Methane combustion catalyst with high stability and preparation method thereof

Abstract

This invention discloses a highly stable methane combustion catalyst and its preparation method, belonging to the field of energy and environmental technology. The invention first prepares a Ti-doped CeO2 composite oxide as a support, then loads it with a non-precious metal Mn-Co based solid solution, adds urea, and grinds the mixture to obtain the catalyst. This invention is not only simple, green, and efficient, but also fully utilizes the synergistic effect between the non-precious metal Mn-Co based solid solution catalyst and the support, significantly improving low-temperature catalytic activity, selectivity, and high heat and poisoning resistance. Furthermore, the catalyst can be recovered and reused, which is beneficial for resource recycling and cost reduction. The catalyst prepared by this invention has advantages such as convenient operation and high conversion rate in low-concentration methane combustion reactions.

Description

Technical Field

[0001] This invention relates to the field of energy and environmental technology, and more specifically to a highly stable methane combustion catalyst and its preparation method. Background Technology

[0002] The CH4 molecule contains highly elastic CH bonds (bond energy approximately 435 kJ·mol⁻¹). -1 This makes its degradation very difficult; traditional methane flame combustion temperatures exceed 1500℃, and it also reacts with N2 in the air to produce NO. x Methane pollutants pose a significant threat to the environment. Furthermore, traditional flame combustion has very low energy efficiency, making it unsuitable for energy-saving and environmentally friendly treatment methods. Therefore, changing the combustion method of methane is currently a key issue, and catalytic oxidation, with its advantages of moderate operating temperature and high removal efficiency, is an economical and effective method for reducing unburned methane and CO emissions.

[0003] For the catalytic combustion of methane, catalysts can be broadly classified into two categories: noble metal catalysts and non-noble metal catalysts. Currently, research on noble metal catalysts is quite mature, with significant achievements in both preparation methods and reaction mechanisms. Although noble metal catalysts exhibit significant activity, their widespread adoption is hindered by their high cost and susceptibility to poisoning. Non-noble metal catalysts, especially transition metal oxide catalysts (TMOs), have attracted considerable attention due to their low cost, good activity, and the advantages of variable valence states and tunable occupied orbitals in redox reactions. However, the activity of TMO catalysts still differs significantly from that of noble metal catalysts. Therefore, improving the catalytic efficiency of TMO catalysts is crucial for promoting the application of deep oxidation technologies in reducing light alkane emissions.

[0004] The reported catalytic systems mainly include Mn-based, Ce-based, Cu-based, Fe-based, and multi-element composite catalyst systems. Among them, Mn-based catalysts... 3+ and Mn 4+ Dual exchange behavior may exist between them, resulting in unique catalytic redox properties. Therefore, Mn-based materials contain a large amount of surface active oxygen, making them a focus of research in catalytic oxidation. In particular, the Mn-based spinel structure, referring to the AB₂O₄ composition (where A and B are metal ions in tetrahedral and octahedral positions, respectively), exhibits excellent reducing power, strong surface acidity, high surface oxygen concentration, and structural stability. Spinel catalysts contain a large amount of active oxygen and abundant acid sites. Studies have found that oxygen vacancies on cobalt-manganese spinels are important active sites for redox reactions. Oxygen vacancies can enhance the mobility and activity of lattice oxygen through transport effects, promoting the reduction and electron migration of the catalyst. This may be due to the stable three-dimensional structure of spinel, which protects the active sites.

[0005] However, long-term stable methane catalysis still faces some obstacles, which are also problems currently faced by methane combustion catalysts. Regulating the oxygen activity on spinel oxides to improve their catalytic activity has always been a challenge in heterogeneous catalytic oxidation reactions; at the same time, due to the lack of appropriate metal-support interactions and anti-poisoning sites, the active metal components are easily aggregated and poisoned by SO2 and H2O at low temperatures for extended periods, resulting in unsatisfactory catalytic stability.

[0006] The chemical etching effect of urea at high temperatures can be used to construct and modulate oxygen vacancies. With increasing oxygen vacancy concentration, the catalytic oxidation activity of various VOCs is significantly enhanced, compared to the original Co. x Mn 3-x Compared to O4 spinel catalysts, the dual activation of lattice oxygen and gaseous molecular oxygen is significantly promoted due to the modification of oxygen vacancy engineering, which has practical significance in the field of environmental catalysis.

[0007] Supported catalysts have gradually become the mainstream catalysts due to their lower cost, improved thermal stability and sulfur resistance, and relatively high catalytic activity compared to pure catalysts or solid solution catalysts, attracting the attention of most researchers. However, different types of supports have a significant impact on the activity, stability, and other properties of the catalyst.

[0008] Therefore, developing a high-performance methane combustion catalyst with excellent low-temperature activity and high resistance to heat and poisoning through interface engineering, and its preparation method, is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0009] In view of this, the present invention provides a highly stable methane combustion catalyst and its preparation method.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] A method for preparing a highly stable methane combustion catalyst includes the following steps:

[0012] (1) Preparation of Ce-Ti oxides by coprecipitation method

[0013] C 12 H 28 O4Ti was dissolved in ethanol, and then Ce(NO3)3·6H2O was added to the solution and stirred to react. The pH was then adjusted with ammonia, and the mixture was stirred again for 2-4 hours. After aging for 2-4 hours, the precipitate was filtered and washed with water. The washed precipitate was dried and then heated in flowing air to obtain nanostructured Ce. xTi 1-x O2 support, namely Ce-Ti oxide, Ce x Ti 1-x In the formula O2, x = 0.1-0.9, preferably 0.5;

[0014] (2) Supporting Mn-Co solid solution on Ce-Ti oxide

[0015] (2.1) Mn-Co solid solution supported on Ce-Ti oxide using the positive drop method

[0016] Co(NO3)2·6H2O and Mn(CH3COO)2·4H2O were dissolved in water and labeled as solution A. Ce-Ti oxide and ammonium bicarbonate solution were then mixed and labeled as solution B. Solution A was slowly added dropwise to solution B, and the reaction was stirred and aged for 1-8 hours. After filtration, the precipitate was washed with ethanol and deionized water until the pH reached 7-7.5, yielding the sample. The sample was dried, calcined, ground with urea, and calcined again to obtain supported XMn. x Co 3-x O4 / Y Ce x Ti 1-x O2 catalyst;

[0017] (2.2) Mn-Co solid solution supported on Ce-Ti oxide using the reverse dropping method

[0018] Co(NO3)2·6H2O, Mn(CH3COO)2·4H2O, and Ce-Ti oxides were dissolved in water, and then ammonium bicarbonate solution was slowly added dropwise. After aging the precipitate with stirring for 6-8 hours, the mixture was filtered, and the precipitate was washed with ethanol and deionized water to a pH of 7-7.5 to obtain the sample. The sample was dried, calcined, ground with urea, and calcined again to obtain supported XMn. x Co 3-x O4 / Y Ce x Ti 1-x O2 catalyst;

[0019] Load-type XMn x Co 3-x O4 / YCe x Ti 1-x In the formula for O2 catalyst, X:Y = 5-8:2-5, Mn x Co 1-x In O4, x = 0.1-3, preferably 0.5; Ce x Ti 1-x In O2, x = 0.1-0.9, preferably 0.5.

[0020] Furthermore, the stirring reaction temperature in step (1) is 60-80℃, and the stirring reaction time is 20-40min.

[0021] Furthermore, the mass concentration of the ammonia water in step (1) is 6%, and the ammonia water is added to the solution at a dropping rate of 5 mL / min to adjust the pH to 8.5-10.

[0022] Furthermore, the drying temperature in step (1) is 80-100℃, and the drying time is 10-12h;

[0023] Furthermore, the heating temperature of the flowing air is 400-500℃, the heating time is 3-4h, and the air flow rate is 20-50ml / min.

[0024] Furthermore, the dropping temperature in step (2.1) is 50-80℃, and the dropping rate is 5ml / min.

[0025] The concentration of the ammonium bicarbonate solution is 1 mol / L.

[0026] Furthermore, the sample drying temperature in step (2.1) is 80-100℃, and the drying time is 6-7h;

[0027] The calcination temperature of the sample was 400-500℃, and the calcination time was 3-4 hours.

[0028] The mass ratio of the sample to urea was 1:4;

[0029] The recalcination temperature is 400-600℃, and the calcination time is 3-4 hours.

[0030] Furthermore, the dropping temperature in step (2.2) is 60-70℃, and the dropping rate is 5ml / min;

[0031] The concentration of the ammonium bicarbonate solution is 1 mol / L.

[0032] Furthermore, the sample drying temperature in step (2.2) is 80-100℃, and the drying time is 6-7h;

[0033] The calcination temperature of the sample was 400-500℃, and the calcination time was 3-4 hours.

[0034] The mass ratio of the sample to urea was 1:4;

[0035] The recalcination temperature is 400-600℃, and the calcination time is 3-4 hours.

[0036] The beneficial effects of this invention are as follows:

[0037] A layered structure was constructed by loading a Mn-Co based solid solution catalyst onto Ti-doped CeO2. Through Ti-induced CeO2 crystal reconstruction, two strong SO2 affinity sites were formed, delaying the influence of sulfate species on the active center and thus improving stability. The presence of "low-temperature active sites" and "dual anti-poisoning sites" endows the catalyst with excellent activity and stability. The layered structure promotes the formation of the active metal-support interface. The strong interaction at the metal-support interface helps suppress the formation of adsorbed hydroxyl groups on the surface and facilitates oxygen migration (including adsorbed oxygen, lattice oxygen, and oxygen vacancies) and metal charge transfer. Furthermore, by constructing and adjusting oxygen vacancies through oxygen vacancy engineering (urea modification: the chemical etching effect of urea at high temperatures), the catalytic oxidation activity is significantly enhanced with increasing oxygen vacancy concentration. This achieves excellent low-temperature activity in a low-concentration methane combustion catalyst, while also exhibiting high stability and resistance to water and sulfur dioxide.

[0038] In this invention, CeO2 possesses abundant surface oxygen vacancies, which can serve as adsorption and activation sites for SO2, protecting the active components from poisoning. However, pure CeO2 degrades rapidly at high temperatures due to a significant reduction in surface area, failing to meet practical application requirements. After doping or surface modification according to this invention, the structural properties of CeO2 can be improved. Introducing other metal ions into the CeO2 lattice to form a CeO2-based solid solution can endow the material with high oxygen storage capacity, thermal stability, and redox performance, thereby exhibiting excellent catalytic performance.

[0039] The catalyst prepared by this invention has excellent low-temperature activity, and the conversion rate of ultra-low concentration methane (methane concentration 0.5%-1.5%) can reach 90% at a temperature of 400℃. It also has high water resistance and sulfur dioxide resistance. Attached Figure Description

[0040] Figure 1 This is a process flow diagram for preparing the highly stable methane combustion catalyst of the present invention;

[0041] Figure 2 The reaction of 100 ppm SO2 with 50% Mn at a concentration of 0.5% methane. 0.5 Co 2.5 O4 / 50%Ce 0.5 Ti 0.5 The effect of O2 catalyst on catalytic performance;

[0042] Figure 3 100 ppm SO2 at 1% methane concentration versus 70% Mn 0.5 Co 2.5 O4 / 30%Ce 0.5 Ti 0.5 The effect of O2 catalyst on catalytic performance;

[0043] Figure 4 The reaction of 100 ppm SO2 with 80% Mn at a concentration of 1.5% methane. 0.5 Co 2.5 O4 / 20%Ce 0.5 Ti 0.5 The effect of O2 catalyst on catalytic performance. Detailed Implementation

[0044] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] Example 1

[0046] A method for preparing a highly stable methane combustion catalyst:

[0047] (1) Preparation of Ce-Ti oxides by coprecipitation method

[0048] C 12 H 28 O₄Ti was dissolved in ethanol, and then Ce(NO₃)₃·6H₂O was added to the solution. The mixture was stirred at 70°C for 30 min, with a Ti to Ce molar ratio of 1:1. The pH was then adjusted to 9 by adding 6% ammonia solution dropwise at a rate of 5 mL / min. After stirring again for 3 h, the mixture was aged for 3 h. The precipitate was filtered and washed with water. The washed precipitate was dried at 90°C for 12 h, and then heated at 450°C for 3.5 h in flowing air at a rate of 30 mL / min to obtain nanostructured Ce. 0.5 Ti 0.5 O2 support, namely Ce-Ti oxide;

[0049] (2) Mn-Co solid solution was supported on Ce-Ti oxide using the positive drop method.

[0050] Co(NO3)2·6H2O and Mn(CH3COO)2·4H2O were dissolved in water, with a molar ratio of Mn to Co of 1:5. The sample was Mn. 0.5 Co 2.5 O4, denoted as solution A, then Ce 0.5 Ti 0.5O2 and 400 ml of 1 mol / L ammonium bicarbonate solution were mixed, denoted as solution B. Solution A was slowly added dropwise to solution B at a rate of 5 ml / min at 65°C. After stirring and aging for 4 hours, the mixture was filtered, and the precipitate was washed with ethanol and deionized water until the pH reached 7, yielding the sample. The sample was dried at 100°C for 6 hours, then calcined at 450°C for 3.5 hours. Urea (4 times the sample mass) was added and the mixture was ground, then calcined again at 500°C for 3.5 hours to obtain the supported 50% MnO2 solution. 0.5 Co 2.5 O4 / 50%Ce 0.5 Ti 0.5 O2 catalyst.

[0051] Example 2

[0052] A method for preparing a highly stable methane combustion catalyst:

[0053] (1) Preparation of Ce-Ti oxides by coprecipitation method

[0054] C 12 H 28 O₄Ti was dissolved in ethanol, and then Ce(NO₃)₃·6H₂O was added to the solution. The mixture was stirred at 70°C for 30 min, with a Ti to Ce molar ratio of 1:1. The pH was then adjusted to 9 by adding 6% ammonia solution dropwise at a rate of 5 mL / min. After stirring again for 3 h, the mixture was aged for 3 h. The precipitate was filtered and washed with water. The washed precipitate was dried at 90°C for 12 h, and then heated at 450°C for 3.5 h in flowing air at a rate of 30 mL / min to obtain nanostructured Ce. 0.5 Ti 0.5 O2 support, namely Ce-Ti oxide;

[0055] (2) Mn-Co solid solution is supported on Ce-Ti oxide by reverse dropping method.

[0056] Co(NO3)2·6H2O, Mn(CH3COO)2·4H2O, and Ce-Ti oxide were dissolved in water at a molar ratio of Mn to Co of 1:5. Then, 400 ml of a 1 mol / L ammonium bicarbonate solution was slowly added dropwise at 5 ml / min at 65 °C. After aging with stirring for 7 h, the precipitate was filtered, washed with ethanol and deionized water to a pH of 7, and the sample was obtained. The sample was dried at 100 °C for 6 h, then calcined at 450 °C for 3.5 h. Urea (4 times the sample mass) was added and the mixture was ground, then calcined again at 500 °C for 3.5 h to obtain a supported 50% Mn oxide. 0.5 Co 2.5 O4 / 50%Ce 0.5 Ti 0.5 O2.

[0057] Example 3

[0058] The preparation steps are basically the same as in Example 1, except that the ratio of Co(NO3)2·6H2O, Mn(CH3COO)2·4H2O and Ce-Ti oxide is adjusted. The product prepared is a supported 70% Mn oxide. 0.5 Co 2.5 O4 / 30%Ce 0.5 Ti 0.5 O2.

[0059] Example 4

[0060] The preparation steps are basically the same as in Example 1, except that the ratio of Co(NO3)2·6H2O, Mn(CH3COO)2·4H2O and Ce-Ti oxide is adjusted. The product prepared is a supported 80% Mn oxide. 0.5 Co 2.5 O4 / 20%Ce 0.5 Ti 0.5 O2.

[0061] Experimental Example 1

[0062] As in the scheme of Example 1, Mn 0.5 Co 2.5 O4 and Ce 0.5 Ti 0.5 O2 is loaded in a 1:1 ratio, denoted as 50% Mn. 0.5 Co 2.5 O4 / 50%Ce 0.5 Ti 0.5 O2; The catalyst was placed in a fixed-bed reactor, and stability tests were conducted at a methane concentration of 0.5%; The temperature was programmed from 0 to 500 °C, with a feed gas ratio of 0.5% methane, 20% O2, and the remainder Ar, and a space velocity of 45000 mL / (gh). The methane conversion rate was observed; 100 ppm SO2 was introduced into the feed gas, and the change in methane conversion rate was observed. The results are as follows. Figure 2 As shown.

[0063] Experimental Example 2

[0064] As in the scheme of Example 3, Mn 0.5 Co 2.5 O4 and Ce 0.5 Ti 0.5 O2 is used in a 7:3 load, denoted as 70% Mn. 0.5 Co 2.5 O4 / 30%Ce 0.5 Ti 0.5O2; The catalyst was placed in a fixed-bed reactor, and stability tests were conducted at a methane concentration of 1%; The temperature was programmed from 0 to 500 °C, with a feed gas ratio of 1% methane, 20% O2, and the remainder Ar, and a space velocity of 45000 mL / (gh). The methane conversion rate was observed; 100 ppm SO2 was introduced into the feed gas, and the change in methane conversion rate was observed. The results are as follows. Figure 3 As shown.

[0065] Experimental Example 3

[0066] As in the scheme of Example 4, Mn 0.5 Co 2.5 O4 and Ce 0.5 Ti 0.5 O2 is subjected to an 8:2 load, denoted as 80% Mn. 0.5 Co 2.5 O4 / 20%Ce 0.5 Ti 0.5 O2; The catalyst was placed in a fixed-bed reactor, and stability tests were conducted at a methane concentration of 1.5%; The temperature was programmed from 0 to 500 °C, with a feed gas ratio of 1.5% methane, 20% O2, and the remainder Ar, and a space velocity of 45000 mL / (gh). The methane conversion rate was observed; 100 ppm SO2 was introduced into the feed gas, and the change in methane conversion rate was observed. The results are as follows. Figure 4 As shown.

[0067] As attached Figure 2-4 As shown, the sulfur resistance performance of catalysts with different loading ratios was studied in a fixed-bed reactor by introducing 100 ppm SO2 into the feed gas. The catalysts all showed good sulfur resistance performance, and their catalytic activity in the sulfur-containing atmosphere was almost the same as that in the sulfur-free atmosphere. This indicates that by loading the Mn-Co based solid solution catalyst onto the Ti-doped CeO2 to construct a stacked structure, the two strong SO2 affinity sites formed by Ti-induced CeO2 crystal reconstruction improved the sulfur resistance performance of the catalyst.

[0068] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing a highly stable methane combustion catalyst, characterized in that, Includes the following steps: (1) Preparation of Ce-Ti oxides by coprecipitation method C 12 H 28 O4Ti was dissolved in ethanol, and then Ce(NO3)3·6H2O was added to the solution and stirred to react. The pH was then adjusted with ammonia, and the mixture was stirred again for 2-4 hours. After aging for 2-4 hours, the precipitate was filtered and washed with water. The washed precipitate was dried and then heated in flowing air to obtain nanostructured Ce. x Ti 1-x O2 support, namely Ce-Ti oxide, Ce x Ti 1-x In formula O2, x = 0.1 - 0.9; (2) Supporting Mn-Co solid solution on Ce-Ti oxide (2.1) Mn-Co solid solution supported on Ce-Ti oxide using the positive drop method Co(NO3)2·6H2O and Mn(CH3COO)2·4H2O were dissolved in water and labeled as solution A. Ce-Ti oxide and ammonium bicarbonate solution were then mixed and labeled as solution B. Solution A was slowly added dropwise to solution B, and the reaction was stirred and aged for 1-8 hours. After filtration, the precipitate was washed with ethanol and deionized water until the pH reached 7-7.5, yielding the sample. The sample was dried, calcined, ground with urea, and calcined again to obtain supported XMn. x Co 3-x O4 / Y Ce x Ti 1-x O2 catalyst; (2.2) Mn-Co solid solution supported on Ce-Ti oxide using the reverse dropping method Co(NO3)2·6H2O, Mn(CH3COO)2·4H2O, and Ce-Ti oxides were dissolved in water, and then ammonium bicarbonate solution was slowly added dropwise. After aging the precipitate with stirring for 6-8 hours, the mixture was filtered, and the precipitate was washed with ethanol and deionized water to a pH of 7-7.5 to obtain the sample. The sample was dried, calcined, ground with urea, and calcined again to obtain supported XMn. x Co 3-x O4 / Y Ce x Ti 1-x O2 catalyst; Load-type X Mn x Co 3-x O4 / Y Ce x Ti 1-x In the formula for O2 catalyst, X:Y = 5-8:2-5, Mn x Co 1-x In O4, x = 0.1 - 3, Ce x Ti 1-x In O2, x = 0.1 - 0.

9.

2. The method for preparing a highly stable methane combustion catalyst according to claim 1, characterized in that, The stirring reaction temperature in step (1) is 60-80℃, and the stirring reaction time is 20-40min.

3. The method for preparing a highly stable methane combustion catalyst according to claim 1, characterized in that, The ammonia solution in step (1) has a mass concentration of 6%, and the ammonia solution is added to the solution at a dropping rate of 5 mL / min to adjust the pH to 8.5-10.

4. The method for preparing a highly stable methane combustion catalyst according to claim 1, characterized in that, The drying temperature in step (1) is 80-100℃, and the drying time is 10-12h; The heating temperature of the flowing air is 400-500℃, the heating time is 3-4h, and the air flow rate is 20-50ml / min.

5. The method for preparing a highly stable methane combustion catalyst according to claim 1, characterized in that, The dripping temperature in step (2.1) is 50-80℃, and the dripping rate is 5ml / min; The concentration of the ammonium bicarbonate solution is 1 mol / L.

6. The method for preparing a highly stable methane combustion catalyst according to claim 1, characterized in that, The sample drying temperature in step (2.1) is 80-100℃, and the drying time is 6-7h; The calcination temperature of the sample was 400-500℃, and the calcination time was 3-4 hours. The mass ratio of the sample to urea was 1:4; The recalcination temperature is 400-600℃, and the calcination time is 3-4 hours.

7. The method for preparing a highly stable methane combustion catalyst according to claim 1, characterized in that, The dripping temperature in step (2.2) is 60-70℃, and the dripping rate is 5ml / min; The concentration of the ammonium bicarbonate solution is 1 mol / L.

8. The method for preparing a highly stable methane combustion catalyst according to claim 1, characterized in that, The sample drying temperature in step (2.2) is 80-100℃, and the drying time is 6-7h; The calcination temperature of the sample was 400-500℃, and the calcination time was 3-4 hours. The mass ratio of the sample to urea was 1:4; The recalcination temperature is 400-600℃, and the calcination time is 3-4 hours.

9. A highly stable methane combustion catalyst, characterized in that, It is prepared by the preparation method described in any one of claims 1-8.

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