A Pt / NiZnFe-LDH@C3N4 catalyst, its preparation method and application

Abstract

The present invention provides a Pt / NiZnFe-LDH@C3N4 catalyst, a preparation method thereof and an application thereof. The catalyst comprises a carrier and active metal nanoparticles supported on the carrier, and the carrier is an organic-inorganic composite carrier composed of g-C3N4 and NiZnFe-LDH. Preferably, the active metal is Pt. This catalyst is applied to the reaction of catalytic hydrogenation of p-chloronitrobenzene to produce p-chloroaniline, and both the conversion rate of p-chloronitrobenzene and the selectivity of p-chloroaniline can reach 99.99%. Pt / NiZnFe-LDH@C3N4 is used to catalyze the hydrogenation of different chloronitrobenzenes to prepare the corresponding aniline compounds, and the selectivity of the target products is all above 99.9%. This novel Pt / NiZnFe-LDH@C3N4 catalyst has a novel catalyst structure, is green and environmentally friendly, and has excellent industrial practical value.

Description

Technical Field

[0001] The present invention belongs to the field of catalysts, and particularly relates to a Pt / NiZnFe-LDH@C3N4 organic-inorganic hybrid catalyst, a preparation method thereof, and an application thereof in the hydrogenation of p-chloronitrobenzene to prepare p-chloroaniline. Background Art

[0002] p-Chloroaniline is an important chemical intermediate and has wide applications in synthetic rubber, medicine, dyes, pesticides, etc. Currently, the commonly used reduction methods for p-chloronitrobenzene include electrochemical reduction method, iron powder reduction method, hydrazine hydrate reduction method, catalytic hydrogenation method, etc. Due to technical limitations, the electrochemical reduction method can only be applied in the laboratory at present; the products of the iron powder reduction method are difficult to separate; the hydrazine hydrate reduction method has the problems that hydrazine hydrate is expensive and toxic; the catalytic hydrogenation method has the advantages of mild reaction conditions, environmental friendliness, easy separation of products, and recyclability of the catalyst, and has the greatest potential for industrial application.

[0003] However, for the catalytic hydrogenation of p-chloronitrobenzene to selectively prepare p-chloroaniline, the dechlorination problem is a huge challenge because the p-chloronitrobenzene molecule contains two active functional groups. While -NO2 is reduced to -NH2, C-Cl may also break, generating the dechlorination by-product aniline. Therefore, it is of great significance to develop a catalyst that can achieve highly selective hydrogenation of halogenated nitrobenzene under mild conditions. In order to prevent dechlorination, reduce the occurrence of dechlorination by-products, and improve the selectivity of p-chloroaniline, the catalyst needs to be modified. Currently, the main modification method is to add a dechlorination inhibitor to the raw materials, which increases the difficulty of product separation. Another method is to modify the catalyst. For example, Patent CN115057782A discloses a method of using a modified polystyrene maleic anhydride polymer to complex a noble metal (Pt, Pd) catalyst precursor, and then modifying it with morpholine, which is applied to the hydrogenation of p-chloronitrobenzene to obtain a conversion rate of p-chloronitrobenzene of 99.9% and a selectivity of p-chloroaniline of 99.99%. However, adding a dechlorination inhibitor to the raw materials or modifying the catalyst with a dechlorination inhibitor both increase the difficulty of product purification and the treatment of P-containing wastewater. Therefore, it is of great significance to directly develop a catalyst that can highly selectively catalyze the synthesis of p-chloroaniline from p-chloronitrobenzene without a dechlorination inhibitor under mild conditions.

[0004] The commonly used catalysts for the preparation of p-chloroaniline by catalytic hydrogenation include transition metal catalysts and noble metal catalysts. Transition metal catalysts include Ni-based catalysts, Fe-based catalysts, Co-based catalysts, etc., and mainly have problems such as general catalytic activity and relatively high reaction conditions; noble metal catalysts include Pt, Pd, Ru, etc., and have advantages such as higher selectivity, reusability, and strong interaction with hydrogen molecules compared with non-noble metal catalysts.

[0005] Patents CN114195648A and CN115304489A respectively disclose Pt catalysts with carbon materials as carriers for the hydrogenation of p-chloronitrobenzene. The conversion rates of p-chloronitrobenzene are 99.98% and 99.9% respectively, and the selectivities to p-chloroaniline are 96.53% and 99.3% respectively. These carbon material carriers have a large specific surface area and good thermal conductivity and are considered to be good catalyst carriers. Loading nano-catalysts on carbon materials can improve the dispersion of nano-particles, thereby increasing the catalytic effect. However, the selectivity to p-chloroaniline still cannot meet the requirements of industrialization.

[0006] In recent years, because g-C3N4 can introduce highly electron-rich nitrogen atoms, loading metal nanoparticles on g-C3N4 may significantly affect the electronic properties of the metal, ensuring a strong electronic interaction with metal species to a large extent. Layered double hydroxides (LDHs) are a class of two-dimensional highly ordered layered materials mainly composed of metal M 2+ and M 3+ cations, which are evenly distributed in the hydrotalcite layer. LDH materials have the advantages of low price, easy preparation, and structural variability, and have extensive practical application potential. Due to its simple preparation method, high cost-effectiveness, and good stability, loading metal nanoparticles into an organic-inorganic composite carrier combined with LDHs and g-C3N4 will open up a new field for the preparation and application of metal catalysts. Summary of the Invention

[0007] Aiming at the problems of the above-mentioned existing technologies, the present invention aims to provide an organic-inorganic hybrid noble metal catalyst and its preparation method, as well as its application in the hydrogenation reaction of p-chloronitrobenzene. Under the action of this catalyst, p-chloronitrobenzene undergoes high-selectivity hydrogenation, and both the conversion rate of p-chloronitrobenzene and the selectivity to p-chloroaniline are above 99.0%. This catalyst can reduce the noble metal loading amount, and is simple to prepare and low in cost.

[0008] To achieve the above object, the present invention adopts the following technical solutions:

[0009] A Pt / NiZnFe-LDH@C3N4 catalyst, the catalyst includes a carrier and active metal nanoparticles loaded on the carrier, and the carrier is an organic-inorganic composite carrier composed of g-C3N4 and NiZnFe-LDH.

[0010] Preferably, the molar ratio of Ni, Zn, and Fe elements in the NiZnFe-LDH is (1.5 - 5):1:1.

[0011] Preferably, in the catalyst, the active metal is Pt.

[0012] Preferably, the active metal accounts for 0.1-0.8% of the mass of the catalyst.

[0013] Preferably, the organic-inorganic composite support is prepared by the following method:

[0014] After stirring g-C3N4 and NiZnFe-LDH in water, water is removed and grinding is carried out to obtain the organic-inorganic composite support.

[0015] Preferably, the stirring time is 12 h. Preferably, the water removal includes a step of drying at 80-110 °C. Preferably, the drying time is 12-24 h.

[0016] Preferably, in the organic-inorganic composite support, the mass fraction of g-C3N4 is 10%-60%, and the mass fraction of NiZnFe-LDH is 40-90%.

[0017] Preferably, the g-C3N4 is prepared by the following method:

[0018] After grinding melamine evenly, it is calcined in a reactor at 450-600 °C to obtain it. Preferably, the heating rate is 5 °C / min.

[0019] Preferably, the calcination time is 1-5 h.

[0020] Preferably, the NiZnFe-LDH is prepared by the following method:

[0021] Mix solution A and solution B for reaction, and then age to obtain the precipitate which is the NiZnFe-LDH; solution A is an aqueous mixed solution of Ni 2+ , Zn 2+ and Fe 3+ , and solution B is an aqueous mixed solution of CO3 2- and OH - .

[0022] Preferably, the method further includes steps of washing, filtering, drying and grinding the precipitate. The drying temperature is 80-110 °C. The drying time is 12-24 h.

[0023] Preferably, the Ni 2+ , Zn 2+ or Fe 3+ is derived from nitrate.

[0024] Preferably, the CO3 2- is derived from Na2CO3, and the OH - is derived from NaOH.

[0025] Preferably, the CO3 2- and OH - have a molar amount that satisfies the following formula:

[0026]

[0027] wherein, is the total molar amount of Ni 2+ and Zn 2+ ; is the molar amount of Fe 3+ .

[0028] Preferably, the temperature of the mixing reaction is 55 to 65 °C.

[0029] Preferably, the pH of the mixing reaction is controlled at 9 to 10.

[0030] Preferably, the temperature of the aging is 55 to 65 °C.

[0031] Preferably, the time of the aging is 6 to 10 h.

[0032] The present invention further provides a method for preparing the Pt / NiZnFe-LDH@C3N4 catalyst, comprising the following steps:

[0033] Disperse the organic-inorganic composite support in water and mix it evenly with an aqueous solution of a precursor of an active metal, and then slowly add a reducing agent to carry out a reduction reaction to obtain the Pt / NiZnFe-LDH@C3N4 catalyst.

[0034] The precursor of the active metal is a compound well known to those skilled in the art for synthesizing the metal nanoparticles. For Pt, the precursor of the active metal is H2PtCl6.

[0035] Preferably, the reducing agent is KBH4, NaBH4, hydrazine hydrate or hydrogen.

[0036] Preferably, the time of the reduction reaction is 1 to 5 h.

[0037] The present invention further provides a method for preparing p-chloroaniline by hydrogenating p-chloronitrobenzene, and the method is as follows:

[0038] Use the Pt / NiZnFe-LDH@C3N4 catalyst to carry out a hydrogenation reaction on p-chloronitrobenzene and hydrogen.

[0039] Preferably, the environment of the hydrogenation reaction is: in a methanol solution. Preferably, the concentration of p-chloronitrobenzene in the methanol solution is 1 g / L to 300 g / L, a preferred value is 30 g / L to 80 g / L, and the best value is 50 g / L to 70 g / L;

[0040] Preferably, the mass ratio of p-chloronitrobenzene to the Pt / NiZnFe-LDH@C3N4 catalyst is 2:0.05-0.07.

[0041] Preferably, the temperature of the hydrogenation reaction is 40-80°C.

[0042] Preferably, the hydrogen pressure of the hydrogenation reaction is 0.1-5.0 MPa.

[0043] Preferably, the hydrogenation reaction time is 0.5 to 4 hours.

[0044] Preferably, the optimal reaction temperature of the hydrogenation reaction is 60° C., the optimal reaction pressure is 2.0 MPa, and the optimal reaction time is 2 h.

[0045] Preferably, the hydrogenation reaction is carried out under stirring conditions. Preferably, the stirring speed is 300-1000 r / min, wherein the optimal stirring speed is 650 r / min.

[0046] The beneficial effects of the present invention are:

[0047] The present invention utilizes an organic-inorganic composite carrier to load active metal nanoparticles. The organic-inorganic composite carrier is formed by fully stirring g-C3N4 and NiZnFe-LDH in water, has an electron-rich structure, can enhance the strong interaction between the carrier and the active metal, and improve the selectivity of chloroaniline.

[0048] (1) The active component of the catalyst of the present invention is a nanostructured active metal, especially Pt, which can reduce the loading amount of the precious metal to achieve a higher catalytic activity, thereby greatly saving the cost of raw materials.

[0049] (2) The NiZnFe-LDH@C3N4 organic-inorganic composite carrier of the present invention has electron vacancies, which ensures a strong electronic interaction between the carrier and the active metal species.

[0050] (3) The preparation process of the catalyst of the present invention is simple and inexpensive, and has high atom economy.

[0051] (4) The catalyst of the present invention is easy to separate from the product after the catalytic liquid-phase hydrogenation reaction of p-chloronitrobenzene is completed. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 XRD patterns of g-C3N4, NiZnFe-LDH, NiZnFe-LDH@C3N4, and Pt / NiZnFe-LDH@C3N4 prepared in Example 1;

[0053] Figure 2FT-IR spectra of g-C3N4, NiZnFe-LDH, NiZnFe-LDH@C3N4, and Pt / NiZnFe-LDH@C3N4 prepared in Example 1;

[0054] Figure 3 SEM images of NiZnFe-LDH, g-C3N4, and Pt / NiZnFe-LDH@g-C3N4 prepared in Example 1.

[0055] Among them, a is NiZnFe-LDH, b is g-C3N4, and c is Pt / NiZnFe-LDH@g-C3N4.

[0056] Figure 4 Adsorption-desorption isotherms and pore size distribution plots of NiZnFe-LDH, g-C3N4, and Pt / NiZnFe-LDH@g-C3N4 prepared in Example 1

[0057] Figure 5 Comparison chart of catalytic effects of different catalysts in Example 13. Detailed implementation methods

[0058] The present invention will be described in more detail below with reference to examples, which do not limit the scope of protection of the present invention.

[0059] Example 1

[0060] Weigh 11.43 g of Ni(NO3)2·3H2O, 7.44 g of Zn(NO3)2·6H2O, and 10.1 g of Fe(NO3)3·10H2O according to the molar ratio of metal elements nickel, zinc, and iron in nickel salt, zinc salt, and iron salt of 2:1:1, and dissolve them in 100 mL of deionized water to prepare a mixed salt solution A.

[0061] According to the formula It is calculated that 6.4 g of NaOH and 5.3 g of Na2CO3 should be taken and dissolved in 60 mL of deionized water to prepare a mixed alkali solution B.

[0062] Pre-add about 10 mL of deionized water into a four-necked flask, heat it to 55 - 65 °C, and simultaneously add solutions A and B into the flask under stirring conditions. During the dropping process, keep the pH of the mixed solution at 9 - 10. After the dropping is completed, continue stirring, age at 60 °C for 6 h. After aging, filter the mixed solution, wash it with deionized water until the pH of the filtrate is 7, and then dry it in an oven at 105 °C for 24 h to obtain NiZnFe-LDH, and grind it into powder for use.

[0063] After grinding melamine evenly, put it into a crucible with a lid, and then place it in a muffle furnace. Heat it at a rate of 5 °C / min to 500 °C and calcine for 3 h to finally obtain light yellow solid g-C3N4.

[0064] Weigh 1 g of g-C3N4 and 1 g of NiZnFe-LDH into a small beaker, add 20 mL of deionized water, stir magnetically for 12 h, then centrifuge, dry, and grind to prepare the NiZnFe-LDH@C3N4 organic-inorganic composite support.

[0065] Take 1 g of NiZnFe-LDH@C3N4 and disperse it in 10 mL of deionized water. Use a pipette to measure 1 mL of an aqueous solution of H2PtCl6 with a Pt content of 0.25 g / mL, stir magnetically for 3 h, then slowly add 10 mL of 0.5 mol / L KBH4 solution and continue stirring for 3 h. After completion, centrifuge, dry, and grind to finally obtain the 0.25% Pt / NiZnFe-LDH@C3N4 catalyst.

[0066] The XRD patterns of the prepared g-C3N4, NiZnFe-LDH, NiZnFe-LDH@C3N4, and Pt / NiZnFe-LDH@C3N4 are as Figure 1 shown.

[0067] The FT-IR patterns of the prepared g-C3N4, NiZnFe-LDH, NiZnFe-LDH@C3N4, and Pt / NiZnFe-LDH@C3N4 are as Figure 2 shown.

[0068] The SEM images of the prepared g-C3N4, NiZnFe-LDH, NiZnFe-LDH@C3N4, and Pt / NiZnFe-LDH@C3N4 are as Figure 3 shown.

[0069] The adsorption-desorption curves and pore size distribution diagrams of the prepared g-C3N4, NiZnFe-LDH, and Pt / NiZnFe-LDH@C3N4 are as Figure 4 shown.

[0070] The specific surface areas and pore volumes of the prepared g-C3N4, NiZnFe-LDH, and Pt / NiZnFe-LDH@C3N4 are shown in Table 1.

[0071] Table 1 Specific surface areas and pore volumes of NiZnFe-LDH, g-C3N4, and Pt / NiZnFe-LDH@g-C3N4

[0072] sample <![CDATA[Specific surface area / m 2 ·g -1 > <![CDATA[Pore volume / cm 3 ·g -1 > NiZnFe-LDH 92.5 0.25 <![CDATA[g-C3N4]]> 11.4 0.07 <![CDATA[Pt / LDH@g-C3N4]]> 45.5 0.24

[0073] As can be seen from Table 1, although the g-C3N4 organic carrier is rich in electrons on its surface, its specific surface area is relatively low. The active centers of the catalyst prepared by loading are few, and its activity for the hydrogenation of p-chloronitrobenzene is low. For the catalyst Pt / LDH / g-C3N4 prepared with the composite carrier, its specific surface area increases, so the activity for the hydrogenation of p-chloronitrobenzene and the selectivity for p-chloroaniline reach the optimum.

[0074] Catalyst performance evaluation: The dosage of the catalyst 0.25% Pt / NiZnFe-LDH@C3N4 is 0.05 g, with 30 mL of 67 g / L p-chloronitrobenzene-ethanol solution, the reaction temperature is 60 °C, the hydrogen pressure is 2 MPa, the stirring speed is 630 rpm, and the reaction time is 2 h. After the reaction, samples are taken for determination and analysis, and the conversion rate of p-chloronitrobenzene is above 99.99%, and the selectivity for p-chloroaniline is above 99.99%. After the catalyst is recycled 10 times, the conversion rate of p-chloronitrobenzene is 99.96%, and the selectivity for p-chloroaniline is above 99.99%, and the activity of the catalyst and the selectivity for p-chloroaniline have no obvious decrease.

[0075] Example 2

[0076] The preparation of NiZnFe-LDH and g-C3N4 is the same as that in Example 1, except that the molar ratio of the metal elements nickel, zinc and iron is 1.5:1:1.

[0077] Weigh 0.2 g of g-C3N4 and 1.8 g of NiZnFe-LDH in a small beaker, add 20 mL of deionized water, stir magnetically for 12 h, then centrifuge, dry and grind to obtain the NiZnFe-LDH@C3N4 composite carrier; finally, disperse 1 g of NiZnFe-LDH@C3N4 in 10 mL of deionized water, use a pipette to measure 0.4 mL of an aqueous H2PtCl6 solution with a Pt content of 0.25 g / mL, stir magnetically for 3 h, then slowly add 10 mL of 0.5 mol / L KBH4 solution and continue stirring for 3 h. After completion, centrifuge, dry and grind to finally obtain the 0.1% Pt / NiZnFe-LDH@C3N4 catalyst.

[0078] The performance evaluation of the catalyst is the same as that in Example 1, except that the hydrogenation reaction time is 0.5 h, the hydrogen pressure is 5.0 MPa, and the reaction temperature is 40 °C, and the conversion rate of p-chloronitrobenzene is 82.1%, and the selectivity for p-chloroaniline is above 99.99%.

[0079] Example 3

[0080] The preparation of ZnFe-LDH and g-C3N4 is the same as that in Example 1, except that the molar ratio of the metal elements nickel, zinc and iron is 3:1:1.

[0081] Weigh 0.4 g of g-C3N4 and 1.6 g of NiZnFe-LDH in a small beaker, add 20 mL of deionized water, stir magnetically for 12 h, then centrifuge, dry, and grind to obtain the NiZnFe-LDH@C3N4 composite support; finally, disperse 1 g of NiZnFe-LDH@C3N4 in 10 mL of deionized water, measure 2 mL of an aqueous H2PtCl6 solution with a pipette gun with a Pt content of 0.25 g / mL, stir magnetically for 3 h, then slowly add 10 mL of 0.5 mol / L KBH4 solution and continue stirring for 3 h. After completion, centrifuge, dry, and grind to finally obtain the 0.5% Pt / NiZnFe-LDH@C3N4 catalyst.

[0082] The performance evaluation of the catalyst was the same as in Example 1, except that the reaction temperature was 80 °C, and the conversion rate of p-chloronitrobenzene was 86.4%, and the selectivity for p-chloroaniline was more than 99.99%.

[0083] Example 4

[0084] The preparation of NiZnFe-LDH and g-C3N4 was the same as in Example 1, except that the molar ratio of the metal elements nickel, zinc, and iron was 5:1:1.

[0085] Weigh 0.6 g of g-C3N4 and 1.4 g of NiZnFe-LDH in a small beaker, add 20 mL of deionized water, stir magnetically for 12 h, then centrifuge, dry, and grind to obtain the NiZnFe-LDH@C3N4 composite support; finally, disperse 1 g of NiZnFe-LDH@C3N4 in 10 mL of deionized water, accurately measure 3.2 mL of an aqueous H2PtCl6 solution with a pipette gun with a Pt content of 0.25 g / mL, stir magnetically for 3 h, then slowly add 10 mL of 0.5 mol / L KBH4 solution and continue stirring for 3 h. After completion, centrifuge, dry, and grind to finally obtain the 0.8% Pt / NiZnFe-LDH@C3N4 catalyst.

[0086] The performance evaluation of the catalyst was the same as in Example 1, and the conversion rate of p-chloronitrobenzene was 89.3%, and the selectivity for p-chloroaniline was more than 99.99%.

[0087] Example 5

[0088] The preparation of NiZnFe-LDH and g-C3N4 was the same as in Example 1.

[0089] Weigh 0.8 g of g-C3N4 and 1.2 g of NiZnFe-LDH in a small beaker, add 20 mL of deionized water, stir magnetically for 12 h, then centrifuge, dry, and grind to obtain the NiZnFe-LDH@C3N4 composite support; finally, disperse 1 g of NiZnFe-LDH@C3N4 in 10 mL of deionized water, accurately pipette 1 mL of an aqueous H2PtCl6 solution with a Pt content of 0.25 g / mL, stir magnetically for 3 h, then slowly add 10 mL of a 0.5 mol / L KBH4 solution, and continue stirring for 3 h. After completion, centrifuge, dry, and grind to finally obtain the 0.25% Pt / NiZnFe-LDH@C3N4 catalyst.

[0090] The performance evaluation of the catalyst was the same as in Example 1, and the conversion rate of p-chloronitrobenzene was 94.5%, and the selectivity for p-chloroaniline was above 99.99%.

[0091] Example 6

[0092] The preparation of NiZnFe-LDH and g-C3N4 was the same as in Example 1.

[0093] Weigh 1.2 g of g-C3N4 and 0.8 g of NiZnFe-LDH in a small beaker, add 20 mL of deionized water, stir magnetically for 12 h, then centrifuge, dry, and grind to obtain the NiZnFe-LDH@C3N4 composite support; finally, disperse 1 g of NiZnFe-LDH@C3N4 in 10 mL of deionized water, accurately pipette 1 mL of an aqueous H2PtCl6 solution with a Pt content of 0.25 g / mL, stir magnetically for 3 h, then slowly add 10 mL of a 0.5 mol / L KBH4 solution, and continue stirring for 3 h. After completion, centrifuge, dry, and grind to finally obtain the 0.25% Pt / NiZnFe-LDH@C3N4 catalyst.

[0094] The performance evaluation of the catalyst was the same as in Example 1, except that the hydrogenation reaction time was 4 h and the hydrogen pressure was 0.1 MPa. The conversion rate of p-chloronitrobenzene was above 99.99%, and the selectivity for p-chloroaniline was above 99.99%.

[0095] Example 7

[0096] The preparation of NiZnFe-LDH, g-C3N4, and NiZnFe-LDH@C3N4 was the same as in Example 1.

[0097] Disperse 1 g of NiZnFe-LDH@C3N4 support in 10 mL of deionized water. Use a pipette to accurately measure 2 mL of an aqueous H2PtCl6 solution with a Pt content of 0.25 g / mL, and stir magnetically for 3 h. Then slowly add 10 mL of 0.5 mol / L KBH4 solution and continue stirring for 3 h. After completion, centrifuge, dry, and grind to finally obtain the 0.50% Pt / NiZnFe-LDH@C3N4 catalyst.

[0098] The performance evaluation of the catalyst was the same as in Example 1, and the conversion rate of p-chloronitrobenzene was above 99.99%, and the selectivity for p-chloroaniline was 99.8%.

[0099] Example 8

[0100] The preparation of NiZnFe-LDH, g-C3N4, and NiZnFe-LDH@C3N4 was the same as in Example 1.

[0101] Disperse 1 g of NiZnFe-LDH@C3N4 in 10 mL of deionized water. Use a pipette to accurately measure 0.8 mL of an aqueous H2PtCl6 solution with a Pt content of 0.25 g / mL, and stir magnetically for 3 h. Then slowly add 10 mL of 0.5 mol / L KBH4 solution and continue stirring for 3 h. After completion, centrifuge, dry, and grind to finally obtain the 0.20% Pt / NiZnFe-LDH@C3N4 catalyst.

[0102] The performance evaluation of the catalyst was the same as in Example 1, and the conversion rate of p-chloronitrobenzene was above 73.6%, and the selectivity for p-chloroaniline was 99.90%.

[0103] Example 9

[0104] The preparation of NiZnFe-LDH, g-C3N4, and NiZnFe-LDH@C3N4 was the same as in Example 1.

[0105] Disperse 1 g of NiZnFe-LDH@C3N4 in 10 mL of deionized water. Use a pipette to accurately measure 1.2 mL of an aqueous H2PtCl6 solution with a Pt content of 0.25 g / mL, and stir magnetically for 3 h. Then slowly add 10 mL of 0.5 mol / L KBH4 solution and continue stirring for 3 h. After completion, centrifuge, dry, and grind to finally obtain the 0.30% Pt / NiZnFe-LDH@C3N4 catalyst.

[0106] The performance evaluation of the catalyst was the same as in Example 1, and the conversion rate of p-chloronitrobenzene was above 99.99%, and the selectivity for p-chloroaniline was 99.94%.

[0107] Example 10

[0108] The preparation of NiZnFe-LDH, g-C3N4 and NiZnFe-LDH@C3N4 was the same as that in Example 1.

[0109] Disperse 1 g of NiZnFe-LDH@C3N4 in 10 mL of deionized water. Use a pipette to accurately measure 1.6 mL of an aqueous H2PtCl6 solution with a Pt content of 0.25 g / mL, and stir magnetically for 3 h. Then slowly add 10 mL of a 0.5 mol / L KBH4 solution and continue stirring for 3 h. After completion, centrifuge, dry, and grind to finally obtain a 0.40% Pt / NiZnFe-LDH@C3N4 catalyst.

[0110] The performance evaluation of the catalyst was the same as that in Example 1, and the conversion rate of p-chloronitrobenzene was above 99.99%, and the selectivity for p-chloroaniline was 99.78%.

[0111] Example 11

[0112] Weigh 11.43 g of Ni(NO3)2·3H2O, 4.96 g of Zn(NO3)2·6H2O, and 6.73 g of Fe(NO3)3·10H2O according to the molar ratio of the metal elements nickel, zinc, and iron in the nickel salt, zinc salt, and iron salt being 3:1:1, and dissolve them in 100 mL of deionized water to prepare a mixed salt solution A.

[0113] According to the formula It was calculated that 5.3 g of NaOH and 3.53 g of Na2CO3 should be taken and dissolved in 60 mL of deionized water to prepare a mixed alkali solution B.

[0114] Pre-add about 10 mL of deionized water to a four-necked flask, heat to 60 °C, and simultaneously add solutions A and B to the flask under stirring conditions. During the dropping process, always maintain the pH of the mixed solution at 9 - 10. After the dropping is completed, continue stirring and age at 60 °C for 6 h. After aging, filter the mixed solution, wash it with deionized water until the pH of the filtrate is 7, and then dry it in an oven at 105 °C for 24 h to obtain NiZnFe-LDH, and grind it into powder for use.

[0115] Grind melamine evenly and put it into a crucible with a lid, then place it in a muffle furnace and heat it to 550 °C at a rate of 5 °C / min, and calcine for 2 h to finally obtain a pale yellow solid g-C3N4.

[0116] Weigh 1 g of g-C3N4 and 1 g of NiZnFe-LDH in a small beaker, add 20 mL of deionized water, stir magnetically for 12 h, then centrifuge, dry, and grind to prepare a NiZnFe-LDH@C3N4 organic-inorganic composite support.

[0117] Disperse 1 g of NiZnFe-LDH@C3N4 in 10 mL of deionized water. Pipette 1 mL of an aqueous H2PtCl6 solution with a Pt content of 0.25 g / mL, and stir magnetically for 3 h. Then slowly add 10 mL of a 0.5 mol / L KBH4 solution and continue stirring for 3 h. After completion, centrifuge, dry, and grind to finally obtain a 0.25% Pt / NiZnFe-LDH@C3N4 catalyst.

[0118] Catalyst performance evaluation: The amount of the 0.25% Pt / NiZnFe-LDH@C3N4 catalyst used is 0.05 g, in a 30 mL 60 g / L p-chloronitrobenzene-ethanol solution, the reaction temperature is 60 °C, the H2 pressure is 1 MPa, the stirring speed is 600 rpm, and the reaction time is 2 h. After the reaction is completed, samples are taken for determination and analysis, and the conversion rate of p-chloronitrobenzene is above 99.99%, and the selectivity for p-chloroaniline is 99.73%. After the catalyst is recycled 10 times, the conversion rate of p-chloronitrobenzene is 99.90%, and the selectivity for p-chloroaniline is 99.45%. There is no obvious decrease in the activity of the catalyst and the selectivity for p-chloroaniline.

[0119] Example 12

[0120] With the molar ratio of the metal elements nickel, zinc, and iron in nickel salt, zinc salt, and iron salt being 2.5:1:1, weigh 11.43 g of Ni(NO3)2·3H2O, 5.95 g of Zn(NO3)2·6H2O, and 8.07 g of Fe(NO3)3·10H2O, dissolve them in 100 mL of deionized water to prepare a mixed salt solution A.

[0121] Secondly, according to the formula It is calculated that 4.8 g of NaOH and 4.24 g of Na2CO3 should be taken and dissolved in 60 mL of deionized water to prepare a mixed alkali solution B.

[0122] Pre-add about 10 mL of deionized water to a four-necked flask, heat to 60 °C, and simultaneously add solutions A and B to the flask under stirring conditions. During the dropping process, always keep the pH of the mixed solution at 9 - 10. After the dropping is completed, continue stirring and age at 60 °C for 6 h. After aging is completed, filter the mixed solution, wash it with deionized water until the pH of the filtrate is 7, and then dry it in an oven at 105 °C for 24 h to obtain NiZnFe-LDH, and grind it into powder for use.

[0123] Grind melamine evenly and put it into a crucible with a lid, then place it in a muffle furnace and heat it to 550 °C at a rate of 5 °C / min, and calcine for 2 h to finally obtain light yellow solid g-C3N4.

[0124] Weigh 1 g of g-C3N4 and 1 g of NiZnFe-LDH into a small beaker, add 20 mL of deionized water, stir magnetically for 12 h, then centrifuge, dry, and grind to obtain the NiZnFe-LDH@C3N4 organic-inorganic composite support.

[0125] Disperse 1 g of NiZnFe-LDH@C3N4 in 10 mL of deionized water, pipette 1 mL of an aqueous H2PtCl6 solution with a Pt content of 0.25 g / mL, stir magnetically for 3 h, then slowly add 10 mL of a 0.5 mol / L KBH4 solution and continue stirring for 3 h. After completion, centrifuge, dry, and grind to finally obtain the 0.25% Pt / NiZnFe-LDH@C3N4 catalyst.

[0126] Catalyst performance evaluation: The amount of the 0.25% Pt / NiZnFe-LDH@C3N4 catalyst used is 0.05 g, in a 30 mL 50 g / L p-chloronitrobenzene-ethanol solution, the reaction temperature is 60 °C, the H2 pressure is 1 MPa, the stirring speed is 550 rpm, and the reaction time is 2 h. After the reaction, samples are taken for determination and analysis, and the conversion rate of p-chloronitrobenzene is above 99.99%, and the selectivity for p-chloroaniline is 99.93%. After the catalyst is recycled 10 times, the conversion rate of p-chloronitrobenzene is 99.92%, and the selectivity for p-chloroaniline is 99.57%, and there is no obvious decrease in the catalyst and the selectivity for p-chloroaniline.

[0127] Example 13

[0128] Prepare the NiZnFe-LDH and g-C3N4 supports using the same method as in Example 1.

[0129] Disperse g-C3N4 in 10 mL of deionized water, pipette the aqueous H2PtCl6 solution, stir magnetically for 3 h, then slowly add 10 mL of a 0.5 mol / L KBH4 solution and continue stirring for 3 h. After completion, centrifuge and dry to obtain Pt / g-C3N4. Weigh Pt / g-C3N4 and NiZnFe-LDH and disperse them in 10 mL of deionized water, stir at room temperature for 6 h. After completion, centrifuge and dry to obtain the (Pt / CN) / LDH catalyst.

[0130] Disperse NiZnFe-LDH in 10 mL of deionized water, pipette the aqueous H2PtCl6 solution, stir magnetically for 3 h, then slowly add 10 mL of a 0.5 mol / L KBH4 solution and continue stirring for 3 h. After completion, centrifuge and dry to obtain the Pt / NiZnFe-LDH catalyst. Weigh g-C3N4 and Pt / NiZnFe-LDH and disperse them in 10 mL of deionized water, stir at room temperature for 6 h. After completion, centrifuge and dry to obtain the (Pt / LDH) / CN catalyst.

[0131] The Pt / NiZnFe-LDH@C3N4 catalyst prepared in Example 1 was used as the Pt / (CN / LDH) catalyst.

[0132] Catalyst performance evaluation:

[0133] With a catalyst dosage of 0.05 g, in a 30 mL 50 g / L p-chloronitrobenzene-ethanol solution, at a reaction temperature of 60 °C, a H2 pressure of 1 MPa, a stirring speed of 550 rpm, and a reaction time of 2 h, the effects of catalysts prepared in different sequences on the hydrogenation of p-chloronitrobenzene were investigated. The results are as Figure 5 shown. It can be seen from the figure that the Pt / (CN / LDH) catalyst has the best catalytic effect, and the conversion rate of p-chloronitrobenzene and the selectivity for p-chloroaniline are both close to 100%; the catalytic effect of (Pt / LDH) / CN is the second best; the worst is (Pt / CN) / LDH.

[0134] It can be seen that the preparation sequence of the catalyst has a great influence on the catalytic performance.

[0135] Example 14

[0136] NiZnFe-LDH and g-C3N4 supports were prepared by the same method as in Example 1.

[0137] g-C3N4, NiZnFe-LDH, and the organic-inorganic composite support prepared in Example 1 were respectively dispersed in 10 mL of deionized water. An aqueous solution of H2PtCl6 was measured with a pipette gun, and magnetic stirring was carried out for 3 h. Then, 10 mL of 0.5 mol / L KBH4 solution was slowly added, and stirring was continued for 3 h. After completion, centrifugation, drying, and grinding were carried out to obtain catalysts supported on different supports.

[0138] The catalysts on different supports and g-C3N4 were respectively used for the hydrogenation of p-chloronitrobenzene to investigate the effects of different supports on the hydrogenation of p-chloronitrobenzene.

[0139] Catalyst performance evaluation:

[0140] The dosage of the catalytic material was 0.05 g, in a 30 mL 67 g / L different chloronitrobenzene-ethanol solution, at a reaction temperature of 60 °C, a H2 pressure of 2 MPa, a stirring speed of 630 rpm, and a reaction time of 2 h. The hydrogenation results are shown in Table 2:

[0141] Table 2 Effects of different catalytic materials on the hydrogenation of nitrobenzene

[0142] catalyst Conversion rate of p-chloronitrobenzene / % Selectivity of p-chloroaniline / % <![CDATA[g-C3N4]]> 29.2 98.2 <![CDATA[0.25% Pt / g-C3N4]]> 92.4 99.7 0.25% Pt / NiZnFe-LDH 100 99.1 <![CDATA[0.25% Pt / NiZnFe-LDH@C3N4]]> 100 100

[0143] As can be seen from Table 1, the catalytic effect of 0.25% Pt / NiZnFe-LDH@C3N4 is the best. This is because the composite support of g-C3N4 and NiZnFe-LDH is conducive to the electron conduction on the surface of the support, increasing the hydrogenation effect of the nitro group.

[0144] Example 15

[0145] The preparation of the Pt / NiZnFe-LDH@C3N4 catalyst was the same as that in Example 1.

[0146] Catalyst performance evaluation: The dosage of the catalyst 0.25% Pt / NiZnFe-LDH@C3N4 was 0.05 g, in 30 mL of 67 g / L different chloronitrobenzene-ethanol solutions, the reaction temperature was 60 °C, the H2 pressure was 2 MPa, the stirring speed was 630 rpm, and the reaction time was 2 h. After the reaction ended, samples were taken for determination and analysis. The conversion rate of chloronitrobenzene and the selectivity of chloroaniline are shown in Table 3. As can be seen from the table, for the hydrogenation of different chloronitrobenzenes catalyzed by the catalyst prepared in Example 1, the selectivity of the products is all above 99.9%.

[0147] Table 3 Reaction effects of preparing corresponding amine compounds by hydrogenating different substrates with the Pt / NiZnFe-LDH@C3N4 catalyst

[0148]

[0149]

Claims

1. A Pt / NiZnFe-LDH@g-C3N4 catalyst, characterized in that, The catalyst includes a support and active metal nanoparticles supported on the support. The support is an organic-inorganic composite support composed of g-C3N4 and NiZnFe-LDH; the organic-inorganic composite support is prepared by the following method: After stirring g-C3N4 and NiZnFe-LDH in water, water is removed and grinding is carried out to obtain the organic-inorganic composite support; The active metal is Pt.

2. The catalyst according to claim 1, characterized in that, The molar ratio of Ni, Zn and Fe elements in the NiZnFe-LDH is (1.5~5):1:

1.

3. The catalyst according to claim 1, wherein The active metal accounts for 0.1~0.8% of the mass of the catalyst.

4. The catalyst according to claim 1, wherein In the organic-inorganic composite support, the mass fraction of g-C3N4 is 10%~60%, and the mass fraction of NiZnFe-LDH is 40~90%.

5. The catalyst according to claim 1, characterized in that, The NiZnFe-LDH is prepared by the following method: Mix solution A and solution B for reaction, and then age it. The obtained precipitate is the NiZnFe-LDH; solution A is an aqueous solution containing Ni 2+ , Zn 2+ and Fe 3+ . Solution B is an aqueous solution containing CO3 2- and OH - .

6. The catalyst according to claim 5, wherein The CO3 2- and OH - amounts of substance satisfy the following formula: ； ； Among them, is the total amount of substance of Ni 2+ , Zn 2+ ; is the amount of substance of Fe 3+ .

7. The preparation method of the Pt / NiZnFe-LDH@g-C3N4 catalyst according to any one of claims 1 to 6, characterized in that, It includes the following steps: The organic-inorganic composite support is dispersed in water and mixed evenly with an aqueous solution of a precursor of the active metal, and then a reducing agent is slowly added for a reduction reaction to obtain the Pt / NiZnFe-LDH@g-C3N4 catalyst.

8. A method for preparing p-chloroaniline by catalytic hydrogenation of p-chloronitrobenzene using the Pt / NiZnFe-LDH@g-C3N4 catalyst according to any one of claims 1-6, characterized in that, The method is: Using the Pt / NiZnFe-LDH@g-C3N4 catalyst, p-chloronitrobenzene and hydrogen are subjected to a hydrogenation reaction.

9. The method according to claim 8, characterized in that The mass ratio of p-chloronitrobenzene to the Pt / NiZnFe-LDH@g-C3N4 catalyst is 2:0.05~0.

07. The temperature of the hydrogenation reaction is 40~80°C, the hydrogen pressure of the hydrogenation reaction is 0.1~5.0 Mpa, and the time of the hydrogenation reaction is 0.5~4 h.

10. The method according to claim 9, wherein The temperature of the hydrogenation reaction is 60°C, the hydrogen pressure of the hydrogenation reaction is 2.0 Mpa, and the time of the hydrogenation reaction is 2 h.

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