Preparation method of doped carbon-based nano noble metal catalyst

Abstract

The present invention belongs to the technical field of the preparation of nano noble metal catalysts, and relates to a preparation method of a doped carbon-based nano noble metal catalyst. In the present invention, phytic acid-doped polyaniline is prepared by chemical oxidative polymerization, and a nitrogen and phosphorus co-doped carbon carrier is obtained by pyrolysis under a nitrogen atmosphere. Gold and palladium bimetals are loaded by a metal colloid adsorption method to obtain a doped carbon-based nano noble metal catalyst. The introduced doped element phosphorus has an anchoring and dispersing effect on the noble metal, and the introduced trace second component metal palladium significantly improves the activity of the catalyst. The catalyst prepared by the present invention has a simple synthesis method, high activity, good selectivity, excellent cyclic stability, is applicable to the hydrogenation of p-chloronitrobenzene to prepare p-chloroaniline, and has a broad application prospect.

Description

Technical Field

[0001] The present invention relates to a preparation method of a doped carbon-based nano noble metal catalyst, belonging to the technical field of the preparation and application of supported noble metal catalysts. Background Art

[0002] p-Chloroaniline is an important organic intermediate, which is widely used in the fields of pesticides, pharmaceuticals, and insecticides. Traditional preparation methods such as iron powder reduction method and sodium sulfide reduction method have problems of environmental pollution and low yield. At present, catalytic hydrogenation method has become the best choice due to its high efficiency and environmental protection advantages. In recent years, nano gold catalysts have shown high selectivity in the hydrogenation reaction of aromatic nitro compounds (Catalysis Letters 2018, 148, 1490-1498; Journal of Nanoscience and Nanotechnology 2018, 18, 301-308), but the low conversion rate limits their industrial application.

[0003] In recent years, carbon-based materials have emerged in the field of catalysis. Their unique advantages such as high and adjustable specific surface area, complex pore structure, and tunable surface chemical properties make them one of the preferred catalyst carriers. It is reported that carbon-based heteroatoms (N, P, S, B, etc.) can assist in anchoring and dispersing metal particles and regulating their electronic states, thereby promoting the improvement of catalytic performance (ChemSusChem 2022, 15, e202200411). Conductive polymers such as polyaniline and polypyrrole, as precursors of carbon-based materials, have attracted great attention from scientific researchers due to their simple preparation methods, reversible doping / dedoping characteristics, and easy dispersion of noble metal precursors (Chemical Engineering Journal 2022, 442, 136055). Loading noble metal nanoparticles on a doped carbon-based carrier, stabilizing the noble metal particles through carbon-based heteroatoms, and modulating the chemical state of the metal surface by the interaction between the heteroatoms and the noble metal, and then regulating the adsorption and activation in the catalytic process, are expected to obtain a highly active and stable supported noble metal catalyst.

[0004] The Chinese patent application with the publication number CN 115121288 A discloses "a novel partially carbonized core-shell polyaniline catalyst and its preparation method and application", which uses a pyrolysis strategy to partially carbonize the PANI layer of Fe3O4@PANI to obtain a magnetic catalyst that can be applied to the catalytic removal of tetracycline by persulfate. It does not involve the doping of carbon materials and the loading of noble metal particles, and its application is also different from that of the present invention. The pure doped carbon carrier has no catalytic effect on the hydrogenation of p-chloronitrobenzene, and the introduction of magnetic particles will interfere with the interaction regulation between the carbon-based carrier and the active metal, which is not conducive to obtaining the target catalyst with high activity and high stability.

[0005] The Chinese invention patent application with publication number CN 115133050 A discloses “a platinum-cobalt alloy catalyst, preparation method and application thereof”. This technology coats a carbon-nitrogen shell on the surface of carbon black by pyrolyzing PANI, and uses an impregnation method to load platinum-cobalt metal nanoparticles on the modified carbon support to obtain a PANI-modified carbon support-supported platinum-cobalt catalyst. The nitrogen doping and alloying effect strengthen the interaction between the metal and the support, reduce the agglomeration of metal particles, and improve the activity and durability of the catalyst when used in fuel cells. This technology does not involve the effect of introducing the P element by doping PANI with phytic acid, and its alloy element type, precious metal loading method and application are different from those of the present invention. The platinum-cobalt alloy content loaded in this technology is ≥20%, and the cost is much higher than that of the catalyst of the present invention. In addition, this technology obtains nitrogen-doped carbon materials by pyrolysis after core-shell coating between carbon black and PANI. The process is more complicated than directly using polyaniline doping to introduce the doping element and then pyrolysis, and the carbon black needs to be pretreated with highly corrosive and oxidizing hydrogen peroxide before use, which poses a great safety hazard during operation.

[0006] Chinese invention patent application publication number CN 117427675 A discloses a "ruthenium-based catalyst, its preparation method, and application." The catalyst uses phytic acid and ruthenium to form a ruthenium complex, Ru-PA, by heating and refluxing. The Ru-PA complex is then mixed with polyaniline in an aqueous solution and stirred to dope the polyaniline. The catalyst is then pyrolyzed at high temperature to uniformly distribute the ruthenium on the surface of PANI and in situ phosphating the ruthenium. Simultaneously, the PANI is pyrolyzed into a carbon material, resulting in a carbon-doped ruthenium-supported catalyst that is used to catalyze the hydrogen-deuterium exchange reaction of hexamethylenediamine. This technology simultaneously introduces phytic acid and the active metal Ru onto PANI in the form of a ruthenium complex, followed by pyrolysis. The complex preparation requires heating and refluxing, making the process relatively complex. Furthermore, the high temperature of the PANI during pyrolysis can easily cause the active metal particles to aggregate and grow, leading to catalyst deactivation. Compared with the above invention, the present invention adopts the strategy of doping polyaniline with phytic acid to introduce phosphorus into the carbon support after pyrolysis. The amount of phosphorus is adjusted by adjusting the amount of doped phytic acid. The method is simpler and more efficient. In addition, the trace amount of the second component palladium introduced in the present invention significantly improves the catalyst's ability to catalyze the hydrogenation of p-chloronitrobenzene to prepare p-chloroaniline.

[0007] The TOF of the 0.05% Pd-0.5% Au / NPC (2:1) catalyst prepared by the present invention for the conversion of p-chloronitrobenzene under the reaction conditions of 1.2 MPa H2 and 373 K is 7086 h -1 The catalyst of the present invention has the advantages of high activity and high stability, and has excellent industrial application prospects. Summary of the Invention

[0008] The present invention provides a preparation method of a doped carbon-based nanometer noble metal catalyst. Nitrogen and phosphorus co-doped carbon carriers are used to stabilize nano gold by pyrolyzing phytic acid-doped polyaniline. By introducing a second component palladium into the nano gold catalyst, the hydrogenation ability of the gold catalyst is significantly improved, and a highly efficient catalyst with high activity and good stability, which can be applied to the hydrogenation of p-chloronitrobenzene to prepare p-chloroaniline, is obtained.

[0009] The present invention is realized through the following technical solutions:

[0010] A preparation method of a doped carbon-based nanometer noble metal catalyst, characterized in that: the carrier of the nanometer noble metal catalyst is a nitrogen and phosphorus co-doped carbon carrier derived from conductive polymer phytic acid-doped polyaniline, the noble metal is a gold-palladium bimetal, and the loading method of the noble metal is the metal colloid adsorption method.

[0011] Among them, phytic acid-doped polyaniline is prepared according to the following steps: 20-40 mmol of aniline, 80-120 mL of deionized water, and 3.2-9.6 mL of phytic acid are stirred and mixed evenly. Subsequently, 1-3 g of ammonium persulfate is dissolved in 10 mL of deionized water and added dropwise to the above aniline phytic acid solution. After reacting in an ice-water bath for 8-*16 h*, phytic acid-doped polyaniline PA-PANI is obtained after washing and drying.

[0012] PA-PANI is pyrolyzed at 600-800 °C for 0.5-2 h (heating rate is 5 °C / min, N2 flow rate is 40 mL / min) in a nitrogen atmosphere to obtain a nitrogen and phosphorus co-doped carbon NPC carrier. The introduction amount of P is adjusted by the dosage of phytic acid in PA-PANI.

[0013] Among them, the loading method of the noble metal is the metal colloid adsorption method, and the metal colloid used is a gold-palladium bimetal colloid solution, which is prepared according to the following steps: First, a gold colloid solution is prepared. 1-2 mL of HAuCl4 solution (9.56 mg / mL) and 0.5-1.5 mL of PVA solution (2 wt%) are dispersed in 400-500 mL of deionized water, stirred in an ice-water bath for 10-40 min, 2-3 mL of NaBH4 solution (0.1 mol / L) is added dropwise, and then slowly stirred for 1-4 h, and stored in a refrigerator at 0-4 °C for later use;

[0014] Subsequently, 30-50 mL of the above self-made gold colloid solution is taken, 2-6 mL of ascorbic acid solution (0.1 mol / L) is added, stirred and dispersed evenly, and then 0.01-0.5 mL of H2PdCl4 solution (1 mg / mL) is added and stirred at room temperature for 8-16 h, and stored in a refrigerator at 0-4 °C for later use;

[0015] Disperse 0.05 - 0.1 g of NPC carrier in 2 - 5 mL of deionized water, add 10 - 34 mL of gold-palladium bimetallic colloid solution, stir and adsorb for 18 - 30 h, then wash and dry to obtain Pd-Au / NPC. Among them, the introduction amount of Pd is adjusted by the dosage of H2PdCl4 solution in the preparation process of gold-palladium bimetallic colloid.

[0016] The catalyst has excellent activity and stability in the reaction of hydrogenation of p-chloronitrobenzene to prepare p-chloroaniline, where the pressure of hydrogen is 0.8 - 1.2 MPa and the reaction temperature is 60 - 120 °C.

[0017] Prepare nitrogen-doped carbon (NC) carrier by pyrolysis of hydrochloric acid-doped polyaniline (HCl-PANI) as a comparison. The preparation is carried out according to the following steps: dissolve 30 - 60 mmol of aniline in 30 - 50 mL of deionized water, add hydrochloric acid to adjust the pH to 0.4, then add 10 - 30 mL of initiator ammonium persulfate solution (2.5 mol / L), stir vigorously for 1 h, stand at room temperature for 24 h, and obtain HCl-PANI after washing and drying. Pyrolyze under the same conditions as PA-PANI to obtain NC carrier. Replace NPC in the preparation process of Pd-Au / NPC with NC to obtain Pd-Au / NC as a comparison.

[0018] Prepare nano-gold catalyst by NaBH4 reduction method, urea precipitation method and gold colloid adsorption method as a comparison. For the NaBH4 reduction method, the preparation is carried out according to the following steps: disperse 0.2 - 0.4 g of the carrier in 20 - 40 mL of deionized water, then add 0.1 - 0.2 mL of HAuCl4 solution (9.56 mg / mL), stir vigorously for 30 min, and then gradually add 8 - 12 mL of aqueous solution containing 0.01 - 0.03 g of NaBH4 dropwise to the carrier gold dispersion. React in an ice-water bath for 10 - 30 min, then wash and dry to obtain Au / NC(NaBH4).

[0019] For the urea precipitation method, the preparation is carried out according to the following steps: dissolve 0.04 - 0.08 g of urea in 8 - 12 mL of water, then add 0.1 - 0.2 mL of HAuCl4 solution (9.56 mg / mL), after dispersing evenly, add 0.1 - 0.3 g of the carrier, stir at 70 - 80 °C for 2 - 6 h, then wash and dry, and calcine in air atmosphere at 150 - 250 °C for 3 - 6 h to obtain Au / NC(UDP).

[0020] Among them, the preparation process of preparing nano-gold catalyst by gold colloid adsorption is the same as the process of preparing Pd-Au / NPC by gold-palladium bimetallic colloid adsorption, only replacing the gold-palladium bimetallic colloid solution with gold colloid solution and the carrier NPC with NC.

[0021] The present invention takes a unique approach and invents a preparation technology for a doped carbon-based nano-precious metal catalyst. This technology integrates the basic principles and cutting-edge achievements in the fields of nanoscience, catalysis science, and polymer science. By pyrolyzing a conductive polymer, a gold catalyst supported on nitrogen and phosphorus co-doped carbon is prepared. With the help of carbon-based heteroatoms to anchor and disperse metal particles, the stability of the nano-gold catalyst is improved. By introducing a trace amount of a second metal element, the activity and stability of the catalyst for the hydrogenation of p-chloronitrobenzene to prepare p-chloroaniline are significantly improved. The catalyst prepared by the present invention has the characteristics of high catalytic activity, good selectivity, and excellent stability in recycling, and can be efficiently applied to the hydrogenation of p-chloronitrobenzene, showing broad application prospects. The implementation of the present invention has important promotional significance for accelerating the research and development and industrial application speed of new catalysts, leading the development of emerging industries, and promoting the transformation of traditional industries. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Catalytic activity diagrams of x%Au / NC catalysts with different gold loadings prepared by the gold colloid adsorption method in Example 1 of the present invention. (x% is the theoretical gold loading, reaction conditions: reaction temperature, 100 °C; H2 pressure, 1.2 MPa; reaction time, 2 h; substrate amount, 0.787 g of p-chloronitrobenzene; solvent amount, 25 mL of methanol).

[0023] Figure 2 Catalytic activity diagrams of 0.5%Au / NC catalysts prepared by different methods in Examples 1-3 of the present invention. (Reaction conditions: reaction temperature, 100 °C; H2 pressure, 1.2 MPa; reaction time, 2 h; substrate amount, 0.787 g of p-chloronitrobenzene; solvent amount, 25 mL of methanol).

[0024] Figure 3 Transmission electron microscope diagrams and gold particle size distribution diagrams of 0.5%Au / NC and 0.05%Pd-0.5%Au / NC catalysts prepared by the metal colloid adsorption method in Examples 1 and 4 of the present invention.

[0025] Figure 4 Catalytic activity diagrams of x%Pd-0.5%Au / NC catalysts with different Pd loadings prepared by the metal colloid adsorption method in Example 4 of the present invention. (Reaction conditions: reaction temperature, 100 °C; H2 pressure, 1.2 MPa; reaction time, 2 h; substrate amount, 0.787 g of p-chloronitrobenzene; solvent amount, 25 mL of methanol).

[0026] Figure 5Catalytic activity diagram of 0.05% Pd-0.5% Au / NPC (x:1) with different amounts of phytic acid prepared by the metal colloid adsorption method in Example 5 of the present invention. (x:1 is the molar ratio of aniline to phytic acid; reaction conditions: reaction temperature, 100 °C; H2 pressure, 1.2 MPa; reaction time, 1 h; substrate amount, 0.787 g of p-chloronitrobenzene; solvent amount, 25 mL of methanol).

[0027] Figure 6 XRD diagrams of the catalysts and NPC support prepared in Examples 1, 5, and 6 of the present invention.

[0028] Figure 7 Transmission electron microscopy and gold size distribution diagrams of the catalysts and NPC support prepared in Examples 5 and 6 of the present invention.

[0029] Figure 8 Au4f XPS spectra of the catalysts prepared in Examples 4 and 6 of the present invention.

[0030] Figure 9 Pd3d XPS spectra of the catalysts prepared in Examples 4 and 6 of the present invention.

[0031] Figure 10 P2p XPS spectra of the NPC support prepared in the present invention and the catalyst prepared in Example 6.

[0032] Figure 11 Catalytic activity diagram of the catalyst prepared in Example 6 of the present invention with changes in temperature and pressure. (Reaction conditions: reaction time, 1 h; substrate amount, 0.787 g of p-chloronitrobenzene; solvent amount, 25 mL of methanol).

[0033] Figure 12 Cyclic activity diagram of the catalyst prepared in Example 6 of the present invention. (Reaction conditions: reaction temperature, 100 °C; H2 pressure, 1.2 MPa; reaction time, 0.5 h; substrate amount, 0.787 g of p-chloronitrobenzene; solvent amount, 25 mL of methanol). Detailed implementation manners

[0034] The present invention will be further explained below in conjunction with specific examples and their accompanying drawings:

[0035] Example 1: Preparation of x% Au / NC catalyst by gold colloid adsorption method

[0036] Dissolve 50 mmol of aniline in 40 mL of deionized water. After adjusting the pH to 0.4 with hydrochloric acid, add 20 mL of ammonium persulfate solution (2.5 mol / L) as the initiator. After vigorously stirring for 1 h, let it stand at room temperature for 24 h. After washing and drying, HCl-PANI is obtained. Pyrolyze HCl-PANI at 800 °C for 1 h under a nitrogen atmosphere (heating rate: 5 °C / min, N2 flow rate: 40 mL / min) to obtain the NC support.

[0037] Subsequently, disperse 1.33 mL of HAuCl4 solution (9.56 mg / mL) and 1 mL of PVA solution (2 wt%) in 431.3 mL of deionized water. Stir in an ice-water bath for 20 min. After adding 2.5 mL of NaBH4 solution (0.1 mol / L), stir slowly for 2 h to obtain a gold colloid solution, which is refrigerated at 0 - 4 °C for later use.

[0038] Disperse 0.1 g of the support NC in 2.5 mL of deionized water. After adding 17 mL of the gold colloid solution and stirring for adsorption for 24 h, wash and dry to obtain 0.5%Au / NC(Sol), where 0.5% is the theoretical gold loading amount, and its value can be optimized and adjusted according to the change in the added amount of the gold colloid solution.

[0039] Through Figure 1 It can be seen that the nano-gold catalyst supported on nitrogen-doped carbon has excellent selectivity, but its conversion rate is relatively low, which is determined by the relatively weak H2 dissociation ability of gold. The conversion rate of 0.5%Au / NC is 11.4%, higher than that of 0.3%Au / NC (2.9%) and 0.7%Au / NC (7.2%). This is because when the gold loading amount is low, the active gold species are relatively few, and when the gold loading amount is high, the active gold species may agglomerate due to the high surface energy. Therefore, the gold loading amount is preferably 0.5%.

[0040] Example 2: Preparation of 0.5%Au / NC catalyst by NaBH4 reduction method

[0041] Dissolve 50 mmol of aniline in 40 mL of deionized water. After adjusting the pH to 0.4 with hydrochloric acid, add 20 mL of ammonium persulfate solution (2.5 mol / L) as the initiator. After vigorously stirring for 1 h, let it stand at room temperature for 24 h. After washing and drying, HCl-PANI is obtained. Pyrolyze HCl-PANI at 800 °C for 1 h under a nitrogen atmosphere (heating rate: 5 °C / min, N2 flow rate: 40 mL / min) to obtain the NC support.

[0042] Disperse 0.3 g of the carrier in 30 mL of deionized water. Subsequently, add 0.157 mL of HAuCl4 solution (9.56 mg / mL). After vigorously stirring for 30 min, gradually add 10 mL of an aqueous solution of NaBH4 containing 0.022 g dropwise to the carrier gold dispersion. After reacting in an ice-water bath for 15 min, wash and dry to obtain 0.5% Au / NC(NaBH4).

[0043] Example 3: Preparation of 0.5% Au / NC catalyst by urea precipitation method

[0044] Dissolve 50 mmol of aniline in 40 mL of deionized water. Add hydrochloric acid to adjust the pH to 0.4, then add 20 mL of initiator ammonium persulfate solution (2.5 mol / L). After vigorously stirring for 1 h, let it stand at room temperature for 24 h. After washing and drying, HCl-PANI is obtained. Pyrolyze HCl-PANI in a nitrogen atmosphere at 800 °C for 1 h (heating rate is 5 °C / min, N2 flow rate is 40 mL / min) to obtain the NC carrier.

[0045] Dissolve 0.06 g of urea in 10 mL of water. Subsequently, add 0.104 mL of HAuCl4 solution (9.56 mg / mL). After dispersing evenly, add 0.2 g of the carrier. After stirring at 80 °C for 4 h, wash and dry, and calcine in an air atmosphere at 200 °C for 5 h to obtain 0.5% Au / NC(UDP).

[0046] Appendix Figure 2 Figure for the catalytic activities of nitrogen-doped carbon-based catalysts with different gold loading methods. When the gold loading is controlled at 0.5% in both cases, the conversion rates of 0.5% Au / NC(NaBH4) and 0.5% Au / NC(UDP) for the hydrogenation of p-chloronitrobenzene are 3.7% and 8.0% respectively, both lower than that of 0.5% Au / NC(Sol). Therefore, the preferred gold loading method is the metal colloid adsorption method.

[0047] Example 4: Preparation of x% Pd-0.5% Au / NC catalyst by metal colloid adsorption method

[0048] Dissolve 50 mmol of aniline in 40 mL of deionized water. Add hydrochloric acid to adjust the pH to 0.4, then add 20 mL of initiator ammonium persulfate solution (2.5 mol / L). After vigorously stirring for 1 h, let it stand at room temperature for 24 h. After washing and drying, HCl-PANI is obtained. Pyrolyze HCl-PANI in a nitrogen atmosphere at 800 °C for 1 h (heating rate is 5 °C / min, N2 flow rate is 40 mL / min) to obtain the NC carrier.

[0049] Take 40 mL of the above self-prepared gold colloid solution, add 3.6 mL of ascorbic acid solution (0.1 mol / L), stir and disperse evenly, then add 0.115 mL of H2PdCl4 solution (1 mg / mL), and stir at room temperature for 12 h to obtain the gold-palladium bimetallic colloid solution.

[0050] Disperse 0.1 g of the support NC in 2.5 mL of deionized water, add 18.75 mL of the gold-palladium bimetallic colloid solution, stir and adsorb for 24 h, then wash and dry to obtain 0.05% Pd-0.5% Au / NC. The modulation of the Pd loading can be achieved by changing the addition amount of the H2PdCl4 solution during the preparation of the bimetallic colloid.

[0051] Appendix Figure 3 Figs. are the transmission electron microscope images and the size distribution diagrams of gold for the catalysts prepared in Example 1 and Example 4. It can be seen from the figures that the gold nanoparticles with a particle size of about 2-5 nm are evenly dispersed on the NC support. And compared with the average particle size of gold in 0.5% Au / NC (3.75 nm), the average particle size of gold in 0.05% Pd-0.5% Au / NC (3.70 nm) is slightly reduced, indicating that the introduction of trace Pd plays a certain physical isolation role on the gold nanoparticles, making the gold particles relatively smaller. Further, after the introduction of Pd, the size and distribution of the noble metal particles do not change much, meaning that Pd is mainly on the Au nanoparticles.

[0052] Figure 4 Figs. are the catalytic activity diagrams of the x% Pd-0.5% Au / NC catalysts with different Pd loadings prepared by the metal colloid adsorption method. From Appendix Figure 1 and Appendix Figure 2 it can be seen that although the gold catalyst has extremely high selectivity, its conversion rate is not satisfactory. For the hydrogenation reaction of p-chloronitrobenzene, the conversion rate of the optimized 0.5% Au / NC catalyst is only 11.4%. By introducing a trace amount of Pd, the hydrogenation efficiency of the catalyst can be significantly improved. As can be seen from Figure 4 , as the Pd content increases, the conversion rate of p-chloronitrobenzene gradually increases. When the loading is 0.05%, the complete conversion of the substrate can be achieved within 2 h and a high p-chloroaniline selectivity close to 100% can be obtained. When the Pd content is further increased, due to the too strong hydrogen dissociation ability of Pd, the selectivity of p-CAN drops sharply. In order to balance the requirements of high conversion efficiency and high selectivity and reduce costs, the introduction amount of Pd is preferably 0.05%.

[0053] Example 5: Preparation of 0.5% Au / NPC catalyst by gold colloid adsorption method

[0054] 16.5 mmol of aniline, 100 mL of deionized water, and 4.8 mL of phytic acid were stirred and mixed evenly. Subsequently, 1.8 g of ammonium persulfate was dissolved in 10 mL of deionized water and added dropwise to the aniline-phytic acid solution. After reacting in an ice-water bath for 12 h, PA-PANI was obtained through washing and drying. PA-PANI was pyrolyzed at 800 °C for 1 h in a nitrogen atmosphere (heating rate: 5 °C / min, N2 flow rate: 40 mL / min) to obtain the NPC support.

[0055] 0.1 g of the support NPC was dispersed in 2.5 mL of deionized water, and 17 mL of gold colloid solution was added. After stirring and adsorbing for 24 h, it was washed and dried to obtain 0.5%Au / NPC.

[0056] When this catalyst was applied to the hydrogenation reaction of p-chloronitrobenzene, its conversion rate was only 5%. Therefore, the nano-gold catalyst supported on the P-doped modified carbon support alone had poor performance.

[0057] Example 6: Preparation of 0.05%Pd-0.5%Au / NPC catalyst by metal colloid adsorption method

[0058] 16.5 mmol of aniline, 100 mL of deionized water, and 4.8 mL of phytic acid were stirred and mixed evenly. Subsequently, 1.8 g of ammonium persulfate was dissolved in 10 mL of deionized water and added dropwise to the aniline-phytic acid solution. After reacting in an ice-water bath for 12 h, PA-PANI was obtained through washing and drying. PA-PANI was pyrolyzed at 800 °C for 1 h in a nitrogen atmosphere (heating rate: 5 °C / min, N2 flow rate: 40 mL / min) to obtain the NPC support. The P element content in the NPC support was regulated by controlling the amount of phytic acid.

[0059] 0.1 g of the support NPC was dispersed in 2.5 mL of deionized water, and 18.75 mL of gold-palladium bimetallic colloid solution was added. After stirring and adsorbing for 24 h, it was washed and dried to obtain 0.05%Pd-0.5%Au / NPC.

[0060] Figure 5Catalytic activity diagrams of 0.05%Pd-0.5%Au / NPC(x:1) with different amounts of phytic acid prepared by the metal colloid adsorption method. It can be seen from the figure that as the molar ratio of aniline to phytic acid decreases, the activity of catalytic hydrogenation of p-chloronitrobenzene to p-chloroaniline first increases and then decreases. When the molar ratio of aniline to phytic acid is 2:1, both the conversion rate and selectivity are 100%. Therefore, the molar ratio of aniline to phytic acid is preferably 2:1. It should be noted that compared with the bimetallic 0.05%Pd-0.5%Au / NC supported on nitrogen-doped carbon, under the same conditions, the time for 0.05%Pd-0.5%Au / NPC to completely convert p-chloronitrobenzene is shortened from 2 h to 1 h, and the introduction of P element significantly improves the catalytic efficiency of the catalyst.

[0061] Figure 6 XRD analysis results of 0.5%Au / NC, 0.5%Au / NPC(2:1), 0.05%Pd-0.5%Au / NPC(2:1) catalysts and NPC(2:1) support are shown. All samples exhibit a broad diffraction peak at 24° attributed to the (002) crystal plane of carbon, indicating that they have an amorphous carbon structure; meanwhile, the characteristic peak at 44° corresponds to the (100) crystal plane of carbon, confirming the successful carbonization of the materials.

[0062] In particular, for the gold-loaded catalysts 0.5%Au / NC and 0.5%Au / NPC(2:1), the characteristic peak of the (111) crystal plane of Au is observed at 2θ = 38.3°, directly proving the effective loading of Au. It should be noted that although the Au loading amounts of both are the same, the intensity of the characteristic peak of the (111) crystal plane of Au in 0.5%Au / NPC(2:1) is weaker, which may be due to the more uniform dispersion or smaller particle size of Au on the NPC(2:1) support.

[0063] Furthermore, when the second active component Pd is introduced on the basis of 0.5%Au / NPC(2:1), no obvious characteristic peaks of Au and Pd are detected in the XRD pattern. This phenomenon means that the particle sizes of Pd and Au may decrease due to the addition of Pd, reaching below the XRD detection limit, or they exist in a highly dispersed form, thus not forming a detectable crystal phase. This indicates that the dispersion of metal particles in the bimetallic catalyst is optimized, which is beneficial to the improvement of catalytic performance.

[0064] Figure 7 Transmission electron microscope images of the catalysts prepared in Example 5 and Example 6 of the present invention, and the attached Figure 2Compared with the catalyst without P doping modification, the average sizes of the gold (3.41 nm) and gold-palladium bimetallic (3.33 nm) catalyst nanoparticles supported on NPC are significantly reduced, indicating that the heteroatom P plays a good role in anchoring and dispersing noble metals. By comparing the data of Example 5 and Example 1, it is found that although the size of Au in Example 5 (0.5%Au / NPC) is smaller than that in Example 1 (0.5%Au / NC), its activity (5%) is lower than that in Example 1 (11.4%). Therefore, the reduction of gold size is not the key factor for the improvement of its catalytic activity. By comparing Example 6 and Example 5, after introducing a small amount of Pd, the size of the nanoparticles only decreases slightly, indicating that Pd is mainly supported on the gold nanoparticles, and the introduction of Pd plays a physical isolation role on the gold nanoparticles, slightly reducing the particle size of the gold particles.

[0065] Figure 8 Figure 4 shows the Au4f XPS spectra of the catalysts prepared in Example 4 and Example 6 of the present invention. As can be seen from the figure, after P doping, the binding energy of Au4f 7 / 2 shifts from 83.98 to 84.20 eV, increasing the surface electron deficiency. The binding energy of the Pd 3d Pd 2+ species shifts from 337.22 to 337.56 eV, and its content increases from 3.4% to 9.2% (attached Figure 9 ). Therefore, it can be determined that the P-doped support has a strong support-noble metal electronic interaction with both Au and Pd. This interaction makes Au and Pd electron-deficient, and the electron-deficient gold-palladium on the surface is beneficial to the adsorption and activation of the substrate p-chloronitrobenzene, thus significantly improving its catalytic activity. Through Figure 10 the P2p XPS spectra of the NPC support and the catalyst prepared in Example 6, it can be seen that in the XPS spectra of NPC after loading the metal, the binding energy of P2p shifts to a lower binding energy relative to the NPC support, further confirming the electron transfer from the noble metals to the support after loading the noble metals, and there is a strong electronic interaction between the noble metals and the support.

[0066] Figure 11Catalytic activity diagram of the catalyst prepared in Example 6 of the present invention varying with temperature and pressure. When the reaction temperature was controlled at 100 °C and the hydrogen pressure was 0.8 MPa, the conversion rate was 80%. As the pressure increased, the overall conversion rate showed an upward trend. When the pressure was 1.2 MPa, the conversion rate reached 100% and the selectivity was close to 100%. Generally speaking, the change in pressure had a relatively obvious effect on the conversion rate, but the selectivity remained almost unchanged, proving that increasing the pressure did not lead to the occurrence of side reactions. The influence of temperature on the reaction had a similar trend. When the pressure was controlled at 1.2 MPa, within the range of 60-120 °C, as the temperature increased, the conversion rate gradually increased until complete conversion, and the selectivity remained basically unchanged. Therefore, the reaction temperature was preferably 100 °C and the reaction pressure was preferably 1.2 MPa.

[0067] Figure 12 Cyclic activity diagram of the 0.05%Pd-0.5%Au / NPC(2:1) catalyst in Example 6. The reaction time was controlled to be only 0.5 h. It can be seen from the figure that after five cycles, the conversion rate of the catalyst only decreased from 82% to 52%, indicating excellent cyclic use ability, which shows that the catalyst of the present invention has the characteristics of high cyclic activity and good stability.

Claims

1. A preparation method of a doped carbon-based nano-precious metal catalyst, characterized in that: The support of the nano noble metal catalyst is a nitrogen and phosphorus co-doped carbon support NPC obtained by pyrolysis of phytic acid-doped polyaniline. The noble metal is a gold-palladium bimetal. The preparation method of the doped carbon-based nano noble metal catalyst is as follows: Disperse 0.05 - 0.1 g of the NPC support in 2 - 5 mL of deionized water, add 10 - 34 mL of the gold-palladium bimetal colloid solution, stir and adsorb for 18 - 30 h, wash and dry to obtain the catalyst doped carbon-based nano noble metal catalyst Pd-Au / NPC; The phytic acid-doped polyaniline is prepared according to the following steps: Stir and mix 20 - 40 mmol of aniline, 80 - 120 mL of deionized water, and 3.2 - 9.6 mL of phytic acid evenly, then dissolve 1 - 3 g of ammonium persulfate in 10 mL of deionized water and add it dropwise to the above solution, react in an ice-water bath for 8 - 16 h, and obtain phytic acid-doped polyaniline PA-PANI after washing and drying.

2. The method for preparing a doped carbon-based nano-precious metal catalyst according to claim 1, characterized in that: The preparation method of the nitrogen and phosphorus co-doped carbon support is as follows: Pyrolyze PA-PANI in a nitrogen atmosphere at 600 - 800 °C for 0.5 - 2 h to obtain the nitrogen and phosphorus co-doped carbon NPC support.

3. The preparation method of a doped carbon-based nano noble metal catalyst according to claim 1, characterized in that: The gold-palladium bimetal colloid solution is prepared according to the following steps: First, prepare the gold colloid solution. Disperse 1 - 2 mL of 9.56 mg / mL HAuCl4 solution and 0.5 - 1.5 mL of 2 wt% PVA solution in 400 - 500 mL of deionized water, stir in an ice-water bath for 10 - 40 min, add 2 - 3 mL of 0.1 mol / L NaBH4 solution and then stir slowly for 1 - 4 h, and store it refrigerated at 0 - 4 °C for later use; Subsequently, take 30 - 50 mL of the above gold colloid solution, add 2 - 6 mL of 0.1 mol / L ascorbic acid solution, stir and disperse evenly, then add 0.01 - 0.5 mL of 1 mg / mL H2PdCl4 solution, and stir at room temperature for 8 - 16 h to obtain the gold-palladium bimetal colloid solution, and store it refrigerated at 0 - 4 °C for later use.

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