JP2004209356A - Exhaust gas treatment catalyst and exhaust gas treatment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust gas treatment catalyst which can efficiently remove harmful components such as CO, NOx contained in exhaust gas and is effective industrially in terms of costs, or the like, and an exhaust gas treatment method using the catalyst. <P>SOLUTION: In the exhaust gas treatment catalyst, a catalyst component A comprising at least one noble metal element selected from the group consisting of Pt, Pd, Rh, Ru, Ir, and Au is supported on a metal oxide containing at least one metal selected from the group consisting of Ti, Al, Si, W, and Zr, and the catalyst is obtained by regenerating catalytic activity. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exhaust gas treatment catalyst and an exhaust gas treatment method using the same. Specifically, carbon monoxide (CO) and the like obtained by regenerating catalytic activity and contained in combustion exhaust gas discharged from various fuel devices such as boilers, gas turbines, diesel engines and gas engines The present invention is directed to an exhaust gas treatment catalyst for efficiently treating harmful components and an exhaust gas treatment method using such a catalyst.
[0002]
[Prior art]
Combustion exhaust gas discharged from various combustion devices such as boilers, gas turbines, diesel engines, and gas engines varies depending on the combustion device, operating conditions, and the like._X, SO_XAnd volatile organic compounds and the like derived from unburned fuel are contained as harmful components. In these combustion devices, while improving the combustion efficiency or heat efficiency, CO and NO_XFor the purpose of efficiently reducing harmful components such as the above, combustion is often performed by increasing the amount of supplied air at the time of combustion to a value greater than the theoretical amount of air required for complete combustion of the fuel gas. By controlling the combustion state, CO and NO contained in the combustion exhaust gas are controlled._XHarmful components such as CO, NO_XEtc. remain at a level deemed harmful. Accordingly, it is necessary to efficiently treat these remaining harmful components, and it is necessary to develop an exhaust gas treatment catalyst and an exhaust gas treatment method that can function effectively in this regard.
[0003]
As such an exhaust gas treatment catalyst, a catalyst in which a metal oxide is used as a carrier and a catalyst component composed of a noble metal element is supported on the carrier is known.
Exhaust gas treatment catalysts made of noble metal-supported metal oxides can exhibit a complex catalytic action of metal oxides and noble metals, and are more efficient than exhaust gas treatment catalysts composed of only metal oxides. It has the advantage that the components can be processed and the range of types of harmful components that can be processed is widened. Specifically, an exhaust gas treatment catalyst in which a precious metal such as Pt or Pd is supported on a binary composite oxide such as a Ti—Si composite oxide or a ternary composite oxide is disclosed. (For example, refer to Patent Document 1.)
However, as for the noble metal element to be supported, there is always a problem that the cost unit price is high even though it is an effective catalyst component as described above, and a new noble metal is supported every time the catalytic activity is deteriorated by exhaust gas treatment. If the catalyst is replaced with a prepared catalyst, it is hardly an effective catalyst because it is industrially efficient.
[0004]
[Patent Document 1]
JP-A-53-146991
[0005]
[Problems to be solved by the invention]
The problem to be solved by the present invention is to solve the problem of CO and NO contained in exhaust gas._XIt is an object of the present invention to provide an exhaust gas treatment catalyst which can efficiently remove harmful components such as odors and is industrially very effective in terms of cost and the like, and an exhaust gas treatment method using the same.
[0006]
[Means for Solving the Problems]
The present inventor has conducted intensive studies in order to solve the above problems. In the process, a catalyst obtained by supporting a catalyst component composed of a specific noble metal element on a carrier obtained from a carrier material containing a single oxide or a composite oxide of a metal element such as titanium. After use, an exhaust gas treatment catalyst obtained by regenerating the catalytic activity, and an exhaust gas treatment method in which an exhaust gas containing CO is brought into contact with the catalyst, have been found to be able to solve the above problems at once. Was confirmed, and the present invention was completed.
[0007]
That is, the exhaust gas treatment catalyst according to the present invention is:
A metal oxide containing at least one metal selected from the group consisting of Ti, Al, Si, W and Zr, and at least one noble metal element selected from the group consisting of Pt, Pd, Rh, Ru, Ir and Au Characterized by being obtained by regeneration of catalytic activity.
Further, the exhaust gas treatment method according to the present invention,
An exhaust gas treatment method for removing CO in exhaust gas, comprising a step of bringing the exhaust gas into contact with the exhaust gas treatment catalyst of the present invention.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the exhaust gas treatment catalyst and the exhaust gas treatment method according to the present invention will be described in detail, but the scope of the present invention is not limited to these descriptions, and other than the following examples, a range that does not impair the spirit of the present invention. Can be carried out as appropriate.
[Exhaust gas]
The exhaust gas treatment catalyst and exhaust gas treatment method of the present invention can be applied to exhaust gas discharged from ordinary various industrial devices and equipment (hereinafter, referred to as a generation source). Specific examples include boilers, gas turbines, diesel engines, gas engines, heating furnaces, and combustion exhaust gases from various industrial processes.
[0009]
Components contained in the flue gas vary depending on the source, and also vary depending on environmental conditions such as emission standards. Specifically, gas components that can adversely affect the environment, that is, harmful components include, for example, carbon monoxide (CO), nitrogen oxides (NO_X), Sulfur oxides (SO_X).
In the case of the combustion exhaust gas, a volatile organic compound which is a component derived from the fuel but has not burned may be contained, and thus, there is a problem that an adverse effect on the environment is caused as a harmful component.
The exhaust gas treatment catalyst according to the present invention is characterized in that carbon monoxide (CO) and nitrogen oxide (NO_X) And the treatment of exhaust gas containing volatile organic compounds, that is, the removal of these harmful components. Also, SO₂Oxidation rate can be kept low. The exhaust gas treatment catalyst of the present invention is particularly effective for the treatment of exhaust gas containing carbon monoxide (CO) (that is, the treatment for removing CO in the exhaust gas).
[0010]
The exhaust gas may be subjected to various types of exhaust gas treatment before performing the treatment step using the exhaust gas treatment catalyst of the present invention. Therefore, there are cases where the components of the exhaust gas discharged from the source are different from those of the exhaust gas which is subjected to the exhaust gas treatment by the exhaust gas treatment catalyst of the present invention.
The exhaust gas treatment catalyst and the exhaust gas treatment method of the present invention are also effective for low-concentration CO-containing exhaust gas, which is difficult to perform efficiently with a conventional exhaust gas treatment catalyst. Specifically, an exhaust gas having a CO concentration of 100 ppm or less Is effective even if
The temperature condition and the speed of the exhaust gas vary depending on the conditions of discharge from the source and the history of the exhaust gas treatment.
[0011]
(Exhaust gas treatment catalyst)
The exhaust gas treatment catalyst of the present invention includes a carrier and a catalyst component, and is obtained by regenerating catalytic activity by having a catalyst component supported on a carrier. Hereinafter, these will be described in detail.
<Carrier>
The carrier used in the exhaust gas treatment catalyst of the present invention is a metal containing at least one metal element selected from the group consisting of Ti (titanium), Si (silicon), Al (aluminum), W (tungsten) and Zr (zirconium). An oxide is essential. Therefore, the metal oxide may be a metal oxide (single oxide) containing only one metal element, specifically, titania, silica, alumina, zirconia, or two or more metal elements. May be a metal oxide (composite oxide) containing, and is not particularly limited. The carrier used in the exhaust gas treatment catalyst of the present invention may be a mixture of two or more of the above-described single oxides, a mixture of two or more of the above-described composite oxides, It may be a mixture of two or more oxides and composite oxides. The carrier may be a mixture of the above-mentioned metal oxide and an oxide which can be generally used for the carrier. Examples of such an oxide include zeolite. Hereinafter, such a mixed form is also referred to as “metal oxide”.
[0012]
It is preferable that the metal oxide includes a titanium-based oxide as an essential component. The titanium-based oxide referred to here may be, specifically, an oxide (titanium oxide) composed of only Ti (titanium), Si (silicon), Al (aluminum), W (tungsten) and A composite oxide obtained by compounding at least one element selected from the group consisting of Zr (zirconium) with Ti may be used, or a composite oxide of this composite oxide (titanium-based composite oxide) and titanium oxide may be used. It may be a mixture. It is to be noted that the metal oxide constituting the carrier is essentially made of a titanium-based oxide, which means that the above-described titanium-based oxide also includes a form in which a non-titanium-based oxide generally usable for a carrier is mixed. Examples of the titanium-based oxide include silica, alumina, silica-alumina, zirconia, zeolite, and the like. Hereinafter, the “titanium-based oxide” includes such a mixed form.
[0013]
When the metal oxide constituting the carrier is a titanium-based oxide, the content of Ti is 5 to 95 mol% with respect to the total number of moles of Ti and other elements in the entire titanium-based oxide. Preferably, it is more preferably 20 to 95 mol%.
The carrier containing the metal oxide not only has the function of simply supporting the catalyst component, but also maintains the supported state of the catalyst component supported on the carrier in a state suitable for the removal of CO. It contributes to the function of enhancing the exhaust gas treatment function. As a result, high CO removal performance can be obtained without increasing the supported amount of the catalyst component. Such effects are particularly remarkable when the metal oxide is a titanium-based oxide.
[0014]
In particular, when a Ti-Si composite oxide is used as the metal oxide constituting the carrier, SO₂It is preferable because it has a low oxidation rate and excellent exhaust gas purification performance.
The carrier used in the exhaust gas treatment catalyst of the present invention is preferably, for example, an integrally molded porous honeycomb carrier obtained by extruding and firing a carrier material.
For the preparation of a metal oxide such as a titanium-based oxide serving as a carrier material, the same means as for a normal metal oxide can be employed. A technique disclosed in JP-A-53-146991 or the like can be mentioned. In particular, a technique disclosed in Japanese Patent Application No. 2000-99593 (Japanese Patent Application Laid-Open No. 2001-062292), which the applicant of the present invention applied for a patent, is cited as a preferable technique.
[0015]
As a raw material for supplying a metal oxide serving as a carrier material, a metal oxide prepared in advance may be used as it is, or a compound material capable of generating a metal oxide by firing may be used. Specifically, any of inorganic and organic compounds may be used. For example, hydroxides containing predetermined metal elements, ammonium salts, ammine complexes, oxalates, halides, sulfates, nitrates, carbonates, alkoxides and the like Can be used.
In the case of manufacturing the above-mentioned integrally formed porous honeycomb carrier, basically, the same manufacturing conditions as those of a normal porous honeycomb carrier can be applied.
[0016]
The porous carrier is a carrier having a porous structure with a fine pore space. The porous carrier can support the catalyst component not only on its outer surface but also inside the fine pore space. The contact area between the exhaust gas and the catalyst component is large, and the treatment reaction is performed efficiently.
When the carrier material contains a metal oxide such as a titanium-based oxide, the function of adsorbing and holding the exhaust gas component in the porous structure is favorably exhibited. The supported catalyst component and the metal oxide such as a titanium-based oxide function synergistically not only on the outer surface of the support but also inside the porous structure to efficiently perform exhaust gas treatment.
[0017]
The honeycomb carrier has a structure in which a large number of gas passages through which exhaust gas passes are arranged vertically and horizontally. The gas passages are separated by relatively thin inner walls. It is a so-called beehive-shaped carrier. Specifically, it has a structure as illustrated in FIG.
The cross-sectional shape of the gas passage is not limited to the same hexagon as the honeycomb, but may be a square, a rectangle, or another polygon. It may include a curved shape such as a circle or an oval.
The size of the gas passage also varies depending on conditions such as the amount of exhaust gas to be circulated and the processing capacity. The length W of one side of the gas passage (also referred to as “opening”) W, the thickness T of the inner wall, the opening ratio, the length of the gas passage, ie, the length of the porous honeycomb carrier in a direction parallel to the flow direction of the exhaust gas during use. The length L, the number of gas passages, and the like can be appropriately set according to the purpose.
[0018]
The gas passages may be arranged vertically and horizontally in a linear lattice, or may be arranged in a staggered or spiral shape.
A square, rectangular or other polygonal shape is employed as the overall cross-sectional shape of the porous honeycomb carrier. A curved shape such as a circle can also be adopted.
<Catalyst component and its support>
(Catalyst component A)
In the exhaust gas treatment catalyst of the present invention, a catalyst component A composed of a noble metal element is used as a catalyst component. The catalyst component is used by being supported on a metal oxide. The exhaust gas treatment catalyst of the present invention may contain a catalyst component other than the above-mentioned catalyst component A as a catalyst component, or may contain other compounds other than the catalyst component, and is not particularly limited. Specifically, for example, at least one selected from the group consisting of Pt, Pd, Rh, Ru, Ir, and Au is used as the noble metal element. The catalyst component A may be a metal composed of the above-mentioned noble metal element, or a compound thereof (such as an oxide).
[0019]
As the feedstock of the catalyst component A, a material used for ordinary catalyst production or the like can be used. Specific examples include nitrates, halides, ammonium salts, ammine complexes, and hydroxides.
As means for supporting the catalyst component A on the carrier, basically, means common to ordinary noble metal-supported metal oxide catalysts can be employed. In the treatment step of supporting the catalyst component A on the carrier, for example, it is preferable that the catalyst component A is supported on the carrier so as to be unevenly distributed at a high concentration near the outer surface of the carrier. That is, they are unevenly distributed on the outer surface and / or inside the carrier near the outer surface.
[0020]
In the case where the catalyst and the exhaust gas are brought into contact with each other at a high space velocity (SV) to remove CO in the exhaust gas, it is considered that most of the purification action by the catalyst occurs in the surface layer of the catalyst. In such a case, the catalyst component A is unevenly distributed and supported on the surface layer of the catalyst in contact with the exhaust gas, whereby the processing efficiency of the exhaust gas by the catalyst can be increased.
The amount of the catalyst component A to be supported varies depending on the combination of materials and the conditions of the supporting treatment, but is usually 0.005 to 2.0% by weight of the catalyst component A based on the total amount of the catalyst, preferably It is used in the range of 0.01 to 1.0% by weight. If the supported amount of the catalyst component A is too small, the catalytic activity becomes low. If the amount of the catalyst component A carried is too large, the effect on the activity improvement cannot be expected, which only impairs the economic efficiency.₂→ SO₃The conversion is also high, which is harmful.
[0021]
The catalyst component A is usually supported on a carrier in the form of particles. The average particle diameter of the catalyst component A is preferably 30 nm or less, more preferably 20 nm or less. The smaller the particle diameter of the catalyst component A and the higher the dispersion state, the higher the activity.
(Catalyst component B)
The exhaust gas treatment catalyst of the present invention may further contain, as a catalyst component, a catalyst component C comprising at least one element contained in Groups I to III of the periodic table. Specific examples of the elements included in Groups I to III of the periodic table include Na, Li, Mg, Ca, Y, Ce, and La. The catalyst component B may be a metal composed of an element included in the above-described groups I to III, or a compound thereof (such as an oxide).
[0022]
When a catalyst that also contains the catalyst component B is used as the catalyst component, the processing performance is improved as compared with the case where only the catalyst component A is supported, and the amount of the catalyst component A used can be effectively reduced. At the same time, when the catalyst component B coexists with the catalyst, SO 2₂Oxidation is suppressed and SO_xResistance and heat resistance are improved, and even when the amount of catalyst component A carried is small, stable processing efficiency can be maintained for a long period of time.
The raw material for the catalyst component B is not particularly limited, and one or more materials used in the production of ordinary catalysts can be used. Preferably, organic acid salts, alkoxides, organometallic complexes and the like are used. Those containing an organic component such as an organic acid in the molecule can be exemplified.
[0023]
The method of supporting the catalyst component B is not particularly limited, either, and the catalyst component B can be supported by a method used in ordinary catalyst production.
The supported amount of the catalyst component B is preferably in the range of 20% by weight or less, more preferably in the range of 0.01 to 20% by weight, and still more preferably in the range of 0.1 to 10% by weight based on the total amount of the catalyst. Range. If the supported amount of the catalyst component B is too small, the above-described effect unique to the catalyst component B cannot be obtained. Even if the supported amount is increased beyond the above range, no effect on the activity improvement can be expected, and conversely, the activity is reduced. Sometimes.
The loading order is not particularly limited. The catalyst component B may be supported after the catalyst component A is supported, the catalyst component B may be supported before the catalyst component A is supported, or the catalyst component A and the catalyst component B are simultaneously supported. Among them, it is preferable to carry the catalyst component B after carrying the catalyst component A, or to carry the catalyst component A and the catalyst component B at the same time.
[0024]
(Loading of catalyst component A and catalyst component B)
The exhaust gas treatment catalyst of the present invention has the above-mentioned catalyst component A supported thereon and, optionally, catalyst component B supported thereon, thereby having the above-described effects. When the supported state of A and the supported state of the catalyst component B are combined as described below, each has a specific effect. Specifically, 1) when the catalyst component A and the catalyst component B are both unevenly distributed on the catalyst surface, and 2) when the catalyst component A is unevenly distributed on the catalyst surface and the catalyst component B is substantially uniformly distributed over the entire catalyst. And when it is present. Note that a description will be given below of a supported state in which the surface is unevenly distributed and a substantially uniform supported state. However, the description of the supported amount and the like is assumed to be independent for the catalyst component A and the catalyst component B.
[0025]
That is, that the catalyst component is unevenly distributed on the surface of the catalyst (surface uneven distribution) means that the catalyst component is supported on the surface of the carrier and / or in the vicinity of the surface. There is no particular limitation as long as it exists or exists near the surface with a distribution area of a certain width in the depth direction than the surface layer, and is not particularly limited (hereinafter, “surface and / or near surface” is simply referred to as “surface and / or near surface”). Sometimes referred to as "surface."). Specifically, for example, in the case of a honeycomb catalyst, an electron probe microanalyzer (EPMA) device is used to change the inner wall portion of the honeycomb catalyst from one outer surface of the inner wall portion to the other outer surface. Between the cross-sectional thickness direction of the inner wall portion of the honeycomb-shaped catalyst and the X-ray intensity I of the catalyst component A or the catalyst component B obtained by continuously measuring (linear analysis measurement) the predetermined catalyst component toward In the figure (graph), the integrated value of the X-ray intensity I over the entire cross-sectional thickness T of the inner wall portion is represented by N₀Where N is the integral value of the X-ray intensity I from the outer surface of the inner wall portion to the portion at the depth T / 4 in the inward direction, and 70 ≦ (N / N₀× 100), and more preferably 80 ≦ (N / N₀× 100), more preferably 90 ≦ (N / N₀× 100), particularly preferably 95 ≦ (N / N₀× 100).
[0026]
More specifically, for example, it is preferable that 70% by weight or more of the total supported amount of the catalyst component on the honeycomb carrier is present in a region from the outer surface of the catalyst to a depth of 100 μm, more preferably 80% by weight. The above amount is more preferably 90% by weight or more, particularly preferably 95% by weight or more. Thus, defining the abundance in the region from the outer surface of the catalyst to a depth of 100 μm depends on the inner wall of the honeycomb catalyst. The thickness is preferably 0.3 mm or more, more preferably 0.3 to 1.0 mm, and still more preferably 0.3 to 0.6 mm.
On the other hand, that the catalyst component is present substantially uniformly throughout the catalyst is not limited to the catalyst component being present in a completely uniform distribution state throughout the catalyst, for example, near the surface. May be distributed more than the average, or conversely, may be distributed more inside the catalyst than on the surface. In short, any form other than the above-described surface uneven distribution may be used. Specifically, N₀Using the above definitions for and N, (N / N₀× 100) <70, and to be more uniform, (N / N₀× 100) <65, and (N / N₀× 100) <60. More specifically, in the same manner as in the case of surface uneven distribution, the amount present in the region from the outer surface of the catalyst to the depth of 100 μm out of the total amount of the catalyst component supported on the honeycomb carrier is less than 70% by weight. And to be more uniform it is less than 65% by weight and even less than 60% by weight.
[0027]
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 Groups I to III of the Periodic Table, have the same loading amount. If they are unevenly distributed, the reaction efficiency can be remarkably improved, and the economy is excellent. Further, the catalyst component B can improve the CO removing activity of the catalyst component A by a so-called cocatalyst effect.
When 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 effects are obtained. That is, in order to obtain a high CO removal activity, it is usually necessary that the catalyst has a high oxidizing power.₂Oxidation (SO₂→ SO₃) There is a demand for selectivity to keep the activity as low as possible. The elements contained in Groups I to III of the periodic table are SO_xCan be effectively captured, resulting in SO₂It is believed that the oxidation activity can also be suppressed. The CO removal reaction occurs mainly on the surface of the catalyst,₂The oxidation reaction of can occur inside the catalyst. Accordingly, 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 substantially uniformly present in the entire catalyst, the above-described selectivity in the catalyst can be improved. It can be improved efficiently.
[0028]
In the present invention, the catalyst component A is preferably supported so as to be unevenly distributed on the catalyst surface, and the catalyst component B is preferably supported so as to be unevenly distributed on the catalyst surface and supported so as to be uniformly present on the entire catalyst. Although it may be acceptable, both of the above-described state of uneven distribution and uniform presence of the surface will be described together.
The treatment method for supporting the catalyst component A or the catalyst component B on the carrier is not particularly limited. For example, impregnation (a feed material of the catalyst component (hereinafter, this feed material is also simply referred to as a catalyst component). ) Is preferably applied by using a solution or a mixed solution (impregnating solution) containing). When the catalyst component is supported by impregnation, the catalyst component is supported by, for example, chemisorption or physical adsorption.Whether the catalyst component is supported by chemisorption or physical adsorption depends on the type of the catalyst component to be adsorbed on the support. Depends on how they are selected and combined. Specifically, for example, when the carrier is silicon, aluminum, a titanium-based oxide containing an oxide of tungsten and zirconium, and the catalyst component is hexaammine platinum hydroxide, the treatment is mainly performed by chemisorption, and the carrier is silicon, In the case of a titanium-based oxide containing an oxide of aluminum, tungsten and zirconium and the like, and the catalyst component is an acetate of an element included in Groups I to III of the periodic table, the treatment is mainly performed by physical adsorption.
[0029]
In general, in the case of chemisorption, since the carrier and the catalyst component can be strongly bonded, once adsorbed, the movement of the catalyst component from the carrier hardly occurs. Therefore, when the impregnating liquid containing the catalyst component is impregnated (for example, when the carrier is impregnated with an aqueous solution in which the catalyst component is dissolved), the impregnating liquid is absorbed or the impregnating liquid (absorbed by the carrier) is absorbed. The catalyst component diffused into the carrier reaches the adsorption point of the carrier, so that the adsorption usually proceeds preferentially from the catalyst surface, and the subsequent movement of the catalyst component by drying hardly occurs. . Therefore, when the catalyst component is unevenly distributed on the surface, the impregnation time may be shortened, and when the catalyst component is present substantially uniformly throughout the catalyst, the impregnation time may be increased. In other words, in the loading of the catalyst component by chemical adsorption, the loading state, such as whether the surface is unevenly distributed or present substantially uniformly, is affected to some extent by the drying conditions, but greatly affected by the impregnation conditions such as the impregnation time. It is considered to receive.
[0030]
In general, in the case of physical adsorption, the bond between the carrier and the catalyst component is weaker than in the case of chemical adsorption. Therefore, when the impregnation liquid containing the catalyst component is impregnated (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 present in the entire catalyst together with the absorption of the impregnation liquid. However, in the subsequent drying, the catalyst component easily moves together with the movement due to the drying of the moisture and the like. Therefore, in the case where the catalyst component is unevenly distributed on the surface, it is preferable that the impregnation time is appropriately shortened, and then, if possible, the catalyst component is dried quickly after the impregnation so that the catalyst component is moved in the direction of the catalyst surface together with the water. In the case where the catalyst is present substantially uniformly, it is preferable to appropriately lengthen the impregnation time and slowly perform drying after the impregnation to moderate the movement of water and suppress the movement of the catalyst component. That is, in the loading of the catalyst component by physical adsorption, the loading state, such as whether the surface is unevenly distributed or substantially uniformly present, is a balance between the impregnation conditions such as the impregnation time and the drying conditions, but usually the drying conditions. Is likely to be significantly affected by
[0031]
Hereinafter, conditions for supporting the catalyst component by chemisorption will be described in detail.
In the loading treatment of the catalyst component A or the catalyst component B by chemical adsorption, first, the carrier is impregnated with the impregnating liquid containing the catalyst component A or the catalyst component B in a heated state. Due to this impregnation, the chemical adsorption is carried out efficiently and the support becomes easy. Specifically, it is preferable that the temperature of the impregnating liquid containing the catalyst component A or the catalyst component B is heated to 40 ° C. or more, and 50 ° C. or more, 60 ° C. or more, 70 ° C. or more, 80 ° C. or more, or 90 ° C. The above is more preferable. If the temperature of the impregnating liquid is too low, a desired amount of the catalyst component may not be supported.
[0032]
Conditions for the impregnation include, for example, the impregnation time, the pH of the impregnating liquid, the concentration of the catalyst component in the impregnating liquid, the impregnation temperature (temperature of the impregnating liquid), and among others, the impregnation time is important. . The impregnation time is defined as the time from the start of impregnation of the carrier with the impregnation liquid containing the catalyst component to the end of impregnation (removal of the carrier from the impregnation liquid) (the same applies to the following description).
The impregnation time is not particularly limited, but is preferably 10 minutes or less, more preferably 5 minutes or less, and still more preferably 3 minutes or less when the catalyst component is unevenly distributed on the surface of the catalyst. If the time exceeds 10 minutes, there is a possibility that uneven distribution on the catalyst surface may not be achieved. On the other hand, when the catalyst component is present substantially uniformly in the entire catalyst, it is preferably at least 15 minutes, more preferably at least 20 minutes, and even more preferably at least 30 minutes. If it is less than 15 minutes, it may not be possible to make the catalyst substantially uniformly present throughout the catalyst.
[0033]
After the above impregnation, a standing time may be appropriately provided between drying and drying described below, if necessary. In particular, when it is desired that the catalyst component be substantially uniformly present in the entire catalyst, not only the impregnation under the above-mentioned preferable impregnation conditions, but also a time period for allowing the catalyst component to stand may be effective.
After the impregnation with the impregnating liquid containing the catalyst component (after the impregnation and drying, if the above-mentioned standing time is provided, the time is also included), and 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, since the catalyst component is easily unevenly distributed on the surface of the support, but is particularly limited. However, specifically, the drying time (the time from the start of drying to the end of the drying) is preferably 1 hour or less, more preferably 30 minutes or less, and further preferably 20 minutes or less. is there. If the drying time exceeds 1 hour, there is a possibility that uneven distribution on the catalyst surface may not be achieved. The drying temperature is preferably from 60 to 300C, more preferably from 100 to 200C. If the drying temperature is lower than 60 ° C., drying may not be sufficiently performed within the above-mentioned preferable drying time. If the drying temperature is higher than 300 ° C., there may be a problem that catalytic activity is lowered. On the other hand, when the catalyst component is present substantially uniformly throughout the catalyst, it is necessary to slowly dry the support over time, if necessary, so that the catalyst component sufficiently penetrates into the interior of the support and substantially throughout the catalyst. However, the drying time (the time from the start of drying to the end of substantially drying) is preferably 2 hours or more, and more preferably. Is at least 3 hours, more preferably at least 5 hours. If the drying time is less than 2 hours, the catalyst component may move to the catalyst surface and may be unevenly distributed on the catalyst surface. Further, the drying temperature is preferably from 10 to 200 ° C, more preferably from 20 to 150 ° C. If the drying temperature is lower than 10 ° C., the drying may take too much time more than necessary. If the drying temperature is higher than 200 ° C., the drying may be performed outside the preferable drying time range. There is a possibility that components may move to the catalyst surface and may be unevenly distributed on the catalyst surface.
[0034]
In the chemical adsorption, the drying may be performed by ventilation drying or airless drying in any of the above cases, and the drying is not particularly limited.In general, when the catalyst component is unevenly distributed on the surface of the catalyst, the drying is preferably performed by ventilation drying. When it is desired to make the catalyst substantially uniform throughout the entire catalyst, it is preferable to perform the drying by airless drying. Therefore, when ventilation drying is performed 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 a desired drying time or the like, and is not particularly limited. It is preferably 0.5 to 50 m / s, more preferably 1 to 30 m / s, and still 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. If it is more than 50 m / s, a large apparatus is required, which is not economical, and the catalyst may be destroyed. The value of the linear velocity during ventilation drying is determined by the gas flow rate (m³/ S) is the cross-sectional area of the catalyst-filled portion of the drying apparatus (however, the cross-sectional area in a state where the catalyst is not charged, that is, a so-called empty tower cross-sectional area) (m).²).
[0035]
Hereinafter, conditions for supporting the catalyst component by physical adsorption will be described in detail.
Conditions for the impregnation include, for example, the impregnation time, the concentration of the catalyst component in the impregnation liquid, and the like. Among them, the impregnation time is particularly important.
The impregnation time is not particularly limited, but is preferably 2 minutes or less, more preferably 1 minute or less, even more preferably 30 seconds or less when the catalyst component is unevenly distributed on the surface of the catalyst. With the above-mentioned impregnation time, the catalyst can be more unevenly distributed on the catalyst surface. On the other hand, when the catalyst component is present substantially uniformly in the entire catalyst, it is preferably at least 1 minute, more preferably at least 2 minutes, further preferably at least 5 minutes. If it is less than 1 minute, it may not be possible to effectively make the catalyst substantially uniform throughout the catalyst.
[0036]
After the above impregnation, a standing time may be appropriately provided between drying and drying described below, if necessary. In particular, when it is desired that the catalyst component be substantially uniformly present in the entire catalyst, not only the impregnation under the above-mentioned preferable impregnation conditions, but also a time period for allowing the catalyst component to stand may be effective.
After the impregnation with the impregnating liquid containing the catalyst component (after the impregnation and drying, if the above-mentioned standing time is provided, the time is also included), and the carrier and the like are dried. Here, when the catalyst component is unevenly distributed on the surface of the catalyst, it is necessary to quickly dry the carrier after impregnation, and the catalyst component moves to the surface of the support and moves unevenly with the movement of moisture and the like in the direction of the catalyst surface during drying. It is preferable because it becomes easy. Specifically, the drying time (the time from the start of drying to the end of substantially 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 well in the direction of the catalyst surface, or may penetrate more inside the catalyst, so that the catalyst component may not be sufficiently localized on the surface. Further, the drying temperature is preferably from 80 to 300 ° C, more preferably from 100 to 200 ° C. If the drying temperature is lower than 80 ° C., the drying may not be sufficiently performed within the above-mentioned preferable drying time, and if it exceeds 300 ° C., there may be a problem that the catalytic activity is lowered. On the other hand, when the catalyst component is present substantially uniformly throughout the catalyst, drying the carrier slowly over time makes it easier to maintain a state in which the catalyst component has sufficiently penetrated into the interior of the carrier. This is preferable because it can be substantially uniformly present throughout. Specifically, the drying time (the time from the start of drying to the end of the drying) is preferably 3 hours or more, more preferably 5 hours or more, and further preferably 10 hours or more. If the drying time is less than 3 hours, there is a possibility that the catalyst component may not be substantially uniformly present in the entire catalyst due to the migration to the catalyst surface and uneven distribution on the catalyst surface. is there. The drying temperature is preferably from 10 to 150 ° C, more preferably from 20 to 120 ° C. If the drying temperature is lower than 10 ° C, the drying may take too much time more than necessary. If the drying temperature is higher than 150 ° C, the catalyst components move to the catalyst surface and are unevenly distributed on the catalyst surface. Could be.
[0037]
In physical adsorption, in any of the above cases, drying may be performed by ventilation drying or non-air drying, and is not particularly limited.In general, when catalyst components are unevenly distributed on the surface of the catalyst, ventilation drying is performed. When it is desired to make the catalyst substantially uniform throughout the entire catalyst, it is preferable to perform the drying by airless drying. Therefore, when ventilation drying is performed 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 a desired drying time or the like, and is not particularly limited. It is preferably from 50 to 50 m / s, more preferably from 2 to 30 m / s, and still more preferably from 5 to 20 m / s. If it is less than 1 m / s, it may not be possible to make the surface unevenly distributed. If it is more than 50 m / s, a large apparatus is required, which is not economical and the catalyst may be destroyed. The definition of the value of the linear velocity at the time of ventilation drying is the same as in the case of the chemical adsorption.
[0038]
Regarding the treatment method for supporting the catalyst component on the carrier, particularly when it is desired to make the catalyst component uniformly exist in the entire catalyst, besides the above-mentioned treatment method for impregnation by the impregnation, (1) the carrier component (or calcination and the carrier component) A method of mixing the powder of the catalyst component or a solution or a mixed solution containing the same with the powder or slurry of the catalyst component, or (2) a solution of a carrier component (or a compound which becomes a carrier component by firing) and a catalyst. A method of mixing with a solution containing components followed by co-precipitation. According to these methods, it is possible to carry out substantially substantially uniformly without controlling and adjusting the drying conditions and the like, which were conditions that can be examined by the above-mentioned loading treatment method by impregnation. Specifically, when the catalyst component B is supported substantially uniformly and the catalyst component A is unevenly distributed on the surface, a powder or slurry containing the carrier component (or a compound which becomes a carrier component by firing) and the catalyst component B is used. Is prepared, molded, dried and fired, and the catalyst component A may be supported on the surface by the above-described impregnation method or the like.
[0039]
(Catalyst component C)
The exhaust gas treatment catalyst of the present invention further contains, as a catalyst component, a catalyst component C comprising at least one element selected from the group consisting of V, W, Mo, Cu, Mn, Ni, Co, Cr and Fe. be able to. The catalyst component C may be a metal composed of the above-mentioned various elements, or a compound thereof (such as an oxide). The catalyst component C may be contained in an amount of 10% by weight or less in terms of atoms of the above various elements (V, W, Mo, Cu, Mn, Ni, Co, Cr and Fe) based on the total amount of the catalyst. More preferably, it is contained in an amount of 0.01 to 10% by weight. By adding these catalyst components C, the processing efficiency for low-concentration CO exhaust gas can be further improved or a denitration function can be imparted.
[0040]
The feedstock of the catalyst component C is not particularly limited, and one or more materials used in ordinary catalyst production can be used. The loading method is also not particularly limited, and the catalyst can be loaded on a carrier by a method used for ordinary catalyst production, such as the method described for the catalyst components A and B. The order of loading is not particularly limited. Specifically, the carrier may support the catalyst component A and the catalyst component C at the same time, may support the catalyst component C after supporting the catalyst component A, or may support the catalyst component C. The catalyst component A may be loaded later. In the case of a catalyst containing the catalyst component B in addition to the catalyst component A, the catalyst component A, the catalyst component B, and the catalyst component C may be simultaneously supported on the carrier, or the catalyst component A and the catalyst component B may be supported on the carrier. After carrying out, the catalyst component C may be carried, or after carrying the catalyst component C, the catalyst component A and the catalyst component B may be carried. The catalyst component C may be unevenly distributed on the surface of the catalyst as in the case of the catalyst component B, or may be uniformly distributed throughout the catalyst without being unevenly distributed.
[0041]
<Other components and their contents>
The exhaust gas treatment catalyst of the present invention further includes, as the other component D, a compound of at least one element selected from the group consisting of B, P, Sb, Pb, Sn, Zn, and In (hereinafter, referred to as compound D ′). ) And / or sulfur compounds. That is, the exhaust gas treatment catalyst of the present invention may also include, as the other component D, a compound of at least one element selected from the group consisting of B, S, P, Sb, Pb, Sn, Zn, and In. .
(Compound D ')
By adding compound D 'as the other component D to the catalyst, the catalyst of the present invention₂It is possible to efficiently remove CO in exhaust gas for a long period of time while keeping oxidation low.
[0042]
The raw material for the compound D 'is not particularly limited, and one or more materials used in ordinary catalyst production can be used. The method for containing the compound D ′ is also not particularly limited, and may be a method in which the compound is supported on a carrier by a method used in ordinary catalyst production, or may be added and mixed at the time of preparing the carrier, or may be used as one of the carrier materials. There can be mentioned a method of containing the compound by using the compound. Among them, when the compound D ′ is supported and supported, the loading order is not particularly limited, but specifically, the catalyst component A and the compound D ′ are simultaneously supported on the carrier, or It is preferable to load the compound D ′ before loading the component A. In the case of the catalyst containing the catalyst component A and the catalyst component B, the catalyst component A and the catalyst component B and the compound D ′ are simultaneously supported on the carrier, or the compound before the catalyst component A and the catalyst component B are supported. It is preferable to carry D '. The compound D 'may be unevenly distributed on the surface of the catalyst similarly to the catalyst component B, or may be uniformly distributed throughout the catalyst without uneven distribution. When both the catalyst component C and the compound D ′ are supported, the loading order of the catalyst component C and the compound D ′ is not particularly limited. Is also good.
[0043]
The compound D ′ is preferably contained in an amount of 10% by weight or less in terms of atoms of the various elements (B, P, Sb, Pb, Sn, Zn and In) based on the total amount of the catalyst, and more preferably. Is 0.005 to 10% by weight, more preferably 0.02 to 5% by weight. When the content of the compound D 'is more than 10% by weight, it becomes a poisoning component for the active ingredient, and may possibly lower the activity.
As the compound D ′, for example, a phosphorus compound can be preferably used, and in that case, it will be described in detail below, but a compound of the above-mentioned various elements other than P (B, P, Sb, Pb, Sn, Zn, and In) Can be used in the same manner as the phosphorus compound as follows.
[0044]
The feed material of the phosphorus compound is not particularly limited, and for example, those exemplified as an inorganic phosphorus compound and an organic phosphorus compound can be preferably used, and examples thereof include phosphoric acid, ammonium phosphate, and ammonium dihydrogen phosphate. It is particularly preferable to use a water-soluble phosphorus compound of the formula (1).
The reason why CO in exhaust gas can be efficiently removed for a long period of time by including a phosphorus compound in a range of 10% by weight or less in terms of phosphorus atoms with respect to the total amount of the catalyst as described above is as follows. Although many parts are not clear, it can be estimated as follows. That is, when a phosphorus compound is contained in the catalyst at a specific ratio as in the present invention, the catalyst itself which is liable to be generated when a high-temperature exhaust gas of about 300 to 500 ° C. containing high concentrations of oxygen and water vapor is treated for a long time. It is considered that a change in the physical properties of the catalyst, for example, a change in the physical properties such as a specific surface area, a pore structure, and a crystal structure can be suppressed, and as a result, a change in the performance of the catalyst itself can be suppressed. Therefore, a catalyst having resistance to thermal load can be obtained without increasing the amount of noble metal carried, and high activity can be obtained even when exposed to high temperature exhaust gas containing high concentration of oxygen and water vapor for a long time. It is a catalyst that can be maintained.
[0045]
The method for incorporating the phosphorus compound into the catalyst is not particularly limited. For example, the phosphorus compound may be added and contained in the step of forming the carrier, or the starting material containing phosphorus when producing the carrier may be used. May be used to contain a phosphorus compound. In addition, similarly to the means used in the production of ordinary catalysts, the carrier can be immersed in an aqueous solution containing a raw material of the phosphorus compound to contain the phosphorus compound.
The order of the addition is not particularly limited either. The phosphorus compound may be contained simultaneously with the loading of the catalyst component A or the catalyst component B, or the phosphorus compound may be contained after the catalyst component A and the catalyst component B are loaded. Although it is possible to make the catalyst contain the phosphorus compound in various orders, it is preferable that the phosphorus compound be contained before the catalyst component A or the catalyst component B is supported.
[0046]
The form in which the phosphorus compound is contained in the carrier is not particularly limited, and the phosphorus compound may be uniformly contained in the carrier or may have a concentration gradient (concentration distribution) in the concentration of the phosphorus compound. The form may be, for example, such that the content is large near the outer surface of the carrier and the content decreases toward the inside of the carrier, but it is particularly preferable that the carrier is uniformly contained in the carrier.
(Sulfur compound)
The catalyst of the present invention may contain, as the other component D, a sulfur compound in an amount of 1% by weight or less in terms of sulfur atoms based on the total amount of the catalyst.
[0047]
Since the catalyst of the present invention contains a sulfur compound, it has a problem of SO during operation.₂The increase in the oxidation rate can be suppressed and kept low, and_XIt has sufficient durability to maintain stable and efficient performance for a long period of time, and unburned volatiles such as CO (especially low-concentration CO) and acetaldehyde in exhaust gas. The organic compound removal performance can be improved.
Usually, sulfur-containing compounds such as hydrogen sulfide and mercaptan are poisonous components to the catalyst, and therefore, it was generally thought that the sulfur content was a factor to decrease the catalytic ability. Have shown that certain sulfur compounds, such as sulfates (SO₄ ^2-)), The removal performance and the like may be improved in some cases, and a more detailed study reveals that it is not necessarily sufficient to increase the content, but it is necessary to control the content to an appropriate level. For example, it was found that the catalyst would be very excellent in the above-mentioned removal performance and the like.
[0048]
By containing the sulfur compound in a range of 1% by weight or less in terms of sulfur atoms with respect to the total amount of the catalyst as described above, CO (particularly low-concentration CO) and unburned volatile organic compounds such as acetaldehyde can be reduced. The reason why the removal performance and the like are improved is not clear at present, but can be estimated as follows. That is, it has been known that a titanium-based oxide containing a sulfate group exhibits a strong acid property not found in a titanium-based oxide alone, and is called a solid superacid. I have. Inferring from such facts, when a sulfur compound is contained in a range of 1% by weight or less in terms of sulfur atoms with respect to the total amount of the catalyst as in the present invention, the sulfur compound (sulfate group) coexists in the titanium-based oxide. The properties, such as the acidity, of the titanium-based oxide serving as a carrier change, and such a change in the properties of the carrier affects the supported state of the catalyst component supported on the carrier, the electronic state, and the like. And more advantageous effects. As a result, unburned volatile organic compounds such as CO (especially low-concentration CO) and acetaldehyde in exhaust gas can be more efficiently purified, and stable performance can be maintained for a long period of time. It is.
[0049]
Sulfur compounds include sulfate groups and sulfite groups. Only one sulfur compound may be used, or two or more sulfur compounds may be used in combination. By containing the sulfur compound as a catalyst component, unburned volatile organic compounds such as CO and aldehydes in exhaust gas can be more efficiently purified.
The method for containing the sulfur compound in the catalyst is not particularly limited, for example, the sulfur compound may be added and contained in the step of molding the carrier, or a starting material comprising a sulfate when producing the carrier Can be used to contain a sulfur compound. In addition, similarly to the means used for ordinary catalyst production, the carrier can be immersed in an aqueous solution containing a sulfur compound feedstock to contain the sulfur compound.
[0050]
Sulfuric acid, sulfurous acid, ammonium sulfate, ammonium sulfite, ammonium bisulfate, and ammonium bisulfite can be used as the feedstock for the sulfur compound.
The order of the addition is not particularly limited, but it is preferable to add the sulfur compound before supporting the catalyst component A or the catalyst component B.
The form in which the sulfur compound is contained in the carrier is not particularly limited, and may be uniformly contained in the carrier, or may have a concentration gradient in the concentration, for example, in the vicinity of the outer surface of the carrier. In which the content is large and the content decreases toward the inside.
[0051]
As described above, the content of the sulfur compound is preferably in the range of 1% by weight or less in terms of sulfur atom, based on the total amount of the catalyst, more preferably 0.01 to 1% by weight, and still more preferably. The range is 0.05 to 0.75% by weight, particularly preferably 0.1 to 0.5% by weight. If the content of the sulfur compound is more than 1% by weight, the active component becomes a poisoning component and conversely decreases the activity, which is not preferable.
<Preparation of catalyst and its physical properties>
The exhaust gas treatment catalyst of the present invention is prepared by using a catalyst component such that a carrier composed essentially of a metal oxide (for example, a porous honeycomb carrier made of a titanium-based oxide) is used so that a predetermined amount of the above-mentioned various raw materials is carried. It is obtained by carrying out drying and calcination treatments after carrying the above and the like, and is also obtained by regenerating the catalytic activity after once using the exhaust gas treatment.
[0052]
The above drying can be usually performed by treating in an air atmosphere, a nitrogen atmosphere, or a flow of these gases at a temperature of 50 to 200 ° C. for 1 to 24 hours. The calcination can be performed by performing a heat treatment in a temperature range of 200 to 900 ° C. for 1 to 10 hours. Usually, the reaction is performed in an air atmosphere or under an air flow, but a gas containing a reducing gas such as nitrogen or hydrogen may be used instead of air.
In obtaining the catalyst of the present invention, the regeneration of the above-mentioned catalytic activity requires at least one selected from the group consisting of hydrogen, hydrocarbons, alcohols, aldehydes, carboxylic acids and carbon monoxide in the catalyst once used for exhaust gas treatment. It is preferable that gas (hereinafter, may be referred to as a regeneration gas) is passed through the catalyst. By flowing the regeneration gas through the catalyst, the catalyst activity can be effectively and efficiently regenerated.
[0053]
In the present invention, the regeneration of the catalyst activity is not limited to the regeneration until the same state as before use (the same state as a new state). Any regeneration level that can maintain the reaction rate may be used.
The processing conditions for the regeneration of the catalyst activity are as follows in more detail.
As the regenerating gas, a gas containing at least 0.1% by volume of at least one kind (predetermined gas component) selected from the group consisting of hydrogen, hydrocarbons, alcohols, aldehydes, carboxylic acids, and carbon monoxide is used. It is preferably 0.5% by volume or more, more preferably 1.0% by volume or more. If the ratio of the predetermined gas component is less than 0.1% by volume, the catalytic activity may not be sufficiently recovered.
[0054]
The regeneration gas preferably has an oxygen content of 50% by volume or less, more preferably 30% by volume or less, and still more preferably an oxygen concentration in air (21% by volume or less). If the proportion of oxygen in the regeneration gas exceeds 50% by volume, the catalytic activity may not be sufficiently restored.
The temperature of the regeneration gas passed through the catalyst is preferably from 100 to 600 ° C, more preferably from 150 to 550 ° C, even more preferably from 200 to 500 ° C. If the temperature of the regeneration gas is lower than 100 ° C., the catalytic activity may not be sufficiently recovered, and if it is higher than 600 ° C., sintering of the active component may occur.
[0055]
The linear velocity of the regeneration gas flowing through the catalyst is preferably 0.01 to 20 m / sec, more preferably 0.05 to 15 m / sec, and still more preferably 0.1 to 10 m / sec. . If the linear velocity of the regenerated gas is less than 0.01 m / sec, the catalytic activity may not be sufficiently restored, and even if the linear velocity is increased to more than 20 m / sec, the regeneration efficiency is not significantly improved. Pressure loss may increase.
The space velocity of the regeneration gas flowing through the catalyst is 100 to 1,000,000 H^-1And more preferably 500 to 500,000H^-1And more preferably 1,000 to 300,000H^-1It is. Space velocity of the regeneration gas is 100H^-1If the amount is less than 1,000,000 H, there is a possibility that the catalyst activity may not be sufficiently recovered.^-1Although the regeneration efficiency does not improve so much even if the space velocity is increased beyond the above range, the amount of regeneration gas required for regeneration per unit amount of catalyst may increase, and the disadvantage may be increased economically.
[0056]
The time for flowing the regeneration gas through the catalyst is preferably 0.5 to 50 hours, more preferably 1 to 30 hours, and even more preferably 2 to 20 hours. If the circulation time is less than 0.5 hour, the catalyst activity may not be sufficiently recovered, and even if it exceeds 50 hours, the time required for sufficient regeneration is prolonged although the regeneration efficiency is not so improved. There is a risk.
The exhaust gas treatment catalyst of the present invention may have a porous structure having fine pores. In this case, diffusion of gas inside the catalyst is affected by the amount of pores. The specific surface area of the catalyst also affects the performance of treating exhaust gas.
[0057]
Usually, the total pore volume is 0.2-0.8 cm³/ G (mercury intrusion method) is appropriate. 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. Usually, the specific surface area is 30 to 250m²/ G (BET method) range, 40-200m²/ G is preferred. If the specific surface area is too small, the catalytic activity may not be sufficient.If the specific surface area is too large, the catalytic activity does not improve so much, but the accumulation of catalyst poisoning components increases or the catalyst life decreases. Such an adverse effect may occur.
[0058]
<Use form of catalyst>
The exhaust gas treatment catalyst of the present invention is usually used by being housed in a catalyst reactor made of metal or the like. The catalyst reactor is provided with an exhaust gas inlet and an outlet, and is provided with a structure that allows the exhaust gas to efficiently contact the catalyst housed therein.
The exhaust gas treatment catalyst of the present invention is obtained by regenerating the catalyst activity, but is not limited to a state in which a new catalyst is used until the activity once decreases, and then the catalyst activity is once regenerated. A catalyst obtained by regenerating the catalyst activity a plurality of times, such as using the catalyst obtained by regeneration until the activity decreases and then regenerating the catalyst activity, may be used. Therefore, as the usage form of the exhaust gas treatment catalyst of the present invention, the accommodation in the above-mentioned predetermined catalyst reactor, the removal, and the regeneration of the catalyst activity are repeatedly used.
[0059]
[Exhaust gas treatment method]
The exhaust gas treatment method of the present invention is characterized in that the exhaust gas treatment method for removing CO in exhaust gas is brought into contact with the exhaust gas treatment catalyst of the present invention.
When carrying out the exhaust gas treatment method of the present invention, basically, an exhaust gas treatment technique using a normal noble metal-supported metal oxide catalyst is applied. Normally, a catalyst reactor containing a catalyst is installed in the middle of a discharge path for exhaust gas or the like. When the exhaust gas passes through the catalytic reactor, the exhaust gas comes into contact with the surface of the catalyst, thereby receiving a predetermined catalytic action.
According to the exhaust gas treatment method of the present invention, not only CO contained in exhaust gas but also unburned volatile organic compounds can be treated at the same time.
[0060]
When exhaust gas is treated using the exhaust gas treatment catalyst of the present invention, the efficiency of exhaust gas treatment by the catalyst is improved by appropriately setting conditions such as temperature and space velocity. For example, a gas temperature of 250 ° C. to 600 ° C., a space velocity of 30,000 H^-1~ 1,000,000H^-1It is preferable to treat the combustion exhaust gas. More preferably, a gas temperature of 300 ° C. to 550 ° C. can be adopted, and a space velocity of 50,000 H^-1~ 500,000H^-1Can be adopted. Furthermore, Linear Velocity (LV) = 0.1 m / s (Normal) or more, or dust 10 mg / m³(Normal) The following processing conditions are preferred.
[0061]
In the exhaust gas treatment method of the present invention, another exhaust gas treatment step using another type of exhaust gas treatment catalyst may be combined before or after the exhaust gas treatment step using the exhaust gas treatment 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 exhaust gas treatment catalyst of the present invention is preferable.
For example, nitrogen oxides (NO_XIn the case of treating the exhaust gas containing (2), the exhaust gas treatment step using the denitration catalyst and the exhaust gas treatment step using the exhaust gas treatment catalyst of the present invention can be combined. In this way, CO and nitrogen oxides (NO_X) Containing nitrogen oxides (NO) together with CO_X) Can also be efficiently removed. In addition, the CO and nitrogen oxides (NO_X) Is preferably performed in an atmosphere of excess molecular oxygen.
[0062]
In the exhaust gas treatment step using the above-described denitration catalyst, the exhaust gas is brought into contact with the denitration catalyst in the presence of a reducing agent. Examples of the reducing agent include ammonia, urea, hydrazine and the like, and these may be used alone or in combination of two or more. The amount of the reducing agent used may be appropriately set depending on the required denitration rate, and is not particularly limited. Specifically, the reducing agent and the nitrogen oxide (NO_X) (Reducing agent / NO)_X) Is preferably less than 2, more preferably less than 1.5, and even more preferably less than 1.2. When the above molar ratio is 2 or more, a large amount of the reducing agent remains in the gas after the denitration treatment, which is not preferable.
[0063]
As mentioned above, CO and NO_XWhen treating an exhaust gas containing the following, an exhaust gas treatment step using an exhaust gas treatment catalyst of the present invention and an exhaust gas treatment step using a denitration catalyst in the presence of a reducing agent are combined. After removing CO in the exhaust gas by contacting with the exhaust gas treatment catalyst, NO._XAnd 2) contacting the exhaust gas with a denitration catalyst in the presence of a reducing agent to reduce NO in the exhaust gas._X, And then contacting the exhaust gas treatment catalyst of the present invention to remove CO in the exhaust gas.
[0064]
The former method 1) is a method for producing SO 2 of the exhaust gas treatment catalyst of the present invention._XThis is preferable in that the degradation of the activity due to the above can be further suppressed. That is, usually, even in the treatment with the denitration catalyst, SO₂→ SO₃Oxidation reaction occurs. The activity degradation of the exhaust gas treatment catalyst according to the present invention is caused by SO₂SO than by₃Is larger. If the exhaust gas treatment catalyst of the present invention is installed ahead of the denitration catalyst, it is expected that this activity deterioration can be suppressed.
In the latter method 2), the excess reducing agent (NH₃Etc.) can be further reduced. That is, NH usually used in the treatment with the denitration catalyst₃Such as NO_XAlthough it is reduced by participating in the removal reaction, etc., depending on the processing conditions, it may be unreacted and mixed into the treated exhaust gas, which poses a problem.₃It is expected that if the exhaust gas treatment catalyst of the present invention is installed behind the denitration catalyst, the unreacted reducing agent can be oxidized and further reduced because the exhaust gas treatment catalyst of the present invention is also provided. Is done. Particularly, when a high denitration rate is required, such as when a strict emission control value is imposed, the method 2) can be used to obtain NH3.₃Oversupply of a reducing agent such as_XThis is very effective because the removal efficiency is made as high as possible, and a large amount of unreacted unreacted reducing agent can be removed by the exhaust gas treatment catalyst of the present invention at a later stage.
[0065]
As the exhaust gas treatment technology using the denitration catalyst, the technology disclosed in Japanese Patent Application Laid-Open No. Hei 10-235206, which was previously filed by the present applicant, 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 (a metal oxide composed of vanadium or tungsten) are combined, and the catalyst component b is supported on the catalyst component a. Have.
In the exhaust gas treatment method of the present invention, nitrogen oxides (NO_X) Can be targeted, and even such an exhaust gas can efficiently remove CO.
[0066]
In the exhaust gas treatment method of the present invention using the exhaust gas treatment catalyst of the present invention, NO_XCan also be removed. In this case, NO_XIn order to increase the efficiency of removing methane, it is preferable to carry out the reaction in the presence of a reducing agent such as ammonia, urea and hydrazine. Further, in these cases, for example, the gas temperature is 250 to 500 ° C., and the space velocity is 2000 to 500,000 H.^-1It is preferable to treat the exhaust gas.
In the exhaust gas treatment method of the present invention, known exhaust gas treatment methods described in JP-A-53-146991, JP-A-62-65721, JP-B-6-4126 and the like can be combined. .
[0067]
In the present invention, as a catalyst for treating CO contained in exhaust gas, for example, an integrally molded porous honeycomb body made of a titanium-based oxide is used as a carrier, and a catalyst component A made of at least one noble metal element is used as a catalyst surface. It is possible to use a honeycomb catalyst supported on the carrier so as to be unevenly distributed. As a result, a very high catalytic activity can be obtained, and a high treatment efficiency can be achieved without increasing the amount of the noble metal to be a catalyst component. As a result, the method is very effective as a method for treating a large amount of CO-containing exhaust gas discharged from a gas turbine or the like. Further, as described above, in the present invention, an exhaust gas treatment catalyst obtained by regenerating catalytic activity is used as a catalyst for treating CO contained in exhaust gas. As long as the hard surface to obtain is kept at a certain level, the catalyst with reduced activity can be reused many times, so that the cost can be kept very low in the long term. Further, in terms of environment, wastes and the like after use of the catalyst can be further reduced, so that environmental pollution and the like can be suppressed.
[0068]
【Example】
Hereinafter, the present invention will be described more specifically with reference to Examples, but the present invention is not limited thereto. In the following, “parts by weight” may be simply referred to as “parts” for convenience. Further, “wt%” may be simply described as “wt%”.
The conditions of the composition analysis and the EPMA sectional line analysis of the catalysts produced in the following Examples and Comparative Examples are shown below.
<Catalyst composition analysis>
The analysis of the catalyst composition was performed by the fluorescent X-ray analysis under the following conditions.
[0069]
Analyzer: Rigaku Corporation, Product name: RIX2000
Sample atmosphere during analysis: vacuum
Sample spin speed: 60 rpm
X-ray source: Rh tube
<EPMA cross section line analysis>
Analyzer: Shimadzu Corporation, Product name: EPMA-1610
X-ray beam diameter: 1 μm
Acceleration voltage: 15 kV
Sample current: 0.1 μA
Measurement interval: 1 μm
Measurement time: 1 second / point
[Production example]
A new exhaust gas treatment catalyst was prepared as follows.
[0070]
Preparation of Ti-Si composite oxide:
100 kg of titanium tetrachloride is gradually added dropwise to 700 liters of water while cooling and stirring.₂Of colloidal silica (Snowtex-20 (trade name), manufactured by Nissan Chemical Industries, Ltd.) was added, and the temperature after the addition was maintained at about 30 ° C., and then ammonia water was stirred well under cooling. The pH was gradually dropped until the pH reached 7.5, and the obtained gel was aged for 2 hours. Thereafter, the resultant was filtered, washed with water, and subsequently dried at 150 ° C. for 10 hours. This was fired at 500 ° C. and further pulverized using a hammer mill to obtain a powder. In the powder X-ray diffraction chart, TiO₂And SiO₂Was not recognized, and the broad diffraction peak confirmed that the composite oxide was a composite oxide of titanium and silicon (Ti-Si composite oxide) having an amorphous fine structure.
[0071]
Manufacture of honeycomb carrier:
To 20 kg of the above-mentioned Ti-Si composite oxide, 1 kg of a phenolic resin (Bellpearl (trade name), manufactured by Kanebo Co., Ltd.) and 0.5 kg of starch as a molding aid are added and mixed. After well kneading, the mixture 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 using an extruder. Next, after drying at 80 ° C., it was fired at 450 ° C. for 5 hours in an air atmosphere to obtain a honeycomb carrier.
The honeycomb carrier has a lattice structure as shown in FIG. 1, and each exhaust gas passage has an opening of 2.1 mm and a lattice wall thickness of 0.4 mm.
[0072]
Preparation of catalyst by supporting catalyst component:
The honeycomb carrier was impregnated with a mixed solution of boiled hexaammine platinum hydroxide and magnesium acetate and dried. Next, by firing at 450 ° C. for 2 hours in an air atmosphere, a catalyst (A) in which Pt was supported as the catalyst component A and Mg was supported as the catalyst component B on the honeycomb carrier was obtained.
Catalyst analysis:
When the composition of the obtained catalyst (A) was analyzed, the ratio was Ti-Si composite oxide: Mg: Pt = 98.4: 1.5: 0.1 (weight ratio).
[0073]
The catalyst (A) was subjected to EPMA cross-sectional line analysis of Pt. As a result, it was confirmed that 90% by weight or more of Pt was present in a region from the surface of the catalyst (A) to a depth of 100 μm. Was. The average particle size of Pt measured using a transmission electron microscope was less than 5 nm.
[Example 1]
The catalyst (A) obtained in Reference Example was exposed to exhaust gas discharged from a gas turbine for about 8,000 hours.
The catalyst activity of the catalyst (A) after the exposure was regenerated under the following conditions to obtain a regenerated catalyst (1).
[0074]
Play conditions:
Regeneration gas composition = H₂: 5% by volume, N₂:balance
Gas linear velocity = 0.1 m / sec (Nomal)
Gas temperature = 350 ° C
Space velocity = 5,000H^-1
Regeneration gas circulation time = 3 hours
For each of the catalyst (A) obtained in the reference example, the catalyst (A) after the exposure, and the regenerated catalyst (1), a CO-containing exhaust gas was brought into contact with the catalyst to remove CO, and the removal rate was determined. .
[0075]
As a result, the CO removal rate (%) was 92% for the catalyst (A) obtained in Reference Example, 85% for the catalyst (A) after the above exposure, and 92% for the regenerated catalyst (1).
The CO removal processing conditions and the CO removal rate calculation formula are as follows.
Processing conditions:
Exhaust gas composition
= CO: 20ppm, O₂: 12%, H₂O: 10%, N₂:balance
Gas temperature = 350 ° C
Space velocity (STP) = 90,000H^-1
CO removal rate calculation formula:
CO removal rate (%) =
[{(Reactor inlet CO concentration)-(Reactor outlet CO concentration)}
/ (Reactor inlet CO concentration)] × 100
[Example 2]
Similarly to Example 1, the catalyst (A) obtained in Reference Example was exposed to exhaust gas discharged from a gas turbine for about 8,000 hours.
[0076]
The catalyst activity of the catalyst (A) after the exposure was regenerated under the following conditions to obtain a regenerated catalyst (2).
Play conditions:
Regeneration gas composition = CH₄: 7% by volume, N₂:balance
Gas linear velocity = 25m / sec (Nomal)
Gas temperature = 350 ° C
Space velocity = 100,000H^-1
Regeneration gas circulation time = 3 hours
With respect to the regenerated catalyst (2), an exhaust gas containing CO was brought into contact with the regenerated catalyst to perform a CO removal treatment, and the removal rate was obtained. The conditions for the CO removal treatment are the same as in the first embodiment.
[0077]
As a result, the CO removal rate (%) of the regenerated catalyst (2) was 92%.
[Example 3]
The regenerated catalyst (2) obtained in Example 2 was subjected to desktop exposure under the following conditions.
Tabletop exposure conditions:
Gas composition = H₂O: 8% by volume, N₂:balance
Gas temperature = 500 ° C
Space velocity = 80,000H^-1
Regeneration gas circulation time = 1,500 hours
Next, the catalyst activity of the catalyst (2) after the desktop exposure was regenerated under the same conditions as in Example 2 to obtain a regenerated catalyst (3).
[0078]
With respect to each of the catalyst (2) and the regenerated catalyst (3) after the desktop exposure, CO was removed by contacting the exhaust gas containing CO, and the removal rate was obtained. The conditions for the CO removal treatment are the same as in the first embodiment.
As a result, the CO removal rate (%) was 83% for the catalyst (2) and 91% for the regenerated catalyst (3) after exposure on the desk.
[0079]
【The invention's effect】
According to the present invention, CO and NO contained in exhaust gas_XIt is possible to provide an exhaust gas treatment catalyst which can efficiently remove harmful components such as exhaust gas and is industrially very effective in terms of cost and the like, and an exhaust gas treatment method using the same.
[Brief description of the drawings]
FIG. 1 is a perspective view of an exhaust gas treatment catalyst according to an embodiment of the present invention.
[Explanation of symbols]
10 Exhaust gas treatment catalyst
11 Porous honeycomb carrier
13 Exhaust gas passage
14 Inner wall

Claims (6)

A metal oxide containing at least one metal selected from the group consisting of Ti, Al, Si, W and Zr, and at least one noble metal element selected from the group consisting of Pt, Pd, Rh, Ru, Ir and Au An exhaust gas treatment catalyst which is obtained by regeneration of catalytic activity, comprising a catalyst component A comprising 2. The exhaust gas treatment catalyst according to claim 1, wherein the regeneration is performed by flowing a gas including at least one selected from the group consisting of hydrogen, hydrocarbon, alcohol, aldehyde, and carboxylic acid through the catalyst. At least one catalyst component selected from the group consisting of catalyst components B, V, W, Mo, Cu, Mn, Ni, Co, Cr and Fe comprising at least one metal element contained in Groups I to III of the periodic table. A catalyst component C comprising an element, and at least one selected from the group consisting of compounds of at least one element selected from the group consisting of B, S, P, Sb, Pb, Sn, Zn and In. Item 3. The exhaust gas treatment catalyst according to Item 1 or 2. An exhaust gas treatment method for removing CO in exhaust gas,
A step of contacting the exhaust gas with the exhaust gas treatment catalyst according to any one of claims 1 to 3,
An exhaust gas treatment method, characterized in that: The exhaust gas also containing NO _X, the exhaust gas treatment method according to claim 4. The method according to claim 5, further comprising a step of contacting the exhaust gas with the denitration catalyst in the presence of a reducing agent before and / or after the step of contacting the exhaust gas with the exhaust gas treatment catalyst according to any one of claims 1 to 3. Exhaust gas treatment method.

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