Preparation method and application of nano metal catalyst

Abstract

The invention relates to the field of catalyst preparation, and discloses a preparation method and application of a nano-metal catalyst, the preparation method comprises the following steps: S1, preparing hydrosol containing metal salt and a carbon source, and adding a protective agent; s2, adding ammonia water to adjust the pH value to 8-10, carrying out water bath for 1.5-2.5 hours at 55-65 DEG C, and inducing gelation; s3, aging, wherein the gel is placed in a drying box to be subjected to aging treatment; s4, drying: drying under a vacuum condition to obtain dry gel; s5, roasting, namely pretreating the dry gel under the protection of inert gas, and then roasting to obtain a Pd / C catalyst; according to the preparation method provided by the invention, the polymer protective agent is introduced, so that metal ions can be better stabilized, and agglomeration in the gelation process is inhibited; and metal is prevented from being oxidized by roasting in an inert atmosphere.

Description

Technical Field

[0001] The invention relates to the field of catalyst preparation, and more specifically, to a preparation method of a nano metal catalyst and application thereof. Background Art

[0002] Nanometal catalysts refer to catalysts composed of metal nanoparticles. Due to their nanoscale particle size (1-100 nanometers), they have a very high specific surface area and high active sites, and exhibit unique catalytic activity and selectivity.

[0003] Supported nanometal catalyst is a type of nanometal catalyst. Supported nanometal catalyst refers to a catalyst system formed by loading nanometal particles on the surface of a certain carrier material. This structure can improve the dispersion of nanometal, expose more active sites, and give the catalyst a certain mechanical strength and anti-coking ability.

[0004] Carbon-supported nanometal catalysts refer to a type of catalyst formed by loading nanometal particles on the surface of carbon materials. The sol-gel method is a commonly used method for preparing nanomaterials, which can better control the particle size, morphology and uniformity of the product. In the preparation of carbon-supported nanometal catalysts, the sol-gel method can dissolve the metal precursor and the carbon precursor in a solvent to form a uniform sol, and then undergo appropriate gelation, aging, drying and other processes, and finally obtain the desired product through high-temperature roasting / reduction. This method can be used to prepare various supported nanometal catalysts, and the metal particle size, dispersibility, etc. are controllable, and it is suitable for chemical reactions, energy conversion, environmental catalysis and other fields. However, there are problems such as complex process, easy agglomeration of products, and insufficient carbonization. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a method for preparing a nano metal catalyst and its application. Specifically: A method for preparing a nano metal catalyst comprises the following steps: S1: preparing a hydrosol containing a metal salt and a carbon source, and adding a protective agent; S2: Add ammonia water to adjust pH to 8-10, temperature to 55-65°C, and bathe in water for 1.5-2.5h to induce gelation; S3: aging, placing the gel in a drying oven for aging; S4: drying, drying under vacuum conditions to obtain a dry gel; S5: Calcination: pretreating the dry gel under the protection of an inert gas, and then calcining the dry gel to obtain a Pd / C catalyst.

[0006] Preferably, the metal salt is palladium chloride (PdCl2).

[0007] Preferably, the carbon source is mannose.

[0008] Preferably: in step S1, the protective agent is polyvinyl pyrrolidone.

[0009] Preferably, in step S2: add ammonia water to adjust the pH to 9, and place in a water bath at 60° C. for 2 h to induce gelation.

[0010] Preferably: in step S3, the gel is placed in a drying oven at 100°C for aging for 12 hours.

[0011] Preferably, in step S4, vacuum drying is performed at 130° C. for 24 h.

[0012] Preferably, in step S5, a pretreatment calcination is first performed: the dry gel is preheated at 300° C. for 2 hours in a nitrogen atmosphere to remove most of the organic matter; Reduction calcination: hydrogen was introduced at 400° C. for 2 hours to reduce the palladium salt to metallic Pd to obtain a Pd / C catalyst.

[0013] Preferably, in step S4, the dry gel is pretreated at 650° C. for 2 h under nitrogen protection, and then calcined at 800° C. for 3 h to obtain a Pd / C catalyst.

[0014] The nano metal catalyst can be applied to the hydrogenation reaction of organic matter.

[0015] The beneficial effects of the present invention are as follows: the preparation method proposed by the present invention can better stabilize metal ions and inhibit agglomeration during the gelation process by introducing a polymer protective agent; by step-by-step high-temperature calcination, pretreatment is first performed to remove organic matter, and then high-temperature calcination is performed to form carbides, thereby improving the graphitization degree of carbon; and by calcining in an inert atmosphere, oxidation of the metal is avoided. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a transmission electron microscope image of the Pd / C catalyst in the implementation of the present invention. DETAILED DESCRIPTION

[0017] The subject matter described herein will now be discussed with reference to example embodiments. It should be understood that the discussion of these embodiments is only to enable those skilled in the art to better understand and implement the subject matter described herein, and the functions and arrangements of the elements discussed may be changed without departing from the scope of protection of the contents of this specification. Each example may omit, replace or add various processes or components as needed. In addition, the features described relative to some examples may also be combined in other examples.

[0018] Example 1 In this embodiment, a method for preparing a nano metal catalyst is proposed, comprising the following steps: S1: preparing a hydrosol containing a metal salt and a carbon source, and adding a protective agent; The metal salt is palladium chloride (PdCl2).

[0019] The carbon source was mannose.

[0020] The protective agent is polyvinyl pyrrolidone (PVP).

[0021] S2: Add ammonia water to adjust pH to 8-10, temperature to 55-65°C, and bathe in water for 1.5-2.5h to induce gelation; In a specific embodiment, the pH can be adjusted to 8 or 10. In this embodiment, the pH is 9; In a specific embodiment, the temperature can be selected to be 55 or 65°C. In this embodiment, the temperature is 60°C.

[0022] In a specific embodiment, the water bath time can be 1.5 hours or 2.5 hours. In this embodiment, the water bath time is 2 hours.

[0023] S3: Aging: the gel was placed in a drying oven at 100 °C for 12 h; S4: drying: vacuum drying at 130°C for 24 h to obtain a dry gel; S5: Calcination, pretreatment calcination: preheat the dry gel at 300 °C in a nitrogen atmosphere for 2 hours to remove most of the organic matter; Reduction calcination: hydrogen was introduced at 400° C. for 2 hours to reduce the palladium salt to metallic Pd to obtain a Pd / C catalyst.

[0024] Example 2 Characterization Tests: 1. Principle: The transmission beam of high-energy electrons after passing through the sample forms a diffraction spot array, which is imaged to directly observe the morphology, size and structure of the sample.

[0025] 2. Instrument: FEI Talos F200X transmission electron microscope (Field Electron and Ion Co.) 3. Configure the sample: S1: preparing a hydrosol containing a metal salt and a carbon source, and adding an appropriate amount of polyvinylpyrrolidone (PVP); The metal salt is palladium chloride (PdCl2), 0.1 mol / L.

[0026] The carbon source was mannose, 0.4 mol / L.

[0027] S2: Add ammonia water to adjust pH = 9, temperature 60 ° C, water bath for 2 h to induce gelation; S3: Aging: the gel was placed in a drying oven at 100 °C for 12 h; S4: drying: vacuum drying at 130°C for 24 h to obtain a dry gel; S5: Calcination: pretreat the dry gel at 650° C. for 2 h under nitrogen protection, and then calcine at 800° C. for 3 h to obtain a Pd / C catalyst.

[0028] 4. Steps; 1) Disperse an appropriate amount of catalyst sample in anhydrous ethanol and perform ultrasonic dispersion for 30 minutes; 2) Add an external accelerator to fully disperse the sample; 3) Take a small amount of suspension and drop it on the copper mesh membrane, and prepare the sample after the solvent evaporates; 4) Place the sample in a transmission electron microscope sample cell and observe and photograph it at an accelerating voltage of 200 kV.

[0029] like Figure 1 As shown, the Pd nanoparticles are relatively uniform, with the particle size mainly concentrated in the range of 2-4 nm, and are well dispersed on the carbon support.

[0030] The particle sizes of more than 100 particles were counted, and the average particle size was 3.1nm.

[0031] Example 3 X-ray powder diffraction (XRD) characterization test: 1. Principle: X-rays are used to diffract with the periodic atomic arrangement of the crystal in the material. The crystal structure and phase composition of the sample can be determined based on the diffraction angle and intensity.

[0032] 2. Instrument: Rigaku Ultima IV X-ray powder diffractometer.

[0033] 3. Steps: (1) Grind an appropriate amount of the catalyst sample in Example 2 into a uniform powder and place it into a sample cell; (2) Continuous scanning was performed using a Cu Kα ray source (λ = 1.5406Å), a tube voltage of 40 kV, and a tube current of 30 mA; (3) Scanning angle range: 10-90°, step size: 0.02°.

[0034] 4. The results are shown in the following table 2θ(degrees) Relative strength (%) Pd crystal plane index (hkl) 40.1 22 111 46.6 100 200 68.1 32 220 82.1 10 311 86.6 7 222 Pd(111), Pd(200), Pd(220), Pd(311), and Pd(222) are different crystal plane indices of palladium (Pd) metal. They correspond to the characteristic X-ray diffraction peaks of different crystal planes in the cubic close-packed structure.

[0035] The first column 2θ represents the diffraction angle value (in degrees); The second column is the relative intensity percentage of the diffraction peak at the corresponding 2θ angle, and the strongest peak is normalized to 100%; The third column (hkl) gives the crystal plane indices corresponding to the diffraction peaks.

[0036] Three obvious diffraction peaks appear at 2θ=40.1°, 46.6° and 68.1°, corresponding to the characteristic peaks of Pd(111), Pd(200) and Pd(220) surfaces, respectively, indicating the presence of nanocrystalline Pd metal in the sample. No other obvious impurity peaks indicate that the product is relatively pure. The average Pd particle size estimated by the Debye-Scherrer formula is about 3.2nm, which is consistent with the results of Example 2.

[0037] Example 4 (Catalytic performance test) Hydrogenation reaction refers to the process in which organic compounds (usually olefins, alkynes, aromatics, etc.) react with hydrogen in the presence of a catalyst to produce saturated compounds. Pd / C catalysts are widely used in such reactions due to their high catalytic activity and stability. Pd / C catalysts in styrene hydrogenation reactions can convert styrene into ethylbenzene.

[0038] 1. Materials and Equipment Catalyst: Pd / C catalyst; Substrate: styrene; Solvent: ethanol or n-hexane; Gas: high purity hydrogen; Reactor: Autoclave; Analytical instrument: Gas chromatography-mass spectrometry (GC-MS); 2. Reaction steps 2.1 Preparation of reaction system: 5 mmol of styrene was added to the autoclave.

[0039] Add solvent to a total volume of 50 mL.

[0040] Pd / C catalyst (0.05 g, 0.5 wt% Pd) was added.

[0041] 2.2 Reaction conditions setting: The system was repeatedly replaced with nitrogen to remove air.

[0042] High purity hydrogen was added and the pressure was adjusted to 20 atm.

[0043] Reaction temperature: 50°C.

[0044] Reaction time: 2 hours.

[0045] Agitation: 800 rpm.

[0046] 2.3 Sample analysis: After the reaction is complete, slowly release the pressure.

[0047] The reaction solution was collected and the product was analyzed by GC-MS.

[0048] 3. Experimental results and analysis Experimental data table of styrene hydrogenation

[0049] 4.0 Experimental Summary Conversion and selectivity: The results show that the Pd / C catalyst exhibits excellent catalytic performance in the hydrogenation of styrene. Within 2 hours, the conversion of styrene reaches 98%, and the selectivity is as high as 97% to ethylbenzene.

[0050] Reactivity and catalytic stability: Experiments show that Pd / C catalyst can effectively catalyze the hydrogenation reaction of styrene and maintain good catalytic stability during the reaction.

[0051] Adaptability to process conditions: The catalyst exhibits efficient catalytic performance under relatively mild conditions, which is economical and practical for industrial applications.

[0052] Example 5 In this embodiment, an application of a nano metal catalyst is proposed. The nano metal catalyst can be applied to the hydrogenation reaction of organic matter.

[0053] In summary, the Pd / C nanocatalyst prepared by the sol-gel method proposed in the present invention has a narrow particle size distribution, high dispersibility and excellent CO oxidation catalytic activity, showing good application prospects in related catalytic fields.

[0054] The above describes an embodiment of the present embodiment, but the present embodiment is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the guidance of the present embodiment, ordinary technicians in this field can also make many forms, all of which are within the protection of the present embodiment.

Claims

1. A method for preparing a nano metal catalyst, characterized in that: The steps include: S1: preparing a hydrosol containing a metal salt and a carbon source, and adding a protective agent, wherein the protective agent is polyvinyl pyrrolidone; S2: Add ammonia water to adjust pH to 8-10, temperature to 55-65°C, and bathe in water for 1.5-2.5h to induce gelation; S3: aging, placing the gel in a drying oven for aging; S4: drying, drying under vacuum conditions to obtain a dry gel; S5: Calcination: pretreating the dry gel under the protection of an inert gas, and then calcining the dry gel to obtain a Pd / C catalyst.

2. The method for preparing a nano metal catalyst according to claim 1, characterized in that: In step S1, the metal salt is palladium chloride.

3. The method for preparing a nano metal catalyst according to claim 1, characterized in that: In step S1, the carbon source is mannose.

4. The method for preparing a nano metal catalyst according to claim 1, characterized in that: In step S2: add ammonia water to adjust the pH to 9, and place in a water bath at 60° C. for 2 h to induce gelation.

5. The method for preparing a nano metal catalyst according to claim 1, characterized in that: In step S3, the gel is placed in a drying oven at 100°C for aging for 12 hours.

6. The method for preparing a nano metal catalyst according to claim 1, characterized in that: In step S4, vacuum drying is performed at 130° C. for 24 h.

7. The method for preparing a nano metal catalyst according to claim 1, characterized in that: In step S5, a pretreatment calcination is first performed: the dry gel is preheated at 300° C. for 2 hours in a nitrogen atmosphere to remove most of the organic matter; Reduction calcination: hydrogen was introduced at 400° C. for 2 hours to reduce the palladium salt to metallic Pd to obtain a Pd / C catalyst.

8. The method for preparing a nano metal catalyst according to claim 1, characterized in that: In step S4, the dry gel is pretreated at 650° C. for 2 h under nitrogen protection, and then calcined at 800° C. for 3 h to obtain a Pd / C catalyst.

9. An application of a catalyst prepared by the method for preparing a nano-metal catalyst according to any one of claims 1 to 8, characterized in that: The catalyst is used in the hydrogenation reaction of organic matter.

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