A palladium catalyst and its preparation method and its application in preparing phenolic compounds

Abstract

The invention discloses a palladium catalyst and a preparation method thereof and an application thereof in the preparation of phenolic compounds, and belongs to the technical field of palladium catalysts. The preparation method adopted by the palladium catalyst of the present invention includes: dispersing palladium chloride and nano-γ-alumina into water to prepare solution A, stirring for a period of time; dispersing sodium borohydride into water to prepare solution B, slowly adding solution B into solution A under ice bath conditions, continuing to stir, centrifugation, washing, drying, and grinding uniformly. The palladium catalyst preparation method of the present invention is simple, conducive to industrial production, can dehydrogenate cyclohexanol compounds to obtain corresponding phenolic compounds, substrate tolerance is good, and the catalyst is easy to recover and can be recycled for multiple times.

Description

Technical Field

[0001] The invention belongs to the technical field of palladium catalysts, and in particular relates to a palladium catalyst and a preparation method thereof and application thereof in the preparation of phenolic compounds. Background Art

[0002] Phenol and its derived phenolic compounds are very important industrial chemicals and are also key structural motifs in various drugs, agricultural chemicals, plastics and resins. At present, there are two main production processes for phenol: the cumene method and the toluene-benzoic acid method. The cumene method is the current mainstream process. This method has low production costs and is easy to control during the reaction process, but the process is relatively cumbersome, the byproduct acetone is inevitable, and the peroxide intermediate has an explosion risk. The toluene-benzoic acid method has a simple process, the raw materials and catalysts used are less toxic, and the cost is low, but the phenol generated in the reaction needs to be removed from the reaction system as soon as possible, otherwise tar is easily produced. The process of dehydrogenating cyclohexanol to produce phenol is simple, has little environmental pollution, and combined with the reaction of phenol hydrogenation, it has a high reversible hydrogen capacity (about 6 wt.%), and is a potential liquid organic hydrogen carrier material that can be used in hydrogen storage systems in future energy systems. Compared with the reaction of hydrogenating phenol to obtain cyclohexanol, the research on the dehydrogenation of cyclohexanol to obtain phenol is relatively small, which deserves further study. Summary of the invention

[0003] The purpose of the present invention is to solve the deficiencies of the prior art and to provide a palladium catalyst and a preparation method thereof and an application thereof in the preparation of phenolic compounds. The palladium catalyst of the present invention can be directly catalyzed on the basis of cyclohexanol compounds to generate a dehydrogenation reaction and efficiently generate phenolic compounds.

[0004] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0005] The present invention provides a method for preparing a palladium catalyst, which is prepared by the following method:

[0006] Prepare an aqueous solution A of palladium chloride and nano-γ-alumina;

[0007] Prepare an aqueous solution B of sodium borohydride;

[0008] Slowly add solution B into solution A at low temperature and stir to obtain a solid;

[0009] The obtained solid is post-treated to obtain the palladium catalyst.

[0010] Furthermore, the molar ratio of the palladium chloride to the nano-γ-alumina is 1:15-30.

[0011] Furthermore, the molar concentration of palladium chloride in the solution A is 5 to 10 mmol·L -1 .

[0012] Furthermore, the molar concentration of the solution B is 0.05 to 0.5 mol·L -1 .

[0013] Furthermore, the molar ratio of the palladium chloride, the nano-γ-alumina, and the sodium borohydride is 1:15-30:3-8.

[0014] Furthermore, the particle size of the nano-γ-alumina is 5-50 nm; the post-treatment is specifically: washing, drying and grinding the obtained solid.

[0015] The present invention also provides a palladium catalyst prepared by the preparation method of the palladium catalyst.

[0016] The invention also provides application of the palladium catalyst in preparing phenolic compounds.

[0017] Furthermore, the use of the palladium catalyst in the preparation of phenolic compounds specifically comprises the following steps: dehydrogenating the cyclohexanol compound represented by formula (I) in the presence of a palladium catalyst to generate a phenolic compound represented by formula (II), and the reaction formula is as follows: ;

[0018] R is an unsubstituted or substituent-substituted group: phenyl, alkyl or amino, and the substituent is a combination of one or more of the following groups: C1-6 alkyl, amino, phenyl.

[0019] Further, the use of the palladium catalyst in the preparation of phenolic compounds, wherein R is a C1-6 alkyl, amino or phenyl group;

[0020] and / or, the dehydrogenation reaction is carried out at 130-160° C.;

[0021] And / or, the dehydrogenation reaction is carried out at a pressure of 0.1 to 2 MPa;

[0022] And / or, the dehydrogenation reaction is carried out in a solvent;

[0023] And / or, the molar ratio of the cyclohexanol compound represented by the formula (I) to the palladium in the palladium catalyst is 1:0.04-0.10.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The invention provides a novel palladium catalyst. The catalytic system formed by the catalyst can directly catalyze cyclohexanol compounds to generate dehydrogenation reactions and efficiently generate phenolic compounds. The catalyst has good substrate tolerance, is easy to recover the catalyst, and is easy to promote and apply.

[0026] The palladium catalyst preparation process of the present invention is simple and does not require high-temperature calcination; the carrier used is cheap and easy to obtain, and is widely used in industry. The present invention utilizes the effect of surface tension to generate capillary pressure, so that the solution containing the active component enters the carrier, and uses sodium borohydride to convert Pd 2+ Restore to Pd 0 After drying and other operations to remove moisture, palladium was successfully loaded on the nano-γ-alumina carrier. The proportion of zero-valent palladium in the catalyst is very high, about 95.4%, Pd 2+ and Pd 0 The ratio of the two valence states is 1:20.8. The palladium loaded on γ-Al2O3 mainly exists in the form of nanoparticles with small particle sizes, almost all of which are below 5 nm.

[0027] The palladium catalyst of the invention is applied to the preparation of phenolic compounds, and a liquid phase dehydrogenation method is adopted under normal pressure conditions, so the reaction temperature is low and the energy consumption is low; the catalyst is easy to separate and recover and can be used multiple times; the dehydrogenation of cyclohexanol is divided into two steps, the first step is to generate an intermediate product cyclohexanone under the catalytic action of palladium, and the second step is to continue dehydrogenation under the catalytic action of palladium with lower dispersion to generate the target product phenol; the palladium in the catalyst has a suitable dispersion, which is conducive to improving the selectivity of phenol; the application range is wide and the substrate tolerance is good. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a HRTEM (high-resolution transmission electron microscope) image of the palladium catalyst Pd / γ-Al2O3 prepared in Example 1 of the present invention; some palladium nanoparticles in the catalyst are circled with small circles, and it can be seen from the figure that the nano-γ-alumina carrier is in a sheet shape;

[0029] Figure 2 This is an XPS (X-ray photoelectron spectroscopy) diagram of the palladium catalyst Pd / γ-Al2O3 prepared in Example 1 of the present invention; the Pd in ​​the catalyst has Pd 2+ and Pd 0 There are two valence states, among which, at 343.1 eV is Pd 2+ 3d 3 / 2 The characteristic peak at 337.6 eV is Pd 2+ 3d 5 / 2 Characteristic peak of Pd 0 3d 3 / 2 The characteristic peaks and Pd 0 3d 5 / 2 The characteristic peaks of Pd and Pd are at 341.1 eV and 335.8 eV respectively. 0 Theoretically, all Pd should be reduced to zero valence by sodium borohydride, and a small amount of Pd 2+ Maybe Pd0 Oxidation by the environment causes Pd 2+ and Pd 0 The ratio of the content of the two valence states is 1:20.8;

[0030] Figure 3 The target product obtained in Example 3 of the present invention 1 H NMR (nuclear magnetic resonance hydrogen spectrum); Phenol, 1 H NMR (500 MHz, Chloroform- d ) δ 7.34 – 7.28 (m, 2H), 7.00 (t, J = 7.4 Hz, 1H), 6.91(d, J = 7.4 Hz, 2H), 5.57 (s, 1H);

[0031] Figure 4 The target product obtained in Example 7 of the present invention 1 H NMR (nuclear magnetic resonance hydrogen spectrum); 3-Aminophenol, 1 H NMR (500 MHz, DMSO- d 6) δ 8.85 (s, 1H), 6.78 (t, J = 8.2 Hz, 1H), 6.00 (s,1H), 5.93 (d, J = 7.9 Hz, 1H), 4.88 (s, 2H), 3.42 (s, 1H);

[0032] Figure 5 The target product obtained in Example 8 of the present invention 1 H NMR (nuclear magnetic resonance hydrogen spectrum), 2-Amino-4-methylphenol, 1 H NMR (500 MHz, DMSO- d 6) δ 8.69 (s, 1H), 6.51 (d, J = 7.7 Hz,1H), 6.40 (s, 1H), 6.19 (d, J = 7.9 Hz, 1H), 4.39 (s, 2H), 2.09 (s, 3H). DETAILED DESCRIPTION

[0033] The present invention is further described in detail below in conjunction with embodiments.

[0034] Those skilled in the art will appreciate that the following examples are only used to illustrate the present invention and should not be considered to limit the scope of the present invention. If no specific techniques or conditions are specified in the examples, they are carried out according to the techniques or conditions described in the literature in this area or according to the product instructions. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased.

[0035] Example 1

[0036] This embodiment provides a palladium catalyst, and the preparation method of the palladium catalyst is as follows:

[0037] Palladium chloride (0.47 mmol) and nano-γ-alumina (particle size 10 nm, 9.80 mmol) were dispersed in 70 mL of water to prepare solution A, and stirred for 1 h; sodium borohydride (2.35 mmol) was dispersed in 9 mL of water to prepare solution B; solution B was slowly added to solution A under ice bath conditions, and continued to stir for a period of time. After stirring, the solid was separated by centrifugation, washed with water 3 times, and dried at 80°C for 12 h. The dried solid was ground evenly to obtain the final palladium catalyst, recorded as Pd / γ-Al2O3.

[0038] Its characterization spectrum is as follows Figure 1 HRTEM (high-resolution transmission electron microscopy) images, Figure 2 XPS (X-ray photoelectron spectroscopy) diagram.

[0039] Example 2

[0040] This embodiment provides a palladium catalyst, and the preparation method of the palladium catalyst is as follows:

[0041] Palladium chloride (0.47 mmol) and nano-γ-alumina (particle size 10 nm, 9.80 mmol) were dispersed in 70 mL of water to prepare solution A, and stirred for 2 h; sodium borohydride (1.88 mmol) was dispersed in 7 mL of water to prepare solution B; solution B was slowly added to solution A under ice bath conditions, and continued to stir for a period of time. After stirring, the solid was separated by centrifugation, washed with water 3 times, and dried at 70°C for 12 h. The dried solid was ground evenly to obtain the final palladium catalyst, recorded as Pd / γ-Al2O3.

[0042] Comparative Example 1

[0043] The only difference from Example 1 is that no sodium borohydride is added to Solution B.

[0044] Comparative Example 2

[0045] The only difference from Example 1 is that nano α-alumina is used.

[0046] Comparative Example 3

[0047] The only difference from Example 1 is that solution B is slowly added into solution A at room temperature.

[0048] The following provides an example of the preparation of phenolic compounds

[0049] The reaction formula is as follows: .

[0050] Examples 3-14

[0051] 0.5 mmol of the cyclohexanol compound represented by formula (I), 100 mg of Pd / γ-Al2O3 prepared in Example 1, and 2 mL of N,N-dimethylacetamide were added to a reaction vessel and reacted at 150°C for 8 h under normal pressure and oxygen conditions. After the reaction was completed and the temperature was lowered, the catalyst and the reaction solution were separated by centrifugation. Ethyl acetate (1 mL×3) was added to extract and collect the organic phase, which was dried and rotary evaporated to obtain a crude product, which can be purified by silica gel column chromatography to obtain the target product. The specific results are shown in Table 1 (yield determined by GC).

[0052] Application Comparative Example 1

[0053] The difference from Example 3 is that the catalyst Pd / γ-Al2O3 is replaced by the catalyst prepared in Comparative Example 1. The specific results are shown in Table 1 (the yield is determined by GC).

[0054] Application Comparative Example 2

[0055] The difference from Example 3 is that the catalyst Pd / γ-Al2O3 is replaced by the catalyst prepared in Comparative Example 2. The specific results are shown in Table 1 (the yield is determined by GC).

[0056] Application Comparative Example 3

[0057] The difference from Example 3 is that the catalyst Pd / γ-Al2O3 is replaced by the catalyst prepared in Comparative Example 3. The specific results are shown in Table 1 (the yield is determined by GC).

[0058] Table 1 Dehydrogenation of cyclohexanol compounds to generate phenolic compounds

[0059]

[0060]

[0061] As can be seen from Table 1 above, under the reaction conditions described in Example 3, the phenol yield is as high as 84%; the results of Comparative Example 1 show that Pd 0 Pd 2+The results of comparative example 2 show that nano-γ-alumina is more suitable as a carrier for the reaction than nano-α-alumina; the results of comparative example 3 show that adding solution B in a low temperature environment is more conducive to the reaction of Pd 2+ Transformed to Pd 0 process; Examples 4-14 illustrate that the palladium catalyst is not only effective for the dehydrogenation of cyclohexanol to prepare phenol, but also for the dehydrogenation of cyclohexanol compounds (including: 2-methylcyclohexanol, 3-methylcyclohexanol, 4-methylcyclohexanol, 3-aminocyclohexanol, 2-amino-4-methylcyclohexanol, 4-ethylcyclohexanol, 4-tert-butylcyclohexanol, 2,3-dimethylcyclohexanol, 2,4-dimethylcyclohexanol, 2,5-dimethylcyclohexanol or 2-phenylcyclohexanol) to prepare corresponding phenolic compounds.

[0062] Application Comparative Example 4

[0063] The difference from Example 3 is that Pd / γ-Al2O3 is replaced by γ-Al2O3. The preparation method of γ-Al2O3 is the same as that of Example 1, but palladium chloride is not added to solution A.

[0064] Specifically: 0.5 mmol cyclohexanol, 100 mg γ-Al2O3, and 2 mL N,N-dimethylacetamide were added to the reaction vessel and reacted at 150°C for 8 h under normal pressure and oxygen conditions. After the reaction was completed and the temperature was lowered, the catalyst and the reaction solution were separated by centrifugation. Ethyl acetate (1 mL×3) was added to extract and collect the organic phase, which was dried and rotary evaporated to obtain a crude product, which was determined by GC. The yield was 0%.

[0065] Application Comparative Example 5

[0066] The difference from Example 3 is that N,N-dimethylacetamide is replaced by dimethyl sulfoxide.

[0067] Specifically, 0.5 mmol of cyclohexanol, 100 mg of Pd / γ-Al2O3 prepared in Example 1, and 2 mL of dimethyl sulfoxide were added to a reaction vessel and reacted at 150°C for 8 h under normal pressure and oxygen conditions. After the reaction was completed and the temperature was lowered, the catalyst and the reaction solution were separated by centrifugation. Ethyl acetate (1 mL×3) was added to extract and collect the organic phase, which was dried and rotary evaporated to obtain a crude product, which was determined by GC. The yield was 3%.

[0068] Embodiment 15

[0069] 0.5 mmol cyclohexanol, 100 mg Pd / γ-Al2O3 prepared in Example 1, and 2 mL N,N-dimethylacetamide were added to the reaction vessel and reacted at 150°C for 16 h under normal pressure and oxygen conditions. After the reaction was completed and the temperature was lowered, the catalyst and the reaction solution were separated by centrifugation. Ethyl acetate (1 mL×3) was added to extract and collect the organic phase, which was dried and rotary evaporated to obtain a crude product, which was determined by GC. The yield was 87%.

[0070] Example 16 Palladium catalyst application experiment (catalyst application experiment is also called catalyst recovery experiment, which is one of the indicators for testing the performance of heterogeneous catalysts)

[0071] 0.5 mmol cyclohexanol, 100 mg Pd / γ-Al2O3 prepared in Example 1, and 2 mL N,N-dimethylacetamide were added to the reaction vessel and reacted at 150°C for 8 h under normal pressure oxygen. After the reaction was completed and the temperature was lowered, the catalyst and the reaction solution were separated by centrifugation. Ethyl acetate (1 mL×3) was added to extract and collect the organic phase, which was dried and rotary evaporated to obtain a crude product. After each cycle, the catalyst was centrifuged, washed with ethyl acetate (1 mL×3) and deionized water (1 mL×3), and dried. The specific results of the palladium catalyst application experiment are shown in Table 2 (yield determined by GC).

[0072] Table 2 Pd / γ-Al2O3 catalyst application experiment

[0073]

[0074] It can be seen from Table 2 that after the Pd / γ-Al2O3 catalyst was used for 6 times, the catalytic effect did not decrease significantly, indicating that the catalyst can be used multiple times and has good catalytic stability.

[0075] The above embodiments describe the implementation methods of the present invention in detail, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge of ordinary technicians in the field without departing from the purpose of the present invention. The above description is only a preferred feasible embodiment of the present invention, and does not limit the scope of rights of the present invention. All equivalent structural changes made by using the contents of the present invention specification are included in the scope of rights of the present invention.

Claims

1. The use of a palladium catalyst in the preparation of a phenolic compound, characterized in that: Specifically, the process comprises the following steps: subjecting the cyclohexanol compound represented by formula (I) to a dehydrogenation reaction in the presence of a palladium catalyst to generate a phenol compound represented by formula (II), and the reaction formula is as follows: ； The preparation method of the palladium catalyst comprises the following steps: Composition: prepare an aqueous solution A of palladium chloride and nano-γ-alumina; prepare an aqueous solution B of sodium borohydride; slowly add the aqueous solution B into the aqueous solution A under ice bath conditions, stir to obtain a solid; wash the obtained solid with water, dry and grind to obtain the palladium catalyst; The molar concentration of palladium chloride in the aqueous solution A is 5 to 10 mmol·L -1 ; The molar concentration of the aqueous solution B is 0.05-0.5 mol·L -1 ; The molar ratio of the palladium chloride, the nano-γ-alumina and the sodium borohydride is 1: (15-30): (3-8); The particle size of the nano-γ-alumina is 5-50 nm; The dehydrogenation reaction is carried out under normal pressure oxygen conditions at 130-160°C; The cyclohexanol compound is cyclohexanol, or at least one selected from 2-methylcyclohexanol, 3-methylcyclohexanol, 4-methylcyclohexanol, 3-aminocyclohexanol, 4-ethylcyclohexanol, 4-tert-butylcyclohexanol and 2-phenylcyclohexanol; The dehydrogenation reaction is carried out in a solvent, N,N-dimethylacetamide; the molar ratio of the cyclohexanol compound represented by the formula (I) to the palladium in the palladium catalyst is 1: (0.04-0.10).

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