Ammonia oxidation catalyst, catalyst system and method for producing the ammonia oxidation catalyst

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 making the ammonia oxidation catalyst, and a catalyst system including the ammonia oxidation catalyst. [Background technology]

[0002] In recent years, due to environmental issues, technologies to reduce greenhouse gases or harmful gases in the atmosphere have been developed. This has led to an increase in demand for new renewable energy sources to replace the use of fossil fuels such as oil and coal. Hydrogen can be mainly used as one of the new renewable energy sources.

[0003] Ammonia (NH3) is a carbon-free fuel that can efficiently store and transport hydrogen. For example, ammonia can be decomposed to produce hydrogen (H2) and nitrogen (N2), and the hydrogen produced from ammonia can be supplied to fuel cells. However, to supply hydrogen through the ammonia decomposition reaction, an excess amount of ammonia is required, and unreacted ammonia that has not been converted into hydrogen can be released into the atmosphere as exhaust.

[0004] Ammonia is flammable and toxic, making it a potential source of secondary pollution. Therefore, it must be converted into environmentally harmless components before being released into the atmosphere. For example, selective ammonia oxidation catalysts can be used to efficiently remove residual ammonia while suppressing the generation of harmful gases. This allows ammonia to be selectively decomposed into nitrogen (N2) and water (H2O).

[0005] However, when high concentrations of oxygen are injected for the selective oxidation of ammonia, the oxygen can react with hydrogen (H2) produced by the ammonia decomposition reaction or with nitrogen to produce nitrogen oxides (NOx) such as NO or NO2. Furthermore, hydrogen is consumed by oxygen, reducing the overall hydrogen production efficiency, and nitrogen oxides can cause environmental pollution. 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 [Problem to be solved by the invention]

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

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

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

[0009] An ammonia oxidation catalyst according to an embodiment of the present disclosure may comprise a metal oxide comprising titanium and chromium, wherein the metal oxide has an energy band gap of less than 1.4 eV as measured by UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS).

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

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

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

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

[0014] In some embodiments, in the ammonia oxidation reaction using the ammonia oxidation catalyst, the amount of nitrogen oxides (NOx) generated may be 200 ppm or less, measured under conditions where the reaction temperature is 200°C to 400°C and the concentration ratio of O2 to NH3 is 2.2 or more.

[0015] In a method for producing an ammonia oxidation catalyst according to an embodiment of the present disclosure, a first mixture may be prepared by mixing a chromium compound and a titanium compound in an organic solvent. A second mixture may be prepared by adding water to the first mixture. A precursor solution may be prepared by gelation of the second mixture. The precursor solution may 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 greater.

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

[0019] A catalyst system according to an embodiment of the present disclosure includes an ammonia decomposition reactor and a catalyst section located downstream of the ammonia decomposition reactor and including an ammonia oxidation catalyst according to the aforementioned embodiment.

[0020] Some embodiments can further include an ammonia supply located upstream of the ammonia decomposition reactor.

[0021] In some embodiments, the catalyst system may further include an ammonia adsorbing section located downstream of the ammonia decomposition reactor and including an ammonia-selective adsorbent.

[0022] In some embodiments, the ammonia adsorbing section can be located in a downstream region of the catalytic section.

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

[0024] The ammonia oxidation catalyst according to the embodiment of the present disclosure can promote the selective reaction of oxygen and ammonia, thereby improving the ammonia removal efficiency while suppressing hydrogen consumption and nitrogen oxide production, even under conditions of low oxygen concentration.

[0025] In the method for producing an ammonia oxidation catalyst according to an embodiment of the present disclosure, chromium oxide and titanium alkoxide can be gelled under predetermined mixing conditions, whereby chromium is substituted for titanium in the crystal lattice of titanium dioxide, resulting in the formation of chromium oxide (CrO x ) can be suppressed.

[0026] A catalyst system according to an embodiment of the present disclosure can include the ammonia oxidation catalyst, which can reduce the amount of oxygen supplied and suppress the generation of nitrogen oxides, thereby providing high-purity hydrogen gas to a fuel cell. [Brief explanation of the drawings]

[0027] [Figure 1] FIG. 1 is a schematic process flow diagram of a method for producing an ammonia decomposition catalyst according to an exemplary embodiment. [Figure 2] FIG. 2 is a process flow diagram illustrating a catalyst system according to an exemplary embodiment. [Figure 3] FIG. 3 is a process flow diagram illustrating a catalyst system according to an exemplary embodiment. [Figure 4] FIG. 4 is an XRD graph of a metal oxide according to an example. [Figure 5] FIG. 5 is a graph showing gas concentrations when the ammonia oxidation catalysts of Example 1 and Comparative Example were used. [Figure 6a] 6a and 6b are graphs showing gas concentrations when the ammonia oxidation catalyst of Example 2 is used. [Figure 6b] 6a and 6b are graphs showing gas concentrations when the ammonia oxidation catalyst of Example 2 is used. [Figure 7] FIG. 7 is a graph showing the gas concentration when the ammonia oxidation catalyst of Example 1 is used. [Figure 8a] 8a to 8d are graphs showing gas concentrations when the ammonia oxidation catalyst of Comparative Example 2 was used. [Figure 8b] 8a to 8d are graphs showing gas concentrations when the ammonia oxidation catalyst of Comparative Example 2 was used. [Figure 8c] 8a to 8d are graphs showing gas concentrations when the ammonia oxidation catalyst of Comparative Example 2 was used. [Figure 8d] 8a to 8d are graphs showing gas concentrations when the ammonia oxidation catalyst of Comparative Example 2 was used. DETAILED DESCRIPTION OF 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 is provided that includes an ammonia oxidation catalyst.

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

[0031] The ammonia oxidation catalyst according to the present disclosure includes a metal oxide containing titanium and chromium. The ammonia oxidation catalyst selectively promotes the oxidation reaction of ammonia (NH3) to convert ammonia into nitrogen gas. The ammonia oxidation reaction refers to the reaction in which ammonia reacts with oxygen (O2) to produce nitrogen gas.

[0032] The metal oxide may have a titanium oxide crystal structure. Chromium may be doped into the titanium oxide. For example, some titanium atoms may be substituted with chromium atoms in the titanium oxide crystal structure, or chromium atoms may be located in oxygen vacancies in the titanium oxide crystal structure, or chromium atoms may be located in open spaces in the titanium and oxygen lattices, resulting in interstitial doping.

[0033] This improves the stability of the ammonia oxidation catalyst, increases the specific surface area and active sites of the catalyst, and further promotes the ammonia oxidation reaction.

[0034] According to an exemplary embodiment, the metal oxide may have a crystalline structure of titanium dioxide (TiO2), for example, the crystal lattice of the metal oxide may be substantially identical to the crystal lattice of titanium dioxide.

[0035] In some embodiments, chromium may be incorporated into the crystalline structure of the titanium dioxide. For example, some of the titanium atoms in the titanium dioxide crystal lattice may be replaced with chromium atoms. By including chromium within the crystalline structure of the ammonia oxidation catalyst while maintaining the crystalline structure of titanium dioxide, both structural stability and catalytic activity can be improved.

[0036] The ammonia oxidation catalyst according to the exemplary embodiment has the above-described crystal structure, which can enhance ammonia selectivity and ammonia removal efficiency. This can improve ammonia removal efficiency even under low-oxygen conditions and prevent hydrogen consumption due to high-oxygen concentrations. Furthermore, the reaction between nitrogen and oxygen is suppressed, thereby reducing the amount of nitrogen oxides produced.

[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 greater than or equal to 0.2 eV and less than 1.4 eV. The energy band gap of the metal oxide may be measured by UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS).

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

[0039] For example, even if the content of chromium atoms in the metal oxide is the same, if the chromium atoms are in titanium oxide (TiO x ) crystal lattice, or when chromium atoms are present in chromium oxide (CrO x The crystalline morphology of the metal oxide may differ depending on whether it exists as a crystalline structure of SiO 2 or a crystalline structure of SiO 2 . Therefore, the catalytic activity and properties of the ammonia oxidation catalyst may differ depending on the crystalline morphology of the metal oxide.

[0040] The change in electronic structure due to the incorporated Cr in the crystal structure of the titanium oxide provides a new valence band, and the energy band gap of the metal oxide can be shifted to a lower value.

[0041] The ammonia oxidation catalyst contains a metal oxide having an energy band gap within the above range, which improves the ammonia oxidation reaction and ammonia selectivity, thereby promoting the selective oxidation reaction of ammonia even at low oxygen partial pressures and reducing hydrogen consumption and nitrogen oxide generation.

[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. In this range, the proportion of chromium oxide in the crystal structure of the metal oxide can be reduced, and the reaction selectivity and reaction efficiency for ammonia can be further improved.

[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 a chromium oxide (e.g., Cr2O3). The peak position may refer to the median value of the peak.

[0044] For example, the peak position 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 peak position in the Cr 2p spectrum of Cr2O3.

[0045] In some embodiments, the metal oxide is chromium oxide (CrO x ) may not be included. For example, the metal oxide may not have a Cr2O3 crystal structure. This can further enhance the ammonia selectivity while further promoting the ammonia oxidation reaction of the ammonia oxidation catalyst. Therefore, it is possible to selectively remove only ammonia while suppressing the reaction between oxygen and hydrogen.

[0046] For example, the crystal structure of the metal oxide can be measured by X-ray diffraction (XRD) analysis. In the XRD graph of the metal oxide, no peak may be observed within the frequency range corresponding to Cr2O3.

[0047] In some embodiments, the chromium content may be 0.05 mol to 0.30 mol per 1 mol of the total of titanium and chromium on an elemental basis. Within this range, ammonia selectivity can be further improved and the reaction of hydrogen or nitrogen with oxygen can be further suppressed. This can increase ammonia removal efficiency while suppressing hydrogen consumption and nitrogen oxide generation.

[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 per mole of the total of titanium and chromium on an elemental basis. Within this range, the ammonia oxidation catalyst has high activity and can further enhance its reactivity to ammonia in a high-temperature environment.

[0049] In some embodiments, the metal oxide can have a crystalline structure, e.g., the metal oxide can be free of an amorphous structure.

[0050] In one embodiment, the metal oxide may have an anatase phase, which may refer to an anatase crystalline phase, and this may further improve the stability and activity of the ammonia oxidation catalyst.

[0051] In one embodiment, the metal oxide can be represented by Formula 1 below:

[0052] [Chemical formula 1] Cr x Ti 1-x O2

[0053] In the above 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~150m 2 / g, or 80m 2 / g~130m 2 The specific surface area may be measured by the BET (Brunauer, Emmett, Teller) method using N2 adsorption.

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

[0056] FIG. 1 is a schematic process flow diagram illustrating a method for producing 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 (eg, step S10).

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

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

[0060] In some embodiments, the chromium compounds can include chromium nitrates, chlorides, bromides, fluorides, hydroxides, carbonates, acetates, sulfates, and the like.

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

[0062] In some embodiments, the titanium compounds can include titanium alkoxides, nitrates, chlorides, bromides, fluorides, hydroxides, carbonates, acetates, sulfates, and the like.

[0063] In one embodiment, the titanium compound may include a titanium alkoxide, which can enhance compatibility and affinity with the alcohol-based solvent and form a titanium oxide crystal structure through a gelation reaction and a heat treatment reaction.

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

[0065] By adding the chromium compound and the titanium compound together to the organic solvent, chromium can be efficiently incorporated into the crystal structure of titanium oxide. For example, if the titanium compound is first added to the organic solvent and mixed, the dispersibility of the first mixture decreases, and chromium oxide having a different crystal morphology from titanium oxide may be formed.

[0066] In one embodiment, the mixing speed 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 carried out for 10 to 240 minutes, 30 to 180 minutes, or 60 to 120 minutes.

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

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

[0070] In one embodiment, the content of chromium in the chromium compound and the titanium compound 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 of the total of titanium and chromium on an elemental basis.

[0071] A second mixture can be produced by adding water to the first mixture (eg, step S20).

[0072] Water may be added to the first mixture to carry out a sol-gel reaction on the second mixture.

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

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

[0075] In some embodiments, the pH of the second mixture may be 5 or greater. For example, the pH of the second mixture may be 5 to 8, or 6 to 8. In this range, gelation of the second mixture more efficiently converts the titanium compound, e.g., titanium oxide, and allows chromium atoms to be readily substituted into the crystal lattice of the titanium oxide.

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

[0077] The second mixture may be gelled to form a precursor solution (eg, step S30).

[0078] As the second mixture gels, chromium atoms can be easily incorporated into the titanium oxide crystal lattice by the heat treatment process described below, thereby substituting titanium atoms for chromium in the titanium oxide crystal structure while suppressing the formation of the chromium oxide crystal structure.

[0079] In one embodiment, the temperature of the gelling step may be 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 gelling step can include stirring and aging the second mixture.

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

[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 another embodiment, the aging step can be carried out for 10 hours to 30 hours, or 20 hours to 30 hours.

[0086] The precursor solution can be heat-treated to produce an ammonia oxidation catalyst (eg, 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 may be dried and calcined at a temperature between 350°C and 600°C, between 400°C and 550°C, or between 450°C and 550°C.

[0089] FIG. 2 is a process flow diagram illustrating a catalyst system according to an exemplary embodiment.

[0090] A catalyst system according to an embodiment of the present disclosure may include an ammonia oxidation catalyst according to the previously described embodiments.

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

[0092] Ammonia can be decomposed in the ammonia decomposition reactor 20. For example, ammonia (NH3) can be decomposed in the ammonia decomposition reactor 20 to produce hydrogen (H2).

[0093] The ammonia decomposition reaction can be a thermal decomposition reaction or a decomposition reaction using a reduction catalyst.

[0094] In one embodiment, ammonia decomposition reactor 20 may include an ammonia decomposition catalyst, which may be arranged in a stack within ammonia decomposition reactor 20. As ammonia passes through ammonia decomposition reactor 20, hydrogen gas may be produced.

[0095] In one embodiment, ammonia decomposition reactor 20 can include a burner that can increase the temperature of ammonia decomposition reactor 20 and provide the thermal energy required to decompose the ammonia.

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

[0097] For example, ammonia gas supplied from the ammonia supply unit 10 can be decomposed in the ammonia decomposition reactor 20 into hydrogen (H2) and nitrogen (N2).

[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 and vaporize liquid ammonia from the ammonia supply unit 10. This allows the ammonia in the gas phase to be supplied to the ammonia decomposition reactor 20.

[0099] In one embodiment, heat exchanger 50 may receive its heat supply from combustion gases exhausted from a burner in ammonia decomposition reactor 20. The heat flow between ammonia decomposition reactor 20 and heat exchanger 50 is shown by the dashed lines in Figures 2 and 3.

[0100] The catalyst unit 30 may be located in a downstream region of the ammonia decomposition reactor 20. The ammonia oxidation catalyst may be arranged in layers within the catalyst unit 30.

[0101] A 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 reaction. The ammonia and oxygen gas undergo an oxidation reaction in the catalyst unit 30, thereby removing the unreacted ammonia.

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

[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 ppm based on the ammonia concentration in the reaction gas. The ammonia oxidation catalyst can selectively promote the oxidation reaction of ammonia even when the supply amount of oxygen gas is small. This allows the supply amount of oxygen gas to be controlled while improving ammonia removal efficiency, thereby suppressing hydrogen gas consumption and nitrogen oxide generation.

[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, hydrogen consumption and nitrogen oxide production can be suppressed, and the ammonia removal efficiency can be further improved.

[0105] In one embodiment, in the ammonia oxidation reaction using the ammonia oxidation catalyst, the amount of nitrogen oxides (NOx) generated may be 200 ppm or less, measured under conditions where the reaction temperature is 200°C to 400°C and the concentration ratio of O2 to NH3 is 2.2 or more.

[0106] For example, the content of NOx generated by the oxidation reaction of ammonia and an oxygen-containing gas by the ammonia oxidation catalyst at a temperature of 200° C. to 400° C. may be 150 ppm or less, or 120 ppm or less. The concentration ratio of O2 to NH3 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 flow diagram illustrating a catalyst system according to an exemplary embodiment.

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

[0109] The ammonia adsorption unit 60 can include an ammonia-selective adsorbent. This allows the ammonia adsorption unit 60 to selectively adsorb and remove unreacted ammonia. The ammonia adsorption unit 60 can reduce the ammonia concentration, allowing high-purity hydrogen to be produced.

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

[0111] In some embodiments, the ammonia adsorption section 60 can be located in a downstream region of the catalyst section 30. This allows ammonia that remains unoxidized in the catalyst section 30 to be removed by the ammonia adsorption section.

[0112] In some embodiments, the ammonia adsorption section 60 may be located in an upstream region of the catalyst section 30. For example, the ammonia adsorption section 60 may be located between the ammonia decomposition reactor 20 and the catalyst section 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 be supported or doped with alkali metal ions (e.g., sodium ions, calcium ions, potassium ions, etc.).

[0114] According to an exemplary embodiment, hydrogen gas purified by the catalyst section 30 or the ammonia adsorption section 60 may 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 can be purified into high-purity hydrogen gas while passing through the catalyst section 30. This can further improve the power generation efficiency of the fuel cell 40.

[0116] In one embodiment, the gas from the completed reaction in the fuel cell 40 can be re-supplied 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, the embodiments of the present disclosure will be further described with reference to specific manufacturing examples. However, the examples and comparative examples included in the manufacturing examples are merely illustrative and do not limit the scope of the appended claims. It is obvious to those skilled in the art that various changes and modifications can be made within the scope and technical idea of ​​the present disclosure, and it is natural that these changes and modifications also fall within the scope of the appended claims.

[0118] Manufacturing example: Manufacturing of ammonia oxidation catalyst (1) Example 1 Chromium nitrate (Cr(NO3)3) and titanium isopropoxide (TTIP) were added to 250 g of isopropyl alcohol (IPA) and stirred at room temperature for 30 minutes at a rotation speed of 450 rpm to prepare a first mixture. The chromium nitrate and titanium isopropoxide were added so that the molar ratio of chromium to titanium was 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 prepare a second mixture, which was then stirred at 450 rpm at 25°C 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 100°C for 24 hours to obtain a powder, which was then heat-treated at 500°C for 4 hours to prepare 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 titanium isopropoxide were added 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 titanium isopropoxide were added so that the molar ratio of chromium to titanium was 5:95.

[0123] (4) Comparative Example 2 6 g of chromium nitrate (Cr(NO3)3) was added to 100 mL of isopropyl alcohol (IPA) and stirred at room temperature at a rotation speed of 450 rpm for 30 minutes to prepare a first mixture. 10 mL of propylene oxide was added to the first mixture to prepare a second mixture, which was then stirred at 25°C and 450 rpm for 12 hours to obtain a gel-like precursor solution. The precursor solution was heat-treated at 100°C for 1 hour to obtain a powder, which was then heat-treated at 400°C for 3 hours to prepare an ammonia oxidation catalyst.

[0124] (5) Comparative Example 3 TiO2 powder with a rutile crystal phase was added to chromium nitrate hydrate (Cr(NO3)3·9H2O) and stirred for 2 hours. After drying at room temperature for 24 hours, it was heat-treated at 500°C for 4 hours to convert chromium oxide (CrO x The amount of Cr supported was adjusted to 10 wt% relative to TiO2.

[0125] (6) Comparative Example 4 An ammonia oxidation catalyst was prepared in which 2 wt% of Pt was supported on an Al2O3 support.

[0126] (7) Energy band gap measurement The metal oxide was subjected to UV-Vis DRS analysis using a UV-Vis spectrometer (UV-VIS-NIR, Cary 5000) at 25°C and atmospheric pressure. The DRS absorption spectrum of the metal oxide was measured, and the (αhν) 1 / 2 The energy band gap was calculated from the plot. 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-mentioned Example and Comparative Example 1 were measured by X-ray diffraction analysis. Specifically, the current was 300mA, the voltage was 50kV, the wavelength of Cu Kα radiation was 1.5428Å, and the temperature was 5 degrees min -1 The crystal structure of the composite oxide was measured by X-ray diffraction (XRD) under the conditions of a scanning speed of 1000 kJ / cm and 2θ=10° to 80°. FIG. 4 is an XRD graph of the metal oxide of the example. Referring to FIG. 4, in the case of Example 1, peaks corresponding to Cr2O3 were observed at 35° to 38° and 42° to 45°. In the case of Example 2 and Comparative Example 1, the XRD spectrum of the metal oxide did not show a crystalline peak corresponding to Cr2O3, but the metal oxide had a crystalline peak corresponding to TiO2.

[0129] (9) Specific surface area analysis The specific surface areas of the metal oxides of the above Examples and Comparative Examples 1 to 3 were measured by the BET method using a specific surface area measuring device (TriStar II Plus, manufactured by MICROMERITCS) based on the amount of nitrogen gas adsorption. 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 specific surface area of ​​100 m 2 / g or more.

[0132] Experimental Example 1 2.5 g of the ammonia catalyst was placed in a fixed-bed reactor and reduced with a mixed gas of H2 and N2 (H2 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 h . -1 It was. The concentrations of oxygen and ammonia were adjusted to about 2,300 ppm and about 1,050 ppm, respectively. The compositions of O2, NH3, H2, He, and N2 in the reaction gas were adjusted as shown in Table 3 below.

[0133] [Table 3]

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

[0135] [Table 4]

[0136] FIG. 5 is a graph showing gas concentrations when the ammonia oxidation catalysts of Example 1 and Comparative Example were used. 5, in Example 1, the NH3 concentration was reduced to 10 ppm or less, and NO was generated in an amount of 10 ppm or less up to 300° C. Furthermore, 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 an active metal, was so low that ammonia could not react with oxygen, and the ammonia concentration did not substantially decrease.

[0138] In the case of Comparative Example 2, the NH3 concentration was reduced to 23 ppm, but the amount of NO generated increased to 300 ppm or more. Furthermore, when the temperature rose to 300°C or higher, the NH3 concentration increased due to the depletion of oxygen caused by the reaction of oxygen with hydrogen.

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

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

[0141] Experimental Example 2 The concentrations of NH3 and NO after the reaction were measured while changing the O2 / NH3 ratio in the reaction gas and the reaction temperature for Example and Comparative Example 2. The concentrations of NH3 and NO were measured after the gas concentrations after the reaction reached normal levels.

[0142] The O2 / NH3 ratio was adjusted by changing only the concentrations of O2 and NH3 in the reaction gas composition in Table 3. H2, He, and N2 were adjusted so as to satisfy the ratios in Table 3, respectively.

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

[0144] Specifically, the concentrations of NH3 and NO were measured as a function of temperature when the O2 / NH3 ratio in the reaction gas was 2.2 and 4.4, respectively.

[0145] 6a and 6b, in Example 2, the concentrations of NH3 and NO in the gas after the reaction were low even when the proportion of O2 and the reaction temperature increased.

[0146] FIG. 7 is a graph showing the gas concentration when the ammonia oxidation catalyst of Example 1 is used.

[0147] Referring to FIG. 7, in Example 1, the concentrations of NH3 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] 8a to 8d are graphs showing gas concentrations when the ammonia oxidation catalyst of Comparative Example 2 was used.

[0149] Specifically, the concentrations of NH3 and NO were measured as a function of temperature when the O2 / NH3 ratio in the reaction gas was 2.2, 4.4, 6.7, and 8.9, respectively.

[0150] 8a to 8d, the concentrations of NH3 and NO in the gas after the reaction were generally high in Comparative Example 2. Furthermore, the amount of NO generated increased significantly as the reaction temperature or the proportion of O2 increased.

Claims

1. containing a metal oxide containing titanium and chromium, an energy band gap of the metal oxide measured by ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS) of less than 1.4 eV;

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 0.10 mol to 0.30 mol per 1 mol of the total of titanium and chromium on an elemental basis.

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

5. 10. 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 against 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; gelation of the second mixture to prepare a precursor solution; and heat-treating the precursor solution, the ammonia oxidation catalyst comprises a metal oxide containing titanium and chromium; The method wherein the metal oxide has an energy band gap of less than 1.4 eV as measured by UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS).

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 pH of the second mixture is 5 or higher.

10. 9. The method for producing an ammonia oxidation catalyst according to claim 8, wherein the step of heat-treating the precursor solution comprises 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 adsorption section located downstream of the ammonia decomposition reactor and comprising an ammonia-selective adsorbent.

14. 14. The catalyst system of claim 13, wherein the ammonia adsorption section is located downstream of the catalyst section.

15. 12. The catalyst system of claim 11, including a fuel cell that receives a supply of hydrogen from the catalyst portion.

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