JP2003205238A - Exhaust gas treatment catalyst and exhaust gas treatment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the treating efficiency of a metal oxide catalyst as a catalyst component for a low concentration CO-containing gas and to achieve high treating efficiency without increasing an amount of the catalyst component and also to stably maintain the efficiency over a long period of time. <P>SOLUTION: In the catalyst for treating the low concentration CO-containing gas, titanium based oxide is used as a carrier and a catalyst component A consisting of at least one kind element selected among Pt, Pd, Rh, Ru, Ir and Au, and a catalyst component B consisting of at least one kind element included in group 1-3 in the periodic table are contained. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas treatment catalyst and an exhaust gas treatment method, and more specifically, it is contained in combustion exhaust gas discharged from various combustion devices such as boilers, gas turbines, diesel engines, gas engines, etc.
Low concentration CO below ppm, or 100ppm
The target is a catalyst for efficiently treating low-concentration CO and volatile organic compounds, and an exhaust gas treatment method using such a 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 and NO _X, SO _X is contained as harmful components. In these combustion devices, in order to improve the combustion efficiency or the thermal efficiency, the volatile organic compound, C
O, for the purpose of reducing the NO _X, the supply air amount at the time of combustion, often causing combustion by more than the theoretical amount of air required to completely combust 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. 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.

Until now, it has been close to the theoretical air ratio for fuel.
Of the combustion exhaust gas emitted from the combustion device that burns under the specified conditions
For purification purposes, this exhaust gas contains almost no oxygen.
No, NO_X, CO and unburned volatile organic compounds included
For example, Pt, Rh / alumina catalyst, etc.
The original catalyst is used and is currently in practical use. This usage
As a condition, the above exhaust gas is under the condition of about 500 to 700 ° C.
Pass Pt, Rh / alumina catalyst (honeycomb catalyst)
NO in the exhaust gas _X, C
Simultaneous removal of O and unburned volatile organic compounds
Is. However, the target exhaust gas to be treated by this method
Because of its origin, it contains almost all oxygen.
And at a processing temperature of about 500-700 ° C
This CO oxidation is assumed to be carried out in
Removal methods involve large amounts of oxygen and water vapor and are usually
CO is emitted at a temperature of 300-500 ℃
As a method for oxidizing CO in exhaust gas containing carbon
Cannot be applied immediately and effectively.

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 a method for detoxifying low concentration CO in lean exhaust gas engine exhaust gas by deoxidizing it, but 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 Patent Laid-Open 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, in the case that contains the SO _X in the exhaust gas, it becomes high SO ₂ → SO ₃ conversion rate, problems such as pipe corrosion by SO ₃ is generated. Further, SO _X in the exhaust gas may affect the catalyst performance itself, and the catalyst for treating the exhaust gas containing low concentration of CO needs to 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.

[0007]

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.

[0008]

According to the research conducted by the present inventors, when treating low-concentration CO contained in exhaust gas, Pt, Pd, Rh, R using Ti-based oxide as a carrier.
a catalyst component A consisting of at least one element selected from the group consisting of u, Ir and Au, and I to III of the periodic table
Catalyst component B consisting of at least one element contained in the group
It has been found that the use of the catalyst containing and improves the treatment performance as compared with the case where only the catalyst component A is supported, and the amount of the catalyst component A used can be reduced. At the same time, the presence of the catalyst component B in the catalyst suppresses SO ₂ oxidation, resulting in SO _x
It has been found that resistance to heat resistance and heat resistance are improved, and stable treatment efficiency can be maintained for a long period of time even when the amount of catalyst component A supported is small.

That is, the exhaust gas treatment catalyst according to the present invention is a catalyst for treating exhaust gas containing low concentration CO,
Using an i-based oxide as a carrier, Pt, Pd, Rh, Ru, Ir
And a catalyst component A composed of at least one element selected from the group consisting of Au and Au, and a catalyst component B composed of at least one element contained in Groups I to III of the periodic table. The exhaust gas treatment method according to the present invention has a CO concentration of 10
A step (a) of contacting exhaust gas of 0 ppm or less with the exhaust gas treatment catalyst according to any one of claims 1 to 4 is included. [Low Concentration CO-Containing Exhaust Gas] It can be applied to low-concentration CO-containing exhaust gas 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,
The negative impact on the environment is a problem. The exhaust gas treatment catalyst of the present invention is also effective for treating exhaust gas containing a volatile compound in addition to low-concentration CO. Exhaust gas may be subjected to various kinds of exhaust gas treatment before being subjected to the treatment process by the catalyst for treating exhaust gas 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 low-concentration CO-containing exhaust gas 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 conditions and speed of the 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, basically, a material common to the ordinary exhaust gas treatment catalysts can be selected and used. <Carrier> A Ti-based oxide is used as a carrier. Ti
It may be an oxide made of only Ti, or a mixture containing Ti as a main component and other elemental components such as Si, Zr, and Al may be used. When Ti and other components are combined, the Ti content is preferably 5 to 95 mol% of the entire carrier. More preferably, 20 to 95 mol%
Is.

The Ti-Si composite oxide has a low SO ₂ oxidation rate and a strong solid acidity, and is advantageous for supporting the catalyst component A composed of a noble metal by chemisorption. For the production of the carrier, a usual technique for producing a carrier composed of a metal oxide serving as a catalyst material is applied. Preparation of Ti-Si composite oxide
The same means as for ordinary Ti-Si composite oxide can be adopted,
The techniques disclosed in the above-mentioned JP-A-53-146991 are mentioned. In particular, the technique disclosed in Japanese Patent Application No. 2000-99593, which the applicant of the present application has previously filed, is mentioned as a preferable technique. As a raw material for supplying the metal oxide as the 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, and for example, a hydroxide containing a predetermined metal, an ammonium salt, an ammine complex, an oxalate salt, a halide, a sulfate salt, a nitrate salt, a carbonate salt or the like is used. You can

<Catalyst component A> As the catalyst component A, Pt,
Pd, Rh, Ru, Ir, Au can be used. It is also possible to combine a plurality of these elements. By using these elements, unburned volatile organic compounds can be efficiently treated at the same time as low-concentration CO contained in exhaust gas. <Catalyst component B> As catalyst component B, I
At least one element from the group can be used. Specifically, Na, Li, Mg, Ca, Y, La and the like can be mentioned.

By adding the catalyst component B to the catalyst component A, the treatment efficiency for low concentration CO-containing exhaust gas is remarkably improved, and SO ₂ oxidation suppression, SO _x resistance and heat resistance are improved, It is possible to stably maintain high processing efficiency for a long period of time. <Catalyst component C> In addition to the catalyst components A and B, the catalyst component C further contains at least one element selected from the group consisting of V, W, Mo, Cu, Mn, Ni, CO, Cr and Fe. Can be made. By adding the catalyst component C, it is possible to further improve the treatment efficiency for the exhaust gas containing low-concentration CO and to add the denitration function.

[Support of Catalyst Component] Of the catalyst components, the catalyst component A is usually supported on the carrier in the form of particles. The shape of the particles may be spherical or any other shape. The average particle size is preferably 30 nm or less. More preferably, the average particle size is 20 nm or less. Catalyst component A
The smaller the particle size and the higher the dispersion state, the higher the activity. As a means for supporting the catalyst component A on the carrier, basically, a means common to the usual noble metal-supported metal oxide catalyst can be adopted. In the treatment step of supporting the particles of the catalyst component A on the carrier, the supporting means and the supporting conditions are selected so that the catalyst component particles can be unevenly distributed on the surface of the catalyst as much as possible.

[0016] Specifically, the technique of supporting the catalyst component A by chemisorption on a prepared support molded body can be preferably applied. According to the chemical adsorption, the catalyst component particles can be more intensively and firmly supported on the surface layer of the carrier, as compared with other supporting techniques such as physical adsorption. The catalyst component A may be in the form of fine particles in a highly dispersed state and may be unevenly distributed on the catalyst surface. In the case of physical adsorption, even if a small amount of energy (heating etc.) is applied, the movement of the catalyst component particles on the carrier, the accompanying aggregation of the catalyst component particles and the deterioration of the dispersibility are likely to occur. In some cases, processing cannot be performed sufficiently.

In the case of chemical adsorption, the catalyst component particles are supported on the surface of the carrier by a chemical bond, so that the movement of the catalyst component particles from the carrier is much less likely to occur than in physical adsorption. As a result, the exhaust gas treating ability on the surface of the catalyst becomes stable and the treating efficiency is improved, which is a preferable means for supporting the catalyst component A in the present invention. As a specific means of chemisorption, when a solution containing the catalyst component A is impregnated into a support in a heated state, chemisorption is efficiently performed,
It is easy to unevenly distribute the catalyst component particles on the surface layer of the carrier.
Specifically, the temperature of the solution containing the catalyst component A is preferably heated to 40 ° C. or higher, and 50 ° C. or higher, 60 ° C.
As described above, 70 ° C or higher, 80 ° C or higher, or 90 ° C or higher is more preferable. If the temperature of the solution is too low, chemisorption does not occur easily and the object of the present invention cannot be achieved.

As the supply source of the catalyst component A, the materials used for ordinary catalysts can be used. In particular,
Examples thereof include nitrates, halides, ammonium salts, ammine complexes, hydroxides and the like. If a basic complex such as an ammine complex or a hydroxide is used, chemisorption can be efficiently performed. The particles of the catalyst component A account for 70% by mass or more of the total amount supported on the carrier at a depth of 1 from the surface of the catalyst.
It is preferable to make it unevenly distributed in the region of up to 00 μm.
Preferably, 80% by mass or more of the total supported amount is unevenly distributed in the region from the surface of the catalyst to a depth of 100 μm. More preferably, 90% by mass or more of the total supported amount is unevenly distributed in the region from the surface of the catalyst to a depth of 100 μm. More preferably, 95% by mass or more of the total supported amount is unevenly distributed in the region from the surface of the catalyst to a depth of 100 μm.

The catalytic reaction is considered to occur in the surface layer portion of the catalyst. Even if the supported amount of the catalyst component is the same,
By increasing the concentration of the catalyst component in the surface layer, the efficiency of exhaust gas treatment by the catalyst is increased. If the catalyst component can be unevenly distributed and carried on the surface layer portion, the carried amount of the catalyst component can be reduced while maintaining high efficiency. Cost can be reduced and S
The O ₂ oxidation rate is also low. The amount of the catalyst component particles supported on the carrier varies depending on the combination of materials and the treatment conditions of the supporting treatment, but is usually in the range of 0.005 to 2.0 mass% of the catalyst component A relative to the total amount of the catalyst. , Preferably 0.01 to 1% by mass. If the supported amount of the catalyst component A is too small, the catalytic activity will be low. Even if the amount of the catalyst component A carried is too large, the catalytic activity cannot be improved so much and the material cost becomes high. If the supported amount of the catalyst component A is too large, the SO ₂ oxidation rate may become too high, or the dispersibility of the catalyst component particles may deteriorate and the catalyst activity may rather decrease.

The catalyst comprising a carrier carrying particles of the catalyst component A 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 0.2-0.8 cm
A range of ³ / g (mercury porosimetry) is appropriate. If the pore volume is too small, the catalytic activity will be low. If the pore volume is too large, the mechanical strength of the catalyst will be low. The specific surface area of the catalyst also affects performance. Usually a specific surface area of 30 to 250
The range of m ² / g (BET method) is adopted, and it is 40 to 200.
m ² / g is preferred. If the specific surface area is too small, the catalytic activity becomes insufficient. If the specific surface area is too large, the catalyst activity is not improved so much, but the harmful effects such as an increase in the accumulation of catalyst poisoning components and a decrease in the catalyst life occur.

There are no particular restrictions on the feedstock for the catalyst component B, and any of the materials commonly used in the production of catalysts can be used, but organic acid salts, alkoxides,
Examples thereof include those containing an organic component such as an organic acid in the molecule such as an organometallic complex. The method for supporting the catalyst component B on the catalyst is not particularly limited, and the catalyst component B can be supported on the catalyst by a method generally used for catalyst production. The order of loading is not particularly limited, but it is preferable to load the catalyst component A and the catalyst component B at the same time. The feedstock for the catalyst component C is not particularly limited, and materials used in ordinary catalyst production can be used. The method for supporting the catalyst is not particularly limited, and it can be supported on the catalyst by a method used in ordinary catalyst production. The order of loading the catalyst component A and the catalyst component B is not particularly limited, either, but the catalyst component A, the catalyst component B and the catalyst component C are loaded at the same time, or the catalyst component A and the catalyst component B are loaded and then the catalyst component is loaded. It is preferable to carry C. In addition,
Like the catalyst component A, the catalyst components B and C may be unevenly distributed on the surface of the catalyst, or may not be unevenly distributed.

The supported amount of the catalyst component B is in the range of 0.01 to 20% by weight, preferably 0.1 to 20% by weight based on the total amount of the catalyst.
It is in the range of 10% by mass. The supported amount of the catalyst component C is in the range of 0.01 to 20% by mass, preferably 0.1 to 10% by mass, based on the total amount of the catalyst. [Catalyst Usage Mode] The catalyst shape is not particularly limited, and a desired shape selected from a plate shape, a corrugated plate shape, a net shape, a honeycomb shape, a columnar shape, a cylindrical shape, and the like can be adopted. It is also possible to use a minute catalyst having a granular shape, a rod shape, a spherical shape, a ring shape, a columnar shape, or the like, which is filled in a container or deposited.

The catalyst is usually used by being housed in a container-shaped catalytic reactor made of metal or the like. 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,
Pt, Pd, Rh, R
a catalyst component A composed of at least one element selected from the group consisting of u, Ir and Au, and I to III of the periodic table.
Catalyst component B consisting of at least one element contained in the group
And V, W, Mo, Cu, and
Since a catalyst containing a catalyst component C composed of at least one element selected from the group consisting of Mn, Ni, CO, Cr and Fe is used, a very high catalytic activity is obtained and SO ₂ oxidation is performed. Is suppressed, and SO _x resistance and heat resistance 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.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION The exhaust gas treatment catalyst 10 shown in FIG. 1 (a) has a honeycomb structure having a lattice-shaped cross section. The catalyst 10 includes a carrier 11 composed of a Ti—Si composite oxide or the like, a catalyst component A made of noble metal particles such as Pt, a catalyst component B made of Na or Ca, and a catalyst component made of V or W. C and C are carried. A large number of penetrating rectangular passages 13 provided in a lattice-shaped carrier 11.
Then, the exhaust gas to be treated is circulated to perform the exhaust gas treatment.

As shown in FIG. 1 (b), in the catalyst 10, the support region 12 for the catalyst component A is unevenly distributed at a certain depth within the carrier 11 from the surface facing the exhaust gas passage 13. . The catalyst components B and C are also present on the center side of the carrying region 12 of the catalyst component A. The graph shown in FIG. 1 (c) schematically shows the distribution of the concentration of the catalyst component A carried on the carrier 11 at each position in the transverse direction of FIG. 1 (b). In the wall of the carrier 11, the concentration of the catalyst component A sharply increases from the surface positions on both sides toward the inside, reaches the maximum concentration in the middle of the carrying region 12, and then sharply decreases to the inner edge of the carrying region 12. At the position, it drops to a very low concentration near zero. The central area of the carrier 11 which is inside the supporting area 12 has a very small amount of the catalyst component A.
Is contained, but the catalyst component A is substantially absent. The inner edge position of the carrying region 12 is arranged on the surface side with respect to the position of 100 μm in depth from the surface of the carrier 11.
The area under the concentration graph represents the amount of catalyst component A supported. Therefore, for the lower area of the whole concentration graph,
If the ratio of the lower area of the concentration graph in the range from the both side surfaces to the position of 100 μm inside is calculated, it is 1 from the surface.
The ratio of the catalyst component A existing up to the position of 00 μm is obtained.

In FIG. 1 (c), of the particles of the catalyst component A supported on the carrier 11, 90% by mass or more of the total supported amount is
It exists in a region from the surface to a depth of 100 μm. The concentration of the catalyst component A in the present invention is the concentration obtained by the EPMA cross section line analysis that gives a concentration graph as shown in FIG. 1 (c). The exhaust gas catalyst 10 having the above structure is arranged in the middle of the exhaust path of the low concentration CO-containing exhaust gas 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 the exhaust gas passage 1
The inner wall surface of 3 contacts the catalyst 10.

Since the inner wall surface of the exhaust gas passage 13 of the catalyst 10 is the loading region 12 in which the concentration of the catalyst component A is high,
The exhaust gas is efficiently subjected to the catalytic action, and the exhaust gas is processed. Although the contact time of the high-speed exhaust gas with the catalyst 10 is short, the exhaust gas is surely treated by the efficient catalytic action described above. Combustion exhaust gas from a gas turbine or the like contains low-concentration CO and unburned volatile organic compounds such as aldehydes as components to be treated. The catalyst 10 can simultaneously treat these low-concentration CO and volatile organic compounds to remove any components.

Next, the results of the evaluation of the performance of the exhaust gas treatment catalyst of the present invention will be described.

[0032]

Example [Production of catalyst] <Example 1> Preparation of Ti-Si composite oxide as a carrier: 700 liters of 10 mass% ammonia water, Snowtex-20 (manufactured by Nissan Kagaku KK, silica sol, about 20 mass%) % Of SiO ₂ ) was added, stirred and mixed, and then a sulfuric acid solution of titanyl sulfate (125 g / liter as TiO ₂ ;
Sulfuric acid concentration (550 g / liter) (340 liters) was gradually added dropwise with stirring. The obtained gel was left for 3 hours, then filtered, washed with water, and then dried at 150 ° C. for 10 hours. This was fired at 500 ° C. and further pulverized using a hammer mill to obtain a powder. The composition of the obtained powder is Ti
O ₂ : SiO ₂ = 8.5: 1.5 (molar ratio), and no clear intrinsic peaks of TiO ₂ and SiO ₂ were observed in the X-ray diffraction chart of the powder, and a broad diffraction peak made it amorphous. It was confirmed to be a composite oxide of titanium and silicon having a fine microstructure (Ti-Si composite oxide).

Manufacture of honeycomb formed body: The above Ti-Si composite oxide 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.
Then, after drying at 80 ° C., it was fired at 450 ° C. for 5 hours in an air atmosphere to obtain a honeycomb formed body. The honeycomb formed body has a lattice structure as shown in FIG.
The opening of each exhaust gas passage is 2.1 mm, and the wall thickness of the lattice wall is 0.4 mm. Production of catalyst by supporting catalyst components: honeycomb formed body,
The mixture was impregnated with a mixed solution of hexaammineplatinum hydrate solution and magnesium acetate and then dried. Then 450
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 Mg 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,
Ti-Si composite oxide: Mg: Pt = 98.9: 1:
It was 0.1 (mass ratio). For catalyst A, Pt E
PMA cross-section line analysis was performed. From the result, it is possible to carry P
90 mass% or more of t is 100 μm deep from the surface of the catalyst A.
It was confirmed that it exists in the region up to m. The average particle size of Pt measured using a transmission electron microscope was less than 5 nm. <Example 2> Example 1 was repeated except that a mixed solution of hexaammineplatinum hydrate and calcium acetate was used in place of the mixed solution of hexaammineplatinum hydrate and magnesium acetate. Catalyst B was obtained in the same process.

The composition of catalyst B is as follows: Ti-Si composite oxide:
It was Ca: Pt = 98.9: 1: 0.1 (mass ratio). As a result of EPMA sectional line analysis of Pt, it was confirmed that 90% by mass or more of Pt supported on the catalyst B existed in a region from the surface to a depth of 100 μm. From the measurement result of the transmission electron microscope, the average particle diameter of Pt was less than 5 nm. <Example 3> Example 1 was the same as Example 1 except that a mixed solution of hexaammine platinum hydrochloride and sodium acetate was used in place of the mixed solution of hexaammine platinum hydrochloride and magnesium acetate. Catalyst C was obtained in the same step.

The composition of catalyst C is as follows: Ti-Si composite oxide:
It was Na: Pt = 98.9: 1: 0.1 (mass ratio). As a result of EPMA sectional line analysis of Pt, it was confirmed that 90% by mass or more of Pt supported on the catalyst B existed in a region from the surface to a depth of 100 μm. From the measurement result of the transmission electron microscope, the average particle diameter of Pt was less than 5 nm. <Example 4> Example 1 was repeated except that a mixed solution of hexaammineplatinum hydrate and lithium acetate was used in place of the mixed solution of hexaammineplatinum hydrate and magnesium acetate. Catalyst D was obtained in the same process.

The composition of catalyst D is as follows: Ti-Si composite oxide:
Li: Pt = 98.9: 1: 0.1 (mass ratio). As a result of EPMA sectional line analysis of Pt, it was confirmed that 90% by mass or more of Pt supported on the catalyst B existed in a region from the surface to a depth of 100 μm. From the measurement result of the transmission electron microscope, the average particle diameter of Pt was less than 5 nm. <Example 5> Example 1 is the same as Example 1 except that a mixed solution of hexaammine platinum hydrochloride and yttrium acetate was used in place of the mixed solution of hexaammine platinum hydrochloride and magnesium acetate. Catalyst E was obtained in the same process.

The composition of the catalyst E is as follows: Ti-Si composite oxide:
It was Y: Pt = 98.9: 1: 0.1 (mass ratio).
As a result of EPMA sectional line analysis of Pt, P supported on catalyst B
It was confirmed that 90 mass% or more of t exists in the region from the surface to a depth of 100 μm. From the measurement result of the transmission electron microscope, the average particle diameter of Pt was less than 5 nm. <Example 6> Example 1 was the same as Example 1 except that a mixed solution of hexaammineplatinum hydrochloride and lanthanum acetate was used in place of the mixed solution of hexaammineplatinum hydrochloride and magnesium acetate. Catalyst F was obtained in the same process.

The composition of catalyst F is as follows: Ti-Si composite oxide:
It was La: Pt = 98.9: 1: 0.1 (mass ratio). As a result of EPMA sectional line analysis of Pt, it was confirmed that 90% by mass or more of Pt supported on the catalyst B existed in a region from the surface to a depth of 100 μm. From the measurement result of the transmission electron microscope, the average particle diameter of Pt was less than 5 nm. <Comparative Example 1> The same steps as in Example 1 were repeated except that a single solution of hexaammineplatinum hydrate was used in place of the mixed solution of hexaammineplatinum hydrate and magnesium acetate. , Catalyst G was obtained.

The composition of catalyst G is as follows: Ti-Si composite oxide:
It was Pt = 99.9: 0.1 (mass ratio). E of Pt
As a result of PMA sectional line analysis, 90% of Pt supported on the catalyst B was detected.
It was confirmed that the mass% or more exists in the region from the surface to a depth of 100 μm. From the measurement result of the transmission electron microscope, the average particle diameter of Pt was 7 nm. [Performance Evaluation] The following performance evaluation tests were conducted using the catalysts obtained in the respective examples and comparative examples. <CO removal test> Test conditions: Exhaust gas composition = CO: 20 ppm, O ₂ : 10%, H ₂ O:
8%, N ₂ : Balance gas temperature = 340 ° C. Space velocity (STP) = 75000 Hr ⁻¹ CO removal rate calculation formula: CO removal rate (%) = [(reactor inlet CO concentration) − (reactor outlet CO concentration) ] / (CO concentration at reactor inlet) × 100 Exposure test: After the CO removal test was performed on the manufactured catalyst in a new state, the exposure test was performed under the following conditions, and the same CO removal was performed on the catalyst after exposure. The test was conducted.

Exposure gas composition = SO ₂ : 100 ppm,
_{O 2: 10%, H 2} O: 8%, N 2: Balance Gas temperature = 340 ° C. The space velocity (STP) = 75000Hr ^-1 exposure time = 500 hours <acetaldehyde removal test> Test conditions: exhaust gas composition = CH ₃ CHO : 20ppm, CO: 20p
pm, O ₂ : 12%, H ₂ O: 8%, N ₂ : balance gas temperature = 350 ° C space velocity (STP) = 80000Hr ^-1 Acetaldehyde removal rate calculation formula: acetaldehyde removal rate (%) = [(reactor inlet concentration of acetaldehyde) - (reactor outlet concentration of acetaldehyde)] / (reactor inlet concentration of acetaldehyde) × 100 <SO ₂ oxidation ability evaluation test> test conditions: exhaust gas composition _{= SO 2: 30ppm, CO:} 20ppm,
O ₂ : 12%, H ₂ O: 8%, N ₂ : Balance gas temperature = 350 ° C Space velocity (STP) = 80000Hr ^-1 SO ₂ Oxidation rate calculation formula: SO ₂ Oxidation rate (%) = Reactor outlet SO ₃ concentration / reactor inlet SO ₂ concentration × 100 <Test Results> The results of the above performance evaluation test are shown in the table below.
The post-exposure CO removal rate test, acetaldehyde removal test, and SO ₂ oxidation capacity evaluation test were carried out in Example 1 and Comparative Example 1.
I went about.

[0042]

[Table 1]

As a result of the above, it was confirmed that, in each of the examples, superior performance to the CO removal rate can be exhibited as compared with the comparative example 1. As for the acetaldehyde removal rate, it is understood that Example 1 is superior to Comparative Example 1. Further, the SO ₂ oxidation rate was smaller in Example 1 than in Comparative Example 1, and SO ₂ oxidation was suppressed. It was also confirmed that Example 1 was superior in SO _x resistance to Comparative Example 1 even after being exposed to the SO ₂ -containing gas for a long time without having a CO removal rate.

[0044]

By using the exhaust gas treatment catalyst of the present invention, low concentrations of CO and volatile organic compounds can be efficiently removed even in the presence of a large amount of oxygen and water vapor. Specifically, the exhaust gas treatment 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 improved as compared with the case of the catalyst component A alone. However, the amount of the 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, by adding the above-mentioned catalyst component C as a catalyst component, it is possible to impart denitration performance to the catalyst. By making the catalyst component A unevenly distributed on the surface of the catalyst, it is possible to significantly improve the treatment efficiency of the exhaust gas.

[Brief description of drawings]

FIG. 1 is a cross-sectional view (a), an enlarged cross-sectional view (b) and a catalyst component A concentration graph (c) of a catalyst that represents an embodiment of the present invention.

[Explanation of symbols]

10 Exhaust gas catalyst 11 Carrier 12 carrying area 13 Exhaust gas passage

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Nobuyuki Masaki             Hyogo prefecture Himeji city             1 Within Nippon Shokubai Co., Ltd. (72) Inventor Noboru Sugishima             Hyogo prefecture Himeji city             1 Within Nippon Shokubai Co., Ltd. (72) Inventor Motonobu Kobayashi             Hyogo prefecture Himeji city             1 Within Nippon Shokubai Co., Ltd. F-term (reference) 3G091 AA06 AA18 AA19 AB02 BA19                       GA06 GB05W GB06W GB07W                       GB10X                 4D048 AA13 AA17 AB01 BA01X                       BA02X BA06X BA07X BA14X                       BA18X BA30X BA41X BB02                 4G069 AA03 AA08 BA03B BC02B                       BC04B BC09A BC09B BC10A                       BC10B BC31A BC33A BC40B                       BC42B BC54A BC58A BC59A                       BC60A BC62A BC66A BC67A                       BC68A BC69A BC75B CA02                       CA03 CA07 CA14 CA15 EA19                       EB19 FB14

Claims (7)

[Claims] 1. A catalyst for treating exhaust gas containing low concentration CO, which comprises a Ti-based oxide as a carrier and comprises at least one element selected from the group consisting of Pt, Pd, Rh, Ru, Ir and Au. Catalyst component A
And an exhaust gas treatment catalyst containing a catalyst component B comprising at least one element contained in Groups I to III of the periodic table. 2. V, W, Mo, Cu, Mn, Ni, CO,
The exhaust gas treatment catalyst according to claim 1, further comprising a catalyst component C composed of at least one element selected from the group consisting of Cr and Fe. 3. The exhaust gas treatment catalyst according to claim 1, wherein the catalyst component A is fine particles having an average particle diameter of 30 nm or less. 4. 70% by mass or more of the total amount of the catalyst component A supported on the carrier is at a depth of 100 from the surface of the catalyst.
The exhaust gas treatment catalyst according to any one of claims 1 to 3, which is unevenly distributed in a region up to µm. 5. The exhaust gas containing low concentration CO has a CO concentration of 1
The exhaust gas treatment catalyst according to any one of claims 1 to 4, which has an exhaust gas content of 00 ppm or less. 6. A method for treating an exhaust gas containing low concentration CO, comprising the step (a) of contacting the exhaust gas having a CO concentration of 100 ppm or less with the exhaust gas treatment catalyst according to any one of claims 1 to 4. Processing method. 7. The exhaust gas further containing a volatile organic compound is used as the exhaust gas in the step (a).
The method for treating exhaust gas according to.