CuxMnyCo3-x-yO4 co-doped catalyst for catalytic oxidation of methane and preparation method of CuxMnyCo3-x-yO4 co-doped catalyst

Abstract

The invention relates to the technical field of catalytic oxidation degradation of methane, in particular to a CuxMnyCo3-x-yO4 co-doped catalyst for catalytic oxidation of methane and a preparation method of the CuxMnyCo3-x-yO4 co-doped catalyst. According to the method, non-noble metal salt serves as a precursor, litchi-shaped solid or hollow microspheres with the particle size of about 7 microns are directly generated through ultrasonic atomization-high-temperature transient cracking, the surfaces of the litchi-shaped solid or hollow microspheres are rich in nanometer protrusions, and high-density exposure of active sites is achieved. The change of the surface structure of the catalyst is realized by doping the transition metal, so that the catalytic oxidation performance of the catalyst is influenced, the conversion rate of the catalyst to low-concentration methane (the volume concentration is 0.3%) at 350 DEG C in a water vapor-containing atmosphere reaches 90%, and the catalyst shows water poisoning resistance and long-period stability which are superior to those of noble metal. The method is simple in process, low in cost, easy to amplify and suitable for the field of low-temperature methane efficient removal of coal mine ventilation gas, natural gas vehicle tail gas and the like.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of catalytic oxidative degradation of methane, and particularly relates to a Cu x Mn y Co 3-x-y O4 co-doped catalyst and a preparation method thereof. BACKGROUND

[0002] Methane is not only the main component of natural gas, but also is widely used in gas power generation and chemical synthesis due to its high calorific value and low pollution characteristics. However, it is also the second largest greenhouse gas after carbon dioxide, and the greenhouse effect potential of unit mass is about twenty times that of CO2. The key to solving the energy-environment dilemma lies in developing efficient and low-energy consumption methane catalytic oxidation technology: while fully utilizing the clean energy properties of natural gas, the disturbance to the climate system is minimized.

[0003] Catalytic oxidation has become a recognized effective path for controlling low-carbon alkane emissions due to its low energy consumption, large treatment capacity and no secondary pollution, and the core of the technology lies in the rational design of the catalyst. Compared with noble metals, transition metal oxides have the advantages of low cost, strong structural plasticity, simple preparation process and good thermal stability. Among them, cobalt-based oxides, which belong to the same group VIII as noble metals, have variable valence and noble metal-like electronic structure, and show comparable or even superior activity to noble metals in the catalytic combustion of alkanes, esters and other VOCs, providing an economically viable solution for methane deep purification.

[0004] Water vapor is a "persistent" poison in the tail gas of CH4 catalytic combustion device: at low temperature, it competes with methane for active sites, twists the reaction path, and makes the light-off temperature rise sharply and the activity drop sharply, which is a common bottleneck faced by the academic and engineering communities. Although noble metals have "water-repellent" surfaces, stable d-band centers and synergistic effects of supports, they are difficult to be large-scale landed due to high cost, resource scarcity and high-temperature sintering. The preparation of traditional noble metal supported catalysts generally adopts a multi-step process of "dipping-drying-calcining", which has defects such as complicated steps, high energy consumption and easy falling off of active components.

[0005] The document with the patent number CN113856705A provides a PdO-PtS / SiO2 catalyst, a preparation method and application thereof. PdO and PtS double active components show very high catalytic activity in the low-temperature catalytic oxidation reaction of methane. The PdO-PtS / SiO2 catalyst with a Pd loading of 3% and a Pt loading of 1% has a methane conversion rate close to 90% at 400℃.

[0006] Patent CN105214682A discloses "A Three-Dimensional Ordered Macroporous Cerium Dioxide-Supported Co-Pd Nanoalloy Catalyst, Preparation Method and Application," which produces novel materials with controllable particle morphology and pore size, exhibiting good catalytic activity and economy. Under conditions of 2.5% methane concentration, a methane to oxygen molar ratio of 1 / 8, and a space velocity of 20000 mL / (gh), the temperatures at which methane conversion on the Co6-Pd / 3DOMCeO2 catalyst reached 10%, 50%, and 90% were 353℃, 430℃, and 475℃, respectively. Furthermore, for the same Co loading... x -Pd catalysts exhibit better catalytic activity than Co catalysts, i.e., supported Co... x -Pd exhibits good catalytic activity.

[0007] Therefore, there is an urgent need to develop a novel methane catalytic oxidation catalyst that combines high and low temperature activity, excellent thermal / hydrothermal stability, and cost-effectiveness. Summary of the Invention

[0008] This invention provides a Cu for catalytic oxidation of methane. x Mn y Co 3-x-y O4 co-doped catalyst, the Cu x Mn y Co 3-x-y The O4 co-doped catalyst has a lychee-like or hollow lychee-like structure; through Cu 、 Mn co-doping with Co3O4 creates more protrusions and oxygen vacancies; this catalyst can achieve 90% methane conversion at a catalytic oxidation temperature of 350℃. The Cu... x Mn y Co 3-x-y In the O4 co-doped catalyst, x = 0.026 and y = 0.388.

[0009] The Cu used for catalytic oxidation of methane x Mn y Co 3-x-y The preparation method of O4 co-doped catalyst includes the following steps: 1) Dissolve soluble divalent copper salt, divalent manganese salt and trivalent cobalt salt in deionized water according to the target stoichiometric ratio to obtain a mixed salt solution; 2) After the mixed salt solution is atomized, it enters a heat-insulated pipe at 60-70℃ under the carrier of an inert gas and vaporizes to form a solid ultrafine particle aerosol containing Co, Mn and Cu nitrates. 3) The aerosol enters an electric furnace at 590-610℃, where it undergoes denitrification and decomposition within a residence time of 0.1-0.5 s. Under high-temperature driving, in-situ solid-phase doping occurs, yielding Cu.x Mn y Co 3-x-y O4 co-doped oxide; 4)Cu x Mn y Co 3-x-y O4 co-doped oxide is flowed into a water absorption bottle with inert gas, and after quenching by water, it is captured by liquid phase to form a uniformly dispersed slurry; the slurry is centrifuged and dried to obtain Cu x Mn y Co 3-x-y O4 co-doped catalyst.

[0010] Preferably, the carrier gas is the inert gas, which includes nitrogen.

[0011] Preferably, the centrifugal speed is 8000 rpm, and the centrifugal time is 5-10 min.

[0012] Preferably, the drying temperature is 80℃, and the drying time is 12 hours.

[0013] Further, the application includes the purification of CH4 gas in automobile exhaust and the purification of CH4 in industrial waste gas.

[0014] Further, the purification temperature of the CH4 gas is 350℃.

[0015] The beneficial effects of the present application are: The present application uses non-noble metal Co, Mn and Cu salt as precursor, and directly generates about 7 μm of lychee-shaped solid or hollow microspheres through ultrasonic atomization-high temperature transient cracking, and the surface is rich in nano protrusions, so that the active site is exposed with high density. The Cu x Mn y Co 3-x-y O4 co-doped catalyst: Mn is responsible for cracking C-H bond and converting hydroxyl group to active oxygen "in situ"; Co provides high redox potential to drive Mars-van Krevelen deep oxidation cycle; Cu replenishes oxygen vacancies with fast electron transfer and inhibits grain sintering. The closed loop of CH4→ Mn → Co → Cu → Mn is still smooth in water vapor atmosphere, realizing the synchronous leap of low-temperature activity and water resistance. This strategy replaces noble metal with transition metal "coordination-division", which greatly reduces the cost without reducing the performance, and provides an expandable new route for efficient and economical catalytic combustion of methane in water-containing exhaust gas. The catalyst has a conversion rate of 90 The present application synthesizes Cu x Mn y Co 3-x-yThe method of the O4 co-doped catalyst can realize synchronous decomposition and lattice reconstruction of the multi-metallic precursor in milliseconds, has simple process route, low energy consumption and high repeatability, and lays a material and process foundation for large-scale application of efficient catalytic oxidation of methane. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 : is a schematic diagram of the reaction device used in the present application; Figure 2 : is a schematic diagram of the change of methane conversion rate with temperature when the catalyst prepared in Examples 8-12 is used for catalytic oxidative degradation of methane; Figure 3 : is a SEM image of the Cu 0.026 Mn 0.388 Co 2.586 : is a SEM image of the O4 co-doped catalyst of different sizes; Figure 4 : is a SEM image of the catalyst obtained in Example 1 (c), Example 5 (b), and Comparative Example 1 (a); Figure 5 : is a TEM image of the catalyst obtained in Example 1; Figure 6 : is an XRD image of the catalyst obtained in Example 1, Example 5, and Comparative Example 1; Figure 7 : is an EPR image of the catalyst obtained in Example 1, Example 5, and Comparative Example 1; g = 2.003 indicates that the unpaired electrons are mainly localized in oxygen vacancy and other defect centers with high symmetry; Figure 8 : is a graph of the change of methane conversion rate with time during the process of catalytic oxidative degradation of methane at 350 DEG C using the catalyst obtained in Example 1; Figure 9 : is a graph of the change of methane conversion rate with temperature when the catalyst obtained in Example 1 and Example 5 is used without water and with water; Figure 10 : is a graph of the change of methane conversion rate with time during the process of water addition persistence experiment at 350 DEG C using the catalyst obtained in Example 1. DETAILED DESCRIPTION

[0017] In order to make the above-mentioned purposes, features and advantages of the present application more simple and easy to understand, the present application will be described in detail below in combination with examples. However, it should be understood that the following examples are only illustrative of the embodiments of the present application, and are not a limitation on the scope of the present application.

[0018] The chemical reaction temperature is controlled by the desorption of carbonates on the surface of the catalyst. The present application uses transition metal doping, high temperature reaction, nano engineering and interface effect to realize the low temperature gasification of carbonates on the surface of the catalyst, thereby releasing active sites, so that the conversion efficiency of CH4 reaches 90% at 350℃.

[0019] The length of the high-purity quartz glass tube in the following examples of the present application is 37 cm, the outer diameter is 1.2 cm, and the inner diameter is 1 cm.

[0020] The reaction device used in the following examples and comparative examples of the present application is shown in Figure 1 The reaction device is composed of an ultrasonic atomization unit, a carrier gas unit, a heating unit, a water quenching collection unit and a heat preservation and conveying unit. The ultrasonic atomization unit includes a quartz bottle and an ultrasonic atomizer built-in at the bottom of the bottle, which is used to uniformly atomize the precursor solution into micron-sized droplets. The carrier gas unit is equipped with a rotor flowmeter to deliver carrier gas to the quartz bottle at a constant flow rate, carrying the droplets into the heating unit. The heating unit is composed of an electric furnace and an electric furnace controller, which can accurately set and maintain the temperature of the high-temperature decomposition zone at 400-900℃. The heat preservation and conveying unit adopts a heating pipeline covered with a heating jacket to continuously send the droplet-carrier gas mixture into the high-temperature decomposition tube in the electric furnace; after the reaction is completed, the product-carrier gas mixture flows through the exhaust pipe and is introduced into the water quenching collection unit. The water quenching collection unit is a multi-stage water absorption bottle containing deionized water, the product nanoparticles are rapidly cooled by water quenching and captured by the water phase, and the tail gas is discharged through the exhaust pipe. The collected slurry is subjected to high-speed centrifugal separation to obtain solid product, which is then dried in a drying box at 80-110℃ to obtain Cu x Mn y Co 3-x-y O4 co-doped catalyst powder.

[0021] Example 1 S1 ultrasonic atomization-vaporization: cobalt nitrate, manganese nitrate and copper nitrate are weighed according to the target stoichiometric ratio and dissolved in deionized water to prepare a mixed salt solution, and the atomic ratio of copper element to manganese element to cobalt element is 0.05:0.75:5; the solution is atomized into micron-sized droplets by an ultrasonic atomizer, and enters the heating pipeline under the carrying of nitrogen gas with a flow rate of 0.8 L min -1 The heating pipeline is accurately controlled by a temperature controller at 60-70℃, and the droplets are vaporized at this moment to form a solid ultrafine particle aerosol containing Co, Mn and Cu nitrates; S2 high-temperature decomposition-lattice doping: the aerosol continues to enter the electric furnace with nitrogen gas, and the temperature of the reaction zone is kept at 600±10℃ by the electric furnace; the aerosol completes denitration and decomposition in the reaction zone within 0.1-0.5 s of residence time, generates CuO, Mn2O3 and Co3O4 nanometer microzones, and undergoes in-situ solid-phase doping under the driving of high temperature, copper and manganese ions partially replace Co in the Co3O4 lattice to form Cu 0.026 Mn0.388 Co 2.586 O4 spinel-type co-doped oxides; S3 Water quenching collection-solid-liquid separation: the spinel-type co-doped oxides are introduced into a water absorption bottle together with nitrogen, and are captured by liquid phase after being rapidly cooled by water quenching, forming a uniformly dispersed slurry; the slurry is centrifuged at 8000 rpm for 5-10 min, and the obtained solid is dried in a drying oven at 80-110°C for 2-4 h, to obtain Cu x Mn y Co 3-x-y O4 co-doped catalyst, denoted as Cu 0.026 Mn 0.388 Co 2.586 O4.

[0022] Nitrogen can be replaced by other inert gases.

[0023] Example 2 is the same as Example 1, except that in Example 2, the atomic ratio of copper element to manganese element to cobalt element is 0.03:0.75:5.

[0024] Example 3 is the same as Example 1, except that in Example 3, the atomic ratio of copper element to manganese element to cobalt element is 0.07:0.75:5.

[0025] Example 4 is the same as Example 1, except that in Example 4, copper nitrate is not added to the soluble salt solution of active metal elements, and the atomic ratio of manganese element to cobalt element is 0.5:5.

[0026] Example 5 is the same as Example 1, except that in Example 5, copper nitrate is not added to the mixed salt solution, and the atomic ratio of manganese element to cobalt element is 0.75:5.

[0027] Example 6 is the same as Example 1, except that in Example 6, copper nitrate is not added to the mixed salt solution, and the atomic ratio of manganese element to cobalt element is 3:5.

[0028] Example 7 is the same as Example 1, except that in Example 7, manganese nitrate is not added to the mixed salt solution, and the atomic ratio of copper element to cobalt element is 3:5.

[0029] Example 8 is the same as Example 1, except that in Example 8, cobalt nitrate and manganese nitrate are added to the mixed salt solution, and the atomic ratio of manganese element to cobalt element is 1:1.

[0030] Example 9 is the same as Example 1, except that in Example 9, cobalt nitrate and nickel nitrate are added to the mixed salt solution, and the atomic ratio of nickel element to cobalt element is 1:1.

[0031] Example 10 is the same as Example 1 except that in Example 10, the mixed salt solution is added with cobalt nitrate and lanthanum nitrate, and the atomic ratio of lanthanum element to cobalt element is 1:1.

[0032] Example 11 is the same as Example 1 except that in Example 11, the mixed salt solution is added with cobalt nitrate and copper nitrate, and the atomic ratio of copper element to cobalt element is 1:1.

[0033] Example 12 is the same as Example 1 except that in Example 12, the mixed salt solution is added with cobalt nitrate and cerium nitrate, and the atomic ratio of cerium element to cobalt element is 1:1.

[0034] Comparative Example 1 Comparative Example 1 is the same as Example 1 except that in Comparative Example 1, the mixed salt solution is added with only cobalt nitrate.

[0035] Performance Test The catalysts obtained in the Examples and Comparative Example of the present application were used to test the performance of catalytic oxidation degradation of methane. The test method is to use a continuous flow quartz reactor filled with different catalyst powders to catalytically oxidize methane. A gas chromatograph (GC9700 II, Fuli, Zhejiang, China) was used to analyze and detect the methane concentration in the gas mixture before and after catalytic oxidation, calculate the methane conversion rate, and record the temperature T 90 (°C) required when the conversion rate reaches 90%. The reaction conditions are as follows: catalyst filling amount: 0.25 g, initial gas mixture methane volume concentration: 0.3%, space velocity: 24000 mL / (gh), gas flow rate: 100 mL / min, oxygen concentration: 10%, nitrogen balance, and balance time: 30 min. The specific test results are shown in Table 1.

[0036] Table 1 Performance test results of Examples 1-12 and Comparative Example 1 on catalytic oxidation degradation of methane

[0037] Figure 2 The performance test results of the catalysts obtained in Examples 8-12 on catalytic oxidation degradation of methane are shown. The reaction conditions are as follows: catalyst filling amount: 0.25 g, initial gas mixture methane volume concentration: 0.3%, space velocity: 24000 mL / (gh), gas flow rate: 100 mL / min, oxygen concentration: 10%, nitrogen balance, and balance time: 30 min.

[0038] The multi-size SEM image of the catalyst obtained in Example 1 is shown in Figure 3 The results show that the Cu 0.026 Mn 0.388 Co 2.586The O4 co-doped catalysts present a lychee-like small ball or hollow lychee-like small ball with a diameter of about 7 μm, and the surface of the ball has many protrusions.

[0039] The SEM images of the catalysts obtained in Example 1, Example 5 and Comparative Example 1 are shown in the description. Figure 4 The results show that: the doping causes anisotropic compression / tension stress after Mn2O3, CuO enter the Co3O4 spinel lattice; to release the strain, the surface atoms migrate and secondary nucleate on the original surface to form protrusions, and the Co 3+ / Co 2+ , Mn 3+ / Mn 4+ , Cu 2+ / Cu + transition is the most intense, and the oxygen vacancy concentration is higher than that of the smooth area, and the oxygen vacancy not only promotes the activation of O2 to generate active O - / O2 - , but also reduces the C–H bond breaking energy barrier of CH4, and the three-element synergy results in a significantly larger number of protrusions than the two-element and single metal oxide, which is in line with the activity results.

[0040] The TEM image of the Cu x Mn y Co 3-x-y O4 co-doped catalyst obtained in Example 1 is shown in the description. Figure 5 The results show that: the Cu x Mn y Co 3-x-y O4 co-doped catalyst presents several lattice fringes with different spacings. Among them, the lattice fringes with spacings of 0.2847 nm and 0.2015 nm correspond to the (400) crystal plane of Co3O4, the lattice fringes with a spacing of 0.252 nm can correspond to the (002) crystal plane of CuO, and the lattice fringes with spacings of 0.2362 nm and 0.1427 nm correspond to the (004) and (226) crystal planes of Mn2O3.

[0041] The XRD images of the catalysts obtained in Example 1, Example 5 and Comparative Example 1 are shown in the description. Figure 6 The results show that: the Cu x Mn y Co 3-x-y O4 co-doped catalyst appears characteristic peaks of (220), (220), (400), (442), (511), (440) and (533) crystal planes of Co3O4 at 31.3°, 36.9°, 44.8°, 55.5°, 59.3°, 65.2° and 77.5°, respectively, indicating that the phase of the catalyst is mainly composed of Co3O4, and the doping of Cu and Mn does not appear new peaks.

[0042] Cu obtained in Example 1 0.026 Mn 0.388 Co 2.586 O4 co-doped catalyst, Mn obtained in Example 5 0.391 Co 2.609 The electron paramagnetic resonance (EPR) images of the O4 co-doped catalyst and the Co3O4 catalyst obtained in Comparative Example 1 are shown below. Figure 7 As shown. Result analysis: The oxygen vacancy order is: Cu 0.026 Mn 0.388 Co 2.586 O4> Mn 0.391 Co 2.609 O4>Co3O4, which corresponds to the density of bumps and activity in the SEM image.

[0043] Cu obtained in Example 1 0.026 Mn 0.388 Co 2.586 O4 co-doped catalyst (Cu-doped) and Mn obtained in Example 5 0.391 Co 2.609 The activity of the O4 co-doped catalyst (non-Cu doped) without water and with water are shown in the figure. Figure 9 As shown. Result analysis: Cu 0.026 Mn 0.388 Co 2.586 The T90 of the O4 co-doped catalyst (Cu-doped) decreased from 350℃ to 385℃ in a 2% H2O water atmosphere, while that of Mn decreased. 0.391 Co 2.609 The T90 of the O4 co-doped catalyst (without Cu) decreased from 360℃ to 450℃ in a 2% H2O water atmosphere. Clearly, Cu... 0.026 Mn 0.388 Co 2.586 The water resistance of O4 co-doped catalysts (Cu-doped) is significantly better than that of Mn. 0.391 Co 2.609 O4 co-doped catalyst (undoped with Cu). Reaction conditions: catalyst mass: 0.25 g, methane concentration: 3000 ppm, space velocity: 24000 mL / (gh), gas flow rate: 100 mL / min, oxygen concentration: 10%, equilibration time: 30 min.

[0044] The Cu obtained in Example 1 at 350°C 0.026 Mn 0.388 Co 2.586 The graph showing the methane conversion rate versus temperature during the continuous water addition experiment with the O4 co-doped catalyst is attached to the instruction manual. Figure 10 As shown. Result analysis: Cu 0.026 Mn 0.388 Co 2.586The O4 co-doped formula catalyst showed excellent performance in the water addition durability experiment at 350°C, and when 1% water was introduced, the methane conversion efficiency only decreased from 90% to 85.2%, and when 2% water was introduced, it only decreased to 81.4%. Reaction conditions: catalyst mass: 0.25 g, methane volume concentration: 0.3%, space velocity: 24000 mL / (gh), gas flow: 100 mL / min, oxygen concentration: 10%, nitrogen balance, balance time: 30 min.

[0045] The above is based on the ideal embodiment of the application. Through the above description, relevant personnel can make various changes and modifications without deviating from the technical idea of the application. The technical scope of the application is not limited to the content of the specification, and must be determined by the scope of the claims.

Claims

1. A Cu x Mn y Co 3-x-y O4 co-doped catalyst for catalytic oxidation of methane, characterized in that, Cu x Mn y Co 3-x-y The Cu, Mn-doped Co3O4 mixture in the Cu-Mn-Co3O4 co-doped catalyst is a mixture of Cu, Mn-doped Co3O4 in the form of lychee-like small spheres or hollow lychee-like small spheres. x Mn y Co 3-x-y In the Cu-Mn-Co3O4 co-doped catalyst, x = 0.026, y = 0.

388.

2. A Cu x Mn y Co 3-x-y O4 co-doped catalyst for catalytic oxidation of methane according to claim 1, characterized in that, It comprises the following steps: 1) dissolving soluble divalent copper salt, divalent manganese salt and trivalent cobalt salt in deionized water according to target stoichiometric ratio to obtain mixed salt solution; 2) after atomization of the mixed salt solution, entering into 60-70 DEG C heat preservation pipeline under inert gas carrying to form solid ultrafine particle aerosol containing Co, Mn and Cu nitrate by vaporization; 3) Aerosol enters the electric furnace at 590-610 °C, and the denitration and decomposition are completed within 0.1-0.5 s of residence time, and in-situ solid-phase doping occurs under high-temperature driving to obtain Cu x Mn y Co 3-x-y O4 co-doped oxides; 4) Cu x Mn y Co 3-x-y The Cu x Mn y Co 3-x-y O4 co-doped oxide is flowed into a water absorption bottle with inert gas, quenched by water, captured by liquid phase to form a uniformly dispersed slurry; the slurry is centrifuged and dried to obtain a Cu x Mn y Co 3-x-y O4 co-doped catalyst.

3. The Cu for catalytic oxidation of methane as described in claim 2 x Mn y Co 3-x-y The method for preparing O4 co-doped catalyst is characterized by, The inert gas is nitrogen.

4. A Cu x Mn y Co 3-x-y O4 co-doped catalyst according to claim 1, characterized in that, The application is used in the purification of CH4 gas in automobile exhaust and the purification of CH4 gas in industrial waste gas.

5. The Cu of claim 4 x Mn y Co 3-x-y O4 co-doped catalyst, characterized in that, The purification temperature of CH4 gas is 350 DEG C.

6. The Cu of claim 4 x Mn y Co 3-x-y application of the O4 co-doped formula catalyst, characterized in that, The volume concentration of methane in automobile exhaust or industrial waste gas is 0.3%.

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