. On the other hand, if the temperature exceeds 1000 ° C., thermal contraction of the support itself tends to occur. The activity tends to decrease.

  Further, the time required for the oxidation treatment according to the present invention is appropriately selected according to the oxidation treatment temperature and the like. If the temperature is low, it takes a long time, and if the temperature is high, it tends to be short. When the oxidation treatment temperature is 500 to 1000 ° C., the time per oxidation treatment step is preferably about 2 seconds to 1 hour. If the oxidation treatment time is less than 2 seconds, the redispersion of the noble metal on the support tends not to proceed sufficiently, whereas if it exceeds 1 hour, the redispersion action of the noble metal tends to be saturated.

  The oxidation treatment according to the present invention may be carried out in a predetermined treatment apparatus after the exhaust gas purification catalyst is taken out from the exhaust system, but is preferably carried out in a state where it is mounted on the exhaust system of the internal combustion engine. As a result, the number of man-hours for the oxidation treatment can be greatly reduced, and furthermore, the oxide of the noble metal can be reduced by circulating the exhaust gas after the oxidation treatment. When the oxidation treatment is performed with the exhaust gas purification catalyst attached to the exhaust system in this manner, for example, a large amount of air is introduced from an air valve provided upstream of the catalyst, or the air-fuel ratio (A / F) of the air-fuel mixture It is possible to increase the air-fuel ratio (A / F) of the air-fuel mixture by increasing the fuel flow rate, or conversely, greatly reducing the amount of fuel supplied. Moreover, as a heating means, a catalyst may be heated with a specific heating apparatus, and you may heat using the reaction heat on a catalyst.

  If the oxidation treatment is executed with the exhaust system mounted as described above, the oxidation treatment can be performed in real time in accordance with the degree of deterioration of the catalyst performance. For example, the oxidation treatment may be performed periodically according to the driving time and travel distance of the automobile, or the catalyst performance is detected by providing a NOx sensor or CO sensor downstream of the catalyst, and the value exceeds the reference value. In some cases, oxidation treatment may be performed.

  The reduction treatment according to the present invention can be carried out by heating the catalyst in an atmosphere in which a reducing gas such as hydrogen or carbon monoxide is present. Therefore, since the engine exhaust as a whole contains a reducing gas even in a stoichiometric atmosphere, the noble metal can be sufficiently reduced. Further, in the reduction treatment, it is sufficient that the reducing gas is contained even a little, but the concentration of the reducing gas is preferably 0.1% by volume or more. If the concentration of the reducing gas is less than the lower limit, the noble metal on the support tends to hardly return to an active state. Moreover, as gas other than the reducing gas in the reducing atmosphere concerning this invention, it is preferable not to contain oxidizing gas, and it is preferable to use nitrogen gas or an inert gas.

  The heating temperature in the reduction treatment according to the present invention may be a temperature at which the oxide of the noble metal oxidized by the oxidation treatment is reduced, but is preferably 200 ° C. or higher, and a temperature in the range of 400 to 1000 ° C. It is preferable that When the reduction treatment temperature is less than 200 ° C., the oxide of the noble metal on the support tends not to be sufficiently reduced. On the other hand, when the upper limit is exceeded, thermal contraction of the support itself tends to occur and the catalytic activity tends to decrease. .

  In addition, the time required for the reduction treatment according to the present invention is appropriately selected according to the reduction treatment temperature and the like. If the temperature is low, it takes a long time, and if the temperature is high, it tends to be short. When the reduction treatment temperature is 200 ° C. or higher, the time per one reduction treatment step is preferably about 2 seconds to 5 minutes. When the reduction treatment time is less than the lower limit, the noble metal oxide tends to be not sufficiently reduced, whereas when the upper limit is exceeded, the reduction action of the noble metal oxide tends to be saturated.

  The reduction process according to the present invention may be performed in a predetermined processing apparatus after the exhaust gas purification catalyst is taken out from the exhaust system, but it is preferably performed in a state where it is mounted on the exhaust system of the internal combustion engine. As a result, the number of reduction treatment steps can be greatly reduced, and the oxide of the noble metal can be reduced simply by circulating the exhaust gas after the oxidation treatment. Thus, when the reduction treatment is performed with the exhaust gas purification catalyst mounted on the exhaust system, for example, in the case of an automobile exhaust gas purification catalyst, the stoichiometric atmosphere or oxygen in a stoichiometric equivalence ratio is insufficient. It is preferable that the exhaust gas in a rich atmosphere is brought into contact with the exhaust gas purifying catalyst. As a result, the oxidation treatment and the reduction treatment can be performed with the exhaust gas purification catalyst mounted on the exhaust system, and the regeneration treatment of the present invention can be performed as part of the air-fuel ratio control. Moreover, as a heating means, a catalyst may be heated with a specific heating apparatus, and you may heat using the heat | fever of waste gas.

  When the oxidation treatment and the reduction treatment are each in one step, the reduction treatment is performed after the oxidation treatment. However, in the regeneration method of the present invention, the oxidation treatment and the reduction treatment may be alternately repeated. In that case, the oxidation treatment may be performed first or the reduction treatment may be performed first. Further, when the oxidation treatment and the reduction treatment are alternately repeated, the total time of the former treatment and the total time of the latter treatment are not particularly limited.

  Then, by performing such a regeneration treatment of the present invention, it is possible to make the particle diameter of the noble metal that has undergone grain growth finer to 3 nm or less (more preferably 2 nm or less). By performing such a regeneration treatment and making the noble metal particles finer to the particle diameter supported on the carrier, it becomes possible to sufficiently regenerate the catalyst activity.

  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
233 g of cerium nitrate aqueous solution (containing 28% by mass as CeO ₂ ), 152 g of zirconium oxynitrate aqueous solution (containing 18% by mass as ZrO ₂ ), 14 g of yttrium nitrate and 10 g of nonionic surfactant (product name: Leocon, manufactured by Lion Corporation) To 2000 g of the mixed aqueous solution contained, 200 g of 25% by mass ammonia water was added and stirred at room temperature for 10 minutes to obtain a coprecipitate. Next, the obtained coprecipitate was filtered and washed, dried at 110 ° C., and further calcined in the atmosphere at 1000 ° C. for 5 hours to cerium-zirconium-yttrium composite oxide (CeO ₂ —ZrO ₂ —Y _2). A carrier consisting of O ₃ ) was obtained. The composition ratio of the resulting composite oxide (CZY) was 68 wt% _CeO 2, 28 wt% _ZrO 2, 4 _wt% Y 2 _{O 3.}

  Next, 100 g of the obtained carrier was stirred in ion-exchanged water, and 3.38 g of barium nitrate was added thereto to obtain a mixed solution. Then, the obtained mixed solution is heated and evaporated to dryness, then dried at a temperature condition of 110 ° C., and further calcined in the atmosphere at a temperature condition of 500 ° C. for 5 hours, and an additive component containing barium in the carrier Was added to obtain an additive-supporting carrier.

Subsequently, the obtained additive-supported carrier was immersed in an aqueous nitric acid solution of dinitrodiamine platinum (platinum concentration: 4% by mass), filtered and washed, then dried at a temperature of 110 ° C., and further 500 ° C. in the atmosphere. The catalyst for exhaust gas purification of the present invention in the form of a powder in which an additive component containing Pt and Ba was supported on the carrier was obtained by calcining for 3 hours under the following temperature conditions. The powdery exhaust gas purifying catalyst of the present invention thus obtained is compacted at a pressure of 1 t / cm ^{2 using} a cold isostatic pressing method (CIP method), and then 0.5 to The catalyst was pulverized to a size of 1 mm to obtain a pellet-shaped catalyst. In the obtained exhaust gas purification catalyst, the supported amount of Pt is 0.5 mass%, the supported amount of Ba in the additive component is 0.000128 mol per 1 g of the carrier, and the amount of Pt and the additive component The molar ratio of the amount of Ba (Ba / Pt) was 5.

(Example 2)
A pellet-shaped exhaust gas purifying catalyst of the present invention was obtained in the same manner as in Example 1 except that 5.62 g of neodymium nitrate hexahydrate was added instead of barium nitrate. The amounts of Pt and Nd supported in the obtained exhaust gas purification catalyst are shown in Table 2.

(Example 3)
Except that the amount of barium nitrate added was changed to 0.677 g, a pellet-shaped exhaust gas purification catalyst of the present invention was obtained in the same manner as in Example 1. Table 2 shows the amounts of supported Pt and Ba in the obtained exhaust gas purification catalyst.

Example 4
Except that the amount of barium nitrate added was changed to 1.35 g, a pellet-shaped exhaust gas purification catalyst of the present invention was obtained in the same manner as in Example 1. Table 2 shows the amounts of supported Pt and Ba in the obtained exhaust gas purification catalyst.

(Example 5)
Except that the amount of barium nitrate added was changed to 6.77 g, a pellet-shaped exhaust gas purification catalyst of the present invention was obtained in the same manner as in Example 1. Table 2 shows the amounts of supported Pt and Ba in the obtained exhaust gas purification catalyst.

(Example 6)
A pellet-shaped exhaust gas purifying catalyst of the present invention was obtained in the same manner as in Example 1 except that the amount of barium nitrate added was changed to 0.677 g, and 1.05 g of iron nitrate was further added to the mixed solution. Table 2 shows the amounts of Pt, Ba, and Fe supported on the obtained exhaust gas purification catalyst.

(Example 7)
Exhaust gas purification according to the present invention in the form of pellets in the same manner as in Example 6 except that a mixed solution of barium nitrate and iron nitrate was further added with an addition amount of nitric acid aqueous solution of dinitrodiamine platinum to carry Pt, Ba and Fe simultaneously. A catalyst was obtained. Table 2 shows the amounts of Pt, Ba, and Fe supported on the obtained exhaust gas purification catalyst.

(Example 8)
A pellet-shaped exhaust gas purifying catalyst of the present invention was obtained in the same manner as in Example 4 except that the calcination temperature condition for obtaining the support was changed from 1000 ° C to 700 ° C. Table 2 shows the amounts of supported Pt and Ba in the obtained exhaust gas purification catalyst.

(Comparative Example 1)
A catalyst for purifying exhaust gas for comparison was manufactured using the same carrier as that used in Example 1. That is, 100 g of the carrier was immersed in an aqueous nitric acid solution of dinitrodiamine platinum (platinum concentration: 4 mass%), filtered, washed, dried at a temperature of 110 ° C., and further dried in the atmosphere at a temperature of 500 ° C. for 3 hours. An exhaust gas purification catalyst for comparison in the form of a powder having Pt supported on a carrier was obtained. The amount of platinum supported in the obtained catalyst was 0.5% by mass. Further, the exhaust gas purifying catalyst for comparison obtained in this way was compacted at a pressure of 1 t / cm ² by adopting a cold isostatic pressing method (CIP method), and then 0.5 The catalyst was pulverized to a size of ˜1 mm to obtain a pellet-shaped catalyst. The amount of Pt supported in the obtained exhaust gas purification catalyst is shown in Table 2.

(Comparative Example 2)
A pellet-like exhaust gas purification catalyst for comparison was obtained in the same manner as in Comparative Example 1 except that a commercially available γ-Al ₂ O ₃ powder (Grace) was used as the carrier. The amount of Pt supported in the obtained exhaust gas purification catalyst is shown in Table 2.

<Durability test>
Durability tests were performed using the pellet-shaped catalysts obtained in Examples 1 to 8 and Comparative Examples 1 and 2, respectively. That is, the catalyst was charged into the reaction vessel, and the rich gas and the lean gas shown in Table 1 were alternately flowed every 5 minutes so that the flow rate per 3 g of the catalyst was 500 cc / min. The precious metal on the support was grown by treatment for 5 hours (endurance test). The average particle diameter of the noble metal after such an endurance test was determined, and the results obtained are shown in Table 2. In addition, the average particle diameter of the noble metal was determined by a CO chemical adsorption method described in JP-A-2004-340637.

<Platinum redispersion test>
Example 9
Oxidation treatment for 30 minutes at 750 ° C. in an oxidizing atmosphere composed of 20% by volume of O ₂ and 80% by volume of N ₂ for each exhaust gas purifying catalyst obtained in Examples 1 to 8 after the durability test. (Redispersion treatment) was performed, and redispersion of the noble metal was attempted. Table 2 shows the average particle diameter of the noble metal particles of each exhaust gas purifying catalyst after such redispersion treatment. In addition, the average particle diameter of the noble metal was determined by a CO chemical adsorption method described in JP-A-2004-340637. With such redispersion treatment and reduction pretreatment by the CO chemical adsorption method, oxidation treatment and reduction treatment for each exhaust gas purification catalyst were realized, and this was designated as regeneration treatment.

(Comparative Example 3)
A redispersion of the noble metal was attempted by adopting the same method as in Example 9 except that the exhaust gas purifying catalyst obtained in Comparative Examples 1 and 2 after the durability test was used. Table 2 shows the average particle diameter of the noble metal of the exhaust gas purifying catalyst after such redispersion treatment.

  As is clear from the results shown in Table 2, it was confirmed that noble metal grain growth was more sufficiently suppressed in the exhaust gas purifying catalysts of the present invention (Examples 1 to 9). In addition, it was confirmed by the regeneration method of the present invention that the noble metal was sufficiently refined in the exhaust gas purifying catalyst of the present invention (Examples 1 to 9), thereby confirming that the catalyst activity could be easily regenerated. It was.

  As described above, according to the present invention, it is possible to sufficiently suppress the occurrence of noble metal particle growth over a long period of time by sufficiently suppressing the aggregation of noble metal particles even when exposed to high temperature exhaust gas for a long time, and thereby the catalytic activity. Can be sufficiently suppressed, and when grain growth occurs during use, the catalytic activity can be easily regenerated by redispersing the precious metal in a short time even in a relatively low temperature range. It is possible to provide an exhaust gas purifying catalyst that can be easily regenerated even when it is mounted on an exhaust system of an internal combustion engine, and a method for regenerating the exhaust gas purifying catalyst.

  Therefore, the present invention is a technique for using an exhaust gas purifying catalyst for removing harmful components such as HC, CO, NOx, etc., in exhaust gas discharged from an automobile engine for a long time without causing deterioration of catalytic activity. As very useful.

Claims (9)

Zirconia A rare earth elements and group 3A and the carrier containing a composite oxide of at least one element selected from the group consisting of elements, said a noble metal supported on a carrier, alkaline earth supported on the support A catalyst comprising an additive component containing at least one element selected from the group consisting of a metal element, a rare earth element, and a group 3A element,
The amount of the noble metal supported is in the range of 0.05 to 2% by mass with respect to the mass of the catalyst, and
The loading amount of the additive component is such that the molar ratio (amount of additive component / amount of noble metal) in the range of 0.5 to 10 in terms of metal relative to the amount of the noble metal,
An exhaust gas purifying catalyst characterized by.   Iron is further supported on the carrier, and the supported amount of iron is such that a molar ratio (amount of iron / amount of noble metal) with respect to the amount of the noble metal in a range of 0.8 to 12 in terms of metal. The exhaust gas-purifying catalyst according to claim 1.   The exhaust gas purifying catalyst according to claim 1 or 2, wherein the complex oxide has a value of bond energy of oxygen 1s orbital of 531 eV or less. The composite oxide, and zirconia, La lanthanum, cerium, neodymium, praseodymium, of claims 1 to 3, characterized in that a composite oxide of at least one element selected from the group consisting of yttrium and scandium The exhaust gas-purifying catalyst according to any one of the above. The element contained in the additive component is at least one element selected from the group consisting of magnesium, calcium, neodymium , praseodymium , barium, lanthanum, cerium, yttrium, and scandium. The exhaust gas-purifying catalyst according to any one of the above.   An exhaust gas purifying catalyst characterized by subjecting the exhaust gas purifying catalyst according to any one of claims 1 to 5 to oxidation treatment and heating treatment in an oxidizing atmosphere containing oxygen. How to play.   The method for regenerating an exhaust gas purifying catalyst according to claim 6, wherein the temperature in the oxidation treatment is 500 to 1000 ° C.   The method for regenerating an exhaust gas purifying catalyst according to claim 6 or 7, wherein the oxygen concentration in the oxidizing atmosphere is 1% by volume or more. The exhaust gas purification catalyst according to any one of claims 6 to 8, wherein the oxidation treatment and the reduction treatment are performed in a state where the exhaust gas purification catalyst is mounted on an exhaust system of an internal combustion engine. How to play.