Patent Application
20250153146
The present application claims priority under 35 U.S.C. § 119 (a) to Korean application number 10-2023-0157334 filed on Nov. 14, 2023, which is incorporated herein by reference in its entirety.
Embodiments of the present disclosure relate to a catalyst for ammonia oxidation (“an ammonia oxidation catalyst”), a method of preparing the ammonia oxidation catalyst and a catalyst system including the ammonia oxidation catalyst.
Recently, due to environmental pollution concerns, techniques for reducing greenhouse gases or harmful gases in the atmosphere are being developed. Accordingly, there is a growing demand for a renewable alternative energy to replace the use of fossil fuels such as petroleum and coal. Hydrogen may be mainly used as one of the renewable alternative energy.
Ammonia (NH3) is a carbon-free fuel and may efficiently store and transport hydrogen. For example, ammonia may be decomposed to generate hydrogen (H2) and nitrogen (N2), and the hydrogen generated from the ammonia may be supplied to a fuel cell and the like. However, in order to supply the hydrogen through a decomposition reaction of ammonia, an excess of ammonia may be required, and unreacted products that have not been converted into hydrogen among the supplied ammonia may be released into the atmosphere as exhaust gases.
However, ammonia is a secondary pollutant because it is flammable and toxic. Hence, it is desirable to convert the ammonia into an environmentally harmless component before releasing it into the atmosphere. For example, a catalyst for selective ammonia oxidation may be used to efficiently remove residual ammonia while suppressing the generation of harmful gases. Accordingly, ammonia may be selectively decomposed into nitrogen (N2) and water (H2O).
However, when a high concentration of oxygen is injected into a reaction for the selective oxidation of ammonia, the oxygen may react with hydrogen (H2) produced through the ammonia decomposition reaction, or react with nitrogen to generate nitrogen oxides (NOx) such as NO or NO2, etc. Since the hydrogen is consumed by the oxygen, an overall production efficiency of hydrogen may be decreased, and environmental pollution may occur due to the nitrogen oxides. Therefore, new solutions are needed to address these issues before ammonia can be used in an environmental friendly manner for producing hydrogen.
Various embodiments of the present disclosure overcome the aforementioned issues of existing ammonia systems.
An embodiment of the present disclosure provides an ammonia oxidation catalyst which may selectively oxidize ammonia.
Another embodiment of the present disclosure provides a method of preparing an ammonia oxidation catalyst.
In addition, another embodiment of the present disclosure provides a catalyst system which includes the above-described ammonia oxidation catalyst.
Embodiments of the present disclosure provide an ammonia oxidation catalyst capable of efficiently removing ammonia while suppressing the consumption of hydrogen and generation of nitrogen oxides.
According to an embodiment of the present disclosure, a catalyst for ammonia oxidation is provided which includes a metal oxide including titanium and chromium. The energy band gap of the metal oxide as measured by UV-Vis diffuse reflectance spectroscopy (DRS) may be less than 1.4 eV.
In some embodiments, the energy band gap of the metal oxide may be 0.2 eV or more and less than 1.4 eV.
In some embodiments, a content of the chromium may be 0.05 to 0.30 moles based on a total 1 mole of titanium and chromium on an elemental basis.
In some embodiments, the metal oxide may have a titanium oxide crystal structure, and the chromium may be doped into the titanium oxide crystal structure.
In some embodiments, the metal oxide may include an anatase phase.
In some embodiments, in an ammonia oxidation reaction by the ammonia oxidation catalyst, an amount of nitrogen oxide (NOx) generated may be 200 ppm or less when measured under conditions where a reaction temperature is 200° C. to 400° C. and a concentration ratio of O2 to NH3 is 2.2 or more.
In a method of preparing a catalyst for ammonia oxidation according to another embodiment of the present disclosure, a chromium compound and a titanium compound may be mixed in an organic solvent to prepare a first mixture. Water may be added to the first mixture to prepare a second mixture. The second mixture may be gelated to prepare a precursor solution. The precursor solution may be subjected to heat treatment.
In some embodiments, the organic solvent may include an alcohol solvent.
In some embodiments, the second mixture may have a pH of 5 or more.
In some embodiments, the operation of performing heat treatment on the precursor solution may include: drying the precursor solution at a temperature of 70° C. to 125° C.; and performing calcination on the precursor solution at a temperature of 350° C. to 600° C.
In yet another embodiment of the present disclosure, a catalyst system may include an ammonia decomposition reactor, and a catalyst unit which is located downstream from the ammonia decomposition reactor and includes the ammonia oxidation catalyst according to the above-described embodiments.
In some embodiments, the catalyst system may further include an ammonia supply unit which is located in an upstream region of the ammonia decomposition reactor.
In some embodiments, the catalyst system may further include an ammonia adsorption unit which is located downstream from, the ammonia decomposition reactor and includes an ammonia selective adsorbent. The ammonia adsorption unit may be located downstream from the catalyst unit.
In some embodiments, the catalyst system may include a fuel cell configured to receive hydrogen from the catalyst unit.
The ammonia oxidation catalyst according to embodiments of the present disclosure may promote a selective reaction between oxygen and ammonia. Therefore, an ammonia removal efficiency may be improved even under conditions of low concentration of oxygen while suppressing the consumption of hydrogen and generation of nitrogen oxides.
In the method of preparing the ammonia oxidation catalyst according to embodiments of the present disclosure, chromium oxide and titanium alkoxide may be gelated under a predetermined mixing condition. Accordingly, chromium may be substituted with titanium in a crystal lattice of titanium dioxide, thus suppressing the generation of chromium oxides (CrOx).
The catalyst system according to embodiments of the present disclosure may include the ammonia oxidation catalyst. Thereby, a supply amount of oxygen may be reduced, and the generation of nitrogen oxides may be suppressed, thus providing a high-purity hydrogen gas to the fuel cell.
The above and other objects, features and other advantages of the embodiments of the present disclosure will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:
According to embodiments of the present disclosure, there is provided an ammonia oxidation catalyst.
According to embodiments of the present disclosure, there is provided a catalyst system including the ammonia oxidation catalyst.
Hereinafter, embodiments of the present disclosure will be described in more detail.
An ammonia oxidation catalyst according to embodiments of the present disclosure includes a metal oxide including titanium and chromium. The ammonia oxidation catalyst may selectively promote an oxidation reaction of ammonia (NH3) to convert the ammonia into a nitrogen gas. The ammonia oxidation reaction refers to a reaction in which ammonia reacts with oxygen (O2) to produce the nitrogen gas.
The metal oxide may have a titanium oxide crystal structure. Chromium may be doped into the titanium oxide within the metal oxide. For example, some of titanium atoms may be substituted with chromium atoms within the crystal structure of the titanium oxide, or chromium atoms may be positioned at oxygen vacancies, which are positions where oxygen is missed in the crystal structure of the titanium oxide, or chromium atoms may be positioned in empty spaces within the lattices of titanium and oxygen, thereby resulting in interstitial doping.
Accordingly, stability of the ammonia oxidation catalyst may be improved, and the specific surface area and the active site area of the catalyst may be increased, thereby further promoting the oxidation reaction of ammonia.
According to various embodiments, the metal oxide may have a crystal structure of titanium dioxide (TiO2). For example, the crystal lattice of the metal oxide may be substantially the same as the crystal lattice of titanium dioxide.
In some embodiments, chromium may be incorporated into the crystal structure of the titanium dioxide. For example, some of the titanium atoms in the crystal lattice of the titanium dioxide may be substituted with chromium atoms. It has been found, rather unexpectedly, that when the ammonia oxidation catalyst has the crystal structure of titanium dioxide and includes chromium in the crystal structure, both the structural stability and the catalytic activity may be improved.
Since the ammonia oxidation catalyst according to an embodiment has the above-described crystal structure, the ammonia selectivity and the ammonia removal efficiency may be increased. Accordingly, the ammonia removal efficiency may be improved even under conditions of low concentration of oxygen, and the consumption of hydrogen due to high concentration of oxygen may be prevented. In addition, a reaction between nitrogen and oxygen may be suppressed, such that an amount of nitrogen oxides generated may be decreased.
An 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 may be measured by UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS).
The energy band gap may be measured as an indicator of the degree that the chromium atoms are substituted or doped into the crystal structure of the titanium dioxide. For example, even if the contents of chromium atoms included in the metal oxide are the same as each other, crystal forms of the metal oxide may be different from each other when the chromium atoms exist in the crystal lattice of titanium oxide (TiOx) and when the chromium atoms exist in the crystal structure of chromium oxide (CrOx). Accordingly, the catalytic activity and properties of the ammonia oxidation catalyst may vary depending on the crystal form of the metal oxide.
A new valence band is provided due to a change in an electronic structure caused by the chromium (Cr) incorporated in the crystal structure of the titanium oxide, and the energy band gap of the metal oxide may be shifted to a lower value.
The ammonia oxidation catalyst may include a metal oxide having the energy band gap within the above range, such that the ammonia oxidation reaction and ammonia selectivity may be improved. Accordingly, the selective oxidation reaction for ammonia may be promoted even at a low oxygen partial pressure, and the consumption of hydrogen and the amount of the nitrogen oxides generated may be decreased.
In some embodiments, the energy band gap of the metal oxide may be 0.2 eV or more and less than 1.4 eV, or 0.5 eV to 1.3 eV, or 0.8 eV to 1.3 eV. Within the above range, a ratio of the chromium oxide in the crystal structure of the metal oxide may be reduced, and the reaction selectivity and reaction efficiency for ammonia may be further enhanced.
In some embodiments, a peak position of a binding energy of Cr in the metal oxide may be higher than the peak position of the binding energy of Cr in the chromium oxide (e.g., Cr2O3). The peak position may refer to the peak median value.
For example, the position of a peak in the Cr 2p energy spectrum of the metal oxide measured by X-ray photoelectron spectroscopy (XPS) measurement may be higher by 0.5 e V or more, for example, 0.5 eV to 1.5 eV, than the position of the peak in the Cr 2p spectrum of the Cr2O3.
In some embodiments, the metal oxide may not include chromium oxide (CrOx). For example, the metal oxide may not have a crystal structure of Cr2O3. Accordingly, the ammonia selectivity may be further enhanced while further promoting the ammonia oxidation reaction of the ammonia oxidation catalyst. Accordingly, only ammonia may be selectively removed while suppressing the reaction between oxygen and hydrogen.
For example, the crystal structure of the metal oxide may be measured through X-ray diffraction (XRD) analysis. In the XRD graph of the metal oxide, no peak may be observed within the wavenumber range corresponding to Cr2O3.
In some embodiments, a content of the chromium may be 0.05 moles to 0.30 moles based on a total 1 mole of titanium and chromium on an elemental basis. Within the above range, the ammonia selectivity may be further improved, and the reaction of hydrogen or nitrogen with oxygen may be further suppressed. Accordingly, the ammonia removal efficiency may be improved while suppressing the consumption of hydrogen and generation of nitrogen oxides.
In some embodiments, the content of the chromium may be 0.10 moles to 0.30 moles, or 0.10 moles to 0.25 moles, or 0.10 moles to 0.20 moles based on the total 1 mole of titanium and chromium on the elemental basis. Within the above range, the reactivity for ammonia in a high-temperature environment may be further enhanced while the ammonia oxidation catalyst has high activity.
In some embodiments, the metal oxide may have a crystalline structure. For example, the metal oxide may not include an amorphous structure.
In some embodiments, the metal oxide may have an anatase phase. For example, an anatase phase may mean an anatase crystal phase. Accordingly, the stability and activity of the ammonia oxidation catalyst may be further improved.
In some embodiments, the metal oxide may be represented by Formula 1 below.
CrxTi1-xO2 Formula 1
In the Formula 1, x may be 0.05 to 0.30, or 0.1 to 0.3, or 0.1 to 0.25, or 0.1 to 0.2.
In some embodiments, the metal oxide may have a specific surface area of, for example, 50 m2/g to 150 m2/g or 80 to 130 m2/g. The specific surface area may be measured through the Brunauer-Emmett-Teller (BET) method by nitrogen (N2) adsorption.
In some embodiments, the metal oxide may have a specific surface area of 85 m2/g to 125 m2/g, or 90 m2/g to 120 m2/g, or 100 m2/g to 120 m2/g. Within the above range, the oxidation reaction and selectivity of ammonia may be further improved.
Referring to
In some embodiments, the organic solvent may include an alcohol solvent. For example, the organic solvent may include ethanol, propanol, isopropanol, butanol and the like. When the organic solvent includes the alcohol solvent, compatibility with precursor compounds may be further enhanced.
In addition, when using the alcohol solvent as a base solvent, a gelation reaction may be promoted even with the addition of a small amount of water.
In some embodiments, the organic solvent may include isopropanol.
In some embodiments, the chromium compound may include a nitrate, chloride, bromide, fluoride, hydroxide, carbonate, acetate, sulfate of chromium, and the like.
In some embodiments, the chromium compound may include chromium nitrate.
In some embodiments, the titanium compound may include an alkoxide, nitrate, chloride, bromide, fluoride, hydroxide, carbonate, acetate, sulfate of titanium, and the like.
In some embodiments, the titanium compound may include titanium alkoxide. When titanium alkoxide is the titanium compound, compatibility and affinity with the alcohol solvent may be further enhanced, and a crystal structure of titanium oxide may be formed through a gelation reaction and a heat treatment reaction.
For example, the titanium compound may include titanium tetraisopropoxide (also known as titanium isopropoxide and having the formula Ti(OCH(CH3)2)4).
The chromium and titanium compounds may be introduced together into the organic solvent, thereby allowing chromium to be more efficiently incorporated into the crystal structure of titanium oxide. For example, when the titanium compound is first introduced into the organic solvent and mixed, dispersibility of the first mixture is reduced, and chromium oxide may be formed having a crystal form separate from the crystal structure of the titanium oxide.
In some embodiments, a mixing speed of the chromium and titanium compounds in the organic solvent may be 300 rpm to 600 rpm, or 350 rpm to 550 rpm, or 400 rpm to 500 rpm.
In some embodiments, the mixing process may be performed for 10 minutes to 240 minutes, or 30 minutes to 180 minutes, or 60 minutes to 120 minutes.
In some embodiments, the temperature in the mixing process may be 2° C. to 40° C.
In some embodiments, the chromium and the titanium compounds may be added so that the chromium is added in an amount of 0.05 moles to 0.30 moles based on the total 1 mole of titanium and chromium on the elemental basis.
In some embodiments, among the chromium and the titanium compounds, the content of chromium may be 0.1 moles to 0.3 moles, or 0.1 moles to 0.25 moles, or 0.1 moles to 0.2 moles based on the total 1 mole of titanium and chromium on the elemental basis.
Water may be added to the first mixture to prepare a second mixture (e.g., operation S20).
Water may be added to the first mixture to perform a sol-gel reaction for the second mixture.
In some embodiments, an amount of water added may be 1 to 30 parts by weight (“wt. parts”) based on 100 wt. parts of the organic solvent. Within the above range, the sol-gel reaction of the second mixture may be performed more efficiently, and the crystallinity of the ammonia oxidation catalyst may be easily controlled to a desired range by heat treatment to be described below.
In some embodiments, the amount of water added may be 1 wt. part to 25 wt. parts, 2 wt. parts to 25 wt. parts, or 2 wt. parts to 20 wt. parts based on 100 wt. parts of the organic solvent.
In some embodiments, the second mixture may have a pH of 5 or more. For example, the second mixture may have a pH of 5 to 8, or 6 to 8. Within the above range, the titanium compound, for example titanium oxide may be more efficiently converted into titanium oxide by gelation of the second mixture, thereby allowing chromium atoms to be easily substituted into the crystal lattice of the titanium oxide.
In some embodiments, nitric acid may be added to the first mixture to perform a sol-gel reaction for the second mixture.
The second mixture may be gelated to form a precursor solution (e.g., operation S30).
As the second mixture is gelated, chromium atoms may be easily incorporated into the crystal lattice of titanium oxide through a heat treatment process to be described below. Accordingly, chromium may be substituted with titanium atoms of the titanium oxide crystal structure while suppressing the production of the crystal structure of chromium oxide.
In some embodiments, the temperature in the gelation process may be 15° C. to 30° C.
In some embodiments, the gelation process may be performed at a rotation speed of 100 rpm to 500 rpm.
In some embodiments, the gelation process may be performed for 15 hours to 30 hours, or 20 hours to 30 hours.
In some embodiments, the gelation process may include a stirring process and an aging process performed on the second mixture.
For example, the second mixture may be stirred at a rotation speed of 100 rpm to 500 rpm, and then left in a constant-temperature device for a predetermined period of time.
In some embodiments, the stirring process may be performed at a temperature of 15° C. to 30° C. for 30 minutes to 4 hours, or 1 hour to 3 hours.
In some embodiments, the aging process may be performed at a temperature in a range of 15° C. to 30° C. In some embodiments, the aging process may be performed for 10 hours to 30 hours, or 20 hours to 30 hours.
An ammonia oxidation catalyst may be prepared by performing heat treatment on the precursor solution (e.g., operation S40).
In some embodiments, the precursor solution may be dried at a temperature of 70° C. to 125° C., 80° C. to 120° C., or 85° C. to 110° C.
In some embodiments, the precursor solution may be dried, and subjected to calcination at a temperature of 350° C. to 600° C., 400° C. to 550° C., or 450° C. to 550° C.
The catalyst system according to embodiments of the present disclosure may include the ammonia oxidation catalyst according to the above-described embodiments.
The catalyst system may include an ammonia decomposition reactor 20 and a catalyst unit 30. The catalyst unit 30 may include the ammonia oxidation catalyst.
Ammonia may be decomposed in the ammonia decomposition reactor 20. For example, ammonia (NH3) may be decomposed to generate hydrogen (H2) within the ammonia decomposition reactor 20.
The ammonia decomposition reaction may include a thermal decomposition reaction or a decomposition reaction using a reduction catalyst.
In some embodiments, the ammonia decomposition reactor 20 may also include an ammonia decomposition catalyst. The ammonia decomposition catalyst may be arranged in a stacked manner within the ammonia decomposition reactor 20. While the ammonia passes through the ammonia decomposition reactor 20, hydrogen gas may be generated.
In some embodiments, the ammonia decomposition reactor 20 may include a burner for increasing the temperature in the ammonia decomposition reactor 20 and supplying the heat energy needed for ammonia decomposition.
The catalyst system may further include an ammonia supply unit 10. The ammonia supply unit 10 may be located in an upstream region of the ammonia decomposition reactor 20. Ammonia may be supplied to the ammonia decomposition reactor 20 through the ammonia supply unit 10. In some embodiments, the ammonia supply unit 10 may include an ammonia storage tank.
For example, the ammonia gas supplied from the ammonia supply unit 10 may be decomposed into hydrogen (H2) and nitrogen (N2) in the ammonia decomposition reactor 20.
In some embodiments, a heat exchanger 50 may be arranged between the ammonia supply unit 10 and the ammonia decomposition reactor 20. The heat exchanger 50 may receive liquid ammonia from the ammonia supply unit 10 and vaporize the same. Accordingly, gaseous ammonia may be supplied to the ammonia decomposition reactor 20.
In some embodiments, the heat exchanger 50 may receive heat from a combustion gas discharged from the burner in the ammonia decomposition reactor 20. Heat flow between the ammonia decomposition reactor 20 and the heat exchanger 50 is indicated by dotted line arrows in
The catalyst unit 30 may be located downstream from the ammonia decomposition reactor 20. The ammonia oxidation catalyst may be arranged in a stacked manner within the catalyst unit 30.
A reaction gas and an oxygen gas may be supplied from the ammonia decomposition reactor 20 to the catalyst unit 30. The reaction gas may contain ammonia that has not reacted during the ammonia decomposition reaction. The ammonia and the oxygen gas may be induced to undergo an oxidation reaction in the presence of the catalyst in the catalyst unit 30, thereby removing any unreacted ammonia.
In some embodiments, the reaction gas supplied from the ammonia decomposition reactor 20 to the catalyst unit 30 may include hydrogen and nitrogen generated during the ammonia decomposition process. The ammonia oxidation catalyst may have high selectivity for ammonia for selectively removing only ammonia without consuming hydrogen generated during the ammonia decomposition process. Accordingly, the concentration of ammonia and the concentration of nitrogen oxides may be decreased while maintaining the concentration of hydrogen at a high level through the catalyst unit 30.
In some embodiments, the amount of oxygen gas supplied may be 8.9 or less, 6.7 or less, 4.4 or less, or 2.2 or less on a ppm basis relative to the ammonia concentration in the reaction gas. Even if the amount of oxygen gas supplied is small, the oxidation reaction for ammonia may be selectively promoted by the ammonia oxidation catalyst. Accordingly, the amount of oxygen gas supplied may be controlled to suppress the consumption of hydrogen gas and generation of nitrogen oxides while improving the ammonia removal efficiency.
In some embodiments, the reaction temperature in the ammonia decomposition reactor 20 may be 250° C. to 500° C., or 280° C. to 450° C., or 300° C. to 400° C. Within the above range, the consumption of hydrogen and generation of nitrogen oxides may be suppressed, and the ammonia removal efficiency may be further increased.
In some embodiments, in the ammonia oxidation reaction using the ammonia oxidation catalyst, an amount of nitrogen oxide (NOx) generated may be 200 ppm or less, which is measured under conditions where the reaction temperature is 200° C. to 400° C. and a concentration ratio of 02 to NH3 is 2.2 or more.
For example, the content of NOx generated by the oxidation reaction of the ammonia oxidation catalyst for ammonia and 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 O2 to NH3 in the reaction gas may be 2.2 to 8.9, or 2.2 to 6.7, or 2.2 to 4.4 on the ppm basis.
Referring to
The ammonia adsorption unit 60 may include an ammonia selective adsorbent. Accordingly, the ammonia adsorption unit 60 may selectively adsorb and remove unreacted ammonia. The ammonia concentration may be decreased by the ammonia adsorption unit 60, and high-purity hydrogen may be produced.
In some embodiments, the ammonia adsorption unit 60 may operate using a pressure swing adsorption (PSA) process or a temperature swing adsorption (TSA) process.
In the illustrated embodiment of
However, it is noted that in some embodiments (not shown), the ammonia adsorption unit 60 may also be located upstream from the catalyst unit 30 meaning that the ammonia adsorption unit 60 may be located between the ammonia decomposition reactor 20 and the catalyst unit 30.
In some embodiments, the ammonia selective adsorbent may include a metal oxide including aluminum and silicon. For example, the ammonia selective adsorbent may include aluminosilicate. In some embodiments, the aluminosilicate may be carried or doped with an alkali metal ion (e.g., sodium ion, calcium ion, potassium ion, etc.).
According to various embodiments, hydrogen gas purified in the catalyst unit 30 or the ammonia adsorption unit 60 may be supplied to a fuel cell 40. For example, the fuel cell 40 may be a hydrogen fuel cell 40.
The concentrations of ammonia and nitrogen oxides may be decreased without consuming hydrogen by the ammonia oxidation catalyst. Accordingly, the gas generated in the ammonia decomposition reactor 20 while passing through the catalyst unit 30 may be purified into high-purity hydrogen gas. Accordingly, a power generation efficiency of the fuel cell 40 may be further improved.
In some embodiments, the gas on which the reaction have been completed in the fuel cell 40 may be supplied back to the bumer of the ammonia decomposition reactor 20. Then, the gas may be used as a heat source for the ammonia decomposition reaction.
Hereinafter, embodiments of the present disclosure will be further described with reference to specific preparative examples. Examples and comparative examples included in the preparative examples only illustrate the scope of the present disclosure and are not intended to limit the appended claims. Those skilled in the art will understand that various alterations and modifications are possible within the scope and technical concepts of the present disclosure. Such alterations and modifications are duly included within the scope of the appended claims.
Chromium nitrate (Cr(NO3) 3) and titanium isopropoxide (TTIP) were added to 250 g of isopropyl alcohol (IPA) and stirred at room temperature at a rotation speed of 450 rpm for 30 minutes to prepare a first mixture. The chromium nitrate and the titanium isopropoxide were added so that a molar ratio of chromium and titanium was 30:70 and a mass of the final oxide catalyst after calcination was 6 g.
An amount of 12 g of deionized water was added to the first mixture to prepare a second mixture. The second mixture was stirred at a temperature of 25° C. and at a rotation speed of 450 rpm for 2 hours, and stored at 25° C. for 24 hours to obtain a precursor solution in the form of a gel.
The precursor solution was subjected to heat treatment at a temperature of 100° C. for 24 hours to obtain a powder. The powder was subjected to heat treatment at a temperature of 500° C. for 4 hours to prepare an ammonia oxidation catalyst.
An ammonia oxidation catalyst was prepared in the same manner as in Example 1, except that the chromium nitrate and the titanium isopropoxide were added so that the molar ratio of chromium and titanium was 15:85.
An ammonia oxidation catalyst was prepared in the same manner as in Example 1, except that the chromium nitrate and the titanium isopropoxide were added so that the molar ratio of chromium and titanium was 5:95.
6 g of chromium nitrate (Cr(NO3)3) was added to 100 mL of isopropyl alcohol (IPA) and stirred at room temperature and a rotation speed of 450 rpm for 30 minutes to prepare a first mixture.
A second mixture was prepared by adding 10 mL of propylene oxide to the first mixture. The second mixture was stirred at a temperature of 25° C. and at a rotation speed of 450 rpm for 12 hours to obtain a precursor solution in the form of a gel.
The precursor solution was subjected to heat treatment at a temperature of 100° C. for 1 hour to obtain a powder. The powder was subjected to heat treatment at a temperature of 400° C. for 3 hours to prepare an ammonia oxidation catalyst.
TiO2 powder having a rutile crystalline phase was added to chromium nitrate hydrate (Cr(NO3)3·9H2O) and stirred for 2 hours. After drying at room temperature for 24 hours, the mixture was subjected to heat treatment at a temperature of 500° C. for 4 hours to produce a metal oxide in which chromium oxide (CrOx) is carried on TiO2. The amount of Cr carried on TiO2 was adjusted to 10% by weight (“wt. %”).
An ammonia oxidation catalyst in which 2 wt. % of Pt is carried on an Al2O3 carrier was prepared.
UV-Vis Diffuse Reflectance Spectroscopy (UV-Vis DRS) analysis was performed on the metal oxides using a UV-Vis spectrometer (UV-VIS-NIR, Cary 5000) under conditions of 25° C. and atmospheric pressure. The DRS absorption spectrum for the metal oxides was measured, and the energy band gap was calculated from the plot of (αhv)1/2 according to the photon energy (hv).
Measurement results are shown in Table 1 below.
Crystal structures of the metal oxides of the examples and Comparative Example 1 were measured through X-ray diffraction analysis.
Specifically, the crystal structures of the composite oxides were measured by X-ray diffraction analysis (XRD) under conditions of 300 mA current, 50 kV voltage, Cu Kα radiation of wavelength (1.5428 Å), scanning speed of 5 degree min−1, and 2θ=10° to 80°.
Referring to
In the case of Example 2 and Comparative Example 1, no crystal peak corresponding to Cr2O3 appeared in the XRD spectrum of the metal oxides, and the metal oxides had crystal peaks corresponding to TiO2.
Specific surface areas of the metal oxides of the examples and Comparative Examples 1 to 3 were measured with the BET method by nitrogen gas adsorption using a specific surface area measuring device (TriStar II Plus, MICROMERITCS).
Measurement results are shown in Table 2 below.
Referring to Table 2 above, the metal oxides of the examples 1 and 2 had higher specific surface areas than the metal oxides of the comparative examples 1, 2, and 3. In the case of Example 2, the metal oxide had a high specific surface area of more than 100 m2/g.
2.5 g of the ammonia catalyst was put into a fixed bed reactor, and subjected to reduction treatment with a mixture of H2 and N2 gas (H2 10% by volume) at a temperature of 400° C. for 1 hour.
Then, ammonia oxidation reaction was evaluated using the reaction gas mixture. The flow rate of the reaction gas was controlled 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 O2, NH3, H2, He, and N2 in the reaction gas were controlled as shown in Table 3 below.
The gas concentration after the reaction was measured by QMS (Dycor 2000, Ametek), and the concentrations of NH3 and NO were measured using a gas analyzer (Airwell 7+e, Tunable Diode Laser Absorption Spectroscopy, Korea Industrial Gas) and a gas analyzer (CLD82 S, ECO Physics), respectively.
The temperature in the reactor was increased from 50° C. to 450° C. at a rate of temperature rise of 10° C./min, and the NH3 concentration and NO concentration at each temperature were measured.
Evaluation results are shown in Table 4 and
Referring to
In the case of Comparative Example 1, the content of chromium, which is an active metal, was low, such that ammonia did not react with oxygen, and the concentration of ammonia was not substantially decreased.
In the case of Comparative Example 2, the concentration of NH3 was reduced to 23 ppm, but the amount of NO generated was increased to 300 ppm or more. In addition, when increasing the temperature to 300° C. or higher, the concentration of NH3 was increased due to the depletion of oxygen caused by the reaction between oxygen and hydrogen.
In the case of Comparative Example 3, all oxygen injected for the oxidation of ammonia in the chromium oxide carried on TiO2 reacted with hydrogen to be consumed, and ammonia was not removed due to the depletion of oxygen.
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.
For the examples and Comparative Example 2, the NH3 concentration and NO concentration after the reaction were measured while changing the ratio of O/NH3 in the reaction gas and the reaction temperature, respectively. The NH3 concentration and NO concentration were measured when the gas concentration after the reaction reached a steady state.
The ratio of O2/NH3 was adjusted by changing only the concentrations of O2 and NH3 in the composition of the reaction gas shown in Table 3, and H2, He and N2 were each controlled to satisfy the ratios shown in Table 3.
Specifically, the NH3 concentration and NO concentration according to the temperature were measured when the ratios of O2/NH3 in the reaction gas were 2.2 and 4.4, respectively.
Referring to
Referring to
Specifically, when the ratios of O2/NH3 in the reaction gas were 2.2, 4.4, 6.7, and 8.9, respectively, the NH3 concentration and NO concentration were measured according to the temperature.
Referring to
Although the invention was described in conjunction with specific embodiments, the invention is not limited to these embodiments only. Many variations of the described embodiments, as well as other embodiments may be envisioned by the skilled person which do not depart from the scope of the appended claims. Furthermore, the embodiments may be combined to form additional embodiments.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2023-0157334 | Nov 2023 | KR | national |
