A process for preparing a highly active alumina-supported platinum catalyst

Abstract

The present invention relates to the technical field of catalyst preparation, and in particular to a process for preparing a high-activity alumina-supported platinum catalyst. The present invention uses aluminum isopropoxide as an aluminum source to prepare an aluminum precursor, then prepares an alumina carrier by two calcinations, and uses polyethylene glycol to modify the alumina carrier, and finally loads metal platinum to prepare the catalyst. The prepared catalyst can catalyze the hydrogenation reaction of styrene, and its specific surface area is 289.5 m 2 / g, with a porous structure and a pore size of 18nm. Within 100min, the catalyst can make the conversion rate of styrene reach 94.5%. In addition, the loaded metal platinum particles are evenly dispersed on the surface of the carrier, and the amount of chloroplatinic acid added can be controlled to prepare a catalyst with a platinum loading of 10.6mg / g, which increases the reactive sites and can therefore exert excellent catalytic activity in the styrene hydrogenation reaction.

Description

Technical Field

[0001] The invention relates to the technical field of catalyst preparation, and in particular to a process for preparing a high-activity alumina-supported platinum catalyst. Background Art

[0002] Alumina is an important carrier material with a porous structure, high specific surface area, good thermal stability and chemical stability, and has shown broad application prospects in the field of catalysis. The precious metal platinum has the advantages of high atomic utilization, good selectivity, and good catalytic performance. Among many precious metal catalysts, it is the most widely used. Alumina is used as a catalytic carrier. Its surface has a large number of sites for enrichment of metal active components, which is conducive to the uniform dispersion of precious metal particles and can significantly improve the efficiency of catalytic reactions. In recent years, there have been a large number of reports on alumina-loaded precious metal catalysts.

[0003] As in the literature Lisa Geerts, Hannelore Geerts-Claes, Alexander Skorikov, Julie Vermeersch, Gina Vanbutsele, Vladimir Galvita, Denis Constales, C. Vinod Chandran, Sambhu Radhakrishnan, Jin Won Seo, Eric Breynaert, Sara Bals, Sreeprasanth Pulinthanathu Sree, Johan A. Martens, Spherical core-shell alumina support particles for model platinum catalysts, Nanoscale, 2021, 13, 4221-4232. Aluminum nitrate and urea solution were used for hydrothermal reaction to synthesize spherical core-shell particles with a particle size of 1 μm as catalyst support materials. Then, Pt nanoparticles with an average size of less than 1 nm were loaded on spherical alumina particles using a strong electrostatic adsorption method. Electron microscopy and X-ray spectroscopy showed that platinum was attached to the alumina surface. These platinum-loaded alumina spheres can achieve acid catalysis. However, the prepared catalyst carrier uses electrostatic adsorption to load platinum, which eventually leads to uneven dispersion of platinum particles on the carrier surface. In the literature Huishan Shang, Wenxing Chen, Zhuoli Jiang, DanniZhoua and Jiatao Zhang, Atomic-dispersed platinum anchored on porous aluminasheets as an efficient catalyst for diboration of alkynes, Chem. Commun., 2020, 56, 3127-3130., atomically dispersed Pt is anchored on defect-rich porous alumina sheets by combining wet impregnation with pyrolysis. These Pt-functionalized nanosheets have a high density of active sites and have excellent catalytic activity and cycle performance in the diboration reaction of alkynes. However, the catalyst in this document has a slow rate of catalyzing the hydrogenation reaction of styrene. Chinese invention patent CN202110615945.4 discloses a metal platinum catalyst, a preparation method and an application thereof. The carrier of the catalyst is mesoporous alumina, and the active component is metal platinum. The mesoporous alumina is prepared by a sol-gel method. The provided metal platinum catalyst has excellent catalytic activity, selectivity and stability, and can be used for the selective hydrogenation of saturated aldehydes to synthesize unsaturated alcohols.However, the alumina catalyst is prepared by a chemical impregnation method, which results in a low loading of metal platinum and a small number of catalytic active sites.

[0004] Ethylbenzene, the product of selective hydrogenation of styrene, has good stability and plays an important role in gasoline production and aromatics industry. How to prepare catalysts for styrene hydrogenation reaction with large specific surface area, fast catalytic rate, high dispersibility and many active sites is the bottleneck in the current catalytic field.

[0005] Therefore, a process for preparing high-activity alumina-supported platinum catalyst was proposed. Summary of the invention

[0006] The object of the present invention is to provide a high-activity alumina-supported platinum catalyst preparation process, wherein an aluminum precursor is prepared by using aluminum isopropoxide as an aluminum source, an alumina carrier is prepared by two calcinations, the alumina carrier is modified by polyethylene glycol, and finally a catalyst is prepared by loading metal platinum. The prepared catalyst can catalyze the hydrogenation reaction of styrene, and the conversion rate of styrene can reach 94.5%. In addition, the loaded metal platinum particles are uniformly dispersed on the surface of the carrier, and can exert excellent catalytic activity in the hydrogenation reaction of styrene.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] On the one hand, the present invention provides a process for preparing a high-activity alumina-supported platinum catalyst, characterized in that it comprises the following steps:

[0009] Weighing aluminum alkoxide, dissolving the aluminum alkoxide in ethanol to obtain an aluminum alkoxide solution; placing the aluminum alkoxide solution in a round-bottom flask, reacting at 30-100° C. in an oil bath for 6 hours to obtain a turbid solution; taking out the turbid solution, centrifuging, washing, and drying to obtain an aluminum precursor;

[0010] The aluminum precursor is placed in a muffle furnace for a first calcination, the temperature of the first calcination is 180-360°C, and the calcination is performed for 1 hour; after the calcination, a second calcination is performed, the temperature of the second calcination is 550-980°C, and the calcination is performed for 3 hours; the heating rate of the muffle furnace is 5°C / min; after the calcination, it is cooled to room temperature to obtain an alumina carrier;

[0011] The alumina carrier is placed in a round-bottom flask, and concentrated nitric acid is added to the alumina carrier to obtain an alumina acid solution; the alumina acid solution is placed in an oil bath, and refluxed at 30-50° C. for 36 hours to obtain a reaction system; the reaction system is separated and centrifuged, and solid insoluble matter is obtained by suction filtration, and the solid insoluble matter is washed with deionized water until neutral, and dried to obtain an intermediate product 1; the intermediate product 1 is dispersed in deionized water to obtain a dispersion; polyethylene glycol is added to the dispersion, and the mixture is reacted at 40° C. for 10 hours to obtain a modified alumina;

[0012] The modified alumina is dispersed in deionized water to obtain a suspension; an equal volume of a metal platinum solution and a 1.0 mg / mL sodium borohydride solution are added to the suspension to obtain a mixed solution; the mixed solution is placed in a microwave tube to perform a microwave reaction; after the reaction is completed, the microwave tube is taken out, cooled to room temperature, and then centrifuged to retain the precipitate; the precipitate is washed and dried to obtain the high-activity alumina-loaded platinum catalyst.

[0013] Preferably, the aluminum alkoxide is aluminum isopropoxide, with a CAS number of 555-31-7; and the concentration of the aluminum alkoxide solution is 0.5-3.5 g / L.

[0014] Preferably, the mass fraction of the concentrated nitric acid is 65%; the ratio of the alumina carrier to the concentrated nitric acid is 1 g:15 mL-30 mL, and the ratio relationship is g:mL.

[0015] Preferably, the mass ratio of the alumina carrier to the polyethylene glycol is 1:1-2.

[0016] Preferably, the polyethylene glycol is aminopolyethylene glycol with CAS number 956496-54-1 and molecular weight of 2000.

[0017] Preferably, the metal platinum solution is a chloroplatinic acid solution.

[0018] Preferably, the concentration of the metal platinum solution is 1-10 g / L.

[0019] Preferably, the mass ratio of the modified alumina to the metal platinum is 10:0.1-1.

[0020] Preferably, the microwave reaction temperature is 85° C. and the microwave reaction time is 2 hours.

[0021] On the other hand, the present invention provides a preparation process of a high-activity alumina-supported platinum catalyst, characterized in that: the high-activity alumina-supported platinum catalyst uses aluminum isopropoxide as an aluminum source, then prepares an alumina carrier by two calcinations, and modifies the alumina carrier with polyethylene glycol, and finally loads a metal platinum composition; the high-activity alumina-supported platinum catalyst is prepared by the preparation process as described above; the high-activity alumina-supported platinum catalyst can catalyze the hydrogenation reaction of styrene, and within 100 minutes, the conversion rate of styrene reaches 94.5%; the high-activity alumina-supported platinum catalyst has a porous structure, the pores are densely and evenly arranged, and the specific surface area reaches 289.5m 2 / g, pore size is 18nm; the high activity alumina supported platinum catalyst has uniform morphology; the catalytic rate constant of the high activity alumina supported platinum catalyst is 1.26×10 -3mol / L·min; the loading amount of metal platinum in the high-activity alumina-supported platinum catalyst is 10.6 mg / g.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. The present invention dissolves aluminum isopropoxide in ethanol to obtain an aluminum isopropoxide solution with a concentration of 1.8 g / L, then takes out after reacting in an oil bath at 80°C for 6 hours, centrifuges, washes, and dries to obtain an aluminum precursor, and uses the aluminum precursor obtained by the method as a precursor to prepare an alumina-supported platinum hydrogenation reaction catalyst, which can catalyze the hydrogenation reaction of styrene. The prepared catalyst achieves a styrene conversion rate of 94.5% within 100 minutes. The present invention uses aluminum isopropoxide as an aluminum source, and the prepared alumina carrier has a porous structure, high crushing strength, large specific surface area, and interacts with active metal particles, and can carry a sufficient amount of active component platinum; at the same time, the porous structure can isolate the metal particles from each other, thereby inhibiting the aggregation of metal platinum particles. The prepared alumina carrier itself is inert and will not react with active ingredients or reactants, and by optimizing the concentration of the aluminum isopropoxide solution, the purpose of improving the styrene conversion rate can be achieved in the styrene hydrogenation reaction.

[0024] 2. The present invention places the aluminum precursor in a muffle furnace for the first calcination, the temperature of the first calcination is 260°C, and the calcination is carried out for 1 hour; after the calcination, the second calcination is carried out at 780°C and the calcination is carried out for 3 hours; the heating rate of the muffle furnace is 5°C / min, and after the calcination, the aluminum oxide carrier is cooled to room temperature to obtain the aluminum oxide carrier. The catalyst prepared by the method has a porous structure, which is densely and evenly arranged, and the specific surface area can reach 289.5m 2 / g, and the most probable pore size is 18nm, indicating that the alumina carrier prepared by the preparation process of the present invention has a three-dimensional ordered interconnected mesoporous structure, which provides more space for the subsequent enrichment of metal platinum, and thus can catalyze the hydrogenation reaction of styrene. The present invention optimizes the temperature of the two calcinations so that the prepared alumina carrier has a porous structure and a large specific surface area, which can reduce the resistance in the mass transfer process of the styrene hydrogenation reaction, so that the reactants can easily diffuse to the active sites, and the products can also easily diffuse outside the pores; secondly, the alumina carrier itself has a limited domain effect on the metal particles, which is beneficial to the subsequent loading and dispersion of the metal platinum particles, and the catalyst calcined at high temperature has better stability.

[0025] 3. The present invention adds 65% concentrated nitric acid by mass to the alumina carrier, the ratio of the alumina carrier to the concentrated nitric acid is 1g:20mL, and the ratio relationship is g:mL; the alumina acid solution is placed in an oil bath pot and refluxed at 40°C for 36 hours to obtain a reaction system; the reaction system is separated and centrifuged, and solid insolubles are obtained by suction filtration, washed with deionized water until neutral, and dried to obtain an intermediate product 1. The present invention activates the surface of the alumina carrier by using concentrated nitric acid, so that the surface has active hydroxyl groups, which is easy to react with subsequent amino polyethylene glycol to form an amide, thereby realizing the modification of polyethylene glycol, and then promoting the loading of active species metal platinum particles on the carrier, and can improve the dispersion of platinum particles, so that the active metal platinum particles are evenly dispersed on the carrier, which can reduce the agglomeration phenomenon of platinum in traditional catalysts when the platinum loading is high, and increase the active sites of the reaction, so that it can play an excellent catalytic activity in the styrene hydrogenation reaction.

[0026] 4. In the present invention, the intermediate product 1 is dispersed in deionized water, and then amino polyethylene glycol is added, the mass ratio of the alumina carrier to the polyethylene glycol is 1:1.7, and the reaction is carried out at 40°C for 10 hours to obtain modified alumina. The modified alumina prepared by the method is used for the subsequent preparation of a high-activity alumina-supported platinum catalyst. The catalytic rate constant of the obtained catalyst is 1.26×10 -3 mol / L·min, and the catalytic rate is fast. The present invention modifies the surface of alumina by aminopolyethylene glycol, and controls the amount of polyethylene glycol added to make the alumina carrier more dispersible, and the amino group and metal platinum have an electrostatic effect, which is conducive to stabilizing the metal platinum particles, so that the platinum particles in the prepared catalyst are not easy to fall off, thereby ensuring the catalytic activity and long-term stability of the catalyst. The polyethylene glycol coupled to the surface of the alumina carrier can effectively inhibit the spontaneous agglomeration of small-sized metal platinum, making the final catalyst morphology uniform, the active sites more uniform, and making the styrene hydrogenation reaction easier to carry out, so the rate constant is large. Control the amount of polyethylene glycol added so that the final prepared catalyst has a uniform morphology and more active sites.

[0027] 5. The present invention disperses the modified alumina in deionized water, then adds an equal volume of 5.5g / L chloroplatinic acid solution and 1.0mg / mL sodium borohydride solution to obtain a mixed solution; the mass ratio of the modified alumina to the chloroplatinic acid is 10:0.5, and the mixed solution is placed in a microwave tube for microwave reaction, the microwave reaction temperature is 85°C, the microwave reaction time is 2 hours, and the microwave tube is taken out after the reaction is completed, cooled to room temperature, and then centrifuged to retain the precipitate; the precipitate is washed and dried to obtain the high-activity alumina-supported platinum catalyst, and the loading amount of the metal platinum is 10.6mg / g. The greater the loading amount of the metal platinum, the more active centers of the catalyst. The present invention prepares an alumina carrier, and after functionalizing its surface, loads metal platinum as an active site, so as to realize catalytic hydrogenation of styrene. The present invention uses platinum as an active metal atom, and its d orbital is in an unfilled state, and there are electron holes. The unpaired electrons in the orbit can promote the interaction of electrons to form bonds, and promote the rate of hydrogenation catalysis. When platinum is loaded on alumina, the present invention adds sodium borohydride as a reducing agent to reduce metal platinum ions to platinum particles, and adopts a microwave-assisted method to enrich the platinum ions on the alumina carrier. The microwave method shortens the preparation process time and can make the metal platinum particles evenly dispersed; the synergistic effect of the alumina carrier and the active metal platinum can also improve the activity of the catalyst to a certain extent, so that the utilization rate of the metal platinum is high. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a scanning electron microscope image of the high-activity alumina-supported platinum catalyst prepared in Example 24 of the present invention. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] See also Figure 1 The present invention provides a process for preparing a high-activity alumina-supported platinum catalyst, and the technical scheme is as follows:

[0031] Example 1

[0032] A process for preparing a high-activity alumina-supported platinum catalyst comprises the following steps:

[0033] Weigh aluminum isopropoxide, dissolve aluminum isopropoxide in ethanol to obtain an aluminum isopropoxide solution with a concentration of 0.5 g / L; place the aluminum isopropoxide solution in a round-bottom flask, react at 30° C. in an oil bath for 6 hours to obtain a turbid solution; take out the turbid solution, centrifuge, wash, and dry to obtain an aluminum precursor;

[0034] The aluminum precursor is placed in a muffle furnace for the first calcination, the temperature of the first calcination is 180°C, and the calcination is carried out for 1 hour; after the calcination, the second calcination is carried out at a temperature of 550°C and the calcination is carried out for 3 hours; the heating rate of the muffle furnace is 5°C / min; after the calcination, the aluminum oxide carrier is cooled to room temperature to obtain;

[0035] An alumina carrier is placed in a round-bottom flask, and concentrated nitric acid with a mass fraction of 65% is added to the alumina carrier to obtain an alumina acid solution; the ratio of the alumina carrier to the concentrated nitric acid is 1g:15mL, and the ratio relationship is g:mL; the alumina acid solution is placed in an oil bath pot, and refluxed at 30°C for 36 hours to obtain a reaction system; the reaction system is separated and centrifuged, and solid insoluble matter is obtained by suction filtration, and the solid insoluble matter is washed with deionized water until neutral, and dried to obtain an intermediate product 1; the intermediate product 1 is dispersed in deionized water to obtain a dispersion; aminopolyethylene glycol is added to the dispersion, and the mass ratio of the alumina carrier to the polyethylene glycol is 1:1.3, and the reaction is carried out at 40°C for 10 hours to obtain modified alumina;

[0036] The modified alumina is dispersed in deionized water to obtain a suspension; an equal volume of a 1 g / L chloroplatinic acid solution and a 1.0 mg / mL sodium borohydride solution are added to the suspension to obtain a mixed solution; the mass ratio of the modified alumina to the chloroplatinic acid is 10:0.1, and the mixed solution is placed in a microwave tube for microwave reaction at a microwave reaction temperature of 85°C for 2 hours. After the reaction is completed, the microwave tube is taken out, cooled to room temperature, and then centrifuged to retain the precipitate; the precipitate is washed and dried to obtain the high-activity alumina-loaded platinum catalyst.

[0037] In this example, aluminum isopropoxide and aminopolyethylene glycol were purchased from Shanghai Aladdin Reagent Co., Ltd.; the remaining chemical reagents can be purchased through conventional channels. The purity specifications of the solvents used are all analytically pure. The raw materials in other examples were purchased from the same manufacturers as in Example 1.

[0038] The concentration of aluminum isopropoxide solution and the oil bath reaction temperature in Example 2-8 are shown in Table 1, and the remaining reagents and operations are the same as in Example 1.

[0039] Table 1 Concentration of aluminum isopropoxide solution and oil bath reaction temperature in Examples 2-8

[0040] Aluminum isopropoxide solution concentration (g / L) Oil bath reaction temperature (℃) Example 2 0.5 50 Example 3 1.8 80 Example 4 2.5 100 Example 5 3.5 50 Example 6 1.8 80 Example 7 2.5 100 Example 8 3.5 30

[0041] Example 9

[0042] The catalytic activity of the highly active alumina-supported platinum catalyst prepared in Examples 1-8 above was detected. The styrene hydrogenation reaction was used as the catalyzed reaction, and the catalyst was added in an amount of 25 mg of catalyst to 1 g of styrene. The catalytic activity was expressed by the conversion rate of styrene at the same time, and the styrene concentration was detected by gas chromatograph. The results are shown in Table 2.

[0043] In Example 6, aluminum isopropoxide is dissolved in ethanol to obtain an aluminum isopropoxide solution with a concentration of 1.8g / L, and then placed in a round-bottom flask, taken out after reacting in an oil bath at 80°C for 6 hours, centrifuged, washed, and dried to obtain an aluminum precursor, and the aluminum precursor obtained by the method is used as a precursor to prepare an alumina-supported platinum hydrogenation reaction catalyst, which can catalyze the hydrogenation reaction of styrene. The catalyst prepared in Example 6 achieves a conversion rate of styrene of 94.5% within 100min. The present invention uses aluminum isopropoxide as an aluminum source, and the prepared alumina carrier has a porous structure, high crushing strength, large specific surface area, and interacts with active metal particles, and can carry a sufficient amount of active component platinum; at the same time, the porous structure can isolate the metal particles from each other, thereby inhibiting the aggregation of metal platinum particles. And the prepared alumina carrier itself is inert, will not react with active ingredients or reactants, and by preferably selecting the concentration of the aluminum isopropoxide solution, it can be achieved in the styrene hydrogenation reaction, improve the conversion rate of styrene, and the catalyst prepared by comprehensive comparison of Example 6 of the present invention has the strongest catalytic activity.

[0044] Table 2 Conversion rate of styrene catalyzed by the high-activity alumina-supported platinum catalyst prepared in Examples 1-8 within 100 min

[0045] Conversion rate of styrene (%) Example 1 85.2 Example 2 81.4 Example 3 77.5 Example 4 76.2 Example 5 71.3 Example 6 94.5 Example 7 88.2 Example 8 79.5

[0046] Example 10

[0047] A process for preparing a high-activity alumina-supported platinum catalyst comprises the following steps:

[0048] Weigh aluminum isopropoxide, dissolve aluminum isopropoxide in ethanol to obtain an aluminum isopropoxide solution with a concentration of 1.8 g / L; place the aluminum isopropoxide solution in a round-bottom flask, react at 80° C. in an oil bath for 6 hours to obtain a turbid liquid; take out the turbid liquid, centrifuge, wash, and dry to obtain an aluminum precursor;

[0049] The aluminum precursor is placed in a muffle furnace for the first calcination, the temperature of the first calcination is 180°C, and the calcination is carried out for 1 hour; after the calcination, the second calcination is carried out at 600°C, and the calcination is carried out for 3 hours; the heating rate of the muffle furnace is 5°C / min; after the calcination, the aluminum oxide carrier is cooled to room temperature to obtain;

[0050] An alumina carrier is placed in a round-bottom flask, and concentrated nitric acid with a mass fraction of 65% is added to the alumina carrier to obtain an alumina acid solution; the ratio of the alumina carrier to the concentrated nitric acid is 1g:15mL, and the ratio relationship is g:mL; the alumina acid solution is placed in an oil bath pot, and refluxed at 30°C for 36 hours to obtain a reaction system; the reaction system is separated and centrifuged, and solid insoluble matter is obtained by suction filtration, and the solid insoluble matter is washed with deionized water until neutral, and dried to obtain an intermediate product 1; the intermediate product 1 is dispersed in deionized water to obtain a dispersion; aminopolyethylene glycol is added to the dispersion, and the mass ratio of the alumina carrier to the polyethylene glycol is 1:1.3, and the reaction is carried out at 40°C for 10 hours to obtain modified alumina;

[0051] The modified alumina is dispersed in deionized water to obtain a suspension; an equal volume of a 1 g / L chloroplatinic acid solution and a 1.0 mg / mL sodium borohydride solution are added to the suspension to obtain a mixed solution; the mass ratio of the modified alumina to the chloroplatinic acid is 10:0.1, and the mixed solution is placed in a microwave tube for microwave reaction at a microwave reaction temperature of 85°C for 2 hours. After the reaction is completed, the microwave tube is taken out, cooled to room temperature, and then centrifuged to retain the precipitate; the precipitate is washed and dried to obtain the high-activity alumina-loaded platinum catalyst.

[0052] The first calcination temperature and the second calcination temperature in Examples 11-18 are shown in Table 3, and the remaining reagents and operations are the same as in Example 10.

[0053] Table 3 The first calcination temperature and the second calcination temperature in Examples 11-18

[0054] First calcination temperature (℃) Second calcination temperature (℃) Embodiment 11 180 650 Example 12 180 780 Embodiment 13 260 650 Embodiment 14 260 780 Embodiment 15 260 850 Example 16 360 650 Embodiment 17 360 780 Embodiment 18 360 980

[0055] Embodiment 19

[0056] The specific surface area and pore size of the high-activity alumina-supported platinum catalyst prepared in the above Examples 10-18 were detected by a low-temperature nitrogen adsorption-desorption experimental method. The instrument was a Kubo 1108 ultra-high-speed specific surface area analyzer produced by Beijing Biode Electronic Technology Co., Ltd. The results were shown in Table 4 by setting a program.

[0057] In Example 14, the aluminum precursor is placed in a muffle furnace for the first calcination, the temperature of the first calcination is 260°C, and the calcination is carried out for 1 hour; after the calcination, the second calcination is carried out at 780°C and the calcination is carried out for 3 hours; the heating rate of the muffle furnace is 5°C / min; after the calcination, it is cooled to room temperature to obtain an alumina carrier. The catalyst prepared by the method has a porous structure, densely and evenly arranged, and the maximum specific surface area can reach 289.5m 2 / g, and the most probable pore size is 18nm, indicating that the alumina carrier prepared by the preparation process of the present invention has a three-dimensional ordered interconnected mesoporous structure, which provides more sites for the subsequent enrichment of metal platinum, and thus can promote the catalytic activity of the styrene hydrogenation reaction. The present invention optimizes the temperature of the two calcinations so that the prepared alumina carrier has a porous structure and a maximum specific surface area, which can reduce the resistance in the mass transfer process of the styrene hydrogenation reaction, so that the reactants can easily diffuse to the active sites, and the products can also easily diffuse outside the pores; secondly, the alumina carrier itself has a limited domain effect on the metal particles, which is beneficial to the subsequent loading and dispersion of the metal platinum particles, and the catalyst calcined at high temperature has better stability.

[0058] Table 4 Specific surface area and pore size of the high activity alumina supported platinum catalyst prepared in Examples 10-18

[0059] <![CDATA[Specific surface area (m 2 / g)]]> Most probable pore size (nm) Example 10 124.1 56 Embodiment 11 86.5 45 Example 12 99.3 11 Embodiment 13 201.1 20 Embodiment 14 289.5 18 Embodiment 15 221.5 28 Example 16 96.6 32 Embodiment 17 152.3 66 Embodiment 18 164.7 54

[0060] Embodiment 20

[0061] A process for preparing a high-activity alumina-supported platinum catalyst comprises the following steps:

[0062] Weigh aluminum isopropoxide, dissolve aluminum isopropoxide in ethanol to obtain an aluminum isopropoxide solution with a concentration of 1.8 g / L; place the aluminum isopropoxide solution in a round-bottom flask, react at 80° C. in an oil bath for 6 hours to obtain a turbid liquid; take out the turbid liquid, centrifuge, wash, and dry to obtain an aluminum precursor;

[0063] The aluminum precursor is placed in a muffle furnace for the first calcination, the temperature of the first calcination is 260°C, and the calcination is carried out for 1 hour; after the calcination, the second calcination is carried out at a temperature of 780°C and the calcination is carried out for 3 hours; the heating rate of the muffle furnace is 5°C / min; after the calcination, it is cooled to room temperature to obtain an alumina carrier;

[0064] An alumina carrier is placed in a round-bottom flask, and concentrated nitric acid with a mass fraction of 65% is added to the alumina carrier to obtain an alumina acid solution; the ratio of the alumina carrier to the concentrated nitric acid is 1g:18mL, and the ratio relationship is g:mL; the alumina acid solution is placed in an oil bath pot, and refluxed at 30°C for 36 hours to obtain a reaction system; the reaction system is separated and centrifuged, and solid insolubles are obtained by suction filtration, and the solid insolubles are washed with deionized water until neutral, and dried to obtain an intermediate product 1; the intermediate product 1 is dispersed in deionized water to obtain a dispersion; amino polyethylene glycol is added to the dispersion, and the mass ratio of the alumina carrier to the polyethylene glycol is 1:1.3, and the reaction is carried out at 40°C for 10 hours to obtain modified alumina;

[0065] The modified alumina is dispersed in deionized water to obtain a suspension; an equal volume of a 1 g / L chloroplatinic acid solution and a 1.0 mg / mL sodium borohydride solution are added to the suspension to obtain a mixed solution; the mass ratio of the modified alumina to the chloroplatinic acid is 10:0.1, and the mixed solution is placed in a microwave tube for microwave reaction at a microwave reaction temperature of 85°C for 2 hours. After the reaction is completed, the microwave tube is taken out, cooled to room temperature, and then centrifuged to retain the precipitate; the precipitate is washed and dried to obtain the high-activity alumina-loaded platinum catalyst.

[0066] The ratio of alumina carrier to concentrated nitric acid and the reflux temperature in Examples 21-28 are shown in Table 5, and the remaining reagents and operations are the same as in Example 20.

[0067] Table 5 Ratio of alumina carrier to concentrated nitric acid and reflux temperature in Examples 21-28

[0068] Ratio of alumina support to concentrated nitric acid (g:mL) Reflux temperature (℃) Embodiment 21 1：25 30 Embodiment 22 1：30 30 Embodiment 23 1：15 40 Embodiment 24 1：20 40 Embodiment 25 1：30 40 Embodiment 26 1：15 50 Embodiment 27 1：20 50 Embodiment 28 1：30 50

[0069] Embodiment 29

[0070] The dispersion uniformity of platinum particles in the high-activity alumina-supported platinum catalysts prepared in Examples 20-28 above was detected by direct observation using a scanning electron microscope (SEM) model SU8020, manufactured by Hitachi, Japan. Figure 1 This is a scanning electron microscope image of the catalyst prepared in Example 24.

[0071] In Example 24, an alumina carrier is placed in a round-bottom flask, and concentrated nitric acid with a mass fraction of 65% is added thereto to obtain an alumina acid solution, the ratio of the alumina carrier to the concentrated nitric acid is 1g:20mL, and the ratio relationship is g:mL; the alumina acid solution is placed in an oil bath pot, and refluxed at 40°C for 36 hours to obtain a reaction system; the reaction system is separated and centrifuged, and solid insolubles are obtained by suction filtration, washed with deionized water until neutral, and dried to obtain an intermediate product 1. The present invention activates the surface of the alumina carrier by using concentrated nitric acid, so that the surface has active hydroxyl groups, which are easy to react with subsequent aminopolyethylene glycol to undergo amide reaction, thereby achieving polyethylene glycol modification, thereby promoting the loading of active species platinum metal particles on the carrier, and can improve the dispersion of platinum particles, so that active metal platinum particles are evenly dispersed on the carrier. The reaction process mainly relies on the strong oxidizing property of concentrated nitric acid, and the surface of the alumina carrier is activated so that the polar groups on the surface of the alumina carrier can react with aminopolyethylene glycol. As the reaction temperature increases, the concentration of concentrated nitric acid decreases, and the reaction generates aluminum nitrate impurities. In the post-treatment process, the solid is separated from the reaction system by separation centrifugation and filtration, and deionized water is washed to neutrality to ensure the removal of dilute nitric acid and aluminum nitrate impurities in the alumina carrier. After drying, the alumina carrier reacts with polyethylene glycol to obtain modified alumina. The reaction temperature is controlled during the reaction to reduce the generation of by-products. When the reaction is at 30°C, the activation process time is long, the activation yield is low, the intermediate surface hydroxyl activity obtained by separation centrifugation is weak, the yield decreases during the reaction with aminopolyethylene glycol, the modification of polyethylene glycol decreases, the loading of platinum metal particles is poor, and the activity of the prepared catalyst is poor. When the temperature rises to 50°C, the concentration of concentrated nitric acid decreases, the dilute nitric acid dissolves the alumina carrier, the generated aluminum nitrate dissolves in the system, the content of activated alumina decreases, the loading amount of platinum particles of the prepared modified alumina decreases, and the catalytic activity decreases. like Figure 1 The figure shows a scanning electron microscope image of the high-activity alumina-supported platinum catalyst prepared in Example 24 of the present invention. It can be seen from the figure that the catalyst prepared by the present invention has a porous structure, in which metal platinum particles are evenly dispersed on the surface, which can reduce the agglomeration of platinum at high loading in traditional catalysts and increase the active sites of the reaction, so it can exert excellent catalytic activity in the styrene hydrogenation reaction. Other Examples Due to the inappropriate ratio of the alumina carrier to concentrated nitric acid, the final prepared catalyst was observed by electron microscopy, and the platinum particles were easily aggregated on the carrier, resulting in poor catalytic effect.

[0072] Embodiment 30

[0073] A process for preparing a high-activity alumina-supported platinum catalyst comprises the following steps:

[0074] Weigh aluminum isopropoxide, dissolve aluminum isopropoxide in ethanol to obtain an aluminum isopropoxide solution with a concentration of 1.8 g / L; place the aluminum isopropoxide solution in a round-bottom flask, react at 80° C. in an oil bath for 6 hours to obtain a turbid liquid; take out the turbid liquid, centrifuge, wash, and dry to obtain an aluminum precursor;

[0075] The aluminum precursor is placed in a muffle furnace for the first calcination, the temperature of the first calcination is 260°C, and the calcination is carried out for 1 hour; after the calcination, the second calcination is carried out at a temperature of 780°C and the calcination is carried out for 3 hours; the heating rate of the muffle furnace is 5°C / min; after the calcination, it is cooled to room temperature to obtain an alumina carrier;

[0076] An alumina carrier is placed in a round-bottom flask, and concentrated nitric acid with a mass fraction of 65% is added to the alumina carrier to obtain an alumina acid solution; the ratio of the alumina carrier to the concentrated nitric acid is 1g:20mL, and the ratio relationship is g:mL; the alumina acid solution is placed in an oil bath pot, and refluxed at 40°C for 36 hours to obtain a reaction system; the reaction system is separated and centrifuged, and solid insoluble matter is obtained by suction filtration, and the solid insoluble matter is washed with deionized water until neutral, and dried to obtain an intermediate product 1; aminopolyethylene glycol is added to the dispersion, and the mass ratio of the alumina carrier to the polyethylene glycol is 1:1.2, and the reaction is carried out at 40°C for 10 hours to obtain modified alumina;

[0077] The modified alumina is dispersed in deionized water to obtain a suspension; an equal volume of a 1 g / L chloroplatinic acid solution and a 1.0 mg / mL sodium borohydride solution are added to the suspension to obtain a mixed solution; the mass ratio of the modified alumina to the chloroplatinic acid is 10:0.1, and the mixed solution is placed in a microwave tube for microwave reaction at a microwave reaction temperature of 85°C for 2 hours. After the reaction is completed, the microwave tube is taken out, cooled to room temperature, and then centrifuged to retain the precipitate; the precipitate is washed and dried to obtain the high-activity alumina-loaded platinum catalyst.

[0078] The mass ratio of the alumina carrier to polyethylene glycol in Examples 31-36 is shown in Table 6, and the remaining reagents and operations are the same as in Example 30.

[0079] Table 6 Mass ratio of alumina support to polyethylene glycol in Examples 31-36

[0080] Mass ratio of alumina support to polyethylene glycol (g:mL) Embodiment 31 1:1 Embodiment 32 1:1.3 Embodiment 33 1:1.5 Embodiment 34 1:1.7 Embodiment 35 1:1.9 Embodiment 36 1:2

[0081] Embodiment 37

[0082] The reaction rate of the styrene hydrogenation reaction catalyzed by the high-activity alumina-supported platinum catalyst prepared in Examples 30-36 above was detected. The reaction rate was characterized by the rate constant. The results are shown in Table 7.

[0083] In Example 34, the intermediate product 1 was dispersed in deionized water, and then amino polyethylene glycol was added. The mass ratio of the alumina carrier to the polyethylene glycol was 1:1.7. The reaction was carried out at 40°C for 10 hours to obtain modified alumina. The modified alumina prepared by the method was used for the subsequent preparation of a high-activity alumina-supported platinum catalyst. The rate constant of the obtained catalyst was 1.26×10 -3 mol / L·min. The present invention modifies the surface of alumina by aminopolyethylene glycol, and controls the amount of polyethylene glycol added to make the alumina carrier more dispersible, and the amino group and metal platinum have an electrostatic effect, which is beneficial to stabilize the metal platinum particles, so that the platinum particles in the prepared catalyst are not easy to fall off, thereby ensuring the catalytic activity and long-term stability of the catalyst. The polyethylene glycol coupled to the surface of the alumina carrier can effectively inhibit the spontaneous agglomeration of small-sized metal platinum, so that the final catalyst morphology is uniform and the active sites are more uniform, making the styrene hydrogenation reaction easier to carry out, so the rate constant is the largest. In other embodiments, due to the inappropriate amount of polyethylene glycol added, the final prepared catalyst has a poor morphology and fewer active sites, so the reaction rate constant of the catalytic styrene hydrogenation reaction is small.

[0084] Table 7 Rate constants of styrene hydrogenation reaction catalyzed by the catalysts prepared in Examples 30-36

[0085] Rate constant of styrene hydrogenation reaction (mol / L·min) Embodiment 30 <![CDATA[3.56×10 -4 ]]> Embodiment 31 <![CDATA[4.21×1 0-4 ]]> Embodiment 32 <![CDATA[3.31×10 -4 ]]> Embodiment 33 <![CDATA[1.10×10 -3 ]]> Embodiment 34 <![CDATA[1.26×10 -3 ]]> Embodiment 35 <![CDATA[2.35×10 -4 ]]> Embodiment 36 <![CDATA[6.62×10 -4 ]]>

[0086] Embodiment 38

[0087] A process for preparing a high-activity alumina-supported platinum catalyst comprises the following steps:

[0088] Weigh aluminum isopropoxide, dissolve aluminum isopropoxide in ethanol to obtain an aluminum isopropoxide solution with a concentration of 1.8 g / L; place the aluminum isopropoxide solution in a round-bottom flask, react at 80° C. in an oil bath for 6 hours to obtain a turbid liquid; take out the turbid liquid, centrifuge, wash, and dry to obtain an aluminum precursor;

[0089] The aluminum precursor is placed in a muffle furnace for the first calcination, the temperature of the first calcination is 260°C, and the calcination is carried out for 1 hour; after the calcination, the second calcination is carried out at a temperature of 780°C and the calcination is carried out for 3 hours; the heating rate of the muffle furnace is 5°C / min; after the calcination, it is cooled to room temperature to obtain an alumina carrier;

[0090] An alumina carrier is placed in a round-bottom flask, and concentrated nitric acid with a mass fraction of 65% is added to the alumina carrier to obtain an alumina acid solution; the ratio of the alumina carrier to the concentrated nitric acid is 1g:20mL, and the ratio relationship is g:mL; the alumina acid solution is placed in an oil bath pot, and refluxed at 40°C for 36 hours to obtain a reaction system; the reaction system is separated and centrifuged, and solid insoluble matter is obtained by suction filtration, and the solid insoluble matter is washed with deionized water until neutral, and dried to obtain an intermediate product 1; the intermediate product 1 is dispersed in deionized water to obtain a dispersion; amino polyethylene glycol is added to the dispersion, and the mass ratio of the alumina carrier to the polyethylene glycol is 1:1.7, and the reaction is carried out at 40°C for 10 hours to obtain modified alumina;

[0091] The modified alumina is dispersed in deionized water to obtain a suspension; an equal volume of a 3.5 g / L chloroplatinic acid solution and a 1.0 mg / mL sodium borohydride solution are added to the suspension to obtain a mixed solution; the mass ratio of the modified alumina to the chloroplatinic acid is 10:0.1, and the mixed solution is placed in a microwave tube for microwave reaction at a microwave reaction temperature of 85°C for 2 hours. After the reaction is completed, the microwave tube is taken out, cooled to room temperature, and then centrifuged to retain the precipitate; the precipitate is washed and dried to obtain the high-activity alumina-loaded platinum catalyst.

[0092] The concentration of chloroplatinic acid solution and the mass ratio of modified alumina to chloroplatinic acid in Examples 39-46 are shown in Table 8, and the remaining reagents and operations are the same as in Example 38.

[0093] Table 8 Concentration of chloroplatinic acid solution and mass ratio of modified alumina to chloroplatinic acid in Examples 39-46

[0094] Chloroplatinic acid solution concentration (g / L) Mass ratio of modified alumina to chloroplatinic acid Embodiment 39 5.5 10:0.1 Embodiment 40 7.5 10:0.1 Embodiment 41 10 10:0.1 Embodiment 42 5.5 10:0.5 Embodiment 43 7.5 10:0.5 Embodiment 44 10 10:0.5 Embodiment 45 5.5 10:1 Embodiment 46 7.5 10:1

[0095] Embodiment 47

[0096] The loading amount of metal platinum on the high-activity alumina-supported platinum catalysts prepared in the above Examples 38-46 was tested. The test results are shown in Table 9.

[0097] In Example 42, the modified alumina is dispersed in deionized water to obtain a suspension; an equal volume of chloroplatinic acid solution with a concentration of 5.5 g / L is added to the suspension to obtain a mixed solution; the mass ratio of modified alumina to chloroplatinic acid is 10:0.5, and the mixed solution is placed in a microwave tube for microwave reaction, the microwave reaction temperature is 85 ° C, the microwave reaction time is 2 hours, and the microwave tube is taken out after the reaction is completed, cooled to room temperature, and then centrifuged to retain the precipitate; the precipitate is washed and dried to obtain the high-activity alumina-supported platinum catalyst, and the loading amount of metal platinum is 10.6 mg / g. The greater the loading amount of metal platinum, the more active centers of the catalyst. The present invention prepares an alumina carrier, and after functionalizing its surface, loads metal platinum as an active site, which can achieve excellent performance in styrene hydrogenation catalysis. The present invention uses platinum as an active metal atom, and its d electron orbit is in an unfilled state, and there are electron holes. The unpaired electrons in the orbit can promote the interaction of electrons to form bonds, thereby promoting the rate of hydrogenation catalysis. When platinum is loaded on alumina, the present invention adds a sodium borohydride solution as a reducing agent to reduce metal platinum ions to platinum particles, and adopts a microwave-assisted method to enrich the platinum ions on the alumina carrier. The microwave method shortens the preparation process time and can make the metal platinum particles evenly dispersed. The synergistic effect between the carrier and the active metal can also improve the activity of the catalyst to a certain extent, so that the utilization rate of the metal platinum is high.

[0098] Table 9 Loading amount of platinum metal on the catalyst prepared in Examples 38-46

[0099] Platinum metal loading (mg / g) Embodiment 38 2.2 Embodiment 39 1.5 Embodiment 40 3.8 Embodiment 41 6.6 Embodiment 42 10.6 Embodiment 43 7.9 Embodiment 44 8.1 Embodiment 45 5.5 Embodiment 46 9.7

[0100] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A process for preparing a high-activity alumina-supported platinum catalyst, characterized in that: The following steps are involved: Weighing aluminum alkoxide, and dissolving the aluminum alkoxide in ethanol to obtain an aluminum alkoxide solution; The aluminum alkoxide solution is placed in a round-bottom flask, and reacted in an oil bath at 30-100° C. for 6 hours to obtain a turbid solution; The turbid liquid is taken out, centrifuged, washed and dried to obtain an aluminum precursor; The aluminum precursor is placed in a muffle furnace for a first calcination, the temperature of the first calcination is 180-360°C, and the calcination is performed for 1 hour; after the calcination, a second calcination is performed, the temperature of the second calcination is 550-980°C, and the calcination is performed for 3 hours; the heating rate of the muffle furnace is 5°C / min; after the calcination, it is cooled to room temperature to obtain an alumina carrier; The alumina carrier is placed in a round-bottom flask, and concentrated nitric acid is added to the alumina carrier to obtain an alumina acid solution; the alumina acid solution is placed in an oil bath, and refluxed at 30-50° C. for 36 hours to obtain a reaction system; the reaction system is separated and centrifuged, and solid insoluble matter is obtained by suction filtration, and the solid insoluble matter is washed with deionized water until neutral, and dried to obtain an intermediate product 1; the intermediate product 1 is dispersed in deionized water to obtain a dispersion; polyethylene glycol is added to the dispersion, and the mixture is reacted at 40° C. for 10 hours to obtain a modified alumina; The modified alumina is dispersed in deionized water to obtain a suspension; an equal volume of a metal platinum solution and a 1.0 mg / mL sodium borohydride solution are added to the suspension to obtain a mixed solution; the mixed solution is placed in a microwave tube to perform a microwave reaction; after the reaction is completed, the microwave tube is taken out and cooled to room temperature, and then centrifuged to retain a precipitate; the precipitate is washed and dried to obtain the high-activity alumina-supported platinum catalyst; The aluminum alkoxide is aluminum isopropoxide, CAS No. 555-31-7; the concentration of the aluminum alkoxide solution is 0.5-3.5 g / L; The polyethylene glycol is amino polyethylene glycol, with CAS No. 956496-54-1 and molecular weight of 2000.

2. A process for preparing a high-activity alumina-supported platinum catalyst according to claim 1, characterized in that: The mass fraction of the concentrated nitric acid is 65%; the ratio of the alumina carrier to the concentrated nitric acid is 1g:15mL-30mL.

3. A process for preparing a high-activity alumina-supported platinum catalyst according to claim 1, characterized in that: The mass ratio of the alumina carrier to the polyethylene glycol is 1:1-2.

4. A process for preparing a high-activity alumina-supported platinum catalyst according to claim 1, characterized in that: The metal platinum solution is a chloroplatinic acid solution.

5. The process for preparing a high-activity alumina-supported platinum catalyst according to claim 1, characterized in that: The concentration of the metal platinum solution is 1-10 g / L.

6. A process for preparing a high-activity alumina-supported platinum catalyst according to claim 1, characterized in that: The mass ratio of the modified alumina to the metal platinum is 10:0.1-1.

7. The process for preparing a high-activity alumina-supported platinum catalyst according to claim 1, characterized in that: The microwave reaction temperature was 85° C., and the microwave reaction time was 2 hours.

8. A high-activity alumina-supported platinum catalyst, characterized in that: The high-activity alumina-supported platinum catalyst uses aluminum isopropoxide as an aluminum source, and then prepares an alumina carrier by two calcinations, and then uses polyethylene glycol to modify the alumina carrier, and finally loads metal platinum. The high-activity alumina-supported platinum catalyst is prepared by the preparation process described in any one of claims 1 to 7. The high-activity alumina-supported platinum catalyst can catalyze the hydrogenation reaction of styrene, and within 100 minutes, the conversion rate of styrene reaches 94.5%; the high-activity alumina-supported platinum catalyst has a porous structure, the pores are densely and evenly arranged, and the specific surface area reaches 289.5m 2 / g, pore size is 18nm; the high activity alumina supported platinum catalyst has uniform morphology; the catalytic rate constant of the high activity alumina supported platinum catalyst is 1.26×10 -3 mol / L·min; the loading amount of metal platinum in the high-activity alumina-supported platinum catalyst is 10.6 mg / g.

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