Method for preparing non-porous metal catalyst by photodeposition method and application of catalyst

Abstract

The invention provides a method for preparing a non-porous metal catalyst through a photodeposition method and application of the catalyst, and relates to the technical field of catalysts. The preparation method of the non-porous metal catalyst comprises the following steps: preparing carbon quantum dots, pickling a carrier material, blocking the carrier material with the carbon quantum dots to prepare a non-porous carrier, and loading a metal active component onto the non-porous carrier through a photodeposition method to prepare the non-porous metal catalyst. And the catalyst can be applied to a nitro compound hydrogenation reaction in a fixed bed. According to the invention, the defects in the prior art are overcome, the metal catalyst is prepared by using the surface non-porous carrier and the photodeposition technology, the dispersity of metal on the surface of the carrier can be improved, the aggregation and accumulation of metal particles can be effectively prevented, the surface smoothness of the non-porous carrier is high, the diffusion path between the metal and reactants is reduced, and the reaction efficiency is improved.

Description

Technical Field

[0001] The invention relates to the technical field of catalysts, and in particular to a method for preparing a non-porous metal catalyst by a photodeposition method and application of the catalyst. Background Art

[0002] Halogenated anilines are widely used in industries such as chemicals, dyes, pesticides and medicines. It is of great significance to develop an efficient continuous catalytic method for hydrogenation of halogenated nitrobenzenes. However, there are some limitations in the preparation of traditional supported nanometal catalysts. First, metal particles tend to aggregate on the surface of the carrier, resulting in a reduction in catalyst active sites and reduced reaction efficiency. Secondly, the dispersibility of supported nanometal catalysts is difficult to control, and metal particles are often unevenly distributed on the carrier, which may cause the diffusion path to be too long and mass transfer limitations. During the preparation process, the control of metal particles on the catalyst surface greatly affects the performance of the catalyst.

[0003] Photodeposition is a special method for depositing metals on catalyst supports. Thiel et al. (RSC Adv., 2022, 12, 30860-30870) used photodeposition to fix platinum nanoparticles on cellulose. The obtained Pt@cellulose catalyst showed narrow and well-dispersed nanoparticles with an average size of 2-5nm. Zhu et al. (Applied Surface Science 504 (2020) 14432) synthesized bimetallic Pt@Cu / TiO2 catalysts with different Cu contents by two-step photodeposition. The characterization results showed that the bimetallic Pt-Cu nanocomposite with Pt as the core and Cu as the shell was formed by the deposition of Cu at specific positions on the surface of Pt particles. For the selective catalytic hydrogenation of pCNB to generate p-CAN, Pt@Cu(0.11) / TiO2 with monolayer dispersion ability showed the best catalytic performance, which was due to its effective blocking of the cleavage of C-Cl bonds at the Pt site. This shows that after fine surface modification, the loaded precious metal can be used as a highly active and selective catalyst for the selective catalytic hydrogenation of p-CNB. On this basis, it is crucial to design a catalyst in which the metals are uniformly dispersed and loaded on a carrier. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention provides a method for preparing a non-porous metal catalyst by a photodeposition method and the application of the catalyst. The catalyst is prepared by a photodeposition method to ensure that the metal is evenly dispersed and loaded on a non-porous carrier with a smooth surface, and is applied to the preparation of halogenated aniline by fixed bed continuous hydrogenation.

[0005] To achieve the above objectives, the technical solution of the present invention is implemented through the following technical solutions:

[0006] A method for preparing a non-porous metal catalyst by photodeposition, the method comprising the following steps:

[0007] S1, mixing a carbon source and a nitrogen source in a mass ratio of 1:0.2-0.6 and dissolving them in water, stirring them evenly and then performing hydrothermal treatment, and then putting them into a dialysis bag for dialysis, collecting the solution outside the dialysis bag, rotary evaporating the solution after dialysis to obtain a solid, and freeze-drying the solid to obtain a carbon quantum dot solid;

[0008] S2, washing the carrier material with acid and then with deionized water until neutral and then drying to obtain a pretreated carrier for use;

[0009] S3, dissolving the above carbon quantum dot solid in deionized water to prepare an aqueous solution of carbon quantum dots with a concentration of 1-5wt%, then adding an equal volume of the carbon quantum dot aqueous solution to the pretreated carrier for impregnation, drying at 120°C after impregnation, and then calcining at 50-200°C under a hydrogen atmosphere for 1-3h, and then repeating the impregnation-drying-calcination operation multiple times to control the surface area coverage to 50%-80%, to obtain a non-porous carrier for standby use;

[0010] S4. The non-porous carrier is mixed with the metal solution and the alcohol sacrificial agent for ultrasonic treatment, and then magnetically stirred and irradiated with an ultraviolet lamp at a wavelength of 260-360nm for photodeposition for 1-3h, and the loading amount of the metal active component in the metal solution is controlled to be 0.1-2.5wt%, and then washed and vacuum dried to obtain a non-porous metal catalyst.

[0011] Preferably, in step S1, the carbon source is any one of glucose, citric acid and polyethylene glycol, and the nitrogen source is any one of ammonia, ethylenediamine, lysine, phenylalanine, proline and glycine.

[0012] Preferably, the temperature of the hydrothermal treatment in step S1 is 180-220° C., and the time of the hydrothermal treatment is 10-24 h.

[0013] Preferably, the molecular cutoff of the dialysis bag in step S1 is 100-500Da, and the dialysis time is 12-24h, and the water is changed every 1h during the dialysis process.

[0014] Preferably, the carrier material in step S2 is any one of alumina, silicon oxide, titanium dioxide, graphite and silicon carbide, and the specific surface area of ​​the carrier material is 5-20 m 2 / g, the shape is any one or more of spherical, granular and columnar, and the particle size is 10-60 mesh.

[0015] Preferably, the pickling in step S2 is performed using any one of hydrochloric acid, nitric acid and sulfuric acid, and the acid concentration is 1-5 vol%, the pickling time is 1-3 h, and the solid-liquid ratio during pickling is 1:5-10.

[0016] Preferably, the metal active component in the metal solution in step S4 is any one or more of platinum, palladium, rhodium, ruthenium, nickel and cobalt.

[0017] Preferably, in step S4, the solid-to-liquid ratio of the non-porous carrier mixed metal solution and the alcohol sacrificial agent is 1:10-20, and the alcohol sacrificial agent is any one of methanol, ethanol, ethylene glycol and isopropanol, and the added amount is 5-10 vol%.

[0018] The non-porous metal catalyst is used in a fixed bed for hydrogenation of halogenated nitro compounds, and the method of using the catalyst comprises the following steps:

[0019] (1) Set the ratio of the fixed bed inner diameter to the non-porous metal catalyst particle size to 50-10:1, and the liquid space velocity to 2-8h -1 , filling the reaction tube with quartz wool, loading the reaction tube with a non-porous metal catalyst, and then adding quartz sand;

[0020] (2) preparing a raw material solution containing halogenated nitrobenzene at a concentration of 0.05-0.8 g / ml, using ammonia water or ammonium bicarbonate as a diluent, and adding ammonia water or ammonium bicarbonate to the raw material solution according to a molar ratio of ammonia water or ammonium bicarbonate to halogenated nitrobenzene of 1:1-20 to prepare a mixed raw material solution;

[0021] (3) Under normal pressure, nitrogen is introduced to replace the air in the reaction tube, and then hydrogen is introduced. After the gas flow stabilizes, the catalyst is reduced at 250-400°C for 2-4 hours;

[0022] (4) After the reduction is completed, turn off the nitrogen and adjust the hydrogen flow rate at the same time, wait for the temperature to drop to 100-220°C, use a high-pressure pump to inject the mixed raw material liquid into the reaction tube, and the gas and liquid flow from top to bottom, with a gas-liquid ratio of 20-200.

[0023] Preferably, the halogenated nitrobenzene in step (2) is any one of p-chloronitrobenzene, m-chloronitrobenzene, o-chloronitrobenzene, 4-chloro-3-nitrotoluene, 6-chloro-2-nitrotoluene and 3,4-dichloronitrobenzene, and the solvent in the raw material liquid is any one of methanol, ethanol and ethyl acetate.

[0024] The present invention provides a method for preparing a non-porous metal catalyst by photodeposition and the application of the catalyst, which has the following advantages over the prior art:

[0025] (1) The present invention uses a non-porous support and a photodeposition technique to prepare a metal catalyst, which can improve the dispersibility of the metal on the support surface, effectively prevent the aggregation and accumulation of metal particles, and the non-porous support has a high surface smoothness, which reduces the diffusion path between the metal and the reactant and improves the reaction efficiency;

[0026] (2) When the catalyst prepared by the present invention is used for the hydrogenation reaction of halogenated nitro compounds, ammonia water or ammonium bicarbonate is added as a diluent, which can reduce the concentration of the nitro compound and improve the selectivity of the reaction, thereby helping to reduce side reactions, prevent excessive hydrogenation and increase product purity, ensuring that the nitro compound content in the product is less than one ten-thousandth. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 TEM images of experimental group 1 (a), control group 1 (b) and control group 2 (c) in the examples of the present invention. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention is clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] Embodiment 1:

[0030] Preparation of non-porous metal catalysts:

[0031] (1) Preparation of carbon quantum dots: weigh glucose and phenylalanine in a mass ratio of 1:0.4 and dissolve them in water. Stir well and then put them into Teflon inner village. Hydrothermally treat at 180°C for 10 hours to synthesize carbon quantum dots; after hydrothermal treatment, put the solution into a dialysis bag with a molecular cutoff of 100Da and dialyze for 24 hours. Change the water every 1 hour and collect the solution outside the dialysis bag; rotary evaporate the solution after dialysis to obtain a solid, and freeze-dry the solid to obtain a carbon quantum dot solid;

[0032] (2) Carrier pretreatment: The carrier is selected with a specific surface area of ​​5m 2 / g of spherical alumina with a particle size of 10-20 mesh. The carrier and a 1vol% hydrochloric acid solution were mixed at a solid-liquid ratio of 1:5 (g / mL), stirred for 1h, washed with deionized water until neutral after acid washing, and then vacuum dried; the synthesized carbon quantum dots were dissolved in deionized water to prepare a carbon quantum dot solution with a concentration of 1wt%, poured into the vacuum-dried carrier for equal volume impregnation, dried at 120°C after impregnation, calcined at 50°C in a hydrogen atmosphere for 3h, and the impregnation-drying-calcination process was repeated until the carrier specific surface area was covered by 50%, to obtain a non-porous carrier blocked by carbon quantum dots;

[0033] (3) Metal loading by photodeposition: A Pt metal solution with a concentration of 0.1 wt% was prepared using 5 vol% methanol, and the metal solution was poured into the above-prepared non-porous carrier at a solid-liquid ratio of 1:10, and ultrasonic treatment was performed for 5 minutes to mix the solution and the carrier evenly; the mixture was stirred on a magnetic stirrer and irradiated under an ultraviolet lamp with a wavelength of 260 nm for 1 hour to achieve uniform dispersion of the metal on the surface of the non-porous carrier blocked by carbon quantum dots, with a loading amount of 0.1 wt%; after photodeposition, the obtained metal-loaded catalyst was washed and vacuum dried to remove the residual solution to obtain a non-porous metal catalyst.

[0034] Referring to the above preparation method, different catalysts were prepared according to the conditions in the following table for the experimental groups 1-10 and the control group 1-2:

[0035] Table 1

[0036]

[0037]

[0038]

[0039] Embodiment 2:

[0040] The catalysts in the experimental group and the control group in Example 1 above were subjected to a fixed bed continuous catalytic hydrogenation experiment:

[0041] The specific method is as follows:

[0042] (1) Set the ratio of the fixed bed inner diameter to the non-porous metal catalyst particle size to 50-10:1, and the liquid space velocity to 2-8h -1 , filling the reaction tube with quartz wool, loading the reaction tube with a non-porous metal catalyst, and then adding quartz sand;

[0043] (2) preparing a raw material solution containing halogenated nitrobenzene at a concentration of 0.05-0.8 g / ml, using ammonia water or ammonium bicarbonate as a diluent, and adding ammonia water or ammonium bicarbonate to the raw material solution according to a molar ratio of ammonia water or ammonium bicarbonate to halogenated nitrobenzene of 1:1-20 to prepare a mixed raw material solution;

[0044] (3) Under normal pressure, nitrogen is introduced to replace the air in the reaction tube, and then hydrogen is introduced. After the gas flow stabilizes, the catalyst is reduced at 250-400°C for 2-4 hours;

[0045] (4) After the reduction is completed, turn off the nitrogen and adjust the hydrogen flow rate at the same time, wait for the temperature to drop to 100-220°C, use a high-pressure pump to inject the mixed raw material liquid into the reaction tube, and the gas and liquid flow from top to bottom, with a gas-liquid ratio of 20-200.

[0046] The specific conditions and results of the fixed bed continuous catalytic hydrogenation experiment carried out by each experimental group and control group according to the above operation are shown in Table 2 below:

[0047] Table 2

[0048]

[0049]

[0050] From Table 2 above, it can be seen that the catalysts prepared in Experimental Groups 1-10 have high conversion rates and selectivities for the fixed-bed continuous catalytic hydrogenation reaction;

[0051] And refer to Figure 1 , comparing the TEM images of experimental group 1, comparative photo 1, and control group 2, the Pt metal particles obtained by the preparation method of experimental group 1 (a) are highly dispersed, and their size is about 2nm; Figure 1 (b) is the Pt metal particles obtained by the preparation method of control group 1. Compared with experimental group 1, this method does not add carbon quantum dots, making the loading of Pt metal more difficult, and the metal size is small and dispersed, within the range of 1-2nm; Figure 1 (c) Pt metal particles obtained by the preparation method of control group 2. This method added carbon quantum dots to obtain a non-porous carrier, but used a hydrothermal method to load metal Pt, resulting in slight agglomeration of Pt particles, and the dispersion was not as high as that of the photodeposition method.

[0052] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a non-porous metal catalyst by photodeposition. It is characterized in that The method comprises the following steps: S1, mixing a carbon source and a nitrogen source in a mass ratio of 1:0.2-0.6 and dissolving them in water, stirring them evenly and then performing hydrothermal treatment, and then putting them into a dialysis bag for dialysis, collecting the solution outside the dialysis bag, rotary evaporating the solution after dialysis to obtain a solid, and freeze-drying the solid to obtain a carbon quantum dot solid; S2, washing the carrier material with acid and then with deionized water until neutral and then drying to obtain a pretreated carrier for use; S3, dissolving the above carbon quantum dot solid in deionized water to prepare an aqueous solution of carbon quantum dots with a concentration of 1-5wt%, then adding an equal volume of the carbon quantum dot aqueous solution to the pretreated carrier for impregnation, drying at 120°C after impregnation, and then calcining at 50-200°C under a hydrogen atmosphere for 1-3h, and then repeating the impregnation-drying-calcination operation multiple times to control the surface area coverage to 50%-80%, to obtain a non-porous carrier for standby use; S4. The non-porous carrier is mixed with the metal solution and the alcohol sacrificial agent for ultrasonic treatment, and then magnetically stirred and irradiated with an ultraviolet lamp at a wavelength of 260-360nm for photodeposition for 1-3h, and the loading amount of the metal active component in the metal solution is controlled to be 0.1-2.5wt%, and then washed and vacuum dried to obtain a non-porous metal catalyst.

2. The method for preparing a non-porous metal catalyst by photodeposition according to claim 1, Features: In step S1, the carbon source is any one of glucose, citric acid and polyethylene glycol, and the nitrogen source is any one of ammonia water, ethylenediamine, lysine, phenylalanine, proline and glycine.

3. The method for preparing a non-porous metal catalyst by photodeposition according to claim 1, Features: The temperature of the hydrothermal treatment in step S1 is 180-220° C., and the time of the hydrothermal treatment is 10-24 hours.

4. The method for preparing a non-porous metal catalyst by photodeposition according to claim 1, Features: In step S1, the molecular cutoff of the dialysis bag is 100-500Da, and the dialysis time is 12-24h, and the water is changed every 1h during the dialysis process.

5. The method for preparing a non-porous metal catalyst by photodeposition according to claim 1, Features: In step S2, the carrier material is any one of aluminum oxide, silicon oxide, titanium dioxide, graphite and silicon carbide, and the specific surface area of ​​the carrier material is 5-20m 2 / g, the shape is any one or more of spherical, granular and columnar, and the particle size is 10-60 mesh.

6. The method for preparing a non-porous metal catalyst by photodeposition according to claim 1, Features: In step S2, pickling is performed using any one of hydrochloric acid, nitric acid and sulfuric acid, and the acid concentration is 1-5 vol%, the pickling time is 1-3 h, and the solid-liquid ratio during pickling is 1:5-10.

7. The method for preparing a non-porous metal catalyst by photodeposition according to claim 1, Features: The metal active component in the metal solution in step S4 is any one or more of platinum, palladium, rhodium, ruthenium, nickel and cobalt, and the solid-liquid ratio of the non-porous carrier mixed metal solution and the alcohol sacrificial agent is 1:10-20, and the alcohol sacrificial agent is any one of methanol, ethanol, ethylene glycol and isopropanol, and the addition amount is 5-10 vol%.

8. Use of the non-porous metal catalyst prepared by the preparation method according to any one of claims 1 to 7 in a fixed bed for hydrogenation of halogenated nitro compounds.

9. The use according to claim 8, It is characterized in that The method of application comprises the following steps: (1) Set the ratio of the fixed bed inner diameter to the non-porous metal catalyst particle size to 50-10:1, and the liquid space velocity to 2-8h -1 , filling the reaction tube with quartz wool, loading the reaction tube with a non-porous metal catalyst, and then adding quartz sand; (2) preparing a raw material solution containing halogenated nitrobenzene at a concentration of 0.05-0.8 g / ml, using ammonia water or ammonium bicarbonate as a diluent, and adding ammonia water or ammonium bicarbonate to the raw material solution according to a molar ratio of ammonia water or ammonium bicarbonate to halogenated nitrobenzene of 1:1-20 to prepare a mixed raw material solution; (3) Under normal pressure, nitrogen is introduced to replace the air in the reaction tube, and then hydrogen is introduced. After the gas flow stabilizes, the catalyst is reduced at 250-400°C for 2-4 hours; (4) After the reduction is completed, turn off the nitrogen and adjust the hydrogen flow rate at the same time, wait for the temperature to drop to 100-220°C, use a high-pressure pump to inject the mixed raw material liquid into the reaction tube, and the gas and liquid flow from top to bottom, with a gas-liquid ratio of 20-200.

10. The use according to claim 8, It is characterized in that In the step (2), the halogenated nitrobenzene is any one of p-chloronitrobenzene, m-chloronitrobenzene, o-chloronitrobenzene, 4-chloro-3-nitrotoluene, 6-chloro-2-nitrotoluene and 3,4-dichloronitrobenzene, and the solvent in the raw material liquid is any one of methanol, ethanol and ethyl acetate.

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