JP2012223768A - Catalyst and method for decomposing ammonia - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decompose ammonia, particularly, the ammonia which is contained in a gas, in a wide range from low concentration to high concentration.SOLUTION: A catalyst for decomposing ammonia is obtained by depositing at least one element (platinum group element) of group 8-10 elements on a metal oxide (metal oxide having low acid strength) having ≥-5.6 acid strength (Hconstant). It is preferable that the metal oxide having low acid strength is aluminum oxide, cerium oxide, magnesium oxide or titanium oxide.

Description

  The present invention provides a catalyst for decomposing ammonia and a method for decomposing ammonia using the catalyst.

  Ammonia is odorous and needs to be treated when it is contained in a gas. Conventionally, a treatment method has been proposed, for example, a method in which oxygen and ammonia are brought into contact with each other to oxidize and decompose, and ammonia is converted to hydrogen. Methods have been proposed. For example, there is a method of decomposing ammonia generated from a coke oven using a platinum alumina catalyst, a manganese alumina catalyst, and an iron alumina catalyst in the presence of air to obtain hydrogen (Patent Document 1). It is often undesirable that new NOx treatment facilities are required, and the ammonia gas generated from the organic waste treatment process is decomposed using nickel, alkaline earth, alumina carrying lanthanoids, silica, etc. to generate hydrogen. However, this method has a low conversion rate and is not practical. Furthermore, in the treatment of ammonia generated from a coke oven, conventional catalysts are iron alumina, platinum alumina, and ruthenium alumina, whereas ammonia is decomposed and hydrogen is decomposed using a catalyst in which ruthenium, alkali metal, and alkaline earth metal are supported on alumina. In this method (Patent Document 3), the conversion rate is low and not practical and not preferable.

JP-A 64-56301 JP 2004-195454 A JP-A-01-119341

  The present invention is a catalyst that can be efficiently decomposed over a wide range of ammonia concentrations from low to high.

As a method for solving the above-mentioned problems, the present inventors have conducted intensive studies, and at least one element of group 8 to group 10 elements (hereinafter also referred to as “platinum group element”) and acid strength (H ₀ constant). Including a metal oxide (hereinafter also referred to as “low acid strength oxide”) having a specific surface area of 5 to 300 m ² / g in nitrogen and hydrogen. The inventors have found a method for decomposing ammonia using an ammonia decomposing catalyst to be converted, and have completed the invention.

  By using the present invention, ammonia, particularly ammonia contained in a gas, can be decomposed over a wide range from a low concentration to a high concentration.

The first invention of the present invention is a metal having at least one element of Group 8 to Group 10, an acid strength (H ₀ constant) of −5.6 or more and a specific surface area of 5 to 300 m ² / g. An ammonia decomposition catalyst comprising an oxide (low acid strength oxide), preferably an acid strength (H ₀ constant) of at least one element of Group 8 to Group 10 elements of −5.6. Ammonia decomposition catalyst supported on the above metal oxide (low acid strength oxide), preferably aluminum oxide, cerium oxide, magnesium oxide, niobium oxide, titanium oxide, vanadium oxide, tantalum oxide, hafnium oxide, yttrium oxide Lanthanum oxide, neodymium oxide, more preferably at least selected from the group consisting of aluminum oxide, cerium oxide, magnesium oxide and titanium oxide Both are kind.

The specific surface area of the low acid strength oxide is preferably 1 to 300 m ² / g.

  The second invention of the present invention is an ammonia decomposing method characterized by decomposing ammonia using the catalyst. Preferably, the ammonia is obtained by decomposing urea, at 180 to 950 ° C. Ammonia decomposition. The present invention is described in detail below.

  Any element may be used as long as it is at least one element of Group 8 to Group 10, but preferably at least one element selected from the group consisting of platinum, palladium, rhodium, ruthenium, iron, cobalt and nickel. More preferred is ruthenium and / or iron, and most preferred is ruthenium.

  As a raw material of at least one element of Group 8 to Group 10, metals, hydroxides, oxides, carbonates, nitrates, chlorides, nitrosyl nitrates, sulfates, and carbonyl complexes can be used. Are nitrates, chlorides, nitrosyl nitrates, carbonyl complexes.

The low acid strength oxide has an acid strength (H ₀ constant) of −5.6 or more, preferably −5.6 to +1.5, and most preferably +1.5 or more. The H ₀ constant is the acid strength expressed using the Hammett acidity function. Any metal oxide may be used as long as the H ₀ constant exhibits the above value, but α-alumina, aluminum oxide, cerium oxide, magnesium oxide, titanium oxide, niobium oxide, vanadium oxide, tantalum oxide, and oxide are preferable. Hafnium, yttrium oxide, lanthanum oxide, and neodymium oxide, and more preferably at least one selected from the group consisting of aluminum oxide, cerium oxide, magnesium oxide, and titanium oxide. These oxides can be used as single oxides or complex oxides. Moreover, even if it is an oxide of the same composition, that whose acid strength is in the said range is preferable.

  In addition to oxides, raw materials for the low acid strength oxides may be oxides such as nitrates and carbonates that are converted to oxides by thermal decomposition.

  The acid strength measurement method is a method of measuring the acid strength of the solid surface with an indicator. Specifically, about 0.1 g of a sample is put in a test tube, and 3 to 5 mL of benzene is added. A method of observing a color change when a small amount of a benzene solution containing an indicator of 0.1% by mass is added can be used.

The low acid strength oxide having a specific surface area of 1~300m ² / g, it is preferred that preferably 5~260m ² / g, further 20 to 200 m ² / g. The BET method is used as a method for measuring the specific surface area. For example, even if it is an oxide of the same composition, it is preferable that it is an oxide within the above range.

  The amount of at least one element of Group 8 to Group 10 elements (in metal equivalent) is 0.1 to 50 parts by weight, preferably 0.5 to 20 parts by weight, based on 100 parts by weight of the low acid strength oxide. More preferably, it is 1.0-6.0 mass parts.

  Other components can be added (added component) to the catalyst, for example, an alkali metal, preferably at least one selected from the group consisting of cesium, rubidium and potassium. The amount of the additive component is 1 to 40 parts by mass, preferably 3 to 20 parts by mass with respect to 100 parts by mass of the low acid strength oxide in terms of element.

  As the ammonia gas, ammonia can be generally used, and ammonia may be generated by thermal decomposition or the like like urea. The ammonia gas may contain other components as long as they do not cause catalyst poisoning.

Ammonia gas per pair catalyst, at SV (space velocity), 1000~20000hr ^-1, preferably 2000～15000Hr ^-1, and most preferably 3000~10000hr ^-1. In addition, per catalyst is the volume of ammonia gas per unit time per volume occupied when the catalyst is packed in the reactor.

  The reaction temperature is 180 to 950 ° C, preferably 300 to 900 ° C, more preferably 400 to 800 ° C. The reaction pressure is 0.002 MPa to 2 MPa, preferably 0.004 MPa to 1 MPa.

  As a method for preparing the catalyst, a general method can be used, a method of mixing a low acid strength oxide and a platinum group element, a method of impregnating a low acid strength oxide with an aqueous solution of a platinum group element, an aqueous solution A method of chemically adsorbing the platinum group element contained in the liquid to the low acid strength oxide can be used. The impregnation method is preferred. More specifically, the preparation method shows a water absorption amount (volume) of the dried low acid strength oxide, and a solution whose concentration is adjusted so that the amount of the platinum group element to be impregnated is just the volume. Is gradually soaked into the dried low acid strength oxide while stirring.

  The catalyst according to the present invention may be in any form as long as it contains at least one element of a platinum group element and a low acid strength oxide. Although it may be in the form of a mixture or in the form of supporting at least one element of a platinum group element on a low acid strength oxide, the latter is preferable.

  Hereinafter, the present invention will be described in detail with reference to examples and comparative examples, but the present invention is not limited to the following examples unless it is contrary to the gist of the present invention.

Example 1
(Catalyst A)
13.365 g of a ruthenium aqueous solution having a ruthenium content of 3.938% by mass is impregnated uniformly into 10 g of a carrier of γ-alumina (BET specific surface area 130 m ² / g), so that it becomes 5% by mass in terms of Ru. After the adjustment, drying was performed at 90 to 120 ° C. Thereafter, hydrogen reduction was performed at 400 ° C. for 4 hours. Ru / Al ₂ O ₃ was obtained.

(Ammonia decomposition reaction)
An ammonia decomposition reaction was performed using ammonia having a purity of 99.9% or more. As a result of carrying out at 300 ° C., SV = 6000 hr ⁻¹ , and normal pressure, the decomposition rate was 7.1%. The result when changing to SV = 15000 hr ⁻¹ was a decomposition rate of 4.5%.

(Example 2)
(Catalyst B)
13.365 g of ruthenium nitrate aqueous solution (manufactured by Tanaka Kikinzoku) with a ruthenium content of 3.938% by mass was impregnated uniformly into 10 g of a carrier of γ-alumina (manufactured by JGC, surface area of 166 m ² / g), and converted to Ru. After adjusting so that it might become 5 mass%, it dried at 90-120 degreeC. Thereafter, hydrogen reduction was performed at 400 ° C. for 4 hours. Ru / Al ₂ O ₃ was obtained.

(Ammonia decomposition reaction)
An ammonia decomposition reaction was performed using ammonia having a purity of 99.9% or more. As a result of carrying out at 300 ° C., SV = 6000 hr ⁻¹ , and normal pressure, the decomposition rate was 3.7%.

(Example 3)
(Catalyst C)
Ce (NO ₃ ) ₃ · 6H ₂ O was dissolved in water to form a 0.2N solution, pH was adjusted to 10 with 5% aqueous ammonia, a precipitate was formed, stirred, allowed to stand, filtered with suction, and washed with pure water. After drying at 100 ° C., calcination was performed in air at 500 ° C. for 3 hours to obtain a CeO ₂ carrier. This was impregnated with a solution in which ruthenium carbonyl Ru ₃ (CO) ₁₂ was dissolved in THF in a mayonnaise bottle. After stirring overnight, the THF was removed with an evaporator, and the temperature was raised to 350 ° C. in nitrogen. The reduction treatment was performed at 350 to 400 ° C. for 4 hours in a hydrogen stream to obtain 2.45 mass% Ru / CeO ₂ . It was 29 m < ² > / g as a result of measuring a BET surface area.

(Ammonia decomposition reaction)
An ammonia decomposition reaction was performed using ammonia having a purity of 99.9% or more. As a result of carrying out at 300 ° C., SV = 6000 hr ⁻¹ , and normal pressure, the decomposition rate was 7.8%. The result when changing to SV = 15000 hr ⁻¹ was a decomposition rate of 4.4%.

Example 4
(Catalyst D)
Basic magnesium carbonate was calcined at 500 ° C. for 3 hours to obtain an MgO carrier. In the catalyst C, except for changing the CeO ₂ support the MgO support by the same preparation method a catalyst C, was obtained 2.44 wt% Ru / MgO. As a result of measuring the BET surface area, it was 126 m ² / g.

(Ammonia decomposition reaction)
An ammonia decomposition reaction was performed using ammonia having a purity of 99.9% or more. As a result of carrying out at 300 ° C., SV = 6000 hr ⁻¹ , and normal pressure, the decomposition rate was 2.7%.

(Example 5)
(Catalyst E)
In the catalyst C, 2.44 mass% Ru / TiO ₂ was obtained by the same preparation method as the catalyst C except that the CeO ₂ support was changed to a rutile type titanium oxide support.

(Ammonia decomposition reaction)
An ammonia decomposition reaction was performed using ammonia having a purity of 99.9% or more. As a result of carrying out at 300 ° C., SV = 6000 hr ⁻¹ , and normal pressure, the decomposition rate was 3.3%.

(Example 6)
(Catalyst F)
Using cesium nitrate, prepare an aqueous solution so that the impregnating liquid having the same volume as the water absorption amount of the dried catalyst A becomes Cs / Ru = 1 (molar ratio), so that it is uniform with respect to the catalyst A. Impregnated. Hydrogen treatment at 400 ° C. was performed for 4 hours to obtain Cs—Ru / Al ₂ O ₃ (Cs / Ru = 1 molar ratio). As a result of measuring the BET surface area, it was 103 m ² / g.

(Ammonia decomposition reaction)
An ammonia decomposition reaction was performed using ammonia having a purity of 99.9% or more. As a result of carrying out at 300 ° C., SV = 6000 hr ⁻¹ and normal pressure, the decomposition rate was 37.5%. The result of changing to SV = 15000 hr ⁻¹ was a decomposition rate of 25.9%. The result at 200 ° C., SV = 6000 hr ⁻¹ , and normal pressure was a decomposition rate of 3.3%. The result when changing to SV = 15000 hr ⁻¹ was a decomposition rate of 1.9%. As a result of carrying out at 450 ° C., SV = 3500 hr ⁻¹ and normal pressure for 25 hours, the decomposition rate was 96.2 to 99.3%. Thereafter, the decomposition rate was 96.0% when carried out at 400 ° C. and SV = 3000 hr ⁻¹ . The result of changing to SV = 6000 hr ⁻¹ was a decomposition rate of 92.9%. When the reaction temperature was carried down to 350 ° C., SV = 3000 hr decomposition rate 73.7% at ^-1, with a degradation rate of 65.6% at SV = 6000 hr ^-1. When the reaction temperature was raised to 500 ° C., SV = 3500 hr ⁻¹ and 7000 hr ⁻¹ both had a decomposition rate of 100%. The results of measuring the decomposition rate at 600 ° C. and 750 ° C. were 100% for both SV = 3500 and 7000.

(Example 7)
(Catalyst G)
In catalyst F, Rb—Ru / Al ₂ O ₃ (Rb / Ru = 1 molar ratio) was obtained in the same manner as catalyst F, except that rubidium nitrate was used instead of cesium nitrate.

(Ammonia decomposition reaction)
An ammonia decomposition reaction was performed using ammonia having a purity of 99.9% or more. As a result of carrying out at 300 ° C., SV = 6000 hr ⁻¹ , and normal pressure, the decomposition rate was 26.0%.

(Example 8)
(Catalyst H)
In the catalyst F, K-Ru / Al ₂ O ₃ (K / Ru = 1 molar ratio) was obtained by the same method as the catalyst F except that potassium nitrate was used instead of cesium nitrate.

(Ammonia decomposition reaction)
An ammonia decomposition reaction was performed using ammonia having a purity of 99.9% or more. As a result of carrying out at 300 ° C., SV = 6000 hr ⁻¹ and normal pressure, the decomposition rate was 20.0%.

Example 9
(Catalyst I)
In the catalyst F, Ru / _Al 2 _{O 3} to changing the catalyst _{C (Ru / Al 2 O 3} ) except for using is impregnated with cesium in the same preparation method as catalysts _{F, Cs-Ru / CeO 2} (Cs / Ru = 1 molar ratio) was obtained. The result of measuring the BET surface area was 24 m ² / g.

(Ammonia decomposition reaction)
An ammonia decomposition reaction was performed using ammonia having a purity of 99.9% or more. As a result of carrying out at 300 ° C., SV = 6000 hr ⁻¹ , and normal pressure, the decomposition rate was 31.4%. The result when changing to SV = 15000 hr ⁻¹ was a decomposition rate of 21.3%. The result at 200 ° C., SV = 6000 hr ⁻¹ , and normal pressure was a decomposition rate of 2.6%. The result when changing to SV = 15000 hr ⁻¹ was a decomposition rate of 1.6%.

(Example 10)
(Catalyst J)
In the catalyst F, except that the ratio of Cs / Ru was changed to Cs / Ru = 8 (molar ratio), Cs—Ru / Al ₂ O ₃ (Cs / Ru = 8 molar ratio) Obtained. It was 46 m < ² > / g as a result of measuring a BET surface area.

(Ammonia decomposition reaction)
An ammonia decomposition reaction was performed using ammonia having a purity of 99.9% or more. As a result of carrying out at 300 ° C., SV = 6000 hr ⁻¹ , and normal pressure, the decomposition rate was 32.4%. The result when changing to SV = 15000 hr ⁻¹ was a decomposition rate of 21.0%. As a result of carrying out at 200 ° C., SV = 6000 hr ⁻¹ , and normal pressure, the decomposition rate was 3.1%. The result when changing to SV = 15000 hr ⁻¹ was a decomposition rate of 1.5%.

(Example 11)
(Catalyst K)
Except for changing the Cs / Ru = 8 (molar ratio) was performed in the same preparation method a catalyst I, was obtained _Cs-Ru / CeO 2 and (Cs / Ru = 8 molar ratio).

(Ammonia decomposition reaction)
An ammonia decomposition reaction was performed using ammonia having a purity of 99.9% or more. As a result of carrying out at 300 ° C., SV = 6000 hr ⁻¹ , and normal pressure, the decomposition rate was 16.6%. The result when changing to SV = 15000 hr ⁻¹ was a decomposition rate of 10.2%.

(Example 12)
(Catalyst L)
Ce (NO ₃ ) ₃ · 6H ₂ O was dissolved in water to form a 0.2N solution, pH was adjusted to 10 with 5% aqueous ammonia, a precipitate was formed, stirred, allowed to stand, filtered with suction, and washed with pure water. After drying at 100 ° C., calcination was performed in air at 500 ° C. for 3 hours to obtain a CeO ₂ carrier. Ni (NO ₃ ) ₂ · 6H ₂ O was dissolved in methanol, and the resulting CeO ₂ was impregnated. Firing was performed in air at 500 ° C. for 1 hour, and after evacuation, reduction was performed in hydrogen for 12 hours. Ni / CeO ₂ was obtained. This was impregnated with a solution in which ruthenium carbonyl Ru ₃ (CO) ₁₂ was dissolved in THF in a mayonnaise bottle, and after stirring was continued overnight, the THF was removed by an evaporator, vacuum dried to 400 ° C., 350 to 400 Reduction treatment was performed in a hydrogen stream at 4 ° C. for 4 hours. 0.48 mass% Ni-2.45 mass% Ru / CeO ₂ was obtained.

(Ammonia decomposition reaction)
An ammonia decomposition reaction was performed using ammonia having a purity of 99.9% or more. As a result of carrying out at 300 ° C., SV = 6000 hr ⁻¹ , and normal pressure, the decomposition rate was 9.0%. The result when changing to SV = 15000 hr ⁻¹ was a decomposition rate of 5.1%.

(Comparative Example 1)
(Catalyst E)
The same preparation method as catalyst B was carried out except that silica alumina (manufactured by JGC, surface area 196 m ² / g, SiO ₂ : 67.5 mass%, Al ₂ O ₃ : 25.6 mass%) was used as the carrier. Mass% Ru / SiO ₂ · Al ₂ O ₃ was obtained.

(Ammonia decomposition reaction)
An ammonia decomposition reaction was performed using ammonia having a purity of 99.9% or more. As a result of carrying out at 300 ° C., SV = 6000 hr ⁻¹ , and normal pressure, the decomposition rate was 1.7%.

  The present invention relates to the decomposition of ammonia, and can be applied to an environmental field in which a gas having an ammonia odor is not brominated, and a field in which ammonia is converted to nitrogen or hydrogen.

Claims (2)

At least one element of group 8 to group 10 elements (hereinafter also referred to as “platinum group element”), an acid strength (H ₀ constant) of −5.6 or more, and a specific surface area of 5 to 300 m ² / g An ammonia decomposition catalyst for converting ammonia into nitrogen and hydrogen, characterized in that it contains a metal oxide (hereinafter also referred to as “low acid strength oxide”). Ammonia decomposition method, wherein ammonia is converted to nitrogen and hydrogen using the catalyst according to claim 1.