A PdMOF catalyst for H2 low-temperature catalysis and a preparation method thereof
By preparing PdMOF catalysts, the problem of poor activity stability of Pd catalysts was solved, and highly dispersed Pd nanoparticles were prepared, which improved catalytic activity and lifespan and reduced costs.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- CHINA STATE SHIPBUILDING CORP LTD RESEARCH INSTITUTE 719
- Filing Date
- 2023-05-17
- Publication Date
- 2026-06-23
AI Technical Summary
Existing Pd catalysts exhibit poor activity stability during low-temperature catalysis, resulting in a significant decrease in catalytic activity over time, making them unsuitable for long-term use.
PdMOF catalysts were synthesized under specific conditions using 1,2,4,5-benzenetetracarboxylic acid and ammonium chloropalladate. By controlling the reaction temperature and reduction method, highly dispersed Pd nanoparticles were prepared, avoiding agglomeration and improving the catalyst's active lifetime.
This improved the activity stability and catalytic activity of the Pd catalyst, reduced the noble metal loading, lowered the cost, and maintained high catalytic performance.
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Figure CN116571238B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of novel MOF adsorption catalyst synthesis, specifically to a PdMOF catalyst for low-temperature H2 catalysis and its preparation method. Background Technology
[0002] Hydrogen is a flammable gas and a clean energy source. Our research on hydrogen reactions, especially its further study on low-temperature catalytic reactions, is of great significance to the future energy field. For example, low-temperature reactions that convert chemical energy into electrical energy will help the further development of new energy batteries. Furthermore, nuclear power plant reactors produce or leak a certain amount of hydrogen. If this hydrogen is not depleted quickly, the accumulated hydrogen concentration can easily lead to an explosion, causing a serious nuclear accident. Low-temperature catalytic combustion of H2 is beneficial for nuclear power plants to deplete hydrogen under low-energy operating conditions, ensuring the safety of nuclear power plants.
[0003] Currently, low-temperature catalytic combustion of H2 technology is a popular research direction, mentioned in many scientific papers. For example, Kramer et al. studied the low-temperature catalytic combustion performance of hydrogen using Pd / γ-Al2O3 as a catalyst. The low temperature in this paper refers to a reaction temperature where the combustion conditions do not exceed 250℃, and the activity temperature is still not ideal. Zhou Ying from Jiangsu University mentioned the catalytic activity of another noble metal, Pt-Al2O3, in her master's thesis, which can achieve complete hydrogen conversion below 100℃, but the cost of Pt is higher than that of Pd. Patent application document with publication number CN 113908831 A provides a hydrophobic catalyst for low-temperature catalytic combustion of hydrogen and its preparation method. The preparation process of 0.1% Pd / Al2O3 described in the specification is as follows: 1.0 mL of palladium precursor aqueous solution (containing 0.001 g Pd) is added to 0.999 g Al2O3, appropriate water is added to make it uniform, and then it is placed in a drying oven at 110℃ for 12 h. The catalyst was allowed to react for 3 hours in a 0.5 mol / L NaBH4 solution to fully reduce it. 1 ml of deionized water was dissolved in 100 ml of anhydrous ethanol. Then, 1 g of the prepared original catalyst was weighed and added to the ethanol solution containing deionized water. The reaction was allowed to proceed at 25°C for 2 hours. The soaked catalyst was then washed with deionized water and dried in a drying oven at 80°C for 8 hours. The resulting catalyst was 0.1% Pd / Al2O3, with a T99 as low as 5°C, exhibiting a significant low-temperature advantage. However, the conversion rate decreased to 64.79% after 2 hours of continuous reaction, 31.27% after 6 hours, and even 4.73% after 100 hours, indicating a relatively short active lifespan. The catalyst's activity stability deteriorated over time, making it unsuitable for long-term use. Summary of the Invention
[0004] The present invention aims to provide a PdMOF catalyst for low-temperature H2 catalysis and its preparation method, so as to solve the technical problem of poor activity and stability of existing Pd catalysts.
[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:
[0006] A method for preparing a PdMOF catalyst for low-temperature H2 catalysis includes the following steps:
[0007] (1) Dissolve 1,2,4,5-benzenetetracarboxylic acid and ammonium chloropalladate in distilled water in a reaction vessel at a molar ratio of 1:5 at room temperature.
[0008] (2) The solution obtained in step (1) is heated at 100-140°C for 4-6 hours to obtain a solid product;
[0009] (3) The solid product obtained in step (2) is washed and dried to obtain a powdered product;
[0010] (4) The powdered product obtained in step (3) is heated to 600-650°C at a heating rate of 1-10°C / min under nitrogen atmosphere protection and held for 2 hours;
[0011] (5) The powder obtained from the heating reaction in step (4) is subjected to a reduction reaction to obtain the PdMOF catalyst.
[0012] Furthermore, the washing process described in step (3) involves washing three times with water and acetone respectively.
[0013] Furthermore, the heating rate in step (4) is 1–2 °C / min.
[0014] Further, the reduction reaction in step (5) is as follows: the powder obtained from the heating reaction in step (4) is dispersed in deionized water, and NaBH4 solution is added dropwise for reduction until no microbubbles are generated. After filtration and drying, the PdMOF catalyst can be obtained.
[0015] Furthermore, the concentration of the NaBH4 solution is 0.1 mol / L.
[0016] This invention also protects PdMOF catalysts prepared using the above-described preparation method.
[0017] Compared with the prior art, the present invention has the following beneficial effects:
[0018] 1. The PdMOF catalyst prepared by this invention is a single-metal center catalyst. It uses a specific organic compound, 1,2,4,5-benzenetetracarboxylic acid, and ammonium chloropalladate to generate a MOF structure under specific reaction conditions. This structure can better disperse and fix the active center Pd, so that the Pd active center will not agglomerate into large particles during the slow carbonization process, and will not cause a sharp decline in catalytic activity during the reaction, thereby improving the active life of the catalyst.
[0019] 2. The Pd particles prepared by the method of this invention can form small nanoparticles, allowing the active Pd centers to be better exposed to contact with the reactant gases, thus improving catalytic activity. High dispersion enhances catalytic activity while also reducing the loading of the precious metal Pd, thereby lowering catalyst costs. Attached Figure Description
[0020] Figure 1 The catalytic activity-temperature graphs of Pd catalysts prepared using different supports are shown.
[0021] Figure 2 The catalytic activity-reaction time curves of Pd catalysts prepared with different supports at 60 °C are shown.
[0022] Figure 3 The catalytic activity-temperature graphs of Pd / C catalysts prepared by different reduction methods are shown.
[0023] Figure 4 The bar chart shows the catalytic activity of Pd / C catalysts prepared with different carbonization heating rates at 60 °C. Detailed Implementation
[0024] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described below in conjunction with various embodiments and accompanying drawings. The implementation of the present invention includes, but is not limited to, the following embodiments.
[0025] Example 1
[0026] The preparation process of the PdMOF catalyst provided in this embodiment is as follows:
[0027] (1) Dissolve 0.4 mol of 1,2,4,5-benzenetetracarboxylic acid (BTEC) and 0.20 mol of ammonium chloropalladate ((NH4)2PdCl4) in 500 mL of distilled water at room temperature by stirring.
[0028] (2) The above solution was placed in a reaction vessel with a polytetrafluoroethylene liner and heated at about 120°C for 4 hours to obtain a solid product.
[0029] (3) The obtained solid was washed with water and acetone three times at room temperature and dried to obtain a powdered product.
[0030] (4) The powder obtained above was heated to 600°C at a heating rate of 2°C / min under N2 protection for 2 hours.
[0031] (5) Disperse the above powder into 200 mL of deionized water, add 0.1 mol / L NaBH4 solution dropwise for reduction until no small bubbles are generated, and obtain the PdMOF catalyst, named Pd / C.
[0032] Catalyst reference standards with the same Pd content were prepared using an impregnation method: Pd / C-commercial, Pd / SBA-15, and Pd / Al2O3, for use in control experiments. The preparation process involved impregnating activated carbon, SBA-15, and Al2O3 in a PdCl2 solution, followed by impregnation with a mixture of H2 and N2 gas (V...). H2 :V N2 At a ratio of 1:5, reduction was carried out at 450℃ for 1 h to obtain Pd / C-commercial, Pd / SBA-15 and Pd / Al2O3 catalyst reference standards.
[0033] like Figure 1 The figure shows the catalytic activity-temperature curves of Pd / C, Pd / C-commercial, Pd / SBA-15, and Pd / Al2O3 catalysts for low-temperature H2 catalysis. It is easy to see that at the same reaction temperature, Pd / C has a higher conversion rate, that is, it has better catalytic activity.
[0034] like Figure 2 The figure shows the catalytic activity-reaction time curves for Pd / C, Pd / C-commercial, Pd / SBA-15, and Pd / Al2O3 catalysts at 60℃ for low-temperature H2 catalysis. Due to the carbonization of the PdMOF structure, Pd nanoparticles are well encapsulated by the carbonized structure, resulting in good activity stability for the Pd / C catalyst. After 100 hours of continuous stability testing, the catalyst still maintains high catalytic activity. In contrast, the activity of Pd / C-commercial and Pd / Al2O3 catalysts supported on ordinary commercial activated carbon decreases rapidly. During long-term reactions, Pd nanoparticles aggregate, reducing the dispersion of active centers and leading to a decline in catalytic activity. The catalytic activity of Pd / SBA-15 also decreases relatively quickly. Compared with Pd / C-commercial catalyst, Pd / SBA-15 has slightly better catalytic activity stability because some Pd nanoparticles are relatively stable in the SBA-15 channel and will not agglomerate due to long-term reaction, thus reducing the decay of catalytic activity. However, its activity decrease rate is still significantly greater than that of Pd / C.
[0035] Example 2
[0036] This embodiment, based on Example 1, explores the reduction method in step (5). First, it investigates the concentration of NaBH4 solution, supplementing the examples with 0.5 mol / L and 1.0 mol / L NaBH4 solutions. It also explores the reduction method using H2. Finally, the catalyst prepared in this embodiment is named Pd / C-0.1, the catalysts prepared with 0.5 mol / L and 1.0 mol / L NaBH4 solutions are named Pd / C-0.5 and Pd / C-1, and the catalyst prepared by H2 reduction is named Pd / C-H2. The results are as follows... Figure 3 As shown, the catalytic activity-temperature curves of Pd / C-0.1, Pd / C-0.5, Pd / C-1, and Pd / C-H2 catalysts for low-temperature H2 catalysis are presented. It is easy to see that Pd / C-0.1, which is reduced with 0.1 mol / NaBH4 solution, has higher catalytic activity. This may be because the mild reduction method can prevent the aggregation of Pd active components, thus better dispersing the active components and improving catalytic activity.
[0037] Example 3
[0038] This embodiment further explores the heating rate in step (4) based on Example 1. Catalysts prepared at heating rates of 1℃ / min, 2℃ / min, 5℃ / min, 10℃ / min, and 20℃ / min are designated as Pd / C-1C, Pd / C-2C, Pd / C-5C, Pd / C-10C, and Pd / C-20C, respectively. Figure 4 As shown, this embodiment compares the catalytic activity of Pd / C prepared at different carbonization heating rates at a reaction temperature of 60°C. Figure 4 It can be seen that excessively rapid carbonization heating rates lead to a decrease in the catalytic activity of the prepared Pd / C. During the carbonization of MOF into carbon materials, an excessively rapid carbonization rate can cause the pore structure to collapse easily, resulting in a reduction in the specific surface area and pore volume of the carbon support, thus decreasing the catalyst activity. At a reaction temperature of 125℃, Pd / C-1C and Pd / C-2C exhibit the highest catalytic activity, with Pd / C-5C, Pd / C-10C, and Pd / C-20C showing a decreasing trend in catalytic activity.
[0039] The above embodiments are merely one of the preferred embodiments of the present invention and should not be used to limit the scope of protection of the present invention. Any modifications or refinements made to the main design concept and spirit of the present invention that are not of substantial significance, but solve the same technical problem as the present invention, should be included within the scope of protection of the present invention.
Claims
1. A method for preparing a PdMOF catalyst for low-temperature H2 catalysis, characterized in that, Includes the following steps: (1) Dissolve 1,2,4,5-benzenetetracarboxylic acid and ammonium chloropalladate in distilled water in a reaction vessel at a molar ratio of 1:5 at room temperature; (2) The solution obtained in step (1) is heated at 100~140℃ for 4~6h to obtain a solid product; (3) Wash and dry the solid product obtained in step (2) to obtain a powdered product; (4) The powdered product obtained in step (3) is heated to 600-650°C at a heating rate of 1-2°C / min under nitrogen atmosphere protection and held for 2 hours; (5) The powder obtained from the heating reaction in step (4) is subjected to a reduction reaction. The reduction reaction is as follows: the powder obtained from the heating reaction in step (4) is dispersed in deionized water, and 0.1 mol / L NaBH4 solution is added dropwise for reduction until no micro bubbles are generated. After filtration and drying, PdMOF catalyst can be obtained.
2. The preparation method according to claim 1, characterized in that, The washing process described in step (3) involves washing three times with water and acetone respectively.
3. A PdMOF catalyst prepared by the preparation method described in claim 1 or 2.