Non-noble metal Cu-Co-based catalyst for efficient catalytic combustion of ultralow-concentration methane and preparation method of non-noble metal Cu-Co-based catalyst

Abstract

The invention relates to the technical field of catalyst synthesis, in particular to a non-noble metal Cu-Co-based catalyst for efficient catalytic combustion of ultralow-concentration methane and a preparation method of the non-noble metal Cu-Co-based catalyst. According to the method, copper nitrate trihydrate, cobalt nitrate hexahydrate, cerium nitrate hexahydrate, anhydrous sodium carbonate and deionized water are used as raw materials, and the catalyst with metal copper (Cu) and metal cobalt (Co) as active components and CeO2 as a carrier is prepared through the steps of carrier preparation, active metal solution preparation, mixing, precipitation, suction filtration, washing, drying, roasting, tabletting, grinding, sieving and the like. Compared with catalysts prepared by various schemes and preparation conditions, the dispersity of active components of the catalyst is greatly improved, and the catalytic activity and the stability are higher.

Description

Technical Field

[0001] This invention relates to the field of catalyst synthesis technology, specifically to a non-precious metal Cu-Co based catalyst for the efficient catalytic combustion of ultra-low concentration methane and its preparation method. Background Technology

[0002] my country possesses abundant coal reserves, but the emission of ultra-low concentration methane (<1%) during coal mining has become a dual challenge for both environmental governance and energy utilization. Statistics show that my country's coal mines emit over 20 billion cubic meters of methane annually, with more than 70% being exhaust gas with a concentration below 1%. This type of gas, due to its insufficient calorific value, cannot be directly utilized through traditional thermal combustion technologies. Direct emission not only wastes resources but also significantly impacts global climate change due to its greenhouse effect being 25 times that of carbon dioxide. While traditional catalytic combustion technology can achieve methane conversion, it faces core challenges such as insufficient low-temperature activity, weak resistance to sintering, and poor resistance to poisoning. Ultra-low concentration methane, in particular, has a stable molecular structure and requires temperatures of 300-500℃ for efficient conversion. Existing catalysts exhibit low activity within this temperature range, failing to meet industrial application requirements. Furthermore, impurities such as sulfides and dust in coal mine exhaust gas can easily deactivate catalysts, further limiting the technology's widespread adoption. Therefore, developing a high-efficiency, stable, and low-cost non-precious metal catalyst is crucial for solving the problem of ultra-low concentration methane emissions.

[0003] In the field of methane catalytic combustion, precious metal catalysts have long dominated, with palladium (Pd) and platinum (Pt) based catalysts being the most typical. Pd exhibits excellent adsorption and activation capabilities for oxygen species, especially at low temperatures (<300℃). Studies have shown that Pd / Al2O3 catalysts can achieve an ignition temperature as low as 250℃ with a methane concentration of 2%, and demonstrate good stability in dry air. However, Pd catalysts have extremely weak resistance to sulfur poisoning; even trace amounts of H2S in coal mine exhaust air can lead to irreversible deactivation of their active centers. While Pt-based catalysts show slightly better tolerance to sulfur, their methane oxidation activity is significantly lower than that of Pd, requiring higher temperatures (>350℃) to achieve efficient conversion. Furthermore, the scarcity of precious metal resources leads to increasingly prominent cost issues—global annual Pd production is less than 300 tons, while Pt reserves are only sufficient to meet demand for the next 20 years, creating an economic bottleneck for the large-scale industrial application of precious metal catalysts. Even more serious is that, under high-temperature steam conditions, precious metal particles are prone to causing the active components to migrate and aggregate. For example, after Pd / Al2O3 was treated in 600℃ steam for 100 hours, the particle size increased from 3nm to 15nm, and the conversion rate decreased by 40%. These defects have prompted researchers to turn their attention to non-precious metal systems.

[0004] In the research of non-precious metal catalysts, transition metal oxides (such as Co, Cu, and Mn) have gradually become a research hotspot due to their abundant reserves, low cost, and excellent resistance to poisoning. Among them, Cu-Co based composite oxides have attracted much attention due to their unique electronic structure and synergistic effect. The electronic structures of Cu and Co are significantly complementary: Cu... 2+ (3d) 9 ) and Co 3+ (3d) 6 Due to differences in electron configuration, unevenly charged regions form at the contact interface. Experiments show that this unique electronic interaction allows ultra-low concentrations of methane to react at even lower temperatures. Research indicates that in the Cu-Co spinel structure, Cu... + Co acts as an electron acceptor, promoting the dissociation of O2. 2+ As adsorption sites activating methane molecules, the synergistic effect of Cu-Co catalysts significantly reduces the complete oxidation temperature of methane. For example, the CuCo2O4 catalyst developed by the French Petroleum Institute exhibits excellent low-temperature activity, with an ignition temperature 80°C lower than that of single-metal catalysts at a methane concentration of 1.69%. However, existing Cu-Co catalysts still suffer from problems such as complex preparation processes and poor batch stability. While the traditional impregnation method is simple to operate and low in cost, the active components are prone to agglomeration, and the metal-support interaction is weak, thus affecting the catalyst stability. The sol-gel method requires strict control of aging time, and the pore structure is difficult to precisely control. In addition, most catalysts have a conversion rate of less than 80% below 450°C, which is insufficient to meet the self-heating combustion requirements of exhaust air in coal mines, and their activity decreases significantly in humid environments, limiting their practical application.

[0005] Despite the significant potential of non-noble metal catalysts, the activity and stability of Cu-Co systems remain highly dependent on elemental ratios and interaction strengths. Existing research largely focuses on single-metal support or equimolar composites, while the understanding of the dynamic changes in electronic structure under asymmetric ratios remains limited. This study aims to explore the structure-activity relationship between electronic synergy and catalytic performance by precisely controlling the ratio of active components, thereby identifying the structure-activity relationship of Cu... 2+ / Cu + With Co 3+ / Co 2+ The optimal ratio for achieving redox cycle efficiency was determined. This discovery provides key parameters for the rational design of non-precious metal catalysts, promoting the industrialization of ultra-low concentration methane catalytic combustion technology. Summary of the Invention

[0006] This invention addresses the technical problem of low activity of non-precious metal catalysts in the catalytic combustion of ultra-low concentration methane by providing a method for preparing a non-precious metal Cu-Co based catalyst for efficient catalytic combustion of ultra-low concentration methane. By varying the loading and comparing preparation methods, this invention utilizes various characterization techniques to conduct in-depth analysis of the catalyst's physicochemical properties. Combined with catalyst performance testing, the optimal preparation method for a high-performance non-precious metal Cu-Co based catalyst is determined.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: a method for preparing a non-precious metal Cu-Co based catalyst for the efficient catalytic combustion of ultra-low concentration methane, comprising the following steps: (1) Preparation of CeO2 support; (2) Using at least one of Cu(NO3)2·3H2O and Co(NO3)2·6H2O as a precursor, add deionized water to dissolve and prepare a solution; (3) Add the CeO2 support to the solution in step (2) and dissolve it completely to obtain sample A; (4) Slowly add Na2CO3 solution to sample A while stirring. Adjust the pH, dry the precipitated solution at room temperature, then filter, wash, and filter again until the pH is neutral. Then put the sample into a preheated drying oven to dry, and obtain sample B. (5) Sample B was placed in a muffle furnace for calcination, and then tableted, ground, and screened to obtain the catalyst.

[0008] As a further limitation of the technical solution of the present invention, the CeO2 support in step (1) is obtained by direct calcination using Ce(NO3)3·6H2O as a precursor, with a calcination temperature of 450 ℃ and a calcination time of 3h.

[0009] As a further limitation of the technical solution of the present invention, the Cu in the solution in step (2) 2+ The concentration is 0-5 wt%, Co 2+ The concentration is 0-5 wt%.

[0010] As a further limitation of the technical solution of the present invention, after mixing in step (3), continue stirring to make the active metal uniformly dispersed in the system, and then let it stand for 1 hour.

[0011] As a further limitation of the technical solution of the present invention, in step (4), the room temperature drying time is 10h; the sodium carbonate solution is 3 mol / L, and the pH is adjusted to 9; the temperature of the preheating drying oven is 110℃, and the drying time is 12h.

[0012] As a further limitation of the technical solution of the present invention, the calcination conditions in step (5) are as follows: in a muffle furnace with static air, the heating rate is 1℃ / min. -1 Raise the temperature to 300℃ and calcine for 1 hour, then increase the temperature at a rate of 2℃ / min. -1 Roast at 600℃ for 3 hours.

[0013] As a further limitation of the technical solution of the present invention, the catalyst screening condition in step (5) is to pass through a 40-60 mesh sieve.

[0014] The present invention also provides a non-precious metal Cu-Co based catalyst for the efficient catalytic combustion of ultra-low concentration methane obtained by the above preparation method.

[0015] Compared with the prior art, the present invention has the following beneficial effects: This invention proposes an optimal preparation method for Cu-Co-based catalysts for the efficient catalytic combustion of ultra-low concentration methane. Compared with conventional methods, this method controls the precipitation rate by slowly adding Na₂CO₃ solution, avoiding local supersaturation and promoting the simultaneous and uniform precipitation of copper and cobalt ions in the liquid phase, achieving a high degree of dispersion and tight binding of the active components. This close interaction effectively induces the formation of more stable Cu-Co spinel structures, which are key to the catalytic active center. Mechanistically, the electronic synergistic effect between copper and cobalt ions in the spinel structure significantly enhances the mobility of lattice oxygen, substantially reducing the energy barrier for methane CH bond activation. Simultaneously, the highly dispersed active sites prevent aggregation and sintering during the reaction process, thereby improving the catalyst's initial low-temperature activity while also significantly enhancing its catalytic stability and anti-sintering ability, ultimately achieving efficient and sustained catalytic combustion of ultra-low concentration methane. Attached Figure Description

[0016] Figure 1 A simplified diagram of the process for preparing a high-efficiency combustion catalyst for ultra-low concentration methane using the traditional impregnation method.

[0017] Figure 2 A simplified diagram of the process for preparing a high-efficiency combustion catalyst for ultra-low concentration methane using conventional combustion methods.

[0018] Figure 3 A simplified diagram of the process for preparing a catalyst for the efficient combustion of ultra-low concentration methane using the sol-gel method.

[0019] Figure 4 This is a simplified diagram illustrating the process of preparing a catalyst for the efficient combustion of ultra-low concentration methane using the method of this invention.

[0020] Figure 5Initial activity test results for 5wt% Cu catalysts prepared by four different methods for the catalytic combustion of methane; Reaction conditions: CH4 / O2 / N2 = 1 / 10 / 89 mL / min, 300℃-700℃, 50℃ intervals, 1 atm, 120000 mL / (h·g) cat ).

[0021] Figure 6 Initial activity test graphs of 5wt%Co catalysts prepared by four different methods for the catalytic combustion of methane; Reaction conditions: CH4 / O2 / N2 = 1 / 10 / 89 mL / min, 300℃-700℃, 50℃ interval, 1 atm, 120000 mL / (h·g) cat ).

[0022] Figure 7 Initial activity test graphs of 4wt%Cu-1wt%Co catalysts prepared by four different methods for the catalytic combustion of methane; reaction conditions: CH4 / O2 / N2 = 1 / 10 / 89 mL / min, 300℃-700℃, 50℃ interval, 1 atm, 120000 mL / (h·g) cat ).

[0023] Figure 8 Initial activity test graphs of 2.5wt%Cu-2.5wt%Co catalysts prepared by four different methods for the catalytic combustion of methane; reaction conditions: CH4 / O2 / N2 = 1 / 10 / 89 mL / min, 300℃-700℃, 50℃ interval, 1 atm, 120000 mL / (h·g) cat ).

[0024] Figure 9 Initial activity test graphs of 1wt%Cu-4wt%Co catalysts prepared by four different methods for the catalytic combustion of methane; reaction conditions: CH4 / O2 / N2 = 1 / 10 / 89 mL / min, 300℃-700℃, 50℃ interval, 1 atm, 120000 mL / (h·g) cat ).

[0025] Figure 10 Stability test results of 1wt%Cu-4wt%Co catalysts with optimal catalytic performance prepared by four different methods after 10 h; Reaction conditions: CH4 / O2 / N2 = 1 / 10 / 89 mL / min, 500℃, 1 atm, 120000 mL / (h·g) cat ).

[0026] Figure 11A comparison of the activity retention rates of catalysts prepared by four different methods after 10 h of reaction; Reaction conditions: CH4 / O2 / N2 = 1 / 10 / 89 mL / min, 500℃, 1 atm, 120000 mL / (h·g) cat ).

[0027] Figure 12 Stability test results of 1wt%Cu-4wt%Co catalysts with optimal catalytic performance prepared by four different methods after 20 h; Reaction conditions: CH4 / O2 / N2 = 1 / 10 / 89 mL / min, 500℃, 1 atm, 120000 mL / (h·g) cat (where a is the traditional impregnation method, b is the conventional combustion method, c is the sol-gel method, and d is the coprecipitation method of this invention).

[0028] Figure 13 A comparison of the activity retention rates of catalysts prepared by four different methods after 20 h of reaction; Reaction conditions: CH4 / O2 / N2 = 1 / 10 / 89 mL / min, 500℃, 1 atm, 120000 mL / (h·g) cat ). Detailed Implementation

[0029] The present invention will be further described below with reference to specific embodiments. Example 1

[0030] like Figure 1 As shown, the traditional impregnation method includes the following steps: using Ce(NO3)3·6H2O as the support precursor, Cu(NO3)2·3H2O and Co(NO3)2·6H2O as the active metal sources, and deionized water as the solvent, a catalyst is prepared. First, an appropriate amount of Ce(NO3)3·6H2O is placed in a muffle furnace and calcined at 450 °C for 3 h to form the support CeO2. Then, the active metal precursor is dissolved in deionized water to prepare an impregnation solution. The dried support is then impregnated, and the impregnation solution is added according to the water absorption of the support. Impregnation is carried out at room temperature for 1 h, with stirring every 10 min to ensure thorough impregnation. After impregnation, the resulting sample is dried at room temperature for 12 h, and then dried in a 110 °C drying oven for another 12 h. Finally, the dried gel is placed in a muffle furnace and heated in air at a rate of 1 °C / min. -1 The temperature was increased to 300 °C at a heating rate and held for 1 hour, then increased at a rate of 2 °C / min. -1 The temperature was increased to 600 °C and held for 3 h. Finally, the catalyst was pressed, ground and sieved to obtain the final catalyst sample. Example 2

[0031] like Figure 2As shown, the conventional combustion method includes the following steps: Ce(NO3)3·6H2O is used as the support precursor, Cu(NO3)2·3H2O and Co(NO3)2·6H2O are the active metal sources, and C2H5NO2 and NH4NO3 are used as the combustion agents. Due to the characteristic that the combustion agents are not easily soluble in ethanol, a water-ethanol mixed solution (containing 10 mL of water per 25 mL solution) is used as the solvent to prepare the catalyst. First, an appropriate amount of Ce(NO3)3·6H2O is placed in a muffle furnace and calcined at 450 °C for 3 h to form the support CeO2. Then, the combustion agent and the active metal precursor are mixed in a molar ratio of 1:1:2 to prepare an impregnation solution. The dried support is impregnated, and the impregnation solution is added according to the water absorption of the support. Impregnation is carried out at room temperature for 1 h, and the mixture is stirred every 10 min to ensure thorough impregnation. After impregnation, the obtained sample is placed in a room temperature environment to dry for 12 h, and then dried in a drying oven at 110 °C for another 12 h. Finally, the dried gel was placed in a muffle furnace and heated at 1 °C / min in air. -1 The temperature was increased to 300 °C at a heating rate and held for 1 h, then increased at a rate of 2 °C / min. -1 The temperature was increased to 600 °C and held for 3 hours. Finally, the catalyst was pressed, ground, and sieved to obtain the final catalyst sample. Example 3

[0032] like Figure 3 As shown, the sol-gel method includes the following steps: using Ce(NO3)3·6H2O as the support precursor, Cu(NO3)2·3H2O and Co(NO3)2·6H2O as the active metal sources, citric acid as the complexing agent, and deionized water as the solvent, a catalyst is prepared. First, an appropriate amount of Ce(NO3)3·6H2O is dissolved in deionized water and stirred at 60 °C for 5 h to form a homogeneous precursor solution. Then, the active metal is added, and stirring continues for 5 h to ensure uniform dispersion of the active metal in the system. During stirring, a certain amount of citric acid solution is added dropwise to achieve metal ion complexation and stabilization. After mixing, the system is placed in a water bath and allowed to react until a wet gel is formed. The resulting gel is dried at 110 °C for 12 h to remove the solvent and some organic components, obtaining a dry gel powder. Finally, the dry gel is placed in a muffle furnace and heated in an air atmosphere at a rate of 1 °C / min. -1 The temperature was increased to 300 °C at a heating rate and held for 1 h, then increased at a rate of 2 °C / min. -1 The temperature was increased to 600℃ and held for 3 hours. Finally, the catalyst was pressed, ground and sieved to obtain the final catalyst sample. Example 4

[0033] like Figure 4As shown, the method of the present invention includes the following steps: using Ce(NO3)3·6H2O as the support precursor, Cu(NO3)2·3H2O and Co(NO3)2·6H2O as active metal sources, anhydrous sodium carbonate as the precipitant, and deionized water as the solvent, a catalyst is prepared. First, an appropriate amount of Ce(NO3)3·6H2O is placed in a muffle furnace and calcined at a calcination temperature of 450 °C for 3 h to form the support CeO2. Subsequently, Cu(NO3)2·3H2O and Co(NO3)2·6H2O were dissolved in deionized water to prepare a solution. CeO2 support was then added, and the mixture was stirred to ensure uniform dispersion of the active metal in the system. After thorough mixing, a precipitant solution of Na2CO3 was slowly added dropwise while stirring, and the pH was adjusted to approximately 9. The precipitated solution was dried at room temperature for 10 h, then filtered, washed, and filtered again until the pH was neutral. The resulting sample was dried at 110 °C for 12 h to remove the solvent. Finally, the sample was placed in a muffle furnace and dried at 1 °C / min in air. -1 The temperature was increased to 300 °C at a heating rate and held for 1 h, then increased at a rate of 2 °C / min. -1 The temperature was increased to 600 °C and held for 3 h. Finally, the catalyst was pressed, ground and sieved to obtain the final catalyst sample.

[0034] In Examples 1-4 above, the amount of Cu(NO3)2·3H2O and Co(NO3)2·6H2O added as precursors in each example is: solutions of five different metal active components (5 wt% Cu, 5 wt% Co, 2.5 wt% Cu-2.5 wt% Co, 4 wt% Cu-1 wt% Co, 1 wt% Cu-4 wt% Co) need to be prepared respectively, that is, five catalysts with different active components are prepared in each example.

[0035] Initial activity tests, stability tests at 10 h and 20 h, and activity retention rates after 10 h and 20 h were conducted on the catalysts used in Examples 1-4 above for the catalytic combustion of methane. The test results are as follows: like Figure 5-9 As shown, the conversion rates of all catalysts gradually increase with increasing reaction temperature. The CH4 conversion rate of the catalyst prepared by the method of this invention is higher than that of catalysts prepared by other methods at all temperatures. In particular, at 570℃, the CH4 conversion rate of 1wt%Cu-4wt%Co / CeO2 reaches 90%, compared to only 69% for 1wt%Cu-4wt%Co / CeO2 prepared by the conventional impregnation method. Comparing different active component ratios, the 1wt%Cu-4wt%Co / CeO2 catalyst exhibits the best catalytic activity under all four methods.

[0036] like Figure 10-11 As shown, in a 10-hour stability test, the performance of 1wt% Cu-4wt% Co / CeO2 catalysts prepared by four different methods (conventional impregnation method, conventional combustion method, sol-gel method, and the co-precipitation method of this invention) was evaluated. The test conditions were a fixed reaction temperature of 500℃, continuous introduction of an ultra-low concentration methane mixture (CH4 / O2 / N2 = 1 / 10 / 89 mL / min), and monitoring of methane conversion over time. The results showed that the catalyst prepared by the co-precipitation method of this invention maintained the highest initial conversion rate (approximately 69%) within 10 hours, with the smallest decline, ultimately decreasing to approximately 67%, a decline rate of less than 2.9%. In contrast, the conventional impregnation method catalyst conversion rate decreased from an initial 48% to approximately 43%, with a decline rate of approximately 10.4%; the conventional combustion method and sol-gel method catalysts decreased to approximately 46% and 57%, respectively, with decline rates of 8% and 5%, respectively. This is attributed to the fact that the co-precipitation method achieves high dispersion of active components and uniform formation of Cu-Co spinel structure through slow drop-feeding of precipitant, which effectively enhances metal-support interaction and thus significantly improves the short-term stability of the catalyst.

[0037] like Figure 12-13 As shown, a 20-hour long-term stability test was conducted to further verify the long-term durability of the catalyst. Under the same reaction conditions, 1wt%Cu-4wt%Co / CeO2 prepared by four methods were compared. All catalysts exhibited varying degrees of activity decline. However, the catalyst prepared by the co-precipitation method of this invention still demonstrated excellent stability, maintaining a methane conversion rate above 65% after 20 h with a decay rate of less than 6%, significantly superior to other methods. The conventional impregnation method catalyst saw its conversion rate drop below 40%, with a decay rate exceeding 16.6%; the conventional combustion method and sol-gel method catalysts decayed to approximately 44% and 54%, respectively, with decay rates of 12% and 10%. These data fully demonstrate that the co-precipitation method, through precise control of the tightly packed Cu-Co synergistic structure and highly dispersed active sites formed during the precipitation process, ensures the sustained and efficient performance of the catalyst in the catalytic combustion of ultra-low concentration methane.

Claims

1. A method for preparing a non-noble metal Cu-Co-based catalyst for efficient catalytic combustion of ultra-low concentration methane, characterized in that, The method comprises the following steps: (1) preparing a CeO2 carrier; (2) dissolving at least one of Cu(NO3)2·3H2O and Co(NO3)2·6H2O in deionized water to prepare a solution; (3) adding the CeO2 carrier into the solution of step (2) and dissolving sufficiently to obtain sample A; (4) adding Na2CO3 solution dropwise into sample A while stirring, adjusting pH, drying the precipitated solution at room temperature, then performing suction filtration, washing, and suction filtering to neutral pH, and then drying the sample in a preheated drying box to obtain sample B; (5) placing sample B into a muffle furnace for calcination, then tabletting, grinding, and screening to obtain a catalyst.

2. The preparation method of a non-noble metal Cu-Co-based catalyst for efficient catalytic combustion of ultra-low concentration methane according to claim 1, characterized in that, The CeO2 carrier in step (1) is prepared by direct calcination using Ce(NO3)3·6H2O as a precursor, with a calcination temperature of 450 ℃ and a calcination time of 3 h.

3. The preparation method of a non-noble metal Cu-Co-based catalyst for efficient catalytic combustion of ultra-low concentration methane according to claim 1, characterized in that, Cu in the solution described in step (2) 2+ The concentration is 0-5 wt%, Co 2+ The concentration is 0-5 wt%.

4. The preparation method of a non-noble metal Cu-Co-based catalyst for efficient catalytic combustion of ultra-low concentration methane according to claim 1, characterized in that, After mixing in step (3), continue to stir to uniformly disperse the active metal in the system, and then stand for 1 h.

5. The preparation method of a non-noble metal Cu-Co-based catalyst for efficient catalytic combustion of ultra-low concentration methane according to claim 1, characterized in that, In step (4), the room temperature drying time is 10 h; the sodium carbonate solution is 3 mol / L, and the pH is adjusted to 9; the preheated drying box has a temperature of 110 ℃, and the drying time is 12 h.

6. The preparation method of a non-noble metal Cu-Co-based catalyst for efficient catalytic combustion of ultra-low concentration methane according to claim 1, characterized in that, The calcination conditions in step (5) are 1 °C / min ramp to 300 °C, 1 h calcination, 2 °C / min ramp to 600 °C, 3 h calcination. -1 The calcination conditions in step (5) are 1 °C / min ramp to 300 °C, 1 h calcination, 2 °C / min ramp to 600 °C, 3 h calcination. -1 The calcination conditions in step (5) are 1 °C / min ramp to 300 °C, 1 h calcination, 2 °C / min ramp to 600 °C, 3 h calcination.

7. The preparation method of a non-noble metal Cu-Co-based catalyst for efficient catalytic combustion of ultra-low concentration methane according to claim 1, characterized in that, In step (5), the catalyst screening condition is passing through a 40-60 mesh screen.

8. A non-noble metal Cu-Co-based catalyst for efficient catalytic combustion of ultra-low concentration methane, prepared by the method according to any one of claims 1-7.

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