CN114452980B - Preparation method of platinum-supported Ni/Mg/Fe hydrotalcite catalyst and application of catalyst in preparation of aniline - Google Patents
Preparation method of platinum-supported Ni/Mg/Fe hydrotalcite catalyst and application of catalyst in preparation of aniline Download PDFInfo
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Abstract
The invention relates to the field of catalyst preparation, and discloses a preparation method of a platinum-supported Ni/Mg/Fe hydrotalcite catalyst and application thereof in aniline preparation, wherein the preparation method comprises the following steps: dissolving nickel salt, magnesium salt and iron salt in water to obtain a mixed solution A; mixing a sodium hydroxide solution and a sodium carbonate solution to obtain a mixed solution B; mixing the mixed solution A and the mixed solution B, and then stirring and aging to obtain a mixed solution C; filtering the mixed solution C, and then sequentially washing, drying and grinding to obtain a catalyst precursor; and soaking in alkali liquor, washing, drying, roasting, cooling, grinding, ultrasonically soaking in chloroplatinic acid solution, taking out, and drying to obtain the platinum-supported Ni/Mg/Fe hydrotalcite catalyst. The invention can increase active sites, improve the load stability of active components, and show excellent conversion efficiency and selectivity in the application of preparing aniline by catalytic hydrogenation of nitrobenzene.
Description
Technical Field
The invention relates to the field of catalyst preparation, in particular to a preparation method of a platinum-supported Ni/Mg/Fe hydrotalcite catalyst and application thereof in aniline preparation.
Background
Aniline (AN), also known as aminobenzene, is AN important industrial chemical intermediate, has a wide application market, is mostly applied to the fields of dyes, organic pigments, printing and dyeing, pesticides, rubber auxiliaries, medicines and the like, is also commonly used as AN intermediate for producing spices, plastics, varnishes, films and the like, and can also be used as a stabilizer in explosives, AN explosion-proof agent in gasoline, a solvent and the like. The preparation method of aniline mainly comprises phenol ammonolysis and nitrobenzene reduction, wherein the nitrobenzene reduction comprises iron powder reduction, hydrazine hydrate reduction and catalytic hydrogenation. The iron powder reduction method has the defects of complex equipment, easy water body environmental pollution caused by the process and the like; the hydrazine hydrate reduction method has less pollution compared with the iron powder reduction method, but is eliminated because large-scale production cannot be realized. The catalytic hydrogenation method makes up the defects of the two methods, is relatively simple to operate, and becomes a main production process of the aniline.
The Chinese patent with publication number CN103288651B discloses a reaction for generating aniline by catalytic hydrogenation of nitrobenzene with a catalyst of nickel-loaded bentonite. The reaction adopts high-purity hydrogen with the flow rate of 30mL/min to reduce the Ni/bentonite catalyst for 2 hours in situ at 400 ℃, then hydrogen is introduced after gasification, continuous reaction is carried out at 300 ℃ and 0.1MPa, 0.19g/h of aniline can be obtained after 1 hour of reaction, and the yield of the aniline is 35.20%. Although the invention utilizes the catalytic hydrogenation method to generate the aniline, the yield of the obtained aniline is low, and the selectivity of the catalytic hydrogenation is poor, thus being not beneficial to industrial mass production.
Disclosure of Invention
In order to solve the technical problems, the invention provides a preparation method of a platinum-supported Ni/Mg/Fe hydrotalcite catalyst and application thereof in preparing aniline, so that the defects of the existing method are overcome, the catalyst consumption is reduced, the selectivity and the conversion rate are improved, the efficient catalytic hydrogenation of a nitro compound to generate aniline is realized, the pollution is reduced, and the green recovery is realized.
The specific technical scheme of the invention is as follows:
in a first aspect, the invention provides a preparation method of a platinum-supported Ni/Mg/Fe hydrotalcite catalyst, which comprises the following steps:
(1) Dissolving nickel salt, magnesium salt and iron salt in water to obtain a mixed solution A; mixing a sodium hydroxide solution and a sodium carbonate solution to obtain a mixed solution B;
(2) Mixing the mixed solution A and the mixed solution B, and then stirring and aging to obtain a mixed solution C;
(3) Filtering the mixed solution C to obtain a precipitate, and sequentially washing, drying and grinding to obtain a catalyst precursor;
(4) Soaking a catalyst precursor in alkali liquor, washing and drying, roasting, cooling and grinding to obtain a Ni/Mg/Fe hydrotalcite catalyst;
(5) Ultrasonically dipping the Ni/Mg/Fe hydrotalcite catalyst into chloroplatinic acid solution, and then taking out and drying to obtain the platinum-supported Ni/Mg/Fe hydrotalcite catalyst.
Hydrotalcite is a layered compound formed by orderly assembling guest anions and a host hydroxide layer with positive charges. The thermal decomposition product of hydrotalcite, i.e., layered metal composite oxide, can be used as a base catalyst, and exhibits good catalytic hydrogenation activity due to the presence of base sites in the oxide. In addition, pt is used as an active component of a hydrogenation catalyst, which can exhibit good catalytic activity and high selectivity in the field of selective hydrogenation. The hydrotalcite layer plate structure assembled by Ni, mg and Fe metal ions and the special cation vacancy effect formed by the hydrotalcite layer plate structure greatly improve the dispersion degree of the Pt active component on the hydrotalcite carrier, thereby increasing the effective contact with reactants. Furthermore, the existence of Mg can ensure the alkalinity of the catalyst, ni and Fe have auxiliary promotion effect on the catalytic activity of Pt, so that the catalyst obtained by combining the metal ions has higher catalytic hydrogenation activity.
In addition, space active sites are increased by roasting hydrotalcite interlamination layout, more space is provided for distribution of Pt at the active sites, and H is adopted 2 PtCl 6 And (3) impregnation is carried out, so that Pt ions are firmly fixed on active sites, and the stability in catalysis is improved. Meanwhile, compared with other metal cations, the Pt metal ions and the Ni, mg and Fe metal ions form firmer combination due to the cation vacancy effect, so that the catalyst has better repeatability and service life.
Preferably, in the step (1), the nickel salt, the magnesium salt and the iron salt are respectively nitrate or chloride of nickel, magnesium and iron; the molar ratio of the metal elements of nickel, magnesium and iron in the nickel salt, the magnesium salt and the iron salt is 4; the molar ratio of sodium hydroxide to sodium carbonate in the sodium hydroxide solution to the sodium carbonate solution is 1:0.5 to 2.
Preferably, in the step (2), the mixing is carried out in a manner of dripping solution, the dripping speed is 3-5 s per drop, and the pH of the mixed solution is kept to be 9-10 in the dripping process; the stirring time is 3-5 h; the aging temperature is 55-65 ℃ and the aging time is 5-6 h.
The range of the dripping speed is to ensure that the pH value is 9-10 in the synthesis process, and the optimal hydrotalcite crystal morphology can be formed. When the aging temperature is too low, hydrotalcite crystals are slowly formed; when the aging temperature is too high, the crystal may be partially broken. The experimental conditions at this stage are controlled to ensure that the catalyst with perfect crystal form is obtained.
Preferably, in the step (3), the drying temperature is 110-120 ℃ and the drying time is 14-18 h.
Preferably, in the step (4), the alkali liquor is a sodium hydroxide solution, and the concentration is 1.5-3 mol/L; the dipping time is 30-50 min; the roasting temperature is 300-450 ℃.
The hydrotalcite catalyst converts hydroxide into oxide by roasting, the hydroxide is not completely decomposed when the roasting temperature is too low, the oxide is further changed into crystalline stone when the roasting temperature is too high, and the crystalline stone hardly has catalytic activity.
Preferably, in the step (5), the mass fraction of platinum in the platinum-supported Ni/Mg/Fe hydrotalcite catalyst is 0.5 to 5%.
Preferably, the step (4) further comprises a modification step of Ni/Mg/Fe hydrotalcite catalyst: mixing the components in a mass ratio of 1:5 to 12 of TiO 2 Mixing the nano particles and dopamine hydrochloride in tris buffer solution, carrying out polymerization reaction, carrying out centrifugal separation after the reaction is finished, adding the obtained product and sodium sulfate into water, and carrying out ultrasonic treatment; then adding Ni/Mg/Fe hydrotalcite catalyst and sodium hydroxide, performing ultrasonic dispersion at 70-80 ℃ for 1.5-3 h and at the frequency of 30-40 KHz, and then performing crystallization at 90-110 ℃ for 6-12 h, performing ultrasonic treatment for 3-8 min every 1h, wherein the amplitude is more than or equal to 40 mu m; then filtering and washing the mixture until the pH value is 6 to 7, and drying the mixture to obtain the modified starchAnd (3) a Ni/Mg/Fe hydrotalcite catalyst.
Hydrotalcite has interlayer anion exchangeability, SO 4 2- The anion can exchange with the object in the precursor hydrotalcite, and the unit cell parameter of the original hydrotalcite is changed to obtain the corresponding intercalated hydrotalcite. The invention is prior to TiO 2 Coating a polydopamine layer on the surface of the nanoparticles by adjusting TiO 2 Inducing the nanoparticles to form a partial coating structure by the mass ratio of the nanoparticles to the dopamine hydrochloride, and then utilizing TiO 2 Nanoparticles, dopamine and SO 4 2- The polydopamine also has certain adhesiveness and can improve SO by absorbing through the interaction of hydrogen bonds between anions 4 2- The surface of the anion is loaded, and the charge density is higher. The anion guest and the precursor hydrotalcite are subjected to anion exchange reaction, and interlayer pillaring generated by introducing anions with larger volume can effectively prevent the hydrotalcite from generating soft agglomeration or hard agglomeration effect, improve the specific surface area and the dispersibility in water, expose more cation vacancies, be beneficial to better anchoring active components and be difficult to lose. In addition, due to TiO 2 The surface effect of the nano particles and the adsorption effect of the polydopamine can improve the loading rate and the loading stability of metal ions to a certain degree, so that the catalyst also has excellent stability in hydrogenation reaction, and still has good conversion efficiency and selectivity after being used for many times.
The ultrasonic crystallization and re-ultrasonic process is to break up the interaction force among the particles in advance, intensify the internal motion among the particles and molecules, help to generate interlayer exchange reaction of large-volume anions, keep the nucleation consistency in the crystallization process, and maximally not influence the nucleation of the mutual particles, thereby finally obtaining the particles with good uniformity and dispersibility.
Preferably, the TiO is 2 The particle size of the nano particles is 10-30 nm; the polymerization is carried out for 6 to 10 hours at the temperature of between 20 and 40 ℃; the mass ratio of the obtained product to sodium sulfate is 1:4.8 to 12; the molar ratio of the Ni/Mg/Fe hydrotalcite catalyst to the sodium sulfate to the sodium hydroxide is 1:0.9 to 3:5 to 9; the drying is carried out for 7 to 10 hours at a temperature of between 60 and 75 ℃.
Controlling TiO 2 The particle size of the nano particles can promote better anion interlayer exchange reaction. The effect of increasing the specific surface area by interlayer column support is not obvious when the particle size is too small; the particle size is too large, which is not beneficial to entering or partially entering hydrotalcite interlamination to generate anion exchange, but can prevent active components from entering the hydrotalcite structure, and the catalytic effect and the stability are poor.
In a second aspect, the invention also provides an application of the catalyst prepared by the preparation method in preparation of aniline by hydrogenation of nitrobenzene.
Preferably, the catalyst is reduced in a hydrogen atmosphere before use at a reduction temperature of 50 to 60 ℃.
Compared with the prior art, the invention has the beneficial effects that:
(1) The Pt active component is loaded on the Ni/Mg/Fe hydrotalcite carrier, so that the catalyst shows good catalytic hydrogenation activity, and particularly shows excellent conversion efficiency and selectivity in the application of preparing aniline by catalytic hydrogenation of nitrobenzene;
(2) The preparation method is improved, so that active sites can be increased, the load stability of the active components is improved, the active components are not easy to lose, and the catalyst still has good catalytic activity after being used for many times.
Detailed Description
The present invention will be further described with reference to the following examples.
Example 1 (active component 0.5% Pt)
1. Preparation of platinum-loaded Ni/Mg/Fe hydrotalcite catalyst
(1) Weighing 8.20g Ni (NO) 3 ) 2 ·3H 2 O、2.24g Mg(NO 3 ) 2 ·6H 2 O、3.56gFe(NO 3 ) 3 ·9H 2 Dissolving O in 40mL of deionized water to prepare a mixed solution A for later use; 4g of NaOH and 21.2g of Na were taken 2 CO 3 Dissolving in 40mL of deionized water to prepare a mixed solution B for later use;
(2) Adding 40mL of deionized water into a flask in advance, heating to the reaction temperature of 60 ℃, adding the mixed solution A and the mixed solution B into the flask at the dropping speed of 4s per drop under the stirring condition, and keeping the pH = 9-10 of the mixed solution in the dropping process all the time; after the dropwise adding is finished, the mixture is stirred vigorously to be aged at the temperature of 60 ℃ for 6 hours, and then a mixed solution C is obtained;
(3) Filtering the mixed solution C, repeatedly washing the mixed solution C with deionized water until the pH of the filtrate is =7, placing the filtrate in an oven at the temperature of 120 ℃ for treatment for 16 hours, and grinding the filtrate into powder to obtain a catalyst precursor;
(4) Soaking 2g of catalyst precursor in 20mL of 2mol/L NaOH solution for 30min, taking out, washing with deionized water to be neutral, and drying in an oven at 80 ℃; then roasting at 450 ℃ to obtain a Ni/Mg/Fe hydrotalcite catalyst;
(5) Dissolving 1g of chloroplatinic acid in 5mL of ethanol to prepare a mixed solution D, putting 1g of Ni/Mg/Fe hydrotalcite catalyst in a sampling bottle, transferring 68 mu L of the mixed solution D by a pipette, soaking for 1h by ultrasonic wave, soaking overnight, and drying in an oven at 80 ℃ to obtain the platinum-supported Ni/Mg/Fe hydrotalcite catalyst.
2. Application of nitrobenzene catalytic hydrogenation to prepare aniline
Adding 0.1g of platinum-supported Ni/Mg/Fe hydrotalcite catalyst into a reaction kettle, adding 10g of nitrobenzene, 0.2g of dicyandiamide and 50mL of ethanol, introducing nitrogen for four times to remove air, replacing for three times with hydrogen, setting the stirring speed at 600r/min, setting the temperature of the reactor at 60 ℃, controlling the hydrogen pressure to be stable at 1MPa, and reacting for 4 hours to obtain aniline.
Example 2
The difference from example 1 is that: active fraction 1% pt.
1. Preparation of platinum-loaded Ni/Mg/Fe hydrotalcite catalyst
(1) Weighing 8.20g Ni (NO) 3 ) 2 ·3H 2 O、2.24g Mg(NO 3 ) 2 ·6H 2 O、3.56gFe(NO 3 ) 3 ·9H 2 Dissolving O in 40mL of deionized water to prepare a mixed solution A for later use; 4g of NaOH and 21.2g of Na were taken 2 CO 3 Dissolving in 40mL of deionized water to prepare a mixed solution B for later use;
(2) Adding 40mL of deionized water into a flask in advance, heating to the reaction temperature of 60 ℃, adding the mixed solution A and the mixed solution B into the flask at the dropping speed of 4s per drop under the stirring condition, and keeping the pH = 9-10 of the mixed solution in the dropping process all the time; after the dropwise adding is finished, the mixture is stirred vigorously to be aged at the temperature of 60 ℃ for 6 hours, and then a mixed solution C is obtained;
(3) Filtering the mixed solution C, repeatedly washing the mixed solution C with deionized water until the pH of the filtrate is =7, placing the filtrate in an oven at 120 ℃ for treatment for 16h, and grinding the filtrate into powder to obtain a catalyst precursor;
(4) Soaking 2g of catalyst precursor in 20mL of 2mol/L NaOH solution for 30min, taking out, washing with deionized water to be neutral, and drying in an oven at 80 ℃; then roasting at 450 ℃ to obtain a Ni/Mg/Fe hydrotalcite catalyst;
(5) Dissolving 1g of chloroplatinic acid in 5mL of ethanol to prepare a mixed solution D, putting 1g of Ni/Mg/Fe hydrotalcite catalyst in a sampling bottle, transferring 136 mu L of the mixed solution D by a pipette, soaking for 1h by ultrasonic wave, soaking overnight, and drying in an oven at 80 ℃ to obtain the platinum-supported Ni/Mg/Fe hydrotalcite catalyst.
2. Application of nitrobenzene catalytic hydrogenation to prepare aniline
Adding 0.1g of platinum-supported Ni/Mg/Fe hydrotalcite catalyst into a reaction kettle, adding 10g of nitrobenzene, 0.2g of dicyandiamide and 50mL of ethanol, introducing nitrogen for four times to remove air, replacing for three times with hydrogen, setting the stirring speed at 600r/min, setting the temperature of the reactor at 60 ℃, controlling the hydrogen pressure to be stable at 1MPa, and reacting for 4 hours to obtain aniline.
Example 3
The difference from example 1 is that: active ingredient was 2% pt.
1. Preparation of platinum-loaded Ni/Mg/Fe hydrotalcite catalyst
(1) Weighing 8.20g Ni (NO) 3 ) 2 ·3H 2 O、2.24g Mg(NO 3 ) 2 ·6H 2 O、3.56gFe(NO 3 ) 3 ·9H 2 Dissolving O in 40mL of deionized water to prepare a mixed solution A for later use; 4g of NaOH and 21.2g of Na were taken 2 CO 3 Dissolving in 40mL of deionized water to prepare a mixed solution B for later use;
(2) Adding 40mL of deionized water into a flask in advance, heating to a reaction temperature of 60 ℃, adding the mixed solution A and the mixed solution B into the flask at a dropping speed of 4s per drop under a stirring condition, and keeping the pH of the mixed solution = 9-10 all the time in the dropping process; after the dropwise adding is finished, the mixture is stirred vigorously to be aged at the temperature of 60 ℃ for 6 hours, and then a mixed solution C is obtained;
(3) Filtering the mixed solution C, repeatedly washing the mixed solution C with deionized water until the pH of the filtrate is =7, placing the filtrate in an oven at 120 ℃ for treatment for 16h, and grinding the filtrate into powder to obtain a catalyst precursor;
(4) Soaking 2g of catalyst precursor in 20mL of 2mol/LNaOH solution for 30min, then taking out, washing with deionized water to be neutral, and drying in an oven at 80 ℃; then roasting at 450 ℃ to obtain a Ni/Mg/Fe hydrotalcite catalyst;
(5) Dissolving 1g of chloroplatinic acid in 5mL of ethanol to prepare a mixed solution D, taking 1g of Ni/Mg/Fe hydrotalcite catalyst in a sampling bottle, transferring 271 mu L of the mixed solution D by a transfer pipette, soaking for 1h by ultrasonic wave, standing overnight, and drying in an oven at 80 ℃ to obtain the platinum-supported Ni/Mg/Fe hydrotalcite catalyst.
2. Application of nitrobenzene catalytic hydrogenation to prepare aniline
Adding 0.1g of platinum-supported Ni/Mg/Fe hydrotalcite catalyst into a reaction kettle, adding 10g of nitrobenzene, 0.2g of dicyandiamide and 50mL of ethanol, introducing nitrogen for four times to remove air, replacing for three times with hydrogen, setting the stirring speed at 600r/min, setting the temperature of the reactor at 60 ℃, controlling the hydrogen pressure to be stable at 1MPa, and reacting for 4 hours to obtain aniline.
Example 4
The difference from example 1 is that: active ingredient 5% pt.
1. Preparation of platinum-loaded Ni/Mg/Fe hydrotalcite catalyst
(1) Weighing 8.20g Ni (NO) 3 ) 2 ·3H 2 O、2.24g Mg(NO 3 ) 2 ·6H 2 O、3.56gFe(NO 3 ) 3 ·9H 2 Dissolving O in 40mL of deionized water to prepare a mixed solution A for later use; 4g of NaOH and 21.2g of Na were taken 2 CO 3 Dissolving in 40mL deionized water to obtain mixed solution BUsing;
(2) Adding 40mL of deionized water into a flask in advance, heating to the reaction temperature of 60 ℃, adding the mixed solution A and the mixed solution B into the flask at the dropping speed of 4s per drop under the stirring condition, and keeping the pH = 9-10 of the mixed solution in the dropping process all the time; after the dropwise adding is finished, the mixture is stirred vigorously to be aged at the temperature of 60 ℃ for 6 hours, and then a mixed solution C is obtained;
(3) Filtering the mixed solution C, repeatedly washing the mixed solution C with deionized water until the pH of the filtrate is =7, placing the filtrate in an oven at 120 ℃ for treatment for 16h, and grinding the filtrate into powder to obtain a catalyst precursor;
(4) Soaking 2g of catalyst precursor in 20mL of 2mol/L NaOH solution for 30min, taking out, washing with deionized water to be neutral, and drying in an oven at 80 ℃; then roasting at 450 ℃ to obtain a Ni/Mg/Fe hydrotalcite catalyst;
(5) Dissolving 2g of chloroplatinic acid in 10mL of ethanol to prepare a mixed solution D, taking 1g of Ni/Mg/Fe hydrotalcite catalyst in a sampling bottle, transferring 6.76mL of the mixed solution D by a transfer pipette, soaking for 1h by ultrasonic wave, soaking overnight, and drying in an oven at 80 ℃ to obtain the platinum-supported Ni/Mg/Fe hydrotalcite catalyst.
2. Application of nitrobenzene catalytic hydrogenation to prepare aniline
Adding 0.1g of platinum-supported Ni/Mg/Fe hydrotalcite catalyst into a reaction kettle, adding 10g of nitrobenzene, 0.2g of dicyandiamide and 50mL of ethanol, introducing nitrogen for four times to remove air, replacing three times with hydrogen, setting the stirring speed at 600r/min, setting the temperature of the reactor at 60 ℃, controlling the hydrogen pressure to be stable at 1MPa, and reacting for 4 hours to obtain aniline.
Example 5
The difference from example 2 is that: the step (4) also comprises a modification step of Ni/Mg/Fe hydrotalcite catalyst.
1. Preparation of platinum-loaded Ni/Mg/Fe hydrotalcite catalyst
(1) Weighing 8.20g Ni (NO) 3 ) 2 ·3H 2 O、2.24g Mg(NO 3 ) 2 ·6H 2 O、3.56gFe(NO 3 ) 3 ·9H 2 Dissolving O in 40mL deionized water to prepare mixed solution AUsing; 4g of NaOH and 21.2g of Na were taken 2 CO 3 Dissolving in 40mL of deionized water to prepare a mixed solution B for later use;
(2) Adding 40mL of deionized water into a flask in advance, heating to the reaction temperature of 60 ℃, adding the mixed solution A and the mixed solution B into the flask at the dropping speed of 4s per drop under the stirring condition, and keeping the pH = 9-10 of the mixed solution in the dropping process all the time; after the dropwise adding is finished, the mixture is stirred vigorously to be aged at the temperature of 60 ℃ for 6 hours, and then a mixed solution C is obtained;
(3) Filtering the mixed solution C, repeatedly washing the mixed solution C with deionized water until the pH of the filtrate is =7, placing the filtrate in an oven at 120 ℃ for treatment for 16h, and grinding the filtrate into powder to obtain a catalyst precursor;
(4) Soaking 2g of catalyst precursor into 20mL of 2mol/L NaOH solution for 30min, taking out, washing with deionized water to be neutral, and drying in an oven at 80 ℃; then roasting at 450 ℃ to obtain a Ni/Mg/Fe hydrotalcite catalyst; 1g of TiO 2 Mixing the nano particles and 8g of dopamine hydrochloride in tris buffer solution, carrying out polymerization reaction for 9h at 30 ℃ 2 The particle size of the nano particles is 15nm, centrifugal separation is carried out after the reaction is finished, 1.5g of the obtained product and 12g of sodium sulfate are added into water and subjected to ultrasonic treatment; then adding Ni/Mg/Fe hydrotalcite catalyst and sodium hydroxide, wherein the molar ratio of the Ni/Mg/Fe hydrotalcite catalyst to the sodium sulfate to the sodium hydroxide is 1:1.6:6, firstly performing ultrasonic dispersion at 70 ℃ for 2 hours and the frequency of 30KHz, and then performing crystallization at 95 ℃ for 7 hours, performing ultrasonic treatment for 4min every 1 hour, wherein the amplitude is 40 mu m; then filtering and washing until the pH value is 6-7, and drying at 60 ℃ for 10 hours to obtain a modified Ni/Mg/Fe hydrotalcite catalyst;
(5) Dissolving 1g of chloroplatinic acid in 5mL of ethanol to prepare a mixed solution D, taking 1g of modified Ni/Mg/Fe hydrotalcite catalyst in a sampling bottle, transferring 136 mu L of the mixed solution D by a transfer pipette, soaking for 1h by ultrasonic, soaking overnight, and drying in an oven at 80 ℃ to obtain the platinum-supported Ni/Mg/Fe hydrotalcite catalyst.
2. Application of nitrobenzene catalytic hydrogenation to prepare aniline
Adding 0.1g of platinum-supported Ni/Mg/Fe hydrotalcite catalyst into a reaction kettle, adding 10g of nitrobenzene, 0.2g of dicyandiamide and 50mL of ethanol, introducing nitrogen for four times to remove air, replacing for three times with hydrogen, setting the stirring speed at 600r/min, setting the temperature of the reactor at 60 ℃, controlling the hydrogen pressure to be stable at 1MPa, and reacting for 4 hours to obtain aniline.
Example 6
The difference from example 2 is that: the step (4) also comprises a modification step of Ni/Mg/Fe hydrotalcite catalyst.
1. Preparation of platinum-loaded Ni/Mg/Fe hydrotalcite catalyst
(1) Weighing 8.20g Ni (NO) 3 ) 2 ·3H 2 O、2.24g Mg(NO 3 ) 2 ·6H 2 O、3.56gFe(NO 3 ) 3 ·9H 2 Dissolving O in 40mL of deionized water to prepare a mixed solution A for later use; 4g of NaOH and 21.2g of Na were taken 2 CO 3 Dissolving in 40mL of deionized water to prepare a mixed solution B for later use;
(2) Adding 40mL of deionized water into a flask in advance, heating to the reaction temperature of 60 ℃, adding the mixed solution A and the mixed solution B into the flask at the dropping speed of 4s per drop under the stirring condition, and keeping the pH = 9-10 of the mixed solution in the dropping process all the time; after the dropwise adding is finished, the mixture is stirred vigorously to be aged at the temperature of 60 ℃ for 6 hours, and then a mixed solution C is obtained;
(3) Filtering the mixed solution C, repeatedly washing the mixed solution C with deionized water until the pH of the filtrate is =7, placing the filtrate in an oven at 120 ℃ for treatment for 16h, and grinding the filtrate into powder to obtain a catalyst precursor;
(4) Soaking 2g of catalyst precursor in 20mL of 2mol/LNaOH solution for 30min, taking out, washing with deionized water to be neutral, and drying in an oven at 80 ℃; then roasting at 450 ℃ to obtain a Ni/Mg/Fe hydrotalcite catalyst; 1g of TiO 2 Mixing the nanoparticles with 10g dopamine hydrochloride in tris buffer solution, polymerizing at 40 deg.C for 7h 2 The particle size of the nano particles is 20nm, centrifugal separation is carried out after the reaction is finished, and 1.5g of the obtained product and 15g of sodium sulfate are added into water and subjected to ultrasonic treatment; adding Ni/Mg/Fe hydrotalcite catalyst and sodium hydroxide, wherein the molar ratio of the Ni/Mg/Fe hydrotalcite catalyst to the sodium sulfate to the sodium hydroxide is 1:2.1:8, firstly performing ultrasonic dispersion for 2 hours at 80 ℃ and crystallizing at 110 ℃ for 8 hours at the frequency of 40KHzPerforming ultrasonic treatment for 7min every 1h, wherein the amplitude is 60 mu m; then filtering and washing until the pH value is 6-7, and drying for 8 hours at 75 ℃ to obtain a modified Ni/Mg/Fe hydrotalcite catalyst;
(5) Dissolving 1g of chloroplatinic acid in 5mL of ethanol to prepare a mixed solution D, taking 1g of modified Ni/Mg/Fe hydrotalcite catalyst in a sampling bottle, transferring 136 mu L of the mixed solution D by a pipette, soaking for 1h by ultrasonic wave, soaking overnight, and drying in an oven at 80 ℃ to obtain the platinum-supported Ni/Mg/Fe hydrotalcite catalyst.
2. Application of nitrobenzene catalytic hydrogenation to prepare aniline
Adding 0.1g of platinum-supported Ni/Mg/Fe hydrotalcite catalyst into a reaction kettle, adding 10g of nitrobenzene, 0.2g of dicyandiamide and 50mL of ethanol, introducing nitrogen for four times to remove air, replacing three times with hydrogen, setting the stirring speed at 600r/min, setting the temperature of the reactor at 60 ℃, controlling the hydrogen pressure to be stable at 1MPa, and reacting for 4 hours to obtain aniline.
Comparative example 1
The difference from example 2 is that: active ingredient 10% mo.
1. Preparation of molybdenum-supported Ni/Mg/Fe hydrotalcite catalyst
(1) Weighing 8.20g Ni (NO) 3 ) 2 ·3H 2 O、2.24g Mg(NO 3 ) 2 ·6H 2 O、3.56gFe(NO 3 ) 3 ·9H 2 Dissolving O in 40mL of deionized water to prepare a mixed solution A for later use; 4g of NaOH and 21.2g of Na were taken 2 CO 3 Dissolving in 40mL of deionized water to prepare a mixed solution B for later use;
(2) Adding 40mL of deionized water into a flask in advance, heating to a reaction temperature of 60 ℃, adding the mixed solution A and the mixed solution B into the flask at a dropping speed of 4s per drop under a stirring condition, and keeping the pH of the mixed solution = 9-10 all the time in the dropping process; after the dropwise adding is finished, the mixture is stirred vigorously to be aged at the temperature of 60 ℃ for 6 hours, and then a mixed solution C is obtained;
(3) Filtering the mixed solution C, repeatedly washing the mixed solution C with deionized water until the pH of the filtrate is =7, placing the filtrate in an oven at 120 ℃ for treatment for 16h, and grinding the filtrate into powder to obtain a catalyst precursor;
(4) Soaking 2g of catalyst precursor in 20mL of 2mol/LNaOH solution for 30min, then taking out, washing with deionized water to be neutral, and drying in an oven at 80 ℃; then roasting at 450 ℃ to obtain a Ni/Mg/Fe hydrotalcite catalyst;
(5) Preparing mesoporous SiO loaded with phosphomolybdic acid (PMA) by using an impregnation method 2 Powder (PMA-SiO) 2 ) Then adding PMA-SiO 2 Powder in H 2 /N 2 Treating at 400 deg.C for 6h under atmosphere to obtain black solid, treating with HF solution for 13h, centrifuging, washing with deionized water and anhydrous ethanol, and drying to obtain MoO 2 A nanoparticle;
1.33g of MoO 2 Dissolving the nano particles in 5mL of ethanol to prepare a mixed solution D, taking 1g of Ni/Mg/Fe hydrotalcite catalyst in a sampling bottle, transferring 500 mu L of the mixed solution D by a pipette, soaking for 1h by ultrasonic waves, soaking overnight, and drying in an oven at 80 ℃ to obtain the molybdenum-supported Ni/Mg/Fe hydrotalcite catalyst.
2. Application of nitrobenzene catalytic hydrogenation to prepare aniline
Adding 0.1g of molybdenum-supported Ni/Mg/Fe hydrotalcite catalyst into a reaction kettle, adding 10g of nitrobenzene, 0.2g of dicyandiamide and 50mL of ethanol, introducing nitrogen for four times to remove air, replacing for three times with hydrogen, setting the stirring speed at 600r/min, setting the temperature of the reactor at 60 ℃, controlling the hydrogen pressure to be stable at 1MPa, and reacting for 4 hours to obtain aniline.
Comparative example 2
The difference from example 2 is that: the active ingredient was 10% cu.
1. Preparation of copper-loaded Ni/Mg/Fe hydrotalcite catalyst
(1) Weighing 8.20g Ni (NO) 3 ) 2 ·3H 2 O、2.24g Mg(NO 3 ) 2 ·6H 2 O、3.56gFe(NO 3 ) 3 ·9H 2 Dissolving O in 40mL of deionized water to prepare a mixed solution A for later use; 4g of NaOH and 21.2g of Na were taken 2 CO 3 Dissolving in 40mL of deionized water to prepare a mixed solution B for later use;
(2) Adding 40mL of deionized water into a flask in advance, heating to the reaction temperature of 60 ℃, adding the mixed solution A and the mixed solution B into the flask at the dropping speed of 4s per drop under the stirring condition, and keeping the pH = 9-10 of the mixed solution in the dropping process all the time; after the dropwise adding is finished, the mixture is stirred vigorously to be aged at the temperature of 60 ℃ for 6 hours, and then a mixed solution C is obtained;
(3) Filtering the mixed solution C, repeatedly washing the mixed solution C with deionized water until the pH of the filtrate is =7, placing the filtrate in an oven at 120 ℃ for treatment for 16h, and grinding the filtrate into powder to obtain a catalyst precursor;
(4) Soaking 2g of catalyst precursor in 20mL of 2mol/LNaOH solution for 30min, then taking out, washing with deionized water to be neutral, and drying in an oven at 80 ℃; then roasting at 450 ℃ to obtain a Ni/Mg/Fe hydrotalcite catalyst;
(5) 1.56g of Cu (NO) 3 ) 2 Dissolving the aqueous solution in 5mL of ethanol to prepare a mixed solution D, putting 1g of Ni/Mg/Fe hydrotalcite catalyst in a sampling bottle, adding the mixed solution D, soaking for 1h by ultrasonic waves, soaking overnight, filtering, and drying the solid in an oven at 80 ℃; and soaking the solid by using the filtrate, drying and repeating for 2 times to obtain the copper-supported Ni/Mg/Fe hydrotalcite catalyst.
2. Application of nitrobenzene catalytic hydrogenation to prepare aniline
Adding 0.1g of copper-supported Ni/Mg/Fe hydrotalcite catalyst into a reaction kettle, adding 10g of nitrobenzene, 0.2g of dicyandiamide and 50mL of ethanol, introducing nitrogen for four times to remove air, replacing three times with hydrogen, setting the stirring speed at 600r/min, setting the temperature of the reactor at 60 ℃, controlling the hydrogen pressure to be stable at 1MPa, and reacting for 4 hours to obtain aniline.
Comparative example 3
The difference from example 2 is that: the calcination temperature in the step (4) was 500 ℃.
1. Preparation of platinum-loaded Ni/Mg/Fe hydrotalcite catalyst
(1) Weighing 8.20g Ni (NO) 3 ) 2 ·3H 2 O、2.24g Mg(NO 3 ) 2 ·6H 2 O、3.56gFe(NO 3 ) 3 ·9H 2 Dissolving O in 40mL of deionized water to prepare a mixed solution A for later use; 4g of NaOH and 21.2g of Na were taken 2 CO 3 Dissolving in 40mL deionized water, and mixingThe solution B is ready for use;
(2) Adding 40mL of deionized water into a flask in advance, heating to a reaction temperature of 60 ℃, adding the mixed solution A and the mixed solution B into the flask at a dropping speed of 4s per drop under a stirring condition, and keeping the pH of the mixed solution = 9-10 all the time in the dropping process; after the dropwise addition is finished, the mixture is stirred vigorously to carry out aging treatment at the temperature of 60 ℃ for 6 hours, and then mixed solution C is obtained;
(3) Filtering the mixed solution C, repeatedly washing the mixed solution C with deionized water until the pH of the filtrate is =7, placing the filtrate in an oven at 120 ℃ for treatment for 16h, and grinding the filtrate into powder to obtain a catalyst precursor;
(4) Soaking 2g of catalyst precursor in 20mL of 2mol/LNaOH solution for 30min, then taking out, washing with deionized water to be neutral, and drying in an oven at 80 ℃; then roasting at the high temperature of 500 ℃ to obtain a Ni/Mg/Fe hydrotalcite catalyst;
(5) Dissolving 1g of chloroplatinic acid in 5mL of ethanol to prepare a mixed solution D, putting 1g of Ni/Mg/Fe hydrotalcite catalyst in a sampling bottle, transferring 136 mu L of the mixed solution D by a pipette, soaking for 1h by ultrasonic wave, soaking overnight, and drying in an oven at 80 ℃ to obtain the platinum-supported Ni/Mg/Fe hydrotalcite catalyst.
2. Application of nitrobenzene catalytic hydrogenation to prepare aniline
Adding 0.1g of platinum-supported Ni/Mg/Fe hydrotalcite catalyst into a reaction kettle, adding 10g of nitrobenzene, 0.2g of dicyandiamide and 50mL of ethanol, introducing nitrogen for four times to remove air, replacing for three times with hydrogen, setting the stirring speed at 600r/min, setting the temperature of the reactor at 60 ℃, controlling the hydrogen pressure to be stable at 1MPa, and reacting for 4 hours to obtain aniline.
Comparative example 4
The difference from example 2 is that: a Ni/Zn/Fe hydrotalcite support was used.
1. Preparation of platinum-loaded Ni/Zn/Fe hydrotalcite catalyst
(1) Weighing 8.20g Ni (NO) 3 ) 2 ·3H 2 O、2.60g Zn(NO 3 ) 2 ·6H 2 O、3.56gFe(NO 3 ) 3 ·9H 2 Dissolving O in 40mL of deionized water to prepare a mixed solution A for later use; 4g of NaOH and 21.2g of NaOH were takenNa 2 CO 3 Dissolving in 40mL of deionized water to prepare a mixed solution B for later use;
(2) Adding 40mL of deionized water into a flask in advance, heating to a reaction temperature of 60 ℃, adding the mixed solution A and the mixed solution B into the flask at a dropping speed of 4s per drop under a stirring condition, and keeping the pH of the mixed solution = 9-10 all the time in the dropping process; after the dropwise adding is finished, the mixture is stirred vigorously to be aged at the temperature of 60 ℃ for 6 hours, and then a mixed solution C is obtained;
(3) Filtering the mixed solution C, repeatedly washing the mixed solution C with deionized water until the pH of the filtrate is =7, placing the filtrate in an oven at 120 ℃ for treatment for 16h, and grinding the filtrate into powder to obtain a catalyst precursor;
(4) Soaking 2g of catalyst precursor in 20mL of 2mol/LNaOH solution for 30min, then taking out, washing with deionized water to be neutral, and drying in an oven at 80 ℃; then roasting at 450 ℃ to obtain a Ni/Zn/Fe hydrotalcite catalyst;
(5) Dissolving 1g of chloroplatinic acid in 5mL of ethanol to prepare a mixed solution D, putting 1g of Ni/Zn/Fe hydrotalcite catalyst in a sampling bottle, transferring 136 mu L of the mixed solution D by a pipette, soaking for 1h by ultrasonic waves, soaking overnight, and drying in an oven at 80 ℃ to obtain the platinum-supported Ni/Zn/Fe hydrotalcite catalyst.
2. Application of nitrobenzene catalytic hydrogenation to prepare aniline
Adding 0.1g of platinum-supported Ni/Zn/Fe hydrotalcite hydrogenation catalyst into a reaction kettle, adding 10g of nitrobenzene, 0.2g of dicyandiamide and 50mL of ethanol, introducing nitrogen for four times to remove air, replacing for three times with hydrogen, setting the stirring speed to be 600r/min, setting the temperature of the reactor to be 60 ℃, controlling the hydrogen pressure to be stable at 1MPa, and reacting for 4 hours to obtain aniline.
Comparative example 5
The difference from example 2 is that: a Ni/Mg/Al hydrotalcite support was used.
1. Preparation of platinum-loaded Ni/Mg/Al hydrotalcite catalyst
(1) Weighing 8.20g Ni (NO) 3 ) 2 ·3H 2 O、2.24g Mg(NO 3 ) 2 ·6H 2 O、3.31gAl(NO 3 ) 3 ·9H 2 O solutionPreparing a mixed solution A in 40mL of deionized water for later use; 4g of NaOH and 21.2g of Na were taken 2 CO 3 Dissolving in 40mL of deionized water to prepare a mixed solution B for later use;
(2) Adding 40mL of deionized water into a flask in advance, heating to the reaction temperature of 60 ℃, adding the mixed solution A and the mixed solution B into the flask at the dropping speed of 4s per drop under the stirring condition, and keeping the pH = 9-10 of the mixed solution in the dropping process all the time; after the dropwise adding is finished, the mixture is stirred vigorously to be aged at the temperature of 60 ℃ for 6 hours, and then a mixed solution C is obtained;
(3) Filtering the mixed solution C, repeatedly washing the mixed solution C with deionized water until the pH of the filtrate is =7, placing the filtrate in an oven at 120 ℃ for treatment for 16h, and grinding the filtrate into powder to obtain a catalyst precursor;
(4) Soaking 2g of catalyst precursor in 20mL of 2mol/LNaOH solution for 30min, then taking out, washing with deionized water to be neutral, and drying in an oven at 80 ℃; then roasting at 450 ℃ to obtain a Ni/Mg/Al hydrotalcite catalyst;
(5) Dissolving 1g of chloroplatinic acid in 5mL of ethanol to prepare a mixed solution D, putting 1g of Ni/Mg/Al hydrotalcite catalyst in a sampling bottle, transferring 136 mu L of the mixed solution D by a pipette, soaking for 1h by ultrasonic waves, soaking overnight, and drying in an oven at 80 ℃ to obtain the platinum-supported Ni/Mg/Al hydrotalcite catalyst.
2. Application of nitrobenzene catalytic hydrogenation to prepare aniline
Adding 0.1g of platinum-supported Ni/Mg/Al hydrotalcite catalyst into a reaction kettle, adding 10g of nitrobenzene, 0.2g of dicyandiamide and 50mL of ethanol, introducing nitrogen for four times to remove air, replacing for three times with hydrogen, setting the stirring speed at 600r/min, setting the temperature of the reactor at 60 ℃, controlling the hydrogen pressure to be stable at 1MPa, and reacting for 4 hours to obtain aniline.
Comparative example 6
The difference from example 2 is that: a Cu/Mg/Fe hydrotalcite support was used.
1. Preparation of platinum-loaded Cu/Mg/Fe hydrotalcite catalyst
(1) Weigh 8.37g Cu (NO) 3 ) 2 ·3H 2 O、2.24g Mg(NO 3 ) 2 ·6H 2 O、3.56gFe(NO 3 ) 3 ·9H 2 Dissolving O in 40mL of deionized water to prepare a mixed solution A for later use; 4g of NaOH and 21.2g of Na were taken 2 CO 3 Dissolving in 40mL of deionized water to prepare a mixed solution B for later use;
(2) Adding 40mL of deionized water into a flask in advance, heating to a reaction temperature of 60 ℃, adding the mixed solution A and the mixed solution B into the flask at a dropping speed of 4s per drop under a stirring condition, and keeping the pH of the mixed solution = 9-10 all the time in the dropping process; after the dropwise adding is finished, the mixture is stirred vigorously to be aged at the temperature of 60 ℃ for 6 hours, and then a mixed solution C is obtained;
(3) Filtering the mixed solution C, repeatedly washing the mixed solution C with deionized water until the pH of the filtrate is =7, placing the filtrate in an oven at 120 ℃ for treatment for 16h, and grinding the filtrate into powder to obtain a catalyst precursor;
(4) Soaking 2g of catalyst precursor in 20mL of 2mol/LNaOH solution for 30min, then taking out, washing with deionized water to be neutral, and drying in an oven at 80 ℃; then roasting at 450 ℃ to obtain a Cu/Mg/Fe hydrotalcite catalyst;
(5) Dissolving 1g of chloroplatinic acid in 5mL of ethanol to prepare a mixed solution D, placing 1g of Cu/Mg/Fe hydrotalcite catalyst in a sampling bottle, transferring 136 mu L of the mixed solution D by a pipette, soaking for 1h by ultrasonic waves, soaking overnight, and placing in a drying oven to dry at 80 ℃ to obtain the platinum-supported Cu/Mg/Fe hydrotalcite catalyst.
2. Application of nitrobenzene catalytic hydrogenation to prepare aniline
Adding 0.1g of platinum-supported Cu/Mg/Fe hydrotalcite catalyst into a reaction kettle, adding 10g of nitrobenzene, 0.2g of dicyandiamide and 50mL of ethanol, introducing nitrogen for four times to remove air, replacing three times with hydrogen, setting the stirring speed at 600r/min, setting the temperature of the reactor at 60 ℃, controlling the hydrogen pressure to be stable at 1MPa, and reacting for 4 hours to obtain aniline.
Comparative example 7
The difference from example 5 is (crystallization process difference):
in the step (4), 2g of catalyst precursor is soaked in 20mL of 2mol/LNaOH solution for 30min, then the catalyst precursor is taken out and washed by deionized water to be neutral, and the catalyst precursor is dried in an oven at 80 ℃; then roasting at 450 ℃ to obtain a Ni/Mg/Fe hydrotalcite catalyst;
1g of TiO 2 Mixing the nano particles and 8g of dopamine hydrochloride in tris buffer solution, carrying out polymerization reaction for 9h at 30 ℃ 2 The particle size of the nano particles is 15nm, centrifugal separation is carried out after the reaction is finished, 1.5g of the obtained product and 12g of sodium sulfate are added into water and subjected to ultrasonic treatment; then adding Ni/Mg/Fe hydrotalcite catalyst and sodium hydroxide, wherein the molar ratio of the Ni/Mg/Fe hydrotalcite catalyst to the sodium sulfate to the sodium hydroxide is 1:1.6:6, stirring for 2 hours at 70 ℃, and crystallizing for 7 hours at 95 ℃; then filtering and washing until the pH value is 6-7, and drying at 60 ℃ for 10h to obtain the modified Ni/Mg/Fe hydrotalcite catalyst.
Comparative example 8
The difference from example 5 is That (TiO) 2 The particle size of the nanoparticles exceeds a defined range):
in the step (4), 2g of the catalyst precursor is immersed in 20mL of 2mol/LNaOH solution for 30min, then taken out, washed to be neutral by deionized water, and placed in an oven at 80 ℃ for drying; then roasting at 450 ℃ to obtain a Ni/Mg/Fe hydrotalcite catalyst;
1g of TiO 2 Mixing the nano particles and 8g of dopamine hydrochloride in tris buffer solution, carrying out polymerization reaction for 9h at 30 ℃ 2 The particle size of the nano particles is 50nm, centrifugal separation is carried out after the reaction is finished, 1.5g of the obtained product and 12g of sodium sulfate are added into water and subjected to ultrasonic treatment; adding Ni/Mg/Fe hydrotalcite catalyst and sodium hydroxide, wherein the molar ratio of the Ni/Mg/Fe hydrotalcite catalyst to the sodium sulfate to the sodium hydroxide is 1:1.6:6, firstly performing ultrasonic dispersion at 70 ℃ for 2 hours and the frequency of 30KHz, and then performing crystallization at 95 ℃ for 7 hours, performing ultrasonic treatment for 4min every 1 hour, wherein the amplitude is 40 mu m; then filtering and washing until the pH value is 6-7, and drying at 60 ℃ for 10h to obtain the modified Ni/Mg/Fe hydrotalcite catalyst.
TABLE 1 conversion and selectivity of catalytic hydrogenation of nitrobenzene to aniline
| Group of | Hydrotalcite carrier | Active component | Temperature of calcination | Conversion of nitrobenzene | Selectivity to aniline |
| Example 1 | Ni/Mg/Fe | 0.5％Pt | 450℃ | 98.10％ | 97.25％ |
| Example 2 | Ni/Mg/Fe | 1％Pt | 450℃ | 100.00％ | 98.42％ |
| Example 3 | Ni/Mg/Fe | 2％Pt | 450℃ | 100.00％ | 90.49％ |
| Example 4 | Ni/Mg/Fe | 5％Pt | 450℃ | 99.50％ | 97.64％ |
| Example 5 | Modified Ni/Mg/Fe | 1％Pt | 450℃ | 100.00％ | 99.56％ |
| Example 6 | Modified Ni/Mg/Fe | 1％Pt | 450℃ | 100.00％ | 99.34％ |
| Comparative example 1 | Ni/Mg/Fe | 10％Mo | 450℃ | 89.66％ | 90.28％ |
| Comparative example 2 | Ni/Mg/Fe | 10％Cu | 450℃ | 79.00％ | 70.81％ |
| Comparative example 3 | Ni/Mg/Fe | 1％Pt | 500℃ | 48.00％ | 50.03％ |
| Comparative example 4 | Ni/Zn/Fe | 1％Pt | 450℃ | 83.66％ | 95.46％ |
| Comparative example 5 | Ni/Mg/Al | 1％Pt | 450℃ | 84.87％ | 93.27％ |
| Comparative example 6 | Cu/Mg/Fe | 1％Pt | 450℃ | 80.34％ | 90.23％ |
| Comparative example 7 | Modified Ni/Mg/Fe | 1％Pt | 450℃ | 94.16％ | 92.69％ |
| Comparative example 8 | Modified Ni/Mg/Fe | 1％Pt | 450℃ | 93.57％ | 93.97％ |
TABLE 2 conversion and selectivity of catalyst for hydrogenation of nitrobenzene to prepare aniline for ten cycles
In tables 1 and 2, the mass fraction of the active component is the mass fraction of the active component in the hydrotalcite carrier; nitrobenzene conversion = [ (mass of nitrobenzene before reaction-mass of nitrobenzene after reaction)/mass of nitrobenzene before reaction ]. 100%; aniline selectivity = [ (mass of aniline after reaction-mass of aniline before reaction)/(mass before nitrobenzene reaction-mass after nitrobenzene reaction) ] + 100%; the aniline in this formula is the product after nitrobenzene reduction.
The specific results are shown in tables 1 and 2, and it can be seen from examples 1-4 that the catalyst prepared by the invention has good catalytic activity and repeatability, and the conversion rate, selectivity and service life of the aniline prepared by catalytic hydrogenation of nitrobenzene all reach higher levels. With the combination of examples 1-4 and comparative examples 1-3, the catalytic activity and service life of the same Ni/Mg/Fe hydrotalcite carrier loaded with different active components are greatly different, and when the roasting temperature during preparation exceeds 450 ℃, the conversion rate and selectivity of nitrobenzene are remarkably reduced, and the activity of the catalyst is also remarkably reduced after the catalyst is recycled for ten times. Combining example 2 and comparative examples 4-6, different metal components were selected to prepare hydrotalcite supports, and the catalytic activity and service life of the obtained catalyst also showed great difference. This shows that under the condition of the preparation method of the present invention, under the synergistic effect of Pt as the active center and Ni/Mg/Fe catalyst precursor, the conversion rate, selectivity and service life of the nitrobenzene-to-aniline reaction can reach higher levels by cooperating with hydrogen reduction.
In addition, compared with example 2, the modified Ni/Mg/Fe hydrotalcite carriers of examples 5 to 6 can improve the conversion rate and selectivity of the catalyst, especially the stability and service life of the catalyst. In combination with example 5 and comparative example 7, the crystallization process does not involve ultrasonic dispersion, which results in large volume of anions not entering or partially entering the interlayer well, and may cause a more serious agglomeration phenomenon, and even may reduce the original conversion rate and selectivity. Combining example 5 and comparative example 8, tiO 2 The particle size of the nano particles is too large, because the long molecular chain part of the polydopamine can extend into the hydrotalcite layers due to the action of hydrogen bonds and anion exchange, and TiO 2 The nanoparticles are easy to agglomerate with the hydrotalcite body at the outside, but can prevent the active component from entering the hydrotalcite structure, and the catalytic effect and the stability are poor.
The raw materials and equipment used in the invention are common raw materials and equipment in the field if not specified; the methods used in the present invention are conventional in the art unless otherwise specified.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and all simple modifications, alterations and equivalents of the above embodiments according to the technical spirit of the present invention are still within the protection scope of the technical solution of the present invention.
Claims (9)
1. A preparation method of a platinum-supported Ni/Mg/Fe hydrotalcite catalyst is characterized by comprising the following steps:
(1) Dissolving nickel salt, magnesium salt and iron salt in water to obtain a mixed solution A; mixing a sodium hydroxide solution and a sodium carbonate solution to obtain a mixed solution B;
(2) Mixing the mixed solution A and the mixed solution B, and then stirring and aging to obtain a mixed solution C;
(3) Filtering the mixed solution C to obtain a precipitate, and sequentially washing, drying and grinding to obtain a catalyst precursor;
(4) Soaking a catalyst precursor in alkali liquor, washing, drying, and roasting at the temperature of 300-450 ℃, cooling and grinding to obtain a Ni/Mg/Fe hydrotalcite catalyst;
the step (4) also comprises a modification step of Ni/Mg/Fe hydrotalcite catalyst:
mixing the components in a mass ratio of 1:5 to 12% TiO 2 Mixing the nano particles and dopamine hydrochloride in a tris buffer solution, carrying out polymerization reaction, carrying out centrifugal separation after the reaction is finished, adding the obtained product and sodium sulfate into water, and carrying out ultrasonic treatment; then adding Ni/Mg/Fe hydrotalcite catalyst and sodium hydroxide, carrying out ultrasonic dispersion at 70-80 ℃ for 1.5-3h and at a frequency of 30-40KHz, and then carrying out crystallization at 90-110 ℃ for 6-12h, carrying out ultrasonic treatment for 3-8min every 1h, wherein the amplitude is more than or equal to 40 mu m; then filtering and washing until the pH value is 6 to 7, and drying to obtain a modified Ni/Mg/Fe hydrotalcite catalyst;
(5) And ultrasonically dipping the modified Ni/Mg/Fe hydrotalcite catalyst into chloroplatinic acid solution, taking out and drying to obtain the platinum-loaded Ni/Mg/Fe hydrotalcite catalyst.
2. The method for preparing the platinum-supported Ni/Mg/Fe hydrotalcite catalyst according to claim 1, wherein in the step (1), the nickel salt, the magnesium salt and the iron salt are respectively nitrate or chloride of nickel, magnesium and iron; the molar ratio of the metal elements of nickel, magnesium and iron in the nickel salt, the magnesium salt and the iron salt is 4; the molar ratio of sodium hydroxide to sodium carbonate in the sodium hydroxide solution to the sodium carbonate solution is 1:0.5 to 2.
3. The preparation method of the platinum-supported Ni/Mg/Fe hydrotalcite catalyst according to claim 1, wherein in the step (2), the mixing is carried out in a manner of dropwise adding the solution, the dropping speed is 3 to 5s per drop, and the pH of the mixed solution is kept to be 9 to 10 in the dropwise adding process; the stirring time is 3 to 5 hours; the temperature of the aging is 55 to 65 ℃, and the time is 5 to 6 hours.
4. The preparation method of the platinum-supported Ni/Mg/Fe hydrotalcite catalyst according to claim 1, wherein in the step (3), the drying temperature is 110 to 120 ℃ and the drying time is 14 to 18h.
5. The preparation method of the platinum-supported Ni/Mg/Fe hydrotalcite catalyst according to claim 1, wherein in the step (4), the alkali solution is a sodium hydroxide solution with a concentration of 1.5 to 3mol/L; the dipping time is 30 to 50min.
6. The preparation method of the platinum-supported Ni/Mg/Fe hydrotalcite catalyst according to claim 1, wherein in the step (5), the mass fraction of platinum in the platinum-supported Ni/Mg/Fe hydrotalcite catalyst is 0.5-5%.
7. The method for preparing the platinum-supported Ni/Mg/Fe hydrotalcite catalyst according to claim 1, wherein in the modification step, the TiO is added 2 The particle size of the nano particles is 10 to 30nm; the polymerization is carried out for 6 to 10 hours at the temperature of 20 to 40 ℃; the mass ratio of the obtained product to sodium sulfate is 1:4.8 to 12; the molar ratio of the Ni/Mg/Fe hydrotalcite catalyst to the sodium sulfate to the sodium hydroxide is 1:0.9 to 3:5 to 9; the drying is carried out for 7 to 10 hours at the temperature of 60 to 75 ℃.
8. The use of the catalyst prepared by the preparation method of any one of claims 1 to 7 in the hydrogenation of nitrobenzene to prepare aniline.
9. The use of claim 8, wherein: the catalyst is reduced in a hydrogen atmosphere before use, and the reduction temperature is 50-60 ℃.
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