Ammonia decomposition catalyst, honeycomb structure, and internal combustion engine

Abstract

The present disclosure relates to: an ammonia decomposition catalyst comprising a composite oxide constituting a perovskite structure by means of at least barium, zirconium, and ruthenium; a honeycomb structure including an ammonia decomposition catalyst; and an internal combustion engine comprising the ammonia decomposition catalyst. The present disclosure makes it possible to provide: an ammonia decomposition catalyst that exhibits excellent heat resistance and initial activity even at low temperatures during ammonia decomposition activity; a honeycomb structure including an ammonia decomposition catalyst; and an internal combustion engine comprising the ammonia decomposition catalyst.

Description

Ammonia decomposition catalyst, honeycomb structure and internal combustion engine

[0001] The present disclosure relates to an ammonia decomposition catalyst, and also to a honeycomb structure and an internal combustion engine.

[0002] Ammonia decomposition catalysts tend to have higher ammonia decomposition activity as the basicity of the catalyst increases, and compositions containing alkali metals or alkaline earth metal elements that improve basicity are known. Patent Document 1 describes a catalyst having the general formula: Ba(Ce １－ｘ Ru ｘ ) O ３ An ammonia decomposition catalyst comprising a compound having a perovskite structure represented by the formula (wherein x is 0.05, 0.25 or 0.5) is disclosed.

[0003] Patent Document 2 describes a ruthenium (Ru)-supported barium zirconate [5 wt% Ru / SrxBa （１－ｘ） ZrO ３ (x=0.125)] is disclosed. ３ and ZrO ２ A catalyst is disclosed in which metal Ru nanoparticles are supported on a support made of the above.

[0004] JP 2010-110697 A JP 2024-9392 A

[0005] "Ruthenium catalyst supported on Ba-modified ZrO2 for ammonia decomposition to COx-free hydrogen," International Journal of Hydrogen Energy, 2019, Vol. 44, pp. 7300-7307

[0006] The ammonia decomposition catalyst disclosed in Patent Document 1 did not have sufficient initial ammonia decomposition activity at 600°C. General formula: BaCeO ３ It is presumed that the ammonia decomposition catalyst in which Ru is dissolved in a compound having a perovskite structure represented by the formula (I) has a low SSA (Specific Surface Area) and does not exhibit sufficient activity.

[0007] On the other hand, in the catalysts disclosed in Patent Document 2 and Non-Patent Document 1, ruthenium is not dissolved in the crystal structure but is simply supported on a carrier, and the ruthenium is not sufficiently fixed to the carrier, so that ruthenium tends to easily aggregate when used at high temperatures. As a result, the dispersibility of the active metal ruthenium is easily reduced, making it difficult to fully demonstrate catalytic performance.

[0008] An object of the present disclosure is to provide an ammonia decomposition catalyst that exhibits excellent initial activity in ammonia decomposition activity even at low temperatures (for example, temperatures of 350°C or higher but lower than 600°C) and exhibits stable and excellent heat resistance even at high temperatures such as 1000°C or higher, as well as a honeycomb structure and an internal combustion engine that include the same. Another object of the present disclosure is to provide an ammonia decomposition catalyst that maintains an ammonia conversion rate of 50% or higher at a temperature of 450°C even after being subjected to a heat treatment at a temperature of 1200°C for 10 hours.

[0009] The ammonia decomposition catalyst according to the present disclosure contains a composite oxide having a perovskite structure composed of at least barium, zirconium, and ruthenium.

[0010] According to the present disclosure, it is possible to provide an ammonia decomposition catalyst that exhibits excellent initial activity in ammonia decomposition activity even at low temperatures (for example, temperatures of 350°C or higher but lower than 600°C) and exhibits stable and excellent heat resistance even at high temperatures such as 1000°C or higher, as well as a honeycomb structure and an internal combustion engine that include the same. According to the present disclosure, it is possible to provide an ammonia decomposition catalyst that has an ammonia conversion rate of 50% or higher at a temperature of 450°C even after being subjected to a heat treatment at a temperature of 1200°C for 10 hours.

[0011] FIG. 1 is a schematic diagram for explaining an internal combustion engine of the present disclosure. FIG. 2 is a schematic diagram for explaining an ammonia decomposition device used in the examples. FIG. 3 is a schematic diagram for explaining the "M" of the ammonia decomposition catalyst of the examples. Ｒｕ / M Ｚｒ " to "M Ｂａ / (M Ｚｒ +M Ｒｕ ) is plotted against

[0012] <Ammonia decomposition catalyst> The ammonia decomposition catalyst of the present disclosure is a catalyst for decomposing ammonia (NH ３ The ammonia decomposition catalyst is an ammonia decomposition catalyst for decomposing ammonium hydroxide (ammonium hydroxide), which comprises a composite oxide (hereinafter also referred to as a first composite oxide) that forms a perovskite structure from at least barium (Ba), zirconium (Zr), and ruthenium (Ru). The ammonia decomposition catalyst preferably comprises a composite oxide that forms a perovskite structure from barium, zirconium, and ruthenium. The presence of the first composite oxide in the ammonia decomposition catalyst can be confirmed by X-ray diffraction (XRD) analysis, elemental mapping by EDX (energy dispersive X-ray spectroscopy) of a TEM (transmission electron microscope), or X-ray absorption fine structure (XAFS) measurement.

[0013] By including the first composite oxide, the ammonia decomposition catalyst can exhibit excellent initial activity and heat resistance in ammonia decomposition activity even at low temperatures. By including the first composite oxide, the ammonia decomposition catalyst can exhibit an ammonia conversion rate of 80% or more at a temperature of 400°C, preferably even after being subjected to heat treatment at a temperature of 1000°C for 2 hours. In this specification, the ammonia conversion rate (%) is determined according to the evaluation method described in the Examples section below.

[0014] General formula: ABO ３ In composite oxides having a perovskite structure represented by the formula (1), it is thought that perovskite composite oxides containing Ba at the A site have high basicity and are oxides with excellent basicity, and as a result, they are more likely to exhibit excellent properties as an ammonia decomposition catalyst. Furthermore, it has been found that perovskite composite oxides containing Zr at the B site tend to have higher heat resistance and have a high SSA than perovskite composite oxides containing Ce at the B site, and are therefore advantageous as catalyst matrices. Furthermore, Zr ４＋ The site is Ru ４＋Since BaZrO is easily dissolved in the perovskite structure, high dispersibility of Ru and heat resistance are ensured, and it is presumed that excellent initial activity and heat resistance can be achieved even at low temperatures in ammonia decomposition activity. ３ Although composite oxides having a perovskite structure represented by the formula (I) are known as catalyst bases for, for example, the oxidation of hydrocarbons, it was quite unexpected that they exhibited high activity in ammonia decomposition, considering that there is no correlation between oxidation activity and ammonia decomposition activity.

[0015] The first composite oxide has the general formula: BaZrO ３ In the perovskite structure represented by the formula (1), a part of Zr constituting the crystal lattice is replaced by Ru, and the resulting solid solution crystal structure (hereinafter referred to as Ru solid solution BaZrO ３ As a result, excellent initial ammonia decomposition activity and heat resistance can be achieved even at low temperatures. ３ In a composite oxide having a perovskite structure represented by the general formula: BaZrO, if at least one of Ru and its oxide is supported without forming a solid solution crystal structure in which part of Zr is substituted with Ru, Ru will not be sufficiently immobilized, and catalytic activity, particularly heat resistance, in ammonia decomposition activity will tend to be difficult to exhibit. ３ It can be confirmed by XRD analysis, TEM-EDX analysis and XAFS analysis that the crystalline structure is a solid solution in which Ru is dispersed and incorporated into the crystal lattice of the perovskite structure represented by the formula:

[0016] When the molar ratio of Ba to Zr in the ammonia decomposition catalyst (hereinafter also referred to as the Ba / Zr ratio) is M1, M1 can satisfy the following formula (1): 0.2≦M1≦5.0 (1) When the ammonia decomposition catalyst further contains a compound containing Ba (hereinafter also referred to as a barium compound) in addition to the first composite oxide, for example as a promoter or a remaining raw material, the Ba in the Ba / Zr ratio is calculated as the sum of the amount of Ba contained in the first composite oxide and the amount of Ba contained in the barium compound.

[0017] The ammonia decomposition catalyst may contain, as the ruthenium component, only Ru present as a solid solution in the crystal lattice of the first composite oxide, and may also contain Ru and Ru oxides (e.g., RuO) present as metals without being solid-solved in the crystal lattice of the first composite oxide in addition to Ru present as a solid solution in the crystal lattice of the first composite oxide. ２ Ru and Ru oxides that are present as metals without being solid-solved in the crystal lattice of the first composite oxide are usually supported on the first composite oxide.

[0018] When the ruthenium component in the ammonia decomposition catalyst is converted to metallic ruthenium, the content of metallic ruthenium is ３ The amount of Ru supported on the first composite oxide may be, for example, 0.4% by mass or more and 20% by mass or less, based on the mass of the first composite oxide (composite oxide having a structure). When at least one of Ru and Ru oxide, which is present as a metal without being solid-solved in the crystal lattice of the first composite oxide, is supported on the first composite oxide, the mass of the first composite oxide also includes the mass of the Ru and Ru oxide supported on the first composite oxide.

[0019] The molar ratio M2 of Ru present as a solid solution in the crystal lattice of the first composite oxide to the metallic ruthenium may be, for example, more than 0 and 1.0 or less, and from the viewpoints of the initial activity at low temperatures and heat resistance in the ammonia decomposition activity, is preferably 0.01 or more and 1.0 or less, more preferably 0.1 or more and 1.0 or less, even more preferably 0.3 or more and 1.0 or less, and particularly preferably 0.5 or more and 1.0 or less.

[0020] The ammonia decomposition catalyst is a catalyst in which the number of moles of Ru contained in the first composite oxide is M Ｒｕ , the mole numbers of Zr and Ba contained in the ammonia decomposition catalyst are M Ｚｒ and M Ｂａ When M is set as above, it is preferable that the following formulae (a) to (c) are satisfied from the viewpoint of heat resistance and catalytic activity: (a) 0.031≦M Ｒｕ / M Ｚｒ ≦0.205 (b) 0.500≦M Ｂａ / (M Ｚｒ +M Ｒｕ )≦1.100 (c) 0<[0.242×MＢａ / (M Ｚｒ +M Ｒｕ ) ]+M Ｒｕ / M Ｚｒ -0.274 M Ｒｕ is the number of moles of Ru constituting the perovskite structure of the first composite oxide, and does not include, for example, Ru and Ru oxides supported on the ammonia decomposition catalyst. Ｚｒ and M Ｂａ is the sum of the number of moles of Zr and Ba contained in the first composite oxide and in other forms.

[0021] By satisfying formulas (a) to (c), the ammonia decomposition catalyst tends to easily exhibit an ammonia conversion rate of 50% or more at a temperature of 450°C even after being subjected to a heat treatment at 1200°C for 10 hours. Ｒｕ / M Ｚｒ If M is less than 0.031, the ammonia conversion rate at 450°C tends to be difficult to achieve at least 50%. Ｒｕ / M Ｚｒ When the value of the first composite oxide is more than 0.205, Ba is contained in addition to the first composite oxide. ４ ZrRu ３ O １２ It is easy to become Ru solid solution BaZrO ３ In this case, it tends to be difficult to obtain a first composite oxide having the structure Ｂａ / (M Ｚｒ +M Ｒｕ When M is less than 0.500, the heat resistance tends to be easily reduced. Ｂａ / (M Ｚｒ +M Ｒｕ ) exceeds 1.100, Ba in addition to the first composite oxide ５ Ru ２ O 10 It is easy to become Ru solid solution BaZrO ３ When formula (c) is satisfied, an ammonia conversion rate (%) of 50% or more at 450°C tends to be easily obtained.

[0022] The left side (lower limit) of formula (c) may preferably be 0.0007 from the viewpoint of an ammonia conversion rate (%) at 450°C of 50% or more.

[0023] From the viewpoint of heat resistance and catalytic activity, the ammonia decomposition catalyst more preferably satisfies the following formulae (a') to (c'): (a') 0.053≦M Ｒｕ / M Ｚｒ ≦0.205 (b') 0.700≦M Ｂａ / (M Ｚｒ +M Ｒｕ )≦1.080 (c') 0<[0.319×M Ｂａ / (M Ｚｒ +M Ｒｕ ) ]+M Ｒｕ / M Ｚｒ -0.381

[0024] By satisfying the formulas (a') to (c'), the ammonia decomposition catalyst tends to easily exhibit an ammonia conversion rate of 70% or more at a temperature of 450°C even after being subjected to a heat treatment at 1200°C for 10 hours. Ｒｕ / M Ｚｒ If M is less than 0.053, the ammonia conversion rate at 450°C tends to be difficult to reach 70% or more. Ｒｕ / M Ｚｒ When the value of the first composite oxide is more than 0.205, the first composite oxide is Ba. ４ ZrRu ３ O １２ It is easy to become Ru solid solution BaZrO ３ In this case, it becomes difficult to obtain a first composite oxide having the structure of formula (b'). Ｂａ / (M Ｚｒ +M Ｒｕ When M is less than 0.700, the heat resistance tends to be easily reduced. Ｂａ / (M Ｚｒ +M Ｒｕ When the formula (c') exceeds 1.080, the ammonia conversion rate at 450°C tends to be difficult to achieve 70% or more. When the formula (c') is satisfied, an ammonia conversion rate (%) at 450°C of 70% or more tends to be easily achieved.

[0025] The left side (lower limit) of formula (c') may preferably be 0.0002 from the viewpoint of an ammonia conversion rate (%) at 450°C of 70% or more.

[0026] From the viewpoint of heat resistance and catalytic activity, the ammonia decomposition catalyst more preferably satisfies the following formulae (a″) to (c″): (a″) 0.075≦M Ｒｕ / M Ｚｒ ≦0.205 (b'') 0.950≦M Ｂａ / (M Ｚｒ +M Ｒｕ )≦1.050 (c'') 0<[1.009×M Ｂａ / (M Ｚｒ +M Ｒｕ ) ]+M Ｒｕ / M Ｚｒ -1.114

[0027] By satisfying the formulas (a'') to (c''), the ammonia decomposition catalyst tends to easily exhibit an ammonia conversion rate of 90% or more at a temperature of 450°C even after being subjected to a heat treatment at 1200°C for 10 hours. Ｒｕ / M Ｚｒ If M is less than 0.075, the ammonia conversion rate at 450°C tends to be difficult to achieve 90% or more. Ｒｕ / M Ｚｒ When the value of the first composite oxide is more than 0.205, the first composite oxide is Ba. ４ ZrRu ３ O １２ Ru solid solution BaZrO ３ In this case, it becomes difficult to obtain a first composite oxide having the structure of formula (b''). Ｂａ / (M Ｚｒ +M Ｒｕ When M is less than 0.950, the heat resistance tends to be easily reduced. Ｂａ / (M Ｚｒ +M Ｒｕ When formula (c'') exceeds 1.050, it tends to be difficult to achieve an ammonia conversion rate of 90% or more at 450°C. By satisfying formula (c''), it tends to be easier to achieve an ammonia conversion rate (%) of 90% or more at 450°C.

[0028] The left side (lower limit) of formula (c'') may preferably be 0.0005 from the viewpoint of an ammonia conversion rate (%) at 450°C of 90% or more.

[0029] Figure 3 shows the "M Ｒｕ / M Ｚｒ " on the Y-axis, "M Ｂａ / (M Ｚｒ +M Ｒｕ ) on the X axis, the "M Ｒｕ / M Ｚｒ " to "M Ｂａ / (M Ｚｒ +M Ｒｕ 3 is a graph plotting the relationship between the kinetic energy of the catalyst and the catalyst temperature. In FIG. 3, the region satisfying formulas (a) to (c) is shown as the first region. In FIG. 3, the region satisfying formulas (a') to (c') is shown as the second region. In FIG. 3, ammonia decomposition catalysts satisfying formulas (a'') to (c'') are shown as being within the third region. In FIG. 3, formulas (c), (c'), and (c'') correspond to the line c constituting the first region, the line c' constituting the second region, and the line c'' constituting the third region, respectively.

[0030] M Ｒｕ , M Ｚｒ and M Ｂａ can be determined from the ratio (molar ratio) of raw materials used in the production of the ammonia decomposition catalyst. Ｒｕ , M Ｚｒ and M Ｂａ The atomic ratio of Ba, Zr, and Ru contained in the ammonia decomposition catalyst or the first composite oxide can be determined by X-ray fluorescence analysis (XRF), inductively coupled plasma (ICP) emission spectroscopy, or the like.

[0031] Furthermore, whether Ru is supported on the ammonia decomposition catalyst or whether Ru is dissolved in the perovskite structure of the first composite oxide can be determined by using X-ray diffraction (XRD), a scanning electron microscope (SEM), a transmission electron microscope (TEM), or the like in combination.

[0032] Furthermore, when Ru supported on the surface of the ammonia decomposition catalyst and Ru dissolved in the perovskite structure of the first composite oxide coexist, the ratio thereof can be calculated using X-ray absorption fine structure (XAFS) measurement or hard X-ray photoelectron spectroscopy (HAXPES).

[0033] More specifically, when the ammonia decomposition catalyst is subjected to a reduction treatment under appropriate conditions, the supported Ru is reduced to a zero-valent state, i.e., a metallic state, while the perovskite structure of the first composite oxide (e.g., BaZrO ３ The Ru in the solid solution state in the first composite oxide (e.g., BaZrO) remains in a cationic state. When the catalyst after such reduction treatment is analyzed by XAFS or HAXPES, the ratio of Ru in the metallic state to Ru in the cationic state can be determined. Furthermore, the Ru in the metallic state that was supported and the Ru in the cationic state are dissolved in the perovskite structure (e.g., BaZrO) of the first composite oxide. ３ ) is considered to be Ru that is solid-dissolved in the ammonia decomposition catalyst, the proportion of Ru that is solid-dissolved in the Ru contained in the ammonia decomposition catalyst can be calculated.

[0034] In XAFS, transmission or fluorescence yield analysis with an analysis depth of several micrometers can be used. In HAXPES, the Ru3d peak overlaps with the C1s peak in the Ru spectrum, so the concentration is calculated using the Ru3p3 peak. It is also desirable to correct the coefficient used to convert the Ru3p3 peak intensity to Ru concentration using a standard sample with a known Ru concentration.

[0035] Note that HAXPES is susceptible to surface contamination of the sample, so caution is required when detecting high concentrations of atoms other than Ba, Zr, Ru, and O. Furthermore, because the maximum analysis depth of HAXPES is approximately 50 nm, analysis by XAFS is preferable when the particle size of the ammonia decomposition catalyst exceeds 50 nm.

[0036] The ammonia decomposition catalyst may further contain one or more promoters selected from the group consisting of magnesium, alkali metals, alkaline earth metals, yttrium (Y), and rare earth elements to enhance basicity. The promoter may be contained in at least one form of oxide, carbonate, hydroxide, or metal. Examples of alkali metals include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), and cesium (Cs). Examples of alkaline earth metals include calcium (Ca), strontium (Sr), and barium (Ba). Examples of rare earth elements include scandium (Sc), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). When the ammonia decomposition catalyst contains a promoter, the content of the promoter may be, for example, less than 50 parts by mass, preferably 30 parts by mass or less, and may be, for example, more than 0 parts by mass, relative to 100 parts by mass of the first composite oxide.

[0037] The ammonia decomposition catalyst may further contain a binder or an organic solvent in order to make it easier to form into a particulate or honeycomb shape or to coat onto a substrate, as described below.

[0038] The content of the first composite oxide in the ammonia decomposition catalyst may be, for example, 100% by mass or less, 95% by mass or less, or 90% by mass or less, or 50% by mass or more, based on the mass of the ammonia decomposition catalyst. When a substrate is coated with the ammonia decomposition catalyst, such as in the honeycomb structure described below, the mass of the ammonia decomposition catalyst refers to the mass of the ammonia decomposition catalyst coated on the substrate, and does not include the mass of the substrate (e.g., a honeycomb-shaped substrate).

[0039] The ammonia decomposition catalyst can be prepared, for example, as follows. ３ , ZrO ２ and RuO ２ To the mixture, pebbles and water are added and wet-mixed to obtain a mixture. Next, the resulting mixture is dried at a temperature of 100-120°C while stirring on a hot plate, and then crushed and sized to obtain particles with particle sizes of several hundred μm to several mm. The resulting particulate sample is then calcined in air at a temperature of 900-1100°C for 2-10 hours. Alternatively, the resulting particulate sample is calcined in air at a temperature of 900-1200°C for 2-10 hours. In this way, an ammonia decomposition catalyst can be obtained.

[0040] The ammonia decomposition catalyst has excellent initial activity even at low temperatures, and can therefore exhibit high ammonia decomposition activity at a temperature of 400°C. Furthermore, the ammonia decomposition catalyst has improved heat resistance, and can exhibit catalytic activity for a long period of time even at relatively high temperatures. The temperature at which the ammonia decomposition catalyst can exhibit catalytic activity may be, for example, 350°C or higher, 400°C or higher, or 500°C or higher, and may be, for example, 900°C or lower, 800°C or lower, or 700°C or lower. After being subjected to a heat treatment at a temperature of 1200°C for 10 hours, the ammonia decomposition catalyst can exhibit an ammonia decomposition activity of preferably 50% or higher, more preferably 70% or higher, and even more preferably 90% or higher at a temperature of 450°C.

[0041] The ammonia decomposition catalyst is capable of exhibiting excellent initial activity and heat resistance in ammonia decomposition activity even at low temperatures, and is therefore suitable for internal combustion engines that use ammonia and engines that produce hydrogen by decomposing ammonia.

[0042] The ammonia decomposition catalyst can be used in the form of a pellet catalyst processed into granules having a size of several mm to several cm, or in the form of a honeycomb catalyst processed into a honeycomb shape.It can also be used as a honeycomb structure described below.

[0043] The ammonia decomposition catalyst can decompose ammonia by heating while in contact with ammonia. The ammonia to be contacted can be ammonia gas (gaseous ammonia). The heating temperature (also referred to as the first heating temperature) when decomposing ammonia by heating while in contact with ammonia may be, for example, 350°C or higher and 900°C or lower. If the heating temperature in the decomposition step is within the above range, it is possible to exhibit the catalytic activity of the ammonia decomposition catalyst. From the viewpoints of suppressing deterioration in catalyst performance and energy costs, the heating temperature is preferably 350°C or higher and 700°C or lower, more preferably 350°C or higher and 600°C or lower, and even more preferably 350°C or higher and 550°C or lower.

[0044] Heating while in contact with ammonia can be performed, for example, by filling a tube with the ammonia decomposition catalyst, introducing ammonia into the tube, and heating the portion of the tube that is in contact with the ammonia decomposition catalyst from the outside. The ammonia decomposition catalyst filled in the tube can be at least one selected from the group consisting of a pellet-shaped catalyst, a honeycomb catalyst (described below), and a honeycomb structure. It can also be an aggregate of the ammonia decomposition catalyst.

[0045] Before contacting ammonia with the ammonia decomposition catalyst, the ammonia decomposition catalyst can be heated to a temperature equal to or higher than the first heating temperature in a reducing atmosphere or under a reducing gas flow, which facilitates enhancing catalytic activity. The reducing atmosphere can be obtained, for example, by diluting hydrogen with nitrogen. Hydrogen alone may be used, or ammonia may be used instead of hydrogen. The heating temperature (hereinafter also referred to as the second heating temperature) when heating ammonia to a temperature equal to or higher than the first heating temperature before contacting the ammonia decomposition catalyst may be, for example, 300°C or higher and 900°C or lower, and from the viewpoints of catalytic activity and energy cost, is preferably 400°C or higher and 800°C or lower, more preferably 600°C or higher and 800°C or lower. The time for heating the ammonia decomposition catalyst at the second heating temperature before contacting ammonia with the ammonia decomposition catalyst may be, for example, 1 to 10 hours.

[0046] <Honeycomb Structure> Another aspect of the present disclosure is a honeycomb structure in which the above-mentioned ammonia decomposition catalyst is applied to a honeycomb-shaped substrate. The honeycomb structure can reduce pressure loss when ammonia gas flows through it. Furthermore, increasing the honeycomb cell density increases the effective surface area, making it easier to increase the ammonia decomposition rate.

[0047] <Ammonia Decomposition Apparatus> An internal combustion engine according to another embodiment of the present disclosure is an internal combustion engine that obtains driving force by burning at least hydrogen, and includes an engine body including a combustion chamber, an ammonia supply unit that supplies ammonia, and a hydrogen generation unit between the ammonia supply unit and the combustion chamber, and the hydrogen generation unit is provided with the above-described ammonia decomposition catalyst.

[0048] Fig. 1 is a schematic diagram of an internal combustion engine according to one embodiment of the present invention. The internal combustion engine 1 shown in Fig. 1 is mounted on, for example, a vehicle and can generate driving force for driving the vehicle. The internal combustion engine 1 includes an engine body 10, an ammonia supply unit 20, a combustion chamber 30, and a hydrogen generation unit 40.

[0049] The engine body 10 obtains driving force by burning at least hydrogen. Ammonia may be burned in addition to hydrogen. The engine body 10 of this embodiment is a spark-ignition type and includes a cylinder block 10b and a cylinder head 10h. A piston 12 is disposed inside the cylinder block 10b, and a combustion chamber 30 is formed by the crown surface of the piston 12 and the cylinder head 10h. A combustion chamber 30 is formed for each cylinder.

[0050] An intake pipe 16 that forms an intake path to the combustion chamber 30 and an exhaust pipe 17 that forms an exhaust path from the combustion chamber 30 are connected to the combustion chamber 30 via the inside of the cylinder block 10b.

[0051] An ignition plug 13 is also fixed to the combustion chamber 30 as an ignition device. The ammonia supply unit 20 supplies ammonia to the hydrogen generation unit 40. The ammonia supply unit 20 is pressurized inside and stores ammonia. The stored ammonia may be liquefied ammonia. The hydrogen generation unit 40 incorporates the above-mentioned ammonia decomposition catalyst (not shown). The hydrogen generation unit 40 heats ammonia to a constant temperature and decomposes ammonia according to the following formula (i): 2NH ３ → N ２ +3H ２ (i) by decomposing it to obtain hydrogen (H ２ The ammonia supplied to the hydrogen generator 40 may be ammonia gas. The hydrogen generated by the hydrogen generator 40 may be hydrogen gas.

[0052] The decomposition reaction of ammonia is an endothermic reaction. Therefore, the hydrogen generator 40 obtains the heat required for the decomposition reaction of ammonia from the heat of the oxidation reaction of ammonia due to the oxidation function of the built-in ammonia decomposition catalyst, or from a heating unit that heats ammonia. The oxidation reaction of ammonia is, for example, represented by the following formula (ii): ３ +30 ２ → 2N ２ +6H ２ O (ii) is the reaction shown in FIG.

[0053] The hydrogen generated by the hydrogen generation unit 40 is supplied to the first supply unit 42 via the first supply pipe 41. The first supply unit 42 is disposed on the intake pipe 16, and is provided downstream of the intake path. Note that what is supplied from the first supply unit 42 to the combustion chamber 30 is not limited to hydrogen; ammonia that was not used in the reaction in the hydrogen generation unit 40 may also be supplied.

[0054] As a modified example, a portion of the ammonia may be directly supplied to the combustion chamber from a second supply pipe provided between the ammonia supply unit 20 and the hydrogen generation unit 40, without being supplied to the hydrogen generation unit 40. As yet another modified example, hydrocarbons may be further supplied to the combustion chamber from a third supply pipe. The supplied hydrocarbons may be hydrocarbon gas. Examples of the hydrocarbons include methane, gasoline, and diesel. As another modified example, a portion of the ammonia may be directly supplied to the exhaust pipe 17 from a fourth supply pipe provided between the ammonia supply unit 20 and the hydrogen generation unit 40, without being supplied to the hydrogen generation unit 40. Furthermore, the ammonia supplied to the combustion chamber 30 may be supplied to the exhaust pipe 17 together with the exhaust gas.

[0055] The present disclosure will now be described in further detail with reference to examples.

[0056] Example 1: BaCO as an ammonia decomposition catalyst material ３ , ZrO ２ and RuO ２ These were weighed out to a molar ratio of Ba:Zr:Ru = 1.00:1.00:0.17, and then mixed with pebbles and water to obtain a mixture. The resulting mixture was dried at 110°C while stirring on a hot plate, and then crushed and sized to obtain a catalyst precursor powder. The catalyst precursor powder was then calcined in air at 1000°C for 2 hours to obtain a Ru solid-solution BaZrO. ３A composite oxide having a perovskite structure as shown above was prepared, and this was used as the ammonia decomposition catalyst of Example 1. The content of metallic ruthenium, calculated as the ruthenium component in the composite oxide in terms of metallic ruthenium, was 5.9 mass% relative to the mass of the composite oxide. [Confirmation of Crystalline Phase] The ammonia decomposition catalysts of the example and comparative example were pulverized in a mortar, and the crystal phase was confirmed by powder XRD measurement (X-ray source: Cu-Kα1). The results are shown in Table 1.

[0057] The TEM (transmission electron microscope) image of the ammonia decomposition catalyst of Example 1 and the element mapping image by EDX (energy dispersive X-ray spectroscopy) in the same field of view revealed that the catalyst had the general formula: BaZrO ３ It was confirmed that the crystalline structure was a solid solution in which Ru was dispersed and incorporated into the crystal lattice of a perovskite structure represented by the formula:

[0058] Comparative Example 1: Commercially available 5 mass % Ru / Al ２ O ３ (Ruthenium supported on alumina) was prepared.

[0059] [Evaluation of Ammonia Decomposition Activity] The ammonia decomposition activity of the catalysts of Example 1 and Comparative Example 1 was evaluated. 0.5 g of catalyst 103 was packed into a reaction tube 101 of an ammonia decomposition apparatus 100 shown in FIG. 2. The catalyst 103 was heated by a heater 102 at a temperature of 600° C. for 2 hours while flowing ammonia at a rate of 42 ml / min. Next, the heater was heated to a temperature of 400° C., and then 100% NH ３ The mixture was heated to 400°C by a heater 102 while being introduced at a rate of 42 ml / min. During the reaction evaluation, the gas discharged from the cracked gas outlet 105 was introduced into a gas chromatograph to measure the ammonia conversion rate (%). ３ Conv. (%) is calculated by the following formula: NH ３ conv. (%)=1-([NH ３ ]t / [NH ３ ]r. t. ) [In the formula, [NH ３ ]t represents the ammonia concentration (%) at temperature t, and [NH ３] r.t. represents the ammonia concentration (%) at the start of the measurement (room temperature). A higher ammonia conversion rate indicates better ammonia decomposition activity (initial activity). The space velocity in both Example 1 and Comparative Example 1 was approximately 5000 ml / (gh). －１ It was.

[0060]

[0061] In Example 1, the ammonia conversion rate at a temperature of 400°C (t = 400°C) was 80% or more, whereas in Comparative Example 1, the ammonia conversion rate at a temperature of 400°C (t = 400°C) was 50% or less.

[0062] The ammonia decomposition catalyst of the present disclosure achieved an ammonia conversion rate of 80% or more at a temperature of 400° C., even after undergoing a heat treatment at 1000° C. during calcination. This demonstrates that the ammonia decomposition catalyst of the present disclosure can exhibit excellent initial activity and thermal stability in ammonia decomposition activity.

[0063] <Examples 2 to 14> BaCO as an ammonia decomposition catalyst material ３ , ZrO ２ and RuO ２ These were prepared and weighed so that the molar ratios of Ba, Zr, and Ru were as shown in Table 2. Cobbles, water, and a binder were added and wet-mixed to obtain a mixture. The resulting mixture was dried at 110°C while stirring on a hot plate, and then crushed and classified to obtain granules with a size of 315 μm to 800 μm. The granular sample was then fired in air at 1200°C for 10 hours, and the resulting powder was further crushed and classified to obtain Ru solid solution BaZrO with a perovskite structure and a size of 510 μm to 700 μm. ３ Catalyst powders containing mainly composite oxides were prepared and used as the ammonia decomposition catalysts of Examples 2 to 14. The ammonia decomposition catalysts of Examples 2 to 14 were pulverized in a mortar, and the crystalline phase was confirmed by powder XRD measurement (X-ray source: Cu-Kα1), which revealed that the catalysts were mainly composed of BaZrO ３Furthermore, from the TEM (transmission electron microscope) images of the ammonia decomposition catalysts of Examples 2 to 14 and elemental mapping images by EDX (energy dispersive X-ray spectroscopy) in the same field of view, it was confirmed that the crystal phase was of the general formula: BaZrO ３ It was confirmed that the crystalline structure was a solid solution in which Ru was dispersed and incorporated into the crystal lattice of the perovskite structure represented by M Ｒｕ / M Ｚｒ and M Ｂａ / (M Ｚｒ +M Ｒｕ ) are shown in Table 3.

[0064]

[0065] Comparative Example 2: BaCO as the material of the ammonia decomposition catalyst support ３ and ZrO ２ These were weighed out so that the molar ratio of Ba:Zr was 0.1:1.0, and then balls and water were added and wet mixed to obtain a mixture. The obtained mixture was dried at a temperature of 110°C while stirring on a hot plate, and then crushed and sized to obtain a precursor powder of the catalyst support. The precursor powder of the catalyst support was then calcined in air at a temperature of 700°C for 6 hours to obtain ZrO ２ Furthermore, RuO was added to the obtained catalyst carrier so that the Ru content was 3 wt %. ２ The mixture was weighed, and then mixed with pebbles, water, and a binder to obtain a mixture. The mixture was dried at 110°C while stirring on a hot plate, and then crushed and classified to obtain granules with a size of 315 μm to 800 μm. The granular sample was then fired in air at 500°C for 3 hours, and the resulting powder was further crushed and classified to obtain 3 wt% Ru-supported Ba-ZrO with a size of 510 μm to 700 μm. ２ 3 wt% Ru-supported Ba-ZrO ２ was pulverized in a mortar and subjected to powder XRD measurement (X-ray source: Cu-Kα1). ２ The second phase is BaZrO ３ Furthermore, it was confirmed by TEM-EDX that Ru was ZrO ２ and / or BaZrO３ Furthermore, it was confirmed that 3 wt % Ru was supported on Ba-ZrO ２ The resultant was calcined at 1200° C. for 10 hours, and used as the ammonia decomposition catalyst of Comparative Example 2.

[0066] Comparative Example 3: BaCO as an ammonia decomposition catalyst material ３、 CeO ２ and RuO ２ These were prepared and weighed to a molar ratio of Ba:Ce:Ru = 1:0.95:0.05, and then balls, water, and a binder were added and wet mixed to obtain a mixture. The obtained mixture was dried at a temperature of 110 ° C while stirring on a hot plate, and then crushed and classified to obtain granules with a size of 315 μm to 800 μm. The granular sample was then fired in air at a temperature of 1000 ° C for 10 hours, and the obtained powder was further crushed and classified to obtain BaCe with a perovskite structure in which Ru was solid-solved with a size of 510 μm to 700 μm. ０．９５ Ru ０．０５ O ３ A composite oxide was prepared. This was used as the ammonia decomposition catalyst of Comparative Example 3. The main phase of the ammonia decomposition catalyst of Comparative Example 3 was BaCeO having a perovskite structure. ３ It was confirmed by powder XRD measurement (X-ray source: Cu-Kα1). Furthermore, it was confirmed that Ru was BaCeO ３ It was confirmed by TEM-EDX that the alloy was in a solid solution state.

[0067] Comparative Example 4: BaCO as the material of the ammonia decomposition catalyst support ３、 SrCO ３ and ZrO ２ These were weighed out so that the molar ratio of Ba:Sr:Zr was 0.875:0.125:1.000, and then balls and water were added and wet mixed to obtain a mixture. The obtained mixture was dried at a temperature of 110°C while stirring on a hot plate, and then crushed and sized to obtain a precursor powder of the catalyst support. The precursor powder of the catalyst support was then calcined in air at a temperature of 1000°C for 2 hours to obtain a catalyst support. ０．８７５ Sr ０．１２５ Zr １．００ O３ Furthermore, RuO was added to the obtained catalyst support so that Ru was 5 wt %. ２ The mixture was weighed, and then mixed with pebbles, water, and a binder to obtain a mixture. The mixture was dried at 110°C while stirring on a hot plate, and then crushed and classified to obtain granules with a size of 510 μm to 700 μm. The granular sample was then fired in air at 600°C for 2 hours to obtain 5 wt% Ru-supported Ba. ０．８７５ Sr ０．１２５ Zr １．００ O ３ A composite oxide was prepared. 5 wt % Ru-supported Ba ０．８７５ Sr ０．１２５ Zr １．００ O ３ The composite oxide was pulverized in a mortar and subjected to powder XRD measurement (X-ray source: Cu-Kα1). ３ Furthermore, it was confirmed by TEM-EDX that Ru was supported on an oxide having a perovskite structure. ０．８７５ Sr ０．１２５ Zr １．００ O ３ The composite oxide was calcined at 1200° C. for 10 hours to prepare an ammonia decomposition catalyst of Comparative Example 4.

[0068] [Evaluation of Ammonia Decomposition Activity] The ammonia decomposition activity of the catalysts of Examples 2 to 14 and Comparative Examples 2 to 4 was evaluated. 0.344 g of catalyst 103 was packed into the reaction tube 101 of the ammonia decomposition apparatus 100 shown in FIG. 2. The catalyst 103 was heated by the heater 102 at a temperature of 600°C for 2 hours while flowing ammonia at a rate of 28.7 ml / min. Next, the heater was heated to a temperature of 450°C, and then 100% NH ３ was introduced at a rate of 28.7 ml / min, and heated to 450°C by a heater 102. During the reaction evaluation, the gas discharged from the cracked gas outlet 105 was introduced into a gas chromatograph to measure the ammonia conversion rate (%). ３ The space velocity in Examples 2 to 14 and Comparative Examples 2 to 4 was about 5000 ml / (gh).－１ The results are shown in Table 3.

[0069]

[0070] In Examples 2 to 5, the ammonia conversion rate at 450°C (t = 450°C) was 50% or higher even after heat treatment at 1200°C for 10 hours. In Examples 6 to 9, the ammonia conversion rate at 450°C (t = 450°C) was 70% or higher even after heat treatment at 1200°C for 10 hours. Furthermore, in Examples 10 to 14, the ammonia conversion rate at 450°C (t = 450°C) was 90% or higher even after heat treatment at 1200°C for 10 hours. In contrast, in both Comparative Examples 2 and 4, the ammonia conversion rate at 450°C (t = 450°C) after heat treatment at 1200°C for 10 hours was less than 50%. In Comparative Example 2, the ammonia conversion rate at 450°C (t = 450°C) was less than 50% despite heat treatment at 1000°C for 10 hours.

[0071] M in Examples 2 to 14 Ｒｕ / M Ｚｒ M Ｂａ / (M Ｚｒ +M Ｒｕ) is shown in Figure 3. The plots for Examples 2 to 4 are linear. Therefore, the slope of the line connecting each plot was determined by the least squares method. Furthermore, the intercepts at which the line with this slope does not exceed each plot were calculated. The line with these slopes and intercepts is line c. Line c constitutes the first region. Similarly, lines c' and c'' were determined for Examples 6 to 8 and 10 to 12. Line c' constitutes the second region, and line c'' constitutes the third region. It can be seen that the ammonia decomposition catalyst in the first region can achieve an ammonia conversion rate of 50% or more at a temperature of 450°C (t = 450°C) after heat treatment at a temperature of 1200°C for 10 hours. It can also be seen that the ammonia decomposition catalyst in the second region can achieve an ammonia conversion rate of 70% or more at a temperature of 450°C (t = 450°C) after heat treatment at a temperature of 1200°C for 10 hours. Furthermore, it can be seen that the ammonia decomposition catalyst in the third region can achieve an ammonia conversion rate of 90% or more at a temperature of 450°C (t=450°C) after being subjected to a heat treatment at a temperature of 1200°C for 10 hours.

[0072] In the above-described embodiments, configurations that can be combined may be combined with each other.

[0073] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present disclosure is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims.

[0074] It will be understood by those skilled in the art that the above-described exemplary embodiments are specific examples of the following aspects: (Item 1) An ammonia decomposition catalyst according to one aspect includes a composite oxide having a perovskite structure formed of at least barium, zirconium, and ruthenium. (Item 2) The ammonia decomposition catalyst according to Item 1 includes a composite oxide having a perovskite structure formed of at least barium, zirconium, and ruthenium, and a molar ratio of ruthenium contained in the composite oxide to M Ｒｕ , the mole numbers of zirconium and barium contained in the ammonia decomposition catalyst are M Ｚｒ and M Ｂａ When M is 0.031 or less, the following formula is satisfied:Ｒｕ / M Ｚｒ ≦0.205 (b) 0.500≦M Ｂａ / (M Ｚｒ +M Ｒｕ )≦1.100 (c) 0<[0.242×M Ｂａ / (M Ｚｒ +M Ｒｕ ) ]+M Ｒｕ / M Ｚｒ (Item 3) The ammonia decomposition catalyst according to item 1 satisfies M Ｒｕ , the mole numbers of zirconium and barium contained in the ammonia decomposition catalyst are M Ｚｒ and M Ｂａ When the following formula is satisfied: (a') 0.053≦M Ｒｕ / M Ｚｒ ≦0.205 (b') 0.700≦M Ｂａ / (M Ｚｒ +M Ｒｕ )≦1.080 (c') 0<[0.319×M Ｂａ / (M Ｚｒ +M Ｒｕ ) ]+M Ｒｕ / M Ｚｒ (Item 4) The ammonia decomposition catalyst according to item 1 satisfies M Ｒｕ , the mole numbers of zirconium and barium contained in the ammonia decomposition catalyst are M Ｚｒ and M Ｂａ When the following formula is satisfied: (a'') 0.075≦M Ｒｕ / M Ｚｒ ≦0.205 (b'') 0.950≦M Ｂａ / (M Ｚｒ +M Ｒｕ )≦1.050 (c'') 0<[1.009×M Ｂａ / (M Ｚｒ +M Ｒｕ ) ]+M Ｒｕ / M Ｚｒ-1.114 is satisfied. (Item 5) When the molar ratio of barium to zirconium (barium / zirconium) in the ammonia decomposition catalyst described in any one of Items 1 to 4 is M1, M1 satisfies the following formula (1): 0.2≦M1≦5.0 (1) (Item 6) When the ruthenium component in the ammonia decomposition catalyst described in any one of Items 1 to 5 is converted to metallic ruthenium, the content of the metallic ruthenium in the ammonia decomposition catalyst is 0.4 mass% or more and 20 mass% or less with respect to the mass of the composite oxide. (Item 7) The ammonia decomposition catalyst described in any one of Items 1 to 6 contains, as a promoter, one or more elements selected from the group consisting of magnesium, alkali metals, alkaline earth metals, yttrium, and rare earth elements. (Item 8) A honeycomb structure including a honeycomb-shaped substrate, the honeycomb-shaped substrate being coated with the ammonia decomposition catalyst according to any one of Items 1 to 7. (Item 9) An internal combustion engine that obtains driving force by the combustion of at least hydrogen, the internal combustion engine comprising an engine body including a combustion chamber, an ammonia supply unit that supplies ammonia, and a hydrogen generation unit between the ammonia supply unit and the combustion chamber, the hydrogen generation unit comprising the ammonia decomposition catalyst according to any one of Items 1 to 7.

[0075] 1 internal combustion engine, 10 engine body, 10b cylinder block, 10h cylinder head, 12 piston, 13 spark plug, 16 intake pipe, 17 exhaust pipe, 20 ammonia supply section, 30 combustion chamber, 40 hydrogen generation section, 41 first supply pipe, 42 first supply section, 100 ammonia decomposition device, 101 reaction tube, 102 heater, 103 catalyst, 104 ammonia inlet, 105 decomposition gas outlet.

Claims

1. An ammonia decomposition catalyst comprising a composite oxide having a perovskite structure composed of at least barium, zirconium and ruthenium.

2. The number of moles of ruthenium contained in the composite oxide is M Ｒｕ The mole numbers of zirconium and barium contained in the ammonia decomposition catalyst are M Ｚｒ and M. Ｂａ When M is 0.031 or less, the following formula is satisfied: Ｒｕ / M Ｚｒ ≦0.205 (b) 0.500≦M Ｂａ / (M Ｚｒ +M Ｒｕ )≦1.100 (c) 0<[0.242×M Ｂａ / (M Ｚｒ +M Ｒｕ ) + M Ｒｕ / M Ｚｒ The ammonia decomposition catalyst according to claim 1, which satisfies -0.

274.

3. The number of moles of ruthenium contained in the composite oxide is M Ｒｕ The mole numbers of zirconium and barium contained in the ammonia decomposition catalyst are M Ｚｒ and M. Ｂａ When M is 0.053 or less, the following formula is satisfied: Ｒｕ / M Ｚｒ ≦0.205 (b') 0.700≦M Ｂａ / (M Ｚｒ +M Ｒｕ )≦1.080 (c') 0<[0.319×M Ｂａ / (M Ｚｒ +M Ｒｕ ) + M Ｒｕ / M Ｚｒ The ammonia decomposition catalyst according to claim 1, which satisfies -0.

381.

4. The number of moles of ruthenium contained in the composite oxide is M Ｒｕ The mole numbers of zirconium and barium contained in the ammonia decomposition catalyst are M Ｚｒ and M. Ｂａ When M is 0.075 or less, the following formula is satisfied: Ｒｕ / M Ｚｒ ≦0.205 (b'') 0.950≦M Ｂａ / (M Ｚｒ +M Ｒｕ )≦1.050 (c'') 0<[1.009×M Ｂａ / (M Ｚｒ +M Ｒｕ ) + M Ｒｕ / M Ｚｒ The ammonia decomposition catalyst according to claim 1, which satisfies −1.

114.

5. The ammonia decomposition catalyst according to any one of claims 1 to 4, which contains, as a promoter, one or more elements selected from the group consisting of magnesium, alkali metals, alkaline earth metals, yttrium, and rare earth elements.

6. A honeycomb structure comprising a honeycomb-shaped substrate, the honeycomb-shaped substrate being coated with the ammonia decomposition catalyst according to any one of claims 1 to 5.

7. An internal combustion engine that obtains driving force by burning at least hydrogen, comprising: an engine body including a combustion chamber; an ammonia supply unit that supplies ammonia; and a hydrogen generation unit between the ammonia supply unit and the combustion chamber, wherein the hydrogen generation unit is equipped with the ammonia decomposition catalyst according to any one of claims 1 to 5.

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