JPH069654B2 - Method for producing catalytic combustion catalyst - Google Patents

Description

The present invention relates to a catalytic combustion catalyst.

(Prior Art) A catalytic combustion method that uses a catalyst to promote the reaction between fuel and oxygen is (1) capable of complete combustion at a low temperature, and (2) a wide range of fuel. Since it is possible to perform stable combustion at an air / air ratio and (3) there is little generation of thermal NOx, it has been particularly noted in recent years.

In order to carry out catalytic combustion, a catalyst in which a catalyst component active in an oxidation reaction is supported on a heat-resistant catalyst carrier is generally used, and a typical one is platinum and / or palladium on an alumina carrier having a large BET specific surface area. It carries a noble metal such as. However, these catalytic combustion catalysts have 100
Under high temperature use conditions such as exceeding 0 ° C., (1) the BET specific surface area of the carrier such as alumina is sharply decreased by fusion of pores, and (2) it is active due to aggregation of finely dispersed active ingredients. There is a drawback that the catalytic activity is lowered due to such factors as the decrease of the number of points and (3) the inactivation of the active ingredient due to the binding between the carrier and the active ingredient. Further, the noble metal catalyst has a drawback that the catalyst cost becomes high. To solve these drawbacks, a large number of thermally stable catalyst carriers or catalysts have been searched for. As a method of stabilizing transferable alumina, Japanese Patent Laid-Open No. 48-14600 discloses that a rare earth oxide such as lanthanum oxide or cerium oxide is added, and calcined at a temperature of about 1000 ° C. or less to transfer to α-alumina. However, this method does not lead to an improvement in the activity of the catalyst, but rather the one that is not stabilized by oxides such as lanthanum and / or cerium is more active. Is high.

JP-A-58-216741 discloses an alumina catalyst using alumina, silica and lanthanide, but the thermal stability is improved only by adding silica to alumina, and the lanthanide is simply acidic. The purpose is to reduce Incidentally, the firing of alumina-silica-lanthanide is performed at about 500 ° C.

Journal of Catharisu Vol. 86, No. 2 (1984
H. C. Yao and Y. F. Yu.Yao's paper shows that the addition of ceria to an alumina-supported noble metal catalyst is
(1) Increased oxygen storage capacity, (2) BE of alumina carrier
Improvement of loss of T specific surface area due to heat, (3) stabilization of finely dispersed active noble metal, (4) CO under oxygen-deficient state
However, the heat treatment after adding ceria is limited to 800 ° C or less, and the heat treatment at a high temperature is limited to the above-mentioned various effects of adding ceria. Is described as diminishing.

Japanese Examined Patent Publication No. 59-41775 relates to a noble metal catalyst using a single-body inert carrier such as a honeycomb, but a surface area of 75 m ² / g or more is maintained at 900 to 1200 ° C with a mixture of ceria, a promoter and activated alumina. However, a method for producing a catalyst is proposed, in which the precalcined product is mixed with a white metal metal or its compound and then coated on a single inert carrier. However, as described in the description of Yao and Yu Yao above, 900 ~
Heat treatment is performed in the high temperature range of 1200 ℃, and the surface area is 75
Maintaining m ² / g or more is an operation requiring extremely precise treatment, and there is a fear that the effect of heat treatment may not be sufficiently achieved.

Japanese Examined Patent Publication No. 60-7537 is intended to obtain a catalyst carrier having excellent durability by calcining a cerium-lanthanum-inorganic porous carrier at a temperature of 700 ° C. or higher.
It is described as unfavorable because the BET specific surface area of the carrier is lowered and the catalytic effect is lowered when the temperature is higher than 0 ° C, and the firing temperature is actually kept at 1000 ° C or lower in the examples.

Japanese Patent Application No. 59-279767 relating to the invention of the present inventors
No. 157345) proposes to improve the heat resistance of the alumina carrier by adding lanthanum and silica in a specific ratio to the alumina carrier, but it is more heat resistant in the catalyst used under severe catalytic combustion reaction conditions. It has been particularly desired to improve the properties of the catalyst, improve the durability of the catalyst, and reduce the cost of the catalyst, thereby widening the field to which the catalytic combustion is applied.

(Problems to be Solved by the Invention) Because of the various problems of the catalytic combustion catalyst as described above, there has conventionally been a demand for a catalytic combustion catalyst which is excellent in heat resistance or durability but inexpensive.

(Means for Solving Problems) An object of the present invention is to improve a catalytic combustion catalyst using a heat-resistant catalyst carrier such as alumina or alumina-silica, and to provide a catalyst having high heat resistance and still being inexpensive. is there.

In order to achieve this object, the present inventors have made extensive studies on the effect of adding a lanthanum compound and a cerium compound to a heat resistant catalyst carrier such as alumina, but as a result, the first method was first applied to the heat resistant catalyst carrier. A lanthanum compound is added as an oxidation catalyst component and a first heat treatment is performed in a temperature range of about 500 to 1000 ° C, and then a cerium compound is added as a second oxidation catalyst component and a first temperature is adjusted in a temperature range of about 1000 to 1300 ° C. It was found that the catalyst obtained by the ^second heat treatment has excellent heat resistance even if it has a low specific surface area of 75 m ² / g or less, and it also functions as a catalytic combustion catalyst. The invention was completed.

As the heat-resistant carrier of the catalyst of the present invention, alumina, silica, titania, all the carriers that have been used as conventional heat-resistant carriers such as zirconia can be used, alumina,
Those mainly containing silica-alumina are preferable. In addition, magnesium, calcium, strontium and / or barium oxide or the like may be added to these as an enhancer.

Examples of the lanthanum compound include lanthanum nitrate, lanthanum carbonate, lanthanum chloride, lanthanum fluoride, lanthanum carbonate, lanthanum oxalate, lanthanum acetate, acetylacetone lanthanum, lanthanum oxide, and mixed rare earth salts containing various lanthanide elements. Can be used. In addition, any method such as a precipitation method, a coprecipitation method, a kneading method, an impregnation method and a combination thereof which are generally used in this field can be used.

The heat treatment after adding the lanthanum compound is preferably about 500 to 1000 ° C. The mixed powder of the carrier-lanthanum compound is heat-treated and then molded into a carrier, or the molded product is heat-treated into a carrier.

The amount of lanthanum compound added is La _{2 with} respect to 100 parts by weight of the carrier.
It is preferably about 1 to 40 parts by weight, especially about 1 to 20 parts by weight, calculated as O ₃ . In this case, the aforementioned Japanese Patent Application No. 59-279767
As described in No. 1, instead of the alumina carrier, alumina 100
It is even more preferred to use silica-alumina as the carrier, which contains about 0.5 to 15 parts by weight of silica per part by weight.

As the cerium compound to be added, various kinds of salts similar to the case of the lanthanum compound can be used as other compounds.

The second heat treatment after the addition of the cerium compound is performed at a high temperature exceeding about 1000 ° C. Due to the effect of preliminary stabilization by adding a lanthanum compound, the heat treatment at such a high temperature in the secondary heat treatment has little influence on the catalytic activity, and as a result, addition of noble metal is sufficient. An excellent catalytic combustion catalyst with high activity can be obtained. The upper limit of the temperature of the second heat treatment is preferably about 1300 ° C.

The addition amount of the cerium compound is C based on 100 parts by weight of the carrier.
Approximately 5 to 40 parts by weight in terms of eO ₂ is preferable from the viewpoint of initial activity and heat resistance.
If it is more than 1 part by weight, the initial activity of the catalyst will be low and the heat resistance will be poor.

The present inventors have found an inexpensive catalytic combustion catalyst excellent in activity and heat resistance without using a precious metal such as platinum and / or palladium. However, when a precious metal such as platinum is added to the catalyst of the present invention, the present invention It was also found to be useful for improving the properties of the catalysts, especially low temperature activity. However, without using a large amount of noble metal as was previously considered, about 0.3% of the total catalyst weight.
It has been found that the addition of small amounts of noble metals, up to%, in particular up to 0.05%, also helps to improve the properties of the catalysts of the invention. Since the addition of such a noble metal is minute, it does not necessarily deviate from the purpose of an inexpensive catalytic combustion catalyst. The use of a catalyst containing a noble metal in the first stage of the reaction and the use of an inexpensive catalyst containing no noble metal in the second stage of the reaction contributes to a reduction in the cost of the catalyst as a whole system.

(Function) The catalyst of the present invention is particularly excellent in heat resistance and has a maximum temperature of 700
It is particularly suitable as a catalyst for catalytic combustion reactions such as reaching ~ 1400 ° C. This catalyst is a catalytic combustion catalyst that is inexpensive and still has excellent durability and activity, and can be applied to areas where the heat resistance and price of conventional catalysts are limited.

(Example) Next, the present invention will be described in more detail by way of examples, but the present invention is not limited thereto.

Example 1 100 g of aluminum hydroxide (61 g as Al ₂ O ₃ ) was taken and calcined at 450 ° C. for 5 hours, then 12.5 g of colloidal silica (containing 2.5 g as SiO ₂ ) was added,
The mixture was kneaded at room temperature for 3 hours. After calcining this at 550 ℃ for 5 hours,
Grinded to 12-24 mesh, alumina 4% by weight silica 96
A weight% silica-alumina carrier (hereinafter referred to as carrier A) was obtained.

40 g of the carrier A was put into a lanthanum nitrate aqueous solution (containing 4 g as La ₂ O ₃ ) and the impregnated product was dried at 400 ° C. This operation of impregnation and drying was repeated 4 times to impregnate the whole amount of lanthanum nitrate, and then, firing was performed at 900 ° C. for 10 hours (primary firing).

The obtained primary fired product containing La ₂ O ₃ was put into an aqueous cerium nitrate solution (containing 4 g of CeO ₂ ), and the impregnated product was dried at 400 ° C. This operation of impregnation and drying was repeated four times to impregnate the entire amount of lanthanum nitrate, and then, firing was performed at 1250 ° C. for 10 hours (secondary firing). The catalyst thus obtained was 10 parts by weight of La ₂ O _{3 with} respect to 100 parts by weight of silica-alumina carrier,
And 10 parts by weight of CeO ₂ (this catalyst is referred to as catalyst A).

Comparative Example 1 A catalyst was produced by the same method as in Example 1 except that the primary calcination was not performed (this catalyst is referred to as catalyst a).

Example 2 300 g of the catalyst A produced according to Example 1 was taken and impregnated with a palladium chloride solution (containing 0.15 as Pd), and the impregnated product was dried at 400 ° C. and then calcined at 1200 ° C. for 10 hours,
A catalyst containing 0.05% of Pd (Catalyst B) was obtained.

Comparative Example 2 A catalyst (catalyst b) was produced in the same manner as in Example 2, except that the catalyst a was used in place of the catalyst A.

Example 3 A reaction tube made of alumina having an inner diameter of 15 mm was filled with 10 cc of a catalyst prepared in 12 to 24 mesh, and the external temperature of the reactor was kept at 900 ° C. with a heater, and then H ₂ 3.0% by volume, CH ₄ 2.0% by volume, Fuel gas consisting of air as the balance was inserted at a rate of 300 / hr. Then, a catalytic combustion reaction test was conducted while adjusting the temperature outside the reactor so that the maximum temperature inside the reactor was maintained at 1250 ° C. The results of testing the catalysts of Examples 1 and 2 and Comparative Examples 1 and 2 were as shown in Table 1 below.

As can be seen from Table 1 above, the catalyst A of Example 1 and the catalyst B of Example 2 according to the present invention are clearly more durable than the corresponding catalyst a of Comparative Example 1 and catalyst b of Comparative Example 2. It has excellent properties.

Examples 4 to 8 and Comparative Example 3 By the same operation as in Example 1, the alumina-silica carrier 1
10 parts by weight of La ₂ O ₃ was carried on 00 parts by weight, and a primary-fired product was produced by firing at 900 ° C. Then, a carrier 100 was prepared in the same manner as in Example 1 except that the impregnation amount of cerium nitrate was changed.
The CeO ₂ amount with respect to parts by weight is 2 parts by weight (Comparative Example 3), 5 parts by weight (Example 4), 15 parts by weight (Example 5), respectively.
20 parts by weight (Example 6), 30 parts by weight (Example 7) and 40 parts by weight (Example 8) were impregnated with cerium nitrate,
After drying, it was calcined at 1200 ° C. for 10 hours to obtain catalysts C, D, E, F. G
And H were produced respectively.

Example 9 Comparative Example 3 was carried out using the catalysts of Examples 4 to 8 (catalysts C to H).
The same test as in Example 3 was performed. The results are shown in Table 2 below.

As can be seen from Table 2 above, the catalytic combustion catalyst of the present invention has extremely good CH ₄ flammability.

Examples 10 to 15 Using catalyst F of Example 6, palladium chloride was impregnated in the same manner as in Example 2, dried at 400 ° C, and then dried at 1150 ° C.
After being calcined for 10 hours, 0.01% by weight of palladium (Example 10), 0.03% by weight (Example 11), 0.05% by weight (Example 12), 0.08% by weight (Example 13) and 0.10% by weight, respectively
Catalysts I, J, K, L, M and N containing (Example 14) and 0.15 wt% (Example 15) were prepared, respectively.

Example 16 Heat treatment of catalysts F, I to N in an electric furnace at 1300 ° C. for 100 hours,
The same alumina reaction tube as in Example 3 was filled with the catalyst. Then 1.0% by volume hydrogen, 0.6% by volume oxygen and nitrogen
While introducing 98.4% by volume of gas, the external temperature of the reactant is 120 ° C /
The temperature at which hydrogen ignites was tested by gradually increasing the temperature from room temperature at a rate of time. The results of the tests are shown in Table 3 below.

As can be seen from Table 3 above, the catalytic combustion catalyst of the present invention had extremely good hydrogen flammability.

(Effects of the Invention) Thus, according to the present invention, it is possible to obtain a catalytic combustion catalyst which is excellent in heat resistance and durability but is inexpensive. Therefore, the present invention is extremely useful industrially.

Although the present invention has been described with reference to specific examples and numerical values, it is needless to say that various changes and modifications of the present invention can be made without departing from the broad spirit and scope of the present invention.

 ─────────────────────────────────────────────────── --- Continuation of the front page (56) References JP 59-160536 (JP, A) JP 59-98730 (JP, A) JP 59-52529 (JP, A) JP 58- 133831 (JP, A)

Claims (2)

[Claims] 1. A lanthanum compound of 1 to 40 parts by weight in terms of La ₂ O ₃ as a first oxidation catalyst component is added to 100 parts by weight of a heat-resistant catalyst carrier, and the first lanthanum compound is added in a temperature range of 500 to 1000 ° C. Next heat treatment is performed, and then Ce as the second oxidation catalyst component
A method for producing a catalytic combustion catalyst, comprising adding 5 to 40 parts by weight of a cerium compound in terms of O ₂ and performing a second heat treatment in a temperature range of 1000 to 1300 ° C. 2. A lanthanum compound of 1 to 40 parts by weight in terms of La ₂ O ₃ as a first oxidation catalyst component is added to 100 parts by weight of a heat-resistant catalyst carrier, and the first lanthanum compound is added in a temperature range of 500 to 1000 ° C. Next heat treatment is performed, and then Ce as the second oxidation catalyst component
The cerium compound is added in an amount of 5 to 40 parts by weight in terms of O ₂ , and the second heat treatment is performed in the temperature range of 1000 to 1300 ° C., and 0.3 to 100 parts by weight of the heat resistant catalyst carrier.
A method for producing a catalytic combustion catalyst, comprising supporting a noble metal element by weight or less as a third oxidation catalyst component.