A platinum-based catalyst, its preparation method, and its application in low-temperature methane combustion.

Abstract

This invention discloses a platinum-based catalyst, its preparation method, and its application in the catalytic combustion of methane. The preparation method includes reacting a catalyst supported on reduced platinum in a mixed atmosphere of methane / nitrous oxide or methane / nitrous oxide / inert gas at the lowest temperature required for the complete catalytic combustion of methane by nitrous oxide, yielding a catalyst supported on low-oxidation-state platinum. This invention achieves a breakthrough reduction in the temperature for complete methane conversion to below 200°C and maintains long-term stability. This invention enables the simultaneous degradation of two greenhouse gases, methane and nitrous oxide, which is beneficial for mitigating the greenhouse effect. The catalyst of this invention has a simple manufacturing process, excellent performance, and long lifespan, and can be widely used in equipment such as flue gas treatment, natural gas vehicle exhaust treatment, and air purifiers.

Description

Technical Field

[0001] This invention relates to the fields of air pollution control and thermocatalysis, specifically to a design method for a highly efficient platinum-based catalyst for low-temperature combustion of methane and synergistic reduction of nitrous oxide. Background Technology

[0002] Methane (CH4), the main component of natural gas, is widely used as a substitute for traditional fossil fuels in power generation, heating, and natural gas vehicles. However, methane is the second largest greenhouse gas globally, with a global warming potential (GWP) approximately 25 times that of carbon dioxide (CO2). Since the Industrial Revolution, atmospheric methane concentrations have more than doubled, and this doubling of methane emissions contributes about 20% to global warming. Considering that methane's lifetime is only 8–11 years, about one-tenth that of carbon dioxide, reducing methane emissions can effectively curb rapid global warming in a relatively short period. Therefore, controlling methane emissions is of great significance in mitigating the greenhouse effect.

[0003] Methane is one of the most chemically stable alkanes, with a CH bond energy as high as 439 kJ / mol and low electron and proton affinity. Direct combustion of methane requires extremely high temperatures, which not only wastes a large amount of energy but also easily produces incomplete combustion byproducts (CO, NO). x(etc.), causing secondary pollution to the environment. Catalytic combustion of methane can completely convert methane into carbon dioxide at relatively low temperatures, making it a highly efficient, environmentally friendly, and economical method for reducing methane emissions. Its core lies in the design and development of highly efficient and stable catalysts. Supported noble metal catalysts typically exhibit excellent low-temperature catalytic methane combustion performance. Among them, platinum-based and palladium-based catalysts can lower the temperature for complete methane combustion to below 400℃ and are widely used in methane catalytic combustion. These supported noble metal catalysts (such as Pt / Pd on TiO2 / CeO2 / MnO2) can significantly affect catalytic activity by adjusting the coordination and interfacial structure of their active phase through in-situ redox reactions. Jiang et al. (Jiang, D.; Wan, G.; Halldin Stenlid, J.; García-Vargas, CE; Zhang, J.; Sun, C.; Li, J.; Abild-Pedersen, F.; Tassone, CJ; Wang, Y., Dynamic and reversible transformations of subnanometre-sized palladium on ceria for efficient methane removal. Nature Catalysis 2023, 6, 618-627.) pre-activated a Pd / CeO2 catalyst in a CO atmosphere containing excess O2, converting isolated Pd single atoms into PdO. x Sub-nano clusters were used to enhance the activity of the catalyst in the methane combustion reaction, achieving a 90% methane conversion rate at 400℃. Yang et al. (Yang, WW; Polo-Garzon, F.; Zhou, H.; Huang, ZN; Chi, MF; Meyer, HM, III; Yu, XB; Li, YY; Wu, ZL, Boosting the Activity of PdSingle Atoms by Tuning Their Local Environment on Ceria for Methane Combustion. Angew. Chem.-Int. Edit. 2023, 62, 7.) found that after one cycle of CH4+O2 combustion reaction, the T2 of the single-atom Pd / CeO2 catalyst increased significantly. 50 The temperature dropped by 130°C, and characterization results showed that the Pd single atom in the catalyst induced the formation of oxygen-coordinated unsaturated Pd during the reaction. δ+The presence of certain species promotes the migration of reactive oxygen species and the decomposition of reaction intermediates, thereby significantly enhancing the reaction activity. Similar phenomena have been reported in Pt / MnO2 catalysts (Yan,D.;Gao,Y.;Qi,M.-Y.;Jia,H.;Xu,Y.-J.,In Situ High-Temperature Reaction-InducedLocal Structural Dynamic Evolution of Single-Atom Pt on OxideSupport.Precision Chemistry 2023,1,299-308.), which is due to the dynamic response between the catalyst's active phase and the reaction atmosphere during the reaction. The lattice near Pt is activated, providing additional electrons to Pt, thus increasing the methane combustion rate. The above studies show that the coordinated unsaturated metal sites induced by the catalyst during the reaction exhibit unique activity for methane combustion. Therefore, the catalyst structure can be adjusted in situ and its performance improved by utilizing the reaction process and changing the reaction atmosphere.

[0004] However, oxygen is a strong oxidant. When O2 is used as the oxidant for methane combustion, the unsaturated metal species generated during the reaction are easily re-oxidized to higher valence states, making these highly reactive metal sites difficult to maintain stably or present in small quantities. Even the most advanced methane combustion catalysts currently available struggle to achieve 100% methane conversion below 400°C under oxygen conditions. Therefore, how to prepare highly efficient catalysts and improve the reaction atmosphere to achieve in-situ dynamic adjustment of the catalyst structure to further reduce the temperature of methane catalytic combustion and maintain stability has become an urgent technical problem to be solved. Summary of the Invention

[0005] To address the aforementioned technical problems and shortcomings in this field, the present invention provides a platinum-based catalyst, its preparation method, and its application.

[0006] [1] A method for preparing a platinum-based catalyst, comprising: reacting a catalyst supported on reduced platinum in a mixed atmosphere of methane / nitrous oxide or methane / nitrous oxide / inert gas at the lowest temperature at which methane is completely catalytically combusted by nitrous oxide to obtain a catalyst supported on low-oxidation-state platinum. In some embodiments, the reaction temperature may be 300–320°C, for example 310°C. In some embodiments, the reaction time may be 1–4 hours, preferably 2–3 hours. In some embodiments, the space velocity of the reaction may be 10–15 L / (g·h), for example 12 L / (g·h), where g represents the mass of the catalyst.

[0007] In some embodiments, the support in the catalyst loaded with reduced platinum may be titanium dioxide. Optionally, the titanium dioxide is in the anatase crystal form. Optionally, the particle size of the titanium dioxide is 20–60 nm, for example, 40 nm.

[0008] In the methane / nitrous oxide / inert gas mixed atmosphere, with the total volume of methane, nitrous oxide and inert gas being 100%, the volume percentage of methane can be 1% to 5%, preferably 2% to 3%, such as 2.5%, etc., and the volume percentage of nitrous oxide can be 4% to 20%, preferably 8% to 12%, such as 10%, etc.

[0009] In the methane / nitrous oxide or methane / nitrous oxide / inert gas mixed atmosphere, the volume ratio of methane to nitrous oxide is preferably 1:4. This is the stoichiometric ratio for complete reaction of methane and nitrous oxide (100% complete catalytic combustion of methane by nitrous oxide).

[0010] In the methane / nitrous oxide / inert gas mixed atmosphere, the inert gas refers to a gas that does not participate in the reaction, such as at least one of nitrogen, rare gases, etc. The rare gas can be at least one of helium, argon, etc.

[0011] The loading of platinum in the catalyst supported on reduced platinum can be 0.8 wt% to 1.2 wt%, for example, 1 wt%.

[0012] In some embodiments, the reduced platinum in the catalyst supported on reduced platinum exists in the form of nanoclusters. Further, the average size of the reduced platinum nanoclusters can be 0.9–1.5 nm, for example, 1.2 nm.

[0013] In some embodiments, the method for preparing the catalyst supported on reduced platinum may include:

[0014] The catalyst supported on reduced platinum was obtained by impregnation, mixing the catalyst support with a platinum precursor solution, drying, calcining, and reducing with hydrogen.

[0015] The platinum precursor solution can be an H₂PtCl₆ solution. The concentration of platinum in the platinum precursor solution can be 35–40 mg. Pt mL -1 For example, 37mg Pt mL -1 .

[0016] The heating rate of the roasting can be 1 to 10 °C / min, for example, 5 °C / min.

[0017] The calcination temperature can be 450-550℃, for example, 500℃.

[0018] The roasting time can be 2 to 4 hours, for example, 3 hours.

[0019] The roasting can be carried out in air.

[0020] In the method for preparing the catalyst supported on reduced platinum, calcination yields a catalyst supported on oxidized platinum.

[0021] The reduction heating rate can be 1 to 10 °C / min, for example, 5 °C / min.

[0022] The heat preservation temperature for the reduction can be 250-400℃, for example, 350℃.

[0023] The heat preservation time for the reduction can be 2 to 4 hours, such as 3 hours.

[0024] The reduction can be carried out in a hydrogen-argon mixture. The volume percentage of hydrogen in the hydrogen-argon mixture can be 1% to 10%, for example, 5%.

[0025] [2] A catalyst supported on low-oxidation-state platinum was prepared according to the preparation method described in [1].

[0026] Furthermore, the catalyst supported on low-oxidation-state platinum may have a valence state of δ, where 0 < δ < 2.

[0027] In some embodiments, the low-oxidation-state platinum in the catalyst supported on low-oxidation-state platinum exists in the form of nanoclusters. Further, the average size of the low-oxidation-state platinum nanoclusters can be 1.2–1.8 nm, for example, 1.5 nm.

[0028] [3] Application of the catalyst supported on low-oxidation-state platinum as described in [2] in the catalytic combustion of methane.

[0029] [4] A method for catalytic combustion of methane, using the catalyst supported on low-oxidation-state platinum as described in [2], with nitrous oxide and / or oxygen as oxidants, to catalyze the combustion of methane.

[0030] The catalyst of this invention, supported on low-oxidation-state platinum, can achieve 100% conversion of CH4 and N2O at 200°C in a mixed atmosphere of 2.5 vol% CH4 / 10 vol% N2O / 87.5 vol% inert gas.

[0031] This invention provides a design method for a highly efficient platinum-based catalyst for the low-temperature combustion of methane and the synergistic reduction of nitrous oxide. Specifically, nitrous oxide is used as the oxidant to replace oxygen. The catalyst, such as Pt / TiO2 supported on reduced platinum, is heat-treated under conditions of methane and nitrous oxide coexistence. This process in situ adjusts the catalyst structure, inducing the generation of highly active, low-oxidation-state (oxygen-coordinating unsaturated) Pt.δ+ (0<δ<2) species to enhance the reactivity of methane combustion.

[0032] Compared with the prior art, the beneficial effects of this invention are as follows:

[0033] 1. The present invention uses nitrous oxide as an oxidant, and preferably sets the volume (molar) ratio of methane to nitrous oxide to be 1:4, which can achieve the simultaneous degradation of the two greenhouse gases and help alleviate the greenhouse effect.

[0034] 2. This invention induces the formation of highly active, low-oxidation-state Pt by heat-treating the catalyst under conditions of coexistence of methane and nitrous oxide. δ+ For species with (0<δ<2), the temperature at which methane is completely converted (T) 100 It has achieved a breakthrough by reducing the temperature to below 200°C and maintaining stability for a long time.

[0035] 3. This catalyst has a simple manufacturing process, excellent performance, and long lifespan, and can be widely used in equipment such as flue gas treatment, natural gas vehicle exhaust treatment, and air purifiers. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the preparation process of the Pt / TiO2 series catalysts in a specific embodiment.

[0037] Figure 2 The images show transmission electron microscopy (TEM) images of reduced Pt / TiO2 (left) and low-oxidation Pt / TiO2-CH4+N2O (right) in the specific embodiments.

[0038] Figure 3 This is a transmission electron microscopy (TEM) image of the elemental distribution of reduced Pt / TiO2 in a specific embodiment.

[0039] Figure 4 The images shown are high-angle annular dark-field scanning transmission electron microscope (HADDF-STEM) images and Pt particle size distribution diagrams of reduced Pt / TiO2 (left image) and low-oxidation Pt / TiO2-CH4+N2O (right image) in the specific embodiment.

[0040] Figure 5 The diagram shows the activity of reduced Pt / TiO2 in a methane and nitrous oxide atmosphere after four cycles in a specific embodiment.

[0041] Figure 6 This is an activity diagram of the catalyst in Example 2 under a methane and oxygen atmosphere.

[0042] Figure 7 The figure shows the stability test results of low oxidation state Pt / TiO2-CH4+N2O in a specific implementation method.

[0043] Figure 8 The above are in-situ X-ray photoelectron spectroscopy (XPS) spectra of the catalyst in Example 2 under different atmospheres. Detailed Implementation

[0044] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Operating methods not specifically specified in the following embodiments are generally performed under conventional conditions or as recommended by the manufacturer. Unless otherwise stated, the raw materials and reagents used in the following embodiments are commercially available or can be prepared by known methods.

[0045] Example 1:

[0046] (1) For catalyst preparation, see Figure 1 :

[0047] Take 4g of anatase TiO2 powder with a particle size of 40nm and add it to 50mL of deionized water, with a concentration of 37mg. Pt mL -1 A Pt precursor (H₂PtCl₆) solution was impregnated and stirred at room temperature for 6 hours to ensure homogeneity and complete reaction. The mixture was then dried overnight in an oven at 100°C. The dried solid was ground into powder and placed in a muffle furnace, where it was heated to 500°C at a constant rate of 5°C / min and calcined for 3 hours. The powder was then cooled to room temperature. Further, the powder was placed in a tube furnace under a hydrogen-argon mixed atmosphere with a hydrogen content of 5 vol%, and heated to 350°C at a constant rate of 5°C / min. After calcination for 3 hours, the powder was then further heated in a hydrogen-argon mixed atmosphere with a hydrogen content of 5 vol%. The catalyst was cooled to room temperature in a hydrogen-argon mixture to obtain a reduced platinum catalyst (reduced Pt / TiO2), with a Pt loading of approximately 1 wt%. Finally, the catalyst powder with a mesh size of 40-60 was screened and placed in an activity evaluation device. The temperature was uniformly increased to 310 °C under a reaction atmosphere of 2.5 vol% CH4 / 10 vol% N2O / 87.5 vol% He, and the reaction was activated for 3 hours to obtain a low oxidation state Pt / TiO2 catalyst (low oxidation state Pt / TiO2-CH4+N2O).

[0048] Figure 2 These are TEM images of the reduced Pt / TiO2 and the low-oxidation Pt / TiO2-CH4+N2O prepared in this embodiment. From... Figure 2 It can be seen that TiO2 is spherical, with small-diameter Pt nanoclusters uniformly distributed on it.

[0049] Figure 3 The image shows a TEM mapping photograph of Pt / TiO2, which confirms the uniform distribution of Pt on the TiO2 support.

[0050] Figure 4 The images show HADDF-STEM images of reduced Pt / TiO2 and low-oxidation Pt / TiO2-CH4+N2O. The images visually demonstrate the uniform distribution of Pt nanoclusters (indicated in circles), with average particle sizes of 1.2 nm and 1.5 nm, respectively.

[0051] (2) Thermal catalytic performance test:

[0052] The performance of reduced Pt / TiO2 was investigated under the following reaction conditions: helium carrier gas, methane concentration of 2.5 vol%, nitrous oxide concentration of 10 vol% (methane to oxygen molar ratio of 1:4), and space velocity of 12000 mL / (g·h) (where g represents catalyst mass). The Tg of this catalyst was determined. 100 The results of the four-cycle reaction tests are shown in Table 1 and Table 2, respectively. Figure 5 As shown. Figure 5 In the figure, the solid curve represents the thermocatalytic performance test results during the cooling process after the first thermocatalytic performance test.

[0053] (3) Thermal stability test:

[0054] The long-term stability of the low oxidation state Pt / TiO2-CH4+N2O was investigated under the following reaction conditions: helium carrier gas, methane concentration of 2.5 vol%, nitrous oxide concentration of 10 vol% (methane to oxygen molar ratio of 1:4), space velocity of 12000 mL / (g·h) (where g represents catalyst mass), and temperature of 200 °C. The activity results of this catalyst within 100 h are as follows: Figure 7 As shown.

[0055] Example 2:

[0056] (1) Catalyst preparation:

[0057] The only difference between the preparation process and Example 1 is that it was not pre-activated in a reaction atmosphere of 2.5 vol% CH4 / 10 vol% N2O / 87.5 vol% He, that is, the catalyst supported on reduced platinum obtained after hydrogen reduction in Example 1 was used directly.

[0058] (2) Thermal catalytic performance test:

[0059] The performance of the catalyst was investigated under the following reaction conditions: helium carrier gas, methane concentration of 2.5 vol%, oxygen concentration of 5 vol% (molar ratio of methane to oxygen atoms of 1:4), and space velocity of 12000 mL / (g·h) (where g represents the mass of the catalyst). The Te of this catalyst was determined. 100 The results of the four-cycle reaction tests are shown in Table 1 and Table 2, respectively. Figure 6 As shown.

[0060] The reaction atmosphere and activity data for different embodiments are shown in Table 1.

[0061] Table 1

[0062] Catalyst composition Reaction Atmosphere <![CDATA[Pre-activated T 100 (℃)]]> <![CDATA[Activated T 100 (℃)]]> Example 1 <![CDATA[Pt / TiO2]]> <![CDATA[CH4+N2O]]> 310 200 Example 2 <![CDATA[Pt / TiO2]]> <![CDATA[CH4+O2]]> 440 440

[0063] The dynamic changes of Pt in the catalyst supported on reduced platinum in Example 2 under different reaction atmospheres were tested using in-situ XPS. The specific test steps and analysis methods are as follows:

[0064] X-ray photoelectron spectroscopy was performed on a ThermoFischer ESCALAB 250Xi instrument. A monochromatic Al-Kα excitation source (hv = 1486.6 eV) with a power of 200 W was used. The sample was compressed into a pellet and vacuum-treated before the reaction, and the resulting spectra were acquired at room temperature. Four different reaction atmospheres were introduced, and the effects of the reaction atmosphere on the structure, valence state, and electronic state of Pt were investigated under different reaction conditions. The test conditions are shown below:

[0065] Test 1: Introduce a 2.5 vol% CH4 / carrier gas He atmosphere and heat the sample to 310 °C at a rate of 10 °C / min. Collect spectra at 10 min and 120 min.

[0066] Test 2: Introduce a 10 vol% N2O / carrier gas He atmosphere and heat the sample to 310 °C at a rate of 10 °C / min. Collect spectra at 10 min and 120 min.

[0067] Test 3: Introduce a 2.5 vol% CH4 / 10 vol% N2O / carrier gas He atmosphere, heat the sample to 310 °C at a rate of 10 °C / min, and collect spectra at 10 min and 120 min;

[0068] Test 4: Introduce a 2.5 vol% CH4 / 5 vol% O2 / carrier gas He atmosphere, heat the sample to 310 °C at a rate of 10 °C / min, and collect spectra at 10 min and 120 min. Then heat to 440 °C and hold for 120 min before collecting spectra.

[0069] The surface charge of the sample was assessed using the C1s value of contaminated carbon (284.8 eV) as an internal standard to correct for the binding energy of the sample. For example... Figure 8 As shown, in-situ XPS tests indicate that a large amount of low-oxidation-state Pt is induced only under conditions where methane and nitrous oxide coexist. δ+ (0<δ<2) Highly reactive species: neither methane alone nor nitrous oxide alone can induce the formation of reactive species, while an atmosphere in which methane and oxygen coexist will lead to the formation of low oxidation state Pt. δ+Highly reactive species are over-oxidized to form divalent Pt species.

[0070] In summary, this invention provides a method for designing a highly efficient platinum-based catalyst for the low-temperature combustion of methane and the synergistic reduction of nitrous oxide, which can prepare highly active Pt catalysts. δ+ A Pt / TiO2 catalyst of the (0<δ<2) species was applied to the methane combustion reaction using nitrous oxide as the oxidant, achieving complete degradation of methane and nitrous oxide at 200℃. This invention has advantages such as simple process, convenient operation, and good stability, and has excellent prospects for practical application.

[0071] Furthermore, it should be understood that after reading the above description of the present invention, those skilled in the art can make various alterations or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A method for preparing a platinum-based catalyst, characterized in that, include: A catalyst supported on reduced platinum is reacted in a mixed atmosphere of methane / nitrous oxide or methane / nitrous oxide / inert gas at the lowest temperature at which methane is completely catalytically combusted by nitrous oxide, to obtain a catalyst supported on low-oxidation-state platinum; in the mixed atmosphere of methane / nitrous oxide or methane / nitrous oxide / inert gas, the volume ratio of methane to nitrous oxide is 1:4; the valence state of the low-oxidation-state platinum is δ, 0 < δ < 2.

2. The preparation method according to claim 1, characterized in that, The reaction temperature is 300–320°C; The reaction time is 1 to 4 hours; The space velocity of the reaction is 10–15 L / (g·h), where g represents the mass of the catalyst.

3. The preparation method according to claim 2, characterized in that, The reaction temperature is 310℃; The reaction takes 2 to 3 hours.

4. The preparation method according to claim 1, characterized in that, In the methane / nitrous oxide / inert gas mixed atmosphere, with the total volume of methane, nitrous oxide, and inert gas being 100%, the volume percentage of methane is 1% to 5%, and the volume percentage of nitrous oxide is 4% to 20%.

5. The preparation method according to claim 4, characterized in that, In the methane / nitrous oxide / inert gas mixed atmosphere, with the total volume of methane, nitrous oxide, and inert gas being 100%, the volume percentage of methane is 2% to 3%, and the volume percentage of nitrous oxide is 8% to 12%.

6. The preparation method according to claim 1, characterized in that, The catalyst supported on reduced platinum is supported on titanium dioxide; the titanium dioxide is in the anatase crystal form; and the particle size of the titanium dioxide is 20–60 nm. The catalyst supported on reduced platinum has a platinum loading of 0.8 wt% to 1.2 wt%. The reduced platinum in the catalyst supported on reduced platinum exists in the form of nanoclusters, with an average size of 0.9–1.5 nm.

7. The preparation method according to claim 1 or 6, characterized in that, The method for preparing the catalyst supported on reduced platinum includes: The catalyst supported on reduced platinum was obtained by impregnation, mixing the catalyst support with a platinum precursor solution, drying, calcining, and reducing with hydrogen.

8. The catalyst supported on low-oxidation-state platinum prepared by the preparation method according to any one of claims 1 to 7.

9. The catalyst supported on low-oxidation-state platinum according to claim 8, characterized in that, In the catalyst supported on low-oxidation-state platinum, the low-oxidation-state platinum exists in the form of nanoclusters, with an average size of 1.2–1.8 nm.

10. The application of the catalyst supported on low-oxidation-state platinum according to claim 8 or 9 in the catalytic combustion of methane.

11. A method for catalytic combustion of methane, characterized in that, The catalyst supported on low-oxidation-state platinum as described in claim 8 or 9 is used to catalyze the combustion of methane using nitrous oxide and / or oxygen as oxidants.

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