JP2008155071A - Exhaust gas purifying catalyst - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a practical exhaust purifying catalyst capable of being replaced with a catalyst using a noble metal such as platinum or the like, expensive and also rare from an aspect of resources and showing an inexpensive good catalytic action. <P>SOLUTION: The exhaust purifying catalyst contains at least one kind of an element M selected from the group consisting of tellurium (Te), ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os) and iridium (Ir) and is characterized in that the value of the molar ratio X of Te to the element M is 0.2<X<4. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention is an exhaust gas purifying catalyst, particularly one or more selected from the group consisting of tellurium (Te) element and ruthenium (Ru), rhodium (Rh), palladium (Pd), osnium (Os), and iridium (Ir). The present invention relates to a catalyst using the additive element as an active component.

In recent years, exhaust gas purification is an important environmental issue, and regulations are becoming stronger from the viewpoint of preventing air pollution, and an immediate response is desired.
In order to remove carbon monoxide (CO) and hydrocarbons (HC) in combustion gas generated from an internal combustion engine and other combustion engines, treatment using an oxidation catalyst is performed.

In general, exhaust gas oxidation catalysts for automobiles and the like are used in which a noble metal such as platinum or palladium is coated on a carrier such as alumina or cordierite.
For example, Patent Document 1 discloses an automobile exhaust gas purification catalyst containing platinum and a composite oxide containing tungsten.

JP 2001-46870 A

  However, since noble metals such as platinum are expensive and scarce in terms of resources, the development of an exhaust gas purifying catalyst that can replace these noble metals is one of the important issues. The conventional exhaust gas purifying catalyst such as Patent Document 1 does not meet such a problem.

  The present invention has been made in view of the above-described problems. That is, an object of the present invention is to provide a practical exhaust gas purifying catalyst that can be replaced with a catalyst using a noble metal such as platinum, which is expensive and resource-rare, and exhibits a good catalytic action at low cost. .

  Various studies have been made so far as metals that replace platinum, but no metal having sufficient activity has been found. Further, as has been studied conventionally, it has been found that it is difficult to achieve the object simply by modifying a single metal catalyst or a metal catalyst with another compound.

  Therefore, as a result of intensive investigations in view of the above circumstances, the present inventors have achieved high catalytic activity by using an alloy or compound containing a Group VIII element such as ruthenium and tellurium, and a catalyst using a noble metal such as platinum. It has been found that an exhaust gas purifying catalyst having utility that can be substituted for the above is obtained. In addition, by depositing this alloy or compound on a carrier, it is possible to obtain an exhaust gas purification catalyst that is inexpensive, has a higher catalytic activity, and has a practical utility that can be substituted for a catalyst using a noble metal such as platinum. I found it.

The present invention has been completed based on such knowledge, and the gist thereof is as follows.
[1] including tellurium (Te) and one or more elements M selected from the group consisting of ruthenium (Ru), rhodium (Rh), palladium (Pd), osnium (Os), and iridium (Ir), A catalyst for exhaust gas purification, wherein the molar ratio X of Te to the element M is 0.2 <X <4.
[2] The exhaust gas-purifying catalyst according to [1], containing Ru.
[3] The exhaust gas purifying catalyst according to [1] or [2], characterized by containing RuTe ₂ .
[4] The exhaust gas-purifying catalyst according to any one of [1] to [3], wherein an active ingredient is deposited on a metal oxide support.

Non-Patent Document 1 below discloses an alloy having a composition represented by Ru _x Te _y (x and y represent the number of moles of Ru and Te, respectively). The value is not disclosed. There is no suggestion of application to a catalyst.
[Non-Patent Document 1] Nuclear Instruments & Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment, 448 (1-2), 2000, 323-326.

  ADVANTAGE OF THE INVENTION According to this invention, the practical exhaust gas purification catalyst which shows a cheap and favorable catalytic action which can substitute for the catalyst using noble metals, such as platinum which is expensive and rare also in resources, is provided.

  Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and various modifications can be made within the scope of the gist of the present invention.

[Exhaust gas purification catalyst]
The exhaust gas purifying catalyst of the present invention contains tellurium (Te) and is further selected from the group consisting of ruthenium (Ru), rhodium (Rh), palladium (Pd), osnium (Os), and iridium (Ir). Contains the above element M.
When the molar ratio of tellurium to element M is X, that is, when the composition of element M and tellurium is expressed as M ₁ Te _X , the value of X satisfies 0.2 <X <4.
The exhaust gas-purifying catalyst of the present invention only needs to have a component (hereinafter sometimes referred to as “active component”) composed of Te and element M. That is, it may be composed of only the active ingredient, or may be one obtained by adhering the active ingredient to the carrier.

  In the following, one or more elements selected from the group consisting of ruthenium (Ru), rhodium (Rh), palladium (Pd), osnium (Os), and iridium (Ir) are referred to as “Group VIII metal elements”. , “M”.

[Active ingredient]
In the exhaust gas purifying catalyst of the present invention, the tellurium in the active ingredient (Te), the abundance ratio of the Group VIII metal element M, the ratio of the number of elements constituting the active ingredients when expressed as M ₁ Te _X, X Is usually X> 0.2, preferably X> 0.3, more preferably X> 1, and the upper limit of X is usually X <4, preferably X <3, more preferably X <2. .5. If the value of X representing the abundance ratio of the group VIII metal element M to tellurium is less than this lower limit, the activity tends to be low, and even if it exceeds the upper limit, the activity may be difficult to be produced.

  In addition, any one of the Group VIII metal elements M may be used alone, or two or more may be used in any combination and ratio. When two or more Group VIII metal elements M are used in combination, the ratio between the total number of elements and the number of tellurium elements only needs to satisfy the above condition.

  The tellurium content in the active ingredient is usually 5% by weight or more, more preferably 6% by weight or more, still more preferably 10% by weight or more, and usually 96% by weight or less, preferably 95% by weight based on the entire active ingredient. % By weight or less, more preferably 93% by weight or less, still more preferably 90% by weight or less, and particularly preferably 87% by weight or less. If the tellurium content in the active ingredient is less than this lower limit, the activity tends to be low, and even if the upper limit is exceeded, the activity may be difficult to occur.

  Further, the content of the group VIII metal element M in the active ingredient is usually 1% by weight or more, preferably 5% by weight or more, more preferably 7% by weight or more, and further preferably 10% by weight with respect to the entire active ingredient. Above, particularly preferably 13% by weight or more, and usually 95% by weight or less, preferably 90% or less, more preferably 88% by weight or less, and further preferably 85% by weight or less. If the content of the group VIII metal element in the active ingredient is below this lower limit, the activity may be easily lowered, and even if the upper limit is exceeded, the activity may be difficult to be obtained. When two or more kinds of Group VIII metal elements M are used in combination, the total amount of the elements only needs to satisfy the above range.

  These tellurium and group VIII metal element M constituting the active ingredient are preferably present with a bond to each other. As the presence form of such an active component, a so-called alloy form is preferable from the viewpoint of thermal stability and the like.

When the active component has an alloy form, specific examples of the composition include RuTe ₂ , RuTe, Ru ₂ Te, OsTe ₂ , RhTe, RhTe ₂ , Rh ₃ Te ₂ , Rh ₃ Te ₄ , Rh ₃ Te ₈ , IrTe ₂ , Ir ₃ Te ₈ , PdTe, Pd ₃ Te ₂ , PdTe ₂ , Pd ₉ Te ₄ , Pd _2.5 Te, Pd ₃ Te, Pd ₂ Te, Pd ₂₀ Te ₇ , Pd ₈ Te ₃ , Pd ₇ Te ₂ , Pd ₇ Te ₃ , Pd ₄ Te, Pd ₁₇ Te _{4 and the} like can be mentioned. Of these, RuTe ₂ , RuTe, and Ru ₂ Te are preferable, and RuTe ₂ is particularly preferable. The group VIII metal element M that forms an alloy by bonding with tellurium may be one type, or two or more types.

  The existence form of the active component in the exhaust gas purifying catalyst of the present invention can be confirmed by X-ray diffraction (XRD). That is, for example, it can be confirmed by irradiating an active ingredient deposited on a carrier described later with X-rays (Cu-Kα rays) and observing the diffraction spectrum thereof. Examples of the measurement apparatus and measurement conditions include the following, but are not limited to the following measurement apparatuses and measurement conditions.

(Powder XRD analysis)
Measuring device X-ray powder analyzer / PANalytical PW1700
Measurement conditions X-ray output (Cu-Kα): 40 kV, 30 mA
Scanning axis: θ / 2θ
Measurement range (2θ): 3.0 ° to 90.0 °
Measurement mode: Continuous
Reading width: 0.05 °
Scanning speed: 3.0 ° / min
DS, SS, RS: 1 °, 1 °, 0.20mm

Specifically, RuTe ₂ only needs to match one of JCPDS PDF # 09-1108, PDF # 044-1015, PDF # 065-3334, and PDF # 088-1380. JCPDS is an abbreviation for Joint Committee for Powder Diffraction Studies (JCPDS), an organization that was established in 1941 and renamed International Center for Diffraction Data (ICDD) in 1978. It maintains a database of a certain Powder Diffraction File (PDF).

[Carrier]
The exhaust gas purifying catalyst of the present invention may be a non-adhered catalyst composed only of the above-mentioned active component, but it is also possible to use the active component by adhering it to a carrier for holding the active component. is there. From the viewpoint of dispersibility and contact efficiency, an adsorbed catalyst in which an active component is adsorbed on a support is preferred.

  Although there is no restriction | limiting in the kind of support | carrier used for the exhaust gas purification catalyst of this invention, A metal oxide support | carrier is suitable. Various metal oxide carriers can be used and are not limited. Examples thereof include silica, alumina, magnesia, titania, zirconia, zeolite, clay and the like. Any one of the carriers may be used alone, or two or more carriers may be used in any combination and ratio.

Although there is no particular limitation on the specific surface area of the support, usually 5 m ² / g or more, preferably 10 m ² / g or more, more preferably 50 m ² / g or more and usually 5000 m ² / g or less, preferably 2000 m ² / g The following is desirable. If the specific surface area is too small, the effective area for depositing the active component is reduced, and the reaction field may be reduced, resulting in insufficient catalytic activity. In addition, when the specific surface area is excessively large, the pore diameter of the support may be small, and even if the active component is deposited in the small pores, sufficient catalytic activity may not be obtained. The specific surface area of the carrier is measured by the BET method.

  The form of the carrier is not particularly limited, but the most commonly used is a powder or a molded article such as a honeycomb.

[Adhesion of active ingredient to carrier]
In the present invention, the active ingredient may be applied to the carrier by, for example, a loading method in which the active ingredient or a supply compound of the active ingredient is mixed with the carrier and calcined, a mixing method in which the active ingredient and the carrier are simply mixed, and other impregnation It can be carried out by a known method such as a method, a precipitation method or an adsorption method. It is also possible to support the slurry of the deposited catalyst on a molded article such as a honeycomb by a known wash coat method or sol-gel method.

  The shape of the active ingredient attached to the carrier is not limited, but the most common is a particulate form. The upper limit of the average particle diameter of the particulate active ingredient is usually 100 μm or less, preferably 1000 nm or less, more preferably 500 nm or less, still more preferably 300 nm or less, and the lower limit is usually 0.5 nm or more, preferably 1.0 nm or more. More preferably, the thickness is 2.0 nm or more. If the particle size of the active ingredient is below this lower limit, it may become unstable and may be easily deactivated, and if it exceeds the upper limit, it may be difficult to obtain high activity.

  The average particle diameter of the active ingredient deposited on the carrier is determined by unifying the direction in which the particle length is measured by a scanning electron microscope (SEM) or transmission electron microscope (TEM). The particle length is measured and indicated as an average value.

  In order to deposit the active ingredient having such a small average particle diameter on the carrier, the production method thereof may be devised as will be described later. In particular, the firing temperature after impregnating and supporting the active ingredient on the carrier is lowered. Controlling the crystal growth state by shortening the firing time can be mentioned.

The deposition ratio of the active ingredient to the carrier is not particularly limited, but the lower limit of the active ingredient / carrier weight ratio is usually 10 ⁻⁵ or more, preferably 0.001 or more, more preferably 0.8. It is 01 or more, more preferably 0.05 or more, and the upper limit is usually 0.95 or less, preferably 0.4 or less, more preferably 0.3 or less. If the deposition ratio of the active ingredient is below this lower limit, it may be difficult to obtain desired activity, and if it exceeds the upper limit, it may be difficult to improve the activity due to deposition.

[Other catalyst components]
In this invention, unless the effect of this invention is impaired, components other than the above-mentioned Te and element M may be contained. Examples of other components include transition metal elements.

  This transition metal element (hereinafter sometimes referred to as “other catalyst component”) is an element belonging to the fourth to sixth periods of Groups IIIA to VIIA, VIII, and IB of the Periodic Table. (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), lanthanum (La), europium (Eu), gold (Au), cerium (Ce), tantalum (Ta), tungsten (W), rhenium (Re), praseodymium (Pr), neodymium (Nd) is exemplified.

  In addition, these other catalyst components may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and ratios.

When other catalyst components are used in combination as a cocatalyst, examples of the combined form of the other catalyst components include the following.
(1) Other catalyst components are mixed with the active component together with the support.
(2) Other catalyst components are supported on the carrier together with the active components.
(3) The active component supported on the carrier is mixed with other catalyst components.
(4) The active component is mixed with another catalyst component supported on another carrier.
(5) The active component supported on the carrier is mixed with other catalyst components supported on the other carrier.

  When other catalyst components are used, the ratio of the other catalyst components is a ratio of the total weight of the other catalyst components to the weight of the active component, and is usually 0.001 or more, preferably 0.01 or more, more preferably as a lower limit. It is preferable to use 0.05 or more, and the upper limit is usually 0.5 or less, preferably 0.4 or less, more preferably 0.3 or less. If the ratio of the other catalyst component to the active component is below this lower limit, it may be difficult to obtain the desired activity, and if it exceeds the upper limit, it may be difficult to improve the activity.

  The other catalyst component is preferably in the form of powder, and the average particle size in this case is usually 1000 nm or less, preferably 500 nm or less, more preferably 300 nm or less as the upper limit, and usually 0.5 nm or more as the lower limit. It is desirable. Below this lower limit, it may become unstable and easily deactivated, and when it exceeds the upper limit, it may be difficult to obtain high activity.

  In the exhaust gas purifying catalyst of the present invention, even if a metal component other than the transition metal element is contained in an amount of several weight% or less based on the weight of the active component, it is acceptable for the purpose and effect of the present invention. it can.

  By using such other catalyst components in combination, the catalyst activity can be enhanced, especially by using the other catalyst components supported on the carrier together with the active components. Although the details of the action mechanism of the catalytic activity improvement effect by using other catalyst components in combination, particularly by supporting the other catalyst components together with the active components on the carrier, the transition metal of the other catalyst components is not necessarily clear. It is estimated that the activity is improved because it functions as a cocatalyst.

Each element supply compound is not limited as long as it can be thermally decomposed.
For example, in the case of tellurium supply compounds, besides tellurium powder (Te), halides such as TeCl ₂ , TeBr ₂ , TeCl ₄ , oxides such as TeO ₂ , TeO ₃ , H ₂ TeO ₃ , H ₆ TeO _6, etc. Examples thereof include inorganic salts such as oxoacids.

  Moreover, as a supply compound of ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), in addition to these halides, oxides, inorganic salts, organic acid salts, etc., Examples include compounds that bind to organic compounds.

Specifically, a halide such as RuCl ₃ .xH ₂ O, RuBr ₃ , an inorganic salt such as Ru (SO ₄ ) ₂ , Ru (NO) (NO ₃ ) ₃ , K ₂ RuO ₄ .H ₂ O, Ru Organic acid salts such as ₂ (OCH ₃ CO) _4, compounds that bind to organic compounds such as Ru (acac) ₃ , halides such as RhCl ₃ · xH ₂ O, RhBr ₃ , KRh (SO ₄ ) ₂ · 12H ₂ Inorganic salts such as O, Rh (NO ₃ ) ₃ .2H ₂ O, organic acid salts such as Rh (OCH ₃ CO) ₃ , PdCl ₂ , PdCl ₂ .2H ₂ O, PdF ₂ , PdCl ₄ , K ₂ PdCl ₄ , Halides such as K ₂ PdCl ₆ , inorganic salts such as Pd (NO ₃ ) ₂ , organic acid salts such as Pd (OCH ₃ CO) ₂ , halides such as OsCl ₃ and K ₂ OsCl ₆ , OsO _2, etc. oxide, IrCl _3, IrBr _3, etc. halides, oxides such as IrO _2, Ir SO ₄₎ inorganic salts such as _2, and the like.

  These feed compounds may be used alone or in combination of two or more in any combination and ratio.

[Production of supported catalyst]
Among the exhaust gas purifying catalysts of the present invention, the carrier-adhered catalyst is produced by adhering an active component to a carrier. Here, the active ingredient may be applied to the carrier by, for example, a loading method in which the active ingredient or a supply compound of the active ingredient is mixed with the carrier and calcined, a mixing method in which the active ingredient and the carrier are simply mixed, and other impregnations. It can be carried out by a known method such as a method, a precipitation method or an adsorption method.

For example, a catalyst in which an active ingredient is supported on a carrier is prepared by dissolving or dispersing a supply compound of an element serving as a catalyst in a solvent such as an aqueous solution at a desired molar ratio, and impregnating the liquid into the carrier or in the liquid. Prepared by applying a step (for example, reduction treatment) for activating the precursor of the active ingredient, if necessary, by depositing the supply compound on the carrier by filtration or distilling off the solvent. . In addition, as a precursor of an active component, the same compound as the compound used for manufacture of a non-adhesion catalyst can be used. Among them, as the ruthenium supply compound, RuCl ₃ · xH ₂ O, Ru (acac) ₃ , Ru (NO) (NO ₃ ) ₃ are preferable (in the above formula, x represents a molar ratio of crystal water). As the tellurium supplying compound, H ₆ TeO ₆ is preferable.

  As a method for synthesizing a carrier-coated catalyst in which an active component is supported on a carrier, a method exemplified below can be given as a method for producing a catalyst containing ruthenium and tellurium as active components.

First, RuCl ₃ or Ru (acac) ₃ which is a ruthenium supply compound and H ₆ TeO ₆ which is a tellurium supply compound are dissolved or dispersed in water at a mixing ratio according to a desired molar ratio. Specifically, the molar ratio of Te to Ru is usually 0.2 or more, preferably 1 or more, and usually 10 or less, preferably 4 or less.

  A predetermined amount of a carrier such as silica, alumina, magnesia, titania, zirconia, zeolite, clay or the like is mixed with the obtained solution or dispersion, and the mixture is mixed for a predetermined time (usually 10 minutes or more, preferably 30 minutes or more, and usually 50 Or less, preferably 30 hours or less). In this case, ultrasonic treatment may be performed.

  Next, if necessary, at a predetermined temperature (usually 60 ° C. or higher, preferably 100 ° C. or higher, and usually 300 ° C. or lower, preferably 200 ° C. or lower) for a predetermined time (usually 10 minutes or longer, preferably 30 minutes or longer). In addition, it is usually heated or refluxed for 50 hours or less, preferably 30 hours or less, and then a precipitate is obtained by filtration or evaporator.

  The resulting precipitate is air-dried at room temperature, and then in an inert gas atmosphere such as nitrogen or argon for a predetermined time (usually 10 minutes or more, preferably 30 minutes or more, and usually 50 hours or less, preferably 30 hours or less) , And drying at a predetermined temperature (usually 100 ° C. or higher, preferably 200 ° C. or higher, and usually 1000 ° C. or lower, preferably 800 ° C. or lower).

  After the drying treatment, the obtained solid is subjected to a predetermined time (usually 10 minutes or more, preferably 30 minutes or more, and usually 50 hours or less, preferably 30 hours or less), a predetermined temperature (usually 100 ° C. or more, preferably 200 However, it may contain an inert gas such as nitrogen or Ar at a temperature of not less than 300 ° C, more preferably not less than 300 ° C, and usually not more than 1000 ° C, preferably not more than 800 ° C. The hydrogen concentration in the gas is not limited, but is usually 1% or more, preferably 10% or more, and usually 100% or less, preferably 80% or less in volume ratio. Thus, an active ingredient containing Ru and Te can be supported on the carrier.

  Thereafter, in an inert gas atmosphere having a low oxygen concentration (eg, oxygen concentration of usually 5% by weight or less, preferably 2% by weight or less) for a predetermined time (usually several tens of minutes, preferably 30 minutes or more, The passivation treatment for forming a passive film can also be performed by treatment at a predetermined temperature (usually around room temperature) usually for 10 hours or less, preferably 5 hours or less.

  Alternatively, the active ingredient may be prepared in advance by the above-described known method, mixed with a carrier, and kneaded in a mortar or the like to adhere the active ingredient to the carrier. This mixing may be dry or wet, but is preferably wet mixed using a medium such as water and then dried at a temperature of about 100 to 200 ° C.

  In the present invention, among the above-described catalyst production methods, a support method in which a metal oxide carrier and an active ingredient and a compound selected from active compound supply compounds are mixed and then calcined is preferable. The activity of the resulting catalyst can be improved. The reason why the activity can be improved by firing in this manner is not necessarily clear, but since the active component is deposited on the metal oxide carrier, sintering of the active component during firing is suppressed. Therefore, it is estimated that the activity is improved.

  When the above-mentioned other catalyst components are deposited on the carrier together with the active component, other catalyst components may be deposited simultaneously in the active component deposition step, and other components may be deposited before or after the active component deposition step. A catalyst component may be deposited. Here, the “active component deposition step” includes the treatment process for depositing the active component, that is, the entire process from the addition of the active component supply compound to the provision of the active component.

  Transition metal supply compounds for depositing other catalyst components on the support include oxides, inorganic acid salts such as nitrates, sulfates and carbonates, organic acid salts such as acetates, halides and hydrides. , A carbonyl compound, an amine compound, an olefin coordination compound, a phosphine coordination compound or a phosphite coordination compound. These may be used alone or in combination of two or more.

  As a specific method for depositing other catalyst components together with the active component on the carrier, for example, the methods described below may be mentioned.

  First, a solution in which a transition metal compound such as chloride is dissolved is added to a catalyst in which an active ingredient containing Ru and Te is supported on a carrier synthesized by the method described above, and a predetermined time (usually 10 minutes or more) is added. And preferably 30 minutes or more, and usually 50 hours or less, preferably 30 hours or less), and then the solvent is distilled off by an evaporator. In this case, ultrasonic treatment may be performed.

  Next, under a gas flow containing hydrogen (which may contain an inert gas such as nitrogen or Ar. However, the hydrogen concentration in the gas is not limited, but is usually 1% by volume). Or more, preferably 10% or more, and usually 100% or less, preferably 80% or less), a predetermined temperature (usually 100 ° C or more, preferably 150 ° C or more, and usually 800 ° C or less, preferably 500 Active component containing Ru and Te and other catalyst components by heating for a predetermined time (usually 10 minutes or more, preferably 30 minutes or more, and usually 50 hours or less, preferably 30 hours or less) As a result, a supported catalyst having a catalyst supported on the carrier can be obtained.

  Thereafter, in an inert gas atmosphere having a low oxygen concentration (eg, oxygen concentration of usually 5% by weight or less, preferably about 2% by weight or less) for a predetermined time (usually several tens of minutes, preferably 30 minutes or more, In addition, a passivation treatment can be performed in which a passive film is formed by treatment at a predetermined temperature (usually around room temperature) usually for 10 hours or less, preferably 5 hours or less.

  As described above, the other catalyst component may be used as it is mixed with the carrier on which the active component is deposited (supported), or the active component may be added to the carrier on which the other catalyst component is deposited (supported). May be used in combination.

[Usage and use of catalyst]
The exhaust gas purifying catalyst of the present invention described above is usually used by coating an integral structure type substrate. Such a substrate can be appropriately selected from known catalyst-supporting substrates, and examples thereof include a monolith carrier and a metal carrier made of a refractory material. Further, the shape of the substrate is not particularly limited, but usually a honeycomb shape is preferable, and the catalyst is applied to the honeycomb-shaped substrate as a slurry of the catalyst powder or a medium such as the catalyst water. . In the case of coating, it is preferable to use alumina, boehmite, silica, a sol thereof, or an arbitrary mixture thereof as a binder in order to improve adhesion. In general, cordierite materials such as ceramics are often used as the honeycomb material, but a honeycomb material made of a metal material such as ferritic stainless steel can also be used. Furthermore, the catalyst powder itself may be formed into a honeycomb shape. The honeycomb shape is effective because the contact area between the catalyst and the exhaust gas is increased and the pressure loss can be suppressed.

Exhaust gas to which the exhaust gas purifying catalyst of the present invention can be applied broadly means exhaust gas discharged from an internal combustion engine such as an automobile, and specifically, CO (carbon monoxide), HC (hydrocarbon). , NO _x (nitrogen oxide), PM (solid carbon fine particles, liquid or solid high molecular weight hydrocarbon fine particles) and the like.

Of these exhaust gas components, the exhaust gas purifying catalyst of the present invention is particularly effective for oxidizing CO, HC, and burning PM. Accordingly, the exhaust gas in a narrow sense refers to CO, HC, NO _x, PM, or a gas containing these components. Particularly preferred is a gas containing HC.

The exhaust gas purifying catalyst of the present invention can also be used as a NO _x removal catalyst. Furthermore, the present invention can be applied to volatile organic compounds (VOC) such as toluene and ethyl acetate discharged at a chemical manufacturing factory or the like. Further, the present invention can also be applied to a CO shift reaction catalyst used as a pretreatment of a fuel cell gas for which a platinum catalyst is effective.

Although the reaction conditions for exhaust gas purification are not limited, for example, when exhaust gas purification is performed on a diesel vehicle or the like, the space velocity (SV) is 50,000 to 100,000 h ⁻¹ , the oxygen concentration is 5 to 10%, and the hydrocarbon concentration is about 1000 ppm. It is common to carry out under conditions. Moreover, the temperature of the exhaust gas of a diesel engine changes in the wide range of 200-600 degreeC. Since the temperature range applied to each exhaust gas is wide, exhaust gas purification capability in a wide temperature range is required.

  EXAMPLES Hereinafter, although an Example demonstrates this invention still in detail, this invention is not limited to these Examples, unless the summary is exceeded.

[Example 1]
[Synthesis of RuTe ₂ / alumina catalyst]
0.47 g of RuCl ₃ and 1.04 g of telluric acid (manufactured by Mitsuwa Chemical Co., Ltd.) were dissolved in water so that the charged molar ratio of Ru and Te was 1: 2. After immersing 4.56 g of alumina pellets in the obtained aqueous solution and evaporating to dryness, a RuTe ₂ precursor supported on alumina (hereinafter referred to as “RuTe ₂ precursor / alumina”) was obtained. Here, the supported amount of RuTe ₂ was adjusted so that the amount of Ru was 5% by weight with respect to the weight of the alumina pellets. This RuTe ₂ precursor / alumina was dried by holding at 300 ° C. for 2 hours in an argon gas stream, and then heated from 300 ° C. to 650 ° C. over 3 hours while flowing hydrogen gas at a flow rate of 3 L / hr. did. Then, after maintaining at 650 ° C. for 2 hours, the catalyst was cooled to room temperature to obtain a catalyst in which RuTe ₂ was supported on alumina (hereinafter referred to as “RuTe ₂ / alumina catalyst”). When the obtained RuTe ₂ / alumina catalyst was analyzed by X-ray diffraction (XRD), RuTe ₂ (JCPDS, PDF # 079-0252, PDF # 044-1015) and alumina (JCPDS, PDF # 010-0425) were analyzed. It was confirmed that it contained. This is referred to as “exhaust gas purifying catalyst of Example 1”.

[Evaluation]
About the exhaust gas purifying catalyst of Example 1 prepared by the above procedure, catalytic activity evaluation with a model gas was performed. The evaluation temperature was 350 ° C., and the gas flow rate was 1.1 L / min (equivalent to SV = 30000 h ⁻¹ ). Table 1 shows the composition of the model gas.

Table 2 shows the results of the catalytic activity test performed on the exhaust gas purification catalyst of Example 1 under the above evaluation conditions. Here, the conversion rate (%) based on the amount of carbon dioxide (CO ₂ ) generated by complete oxidation of HC was used as an index representing the hydrocarbon purification performance of the exhaust gas purification catalyst.

  According to the present invention, since an inexpensive exhaust gas purification catalyst is provided, CO, HC, etc. contained in exhaust gas from an internal combustion engine such as a diesel car or other combustion engine, and purification for PM combustion are provided. In addition to the catalyst, removal of nitrogen oxides, purification of volatile organic substances discharged from factories, and practical application to CO shift catalysts are promoted.

Claims (4)

  Including tellurium (Te) and one or more elements M selected from the group consisting of ruthenium (Ru), rhodium (Rh), palladium (Pd), osnium (Os), and iridium (Ir), and A catalyst for exhaust gas purification, wherein the molar ratio X of Te is 0.2 <X <4.   The exhaust gas-purifying catalyst according to claim 1, wherein the element M contains at least ruthenium. The exhaust gas-purifying catalyst according to claim 1 or ₂ , comprising RuTe2.   The exhaust gas-purifying catalyst according to any one of claims 1 to 3, wherein an active component containing Te and the element M is deposited on a metal oxide support.