Preparation method and application of Pd nano-catalyst with core-shell structure

Abstract

The invention discloses a preparation method and application of a Pd nano-catalyst with a core-shell structure, the Pd nano-catalyst with the Pd nano-catalyst as a core and other transition metals as a shell structure is synthesized by adopting a microwave-assisted microemulsion-atmosphere induction method, and the Pd nano-catalyst with the core-shell structure is used for hydrogen production reaction through oxidative decomposition of ammonia. The catalyst has strong oxidation resistance and hydrogen transfer capability, so that the catalyst has excellent activity and selectivity in hydrogen production reaction through oxidative decomposition of ammonia.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalyst preparation, and particularly relates to the application of a core-shell structured Pd nanocatalyst in the oxidative dehydrogenation reaction of ammonia. Background Art

[0002] The ammonia decomposition to hydrogen technology is an efficient method to obtain carbon-free "green hydrogen". Combined with hydrogen-oxygen fuel cell technology, it is of great significance for achieving the goals of "carbon neutrality" and "carbon peak". However, due to the thermodynamic limitations of the reaction, the ammonia decomposition temperature is generally above 400 °C, resulting in a large amount of energy consumption and limiting its large-scale application. Therefore, it is necessary to develop a technology for NH3 decomposition to hydrogen at a lower temperature to meet the requirements of fuel cell technology.

[0003] The oxidative dehydrogenation technology of NH3 is a method to control the hydrogen production rate by regulating conditions such as oxygen partial pressure. Its principle is that oxygen first oxidizes the metal catalyst and surface defect sites, and the generated heat is supplied to the dehydrogenation reaction of NH3, thereby realizing the continuous oxidative dehydrogenation of NH3. However, if the oxygen concentration is too high, by-products such as NO x will be produced, and if the oxygen concentration is too low, the reaction heat will not be sufficient to maintain the decomposition dehydrogenation of ammonia. Therefore, reasonable control of conditions such as oxygen partial pressure and catalyst structure is crucial for realizing an efficient NH3 oxidative dehydrogenation process. For example, Japanese scientists Katsutoshi Nagaoka et al. proposed that the oxidative dehydrogenation process of NH3 can achieve hydrogen production technology close to room temperature. The literature [ACS Sustainable Chem. Eng. 2020, 8, 13369−13376] reported a Ru / Ce 0.5 Zr 0.5 O2 catalyst, which can achieve the oxidative dehydrogenation of ammonia for 100 h, but the catalyst has weak antioxidant properties and insufficient hydrogen transfer ability, resulting in intermittent reactions and unable to continuously produce hydrogen.

[0004] In recent years, due to the special energy transfer and conversion mode of microwaves, as a special green heating method, it has been widely used in catalyst preparation. Compared with traditional methods, microwave technology has significant advantages such as high efficiency, fast speed, high resource recovery and utilization rate, low energy consumption, and no environmental pollution. For example, Patent CN102658207A successfully prepared a highly dispersed Pd catalyst using microwave reaction technology, but a large amount of organotin solvent was introduced in the preparation process, which caused great damage to the environment and restricted the development of this method; Patent CN105268433A also successfully prepared a series of highly dispersed platinum group series catalysts using microwave heating method, but a large amount of alcohol reducing agents and polymer protectants were introduced in this preparation process, making the preparation process complex and increasing the production cost input, resulting in the difficulty of industrialization of this scheme. C.Y. Lu et al. reported a method for synthesizing Fe3O4@SiO2 core-shell nanomaterials by microwave-assisted reverse microemulsion (RSC Adv., 2016, 6, 88762-88769). They found that compared with the synthesis method without microwave assistance, the introduction of microwaves could successfully reduce the thickness of the shell layer SiO2. They thought this might be related to the short microwave irradiation time. However, due to the compactness of the shell layer SiO2, it was difficult for reaction molecules to contact the metal active species inside. Therefore, it was difficult to apply to the oxidative dehydrogenation reaction of ammonia. Nasrullah Shah et al. reported a preparation method for coating nanoparticles with a polymer shell (MAAm-co-AA) by microwave-assisted precipitation polymerization (Appl Nanosci 12, 3547–3554 (2022)). They successfully prepared nanoparticles with Fe3O4@SiO2 as the magnetic core and organic polymer as the shell, and showed excellent application prospects in the biomedical field. However, due to the complex preparation method and environmental pollution caused by the use of organic reagents, it was difficult to achieve industrial application. Summary of the Invention

[0005] Aiming at the problems of high temperature, discontinuous hydrogen production, low antioxidant capacity of the catalyst, and large pollution in the decomposition of NH3 to produce hydrogen, the present invention synthesizes a core-shell structured Pd nanocatalyst by a microwave-assisted microemulsion-atmosphere induction method, with the Pd nanocatalyst as the core and other transition metals as the shell structure. In the present invention, by reasonably regulating the microwave power and the metal precursor solution, Pd nanoparticles catalysts wrapped by transition metals that are uniform and stable can be obtained quickly. The two have a strong interaction and are not easy to fall off. Subsequently, a metal-state catalyst sample is obtained by combining a reduction method; the preparation method has the advantages of simple process, low preparation cost, no pollution, easy scale-up, and high controllability. The core-shell structured Pd nanocatalyst is used for the oxidative decomposition of ammonia to produce hydrogen, and has strong antioxidant and hydrogen transfer capabilities, making it have excellent activity and selectivity in the oxidative decomposition of ammonia to produce hydrogen.

[0006] In the first aspect of the present invention, a method for preparing a core-shell structured Pd nanocatalyst is provided, and the core-shell structured Pd nanocatalyst is prepared by a microwave-assisted microemulsion-atmosphere induction method.

[0007] Optionally, the method for preparing the core-shell structured Pd nanocatalyst includes the following steps: (1) Mix the microemulsion system A containing Pd salt and the microemulsion system B containing other transition metal salts, adjust the pH, and carry out microwave hydrothermal reaction in a microwave reaction kettle; (2) Wash, filter, and dry to obtain a precursor, and calcine and activate it in an atmosphere containing a reducing gas to obtain a core-shell structured Pd nanocatalyst.

[0008] Optionally, the microemulsion system A containing Pd salt includes: a salt solution of Pd, a solvent A, and a surfactant A. The solvent A is selected from C6-C8 straight-chain alkanes or cycloalkanes. The surfactant A is selected from sodium dodecyl sulfate, sodium diisooctyl sulfosuccinate, sodium dodecyl sulfonate, polyoxyethylene ethers, polyethylene glycol types, etc., and the surfactant A accounts for 5-10% of the volume of the solvent A.

[0009] Optionally, the emulsion system B includes: a salt solution of other transition metals, a solvent B, and a surfactant B. The solvent B is selected from C6-C8 straight-chain alkanes or cycloalkanes. The surfactant B is selected from sodium dodecyl sulfate, sodium diisooctyl sulfosuccinate, sodium dodecyl sulfonate, polyoxyethylene ethers, polyethylene glycol types, etc., and the surfactant B accounts for 5-10% of the volume of the solvent B. The surfactant A and the surfactant B are the same or different, and the solvent A and the solvent B are the same or different.

[0010] Optionally, other transition metals are selected from one or more of Ni, Co, Fe, Cu, Zn, Mn, Cr, V, etc.

[0011] Optionally, the Pd salt and other transition metal salts are selected from inorganic salts or organic salts, such as chlorides, nitrates, sulfates for inorganic salts, and acetates for organic salts.

[0012] Optionally, the molar ratio range of Pd to other transition metals is between 1:1 and 10:1.

[0013] Optionally, the microwave hydrothermal reaction conditions include: the reaction duration is 1-4 h, the pressure is 0.1-2.0 MPa, the temperature is 150-300 °C, and the microwave power is 0.6-1.0 kW. Preferably, the microwave power is 0.6-0.8 kW.

[0014] Optionally, the pH is between 4 and 10. The pH regulators include sulfuric acid, hydrochloric acid, sodium hydroxide, sodium carbonate, sodium bicarbonate, potassium bicarbonate, urea, ammonia water, ammonium carbonate, etc.

[0015] Optionally, the atmosphere containing reducing gas includes reducing gas and inert gas; the reducing gas includes gases such as CO, H2, CH4, etc., and the inert gas includes argon, nitrogen, helium, etc. The volume fraction of the reducing gas is 5-20%.

[0016] Optionally, the calcination activation temperature is 300-600 °C, the time is 2-6 h, and the pressure is atmospheric pressure.

[0017] The second aspect of the present invention provides the application of the core-shell structured Pd nanocatalyst, and the core-shell structured Pd nanocatalyst is used for the oxidative dehydrogenation reaction of ammonia.

[0018] Optionally, the gas composition of the oxidative dehydrogenation reaction of ammonia is NH3:O2:Ar = 4-10:1:1 (volume ratio), and the space velocity is 8000-60000 mL g cat -1 h -1 , and the reaction temperature is 75-300 °C. When the reaction temperature is 75-300 °C, the actual bed temperature is 90-350 °C.

[0019] The core-shell structured Pd catalyst prepared by the present invention exhibits excellent activity and stability in the oxidative dehydrogenation reaction of ammonia, and the raw materials required for this method, such as metal salts, solvents, surfactants, etc., are all bulk commercial chemicals with low costs. Compared with the prior art, the beneficial effects of the catalyst provided by the present invention include: 1. A Pd nanocatalyst with a core-shell structure was successfully prepared by the microwave-assisted microemulsion-atmosphere induction method and was successfully applied in the oxidative dehydrogenation reaction of ammonia, showing excellent performance; 2. The low-temperature (≤300 °C) and continuous ammonia decomposition to produce hydrogen process was successfully achieved and has great stability, which is of great significance for the large-scale use of "green hydrogen"; 3. For the preparation method of the catalyst provided by the present invention, the raw materials required, such as metal salts, solvents, surfactants, etc., are all bulk chemicals with low costs; 4. The preparation method of the catalyst provided by the present invention has the advantages of simple and safe preparation process, energy conservation and environmental protection, adjustable core-shell layer structure, easy scale-up, etc. Description of the Drawings

[0020] Figure 1 Schematic diagrams of STEM and EDX-Mapping for Example 1; Figure 2 Results of the stability test for the oxidative dehydrogenation reaction of ammonia in Example 1 and Comparative Examples 1-4; Figure 3 Schematic diagrams of STEM and EDX-Mapping for Comparative Example 3; Figure 4 Schematic diagrams of STEM and EDX-Mapping for Comparative Example 4. Detailed implementation manners

[0021] The present invention will be described in detail below in conjunction with the embodiments, but is not limited to the described embodiments.

[0022] Unless otherwise specified, all numbers appearing in the specification and claims of the present invention, such as values of loading, temperature, time, conversion rate, etc., should not be understood as absolute exact values. Due to the standard deviation of measurement techniques, there will inevitably be certain experimental errors in the measured values.

[0023] The microwave hydrothermal reaction is carried out in a microwave reaction furnace, which is purchased from Beijing Xianghu Technology Development Co., Ltd., with the model of Hydrocube XH-800SE. The maximum power used does not exceed 2 kW, and the maximum temperature does not exceed 600 °C.

[0024] All catalysts are evaluated for activity in a fixed-bed reactor equipped with an infrared temperature measurement device. Before the reaction, at room temperature, 10% NH3 / Ar is first passed through to adsorb sufficient NH3 on the catalyst surface to avoid competitive adsorption with O2. Then, in the programmed temperature control device, the reaction temperature is controlled at 75-300 °C, and the reaction gas is passed in according to a certain ratio of NH3:O2:Ar, and the space velocity is controlled at 8000-60000 mL g cat -1 h -1 , and a gas chromatograph is used to track the amounts of NH3, O2, and H2 in the tail gas, and the conversion rate is calculated.

[0025] The metal loading is tested and completed by an inductively coupled plasma instrument.

[0026] The metal dispersion state (STEM) and the core-shell structure (EDX-Mapping) are observed by high-angle annular dark-field imaging of the sample using a spherical aberration corrected electron microscope of the American ThermoFisher model.

[0027] Example 1

[0028] First, take 20 mL of Na2PdCl4 solution (31.34 mg / mL), then add 100 mL of cyclohexane and 7 mL of sodium dodecyl sulfate solution (0.2 mol / L), stir and disperse evenly to obtain a homogeneous emulsion A. Disperse 0.7 g of Co(NO3)2·6H2O powder into 10 mL of water, then add 100 mL of cyclohexane and 8.6 g of polyethylene glycol 400 solution, stir and disperse evenly to obtain a homogeneous emulsion B. Stir and mix the two evenly, and add Na2CO3 to adjust the pH to between 6 and 7. Control the temperature at 200 °C (microwave input power 800 W) and the pressure at 0.4 MPa in a microwave reactor, stir and react for 3 h. Take the filtrate after the reaction and wash it by centrifugation for multiple times. Take the brown solid precipitate in the lower layer, dry it and transfer it to a tubular furnace, introduce 5% H2 / Ar and reduce and activate it at 400 °C for 2 h to obtain Pd 0.7 Co 0.3 Core-shell structured catalyst.

[0029] After that, pretreat 0.1 g of Pd by introducing 10% NH3 / Ar at room temperature for 5 - 10 min. Introduce the reaction gas, a mixed gas of NH3:O2:Ar = 4:1:1, into the reaction tube, control the reaction space velocity at 24000 mL g 0.7 Co 0.3 h cat -1 h -1 , the reaction temperature is 75 °C at atmospheric pressure. Analyze the composition of the tail gas by gas chromatography and calculate the conversion rates of NH3, O2, and H2.

[0030] It can be found from Table 1 that the actual bed temperature of this catalyst is about 90 °C, and the hydrogen production rate is about 322 mmol g cat -1 h -1 , which is much higher than the activity of the catalyst in the comparative example.

[0031] From Figure 1 it can be found that: this catalyst has a core-shell structure, the inner core is Pd nanoparticles, and the outer shell is uniformly distributed Co nanoparticles with a size of about 10 nm.

[0032] Example 2

[0033] First, disperse 4.4 g of Pd(CH3COO)2 in 10 mL of water, then add 70 mL of octane and 6 mL of sodium dioctyl sulfosuccinate solution, and stir to disperse evenly to obtain a homogeneous emulsion A. Disperse 0.2 g of Co(Cl)2·6H2O powder in 10 mL of water, then add 70 mL of octane and 5.6 g of sodium dodecyl sulfate solution (0.2 mol / L), and stir to disperse evenly to obtain a homogeneous emulsion B. Stir and mix the two evenly, and add ammonia water to adjust the pH to between 4 and 5. Control the temperature at 150 °C (microwave input power 600 W) and the pressure at 0.1 MPa in a microwave reactor, and stir and react for 3 h. Take the filtrate after the reaction and wash it by centrifugation multiple times. Take the brown solid precipitate in the lower layer, dry it, and transfer it to a tubular furnace. Pass 5% CO / Ar and reduce and activate it at 600 °C for 2 h to obtain Pd1Co 0.1 Core-shell structure catalyst.

[0034] After that, pretreat 0.1 g of Pd1Co catalyst with 10% NH3 / Ar at room temperature for 5 - 10 min. Pass the reaction gas mixture of NH3:O2:Ar = 10:1:1 into the reaction tube, and control the reaction space velocity at 8000 mL g 0.1 h cat -1 -1 , and the reaction temperature is 85 °C at atmospheric pressure. Analyze the composition of the tail gas by gas chromatography and calculate the conversion rates of NH3, O2, and H2.

[0035] Example 3

[0036] First, disperse 4.9 g of Pd(NO3)2 in 10 mL of water, then add 80 mL of heptane and 4 mL of polyoxyethylene ether solution, and stir to disperse evenly to obtain a homogeneous emulsion A. Disperse 2.1 g of Co(CH3COO)2 powder in 10 mL of water, then add 90 mL of heptane and 7.3 g of sodium dodecyl sulfate solution (0.2 mol / L), and stir to disperse evenly to obtain a homogeneous emulsion B. Stir and mix the two evenly, and add potassium hydroxide to adjust the pH to between 9 and 10. Control the temperature at 300 °C (microwave input power 1000 W) and the pressure at 2 MPa in a microwave reactor, and stir and react for 1 h. Take the filtrate after the reaction and wash it by centrifugation multiple times. Take the black-brown solid precipitate in the lower layer, dry it, and transfer it to a tubular furnace. Pass 5% CH4 / Ar and reduce and activate it at 300 °C for 2 h to obtain Pd1Co1 core-shell structure catalyst.

[0037] After that, pretreat 0.1 g of Pd1Co catalyst with 10% NH3 / Ar at room temperature for 5 - 10 min. 0.1 Pass the reaction gas mixture of NH3:O2:Ar = 7:1:1 into the reaction tube, and control the reaction space velocity at 60000 mL gcat -1 h -1 , the reaction temperature was 300 °C at atmospheric pressure. The composition of the tail gas was analyzed by gas chromatography, and the conversion rates of NH3, O2, and H2 were calculated.

[0038] Example 4

[0039] The operation was the same as that in Example 1, except that Co(NO3)2·6H2O powder was replaced by Fe(Cl)3·6H2O, and the relative mass was adjusted according to the set ratio to prepare Pd 0.7 Fe 0.3 core-shell structure catalyst.

[0040] After that, 10% NH3 / Ar was introduced at room temperature to pretreat 0.1 g of Pd 0.7 Fe 0.3 catalyst for 5 - 10 min. A mixed gas of reaction gas NH3:O2:Ar = 4:1:1 was introduced into the reaction tube, and the reaction space velocity was controlled to be 24000 mL g cat -1 h -1 , the reaction temperature was 75 °C at atmospheric pressure. The composition of the tail gas was analyzed by gas chromatography, and the conversion rates of NH3, O2, and H2 were calculated.

[0041] Example 5

[0042] The operation was the same as that in Example 1, except that Co(NO3)2·6H2O powder was replaced by Cu(NO3)2·3H2O, and the relative mass was adjusted according to the set ratio to prepare Pd 0.7 Cu 0.3 core-shell structure catalyst.

[0043] After that, 10% NH3 / Ar was introduced at room temperature to pretreat 0.1 g of Pd 0.7 Cu 0.3 catalyst for 5 - 10 min. A mixed gas of reaction gas NH3:O2:Ar = 4:1:1 was introduced into the reaction tube, and the reaction space velocity was controlled to be 24000 mL g cat -1 h -1 , the reaction temperature was 75 °C at atmospheric pressure. The composition of the tail gas was analyzed by gas chromatography, and the conversion rates of NH3, O2, and H2 were calculated.

[0044] Example 6

[0045] The operation was the same as that in Example 1, except that Co(NO3)2·6H2O powder was replaced by Zn(NO3)2·6H2O, and the relative mass was adjusted according to the set ratio to prepare Pd 0.7 Zn 0.3Core-shell structured catalyst.

[0046] After that, 0.1 g of Pd catalyst was pretreated with 10% NH3 / Ar at room temperature for 5 - 10 min, and the reaction gas mixture of NH3:O2:Ar = 4:1:1 was introduced into the reaction tube, controlling the reaction space velocity to be 24000 mL g 0.7 Zn 0.3 -1 h cat -1 h -1 , the reaction temperature was 75 °C at atmospheric pressure, and the composition of the tail gas was analyzed by gas chromatography, and the conversion rates of NH3, O2, and H2 were calculated.

[0047] Example 7

[0048] The operation was the same as in Example 1, except that Co(NO3)2·6H2O powder was replaced by Ni(NO3)2·6H2O, and the relative mass was adjusted according to the set ratio to prepare Pd 0.7 Ni 0.3 core-shell structured catalyst.

[0049] After that, 0.1 g of Pd 0.7 Ni 0.3 catalyst was pretreated with 10% NH3 / Ar at room temperature for 5 - 10 min, and the reaction gas mixture of NH3:O2:Ar = 4:1:1 was introduced into the reaction tube, controlling the reaction space velocity to be 24000 mL g cat -1 h -1 , the reaction temperature was 125 °C at atmospheric pressure, and the composition of the tail gas was analyzed by gas chromatography, and the conversion rates of NH3, O2, and H2 were calculated.

[0050] Example 8

[0051] The operation was the same as in Example 1, except that Co(NO3)2·6H2O powder was replaced by Cr(Cl)3·6H2O, and the relative mass was adjusted according to the set ratio to prepare Pd 0.7 Cr 0.3 core-shell structured catalyst.

[0052] After that, 0.1 g of Pd 0.7 Cr 0.3 catalyst was pretreated with 10% NH3 / Ar at room temperature for 5 - 10 min, and the reaction gas mixture of NH3:O2:Ar = 4:1:1 was introduced into the reaction tube, controlling the reaction space velocity to be 24000 mL g cat -1 h -1 , the reaction temperature was 185 °C at atmospheric pressure, and the composition of the tail gas was analyzed by gas chromatography, and the conversion rates of NH3, O2, and H2 were calculated.

[0053] Example 9

[0054] The operation is the same as that in Example 1, except that Co(NO3)2·6H2O powder is replaced by Mn(CH3COO)2·4H2O, and the relative mass is adjusted according to the set ratio to prepare Pd 0.7 Mn 0.3 core-shell structure catalyst.

[0055] After that, 0.1 g of Pd is pretreated with 10% NH3 / Ar at room temperature for 5 - 10 min, and the reaction gas mixture of NH3:O2:Ar = 4:1:1 is introduced into the reaction tube, controlling the reaction space velocity to be 24000 mL g 0.7 Mn 0.3 catalyst for 5 - 10 min, and the reaction temperature is 125 °C at atmospheric pressure. The composition of the tail gas is analyzed by gas chromatography, and the conversion rates of NH3, O2, and H2 are calculated. cat -1 h -1

[0056] Comparative Example 1

[0057] The operation is the same as that in Example 1, except that emulsion B is not added to prepare Pd catalyst.

[0058] After that, 0.1 g of Pd catalyst is pretreated with 10% NH3 / Ar at room temperature for 5 - 10 min, and the reaction gas mixture of NH3:O2:Ar = 4:1:1 is introduced into the reaction tube, controlling the reaction space velocity to be 24000 mL g cat -1 h -1

[0059] It can be found from Table 1 that the actual bed temperature of this catalyst is about 78 °C, and the hydrogen production rate is only 2 mmol g cat -1 h -1

[0060] Comparative Example 2

[0061] The operation is the same as that in Example 1, except that emulsion A is not added to prepare Co catalyst.

[0062] After that, 0.1 g of Pd catalyst is pretreated with 10% NH3 / Ar at room temperature for 5 - 10 min, and the reaction gas mixture of NH3:O2:Ar = 4:1:1 is introduced into the reaction tube, controlling the reaction space velocity to be 24000 mL g cat -1 h-1 The reaction temperature was 75 °C at atmospheric pressure. The composition of the tail gas was analyzed by gas chromatography, and the conversion rates of NH3, O2, and H2 were calculated.

[0063] It can be found from Table 1 that the actual bed temperature of the catalyst was about 74 °C, and the hydrogen production rate was 7 mmol g cat -1 h -1 .

[0064] Comparative Example 3

[0065] The operation was the same as that in Example 1, except that the hydrothermal process was carried out without microwave assistance and changed to a common hydrothermal reaction at 200 °C to prepare a Pd 0.7 Co 0.3 catalyst.

[0066] After that, at room temperature, 10% NH3 / Ar was introduced to pretreat 0.1 g of the Pd catalyst for 5 - 10 min. The reaction gas mixture of NH3:O2:Ar = 4:1:1 was introduced into the reaction tube, and the reaction space velocity was controlled to be 24000 mL g cat -1 h -1 The reaction temperature was 75 °C at atmospheric pressure. The composition of the tail gas was analyzed by gas chromatography, and the conversion rates of NH3, O2, and H2 were calculated.

[0067] It can be found from Table 1 that the actual bed temperature of the catalyst was about 135 °C, and the hydrogen production rate was 122 mmol g cat -1 h -1 .

[0068] Comparative Example 4

[0069] The operation was the same as that in Example 1, except that the microwave power was adjusted to 2.0 kW and the hydrothermal temperature was controlled to be 200 °C to prepare a Pd 0.7 Co 0.3 catalyst.

[0070] After that, at room temperature, 10% NH3 / Ar was introduced to pretreat 0.1 g of the Pd catalyst for 5 - 10 min. The reaction gas mixture of NH3:O2:Ar = 4:1:1 was introduced into the reaction tube, and the reaction space velocity was controlled to be 24000 mL g cat -1 h -1 The reaction temperature was 75 °C at atmospheric pressure. The composition of the tail gas was analyzed by gas chromatography, and the conversion rates of NH3, O2, and H2 were calculated.

[0071] It can be found from Table 1 that the actual bed temperature of the catalyst was about 116 °C, and the hydrogen production rate was 98 mmol gcat -1 h -1 。

[0072] Table 1 presents the physicochemical properties of the catalysts in Examples 1-9 and Comparative Examples 1-4. It can be seen that the core-shell structured Pd nanocatalyst prepared by microwave-assisted microemulsion-atmosphere induced activation has the advantages of adjustable intake components and high hydrogen production rate, providing a reference for the realization of low-temperature continuous NH3 oxidative dehydrogenation technology.

[0073] Table 1 Comparison of Physicochemical Properties of Different Catalysts

[0074] Example 10 Stability Test The catalysts in Example 1 and Comparative Examples 1-4 above were subjected to a stability test in a fixed-bed reactor. The catalysts were tested for activity changes under the same conditions (reaction temperature 75 °C at atmospheric pressure, NH3:O2:Ar = 4:1:1, space velocity 24000 mL g cat -1 h -1 )

[0075] It can be seen from Figure 2 that the catalyst in Example 1 has high stability and hydrogen production rate, and also has a significant improvement in activity compared to the catalysts in Comparative Examples 1 and 2, indicating that the presence of the PdCo interface is crucial for the reaction; at the same time, in combination with Comparative Example 3 and Figure 3 it can be seen that the presence of microwaves is crucial for the formation of the core-shell structure. Simple hydrothermal treatment without microwaves hardly forms a core-shell structure, only simple Co nanoparticles and Pd nanoparticles; at the same time, in combination with Comparative Example 4 and Figure 4 it can be seen that too high microwave power will result in the formation of uniform CoPd alloy particles and will not form a core-shell structure either. Both of these situations cause a decrease in reaction activity, and the CoPd alloy particles have very poor stability.

[0076] The above are only several embodiments of the present invention and do not impose any form of limitation on the present invention. Although the present invention is disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the relevant art, without departing from the technical scope of the present invention, making some changes or modifications using the technical content disclosed above is equivalent to equivalent embodiments and all fall within the technical scope.

Claims

1. A preparation method of a core-shell structured Pd nanocatalyst, which uses a microwave-assisted microemulsion-atmosphere induction method to prepare the core-shell structured Pd nanocatalyst.

2. The preparation method according to claim 1, characterized in that, It includes the following steps: (1) Mix the microemulsion system A containing Pd salt and the microemulsion system B containing other transition metal salts, adjust the pH, and carry out microwave hydrothermal reaction in a microwave reaction kettle; (2) Wash, filter, and dry to obtain a precursor, and calcine and activate it in an atmosphere containing a reducing gas to obtain a core-shell structured Pd nanocatalyst.

3. The preparation method according to claim 2, characterized in that, The microemulsion system A containing Pd salt includes: a salt solution of Pd, a solvent A, and a surfactant A.

4. The preparation method according to claim 2, characterized in that, The emulsion system B includes: a salt solution of other transition metals, a solvent B, and a surfactant B.

5. The preparation method according to claim 2, wherein The other transition metals are selected from one or more of Ni, Co, Fe, Cu, Zn, Mn, Cr, and V.

6. The preparation method according to claim 2, characterized in that, The molar ratio range of Pd to other transition metals is between 1:1 and 10:

1.

7. The preparation method according to claim 2, wherein The temperature of the microwave hydrothermal reaction is 150-300 °C, and the microwave power is 0.6-1.0 kW.

8. The preparation method according to claim 2, characterized in that, The atmosphere containing a reducing gas includes a reducing gas and an inert gas.

9. Application of the core-shell structured Pd nanocatalyst prepared by the preparation method according to any one of claims 1-8, wherein the core-shell structured Pd nanocatalyst is used for the oxidative dehydrogenation reaction of ammonia.

10. The application according to claim 9, characterized in that, The gas composition for the oxidative dehydrogenation reaction of ammonia is NH3:O2:Ar = 4 - 10:1:1 (volume ratio), the space velocity is 8000 - 60000 mL g cat -1 h -1 , and the reaction temperature is 75 - 300 °C.

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