Preparation method of doped carbon-based nano noble metal catalyst

Abstract

The invention belongs to the technical field of preparation of nano noble metal catalysts, and relates to a preparation method of a doped carbon-based nano noble metal catalyst. Phytic acid doped polyaniline is prepared through chemical oxidative polymerization, a nitrogen and phosphorus co-doped carbon carrier is obtained through pyrolysis under the nitrogen atmosphere, gold and palladium bimetal is loaded through a metal colloid adsorption method, the doped carbon-based nano noble metal catalyst is obtained, the introduced doped element phosphorus has anchoring and dispersing effects on noble metal, and the noble metal is more stable in performance. The activity of the catalyst is remarkably improved by introducing a trace amount of second component metal palladium. The catalyst prepared by the invention is simple in synthesis method, high in activity, good in selectivity and excellent in cycling stability, is suitable for preparing parachloroaniline by hydrogenation of parachloronitrobenzene, and has a relatively wide application prospect.

Description

Technical Field

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

[0002] p-Chloroaniline is an important organic intermediate widely used in pesticides, medicines and insecticides. Traditional preparation methods such as iron powder reduction and alkali sulfide reduction have problems of environmental pollution and low yield. At present, catalytic hydrogenation has become the best choice due to its high efficiency and environmental 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 its 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 adjustable surface chemical properties, make them one of the preferred catalyst carriers. It is reported that carbon-based heteroatoms (N, P, S, B, etc.) can help anchor and disperse metal particles and regulate their electronic state, 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 properties, and easy dispersion of precious metal precursors (Chemical Engineering Journal 2022, 442, 136055). By loading precious metal nanoparticles on doped carbon-based carriers, stabilizing precious metal particles through carbon-based heteroatoms, and modulating the chemical state of the metal surface through the interaction between heteroatoms and precious metals, and then regulating the adsorption and activation during the catalytic process, it is expected to obtain highly active and stable supported precious metal catalysts.

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

[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 the 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 carrier to obtain a platinum-cobalt catalyst loaded on a PANI modified carbon carrier. Nitrogen doping and alloying effects strengthen the interaction between the metal and the carrier, reduce the agglomeration of metal particles, and improve the activity and durability of the catalyst when applied to a fuel cell. This technology does not involve the effect of introducing the P element by doping PANI with phytic acid, and its alloy element types, precious metal loading methods and applications are different from those of the present invention. The platinum-cobalt alloy content loaded by 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 relatively complicated compared to directly using polyaniline doping to introduce doping elements and then pyrolysis, and carbon black needs to be pretreated with highly corrosive and oxidizing hydrogen peroxide before use, and there are great safety hazards during operation.

[0006] The Chinese invention patent application with publication number CN 117427675 A discloses a "ruthenium-based catalyst and its preparation method and application", which uses phytic acid and ruthenium to heat and reflux to form a ruthenium complex Ru-PA, then mixes and stirs the complex Ru-PA with polyaniline in an aqueous solution to dope it into the polyaniline, and then pyrolyzes it at high temperature to evenly distribute ruthenium on the surface of PANI and phosphate it in situ, and pyrolyzes PANI into carbon material to obtain a doped carbon-supported ruthenium catalyst and applies it to catalyze the hydrogen-deuterium exchange reaction of hexamethylenediamine. This technology introduces phytic acid and active metal Ru on PANI in the form of a ruthenium complex and then pyrolyzes it. The preparation of the complex requires heating and reflux, and the process is relatively complicated. In addition, the high temperature process of PANI during the pyrolysis process easily causes the aggregation and growth of active metal particles, causing the catalyst to deactivate. Compared with the above invention, the present invention adopts the strategy of doping polyaniline with phytic acid to introduce phosphorus into the carbon carrier after pyrolysis. The amount of phosphorus is adjusted by adjusting the amount of doped phytic acid. The method is simpler and more efficient. 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 method for preparing a doped carbon-based nano noble metal catalyst. The nitrogen-phosphorus co-doped carbon carrier stabilized nano gold is prepared by pyrolysis of phytic acid-doped polyaniline, and the hydrogenation capacity of the gold catalyst is significantly improved by introducing a second component of palladium into the nano gold catalyst, thereby obtaining a highly active and stable catalyst that can be used for hydrogenation of p-chloronitrobenzene to prepare p-chloroaniline.

[0009] The present invention is achieved through the following technical solutions: A method for preparing a doped carbon-based nano noble metal catalyst, characterized in that: the carrier of the nano noble metal catalyst is a nitrogen-phosphorus co-doped carbon carrier derived from conductive polymer phytic acid-doped polyaniline, the noble metal is a gold-palladium bimetallic, and the loading method of the noble metal is a metal colloid adsorption method.

[0010] Phytic acid-doped polyaniline is prepared according to the following steps: 20-40 mmol aniline, 80-120 mL deionized water, and 3.2-9.6 mL phytic acid are stirred and evenly mixed, then 1-3 g ammonium persulfate is dissolved in 10 mL deionized water and added dropwise to the above aniline phytic acid solution, and the mixture is reacted in an ice-water bath for 8-16 h, and then washed and dried to obtain phytic acid-doped polyaniline PA-PANI.

[0011] The nitrogen-phosphorus co-doped carbon NPC support was obtained by pyrolyzing PA-PANI at 600-800 °C for 0.5-2 h (heating rate of 5 °C / min, N2 flow rate of 40 mL / min) under nitrogen atmosphere. The amount of P introduced was adjusted by the amount of phytic acid in PA-PANI.

[0012] The loading method of the precious metal is the metal colloid adsorption method. The metal colloid used is a gold-palladium bimetallic colloid solution, which is prepared according to the following steps: first, prepare the gold colloid solution, disperse 1-2 mL HAuCl4 solution (9.56 mg / mL) and 0.5-1.5 mL PVA solution (2 wt%) in 400-500 mL deionized water, stir in an ice water bath for 10-40 min, add 2-3 mL NaBH4 solution (0.1 mol / L) dropwise, stir slowly for 1-4 h, and refrigerate at 0-4 °C for later use; Then, take 30-50 mL of the self-made gold colloid solution, add 2-6 mL of ascorbic acid solution (0.1 mol / L), stir and disperse evenly, then add 0.01-0.5 mL of H2PdCl4 solution (1 mg / mL), stir at room temperature for 8-16 h, and refrigerate at 0-4 °C for later use; 0.05-0.1 g of NPC carrier was dispersed in 2-5 mL of deionized water, and 10-34 mL of gold-palladium bimetallic colloid solution was added. After stirring and adsorbing for 18-30 h, Pd-Au / NPC was obtained by washing and drying. The amount of Pd introduced was adjusted by the amount of H2PdCl4 solution used in the preparation of gold-palladium bimetallic colloid.

[0013] The catalyst has excellent activity and stability when applied to the reaction of preparing p-chloroaniline by hydrogenation of p-chloronitrobenzene, wherein the pressure of hydrogen is 0.8-1.2 MPa and the reaction temperature is 60-120°C.

[0014] The nitrogen-doped carbon (NC) carrier was prepared by pyrolysis of hydrochloric acid-doped polyaniline (HCl-PANI) as a comparison. The preparation was carried out according to the following steps: 30-60 mmol aniline was dissolved in 30-50 mL deionized water, and hydrochloric acid was added to adjust the pH to 0.4, and then 10-30 mL of initiator ammonium persulfate solution (2.5 mol / L) was added. After vigorous stirring for 1 h, it was allowed to stand at room temperature for 24 h, and HCl-PANI was obtained after washing and drying. The NC carrier was obtained by pyrolysis under the same conditions as PA-PANI. Pd-Au / NC was obtained by replacing NPC in the preparation process of Pd-Au / NPC with NC as a comparison.

[0015] Nano-gold catalysts were prepared by NaBH4 reduction method, urea precipitation method and gold colloid adsorption method for comparison. The NaBH4 reduction method was prepared according to the following steps: 0.2~0.4 g of the carrier was dispersed in 20~40 mL of deionized water, and then 0.1~0.2 mL of HAuCl4 solution (9.56 mg / mL) was added. After vigorous stirring for 30 min, 8~12 mL of NaBH4 aqueous solution containing 0.01~0.03 g was added dropwise to the carrier gold dispersion. After reacting in an ice-water bath for 10~30 min, Au / NC (NaBH4) was obtained by washing and drying.

[0016] The urea precipitation method was prepared according to the following steps: 0.04-0.08 g urea was dissolved in 8-12 mL water, and then 0.1-0.2 mL HAuCl4 solution (9.56 mg / mL) was added. After uniform dispersion, 0.1-0.3 g carrier was added. The mixture was stirred at 70-80 °C for 2-6 h, washed and dried, and calcined at 150-250 °C in air atmosphere for 3-6 h to obtain Au / NC(UDP).

[0017] Among them, the preparation process of gold colloid adsorption to prepare nano-gold catalyst is consistent with the process of gold-palladium bimetallic colloid adsorption to prepare Pd-Au / NPC, except that the gold-palladium bimetallic colloid solution is replaced by gold colloid solution, and the carrier NPC is replaced by NC.

[0018] The present invention is unique and invents a preparation technology for doped carbon-based nano-precious metal catalysts. This technology integrates the basic principles and cutting-edge achievements in the fields of nanoscience, catalytic science, and polymer science. A nitrogen-phosphorus co-doped carbon-loaded gold catalyst is prepared by pyrolysis of a conductive polymer, and metal particles are anchored and dispersed with the help of carbon-based heteroatoms to improve the stability of the nano-gold catalyst. By introducing a trace amount of a second metal element, the activity and stability of the catalyst in catalyzing 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 cyclic stability. It can be efficiently applied to the hydrogenation of p-chloronitrobenzene and has broad application prospects. The implementation of the present invention has important promoting significance for accelerating the research and development of new catalysts and the speed of industrial application, leading the development of emerging industries, and promoting the transformation of traditional industries. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The catalytic activity diagram of the x% Au / NC catalyst with different gold loadings prepared by the gold colloid adsorption method in Example 1 of the present invention. (x% is the theoretical loading of gold, reaction conditions: reaction temperature, 100°C; H2 pressure, 1.2 MPa; reaction time, 2h; substrate amount, 0.787 g p-chloronitrobenzene; solvent amount, 25 mL methanol).

[0020] Figure 2 The catalytic activity diagram of 0.5% Au / NC catalyst 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 p-chloronitrobenzene; solvent amount, 25 mL methanol).

[0021] Figure 3 Transmission electron microscopy images and gold particle size distribution diagrams of 0.5% Au / NC and 0.05% Pd-0.5% Au / NC catalysts prepared by metal colloid adsorption method in Examples 1 and 4 of the present invention.

[0022] Figure 4 The catalytic activity diagram of x%Pd-0.5%Au / NC catalysts with different Pd loadings prepared by 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 p-chloronitrobenzene; solvent amount, 25 mL methanol).

[0023] Figure 5The catalytic activity diagram of 0.05% Pd-0.5% Au / NPC (x:1) with different phytic acid dosages prepared by 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 p-chloronitrobenzene; solvent amount, 25 mL methanol).

[0024] Figure 6 XRD diagrams of the catalysts and NPC carriers prepared in Examples 1, 5, and 6 of the present invention.

[0025] Figure 7 Transmission electron microscopy and gold size distribution diagram of the catalyst and NPC carrier prepared in Examples 5 and 6 of the present invention.

[0026] Figure 8 Au4f XPS spectra of the catalysts prepared in Examples 4 and 6 of the present invention.

[0027] Fig. 9 Pd3d XPS spectra of the catalysts prepared in Examples 4 and 6 of the present invention.

[0028] Fig.10 P2p XPS spectra of the NPC support prepared in the present invention and the catalyst prepared in Example 6.

[0029] Fig.11 The catalytic activity diagram of the catalyst prepared in Example 6 of the present invention as a function of temperature and pressure (reaction conditions: reaction time, 1 h; substrate amount, 0.787 g p-chloronitrobenzene; solvent amount, 25 mL methanol).

[0030] Fig.12 This is a 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 p-chloronitrobenzene; solvent amount, 25 mL methanol). DETAILED DESCRIPTION

[0031] The present invention will be further explained below in conjunction with specific embodiments and accompanying drawings: Example 1: Preparation of x% Au / NC catalyst by gold colloid adsorption method 50 mmol of aniline was dissolved in 40 mL of deionized water, and hydrochloric acid was added to adjust the pH to 0.4, and then 20 mL of initiator ammonium persulfate solution (2.5 mol / L) was added. After vigorous stirring for 1 h, the mixture was allowed to stand at room temperature for 24 h, and HCl-PANI was obtained after washing and drying. HCl-PANI was pyrolyzed at 800 °C for 1 h in a nitrogen atmosphere (heating rate of 5 °C / min, N2 flow rate of 40 mL / min) to obtain the NC carrier.

[0032] Subsequently, 1.33 mL of HAuCl4 solution (9.56 mg / mL) and 1 mL of PVA solution (2 wt%) were dispersed in 431.3 mL of deionized water, stirred in an ice-water bath for 20 min, and 2.5 mL of NaBH4 solution (0.1 mol / L) was added dropwise and slowly stirred for 2 h to obtain a gold colloidal solution, which was refrigerated at 0-4 °C for later use.

[0033] 0.1 g of carrier NC was dispersed in 2.5 mL of deionized water, and 17 mL of gold colloid solution was added and stirred for 24 h. Then, 0.5% Au / NC(Sol) was obtained by washing and drying, where 0.5% is the theoretical loading amount of gold, and its size can be optimized and adjusted according to the change in the amount of gold colloid solution added.

[0034] pass Figure 1 It can be seen that the nitrogen-carbon-supported nano-gold catalyst 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%, which is higher than 0.3% Au / NC (2.9%) and 0.7% Au / NC (7.2%). This is because when the gold loading is low, the active gold species are relatively few, and when the gold loading is high, the active gold species may agglomerate due to the high surface energy. Therefore, the gold loading is preferably 0.5%.

[0035] Example 2: Preparation of 0.5% Au / NC catalyst by NaBH4 reduction method 50 mmol of aniline was dissolved in 40 mL of deionized water, and hydrochloric acid was added to adjust the pH to 0.4, and then 20 mL of initiator ammonium persulfate solution (2.5 mol / L) was added. After vigorous stirring for 1 h, the mixture was allowed to stand at room temperature for 24 h, and HCl-PANI was obtained after washing and drying. HCl-PANI was pyrolyzed at 800 °C for 1 h in a nitrogen atmosphere (heating rate of 5 °C / min, N2 flow rate of 40 mL / min) to obtain the NC carrier.

[0036] 0.3 g of the carrier was dispersed in 30 mL of deionized water, and then 0.157 mL of HAuCl4 solution (9.56 mg / mL) was added. After vigorous stirring for 30 min, 10 mL of aqueous NaBH4 solution containing 0.022 g was added dropwise to the carrier gold dispersion. After reacting in an ice-water bath for 15 min, 0.5% Au / NC (NaBH4) was obtained by washing and drying.

[0037] Example 3: Preparation of 0.5% Au / NC catalyst by urea precipitation method 50 mmol of aniline was dissolved in 40 mL of deionized water, and hydrochloric acid was added to adjust the pH to 0.4, and then 20 mL of initiator ammonium persulfate solution (2.5 mol / L) was added. After vigorous stirring for 1 h, the mixture was allowed to stand at room temperature for 24 h, and HCl-PANI was obtained after washing and drying. HCl-PANI was pyrolyzed at 800 °C for 1 h in a nitrogen atmosphere (heating rate of 5 °C / min, N2 flow rate of 40 mL / min) to obtain the NC carrier.

[0038] 0.06 g urea was dissolved in 10 mL water, and then 0.104 mL HAuCl4 solution (9.56 mg / mL) was added. After uniform dispersion, 0.2 g carrier was added, stirred at 80 °C for 4 h, washed and dried, and calcined at 200 °C in air atmosphere for 5 h to obtain 0.5% Au / NC(UDP).

[0039] Attached Figure 2 The catalytic activity diagram of nitrogen-carbon-based catalysts with different gold loading methods. When the gold loading is controlled at 0.5%, the conversion rates of 0.5%Au / NC(NaBH4) and 0.5%Au / NC(UDP) for hydrogenation of p-chloronitrobenzene are 3.7% and 8.0%, respectively, which are lower than 0.5%Au / NC(Sol). Therefore, the preferred gold loading method is metal colloid adsorption.

[0040] Example 4: Preparation of x%Pd-0.5%Au / NC Catalyst by Metal Colloid Adsorption 50 mmol of aniline was dissolved in 40 mL of deionized water, and hydrochloric acid was added to adjust the pH to 0.4, and then 20 mL of initiator ammonium persulfate solution (2.5 mol / L) was added. After vigorous stirring for 1 h, the mixture was allowed to stand at room temperature for 24 h, and HCl-PANI was obtained after washing and drying. HCl-PANI was pyrolyzed at 800 °C for 1 h in a nitrogen atmosphere (heating rate of 5 °C / min, N2 flow rate of 40 mL / min) to obtain the NC carrier.

[0041] Take 40 mL of the self-made gold colloidal 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 a gold-palladium bimetallic colloidal solution.

[0042] 0.1 g of carrier NC 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, 0.05%Pd-0.5%Au / NC was obtained by washing and drying. The Pd loading can be adjusted by changing the amount of H2PdCl4 solution added during the preparation of the bimetallic colloid.

[0043] Attached Figure 3 The transmission electron microscope images and gold size distribution diagrams of the catalysts prepared in Example 1 and Example 4. It can be seen from the figure that the gold nanoparticles with a particle size of about 2-5 nm are evenly dispersed on the NC carrier, and the average particle size of gold in 0.05%Pd-0.5%Au / NC (3.70 nm) is slightly reduced compared to the average particle size of gold in 0.5%Au / NC (3.75 nm), indicating that the introduction of trace amounts of Pd plays a certain role in physical isolation of gold nanoparticles, making the gold particles relatively small. Furthermore, the size and distribution of the precious metal particles do not change much after the introduction of Pd, which means that Pd is mainly on the Au nanoparticles.

[0044] Figure 4 The catalytic activity diagram of x%Pd-0.5%Au / NC catalysts with different Pd loadings prepared by metal colloid adsorption method. Figure 1 and attached 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 0.5% Au / NC catalyst obtained by optimization is only 11.4%. By introducing a trace amount of Pd, the hydrogenation efficiency of the catalyst can be significantly improved. Figure 4 It can be seen that with the increase of Pd content, the conversion rate of p-chloronitrobenzene gradually increases. When the loading amount is 0.05%, the substrate can be completely converted within 2 h and has a high p-chloroaniline selectivity close to 100%. When the Pd content is further increased, the selectivity of p-CAN drops sharply due to the strong dissociation ability of Pd for hydrogen. 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%.

[0045] Example 5: Preparation of 0.5% Au / NPC catalyst by gold colloid adsorption method 16.5 mmol aniline, 100 mL deionized water, and 4.8 mL phytic acid were stirred and mixed evenly, and then 1.8 g ammonium persulfate was dissolved in 10 mL 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 by washing and drying. PA-PANI was pyrolyzed at 800 °C for 1 h in a nitrogen atmosphere (heating rate of 5 °C / min, N2 flow rate of 40 mL / min) to obtain the NPC carrier.

[0046] 0.1 g of carrier NPC was dispersed in 2.5 mL of deionized water, and 17 mL of gold colloid solution was added and stirred for 24 h. Then, 0.5% Au / NPC was obtained by washing and drying.

[0047] This catalyst was applied to the hydrogenation reaction of p-chloronitrobenzene, and its conversion rate was only 5%. Therefore, the nano-gold catalyst supported on the P-doped modified carbon carrier was not effective.

[0048] Example 6: Preparation of 0.05% Pd-0.5% Au / NPC catalyst by metal colloid adsorption method 16.5 mmol aniline, 100 mL deionized water, and 4.8 mL phytic acid were stirred and mixed evenly. Then 1.8 g ammonium persulfate was dissolved in 10 mL 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 by washing and drying. The NPC carrier was obtained by pyrolyzing PA-PANI at 800 °C for 1 h in a nitrogen atmosphere (heating rate of 5 °C / min, N2 flow rate of 40 mL / min). The P content in the NPC carrier was regulated by controlling the amount of phytic acid.

[0049] 0.1 g of carrier 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, 0.05%Pd-0.5%Au / NPC was obtained by washing and drying.

[0050] Figure 5 The catalytic activity diagram of 0.05%Pd-0.5%Au / NPC (x:1) with different phytic acid dosages prepared by metal colloid adsorption method shows that as the molar ratio of aniline to phytic acid decreases, its activity in catalyzing the hydrogenation of p-chloronitrobenzene to prepare p-chloroaniline increases first and then decreases. When the molar ratio of aniline to phytic acid is 2:1, its conversion rate and selectivity are both 100%. Therefore, the molar ratio of aniline to phytic acid is preferably 2:1. It is worth noting that compared with the bimetallic 0.05%Pd-0.5%Au / NC supported by nitrogen-doped carbon, under the same conditions, the time for the complete conversion of p-chloronitrobenzene catalyzed by 0.05%Pd-0.5%Au / NPC is shortened from 2h to 1h, and the introduction of P element significantly improves the catalytic efficiency of the catalyst.

[0051] Figure 6 The 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) carriers are shown. All samples show a broad diffraction peak at 24°, which is attributed to the (002) crystal plane of carbon, indicating that they have an amorphous carbon structure; at the same time, the characteristic peak at 44° corresponds to the (100) crystal plane of carbon, confirming the successful carbonization of the material.

[0052] In particular, for the gold-loaded catalysts 0.5%Au / NC and 0.5%Au / NPC(2:1), the characteristic peak of Au (111) was observed at 2θ = 38.3°, directly proving the effective loading of Au. It is worth noting that although the Au loading is the same for both, the intensity of the characteristic peak of Au (111) in 0.5%Au / NPC(2:1) is weaker, which may be due to the more uniform dispersion of Au on the NPC(2:1) support or the smaller particle size.

[0053] Furthermore, when the second active component Pd was introduced on the basis of 0.5% Au / NPC (2:1), no obvious Au and Pd characteristic peaks were detected in the XRD spectrum. This phenomenon means that the particle size of Pd and Au may be reduced due to the addition of Pd, reaching below the XRD detection limit, or they exist in a highly dispersed form, thus failing to form a detectable crystalline phase. This indicates that the dispersion of metal particles in the bimetallic catalyst has been optimized, which is beneficial to the improvement of catalytic performance.

[0054] Figure 7 The transmission electron microscope images of the catalysts prepared in Examples 5 and 6 of the present invention are shown in the accompanying Figure 2 Compared with the catalysts without P doping modification, the average size of the gold (3.41 nm) and gold-palladium bimetallic (3.33 nm) catalyst nanoparticles loaded by NPC is significantly reduced, indicating that the heteroatom P plays a good role in anchoring and dispersing the precious metal. 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 improving its catalytic activity. Comparing Example 6 and Example 5, after introducing a trace amount of Pd, the size of the nanoparticles is only slightly reduced, indicating that Pd is mainly loaded on the nanogold particles, and the introduction of Pd plays a physical isolation role on the gold nanoparticles, which slightly reduces the particle size of the gold particles.

[0055] Figure 8The XPS spectra of Au4f prepared in Examples 4 and 6 of the present invention are shown in Figure 1. As can be seen from the figure, after P doping, Au4f 7 / 2 The binding energy of Pd 3d Pd 2+ The binding energy of the species shifted from 337.22 to 337.56 eV, and its content increased from 3.4% to 9.2% (see Appendix). Fig. 9 ). Therefore, it can be determined that the P-doped carrier has a strong carrier-noble metal electronic interaction with Au and Pd. This interaction makes Au and Pd electron-deficient, and the electron-deficient gold palladium on the surface is conducive to the adsorption and activation of the substrate p-chloronitrobenzene, thus significantly improving its catalytic activity. Fig.10 From the P2p XPS spectra of the NPC carrier and the catalyst prepared in Example 6, it can be seen that the binding energy of P2p in the XPS spectrum of the NPC after metal loading is shifted to low binding energy relative to the NPC carrier, which once again confirms the electron transfer from gold and palladium to the carrier after precious metal loading, and there is a strong electronic interaction between the precious metal and the carrier.

[0056] Fig.11 The catalytic activity diagram of the catalyst prepared for Example 6 of the present invention as a function of temperature and pressure. When the reaction temperature is controlled to be 100 ° C, the conversion rate is 80% when the hydrogen pressure is 0.8 MPa. As the pressure increases, the overall conversion rate shows an upward trend. When the pressure is 1.2 MPa, the conversion rate reaches 100%, and the selectivity is close to 100%. Overall, the change in pressure has a more obvious effect on the conversion rate, but the selectivity remains almost unchanged, proving that increasing the pressure does not lead to the occurrence of side reactions. The effect of temperature on the reaction has a similar trend. The control pressure is 1.2 MPa. In the range of 60~120 ° C, as the temperature increases, the conversion rate gradually increases until the conversion is complete, and the selectivity remains basically unchanged, so the reaction temperature is preferably 100 ° C, and the reaction pressure is preferably 1.2 MPa.

[0057] Fig.12 This is the cyclic activity diagram of the 0.05% Pd-0.5% Au / NPC (2:1) catalyst of Example 6. The reaction time is 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 decreases from 82% to 52%, which has excellent recycling ability, indicating that the catalyst of the present invention has the characteristics of high cyclic activity and good stability.

Claims

1. A method for preparing a doped carbon-based nano-precious metal catalyst, characterized in that: The carrier of the nano noble metal catalyst is a nitrogen-phosphorus co-doped carbon carrier NPC obtained by pyrolysis of phytic acid-doped polyaniline, the noble metal is a gold-palladium bimetallic, and the preparation method of the doped carbon-based nano noble metal catalyst is as follows: 0.05-0.1 g of the NPC carrier is dispersed in 2-5 mL of deionized water, 10-34 mL of a gold-palladium bimetallic colloid solution is added, the mixture is stirred and adsorbed for 18-30 h, and the catalyst-doped carbon-based nano noble metal catalyst Pd-Au / NPC is obtained by washing and drying.

2. The method for preparing a doped carbon-based nano-precious metal catalyst according to claim 1, characterized in that: The phytic acid-doped polyaniline is prepared according to the following steps: 20-40 mmol aniline, 80-120 mL deionized water, and 3.2-9.6 mL phytic acid are stirred and mixed evenly, then 1-3 g ammonium persulfate is dissolved in 10 mL deionized water and added dropwise to the above solution, reacted in an ice-water bath for 8-16 h, and phytic acid-doped polyaniline PA-PANI is obtained after washing and drying.

3. 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-phosphorus co-doped carbon carrier is as follows: pyrolyzing PA-PANI at 600-800° C. for 0.5-2 h in a nitrogen atmosphere to obtain the nitrogen-phosphorus co-doped carbon NPC carrier.

4. The method for preparing a doped carbon-based nano-precious metal catalyst according to claim 1, characterized in that: The gold-palladium bimetallic colloid solution is prepared according to the following steps: first, a gold colloid solution is prepared, 1-2 mL of a 9.56 mg / mL HAuCl4 solution and 0.5-1.5 mL of a 2 wt% PVA solution are dispersed in 400-500 mL of deionized water, stirred in an ice-water bath for 10-40 min, 2-3 mL of a 0.1 mol / L NaBH4 solution is added dropwise, and then slowly stirred for 1-4 h, and refrigerated at 0-4°C for use; then, 30-50 mL of the above gold colloid solution is taken, 2-6 mL of a 0.1 mol / L ascorbic acid solution is added, and after stirring and dispersing evenly, 0.01-0.5 mL of a 1 mg / mL H2PdCl4 solution is added, and stirred at room temperature for 8-16 h to obtain a gold-palladium bimetallic colloid solution, which is refrigerated at 0-4°C for use.

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