Ammonia purification metal oxide catalyst as well as preparation method and application thereof

Abstract

The invention provides an ammonia purification metal oxide catalyst as well as a preparation method and application thereof. The ammonia purification metal oxide catalyst comprises a defect type cerium dioxide carrier, a first active component and a second active component, wherein the first active component and the second active component are loaded on the defect type cerium dioxide carrier; the element of the first active component is iridium; elements of the first active component comprise any one or a combination of at least two of tungsten, molybdenum or niobium. The carrier, the first active component and the second active component are screened and synergistically compounded, and the first active component and the second active component are uniformly dispersed on the surface of the defective cerium dioxide carrier, so that close coupling of double functional sites of ammoxidation and nitrogen oxide reduction is realized; the obtained catalyst has excellent ammonia purification low-temperature activity and nitrogen selectivity.

Description

Technical Field

[0001] The invention belongs to the technical field of ammonia internal combustion engine tail gas purification, and relates to an ammonia purification metal oxide catalyst and a preparation method and application thereof. Background Art

[0002] At present, due to the shortage of fossil fuels, ammonia is an ideal energy storage material. Its molecules do not contain carbon elements, and the only products of complete combustion are water and nitrogen. Compared with most gaseous fuels, it can be easily compressed into liquid, making it convenient for storage and transportation. As the second largest chemical product in the world, ammonia's related storage and transportation facilities are relatively complete. Therefore, ammonia has the potential to become an alternative fuel for internal combustion engines.

[0003] CN117722269A discloses an ammonia internal combustion engine system and a control method thereof, the system comprising: an ammonia online decomposition device, a combustion chamber, a purification device and a control system, wherein the ammonia online decomposition device comprises a plurality of electric heating catalytic units for decomposing ammonia fuel into a mixed gas containing ammonia, hydrogen and nitrogen, the number of which is determined according to the maximum ammonia decomposition hydrogen production; the combustion chamber is suitable for premixing the mixed gas with air before combustion; the purification device is suitable for purifying unburned ammonia and nitrogen oxides produced in the combustion chamber; the control system is used to adjust the number of energized electric heating catalytic units and the heating temperature according to the hydrogen-ammonia ratio required for ignition and combustion of the combustion chamber. Because part of the fuel ammonia in the ammonia internal combustion engine is still not fully burned during the combustion process, it enters the atmosphere with the exhaust gas and causes pollution, therefore, the ammonia in the exhaust gas needs to be catalytically purified by the purification device.

[0004] However, the above scheme does not provide an ammonia purification catalyst loaded in the purification device, and the existing single-component catalyst cannot take into account both good ammonia purification low-temperature activity and nitrogen selectivity. Common precious metal ammonia purification catalysts have good ammonia purification low-temperature activity, but their nitrogen selectivity is poor and they are prone to produce nitrogen oxides, causing secondary pollution; while transition metal ammonia purification catalysts show good nitrogen selectivity, but their ammonia purification low-temperature activity is poor. These single-component catalysts cannot meet the needs of ammonia internal combustion engines for efficient purification of unburned ammonia and reduction of nitrogen oxide emissions.

[0005] In summary, providing an ammonia purification catalyst having both high ammonia purification activity and high nitrogen selectivity and a preparation method thereof is an issue that needs to be urgently addressed by those skilled in the art. Summary of the invention

[0006] In view of the shortcomings of the prior art, the purpose of the present invention is to provide an ammonia purification metal oxide catalyst and a preparation method and application thereof. By screening and synergistic compounding of a carrier, a first active component and a second active component, and uniformly dispersing the first active component and the second active component on the surface of a defective ceria carrier, a close coupling of the dual functional sites of ammonia oxidation and nitrogen oxide reduction is achieved, and the resulting catalyst has excellent low-temperature activity for ammonia purification and nitrogen selectivity.

[0007] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides an ammonia purification metal oxide catalyst, the ammonia purification metal oxide catalyst comprising a defective ceria carrier and a first active component and a second active component supported on the defective ceria carrier;

[0009] The element of the first active component is iridium;

[0010] The elements of the first active component include any one of tungsten, molybdenum or niobium, or a combination of at least two of them.

[0011] The ammonia purification metal oxide catalyst provided by the present invention achieves tight coupling of dual functional sites of ammonia oxidation and nitrogen oxide reduction by screening and synergistically compounding a carrier, a first active component, and a second active component, and uniformly dispersing the first active component and the second active component on the surface of a defective ceria carrier, thereby ensuring that while the first active component exerts good ammonia purification activity, the second active component achieves a synergistic effect through nitrogen oxide reduction, thereby significantly improving the nitrogen selectivity of the catalyst.

[0012] It is worth noting that the defective ceria carrier in the ammonia purification metal oxide catalyst has a large specific surface area and is rich in surface oxygen vacancies, which is not only beneficial to improving the dispersibility of the active components on its surface, but also beneficial to improving the catalytic activity. The first active component is dispersed on the surface of the defective ceria carrier at the atomic level and has high activity. The second active component is uniformly dispersed on the surface of the defective ceria carrier in the form of metal oxide, and a synergistic effect is achieved through nitrogen oxide reduction, further enhancing the redox capacity, thereby improving the catalytic activity.

[0013] As a preferred technical solution of the present invention, based on 100% by mass, the ammonia purification metal oxide catalyst includes: 0.5%-2% of the first active component, 1%-8% of the second active component, and the remainder is a defective ceria carrier.

[0014] In the present invention, the content of the first active component is 0.5%-2%, for example, it can be 0.6%, 0.8%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8% or 1.9%, etc., and the content of the second active component is 1%-8%, for example, it can be 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7% or 7.5%, etc., but is not limited to the listed values, and other unlisted values ​​within the range are equally applicable.

[0015] In the present invention, the contents of the first active component and the second active component are measured by inductively coupled plasma mass spectrometry (ICP-MS).

[0016] In the present invention, the contents of the first active component and the second active component in the catalyst are further controlled to ensure efficient ammonia purification reaction in a low-oxygen environment, thereby meeting the purification requirements of an ammonia internal combustion engine for unburned ammonia.

[0017] Preferably, the mass percentage content of the second active component includes the following:

[0018] When the second active component is tungsten, the content of the second active component is 5%-8%, for example, it can be 5.2%, 5.4%, 5.5%, 5.6%, 5.8%, 6%, 6.2%, 6.4%, 6.5%, 6.6%, 6.8%, 7%, 7.2%, 7.4%, 7.5%, 7.6% or 7.8%, etc., but is not limited to the listed values, and other values ​​not listed in the range are also applicable; or

[0019] When the second active component is molybdenum and / or niobium, the content of the second active component is 1%-5%, for example, it can be 1.2%, 1.4%, 1.5%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.5%, 2.6%, 2.8%, 3%, 3.2%, 3.4%, 3.5%, 3.6%, 3.8%, 4%, 4.2%, 4.4%, 4.5%, 4.6% or 4.8%, etc., but is not limited to the listed values, and other values ​​not listed within the range are also applicable.

[0020] As a preferred technical solution of the present invention, the specific surface area of ​​the defective ceria carrier is 60-70m 2 / g, for example, it can be 61m 2 / g, 62m 2 / g, 63m 2 / g, 64m 2 / g, 65m 2 / g, 66m 2 / g, 67m 2 / g, 68m 2 / g or 69m 2 / g, etc., but are not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0021] In the present invention, the specific surface area of ​​the defective ceria carrier is measured by the BET method.

[0022] In the present invention, the surface defect sites of the defective ceria carrier are controlled, which is beneficial to improving the dispersibility of the active components on the surface thereof.

[0023] Preferably, the oxygen vacancy concentration on the surface of the defective cerium dioxide carrier is 30%-40%, for example, it can be 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38% or 39%, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0024] In the present invention, the oxygen vacancy concentration on the surface of the defective ceria carrier is expressed as the peak area ratio percentage of vacant oxygen in the O1s orbital / (surface oxygen+lattice oxygen) in the XPS spectrum; wherein the oxygen vacancies are measured using an X-ray photoelectron spectroscopy analyzer (XPS).

[0025] In the present invention, the surface of the defective ceria carrier is rich in oxygen vacancies, which is beneficial to enhancing the redox ability of the catalyst, strengthening the interaction between the carrier and the two active components, and thus improving the catalytic activity.

[0026] In a second aspect, the present invention provides a method for preparing the ammonia purification metal oxide catalyst as described in the first aspect, the preparation method comprising the following steps:

[0027] (1) performing a first calcination on a cerium precursor to obtain a defective cerium dioxide carrier;

[0028] (2) mixing a first active component precursor, a second active component precursor, a solvent and the defective ceria carrier obtained in step (1), and then sequentially performing solid-liquid separation, drying and a second calcination to obtain an ammonia purification metal oxide catalyst.

[0029] In the present invention, the mixing method of step (2) includes: impregnating the solution of the active component precursor on the defective ceria carrier by co-impregnation or step-by-step. The solvent of step (2) includes water, for example, deionized water or industrial recycled water that meets the requirements.

[0030] The preparation method provided by the present invention prepares a defective cerium dioxide carrier with a high specific surface area and rich in oxygen vacancies by calcination, which is not only beneficial to improving the dispersibility of the active component on its surface, but also beneficial to improving the catalytic activity. Then, two active components with different functions are loaded on the defective cerium dioxide carrier by impregnation. After the second calcination, the first active component is dispersed at the atomic level on the carrier, and the second active component exists in the form of uniformly dispersed metal oxides, thereby achieving a tight coupling of the dual functional sites of ammonia oxidation and nitrogen oxide reduction, ensuring that while the first active component exerts good ammonia purification activity, the second active component achieves a synergistic effect through nitrogen oxide reduction, thereby significantly improving the nitrogen selectivity of the catalyst.

[0031] As a preferred technical solution of the present invention, the cerium precursor in step (1) includes any one of cerium nitrate, cerium acetate or cerium carbonate, or a combination of at least two of them.

[0032] Preferably, the first calcination in step (1) is carried out in an air atmosphere.

[0033] Preferably, the temperature of the first calcination in step (1) is 300-400°C, for example, it can be 310°C, 320°C, 330°C, 340°C, 350°C, 360°C, 370°C, 380°C or 390°C, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0034] In the present invention, by controlling the first calcination to be carried out in an air atmosphere at a temperature within the range of 300-400° C., the obtained defective cerium dioxide carrier has a larger specific surface area and is conducive to the formation of surface oxygen vacancies.

[0035] Preferably, the holding time of the first calcination in step (1) is 2-3 h, for example, it can be 2.1 h, 2.2 h, 2.3 h, 2.4 h, 2.5 h, 2.6 h, 2.7 h, 2.8 h or 2.9 h, but is not limited to the listed values, and other values ​​not listed within the range are also applicable.

[0036] Preferably, in step (1), grinding is further performed after the first calcination.

[0037] In the present invention, there is no specific limitation on the parameters related to grinding, as long as the particle size after grinding meets the requirements, those skilled in the art can determine it according to actual needs.

[0038] As a preferred technical solution of the present invention, in step (1), the first active component precursor includes an iridium source.

[0039] Preferably, the iridium source includes any one of iridium tetrachloride, iridium trichloride or chloroiridic acid, or a combination of at least two thereof.

[0040] Preferably, in step (1), the second active component precursor comprises any one of a tungsten source, a molybdenum source or a niobium source, or a combination of at least two of them.

[0041] Preferably, the tungsten source includes any one of ammonium metatungstate, ammonium paratungstate or ammonium tungstate, or a combination of at least two thereof.

[0042] Preferably, the molybdenum source comprises ammonium heptamolybdate and / or ammonium tetramolybdate.

[0043] Preferably, the niobium source comprises niobium oxalate and / or ammonium niobium oxalate.

[0044] As a preferred technical solution of the present invention, the mass ratio of the defective cerium dioxide carrier to the first active component element in the first active component precursor is 1:(0.005-0.02), for example, it can be 1:0.006, 1:0.008, 1:0.01, 1:0.012, 1:0.014, 1:0.015, 1:0.016, 1:0.018 or 1:0.019, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0045] Preferably, the mass ratio of the defective cerium dioxide carrier to the second active component element in the second active component precursor is 1:(0.01-0.08), for example, it can be 1:0.02, 1:0.03, 1:0.04, 1:0.05, 1:0.06 or 1:0.07, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0046] As a preferred technical solution of the present invention, the mixing in step (2) is carried out under stirring.

[0047] Preferably, the mixing temperature in step (2) is 20-35°C, for example, it can be 22°C, 24°C, 25°C, 26°C, 28°C, 30°C, 32°C or 34°C, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0048] Preferably, the mixing time in step (2) is 1-3 h, for example, it can be 1.1 h, 1.2 h, 1.3 h, 1.4 h, 1.5 h, 1.6 h, 1.7 h, 1.8 h, 1.9 h, 2 h, 2.1 h, 2.2 h, 2.3 h, 2.4 h, 2.5 h, 2.6 h, 2.7 h, 2.8 h or 2.9 h, but is not limited to the listed values, and other values ​​not listed within the range are also applicable.

[0049] Preferably, the drying temperature in step (2) is 30-90°C, for example, it can be 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C or 85°C, but is not limited to the listed values, and other values ​​not listed within the range are also applicable.

[0050] As a preferred technical solution of the present invention, the temperature of the second calcination in step (2) is 300-450°C, for example, it can be 310°C, 320°C, 330°C, 340°C, 350°C, 360°C, 370°C, 380°C, 390°C, 400°C, 410°C, 420°C, 430°C or 440°C, but is not limited to the listed values, and other unlisted values ​​within the range are equally applicable.

[0051] In the present invention, the second calcination is performed in an air atmosphere.

[0052] Preferably, the holding time for the second calcination in step (2) is 3-5 h, for example, it can be 3.1 h, 3.2 h, 3.3 h, 3.4 h, 3.5 h, 3.6 h, 3.7 h, 3.8 h, 3.9 h, 4 h, 4.1 h, 4.2 h, 4.3 h, 4.4 h, 4.5 h, 4.6 h, 4.7 h, 4.8 h or 4.9 h, but is not limited to the listed values, and other values ​​not listed within the range are also applicable.

[0053] In a third aspect, the present invention provides an application of an ammonia purification metal oxide catalyst, the application comprising using the ammonia purification metal oxide catalyst described in the first aspect to catalytically purify exhaust gas generated during the operation of an ammonia internal combustion engine.

[0054] The ammonia purification metal oxide catalyst provided by the present invention has high activity in the range of 200-300°C and in the presence of 5% oxygen, and can meet the requirements of the catalyst for purifying ammonia under high temperature and high oxygen conditions of an ammonia internal combustion engine; at the same time, it also has high nitrogen selectivity in the range of 200-350°C, meeting the requirements for purifying gas in an ammonia internal combustion engine.

[0055] Preferably, the temperature of the catalytic purification is 150-350°C, for example, it can be 160°C, 180°C, 200°C, 220°C, 240°C, 250°C, 260°C, 280°C, 300°C, 320°C or 340°C, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0056] Preferably, based on 100% by volume, the oxygen content in the exhaust gas of the ammonia internal combustion engine is 2%-10%, for example, it can be 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9% or 9.5%, etc., but is not limited to the listed values, and other values ​​not listed within the range are also applicable.

[0057] Preferably, the volume concentration of ammonia in the tail gas formed during the operation of the ammonia internal combustion engine is 300-1500ppm, for example, it can be 400ppm, 500ppm, 600ppm, 700ppm, 800ppm, 900ppm, 1000ppm, 1100ppm, 1200ppm, 1300ppm or 1400ppm, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0058] Compared with the prior art, the present invention has the following beneficial effects:

[0059] (1) The ammonia purification metal oxide catalyst provided by the present invention achieves a tight coupling of the dual functional sites of ammonia oxidation and nitrogen oxide reduction by screening and synergistically compounding the carrier, the first active component, and the second active component, and uniformly dispersing the first active component and the second active component on the surface of the defective ceria carrier, thereby ensuring that while the first active component exerts good ammonia purification activity, the second active component achieves a synergistic effect through nitrogen oxide reduction, thereby significantly improving the nitrogen selectivity of the catalyst;

[0060] (2) The ammonia purification metal oxide catalyst provided by the present invention has high activity in the range of 200-300°C and in the presence of 5% oxygen, which can meet the requirements of the catalyst for purifying ammonia under high temperature and high oxygen conditions of an ammonia internal combustion engine; at the same time, it also has high nitrogen selectivity in the range of 200-350°C, meeting the requirements for purifying gas in an ammonia internal combustion engine;

[0061] (3) The preparation method provided by the present invention is to prepare a defective cerium dioxide carrier with a high specific surface area and rich in oxygen vacancies by calcination, which is not only beneficial to improving the dispersion of the active components on its surface, but also beneficial to improving the catalytic activity. Then, two active components with different functions are loaded on the defective cerium dioxide carrier by impregnation. After the second calcination, the first active component is dispersed at the atomic level on the carrier, and the second active component exists in the form of a uniformly dispersed metal oxide. The prepared catalyst has high catalytic activity and nitrogen selectivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1 It is the Ce3d XPS graph of the defective cerium dioxide carrier prepared in Example 1 and the commercially available cerium dioxide carrier in Example 6.

[0063] Figure 2 It is the O1s XPS graph of the defective cerium dioxide carrier prepared in Example 1 and the commercially available cerium dioxide carrier in Example 6.

[0064] Figure 3 The graph is a graph of ammonia conversion and nitrogen selectivity of the ammonia-purifying metal oxide catalyst prepared in Example 1 for the catalytic purification reaction of ammonia in the exhaust gas of an ammonia internal combustion engine. DETAILED DESCRIPTION

[0065] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0066] Unless otherwise specified, the raw materials used in the following examples and comparative examples were obtained through commercial sources.

[0067] Example 1

[0068] This embodiment provides an ammonia purification metal oxide catalyst and a preparation method thereof, wherein the ammonia purification metal oxide catalyst comprises, based on a mass percentage of 100%, 1% of a first active component, 7% of a second active component, and the remainder being a defective ceria carrier;

[0069] The element of the first active component is iridium; the element of the second active component is tungsten;

[0070] The specific surface area of ​​the defective ceria carrier is 65 m 2 / g, the surface oxygen vacancy concentration is 40%;

[0071] The preparation method comprises the following steps:

[0072] (1) calcining cerium nitrate in an air atmosphere at a temperature of 350° C. for 2 h, and then grinding to obtain a defective cerium dioxide carrier;

[0073] (2) dissolving iridium tetrachloride and ammonium metatungstate in deionized water to prepare a precursor solution;

[0074] The mass ratio of the defective cerium dioxide support to the iridium element in the precursor solution is 1:0.01, and the mass ratio of the defective cerium dioxide support to the tungsten element in the precursor solution is 1:0.07;

[0075] (3) mixing the defective cerium dioxide support obtained in step (1) and the precursor solution obtained in step (2) at room temperature for 2 hours, centrifuging, drying at 60° C., and then calcining for a second time in an air atmosphere at 400° C. for 3 hours to obtain an ammonia purification metal oxide catalyst;

[0076] There is no particular order in which steps (1) and (2) are performed.

[0077] In this example, the defective ceria carrier obtained in step (1) was characterized. Figure 1-2 It can be known. Figure 1 It can be seen that the surface of the defective ceria carrier prepared by the present invention contains Ce 3+ In addition, Ce 3+ The diffraction peak area of ​​​​the cerium dioxide is higher than that of commercial cerium dioxide, indicating that a large number of oxygen atoms are missing around the Ce surface, resulting in the generation of more oxygen vacancies. Figure 2 It can be seen that the existence of oxygen vacancies in the defective cerium dioxide carrier prepared by the present invention is further confirmed. Compared with commercial cerium dioxide, the prepared CeO2 has a higher surface oxygen diffraction peak area ratio, indicating that its surface contains more oxygen vacancies.

[0078] Example 2

[0079] This embodiment provides an ammonia purification metal oxide catalyst and a preparation method thereof. The ammonia purification metal oxide catalyst comprises, based on a mass percentage of 100%, 1% of a first active component, 5% of a second active component, and the remainder being a defective ceria carrier;

[0080] The element of the first active component is iridium; the element of the second active component is tungsten;

[0081] The specific surface area of ​​the defective ceria carrier is 60 m 2 / g, the surface oxygen vacancy concentration is 35%;

[0082] The preparation method comprises the following steps:

[0083] (1) calcining cerium nitrate in an air atmosphere at a temperature of 350° C. for 2 h, and then grinding to obtain a defective cerium dioxide carrier;

[0084] (2) dissolving iridium tetrachloride in deionized water to prepare a first precursor solution; dissolving ammonium metatungstate in deionized water to prepare a second precursor solution;

[0085] The mass ratio of the defective ceria support to the iridium element in the first precursor solution is 1:0.01, and the mass ratio of the defective ceria support to the tungsten element in the second precursor solution is 1:0.05;

[0086] (3) mixing the defective cerium dioxide carrier obtained in step (1) and the first precursor solution obtained in step (2) at room temperature for 1 hour, then adding the second precursor solution obtained in step (2) thereto and continuing to mix and stir for 1 hour, centrifuging, drying at 60° C., and then performing a second calcination at 450° C. in an air atmosphere for 4 hours to obtain an ammonia purification metal oxide catalyst;

[0087] There is no particular order in which steps (1) and (2) are performed.

[0088] Example 3

[0089] This embodiment provides an ammonia purification metal oxide catalyst and a preparation method thereof, wherein the ammonia purification metal oxide catalyst comprises, based on a mass percentage of 100%, 1% of a first active component, 3% of a second active component, and the remainder being a defective ceria carrier;

[0090] The element of the first active component is iridium; the element of the second active component is niobium;

[0091] The specific surface area of ​​the defective ceria carrier is 57 m 2 / g, the surface oxygen vacancy concentration is 30%;

[0092] The preparation method comprises the following steps:

[0093] (1) calcining cerium nitrate in an air atmosphere at 400° C. for 2 h, and then grinding to obtain a defective cerium dioxide carrier;

[0094] (2) dissolving iridium tetrachloride and niobium oxalate in deionized water to prepare a precursor solution;

[0095] The mass ratio of the defective cerium dioxide support to the iridium element in the precursor solution is 1:0.01, and the mass ratio of the defective cerium dioxide support to the niobium element in the precursor solution is 1:0.03;

[0096] (3) mixing the defective cerium dioxide support obtained in step (1) and the precursor solution obtained in step (2) at room temperature for 2 hours, centrifuging, drying at 60° C., and then calcining for a second time in an air atmosphere at 350° C. for 5 hours to obtain an ammonia purification metal oxide catalyst;

[0097] There is no particular order in which steps (1) and (2) are performed.

[0098] Example 4

[0099] This embodiment provides an ammonia purification metal oxide catalyst and a preparation method thereof, except that the ammonia purification metal oxide catalyst comprises: 2% of a first active component, 0.05% of a second active component, and the remainder is a defective cerium dioxide carrier, with the other conditions being the same as those in Example 1.

[0100] Example 5

[0101] This embodiment provides an ammonia purification metal oxide catalyst and a preparation method thereof, except that the ammonia purification metal oxide catalyst comprises: 2% of a first active component, 10% of a second active component, and the remainder is a defective cerium dioxide carrier, with the other conditions being the same as those in Example 1.

[0102] Example 6

[0103] This embodiment provides an ammonia purification metal oxide catalyst and a preparation method thereof, except that the defective cerium dioxide carrier is commercially available cerium dioxide (1306-38-3, Aladdin); other conditions are the same as those in Example 1.

[0104] Example 7

[0105] This embodiment provides an ammonia purification metal oxide catalyst and a preparation method thereof, except that the temperature of the first calcination is 200° C.; other conditions are the same as those in Embodiment 1.

[0106] Example 8

[0107] This embodiment provides an ammonia purification metal oxide catalyst and a preparation method thereof, except that the temperature of the first calcination is 500° C.; other conditions are the same as those in Embodiment 1.

[0108] Example 9

[0109] This embodiment provides an ammonia purification metal oxide catalyst and a preparation method thereof, except that the temperature of the second calcination is 300° C.; other conditions are the same as those in Embodiment 1.

[0110] Example 10

[0111] This embodiment provides an ammonia purification metal oxide catalyst and a preparation method thereof, except that the temperature of the second calcination is 550° C.; other conditions are the same as those in Embodiment 1.

[0112] Comparative Example 1

[0113] This comparative example provides an ammonia purification metal oxide catalyst and a preparation method thereof, wherein the ammonia purification metal oxide catalyst comprises, by weight percentage, 2% of a first active component and the remainder being a defective cerium dioxide carrier, i.e., does not contain a second active component; other conditions are the same as those in Example 1.

[0114] Comparative Example 2

[0115] This comparative example provides an ammonia purification metal oxide catalyst and a preparation method thereof, wherein the ammonia purification metal oxide catalyst comprises, by weight percentage, 8% of a second active component and the remainder being a defective cerium dioxide carrier, i.e., does not contain a first active component; other conditions are the same as those in Example 1.

[0116] Comparative Example 3

[0117] This comparative example provides an ammonia purification metal oxide catalyst and a preparation method thereof, except that the first active component is platinum; other conditions are the same as those in Example 1.

[0118] Comparative Example 4

[0119] This comparative example provides an ammonia purification metal oxide catalyst and a preparation method thereof, except that the first active component is gadolinium; other conditions are the same as those in Example 1.

[0120] Comparative Example 5

[0121] This comparative example provides an ammonia purification metal oxide catalyst and a preparation method thereof, except that the second active component is copper; other conditions are the same as those in Example 1.

[0122] Comparative Example 6

[0123] This comparative example provides an ammonia purification metal oxide catalyst and a preparation method thereof, except that the defective cerium dioxide carrier is replaced by a titanium dioxide carrier; other conditions are the same as those in Example 1.

[0124] The ammonia purification metal oxide catalyst prepared in the above embodiment and comparative example was used to catalytically purify ammonia in a simulated ammonia internal combustion engine. The catalytic purification temperature was 225°C. The oxygen content in the tail gas of the ammonia internal combustion engine was 5% based on 100% by volume. The total gas flow rate in the tail gas of the ammonia internal combustion engine was 500 mL / min, and the air velocity was 70000 h / min. -1 ; The volume concentration of ammonia in the exhaust gas formed during the operation of the ammonia internal combustion engine is 1000ppm.

[0125] The purified gas was measured by infrared spectrometer. The indicators of the purified gas are shown in Table 1.

[0126] Table 1

[0127]

[0128]

[0129] From Table 1, we can see that:

[0130] (1) The ammonia purification metal oxide catalyst and preparation method thereof provided in Examples 1-3 of the present invention achieves close coupling of dual functional sites of ammonia oxidation and nitrogen oxide reduction by screening and synergistic compounding of a carrier, a first active component, and a second active component, and uniformly dispersing the first active component and the second active component with different functions on the surface of a defective ceria carrier. The obtained metal oxide catalyst has excellent low-temperature activity for ammonia purification and nitrogen selectivity. Among them, at a catalytic purification temperature of 225° C., the ammonia conversion rate is greater than 98% and the nitrogen selectivity is greater than 98%;

[0131] (2) From the comparison between Example 1 and Examples 4-5, it can be seen that when the content of the second active component is too low, the nitrogen oxide reduction ability of the catalyst is insufficient, resulting in a significant decrease in the nitrogen selectivity of the catalyst; when the content of the second active component is too high, the dispersion effect of the first active component is affected, resulting in a significant decrease in the low-temperature activity of the catalyst for ammonia purification;

[0132] (3) It can be seen from the comparison between Example 1 and Examples 6-8 that when commercially available ceria is used as a carrier, the performance of the catalyst is reduced due to the lack of sufficient oxygen vacancies; when the temperature of the first calcination is too low, the structure of the defective ceria carrier is unstable due to incomplete decomposition of the precursor; when the temperature of the second calcination is too high, the carrier is sintered, resulting in excessive crystallinity of the defective ceria carrier and insufficient oxygen vacancy content;

[0133] (4) From the comparison between Example 1 and Examples 9-10, it can be seen that when the temperature of the second calcination is too low, the performance of the catalyst is reduced due to incomplete decomposition of the precursor; when the temperature of the second calcination is too high, the performance of the catalyst is reduced due to sintering and agglomeration of the active components;

[0134] (5) It can be seen from the comparison between Example 1 and Comparative Examples 1-2 that if only one active component is contained, the synergistic effect of the two components cannot be exerted, resulting in a decrease in the low-temperature activity of the catalyst for ammonia purification or the nitrogen selectivity;

[0135] (6) By comparing Example 1 with Comparative Examples 3-6, it can be seen that if the first active component is other precious metal platinum or rare earth metal gadolinium, the ammonia purification activity of the catalyst is significantly weakened due to poor compatibility with cerium dioxide or lack of ammonia purification activity itself; if the second active component is copper, its nitrogen oxide reduction activity is weak, resulting in insufficient nitrogen oxide reduction ability of the catalyst; if the carrier is titanium dioxide carrier, its interaction with the active component is weaker than that of cerium dioxide, resulting in decreased performance of the catalyst.

[0136] The ammonia purification metal oxide catalyst prepared in Example 1 was used to catalytically purify ammonia in a simulated ammonia internal combustion engine, and a gradient temperature test was conducted on the catalytic purification temperature, and the temperatures were 150°C, 175°C, 200°C, 225°C, 250°C, 275°C, 300°C, 325°C, and 350°C respectively;

[0137] Taking the volume percentage as 100%, the oxygen content in the tail gas of the ammonia internal combustion engine is 5%; the total gas flow rate in the tail gas of the ammonia internal combustion engine is 500mL / min, and the air velocity is 70000h -1 ; The volume concentration of ammonia in the exhaust gas formed during the operation of the ammonia internal combustion engine is 1000ppm.

[0138] The results of the purified gas are shown in Figure 3 .

[0139] Depend on Figure 3 It can be seen that the ammonia purification metal oxide catalyst and the preparation method thereof provided by the present invention, a defective cerium dioxide carrier with high specific surface area and rich in oxygen vacancies is prepared by calcination, which is not only beneficial to improving the dispersibility of the active component on its surface, but also beneficial to improving the catalytic activity, and then two active components with different functions are loaded on the defective cerium dioxide carrier by impregnation. After the second calcination, the first active component is dispersed at the atomic level on the carrier, and the second active component exists in the form of uniformly dispersed metal oxide. The obtained catalyst has high catalytic activity and nitrogen selectivity through the screening and synergistic compounding of the carrier, the first active component and the second active component.

[0140] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. An ammonia purification metal oxide catalyst, characterized in that: The ammonia purification metal oxide catalyst comprises a defective ceria carrier and a first active component and a second active component supported on the defective ceria carrier; The element of the first active component is iridium; The elements of the first active component include any one of tungsten, molybdenum or niobium, or a combination of at least two of them.

2. The ammonia purification metal oxide catalyst according to claim 1, characterized in that The ammonia purification metal oxide catalyst comprises, based on a mass percentage of 100%, 0.5%-2% of a first active component, 1%-8% of a second active component, and the remainder being a defective cerium dioxide carrier; Preferably, the mass percentage content of the second active component includes the following: When the second active component is tungsten, the content of the second active component is 5%-8%; or When the second active component is molybdenum and / or niobium, the content of the second active component is 1%-5%.

3. The ammonia purification metal oxide catalyst according to claim 1 or 2, characterized in that: The specific surface area of ​​the defective ceria carrier is 60-70 m 2 / g; Preferably, the oxygen vacancy concentration on the surface of the defective ceria carrier is 30%-40%.

4. A method for preparing an ammonia purification metal oxide catalyst according to any one of claims 1 to 3, characterized in that: The preparation method comprises the following steps: (1) performing a first calcination on a cerium precursor to obtain a defective cerium dioxide carrier; (2) mixing a first active component precursor, a second active component precursor, a solvent and the defective ceria carrier obtained in step (1), and then sequentially performing solid-liquid separation, drying and a second calcination to obtain an ammonia purification metal oxide catalyst.

5. The preparation method according to claim 4, characterized in that: The cerium precursor in step (1) includes any one of cerium nitrate, cerium acetate or cerium carbonate, or a combination of at least two thereof; Preferably, the first calcination in step (1) is carried out in an air atmosphere; Preferably, the temperature of the first calcination in step (1) is 300-400°C; Preferably, the holding time of the first roasting in step (1) is 2-3 hours; Preferably, in step (1), grinding is further performed after the first calcination.

6. The preparation method according to claim 4 or 5, characterized in that: Step (1) The first active component precursor includes an iridium source; Preferably, the iridium source comprises any one of iridium tetrachloride, iridium trichloride or chloroiridic acid, or a combination of at least two thereof; Preferably, the second active component precursor in step (1) comprises any one of a tungsten source, a molybdenum source or a niobium source, or a combination of at least two thereof; Preferably, the tungsten source includes any one of ammonium metatungstate, ammonium paratungstate or ammonium tungstate, or a combination of at least two thereof; Preferably, the molybdenum source comprises ammonium heptamolybdate and / or ammonium tetramolybdate; Preferably, the niobium source comprises niobium oxalate and / or ammonium niobium oxalate.

7. The preparation method according to any one of claims 4 to 6, characterized in that: The mass ratio of the defective ceria carrier to the first active component element in the first active component precursor is 1:(0.005-0.02); Preferably, the mass ratio of the defective ceria carrier to the second active component element in the second active component precursor is 1:(0.01-0.08).

8. The preparation method according to any one of claims 4 to 7, characterized in that: The mixing in step (2) is carried out under stirring; Preferably, the mixing temperature in step (2) is 20-35°C; Preferably, the mixing time in step (2) is 1-3 hours; Preferably, the drying temperature in step (2) is 30-90°C.

9. The preparation method according to any one of claims 4 to 8, characterized in that: Step (2) the second calcination temperature is 350-450°C; Preferably, the holding time of the second calcination in step (2) is 3-5 hours.

10. An application of ammonia purification metal oxide catalyst, characterized in that: The application includes using the ammonia purification metal oxide catalyst according to any one of claims 1 to 3 to catalytically purify the exhaust gas generated during the operation of an ammonia internal combustion engine; Preferably, the temperature of the catalytic purification is 150-350°C; Preferably, based on 100% by volume, the oxygen content in the tail gas of the ammonia internal combustion engine is 2%-10%; Preferably, the volume concentration of ammonia in the tail gas formed during the operation of the ammonia internal combustion engine is 300-1500 ppm.

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