JP2003305365A - Aqueous gas treatment catalyst and waste gas treatment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an aqueous gas treatment catalyst, which is a catalytic component-bearing metal oxide catalyst, having a further improved treatment efficiency to a waste gas containing CO at a low concentration, particularly achieving a high treatment efficiency without increasing the deposition amount of the catalytic component and keeping the high treatment efficiency stably for a long period, and to provide a waste gas treatment method. <P>SOLUTION: The aqueous gas treatment catalyst is the one for treating the waste gas containing CO at the low concentration and comprises an oxide containing a metal element other than titanium as a carrier and catalytic component A of at least one of noble metals and a catalytic component B of at least one element belonging to Groups I to III elements in the periodic table both deposited on the carrier. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an exhaust gas treatment catalyst and an exhaust gas treatment method. For more information, boiler,
TECHNICAL FIELD The present invention relates to an exhaust gas treatment catalyst that efficiently treats low-concentration CO contained in exhaust gas emitted from a gas turbine, a diesel engine, a gas engine, and various other combustion devices, and an exhaust gas treatment method using the exhaust gas treatment catalyst. .

[0002]

2. Description of the Related Art In the combustion exhaust gas discharged from various combustion devices such as a boiler, a gas turbine, a diesel engine, and a gas engine, volatility derived from unburned fuel is generally generated, although it varies depending on the combustion device and operating conditions. Organic compounds, CO, NO _x , and SO _x are contained as harmful components. In these combustion devices, in order to improve the combustion efficiency or the thermal efficiency, the volatile organic compound, C
For the purpose of reducing O and NO _x , combustion is often performed by making the supply air amount at the time of combustion larger than the theoretical air amount required to completely burn the fuel gas. Although the volatile organic compounds, CO, and NO _x in the combustion exhaust gas have been reduced by such control of the combustion state, the volatile organic compounds and a trace amount of CO still remain, and therefore, these It is necessary to treat harmful ingredients,
These combustion exhaust gases contain a large amount of oxygen corresponding to the excess air and steam generated as a result of combustion,
Therefore, in order to oxidize and treat volatile organic compounds and trace amounts of CO therein, it is necessary to develop a treatment catalyst and a treatment method that can be effectively applied even if they are contained.

Up to now, for purification of combustion exhaust gas discharged from a combustion device that burns fuel under a condition close to the theoretical air ratio, the exhaust gas contains almost no oxygen, NO _x , CO and unreacted oxygen. Since it contains a volatile organic compound of fuel, for example, a three-way catalyst such as Pt, Rh / alumina catalyst is used and has been put into practical use. This usage is carried out by passing the exhaust gas through Pt, Rh / alumina catalyst (honeycomb catalyst) under the condition of about 500 to 700 ° C., whereby NO _x in the exhaust gas,
It removes CO and unburned volatile organic compounds at the same time. However, since the target exhaust gas to be treated by this method is based on its origin, it is premised that the exhaust gas contains almost no oxygen and that the treatment temperature is about 500 to 700 ° C. This CO oxidation removal method contains a large amount of oxygen and water vapor, and is usually discharged at about 300 to 500 ° C.
It cannot be applied immediately as a method for oxidizing CO in exhaust gas containing carbon.

On the other hand, low concentration C in exhaust gas discharged at a temperature of about 300 to 500 ° C. and containing a large amount of oxygen and water vapor.
As a method of oxidizing O to render it harmless, for example, JP-A-7-241467 and JP-A-7-241468 describe a method for removing low-concentration CO oxidation in lean exhaust gas engine exhaust gas. Japanese Unexamined Patent Publication No. 7-241467 relates to a catalyst and method for oxidizing low-concentration CO in lean exhaust gas engine exhaust gas to render it harmless. This catalyst is a platinum / alumina catalyst supported on a honeycomb carrier. In addition, the amount of platinum supported is 1.2 to 2.5 g / liter. On the other hand, Japanese Unexamined Patent Publication No. 7-241468 relates to a catalyst and a method for detoxifying low-concentration CO in lean exhaust gas engine exhaust gas by deoxidizing it, but platinum-palladium / alumina supported on a honeycomb carrier as a catalyst. Alternatively, it is characterized by using a platinum-rhodium / alumina catalyst.

In the technique described in Japanese Patent Laid-Open No. 7-241467, in order to stably and effectively oxidize and remove low-concentration CO in exhaust gas discharged from a lean burn gas engine over a long period of time, it is supported on a honeycomb carrier together with alumina. It is necessary to set the supported amount of platinum to be in the range of 1.2 to 2.5 g / liter, and when the supported amount of platinum is reduced to 1 g / liter or less, low concentration CO in exhaust gas is kept for a long period of time. It could not be stably and effectively oxidized and removed. Further, in the technique described in JP-A-7-241468, the platinum / alumina catalyst supported on the honeycomb carrier is changed to platinum-palladium / alumina or platinum-rhodium / alumina catalyst, and the technique disclosed in JP-A-7-241467 is used. Problem, that is, low concentration CO in exhaust gas
It is stated that the platinum loading amount can be selected without being restricted by increasing the platinum loading amount in order to stably and effectively oxidize and remove it over a long period of time and to set it to a certain specific range. However, for that purpose, it was necessary to support palladium and rhodium, which are expensive precious metals similar to platinum, in the same amount as platinum.

In the low concentration CO removal catalyst supporting a noble metal, it is expected that the catalytic function will be improved by increasing the supported amount of the noble metal, but the material cost of the noble metal is increased by the increased supported amount, resulting in economical efficiency. Will be inferior to. Moreover, when SO _x is contained in the exhaust gas, the SO ₂ → SO ₃ conversion rate becomes high, and problems such as pipe corrosion due to SO ₃ occur. Further, it is considered that SO _x in the exhaust gas affects the catalyst performance itself, and therefore the catalyst for treating the exhaust gas containing low concentration CO must have resistance to SO _x in the exhaust gas. However, in JP-A-7-241467 and JP-A-7-241468, there is no mention of the effect of SO _x when oxidizing and detoxifying low-concentration CO in exhaust gas.

By the way, in a reaction using a catalyst, it is generally preferable that stable treatment efficiency is maintained for a long period of time. However, when the catalyst is used for a long period of time, the treatment efficiency is usually decreased due to abrasion of the surface.

[0008]

An object of the present invention is to further improve the treatment efficiency of the above-mentioned catalyst component-supporting metal oxide catalyst for exhaust gas containing low concentration CO. In particular, it is possible to achieve high treatment efficiency and to stably maintain high treatment efficiency for a long period of time without increasing the supported amount of the catalyst component.

[0009]

According to the research conducted by the present inventors, when treating low-concentration CO contained in exhaust gas, a carrier and a catalyst containing at least one noble metal element and a periodical law are used. When a catalyst supporting a catalyst component composed of at least one element contained in Tables I to III is used, the treatment performance is improved as compared with the case where only the precious metal element is supported as a catalyst component, and the use of the precious metal element is used. It was found that the amount can be reduced. At the same time, the presence of at least one element contained in Groups I to III of the Periodic Table in the catalyst suppresses SO ₂ oxidation, improves resistance to SO _x and thermal durability, and increases the amount supported. It was found that it is possible to maintain stable treatment efficiency for a long period of time even if the amount is small.

That is, an exhaust gas treating catalyst according to the present invention is a catalyst for treating an exhaust gas containing low concentration CO,
An oxide containing a metal element other than titanium is used as a carrier, and a catalyst component A composed of at least one noble metal element and a catalyst component B composed of at least one element contained in Groups I to III of the periodic table are supported. It is characterized by being done. An exhaust gas treatment method according to the present invention is a method for treating low concentration CO-containing exhaust gas, and includes a step (a) of contacting the low concentration CO-containing exhaust gas having a CO concentration of 100 ppm or less with the exhaust gas treatment catalyst of the present invention. It is characterized by

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION [Exhaust Gas Containing Low Concentration CO] The present invention can be applied to exhaust gas containing low concentration CO discharged from various ordinary industrial equipment and facilities. Specific examples include combustion exhaust gas from boilers, gas turbines, diesel engines, gas engines, heating furnaces, and various other industrial processes. In the case of combustion exhaust gas, unburned volatile compounds which are components derived from fuel but which have not been burned are contained, and their adverse effect on the environment is a problem. The exhaust gas treatment catalyst of the present invention has a low concentration C
It is also effective for treating exhaust gas containing a volatile compound in addition to O 2.

Exhaust gas may be subjected to various kinds of exhaust gas treatment before being subjected to the treatment step by the exhaust gas treatment catalyst of the present invention. Therefore, the exhaust gas discharged from the supply source and the exhaust gas processed at the exhaust gas treatment catalyst of the present invention may have different components. INDUSTRIAL APPLICABILITY The present invention is effective for exhaust gas containing low-concentration CO that is difficult to be efficiently treated by the conventional exhaust gas treatment catalyst. Specifically, it is suitable for exhaust gas having a CO concentration of 100 ppm or less. The temperature and speed of exhaust gas change depending on the discharge conditions from the supply source and the history of exhaust gas treatment.

[Catalyst Material] As the catalyst material, it is basically possible to select and use from among the materials common to the usual exhaust gas treatment catalysts. <Carrier> As the carrier, an oxide containing a metal element other than titanium is used. Examples of the oxide containing a metal element other than titanium include oxides containing a metal element such as silicon, aluminum and zirconium. For the production of the carrier, a usual technique for producing a carrier composed of a metal oxide serving as a catalyst material can be applied.

As the raw material for supplying the metal oxide serving as a carrier, a metal oxide prepared in advance can be used as it is, or a material that produces an oxide by firing can be used.
Specifically, it may be either an inorganic compound or an organic compound, for example, a hydroxide containing a predetermined metal, an ammonium salt, an ammine complex, an oxalate, a halide, a sulfate, a nitrate, a carbonate, an alkoxide, or the like. Can be used. <Catalyst component A> As the catalyst component A, at least one kind of noble metal element can be used. Specifically, for example, Pt,
Pd, Rh, Ru, Ir, Au and the like can be used. By using these elements, unburned volatile organic compounds can be efficiently treated at the same time as low-concentration CO contained in exhaust gas.

As the feedstock for the catalyst component A, materials used in ordinary catalyst production can be used. Specific examples include nitrates, halides, ammonium salts, ammine complexes, hydroxides and the like. The catalyst component A is usually supported on the carrier in the form of particles. The particle diameter of the catalyst component A is preferably an average particle diameter of 30 nm or less,
More preferably, it is 20 nm or less. The smaller the particle size of the catalyst component A and the more highly dispersed it is, the higher the activity becomes. <Catalyst component B> As catalyst component B, I
At least one element from the family can be used. Specifically, for example, Na, Li, Mg, Ca, Y, La
And Ce and the like. By adding the catalyst component B to the catalyst component A, the amount of the catalyst component A (noble metal element) used can be reduced, the treatment efficiency for low-concentration CO-containing exhaust gas is significantly improved, and SO ₂ oxidation is suppressed. The SO _x resistance and heat durability are improved, and it becomes possible to stably maintain high treatment efficiency for a long period of time.

The feed material for the catalyst component B is not particularly limited, and one or more kinds of materials used in ordinary catalyst production can be used, but organic acid salts, alkoxides and organic materials are preferable. Examples thereof include those containing an organic component such as an organic acid in the molecule such as a metal complex. <Catalyst component C (other catalyst component)> A catalyst containing the catalyst component A and the catalyst component B, V as another catalyst component,
At least one element (catalyst component C) selected from the group consisting of W, Mo, Cu, Mn, Ni, Co, Cr and Fe can be further contained. By adding these catalyst components C, it is possible to further improve the treatment efficiency for the low-concentration CO exhaust gas and to add a denitration function.

The feedstock for the catalyst component C is not particularly limited, and may be one or two types used in ordinary catalyst production.
More than one material can be used. [Support of Catalyst Component] <Support of Catalyst Component A and Catalyst Component B> The means for supporting the catalyst component A on the carrier is not particularly limited, and is basically a normal noble metal-supported metal oxide catalyst. The same means as can be adopted. The supported amount of the catalyst component A varies depending on the combination of materials and the conditions of the supporting treatment, but usually the supported amount of the catalyst component A is 0.0 with respect to the total amount of the catalyst.
05 to 2.0% by weight, preferably 0.01 to 1.
Used in the range of 0% by weight. If the supported amount of the catalyst component A is too small, the catalytic activity will be low. If the amount of the catalyst component A carried is too large, the effect for improving the activity cannot be expected, and the economical efficiency may be impaired.

The means for supporting the catalyst component B on the carrier is not particularly limited, and it can be supported by a method used in ordinary catalyst production. The supported amount of the catalyst component B is usually 0.01 to 2 with respect to the total amount of the catalyst.
The range of 0% by weight is preferable, and 0.1 to 1 is more preferable.
It is 0% by weight. If the supported amount of the catalyst component B is too small, the effect cannot be obtained, and even if the supported amount is increased beyond the above range, the effect for improving the activity cannot be expected, and the activity may be decreased on the contrary. The order of supporting the catalyst component A and the catalyst component B is not particularly limited. The catalyst component B may be loaded after the catalyst component A is loaded, the catalyst component B may be loaded before the catalyst component A is loaded, or the catalyst component A and the catalyst component B are loaded simultaneously. However, it is preferable that the catalyst component B is loaded after the catalyst component A is loaded, or the catalyst component A and the catalyst component B are loaded simultaneously.

In the treatment step of supporting the catalyst component A and the catalyst component B on the carrier, the supporting means and the supporting conditions may be selected such that the catalyst component A and the catalyst component B are unevenly distributed on the surface of the obtained catalyst as much as possible. The supporting means, supporting conditions, etc. may be selected so that they are substantially uniformly present in the entire catalyst, and there is no particular limitation. Usually, it is considered that the catalytic reaction of the catalyst components A and B occurs in the surface layer portion of the catalyst which is the contact portion with the exhaust gas. Therefore,
Even if the amount of catalyst component A or catalyst component B is the same, the exhaust gas treatment efficiency of the catalyst is enhanced by making the catalyst component unevenly distributed on the catalyst surface as much as possible, and the amount of catalyst component A, B supported is reduced while maintaining high efficiency. it can. Therefore, the cost can be reduced and the SO ₂ oxidation rate can be lowered. On the other hand, regarding the catalytic reaction of the catalyst components A and B, it is preferable that stable treatment efficiency be maintained for a long period of time. However, if the catalyst is used for a long period of time, the surface may be abraded and the treatment efficiency may gradually decrease depending on the treatment conditions. Here, even if the catalyst components A and B have the same loading amount, by making the catalyst components A and B substantially evenly present in the entire catalyst, stable treatment efficiency can be obtained even if the catalyst is worn for a long period of time. Can be maintained. Therefore, in the long term, the cost can be reduced and the state where the SO ₂ oxidation rate is low can be maintained for a long time.

Here, the fact that the catalyst component is unevenly distributed on the surface of the catalyst (surface uneven distribution) means that the catalyst is present in the surface layer of the catalyst, or to some extent in the depth direction from the surface layer. There is no particular limitation as long as it exists in the vicinity of the surface with a wide distribution range, and specifically, for example, from the surface of the catalyst to a depth of 1/4 of the inner wall thickness of the catalyst shown in FIG. 2 (a). It is preferable that 70% by weight or more of the total amount supported on the carrier is present in the region of
It is more preferably 80% by weight or more of the total supported amount, even more preferably 90% by weight or more of the total supported amount, and particularly preferably 95% by weight or more of the total supported amount.

The fact that the catalyst component is substantially uniformly present in the entire catalyst is not limited to the fact that the catalyst component is dispersed and present in a completely uniform distribution state in the entire catalyst. The area in the vicinity of the surface may be distributed more than the average, or may be distributed more in the inside than on the surface of the catalyst, but specifically, in the presence form other than the uneven distribution of the surface. Well, for example, less than 70% by weight of the total amount supported on the carrier is present in the region shown in FIG. 2A from the surface of the catalyst to a depth of 1/4 of the inner wall thickness of the catalyst. It is more preferably less than 65% by weight of the total loading, and even more preferably less than 60% by weight of the total loading.

Further, FIG. 2 (a) generally shows a catalyst component carrying region for a catalyst formed by integral molding. However, in the form shown in FIG. 2 (b), that is, the catalyst is a metal carrier. In the case of a form in which it is layered on another carrier 14 which is not active per se, such as a cordierite carrier or a cordierite carrier, the above-mentioned “inner wall thickness of the catalyst” means the total inner wall thickness of another carrier. After the thickness of 14 is subtracted from the thickness, the above-described range of the amount of loading is preferable in the "region from both surfaces of the catalyst to the depth of 1/4 of the thickness of the inner wall of the catalyst". However, for example, T in FIG.
_{When 1} is less than 1/4 T '(where T' =
T ₁ + T ₂ ) is the above in the “region from the surface to a depth of 1 / 2T ₂ ” only for the catalyst coat layer having the thickness T ₂ regardless of the amount of the catalyst coat layer having the thickness T ₁ carried on the catalyst coat layer. It is preferable that the supported amount range is

Further, even in the form in which the catalyst is coated on the other carrier 14 as described above, as shown in FIG. 2C, only on one surface of the other carrier 14. When the catalyst is coated, the thickness of only the coated catalyst portion is defined as the "inner wall thickness of the catalyst", and,
The above range of loading amount is preferable after the above "region from the catalyst surface to a depth of 1/4 of the inner wall thickness of the catalyst" is "region from the catalyst surface to a depth of 1/2 of the inner wall thickness of the catalyst". And 2 (a), 2 (b) and 2
It is assumed that all of (c) represent cross sections in the thickness direction of the inner wall of various catalysts.

The exhaust gas treating catalyst of the present invention has the above-mentioned catalyst component A and catalyst component B supported thereon, and thereby has the above-mentioned action and effect. It is more preferable to combine the state and the loaded state of the catalyst component B as follows, and each has a specific action and effect. That is, when 1) both catalyst component A and catalyst component B are unevenly distributed on the catalyst surface, 2) catalyst component A is unevenly distributed on the catalyst surface, and catalyst component B
Is present substantially uniformly throughout the catalyst, 3) both catalyst component A and catalyst component B are substantially uniformly present throughout the catalyst, and 4) catalyst component A is substantially present throughout the catalyst. When the catalyst component B is unevenly distributed on the catalyst surface. The surface unevenly loaded state and the substantially uniformly loaded state are the same as defined above.

When both the catalyst component A and the catalyst component B are unevenly distributed on the catalyst surface, the following operational effects are obtained. That is, since the CO removal reaction mainly occurs on the surface of the catalyst, both the catalyst component A, which is a noble metal, and the catalyst component B, which is an element included in Group I to III of the periodic table, are surface-coated even with the same loading amount. By making them unevenly distributed, the reaction efficiency can be markedly improved and the economy is excellent. Further, the catalyst component B can improve the CO removal activity of the catalyst component A by the so-called co-catalyst effect. In the case where the catalyst component A is unevenly distributed on the catalyst surface and the catalyst component B is substantially uniformly present in the entire catalyst, the following operational effects are obtained. That is, it is usually necessary for the catalyst to have a high oxidizing power in order to obtain a high CO removal activity, but there is a demand for selectivity to suppress the SO ₂ oxidation (SO ₂ → SO ₃ ) activity as low as possible. . Further, it is considered that the elements included in Groups I to III of the periodic table can effectively capture SO _x , and consequently can suppress SO ₂ oxidation activity. The CO removal reaction mainly occurs on the surface of the catalyst, and the SO ₂ oxidation reaction can also occur inside the catalyst. Therefore, if the catalyst component A, which is a noble metal, is unevenly distributed on the surface and the catalyst component B, which is an element contained in Groups I to III of the periodic table, is present substantially uniformly over the entire catalyst, the above selectivity in the catalyst can be improved. It can be improved efficiently.

When both the catalyst component A and the catalyst component B are substantially uniformly present in the entire catalyst, the following operational effects are obtained. That is, usually, the poisonous substance accumulates on the catalyst most on the catalyst surface, and the wear of the catalyst also progresses from the catalyst surface. Therefore, the catalyst component A, which is a noble metal, and the periodic table group I to III are included. By allowing the catalyst component B, which is an element to be contained, to exist substantially uniformly throughout the catalyst, high catalytic activity and treatment efficiency can be stably maintained for a long period of time. Further, the catalyst component B is
The so-called co-catalyst effect can improve the CO removal activity of the catalyst component A.

In the case where the catalyst component A is substantially uniformly present on the entire catalyst and the catalyst component B is unevenly distributed on the catalyst surface, the following operational effects are obtained. That is, normally
Even if an extremely small amount of SO _x (especially SO ₃ ) contained in exhaust gas has a great influence on the catalytic activity, various SO
_In order to capture _x as much as possible near the catalyst surface, the SO _x resistance of the entire catalyst is improved, that is, S
It is considered that this leads to the prevention of the decrease in the catalytic activity due to O _x, especially SO ₃ (SO ₃ is generated by the oxidation of SO _2. The catalytic component A has this oxidizing activity). The elements contained in Groups I to III of the periodic table can effectively capture SO _x . Further, the exhaust gas usually diffuses from the surface of the catalyst to the inside. Therefore, if the catalyst component B, which is an element included in Group I to III of the periodic table, is unevenly distributed on the surface and the catalyst component A, which is a noble metal, is present substantially uniformly over the entire catalyst, the catalyst component B near the surface of the catalyst The SO ₂ oxidation (SO ₂ → SO ₃ ) activity of the catalyst component A of the above is reduced, and various SO _x are trapped in the vicinity of the surface as much as possible.
Therefore, the SO _x resistance can be improved. The catalyst component A and the catalyst component B shown in the above 1) to 4) are in a supported state, and are appropriately selected depending on the properties of the low-concentration CO-containing exhaust gas to be treated, the treatment conditions, the required treatment performance, and the like. be able to.

The treatment method for supporting the catalyst component A or the catalyst component B on the carrier is not particularly limited, but for example, impregnation (solution containing catalyst component or mixed liquid (impregnation liquid))
The technique of supporting by impregnation) can be preferably applied. When the catalyst component is supported by impregnation, the catalyst component is supported by, for example, chemical adsorption or physical adsorption. Whether the catalyst component is supported by chemical adsorption or physical adsorption depends on the type of the carrier and the catalyst component to be adsorbed. It depends on how you choose and combine. Specifically, for example, when the carrier is an oxide of silicon, aluminum and zirconium and the catalyst component is hexaammine platinum hydroxide, the treatment is mainly by chemisorption, and when the carrier is an oxide of silicon, aluminum and zirconium, etc. When the catalyst component is an acetate salt of an element included in Groups I to III of the Periodic Table, the treatment is mainly physical adsorption.

In general, in the case of chemisorption, since the carrier and the catalyst component can be firmly bound to each other, once adsorbed, the catalyst component is less likely to move from the carrier. Therefore, when impregnated with the impregnating liquid containing the catalyst component (for example, when impregnating the carrier with an aqueous solution in which the catalyst component is dissolved, etc.), the impregnating liquid is absorbed, or the impregnating liquid (absorbed by the carrier is absorbed). When the catalyst component diffused in the solution (before being treated) reaches the adsorption point of the carrier, adsorption usually proceeds preferentially from the catalyst surface, and subsequent catalyst component migration is less likely to occur due to drying. . Therefore, for example, when the catalyst component is desired to be unevenly distributed on the surface, the impregnation time may be shortened, and when it is desired to disperse the catalyst component substantially uniformly throughout the catalyst,
The impregnation time may be lengthened. That is, in the loading of the catalyst component by chemisorption, the loading state such as surface uneven distribution or substantially uniform presence is affected to some extent by the drying conditions, but is greatly affected by the impregnation conditions such as the impregnation time. It is thought to receive.

Generally, in the case of physical adsorption, the bond between the carrier and the catalyst component is weaker than in chemical adsorption. Therefore, when impregnated with an impregnating liquid containing a catalyst component (for example,
When the carrier is impregnated with an aqueous solution or the like in which the catalyst component is dissolved, the catalyst component can be dispersed and present in the entire catalyst along with absorption of the impregnating liquid. The components are also easy to move. Therefore, for example, when it is desired to unevenly distribute the catalyst component on the surface, it is preferable that the impregnation time is appropriately shortened, and if possible, the catalyst component is quickly dried after impregnation so that the catalyst component moves in the catalyst surface direction together with water. If you want to disperse the catalyst in a substantially uniform manner throughout the catalyst, make the impregnation time moderately and slow the drying after impregnation to moderate the moisture movement and suppress the movement of the catalyst components. Is preferred. That is, in the loading of the catalyst component by physical adsorption, the loading state such as surface uneven distribution or substantially uniform presence is a balance between the impregnation conditions such as impregnation time and the drying conditions, but usually the drying conditions It is thought that this will be greatly affected by.

The conditions for supporting the catalyst component by chemisorption will be described in detail below. In the supporting treatment of the catalyst components A and B by chemisorption, first, the impregnation liquid containing the catalyst components A and B is impregnated into the carrier in a heated state. By this impregnation, chemisorption is efficiently performed, and it becomes easy to carry. Specifically, the temperature of the impregnating liquid containing the catalyst components A and B is preferably heated to 40 ° C. or higher, and 50 ° C.
Above, 60 ℃ or more, 70 ℃ or more, 80 ℃ or more or 9
0 ° C or higher is more preferable. If the temperature of the impregnating liquid is too low,
Chemisorption may be less likely to occur. The conditions for impregnation include, for example, impregnation time, pH of impregnation liquid,
Concentration of catalyst component in impregnation liquid, impregnation temperature (temperature of impregnation liquid)
Among them, the impregnation time is important. The impregnation time is defined as the time from when the carrier is impregnated with the impregnating solution containing the catalyst component until when the impregnation is completed (the carrier is taken out from the impregnating solution) (the same applies below).

The impregnation time is not particularly limited, but when the catalyst component is unevenly distributed on the surface of the catalyst, it is preferably 10 minutes or less, more preferably 5 minutes or less,
Even more preferably, it is 3 minutes or less. If it exceeds 10 minutes, it may not be possible to make the catalyst unevenly distributed on the catalyst surface. On the other hand, when the catalyst component is substantially uniformly present in the entire catalyst, it is preferably 15 minutes or more,
More preferably 20 minutes or more, even more preferably 30
More than a minute. If it is less than 15 minutes, it may not be possible to allow the catalyst to exist substantially uniformly throughout the catalyst. If necessary, a leaving time may be provided between the impregnation and the drying described below. In particular, when it is desired to allow the catalyst component to exist substantially uniformly throughout the catalyst, it may be effective not only to impregnate under the above-mentioned suitable impregnation conditions, but also to provide a time for leaving it thereafter.

After impregnation with the impregnating liquid containing the above catalyst component (including the above-mentioned standing time, if any, after the impregnation and before drying), the carrier and the like are dried. Here, when the catalyst component is unevenly distributed on the surface of the catalyst, it is preferable to quickly dry the carrier after impregnation, if necessary, because the catalyst component tends to be unevenly distributed on the surface of the carrier, but it is not particularly limited. However, specifically, the drying time (the time from the start of drying to the end of substantially drying) is preferably 1 hour or less, more preferably 30 minutes or less, and even more preferably 20 minutes or less. Is. Under the condition that the drying time exceeds 1 hour, the catalyst surface may not be unevenly distributed. The drying temperature is 60 to 300.
C is preferable, and more preferably 100 to 200C. If the drying temperature is lower than 60 ° C, the drying may not be sufficiently performed within the preferable drying time range,
If it exceeds 300 ° C, there is a possibility that the catalyst activity may be lowered. On the other hand, when the catalyst component is substantially uniformly present in the entire catalyst, if necessary, the carrier may be dried slowly over a period of time so that the catalyst component is sufficiently permeated to the inside of the carrier and is substantially dispersed in the entire catalyst. It is preferable that it can be uniformly present in the solution. However, it is not particularly limited, and specifically, the drying time (the time from the start of drying to the end of substantially drying) is preferably 2 hours or more,
It is more preferably 3 hours or longer, and even more preferably 5 hours or longer. If the drying time is less than 2 hours, the catalyst component may move to the catalyst surface and become unevenly distributed on the catalyst surface. The drying temperature is
10-200 degreeC is preferable, More preferably, it is 20-15.
It is 0 ° C. If the drying temperature is lower than 10 ° C., it may take too long to dry more than necessary,
If it exceeds 200 ° C., drying may occur outside the preferable drying time range, and the catalyst components may migrate to the catalyst surface, resulting in uneven distribution on the catalyst surface.

In the chemical adsorption, in any of the above-mentioned cases, the drying may be performed by ventilation drying or non-air drying, and is not particularly limited, but usually when the catalyst component is unevenly distributed on the surface of the catalyst. In the case where it is desired to carry out ventilation drying and to make the catalyst substantially uniformly exist in the whole catalyst, it is preferable to carry out drying without air. Therefore, in the case of performing ventilation drying for the purpose of unevenly distributing the catalyst component on the surface of the catalyst, the linear velocity may be appropriately set so as to satisfy the desired drying time and the like, and is not particularly limited, but specifically, 0 0.5 to 50 m
/ S is preferable, and more preferably 1 to 30 m.
/ S, and even more preferably 2 to 20 m / s.
If it is less than 0.5 m / s, it may not be possible to make the surface unevenly distributed, and if it exceeds 50 m / s, a large apparatus is required, which is not economical and the catalyst may be destroyed. The value of the linear velocity at the time of ventilation drying is the gas flow rate (m ³ / s) to be ventilated, and the cross-sectional area of the portion of the device for drying that is filled with the catalyst (however, Area, so-called empty tower cross-sectional area.)
The value is divided by (m ² ).

The conditions for supporting the catalyst component by physical adsorption will be described in detail below. The conditions for impregnation include, for example, the impregnation time and the concentration of the catalyst component in the impregnation liquid, but the impregnation time is particularly important. The impregnation time is not particularly limited, but when the catalyst component is unevenly distributed on the surface of the catalyst, it is preferably 2 minutes or less, more preferably 1 minute or less, still more preferably 30 seconds or less. With the above-mentioned impregnation time, it can be made to be unevenly distributed on the catalyst surface. On the other hand, when the catalyst component is substantially uniformly present in the entire catalyst, it is preferably 1 minute or longer, more preferably 2 minutes or longer, still more preferably 5 minutes or longer. If it is less than 1 minute, it may not be possible to successfully make it exist substantially uniformly throughout the catalyst.

If necessary, a standing time may be provided between the impregnation and the drying described below. In particular, when it is desired to allow the catalyst component to exist substantially uniformly throughout the catalyst, it may be effective not only to impregnate under the above-mentioned suitable impregnation conditions, but also to provide a time for leaving it thereafter. After impregnation with the impregnating solution containing the above catalyst component (including the above-mentioned standing time if the above-mentioned standing time is provided after the impregnation), the carrier and the like are dried. Here, when the catalyst component is unevenly distributed on the surface of the catalyst, it is possible to quickly dry the carrier after impregnation,
It is preferable that the catalyst component moves to the surface of the carrier and tends to be unevenly distributed with the movement of water or the like toward the surface of the catalyst during drying. Specifically, the drying time (the time from the start of drying to the end of substantial drying) is preferably 30 minutes or less, more preferably 20 minutes or less, and even more preferably 10 minutes or less. If the drying time exceeds 30 minutes, the catalyst component may not be able to move toward the surface of the catalyst well, or may penetrate into the inside of the catalyst, so that the catalyst may not be sufficiently unevenly distributed on the surface. The drying temperature is preferably 80 to 300 ° C, more preferably 100 to 200 ° C. If the drying temperature is lower than 80 ° C, the drying may not be sufficiently performed within the preferable drying time range, and if the drying temperature is higher than 300 ° C, the catalytic activity may be lowered. On the other hand, in the case where the catalyst component is substantially uniformly present in the entire catalyst, slowly drying the carrier over time makes it easier to maintain the state where the catalyst component is sufficiently penetrated into the carrier, resulting in It is preferable because it is likely to exist substantially uniformly over the whole. Specifically, the drying time (the time from the beginning of drying until the end of drying)
Is preferably 3 hours or longer, more preferably 5 hours or longer, and even more preferably 10 hours or longer. If the drying time is less than 3 hours, the above catalyst components may not be allowed to exist substantially uniformly over the entire catalyst due to migration of the above catalyst components to the catalyst surface and uneven distribution on the catalyst surface. There is. The drying temperature is 10
To 150 ° C is preferable, and more preferably 20 to 120 ° C.
Is. If the drying temperature is lower than 10 ° C., it may take too long to dry more than necessary.
If the temperature exceeds 0 ° C, the above-mentioned catalyst component may move to the catalyst surface and may be unevenly distributed on the catalyst surface.

In the physical adsorption, in any of the above-mentioned cases, the drying may be performed by ventilation drying or non-air drying, and is not particularly limited, but usually when the catalyst component is unevenly distributed on the surface of the catalyst. In the case where it is desired to carry out ventilation drying and to make the catalyst substantially uniformly exist in the whole catalyst, it is preferable to carry out drying without air. Therefore, in the case of performing ventilation drying for the purpose of unevenly distributing the catalyst component on the surface of the catalyst, the linear velocity thereof may be appropriately set so as to satisfy the desired drying time and the like, but is not particularly limited. ~ 50m / s
Is preferable, and more preferably 2 to 30 m /
s, and even more preferably 5 to 20 m / s. 1m
If it is less than / s, it may not be possible to make the surface unevenly distributed, and if it exceeds 50 m / s, a large device is required, which is not economical and the catalyst may be destroyed. Regarding the definition of the value of the linear velocity during ventilation drying,
This is similar to the case of the above chemical adsorption.

Regarding the treatment method for supporting the catalyst component A or the catalyst component B on the carrier, in particular, when it is desired to make the catalyst component uniformly exist in the whole catalyst, in addition to the above-mentioned supporting treatment method by impregnation, the carrier component (or calcination) is used. And a method of mixing a powder or a slurry of the catalyst component) or a solution or a mixed solution containing the powder of the catalyst component,
Examples thereof include a method of mixing a solution of a carrier component (or a compound that becomes a carrier component when calcined) and a solution containing a catalyst component and then performing coprecipitation. According to these methods, it is possible to carry out the loading substantially evenly without controlling and adjusting the drying conditions, which were the conditions that can be studied in the loading treatment method by impregnation. Specifically, for example, when it is desired to support the catalyst components A and B substantially uniformly, a powder or slurry containing a carrier component (or a compound that becomes a carrier component by firing) and both catalyst components is prepared. ,
The catalyst can be prepared by molding or coating on a carrier substrate made of metal or cordierite and then drying and firing. When only one catalyst component is supported substantially uniformly and the other is to be unevenly distributed on the surface, a powder or slurry containing a carrier component (or a compound which becomes a carrier component by firing) and one catalyst component is used. After preparation, molding or coating on a carrier substrate made of metal or cordierite, and then drying (and calcination if necessary), the other catalyst component is supported on the surface by the above-mentioned impregnation method or the like. Good.

<Supporting of catalyst component C (other catalyst component)>
The method for supporting the catalyst component C is not particularly limited, and it can be supported on the catalyst by using a method used in ordinary catalyst production. The order of loading is also not particularly limited, but the catalyst component A, the catalyst component B and the catalyst component C are loaded simultaneously, or the catalyst component C is loaded after the catalyst component A and the catalyst component B are loaded. It is preferable. The catalyst component C may be unevenly distributed on the surface of the catalyst, like the catalyst components A and B, or may be supported substantially uniformly on the entire catalyst without being unevenly distributed on the surface.

The loading amount of the catalyst component C is preferably 0.01 to 20% by weight, more preferably 0.1 to 10% by weight, based on the total amount of the catalyst.
After various catalyst components are supported on the oxide carrier containing a metal element other than titanium so as to have a predetermined supported amount from various feed materials, drying and calcination treatments can be performed, if necessary. Drying can usually be performed by treating in an air atmosphere, a nitrogen atmosphere, or a flow of these gases at a temperature range of 50 to 200 ° C. for 1 to 24 hours.
The firing can be performed by heat treatment in the temperature range of 200 to 900 ° C. for 1 to 10 hours. Usually, it is performed in an air atmosphere or under air circulation, but a gas containing a reducing gas such as nitrogen or hydrogen may be used instead of air.

The catalyst composed of a carrier supporting the catalyst component preferably has a porous structure having fine pores. The amount of pores affects the flow of exhaust gas and the loading of catalyst component particles. Usually, the total pore volume is 0.2-
A range of 0.8 cm ³ / g (mercury intrusion method) is preferable.
If the pore volume is too small, the catalytic activity may be low, and if the pore volume is too large, the mechanical strength of the catalyst may be low. The specific surface area of the catalyst also affects performance. Normally, the specific surface area is 20 to 400 m ² / g (BET
Method) is preferably adopted and is 30 to 300 m ² / g
Is more preferable. If the specific surface area is too small, the catalyst activity may not be sufficient, and if the specific surface area is too large, the catalyst activity will not increase so much, but the accumulation of catalyst poisoning components will increase or the catalyst life will decrease. There is a possibility that such adverse effects will occur.

Regarding the total pore volume and the specific surface area, it is assumed that only the portion of the entire catalyst in which the oxide containing a metal element other than titanium serves as a carrier and the catalyst component is supported on the carrier. , For example, in the case where such a portion is the whole catalyst coated and coated on yet another carrier substrate such as a non-water-absorbing heat-resistant substrate described later, the other carrier substrate The part (1) is not to be a target part for measuring the total pore volume and the specific surface area. [Catalyst Usage] The shape of the catalyst is not particularly limited, and various shapes such as a honeycomb shape, a plate shape, a net shape, a cylindrical shape, a cylindrical shape, a corrugated shape, a pipe shape, and a donut shape can be used. Incidentally, the catalyst body having various shapes as described above has a catalyst composition in which, for example, a metal oxide powder other than titanium is formed into a desired shape by using an extruder or the like, and then a catalyst component is supported. It may be an integrally molded product consisting of only the object, or a non-water-absorbing heat-resistant substrate having a desired shape may be coated with a metal oxide other than titanium, coated, and then loaded with a catalyst component. It may be In addition, a reinforcing material such as glass fiber, whiskers, or silica particles can be added to the above carrier in order to improve the strength. Further, a plurality of types of reinforcing materials may be blended as necessary. Examples of the non-water-absorbing heat-resistant base material include metal such as stainless steel, ceramics such as cordierite, mullite, and SiC, and ceramic paper manufactured by making fibrous ceramics into a paper-like material, honeycomb-shaped, plate-shaped, and net-shaped. , Columnar, cylindrical, corrugated (corrugated), pipe, donut, lattice, plate (a stack of multiple corrugated plates with a space between adjacent plates), corrugated It is possible to exemplify those processed into a shape such as.

The catalyst is usually housed in a container-shaped catalytic reactor made of metal or the like for use. The catalytic reactor is provided with an exhaust gas inlet and an exhaust port, and is provided with a structure that allows the exhaust gas to efficiently contact the catalyst housed inside. [Exhaust gas treatment method] Basically, an exhaust gas treatment technique using a normal noble metal-supported metal oxide catalyst is applied. Usually, a catalytic reactor in which a catalyst is stored is installed in the middle of an exhaust path for exhaust gas and the like. When the exhaust gas passes through the catalytic reactor, it comes into contact with the surface of the catalyst to undergo a predetermined catalytic action.

The catalyst of the present invention can simultaneously treat low-concentration CO contained in exhaust gas and unburned volatile organic compounds. By appropriately setting the conditions such as the temperature and space velocity of the combustion exhaust gas, the efficiency of exhaust gas treatment by the catalyst is improved. For example, it is preferable to treat a combustion exhaust gas having a gas temperature of 250 ° C. to 500 ° C. and a space velocity of 30,000 H ^{−1 to} 1,000,000 H ⁻¹ . More preferably, a gas temperature of 300 ° C to 450 ° C can be adopted, and the space velocity is 50,0.
00H ^{-1 to} 500,000H ^-1 can be adopted. further,
LV = 0.1 m / s (Normal) or more, or
A processing condition of less than 10 mg / m ³ (Normal) of dust is preferable.

Another exhaust gas treatment step may be combined before or after the exhaust gas treatment step using the catalyst of the present invention. As another exhaust gas treatment step, a step capable of efficiently treating components that are difficult to treat with the catalyst of the present invention is preferable. For example, if the exhaust gas treatment step with a denitration catalyst is combined with the exhaust gas treatment step with a catalyst of the present invention, nitrogen oxides can be efficiently treated with the denitration catalyst. On the other hand, in the exhaust gas treatment step using the catalyst of the present invention, it becomes possible to efficiently treat even low concentration CO and unburned volatile organic compounds. As the exhaust gas treatment technology using the above-mentioned denitration catalyst, the applicant of the present patent has previously filed a patent application.
The technology disclosed in Japanese Unexamined Patent Publication No. 0-235206 can be applied. The denitration catalyst used in this technique has a structure in which a catalyst component a (titanium oxide) and a catalyst component b (an oxide of a metal composed of vanadium or tungsten) are combined to support the catalyst component b on the catalyst component a. Have.

The known exhaust gas treatment methods described in JP-B-63-146991, JP-A-62-65721, JP-B-6-4126 and the like can be combined with the exhaust gas treatment method of the present invention. . In the present invention,
As a catalyst for treating low concentration CO contained in exhaust gas,
Noble metal element because an oxide containing a metal element other than titanium is used as a carrier, the catalyst component A and the catalyst component B are supported, and a catalyst containing the catalyst component C as necessary is used. it is possible to reduce the amount of the catalyst component comprising, or obtained very high catalytic activity, sO ₂
Oxidation is suppressed, SO _x resistance and thermal durability are improved, and stable treatment efficiency can be maintained for a long period of time. As a result, it is a very effective method for treating a large amount of low-concentration CO-containing exhaust gas discharged from a gas turbine or the like. Further, similar to the contents described in the description of the exhaust gas treatment catalyst of the present invention, a catalyst in which each of the catalyst component A and the catalyst component B is characteristically supported on a carrier, specifically, surface unevenly distributed. By using one of the four forms of catalyst depending on whether they are supported or substantially uniformly, the above-mentioned unique excellent effects can be obtained, which is a very effective method.

Exhaust gas treatment catalyst 10 shown in FIG.
Is an integrally molded catalyst, and has a honeycomb structure having a lattice-shaped cross section. The catalyst 10 includes a carrier 11 composed of an oxide containing a metal element other than titanium, a catalyst component A composed of a noble metal element such as Pt, and elements contained in Groups I to III of the periodic table such as Na and Ca. Catalyst component B consisting of
And a catalyst component C composed of V, W, etc., if necessary. Exhaust gas treatment is performed by circulating exhaust gas to be treated through a large number of rectangular passages 13 that penetrate through the lattice-shaped carrier 11. As shown in FIG. 1 (b), in the carrying region 12 of the catalyst 10, the catalyst component A and / or the catalyst component B is formed in a portion at a certain distance inside the carrier 11 from the surface facing the exhaust gas passage 13. This is a catalyst component carrying region when unevenly distributed. Further, in the case of the catalyst component that is not unevenly distributed on the surface, it is substantially uniformly present in the entire catalyst 10 including the supporting region 12.

The graph shown in FIG. 1 (c) schematically shows the concentration distribution at each position of the catalyst component carried on the carrier 11 in the transverse direction of FIG. 1 (b). The concentration distribution is usually measured for each catalyst component, more specifically for each element.
As shown in the graph represented by the solid line in FIG. 1C, for example, the concentration of the catalyst component unevenly distributed on the surface sharply increases inward from the surface positions on both sides of the wall of the carrier 11. However, after reaching the maximum concentration in the middle of the carrying region 12, it rapidly decreases, and at the inner edge position of the carrying region 12, it drops to an extremely low concentration. In the central region of the carrier 11 which is inside the supporting region 12, the catalyst component is contained in a very small amount. The inner edge position of the carrying region 12 may be on the surface side including the position having a depth of 1/4 thickness (1/4 of the wall thickness of the carrier 11) from the surface of the carrier 11.
The area under the concentration graph represents the amount of the catalyst component carried on the surface that is unevenly distributed. Therefore, if the ratio of the lower area of the concentration graph in the range from the both side surfaces to the position of the depth of 1/4 of the lower area of the entire concentration graph is calculated,
The ratio of the catalyst component existing from the surface to the position where the depth is 1/4 of the thickness is obtained. In FIG. 1 (c), 70% by weight or more of the total supported amount of the catalyst component unevenly distributed on the surface is present in the region from the surface to the depth 1/4 of the thickness. In the exhaust gas treating catalyst of the present invention, when the catalyst component A and / or the catalyst component B are unevenly distributed on the surface, the concentration of the catalyst component is obtained as a concentration graph as shown by the solid line in FIG. 1 (c). The concentration is preferably determined by EPMA cross-section line analysis.

Further, as shown in the graph represented by the broken line in FIG. 1 (c), for example, the concentration of the catalyst component which is substantially uniformly present is such that the surface of both sides of the wall of the carrier 11 is It exists at a certain concentration or more at all positions from the position to the inside, and the same is true at the inner edge position of the carrying region 12. In the carrying region 12, the concentration may be slightly higher than the inner edge position of the carrying region 12. The inner edge position of the carrying region 12, which serves as a reference position for substantially uniformly existing in the entire catalyst or unevenly distributed on the catalyst surface, has a depth of 1/4 thickness (wall thickness of the carrier 11 from the surface of the carrier 11. It is sufficient that it is on the front surface side including the position of 1/4).
The area under the concentration graph represents the amount of catalyst components carried in the entire catalyst. Therefore, if the ratio of the lower area of the concentration graph in the range from the both side surfaces to the position of the depth of 1/4 thickness with respect to the lower area of the entire concentration graph is calculated, from the surface to the position of the depth of 1/4 thickness The proportion of catalyst components present between the two is determined. In FIG. 1 (c), with respect to the above-mentioned catalyst components that are substantially uniformly present, the loading amount present in the region from the surface to the depth 1/4 thickness is less than 70% by weight of the total loading amount. Is. In the exhaust gas treatment catalyst of the present invention, the concentration of the catalyst component when the catalyst component A and / or the catalyst component B is substantially uniformly present,
It is preferable that the concentration is obtained by EPMA cross-section line analysis, which gives a concentration graph as shown by the broken line in FIG.

The exhaust gas catalyst 10 having the above-mentioned structure is arranged in the middle of the exhaust passage of the exhaust gas containing low concentration CO in a gas turbine or the like. Exhaust gas having a relatively high temperature and a high velocity passes through the exhaust gas passage 13 of the catalyst 10 and contacts the catalyst 10 on the inner wall surface of the exhaust gas passage 13. As the catalyst 10,
Similar to the content described in the description of the exhaust gas treatment catalyst of the present invention, a catalyst in which each of the catalyst component A and the catalyst component B is characteristically supported on a carrier, specifically, the catalyst is unevenly distributed on the surface or 4 depending on whether or not it is supported substantially uniformly
By using any one of the catalysts in the form, the above-mentioned unique excellent effects can be obtained, which is a very effective method in exhaust gas treatment.

Combustion exhaust gas from a gas turbine or the like contains unburned volatile organic compounds such as aldehyde as a component to be treated together with low concentration CO. Catalyst 1
At 0, these low concentrations of CO and volatile organic compounds can be treated simultaneously to remove any components. Next, the results of the specific evaluation of the performance of the exhaust gas treatment catalyst of the present invention will be described.

[0052]

Examples <Example 1-1> Production of honeycomb formed body: 20 kg of commercially available silica-containing alumina powder (manufactured by SASOL, trade name: SIRALOX, containing about 5% by weight of SiO ₂ ) was used as a forming aid. Starch 4
00 g was added and mixed, and after kneading with a kneader, it was formed into a honeycomb shape having an outer shape of 80 mm square, an opening of 2.1 mm, a wall thickness of 0.4 mm and a length of 500 mm by an extrusion molding machine.
Next, after drying at 80 ° C., firing was performed at 450 ° C. for 5 hours in an air atmosphere to obtain a honeycomb formed body.

The obtained honeycomb molded body has a lattice structure as shown in FIG. 1 (a), each exhaust gas passage has an opening of 2.1 mm, and a lattice wall has a wall thickness of 0.4 mm. . Production of catalyst by supporting catalyst component: A honeycomb formed body was cut into a length of 100 mm, impregnated with an aqueous solution of hexaammineplatinum hydrate for 30 seconds, and then air-dried at 150 ° C for 20 minutes. Then, it was baked at 450 ° C. for 2 hours in an air atmosphere. Furthermore, after impregnating with an aqueous solution of calcium acetate for 30 seconds, it is air-dried at 150 ° C. for 20 minutes,
The mixture was fired at 2 ° C. for 2 hours in an air atmosphere to obtain a catalyst A in which Pt as a catalyst component A and Ca as a catalyst component B were supported on a carrier formed of a honeycomb formed body.

When the composition of the obtained catalyst A was analyzed,
Al ₂ O ₃ : SiO ₂ : Ca: Pt = 93.9: 4.9:
It was 1: 0.2 (weight ratio). The catalyst composition was analyzed by fluorescent X-ray analysis. Specifically, it was performed under the following conditions. Analytical apparatus: RIX2000 manufactured by Rigaku Corporation Sample atmosphere during analysis: Vacuum sample spin rate: 60 rpm X-ray source: Rh tube catalyst A was subjected to EPMA cross-section analysis of Pt and Ca. As a result, with respect to the amount of Pt supported, 70% by weight or more of the total amount of Pt supported in the entire catalyst was present in the region from the surface of the catalyst to a depth of 100 μm. Also,
Regarding the loading amount of Ca, less than 70% by weight of the total loading amount of the entire catalyst is 100 μm deep from the surface of the catalyst.
Existed in the area up to.

<Example 1-2> The honeycomb formed body used in Example 1-1 was cut into a length of 100 mm and impregnated with an aqueous solution of hexaammineplatinum hydrate for 20 minutes.
It was dried in a drier at 0 ° C for 1 day. Then 2 at 450 ° C
It was fired for an hour in an air atmosphere. Further, after impregnating with an aqueous solution of calcium acetate for 20 minutes, it is dried in a dryer at 120 ° C. for 1 day and fired at 450 ° C. for 2 hours in an air atmosphere, and Pt as a catalyst component A is added to a carrier made of a honeycomb formed body as a catalyst component A. A catalyst B carrying Ca as the catalyst component B was obtained. When the composition of the catalyst B was analyzed by the same method as in Example 1-1, Al ₂ O ₃ : SiO ₂ : Ca: Pt = 9.
It was 3.9: 4.9: 1: 0.2 (weight ratio).

EPM of Pt and Ca for Catalyst B
A cross section analysis was performed. As a result, regarding the amount of Pt supported, less than 70% by weight of the total amount of Pt supported in the entire catalyst was present in the region from the surface of the catalyst to a depth of 100 μm. Regarding the amount of Ca carried, less than 70% by weight of the total amount carried in the entire catalyst was present in the region from the surface of the catalyst to a depth of 100 μm. [Performance Evaluation] Using the catalysts obtained in Examples 1-1 and 1-2, the following performance evaluation tests were conducted.

<CO and acetaldehyde removal test> Test conditions: Exhaust gas composition = CH ₃ CHO: 20 ppm, CO: 20 p
pm, O ₂ : 13%, H ₂ O: 6%, N ₂ : balance gas temperature = 370 ° C space velocity (STP) = 70000Hr ^-1 CO removal rate calculation formula: CO removal rate (%) = [(reactor Inlet CO concentration)-(Reactor outlet CO concentration)] / (Reactor inlet CO concentration) x 100 Acetaldehyde removal rate calculation formula: Acetaldehyde removal rate (%) = [(Reactor inlet acetaldehyde concentration)-(Reactor outlet acetaldehyde) Concentration)] / (reactor inlet acetaldehyde concentration) × 100 <Test Results> The results of the above performance evaluation test are shown in Table 1.

[0058]

[Table 1]

<Example 2> Manufacture of honeycomb formed body: Zirconia powder was prepared by the following procedure. To 500 liters of 10 wt% ammonia water,
300 liters of zirconyl oxynitrate solution (containing about 18% by weight of ZrO ₂ ) was gradually added dropwise with stirring. The precipitate obtained is left for 3 hours, then filtered and washed with water, followed by 1
It was dried at 20 ° C. for 10 hours. Then, it was baked at 450 ° C. to obtain a zirconia powder. 20kg of this zirconia powder
To the above, 400 g of starch as a molding aid was added and mixed, and after kneading with a kneader, an external shape of 80 mm was obtained with an extrusion molding machine.
Corner, opening 2.1 mm, wall thickness 0.4 mm, length 500 m
m was formed into a honeycomb shape. Next, after drying at 80 ° C., firing was performed at 450 ° C. for 5 hours in an air atmosphere to obtain a honeycomb formed body.

The obtained honeycomb molded body has a lattice structure as shown in FIG. 1 (a), each exhaust gas passage has an opening of 2.1 mm, and a lattice wall has a wall thickness of 0.4 mm. . Production of catalyst by supporting catalyst component: A honeycomb formed body was cut into a length of 100 mm, impregnated with an aqueous solution of hexaammineplatinum hydrate for 30 seconds, and then air-dried at 150 ° C for 20 minutes. Then, it was baked at 450 ° C. for 2 hours in an air atmosphere. Furthermore, after impregnating with an aqueous solution of magnesium acetate for 20 minutes, it is dried for 1 day in a dryer at 120 ° C.
Firing was performed at 50 ° C. for 2 hours in an air atmosphere to obtain a catalyst C in which Pt as a catalyst component A and Mg as a catalyst component B were supported on a carrier formed of a honeycomb formed body.

When the composition of the catalyst C was analyzed by the same method as in Example 1-1, ZrO ₂ : Mg: Pt = 98.
It was 9: 1: 0.1 (weight ratio). For catalyst C,
EPMA cross-section analysis of Pt and Mg was performed. As a result, with respect to the amount of Pt supported, 70% by weight or more of the total amount of Pt supported in the entire catalyst is 100% deep from the surface of the catalyst.
It existed in the region up to μm. Regarding the amount of supported Mg, less than 70% by weight of the total supported amount in the entire catalyst was present in the region from the surface of the catalyst to a depth of 100 μm. <Comparative Example 1> Pt as a catalyst component A was loaded on a carrier made of a honeycomb molded body by the same operation as in Example 2 except that the impregnation of magnesium acetate and the subsequent drying were not carried out. Catalyst D was obtained.

When the composition of catalyst D was analyzed by the same method as in Example 1-1, ZrO ₂ : Pt = 99.9:
It was 0.1 (weight ratio). For catalyst D, Pt E
PMA cross section analysis was performed. As a result, the loading amount of Pt was 70% by weight of the total loading amount of the entire catalyst.
The above was present in the region from the surface of the catalyst to a depth of 100 μm. [Performance Evaluation] Using the catalysts obtained in Example 2 and Comparative Example 1, the following performance evaluation tests were conducted.

<CO, acetaldehyde removal test and
SO₂Oxidation capacity evaluation test> Test condition: Exhaust gas composition = CH₃CHO: 20ppm, CO: 20p
pm, SO₂: 20ppm, O ₂: 12%, H₂O: 4.
5%, N₂:balance Gas temperature = 355 ℃ Space velocity (STP) = 85000 Hr^-1 CO removal rate calculation formula: CO removal rate (%) = [(reactor inlet CO concentration)-(reaction
CO concentration at reactor outlet)] / (CO concentration at reactor inlet) x 100 Acetaldehyde removal rate calculation formula: Acetaldehyde removal rate (%) = [(reactor inlet acetaldehyde
Aldehyde concentration)-(Reactor outlet acetaldehyde concentration
Degree)] / (reactor inlet acetaldehyde concentration) × 100 SO₂Oxidation rate calculation formula: SO₂Oxidation rate (%) = reactor outlet S
O₃Concentration / reactor inlet SO₂Concentration x 100 <Test Results> The results of the above performance evaluation test are shown in Table 2.

[0064]

[Table 2]

<Example 3-1> Production of honeycomb formed body: In Example 1-1, a commercially available alumina powder (manufactured by SASOL, trade name: PURALOX NGa) was used instead of the commercially available silica-containing alumina powder.
A honeycomb molded body was obtained by the same operation as in Example 1-1, except that −150) was used. The obtained honeycomb molded body had a lattice-like structure as shown in FIG. 1 (a), the individual exhaust gas passage openings were 2.1 mm, and the lattice wall thickness was 0.
It is 4 mm. Production of catalyst by supporting catalyst component: A honeycomb formed body was cut into a length of 100 mm, impregnated with an aqueous solution of hexaammineplatinum hydrate for 20 minutes, and then dried in a drier at 120 ° C for 1 day. Then, it was baked at 450 ° C. for 2 hours in an air atmosphere. Furthermore, after impregnating with a lanthanum acetate aqueous solution for 20 minutes, it is dried in a dryer at 120 ° C. for 1 day,
After being baked in an air atmosphere at 0 ° C. for 2 hours, Pt as a catalyst component A and a catalyst component B are added to a carrier formed of a honeycomb molded body.
As a result, a catalyst E carrying La was obtained.

When the composition of the catalyst A was analyzed by the same method as in Example 1-1, Al ₂ O ₃ : La: Pt = 98.
It was 8: 1: 0.2 (weight ratio). For catalyst E,
EPMA cross-section analysis of Pt and La was performed. As a result, with respect to the amount of Pt supported, less than 70% by weight of the total amount of Pt supported in the entire catalyst was 100 depth from the surface of the catalyst.
It existed in the region up to μm. Regarding the amount of La carried, less than 70% by weight of the total amount carried in the entire catalyst was present in the region from the surface of the catalyst to a depth of 100 μm. <Example 3-2> The honeycomb formed body used in Example 3-1 was cut to a length of 100 mm, impregnated with an aqueous solution of hexaammineplatinum hydrate for 30 seconds, and then air-dried at 150 ° C for 20 minutes. . Then, it was baked at 450 ° C. for 2 hours in an air atmosphere. In addition, 30% lanthanum acetate solution
After impregnating for 2 seconds, air-dry at 150 ° C for 20 minutes,
Firing was performed at 450 ° C. for 2 hours in an air atmosphere to obtain a catalyst F in which Pt as a catalyst component A and La as a catalyst component B were supported on a carrier formed of a honeycomb molded body.

When the composition of the catalyst F was analyzed by the same method as in Example 1-1, Al ₂ O ₃ : La: Pt = 98.
It was 8: 1: 0.2 (weight ratio). For catalyst F,
EPMA cross-section analysis of Pt and La was performed. As a result, with respect to the amount of Pt supported, 70% by weight or more of the total amount of Pt supported in the entire catalyst is 100% deep from the surface of the catalyst.
It existed in the region up to μm. Regarding the amount of La carried, 70% by weight or more of the total amount carried in the entire catalyst was in the region from the surface of the catalyst to a depth of 100 μm. [Performance Evaluation] 50 g / m ³ (N) of silica sand having an average particle diameter of about 40 μm was added to the catalysts obtained in Examples 3-1 and 3-2.
3) at a speed of 30 m / sec
Passed for 0 minutes. The following performance evaluation test was performed using the catalyst whose surface was worn in this way.

<CO and acetaldehyde removal test> Test conditions: Exhaust gas composition = CH ₃ CHO: 20 ppm, CO: 20 p
pm, O ₂ : 14%, H ₂ O: 5%, N ₂ : balance gas temperature = 385 ° C space velocity (STP) = 50000Hr ^-1 CO removal rate calculation formula: CO removal rate (%) = [(reactor Inlet CO concentration)-(Reactor outlet CO concentration)] / (Reactor inlet CO concentration) x 100 Acetaldehyde removal rate calculation formula: Acetaldehyde removal rate (%) = [(Reactor inlet acetaldehyde concentration)-(Reactor outlet acetaldehyde) (Concentration)] / (concentration of acetaldehyde at reactor inlet) × 100 <Test Results> The results of the above performance evaluation test are shown in Table 3.

[0069]

[Table 3]

<Example 4> Manufacture of honeycomb molded body: The honeycomb molded body used in Example 2 was cut into a length of 100 mm, impregnated with an aqueous solution of hexaammineplatinum hydrate for 20 minutes, and dried at 120 ° C. It was dried in the machine for one day. Then, it was baked at 450 ° C. for 2 hours in an air atmosphere. Further, after impregnating with an aqueous solution of sodium acetate for 30 seconds, it is dried by ventilation at 150 ° C. for 20 minutes, and fired at 450 ° C. for 2 hours in an air atmosphere to form Pt as a catalyst component A on the carrier made of a honeycomb formed body, A catalyst G supporting Na as a catalyst component B was obtained.

When the composition of catalyst G was analyzed by the same method as in Example 1-1, ZrO ₂ : Na: Pt = 98.
It was 8: 1: 0.2 (weight ratio). For catalyst G,
EPMA cross section analysis of Pt and Na was performed. As a result, with respect to the amount of Pt supported, less than 70% by weight of the total amount of Pt supported in the entire catalyst was 100 depth from the surface of the catalyst.
It existed in the region up to μm. As for the amount of Na supported, 70% by weight or more of the total amount supported in the entire catalyst was present in the region from the surface of the catalyst to a depth of 100 μm. <Comparative Example 2> Pt as a catalyst component A was loaded on a carrier formed of a honeycomb molded body by the same operation as in Example 4 except that impregnation with sodium acetate and drying after impregnation were not performed in Example 4. The obtained catalyst H was obtained.

When the composition of the catalyst H was analyzed by the same method as in Example 1-1, ZrO ₂ : Pt = 99.8:
It was 0.2 (weight ratio). For catalyst H, Pt E
PMA cross section analysis was performed. As a result, the loading amount of Pt was 70% by weight of the total loading amount of the entire catalyst.
Less than 100 μm was present in the region from the surface of the catalyst to a depth of 100 μm. [Performance Evaluation] Using the catalysts obtained in Example 4 and Comparative Example 2, the gas was exposed under the following conditions, and then the following performance evaluation tests were performed under the same gas conditions.

<SO _x exposure and CO / acetaldehyde removal test> Test conditions: Exhaust gas composition = CH ₃ CHO: 20 ppm, CO: 20 p
pm, SO ₂ : 300 ppm, O ₂ : 12%, H ₂ O:
8.5%, N ₂ : balance gas temperature = 325 ° C space velocity (STP) = 73000 Hr ^-1 exposure time = 130 hours CO removal rate calculation formula: CO removal rate (%) = [(reactor inlet CO concentration)- (Reactor outlet CO concentration)] / (Reactor inlet CO concentration) × 100 Acetaldehyde removal rate calculation formula: Acetaldehyde removal rate (%) = [(Reactor inlet acetaldehyde concentration)-(Reactor outlet acetaldehyde concentration)] / ( Reactor inlet acetaldehyde concentration) × 100 <Test results> Table 4 shows the results of the above performance evaluation test.

[0074]

[Table 4]

[0075]

By using the exhaust gas treatment catalyst of the present invention,
It is possible to efficiently remove low concentrations of CO and volatile organic compounds even in the presence of a large amount of oxygen and water vapor. Specifically, the exhaust gas treating catalyst of the present invention contains the catalyst component B in addition to the catalyst component A as a catalyst component, so that the CO removal performance is higher than that of the catalyst component A alone. As a result, the amount of catalyst component A used can be reduced.
Further, by adding the catalyst component B, the SO ₂ → SO ₃ oxidation rate, which is a problem during operation, can be suppressed, and the SO _x resistance and heat durability of the catalyst are also improved. Further, when the catalyst component C is further added as a catalyst component, it is possible to impart denitration performance to the catalyst.

Further, in the exhaust gas treatment catalyst of the present invention, by controlling the existence state (surface uneven distribution, uniform presence) of the catalyst component A and the catalyst component B, the treatment efficiency of exhaust gas can be remarkably improved and It is possible to keep the processing efficiency stable over a period of time.

[Brief description of drawings]

FIG. 1 is a sectional view (a), an enlarged sectional view (b) and a catalyst component concentration graph (c) showing an embodiment of an exhaust gas treating catalyst of the present invention.

FIG. 2 is an enlarged cross-sectional view ((a), (b), (c)) of a catalyst showing an embodiment of an exhaust gas treating catalyst of the present invention.

[Explanation of symbols]

10 Exhaust gas treatment catalyst 11 Carrier 12 Catalyst component loading area (uneven surface distribution) 13 Exhaust gas passage

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F01N 3/28 301 B01D 53/36 Z G (72) Inventor Nobuyuki Masaki 992, Okihama Nishi, Aboshi-ku, Himeji-shi, Hyogo Prefecture No. 1 in Nippon Shokubai Co., Ltd. (72) Noboru Sugishima, inventor No. 992 Nishikioki, Hamahama-shi, Himeji-shi, Hyogo Prefecture No. 1 Incorporated in Japan Co., Ltd. (72) Motonobu Kobayashi No. 1, Nishikioki, Kibohama, Aboshi-ku, Himeji-shi, Hyogo 1 Co., Ltd. F-Term in Japan catalyst (reference) 3G091 AB02 BA01 BA19 GA06 GB03W GB04W GB05W GB10X 4D048 AA13 AA19 BA01X BA02X BA03X BA06X BA08X BA14X BA15X BA18X BA30X BA31Y BC32Y BA33BBABBABBBAABABBBAABABB05B01A02B01A02B01A02B01A02B01A02B01A02B01A02B01A02B01B02B01A02B01B02A02B01A02B01B02B01A02B03B01B02BA01A02 BC32A BC33A BC38A BC42B BC69A BC75B CA02 CA03 CA11 CA14 DA06 EA19 EC29 FA01 FA02 FB19 FB30

Claims (7)

[Claims] 1. A catalyst for treating an exhaust gas containing low concentration CO, wherein an oxide containing a metal element other than titanium is used as a carrier.
A catalyst for exhaust gas treatment, comprising: a catalyst component A composed of at least one precious metal element; and a catalyst component B composed of at least one element contained in Groups I to III of the periodic table. . 2. The exhaust gas treatment catalyst according to claim 1, wherein both the catalyst component A and the catalyst component B are unevenly distributed on the catalyst surface. 3. The catalyst component A is unevenly distributed on the surface of the catalyst, and the catalyst component B is substantially uniformly present in the entire catalyst.
The exhaust gas treatment catalyst according to claim 1. 4. The exhaust gas treatment catalyst according to claim 1, wherein both the catalyst component A and the catalyst component B are substantially uniformly present in the entire catalyst. 5. The catalyst component A is present substantially uniformly throughout the catalyst, and the catalyst component B is unevenly distributed on the catalyst surface.
The exhaust gas treatment catalyst according to claim 1. 6. The exhaust gas treatment according to claim 1, wherein the oxide containing a metal element other than titanium is at least one oxide selected from the group consisting of silicon, aluminum and zirconium. Catalyst. 7. A method for treating an exhaust gas containing low concentration CO, comprising the step of contacting the exhaust gas containing low concentration CO having a CO concentration of 100 ppm or less with the exhaust gas treatment catalyst according to any one of claims 1 to 6. An exhaust gas treatment method including (a).