A highly efficient catalytic oxidation of methane using Pd / Co5Mn1O x / NF-Al2O3 catalyst and its preparation method

Abstract

Pd / Co5Mn1O catalyst for efficient catalytic oxidation of methane x The application relates to a Pd / Co5Mn1O catalyst for efficient catalytic oxidation of methane and a preparation method thereof, and belongs to the fields of catalytic chemistry and environmental chemistry. Nano-flower-shaped Al2O3 (NF-Al2O3) is prepared by a hydrothermal method, Co5Mn1O and Pd particles are loaded onto the NF-Al2O3 carrier by adopting an oxalic acid synchronous complexing method and a NaBH4 reduction method respectively, and finally, the Pd / Co5Mn1O / NF-Al2O3 catalyst is obtained by high-temperature calcination treatment at 550 DEG C. x The Pd / Co5Mn1O / NF-Al2O3 catalyst prepared by the application has the advantages of simple preparation process, long service life, excellent catalytic activity for catalytic oxidation of methane, excellent catalytic stability and good application prospect in the field of atmospheric pollution control. x x The Pd / Co5Mn1O / NF-Al2O3 catalyst prepared by the application has the advantages of simple preparation process, long service life, excellent catalytic activity for catalytic oxidation of methane, excellent catalytic stability and good application prospect in the field of atmospheric pollution control.​

Description

Technical Field

[0001] This invention relates to a Pd / Co5Mn1O4 catalyst for efficient catalytic oxidation of methane. x The / NF-Al2O3 catalyst and its preparation method are described. Specifically, nano-flower-like Al2O3 (NF-Al2O3) is first prepared by hydrothermal method, and then Co5Mn1O3 is synthesized by simultaneous complexation with oxalic acid and reduction with NaBH4, respectively. x Pd particles were loaded onto an NF-Al2O3 support, and then Pd / Co5Mn1O was prepared by high-temperature calcination. x The / NF-Al2O3 catalyst exhibits excellent catalytic activity for methane oxidation. It belongs to the fields of catalytic chemistry and environmental chemistry. Background Technology

[0002] Natural gas is widely used in industry, power plants, and automobiles due to its advantages such as high energy density, abundant reserves, and low pollution emissions. However, its practical application is often accompanied by the emission of unburned methane. Although CO2 accounts for the largest share of greenhouse gases, methane's global warming potential is approximately 25 times that of CO2 (WW Yang et al., Angew. Chem. Int. Ed., 2023, 62:e202217323.), causing serious harm to the atmospheric environment. Therefore, reducing and controlling methane emissions is crucial for the clean utilization of natural gas. Among many methods, catalytic oxidation of methane is one of the most effective. However, the exceptionally stable CH bond in the methane molecule poses a significant challenge to methane oxidation, requiring higher temperatures to eliminate methane. Supported Pd-based catalysts have been extensively studied due to their high activity in methane oxidation (Z. Zhang et al., Appl. Surf. Sci., 2019, 494: 1044–1054.), but they still face problems such as poor activity at low temperatures and susceptibility to poisoning by H2O and SO2 (H. Xiong et al., Nat. Catal., 2021, 4: 830–839.). Therefore, there is an urgent need to develop catalysts with high activity and stability at low temperatures for the catalytic oxidation of methane.

[0003] γ-Al₂O₃ is widely used as a catalyst support due to its large specific surface area, excellent chemical stability, and mechanical strength. It has been reported that the unsaturated five-coordinated Al₂O₃... 3+ (Al 3+ penta Al can serve as a binding site for anchoring metal atoms, in order to better utilize Al 3+ pentaTo stabilize metals and improve mass transfer between reactants and products, researchers synthesized Al₂O₃ nanosheets with a two-dimensional structure. However, these individual nanosheets often aggregate or clump together at high temperatures, reducing catalyst performance (L. Shi et al., Angew. Chem. Int. Ed., 2015, 54: 13994-13998). Composite metal oxides have been widely welcomed in the field of catalysis due to their low cost, good electron mobility, and strong oxidizing properties. They utilize the synergistic effects and interactions between metals to promote redox cycles and effectively improve catalyst performance. However, most currently prepared composite metal oxides suffer from problems such as low specific surface area, unfavorable dispersion and loading of noble metals, and limited efficiency in eliminating methane at low temperatures. Based on these considerations, this invention successfully prepared Pd / Co₅Mn₁O₃. x The / NF-Al2O3 catalyst can efficiently catalyze the elimination of methane, and compared with the traditional Pd / Al2O3 catalyst, this catalyst exhibits higher catalytic activity and better stability.

[0004] To the best of our knowledge, there are currently no literature or patent reports on the use of Pd / Co5Mn1O x There have been previous reports on the catalytic oxidation of methane using / NF-Al2O3 catalysts. Therefore, this invention is innovative, and the related research results are expected to provide a feasible method for the efficient low-temperature elimination of methane. Summary of the Invention

[0005] The purpose of this invention is to first prepare nano-flower-like Al2O3 (NF-Al2O3) using a hydrothermal method, and then to synthesize Co5Mn1O3 using both the oxalic acid simultaneous complexation method and the NaBH4 reduction method. x Pd particles were loaded onto an NF-Al2O3 support, and finally Pd / Co5Mn1O was obtained by high-temperature calcination. x / NF-Al2O3 catalyst is used to catalyze the oxidation of methane.

[0006] A catalyst for the catalytic oxidation of methane and a method for its preparation, the present invention specifically includes the following steps:

[0007] (1) Preparation of nanoflower-like Al2O3, i.e., NF-Al2O3: NF-Al2O3 was synthesized according to the method reported in the literature (WMLiu et al., Appl. Catal. B, 2021, 292: 120171.). The specific steps are as follows: Al(NO3)3·9H2O, K2SO4 and CO(NH2)2 were dissolved in an appropriate amount of deionized water, and the resulting mixture was transferred to a 100 mL autoclave with a polytetrafluoroethylene liner. The mixture was heated at 180 °C for 3 h, cooled to room temperature, filtered and collected the white precipitate, dried at 80 °C for 12 h, and finally calcined at 500 °C for 2 h.

[0008] (2) Co5Mn1O x Preparation of / NF-Al2O3: Co(CH3COO)2·4H2O, Mn(CH3COO)2·4H2O, C2H2O4·2H2O and NF-Al2O3 were dissolved in deionized water and mixed. The resulting solution was then centrifuged, washed three times with ethanol and deionized water, and dried overnight in an oven at 80°C. Finally, the dried powder was calcined at 650°C for 4 hours to obtain the support.

[0009] When the molar ratios of added Co(CH3COO)2·4H2O and Mn(CH3COO)2·4H2O are 1:1, 5:1, and 10:1, the resulting catalysts are Co1Mn1O, respectively. x / NF-Al2O3、Co5Mn1O x / NF-Al2O3 and Co 10 Mn1O x / NF-Al2O3 carrier.

[0010] (3)Pd / Co5Mn1O x Preparation of / NF-Al2O3: A certain amount of PdCl2 aqueous solution was added to a polyvinyl alcohol solution and stirred for 1 hour to obtain a suspension; then a certain amount of support such as Co5Mn1O was added to the above suspension. x The / NF-Al2O3 support was stirred in an ice-water bath for 30 min, then a certain amount of NaBH4 aqueous solution was rapidly added, and the mixture was stirred for 12 h. The mixed solution was filtered, dried in an oven at 80 °C for 24 h, and calcined at 550 °C for 6 h under air conditions.

[0011] Additionally, Pd / Co1Mn1O x / NF-Al2O3、Pd / Co 10 Mn1O xThe preparation processes of comparative catalysts such as / NF-Al2O3, Pd / NF-Al2O3, and Pd / Com-Al2O3 (commercial Al2O3) are similar to those of Pd / Co5Mn1O x The preparation process of / NF-Al2O3 is the same.

[0012] The Pd loading in the above catalyst is 2.0 to 2.1 wt%.

[0013] The catalyst obtained in this invention is used for the catalytic oxidation of methane to carbon dioxide and water.

[0014] Catalyst performance evaluation:

[0015] In the methane oxidation activity evaluation system, the reaction gas composition was 1 vol% CH4 + 20 vol% O2 + N2 (equilibrium gas), the space velocity was 20000 mL / (g·h), and the optimal catalyst was Pd / Co5Mn1O. x / NF-Al2O3 of T 50％ (The reaction temperature required for methane conversion to reach 50%) and T 90％ The reaction temperatures required to achieve a 90% methane conversion rate are 285℃ and 323℃, respectively, indicating that the catalyst has excellent catalytic activity and long-term stability.

[0016] The catalyst of this invention has a simple preparation process and exhibits excellent catalytic activity and stability for methane oxidation, showing promising application prospects in the field of methane catalytic oxidation. Attached Figure Description

[0017] Figure 1 The image shows the XRD pattern of the prepared catalyst.

[0018] Figure 2 Figures (A), (B), and (C) show SEM images of the prepared NF-Al₂O₃ support. Figures (D) and (E) show Pd / Co₅Mn₁O₃... x TEM images of the / NF-Al2O3 catalyst, Figures (F) and (G) show Pd / Co5Mn1O x Elemental scan pattern of / NF-Al2O3 catalyst.

[0019] Figure 3 Pd / Co5Mn1O x The catalytic activity of / NF-Al2O3 and the comparative catalyst for the catalytic oxidation of methane was compared under the following reaction conditions: 1 vol% CH4 + 20 vol% O2 + N2 (equilibrium gas) and space velocity of 20000 mL / (g·h).

[0020] Figure 4 Pd / Co5Mn1O xCatalytic stability of / NF-Al2O3 catalyst. Detailed Implementation

[0021] To further illustrate the present invention, the following detailed description is provided with reference to embodiments, but the invention is not limited to the following embodiments.

[0022] Example 1

[0023] (1) Preparation of NF-Al2O3: NF-Al2O3 was synthesized according to the method reported in the literature (WMLiu et al., Appl. Catal. B, 2021, 292: 120171.). The specific steps are as follows: 1.51 g Al(NO3)3·9H2O, 0.70 g K2SO4 and 0.50 g CO(NH2)2 were dissolved in 80 mL of deionized water. The resulting mixture was then transferred to a 100 mL autoclave with a polytetrafluoroethylene liner and heated at 180 °C for 3 h. After cooling to room temperature, the collected white precipitate was filtered and dried at 80 °C for 12 h. Finally, it was calcined at 500 °C for 2 h.

[0024] (2) Co5Mn1O x Preparation of / NF-Al2O3: 0.4 mmol Co(CH3COO)2·4H2O, 0.08 mmol Mn(CH3COO)2·4H2O, 0.72 mmol C2H2O4·2H2O, and 0.2979 g NF-Al2O3 were dissolved in 25 mL of deionized water, respectively. The resulting solutions were then centrifuged, washed three times with ethanol and deionized water, and dried overnight in an oven at 80 °C. Finally, the obtained solid powder was calcined at 650 °C for 4 h.

[0025] (3)Pd / Co5Mn1O x Preparation of / NF-Al2O3: A certain amount of PdCl2 aqueous solution (1.0 g / L) was added to a polyvinyl alcohol (PVA; 2.0 g / L, Pd / PVA mass ratio = 1.0:1.2) solution and stirred for 1 h. Then, a certain amount (0.5 g) of carrier was added to the above suspension and stirred in an ice-water bath for 30 min. Then, a certain amount of NaBH4 aqueous solution (2.0 g / L; Pd:NaBH4 = 1:5 mol / mol) was rapidly added to the above precursor solution and stirred for 12 h. The mixed solution was filtered, dried in an oven at 80 °C for 24 h, and calcined at 550 °C for 6 h.

[0026] Pd / Co5Mn1O x / NF-Al2O3 catalyst was used for the catalytic oxidation of methane. 50 mg of catalyst (particle size 40–60 mesh) was weighed and loaded into a quartz stationary reactor. A reaction gas with a composition of 1 vol% CH4 + 20 vol% O2 + N2 (equilibrium gas) was introduced into the reactor at a space velocity of 20000 mL / (g·h). Pd / Co5Mn1O x / NF-Al2O3 of T 50％ (The reaction temperature required for methane conversion to reach 50%) and T 90％ The reaction temperatures required to achieve a 90% methane conversion rate are 285℃ and 323℃, respectively, indicating that the catalyst has excellent catalytic activity and excellent catalytic stability during the methane oxidation reaction at 320℃ for 40 hours.

Claims

1. A method for preparing a Pd / Co5Mn1O x / NF-Al2O3 catalyst for efficient catalytic oxidation of methane, characterized by, comprising the steps of: (1) Co5Mn1O x Preparation of Co5Mn1O / NF-Al2O3: Co(CH3COO)2-4H2O, Mn(CH3COO)2-4H2O, C2H2O4-2H2O and NF-Al2O3 were dissolved in deionized water and mixed, and then the obtained solution was centrifuged, washed with ethanol and deionized water for three times, and dried in an oven at 80 °C overnight; finally, the dried powder was calcined at 650 °C for 4 h to obtain the carrier; The molar ratio of Co(CH3COO)2-4H2O and Mn(CH3COO)2-4H2O added is 5:1, and the obtained catalyst carrier is Co5Mn1O x / NF-Al2O3, NF-Al2O3 is nanoflower-like Al2O3; (2) Pd / Co5Mn1O x Preparation of Pd / Co5Mn1O / NF-Al2O3: a certain amount of PdCl2 aqueous solution was added to a polyvinyl alcohol solution, stirred for 1 h to obtain a suspension; then a certain amount of Co5Mn1O x / NF-Al2O3 support was added to the above suspension, stirred in an ice water bath for 30 min, then a certain amount of NaBH4 aqueous solution was quickly added, and stirred for 12 h; the mixed solution was filtered, dried in an oven at 80°C for 24 h, and calcined at 550°C for 6 h under air conditions; The loading of Pd in the catalyst prepared in step (2) is 2.0-2.1 wt%.

2. Catalyst prepared according to the process of claim 1.

3. Use of the catalyst prepared according to the process of claim 1 for catalyzing the oxidation of methane.

4. According to the application described in claim 3, 50 mg of catalyst with a particle size of 40-60 mesh is weighed and placed in a quartz stationary reactor. A reaction gas with a composition of 1 vol% CH4 + 20 vol% O2 + N2 is introduced into the stationary reactor at a space velocity of 20000 mL / (g∙h). The Pd / Co5Mn1O x / NF-Al2O3 of T 50% and T 90% The temperatures were 285℃ and 323℃, respectively.

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