Methane catalytic combustion catalyst as well as preparation method and application thereof

Abstract

The invention provides a methane catalytic combustion catalyst and a preparation method and application thereof. The methane catalytic combustion catalyst comprises a carrier and an active component loaded on the carrier, the carrier is a metal oxide, the active component is a noble metal, and a precursor of the noble metal is a nitrogen-rich compound pre-coordinated noble metal material. Nitrogen-rich compounds are introduced to pre-coordinate precious metal materials, precious metal dispersion is promoted, a large amount of gas is released through pyrolysis of the nitrogen-rich compounds, and a local non-oxidation chemical environment is constructed, so that the electronic structure and the local environment of the precious metal and the carrier are effectively regulated and controlled, more coordinated unsaturated sites are provided, and the catalytic activity of the carrier is improved. The catalyst with low-temperature high activity, excellent stability and strong water resistance is finally prepared, and T90 can be as low as 367 DEG C.

Description

Technical Field

[0001] The invention belongs to the field of environmental catalysis, and specifically relates to a methane catalytic combustion catalyst and a preparation method and application thereof. Background Art

[0002] With the mining of coal, the production and utilization of oil and natural gas, methane emissions have increased rapidly. Various fixed and mobile sources produce a large amount of low-concentration methane (0.1-1.0 vol%), which is discharged into the atmosphere without any treatment, such as methane in mine ventilation air, automobile exhaust, and methane in mixed coalbed methane. Methane itself is a greenhouse gas, and its potential value for greenhouse effect is more than twenty times that of CO2. Therefore, with the increasing use of natural gas year by year, the greenhouse effect problem has become more serious. In today's environment of emission reduction and energy conservation, global climate change and greenhouse effect have become the focus of attention in the environmental field, and methane emission reduction is urgent. Methane has a symmetrical structure and stable properties. The first CH bond energy is as high as 450 kJ / mol, which is difficult to activate. Therefore, designing and synthesizing catalysts that can activate methane at low temperatures is still a hot topic and challenge.

[0003] Patent CN116212864A uses a coprecipitation method to prepare a PdCeO composite oxide methane combustion catalyst using rare earth oxide CeO2 as the main component and Pd combined with another transition metal element. PdCeMnO has the best catalytic activity for methane combustion, reaching a temperature T of 10% methane conversion rate. 10 =290℃, T50 is about 470℃. Patent CN108636403A uses precious metal as the first active component and SnO2 as the second active component. Part of the precious metal enters the SnO2 lattice to replace Sn 2+ , and can also increase the hole concentration, thereby reducing the free electron concentration, forming adsorbed oxygen ions on the catalyst surface, which is beneficial to methane activation. Among them, Pd / SnO2 has the best catalytic activity for methane combustion, reaching a temperature of 90% methane conversion rate T 90 =440℃. Patent CN118079906A first prepares a composite oxide with a core-shell structure as a carrier, and then loads it with precious metal palladium, using the synergistic effect between the precious metal palladium and the carrier to improve the catalytic activity, selectivity and stability. The temperature T of Pd / CeO2@SiO2 for methane combustion to reach 90% methane conversion rate 90 =510℃.

[0004] In summary, precious metal Pd-based catalysts have been widely studied in methane combustion reactions and have good low-temperature catalytic activity for methane. However, the Pd catalysts in the above-mentioned prior art are still largely limited by their insufficient reactivity at low temperatures (<400°C) and the effects of H2O and SO x / Limitation of H2S deactivation.

[0005] Therefore, designing a methane combustion catalyst with low temperature and high activity has great practical significance for methane degradation. Summary of the invention

[0006] In view of the shortcomings of the prior art, the present invention aims to provide a methane catalytic combustion catalyst and its preparation method and application. The present invention introduces nitrogen-rich compounds to pre-coordinate precious metal materials to promote the dispersion of precious metals, and utilizes the pyrolysis of nitrogen-rich compounds to release a large amount of gas to construct a local oxygen-free chemical environment, thereby effectively regulating the electronic structure and local environment of the precious metal and the carrier to provide more coordination unsaturated sites, and finally prepares a catalyst with high activity at low temperature, excellent stability and strong water resistance. 90 Can be as low as 367℃.

[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 a catalyst for catalytic combustion of methane, wherein the methane catalytic combustion catalyst comprises a carrier and an active component loaded on the carrier, wherein the carrier is a metal oxide, the active component is a noble metal, and the precursor of the noble metal is a noble metal material pre-coordinated with a nitrogen-rich compound.

[0009] The present invention promotes the dispersion of precious metals by introducing nitrogen-rich compounds to pre-coordinate precious metal materials, and utilizes the pyrolysis of nitrogen-rich compounds to release a large amount of gas to construct a local oxygen-free chemical environment, thereby effectively regulating the electronic structure and local environment of the precious metals and the carrier to provide more coordinated unsaturated sites, and ultimately preparing a catalyst with high activity at low temperature, excellent stability and strong water resistance.

[0010] The catalyst provided by the present invention can completely convert methane into CO2 and H2O at a relatively low temperature. 90 Can be as low as 367℃.

[0011] Preferably, the nitrogen-rich compound comprises graphite-like carbon nitride.

[0012] In the present invention, graphite-like carbon nitride is used as an anchoring agent, and its advantage of containing electron-rich N is fully utilized. The carbon nitride N-rich cavity is used to anchor the noble metal, and then the local oxygen-free chemical environment formed by releasing a large amount of gas during the pyrolysis process of carbon nitride is used to change the coordination environment of the noble metal.

[0013] Preferably, in the precious metal precursor, the mass content of the precious metal material is 0.1-3wt%, for example, it can be 0.1wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt% or 3wt%.

[0014] In the present invention, the mass content of the precious metal material is 0.1-3wt%, and the mass content of the nitrogen-rich compound is 97-99.9wt%. The appropriate content of the nitrogen-rich compound is conducive to better anchoring the precious metal material.

[0015] Preferably, the metal oxide comprises ceria.

[0016] Preferably, the noble metal includes any one of Pt, Pd or Rh, or a combination of at least two of them.

[0017] Preferably, in the catalyst, the mass content of the precious metal is 0.2-3wt%, for example, it can be 0.2wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt% or 3wt%.

[0018] In a second aspect, the present invention provides a method for preparing the methane catalytic combustion catalyst as described in the first aspect, the preparation method comprising the following steps:

[0019] The noble metal salt solution and the solution containing the nitrogen-rich compound are mixed and calcined once to obtain a noble metal precursor.

[0020] The precursor solution of the metal oxide and the precursor of the noble metal are mixed and subjected to loading treatment to obtain the methane catalytic combustion catalyst.

[0021] The preparation method provided by the invention is simple to operate, the raw materials are easily available, the methane degradation effect is good, and the application prospect is very good.

[0022] Preferably, in the solution containing the nitrogen-rich compound, the solvent comprises water.

[0023] Preferably, the mass volume ratio of the solution containing the nitrogen-rich compound is 0.05-0.1 g / mL, for example, it can be 0.05 g / mL, 0.06 g / mL, 0.07 g / mL, 0.08 g / mL, 0.09 g / mL or 0.1 g / mL.

[0024] It should be noted that the mass-to-volume ratio refers to the ratio of the mass of the solute to the volume of the solvent.

[0025] Preferably, the method for preparing the nitrogen-rich compound comprises: sintering an organic nitrogen source to obtain the nitrogen-rich compound.

[0026] Preferably, the organic nitrogen source comprises melamine and / or urea.

[0027] Preferably, the sintering temperature is 500-550°C, for example, 500°C, 510°C, 520°C, 530°C, 540°C or 550°C.

[0028] In the present invention, if the sintering temperature is too high, the yield will be reduced, and if the temperature is too low, it will be difficult to form a graphite-like phase structure.

[0029] Preferably, the holding time of the sintering treatment is 4-6 hours, for example, it can be 4 hours, 4.5 hours, 5 hours, 5.5 hours or 6 hours.

[0030] In the present invention, if the holding time of the sintering treatment is too long, the yield will be reduced.

[0031] Preferably, the noble metal salt solution includes any one of a platinum salt solution, a palladium salt solution or a rhodium salt solution, or a combination of at least two of them.

[0032] Preferably, the platinum salt solution includes any one of a platinum nitrate solution, a chloroplatinic acid solution or a tetraamine platinum nitrate solution, or a combination of at least two thereof.

[0033] Preferably, the palladium salt solution includes any one of a palladium nitrate solution, a sodium tetrachloropalladate solution, a palladium nitrate dihydrate solution or a tetraammine palladium nitrate solution, or a combination of at least two thereof.

[0034] Preferably, the rhodium salt solution includes any one of rhodium nitrate solution, rhodium chloride solution or ammonium chlororhodate solution, or a combination of at least two thereof.

[0035] Preferably, the primary calcination temperature is 500-550°C, for example, 500°C, 510°C, 520°C, 530°C, 540°C or 550°C.

[0036] Preferably, the holding time of the primary calcination is 4-6 h, for example, 4 h, 4.5 h, 5 h, 5.5 h or 6 h.

[0037] Preferably, the atmosphere of the primary calcination is an inert atmosphere, for example, argon gas or the like.

[0038] In the present invention, a single calcination is carried out in an inert atmosphere, which is beneficial for the nitrogen-rich compound to better anchor the precious metal.

[0039] Preferably, the metal oxide precursor solution comprises a cerium salt solution.

[0040] Preferably, the cerium salt solution includes any one of cerium nitrate, acetate, sulfate or ammonium salt, or a combination of at least two of them.

[0041] Preferably, in the metal oxide precursor solution, the solvent includes water and alcohol.

[0042] Preferably, the loading treatment method includes an impregnation method or a hydrothermal method.

[0043] Preferably, the specific steps of the impregnation method include:

[0044] The precursor solution of the metal oxide is impregnated with the precursor of the precious metal, and then a secondary calcination is performed to complete the loading.

[0045] Preferably, the atmosphere of the secondary calcination is an air atmosphere.

[0046] Preferably, in the impregnation method, the volume ratio of water to alcohol in the solvent of the metal oxide precursor solution is (1-4):1, for example, it can be 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1 or 4:1.

[0047] Preferably, the temperature of the secondary calcination is 600-650°C, for example, 600°C, 610°C, 620°C, 630°C, 640°C or 650°C.

[0048] In the present invention, if the temperature of the secondary calcination is too low, the nitrogen-rich compounds introduced into the catalyst cannot be completely removed, thus affecting the activity and stability of the catalyst.

[0049] Preferably, the secondary calcination time is 4-6 h, for example, 4 h, 4.5 h, 5 h, 5.5 h or 6 h.

[0050] Preferably, the specific steps of the hydrothermal method include:

[0051] The precursor solution of the metal oxide, the precursor of the noble metal, the organic template agent and the regulator are mixed to obtain a mixed solution, the mixed solution is subjected to a hydrothermal reaction, and then calcined three times to complete the loading.

[0052] In the present invention, the carrier synthesized by the hydrothermal method has a larger specific surface area and more surface defects, and can cooperate with nitrogen-rich compounds to regulate the local environment of the carrier and the active metal, thereby improving the methane catalytic combustion activity of the catalyst.

[0053] Preferably, in the hydrothermal method, the volume ratio of water to alcohol in the solvent of the metal oxide precursor solution is (0.1-0.5):1, for example, it can be 0.1:1, 0.2:1, 0.3:1, 0.4:1 or 0.5:1.

[0054] Preferably, the organic template comprises any one of trimesic acid, phthalic acid or terephthalic acid, or a combination of at least two thereof.

[0055] Preferably, the regulator comprises any one of formic acid, acetic acid, hydrochloric acid or benzoic acid, or a combination of at least two thereof.

[0056] Preferably, in the hydrothermal method, the molar ratio of the organic template to the metal ions in the mixed solution is (2-4):1, for example, 2:1, 2.5:1, 3:1, 3.5:1 or 4:1.

[0057] Preferably, the temperature of the hydrothermal reaction is 100-140°C, for example, 100°C, 110°C, 120°C, 130°C or 140°C, etc., and the time is 12-24h, for example, 12h, 16h, 20h or 24h, etc.

[0058] Preferably, the three calcinations are step-by-step calcinations, and the step-by-step calcinations include pre-calcination and final calcination.

[0059] Preferably, the pre-firing atmosphere is an inert atmosphere, for example, argon gas or the like.

[0060] Preferably, the atmosphere of the final firing is an air atmosphere.

[0061] Preferably, the pre-burning temperature is 300-400°C, for example, 300°C, 320°C, 340°C, 360°C, 380°C or 400°C, etc., and the holding time is 1-3h, for example, 1h, 1.5h, 2h, 2.5h or 3h, etc.

[0062] Preferably, the final firing temperature is 450-600°C, for example, it can be 450°C, 460°C, 470°C, 480°C, 490°C, 500°C, 550°C or 600°C, and the insulation time is 4-6h, for example, it can be 4h, 4.5h, 5h, 5.5h or 6h.

[0063] In the present invention, if the final calcination temperature is too low, the nitrogen-rich compounds and organic templates introduced into the catalyst cannot be completely removed, thus affecting the activity and stability of the catalyst.

[0064] Preferably, the preparation method comprises the following steps:

[0065] (1) In an air atmosphere, an organic nitrogen source is heated to 500-550° C. at a heating rate of 5-10° C. / min (e.g., 5° C. / min, 6° C. / min, 7° C. / min, 8° C. / min, 9° C. / min, or 10° C. / min, etc.) for sintering and the heat preservation time is 4-6 hours to obtain a nitrogen-rich compound.

[0066] (2) adding the nitrogen-rich compound to the solvent, stirring and mixing for 4-12 hours (for example, 4 hours, 6 hours, 8 hours, 10 hours or 12 hours, etc.), to obtain a solution containing the nitrogen-rich compound with a mass volume ratio of 0.05-0.1 g / mL.

[0067] The nitrogen-rich compound solution and the noble metal salt solution are stirred and mixed for 4-12 hours (for example, 4 hours, 6 hours, 8 hours, 10 hours or 12 hours, etc.), and dried at 60-80°C (for example, 60°C, 70°C or 80°C, etc.) for 6-12 hours (for example, 6 hours, 8 hours, 10 hours or 12 hours, etc.) to obtain a powder to be calcined.

[0068] In an inert atmosphere, the powder to be calcined is heated to 500-550°C at a heating rate of 5-10°C / min (for example, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min or 10°C / min, etc.) and kept at this temperature for 4-6 hours to obtain a precursor of a precious metal.

[0069] (3) impregnating the precious metal precursor with a cerium salt solution and stirring and mixing for 4-12 hours (for example, 4 hours, 6 hours, 8 hours, 10 hours or 12 hours, etc.), then drying at 60-80°C (for example, 60°C, 70°C or 80°C, etc.) for 6-12 hours (for example, 6 hours, 8 hours, 10 hours or 12 hours, etc.), and then heating the obtained powder to 600-650°C in an air atmosphere at a heating rate of 5-10°C / min (for example, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min or 10°C / min, etc.) for secondary calcination, with a holding time of 4-6 hours, to complete the loading and obtain the catalyst; or,

[0070] A cerium salt solution, a noble metal precursor, an organic template and a regulator are mixed to obtain a mixed solution, and the mixed solution is subjected to a hydrothermal reaction at 100-140° C. for 12-24 hours, centrifuged, washed (the washing agent may be, for example, water and / or alcohol, and the number of times may be, for example, 4-6 times), and dried (the drying temperature may be, for example, 60-80° C., and the time may be, for example, 10-12 hours), and then heated to 300-400° C. for 1-3 hours in an inert atmosphere at a heating rate of 5-10° C. / min (for example, 5° C. / min, 6° C. / min, 7° C. / min, 8° C. / min, 9° C. / min or 10° C. / min, etc.), and then pre-calcined to 450-600° C. for 4-6 hours in an air atmosphere at a heating rate of 5-10° C. / min (for example, 5° C. / min, 6° C. / min, 7° C. / min, 8° C. / min, 9° C. / min or 10° C. / min, etc.), to complete the loading and obtain a catalyst.

[0071] In a third aspect, the present invention provides an application of the methane catalytic combustion catalyst as described in the first aspect, wherein the methane catalytic combustion catalyst is applied to catalytic combustion of methane and is completely oxidized into carbon dioxide and water.

[0072] Preferably, the methane complete conversion temperature of the methane catalytic combustion catalyst used in the methane catalytic combustion is less than or equal to 400°C, for example, it can be 400°C, 380°C, 360°C or 340°C.

[0073] The numerical range described in the present invention not only includes the point values ​​listed above, but also includes any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0074] Compared with the prior art, the present invention has the following beneficial effects:

[0075] (1) The present invention promotes the dispersion of precious metals by introducing nitrogen-rich compounds to pre-coordinate precious metal materials, and utilizes the pyrolysis of nitrogen-rich compounds to release a large amount of gas to construct a local oxygen-free chemical environment, thereby effectively regulating the electronic structure and local environment of the precious metals and the carrier to provide more coordinated unsaturated sites, and finally preparing a catalyst with high activity at low temperature, excellent stability and strong water resistance.

[0076] (2) The catalyst provided by the present invention can completely convert methane into CO2 and H2O at a relatively low temperature. 90 Can be as low as 367℃.

[0077] (3) The preparation method provided by the present invention is simple to operate, the raw materials are easily available, the methane degradation effect is good, and it has a good application prospect. BRIEF DESCRIPTION OF THE DRAWINGS

[0078] Figure 1 This is a stability test curve of the catalyst provided in Example 1 of the present invention for catalytic combustion of methane.

[0079] Figure 2 This is a test curve of water resistance of the catalyst provided in Example 1 of the present invention for catalytic combustion of methane.

[0080] Figure 3 Activity test curves of methane catalytic combustion performed on the catalysts provided in Example 4, Comparative Examples 3-5 and Comparative Example 7 of the present invention. DETAILED DESCRIPTION

[0081] 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.

[0082] It should be noted that the room temperature below refers to 25°C.

[0083] Example 1

[0084] This embodiment provides a catalyst for catalytic combustion of methane, wherein the catalyst includes a carrier and an active component supported on the carrier, wherein the carrier is cerium dioxide, the active component is a precious metal Pd, and the precursor of the precious metal is a precious metal material pre-coordinated with graphite-like carbon nitride, denoted as Pd / C3N4.

[0085] In the precursor of the precious metal, the mass content of the precious metal material is 1wt%; in the catalyst, the mass content of the precious metal is 1wt%.

[0086] This embodiment also provides a method for preparing the above catalyst, which comprises the following steps:

[0087] (1) In an air atmosphere, melamine was sintered at a heating rate of 5°C / min to 550°C for 4 h, and then ground to obtain graphite-like carbon nitride.

[0088] (2) 0.5 g of the graphite-like carbon nitride was added to 10 mL of water, and the mixture was stirred at room temperature for 8 h to obtain a solution containing the graphite-like carbon nitride at a mass volume ratio of 0.05 g / mL.

[0089] 0.0278 g of Pd(NO3)2 solution (Pd content: 18.2 wt.%) was added to the solution containing graphite-like carbon nitride, stirred and mixed for 12 h, and dried at 60°C for 12 h to obtain a powder to be calcined.

[0090] In a tubular furnace in an argon atmosphere, the powder to be calcined was heated to 550° C. at a heating rate of 5° C. / min and the heat preservation time was 4 h to obtain a precursor of precious metal Pd.

[0091] (3) 2.5228 g of Ce(NO3)2·6H2O was added to 8 mL of water and 2 mL of ethanol, and the mixture was dissolved by stirring at room temperature to obtain a Ce(NO3)2 solution. The precursor of the precious metal Pd was then impregnated with the Ce(NO3)2 solution and stirred for 4 h. The mixture was then dried at 60°C for 12 h. The powder was then heated to 600°C in an air atmosphere at a heating rate of 5°C / min and calcined for a second time. The temperature was kept at this temperature for 4 h to complete the loading and obtain the catalyst.

[0092] Stability test:

[0093] The catalyst prepared in Example 1 was used for stability testing. The testing method was as follows: when the gas composition was methane and air, the volume percentage of methane was 1 vol%, and the space velocity was 60000 mL·g -1 ·h -1The fixed bed reactor was reacted continuously for 50 hours at a temperature of 500°C. The methane conversion rate was calculated by the methane concentration at the outlet of the gas chromatography molecular fixed bed. The methane conversion rate within 50 hours was as follows: Figure 1 As shown, from Figure 1 It can be seen that as the reaction time increases, the methane conversion first increases and then stabilizes at about 97%, indicating that the methane combustion catalyst provided by the present invention has high stability.

[0094] Water resistance test:

[0095] The water resistance test of the methane combustion catalyst prepared in Example 1 was carried out. The test method was as follows: first, the gas composition was methane and air, the volume percentage of methane was 1 vol%, and the air velocity was 60000 mL·g -1 ·h -1 , the fixed bed reactor was reacted at 500°C for 20h, and then the gas composition was changed to methane, water vapor and air at 500°C, where the methane volume fraction was 1vol%, and the water vapor volume fraction was 5vol%, and the reaction was continued. The methane conversion rate was calculated using the methane concentration at the outlet of the gas chromatography molecular fixed bed. The methane conversion rate of the above process is as follows Figure 2 As shown, from Figure 2 It can be seen that when water vapor is not introduced, the methane conversion first increases and then stabilizes at about 97%. After 5 vol% water vapor is introduced, the methane conversion rate remains basically unchanged. As the reaction time increases, the methane conversion rate can still be stabilized at about 94%, indicating that the methane combustion catalyst provided by the present invention has excellent water resistance.

[0096] Example 2

[0097] The difference between this embodiment and embodiment 1 is that the mass content of the precious metal material in the precious metal precursor is 0.2 wt %, that is, the mass of the Pd(NO 3 ) 2 solution in the adjustment step (2) is 0.0055 g.

[0098] The rest of the preparation methods and parameters were the same as those in Example 1.

[0099] Example 3

[0100] The difference between this embodiment and embodiment 1 is that the mass content of the precious metal material in the precious metal precursor is 2 wt %, that is, the mass of the Pd(NO 3 ) 2 solution in the adjustment step (2) is 0.0561 g.

[0101] The rest of the preparation methods and parameters were the same as those in Example 1.

[0102] Example 4

[0103] The difference between this embodiment and embodiment 1 is that step (3) is:

[0104] Take 3.23g of trimesic acid, then add 12mL of water and 38mL of ethanol, stir to dissolve, then add 1.5609g of cerium acetate, 2mL of acetic acid and a precious metal precursor to mix to obtain a mixed solution, stir at room temperature for 2h, and then perform a hydrothermal reaction on the mixed solution at 120°C for 24h. After the reaction is completed, cool and centrifuge to separate the precipitate, and wash it with deionized water 3 times and ethanol once, then vacuum dry it at 60°C for 12h, and then heat it to 350°C in an argon atmosphere at a heating rate of 5°C / min for 2h of pre-calcination, and then heat it to 450°C in an air atmosphere at a heating rate of 5°C / min for 6h of final calcination to complete the loading and obtain the catalyst.

[0105] The rest of the preparation methods and parameters were the same as those in Example 1.

[0106] Example 5

[0107] The difference between this embodiment and embodiment 1 is that the precious metal is Pt.

[0108] The rest of the preparation methods and parameters were the same as those in Example 1.

[0109] Example 6

[0110] The difference between this embodiment and embodiment 1 is that the precious metal is Rh.

[0111] The rest of the preparation methods and parameters were the same as those in Example 1.

[0112] Example 7

[0113] The difference between this embodiment and embodiment 1 is that melamine in step (1) is replaced by urea.

[0114] The rest of the preparation methods and parameters were the same as those in Example 1.

[0115] Example 8

[0116] The difference between this embodiment and embodiment 4 is that the mass content of the precious metal in the catalyst is 0.2 wt%.

[0117] The rest of the preparation methods and parameters were the same as those in Example 4.

[0118] Example 9

[0119] The difference between this embodiment and embodiment 4 is that the mass content of the precious metal in the catalyst is 0.5 wt %.

[0120] The rest of the preparation methods and parameters were the same as those in Example 4.

[0121] Example 10

[0122] The difference between this embodiment and embodiment 4 is that the final firing temperature is 500°C.

[0123] The rest of the preparation methods and parameters were the same as those in Example 4.

[0124] Embodiment 11

[0125] The difference between this embodiment and embodiment 4 is that the final firing temperature is 600°C.

[0126] The rest of the preparation methods and parameters were the same as those in Example 4.

[0127] Example 12

[0128] The difference between this embodiment and embodiment 4 is that the final firing temperature is 700°C.

[0129] The rest of the preparation methods and parameters were the same as those in Example 4.

[0130] Embodiment 13

[0131] The difference between this embodiment and embodiment 4 is that the final firing temperature is 800°C.

[0132] The rest of the preparation methods and parameters were the same as those in Example 4.

[0133] Embodiment 14

[0134] The difference between this embodiment and embodiment 4 is that the mass content of the precious metal material in the precious metal precursor is 4 wt %, that is, the mass of the Pd(NO 3 ) 2 solution in the adjustment step (2) is 0.1110 g.

[0135] The rest of the preparation methods and parameters were the same as those in Example 4.

[0136] Embodiment 15

[0137] The difference between this embodiment and embodiment 4 is that the atmosphere of the primary calcination is an air atmosphere.

[0138] The rest of the preparation methods and parameters were the same as those in Example 4.

[0139] Comparative Example 1

[0140] This comparative example provides a catalyst for catalytic combustion of methane, wherein the catalyst is pure CeO2.

[0141] This comparative example also provides a method for preparing the above-mentioned catalyst for catalytic combustion of methane, comprising the following steps:

[0142] 2.5228 g of Ce(NO3)2·6H2O was placed in a crucible, placed in a muffle furnace, heated to 600°C at a heating rate of 5°C / min, and calcined in air for 4 hours to obtain the catalyst.

[0143] Comparative Example 2

[0144] This comparative example provides a catalyst for catalytic combustion of methane, wherein the catalyst is pure CeO2, and the CeO2 is formed by pretreatment with carbon nitride.

[0145] This comparative example also provides a method for preparing the above-mentioned catalyst for catalytic combustion of methane, comprising the following steps:

[0146] 1 g of carbon nitride was added to 8 mL of water and stirred at room temperature for 4 h to fully disperse it. Then, 2.5228 g of Ce(NO3)2·6H2O and 2 mL of ethanol were added and mixed and stirred for 4 h. After stirring and evaporating at 80°C, the mixture was dried at 60°C for 12 h. The resulting powder was heated to 600°C at a heating rate of 5°C / min and calcined in air for 4 h to obtain the catalyst.

[0147] Comparative Example 3

[0148] This comparative example provides a catalyst for catalytic combustion of methane, wherein the catalyst is pure CeO2.

[0149] This comparative example also provides a method for preparing the above-mentioned catalyst for catalytic combustion of methane, comprising the following steps:

[0150] Take 3.23g of trimesic acid, then add 12mL of water and 38mL of ethanol, stir to dissolve, then add 1.6763g of cerium acetate solution and 2mL of acetic acid to mix to obtain a mixed solution, stir at room temperature for 2h, and then perform a hydrothermal reaction on the mixed solution at 120°C for 24h. After the reaction is completed, cool and centrifuge to separate the precipitate, and wash it with deionized water 3 times and ethanol once, then vacuum dry it at 60°C for 12h, and then heat it to 350°C in an argon atmosphere at a heating rate of 5°C / min for 2h, and then heat it to 450°C in an air atmosphere at a heating rate of 5°C / min for 6h to obtain a catalyst.

[0151] Comparative Example 4

[0152] The difference between this comparative example and Example 4 is that the precursor of the precious metal is Pd(NO3)2, that is, step (1) is not performed, and steps (2) and (3) are replaced by the following steps:

[0153] S1. Take 2.5228g of Ce(NO3)2·6H2O in a crucible, put it in a muffle furnace, heat it to 600℃ at a heating rate of 5℃ / min, and roast it in air for 4h to obtain CeO2; S2. Take 1g of the CeO2, add 10mL of water and 0.0555g of Pd(NO3)2, mix and stir for 4h, evaporate to dryness with stirring at 80℃, and dry at 60℃ for 12h. The obtained powder is heated to 600℃ at a heating rate of 5℃ / min and roasted in air for 4h to obtain the catalyst.

[0154] The remaining parameters remain the same as those in Example 4.

[0155] Comparative Example 5

[0156] The difference between this comparative example and comparative example 4 is that step S1 is replaced by the preparation step of pure CeO2 in comparative example 3.

[0157] The rest of the preparation methods and parameters were the same as those in Comparative Example 4.

[0158] Comparative Example 6

[0159] The difference between this comparative example and comparative example 4 is that step S1 is not performed, and CeO2 in step S2 is replaced by commercial Al2O3.

[0160] The rest of the preparation methods and parameters were the same as those in Comparative Example 4.

[0161] Comparative Example 7

[0162] The difference between this comparative example and Example 4 is that the precursor of the precious metal is Na2PdCl4, that is, the precursor of the precious metal in step (3) is replaced by 0.0235 g of Na2PdCl4.

[0163] The rest of the preparation methods and parameters were the same as those in Example 4.

[0164] Comparative Example 8

[0165] The difference between this comparative example and comparative example 7 is that the mass content of the precious metal in the catalyst is 0.2 wt %.

[0166] The rest of the preparation methods and parameters were the same as those in Comparative Example 7.

[0167] Comparative Example 9

[0168] The difference between this comparative example and comparative example 7 is that the mass content of the precious metal in the catalyst is 0.5 wt %.

[0169] The rest of the preparation methods and parameters were the same as those in Comparative Example 7.

[0170] Comparative Example 10

[0171] The difference between this comparative example and comparative example 7 is that the final firing temperature is 500°C.

[0172] The rest of the preparation methods and parameters were consistent with those of Comparative Example 7.

[0173] Comparative Example 11

[0174] The difference between this comparative example and comparative example 7 is that the final firing temperature is 600°C.

[0175] The rest of the preparation methods and parameters were consistent with those of Comparative Example 7.

[0176] Comparative Example 12

[0177] The difference between this comparative example and comparative example 7 is that the final firing temperature is 700°C.

[0178] The rest of the preparation methods and parameters were consistent with those of Comparative Example 7.

[0179] Comparative Example 13

[0180] The difference between this comparative example and comparative example 7 is that the final firing temperature is 800°C.

[0181] The rest of the preparation methods and parameters were consistent with those of Comparative Example 7.

[0182] Performance Testing

[0183] The catalysts provided in the above examples and comparative examples were tested for methane catalytic combustion activity, and the test method was as follows:

[0184] When the gas composition is methane and air, and the volume percentage of methane is 1 vol.%, the air velocity is 60000 mL·g -1 ·h -1 Under the conditions, the catalytic performance was tested by programming the temperature of the fixed bed reactor, and the methane conversion rate was calculated by the methane concentration at the outlet of the gas chromatography molecular fixed bed. When the methane conversion rate reached 50%, the corresponding reaction temperature, i.e., T 50 When the methane conversion rate reaches 90%, record the corresponding reaction temperature, i.e., T 90 , the results are shown in Table 1.

[0185] Figure 3 The activity test curve of methane catalytic combustion of the catalysts provided in Example 4, Comparative Examples 3-5 and Comparative Example 7 of the present invention is as follows: Figure 3 It can be seen that Example 4 has the best activity, T 90is 367°C, indicating that the simultaneous regulation of the local environment of active metals and carriers can significantly improve the catalytic activity of methane combustion. On the one hand, carbon nitride is used to adjust the dispersion and local environment of precious metals. On the other hand, the hydrothermally synthesized Ce-MOF carrier has a larger specific surface area and more surface defects, which are more conducive to the adsorption and diffusion of reaction molecules. At the same time, the local environment of the carrier and active metal is regulated, thereby promoting methane activation.

[0186] Table 1

[0187]

[0188]

[0189]

[0190] analyze:

[0191] It can be seen from the above table that the catalyst provided by the present invention has strong low-temperature catalytic activity and can significantly reduce the reaction temperature of methane catalytic combustion. Under more optimal conditions, the T90 of the methane catalytic combustion process can be as low as 367°C, showing better methane catalytic combustion activity than commercial Pd / Al2O3 catalysts.

[0192] It can be seen from Examples 1-3 that in Example 1, T 50 It is significantly lower than that in Example 2 and Implementation 3, indicating that as the mass content of the precious metal material in the precious metal precursor increases, the catalytic activity of the catalyst first increases and then decreases. This is because the amount of graphite-like carbon nitride affects the dispersion degree of the precious metal. It can be seen that an appropriate amount of graphite-like carbon nitride can further enhance the catalytic activity.

[0193] By comparing Example 1 with Example 4, it can be seen that in Example 4, T 50 It is significantly lower than Example 1. This is because the carrier constructed by the hydrothermal method has a larger specific surface area and more defective structures on the surface, which is more conducive to methane activation.

[0194] It can be seen from the comparison between Example 4 and Examples 10-13, or from the comparison between Comparative Example 7 and Comparative Examples 10-13 that as the calcination temperature increases, the methane catalytic combustion activity decreases. This is because the increase in calcination temperature causes the precious metal particles to sinter, affecting the number of exposed active sites. It can be seen that a suitable calcination temperature can further enhance the catalytic activity.

[0195] From the comparison between Example 4 and Example 14, it can be seen that if the mass content of the precious metal material in the precious metal precursor is too high, it is not conducive to the anchoring and dispersion of the precious metal.

[0196] By comparing Example 4 with Example 15, it can be seen that if the atmosphere of the primary calcination is an air atmosphere, it is not conducive to synthesizing a cerium oxide carrier with more defective structures, thereby affecting the catalytic activity.

[0197] It can be seen from Example 1 and Comparative Example 4 that in Example 1, T 50 It is obviously lower than that of Comparative Example 4, indicating that the catalyst provided by the present invention is more conducive to methane activation. The same rule can be found in the comparison between Example 4 and Comparative Example 7.

[0198] In summary, the present invention introduces nitrogen-rich compounds to pre-coordinate precious metal materials, and then utilizes the pyrolysis of nitrogen-rich compounds to release micro-reducing gases to promote the dispersion of precious metals, so that the catalyst has a richer coordination unsaturated structure; secondly, the present invention uses different carrier preparation methods to obtain cerium dioxide, and it is found that the coordination unsaturated catalysts constructed based on different cerium dioxide carriers have a promoting effect on the activation of methane. On the one hand, the present invention utilizes nitrogen-rich compounds to adjust the dispersion and local environment of precious metals. On the other hand, the hydrothermally synthesized cerium dioxide carrier has a larger specific surface area and more surface defects, and at the same time regulates the local environment of the carrier and the active metal, thereby promoting the activation of methane; the preparation method has a relatively simple process flow, the raw materials are easily available, the cost is low, and it has good industrial application.

[0199] The applicant declares that the present invention illustrates the process method of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned process steps, that is, it does not mean that the present invention must rely on the above-mentioned process steps to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the raw materials selected by the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A methane catalytic combustion catalyst, characterized in that: The methane catalytic combustion catalyst comprises a carrier and an active component loaded on the carrier, the carrier is a metal oxide, the active component is a noble metal, and the precursor of the noble metal is a noble metal material pre-coordinated with a nitrogen-rich compound.

2. The methane catalytic combustion catalyst according to claim 1, characterized in that: The nitrogen-rich compound includes graphite-like carbon nitride; Preferably, in the precious metal precursor, the mass content of the precious metal material is 0.1-3wt%.

3. The methane catalytic combustion catalyst according to claim 1 or 2, characterized in that: The metal oxide includes ceria; Preferably, the noble metal includes any one or a combination of at least two of Pt, Pd or Rh; Preferably, in the catalyst, the mass content of the noble metal is 0.2-3wt%.

4. A method for preparing a methane catalytic combustion catalyst according to any one of claims 1 to 3, characterized in that: The preparation method comprises the following steps: The noble metal salt solution and the solution containing the nitrogen-rich compound are mixed and calcined once to obtain a noble metal precursor; The precursor solution of the metal oxide and the precursor of the noble metal are mixed and subjected to loading treatment to obtain the methane catalytic combustion catalyst.

5. The preparation method according to claim 4, characterized in that: In the solution containing the nitrogen-rich compound, the solvent includes water; Preferably, the mass volume ratio of the solution containing the nitrogen-rich compound is 0.05-0.1 g / mL; Preferably, the method for preparing the nitrogen-rich compound comprises: sintering an organic nitrogen source to obtain the nitrogen-rich compound; Preferably, the organic nitrogen source comprises melamine and / or urea; Preferably, the sintering temperature is 500-550°C; Preferably, the holding time of the sintering treatment is 4-6 hours.

6. The preparation method according to claim 4 or 5, characterized in that: The noble metal salt solution includes any one of a platinum salt solution, a palladium salt solution or a rhodium salt solution, or a combination of at least two thereof; Preferably, the primary calcination temperature is 500-550°C; Preferably, the holding time of the primary calcination is 4-6 hours.

7. The preparation method according to any one of claims 4 to 6, characterized in that: The metal oxide precursor solution includes a cerium salt solution; Preferably, in the metal oxide precursor solution, the solvent includes water and alcohol; Preferably, the loading treatment method includes an immersion method or a hydrothermal method; Preferably, the specific steps of the impregnation method include: The precursor solution of the metal oxide is impregnated with the precursor of the precious metal, and then a secondary calcination is performed to complete the loading; Preferably, the secondary calcination temperature is 600-650°C; Preferably, the secondary roasting time is 4-6h; Preferably, the specific steps of the hydrothermal method include: A metal oxide precursor solution, a noble metal precursor, an organic template and a regulator are mixed to obtain a mixed solution, the mixed solution is subjected to a hydrothermal reaction, and then calcined three times to complete the loading; Preferably, the organic template comprises any one of trimesic acid, phthalic acid or terephthalic acid, or a combination of at least two thereof; Preferably, the regulator comprises any one or a combination of at least two of formic acid, acetic acid, hydrochloric acid or benzoic acid; Preferably, in the hydrothermal method, the molar ratio of the organic template to the metal ion in the mixed solution is (2-4):1; Preferably, the temperature of the hydrothermal reaction is 100-140°C and the time is 12-24h; Preferably, the three calcinations are step-by-step calcinations, and the step-by-step calcinations include pre-calcination and final calcination; Preferably, the pre-burning temperature is 300-400°C and the holding time is 1-3h; Preferably, the final calcination temperature is 450-600° C., and the holding time is 4-6 hours.

8. The preparation method according to any one of claims 4 to 7, characterized in that: The preparation method comprises the following steps: (1) In an air atmosphere, the organic nitrogen source is heated to 500-550° C. at a heating rate of 5-10° C. / min for sintering, and the heat preservation time is 4-6 hours to obtain a nitrogen-rich compound; (2) adding the nitrogen-rich compound to the solvent, stirring and mixing for 4-12 hours, and obtaining a solution containing the nitrogen-rich compound with a mass volume ratio of 0.05-0.1 g / mL; The nitrogen-rich compound solution and the noble metal salt solution are stirred and mixed for 4-12 hours, and dried at 60-80° C. for 6-12 hours to obtain a powder to be calcined; In an inert atmosphere, the powder to be calcined is heated to 500-550° C. at a heating rate of 5-10° C. / min and kept at this temperature for 4-6 hours to obtain a precursor of a precious metal; (3) impregnating the precious metal precursor with a cerium salt solution, stirring and mixing for 4-12 hours, and then drying at 60-80° C. for 6-12 hours, and then heating the obtained powder to 600-650° C. at a heating rate of 5-10° C. / min in an air atmosphere for secondary calcination, with a holding time of 4-6 hours, to complete the loading and obtain a catalyst; or, A cerium salt solution, a noble metal precursor, an organic template and a regulator are mixed to obtain a mixed solution, and the mixed solution is subjected to a hydrothermal reaction at 100-140°C for 12-24 hours, centrifuged, washed, dried, and then pre-calcined at a heating rate of 5-10°C / min to 300-400°C in an inert atmosphere for 1-3 hours, and then finally calcined at a heating rate of 5-10°C / min to 450-600°C in an air atmosphere for 4-6 hours to complete the loading and obtain a catalyst.

9. Use of the methane catalytic combustion catalyst according to any one of claims 1 to 3, characterized in that: The methane catalytic combustion catalyst is used for catalytic combustion of methane and complete oxidation of methane into carbon dioxide and water.

10. The use according to claim 9, characterized in that: The methane catalytic combustion catalyst is applied to methane catalytic combustion and the methane complete conversion temperature is less than or equal to 400°C.

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