JP2002233755A - Catalyst for oxidizing saturated hydrocarbon - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve oxidation activity to saturated hydrocarbons in a low- temperature region, and also improve high-temperature durability by effectively using active spots reduced by grain growth of a noble metal. SOLUTION: Pd is carried on a carrier mainly composed of hollow particles having an acidity in an appropriate range. Thereby, gas diffusibility into the carrier can be improved and the insides of the hollow particles can be used as a reaction field, which improves a contact probability between the carried Pd and a gas. Pd has a high oxidation activity to saturated hydrocarbons. When the acidity of the carrier is too low, the electron-donating of the carrier is increased, so that a Pd-O bonding force becomes too high, which lowers the oxidation activity, When the acidity of the carrier is too high, the electron- withdrawing the carrier is increased, so that the Pd-O bonding force becomes too low, which also lowers the oxidation activity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a catalyst for oxidizing and decomposing a saturated hydrocarbon. INDUSTRIAL APPLICABILITY The catalyst of the present invention is useful for purification of automobile exhaust gas, purification of factory exhaust gas, and the like, and can also be used for oxidative purification of methane, which is considered difficult to purify by oxidation.

[0002]

2. Description of the Related Art Three-way catalysts have been widely used as exhaust gas purifying catalysts for purifying exhaust gas from automobiles.
This three-way catalyst uses platinum (P) on a porous carrier such as alumina.
t) and other precious metals.
O, it is possible to efficiently purify HC and NO _x.

By the way, the noble metal supported on the three-way catalyst does not cause a catalytic reaction in a temperature range lower than its activation temperature. Therefore, the three-way catalyst does not function sufficiently in exhaust gas in a low temperature range such as when the engine is started, and there is a problem that a large amount of HC is emitted. At the time of cold start, the air-fuel ratio is often set to a fuel-rich atmosphere, and the HC in the exhaust gas
The large amount also contributes to the above problem.

Therefore, improvement of the low-temperature activity of the three-way catalyst has become an issue. For example, the catalyst has been arranged immediately below the engine. In this way, the heat of the exhaust gas is quickly transmitted to the catalyst, and the temperature can be quickly raised to the activation temperature. Precious metals are also supported at a high concentration at the upstream end of the exhaust gas stream of the catalyst. The upstream end rises to the activation temperature earlier than the downstream end, and the reaction is active at the upstream end where the activation temperature is raised. As a result, the activity of the catalyst as a whole in a low temperature range is improved.

[0005] Among HCs, olefinic hydrocarbons are relatively easy to purify, but saturated hydrocarbons are more difficult to purify than olefinic hydrocarbons, and methane is a saturated hydrocarbon that is particularly difficult to purify by oxidation. Therefore, the development of a catalyst capable of purifying methane has been promoted, and palladium (P
d) has been found to be effective. For example, JP-A-11-137998 discloses that Pd, Ru,
A catalyst that supports at least one selected from Ir and Cu and exhibits methane purification ability is disclosed. In addition, JP-A-7-05
Japanese Patent No. 3976 discloses a methane oxidation catalyst using a coprecipitate of Pd and Co as a catalyst metal.

[0006]

However, even if the above-mentioned means are used, purification of HC in exhaust gas in a low temperature range is still insufficient, and further improvement in low temperature activation is required.

Further, the catalyst disclosed in Japanese Patent Application Laid-Open No. 11-137998 has a problem that when a high-temperature durability test at 700 ° C. or more is performed, Pd grows in a large grain size and the activity is significantly deteriorated.

[0008] The catalyst disclosed in Japanese Patent Application Laid-Open No. 7-053976 has a drawback that the particles in the coprecipitate of Pd and Co are coarse because the carrier is not used, and the activity decreases particularly after the durability test. The publication also states that a slurry is prepared by adding a binder to the coprecipitate, and honeycomb-shaped alumina,
It is described that it may be used after being applied to a refractory substrate such as magnesia or cordierite. However, also in this case, the co-precipitate of Pd and Co is on the surface of the substrate such as alumina, and is not supported, so that the interaction between the substrate and the co-precipitate is weak and coarse. The activity is significantly reduced after the durability test due to the formation of the resin.

[0009] The inventors of the present invention have conducted intensive studies,
We have developed a catalyst that supports a noble metal and a transition metal such as Fe, Co, Ni, and Sn on an oxide support. According to this catalyst, by supporting the noble metal and the transition metal in a composite manner, the mutual growth of each other is suppressed, so that the activity is improved and the high-temperature durability is improved. Further, it is considered that a part of the noble metal and the transition metal form a composite, and the thermal stability of the noble metal is improved.

Further, the transition metal has a higher oxide stability than the noble metal, and releases the lattice oxygen in the transition metal oxide in a high temperature range where the noble metal oxide is decomposed. By virtue of the presence, active oxygen can be supplied on the noble metal, and the oxidation activity of the hydrocarbon can be maintained.

However, this catalyst showed good results in an endurance test at about 800 ° C., but it was found that the activity decreased when an endurance test at 900 ° C. or higher was carried out.
Further, it has been found that Pd, which has a particularly high oxidation activity of saturated hydrocarbons, is most desirable as the noble metal. However, metal Pd or PdO, which is an active species, tends to grow grains, and in the above catalyst carrying Pd, those with Pd particle size of 10 nm or less after 800 ° C durability test are subjected to 900 ° C durability test. When
It became clear that the grains grew to 20 to 30 nm.

The present invention has been made in view of such circumstances, and by improving the oxidation activity of saturated hydrocarbons in a low temperature range and effectively utilizing active sites reduced by grain growth of noble metals. It is intended to further improve high-temperature durability.

[0013]

The feature of the catalyst for oxidizing a saturated hydrocarbon of the present invention that solves the above-mentioned problems is that an oxide carrier composed of hollow particles and at least an oxide carrier supported on the oxide carrier are provided.
And Pd.

The oxide carrier is preferably an oxide of at least one metal selected from the group consisting of Al, Ti, Zr and Hf, and particularly preferably contains Al ₂ O ₃ as a main component. The shell thickness is 50 nm or less, the particle size is 5 μm or less, the specific surface area is 30 m ² / g or more, and the pore volume is 2 μm or less.
It is desirably at least cc / g.

Further, it is desirable that the amount of Pd carried is 0.5 to 15% by weight.

Further, n kinds of metal elements constituting the oxide carrier
It is desirable that the average oxidation-reduction potential E of M ₁ , M ₂ ... _Mn is in the range of −1.7 <E <−1.5. Where the average oxidation-reduction potential E
Is a value given by Equation 1.

The oxide carrier having such E is Al ₂ O ₃
And at least one element selected from the group consisting of alkali metals, alkaline earth metals, and elements of Group 3 of the periodic table having a redox potential lower than that of Al is preferably not contained in an amount of 10 mol% or more with respect to Al. It is more desirable not to contain not less than mol%.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The catalyst of the present invention comprises an oxide carrier comprising hollow particles, and at least one supported on the oxide carrier.
Pd.

Solid alumina particles usually have a particle size of several μm.
An aggregate having pores of about 10 nm is formed inside at m. Therefore, in the case of using such a powder of solid alumina particles as an oxide carrier and supporting a noble metal on the catalyst, most of the noble metal is supported inside the aggregate. However, when exhaust gas is introduced into this catalyst at high speed, it is difficult for the exhaust gas to sufficiently diffuse into the pores of the aggregate, so the noble metal supported inside the aggregate must be used effectively. Can not.

However, in the present invention, an oxide carrier composed of hollow particles is used. Therefore, gas diffusibility into the carrier is improved, and the inside of the hollow particles can be used as a reaction field, so that the contact probability between the supported catalyst metal and the gas is improved, and the activity is further improved.

In the present invention, at least Pd is supported on the oxide carrier. Since Pd has a particularly high oxidizing activity for saturated hydrocarbons, it can oxidize saturated hydrocarbons very efficiently from a low temperature range by a synergistic effect with the hollow particles described above.

For example, the reaction in which methane is oxidized by Pd is presumed to proceed by active oxygen adsorbed or bound to Pd or PdO. Therefore, the binding state of Pd-O is considered to be an important factor for the catalytic activity. I mean
If the Pd-O bonding force is too strong, the reactivity of oxygen decreases.If the Pd-O bonding force is too weak, it becomes difficult to hold oxygen necessary for the oxidation reaction on Pd until the temperature at which methane reacts with oxygen, and the activity decreases. Conceivable. In the case of metal Pd, it is considered that oxygen is adsorbed on the surface during the oxidation reaction, so the basic mechanism is the same.

It has been clarified that the binding state of Pd-O is greatly affected by the acidity of the carrier. In other words, when the acidity of the carrier is too small, the electron donating property of the carrier becomes strong.
It was found that if the Pd-O binding force was too strong and the acidity of the carrier was too large, the electron-withdrawing property of the carrier was too strong and the Pd-O binding force was too weak. Therefore, when supporting Pd, the acidity of the carrier is important.

One measure of the acidity of the support is the oxidation-reduction potential of the metal element. The lower the redox potential, the lower the acidity, and the higher the redox potential, the higher the acidity. As the oxide carrier used in the saturated hydrocarbon oxidation catalyst of the present invention is therefore, the average oxidation-reduction potential E of the oxide n kinds of metal elements constituting the carrier M _1, M ₂ ·· M _n is -1.7 <E < -1.5
Is desirably within the range. The average oxidation-reduction potential E
Is a value given by Equation 1.

When the average oxidation-reduction potential E is -1.7 or less, the acidity becomes too low, and when it is -1.5 or more, the acidity becomes too high. By setting the average oxidation-reduction potential E in the above range, the acidity of the oxide carrier can be set in an optimum range, and the activity of the supported Pd can be maximized.

Al, Ti, Zr and Hf exist as metal elements having an average oxidation-reduction potential E in the above range. Therefore, when an oxide carrier containing at least one oxide selected from these as a main component is used. Good. Above all, it is particularly desirable to use an oxide carrier containing Al ₂ O ₃ as a main component, since hollow particles can be easily produced and thin hollow particles can be produced.

However, when an oxide carrier mainly composed of Al ₂ O ₃ is used, if the element having a lower oxidation-reduction potential than Al is contained in a large amount, the above average oxidation-reduction potential E may be -1.7 or less. is there. Therefore, the element having a lower oxidation-reduction potential than Al needs to be less than 10 mol%. Further, even if the content of elements having a redox potential lower than that of Al is less than 10 mol%, it is not preferable that the average redox potential E is close to -1.7, so that the content of these elements is less than 2 mol%. It is more desirable to do. Examples of the element having a lower oxidation-reduction potential than Al include an alkali metal, an alkaline earth metal, and an element of Group 3 of the periodic table.

[0028] For example, when the La is a third group element is added to the Al ₂ O _3, heat stability of the Al ₂ O ₃ carrier is known to be improved. However, when Pd is supported, if too much La is added, the average oxidation-reduction potential E decreases, the acidity decreases, and the oxidation activity decreases as described above. Therefore, when La is added, it is preferably at most 10 mol%, particularly preferably at most 2 mol%.

In the case of using an oxide carrier containing Al ₂ O ₃ as a main component, when an element having a higher oxidation-reduction potential than Al is contained in an amount of 1 mol% or more, the average oxidation-reduction potential E becomes -1.5 or more. There are cases. Therefore, these elements are desirably less than 1 mol% which can be regarded as an impurity level. If Al
If it is unavoidable to mix elements with higher oxidation-reduction potential,
It is preferable that the oxidation-reduction potential is close to Al and not extremely high, and Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Ga, Zr, Nb, M
It is preferable to use at least one selected from o, Cd, In, Sn, Hf, Ta, Tl and Pb. Among them, Ti, V, Cr, Mn, Zn, Zr, Nb, Hf and Ta having a difference in oxidation-reduction potential from Al within 1 V are preferable. When the amount of the unavoidable impurity element increases, the specific surface area may decrease. Oxidation activity of an oxide carrier containing Al ₂ O ₃ as a main component may be improved by the addition of such a trace element.

In the case of an oxide carrier composed of hollow particles, hollow particles make it possible to achieve both a large primary particle diameter and a large specific surface area, and are suitable as a catalyst carrier.
Note that a hollow shape means having an internal space, and a shell between the internal space and the external space preferably has an opening. Although the number of internal spaces is not limited, a porous body having a larger volume occupied by the internal spaces is more preferable.

The specific surface area of the oxide carrier composed of hollow particles is almost inversely proportional to the shell thickness. If the shell thickness is too large, the specific surface area becomes small. Therefore, the thickness of the shell is desirably 100 nm or less, particularly desirably 50 nm or less.
It is more desirable that it be less than nm. 100nm shell thickness
By setting it as follows, a specific surface area preferable as a catalyst carrier can be secured.

The outer diameter of the hollow particles is preferably 50 nm to 5 μm, and the ratio of the inner diameter to the outer diameter is preferably 0.5 to 0.99. As a result, the thickness of the shell can be made extremely thin, and hollow particles having a specific surface area of 30 m ² / g or more can be obtained. When the outer diameter is smaller than 50 nm, no hollow portion exists, and it is difficult to produce hollow particles having an outer diameter of more than 5 μm with the current technology. Such hollow particles have a pore structure on the order of 100 nm, which is thought to contribute effectively to gas diffusion. Further, the pore volume of the hollow particles is desirably 2 cc / g or more. This further improves the gas diffusibility and the function as a reaction field.

The method for producing the above hollow particles is described as follows.
The case of producing hollow particles made of l ₂ O ₃ will be described. First, a W / O emulsion is prepared by dispersing an aqueous solution containing a compound containing aluminum as a main component in an organic solvent, and the W / O emulsion is spray-burned to produce alumina particles comprising hollow particles. Is done.

In the spray combustion of a W / O emulsion, the diameter of one dispersed water droplet (several nm to several μm) in the emulsion becomes the size of one reaction field. That is, in the sprayed mist, the dispersed particles in the emulsion become atomized particles composed of an aqueous phase covered with an oil film composed of an organic solvent, and once ignited, the combustion of the oil film is induced. Due to this heat generation, the metal in the aqueous phase inside the atomized particles exposed to the high temperature is oxidized to generate oxide powder. Since the atomized particles are fine, generation of a temperature distribution among the particles can be suppressed, and a homogeneous composite oxide powder can be obtained.
Also, an amorphous composite oxide powder can be easily produced.

Then, the dispersed particles of the W / O emulsion are
Since the Al element is a main component, very thin and porous hollow particles having a shell thickness of several tens nm are formed by spray combustion.
Although the cause is not clear at present, the surface oxide film is formed on the particle surface at a small stage of particle shrinkage due to the high rate of formation of the surface oxide film of Al ions, and as a result, a very thin porous hollow shell is formed. Presumed to be a body.

In the spray combustion of a W / O type emulsion, as described above, one dispersed water droplet diameter serves as one reaction site. However, if the dispersed water droplet diameter in the emulsion is smaller than 100 nm, before the surface oxide film is formed. The particles shrink completely and do not become hollow, which is not preferable. On the other hand, if the diameter of the dispersed water droplets is larger than 10 μm, the reaction field becomes too large and may become inhomogeneous. If the diameter of the water droplet dispersed in the emulsion is in the range of 100 nm to 10 μm, the outer diameter of the hollow particles to be produced is 50 nm to 5 μm.

The combustion temperature during spray combustion is 1000 ° C. or less,
More preferably, the temperature is set to 700 to 900 ° C. If the combustion temperature exceeds 900 ° C., a part of the product grows to form a crystalline powder, and the specific surface area may decrease. On the other hand, if the combustion temperature is too low, the organic component does not completely burn and the carbon component may remain. Further, the metal concentration in the dispersed water droplets in the W / O emulsion is 0.2 to 0.2 in terms of metal.
Desirably, it is 2.4 mol / L. If the concentration is lower than this range, it is difficult to form hollow particles, and it is difficult to make the concentration higher than this range from the solubility.

A W / O emulsion can be formed by stirring an aqueous solution of a metal salt and an organic solvent via a dispersant. Hexane, octane,
Any organic solvent such as kerosene or gasoline that can form a W / O emulsion with an aqueous solution may be used. The type and amount of the dispersant used are not particularly limited. Any of a cationic surfactant, an anionic surfactant, and a nonionic surfactant may be used.The type and amount of the dispersant are changed according to the type of the aqueous solution, the organic solvent, and the required dispersion particle size of the emulsion. It should be done.

The atmosphere in which the W / O emulsion is sprayed and burned is not particularly limited. However, if oxygen is not sufficient, carbon components in the organic solvent may remain due to incomplete combustion. Therefore, it is desirable to supply oxygen (air) to such an extent that the organic solvent in the emulsion can be completely burned.

In the catalyst of the present invention in which Pd is supported on the oxide carrier composed of such hollow particles, Pd exists in a highly dispersed state to some extent, and since it acts effectively, high activity is exhibited. . And after endurance at a high temperature of about 900 ° C
Although Pd grows to some extent, in the catalyst of the present invention, the activity of Pd is high due to the interaction with the support, and the active sites can be effectively used structurally of the support. There is too much. Therefore, it can be used under high temperature conditions and is useful as a high temperature saturated hydrocarbon oxidation catalyst.

Although a certain amount of Pd is supported when a certain amount of Pd is supported, it is desirable that the Pd be in the range of 0.5 to 15% by weight of the whole catalyst. If the supported amount of Pd is less than this range, the dispersibility will be reduced and the oxidation activity of the saturated hydrocarbon will be too low to be practical, and if it is supported more than this range, the activity will be saturated and the cost will be disadvantageous. .

[0042]

The present invention will be specifically described below with reference to examples and comparative examples.

Example 1 A 2 mol / L aluminum nitrate aqueous solution prepared by dissolving commercially available aluminum nitrate nonahydrate in deionized water was used as an aqueous phase.

A commercially available kerosene was used as the organic solvent, and "Solgen 90" manufactured by Daiichi Kogyo Seiyaku was used as the dispersant. The amount of the dispersant added was 1 to 5% by weight based on kerosene. The kerosene containing the dispersant was used as an oil phase and mixed so that an aqueous phase / oil phase = 40 to 70/60 to 30 (vol%).
The W / O emulsion was obtained by stirring the mixed solution using a homogenizer at 1,000 to 20,000 rpm for 5 to 30 minutes. From the result of observation with an optical microscope, the dispersed particle size in the above emulsion was about 1 to 2 μm.

The W / O emulsion prepared above was
Spraying using the emulsion combustion reactor described in JP-A-7-81905, burning the oil phase and oxidizing Al ions present in the aqueous phase, synthesized Al ₂ O ₃ powder consisting of hollow particles. .

In this synthesis, the spray flow rate of the emulsion and the amount of air (the amount of oxygen) are set so that the sprayed emulsion completely burns and the temperature of the center of the flame becomes a constant temperature of about 800 ° C.
And so on. The obtained powder was collected by a bag filter installed at the rear of the reaction tube. further,
Since there is a possibility that unburned carbon components may adhere to the obtained powder, heat treatment was performed at 800 to 1000 ° C. for 1 to 10 hours in the air.

The particles of the obtained oxide powder are hollow, and the average oxidation-reduction potential E of the metal element is -1.66 V, B
ET specific surface area 50m ² / g, shell thickness about 10nm, average particle size
0.6 μm and the pore volume was 4 cc / g.

Next, a predetermined amount of the above oxide powder was mixed with an aqueous solution of palladium nitrate having a predetermined concentration, evaporated and dried, and then baked in the air at 300 ° C. for 2 hours to carry Pd. The supported amount of Pd is 5 g per 120 g of the oxide powder. The resulting catalyst powder was compacted and then pulverized to form a pellet having a particle size of 0.5 to 1 mm to obtain a pellet catalyst.

Example 2 An oxide powder was prepared in the same manner as in Example 1, except that a mixed aqueous solution of aluminum nitrate and zinc nitrate (molar ratio Zn / Al = 0.10) was used as an aqueous phase. A catalyst was obtained. The particles of the oxide powder were hollow, and the average oxidation-reduction potential E of the metal element was -1.58 V
Met.

Example 3 An oxide powder was prepared in the same manner as in Example 1 except that a mixed aqueous solution of aluminum nitrate and chromium nitrate (molar ratio: Cr / Al = 0.10) was used as an aqueous phase. A catalyst was obtained. The particles of the oxide powder are hollow, and the average oxidation-reduction potential E of the metal element is -1.58.
V.

Example 4 An oxide powder was prepared in the same manner as in Example 1 except that a mixed aqueous solution of aluminum nitrate and zirconium oxynitrate (molar ratio Zr / Al = 0.10) was used as an aqueous phase. A pellet catalyst was obtained. The particles of the oxide powder were hollow, and the average oxidation-reduction potential E of the metal element was -1.65 V.

(Example 5) An oxide powder was prepared in the same manner as in Example 1, except that a mixed aqueous solution of aluminum nitrate and titanium tetrachloride (molar ratio Ti / Al = 0.10) was used as an aqueous phase.
Similarly, a pellet catalyst was obtained. The particles of the oxide powder are hollow, and the average oxidation-reduction potential E of the metal element is −1.
It was 65V.

Example 6 Same as Example 1 except that a mixed aqueous solution (molar ratio Zr / Ti / Al = 0.05 / 0.05 / 1.00) of aluminum nitrate, zirconium oxynitrate and tetragonal titanium was used as an aqueous phase. To prepare an oxide powder, and similarly a pellet catalyst was obtained. The particles of the oxide powder were hollow, and the average oxidation-reduction potential E of the metal element was -1.65 V.

Example 7 An oxide powder was prepared in the same manner as in Example 1 except that a mixed aqueous solution of aluminum nitrate and nickel nitrate (molar ratio Ni / Al = 0.10) was used as an aqueous phase.
Similarly, a pellet catalyst was obtained. The particles of the oxide powder are hollow, and the average oxidation-reduction potential E of the metal element is −1.
It was 53V.

Example 8 An oxide powder was prepared in the same manner as in Example 1 except that a mixed aqueous solution of aluminum nitrate and iron nitrate (molar ratio Fe / Al = 0.10) was used as an aqueous phase, and pellets were similarly formed. A catalyst was obtained. The particles of the oxide powder were hollow, and the average oxidation-reduction potential E of the metal element was -1.55 V.

Example 9 An oxide powder was prepared in the same manner as in Example 1 except that a mixed aqueous solution of aluminum nitrate and cobalt nitrate (molar ratio Co / Al = 0.10) was used as an aqueous phase.
Similarly, a pellet catalyst was obtained. The particles of the oxide powder are hollow, and the average oxidation-reduction potential E of the metal element is −1.
It was 54V.

Example 10 An oxide powder was prepared in the same manner as in Example 1 except that a mixed aqueous solution of aluminum nitrate and lanthanum nitrate (molar ratio La / Al = 0.10) was used as an aqueous phase.
Similarly, a pellet catalyst was obtained. The particles of the oxide powder are hollow, and the average oxidation-reduction potential E of the metal element is −1.
It was 74V.

Example 11 An oxide powder was prepared in the same manner as in Example 1, except that a mixed aqueous solution of aluminum nitrate and chromium nitrate (molar ratio La / Al = 0.02) was used as an aqueous phase. A catalyst was obtained. The particles of the oxide powder are hollow, and the average oxidation-reduction potential E of the metal element is -1.68.
V.

Example 12 An oxide powder was prepared in the same manner as in Example 1, except that a mixed aqueous solution of aluminum nitrate and copper nitrate (molar ratio Cu / Al = 0.10) was used as an aqueous phase. A catalyst was obtained. The particles of the oxide powder were hollow, and the average oxidation-reduction potential E of the metal element was -1.48 V.

(Comparative Example 1) Solid as a commercially available oxide powder
A pellet catalyst was prepared in the same manner as in Example 1 except that Al ₂ O ₃ powder was used. The average redox potential E of commercially available solid Al ₂ O ₃ powder is -1.66V.

<Test / Evaluation> FIG. 1 shows a TEM image of the particles of the oxide powder synthesized in Example 1. This particle
It is a hollow body with submicron particle size and shell thickness of about 10 nm, with openings. The specific surface area of the particles measured by the BET method was 50 m ² / g, and the pore volume measured by the Hg intrusion method was 4 cc / g.

The same measurement was performed on the particles of the oxide powders synthesized in Examples 2 to 12, and although there was some variation depending on the composition, the shell thickness was in the range of about 10 to 20 nm. Accordingly, the specific surface area is 30-50 m ² / g, and the pore volume is
2.5 to 4 cc / g, average particle size was in the range of 0.5 to 0.9 μm. In addition, all the particles were hollow particles having the same appearance as in Example 1.

Next, each of the pellet catalysts was placed in a normal pressure flow type endurance test apparatus, and while the lean gas and the rich gas shown in Table 1 were alternately passed under the conditions of 5 minutes and 5 seconds, the temperature of the gas containing the catalyst was 900 ° C. For 5 hours. Space velocity of model gas is 10,000h ^-1 each
It is.

[0064]

[Table 1]

Then, 0.5 g of each pellet catalyst after the durability test
Was placed in a normal pressure flow reactor, and the temperature was raised from room temperature to 500 ° C. at a rate of 12 ° C./min while flowing a model gas shown in Table 2 corresponding to a lean steady atmosphere at a flow rate of 3.5 L / min. The purification rate of CH ₄ at the time of heating was measured almost continuously, and the temperature (CH ₄ -T50) at the time of 50% purification was determined. Table 3 shows the results.

[0066]

[Table 2]

[0067]

[Table 3]

From Table 3, it can be seen that the catalysts of the examples have CH ₄ -T50
It is 410 ° C. or lower, which indicates that the purification activity of methane is higher than that of the catalyst of Comparative Example 1. This is apparently due to the effect of using the hollow oxide carrier.

On the other hand, from the comparison between the examples, the catalysts of Examples 10 and 12 in which the average oxidation-reduction potential E of the oxide carrier is not in the range of -1.7 <E <-1.5, as compared with the other catalysts. CH ₄
-It turns out that T50 is high. In other words, it is clear that the acidity of the oxide carrier greatly affects the methane oxidation activity.

Further, from the results of the catalysts of Examples 10 and 11, even when La having a redox potential lower than that of Al was added, 2 mol%
Below, it can be seen that relatively good performance is maintained.

Further, the catalysts of Examples 2 to 6 were comparable to those of Example 1 in the oxidizing activity of methane, and showed that Zn, Cr, Zr and Ti
Can be used within a range of up to 10 mol%. However, it can be seen that the content of Ni, Fe, Co and Cu is preferably further reduced because the methane oxidation activity is slightly reduced at 10 mol%.

[0072]

According to the catalyst for oxidizing saturated hydrocarbons of the present invention, the oxidizing activity of saturated hydrocarbons in a low temperature range is extremely high, and methane which has conventionally been difficult to oxidatively decompose can be decomposed and removed. It shows high oxidation activity even after a high temperature durability test, and has excellent durability.

[Brief description of the drawings]

FIG. 1 is a TEM photograph showing a particle structure of an oxide carrier manufactured in Example 1 of the present invention.

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[Procedure amendment]

[Submission date] March 15, 2001 (2001.3.1.1)
5)

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] Fig. 1

[Correction method] Change

[Correction contents]

FIG.

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Claims (11)

[Claims] 1. A catalyst for oxidizing saturated hydrocarbons, comprising: an oxide carrier composed of hollow particles; and at least Pd supported on the oxide carrier. 2. The catalyst for oxidizing a saturated hydrocarbon according to claim 1, wherein the oxide carrier is an oxide of at least one metal selected from Al, Ti, Zr and Hf. 3. The catalyst for oxidizing a saturated hydrocarbon according to claim 2, wherein the oxide carrier contains Al ₂ O ₃ as a main component. 4. The catalyst for oxidizing saturated hydrocarbons according to claim 1, wherein the shell thickness of the oxide carrier is 50 nm or less. 5. The catalyst for oxidizing a saturated hydrocarbon according to claim 1, wherein the particle diameter of the oxide carrier is 5 μm or less. 6. The catalyst for oxidizing a saturated hydrocarbon according to claim 1, wherein the specific surface area of the oxide carrier is 30 m ² / g or more. 7. The catalyst for oxidizing saturated hydrocarbons according to claim 1, wherein the pore volume of the oxide carrier is 2 cc / g or more. 8. The catalyst for oxidizing a saturated hydrocarbon according to claim 1, wherein the carried amount of Pd is 0.5 to 15% by weight. 9. average oxidation-reduction potential E of the n kinds of metal elements constituting the oxide carrier M _1, M ₂ ·· M _n is -1.7 <E <-1.5
The catalyst for oxidizing a saturated hydrocarbon according to claim 1, wherein Here, the average oxidation-reduction potential E is a value given by Expression 1. (Equation 1) 10. The oxide carrier contains Al ₂ O ₃ as a main component,
10. The composition according to claim 9, wherein at least one element selected from the group consisting of an alkali metal, an alkaline earth metal, and a Group 3A element in the periodic table, which has a redox potential lower than that of Al, is not contained in an amount of 10 mol% or more based on Al. For the oxidation of saturated hydrocarbons. 11. The oxide carrier, wherein at least one element selected from an alkali metal, an alkaline earth metal and an element of Group 3 of the periodic table is not contained in an amount of 2 mol% or more based on Al. 11. The catalyst for oxidizing saturated hydrocarbon according to 10.