Pd / Co5Mn1Ox / NF-Al2O3 catalyst for efficient catalytic oxidation of methane and preparation method of Pd / Co5Mn1Ox / NF-Al2O3 catalyst

Abstract

The invention discloses a Pd / Co5Mn1Ox / NF-Al2O3 catalyst for efficient catalytic oxidation of methane and a preparation method of the Pd / Co5Mn1Ox / NF-Al2O3 catalyst, and belongs to the field of catalytic chemistry and environmental chemistry. The preparation method comprises the following steps: firstly, preparing nanoflower-shaped Al2O3 (NF-Al2O3) by adopting a hydrothermal method, then loading Co5Mn1Ox and Pd particles onto an NF-Al2O3 carrier by adopting an oxalic acid synchronous complexation method and an NaBH4 reduction method respectively, and finally, carrying out high-temperature roasting treatment at 550 DEG C to obtain the Pd / Co5Mn1Ox / NF-Al2O3 catalyst. The Pd / Co5Mn1Ox / NF-Al2O3 catalyst prepared by the invention is simple in preparation process and long in service life, shows excellent catalytic activity on methane catalytic oxidation, has excellent catalytic stability, and has a good application prospect in the field of air pollution control.

Description

Technical Field

[0001] The present invention relates to a Pd / Co5Mn1O catalyst for high-efficiency catalytic oxidation of methane. x / NF-Al2O3 catalyst and preparation method thereof, specifically, firstly preparing nano flower-like Al2O3 (NF-Al2O3) by hydrothermal method, and then using oxalic acid synchronous complexation method and NaBH4 reduction method to convert Co5Mn1O x The Pd / Co5Mn1O x / NF-Al2O3 catalyst, which exhibits good catalytic methane oxidation activity. It belongs to the field of catalytic chemistry and environmental chemistry. Background Art

[0002] Natural gas is widely used in industries, power plants, automobiles, etc. due to its advantages such as high energy density, abundant reserves and low pollution emissions. However, in actual application, it is often accompanied by unburned methane emissions. Although CO2 accounts for the largest proportion of greenhouse gases, the global warming potential of methane is about 25 times that of CO2 (WW Yang et al., Angew. Chem. Int. Ed., 2023, 62: e202217323.), which has caused serious harm to the atmospheric environment. Therefore, reducing and controlling methane emissions is crucial for the clean use of natural gas. Among many methods, methane catalytic oxidation is one of the most effective methods. However, the abnormally stable CH bond in the methane molecule poses a huge challenge to methane oxidation, resulting in the need for higher temperatures to eliminate methane. Supported Pd-based catalysts have been widely studied due to their high activity for methane oxidation (Z. Zhang et al., Appl. Surf. Sci., 2019, 494: 1044–1054.), but they still face problems such as poor low-temperature activity and easy 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 catalytic oxidation of methane.

[0003] γ-Al2O3 is widely used as a catalyst carrier due to its large specific surface area, excellent chemical stability and mechanical strength. 3+ (Al 3+ penta ) can be used as binding sites for anchoring metal atoms. 3+ pentaIn order to stabilize metals and improve the mass transfer effect between reactants and products, researchers synthesized Al2O3 nanosheets with a two-dimensional structure. However, these independent nanosheets tend to accumulate or aggregate into blocks at high temperatures, reducing the performance of the catalyst (L. Shi et al., Angew. Chem. Int. Ed., 2015, 54: 13994-13998.). Composite metal oxides have been greatly welcomed in the field of catalysis due to their low cost, good electron mobility and strong oxidizing properties. The synergy and interaction between metals are used to promote the redox cycle and effectively improve the performance of the catalyst. However, most of the composite metal oxides prepared at present have problems such as low specific surface area, unfavorable dispersion and loading of precious metals, and limited efficiency in eliminating methane at low temperature. Based on the above considerations, the present invention successfully prepared Pd / Co5Mn1O x / NF-Al2O3 catalyst, which 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] As far as we know, there is no literature or patent report on the use of Pd / Co5Mn1O x / NF-Al2O3 catalyst catalytic oxidation of methane. Therefore, the present invention is innovative, and the relevant research results are expected to provide a feasible method for efficient low-temperature elimination of methane. Summary of the invention

[0005] The purpose of the present invention is to prepare nano-flower-shaped Al2O3 (NF-Al2O3) by hydrothermal method, and then use oxalic acid synchronous complexation method and NaBH4 reduction method to convert Co5Mn1O x The Pd and Pd particles were loaded onto the NF-Al2O3 carrier and finally calcined to obtain Pd / Co5Mn1O x / NF-Al2O3 catalyst for catalytic methane oxidation reaction.

[0006] A catalyst for catalytic oxidation of methane and a preparation method thereof, the present invention specifically comprises 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 (WM Liu 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 then the obtained mixture was transferred to a 100 mL polytetrafluoroethylene-lined autoclave, heated at 180°C for 3 h, cooled to room temperature, filtered to collect the white precipitate, then 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 are dissolved in deionized water and mixed, and then the obtained solution is centrifuged, washed three times with ethanol and deionized water, and dried, such as in an oven at 80°C overnight; finally, the dried powder is calcined at 650°C for 4h to obtain the carrier;

[0009] When the molar ratio of Co(CH3COO)2·4H2O to Mn(CH3COO)2·4H2O was 1:1, 5:1 and 10:1 respectively, the obtained catalysts were Co1Mn1O x / NF-Al2O3、Co5Mn1O x / NF-Al2O3 and Co 10 Mn1O x / NF-Al2O3 support.

[0010] (3) Pd / Co5Mn1O x Preparation of NF-Al2O3: Add a certain amount of PdCl2 aqueous solution to polyvinyl alcohol solution and stir for 1 h to obtain a suspension; then add a certain amount of carrier such as Co5Mn1O x / NF-Al2O3 support, after stirring in an ice-water bath for 30 minutes, quickly add a certain amount of NaBH4 aqueous solution and stir for 12 hours. Filter the mixed solution, dry it in an oven at 80°C for 24 hours, and calcine it at 550°C for 6 hours under air conditions.

[0011] In addition, Pd / Co1Mn1O x / NF-Al2O3、Pd / Co 10 Mn1O xThe preparation process of the comparative catalysts such as Pd / Co5Mn1O x The preparation process of / NF-Al2O3 is the same.

[0012] The Pd loading in the above catalyst is 2.0-2.1 wt% (mass percentage).

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

[0014] Catalyst performance evaluation:

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

[0016] The catalyst of the invention has a simple preparation process, exhibits excellent catalytic activity and stability for methane oxidation, and has good application prospects in the field of methane catalytic oxidation. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is the XRD spectrum of the prepared catalyst.

[0018] Figure 2 Figures (A), (B) and (C) are SEM images of the prepared NF-Al2O3 support. Figures (D) and (E) are SEM images of Pd / Co5Mn1O x TEM images of Pd / Co5Mn1O / NF-Al2O3 catalysts. Figures (F) and (G) are TEM images of Pd / Co5Mn1O / NF-Al2O3 catalysts. x Elemental scanning patterns 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, the reaction conditions are 1 vol% CH4 + 20 vol% O2 + N2 (balance gas), and the space velocity is 20000 mL / (g·h).

[0020] Figure 4 Pd / Co5Mn1O x / catalytic stability of NF-Al2O3 catalyst. DETAILED DESCRIPTION

[0021] In order to further illustrate the present invention, the following embodiments are described in detail, but the present 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 (WM Liu 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 deionized water, and then the obtained mixture was transferred to a 100 mL polytetrafluoroethylene-lined autoclave, heated at 180°C for 3 h, cooled to room temperature, and the white precipitate collected by filtration was dried at 80°C for 12 h, and finally calcined at 500°C for 2 h.

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

[0025] (3) Pd / Co5Mn1O x Preparation of NF-Al2O3: Add a certain amount of PdCl2 aqueous solution (1.0 g / L) to polyvinyl alcohol (PVA; 2.0 g / L, Pd / PVA mass ratio = 1.0:1.2) solution and stir for 1 hour; then add a certain amount (0.5 g) of carrier to the above suspension and stir in an ice-water bath for 30 minutes. Then quickly add a certain amount of NaBH4 aqueous solution (2.0 g / L; Pd:NaBH4 = 1:5 mol / mol) to the above precursor solution and stir for 12 hours. Filter the mixed solution, dry it in an oven at 80°C for 24 hours, and calcine it at 550°C for 6 hours.

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

Claims

1. A Pd / Co5Mn1O for efficient catalytic oxidation of methane x / A method for preparing NF-Al2O3 catalyst, characterized in that: The following steps are involved: (1) Co5Mn1O x Preparation of / NF-Al2O3: Co(CH3COO)2·4H2O, Mn(CH3COO)2·4H2O, C2H2O4·2H2O and NF-Al2O3 are dissolved in deionized water and mixed, and then the obtained solution is centrifuged, washed three times with ethanol and deionized water, and dried, such as in an oven at 80°C overnight; finally, the dried powder is calcined at 650°C for 4h to obtain the carrier; When the molar ratio of Co(CH3COO)2·4H2O to Mn(CH3COO)2·4H2O was 1:1, 5:1 and 10:1 respectively, the obtained catalysts were Co1Mn1O x / NF-Al2O3、Co5Mn1O x / NF-Al2O3 and Co 10 Mn1O x / NF-Al2O3 support; (2) Pd / Co5Mn1O x Preparation of NF-Al2O3: Add a certain amount of PdCl2 aqueous solution to polyvinyl alcohol solution and stir for 1 h to obtain a suspension; then add a certain amount of carrier such as Co5Mn1O x / NF-Al2O3 support, after stirring in an ice-water bath for 30 minutes, quickly add a certain amount of NaBH4 aqueous solution and stir for 12 hours. Filter the mixed solution, dry it in an oven at 80°C for 24 hours, and calcine it at 550°C for 6 hours under air conditions.

2. The method according to claim 1, characterized in that The Pd loading in the catalyst prepared in step (2) is 2.0-2.1 wt%.

3. The catalyst prepared according to the method of claim 1 or 2.

4. Use of the catalyst prepared by the method according to claim 1 or 2 for catalytic methane oxidation.

5. According to the use of claim 4, 50 mg of catalyst (particle size of 40-60 mesh) is weighed and loaded into a quartz fixed reactor, and a reaction gas composed of 1 vol% CH4 + 20 vol% O2 + N2 (balance gas) is introduced into the fixed reactor at an air velocity of 20000 mL / (g·h), Pd / Co5Mn1O x T of / NF-Al2O3 50％ (reaction temperature required for methane conversion to reach 50%) and T 90％ (reaction temperature required for methane conversion rate to reach 90%) were 285℃ and 323℃ respectively; the prepared Pd / Co5Mn1O x / NF-Al2O3 catalyst can still maintain good catalytic stability after 40h of methane catalytic oxidation reaction.

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