CN114433231B - Preparation method and application of polyacid-supported metal nickel hydroalkylation bifunctional catalyst - Google Patents

Abstract

The invention discloses a preparation method and application of a multi-acid supported metal nickel hydroalkylation bifunctional catalyst. In this method, the flower-shaped nickel-aluminum hydrotalcite is firstly synthesized by hydrothermal method, and then the nickel-aluminum composite metal oxide is obtained by roasting under _reducing atmosphere; A multi-acid-supported metal nickel hydroalkylation bifunctional catalyst was obtained by in-situ co-reduction. Compared with traditional supported and mixed hydroalkylation catalysts, the prepared multi-acid-supported nano-metallic nickel hydroalkylation bifunctional catalyst has good matching of hydrogenation activity and alkylation activity, and is thermally stable. It has the advantages of high safety, green, cheap, non-toxic, high efficiency and strong cycle stability. It is used to catalyze the reaction of benzene hydroalkylation to prepare cyclohexylbenzene, and has excellent catalytic activity and selectivity.

Description

A preparation method and application of a polyacid-supported nickel metal hydroalkylation bifunctional catalyst

Technical Field

The invention belongs to the technical field of catalyst preparation, and in particular relates to a preparation method and application of a polyacid-supported metal nickel hydroalkylation bifunctional catalyst.

Background Art

90% of the world's phenol production uses the cumene oxidation decomposition method to generate equal amounts of phenol and acetone. However, in recent years, the growth rate of market demand for phenol has exceeded that of acetone, so the economic efficiency of this method has gradually decreased. Cyclohexylbenzene is an important chemical intermediate. Phenol and cyclohexanone can be co-produced through oxidation-decomposition reactions. This technical route can produce two high-value basic organic chemical raw materials on the same device. It is considered to be a new phenol production route that can replace the traditional cumene method. In addition, cyclohexylbenzene has a high boiling point and a freezing point close to room temperature, and has some special physical and chemical properties. It is a high-boiling point solvent for the preparation of coatings, plastics and adhesives, and is also an excellent anti-overcharge additive for lithium-ion battery electrolytes. Cyclohexylbenzene has a high cetane number and is a high-quality diesel additive; cyclohexylbenzene is also an important organic synthesis intermediate and can be used as a raw material for the synthesis of TFT liquid crystals. With the large-scale application of cyclohexylbenzene oxidation technology to produce phenol and the rise of the electric revolution, the demand for cyclohexylbenzene will continue to increase, and its preparation and production have received widespread attention.

The preparation methods of cyclohexylbenzene mainly include the alkylation of benzene with cyclohexene, the hydrogenation of biphenyl, and the direct hydrogenation of benzene. The first two routes are limited by the source of raw materials and are not suitable for large-scale industrial production. The benzene hydrogenation alkylation method uses benzene as raw material and synthesizes cyclohexylbenzene in one step under the action of a bifunctional catalyst. Due to the simplicity of the process, the low price of raw materials, and the high stability of the catalyst, it has certain industrial prospects; however, its reaction path is complex, there are many reaction products, and the reaction is difficult to effectively control. The hydrogenation alkylation catalyst needs to have both suitable hydrogenation activity and acidity. Excessive hydrogenation activity will lead to excessive hydrogenation of benzene to produce by-products such as cyclohexane, while excessive acidity will lead to an increase in by-products such as polyalkylbenzenes. Therefore, designing the dual-activity structure of the catalyst to show higher activity and selectivity for cyclohexylbenzene has become a key issue in the benzene hydrogenation alkylation reaction.

Summary of the invention

Based on the fact that the traditional nano-metal nickel catalyst has poor stability, is easy to agglomerate at high temperature, and the heteropoly acid has a small specific surface area and needs to be immobilized to better exert its acid activity, the present invention provides a method for preparing a polyacid-loaded nano-metal nickel hydrogenation alkylation bifunctional catalyst by two-step reduction using flower-shaped nickel aluminum hydrotalcite as a precursor, and the prepared catalyst is used to catalyze the reaction of benzene hydrogenation alkylation to prepare cyclohexylbenzene, which has excellent catalytic activity and selectivity. The present invention uses ammonium fluoride as a structure-directing agent to obtain a nickel aluminum hydrotalcite with a three-dimensional nano-flower-like structure, and the flower-shaped hydrotalcite has the characteristics of large specific surface area and good dispersion; then, through the in-situ structural topological transformation process, a highly dispersed and high surface defect concentration supported metal nickel nano-catalyst is obtained; finally, the Ni surface defect is used as the nucleation center, and the polyacid is selectively anchored on the surface of the metal nickel nanoparticle through impregnation-reduction induction, so as to obtain a polyacid-loaded nano-metal nickel hydrogenation alkylation bifunctional catalyst with high dispersion and strong stability.

The preparation method of the polyacid-supported metal nickel hydrogenation alkylation bifunctional catalyst of the present invention is as follows: firstly, flower-shaped nickel aluminum hydrotalcite is synthesized by a hydrothermal method, and then calcined in a reducing atmosphere to obtain a nickel aluminum composite metal oxide; a heteropoly acid is impregnated and supported on the nickel aluminum composite metal oxide, and finally, the polyacid-supported metal nickel hydrogenation alkylation bifunctional catalyst is obtained by in-situ co-reduction in a _H2 atmosphere.

The specific preparation steps of the flower-shaped nickel-aluminum hydrotalcite are as follows: dissolving a soluble nickel salt, a soluble aluminum salt, urea and ammonium fluoride in 100-200 mL of deionized water to obtain a transparent mixed solution, wherein the concentrations of nickel nitrate, aluminum nitrate, urea and ammonium fluoride are 0.05-0.2 M, 0.025-0.1 M, 0.5-2 M and 0.2-0.8 M, respectively; then transferring the mixed solution to a high-pressure reactor, sealing and reacting at 100-140° C. for 12-48 hours, and finally washing the obtained precipitate with deionized water until it is neutral, and drying to obtain the flower-shaped nickel-aluminum hydrotalcite.

The soluble nickel salt is nickel nitrate or nickel chloride; the soluble aluminum salt is aluminum nitrate or aluminum chloride.

The specific preparation steps of the nickel-aluminum composite metal oxide are: fully grinding the flower-shaped nickel-aluminum hydrotalcite, then heating the temperature to 450-600°C at an initial heating rate of 2-10°C/min in a hydrogen gas flow of 20-60mL/min, maintaining the temperature for 2-6h, and then slowly cooling the temperature to room temperature in a nitrogen gas flow to obtain the nickel-aluminum composite metal oxide.

The specific steps of impregnating the nickel-aluminum composite metal oxide with the heteropoly acid are as follows: dispersing 0.4-1.0 g of the nickel-aluminum composite metal oxide in 1-10 mL of a solution containing 0.1-0.3 g of the heteropoly acid, ultrasonicating for 10-30 minutes, and then drying the slurry in an oven at 60-100° C.

The heteropoly acid is selected from one or more of phosphotungstic acid, phosphomolybdic acid and silicotungstic acid.

The specific conditions of the in-situ co-reduction are: in a mixed gas flow of hydrogen and nitrogen at 15-60 mL/min, heating from room temperature to 250-450° C. at a heating rate of 2-15° C./min, keeping the temperature for 2-8 hours, and then slowly cooling to room temperature in a nitrogen gas flow.

The polyacid-supported metal nickel hydroalkylation bifunctional catalyst prepared above needs to be sealed and stored.

The polyacid-supported metal nickel hydroalkylation bifunctional catalyst prepared above is used to catalyze the hydroalkylation of benzene to produce cyclohexylbenzene.

The reaction conditions for catalyzing benzene hydrogenation and alkylation to prepare cyclohexylbenzene are as follows: 5-40 mL of benzene and 0.1-0.5 g of a polyacid-supported metal nickel hydrogenation and alkylation bifunctional catalyst are added to a high-pressure hydrogenation reactor, and 0.5-2 MPa of hydrogen is first used for 3-10 gas replacement to exhaust the air in the reactor; and then the reactor is sealed and reacted for 3-5 hours at 170-220° C., 0.5-2.5 MPa of hydrogen, and a stirring speed of 500-1000 r/min.

After the above-mentioned catalytic benzene hydrogenation alkylation reaction to produce cyclohexylbenzene is completed, the catalyst is separated and dried for continuous and repeated use.

The present invention introduces nickel into a hydrotalcite layer plate by an endogenous method, and after different calcination temperature treatments, a supported Ni-based catalyst with a high surface defect concentration is obtained. Then, with Ni surface defects as the loading center, polyacids are induced to anchor at Ni surface defect sites, and polyacid-loaded nano metal nickel catalysts with heterogeneous structures are obtained through co-reduction treatment. The main feature of this method is that hydrotalcite undergoes a structural topological transformation under thermal reduction conditions, and nickel metal cations present atomic-level dispersion. Based on the self-consistency of the structural topological transformation, a nickel nano catalyst with high dispersion, high stability and high surface defect concentration can be obtained. Heteropolyacids are loaded on this nickel nano catalyst, which can not only solve the problem of the immobilization of heteropolyacids and increase its surface area, but also make the hydrogenation center and the alkylation center adjacent to each other, which is more conducive to the diffusion of intermediate products between the two centers, and improves the selectivity of hydrogenation alkylation products. At the same time, polyacids are anchored on Ni to form a heterogeneous structure, and by adjusting the conditions of polyacid reduction, polyacids and Ni active site structures are regulated, thereby affecting the matching of the catalyst hydrogenation active center and the alkylation active center, thereby changing the activity of the reaction. Compared with traditional supported and mixed hydroalkylation catalysts, the prepared polyacid-supported nano-metal nickel hydroalkylation bifunctional catalyst has the advantages of good matching of hydrogenation activity and alkylation activity, high thermal stability, green, cheap, non-toxic, high efficiency and strong cycle stability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an XRD diagram of the flower-like nickel-aluminum hydrotalcite prepared in Example 2.

FIG. 2 is a SEM image of the flower-like nickel-aluminum hydrotalcite prepared in Example 2.

FIG. 3 is an XRD diagram of the polyacid-supported metal nickel hydroalkylation bifunctional catalyst prepared in Example 2.

FIG. 4 is a SEM image of the polyacid-supported metal nickel hydroalkylation bifunctional catalyst prepared in Example 2.

FIG. 5 is a TEM image of the polyacid-supported metal nickel hydroalkylation bifunctional catalyst prepared in Example 2.

FIG. 6 is a HAADF-STEM image and EDS line scan of the polyacid-supported metal nickel hydroalkylation bifunctional catalyst prepared in Example 2.

DETAILED DESCRIPTION

Example 1

(1) Under room temperature, 5.8 g of nickel nitrate, 3.7 g of aluminum nitrate, 12 g of urea and 3 g of ammonium fluoride were weighed and dissolved in 400 mL of deionized water to form a transparent dispersed solution; the solution was transferred to a stainless steel hydrothermal autoclave, placed in an oven at 110° C. for reaction for 24 h, and then taken out, the precipitate was centrifuged and washed until neutral and dried to obtain a flower-like nickel-aluminum hydrotalcite.

(2) After the flower-like nickel-aluminum hydrotalcite is fully ground, it is placed in a hydrogen atmosphere furnace for calcination and reduction. The temperature is raised to 450°C at an initial heating rate of 9°C/min and the hydrogen flow rate is 40 mL/min. After maintaining for 5 hours, the temperature is slowly cooled to room temperature in a nitrogen flow to prepare a nickel-aluminum composite metal oxide.

(3) Weigh 0.10 g of phosphotungstic acid and 0.4 g of nickel-aluminum composite metal oxide and add them together with 5 mL of deionized water into a 50 mL beaker, ultrasonicate for 30 min, and place the resulting slurry in a 60° C. oven to fully dry.

(4) The solid powder obtained in step (3) was evenly dispersed in a porcelain boat, and placed in an atmosphere furnace with a reducing atmosphere. The temperature was raised to 325° C. at a rate of 5° C./min in a mixed gas flow of H ₂ /N ₂ (volume ratio 1:9) with a flow rate of 30 mL/min. After maintaining for 4 hours, the mixture was cooled to room temperature in a nitrogen gas flow to prepare a polyacid-supported metal nickel hydroalkylation bifunctional catalyst.

0.2g of the prepared polyacid-supported metal nickel hydroalkylation bifunctional catalyst was placed in a stainless steel high-pressure reactor, 5.7ml of benzene was added, and after adding a cylindrical magnet, the reactor was sealed and placed in a heating device with magnetic stirring. The air in the reactor was replaced with 1MPa hydrogen for 3 times. Finally, the pressure condition of 1.5MPa, the temperature condition of 200℃ and the speed of 700r/min in the reactor were maintained by replenishing hydrogen every hour, and the reaction time was 3h.

After testing, the conversion rate of the polyacid-supported metal nickel hydroalkylation bifunctional catalyst for the reaction of benzene hydroalkylation to cyclohexylbenzene was 55%, the selectivity was 68%, and the yield was 37%. Compared with the _catalyst HPW/Ni/ _Al2O3 in which phosphotungstic acid and _Ni are co-supported on _Al2O3 (benzene conversion rate is 19%, cyclohexylbenzene selectivity is 57%), the catalytic performance has been greatly improved. (The Ni loading amount, polyacid loading amount and synthesis conditions of the control _catalyst HPW/Ni/ _Al2O3 are consistent with those of the polyacid-supported metal nickel hydroalkylation bifunctional catalyst).

Example 2

(1) Under room temperature, 2.9 g nickel nitrate, 1.9 g aluminum nitrate, 6.1 g urea and 1.5 g ammonium fluoride were weighed and dissolved in 200 mL deionized water to form a transparent dispersed solution; the solution was poured into a 200 mL stainless steel hydrothermal kettle, placed in a 120° C. oven for reaction for 18 h, then taken out, the precipitate was centrifuged and washed until neutral, and placed in a 60° C. oven for drying for 24 h to obtain flower-like nickel-aluminum hydrotalcite.

(2) After the flower-like nickel-aluminum hydrotalcite is fully ground, it is placed in a hydrogen atmosphere furnace for calcination and reduction, with an initial heating rate of 2°C/min to 500°C and a hydrogen gas flow rate of 30 mL/min for 4 hours to prepare a nickel-aluminum composite metal oxide.

(3) Weigh 0.13 g of phosphotungstic acid and 0.50 g of nickel-aluminum composite metal oxide and add them together with 5 mL of deionized water into a 50 mL beaker, ultrasonicate for 30 min, and place the resulting slurry in a 60° C. oven to fully dry.

(4) The solid powder obtained in step (3) was evenly dispersed in a porcelain boat, and placed in an atmosphere furnace with a reducing atmosphere. The temperature was raised to 300° C. at a rate of 5° C./min in a mixed gas flow of H ₂ /N ₂ (volume ratio 1:9) with a flow rate of 30 mL/min. After maintaining for 4 hours, the mixture was cooled to room temperature in a nitrogen gas flow to prepare a polyacid-supported metal nickel hydroalkylation bifunctional catalyst.

0.2g of the prepared polyacid-supported metal nickel hydroalkylation bifunctional catalyst was placed in a stainless steel high-pressure reactor, 5.7ml of benzene was added, and after adding a cylindrical magnet, the reactor was sealed and placed in a heating device with magnetic stirring. The air in the reactor was replaced with 1MPa hydrogen for 3 times. Finally, hydrogen was added every 1h, and the pressure conditions of _1.5MPaH2 , the temperature conditions of 200℃ and the speed of 700r/min in the reactor were maintained for 4h.

After testing, the polyacid-supported metal nickel hydroalkylation bifunctional catalyst has a conversion rate of 71%, a selectivity of 58%, and a yield of 41% for the reaction of benzene hydroalkylation to cyclohexylbenzene. After five cycles, the conversion rate of the reaction is still greater than 69%, and the selectivity is greater than 57%. (Cycle 1: conversion rate 71%, selectivity 58%; cycle 2: conversion rate 73%, selectivity 55%; cycle 3: conversion rate 74%, selectivity 57%; cycle 4: conversion rate 69%, selectivity 58%; cycle 5: conversion rate 70%, selectivity 58%).

The catalytic performance of the polyacid-supported nickel hydroalkylation bifunctional catalyst prepared above and the existing bifunctional catalyst for benzene hydroalkylation reaction is compared and the results are shown in Table 1 below:

Table 1 Comparison of catalytic performance of different catalysts for benzene hydroalkylation reaction

Claims (6)

1. A method for preparing a polyacid-supported metal nickel hydroalkylation bifunctional catalyst, characterized in that the specific steps of the preparation method are: firstly synthesizing flower-shaped nickel aluminum hydrotalcite by a hydrothermal method, and then calcining in a reducing atmosphere to obtain a nickel aluminum composite metal oxide; impregnating a heteropoly acid onto the nickel aluminum composite metal oxide, and finally in situ co-reducing in a _H2 atmosphere to obtain a polyacid-supported metal nickel hydroalkylation bifunctional catalyst; The specific preparation steps of the flower-shaped nickel-aluminum hydrotalcite are as follows: dissolving a soluble nickel salt, a soluble aluminum salt, urea and ammonium fluoride in 100-200 mL of deionized water to obtain a transparent mixed solution, wherein the concentrations of nickel nitrate, aluminum nitrate, urea and ammonium fluoride are 0.05-0.2 M, 0.025-0.1 M, 0.5-2 M and 0.2-0.8 M, respectively; then transferring the mixed solution to a high-pressure reactor, sealing and reacting at 100-140°C for 12-48 hours, and finally washing the obtained precipitate with deionized water until it is neutral, and drying to obtain the flower-shaped nickel-aluminum hydrotalcite; The specific preparation steps of the nickel-aluminum composite metal oxide are: fully grinding the flower-shaped nickel-aluminum hydrotalcite, then heating the temperature to 450-600°C at an initial heating rate of 2-10°C/min in a hydrogen gas flow of 20-60 mL/min, maintaining the temperature for 2-6 hours, and then slowly cooling the temperature to room temperature in a nitrogen gas flow to obtain the nickel-aluminum composite metal oxide; The specific steps of impregnating the nickel-aluminum composite metal oxide with the heteropoly acid are as follows: dispersing 0.4-1.0 g of the nickel-aluminum composite metal oxide in 1-10 mL of a solution containing 0.1-0.3 g of the heteropoly acid, ultrasonicating for 10-30 min, and then drying the slurry in an oven at 60-100°C. 2. The preparation method according to claim 1 is characterized in that the heteropoly acid is selected from one or more of phosphotungstic acid, phosphomolybdic acid and silicotungstic acid. 3. The preparation method according to claim 1 is characterized in that the specific conditions of the in-situ co-reduction are: in a mixed gas flow of hydrogen and nitrogen at 15-60 mL/min, the temperature is increased from room temperature to 250-450°C at a heating rate of 2-15°C/min, and then the temperature is slowly cooled to room temperature in a nitrogen gas flow after keeping the temperature for 2-8 hours. 4. Use of the polyacid-supported metal nickel hydroalkylation bifunctional catalyst prepared according to the method of any one of claims 1 to 3 to catalyze the hydroalkylation of benzene to produce cyclohexylbenzene. 5. The use according to claim 4, characterized in that the reaction conditions for catalyzing benzene hydrogenation and alkylation to prepare cyclohexylbenzene are as follows: 5-40 mL of benzene and 0.1-0.5 g of a polyacid-supported metal nickel hydrogenation and alkylation bifunctional catalyst are added to a high-pressure hydrogenation reactor, and the gas is replaced 3-10 times with 0.5-2 MPa hydrogen to exhaust the air in the reactor; and then the reaction is sealed and reacted for 3-5 hours at 170-220°C, 0.5-2.5 MPa of hydrogen, and a stirring speed of 500-1000 r/min. 6. The use according to claim 5, characterized in that after the reaction of catalyzing benzene hydrogenation alkylation to produce cyclohexylbenzene is completed, the catalyst is separated and dried so that the catalyst can be continuously recycled.

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