Atomic dispersed Pd-Pt catalyst for dinitrotoluene hydrogenation reaction and preparation method and application thereof

Abstract

The invention discloses an atomically dispersed Pd-Pt catalyst for dinitrotoluene hydrogenation reaction and its preparation method and application, and belongs to the technical field of organic chemical raw material synthesis. The catalyst is loaded on the surface of a nanocarrier in the form of a Pd-Pt atomically dispersed cluster by a coprecipitation method to obtain the atomically dispersed Pd-Pt catalyst. The loading amount of Pd in ​​the catalyst is 0.1-2.0wt%, and the content of Pt is 0.1-2.0wt%. The present invention utilizes atomic dispersion and Pd-Pt synergistic effects to enhance catalytic activity, effectively reducing catalyst costs. The catalyst of the present invention has strong hydrogenation activity and selectivity, and is very suitable for the application of catalyzing dinitrotoluene hydrogenation to prepare toluenediamine under mild conditions (20-60°C, 0.2-1.0MPa). The catalyst has low raw material cost, simple preparation process, stable performance and high catalytic activity.

Description

Technical Field

[0001] The invention relates to the technical field of organic chemical raw material synthesis, and in particular to an atomic-level Pd-Pt catalyst for dinitrotoluene hydrogenation reaction, and a preparation method and application thereof. Background Art

[0002] Toluenediamine (TDA) is the raw material for the preparation of toluene diisocyanate (TDI) and an important raw material for the polyurethane (PU) industry. It is widely used in coatings, foam plastics, fibers, adhesives and other industries. Toluenediamine is usually converted from dinitrotoluene (DNT). Since dinitrotoluene contains two unsaturated nitro groups, the reaction process is a multi-step hydrogenation. The conversion of the first nitro group (electron-withdrawing group) to an amine group (electron-donating group) will reduce the electron defect in the ring and hinder the further reduction of the second nitro group, making it difficult to achieve complete conversion to toluenediamine. The liquid phase catalytic hydrogenation method is mainly used in industry. The catalysts used are mainly Raney nickel catalysts and supported precious metal (Pd / C, Pt / C) catalysts. However, these commercial catalysts need to be used under high temperature and high pressure conditions. Since nitro hydrogenation is a strongly exothermic reaction, excessively high reaction temperatures can easily cause temperature runaway and affect the activity and life of the catalyst. In addition, these catalysts cannot avoid the formation of a small amount of azo compounds, dimers and polymers, which increases the production cost by adding additional purification steps.

[0003] Patent CN113145112A reports a catalyst using activated carbon as a carrier and loaded with Pd-Pt nanoparticles. Under the same conditions (110°C, 1.0MPa), the catalyst activity is higher than that of Pt / C prepared by the same method. However, its toluenediamine yield is low, the production temperature is high, and the main reaction is a highly exothermic reaction, which is easy to cause temperature runaway, affecting the catalyst life and selectivity. Patent CN114797934A reports a catalyst of nitrogen-doped carbon nanotubes loaded with palladium-platinum bimetallic nanoparticles, which is used for catalytic hydrogenation of meta-dinitrobenzene to produce meta-phenylenediamine. In its embodiment, the meta-dinitrobenzene conversion rate is greater than 99%, but the meta-phenylenediamine yield is low and requires a higher reaction pressure.

[0004] Heterogeneous catalytic reactions only occur on the surface of metal nanoparticles, while most of the metal atoms in the core do not show any catalytic activity. In some catalytic reactions, supported metal nanoparticle catalysts have limited metal utilization and low catalytic activity, requiring harsh reaction conditions, and also increasing the cost of using the catalyst. Current research has found that when the size of the active metal on the surface of the carrier reaches the atomic level, the utilization rate of the active metal can be improved, and the catalytic effect of the active metal can be optimized, thereby showing excellent catalytic performance in many reactions. Therefore, the development of atomically dispersed metal catalysts can greatly improve the utilization efficiency of metals, especially reduce the cost of precious metal catalysts. Summary of the invention

[0005] In order to solve the problems of low utilization rate of active metals in the catalyst of the current dinitrotoluene hydrogenation reaction process, poor reaction activity, and harsh reaction conditions, the present invention provides an atomic-level dispersed Pd-Pt catalyst for dinitrotoluene hydrogenation reaction and its preparation method and application, in which the Pd-Pt active metal component is uniformly loaded on a nanocarrier by a coprecipitation method, and is bonded to defects / vacancies on the carrier to form atomic-level dispersed Pd-Pt clusters, which greatly improves the utilization rate of metal atoms; the synergistic effect of Pd-Pt hydrogenation is utilized to improve the catalytic efficiency and realize the efficient hydrogenation of dinitrotoluene. The atomic-level dispersed loaded Pd-Pt metal catalyst for catalyzing the hydrogenation reaction of dinitrotoluene has high utilization rate of active metal atoms, high activity and high selectivity, and can efficiently synthesize toluenediamine under mild reaction conditions.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] An atomically dispersed Pd-Pt catalyst for dinitrotoluene hydrogenation reaction, the catalyst is composed of a nano-carrier and an active metal component loaded on the carrier; wherein the active metal component is uniformly loaded on the nano-carrier and bonds with defects / vacancies on the carrier to form atomically dispersed Pd-Pt clusters.

[0008] The nanocarrier is one or more of nanodiamond, nanographene, graphene / nanodiamond composite material, nano activated carbon, nanosilicon dioxide, nanoalumina and nanotitanium dioxide, preferably graphene / nanodiamond composite material, nanographene or nanoalumina, in particular, the graphene / nanodiamond composite material is a nanodiamond core and defect-rich graphene shell with sp 3 Carbon nucleus sp 2 Carbon shell hybrid core-shell structure materials.

[0009] The active metal components are Pd and Pt, the loading amount of Pd is 0.1wt%-2.0wt%, and the loading amount of Pt is 0.1wt%-2.0wt%. The Pd and Pt are uniformly loaded on the nanocarrier in the form of atomic-level dispersed clusters; the Pd-Pt atomic cluster is the active center of the Pd-Pt catalyst.

[0010] The method for preparing the atomically dispersed Pd-Pt catalyst for dinitrotoluene hydrogenation reaction comprises the following steps:

[0011] (1) Preparing a mother liquor containing active metals: dissolving a Pd metal salt in deionized water to obtain a Pd metal mother liquor having a Pd concentration of 20 g / L; dissolving a Pt metal salt in deionized water to obtain a Pt metal mother liquor having a Pt concentration of 20 g / L; measuring the Pd metal mother liquor and the Pt metal mother liquor according to the required Pd and Pt loading amounts in the catalyst, respectively, mixing, adding deionized water to dilute, and ultrasonically dispersing to obtain a mother liquor containing active metals.

[0012] (2) The active metals Pd and Pt are loaded onto the carrier by a co-precipitation method to obtain the atomically dispersed Pd-Pt catalyst.

[0013] In the above step (1), the Pd metal salt is any one of palladium chloride (PdCl2), sodium tetrachloropalladate (Na2PdCl4), and palladium nitrate (Pd(NO3)2).

[0014] In the above step (1), the Pt metal salt is any one of chloroplatinic acid (H2PtCl6·6H2O) and platinum tetrachloride (PtCl4).

[0015] The process of the coprecipitation method in step (2) above is as follows:

[0016] The nanocarrier powder and deionized water are added to a flask and ultrasonically dispersed to obtain a nanocarrier dispersion; the obtained dispersion is placed in an oil bath for heating and stirring, and a precipitant solid powder is added to the dispersion, and then the mother liquor containing active metals prepared in step (1) is slowly added dropwise according to a proportion, and the mixture is stirred and refluxed and allowed to stand for a period of time; after filtration and drying, the mixture is reduced in a mixed atmosphere of H2 and He to obtain an atomically dispersed Pd-Pt catalyst.

[0017] In the coprecipitation method, the precipitant is one or more of sodium formate, sodium carbonate and sodium bicarbonate, preferably sodium formate, and the molar ratio of the precipitant to the active metal component (Pd+Pt) is 800:1-1000:1.

[0018] In the co-precipitation method, the amount of nanocarrier powder used is 200 mg, the amount of deionized water used is 20-40 mL, the ultrasonic dispersion time is 10-50 min, the heating temperature of the oil bath is 80-100° C., and the dispersion is stirred in the oil bath for 10-50 min; the stirring and reflux time is 1-2 h, and after stirring and reflux, the flask is taken out and cooled, and then filtered after standing for 6-12 h; the drying is carried out in a vacuum drying oven, the drying temperature is 60° C., and the drying time is 12 h; in the mixed atmosphere of H2 and He, the volume ratio of H2 is 10%; the reduction temperature is 150-300° C., and the reduction time is 2 h.

[0019] The atomic-level dispersed Pd-Pt catalyst can be used for catalytic hydrogenation reaction of nitro compounds, and is particularly suitable for catalytic hydrogenation reaction of dinitrotoluene to prepare toluenediamine.

[0020] Preferably, the present invention provides a method for preparing toluenediamine by efficiently hydrogenating dinitrotoluene. The method is carried out in a kettle reactor and uses the Pd-Pt catalyst of the present invention to hydrogenate dinitrotoluene and hydrogen raw materials to prepare toluenediamine.

[0021] The process of preparing toluenediamine by hydrogenation of dinitrotoluene is as follows:

[0022] Weigh the atomically dispersed Pd-Pt catalyst, solvent and dinitrotoluene and put them into the reactor; fill it with nitrogen at room temperature and check the air tightness. After the air tightness is good, replace the reactor with nitrogen and hydrogen three times respectively. After the replacement is completed, heat it to the specified temperature at a rate of 5℃ / min, and introduce hydrogen to the specified pressure. React under stirring conditions, and continue to introduce hydrogen during the reaction process to maintain a constant pressure.

[0023] The solvent is any one of methanol, ethanol, tetrahydrofuran, cyclohexane and toluene, preferably methanol, and the amount of the solvent is 10 mL.

[0024] The molar concentration of the dinitrotoluene is 0.1-1.0 mol / L.

[0025] The reaction temperature is 20-60°C.

[0026] The pressure of the hydrogen is 0.2-1.0 MPa.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] (1) The present invention uses a one-step co-precipitation method to evenly disperse Pd-Pt species on the surface of the nanocarrier. The defects / vacancies on the carrier surface provide anchoring points for the active component Pd-Pt, forming Pd-Pt atomic clusters, thereby improving the dispersibility of the Pd-Pt active metal on the carrier surface and effectively preventing the agglomeration of metal nanoparticles. A high-activity catalyst with atomic-level dispersion is obtained, which greatly improves the utilization rate of active metal atoms and the catalyst performance.

[0029] (2) The present invention regulates the catalyst performance through the Pd-Pt synergistic effect, effectively improving the catalytic activity and reducing the catalyst cost.

[0030] (3) The Pd-Pt catalyst prepared by the present invention is applied to the hydrogenation of dinitrotoluene to produce toluenediamine, achieving high conversion rate and high selectivity synthesis of toluenediamine under mild conditions, with low energy consumption, high safety and good economic benefits.

[0031] (4) The catalyst used in the present invention has low raw material cost, simple preparation, and is environmentally friendly and efficient. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The scanning transmission electron micrograph and mapping diagram of the Pd-Pt atomic-level cluster catalyst in Example 1; wherein: (a) and (b) are scanning transmission electron micrographs of the catalyst at different observation magnifications; (c) is the Pd element distribution; and (d) is the Pt element distribution.

[0033] Figure 2 This is a scanning transmission electron microscopy image of the Pd atomic cluster catalyst prepared in Comparative Example 1;

[0034] Figure 3 This is a scanning transmission electron microscopy image of the Pt atomic-level cluster catalyst prepared in Comparative Example 2. DETAILED DESCRIPTION

[0035] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0036] In the following examples and comparative examples, specific catalysts are represented by element symbols and English abbreviations, where Pd is palladium, Pt is platinum, G is graphene, NDG is graphene / nano-diamond composite material, and Al2O3 is aluminum oxide.

[0037] Embodiment 1:

[0038] 1) Catalyst preparation:

[0039] Take a certain amount of Pd(NO3)2 and H2PtCl6·6H2O mother liquor (Pd content is 0.5wt%, Pt content is 0.5wt%), add deionized water to dilute to 2mL, ultrasonically disperse, and obtain a metal precursor solution. Add 200mg NDG powder and 30mL deionized water to the flask and mix, and ultrasonically disperse for 30min. Place the resulting dispersion in an oil bath pot at 100℃ and stir for 30min. At the same time, add sodium bicarbonate solid powder to the dispersion (the total molar ratio of sodium bicarbonate and active metal is 900:1), then add the metal precursor solution dropwise, stir and reflux for 1h, take out the flask and cool it down and let it stand for 8h, filter it and dry it in a vacuum drying oven at 60℃ for 12h, then reduce it at 200℃ for 2h in a H2 / He mixed atmosphere (H2 accounts for 10vol.%) to obtain a NDG-loaded Pd-Pt catalyst, recorded as 05Pd05Pt / NDG. Figure 1 The SEM images and mapping of the catalysts are shown when the Pd and Pt loadings are both 0.5 wt.%. It can be seen that the Pd-Pt species are mainly dispersed on the nanocarbon carrier in the form of atomically dispersed Pd-Pt clusters.

[0040] 2) Preparation of toluenediamine by hydrogenation of dinitrotoluene:

[0041] Weigh 5mg 05Pd05Pt / NDG, 10mL methanol, 2mmol dinitrotoluene, and put them into a reactor. At room temperature, first fill it with nitrogen and check the air tightness. The air tightness is good, and the reactor is replaced with nitrogen and hydrogen three times respectively. After the replacement is completed, hydrogen is introduced to 1.0MPa at 20°C, and the reaction is stirred at 700rpm for 120min. Hydrogen is continuously introduced during the reaction process to maintain a constant pressure. The conversion rate of dinitrotoluene is 97.2%, and the selectivity is 96.8%.

[0042] Example 2

[0043] 1) Catalyst preparation:

[0044] Take a certain amount of PdCl2 and PtCl4 mother liquor (Pd content is 0.5wt%, Pt content is 1.0wt%), add deionized water to dilute to 2mL, ultrasonic dispersion, and obtain a metal precursor solution. 200mg nanographene powder and 40mL deionized water are added to a flask and mixed, and ultrasonic dispersion is performed for 30min. The resulting dispersion is placed in an oil bath pot and stirred at 100℃ oil bath for 30min, and sodium formate solid powder (sodium formate and active metal total molar ratio is 800:1) is added to the dispersion, and then the metal precursor solution is added dropwise, and after stirring and refluxing for 1h, the flask is taken out to cool and stand for 8h, filtered and dried in a 60℃ vacuum drying oven for 12h, and then reduced at 200℃ for 2h under a H2 / He mixed atmosphere (H2 accounts for 10vol.%) to obtain a nanographene-loaded Pd-Pt catalyst, recorded as 05Pd10Pt / G.

[0045] 2) Preparation of toluenediamine by hydrogenation of dinitrotoluene:

[0046] Weigh 5mg 05Pd10Pt / G, 10mL methanol, and 2mmol dinitrotoluene and put them into a reactor. At room temperature, first fill it with nitrogen and check the air tightness. The air tightness is good, and the reactor is replaced with nitrogen and hydrogen three times respectively. After the replacement is completed, the temperature is raised to 60°C at a rate of 5°C / min, and hydrogen is introduced to 1.0MPa. The reaction is stirred at 700rpm for 30min. Hydrogen is continuously introduced during the reaction process to maintain a constant pressure. The conversion rate of dinitrotoluene is >99.9%, and the selectivity is 99.4%.

[0047] Example 3

[0048] 1) Catalyst preparation:

[0049] Take a certain amount of Na2PdCl4 and PtCl4 mother liquor and mix them (Pd content is 0.5wt%, Pt content is 1.0wt%), add deionized water to dilute to 2mL, and ultrasonically disperse to obtain a metal precursor solution. Add 200mg of nano-alumina powder and 20mL of deionized water to a flask and mix, and ultrasonically disperse for 30min. The resulting dispersion is placed in an oil bath pot and stirred at 100℃ for 30min. At the same time, sodium formate solid powder is added to the dispersion (the total molar ratio of sodium formate and active metal is 1000:1), and then the metal precursor solution is added dropwise. After stirring and refluxing for 1h, take out the flask and cool it down and stand for 8h, filter it and dry it in a vacuum drying oven at 60℃ for 12h, then reduce it at 200℃ for 2h in a H2 / He mixed atmosphere (H2 accounts for 10vol.%) to obtain a nano-alumina-supported Pd-Pt catalyst, recorded as 05Pd10Pt / Al2O3.

[0050] 2) Preparation of toluenediamine by hydrogenation of dinitrotoluene:

[0051] Weigh 5mg 05Pd10Pt / Al2O3, 10mL methanol, and 2mmol dinitrotoluene and put them into a reactor. At room temperature, first fill it with nitrogen and check the air tightness. The air tightness is good, and the reactor is replaced with nitrogen and hydrogen three times respectively. After the replacement is completed, the temperature is raised to 60°C at a rate of 5°C / min, and hydrogen is introduced to 1.0MPa. The reaction is stirred at 700rpm for 30min. Hydrogen is continuously introduced during the reaction process to maintain a constant pressure. The conversion rate of dinitrotoluene is >99.9%, and the selectivity is 97.9%.

[0052] Example 4

[0053] 1) Catalyst preparation:

[0054] Take a certain amount of Pd(NO3)2 and H2PtCl6·6H2O mother liquor (Pd content is 0.5wt%, Pt content is 2.0wt%), add deionized water to dilute to 2mL, ultrasonically disperse, and obtain a metal precursor solution. Add 200mg NDG powder and 25mL deionized water to the flask and mix, and ultrasonically disperse for 30min. The resulting dispersion is placed in an oil bath pot and stirred at 80℃ for 30min. At the same time, sodium formate solid powder is added to the dispersion (the total molar ratio of sodium formate and active metal is 1000:1), and then the metal precursor solution is added dropwise. After stirring and refluxing for 1h, take out the flask and cool it down and stand for 8h, filter it and dry it in a vacuum drying oven at 60℃ for 12h, then reduce it at 200℃ for 2h in a H2 / He mixed atmosphere (H2 accounts for 10vol.%) to obtain a NDG-loaded Pd-Pt catalyst, recorded as 05Pd20Pt / NDG.

[0055] 2) Preparation of toluenediamine by hydrogenation of dinitrotoluene:

[0056] Weigh 5mg 05Pd20Pt / NDG, 10mL tetrahydrofuran, and 2mmol dinitrotoluene and put them into a reactor. At room temperature, first fill it with nitrogen and check the air tightness. The air tightness is good, and the reactor is replaced with nitrogen and hydrogen three times respectively. After the replacement is completed, the temperature is raised to 40°C at a rate of 5°C / min, and hydrogen is introduced to 1.0MPa. The reaction is carried out for 60min under stirring at 700rpm. Hydrogen is continuously introduced during the reaction process to maintain a constant pressure. The conversion rate of dinitrotoluene is >99.9%, and the selectivity is 97.5%.

[0057] Example 5

[0058] 1) Catalyst preparation:

[0059] Take a certain amount of Pd(NO3)2 and H2PtCl6·6H2O mother liquor (Pd content is 2.0wt%, Pt content is 0.5wt%), add deionized water to dilute to 2mL, ultrasonically disperse, and obtain a metal precursor solution. Add 200mg NDG powder and 30mL deionized water to the flask and mix, and ultrasonically disperse for 30min. The resulting dispersion is placed in an oil bath pot and stirred at 100℃ for 30min. At the same time, sodium formate solid powder is added to the dispersion (the total molar ratio of sodium formate and active metal is 900:1), and then the metal precursor solution is added dropwise. After stirring and refluxing for 1h, take out the flask and cool it down and stand for 8h, filter it and dry it in a vacuum drying oven at 60℃ for 12h, then reduce it at 200℃ for 2h in a H2 / He mixed atmosphere (H2 accounts for 10vol.%) to obtain a NDG-loaded Pd-Pt catalyst, recorded as 20Pd05Pt / NDG.

[0060] 2) Preparation of toluenediamine by hydrogenation of dinitrotoluene:

[0061] Weigh 5mg 20Pd05Pt / NDG, 10mL toluene, and 2mmol dinitrotoluene into a reactor. At room temperature, first fill with nitrogen and check the air tightness. The air tightness is good, and the reactor is replaced with nitrogen and hydrogen three times respectively. After the replacement is completed, the temperature is raised to 60°C at a rate of 5°C / min, and hydrogen is introduced to 0.4MPa. The reaction is stirred at 700rpm for 120min. Hydrogen is continuously introduced during the reaction process to maintain a constant pressure. The conversion rate of dinitrotoluene is 96.9%, and the selectivity is 94.2%.

[0062] Example 6

[0063] 1) Catalyst preparation:

[0064] Take a certain amount of Pd(NO3)2 and H2PtCl6·6H2O mother liquor (Pd content is 0.1wt%, Pt content is 0.5wt%), add deionized water to dilute to 2mL, ultrasonically disperse, and obtain a metal precursor solution. Add 200mg NDG powder and 30mL deionized water to the flask and mix, and ultrasonically disperse for 30min. Place the resulting dispersion in an oil bath pot at 100℃ and stir for 30min. At the same time, add sodium formate solid powder to the dispersion (the total molar ratio of sodium formate and active metal is 1000:1), then add the metal precursor solution dropwise, stir and reflux for 1h, take out the flask and cool it down and let it stand for 8h, filter it and dry it in a vacuum drying oven at 60℃ for 12h, then reduce it at 200℃ for 2h in a H2 / He mixed atmosphere (H2 accounts for 10vol.%) to obtain a NDG-loaded Pd-Pt catalyst, recorded as 01Pd05Pt / NDG.

[0065] 2) Preparation of toluenediamine by hydrogenation of dinitrotoluene:

[0066] Weigh 5mg 01Pd05Pt / NDG, 10mL methanol, and 2mmol dinitrotoluene and put them into a reactor. At room temperature, first fill it with nitrogen and check the air tightness. The air tightness is good. Replace the reactor with nitrogen and hydrogen three times respectively. After the replacement is completed, heat it to 50°C at a rate of 5°C / min, and introduce hydrogen to 0.6MPa. React for 30min under stirring at 700rpm. During the reaction process, hydrogen is continuously introduced to maintain a constant pressure. The conversion rate of dinitrotoluene is >99.9%, and the selectivity is 99.0%.

[0067] Example 7

[0068] 1) Catalyst preparation:

[0069] Take a certain amount of Pd(NO3)2 and H2PtCl6·6H2O mother liquor (Pd content is 0.5wt%, Pt content is 0.1wt%), add deionized water to dilute to 2mL, ultrasonically disperse, and obtain a metal precursor solution. Add 200mg NDG powder and 30mL deionized water to the flask and mix, and ultrasonically disperse for 30min. Place the resulting dispersion in an oil bath pot at 100℃ and stir for 30min. At the same time, add sodium formate solid powder to the dispersion (the total molar ratio of sodium formate and active metal is 900:1), then add the metal precursor solution dropwise, stir and reflux for 1h, take out the flask and cool it down and let it stand for 8h, filter it and dry it in a vacuum drying oven at 60℃ for 12h, then reduce it at 200℃ for 2h in a H2 / He mixed atmosphere (H2 accounts for 10vol.%) to obtain a NDG-loaded Pd-Pt catalyst, recorded as 05Pd01Pt / NDG.

[0070] 2) Preparation of toluenediamine by hydrogenation of dinitrotoluene:

[0071] Weigh 5mg 05Pd01Pt / NDG, 10mL methanol, and 2mmol dinitrotoluene and put them into a reactor. At room temperature, first fill it with nitrogen and check the air tightness. The air tightness is good, and the reactor is replaced with nitrogen and hydrogen three times respectively. After the replacement is completed, the temperature is raised to 60°C at a rate of 5°C / min, and hydrogen is introduced to 0.6MPa. The reaction is stirred at 700rpm for 30min. Hydrogen is continuously introduced during the reaction process to maintain a constant pressure. The conversion rate of dinitrotoluene is >99.9%, and the selectivity is >99.9%.

[0072] Example 8

[0073] 1) Catalyst preparation:

[0074] Take a certain amount of Pd(NO3)2 and H2PtCl6·6H2O mother liquor (Pd content is 0.5wt%, Pt content is 1.0wt%), add deionized water to dilute to 2mL, ultrasonically disperse, and obtain a metal precursor solution. Add 200mg NDG powder and 30mL deionized water to the flask and mix, and ultrasonically disperse for 30min. Place the resulting dispersion in an oil bath pot at 100℃ and stir for 30min. At the same time, add sodium formate solid powder to the dispersion (the total molar ratio of sodium formate and active metal is 900:1), then add the metal precursor solution dropwise, stir and reflux for 1h, take out the flask and cool it down and stand for 8h, filter it and dry it in a vacuum drying oven at 60℃ for 12h, then reduce it at 200℃ for 2h in a H2 / He mixed atmosphere (H2 accounts for 10vol.%) to obtain a NDG-loaded Pd-Pt catalyst, recorded as 05Pd10Pt / NDG.

[0075] 2) Preparation of toluenediamine by hydrogenation of dinitrotoluene:

[0076] Weigh 5mg 05Pd10Pt / NDG, 10mL methanol, and 2mmol dinitrotoluene and put them into a reactor. At room temperature, first fill it with nitrogen and check the air tightness. The air tightness is good. Replace the reactor with nitrogen and hydrogen three times respectively. After the replacement is completed, heat it to 60℃ at a rate of 5℃ / min, and introduce hydrogen to 1.0MPa. React for 10min under stirring at 700rpm. During the reaction process, hydrogen is continuously introduced to maintain a constant pressure. The conversion rate of dinitrotoluene is >99.9%, and the selectivity is >99.9%.

[0077] Example 9

[0078] 1) Catalyst preparation:

[0079] The catalyst was prepared by referring to the method of Example 1 and was recorded as 05Pd10Pt / NDG.

[0080] 2) Preparation of toluenediamine by hydrogenation of dinitrotoluene:

[0081] Weigh 5mg 05Pd10Pt / NDG, 10mL methanol, and 10mmol dinitrotoluene and put them into a reactor. At room temperature, first fill it with nitrogen and check the air tightness. The air tightness is good. Replace the reactor with nitrogen and hydrogen three times respectively. After the replacement is completed, heat it to 60℃ at a rate of 5℃ / min, and introduce hydrogen to 0.6MPa. React for 60min under stirring at 700rpm. During the reaction process, hydrogen is continuously introduced to maintain a constant pressure. The conversion rate of dinitrotoluene is >99.9%, and the selectivity is >99.9%.

[0082] Example 10

[0083] 1) Catalyst preparation:

[0084] The catalyst was prepared by referring to the method of Example 1, and was recorded as 05Pd05Pt / NDG. (The catalyst preparation scheme of Example 1 was used to carry out substrate expansion experiment)

[0085] 2) Preparation of toluenediamine by hydrogenation of dinitrotoluene:

[0086] The substrates are 2,4-dinitrochlorobenzene, 2,4-dinitroaniline, 2,4-dinitrobenzaldehyde, 2,4-dinitroanisole, and 3,5-dinitrobenzoic acid methyl ester. Weigh 5mg 05Pd05Pt / NDG, 10mL methanol, and 2mmol substrate and put them into the reactor. At room temperature, fill it with nitrogen and check the air tightness. The air tightness is good. The reactor is replaced with nitrogen and hydrogen three times respectively. After the replacement is completed, the temperature is raised to 60°C at a rate of 5°C / min, and hydrogen is introduced to 1.0MPa. The reaction is stirred at 700rpm for 20min. Hydrogen is continuously introduced during the reaction process to maintain a constant pressure. The specific reaction time and results are shown in Table 1.

[0087] Comparative Example 1

[0088] 1) Catalyst preparation:

[0089] The method of Example 1 is referred to, except that in step 1), only Pd(NO3)2 (Pd content is 0.5wt%) metal mother liquor is added, and other operations remain unchanged to obtain a catalyst, which is recorded as 05Pd / NDG. Figure 2 The figure shows the SEM image of the catalyst when the Pd loading is 0.5wt.%. It can be seen that the Pd species are mainly dispersed on the nanocarbon support in the form of atomically dispersed Pd clusters.

[0090] 2) Preparation of toluenediamine by hydrogenation of dinitrotoluene:

[0091] Weigh 5mg 05Pd / NDG, 10mL methanol, 2mmol dinitrotoluene, and put them into a reactor. At room temperature, first fill with nitrogen and check the air tightness. The air tightness is good, and the reactor is replaced with nitrogen and hydrogen three times respectively. After the replacement is completed, the temperature is raised to 60°C at a rate of 5°C / min, and hydrogen is introduced to 1.0MPa. The reaction is stirred at 700rpm for 10min. Hydrogen is continuously introduced during the reaction process to maintain a constant pressure. The conversion rate of dinitrotoluene is >99.9, and the selectivity is 62.1%.

[0092] Comparative Example 2

[0093] 1) Catalyst preparation:

[0094] The method of Example 1 is referred to, except that in step 1), only H2PtCl6·6H2O (Pt content is 0.5wt%) metal mother liquor is added, and other operations remain unchanged to obtain a catalyst, which is recorded as 05Pt / NDG. Figure 3 The SEM image of the catalyst with a Pt loading of 0.5 wt.% is shown. It can be seen that the Pt species are mainly dispersed on the nanocarbon support in the form of atomically dispersed Pt clusters.

[0095] 2) Preparation of toluenediamine by hydrogenation of dinitrotoluene:

[0096] Weigh 5mg 05Pt / NDG, 10mL methanol, 2mmol dinitrotoluene, and put them into a reactor. At room temperature, first fill it with nitrogen and check the air tightness. The air tightness is good, and the reactor is replaced with nitrogen and hydrogen three times respectively. After the replacement is completed, the temperature is raised to 60°C at a rate of 5°C / min, and hydrogen is introduced to 1.0MPa. The reaction is stirred at 700rpm for 10min. Hydrogen is continuously introduced during the reaction process to maintain a constant pressure. The conversion rate of dinitrotoluene is 97.0%, and the selectivity is 32.7%.

[0097] Table 1 Catalyst activity evaluation results of Example 10

[0098]

[0099] The above examples are for reference only. Technical solutions that are similar to the present invention or extended from the concept of this patent are all within the protection scope of the present invention.

Claims

1. An application of an atomically dispersed Pd-Pt catalyst for dinitrotoluene hydrogenation reaction, characterized in that: The atomic-level dispersed Pd-Pt catalyst is used to catalyze the hydrogenation reaction of dinitrotoluene to prepare toluenediamine; the reaction process uses dinitrotoluene and hydrogen as raw materials, and the reaction temperature is 20-60°C; The catalyst is composed of a nano-carrier and an active metal component; wherein the active metal component is uniformly loaded on the nano-carrier and bonds with defects / vacancies on the carrier to form atomically dispersed Pd-Pt clusters; The active metal components are Pd and Pt, the loading amount of Pd is 0.1-2.0wt%, and the loading amount of Pt is 0.1-2.0wt%. The Pd and Pt are uniformly loaded on the nanocarrier in the form of atomically dispersed Pd-Pt clusters; the Pd-Pt clusters are the active centers of the Pd-Pt catalyst; The nano-carrier is one or more of nano-diamond, nano-graphene, graphene / nano-diamond composite material, nano-activated carbon, nano-silicon dioxide, nano-aluminum oxide and nano-titanium dioxide.

2. The use of the atomically dispersed Pd-Pt catalyst for dinitrotoluene hydrogenation reaction according to claim 1, characterized in that: The graphene / nano-diamond composite material is a sp 3 Carbon nucleus sp 2 Carbon shell hybrid core-shell structure materials.

3. The use of the atomically dispersed Pd-Pt catalyst for dinitrotoluene hydrogenation reaction according to claim 1, characterized in that: The preparation method of the catalyst comprises the following steps: (1) preparing a mother liquor containing active metals: dissolving a Pd metal salt in deionized water to obtain a Pd metal mother liquor having a Pd concentration of 20 g / L; dissolving a Pt metal salt in deionized water to obtain a Pt metal mother liquor having a Pt concentration of 20 g / L; measuring the Pd metal mother liquor and the Pt metal mother liquor according to the required Pd and Pt loading amounts in the catalyst, respectively, mixing, adding deionized water to dilute, and ultrasonically dispersing to obtain a mother liquor containing active metals; (2) The active metal components are dispersed on the carrier by a coprecipitation method to obtain the atomically dispersed Pd-Pt catalyst; the process of the coprecipitation method is as follows: Add nanocarriers and deionized water into a flask and perform ultrasonic dispersion to obtain a nanocarrier dispersion; place the nanocarrier dispersion in an oil bath for heating and stirring, add a precipitant solid powder into the dispersion, then slowly dropwise add the mother solution containing active metals prepared in step (1) according to a certain proportion, stir and reflux, and then let stand for a period of time; After filtration and drying, the product is reduced in a mixed atmosphere of H2 and He to obtain an atomically dispersed Pd-Pt catalyst.

4. The use of the atomically dispersed Pd-Pt catalyst for dinitrotoluene hydrogenation reaction according to claim 3, characterized in that: The Pd metal salt is selected from any one of palladium chloride, sodium tetrachloropalladate and palladium nitrate, and the Pt metal salt is selected from any one of chloroplatinic acid and platinum tetrachloride.

5. The use of the atomically dispersed Pd-Pt catalyst for dinitrotoluene hydrogenation reaction according to claim 3, characterized in that: In the co-precipitation method of step (2), the precipitant is one or more of sodium formate, sodium carbonate and sodium bicarbonate; and the molar ratio of the precipitant to the total of the active metal components Pd and Pt is 800:1-1000:

1.

6. The use of the atomically dispersed Pd-Pt catalyst for dinitrotoluene hydrogenation reaction according to claim 3, characterized in that: In the co-precipitation method of step (2), the amount of nanocarrier is 200 mg, the amount of deionized water is 20-40 mL, and the ultrasonic time is 10-50 min; the temperature of the oil bath is 80-100° C., the dispersion is stirred in the oil bath for 10-50 min, the stirring and reflux time is 1-2 h, and after stirring and reflux, the flask is taken out and cooled, and then filtered after standing for 6-12 h; the drying is carried out in a vacuum drying oven, the drying temperature is 60° C., and the drying time is 12 h; in the mixed atmosphere of H2 and He, the volume ratio of H2 is 10%; the reduction temperature is 150-300° C., and the reduction time is 2 h.

7. The use of the atomically dispersed Pd-Pt catalyst for dinitrotoluene hydrogenation reaction according to claim 1, characterized in that: The reaction process is carried out in a kettle reactor, and the Pd-Pt catalyst is used to prepare toluenediamine through a hydrogenation reaction; in the dinitrotoluene hydrogenation reaction process, the solvent is any one of methanol, ethanol, tetrahydrofuran, cyclohexane and toluene, the molar concentration of dinitrotoluene is 0.1-1.0 mol / L, and the pressure of hydrogen is 0.2-1.0 MPa.

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