Preparation method of trace Co-doped Pd (at) Pt mesoporous core-shell catalyst for ammoxidation

Abstract

The invention discloses a preparation method of a trace Co-doped Pd-Pt mesoporous core-shell catalyst for ammoxidation. The preparation method comprises the following steps: firstly, fully dissolving sodium chloropalladate, potassium chloroplatinate, cobalt acetate and polyether F127 in ultrapure water to obtain a light yellow solution; adding a hydrogen chloride solution into the obtained light yellow solution to obtain a light yellow solution; and adding ascorbic acid into the light yellow solution, carrying out ultrasonic treatment on the whole solution system at 35 DEG C for 3 hours, centrifuging, washing and drying to obtain the trace Co-doped Pd-Pt mesoporous core-shell catalyst. The catalyst has high atom utilization rate and excellent structural stability; the material has high specific surface area, rich active sites and accessible pores, and is beneficial to effective quality and electron transfer; the doping of a trace amount of Co can promote electron transfer, so that the catalytic activity is further improved. The catalyst not only has remarkable ammonia oxidation catalytic performance, but also is good in stability and simple in preparation process.

Description

Technical Field

[0001] The invention relates to a method for preparing a trace Co-doped Pd@Pt mesoporous core-shell catalyst for ammonia oxidation, and belongs to the field of novel functional nanomaterials. Background Art

[0002] Ammonia has become an important clean, efficient and sustainable fuel worldwide due to its wide availability, zero carbon emissions and high energy density. As a promising fuel, it has been demonstrated that ammonia can be directly used as the anode fuel of ammonia fuel cells. However, as the core of the anode of ammonia fuel cells, the ammonia oxidation reaction (AOR) is currently facing the challenges of complex kinetics and slow reaction rate. In practical applications, a large overpotential is required to drive the reaction, which has become a bottleneck restricting its widespread application. Therefore, there is an urgent need to find efficient catalysts to increase the AOR reaction rate.

[0003] Platinum (Pt) catalysts are widely considered to be the most promising AOR catalysts. Among them, Pt-based core-shell catalysts have the advantages of high atomic utilization and stable structure, and are a promising high-performance AOR catalyst. The addition of palladium (Pd) can change the electronic structure of Pt, so that it has a suitable coupled d-band orbital center structure, thereby optimizing the adsorption and desorption free energy of nitrogen active species (*N) during the AOR reaction, greatly promoting the AOR performance of Pt-based core-shell catalysts. However, the traditional Pd@Pt core-shell catalysts hinder the contact between the reactants and the core due to the lack of effective nanopore structure, which seriously affects the mass transfer process of the catalyst. Mesoporous core-shell catalysts not only have the high catalytic activity of the core-shell structure, but also have the unique advantages of the mesoporous structure, which exposes more active sites through its enlarged surface area, thereby promoting catalytic efficiency. In addition, trace element doping is also a promising strategy to improve catalytic activity, which can further increase the active sites and promote electron transfer. Therefore, a simple and efficient method is urgently needed to develop and design trace element doped Pd@Pt mesoporous core-shell catalysts.

[0004] The methods reported so far for preparing trace element doped Pd@Pt mesoporous core-shell catalysts still have the disadvantages of complex preparation process, high cost, poor AOR performance, etc., which are not conducive to their practical application. In addition, the research on trace element doped Pd@Pt mesoporous core-shell catalysts is still limited to a few types. Therefore, it is necessary to develop novel and simple preparation methods for trace element doped Pd@Pt mesoporous core-shell catalysts with high AOR catalytic performance. Summary of the invention

[0005] In order to avoid the shortcomings of the prior art, the present invention provides a method for preparing a trace Co-doped Pd@Pt mesoporous core-shell catalyst.

[0006] One of the purposes of the present invention is to provide a novel trace Co-doped Pd@Pt mesoporous core-shell catalyst.

[0007] The second object of the present invention is to provide a simple and easy one-step reduction method.

[0008] A third object of the present invention is to provide a catalyst having significant and efficient AOR catalytic activity.

[0009] The trace Co-doped Pd@Pt and Pd@Pt mesoporous core-shell catalysts prepared by the present invention are prepared by a one-step reduction method using sodium chloropalladate (Na2PdCl4), potassium chloroplatinate (K2PtCl4), cobalt acetate (Co(CH3COO)2), hydrogen chloride (HCl) solution, polyether F127 (F127) and ascorbic acid (AA) as raw materials, and the preparation process includes the following specific steps: 1. First, fully dissolve 10-20 mg of Na2PdCl4, 40-60 mg of K2PtCl4, 0-0.6 mg of Co(CH3COO)2, and 90-130 mg of F127 in 8-10 mL of ultrapure water to obtain a light yellow solution; 2. Add 2-4 mL of HCl solution to the light yellow solution obtained in step 1 to obtain a light yellow solution; 3. Add 200-300 mg of AA to the light yellow solution obtained in step 2, and ultrasonically treat the entire solution system at 25-45 °C for 2-4 hours to obtain a black solution; 4. Centrifuge the black solution obtained in step 3 at 10,000 rpm for 5 minutes using a high-speed centrifuge, remove the supernatant in the centrifuge tube, and wash with water several times to obtain a black precipitate; 5. The black precipitate obtained in step 4 is placed in an oven at 40-80°C and dried for 4-8 hours to obtain a trace Co-doped Pd@Pt mesoporous core-shell catalyst.

[0010] Beneficial effects of the present invention: 1. The present invention provides a method for preparing a trace Co-doped Pd@Pt mesoporous core-shell catalyst for ammonia oxidation, which is characterized in that the catalyst is prepared by a one-step reduction method using Na2PdCl4, K2PtCl4, Co(CH3COO)2, HCl solution, F127 and AA as raw materials, and only requires common laboratory equipment without special equipment, and the process is simple and easy to operate; 2. This method provides a novel trace Co-doped Pd@Pt mesoporous core-shell catalyst, which is an efficient catalyst for ammonia oxidation reaction; 3. The trace Co-doped Pd@Pt mesoporous core-shell catalyst obtained by this method has a high conductivity at 5 mV s -1The peak current density was 28.14 mA cm -2 , the AOR performance and stability are significantly better than those of Pd@Pt mesoporous core-shell catalysts and commercial Pt / C catalysts; 4. The drugs used in the present invention are non-toxic and harmless, and are simple to prepare and take a short time. No complicated and tedious steps are required after preparation, and they are particularly suitable for batch preparation, and are suitable for industrial-scale production and commercial applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the embodiments or the description of the prior art will be briefly introduced with drawings below, but the drawings in the following description are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0012] Figure 1 This is a transmission electron micrograph of the trace Co-doped Pd@Pt mesoporous core-shell catalyst prepared in the present invention.

[0013] Figure 2 A high-angle annular dark-field transmission electron micrograph of the trace Co-doped Pd@Pt mesoporous core-shell catalyst prepared in the present invention and a corresponding elemental analysis graph.

[0014] Figure 3 This is the X-ray photoelectron spectrum of trace Co-doped Pd@Pt and Pd@Pt mesoporous core-shell catalysts prepared in the present invention.

[0015] Figure 4 This is a test diagram of the AOR performance of trace Co-doped Pd@Pt, Pd@Pt mesoporous core-shell catalysts and commercial Pt / C catalysts prepared in the present invention.

[0016] Figure 5 This is a stability performance test chart of the trace Co-doped Pd@Pt, Pd@Pt mesoporous core-shell catalyst and commercial Pt / C catalyst prepared in the present invention. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0018] Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without making any creative work shall fall within the scope of protection of the present invention.

[0019] Unless otherwise specified, the experimental methods described in the following examples are all conventional methods; the reagents and materials described are all commercially available unless otherwise specified.

[0020] Embodiment 1: First, 15 mg of Na2PdCl4, 50 mg of K2PtCl4, 0.3 mg of Co(CH3COO)2, and 110 mg of F127 were fully dissolved in 9 mL of ultrapure water to obtain a light yellow solution; 3 mL of HCl solution was added to the obtained light yellow solution to obtain a light yellow solution; 250 mg of AA was added to the light yellow solution, and the entire solution system was ultrasonically treated at 35 °C for 3 hours to obtain a black solution; the black solution was centrifuged and washed to obtain a black precipitate; the black precipitate was placed in a 60 °C oven and dried for 6 hours to obtain a trace Co-doped Pd@Pt mesoporous core-shell catalyst.

[0021] Embodiment 2: First, 10 mg of Na2PdCl4, 60 mg of K2PtCl4, and 90 mg of F127 were fully dissolved in 10 mL of ultrapure water to obtain a light yellow solution; 4 mL of HCl solution was added to the obtained light yellow solution to obtain a light yellow solution; 300 mg of AA was added to the light yellow solution, and the entire solution system was ultrasonically treated at 45 °C for 2 hours to obtain a black solution; the black solution was centrifuged and washed to obtain a black precipitate; the black precipitate was placed in a 40 °C oven and dried for 8 hours to obtain a Pd@Pt mesoporous core-shell catalyst.

[0022] Embodiment 3: First, 20 mg of Na2PdCl4, 40 mg of K2PtCl4, 0.6 mg of Co(CH3COO)2, and 130 mg of F127 were fully dissolved in 8 mL of ultrapure water to obtain a light yellow solution; 2 mL of HCl solution was added to the obtained light yellow solution to obtain a light yellow solution; 200 mg of AA was added to the light yellow solution, and the entire solution system was ultrasonically treated at 25 °C for 4 hours to obtain a black solution; the black solution was centrifuged and washed to obtain a black precipitate; the black precipitate was placed in an oven at 80 °C and dried for 4 hours to obtain a trace Co-doped Pd@Pt mesoporous core-shell catalyst.

[0023] Figure 1 This is a transmission electron micrograph of the trace Co-doped Pd@Pt mesoporous core-shell catalyst prepared in Example 1. Figure 1 It can be seen that the synthesized trace Co-doped Pd@Pt mesoporous core-shell catalyst has a clear mesoporous structure on its surface.

[0024] Figure 2This is a high-angle annular dark-field transmission electron microscopy image of the trace Co-doped Pd@Pt mesoporous core-shell catalyst prepared in Example 1 and the corresponding elemental analysis image. Figure 2 It can be seen that Pt, Pd and trace Co elements are distributed in the trace Co-doped Pd@Pt mesoporous core-shell catalyst. It is worth noting that most of the Pd element is concentrated in the center, while Pt and Co are evenly distributed throughout the nanosphere, showing the core-shell structure of trace Co-doped Pd@Pt.

[0025] Figure 3 The X-ray photoelectron spectra of the trace Co-doped Pd@Pt and Pd@Pt mesoporous core-shell catalysts prepared in Example 1-2 are shown in FIG. Figure 3 It can be seen that the Pt 4f 7 / 2 The peak binding energy is located at 71.3 eV, which is lower than the binding energy of Pd@Pt (71.6 eV). This phenomenon proves the transfer process of electrons from Co atoms to Pt atoms. The Pt electronic structure of trace Co doped Pd@Pt is expected to reduce the adsorption of electrons on intermediates, increase the electron transfer rate, and enhance the catalytic activity.

[0026] Figure 4 The AOR performance test diagram of the trace Co-doped Pd@Pt, Pd@Pt mesoporous core-shell catalyst and commercial Pt / C catalyst prepared in Examples 1-3. Figure 4 It can be seen that at 5 mV s -1 Under the test conditions, the peak current density of the trace Co-doped Pd@Pt mesoporous core-shell catalyst prepared in Example 1 was 28.14 mA cm -2 , which is significantly higher than the Pd@Pt prepared in Examples 2 and 3, the trace Co-doped Pd@Pt mesoporous core-shell catalyst and the commercial Pt / C catalyst, indicating that the trace Co-doped Pd@Pt mesoporous core-shell catalyst prepared in Example 1 has excellent AOR performance.

[0027] Figure 5 The stability performance test diagram of the trace Co-doped Pd@Pt, Pd@Pt mesoporous core-shell catalyst and commercial Pt / C catalyst prepared in Examples 1-3. Figure 5 It can be seen that under the constant voltage test condition of 0.7 V, after 500 s, the current density of the trace Co-doped Pd@Pt mesoporous core-shell catalyst prepared in Example 1 was 2.47 mA cm -2 , which is higher than the Pd@Pt, trace Co-doped Pd@Pt mesoporous core-shell catalyst and commercial Pt / C catalyst prepared in Examples 2 and 3. This shows that the trace Co-doped Pd@Pt mesoporous core-shell catalyst prepared in Example 1 has excellent stability.

[0028] Obviously, those skilled in the art can make various changes and modifications to the method for preparing a trace Co-doped Pd@Pt mesoporous core-shell catalyst for ammonia oxidation described in the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for preparing a trace amount of Co-doped Pd@Pt mesoporous core-shell catalyst for ammonia oxidation, comprising the following steps: First, 10-20 mg of Na2PdCl4, 40-60 mg of K2PtCl4, 0-0.6 mg of Co(CH3COO)2, and 90-130 mg of F127 are fully dissolved in 8-10 mL of ultrapure water to obtain a light yellow solution; 2-4 mL of HCl solution is added to the obtained light yellow solution to obtain a light yellow solution; 200-300 mg of AA is added to the light yellow solution, and the entire solution system is ultrasonically treated at 25-45 °C for 2-4 hours to obtain a black solution; The black solution was centrifuged and washed to obtain a black precipitate; the obtained black precipitate was placed in a 40-80° C. oven and dried for 4-8 hours to obtain a trace Co-doped Pd@Pt mesoporous core-shell catalyst.

2. The method for preparing a trace Co-doped Pd@Pt mesoporous core-shell catalyst according to claim 1, characterized in that: The amount of Na2PdCl4 used is 15 mg, the amount of K2PtCl4 used is 50 mg, and the amount of Co(CH3COO)2 used is 0.3 mg.

3. The method for preparing a trace Co-doped Pd@Pt mesoporous core-shell catalyst according to claim 1, characterized in that: The amount of F127 used was 110 mg, the amount of HCl solution used was 3 mL, and the amount of AA used was 250 mg.

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