Preparation method of methane combustion catalyst with water resistance

Abstract

The invention discloses a preparation method of a methane combustion catalyst with water resistance. According to the method, cobaltous acetate and ethylene glycol are taken as raw materials and mixed to form a uniform turbid solution, and the turbid solution is heated under the protection of argon; then, dropwise adding a sodium carbonate solution into the cobalt acetate solution in a protective atmosphere, standing, aging, cooling to room temperature, centrifugally separating, washing with deionized water, dispersing with ethanol, and filtering to obtain a primary solid; and drying the obtained solid in a vacuum environment, and calcining to prepare the cobalt oxide nano material. The method comprises the following steps: dissolving and dispersing palladium nitrate in water, dropwise adding the solution into cobalt oxide under the protection of argon, mixing to form viscous slurry, drying, and calcining in a muffle furnace to finally obtain the Pd / Co3O4 catalyst. The prepared Pd / Co3O4 catalyst has high oxygen vacancy density, excellent methane combustion catalytic activity and water resistance, the activity loss is less than 3% when the Pd / Co3O4 catalyst continuously operates for 100 hours under the condition of containing 3% of water vapor, and the Pd / Co3O4 catalyst is especially suitable for methane combustion reaction and shows excellent catalytic efficiency and long-term stability.

Description

Technical Field

[0001] The present invention belongs to the fields of energy chemistry and environmental catalysis science and technology, and specifically relates to a preparation method of a methane combustion catalyst with high water resistance. Background Art

[0002] With the increasing global emphasis on environmental protection and the continuous growth of energy demand, the gradual depletion of traditional energy sources (such as petroleum) has promoted the development and utilization of new energy sources (such as liquefied natural gas) and oxygen-rich coalbed methane to become research hotspots. These new energy sources have significant economic and social benefits, and methane, as their main component, its efficient combustion technology is crucial for achieving the sustainable utilization of energy. In addition, methane is a potent greenhouse gas with a relatively high global warming potential, and its greenhouse effect value is more than 20 times that of carbon dioxide. The emission of methane not only exacerbates global warming but also has a profound impact on climate change. Therefore, achieving the efficient combustion and conversion of methane is of great significance for reducing greenhouse gas emissions and alleviating global warming.

[0003] However, the methane combustion reaction has high requirements for the performance of the catalyst. On the one hand, the methane molecular structure is stable and difficult to activate; on the other hand, the methane combustion usually occurs in an environment rich in water vapor, and the presence of water will accelerate the deactivation of the catalyst.

[0004] Palladium-based catalysts have become one of the most widely used noble metal catalysts in the methane combustion reaction due to their high activity. However, palladium-based catalysts are prone to sintering and particle growth of palladium nanoparticles under high-temperature reaction conditions, resulting in a significant decline in the activity and stability of the catalyst. At the same time, in a high-humidity environment, such as industrial exhaust gas and automotive exhaust gas treatment conditions, the stability of palladium-based catalysts is also severely affected by water vapor. Research shows that in the presence of water vapor, palladium species are prone to form palladium hydroxide, which will cover the active sites of the catalyst, leading to rapid deactivation of the catalyst. Although the existing palladium-based catalysts show good initial activity in the methane combustion reaction, their water resistance is still relatively limited, resulting in a rapid decline in activity over time.

[0005] Among many metal oxide supports, cobalt-based oxides, especially cobalt tetroxide (Co 3 O 4 ), due to its incompletely filled 3d orbitals, the rapid redox cycle ability between Co 2+ and Co 3+ ), rich surface defects, and excellent oxygen supply ability, have broad application prospects in the field of catalysis. Based on this, the present invention develops a catalyst based on palladium supported on cobalt tetroxide, and enhances the interaction between the noble metal and the support by optimizing the preparation method, thereby improving the water resistance and stability of the catalyst, which is of great significance for achieving the efficiency and sustainability of the methane combustion reaction.

[0006] The present invention aims to design and synthesize a palladium-loaded cobalt tetroxide catalyst with excellent water resistance to solve the problem of the decline in activity and stability of existing catalysts in a high-humidity environment and to provide an efficient and stable catalytic material for the methane combustion reaction. Summary of the Invention

[0007] The object of the present invention is to provide a preparation method of a methane combustion catalyst with high water resistance for the problem of poor water resistance of palladium-based catalysts prepared by the prior art for methane combustion. After mixing cobalt acetate and ethylene glycol, heating is carried out under a protective atmosphere. Then, a sodium carbonate solution is dropped into the cobalt acetate solution under argon protection. After centrifugal washing with water, ethanol dispersion, vacuum filtration, drying, and calcination, cobalt tetroxide nanomaterials are obtained. Then, palladium nitrate is dropped into cobalt tetroxide under atmosphere protection, and after drying and calcination, Pd / Co 3 O 4 catalyst is obtained. Compared with the traditional catalyst prepared by the deposition method directly at 80-100 °C, the preparation method of the Pd / Co 3 O 4 catalyst prepared by this method is simple and practical, and the reagents used are pollution-free. The traditional method first prepares a colloidal sample by the deposition precipitation method and then calcines it. The specific surface area of the prepared sample is small, and it forms a massive sample with fewer oxygen vacancies in Co 3 O 4 . In contrast, in the present invention, by introducing a protective atmosphere during the synthesis process at a high temperature (≥150 °C), Co 3 O 4 is prevented from being oxidized during the nucleation and crystallization process, so that Co 3 O 4 has higher crystallinity and more oxygen vacancies. For the traditional Pd / Co 3 O 4 sample during preparation, palladium nitrate precipitates together with cobalt nitrate and ammonium hydroxide, and the Pd particles in the prepared sample are larger and have poor dispersion. In the present invention, during the process of loading noble metals, by using a protective atmosphere, the Pd / Co 3 O 4 catalyst has a stronger interaction between Pd and Co 3 O 4 , thus having excellent activity and long-term stable water resistance for the methane combustion reaction in a wet reaction environment. Under the condition of containing 3 wt% water vapor, continuous operation for 100 hours results in an activity loss of less than 3%, and its long-term water stability is much higher than that of the Pd / Co 3 O 4 and Pd / CoAlO x series catalysts prepared by the traditional method. Therefore, the preparation method of the present invention is one of the synthesis methods with application prospects.

[0008] To achieve the above object, the present invention adopts the following technical solutions: A preparation method of a methane combustion catalyst with high water resistance, comprising the following steps: Step 1): Weigh a certain amount of (CH 3 COO) 2 Co·4H 2 O, and add 30 mL of ethylene glycol, and stir for 15 min at room temperature (20 - 35 °C) under an inert atmosphere; Step 2): Under the stirring state, heat the cobalt acetate solution obtained in Step 1), raise the temperature and maintain it at 150 - 170 °C; Step 3): Under the stirring state, add a solution of Na 2 CO 3 dropwise to the solution obtained in Step 2); Step 4): After dropping the solution of Na 2 CO 3 dropwise, stop stirring and age at 150 - 170 °C.

[0009] Step 5): Stir and cool the sample obtained in Step 4) to room temperature (20 - 35 °C) under the protection of an inert atmosphere.

[0010] Step 6): After centrifuging and washing the product obtained in Step 5), disperse it in absolute ethanol for cleaning, and then separate.

[0011] Step 7): Place the product obtained in Step 6) in an oven and dry for 12 hours.

[0012] Step 8): Place the product obtained in Step 7) in a muffle furnace and calcine at 450 °C to obtain Co 3 O 4 nanomaterials.

[0013] Step 9): Weigh an appropriate amount of palladium nitrate and dissolve it in deionized water. After ultrasonic dispersion, slowly drop it into an appropriate amount of Co 3 O 4 nanomaterials under the protection of an inert gas, and stir.

[0014] Step 10): Stir the sample in Step 9) until the solution becomes viscous, and place it in an oven to dry.

[0015] Step 11): Grind the sample obtained in Step 10), place it in a muffle furnace, and calcine at 450 °C to obtain a Pd / Co 3 O 4 catalyst.

[0016] Further, the mass of cobalt acetate tetrahydrate described in step 1) is 2.5 g, the inert atmosphere is argon (gas purity ≥ 99.99%), and the stirring rate is 300 - 500 rpm / min.

[0017] Further, in step 2), the holding time is 10 - 20 min at 150 - 170 °C.

[0018] Further, in step 3), the 2 CO 3 dropwise addition rate of the solution is 1.0 - 1.5 mL / min.

[0019] Further, the concentration of the sodium carbonate solution described in step 3) is 0.2 M, and the volume is 100 mL.

[0020] Further, the aging time described in step 4) is 1 hour.

[0021] Further, the protective atmosphere described in step 5) is argon (gas purity ≥ 99.99%), and the stirring rate is 300 - 500 rpm / min.

[0022] Further, steps 1) - 5) are all carried out under the protection of an inert atmosphere, where the protective atmosphere is argon (gas purity ≥ 99.99%).

[0023] Further, the number of times of washing and centrifuging described in step 6) is 6 - 10 times.

[0024] Further, the drying step described in step 7) is vacuum drying at 60 - 90 °C.

[0025] Further, the calcination time described in step 8) is 2 h, and the heating rate is 2 °C / min.

[0026] Further, the mass ratio of palladium nitrate to Co 3 O 4 in step 9) is 1:10, the protective atmosphere is argon (gas purity ≥ 99.99%), and the stirring rate is 300 - 500 rpm / min.

[0027] Further, the drying temperature described in step 10) is 60 - 90 °C, and the time is 12 h.

[0028] Further, the calcination time described in step 11) is 2 h, and the heating rate is 2 °C / min.

[0029] Pd / Co prepared by the synthesis method as described above 3 O 4The nano-catalyst is applied to the methane combustion reaction in a wet reaction environment and has excellent activity and water resistance for the reaction.

[0030] The beneficial effects of the present invention are as follows: (1) The present invention provides a synthesis method of a Pd / Co 3 O 4 catalyst. Using (CH 3 COO) 2 Co·4H 2 O, ethylene glycol, and Na 2 CO 3 as raw materials, and under the protection of high temperature and argon atmosphere, Co 3 O 4 nano-materials with more oxygen vacancies are prepared, and further Pd is loaded onto the Co 3 O 4 nano-materials under an inert atmosphere. The preparation process of the present invention is simple and easy to implement, with simple and safe operation, and easy control of process parameters, having high practical value; (2) Through the control of certain conditions, the present invention prepares a Pd / Co 3 O 4 catalyst, which has more oxygen vacancies and stronger interaction between Pd and the Co 3 O 4 carrier. Through the activity test of the methane combustion reaction, this catalyst has excellent catalytic activity for the methane combustion reaction, and at the same time shows excellent stability in the methane combustion reaction in a wet reaction environment containing water. Under the condition of containing 3wt% water vapor, it operates continuously for 100 hours, and the activity loss is less than 3%, indicating that this catalyst has excellent water resistance for the methane combustion reaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is the X-ray powder diffraction pattern (XRD) of the Co 3 O 4 and Pd / Co 3 O 4 catalysts prepared in Example 1 of the present invention.

[0032] Figure 2 is the high-resolution field emission transmission electron microscope image (HR-TEM) of the Pd / Co 3 O 4 catalyst prepared in Example 1 of the present invention.

[0033] Figure 3 is the Co 3 O 4 and Pd / Co 3 O 4Raman spectrum of the catalyst.

[0034] Figure 4 Pd / Co prepared in Example 1 of the present invention 3 O 4 H 2 -TPR diagram of the catalyst.

[0035] Figure 5 Co prepared in Example 1 of the present invention 3 O 4 、Pd / Co 3 O 4 and commercial Pd / Al 2 O 3 Stability diagrams of the methane combustion reaction of the catalysts. (a) Curve of methane combustion conversion rate of the catalyst varying with temperature. (b) Diagram of activation energy of the methane combustion reaction of the catalyst. (c) Stability of the dry methane combustion reaction of the catalyst at 350 °C. (d) Stability of the wet methane combustion reaction of the catalyst at 350 °C (containing 3% water vapor). Detailed implementation manners

[0036] To make the content of the present invention more understandable, the technical solutions of the present invention are further described below in conjunction with specific implementation manners, but the present invention is not limited thereto.

[0037] Example 1 A preparation method of a methane combustion catalyst with high water resistance, comprising the following steps: Step 1): Weigh 2.5 g of (CH 3 COO) 2 Co·4H 2 O, and add 30 mL of ethylene glycol, and stir at 300 rpm / min for 15 min at room temperature under an argon (gas purity ≥ 99.99%) atmosphere; Step 2): Under stirring and an argon atmosphere, heat the cobalt acetate solution obtained in Step 1), raise the temperature and maintain it at 150 °C for 10 min; Step 3): Under stirring and an argon atmosphere, use a syringe pump to drop 100 mL of 0.2M Na 2 CO 3 solution into the three-necked flask at a rate of 1.0 mL / min; After dropping the Na 2 CO 3 solution, stop stirring and age at 150 °C for 1 hour under an argon atmosphere.

[0038] Step 5): Cool the sample obtained in Step 4) to room temperature at a stirring rate of 300 rpm under the protection of an argon (gas purity ≥ 99.99%) atmosphere.

[0039] Step 6): The product obtained in Step 5) is washed 6 times by centrifugation with water and then dispersed in absolute ethanol, and then separated.

[0040] Step 7): The product obtained in Step 6) is placed in an oven at 60 °C and vacuum dried for 12 hours.

[0041] Step 8): The product obtained in Step 7) is placed in a muffle furnace and calcined at 450 °C for 2 hours at a heating rate of 2 °C / min to obtain Co 3 O 4 nanomaterials.

[0042] Step 9): Weigh 0.1 g of palladium nitrate and dissolve it in 2 mL of deionized water. After ultrasonic dispersion, it is slowly dropped into 1 g of Co 3 O 4 nanomaterials under the protection of argon gas (gas purity ≥ 99.99%), and stir at a rate of 300 rpm / min.

[0043] Step 10): The sample in Step 9) is stirred until the solution becomes viscous and then placed in an oven at 60 °C and dried for 12 hours.

[0044] Step 11): The sample obtained in Step 10) is ground and then placed in a muffle furnace and calcined at 450 °C for 2 hours at a heating rate of 2 °C / min to obtain Pd / Co 3 O 4 catalyst.

[0045] Comparative Example 1 (CN108906078A): Step 1): Mix 25 mL of a cobalt nitrate solution with a concentration of 0.04 g / mL and 2.5 mL of a palladium nitrate solution with a concentration of 0.02 g / mL, and while magnetically stirring it at a speed of 200 rpm, inject 5 mL of an ammonium bicarbonate solution with a concentration of 0.1 g / mL into it to form a mixed solution; Step 2): Let the precipitate formed in the above mixed solution stand and then filter it by suction to obtain a solid sample; Step 3): Add deionized water to the solid sample and grind the mixture of the solid sample and deionized water for 15 min under the condition of a viscosity of 2400 cP to obtain a colloidal sample; Step 4): Inject the colloidal sample into a mold and dry it at 100 °C for 2 h to form a dried sample; Step 5): Calcine the dried sample at 500 °C for 2 h and cool it to obtain Pd / Co 3 O 4 bulk catalyst.

[0046] Example 2 I. Co 3 O 4 and Pd / Co 3 O 4 Catalyst Characterization To identify the characteristics of the Co 3 O 4 catalyst prepared in Example 1 of the present invention and the Pd / Co 3 O 4 catalyst prepared in Example 1, XRD and HE-TEM were used to characterize the crystal structure and microstructure of the catalysts.

[0047] As Figure 1 shown, the synthesized Co 3 O 4 and Pd / Co 3 O 4 showed diffraction signal peaks at 19.0, 31.3, 36.8, 44.8, 55.6, 59.3 and 65.2°, corresponding to the (111), (220), (311), (400), (422), (511) and (440) crystal planes of Co 3 O 4 crystals (JCPDS-46-1003). No obvious signal peaks of Pd species were observed, indicating that the Pd species were well dispersed on Co 3 O 4 . In Comparative Example 1, Pd was directly co-precipitated with Co 3 O 4 by deposition precipitation to obtain a bulk Pd / Co 3 O 4 catalyst with poor Pd dispersion, forming larger particles, as shown in the attached Figure 2 and attached Figure 5 of Comparative Example 1 - Patent CN108906078A. The XRD pattern of the catalyst after reaction (labeled as spent) was consistent with that of the fresh catalyst (labeled as fresh), indicating that the catalyst still maintained its structure after the COM reaction. The microstructure of the Pd / Co Figure 1 O 3 O 4 catalyst used in the COM reaction was further studied by high-resolution transmission electron microscopy (HR-TEM). As Figure 2 shown, the Pd / Co 3 O 4 catalyst was well crystallized, and lattice fringes could be clearly observed from the high-resolution STEM image. The Pd / Co 3 O 4Particles with a size of about 2 - 10 nm can be observed in the catalyst, and these particles belong to Pd species. The lattice fringes of the catalyst were measured, and the lattice spacings were 0.24 and 0.22 nm, corresponding to the (311) crystal plane of Co 3 O 4 and the (111) crystal plane of metallic Pd, respectively.

[0048] Raman spectroscopy has been widely used to analyze the information on the structural properties of spinel crystals. As Figure 3 shown, five characteristic Raman peaks were observed in the fresh Co 3 O 4 catalyst at 189.5, 467.1, 509.4, 603.6, and 668.6 cm -1 . With the addition of Pd, the characteristic peak at 668.6 cm -1 shifted to a lower wavenumber (660.4 cm -1 ) and the peak width broadened, which is related to the lattice distortion or residual stress of the spinel structure. The red shift of the characteristic peak indicates that the fresh catalyst Pd / Co 3 O 4 has more structural defects due to the supported nano Pd particles. The Raman spectroscopy results show that the Co 3 O 4 and Pd / Co 3 O 4 prepared in this invention have more oxygen vacancies. This benefits from the use of an inert atmosphere protection measure during the catalyst preparation process under high-temperature synthesis conditions, effectively avoiding the interference of air on the catalyst synthesis during the synthesis process. In Comparative Example 1, it was directly synthesized in an air atmosphere, and the influence of air could not be avoided. Therefore, the catalyst has relatively fewer oxygen vacancies.

[0049] The reduction properties of the catalyst were analyzed by H 2 -TPR. As Figure 4 shown, two reduction peaks located at 308 and 521 °C were observed in the H 3 O 4 -TPR spectrum of Co 2 , which were attributed to the reduction of Co 3+ to Co 2+ and the reduction of Co 2+ to Co 0 , respectively. In contrast, Pd / Co 3 O 4 showed a reduction peak at 102 °C, corresponding to the reduction of surface PdO x to the metallic phase Pd. In addition, the H 2 consumption of this reduction peak was 2.4 mmol / g, which is higher than that for reducing PdO x to Pd 0The theoretical amount (0.379 mmol / g) is shown in Table 1. The additional H 2 consumption can be attributed to the reverse oxygen spillover from Co 3 O 4 to Pd species. Meanwhile, the reduction peak of Pd / Co 3 O 4 located at 307 °C is attributed to the reduction of Co 3 O 4 lattice oxygen. The H 2 -TPR results indicate that the introduction of Pd significantly reduces the reduction temperature of Co 3 O 4 lattice oxygen, suggesting that the interaction between Pd and Co 3 O 4 weakens the Co-O bond. This means that the reactivity of Co 3 O 4 lattice oxygen at the interface is enhanced, and the migration of oxygen on the interface increases, thus facilitating the formation of oxygen vacancies and being beneficial to the adsorption of oxygen. The H 2 -TPR results illustrate that there is a stronger interaction between Pd and Co 3 O 4 in the Pd / Co 3 O 4 catalyst prepared in the present invention.

[0050] Table 1 H consumption in the H-TPR of the catalyst prepared in Example 1 of the present invention 2 -TPR 2 II. Methane combustion reaction activity and stability of Co 3 O 4 , Pd / Co 3 O 4 and commercial Pd / Al 2 O 3 catalysts.

[0051] The catalytic activity of Co 3 O 4 prepared in Example 1, Pd / Co 3 O 4 and commercial Pd / Al 2 O 3 catalysts for methane combustion reaction (COM) was investigated in a fixed-bed flow reactor. The dosage of each catalyst was 100 mg, which was mixed with 300 mg of quartz sand to prevent heat transfer and diffusion limitations in the reactor. In a volume fraction of 10% CH 4 / Ar at 20 mL / min and pure O 2 ​In the flowing mixed atmosphere, the catalytic performance of the catalyst was investigated in the temperature range of 200 - 500 °C, and the space velocity was 18000 mL / g / h. In the experiment, no CO was detected in the activity test of all catalysts. As Figure 5 shown in a of 4 Pd / Al 2 O 3 and Pd / Co 3 O 4 the conversion rate on is higher than that on Co 3 O 4 , indicating that the loaded Pd can improve the catalytic activity of the catalyst for COM. At 400 °C, the CH 3 conversion rates on Co 4 O 2 , Pd / Al 3 O 3 and Pd / Co 4 O 4 reach 87.9%, 99.9% and 99.9% respectively. The Pd / Co 3 O 4 catalyst prepared in this invention has higher methane combustion activity than the reported Pd-based catalysts (such as Patent CN119236929A attached Figure 1 ). The temperatures for 50% CH 2 conversion on Pd / Al 3 O 3 , Pd / Co 4 O 3 and Co 4 O 4 are 314, 318 and 338 °C respectively, which are lower than the temperatures of Pd / Co 3 O 4 and Pd / CoAlO x reported in the current prior art (Table 3 of Patent CN116920874), indicating that Pd nanoparticles (NPs) are very important for enhancing the catalytic activity of the methane combustion reaction.

[0052] To further study the activity differences among the catalysts, the apparent activation energy of the catalysts was tested at 220 - 300 °C, and the conversion rate of CH 4 was kept below 20% during the test to ensure being within the range of kinetic control. As Figure 5 shown in b of 3 , the E 4 value of the measured Co a O 3 is 92.5 kJ / mol, which is consistent with the literature report. The E 4 value of Pd / Co aThe value is 68.8 kJ / mol, Pd / Al 2 O 3 has an E a value of 72.9 kJ / mol, indicating that CH 4 molecules are more likely to be adsorbed and activated on the sample. Therefore, the supported Pd catalyst can improve the catalytic activity of the methane combustion reaction.

[0053] The stability of the catalyst for the methane combustion reaction was evaluated at 350 °C. As Figure 5 shown in c, the initial CH 2 O 3 conversion rates of Pd / Al 3 O 4 and Co 3 O 4 catalysts were 69.1%, 53.5% and 33.9% respectively. After the Pd / Co 4 O 3 catalyst was run for 100 hours, no obvious loss of catalytic activity was observed. For Co 4 O 3 O 4 2 3 O 2 2 2 3 3 4 3 O 4 2 3 O 2 3

[0054] The water tolerance is a key aspect in evaluating the potential application of Pd-based catalysts. When Pd-based catalysts are exposed to high-concentration water vapor, it may lead to the loss of active centers, resulting in a significant decrease in catalytic activity. Therefore, the water tolerance of the catalysts was investigated under the condition of containing 3 wt% water vapor, as Figure 5 shown in d. Under wet conditions, Co 3 O 4 showed a lower methane conversion rate. In addition, Pd / Al 2 O 3 showed poor stability under wet conditions. After continuous operation for 100 hours, Pd / Al 2 O 3The methane conversion rate decreased by 55.5%. In contrast, Pd / Co 3 O 4 After the catalyst ran for 100 hours, its catalytic performance only decreased slightly. The results of the long-term water resistance test showed that Pd / Co 3 O 4 has great application potential for the complete oxidation of methane under wet conditions. Compared with Comparative Example 1 (Patent CN108906078A), Patent CN119236929A (this patent is attached Figure 2 ), and Patent CN116920874A (this patent is attached Figure 2 ), etc., which only tested the water resistance at different temperatures and did not show the change of the catalyst's water resistance over time. At the same time, in Comparative Example 1 (Patent CN108906078A), Patent CN119236929A (this patent is attached Figure 2 ), and Patent CN116920874A (this patent is attached Figure 2 ), etc., the activity of the catalyst decreased significantly under water vapor conditions. The catalyst prepared in the present invention still maintained excellent activity after continuously running for 100 hours under water vapor conditions. The present invention fully demonstrated the change of the catalyst's water resistance over time and proved its practicality of water resistance. Therefore, the Pd / Co 3 O 4 prepared in the present invention has excellent water resistance performance for methane combustion and has good application prospects.

[0055] The above are only the preferred embodiments of the present invention, and all equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope covered by the present invention.

Claims

1. A method for preparing a water-resistant methane combustion catalyst, characterized in that: The following steps are involved: 1) Weigh a certain amount of (CH3COO)2Co·4H2O, add ethylene glycol, and stir at room temperature under inert atmosphere for 15 min; 2) heating the cobalt acetate solution obtained in step 1) under stirring, raising the temperature and maintaining it at 150-170° C.; 3) Under stirring, add Na2CO3 solution dropwise to the solution obtained in step 2); 4) After the Na2CO3 solution is added, stop stirring and age at 150-170°C; 5) stirring the sample obtained in step 4) under an inert atmosphere and cooling it to room temperature; 6) The product obtained in step 5) is centrifuged and washed with water, then dispersed in anhydrous ethanol for cleaning, and then separated; 7) placing the product obtained in step 6) in an oven and drying for 12 hours; 8) placing the product obtained in step 7) in a muffle furnace and calcining at 450° C. to obtain Co3O4 nanomaterials; 9) Weigh an appropriate amount of palladium nitrate and dissolve it in deionized water. After ultrasonic dispersion, slowly drop it into an appropriate amount of Co3O4 nanomaterial under the protection of inert gas and stir; 10) Stir the sample in step 9) until the solution becomes viscous, and place it in an oven to dry; 11) The sample obtained in step 10) was ground, placed in a muffle furnace, and calcined at 450° C. to obtain a Pd / Co3O4 catalyst.

2. The method according to claim 1, characterized in that: In step 1), the mass of (CH3COO)2Co·4H2O is 2.5 g, the amount of ethylene glycol is 30 mL, the inert atmosphere is argon, and the stirring rate is 300-500 rpm / min.

3. The method according to claim 1, characterized in that: In step 2), the temperature is maintained at 150-170° C. for 10-20 min.

4. The method according to claim 1, characterized in that: In step 3), the concentration of the Na2CO3 solution is 0.2 M, the volume is 100 mL, and the dropping rate is 1.0-1.5 mL / min.

5. The method according to claim 1, characterized in that: The aging time in step 4) is 1 hour.

6. The method according to claim 1, characterized in that: The calcination time in step 8) is 2 h, and the heating rate is 2 °C / min.

7. The method according to claim 1, characterized in that: In step 9), the mass ratio of palladium nitrate to Co3O4 is 1:10, the inert atmosphere is argon, and the stirring rate is 300-500 rpm / min.

8. The method according to claim 1, characterized in that: In step 11), the calcination time is 2 h and the heating rate is 2 °C / min.

9. A Pd / Co3O4 nanocatalyst prepared by the method according to any one of claims 1 to 8.

10. An application of the Pd / Co3O4 nanocatalyst as claimed in claim 9, characterized in that: The catalyst is applied to methane combustion reaction in a water-containing reaction environment.

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