JPH0616848B2 - Heat resistant combustion catalyst and catalytic combustion method using the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a heat resistant combustion catalyst and a catalytic combustion method using the same, and particularly to a heat resistant combustion suitable for combustion in a temperature range of 800 ° C. to 1500 ° C. Regarding catalysts.

[Conventional technology]

The catalysts that have been used as high temperature catalysts have been alumina, silica, silica-alumina, etc., on which a noble metal or base metal is supported, or ceramic materials such as zirconia, aluminum titanate, cordierite, and silicon nitride. A carrier in which activated alumina or the like is coated as a carrier and a precious metal component is supported on the surface has been used. However, these catalysts usually
At temperatures above 0 ° C, the crystal structure of the carrier changes (for example, the phase transition from γ type to α type in the case of alumina) and the specific surface area decreases with crystal growth. Decrease and the catalytic activity decreases. For example,
In the case of a catalyst in which palladium is supported on a conventional alumina carrier, the specific surface area is about 150 m ² /
g, the particle size of palladium is 30 Å, but when heated at 1200 ° C. for 2 hours, the comparative area is about 3 m ² /
The particle size of g and palladium is about 2000 angstrom. That is, by heat treatment at a high temperature, the palladium particles highly dispersed on the carrier aggregate with the decrease of the specific surface area of the carrier and become huge particles, so that the active sites are reduced and the activity as a catalyst is reduced. descend.

As a catalyst that has improved such drawbacks of the high temperature catalyst, γ
-A catalyst that suppresses agglomeration of noble metals as a carrier by coating a mixture of alumina and cerium, lanthanum, strontium, tin, zirconium, magnesium and ceramic whiskers on a heat-resistant carrier (JP-A-59-5252).
9) and γ-alumina mixed with lanthanum, cerium and strontium, coated on a heat resistant carrier, and then brought into contact with base metal particles such as nickel, chromium and cobalt, and platinum or palladium deposited on the surface of the catalyst ( JP-A-59-169536) has been proposed. Although each of these catalysts has advantages, it is not sufficient in terms of heat resistance.

[Problems to be Solved by the Invention]

An improvement of the above thermal instability, supported lanthanum · beta alumina particles of the active ingredient is obtained by adding lanthanum to aluminum for suppressing carriers to aggregate (La ₂ O ₃ · 11~14Al It has been found that a catalyst obtained by combining a ₂ O ₃ ) carrier with a catalytically active component, such as a noble metal or a transition metal, is very effective (JP-A-60-222145).
Lanthanum / β-alumina showed that the decrease in specific surface area under high temperature conditions was small, and it was revealed from the nitrogen adsorption experiment.The particle size of the active ingredient at this time was observed with an electron microscope. It became clear that For example, in a catalyst obtained by supporting palladium (Pb) on lanthanum or β-alumina calcined at 1200 ° C., the specific surface area is about 30 m ² / g, and the particle diameter of palladium (Pd) is about 7
The heat resistance was 00Å, which was superior to that of the above-described carrier using only alumina. In the catalyst in which the noble metal / base metal that is the catalytically active component is supported on this lanthanum / β-alumina carrier, the aggregation of the active component due to the decrease in the specific surface area of the carrier does not easily occur in the use at high temperature, but the change of the carrier at high temperature Aggregation of the active ingredient fine particles may occur irrespectively, so it is necessary to suppress the aggregation of the active ingredient fine particles to further improve the heat resistance of the catalyst. Therefore, an object of the present invention is to provide a heat-resistant combustion catalyst in which the agglomeration of active ingredient fine particles is suppressed and the heat resistance of the catalyst is improved.

[Means for Solving the Problems]

The above-mentioned object is at least one heat-resistant inorganic carrier selected from the group consisting of oxides, carbides and nitrides of Group IIa, Group IIIa and Group IV elements of the Periodic Table, and a platinum group supported on the carrier. And a particle of at least one catalytically active component of an element, wherein the oxide particles of magnesium are dispersed at least on the particles of the platinum group element.

Since the heat-resistant catalyst of the present invention has excellent heat resistance, it is particularly effective when used for catalytic combustion of hydrocarbons and carbon monoxide.
Therefore, according to the present invention, there is proposed a catalytic combustion method in which the heat resistant catalyst and a combustible gas are brought into contact with each other in the presence of oxygen.

When heat resistance is required, the carrier has a specific surface area of 1
Most preferably, 0 m ² / g or more of lanthanum / β-alumina is used, but other carrier components can be used. That is, in addition to lanthanum / β-alumina, γ-alumina or lanthanum oxide and alumina in other crystal form may be used. These supports may contain excess uncombined alumina and / or lanthanum oxide. Instead of lanthanum, other rare earths, for example, one or more selected from the group consisting of cerium, praseodymium, promethium, samarium, europium, gadolinium, erbium, ytterbium, yttrium, scandium, and lutetium can be used.

Further, oxides, nitrides and carbides of IIa, IIIa and IVa elements such as silica, magnesia, calcia, barium oxide, beryllia, zirconia, titania, thoria, cordierite, mullite, sponge yumen, aluminum titanate, silicon carbide, silicon nitride. It is possible to use one or more selected from compounds such as elementary substances.

The carrier material itself is not a feature of the present invention, and the selection of the carrier material depends on the application, the required heat resistance, the cost and the like.

The catalytically active component carried on the heat-resistant carrier is most preferably palladium in the case of a catalyst used for catalytic combustion of hydrocarbons, but other noble metals may be used. That is, other catalyst component, for example, nickel, cobalt, iron in the case of an oxidation or combustion catalyst may be added to one selected from the group consisting of platinum, rhodium and ruthenium.

In addition, as a component that suppresses the aggregation of the noble metal particles, an oxide of a base metal element having an ionic radius smaller than that of palladium is generally most effective. That is, it is preferable to use a base metal made of magnesium whose ionic radius is the same as or smaller than that of the noble metal.

The amount of the noble metal of the active ingredient supported on the heat-resistant carrier is in the range of 0.05% by weight to 10% by weight, preferably in the range of 0.1% by weight to 1.0% by weight, based on the weight of the heat-resistant carrier. ．
If it is less than 05% by weight, the combustion activity is insufficient, and if it is more than 10% by weight, it is not economical.

The base metal added to suppress the agglomeration of the noble metal particles is in the range of 0.1 to 10 gram atom of the base metal per gram atom of the noble metal, preferably 5 to 10 gram atom of the base metal per gram atom of the noble metal. It is a range. If the amount of the base metal is 0.1 gram atom or less per 1 gram atom of the noble metal, the noble metal particles are likely to aggregate and the catalytic activity becomes low. When the base metal is 10 g atom or more per 1 gram atom of the noble metal, the active sites of the noble metal are covered with the base metal and the catalytic activity is lowered.

As a means for preparing the heat-resistant catalyst of the present invention, a heat-resistant carrier is impregnated with a solution of a salt of a platinum group element by an ordinary impregnation method or an immersion method, dried and fired, followed by impregnation with a base metal salt, and dried and fired. Most preferably, the base metal-platinum group-heat resistant carrier is used. That is, it is necessary to use a catalyst in a state in which base metal oxide particles can exist on the surface of platinum group element particles.

The heat-resistant catalyst obtained by the present invention is 800 ° C., preferably 1
Suitable for use at temperatures above 000 ° C. The upper limit of the operating temperature is 1500 ° C., the specific surface area of the catalyst in this case is 5 m ² / g or more, and the particle diameter of palladium is preferably 10,000 angstrom (Å) or less.

Further, the heat-resistant catalyst of the present invention, in the presence of the catalyst,
It can be used as a catalyst for performing a chemical reaction such as an oxidation reaction or a combustion reaction of a substance composed of an inorganic substance and / or an organic substance in a temperature range of 0 to 1500 ° C. In particular, it can be used for gas heating appliances utilizing catalytic combustion, glass turbine combustors, automobile exhaust gas cleaning combustors, malodor removing combustors, and other chemical reaction devices operated at relatively high temperatures.

[Action]

As a conventional heat-resistant combustion catalyst, a noble metal such as platinum (Pt), palladium (Pd), rhodium (Rh), and ruthenium (Ru) is used as an active component in a porous carrier such as γ-alumina.
It is most common to carry such as. Further, a ceramic honeycomb base material such as cordierite or mullite coated with porous alumina and then carrying a noble metal component is also used. In this case, the larger the specific surface area of the carrier, the higher the dispersion of the noble metal component on the carrier, and the more the active sites tend to increase. The present invention suppresses agglomeration of the noble metal particles supported on the carrier, so that magnesium oxide particles are made to coexist, particularly finely coexisted also on the noble metal particles, and when mixed or impregnated in the carrier in advance. The heat resistance of the catalyst is much higher than that of.

This effect of suppressing aggregation was clarified by the CO gas adsorption method of the heat resistant catalyst and the observation of an electron microscope. Moreover, these aggregation suppressing components are oxide carriers such as alumina, silica, magnesia, calcia, beryllia, zirconia, titania and thoria and / or compounds such as cordierite, mullite, sponge yumen, aluminum titanate, silicon carbide and silicon nitride. It was revealed that the effect can be exhibited by combining with a carrier. That is, when a noble metal component is supported on a conventional carrier such as activated alumina, the effect is exhibited at a high temperature, particularly in the range of 800 to 1000 ° C., and at 1000 ° C. or higher, the lanthanum / β-alumina carrier exhibits the effect remarkably. Demonstrate. Therefore, the effect of the aggregation inhibiting component of the present invention can be sufficiently volatilized by combining not only the lanthanum / β-alumina carrier but also a heat-resistant inorganic carrier such as an activated alumina carrier. The effect of the additive for suppressing the aggregation of platinum fine particles, that is, the oxide of Mg, is presumed as follows. Many of the inorganic compounds, especially those in the solid state of oxides, are ionic-bonding and greatly affect the ionic radius, valence, and crystal structure. In particular, Pd is considered to form a kind of solid solution with the oxide in the solid state, depending on whether the ionic radius is the same as or smaller than that of the active component. It is considered that the solid solution is formed not on the entire catalyst but on a very micro portion of the catalyst surface. Table 1 shows the ionic radii of various cations. Pd on the catalyst surface
Is considered to exist as PdO. That is, it has a divalent valence and an ionic radius of 0.8Å. Among the base metal oxides added to Pd, Ba, Ag, La, Ce, and Ca, which have little effect, have a large ionic radius. Therefore, it is not possible to form a solid solution of the oxide in the crystal lattice of Pd ions, and rather, Pd forms a solid solution in the oxide to exhibit low activity. On the other hand, M of the present invention
It is considered that g has an ionic radius smaller than that of Pd, and a part of Mg or Mg oxide is solid-solved in the crystal lattice of Pd to firmly capture Pd particles and suppress aggregation.

[Examples] Hereinafter, the content of the present invention will be described more specifically with reference to Examples, but the present invention is not limited to these Examples.

Example 1 3 ml of a palladium nitrate solution (50 g / as Pd) was diluted with distilled water to a total amount of 17 ml.

This solution was molded into a cylinder with a diameter of 3 mm and a height of 3 mm,
50 g of a lanthanum / β-alumina carrier calcined at 0 ° C. was impregnated, dried at 180 ° C., and calcined at 600 ° C. to decompose the nitrate by calcination to obtain a lanthanum / β-alumina catalyst with palladium. The production method of the lanthanum / β-alumina carrier is described in detail in JP-A-60-222145, and the carrier of this example was produced by the method of Example 1 of the same publication.

1.81 g of magnesium nitrate was dissolved in 17 ml of distilled water. This solution was impregnated into a lanthanum β-alumina catalyst with palladium, dried at 180 ° C., and calcined at 1300 for 20 hours to obtain a heat resistance evaluation catalyst (Example catalyst 1). This catalyst is
It has a form of Mg-Pd-La-βAl ₂ O ₃ ,
Palladium was 0.3% by weight with respect to the total weight of the lanthanum / β-alumina carrier, and the atomic ratio of palladium to magnesium was Pd / Mg = 1/5. Note that here, 130
The catalyst was previously heat-treated at 0 ° C. for 20 hours in order to examine the catalyst durability at high temperature. For example, a gas combustion heater (commonly known as a gas fan motor) is 1000 ° C.
It is operated for a long time (several thousand hours) in a combustion range of 1100 ° C. Therefore, in order to evaluate whether the catalyst of the present invention can be used for a gas fan heater, the catalyst of the present invention is used.
After heat treatment was applied at 00 ° C. for 20 hours, the ignition temperature was measured by a methane combustion test to evaluate the heat resistance of the catalyst. In this case, those having a low ignition temperature have high activity and high heat resistance.

In order to subject the catalyst of the present invention to ordinary use, a usual catalyst calcination temperature, for example, 500 to 1200 ° C., particularly 700 to 1100
It suffices to use it after firing at ℃.

Example 2 (Reference Example) In Example 1, instead of magnesium nitrate, manganese nitrate, zirconium nitrate, nickel nitrate, cobalt nitrate, titania, chromium nitrate, zinc chloride, stannic chloride, calcium nitrate, cerium nitrate, Example catalyst samples 2 to 10 and comparative catalysts 1 to 6 were obtained in the same manner as in Example 1 using lanthanum nitrate, barium nitrate and silver nitrate.

Example catalyst 2 Mn-Pd-La-βAl ₂ O ₃ 〃 3 Sr-Pd-La-βAl ₂ O ₃ 〃 4 Zr-Pd-La-βAl ₂ O ₃ 〃 5 Ni-Pd-La-βAl ₂ O ₃ 〃 6 Co-Pd-La-βAl ₂ O ₃ 〃 7 Cr-Pd-La-βAl ₂ O ₃ 〃 8 Zn-Pd-La-βAl ₂ O ₃ 〃 9 Sn-Pd-La-βAl ₂ O ₃ 〃 10 Nb-Pd-La-βAl ₂ O ₃ Comparative Example Catalyst 1 Ti-Pd-La-βAl ₂ O ₃ 〃 2 Ca-Pd-La-βAl ₂ O ₃ 〃 3 Ce-Pd-La-βAl ₂ O ₃ 〃 4 _{La-Pd-La-βAl 2} O 3 〃 5 Ba-Pd-La-βAl 2 O 3 Comparative example catalyst 6 Ag-Pd-La-βAl 2 O 3 in these catalysts, the amount of palladium lanthanum · beta
It is 0.3% by weight based on the weight of the alumina carrier. The addition amount of the second component of manganese oxide, zirconium oxide, nickel oxide, cobalt oxide, chromium oxide, zinc oxide, tin oxide, calcium oxide, cerium oxide, lanthanum oxide, barium oxide and silver oxide to Pd is the second component. The metal atomic ratio was adjusted to be 1: 5.

Example 3 Example catalysts 11 to 16 were prepared by varying the addition amount of magnesium nitrate in the catalyst preparation of Example 1. The atomic ratio of palladium to magnesium in each catalyst is as follows.

Example catalyst 11 Pd / Mg = 10/1 〃 12 Pd / Mg = 1/1 〃 13 Mg / Pd = 20/1 〃 14 Mg / Pd = 20/1 〃 15 Mg / Pd = 20/1 〃 16 Mg / Pd = 20/1 Comparative Example 1 As a comparative example in the case of adding no aggregation inhibitor, 3 ml of a palladium nitrate solution (50 g / as Pd metal) is diluted with distilled water to make the total amount 17 ml. This solution is 3m in diameter
A lanthanum / β-alumina carrier (50 g) molded in a columnar shape with m and a height of 3 mm was impregnated, dried at 180 ° C., and calcined at 1300 ° C. for 20 hours to obtain a heat resistance evaluation catalyst (Comparative Example catalyst 7). This catalyst had 0.3% by weight of palladium supported on the total weight of the lanthanum / β-alumina carrier.

Comparative Example 2 1.81 g of magnesium nitrate is dissolved in 17 ml of distilled water. This solution was impregnated into a columnar 50 g lanthanum / β-alumina carrier having a diameter of 3 mm and a height of 3 mm and impregnated at 180 ° C.
After being dried at 4, the silver nitrate is baked and removed by baking at 600 ° C. to obtain a lanthanum / β-alumina catalyst with magnesium. 3 ml of a palladium nitrate solution (50 g / as Pd metal) is diluted with distilled water to make the total amount 17 ml. Comparative Example catalyst 8 was obtained in the same manner as in Example 1 except that this solution was impregnated with a lanthanum / β-alumina catalyst with magnesium.

Comparative Example 3 Palladium nitrate solution (50 g / as Pd metal) 3 m
1 and 1.81 g of magnesium nitrate are mixed and diluted with distilled water to make the total volume 17 ml. This solution was impregnated into 50 g of a lanthanum / β-alumina carrier shaped into a column having a diameter of 3 mm and a height of 3 mm, dried at 180 ° C., and Comparative Example catalyst 9 was obtained in the same manner as in Example 1.

Example 4 (Methane Combustion Test) For the example catalysts 1 to 16 and the comparative example catalysts 7 to 9, the combustion reaction of methane was 1000 ppm of methane and the space velocity was 3,0.
The activity test was conducted under the condition of 00h ^-1 . The activity was evaluated by the ignition temperature required to maintain a methane combustion rate of 50%. The results are shown in Table 2 and Table 2. In the table, the numbers in Katsuko are atomic ratios of base metals and platinum group. The ignition temperature (combustion start temperature) of a combustion catalyst used in a gas turbine, a gas fan heater, etc. is usually 400 ° C to 6 ° C.
Since the temperature was in the range of 10 ° C, in this test, the one having an ignition temperature of 610 ° C or lower was regarded as suitable (◯).

As is clear from the table, it was confirmed that the catalyst Nos. 1 to 15 of the example had a lower ignition temperature of 610 ° C. or lower and the heat resistance was superior to those of the catalysts No. 1 to 9 of the comparative example.

It should be noted that when the atomic ratio of Mg to Pd is in the range of 0.1 to 10, the ignition temperature is 600 ° C. or lower, which is a satisfactory result.
However, when the atomic ratio of Mg / Pd becomes 20, the ratio of the surface of Pd covered with MgO increases, the active sites of the catalyst decrease, and the ignition temperature rises.

Regarding Example Catalyst 1 and Comparative Example Catalysts 7 and 8, 1300
The particle structure after heat treatment at ℃, 20 hours after electron microscopy (2
(Observed at a magnification of 10,000). The results are shown in Fig. 1.
The circular part in the center is the palladium particles. As is clear from the results in the figure, in the comparative catalyst 7 (Fig. B), the particle size of Pd was about 15,000Å. On the other hand, in Example catalyst 1 (Fig. A), the particle size of Pd was as small as about 5000Å. Further, in the comparative catalyst 8 (Fig. C), about 15,000-
It was as large as 20,000Å. From the above,
It was confirmed that the catalyst of the present invention controls the aggregation of the Pd particles of the first component by the base metal. Comparative example catalyst 8 is M
The carrier was impregnated with the g compound and then with the Pd compound, but the ignition temperature was 650 ° C. and the activity was low. The catalyst of Comparative Example 9 was prepared by mixing the compound of Mg and Pd and impregnated into the carrier. In this case as well, the heat resistance of the catalyst was not improved as compared with the untreated catalyst (Catalyst of Comparative Example 7).

Moreover, when the addition amount (atomic ratio) of the base metal element to Pd and the ignition temperature were measured for Comparative Example catalysts 1 to 4, the results shown in FIG. 6 were obtained. Thus, the atomic ratio of α / Pd is 610 ° C. or lower in the range of 0.1 to 10 (α is M
g, Mn). In the case of Sr and Zr, the range is narrow, but 6
A catalyst having an ignition temperature of 10 ° C. or lower can be obtained.

Comparative Example 4 A γ-alumina carrier was used instead of the La · βAl ₂ O ₃ carrier. Palladium nitrate solution (50 g / Pd metal /
) Dilute 3 ml with distilled water to bring the total volume to 17 ml.
This solution was molded into a cylindrical shape with a diameter of 3 mm and a height of 3 mm 50
g of gamma-alumina carrier, and dried at 180 ° C.
The nitrate was baked and removed by baking at 1300 ° C. for 2 hours to obtain a gamma-alumina catalyst with palladium (comparative example catalyst 10). This catalyst has the form of Pd-Al ₂ O ₃ ,
0.3% by weight of palladium based on the total weight of the alumina carrier
Is.

Example 5 A γ-alumina carrier was used in place of the lanthanum / β-alumina carrier. Palladium nitrate solution (50 as Pd metal
Dilute g / 3 ml with distilled water to bring the total volume to 17 ml. This solution was impregnated into 50 g of a γ-alumina carrier formed into a cylindrical shape having a diameter of 3 mm and a height of 3 mm, dried at 180 ° C., and calcined at 600 ° C. to remove nitrates by calcination to obtain a γ-alumina catalyst with palladium. Obtained. Magnesium nitrate 1.8
1 g was dissolved in 17 ml of distilled water. This solution was impregnated in a γ-alumina catalyst with palladium, dried at 180 ° C, and
It was calcined at 00 ° C. for 20 hours to obtain a catalyst (Example catalyst 17). This catalyst has a form of M-Pd-Al ₂ O ₃ , and has 0.3% by weight of palladium based on the total weight of the lanthanum / β-alumina carrier, and the atomic ratio of palladium to magnesium Mg / Pd is 5/1. It was.

Regarding Comparative Example Catalyst 10 and Example Catalyst 17, 1300
After the heat treatment for 2 hours at ℃, the state of electron microscope (2,00
(0 times). Results are shown in FIG. As is clear from the results shown in the figure, in the comparative catalyst 10 (FIG. 5B), P
The particle diameter of d was about 10,000Å. On the other hand, in Example catalyst 17 (Fig. A), the particle size of Pd is as small as about 3,000Å. From the above, it was confirmed that the aggregation of Pd particles was suppressed even when the γ-alumina carrier was used.

Example 6 (CO gas adsorption test) Carbon monoxide (CO) gas was adsorbed on the catalyst surface by the pulse method, and the surface structure of the catalyst was analyzed. 32 to reaction tube
10 g of the sample ground to 48 mesh was filled and helium (He) was flowed at 400 ° C. for 1 hour to remove impurities such as oxygen and water adsorbed on the surface of the sample. 80 ° C
Adsorbed gas (CO concentration: 0.98% by volume, residual He) 10
ml was sampled by an adsorption gas introduction tube, introduced into the reaction tube at regular intervals and adsorbed on the sample. The CO concentration of the outlet gas was analyzed by a heat conduction type gas chromatograph and this concentration was
The CO adsorption was completed when the concentration became equal. The total amount of CO adsorbed was calculated from the difference in concentration between the inlet and the outlet. Note that C
As the sample for O adsorption, the catalyst of Example 1 and the catalysts of Comparative Examples 1 and 2 which had been calcined at 1300 ° C. for 20 hours were used.

As is clear from the results shown in FIG. 3, Pd-La-β.
Al ₂ O ₃ catalyst (La.βAl ₂ O ₃ carrier carrying Pd) and Pd-Mg-La · β · Al ₂ O ₃ catalyst (La · β · Al
₂ O ₃ carrier carrying Mg, then Pd) is the same C
The amount of O adsorption was shown. In addition, Mg-Pd-La / β / Al
The CO adsorption amount of the ₂ O ₃ catalyst (La.β · Al ₂ O ₃ carrier loaded with Pd and then Mg) was Pd-La · β · Al.
It was about 1/2 of that of the ₂ O ₃ catalyst and the Pd-Mg-La.β-Al ₂ O ₃ catalyst. From this result, as shown in FIG. 4, Pd particles and Mg particles or MgO particles were present on the La.β.Al ₂ O ₃ carrier, and Mg or MgO particles were scattered on the Pd particles. Therefore, it is considered that the Pd particles are suppressed from approaching each other and the Pd aggregation is suppressed.

Example 7 Using the chloroplatinic acid solution, the rhodium chloride solution, and the ruthenium chloride solution in place of the palladium nitrate solution, the catalysts of Examples 18 to 20 were prepared in the same manner as in Example 1.

Example Medium 18 Mg-Pt-La-βAl ₂ O ₃ 〃 19 Mg-Rh-La-βAl ₂ O ₃ 〃 20 Mg-Ru-La-βAl ₂ O _{3 In} these catalysts, the platinum group element is lanthanum.・ Β ・ A
It is 0.3% by weight based on the total weight of the l ₂ O ₃ carrier, and the ratio of platinum group to magnesium is 1: 5 in atomic ratio.

Comparative Example 5 Comparative catalysts 11 to 13 prepared by the manufacturing method of Example 7 and containing no magnesium oxide were prepared.

Using the example catalysts 18 to 20 and the comparative example catalysts 11 to 13,
Propane 1, which has undergone a 10-hour propane continuous combustion test
%, The gas consisting of the remaining space was passed through the catalyst at a space velocity of 60,000 h ⁻¹ preheated to 500 ° C. The temperature of the catalyst layer rises due to the combustion of propane, and reaches 1100 ° C. at the maximum. The propane reaction rate of each catalyst after 10 hours
Shown in the table. As is clear from the table, the example catalysts 18 to 20 to which magnesium oxide, which is a platinum group aggregation inhibitor, was added,
It shows a high propane reaction rate, indicating that it has excellent heat resistance.

On the other hand, in the comparative catalysts 11 to 13 to which magnesium oxide was not added, the catalytic activity was about 10% in propane reaction rate.
Low.

Example 8 A honeycomb structure made of lanthanum / β / alumina (diameter 90 mm, length 75 mm) was impregnated with palladium nitrate so that the amount of palladium was 0.3% by weight. After drying at 120 ° C, it was baked at 600 ° C for 2 hours. Palladium-lanthanum β-alumina catalyst with magnesium nitrate palladium 1
The honeycomb catalyst (Example catalyst 21) was obtained by impregnating so that 5 g of magnesium was added to g atoms, dried at 120 ° C., and fired at 1300 ° C. for 20 hours. The specific surface area of this honeycomb catalyst was 15 m ² / g, and the palladium particle diameter was 4000 Å.

Comparative Example 6 A comparative catalyst 14 was prepared in the same manner as in Example 8 except that magnesium was not added.

Example 9 A honeycomb structure made of a commercially available cordieride substrate (diameter 90 mm, length 75 mm) was impregnated with 20% by weight of a composite oxide slurry containing lanthanum / β-alumina in 5 batches. After drying at 120 ° C, it was baked at 600 ° C for 2 hours. This cordierite substrate with lanthanum / β-alumina was impregnated with palladium nitrate so that the palladium content would be 0.3% by weight. After drying at 120 ° C, baking is performed at 600 ° C for 2 hours. A palladium-lanthanum .beta..alumina catalyst was impregnated with magnesium nitrate so that 5 g of magnesium was added to 1 g of palladium, dried at 120.degree. C., and calcined at 1300.degree. C. for 20 hours to obtain a Hachicom catalyst (Example catalyst 22). ) Got. The specific surface area of this honeycomb catalyst is 10.0 m ² / g, and the palladium particle size is 5000 Å
It was.

Comparative Example 7 A comparative catalyst 15 of Example 9 containing no magnesium was prepared.

For the catalysts 21 to 22 of Examples 8 and 9 and the catalysts 14 to 15 of Comparative Examples, the methane combustion reaction was carried out under the conditions of 1000 ppm of methane and a space velocity of 30,000 h ^-1 . The activity was evaluated by the ignition temperature required to maintain a methane combustion rate of 50%. The result is shown in FIG.

As can be seen, the example catalysts 21 (curve A) and 22 (curve B) are comparative catalysts 14 (curve C) and 15 (curve C).
It was found that the ignition temperature was lower than that of (curve D) and the heat resistance was excellent.

Example 10 Palladium nitrate solution (50 g / Pd metal) 3 m
1 was diluted with distilled water to make the total volume 17 ml. This solution was molded into a cylindrical shape with a diameter of 3 mm and a height of 3 mm.
50g of alumina carrier was impregnated and dried at 180 ℃, then 60
It was calcined at 0 ° C. to remove the nitrate by calcination to obtain a lanthanum / β-alumina catalyst with palladium.

A lanthanum / β-alumina catalyst with palladium was impregnated with magnesium nitrate, dried and then calcined at 900 ° C. for 2 hours to obtain a catalyst 23 of Example. This catalyst contained 0.3% by weight of palladium based on the total weight of the lanthanum β-alumina carrier, and the atomic ratio of palladium to magnesium was Pd / Mg = 1/5.

Example 11 A honeycomb structure made of a commercially available mullite substrate (diameter 90)
mm x length 75 mm) lantern to be 20% by weight
The slurry of the complex oxide containing β-alumina is impregnated into 5 times. After drying at 120 ° C, it was baked at 600 ° C for 2 hours. This lanthanum / β-alumina-attached mullite substrate is impregnated with palladium nitrate so that the palladium content will be 0.3% by weight. After drying at 120 ° C., it was calcined at 600 ° C. for 2 hours to obtain Example catalyst 24. The following preparation method is the same as in Example 9. The specific surface area of this honeycomb catalyst is 80 m ² / g,
The palladium particle size was 5500Å.

Comparative Example 8 Comparative catalyst 16 in which magnesium was not added in Example 11 was prepared.

Example 12 A honeycomb structure (diameter 90 mm, length 75 mm) made of a commercially available aluminum titanate substrate was impregnated with a slurry of a complex oxide containing lanthanum / β-alumina in 5 times so as to be 20% by weight. . The following preparation method is the same as in Example 10. This honeycomb catalyst (Example catalyst 25) had a specific surface area of 95 m ² / g and a palladium particle diameter of 5000.
It was Å.

Comparative Example 9 A comparative catalyst 17 of Example 12 was prepared without adding magnesium.

Example 13 Honeycomb structure made of a commercially available zirconia substrate (diameter 9
The slurry of the composite oxide containing lanthanum / β-alumina was impregnated into 0 mm × 75 mm length) in an amount of 20% by weight in 5 batches. The following preparation method is the same as in Example 9. The specific surface area of this honeycomb catalyst (Example catalyst 26) is 110.
It was m ² / g and the palladium particle size was 400Å.

Comparative Example 10 Comparative Example catalyst 18 in which magnesium was not added in Example 13 was prepared.

Example 14 A honeycomb structure made of a commercially available silicon carbide substrate (diameter: 9)
The slurry of the composite oxide containing lanthanum / β-alumina was impregnated into 5 times so as to be 20% by weight in 0 mm and 75 mm in length. The following preparation method is the same as in Example 10.
The specific surface area of this honeycomb catalyst (Example catalyst 27) is 90.
It was m ² / g and the palladium particle size was 4800Å.

Comparative Example 11 A comparative catalyst 19 of Example 14 was prepared without adding magnesium.

Example 15 With respect to the example catalysts 21 to 27 and the comparative example catalysts 4 to 19, the combustion reaction of methane was conducted at 1000 ppm of methane and a space velocity of 3
An activity test was conducted under the condition of 10,000 h ⁻¹ , and the activity was evaluated by the ignition temperature required to maintain a methane combustion rate of 50%. The results are shown in Table 4. As is clear from the table, it was found that the example catalysts 21 to 27 had a lower deposition ratio temperature and excellent heat resistance than the comparative catalyst.

[Advantages of the Invention] As described above, according to the present invention, the aggregation of noble metal particles such as palladium can be controlled even at high temperatures, so that stable catalytic activity can be exhibited for a long period of time.

[Brief description of drawings]

FIG. 1 (a) shows Example catalyst 1 (Mg-Pd-La.β).
・ Al ₂ O ₃ ), (b) is comparative example catalyst 7 (Pd-La.
β.Al ₂ O ₃ ), (c) is comparative example catalyst 8 (Pd-Mg)
Is an electron micrograph showing a white metal grain structure _{-La · β · Al 2 O 3} ). FIG. 2 (a) shows Example catalyst 15 (M
g-Pd-γ · Al ₂ O ₃ ), (b) is a comparative example catalyst 10
Is an electron micrograph showing the structure of a _{(Pd-γ · Al 2 O} 3) a noble metal particles. FIG. 3 is a diagram showing the CO adsorption amounts of the example catalyst 1 and the comparative example catalysts 7 and 8, and FIG. 4 is the example catalyst 1
FIG. 5 is a schematic diagram of the surface structure of the catalyst of Example 2 according to the present invention.
It is a figure which shows the relationship between the ignition temperature and methane combustion rate of 1 and 22 and comparative example catalysts 15 and 16. FIG. 6 is a graph showing the ignition temperature when the atomic ratio of the base metal element to Pd is variously changed. 1 ... Mg particle, 2 ... Pd particle, 3 ... La ・ β ・ A
l ₂ O ₃ carrier, curve A ... Example catalyst 21, curve B ... Example catalyst 22, curve C ... Comparative example catalyst 15, curve D ...
Comparative catalyst 16.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akira Kato 4026 Kuji Town, Hitachi City, Ibaraki Prefecture Hitate Manufacturing Co., Ltd.Hitachi Laboratory Ltd. (72) Noriko Watanabe 4026 Kuji Town, Hitachi City Ibaraki Prefecture Hitate Manufacturing Co., Ltd. Hitachi Research Laboratory (72) Inventor Shinpei Matsuda 4026 Kuji Town, Hitachi City, Ibaraki Prefecture Hitachi Research Laboratory, Hitachi, Ltd.

Claims (7)

[Claims] 1. A heat-resistant inorganic carrier selected from the group consisting of oxides, carbides and nitrides of Group IIa, Group IIIa and Group IV elements of the Periodic Table, and a carrier supported on the carrier. A heat-resistant combustion catalyst, comprising particles of at least one catalytically active component of a platinum group element, and magnesium oxide particles dispersed at least on the particles of the platinum group element. 2. The heat-resistant combustion catalyst according to claim 1, wherein the atomic ratio of magnesium to the catalytically active component is 0.1 to 10. 3. The heat-resistant inorganic carrier is selected from the group consisting of alumina, silica, magnesia, calcia, barium oxide, beryllia, zirconia, titania, thoria, cordierite, mullite, sponge yumen, aluminum titanate, silicon carbide and silicon nitride. The heat-resistant combustion catalyst according to claim 1, which is at least one selected from the group consisting of: 4. A heat-resistant inorganic carrier of at least one selected from the group consisting of oxides, carbides and nitrides of elements IIa, IIIa and IV of the periodic table, and at least one platinum group element. Impregnating the impregnated product with a solution of the compound of the catalytically active component, calcining the impregnated product at a temperature sufficient to decompose the compound; and impregnating the calcined product with a solution of the magnesium compound. Calcination of the impregnated product at a temperature sufficient to decompose the magnesium compound. 5. The method for producing a heat-resistant combustion catalyst according to claim 4, wherein the atomic ratio of magnesium to the catalytically active component is 0.1 to 10. 6. A heat-resistant inorganic carrier selected from the group consisting of oxides, carbides and nitrides of Group IIa, Group IIIa and Group IV elements of the Periodic Table, and dispersed and carried on the carrier. And a hydrocarbon gas fuel in the presence of oxygen, a heat-resistant combustion catalyst having at least one catalytically active component particle of a platinum group element and magnesium oxide particles dispersed on the catalytically active component particle. A catalytic combustion method characterized by: 7. The catalytic combustion method according to claim 6, wherein the atomic ratio of magnesium to the catalytically active component is 0.1 to 10.