Catalyst for ammonia oxidation, catalyst system and method of preparing catalyst for ammonia oxidation

Abstract

To provide a catalyst for ammonia oxidation which selectively oxidizes ammonia, a method of preparing a catalyst for ammonia oxidation, and a catalyst system.SOLUTION: According to embodiments of the present disclosure, a catalyst for ammonia oxidation includes a metal oxide including titanium and chromium, wherein an energy band gap of the metal oxide measured by UV-Vis DRS is less than 1.4 eV. A catalyst system according to embodiments of the present disclosure includes: an ammonia decomposition reactor; and a catalyst unit which is located in a downstream region of the ammonia decomposition reactor, and includes the above-described ammonia oxidation catalyst.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to an ammonia oxidation catalyst, a method for manufacturing an ammonia oxidation catalyst, and a catalyst system including the ammonia oxidation catalyst.

Background Art

[0002] In recent years, due to environmental problems, technologies for reducing greenhouse gases or harmful gases in the atmosphere have been developed. As a result, the demand for new renewable energy is increasing to replace the use of fossil fuels such as petroleum and coal. As one of the new renewable energies, hydrogen can mainly be used.

[0003] Ammonia (NH 3 ) is a carbon-free fuel and can efficiently store and transport hydrogen. For example, ammonia can be decomposed to generate hydrogen (H 2 ) and nitrogen (N 2 ), and the hydrogen generated from ammonia can be supplied to a fuel cell or the like. However, in order to supply hydrogen by the decomposition reaction of ammonia, an excessive amount of ammonia is required, and unreacted substances that have not been converted to hydrogen among the supplied ammonia can be released into the atmosphere as exhaust gas.

[0004] Since ammonia is flammable and toxic, it may become a secondary pollution source. Therefore, before ammonia is released into the atmosphere, it is necessary to convert it into environmentally harmless components. For example, a selective ammonia oxidation catalyst can be used to efficiently remove residual ammonia while suppressing the generation of harmful gases. Thereby, ammonia can be selectively decomposed into nitrogen (N 2 ) and water (H 2 O).

[0005] However, when a high concentration of oxygen is injected for the selective oxidation reaction of ammonia, oxygen reacts with hydrogen (H2 ) reacts or reacts with nitrogen to generate nitrogen oxides (NOx) such as NO or NO 2 . In addition, hydrogen may be consumed by oxygen, resulting in a decrease in the overall hydrogen production efficiency, and environmental pollution may be caused by nitrogen oxides. Therefore, there is a need to develop an ammonia oxidation catalyst that can efficiently remove ammonia while suppressing hydrogen consumption and nitrogen oxide generation.

Summary of the Invention

Problems to be Solved by the Invention

[0006] One problem of the present disclosure is to provide an ammonia oxidation catalyst that selectively oxidizes ammonia.

[0007] One problem of the present disclosure is to provide a method for manufacturing an ammonia oxidation catalyst.

[0008] One problem of the present disclosure is to provide a catalyst system including the aforementioned ammonia oxidation catalyst.

Means for Solving the Problems

[0009] The ammonia oxidation catalyst according to an embodiment of the present disclosure includes a metal oxide containing titanium and chromium, and the energy band gap of the metal oxide measured by ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS; diffuse reflectance spectroscopy) may be less than 1.4 eV.

[0010] In one embodiment, the energy band gap of the metal oxide may be 0.2 eV or more and less than 1.4 eV.

[0011] In some embodiments, the chromium content may be 0.1 mol to 0.3 mol based on the total of 1 mol of titanium and chromium on an elemental basis.

[0012] In some embodiments, the metal oxide has a crystal structure of titanium oxide, and the chromium can be doped into the crystal structure of the titanium oxide.

[0013] In some embodiments, the metal oxide can include an anatase phase.

[0014] In some embodiments, in the ammonia oxidation reaction by the ammonia oxidation catalyst, the reaction temperature is 200°C to 400°C, and the generation amount of nitrogen oxides (NOx) measured under the condition that the concentration ratio of O 3 to NH 2 is 2.2 or more may be 200 ppm or less.

[0015] In the method for manufacturing an ammonia oxidation catalyst according to an embodiment of the present disclosure, a chromium compound and a titanium compound can be mixed in an organic solvent to produce a first mixture. Water can be added to the first mixture to produce a second mixture. The second mixture can be gelled to produce a precursor solution. The precursor solution can be heat-treated.

[0016] In some embodiments, the organic solvent can include an alcohol-based solvent.

[0017] In some embodiments, the pH of the second mixture may be 5 or more.

[0018] In some embodiments, the step of heat-treating the precursor solution can include drying the precursor solution at a temperature of 70°C to 125°C and calcining the precursor solution at a temperature of 350°C to 600°C.

[0019] The catalyst system according to an embodiment of the present disclosure includes an ammonia decomposition reactor and a catalyst section located in a downstream region of the ammonia decomposition reactor and including the ammonia oxidation catalyst according to the above-described embodiment.

[0020] In some embodiments, an ammonia supply unit located in the upstream region of the ammonia decomposition reactor may further be included.

[0021] In some embodiments, the catalyst system may further include an ammonia adsorption unit located in the downstream region of the ammonia decomposition reactor and including an ammonia selective adsorbent.

[0022] In some embodiments, the ammonia adsorption unit may be located in the downstream region of the catalyst unit.

[0023] In some embodiments, the catalyst system may include a fuel cell that receives a supply of hydrogen from the catalyst unit.

Advantages of the Invention

[0024] The ammonia oxidation catalyst according to the embodiments of the present disclosure can promote the selective reaction between oxygen and ammonia. Thereby, even under conditions of low oxygen concentration, the ammonia removal efficiency can be improved while suppressing hydrogen consumption and nitrogen oxide generation.

[0025] In the method for manufacturing an ammonia oxidation catalyst according to the embodiments of the present disclosure, chromium oxide and titanium alkoxide can be gelled under predetermined mixing conditions. Thereby, chromium is substituted for titanium within the crystal lattice of titanium dioxide, and the generation of chromium oxide (CrO x ) can be suppressed.

[0026] The catalyst system according to the embodiments of the present disclosure can include the ammonia oxidation catalyst. The supply amount of oxygen can be reduced, the generation of nitrogen oxides can be suppressed, and high-purity hydrogen gas can be provided to the fuel cell.

Brief Description of the Drawings

[0027]

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Embodiments for Carrying Out the Invention

[0028] According to an embodiment of the present disclosure, an ammonia oxidation catalyst is provided.

[0029] According to an embodiment of the present disclosure, a catalyst system including an ammonia oxidation catalyst is provided.

[0030] Hereinafter, the embodiments of the present disclosure will be described more specifically.

[0031] The ammonia oxidation catalyst according to an embodiment of the present disclosure includes a metal oxide containing titanium and chromium. The ammonia oxidation catalyst can selectively promote the oxidation reaction of ammonia (NH 3 ) to convert ammonia into nitrogen gas. The ammonia oxidation reaction means a reaction in which ammonia reacts with oxygen (O 2 ) to produce nitrogen gas.

[0032] The metal oxide can have a crystal structure of titanium oxide. In the metal oxide, chromium can be doped into the titanium oxide. For example, a part of titanium atoms in the crystal structure of the titanium oxide is replaced by chromium atoms, or chromium atoms are located at oxygen vacancies where oxygen has escaped in the crystal structure of the titanium oxide, or chromium atoms can be located in the vacant space within the lattice of titanium and oxygen for interstitial doping.

[0033] Thereby, the stability of the ammonia oxidation catalyst can be improved, the specific surface area and active sites of the catalyst are increased, and the oxidation reaction of ammonia can be further promoted.

[0034] According to an exemplary embodiment, the metal oxide can have a crystal structure of titanium dioxide (TiO 2 ). For example, the crystal lattice of the metal oxide may be substantially the same as the crystal lattice of titanium dioxide.

[0035] In some embodiments, chromium may be incorporated into the crystal structure of the titanium dioxide. For example, a part of the titanium atoms in the crystal lattice of the titanium dioxide can be replaced by chromium atoms. By having the ammonia oxidation catalyst have a crystal structure of titanium dioxide and containing chromium within the crystal structure, both the structural stability and the activity of the catalyst can be improved.

[0036] Due to the ammonia oxidation catalyst according to the exemplary embodiment having the aforementioned crystal structure, the ammonia selectivity and ammonia removal efficiency can be enhanced. Thereby, the ammonia removal efficiency can be improved even under low-concentration oxygen conditions, and the consumption of hydrogen by high-concentration oxygen can be prevented. Also, the reaction between nitrogen and oxygen is suppressed, and the generation amount of nitrogen oxides can be reduced.

[0037] The energy band gap of the metal oxide may be less than 1.4 eV. For example, the energy band gap of the metal oxide may be 0.2 eV or more and less than 1.4 eV. The energy band gap of the metal oxide can be measured by ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS).

[0038] The energy band gap can be measured as an index indicating the degree to which chromium atoms are substituted or doped within the crystal structure of the titanium dioxide.

[0039] For example, even if the content of chromium atoms contained in the metal oxide is the same, the crystal form of the metal oxide can be different between the case where the chromium atoms are present within the crystal lattice of titanium oxide (TiO x ) and the case where the chromium atoms are present as the crystal structure of chromium oxide (CrO x ). Therefore, the catalytic activity and characteristics of the ammonia oxidation catalyst can differ depending on the crystal form of the metal oxide.

[0040] Due to the change in the electronic structure caused by the incorporated Cr in the crystal structure of the titanium oxide, a new valence band is provided, and the energy band gap of the metal oxide can be shifted to a low value.

[0041] By including a metal oxide having an energy band gap within the above range in the ammonia oxidation catalyst, the ammonia oxidation reaction and ammonia selectivity can be improved. As a result, even at a low oxygen partial pressure, a selective oxidation reaction for ammonia can be promoted, and the consumption amount of hydrogen and the generation amount of nitrogen oxides can be reduced.

[0042] In one embodiment, the energy band gap of the metal oxide may be 0.5 eV or more and less than 1.4 eV, 0.2 eV to 1.3 eV, or 0.8 eV to 1.3 eV. Within the above range, the ratio of chromium oxide in the crystal structure of the metal oxide can be lowered, and the reaction selectivity and reaction efficiency for ammonia can be further enhanced.

[0043] In some embodiments, the peak position of the binding energy of Cr in the metal oxide may be higher than the peak position of the binding energy of Cr in chromium oxide (for example, Cr 2 O 3 ). The peak position can mean the median value of the peak.

[0044] For example, the position of the peak in the Cr 2p energy spectrum of the metal oxide measured by XPS (X-ray photoelectron spectroscopy measurement) may be 0.5 eV or more, for example, 0.5 eV to 1.5 eV higher than the position of the peak in the Cr 2p spectrum of Cr 2 O 3 .

[0045] In some embodiments, the metal oxide may not contain chromium oxide (CrO x ). For example, the metal oxide is Cr 2 O 3It does not necessarily have the crystal structure. As a result, while promoting the ammonia oxidation reaction of the ammonia oxidation catalyst more, the ammonia selectivity can be further increased. Therefore, only ammonia can be selectively removed while suppressing the reaction between oxygen and hydrogen.

[0046] For example, the crystal structure of the metal oxide can be measured by XRD (X-Ray Diffraction) analysis. In the XRD graph of the metal oxide, peaks may not be observed within the frequency range corresponding to Cr 2 O 3 either.

[0047] In some embodiments, the chromium content may be 0.05 mol to 0.30 mol based on the total of titanium and chromium on an elemental basis. Within this range, the ammonia selectivity can be further improved, and the reaction between hydrogen or nitrogen and oxygen can be further suppressed. As a result, the ammonia removal efficiency can be increased while suppressing the consumption of hydrogen and the generation of nitrogen oxides.

[0048] In one embodiment, the chromium content may be 0.10 mol to 0.30 mol, 0.10 mol to 0.25 mol, or 0.10 mol to 0.20 mol based on the total of titanium and chromium on an elemental basis. Within this range, the ammonia oxidation catalyst has high activity and can further enhance the reactivity with respect to ammonia in a high-temperature environment.

[0049] In some embodiments, the metal oxide can have a crystalline structure. For example, the metal oxide may not contain an amorphous structure.

[0050] In one embodiment, the metal oxide can have an anatase phase. The anatase phase can mean an anatase crystalline phase. Thereby, the stability and activity of the ammonia oxidation catalyst can be further improved.

[0051] In one embodiment, the metal oxide can be represented by the following Chemical Formula 1.

[0052] [Chemical Formula 1] Cr x Ti 1-x O 2

[0053] In Chemical Formula 1, x may be 0.05 to 0.30, 0.1 to 0.3, 0.1 to 0.25, or 0.1 to 0.2.

[0054] In some embodiments, the specific surface area of the metal oxide is, for example, 50 m 2 / g to 150 m 2 / g, or 80 m 2 / g to 130 m 2 / g. The specific surface area can be measured by the BET (Brunauer, Emmett, Teller) method by adsorption of N 2 .

[0055] In one embodiment, the specific surface area of the metal oxide is 85 m 2 / g to 125 m 2 / g, 90 m 2 / g to 120 m 2 / g, or 100 m 2 / g to 120 m 2 / g. Within this range, the oxidation reaction and selectivity of ammonia can be further improved.

[0056] FIG. 1 is a schematic process flowchart for explaining a method for manufacturing an ammonia oxidation catalyst according to an exemplary embodiment.

[0057] Referring to FIG. 1, a chromium compound and a titanium compound can be mixed in an organic solvent to produce a first mixture (for example, step S10).

[0058] In some embodiments, the organic solvent can include an alcohol-based solvent. For example, the organic solvent can include ethanol, propanol, isopropanol, butanol, etc. By including an alcohol-based solvent in the organic solvent, the compatibility with the precursor compound can be further enhanced. Also, by using an alcohol-based solvent as the base solvent, the gelation reaction can be promoted even when a small amount of water is added.

[0059] In one embodiment, the organic solvent can include isopropanol.

[0060] In some embodiments, the chromium compound can include chromium nitrate, chloride, bromide, fluoride, hydroxide, carbonate, acetate, sulfate, etc.

[0061] In one embodiment, the chromium compound can include chromium nitrate.

[0062] In some embodiments, the titanium compound can include titanium alkoxide, nitrate, chloride, bromide, fluoride, hydroxide, carbonate, acetate, sulfate, etc.

[0063] In one embodiment, the titanium compound can include titanium alkoxide. By including titanium alkoxide as the titanium compound, the compatibility and affinity with the alcohol-based solvent can be further enhanced, and the crystal structure of titanium oxide can be formed by the gelation reaction and the heat treatment reaction.

[0064] For example, the titanium compound can include titanium tetraisopropoxide.

[0065] By introducing the chromium compound and the titanium compound together into an organic solvent, chromium can be efficiently incorporated into the crystal structure of titanium oxide. For example, if the titanium compound is first introduced and mixed in an organic solvent, the dispersibility of the first mixture may decrease, and chromium oxide having a crystal form different from that of titanium oxide may be formed.

[0066] In one embodiment, the mixing rate of the chromium compound, the titanium compound, and the organic solvent may be 300 rpm to 600 rpm, 350 rpm to 550 rpm, or 400 rpm to 500 rpm.

[0067] In one embodiment, the mixing step can be performed for 10 minutes to 240 minutes, 30 minutes to 180 minutes, or 60 minutes to 120 minutes.

[0068] In one embodiment, the temperature of the mixing step may be 2°C to 40°C.

[0069] In some embodiments, the chromium compound and the titanium compound can be added such that the chromium is 0.05 mol to 0.30 mol per 1 mol in total of titanium and chromium on an elemental basis.

[0070] In one embodiment, in the chromium compound and the titanium compound, the content of the chromium may be 0.1 mol to 0.3 mol, 0.1 mol to 0.25 mol, or 0.1 mol to 0.2 mol per 1 mol in total of titanium and chromium on an elemental basis.

[0071] Water can be added to the first mixture to produce a second mixture (for example, step S20).

[0072] Water can be added to the first mixture to perform a sol-gel reaction on the second mixture.

[0073] In some embodiments, the amount of water added may be from 1 part by weight to 30 parts by weight with respect to 100 parts by weight of the organic solvent. Within this range, the sol-gel reaction of the second mixture can be carried out more efficiently, and by the heat treatment described later, the crystallinity of the ammonia oxidation catalyst can be easily adjusted to a desired range.

[0074] In one embodiment, the amount of water added may be from 1 part by weight to 25 parts by weight, from 2 parts by weight to 25 parts by weight, or from 2 parts by weight to 20 parts by weight with respect to 100 parts by weight of the organic solvent.

[0075] In some embodiments, the pH of the second mixture may be 5 or more. For example, the pH of the second mixture may be from 5 to 8, or from 6 to 8. Within this range, titanium compounds, such as titanium oxides, are more efficiently converted by the gelation of the second mixture, and chromium atoms can be easily substituted into the crystal lattice of the titanium oxide.

[0076] In one embodiment, nitric acid can also be added to the first mixture to perform a sol-gel reaction on the second mixture.

[0077] The second mixture can be gelled to form a precursor solution (e.g., step S30).

[0078] With the gelation of the second mixture, chromium atoms can be easily incorporated into the crystal lattice of the titanium oxide by the heat treatment step described later. Thereby, chromium can be substituted for titanium atoms in the crystal structure of the titanium oxide while suppressing the formation of the crystal structure of chromium oxide.

[0079] In one embodiment, the temperature of the gelation step may be from 15°C to 30°C.

[0080] In one embodiment, the gelation step can be carried out at a rotation speed of 100 rpm to 500 rpm.

[0081] In one embodiment, the gelation step can be carried out for 15 to 30 hours, or 20 to 30 hours.

[0082] In some embodiments, the gelation step can include a stirring step and an aging step for the second mixture.

[0083] For example, the second mixture can be stirred at a rotation speed of 100 rpm to 500 rpm and left standing for a certain period of time in a constant temperature device.

[0084] In one embodiment, the stirring step can be carried out at a temperature of 15°C to 30°C for 30 minutes to 4 hours, or 1 hour to 3 hours.

[0085] In one embodiment, the aging step can be carried out at a temperature in the range of 15°C to 30°C. In one embodiment, the aging step can be carried out for 10 to 30 hours, or 20 to 30 hours.

[0086] The precursor solution can be heat-treated to produce an ammonia oxidation catalyst (for example, step S40).

[0087] In one embodiment, the precursor solution can be dried at a temperature of 70°C to 125°C, 80°C to 120°C, or 85°C to 110°C.

[0088] In one embodiment, the precursor solution can be dried and calcined at a temperature of 350°C to 600°C, 400°C to 550°C, or 450°C to 550°C.

[0089] Figure 2 is a process flow chart for explaining a catalyst system according to an exemplary embodiment.

[0090] The catalyst system according to an embodiment of the present disclosure can include the ammonia oxidation catalyst according to the foregoing embodiment.

[0091] The catalyst system can include an ammonia decomposition reactor 20 and a catalyst section 30. The catalyst section 30 can include the ammonia oxidation catalyst.

[0092] In the ammonia decomposition reactor 20, ammonia can be decomposed. For example, ammonia (NH 3 ) is decomposed in the ammonia decomposition reactor 20, and hydrogen (H 2 ) can be generated.

[0093] As the ammonia decomposition reaction, a thermal decomposition reaction or a decomposition reaction using a reduction catalyst can be carried out.

[0094] In one embodiment, the ammonia decomposition reactor 20 may include an ammonia decomposition catalyst. The ammonia decomposition catalyst can be stacked and arranged in the ammonia decomposition reactor 20. Hydrogen gas can be generated while ammonia passes through the ammonia decomposition reactor 20.

[0095] In one embodiment, the ammonia decomposition reactor 20 can include a burner. By the burner, the temperature of the ammonia decomposition reactor 20 can be increased, and the thermal energy required for the decomposition of ammonia can be supplied.

[0096] The catalyst system can further include an ammonia supply section 10. The ammonia supply section 10 can be located in the upstream region of the ammonia decomposition reactor 20. The ammonia supply section 10 can supply ammonia to the ammonia decomposition reactor 20. In one embodiment, the ammonia supply section 10 can include an ammonia storage tank.

[0097] For example, the ammonia gas supplied from the ammonia supply section 10 is decomposed in the ammonia decomposition reactor 20 and can be decomposed into hydrogen (H 2 ) and nitrogen (N 2 ).

[0098] In some embodiments, a heat exchanger 50 can be disposed between the ammonia supply unit 10 and the ammonia decomposition reactor 20. The heat exchanger 50 can receive the supply of liquid ammonia from the ammonia supply unit 10 and vaporize it. Thereby, gaseous ammonia can be supplied to the ammonia decomposition reactor 20.

[0099] In one embodiment, the heat exchanger 50 can receive heat supply from the combustion gas discharged from the burner in the ammonia decomposition reactor 20. The heat flow between the ammonia decomposition reactor 20 and the heat exchanger 50 is shown by a dashed line in FIGS. 2 and 3.

[0100] The catalyst unit 30 can be located in the downstream region of the ammonia decomposition reactor 20. The ammonia oxidation catalyst can be stacked and disposed in the catalyst unit 30.

[0101] The reaction gas and oxygen gas can be supplied from the ammonia decomposition reactor 20 to the catalyst unit 30. The reaction gas can contain ammonia that did not react during the ammonia decomposition process. The ammonia and oxygen gas can undergo an oxidation reaction in the catalyst unit 30 to remove the unreacted ammonia.

[0102] In one embodiment, the reaction gas supplied from the ammonia decomposition reactor 20 to the catalyst unit 30 can contain hydrogen and nitrogen generated during the decomposition process of ammonia. Since the ammonia oxidation catalyst has a high selectivity for ammonia, it can selectively remove only ammonia without consuming the hydrogen generated during the decomposition process of ammonia. Therefore, the concentration of ammonia and the concentration of nitrogen oxides can be lowered while maintaining a high concentration of hydrogen by the catalyst unit 30.

[0103] In one embodiment, the supply amount of the oxygen gas may be 8.9 or less, 6.7 or less, 4.4 or less, or 2.2 or less on a ppm basis with respect to the ammonia concentration in the reaction gas. Even with a small supply amount of oxygen gas, the ammonia oxidation catalyst can selectively promote the oxidation reaction with respect to ammonia. Thereby, while improving the ammonia removal efficiency, the supply amount of oxygen gas can be controlled to suppress the consumption of hydrogen gas and the generation of nitrogen oxides.

[0104] In one embodiment, the reaction temperature of the ammonia decomposition reactor 20 may be 250°C to 500°C, 280°C to 450°C, or 300°C to 400°C. Within this range, the consumption of hydrogen and the generation of nitrogen oxides can be suppressed, and the ammonia removal efficiency can be further increased.

[0105] In one embodiment, in the ammonia oxidation reaction by the ammonia oxidation catalyst, the reaction temperature is 200°C to 400°C, and the amount of nitrogen oxides (NOx) generated measured under the condition that the concentration ratio of O 3 to NH 2 is 2.2 or more may be 200 ppm or less.

[0106] For example, the content of NOx generated by the oxidation reaction of the ammonia oxidation catalyst with respect to ammonia and an oxygen-containing gas under the conditions of 200°C to 400°C may be 150 ppm or less, or 120 ppm or less. The concentration ratio of O 3 to NH 2 in the reaction gas may be 2.2 to 8.9, 2.2 to 6.7, or 2.2 to 4.4 on a ppm basis.

[0107] FIG. 3 is a process flowchart for explaining a catalyst system according to an exemplary embodiment.

[0108] Referring to FIG. 3, the catalyst system may further include an ammonia adsorption unit 60. The ammonia adsorption unit 60 can be located in the downstream region of the ammonia decomposition reactor 20.

[0109] The ammonia adsorption unit 60 can include an ammonia selective adsorbent. Thereby, the ammonia adsorption unit 60 can selectively adsorb and remove unreacted ammonia. The concentration of ammonia can be reduced by the ammonia adsorption unit 60, and high-purity hydrogen can be produced.

[0110] In some embodiments, the ammonia adsorption unit 60 can have a pressure swing adsorption (PSA) or temperature swing adsorption (TSA) method.

[0111] In some embodiments, the ammonia adsorption unit 60 can be located in the downstream region of the catalyst unit 30. Thereby, ammonia remaining without being oxidized in the catalyst unit 30 can be removed by the ammonia adsorption unit.

[0112] In some embodiments, the ammonia adsorption unit 60 can also be located in the upstream region of the catalyst unit 30. For example, the ammonia adsorption unit 60 can be located between the ammonia decomposition reactor 20 and the catalyst unit 30.

[0113] In one embodiment, the ammonia selective adsorbent can include a metal oxide containing aluminum and silicon. For example, the ammonia selective adsorbent can include an aluminosilicate. In one embodiment, the aluminosilicate can carry or dope alkali metal ions (e.g., sodium ions, calcium ions, potassium ions, etc.).

[0114] According to an exemplary embodiment, the hydrogen gas purified by the catalyst unit 30 or the ammonia adsorption unit 60 can be supplied to the fuel cell 40. For example, the fuel cell 40 may be a hydrogen fuel cell 40.

[0115] The ammonia oxidation catalyst can reduce the concentrations of ammonia and nitrogen oxides without consuming hydrogen. As a result, the gas generated in the ammonia decomposition reactor 20 while passing through the catalyst unit 30 can be purified as high-purity hydrogen gas. Thereby, the power generation efficiency of the fuel cell 40 can be further improved.

[0116] In one embodiment, the gas that has completed the reaction in the fuel cell 40 can be resupplied to the burner of the ammonia decomposition reactor 20. The gas can be used as a heat source for the ammonia decomposition reaction.

[0117] Hereinafter, embodiments of the present disclosure will be further described with reference to specific production examples. However, the examples and comparative examples included in the production examples are merely illustrative and do not limit the appended claims. It is obvious to those skilled in the art that various changes and modifications can be made within the scope of the present disclosure and the scope of the technical idea, and it is natural that these modifications and changes belong to the appended claims.

[0118] Production Example: Production of Ammonia Oxidation Catalyst (1) Example 1 Chromium nitrate (Cr(NO 3 ) 3 ) and titanium isopropoxide (TTIP) were added to 250 g of isopropyl alcohol (IPA), and the mixture was stirred at room temperature at a rotation speed of 450 rpm for 30 minutes to produce a first mixture. The chromium nitrate and the titanium isopropoxide were added so that the molar ratio of chromium to titanium satisfied 30:70 and the final mass of the oxide catalyst after calcination was 6 g.

[0119] 12 g of deionized water was added to the first mixture to produce a second mixture. The second mixture was stirred at a temperature of 25°C at a rotation speed of 450 rpm for 2 hours and stored at 25°C for 24 hours to obtain a gel-like precursor solution.

[0120] The precursor solution was heat-treated at a temperature of 100°C for 24 hours to obtain a powder. The powder was heat-treated at a temperature of 500°C for 4 hours to produce an ammonia oxidation catalyst.

[0121] (2) Example 2 An ammonia oxidation catalyst was produced in the same manner as in Example 1, except that the chromium nitrate and the titanium isopropoxide were introduced so that the molar ratio of chromium to titanium was 15:85.

[0122] (3) Comparative Example 1 An ammonia oxidation catalyst was produced in the same manner as in Example 1, except that the chromium nitrate and the titanium isopropoxide were introduced so that the molar ratio of chromium to titanium was 5:95.

[0123] (4) Comparative Example 2 6 g of chromium nitrate (Cr(NO 3 ) 3 ) was added to 100 mL of isopropyl alcohol (IPA), and the mixture was stirred at a rotation speed of 450 rpm for 30 minutes at room temperature to produce a first mixture. 10 mL of propylene oxide was added to the first mixture to produce a second mixture. The second mixture was stirred at a rotation speed of 450 rpm at a temperature of 25°C for 12 hours to obtain a gel-like precursor solution. The precursor solution was heat-treated at a temperature of 100°C for 1 hour to obtain a powder. The powder was heat-treated at a temperature of 400°C for 3 hours to produce an ammonia oxidation catalyst.

[0124] (5) Comparative Example 3 Powder of rutile crystal phase-containing TiO 3 ) 3 ·9H 2 O was added to chromium nitrate hydrate (Cr(NO 2 ), and the mixture was stirred for 2 hours. After drying at room temperature for 24 hours, it was heat-treated at a temperature of 500°C for 4 hours to produce a metal oxide with chromium oxide (CrO 2 ) supported on TiO x . The supported amount of Cr was adjusted to 10% by weight based on TiO 2 .

[0125] (6) Comparative Example 4 Al 2 O 3 An ammonia oxidation catalyst with 2 wt% Pt supported on the carrier was prepared.

[0126] (7) Measurement of energy band gap For the metal oxide, UV-Vis DRS analysis was performed at 25 °C and atmospheric pressure using a UV-Vis spectrometer (UV-VIS-NIR, Cary 5000). The DRS absorption spectrum of the metal oxide was measured, and the energy band gap was calculated from the plot of (αhν) against photon energy (hν). 1 / 2 The measurement results are shown in Table 1 below.

[0127]

Table 1

[0128] (8) XRD analysis The crystal structures of the metal oxides of the above Examples and Comparative Example 1 were measured by X-ray diffraction analysis. Specifically, the crystal structure of the composite oxide was measured by X-ray diffraction analysis (X-ray Diffraction, XRD) under the conditions of a current of 300 mA, a voltage of 50 kV, a wavelength of Cu Kα line (1.5428 Å), a scanning speed of 5 degree min -1 and 2θ = 10° to 80°. Figure 4 is an XRD graph of the metal oxide of the Example. Referring to Figure 4, in the case of Example 1, peaks corresponding to Cr 2 O 3 were shown. In the cases of Example 2 and Comparative Example 1, no crystal peaks corresponding to Cr 2 O 3 were shown, and the metal oxide had crystal peaks corresponding to TiO 2 . ​

[0129] (9) Analysis of specific surface area The specific surface areas of the metal oxides of the above Examples and Comparative Examples 1 to 3 were measured by the BET method based on the nitrogen gas adsorption amount using a specific surface area measuring device (TriStar II Plus, manufactured by MICROMERITCS). The measurement results are shown in Table 2 below.

[0130]

Table 2

[0131] Referring to Table 2 above, the metal oxides of the Examples have a higher specific surface area than the metal oxides of the Comparative Examples. In the case of Example 2, the metal oxide has a high specific surface area of 100 m 2 / g or more.

[0132] Experimental Example 1 Put 2.5 g of the ammonia catalyst into a fixed-bed reactor and reduce it with a mixed gas of H 2 and N 2 (H 2 10 vol%) at a temperature of 400 °C for 1 hour. The ammonia oxidation reaction was evaluated using a reaction gas mixture. The flow rate of the reaction gas was adjusted using a mass flow meter, and the space velocity of the reaction gas was 30,000 hr -1 . The concentrations of oxygen and ammonia were adjusted to be about 2,300 ppm and about 1,050 ppm, respectively. The compositions of O 2 , NH 3 , H 2 , He, and N 2 in the reaction gas were adjusted as shown in Table 3 below.

[0133]

Table 3

[0134] The gas concentration after the reaction was measured by QMS (Dycor 2000, manufactured by Ametek), and NH 3The concentrations of NH₃ and NO were measured using a gas analyzer (Airwell 7+e, Tunable Diode Laser Absorption Spectroscopy, manufactured by Korea Industrial Gases Co., Ltd.) and a gas analyzer (CLD82 S, manufactured by ECO Physics), respectively. While increasing the temperature of the reactor from 50 °C to 450 °C at a heating rate of 10 °C / min, the concentrations of NH₃ 3 and NO were measured at each temperature. The results of the evaluation are shown in Table 4 and Figure 5.

[0135]

Table 4

[0136] Figure 5 is a graph showing the gas concentrations when using the ammonia oxidation catalysts of Example 1 and the Comparative Example. Referring to Figure 5, in the case of Example 1, the concentration of NH₃ 3 decreased to 10 ppm or less, and NO was generated in an amount of 10 ppm or less up to 300 °C. Also, the amount of NO generated at 400 °C was measured to be 130 ppm or less.

[0137] In the case of Comparative Example 1, the content of chromium, which is the active metal, was low and ammonia could not react with oxygen, and the concentration of ammonia did not substantially decrease.

[0138] In the case of Comparative Example 2, the concentration of NH₃ 3 decreased to 23 ppm, but the amount of NO generated increased to 300 ppm or more. Also, when the temperature rose above 300 °C, the concentration of NH₃ 3 increased due to the depletion of oxygen by the reaction of oxygen and hydrogen.

[0139] In the case of Comparative Example 3, the oxygen injected for the oxidation of ammonia in the chromium oxide supported on TiO₂ 2 completely reacted with hydrogen and was consumed. Due to the depletion of oxygen, ammonia was not removed.

[0140] In the case of Comparative Example 4, ammonia did not react with oxygen, and the ammonia concentration was measured to be high in all temperature ranges.

[0141] Experimental Example 2 For Example and Comparative Example 2, while changing the ratio of O 2 / NH 3 and the reaction temperature in the reaction gas respectively, the concentrations of NH 3 and NO after the reaction were measured. The concentrations of NH 3 and NO were measured after the gas concentration after the reaction reached the normal state.

[0142] O 2 / NH 3 The ratio was adjusted by changing only the concentrations of O 2 and NH 3 in the composition of the reaction gas in Table 3 above. H 2 , He and N 2 were adjusted to satisfy the ratios in Table 3 respectively.

[0143] Figures 6a and 6b are graphs showing the gas concentrations when the ammonia oxidation catalyst of Example 2 was used.

[0144] Specifically, when the ratio of O 2 / NH 3 was 2.2 and 4.4 respectively in the reaction gas, the concentrations of NH 3 and NO depending on the temperature were measured.

[0145] Referring to Figures 6a and 6b, in the case of Example 2, even when the ratio of O 2 and the reaction temperature increased, the concentrations of NH 3 and NO in the gas after the reaction were low.

[0146] Figure 7 is a graph showing the gas concentrations when the ammonia oxidation catalyst of Example 1 was used.

[0147] Referring to Figure 7, in the case of Example 1, the concentrations of NH 3 and NO in the gas after the reaction were generally low, and the amount of NO generated did not increase even when the reaction temperature increased.

[0148] Figs. 8a to 8d are graphs showing the gas concentrations when the ammonia oxidation catalyst of Comparative Example 2 was used.

[0149] Specifically, when the ratios of O 2 / NH 3 are 2.2, 4.4, 6.7, and 8.9, respectively, the concentrations of NH 3 and NO were measured as a function of temperature.

[0150] Referring to Figs. 8a to 8d, in the case of Comparative Example 2, the concentrations of NH 3 and NO in the gas after the reaction were generally high. Also, as the reaction temperature increased or the ratio of O 2 increased, the amount of NO generated increased significantly.

Claims

1. Metal oxides including titanium and chromium, The ammonia oxidation catalyst, wherein the energy band gap of the metal oxide is less than 1.4 eV as measured by UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS).

2. 2. The ammonia oxidation catalyst of claim 1, wherein the energy band gap of the metal oxide is greater than or equal to 0.2 eV and less than 1.4 eV.

3. 2. The ammonia oxidation catalyst according to claim 1, wherein the content of the chromium is, on an elemental basis, 0.10 mol to 0.30 mol per 1 mol of the total of titanium and chromium.

4. 2. The ammonia oxidation catalyst of claim 1, wherein the metal oxide has a crystal structure of titanium oxide and the chromium is doped into the crystal structure of titanium oxide.

5. 2. The ammonia oxidation catalyst of claim 1, wherein the metal oxide comprises an anatase phase.

6. In the ammonia oxidation reaction using the ammonia oxidation catalyst, the reaction temperature is 200° C. to 400° C., and NH ３ O ２ 2. The ammonia oxidation catalyst according to claim 1, wherein the amount of nitrogen oxides (NOx) generated is 200 ppm or less when measured under conditions where the concentration ratio of

7. mixing a chromium compound and a titanium compound in an organic solvent to produce a first mixture; adding water to the first mixture to produce a second mixture; gelating the second mixture to prepare a precursor solution; and heat-treating the precursor solution.

8. The method for producing an ammonia oxidation catalyst according to claim 7 , wherein the organic solvent comprises an alcohol-based solvent.

9. The method for producing an ammonia oxidation catalyst according to claim 8, wherein the second mixture has a pH of 5 or more.

10. 9. The method for producing an ammonia oxidation catalyst according to claim 8, wherein the step of heat treating the precursor solution includes the steps of drying at a temperature of 70°C to 125°C and calcining at a temperature of 350°C to 600°C.

11. an ammonia decomposition reactor; a catalyst section located downstream of the ammonia decomposition reactor, the catalyst section comprising the ammonia oxidation catalyst of claim 1.

12. 12. The catalyst system of claim 11 further comprising an ammonia supply located in an upstream region of the ammonia decomposition reactor.

13. 12. The catalyst system of claim 11, further comprising an ammonia adsorbing section located in a downstream region of the ammonia decomposition reactor and comprising an ammonia-selective adsorbent.

14. 14. The catalyst system of claim 13, wherein the ammonia adsorbing section is located in a downstream region of the catalyst section.

15. 12. The catalyst system of claim 11, further comprising a fuel cell receiving a supply of hydrogen from the catalyst portion.

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