JP2012223769A - Method for producing ammonia decomposition catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an ammonia decomposition catalyst with which ammonia of a wide concentration range from low concentration to high concentration can be efficiently decomposed.SOLUTION: The ammonia decomposition catalyst contains: at least one element (active element) selected from the group comprising group 8-10 elements; a compound (addition component A) of an element having ≤1.3 Pauling's electronegativity; and a metal oxide. The method for producing the ammonia decomposition catalyst for converting ammonia into nitrogen and hydrogen comprises the steps of: measuring the amount (volume) of water to be absorbed in the metal oxide when producing the catalyst; impregnating the metal oxide with a solution the concentration of which is adjusted so that the amount of the active element to be impregnated becomes the measured volume exactly; and treating the impregnated metal oxide with hydrogen.

Description

  The present invention provides a method for producing ammonia decomposition for decomposing ammonia.

  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 result of diligent studies, the present inventors have determined that at least one element selected from the group consisting of Group 8 to Group 10 elements (hereinafter referred to as “active element”), electronegativity, A method for producing an ammonia decomposition catalyst comprising a compound of an element having a Pauling's electronegativity of 1.3 or less (hereinafter referred to as “additive component A”) and a metal oxide has been found and the invention has been completed. Is.

  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 present invention relates to at least one element selected from the group consisting of elements from Group 8 to Group 10 (hereinafter referred to as “active element”), a compound of an element having an electronegativity of 1.3 or less in Pauling's electronegativity (Hereinafter referred to as “additive component A”) and a metal oxide,
The amount of water absorption (volume) of the metal oxide is measured during the production of the catalyst, and a solution whose concentration is adjusted so that the amount of the active element to be impregnated is just the volume is soaked in the metal oxide.
Further, the present invention is a method for producing an ammonia decomposition catalyst which converts ammonia into nitrogen and hydrogen.

  Ammonia can be decomposed using the catalyst obtained by the present invention. Preferably, ammonia decomposition at 180 to 950 ° C., or one obtained by decomposing urea into urea can be used. The ammonia gas may contain other components as long as they do not cause catalyst poisoning.

  The active element may be any element as long as it is an element belonging to Group 8 to Group 10, but preferably at least selected from the group consisting of platinum, palladium, rhodium, ruthenium, iron, cobalt, and nickel. 1 type, more preferably ruthenium and / or iron, and most preferably ruthenium.

  As the raw material of the active element, metals, hydroxides, oxides, carbonates, nitrates, chlorides, nitrosyl nitrates, sulfates, and carbonyl complexes can be used, preferably nitrates, chlorides, nitrosyl nitrates, carbonyls. It is a complex.

  The additive component A has an electronegativity of 1.3 or less, preferably 0.7 to 1.12. For example, it is a compound showing alkalinity, preferably an alkali metal, an alkaline earth metal, and more preferably an alkali metal compound. The raw material of additive component A may be an oxide, hydroxide, sulfide, chloride, fluoride, bromide, phosphate, carbonate, or nitrate, but is preferably a hydroxide or nitrate.

  The metal oxide may be any oxide, but preferably aluminum oxide, cerium oxide, magnesium oxide, niobium oxide, titanium oxide, vanadium oxide, tantalum oxide, hafnium oxide, yttrium oxide, oxide At least one selected from the group consisting of lanthanum and neodymium oxide, 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.

  Further, depending on the case, additive component B can be used in combination, for example, at least one selected from the group consisting of Ni, Fe, Mo, Co, Pd, Pt and Rh. More preferred is ruthenium and / or iron, and most preferred is ruthenium.

  With respect to 100 parts by mass of the metal oxide, the active element (in metal equivalent) is 0.1 to 30 parts by mass, preferably 1 to 6, and the additive component A (in element equivalent) is 1 to 40 parts by mass. Preferably it is 3-20.

As the ammonia gas, ammonia can be generally used, and ammonia may be generated by thermal decomposition or the like like urea. Ammonia 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, generally, a method can be used. A method of mixing an active element, an additive component A and a metal oxide, drying and firing appropriately (mixing method), an active element, and the additive component A being an aqueous liquid And a method of impregnating a metal oxide (impregnation method), a method of chemically adsorbing an active element contained in an aqueous liquid to a mixture of an additive component and a metal oxide (chemical adsorption method), etc. Preferably, it is a method of impregnation.

  More specifically, the preparation method is to measure the water absorption (volume) of the dried metal oxide, and dry the solution whose concentration is adjusted so that the amount of the active element to be impregnated is just the volume. In this method, the metal oxide is gradually soaked with stirring.

  The catalyst may be in any form as long as it contains an active element, an additive component, and a metal oxide, but is preferably a mixture of the active element, additive component, and metal oxide, active element, and additive component. Is supported on a metal oxide. A supported form is preferred.

  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 uniformly impregnated into 10 g of a carrier of γ-alumina (BET specific surface area 103 m ² / g), so that it is 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. 5 wt% Ru / _Al 2 _{O 3} was obtained. Next, 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 is Cs / Ru = 1 (molar ratio), so that it is uniform with respect to the catalyst. 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 lowered to 350 ° C., the decomposition rate was 73.7% at SV = 3000, and the decomposition rate was 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%. Moreover, the result of measuring the decomposition rate at 600 ° C. and 750 ° C. was 100% for both SV = 3500 hr ⁻¹ and 7000 hr ⁻¹ .

(Example 2)
(Catalyst B)
In catalyst A, Rb—Ru / Al ₂ O ₃ (Rb / Ru = 1 molar ratio) was obtained in the same manner as in catalyst A, 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 3)
(Catalyst C)
In the catalyst A, K-Ru / Al ₂ O ₃ (K / Ru = 1 molar ratio) was obtained in the same manner as the catalyst A 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 4
(Catalyst D)
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 in a hydrogen stream at 350 to 400 ° C. for 4 hours. 2.45 mass% Ru / CeO ₂ was obtained. It was 29 m < ² > / g as a result of measuring a BET surface area. Csium was impregnated by the same preparation method as catalyst A to obtain Cs-Ru / CeO ₂ (Cs / Ru = 1 molar ratio). 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 5)
(Catalyst E)
The catalyst A was prepared in the same manner as the catalyst A except that Cs / Ru = 1 (molar ratio) was changed to Cs / Ru = 8 (molar ratio), and Cs-Ru / Al ₂ O ₃ (Cs / Ru = 8 molar ratio). 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 6)
(Catalyst F)
Cs-Ru / CeO ₂ (Cs / Ru = 8 molar ratio) in the same preparation method as catalyst D except that Cs / Ru = 1 (molar ratio) was changed to Cs / Ru = 8 (molar ratio) in catalyst D Got.
(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 7)
(Catalyst G)
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. 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 in a hydrogen stream at 350 to 400 ° 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 H)
5% Ru / Al ₂ O ₃ manufactured by Wako Pure Chemical (first grade) was compression molded for reaction evaluation. As a result of measuring the BET surface area, it was 130 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, 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%. There was no activity at 200 ° C. and SV = 6000 hr ⁻¹ .

(Comparative Example 2)
(Catalyst I)
A CeO ₂ carrier was obtained using Ce (NO ₃ ) ₃ .6H ₂ O by the same adjustment method as that for catalyst D. In the same manner as Catalyst D, ruthenium carbonyl Ru ₃ (CO) ₁₂ was impregnated and reduced 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%. There was no activity at 200 ° C. and SV = 6000 hr ⁻¹ .

  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 (1)

At least one element selected from the group consisting of Group 8 to Group 10 elements (hereinafter referred to as “active element”), a compound of an element having an electronegativity of 1.3 or less in Pauling's electronegativity (hereinafter referred to as “ A catalyst comprising a metal oxide, referred to as additive component A ”,
The amount of water absorption (volume) of the metal oxide is measured during the production of the catalyst, and a solution whose concentration is adjusted so that the amount of the active element to be impregnated is just the volume is soaked in the metal oxide.
A method for producing an ammonia decomposition catalyst for converting ammonia into nitrogen and hydrogen, further characterized by hydrogen treatment.