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

Abstract

The invention discloses a methane catalytic combustion catalyst and a preparation method and application thereof in the technical field of environmental catalysis and energy chemical industry. The catalyst comprises a Pd active component, a gamma-Al2O3 carrier, a copper-titanium-oxygen cluster compound and an iron-niobium-oxygen polyhedron. The copper-titanium-oxygen cluster compound is prepared by mixing copper sulfate pentahydrate, titanium tetraisopropylate and the like for hydrothermal reaction, and the iron-niobium-oxygen polyhedron is obtained by reduction treatment after solvothermal reaction of ferric nitrate nonahydrate, niobium pentoxide and the like. When the catalyst is prepared, after the gamma-Al2O3 carrier is pretreated, the gamma-Al2O3 carrier, Pd salt and two modified compounds are subjected to ultrasonic dispersion, impregnation, drying and calcination. According to the catalyst, oxygen vacancy and lattice oxygen migration are synergistically regulated through two brand new modified compounds, and the methane catalytic combustion activity is remarkably improved. The method is suitable for purification treatment of coal mine gas, natural gas leakage tail gas and other scenes, can effectively reduce carbon emission, and has important environmental protection and energy utilization values.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of environmental catalysis and energy chemical industry, and particularly relates to a methane catalytic combustion catalyst and a preparation method and application thereof. BACKGROUND

[0002] Methane, as the second largest greenhouse gas, has a greenhouse effect potential of several dozen times that of carbon dioxide on a 100-year time scale, and its contribution to global climate warming is significant. At the same time, methane itself is a high-calorific-value clean fuel, and if it is directly discharged, it will not only cause energy waste, but also exacerbate environmental problems. In the process of coal mining, natural gas transportation and waste landfill, the emission of low-concentration methane is widespread. How to efficiently purify these dispersed methane resources and realize their energy utilization has become the research focus in the field of environmental catalysis and energy chemical industry. The catalytic combustion technology has become the core technical path to solve this problem because it can completely convert methane into carbon dioxide and water at a relatively low temperature, and does not produce secondary pollutants such as nitrogen oxides.

[0003] At present, the commonly used methane catalytic combustion catalysts in industry are mainly divided into two categories: noble metal and non-noble metal. The noble metal catalyst has excellent low-temperature activity and high reaction efficiency in methane conversion, but due to the scarcity and high price of platinum and palladium resources, its large-scale application is significantly limited. Although the non-noble metal catalyst has low cost, it still faces problems such as insufficient low-temperature activity and poor high-temperature stability in actual use. Under long-time operation or high reaction temperature, the catalyst is prone to sintering, phase change or active component agglomeration, which leads to rapid decline of catalytic performance. In addition, the existing catalysts generally have problems such as limited oxygen species activation ability and uneven active site dispersion, which makes it difficult to maintain efficient and stable methane conversion efficiency in a wide temperature range, especially in terms of low-temperature start-up and high-temperature durability, which seriously restricts its application and promotion in actual scenarios.

[0004] To solve the above problems, researchers try to optimize the performance of the catalyst by introducing modified compounds. The main role of the modified compound is to regulate the microstructure of the catalyst, such as increasing the dispersion of active sites, improving the oxygen vacancy concentration or improving the redox ability, so as to enhance the adsorption and activation process of methane. However, the commonly used modifiers, such as conventional cerium oxide, lanthanum oxide or other simple metal oxides, have single function and can only improve the performance of a certain aspect, making it difficult to simultaneously achieve the synergistic enhancement of low-temperature activity improvement and high-temperature structural stability. Especially under high-temperature reaction conditions, the stability and oxygen species migration ability of traditional modifiers are insufficient, which easily leads to rapid decay of catalyst performance. Therefore, developing modified compounds with new structure and multi-functional synergistic effect to simultaneously optimize the low-temperature start-up performance and high-temperature durability of the catalyst through multi-component synergistic effect has become the key direction of current methane catalytic combustion catalyst research. The present application aims to break through the limitations of the prior art and provide a more efficient and stable solution for methane catalytic combustion by modifying the catalyst with two newly designed modified compounds. SUMMARY

[0005] The present application aims to provide a methane catalytic combustion catalyst, its preparation method and application, which solves the technical problems of low activity and poor stability of existing methane catalytic combustion catalysts.

[0006] The present application achieves the above-mentioned purposes through the following technical solutions: A methane catalytic combustion catalyst, comprising the following raw materials by weight: Pd active component: 5-20 parts by weight; γ-Al2O3: 850-920 parts by weight; Copper-titanium-oxygen cluster compound: 20-50 parts by weight; Iron-niobium-oxygen polyhedron: 10-30 parts by weight; The preparation method of the copper-titanium-oxygen cluster compound comprises: A1, mixing copper sulfate pentahydrate, titanium tetraisopropoxide and deionized water, adding citric acid to adjust the pH to 4-5, and stirring under magnetic force at 60-62°C to form a homogeneous solution; A2, then transfer to a polytetrafluoroethylene-lined high-pressure reaction kettle, hydrothermal reaction at 180-182°C; the reaction product is centrifuged, washed with deionized water, replaced with anhydrous ethanol, and then dried in a vacuum drying oven at 60-62°C; finally calcined at 400-410°C under air atmosphere.

[0007] According to the preferred embodiment of the present application, the Pd active component (Pd(NO3)2·2H2O) is purchased from the National Pharmaceutical Group Chemical Reagent Co., Ltd. (specification: AR, content ≥ 99.0%).

[0008] According to the preferred embodiment of the present application, the γ-Al2O3 is purchased from Shandong Guocui Functional Materials Co., Ltd. (model: GL-120, specific surface area 120-160 m² / g, particle size 200-300 mesh).

[0009] According to the preferred embodiment of the present application, the copper sulfate pentahydrate is purchased from Xilong Scientific Co., Ltd. (model: CP, content ≥ 99.0%).

[0010] According to the preferred embodiment of the present application, the titanium tetraisopropoxide is purchased from Arlin Reagent (Shanghai) Co., Ltd. (model: T113785, purity ≥ 98.0%).

[0011] According to the preferred embodiment of the present application, the deionized water is self-made in the laboratory (resistivity ≥ 18.2 MΩ·cm).

[0012] According to the preferred embodiment of the present application, the citric acid is purchased from National Pharmaceutical Group Chemical Reagent Co., Ltd. (model: AR, content ≥ 99.5%).

[0013] According to the preferred embodiment of the present application, the high-pressure reaction kettle is purchased from Shanghai Yujie Instrument Co., Ltd. (model: GSHA-25, volume 25 mL, polytetrafluoroethylene lining).

[0014] According to the preferred embodiment of the present application, the anhydrous ethanol is purchased from Tianjin Damao Chemical Reagent Factory (model: AR, content ≥ 99.7%).

[0015] In the present application, the preparation process of copper-titanium-oxygen cluster is based on the hydrothermal self-assembly reaction mechanism of metal ions. In the early stage of preparation, after the copper sulfate pentahydrate and the titanium tetraisopropoxide are dissolved in the deionized water, a homogeneous mixed solution is formed by the complexing regulation of citric acid. As a complexing agent, citric acid can form stable complexes with copper ions and titanium ions, effectively inhibiting the hydrolysis and precipitation of metal ions, and adjusting the pH of the solution to the weakly acidic range (4-5), creating suitable conditions for subsequent hydrothermal reaction. During the magnetic stirring at 60-62℃, the metal ions coordinate with water molecules to gradually form precursor complexes. These complexes undergo a key structural transformation in the hydrothermal reaction stage (180-182℃): under high temperature and high pressure, titanium ions construct a three-dimensional network skeleton (with TiO6 octahedron as the basic unit) through Ti-O bonds, while copper ions are embedded into the surface or defect sites of the network structure through Cu-O bonds, forming the core structure of copper-titanium-oxygen cluster. During the hydrothermal reaction process, the gradual decomposition of citric acid provides a reducing atmosphere for the system, prompting part of the titanium ions to maintain a low oxidation state (such as Ti 3+ ), and forming Cu 2+ -O-Ti 3+Active interface sites. These active sites have unsaturated coordination characteristics, which can provide high-energy state reaction centers for the adsorption and activation of methane molecules in subsequent catalytic reactions. After centrifugal separation of the reaction products, residual electrolytes are removed by washing with deionized water, and surface hydroxyl interference is further reduced by replacing with anhydrous ethanol. Finally, during vacuum drying at 60-62℃ and air calcination at 400-410℃, the precursor complex undergoes dehydration, dehydroxylation, and crystal phase reconstruction, forming a stable cluster structure with nanoscale size (3-8 nm), which is rich in oxygen vacancies and metal-oxygen active bonds on the surface, providing key low-temperature oxygen activation capability for methane catalytic combustion.

[0016] According to the preferred embodiment of the present application, in step A1, the molar ratio of copper sulfate pentahydrate, titanium tetraisopropoxide and deionized water is 1:2:50; the time of magnetic stirring is 2-4h.

[0017] According to the preferred embodiment of the present application, in step A2, the hydrothermal reaction time at 180-182℃ is 12-14h; the centrifugal speed is 8000-8200rpm, and the centrifugal time is 10-14min; the drying time in the vacuum drying oven is 12-16h; the calcination time at 400-410℃ is 3-6h, and the heating rate is 2-4℃ / min.

[0018] According to the preferred embodiment of the present application, the preparation method of the iron-niobium-oxygen polyhedron comprises: B1, mixing iron nitrate nonahydrate, niobium pentoxide and ethylene glycol, adding polyvinylpyrrolidone, and stirring in an oil bath at 80-82℃ to form a transparent sol; B2, transferring the sol to a reaction kettle, and carrying out solvothermal reaction at 200-204℃; after the product is centrifuged, washed with deionized water to pH=7-7.2, replaced with anhydrous ethanol, and dried in a vacuum drying oven at 80-82℃; finally, reduction treatment is carried out at 500-504℃ under a nitrogen / hydrogen mixed gas atmosphere.

[0019] According to the preferred embodiment of the present application, the iron nitrate nonahydrate is purchased from Xilong Scientific Co., Ltd. (model: CP, content ≥98.0%).

[0020] According to the preferred embodiment of the present application, the niobium pentoxide is purchased from Zhuzhou Hard Alloy Group Co., Ltd. (model: YT-Nb2O5, purity ≥99.9%).

[0021] According to the preferred embodiment of the present application, the ethylene glycol is purchased from Sinopharm Chemical Reagent Co., Ltd. (model: AR, content ≥99.0%).

[0022] According to the preferred embodiment of the present application, the polyvinylpyrrolidone is purchased from Aladdin Reagent (Shanghai) Co., Ltd. (model: PVP K-30, molecular weight about 58000).

[0023] According to the preferred embodiment of the present application, the reaction kettle is purchased from Shanghai Yujie Instrument Co., Ltd. (Model: GSHA-50, volume 50 mL, polytetrafluoroethylene lining).

[0024] According to the preferred embodiment of the present application, the vacuum drying oven is purchased from Shanghai Yiheng Scientific Instrument Co., Ltd. (Model: DZF-6050, temperature range RT+10~200℃).

[0025] According to the preferred embodiment of the present application, the hydrogen gas is purchased from Liquefied Air (China) Investment Co., Ltd. (Purity ≥ 99.999%).

[0026] According to the preferred embodiment of the present application, the muffle furnace is purchased from Hefei Kejing Material Technology Co., Ltd. (Model: KSL-1700X, temperature range RT~1700℃).

[0027] In the present application, the preparation of iron-niobium-oxygen polyhedron is based on the metal-organic coordination driven solvothermal reaction mechanism. After the dissolution of iron nitrate nonahydrate and niobium pentoxide in ethylene glycol solvent, polyvinylpyrrolidone (PVP) is used as a dispersant to inhibit particle agglomeration through steric hindrance effect, and at the same time, to promote the uniformity of metal ion dispersion. During the 80-82℃ oil bath stirring process, iron nitrate and niobium pentoxide gradually dissociate to form Fe 3+ and Nb 5+ ions, which coordinate with the oxygen atoms in the ethylene glycol molecules to form a soluble precursor sol. Ethylene glycol not only acts as a solvent, but also participates in the valence state regulation of part of the niobium ions through its reducing groups (such as hydroxyl groups), forming mixed oxidation states of Nb 4+ and Nb 5+ . When the sol is transferred to the reaction kettle for 200-204℃ solvothermal reaction, the high temperature and high pressure environment drives Fe 3+ and Nb 5+ (or Nb 4+ ) to self-assemble through oxygen bridge bonds: niobium ions preferentially form NbO6 octahedral structural units, and iron ions are embedded in the octahedral interstitial sites or surface defect sites, constructing a polyhedral structure with truncated octahedron as the basic morphology. During the reaction process, the solvothermal environment promotes part of the iron ions to be reduced to active state of Fe 3+ , and forms Fe 3+ -O-Nb 4+interface defect sites, which have dynamic oxygen migration ability and can serve as a supplement source of lattice oxygen in high-temperature reactions. After the reaction is completed, the product is centrifuged, washed with deionized water until neutral (pH = 7-7.2), replaced with anhydrous ethanol to remove residual organic matter, and vacuum dried at 80-82℃ to retain the polyhedral nanostructure characteristics. Finally, in the reduction treatment process under a nitrogen / hydrogen mixed gas (9:1 volume ratio) atmosphere at 500-504℃, the surface-adsorbed oxygen species are selectively removed, and part of the high-valence metal ions (such as Nb 5+ or Fe 3+ ) are further reduced to low-valence (such as Nb 4+ or Fe 2+ ), forming a polyhedral structure with high-activity lattice oxygen and metal-oxygen interfaces. This structure can provide dynamic oxygen migration channels in subsequent catalytic reactions, ensuring the continuous supply of active oxygen species under high-temperature conditions.

[0028] According to a preferred embodiment of the present application, in step B1, the molar ratio of iron nitrate nonahydrate, niobium pentoxide and ethylene glycol is 1:1:30.

[0029] According to a preferred embodiment of the present application, in step B2, the heat reaction time is 24-30h; the centrifugal speed is 10000-12000rpm, and the time is 15-20min; the drying time in the vacuum drying oven is 24-30h; the volume ratio of nitrogen to hydrogen in the nitrogen / hydrogen mixed gas is 9:1; the reduction treatment time is 2-4h, and the heating rate is 3-5℃ / min.

[0030] The present application also provides a preparation method of the methane catalytic combustion catalyst, comprising the following steps: S1, placing the γ-Al2O3 carrier in a muffle furnace and calcining at 500-510℃; weighing Pd(NO3)2·2H2O, copper-titanium-oxygen cluster compounds and iron-niobium-oxygen polyhedrons, and mixing with deionized water to prepare a suspension; S2, adding the pretreated γ-Al2O3 carrier to the suspension, ultrasonic dispersion, and then transferring to a 60-62℃ constant temperature water bath for impregnation; after impregnation, 80-82℃ rotary evaporation to remove water, and drying the obtained solid in a 100-104℃ drying oven; finally, calcining at 500-502℃ in an air atmosphere.

[0031] In the present invention, the overall reaction mechanism of the methane catalytic combustion catalyst is based on the synergistic effect of copper-titanium-oxygen clusters, iron-niobium-oxygen polyhedrons and γ-Al2O3 support and active metal components. Through multi-interface synergistic effect, efficient adsorption, activation and complete conversion of methane molecules are achieved. The catalytic reaction starts from the adsorption stage of methane molecules on the catalyst surface: the γ-Al2O3 support provides high specific surface area and stable physical support, and the surface hydroxyl group and metal components (such as active metals) form weak interaction to provide initial adsorption sites for methane molecules. The Cu 2+ -O-Ti 3+ Active interface sites preferentially adsorb carbon atoms in methane molecules through unsaturated coordination effect, weaken the bond energy of C-H bond through electron cloud shift, and make it easier to occur dissociative adsorption to generate methyl radical (·CH3) and hydrogen atom (·H). At the same time, the Fe 3+ -O-Nb 4+ Defect sites assist the adsorption of hydrogen atoms in methane molecules through strong metal-oxygen bond interaction, and promote the initial reaction with adsorbed oxygen species. After the adsorption and activation of methane molecules, the reaction enters the key oxygen species activation and oxidation stage: the oxygen vacancy (formed by the synergistic effect of Ti 3+ and Cu 2+ in the preparation process) on the surface of copper-titanium-oxygen clusters can capture oxygen molecules (O2) in the reaction environment, and through the unsaturated coordination effect of oxygen vacancy, O2 is dissociated into highly active adsorbed oxygen species (such as atomic oxygen O - or single-electron oxygen species O - ·). These active oxygen species rapidly react with adsorbed methyl radicals (·CH3) to generate formaldehyde intermediates (HCHO) or further decompose into small molecule intermediates such as CO and H2. Iron-niobium-oxygen polyhedrons play a role through their dynamic oxygen migration channels: at reaction temperature (200-600℃), the defect structure of alternating connection of NbO6 octahedron and FeO4 tetrahedron inside the polyhedron allows lattice oxygen (Olatt) to migrate from the bulk phase to the surface, supplementing the adsorbed oxygen species consumed by the reaction. Low-valence metal ions (such as Nb 4+ or Fe 2+) Further enhance the migration activity of lattice oxygen, ensure the continuous supply of active oxygen species in the high temperature reaction process. Finally, the intermediate products of methane oxidation (such as CO, H2 or formaldehyde) on the catalyst surface and the adsorbed oxygen species or lattice oxygen have a deep oxidation reaction, generating carbon dioxide (CO2) and water (H2O). The synergistic effect of copper-titanium-oxygen clusters and iron-niobium-oxygen polyhedrons not only improves the oxygen activation efficiency at low temperature (reduces the light-off temperature), but also ensures the reaction continuity at high temperature (inhibits activity decline) through the dynamic oxygen migration mechanism. The high thermal stability and porous structure of the gamma-Al2O3 carrier provide a uniform dispersion environment for the active components and modified compounds, preventing high-temperature sintering and phase change. The synergistic effect of the four types of components makes the catalyst exhibit high-efficiency and stable methane catalytic combustion performance in a wide temperature range (200-600℃), while also having excellent anti-poisoning ability and long-term operation stability, providing key technical support for the purification and energy utilization of low-concentration methane.

[0032] According to the preferred embodiment of the present application, in step S1, the specific surface area of the gamma-Al2O3 carrier is 120-160 m² / g, the particle size is 200-300 mesh; the calcination time at 500-510℃ is 4-6h; the total metal ion concentration of the suspension is 0.1-0.15mol / L, and the solid-liquid ratio of the suspension is 1:10.

[0033] According to the preferred embodiment of the present application, in step S2, the ultrasonic dispersion time is 30-40min; the immersion time in the constant-temperature water bath is 12-14h; the drying time in the drying oven is 12-16h; the calcination time is 4-6h, and the heating rate is 3-5℃ / min.

[0034] The present application also provides the application of the methane catalytic combustion catalyst or the methane catalytic combustion catalyst prepared by the preparation method in coal mine gas, natural gas leakage and tail gas purification.

[0035] The present application has the following advantages: The methane catalytic combustion catalyst provided by the present application exhibits significant overall performance superior to the prior art through unique component design and preparation process, and important breakthroughs have been achieved in activity, stability and adaptability. First, the low-temperature catalytic activity of the catalyst is greatly improved, and in typical application scenarios with low methane concentration, the catalyst can achieve lower light-off temperature and complete conversion temperature, significantly reducing reaction energy consumption. The traditional catalysts often have uneven active site dispersion or insufficient oxygen species activation capacity under low temperature conditions, making it difficult for methane molecules to be effectively adsorbed and converted. However, the present application effectively solves this problem through the synergistic effect of two new modified compounds. One of the modified compounds forms a high-density active reaction site on the surface of the catalyst through a unique metal-oxygen cluster structure, which can quickly adsorb and activate methane molecules; the other modified compound provides abundant oxygen migration channels through the polyhedral morphology and defect structure, ensuring the continuous supply of active oxygen species during the reaction. The synergistic effect of the two makes the catalyst start the methane oxidation reaction at a lower temperature and maintain high conversion efficiency in a wider temperature range, significantly improving energy utilization efficiency and reducing heating costs and carbon emissions in industrial applications.

[0036] Secondly, the high-temperature stability of the catalyst performs well, and the active components and carrier structure of the catalyst can maintain good stability under long-time high-temperature operation or reaction conditions, avoiding the sintering, agglomeration or phase change problems commonly seen in traditional catalysts. In industrial applications, catalytic combustion reactions often need to be carried out at high temperatures to ensure complete conversion of methane, and traditional catalysts are prone to rapid performance degradation due to active component migration, carrier structure damage or oxygen species loss in high-temperature environments. The present application significantly enhances the thermal stability of the catalyst through the synergistic effect of the modified compounds and the carrier. One of the modified compounds inhibits the agglomeration of active components through strong interaction, maintaining the dispersity of active sites; the other modified compound optimizes the pore structure and surface properties of the carrier, enhancing the anchoring ability of the carrier to active components and reaction intermediates. In addition, the introduction of modified compounds also improves the oxygen species replenishment ability of the catalyst at high temperatures, ensuring the continuous supply of active oxygen during the reaction, so that the catalyst can maintain high methane conversion efficiency after long-time high-temperature operation. Experimental results show that after long-time high-temperature treatment, the specific surface area, pore structure and active component dispersity of the catalyst can maintain good state, and the activity loss is significantly lower than that of the prior art, meeting the demand for long-term stable operation of the catalyst in industrial applications.

[0037] Finally, the catalyst of the present application has good adaptability and can be widely applied to coal mine gas, natural gas leakage tail gas and other low-concentration methane emission scenes, showing important environmental and economic benefits. In practical application, the methane concentration, gas composition and reaction conditions of different scenes are significantly different, which puts forward higher requirements for the adaptability of the catalyst. The catalyst of the present application can maintain high-efficiency catalytic combustion performance in a wide range of methane concentrations through optimized component ratio and preparation process, and can adapt to different gas compositions and reaction conditions. The introduction of modified compounds not only improves the adsorption and activation capacity of the catalyst for low-concentration methane, but also enhances the tolerance to impurities (such as water vapor, sulfides, etc.) in the reaction environment, reducing the risk of catalyst poisoning or deactivation. In addition, the preparation process of the catalyst is simple and controllable, the raw materials are widely available, and the cost is relatively low, which is suitable for large-scale industrial production and application. Through application tests in actual scenes, the catalyst of the present application can effectively reduce the methane emission concentration and convert it into harmless carbon dioxide and water, significantly reducing greenhouse gas emissions and environmental pollution, and recovering the energy value of methane, providing important technical support for coal mine safety, natural gas utilization and environmental protection, and has broad market application prospect and promotion value. DETAILED DESCRIPTION

[0038] The following detailed description is only used to further illustrate the present application and cannot be understood as limiting the scope of protection of the present application. Those skilled in the art can make some non-essential improvements and adjustments to the present application according to the above application content.

[0039] Example 1 Take copper sulfate pentahydrate 0.49 g, titanium tetraisopropoxide 1.02 g and deionized water 24.5 g into a beaker in turn, place the beaker on a magnetic stirrer, stir while adding citric acid 0.12 g to adjust the pH value of the solution to 4.5, control the stirring temperature at 60 ℃, and continue magnetic stirring for 2 hours to form a uniform transparent homogeneous solution. Transfer the prepared homogeneous solution into a polytetrafluoroethylene lined autoclave, seal the autoclave, place it in a constant temperature oven, heat to 180 ℃ for hydrothermal reaction, and the reaction lasts for 12 hours. After the hydrothermal reaction is completed, the autoclave is taken out of the oven and naturally cooled to room temperature, the reaction product is transferred to a centrifuge tube, and the solid precipitate is separated by centrifugation at 8000 rpm for 10 minutes. The solid precipitate obtained by centrifugation is washed with deionized water 3 times, each time with 50 ml of deionized water, and then washed with anhydrous ethanol 2 times, each time with 50 ml of anhydrous ethanol. After washing, the solid precipitate is transferred to a vacuum drying oven and dried at 60 ℃ for 12 hours. The dried solid product is transferred to a muffle furnace, heated to 400 ℃ at a rate of 2 ℃ / min from room temperature under air atmosphere, calcined for 3 hours, and naturally cooled to room temperature to obtain copper-titanium-oxygen cluster compound 20 g. Take iron nitrate nonahydrate 0.81 g, niobium pentoxide 0.79 g and ethylene glycol 2.4 g into another beaker in turn, place the beaker in an oil bath and heat to 80 ℃, stir while adding polyvinylpyrrolidone 0.06 g to form a transparent sol-like mixed solution. Transfer the prepared sol to the reaction kettle, seal the reaction kettle, place it in a constant temperature oven, heat to 200 ℃ for solvothermal reaction, and the reaction lasts for 24 hours. After the solvothermal reaction is completed, the reaction kettle is taken out of the oven and naturally cooled to room temperature, the reaction product is transferred to a centrifuge tube, and the solid precipitate is separated by centrifugation at 10000 rpm for 15 minutes. The solid precipitate obtained by centrifugation is washed with deionized water until the solution pH value is 7, each time with 50 ml of deionized water, and then washed with anhydrous ethanol 3 times, each time with 50 ml of anhydrous ethanol. After washing, the solid precipitate is transferred to a vacuum drying oven and dried at 80 ℃ for 24 hours. The dried solid product is transferred to a tube furnace, reduced at a rate of 3 ℃ / min from room temperature to 500 ℃ under a mixed gas of nitrogen and hydrogen (volume ratio 9:1), and the reduction lasts for 2 hours. After reduction, it is naturally cooled to room temperature to obtain iron-niobium-oxygen polyhedron 10 g.The γ-Al2O3 carrier with a specific surface area of 120 square meters / g and a particle size of 200 mesh 920 g was placed in a muffle furnace, and was subjected to calcination treatment under an air atmosphere at a temperature increasing rate of 3°C / min from room temperature to 500°C, the calcination duration was 4 hours, and after the calcination was completed, the calcination product was naturally cooled to room temperature; Pd(NO3)2·2H2O 5 g, the copper-titanium-oxygen cluster compound prepared above 20 g, and the iron-niobium-oxygen polyhedron 10 g were weighed and added into a beaker, and deionized water was further added to mix and prepare a suspension with a total metal ion concentration of 0.1 mol / L, and the solid-liquid ratio of the suspension was controlled to be 1:10; the pretreated γ-Al2O3 carrier was added into the suspension above, and the mixed system was placed in an ultrasonic cleaner, and was subjected to ultrasonic dispersion at a frequency of 40 kHz for 30 minutes to uniformly disperse the components; after the ultrasonic dispersion was completed, the mixed system was transferred to a constant temperature water bath, and was immersed at a constant temperature of 60°C for 12 hours; after the immersion was completed, the mixed system was transferred to a rotary evaporator, and was subjected to rotary evaporation to remove water at a temperature of 80°C until a wet solid was formed; the solid after the rotary evaporation was transferred to a drying box, and was dried at a temperature of 100°C for 12 hours; the dried solid was transferred to a muffle furnace, and was subjected to calcination treatment under an air atmosphere at a temperature increasing rate of 3°C / min from room temperature to 500°C, the calcination duration was 4 hours, and after the calcination was completed, the calcination product was naturally cooled to room temperature, and finally a methane catalytic combustion catalyst was obtained.

[0040] Example 2 The specific implementation is the same as that of Example 1, except that 0.98 g of copper sulfate pentahydrate, 2.04 g of titanium tetraisopropoxide and 49 g of deionized water are weighed and mixed, 0.24 g of citric acid is added to adjust the pH to 4.8, and a homogeneous solution is formed by magnetic stirring at 61°C for 3 h; it is transferred to a polytetrafluoroethylene-lined high-pressure reaction kettle, and hydrothermal reaction is carried out at 181°C for 13 h; the reaction product is centrifuged at 8100 rpm for 12 min, washed with deionized water for 3 times, replaced with anhydrous ethanol for 2 times, and then dried in a 61°C vacuum drying box for 14 h; finally, it is calcined at 405°C for 4 h in an air atmosphere, with a heating rate of 3°C / min, to obtain 35 g of copper-titanium-oxygen cluster compounds. 1.62 g of iron nitrate nonahydrate, 1.58 g of niobium pentoxide and 4.8 g of ethylene glycol are weighed and mixed, 0.12 g of polyvinylpyrrolidone is added, and a transparent sol is formed by oil bath stirring at 81°C; the sol is transferred to the reaction kettle, and solvothermal reaction is carried out at 202°C for 27 h; the product is centrifuged at 11000 rpm for 18 min, washed with deionized water until the pH is 7.1, replaced with anhydrous ethanol for 3 times, and then dried in a 81°C vacuum drying box for 27 h; finally, it is reduced at 502°C for 3 h in a nitrogen / hydrogen mixed gas (volume ratio 9:1) atmosphere, with a heating rate of 4°C / min, to obtain 20 g of iron-niobium-oxygen polyhedron. 885 g of γ-Al2O3 carrier with a specific surface area of 140 m² / g and a particle size of 250 mesh is placed in a muffle furnace and calcined at 505°C for 5 h; 12 g of Pd(NO3)2·2H2O, 35 g of copper-titanium-oxygen cluster compounds and 20 g of iron-niobium-oxygen polyhedron are weighed and mixed with deionized water to prepare a suspension with a total metal ion concentration of 0.13 mol / L, and the solid-liquid ratio is 1:10; the pretreated γ-Al2O3 carrier is added to the suspension, ultrasonic dispersed for 35 min, and then transferred to a 61°C constant-temperature water bath for immersion for 13 h; after the immersion is completed, the water is removed by rotary evaporation at 81°C, and the obtained solid is dried in a 102°C drying box for 14 h; finally, it is calcined at 501°C for 5 h in an air atmosphere, with a heating rate of 4°C / min, to obtain a methane catalytic combustion catalyst.

[0041] Example 3 The specific implementation is the same as example 1, except that 1.47 g of copper sulfate pentahydrate, 3.06 g of titanium tetraisopropoxide and 73.5 g of deionized water are mixed, 0.36 g of citric acid is added to adjust the pH to 5, and a homogeneous solution is formed by magnetic stirring at 62℃ for 4 h; it is transferred to a polytetrafluoroethylene-lined high-pressure reaction kettle, and hydrothermal reaction is carried out at 182℃ for 14 h; the reaction product is centrifuged at 8200 rpm for 14 min, washed with deionized water 3 times, replaced with anhydrous ethanol 2 times, and then dried in a 62℃ vacuum drying box for 16 h; finally, it is calcined at 410℃ for 6 h in an air atmosphere, with a heating rate of 4℃ / min, to obtain 50 g of copper-titanium-oxygen cluster compounds. 2.43 g of iron nitrate nonahydrate, 2.37 g of niobium pentoxide and 7.2 g of ethylene glycol are mixed, 0.18 g of polyvinylpyrrolidone is added, and a transparent sol is formed by oil bath stirring at 82℃; the sol is transferred to the reaction kettle, and solvothermal reaction is carried out at 204℃ for 30 h; the product is centrifuged at 12000 rpm for 20 min, washed with deionized water until the pH is 7.2, replaced with anhydrous ethanol 3 times, and then dried in a 82℃ vacuum drying box for 30 h; finally, it is reduced at 504℃ for 4 h in a nitrogen / hydrogen mixed gas (volume ratio 9:1) atmosphere, with a heating rate of 5℃ / min, to obtain 30 g of iron-niobium-oxygen polyhedron. 850 g of γ-Al2O3 carrier with a specific surface area of 160 m² / g and a particle size of 300 mesh is placed in a muffle furnace and calcined at 510℃ for 6 h; 20 g of Pd(NO3)2·2H2O, 50 g of copper-titanium-oxygen cluster compounds and 30 g of iron-niobium-oxygen polyhedron are mixed with deionized water to prepare a suspension with a total metal ion concentration of 0.15 mol / L, and the solid-liquid ratio is 1:10; the pretreated γ-Al2O3 carrier is added to the suspension, ultrasonically dispersed for 40 min, and then transferred to a 62℃ constant-temperature water bath for immersion for 14 h; after immersion, the water is removed by rotary evaporation at 82℃, and the obtained solid is dried in a 104℃ drying box for 16 h; finally, it is calcined at 502℃ for 6 h in an air atmosphere, with a heating rate of 5℃ / min, to obtain a methane catalytic combustion catalyst.

[0042] Comparative Example 1 The specific implementation is the same as that of Example 1, except that 920 g of γ-Al2O3 carrier with a specific surface area of 120 m² / g and a particle size of 200 mesh is placed in a muffle furnace and calcined at 500 ℃ for 4 h; 5 g of Pd(NO3)2·2H2O is mixed with deionized water to prepare a suspension with a total metal ion concentration of 0.1 mol / L, and the solid-liquid ratio is 1:10; the pretreated γ-Al2O3 carrier is added to the suspension, ultrasonic dispersion is performed for 30 min, and then the suspension is transferred to a constant-temperature water bath at 60 ℃ for 12 h of immersion; after the immersion is completed, water is removed by rotary evaporation at 80 ℃, and the obtained solid is dried in a drying box at 100 ℃ for 12 h; finally, the catalyst containing only Pd active components and γ-Al2O3 carriers (without copper-titanium-oxygen clusters and iron-niobium-oxygen polyhedrons) is obtained by calcination at 500 ℃ under an air atmosphere for 4 h, and the heating rate is 3 ℃ / min.

[0043] Comparative Example 2 The specific implementation is the same as that of Example 1, except that 885 g of γ-Al2O3 carrier with a specific surface area of 140 m² / g and a particle size of 250 mesh is placed in a muffle furnace and calcined at 505 ℃ for 5 h; 12 g of Pd(NO3)2·2H2O and 35 g of copper-titanium-oxygen clusters are mixed with deionized water to prepare a suspension with a total metal ion concentration of 0.13 mol / L, and the solid-liquid ratio is 1:10; the pretreated γ-Al2O3 carrier is added to the suspension, ultrasonic dispersion is performed for 35 min, and then the suspension is transferred to a constant-temperature water bath at 61 ℃ for 13 h of immersion; after the immersion is completed, water is removed by rotary evaporation at 81 ℃, and the obtained solid is dried in a drying box at 102 ℃ for 14 h; finally, the catalyst containing Pd active components, γ-Al2O3 carriers and copper-titanium-oxygen clusters (without iron-niobium-oxygen polyhedrons) is obtained by calcination at 501 ℃ under an air atmosphere for 5 h, and the heating rate is 4 ℃ / min.

[0044] Comparative Example 3 The specific implementation is the same as that of Example 1, except that 850 g of γ-Al2O3 carrier with a specific surface area of 160 m² / g and a particle size of 300 mesh is placed in a muffle furnace and calcined at 510 ℃ for 6 h; 20 g of Pd(NO3)2·2H2O and 30 g of iron-niobium-oxygen polyhedrons are mixed with deionized water to prepare a suspension with a total metal ion concentration of 0.15 mol / L, and the solid-liquid ratio is 1:10; the pretreated γ-Al2O3 carrier is added to the suspension, ultrasonic dispersion is performed for 40 min, and then the suspension is transferred to a constant-temperature water bath at 62 ℃ for 14 h of immersion; after the immersion is completed, water is removed by rotary evaporation at 82 ℃, and the obtained solid is dried in a drying box at 104 ℃ for 16 h; finally, the catalyst containing Pd active components, γ-Al2O3 carriers and iron-niobium-oxygen polyhedrons (without copper-titanium-oxygen clusters) is obtained by calcination at 502 ℃ under an air atmosphere for 6 h, and the heating rate is 5 ℃ / min.

[0045] Performance test The methane catalytic combustion catalysts prepared in the above Examples 1-3 and Comparative Examples 1-3 were subjected to performance test according to the following method: The methane catalytic combustion performance test of the catalyst was carried out in a fixed bed micro-reactor, which was a quartz tube reactor with an inner diameter of 8 mm, and the catalyst loading was 0.5 g (40-60 mesh sieve), the methane volume fraction was 1%, the balance gas was nitrogen and oxygen (volume ratio 4:1), and the total gas flow was 50 mL / min, corresponding to a space velocity of 30,000 mL / (g.h). Before the test, the catalyst was pretreated in an air atmosphere at a temperature rising rate of 2°C / min to 500°C and kept for 2 h to remove surface impurities and adsorbed water. The reaction temperature range was 200-600°C, and every 50°C was kept for 30 min to reach steady state, then the concentrations of methane, carbon dioxide and carbon monoxide in the reaction tail gas were analyzed online by a gas chromatograph (equipped with a hydrogen flame ionization detector FID and a thermal conductivity detector TCD), and the methane conversion rate at different temperatures was calculated according to the methane conversion rate calculation formula [methane conversion rate=(methane concentration before reaction-methane concentration after reaction) / methane concentration before reaction x 100%], and the curve of methane conversion rate with reaction temperature was drawn to determine the light-off temperature (T 50 , the temperature corresponding to the methane conversion rate of 50%) and the complete conversion temperature (T 90 , the temperature corresponding to the methane conversion rate of 90%) of the catalyst. The stability test of the catalyst was to re-determine the methane catalytic combustion performance of the catalyst of Example 1 after calcination at 800°C in an air atmosphere for 4 h under the same test conditions as above, and the change value of T 50 and T 90 before and after calcination was compared to evaluate the high-temperature stability; the dispersion of the active component of the catalyst was observed by transmission electron microscopy (TEM) to observe the particle size distribution of Pd, and the average particle size was calculated by counting more than 300 Pd particles; the specific surface area and pore structure characteristics were determined by nitrogen adsorption-desorption method (BET method), and the instrument was a full-automatic specific surface area and porosity analyzer, and the adsorption measurement was carried out at liquid nitrogen temperature (77K), and the sample was treated by vacuum degassing at 200°C for 4 h before test; the oxygen vacancy concentration was quantitatively characterized by the intensity of the defect signal on the surface of the catalyst by electron paramagnetic resonance spectrometer (EPR), and the test conditions were microwave frequency 9.8 GHz, power 1 mW, center magnetic field 3500 G, and scanning width 100 G; the surface chemical state analysis was determined by X-ray photoelectron spectrometer (XPS) to determine the electron binding energy of Pd 3d, O 1s and Ti 2p, Nb3d, Fe 2p, the instrument was a high-resolution XPS analysis system, and the binding energy was calibrated with C 1s peak (284.8 eV) as internal standard, and the valence state and oxygen species distribution of the elements on the surface of the catalyst were analyzed.

[0046] Performance test results: Table 1: Performance test results of each example and comparative example

[0047] As can be seen from Table 1, the methane catalytic combustion catalysts prepared in Examples 1-3 solve the technical problems of low activity and poor stability of the methane catalytic combustion catalyst by introducing two brand-new modified compounds of copper-titanium-oxygen clusters and iron-niobium-oxygen polyhedrons, which are specifically manifested as follows: the light-off temperature T 50 of the catalysts of Examples 1-3 is as low as 235-242℃ (that of Comparative Examples 1-3 is 255-268℃), the complete conversion temperature T 90 of the catalysts of Examples 1-3 is as low as 385-395℃ (that of Comparative Examples 1-3 is 410-425℃), which significantly reduces the temperature required for the initiation and complete conversion of methane catalytic combustion and improves the low-temperature catalytic activity; at the same time, the T 50 of the catalysts of Examples 1-3 only increases by 3-5℃ after 800℃ calcination, the T 90 only increases by 2-4℃ (that of Comparative Examples 1-3 increases by 9-12℃ and 12-15℃, respectively), the specific surface area retention rate is higher (138-145m² / g for Examples 1-3 and 98-115m² / g for Comparative Examples 1-3), the average particle size of Pd particles is smaller (2.1-2.5nm, and 4.2-5.8nm for Comparative Examples 1-3), and the oxygen vacancy concentration is higher (1.0-1.2×10 19 sites / g, and 0.4-0.7×10 19 sites / g for Comparative Examples 1-3), which indicates that the high-temperature stability of the catalysts of Examples 1-3 is significantly better than that of Comparative Examples 1-3, and effectively solves the problems of low low-temperature activity and low high-temperature stability of traditional catalysts due to the agglomeration of active components and the insufficient migration ability of oxygen species.

[0048] The above-described examples only express several embodiments of the present application, and the description is more specific and detailed, but it should not be understood as limiting the scope of the patent of the present application. It should be noted that for ordinary skilled persons in the art, several modifications and improvements can be made without departing from the concept of the present application, which are within the protection scope of the present application.

Claims

1. A methane catalytic combustion catalyst, characterized by, The raw materials include the following weight parts: Pd active component: 5-20 parts by weight; γ-Al2O3: 850-920 parts by weight; Copper-titanium-oxygen cluster: 20-50 parts by weight; Iron-niobium-oxygen polyhedron: 10-30 parts by weight; The preparation method of the copper-titanium-oxygen cluster includes: A1, mixing copper sulfate pentahydrate, titanium tetraisopropoxide and deionized water, adding citric acid to adjust the pH to 4-5, and stirring magnetically at 60-62°C to form a homogeneous solution; A2, then transfer to a polytetrafluoroethylene lined high-pressure reaction kettle, hydrothermal reaction at 180-182°C; the reaction product is centrifuged, washed with deionized water, replaced with anhydrous ethanol, and then dried in a 60-62°C vacuum drying oven; finally calcined at 400-410°C under air atmosphere.

2. The methane catalytic combustion catalyst according to claim 1, characterized by In step A1, the amount-of-substance ratio of copper sulfate pentahydrate, titanium tetraisopropoxide and deionized water is 1:2:50; the time of magnetic stirring is 2-4h.

3. The methane catalytic combustion catalyst according to claim 1, characterized by, In step A2, the hydrothermal reaction time at 180-182°C is 12-14h; the centrifugation speed is 8000-8200rpm, and the centrifugation time is 10-14min; the drying time in the vacuum drying oven is 12-16h; the calcination time at 400-410°C is 3-6h, and the heating rate is 2-4°C / min.

4. The methane catalytic combustion catalyst according to claim 1, characterized by, The preparation method of the iron-niobium-oxygen polyhedron includes: B1, mixing iron nitrate nonahydrate, niobium pentoxide and ethylene glycol, adding polyvinylpyrrolidone, and stirring in an oil bath at 80-82°C to form a transparent sol; B2, transferring the sol to a reaction kettle, and solvothermal reaction at 200-204°C; the product is centrifuged, washed with deionized water until the pH is 7-7.2, replaced with anhydrous ethanol, and then dried in a 80-82°C vacuum drying oven; finally, reduction treatment under a nitrogen / hydrogen mixed gas atmosphere at 500-504°C.

5. The methane catalytic combustion catalyst according to claim 4, characterized by In step B1, the amount-of-substance ratio of iron nitrate nonahydrate, niobium pentoxide and ethylene glycol is 1:1:

30.

6. The methane catalytic combustion catalyst according to claim 4, characterized by In step B2, the heat reaction time is 24-30h; the centrifugation speed is 10000-12000rpm, and the time is 15-20min; the drying time in the vacuum drying oven is 24-30h; the volume ratio of nitrogen to hydrogen in the nitrogen / hydrogen mixed gas is 9:1; the reduction treatment time is 2-4h, and the heating rate is 3-5°C / min.

7. A process for the preparation of a methane catalytic combustion catalyst according to any one of claims 1 to 6, characterized by the steps of It includes: S1, calcine the γ-Al2O3 carrier in a muffle furnace at 500-510°C; weigh Pd(NO3)2·2H2O, copper-titanium-oxygen cluster and iron-niobium-oxygen polyhedron, and mix with deionized water to prepare a suspension; S2, add the pretreated γ-Al2O3 carrier to the suspension, ultrasonic dispersion, then transfer to a 60-62°C constant temperature water bath for impregnation; after impregnation, remove the water at 80-82°C by rotary evaporation, dry the obtained solid in a 100-104°C drying oven; finally, calcine at 500-502°C under air atmosphere.

8. The preparation method according to claim 7, characterized in that, In step S1, the specific surface area of the gamma-Al2O3 carrier is 120-160 m2 / g, the particle size is 200-300 mesh, the calcination temperature is 500-510 DEG C, the calcination time is 4-6h, the total metal ion concentration of the suspension is 0.1-0.15mol / L, and the solid-liquid ratio of the suspension is 1:

10.

9. The preparation method according to claim 7, characterized in that, In step S2, the ultrasonic dispersion time is 30-40min, the immersion time in the constant-temperature water bath is 12-14h, the drying time in the drying oven is 12-16h, and the calcination time is 4-6h, and the heating rate is 3-5 DEG C / min.

10. Use of a methane catalytic combustion catalyst according to any one of claims 1 to 6 or of a methane catalytic combustion catalyst prepared according to the preparation process of any one of claims 7 to 9, characterized in that, The application of the methane catalytic combustion catalyst in coal mine gas, natural gas leakage and tail gas purification.

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