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Composite oxide, metal-supported material, and ammonia synthesis catalyst

Foreign code F210010549
File No. AF40-05WO
Posted date 2021年8月2日
Country 欧州特許庁(EPO)
Application number 19799121
Gazette No. 3805159
Date of filing 令和元年5月7日(2019.5.7)
Gazette Date 令和3年4月14日(2021.4.14)
International application number JP2019018225
International publication number WO2019216304
Date of international filing 令和元年5月7日(2019.5.7)
Date of international publication 令和元年11月14日(2019.11.14)
Priority data
  • 特願2018-089516 (2018.5.7) JP
  • 2018JP34515 (2018.9.18) WO
  • 特願2019-059200 (2019.3.26) JP
  • 2019JP18225 (2019.5.7) WO
Title Composite oxide, metal-supported material, and ammonia synthesis catalyst
Abstract The present invention is a composite oxide including a metal element represented by the composition of general formula (6), wherein the composite oxide comprises an oxide of A and an oxide of X in a mixed state. General formula (6) : AnXy (in the general formula (6), A represents an element selected from the group consisting of Sc, Y, and a trivalent lanthanoid; X represents an element selected from the group consisting of Ca, Sr, and Ba; n is 0 < n < 1; y is 0 < y < 1; and n + y = 1). The present invention is also a metal-supported material in which cobalt particles are supported on the composite oxide.
Outline of related art and contending technology Background Art
Ammonia is an important raw material in the modern chemical industry. Not less than 80% of the ammonia produced is used to produce chemical fertilizers for cultivated crops. In addition, ammonia has received much attention as an energy and hydrogen carrier. This is because (1) the hydrogen content in ammonia is high (17.6wt%), (2) the energy density of ammonia is high (12.8 GJ/m3) , and (3) carbon dioxide is not generated when ammonia is decomposed to produce hydrogen. If ammonia can be efficiently produced from renewable energy such as solar energy and wind power, global problems related to the energy and food crisis will be mitigated.
Currently, the Harber-Bosch process used to produce ammonia consumes a large amount of energy, which accounts for about 1 to 2% of the world' s energy consumption. In this method, about 60% of the consumed energy is recovered and secured as the enthalpyof ammonia. However, most of the remaining energy is lost during the production of hydrogen from natural gas, the synthesis of ammonia, and the separation of the gas. Since ammonia synthesis by the Harber-Bosch process is performed at very high temperatures (>450°C) and high pressures (>20 MPa), it is required to reduce the large amount of energy used in this process. To reduce global energy consumption, a catalyst that can synthesize ammonia under milder conditions (lower temperature and lower pressure) than iron-based catalysts used in the Harber-Bosch process has been required.
Recently, a method for producing ammonia under a low-pressure condition of about 1 MPa (10 atm pressure) is known. A ruthenium catalyst used for ammonia production is generally supported on a carrier. For example, Patent Literature 1 discloses that when a rare earth oxide is used as a carrier for supporting ruthenium, the amount of ruthenium used can be reduced and the reaction temperature can be lowered. However, in the ammonia production method of Patent Literature 1, the ammonia yield when producing ammonia under a lower pressure condition is not satisfactory. Therefore, the present inventors have developed a ruthenium catalyst using La0.5Ce0.5O1.75 reduced at 650°C as a support and reported that such a catalyst exhibits excellent characteristics even under low pressure conditions (Non Patent Literature 4).
In addition to Patent Literature 1 and Non Patent Literature 4, ammonia synthesis catalysts in which ruthenium is supported on various rare earth oxide supports are disclosed in various patent literatures. Typical examples include Patent Literatures 2 to 4 and Non Patent Literatures 1 to 3. Patent Literatures 2 and 4 disclose lanthanoid oxides, Patent Literature 3 discloses praseodymium oxide, and Non Patent Literature 1 discloses Ce oxide as supports. Non Patent Literature 2 discloses a Ru/CeO2-La2O3-based catalyst produced by coprecipitation of hydroxides of Ru, Ce, and La, followed by drying and activating.
Prior art literatures including Patent Literatures 1, 2, and 4, and Non Patent Literature 1 describe that ruthenium catalysts used for ammonia synthesis have Ru as particles on the support surface. There is a report that when Ru is present as particles, the average diameter is greater than 5 nm (see Non Patent Literature 2), and there is a report that the average diameter of such Ru particles is less than 2 nm (Non Patent Literature 4). Further, Patent Literature 3 describes that Ru has an egg-shell structure.
On the other hand, regarding the support, Non Patent Literature 3 discloses that for the support oxide before supporting Ru in evaluating an ammonia synthesis activity of an Ru-supported Y(La)-M-O (M is Ca, Sr, or Ba) catalyst, the support oxide with a calcination temperature of 450°C had a large specific surface area, and the support with a calcination temperature increased to 650°C had a reduced specific surface area.
In view of the fact that Ru is expensive, an ammonia synthesis catalyst in which a transition metal compound other than Ru, such as Co, is supported on a support has also been proposed (see, for example, Non Patent Literature 5 and Non Patent Literature 6). However, Non Patent Literature 6 discloses Co-BaO/C in which cobalt was supported on barium oxide, but its ammonia synthesis activity was low. Further, in Non Patent Literature 5, calcium amide (Co/Ba-Ca(NH2)2)) is used instead of the oxide, but the ammonia yield at 1 MPa of the Co-supported catalyst was not as good as the catalyst on which Ru was supported.
Catalysts for synthesis are generally required to have high synthesis activity. There is a continuing need for highly active ruthenium catalysts for ammonia synthesis that are still under development enabling higher yields. In an equilibrium reaction in which 2 moles of ammonia are synthesized from 1 mole of nitrogen and 3 moles of hydrogen, high pressure conditions should be more convenient in terms of chemical equilibrium in order to improve the ammonia yield. Therefore, it can be considered that the ammonia yield is improved by reacting at a pressure higher than 1 MPa instead of the reaction at 1 MPa. However, a known ruthenium catalyst for synthesizing ammonia is liable to decrease its catalytic activity due to poisoning with hydrogen. Many existing Ru-based catalysts aim at higher ammonia synthesis activity under low-pressure conditions than the Harber-Bosch method, but it is not suitable to improve the yield under high-pressure conditions.
In addition, since a catalyst is loaded into a synthesis reactor and used and needs to be replaced periodically, it is also required that the catalyst be easy to handle. As for ruthenium catalysts for ammonia synthesis, there is still a demand for improved handling.
Citation List
Patent Literature
Patent Literature 1: JP 6-079177 A
Patent Literature 2: JP 2013-111562 A
Patent Literature 3: WO 2016/133213 A
Patent Literature 4: JP 2017-018907 A

Non Patent Literature
Non Patent Literature 1: Y. Niwa and K. Aika, Chemistry Letters, (1996) 3-4
Non Patent literature 2: X. Luo et al., Catalysis Letters 133, 382 (2009)
Non Patent Literature 3: A. S. Ivanova et al., Kinetics and Catalysis, Vol.45, No.4, 2004, pp. 541-546. Translated from Kinetika i Kataliz, Vol. 45, No.4, 2004, pp. 574-579.
Non Patent Literature 4: Y. Ogura et al., "Efficient ammonia synthesis over a Ru/La0.5Ce0.5O1.75 catalyst pre-reduced at high temperature", Chemical Science, vol.9, pp. 2230-2237
Non Patent Literature 5: M. Kitano et al., Angew. Chem. Int. Ed., 130(2018)2678
Non Patent Literature 6: W. Gao et. al., ACS Catal., 7 (2017) 3654
Scope of claims [claim1]
1. A composite oxide comprising a metal element represented by the composition of general formula (6):
        AnXy     (6),

the composite oxide comprising an oxide of A and an oxide of X in a mixed state (in the general formula (6),
A represents an element selected from the group consisting of Sc, Y, and a trivalent lanthanoid;
X represents an element selected from the group consisting of Ca, Sr and Ba;
n is 0 < n < 1;
y is 0 < y < 1; and
n + y = 1) .

[claim2]
2. A composite oxide comprising a metal element represented by the composition of general formula (7):
        AnXyOx     (7),

the composite oxide comprising an oxide of A and an oxide of X in a mixed state (in the general formula (7),
A represents an element selected from the group consisting of Sc, Y, and a trivalent lanthanoid;
X represents an element selected from the group consisting of Ca, Sr and Ba;
n is 0 < n < 1;
y is 0 < y < 1;
n + y = 1; and
x represents the number of oxygen atoms necessary for the composite oxide to remain electrically neutral).

[claim3]
3. The composite oxide according to claim 1 or 2, wherein the A is selected from the group consisting of Sc, Y, La, Nd, Pm, Sm, Eu, Gd, Dy, Ho, Er, Tm, and Lu.

[claim4]
4. The composite oxide according to claim 1 or 2, wherein the A is La and X is Ba.

[claim5]
5. The composite oxide according to claim 1 or 2, wherein the amount of carbonate ions is 10 mol% or less with respect to the X.

[claim6]
6. The composite oxide according to claim 5, wherein oxide particles of the X are deposited on a surface of oxide particles of the A.

[claim7]
7. The composite oxide according to claim 1, comprising a metal element represented by the composition of general formula (6A):
        AnXyMm     (6A)
(in the general formula (6A),
A and X are as defined in claim 1;
M is any of a group 1 element, a group 2 element selected from the group consisting of Ca, Sr, and Ba, or a lanthanoid, in the periodic table, and represents an element different from the A and X;
n is 0 < n < 1;
y is 0 < y < 1;
m is 0 ≤ m < 1; and
n + y + m = 1) .

[claim8]
8. The composite oxide according to claim 7, comprising a tetragonal or cubic solid solution.

[claim9]
9. The composite oxide according to claim 7, wherein at least one of the elements A, X, and M included in the composite oxide is a strongly basic element having a partial negative charge (-δo) value of oxygen in the oxide state of 0.50 or more.

[claim10]
10. The composite oxide according to claim 7, wherein when the composition ratio of each element contained in the composite oxide is expressed as ni (i shows all elements in the composite oxide including A, X, M, and O) and the Sanderson electronegativity of each element is expressed as χi (i shows all elements in the composite oxide including A, X, M, and O), the partial negative charge value (-δo) of oxygen represented by the following formula (A) is 0.52 or more.
Πχini∧1/Σni-5.21/-4.75

[claim11]
11. The composite oxide according to claim 7, wherein X in the general formula (6A) is Ba, and the amount of the carbonate ions contained in the composite oxide is 10 mol% or less with respect to Ba.

[claim12]
12. A metal-supported material, wherein cobalt particles are supported on the composite oxide according to claim 1.

[claim13]
13. The metal-supported material according to claim 12, wherein a layer comprising fine particles composed of the oxide of A and the oxide of X is provided on the cobalt particles.

[claim14]
14. The metal-supported material according to claim 12, wherein a ratio between the Co dispersity (Dads) determined by the H2 pulse chemisorption method and the Co dispersity (DTEM) expected from the average particle diameter of the Co particles determined from the TEM image satisfies the following formula:
0 < Dad/DTEM < 1.

[claim15]
15. The metal-supported material according to claim 12, wherein an average particle diameter of the cobalt particles supported on the composite oxide is 100 nm or less.

[claim16]
16. An ammonia synthesis catalyst using the metal-supported material according to claim 12.

[claim17]
17. A method for producing the metal-supported material according to claim 12, the method comprising:
a mixing step of mixing an A precursor containing the A and an X precursor containing the X to obtain a mixture;
a calcination step of calcining the mixture at a temperature of 600°C or more to obtain a support composed of a composite oxide;
a supporting step of preparing a supported material before pre-reduction treatment, by supporting a compound containing cobalt on the composite oxide; and
a reduction step of reducing the supported material before pre-reduction treatment, at a temperature of 400°C or more.

[claim18]
18. A method for producing ammonia by bringing hydrogen and nitrogen into contact with a catalyst, wherein the catalyst is the ammonia synthesis catalyst according to claim 16.
  • Applicant
  • JAPAN SCIENCE AND TECHNOLOGY AGENCY
  • Inventor
  • NAGAOKA KATSUTOSHI
  • OGURA YUTA
  • SATO KATSUTOSHI
IPC(International Patent Classification)
Specified countries Contracting States: AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR
Extension States: BA ME
Reference ( R and D project ) CREST Creation of Innovative Core Technology for Manufacture and Use of Energy Carriers from Renewable Energy AREA
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