JPH0899039A - Amorphous alloy catalyst for nitrogen oxide decomposition - Google Patents

Abstract

PURPOSE: To obtain an amorphous alloy catalyst which has high activity and good selectivity and decomposes NOx contained in exhaust gas by covering an amorphous alloy containing Ni, Ta, and Pd as indispensable components with ceramics with a large specific surface area by a PVD method. CONSTITUTION: A catalyst for NOx decomposition is made by covering a ceramic with an amorphous alloy containing 10-50 atomic % Ta, 0.5-40 atomic % Pd, and the rest containing substantially 30 atomic % or more Ni by a PVD method, or by covering it similarly with an amorphous alloy containing 10-50 atomic % Ta, 0.5-40 atomic % Pd, 10 atomic % or less Co, the rest comprising substantially Ni, and containing at least 30 atomic % the total of Ni and Co. In another method, the ceramic is covered similarly with an amorphous alloy containing less than 50 atomic % Ta, 10-50 atomic % total of Ta and at least one kind of Nb, Ti, and Zr, 0.5-40 atomic % Pd, and the rest containing substantially 30 atomic % or more Ni to make the catalyst.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly active amorphous alloy catalyst for decomposing NOx contained in combustion exhaust gas.

[0002]

2. Description of the Related Art In devices and engines that burn various organic substances,
NOx is generated by the reaction between nitrogen and oxygen in the atmosphere heated to a high temperature, and NOx is contained in the exhaust gas and discharged. Not only is it harmful to living organisms, but it also has a greenhouse effect and destroys the ozone layer. For the removal of NOx, a method of converting nitrogen and water vapor by reaction with ammonia is currently used in large-scale combustion facilities. A reaction based on the principle of changing to carbon dioxide and nitrogen gas by a reaction with a carbon compound contained in exhaust gas due to incomplete combustion is performed using a platinum group element supported on ceramics as a catalyst.

On the other hand, three of the inventors of the present invention convert carbon compounds into carbon dioxide and water from a gas containing NOx, CO and unburned hydrocarbons discharged from an apparatus for burning various organic substances, an engine, and nitrogen. We have found an amorphous alloy catalyst that can perform an exhaust gas purification reaction based on the principle of changing oxides to nitrogen gas even at a temperature close to room temperature, is highly active, and can be easily produced and regenerated.
Filed as No. 6. Japanese Patent Application No. 1-262986 comprises the following three inventions.

(1) One or two of Nb and Ta 2
Amorphous alloy consisting of 0-70 atom%, 0.5-20 atom% of one or more elements selected from the group of Ru, Pd, Rh, Pt and Ir, and the balance substantially one or two of Ni and Co. A catalyst for purifying exhaust gas, wherein the catalyst is subjected to activation treatment by dipping in hydrofluoric acid. (2) One or two kinds of Ti and Zr, 20-80 atomic%, Ru, Pd,
0.5-20 atomic% of one or more elements selected from the group of Rh, Pt and Ir, the balance being substantially 1 of Ni and Co.
A catalyst for purifying exhaust gas, which is obtained by subjecting an amorphous alloy of 10% by atom or more of 2 or more types to activation treatment by dipping in hydrofluoric acid. (3) One or two kinds of Nb and Ta, 70 atomic% or less, and one or two kinds of Ti and Zr
20-80 atomic% of the total amount with the seeds (including the amount of one or two of the above Nb and Ta), Ru, Pd, Rh, Pt.
And at least one element selected from the group of Ir 0.5-2
0 atomic%, the balance substantially one of Ni and Co or 2
An exhaust gas purifying catalyst, characterized by subjecting an amorphous alloy containing 10 atomic% or more of seed to activation treatment by dipping in hydrofluoric acid.

[0005]

Conventionally, the decomposition of NOx is based on the reduction to nitrogen using ammonia or CO. However, NOx is generated by the reaction between nitrogen and oxygen at high temperature, and it is thermodynamically stable to decompose into nitrogen and oxygen at low temperature.
The advent of high-performance catalysts that directly decompose NOx is awaited as a treatment method for treating exhaust gas of diesel engines in which combustion conditions are difficult to control and for using ammonia in large-scale combustion facilities.

[0006]

The inventors of the present invention have found that amorphous alloys containing Ni, Ta and Pd as essential elements, including alloys having compositions other than the composition applied for in Japanese Patent Application No. 1-262986, are liquid quenched. Japanese Patent Application No. 1-26
It has been found that it can be a high-performance catalyst that directly decomposes NOx without performing the activation treatment by dipping in hydrofluoric acid specified in No. 2986. Furthermore, even if amorphous alloys exhibiting various catalytic properties were obtained, the amorphous alloys produced by the usual method had a drawback that the specific surface area as a catalyst was small and it was difficult to put them into practical use. Alloy P on ceramics with a large specific surface area
The present invention has been achieved by improving the specific surface area by using the VD method to overcome this drawback.

The present invention consists of claims 1 to 4, and includes an amorphous alloy containing Ni, Ta and Pd as essential components and an amorphous alloy obtained by substituting a part of Ta with Nb, Ti and Zr. It is intended to provide a catalyst for NOx decomposition having high activity and excellent reaction selectivity in which an amorphous alloy partially substituted with Co is coated on a ceramic having a large specific surface area by a PVD method.

Table 1 below shows the constituent elements and the contents of these first to fourth inventions.

[0009]

In order to obtain a catalyst which has a high selective catalytic activity for a specific chemical reaction and which can be easily produced and regenerated,
It is more convenient to use an alloy containing a necessary amount of an effective element than to support a platinum group element on ceramics such as alumina, titania, and silica. However, in the case of a crystalline metal produced by an ordinary method, addition of a large amount of various alloying elements often results in a multiphase structure having different chemical properties, and it is not possible to have predetermined properties. Moreover, since it is brittle, it is difficult to obtain a material having a large specific surface area required as a catalyst.

On the other hand, in the amorphous alloy of the present invention having the above composition obtained by the PVD method, the constituent elements are not allowed to be localized and the predetermined elements are uniformly solid-dissolved. When these alloys are formed on a ceramic having a large specific surface area by the PVD method, they have excellent catalytic activity peculiar to the amorphous alloy of the present invention, which has not been realized in the past, and the specific surface area is large like a normal catalyst and rapidly. A catalyst is generated that decomposes NOx.

That is, NOx contained in the combustion exhaust gas
The highly active amorphous alloy catalyst for decomposing the is realized by the catalyst of the present invention in which the alloy having the above composition is coated on the ceramic having a large specific surface area. The ceramics referred to in the present invention is a powdery, porous granular or plate-like body, and can be arbitrarily selected according to the application site.

Next, the reasons for limiting the composition of each component in the present invention will be described.

Ni and Co are elements that form the basis of the alloy of the present invention, and are valve metals such as Ta, Ti, Zr, and
It is an element that forms an amorphous structure in coexistence with one or more kinds of Nb. Further, Pd is a basic element that imparts catalytic activity for NOx decomposition. Of these, an amorphous alloy containing no Ni or Ta cannot obtain high activity for NOx decomposition unless it is immersed in hydrofluoric acid to selectively dissolve the valve metal and Ni and Co to concentrate Pd on the alloy surface. However, in the case of a catalyst in which the highly active amorphous alloy of the present invention is coated on ceramics, when immersed in hydrofluoric acid, the ceramics itself is attacked and the catalyst is destroyed. On the other hand, the amorphous alloy of the present invention containing Ni, Ta and Pd as basic components is a highly active catalyst without the treatment of concentrating Pd on the surface by dipping in hydrofluoric acid. Ta and Pd
Must be the basic ingredient. In this case, the concentration of Ta that is most likely to form an amorphous alloy is 10 to 50 atom%, and therefore Ta in Claim 1 and Claim 2 of the present invention is the same.
Content of 10-50 atomic% is required. Also, T
Although substituting a with Nb, Ti and Zr does not hinder obtaining an amorphous alloy, since Ta is an essential element for the purpose of the present invention, claims 3 and 4 of the present invention. In, Ta contains less than 50 atomic%,
It is necessary to make the total of at least one of Nb, Ti and Zr and Ta 10-50 atomic%. Pd is an essential element that gives catalytic activity for NOx decomposition, but addition of a large amount only raises the cost of the catalyst and is useless with a highly active catalyst such as the catalyst of the present invention. %. Ni is an essential element that forms an amorphous alloy with Ta and other valve metals, but replacing Ni with Pd does not hinder the formation of the amorphous alloy. However, since the use of a large amount of Pd is wasteful as described above, the Ni content in claims 1 and 3 of the present invention is large.
Is required to be 30 atomic% or more as a substantial balance. Also,
Co is also an element that replaces Ni to form an amorphous alloy. However, if Ni is replaced by Co in a large amount, the catalytic activity tends to decrease. Therefore, the addition of Co is 10 in Claims 2 and 4 of the present invention. Limited to less than atomic%. Also,
The addition of various platinum group elements other than Pd does not hinder the purpose of the present invention.

[0015]

EXAMPLES The present invention will now be described with reference to examples.

Example 1 A gamma-alumina powder having a particle size of 0.006 μm was suspended in butanol and applied on a glass plate, and then butanol was evaporated to obtain a ceramics substrate for sputtering having a large specific surface area. As shown in FIG. 1, a Ta disk having a diameter of 100 mm and a thickness of 6 mm was mounted with 6 pieces of 20 mm square Ni and 4 pieces of 10 mm square Pd plate on a circumference having a radius of 29 mm from the center. 5 ml Ar using the device
While maintaining a vacuum of 2 × 10 ⁴ Torr while flowing at a speed of / min, sputter deposition was performed on the substrate rotating and revolving at an output of about 400 W. As a result of X-ray diffraction of an alloy simultaneously deposited using a glass plate as a direct substrate, it was confirmed that the resulting alloy was amorphous. An analysis using an X-ray microanalyzer revealed that the composition of the amorphous alloy was Ni at 50 atomic%, Ta at 34 atomic%, and Pd at 16 atomic%. 3% by weight of Pd was contained per 1 g of the total amount of alumina and the amorphous alloy. 1 g of this catalyst was filled in the central part of a quartz tube having an inner diameter of 8 mm and a length of 500 mm, and while heating the temperature, NO in He was adjusted to 50%.
A gas containing 00 ppm is caused to flow at a rate of 30 ml / min,
The reaction was carried out at various temperatures, and the gas after the reaction was analyzed by gas chromatography. Table 2 shows the conversion rates of NO at various temperatures.

[0017]

As described above, the catalyst obtained by coating the fine alumina powder of the present invention with the amorphous Ni-34 at% Ta-16 at% Pd alloy is a high-performance catalyst for NOx decomposition.

Example 2 Gamma-alumina powder having a particle size of 0.006 μm was suspended in butanol and applied on a glass plate, and then butanol was evaporated to obtain a ceramics substrate for sputtering having a large specific surface area. A target having a 20 mm square Ni plate, a 10 mm square Pd plate and various metal elements placed on a circumference of a radius of 29 mm from the center of a Ta disk having a diameter of 100 mm and a thickness of 6 mm is shown in FIG. Using the device, A
2 × 10 4 To while flowing r at a rate of 5 ml / min
A vacuum deposition of rr was carried out, and sputter deposition was performed at an output of about 400 W on the rotating and revolving substrate. As a result of X-ray diffraction of an alloy simultaneously deposited using a glass plate as a direct substrate, it was confirmed that the resulting alloy was amorphous. The composition of the amorphous alloy was analyzed using an X-ray microanalyzer. 1g of these catalysts, 8mm inner diameter and 500mm length
The central part of the quartz tube of NO is filled with NO in He at 5000p.
Gas containing pm is flowed at a speed of 30 ml / min to 900
The gas after the reaction was analyzed by gas chromatography at 0 ° C. The results are shown in Table 3.

Table 3 Amorphous alloy composition of a catalyst prepared by coating an amorphous alloy on a glass plate supporting the fine alumina powder of the present invention and NO conversion to N ₂ and O _{2 at} 900 ° C. (%) Alloy composition ( Atomic%) Conversion rate of NO to N ₂ and O 2 at 900 ° C. (%) Ni-10Ta-0.5Pd 50 Ni-16Ta-26Pd 80 Ni-20Ta-10Pd 70 Ni-20Ta-20Pd 78 Ni-20Ta- 40Pd 90 Ni-30Ta-0.5Pd 48 Ni-30Ta-10Pd 65 Ni-30Ta-20Pd 75 Ni-30Ta-40Pd 81 Ni-40Ta-0.5Pd 45 Ni-40Ta-10Pd 62 Ni-40Ta-14Pd 65 Ni- 40Ta-20Pd 72 Ni-40Ta-30Pd 76 Ni-50 Ta-0.5Pd 42 Ni-50Ta-10Pd 61 Ni-50Ta-20Pd 69 Ni-10Co-20Ta-40Pd 85 Ni-5Co-20Ta-40Pd 87 Ni-1Co-20Ta-40Pd 90 Ni-10Co-30Ta-40Pd 75 Ni-5Co-30Ta-40Pd 78 Ni-1Co-30Ta-40Pd 81 Ni-10Co-40Ta-30Pd 70 Ni-5Co-40Ta-30Pd 73 Ni-1Co-40Ta-30Pd 76 Ni-10Co-50Ta-20Pd 60 Ni- 5Co-50Ta-20Pd 65 Ni-1Co-50Ta-20Pd 69 Ni-20Ti-40Pd 65 Ni-1Ta-20Ti-40Pd 65 Ni-5Ta-20Ti-40Pd 62 Ni-10Ta-20Ti- 0Pd 61 Ni-20Ta-20Ti-30Pd 58 Ni-30Ta-20Ti-20Pd 50 Ni-20Zr-40Pd 50 Ni-1Ta-20Zr-40Pd 50 Ni-5Ta-20Zr-40Pd 48 Ni-10Ta-20Zr-40Pd 45. 20Ta-20Zr-30Pd 42 Ni-30Ta-20Zr-20Pd 40 Ni-20Nb-40Pd 65 Ni-1Ta-20Nb-40Pd 65 Ni-5Ta-20Nb-40Pd 63 Ni-10Ta-20Nb-40Pd 62Ni-20-20a- 30Pd 59 Ni-30Ta-20Nb-20Pd 51 Ni-30Ti-40Pd 55 Ni-10Ta-30Ti-30Pd 45 Ni-20Ta-30Ti-20Pd 38 Ni-30Zr-40P 45 Ni-10Ta-30Zr-30Pd 38 Ni-20Ta-30Zr-20Pd 31 Ni-30Nb-40Pd 56 Ni-10Ta-30Nb-30Pd 43 Ni-20Ta-30Nb-20Pd 37 Ni-40Ti-30Pd 42Ni-10Ta-40 -20Pd 34 Ni-40Zr-40Pd 35 Ni-10Ta-40Zr-30Pd 28 Ni-40Nb-40Pd 43 Ni-10Ta-40Nb-30Pd 31 Ni-10Co-20Ti-40Pd 52 Ni-5Co-20Ti-40Pd 58 Ni-1Co. -20Ti-40Pd 65 Ni-10Co-20Zr-40Pd 39 Ni-5Co-20Zr-40Pd 46 Ni-1Co-20Zr-40Pd 50 Ni-10Co-20Nb-40Pd 51 i-5Co-20Nb-40Pd 55 Ni-1Co-20Nb-40Pd 65 Ni-10Ta-0.5Pd 48 Ni-10Ta-10Pd 65 Ni-10Ta-20Pd 75 Ni-10Ta-40Pd 85 Ni-15Ta-0.5Pd 52 Ni-15Ta-10Pd 69 Ni-15Ta-20Pd 82 Ni-15Ta-40Pd 91 Ni-10Co-10Ta-40Pd 80 Ni-5Co-10Ta-40Pd 82 Ni-1Co-10Ta-40Pd 85 Ni-10Co-15Ta-40Pd 77 Ni-5Co-15Ta-40Pd 80 Ni-1Co-15Ta-40Pd 91 Ni-10Zr-40Pd 55 Ni-1Ta-10Zr-40Pd 55 Ni-5Ta-10Zr-40Pd 51 Ni-10Ta-10Z r-40Pd 47 Ni-20Ta-10Zr-40Pd 43 Ni-30Ta-10Zr-30Pd 41 Ni-40Ta-10Zr-20Pd 41 Ni-10Ti-40Pd 70 Ni-1Ta-10Ti-40Pd 70 Ni-5Ta-10Ti-40Pd 68 Ni-10Ta-10Ti-40Pd 64 Ni-20Ta-10Ti-40Pd 62 Ni-30Ta-10Ti-30Pd 55 Ni-40Ta-10Ti-20Pd 50 Ni-10Nb-40Pd 71 Ni-1Ta-10Nb-40Pd 71 Ni-5Ta- 10Nb-40Pd 67 Ni-10Ta-10Nb-40Pd 64 Ni-20Ta-10Nb-40Pd 62 Ni-30Ta-10Nb-30Pd 55 Ni-40Ta-10Nb-20Pd 50 Ni-1 Co-10Ti-40Pd 55 Ni-5Co-10Ti-40Pd 66 Ni-1Co-10Ti-40Pd 70 Ni-10Co-10Zr-40Pd 42 Ni-5Co-10Zr-40Pd 49 Ni-1Co-10Zr-40Pd 55 Ni-10Co- 10Nb-40Pd 54 Ni-5Co- 10Nb-40Pd 64 Ni-1Co-10Nb-40Pd degradation at 70 Comparative example Cu-ZSM- ₅ 500 ℃ or more catalytically active reduced Ag-Co ₃ O ₄ 700 ℃ or Co ₃ O ₄ 700 Deterioration above ℃ La ₁₅ Sr _0.5 CuO ₄ 40 (800 ℃) BaFeO _3-x 19 (800 ℃) As described above, the catalyst of the present invention, which is obtained by coating the alumina fine powder with the amorphous alloy, is a high-performance catalyst for NOx decomposition. .

[0021]

As described above, the catalyst of the present invention in which the ceramic having a large specific surface area is coated with the amorphous alloy is a high-performance catalyst for decomposing NOx.

Further, the highly active catalyst for decomposing NOx of the present invention is excellent in practicability since it can be easily formed on a suitable ceramic having a large specific surface area by the PVD method.

[Brief description of drawings]

FIG. 1 is a schematic head showing an example of a sputtering apparatus for producing an amorphous alloy of the present invention.

[Explanation of symbols]

 1 Substrate's revolution axis 2 Rotating substrate 3 Target 6 Target 6 Sputter chamber

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B01J 37/02 301 P C22C 45/04 D C23C 14/18 8939-4K (72) Inventor Katsuhiko Asami 2-5-3 Taichiro, Taichiro-ku, Sendai-shi, Miyagi Prefecture 72-72 Inventor Hiroki widthzaki 6-10-111, Nagamachi, Taichiro-ku, Sendai-shi Miyagi Prefecture (72) Eiji Akiyama 2-chome, Mukaiyama, Taichiro-ku, Sendai-shi, Miyagi Prefecture 13-5 High Rubens 210

Claims (5)

[Claims] 1. Ta: 10-50 atomic%, Pd: 0.5
A catalyst for NOx decomposition in which a ceramic is coated with an amorphous alloy containing -40 atom% and the balance substantially 30 atom% or more of Ni by PVD method. 2. Ta of 10-50 atomic% and Pd of 0.5
-40 atomic% and Co less than 10 atomic% with the balance being substantially N
A catalyst for NOx decomposition in which an amorphous alloy containing i and containing 30 atomic% or more of Ni and Co in total is coated on ceramics by a PVD method. 3. A total of less than 50 atomic% Ta and at least one of Nb, Ti and Zr is 10-50 atomic%,
A catalyst for NOx decomposition in which a ceramic is coated with an amorphous alloy containing 0.5 to 40 atomic% of Pd and the balance of substantially 30 atomic% or more of Ni by a PVD method. 4. A total of Ta of less than 50 atomic% and at least one of Nb, Ti and Zr is 10-50 atomic%,
NOx decomposition in which Pd is 0.5-40 atomic% and Co is less than 10 atomic% and the balance substantially consists of Ni, and an amorphous alloy containing 30 atomic% or more in total of Ni and Co is coated on ceramics by the PVD method. Catalyst. 5. The catalyst for decomposing NOx according to claim 1, wherein the ceramic is powdery or molded porous.