A Mg / Ba dual-doped catalyst for methane catalytic combustion, and its preparation method and application

Abstract

The present invention discloses a Mg / Ba dual-doped catalyst for the catalytic combustion of methane, its preparation method, and application. The catalyst uses La2Ce2O7 as a carrier and Mg and Ba oxides as active components. The carrier and active components are combined using a hydrothermal method, and the catalyst is then uniformly loaded using a colloidal crystal template method. This pyrochlore-type compound (A2B2O7) has high thermal stability, meeting the requirements of a methane oxidative coupling (OCM) catalyst. The catalyst is highly selective, exhibits high catalytic activity in the OCM reaction at low temperatures (<650°C), exhibits high methane removal rates, and produces high yields of C2 products (C2H4 and C2H6), promising broad market applications.

Description

Technical Field

[0001] The invention provides a Mg / Ba double-doped catalyst for methane catalytic combustion and a preparation method thereof, belonging to the field of environmentally friendly catalytic materials and air pollution control. Background Art

[0002] Methane (CH4) is the main component of natural gas. It is also a greenhouse gas, second only to CO2 in greenhouse gas emissions, and its greenhouse effect is 21 times that of CO2. Compared with other alkanes, CH4 has a higher ionization potential (12.5eV), a lower electron affinity (4.4eV) and a higher C-H bond energy (443kJ·mol -1 ), while CH4's stable and highly symmetrical structure makes it difficult to activate. Therefore, promoting complete combustion of CH4 and improving its purification efficiency are currently significant challenges. Catalysts based on precious metals such as palladium (Pd), platinum (Pt), iridium (Ir), and rhodium (Rh) exhibit high catalytic activity for CH4 combustion. However, considering their economic viability, there is an urgent need to find low-cost and efficient non-precious metal catalysts.

[0003] Among the existing patents, patent CN202311088709 prepares a N / MnCo3O4 / ZSM5 catalyst for catalytic combustion of methane. The authors mix water, an alkali source, and an aluminum source, add a template, a cobalt salt, and a silicon source to the mixture, and further mix them to obtain a ZSM5 crystallization precursor solution. The crystallized precursor solution is subjected to hydrothermal crystallization under stirring. Manganese salt is sequentially added to the hydrothermal crystallization solution, and the hydrothermal crystallization treatment is further carried out under stirring. After that, the solution is filtered and the filter cake is dried to obtain a MnCo3O4 / ZSM5 catalyst precursor. Finally, the precursor is calcined under a nitrogen atmosphere. Patent CN202310516128 constructs a high-stability methane combustion catalyst with the structural formula M+PdPt / HMCM22. The preparation process is as follows: palladium and platinum precursors are completely dissolved in a solvent, and then HMCM22 molecular sieves are added. The solid powder is evaporated to obtain a solid powder, and the solid powder is calcined at 450-550°C for 32 hours. The catalyst can confine the interface and stabilize the microstructure of the active Pd-Pt site by adding HMCM-22 molecular sieve. Patent 202310212303.9 discloses an encapsulated Pd-based catalyst for methane catalytic combustion and its preparation method. It includes the following steps: first, the template is mixed with a silicon source to obtain a molecular sieve gel, then a Pd metal precursor solution with ethylenediamine as a ligand is mixed with the above-mentioned molecular sieve gel, and a series of catalysts with different particle sizes are obtained by regulating the molar ratio between ethylenediamine and metal Pd. This catalyst is suitable for the field of low-concentration methane catalytic combustion, solves the problem that the current encapsulated catalyst cannot accurately control the size, and improves the catalytic activity of the catalyst for methane combustion. Most of the methane combustion catalysts on the market are mainly based on precious metal Pd / Pt, which are relatively expensive, so the development of a non-precious metal catalyst has broad market prospects.

[0004] In recent years, with the implementation of national strategies such as carbon peak and carbon neutrality, more and more researchers have focused on greenhouse gas control and reduction, and the catalytic combustion of methane is an inevitable part of this process. Therefore, the development of a new type of high-loaded non-precious metal catalyst is of great significance. Summary of the Invention

[0005] The present invention is aimed at the current status and problems of methane catalytic combustion technology and catalyst research, and proposes a La2Ce2O7 Mg / Ba dual-doped catalyst. Another object of the present invention is to provide a preparation method of the above dual-doped catalyst.

[0006] A method for preparing a Mg / Ba dual-doped catalyst for catalytic combustion of methane, the preparation method of the catalyst is as follows:

[0007] (1) Synthesis of PMMA microspheres

[0008] A 60-90°C potassium persulfate solution is added to a 60-90°C methyl methacrylate (MMA) solution for reaction, and after the reaction is completed, the solution is cooled to room temperature and filtered to obtain a uniform latex of monodispersed PMMA microspheres.

[0009] (2) Synthesis of CCT

[0010] A highly ordered PMMA-CCT template was obtained by centrifuging the homogenous latex of PMMA microspheres and drying the resulting solid mass;

[0011] (3) Catalyst preparation

[0012] The PMMA-CCT template is immersed in a mixture of lanthanum salt, cerium salt, barium salt and magnesium salt, and then filtered to obtain a PMMA-CCT mixture filled with metal oxide precursors. The mixture is dried and then calcined twice to obtain the target product.

[0013] In the above preparation method: the reaction in step (1) is carried out under stirring, and the stirring speed is 300-400 r min -1 ; The reaction temperature is 60-90°C, and the reaction time is 1-3h.

[0014] In the above preparation method: the concentration of the potassium persulfate solution in step (1) is 20-70 mmol / L, the mass concentration of the methyl methacrylate (MMA) solution is 10-30%; and the volume ratio of the potassium persulfate solution to methyl methacrylate is 1:(2.5-5).

[0015] In the above preparation method: the filter paper used for microporous filtration in step (1) has a size of 0.5 to 2 μm.

[0016] In the above preparation method: the drying temperature in step (2) is 50-70° C., and the drying time is 35-40 hours.

[0017] In the above preparation method: the salts of the lanthanum salt, cerium salt, magnesium salt and barium salt are in the form of nitrates, and the molar concentrations of the lanthanum salt, cerium salt, magnesium salt and barium salt in the mixed solution are 250-350 mmol / L, 250-350 mmol / L, 50-110 mmol / L and 20-60 mmol / L, respectively.

[0018] In the above preparation method: the complete immersion time described in step (3) is 8 to 12 hours, the drying temperature is 50 to 80° C., and the drying time is 20 to 28 hours.

[0019] In the above preparation method: the first calcination temperature in step (3) is 240-320° C., and the calcination time is 2-4 hours; the second calcination temperature is 700-850° C., and the calcination time is 3-5 hours.

[0020] A Mg / Ba dual-doped catalyst for catalytic combustion of methane. The catalyst uses La2Ce2O7 as a carrier, and the mass ratio of lanthanum oxide:cerium oxide:magnesium oxide:barium oxide in the catalyst is 10:8-10:(1-3):(0.5-2).

[0021] A Mg / Ba dual-doped catalyst for catalytic combustion of methane is prepared by the above method.

[0022] In the technical solution of the present invention, the catalyst prepared by the above method is used to remove methane from the atmosphere.

[0023] Beneficial effects

[0024] Methane can be directly converted to C2H4, and rare earth oxide-based catalysts have been extensively studied for the OCM reaction. A2B2O7-type composite oxides possess high thermal stability and oxygen mobility, which essentially meet the requirements for suitable OCM catalysts. Furthermore, optimization strategies such as doping, defect introduction, and surface modification of oxide catalysts have been widely adopted to further enhance their catalytic performance. In A2B2O7-type oxide catalysts, both the A and B sites can be partially substituted with other metal ions of similar radius, while maintaining the integrity of the crystal structure, but with the formation of anionic defects. Substitution of the A and B sites in the A2B2O7 structure can modulate the density of lattice vacancies and active oxygen species, thereby adjusting catalyst performance. La2Ce2O7 catalysts exhibit high catalytic activity in the OCM reaction. It has also been found that partial substitution of cations in metal oxide catalysts with lanthanides, alkali metals, and alkaline earth metals can increase the number of oxygen vacancies. The increase in oxygen vacancies in the catalyst enhances the activation of O2 molecules into active oxygen species, which improves the catalytic activity for the OCM reaction at low temperatures (<650°C). The dual doping of alkaline earth metals (Mg and Ba) to replace the A or B position in La2Ce2O7 compounds is of great significance in promoting the catalytic activity of the OCM reaction. This catalyst shows excellent catalytic effect in low-temperature catalysis and has broad market value. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is the methane removal rate of the catalyst in Examples 1 to 3 and Comparative Examples 1 to 3.

[0026] Figure 2 It is the yield of C2 product of the catalyst in Examples 1 to 3 and Comparative Examples 1 to 3. DETAILED DESCRIPTION

[0027] The present invention will be further described below with reference to the following examples, but the scope of protection of the present invention is not limited thereto: Example 1

[0028] (1) Synthesis of PMMA microspheres

[0029] 500 ml of deionized water was poured into a four-necked round-bottom flask (2000 ml). When the solvent was heated to 80°C in a hot water bath, 120 ml of MMA monomer was then added. 0.72 g of KPS was added to 40 ml of deionized water to form a solution, and maintained at 80°C in a hot water bath. After stabilization for 20 min, the KPS solution was quickly added to the flask. The mixture was heated at 80°C at 350 r min under nitrogen protection. -1 After the polymerization reaction was completed, the reaction system was naturally cooled to room temperature and filtered with a 1 μm microporous filter paper to obtain a uniform latex of monodispersed PMMA microspheres.

[0030] (2) Synthesis of CCT

[0031] The filtered latex was heated for 3000 min. -1 The mixture was centrifuged for a period of time to form a colloidal crystal template (CCT). The supernatant was decanted to clarify the liquid, and the solid block was dried at 60°C for 40 h. Finally, a highly ordered PMMA template was obtained.

[0032] (3) Catalyst preparation

[0033] 3.43 g La(NO3)3·6H2O, 2.21 g Ce(NO3)3·6H2O, 0.78 g Mg(NO3)2·6H2O and 0.44 g Ba(NO3)2 were dissolved in 30 ml ethylene glycol and methanol to obtain a homogeneous solution (V 乙二醇 :V 甲醇 =1:2). Subsequently, the PMMA-CCT template was added to the solution, and the CCT was completely immersed in the solution for 10 hours. After immersion, the excess precursor solution was removed using vacuum filtration on a Buchner funnel to obtain a PMMA-CCT mixture filled with the metal oxide precursor, which was then dried in an oven at 60°C for 24 hours. The dried mixture was first calcined in air at 300°C for 2 hours, then the temperature was increased to 800°C at a rate of 2°C / min and calcined for an additional 4 hours.

[0034] (4) Catalytic activity test

[0035] 200 mg of the prepared 40-60 mesh catalyst was loaded into a catalyst performance evaluation reactor. The simulated gas composition was: CH4 / O2 / N2 = 4 / 1 / 5, with a flow rate of 120 ml / min. Prior to the reaction, the catalyst was pretreated at 800°C for 30 minutes under an N2 atmosphere, then cooled to 500°C for activity testing. The catalytic reaction was tested at a temperature range of 550-800°C. Test results showed a methane removal rate of 38.2% at 650°C, and a C2 product yield of 26.1%.

[0036] Example 2

[0037] (1) Synthesis of PMMA microspheres

[0038] 500 ml of deionized water was poured into a four-necked round-bottom flask (2000 ml). When the solvent was heated to 80°C in a hot water bath, 100 ml of MMA monomer was then added. 0.57 g of KPS was added to 40 ml of deionized water to form a solution, and maintained at 80°C in a hot water bath. After stabilization for 20 minutes, the KPS solution was quickly added to the flask. The mixture was heated at 80°C at 350 r min under nitrogen protection. -1 After the polymerization reaction was completed, the reaction system was naturally cooled to room temperature and filtered with a 1 μm microporous filter paper to obtain a uniform latex of monodispersed PMMA microspheres.

[0039] (2) Synthesis of CCT

[0040] The filtered latex was heated for 3000 min. -1 The mixture was centrifuged for a period of time to form a colloidal crystal template (CCT). The supernatant was decanted to clarify the liquid, and the solid block was dried at 60°C for 40 h. Finally, a highly ordered PMMA template was obtained.

[0041] (3) Catalyst preparation

[0042] 2.73 g La(NO3)3·6H2O, 1.87 g Ce(NO3)3·6H2O, 0.43 g Mg(NO3)2·6H2O and 0.22 g Ba(NO3)2 were dissolved in 30 ml ethylene glycol and methanol to obtain a homogeneous solution (V 乙二醇 :V 甲醇 =1:3). Subsequently, the PMMA-CCT template was added to the solution, and the CCT was completely immersed in the solution for 10 hours. After immersion, the excess precursor solution was removed using vacuum filtration on a Buchner funnel to obtain a PMMA-CCT mixture filled with the metal oxide precursor, which was then dried in an oven at 60°C for 24 hours. The dried mixture was first calcined in air at 300°C for 2 hours, then the temperature was increased to 800°C at a rate of 2°C / min and calcined for an additional 4 hours.

[0043] (4) Catalytic activity test

[0044] 200 mg of the prepared 40-60 mesh catalyst was loaded into a catalyst performance evaluation reactor. The simulated gas composition was: CH4 / O2 / N2 = 4 / 1 / 5, with a flow rate of 120 ml / min. Prior to the reaction, the catalyst was pretreated at 800°C for 30 minutes under an N2 atmosphere, then cooled to 500°C for activity testing. The catalytic reaction was tested at a temperature range of 550-800°C. Test results showed a methane removal rate of 32.5% at 650°C, and a C2 product yield of 20.4%.

[0045] Example 3

[0046] (1) Synthesis of PMMA microspheres

[0047] 500 ml of deionized water was poured into a four-necked round-bottom flask (2000 ml). When the solvent was heated to 80°C in a hot water bath, 180 ml of MMA monomer was then added. 0.42 g of KPS was added to 40 ml of deionized water to form a solution, and maintained at 80°C in a hot water bath. After stabilization for 20 min, the KPS solution was quickly added to the flask. The mixture was heated at 80°C at 350 r min under nitrogen protection. -1 After the polymerization reaction was completed, the reaction system was naturally cooled to room temperature and filtered with a 1 μm microporous filter paper to obtain a uniform latex of monodispersed PMMA microspheres.

[0048] (2) Synthesis of CCT

[0049] The filtered latex was heated for 3000 min. -1 The mixture was centrifuged for a period of time to form a colloidal crystal template (CCT). The supernatant was decanted to clarify the liquid, and the solid block was dried at 60°C for 40 h. Finally, a highly ordered PMMA template was obtained.

[0050] (3) Catalyst preparation

[0051] 3.23 g La(NO3)3·6H2O, 1.92 g Ce(NO3)3·6H2O, 0.63 g Mg(NO3)2·6H2O and 0.46 g Ba(NO3)2 were dissolved in 30 ml ethylene glycol and methanol to obtain a homogeneous solution (V 乙二醇 :V 甲醇 =2:1). Subsequently, the PMMA-CCT template was added to the solution, and the CCT was completely immersed in the solution for 10 hours. After immersion, the excess precursor solution was removed using vacuum filtration on a Buchner funnel to obtain a PMMA-CCT mixture filled with the metal oxide precursor, which was then dried in an oven at 60°C for 24 hours. The dried mixture was first calcined in air at 300°C for 2 hours, then the temperature was increased to 800°C at a rate of 2°C / min and calcined for an additional 4 hours.

[0052] (4) Catalytic activity test

[0053] 200 mg of the prepared 40-60 mesh catalyst was loaded into a catalyst performance evaluation reactor. The simulated gas composition was: CH4 / O2 / N2 = 4 / 1 / 5, with a flow rate of 120 ml / min. Prior to the reaction, the catalyst was pretreated at 800°C for 30 minutes under an N2 atmosphere, then cooled to 500°C for activity testing. The catalytic reaction was tested at a temperature range of 550-800°C. Test results showed a methane removal rate of 34.7% at 650°C, and a C2 product yield of 24.7%.

[0054] Comparative Example 1

[0055] (1) Synthesis of PMMA microspheres

[0056] The conditions are the same as step (1) in Example 1;

[0057] (2) Synthesis of CCT

[0058] The conditions are the same as step (2) in Example 1;

[0059] (3) Catalyst preparation

[0060] Without adding Ba(NO3)2·2H2O and Mg(NO3)2·6H2O, other conditions are the same as step (3) in Example 1

[0061] (4) Catalytic activity test

[0062] 200 mg of the prepared 40-60 mesh catalyst was loaded into a catalyst performance evaluation reactor. The simulated gas composition was: CH4 / O2 / N2 = 4 / 1 / 5, with a flow rate of 120 ml / min. Prior to the reaction, the catalyst was pretreated at 800°C for 30 minutes under an N2 atmosphere, then cooled to 500°C for activity testing. The catalytic reaction was tested at a temperature range of 550-800°C. Test results showed an 18.7% methane removal rate and an 11.4% C2 product yield at 650°C.

[0063] (5) Contrast effect

[0064] Compared with Example 1, Ba(NO3)2·2H2O and Mg(NO3)2·6H2O were not added in step (3). The methane removal efficiency and C2 product selectivity of the prepared catalyst were significantly reduced. The decrease in the specific surface area of ​​the catalyst led to a decrease in the adsorption and activation performance of CH4 and O2.

[0065] Comparative Example 2

[0066] (1) Synthesis of PMMA microspheres

[0067] The conditions are the same as step (1) in Example 1;

[0068] (2) Synthesis of CCT

[0069] The conditions are the same as step (2) in Example 1;

[0070] (3) Catalyst preparation

[0071] Without adding Ba(NO3)2, other conditions are the same as step (3) in Example 1

[0072] (4) Catalytic activity test

[0073] 200 mg of the prepared 40-60 mesh catalyst was loaded into a catalyst performance evaluation reactor. The simulated gas composition was: CH4 / O2 / N2 = 4 / 1 / 5, with a flow rate of 120 ml / min. Prior to the reaction, the catalyst was pretreated at 800°C for 30 minutes under an N2 atmosphere, then cooled to 500°C for activity testing. The catalytic reaction was tested at a temperature range of 550-800°C. Test results showed a methane removal rate of 21.7% at 650°C, and a C2 product yield of 16.3%.

[0074] (5) Contrast effect

[0075] Compared with Example 1, Ba(NO3)2·2H2O was not added in step (3). The methane removal efficiency and C2 product selectivity of the prepared catalyst were significantly reduced, which may be due to the lack of Ba doping, resulting in a decrease in active sites in the catalyst and a poor OCM reaction effect.

[0076] Comparative Example 3

[0077] (1) Synthesis of PMMA microspheres

[0078] The conditions are the same as step (1) in Example 1;

[0079] (2) Synthesis of CCT

[0080] The conditions are the same as step (2) in Example 1;

[0081] (3) Catalyst preparation

[0082] No Mg(NO3)2·6H2O was added, and other conditions were the same as step (3) in Example 1.

[0083] (4) Catalytic activity test

[0084] 200 mg of the prepared 40-60 mesh catalyst was loaded into a catalyst performance evaluation reactor. The simulated gas composition was: CH4 / O2 / N2 = 4 / 1 / 5, with a flow rate of 120 ml / min. Before the reaction, the catalyst was pretreated at 800°C for 30 minutes under an N2 atmosphere, then cooled to 500°C for activity testing. The catalytic reaction was tested at a temperature range of 550-800°C. Test results showed a methane removal rate of 19.4% at 650°C, and a C2 product yield of 14.8%.

[0085] (5) Contrast effect

[0086] Compared with Example 1, Mg(NO3)2·6H2O was not added in step (3). The methane removal efficiency and C2 product selectivity of the prepared catalyst were significantly reduced, which may be due to the lack of Mg doping, resulting in a decrease in active sites in the catalyst and a poor OCM reaction effect.

Claims

1. A method for preparing a Mg / Ba dual-doped catalyst for catalytic combustion of methane, characterized by: The preparation method of the catalyst is as follows: (1) Synthesis of PMMA microspheres A 60-90°C potassium persulfate solution is added to a 60-90°C methyl methacrylate (MMA) solution for reaction, and after the reaction is completed, the solution is cooled to room temperature and filtered to obtain a uniform latex of monodispersed PMMA microspheres. (2) Synthesis of colloidal crystal template CCT A highly ordered PMMA-CCT template was obtained by centrifuging the homogenous latex of PMMA microspheres and drying the resulting solid mass; (3) Catalyst preparation The PMMA-CCT template is immersed in a mixture of lanthanum salt, cerium salt, barium salt and magnesium salt, and then filtered to obtain a PMMA-CCT mixture filled with metal oxide precursors. The mixture is dried and then calcined twice to obtain the target product. The salts of the lanthanum salt, cerium salt, magnesium salt and barium salt described in step (3) are in the form of nitrates, and the molar concentrations of the lanthanum salt, cerium salt, magnesium salt and barium salt in the mixed solution are 250-350 mmol / L, 250-350 mmol / L, 50-110 mmol / L and 20-60 mmol / L, respectively; In step (3), the first calcination temperature of the secondary calcination is 240-320°C, and the calcination time is 2-4 hours; the second calcination temperature of the secondary calcination is 700-850°C, and the calcination time is 3-5 hours.

2. The preparation method according to claim 1, wherein: The reaction in step (1) is carried out under stirring at a speed of 300-400 r min -1 ; The reaction temperature is 60~90°C, and the reaction time is 1~3h.

3. The preparation method according to claim 1, wherein: In step (1), the concentration of the potassium persulfate solution is 20-70 mmol / L, the mass concentration of the methyl methacrylate (MMA) solution is 10-30%, and the volume ratio of the potassium persulfate solution to the methyl methacrylate is 1:(2.5-5).

4. The preparation method according to claim 1, wherein: The filter paper used for filtration in step (1) has a size of 0.5 to 2 μm.

5. The preparation method according to claim 1, wherein: The drying temperature in step (2) is 50-70°C and the drying time is 35-40h.

6. The preparation method according to claim 1, wherein: The immersion time described in step (3) is 8 to 12 hours, the drying temperature is 50 to 80°C, and the drying time is 20 to 28 hours.

7. A Mg / Ba dual-doped catalyst for catalytic combustion of methane, characterized by: The catalyst is prepared by the method according to any one of claims 1 to 6.

8. The Mg / Ba dual-doped catalyst for catalytic combustion of methane according to claim 7, characterized in that: The catalyst uses La2Ce2O7 as a carrier, and the mass ratio of lanthanum oxide: cerium oxide: magnesium oxide: barium oxide in the catalyst is 10:8~10: (1~3): (0.5~2).

9. Use of the catalyst prepared by the method of claim 1 in removing methane from the atmosphere.

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