Preparation method of Cu-based reverse phase catalyst and application of Cu-based reverse phase catalyst in preparation of dihydric alcohol through intramolecular lactone hydrogenation

Abstract

This invention discloses a method for preparing a Cu-based reverse-phase catalyst and its application in the hydrogenation of cyclic lactones to prepare diols, belonging to the field of catalytic hydrogenation technology for cyclic lactones. The catalyst consists of a metal oxide ZnO supported on a Cu species, forming an oxide / metal reverse-phase interface structure, denoted as ZnO / Cu. This reverse-phase interface structure enhances the adsorption and activation capacity for ester carbonyl groups, promotes the hydrogenation ring-opening process, and achieves highly selective preparation of the corresponding diols, which is of great significance for promoting the high-value utilization of resources.

Description

Technical Field

[0001] This invention belongs to the field of catalytic hydrogenation technology of cyclic lactones, specifically relating to a Cu-based reversed-phase catalyst and its application in the catalytic hydrogenation of cyclic lactones to prepare diols. Background Technology

[0002] Cyclic lactones (such as γ-butyrolactone, γ-pentanolide, ε-caprolactone, etc., as shown in formula (I)) serve as important platform molecules. Catalytic hydrogenation to convert them into high-value-added diols (such as 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, etc.) is one of the key pathways to achieve high-value utilization of resources.

[0003]

[0004] Non-precious metal Cu-based catalytic systems are widely used in ester hydrogenation reactions due to their excellent C=O and CO bond activation properties and low cost. For example, CN115448814A reported a copper / cobalt bimetallic supported catalyst for the hydrogenation of γ-butyrolactone to 1,4-butanediol at 140–200 °C and 3–7 MPa hydrogen pressure, and the catalytic activity was improved by the synergistic effect of the bimetallic catalyst. The activity of ester hydrogenation reaction is related to the dispersion of active sites and Cu. 0 / Cu + The ratio and support are closely related; however, the ester group in the cyclic lactone molecule is embedded in the cyclic skeleton (as shown in formula (I)), and its adsorption and bond activation are more difficult than those of linear esters, thus requiring higher catalysts.

[0005] Existing Cu-based ester hydrogenation catalysts typically employ a traditional normal-phase supported structure, where metallic Cu species are supported on a metal oxide support. While this structure can achieve ester hydrogenation conversion, the metal-support interfacial interaction is relatively limited, making it difficult to effectively regulate interfacial active sites. Furthermore, under certain reaction conditions, Cu is prone to migration, aggregation, or sintering, leading to decreased activity. These problems are particularly pronounced in the hydrogenation of cyclic lactones (due to the structural characteristics of cyclic lactones and harsh reaction conditions). Therefore, constructing a non-noble metal reverse-phase catalytic system using metallic Cu species as the support and metal oxide as the supported phase has become a reasonable strategy to improve the activity and selectivity of cyclic lactone hydrogenation reactions. Summary of the Invention

[0006] To address the problems of insufficient catalyst activity and poor selectivity in existing reactions of hydrogenating cyclic lactones to diols, the present invention aims to provide a highly active and selective reverse-phase ZnO / Cu catalyst, its preparation method, and its application in the catalytic hydrogenation of cyclic lactones to diols.

[0007] The reversed-phase catalyst provided by this invention uses ZnO metal oxide as the supporting phase supported on a Cu metal support to form a nano-oxide / metal reversed-phase interface structure, denoted as ZnO / Cu. The molar ratio of ZnO to Cu is the molar ratio of Zn element to Cu element, and this molar ratio ranges from 10:90 to 95:5.

[0008] The preparation method of the reversed-phase catalyst is as follows: A Cu precursor salt is dissolved and dispersed in a solvent, and a suitable proportion of precipitant solution is added to form a dispersed Cu precipitate solution. Under a stirring speed of 200–1000 r / min, the Zn precursor solution and precipitant solution are added to the dispersed Cu precipitate solution at the same volumetric flow rate using a syringe pump at a rate of 0.5–2 mL / min. After injection, stirring is continued for 3–6 h. After stirring, the CuZn precipitate solution is centrifuged and dried at 80–120 °C for 12–24 h. The dried sample is then heated to 300–380 °C in air at a heating rate of 2–5 °C / min and calcined for 4–6 h. Subsequently, it is reduced in a hydrogen atmosphere at 220–300 °C for 2–6 h to obtain the reversed-phase ZnO / Cu catalyst, wherein the hydrogen gas fraction in the reducing atmosphere is not less than 10%.

[0009] The Cu precursor is one or more of copper nitrate, copper acetate, copper chloride, and copper sulfate, and the Zn precursor is one or more of zinc nitrate, zinc acetate, zinc chloride, and zinc sulfate.

[0010] The solvents used in the Cu precursor solution and Zn precursor solution are one or more of water, ethanol, isopropanol, and n-butanol.

[0011] The precipitant solution is one or more of the following: oxalic acid aqueous solution, oxalic acid ethanol solution, oxalic acid isopropanol solution, and oxalic acid n-butanol solution. The molar ratio of metal ions to precipitant during the process is 1:1.0–1.1.

[0012] The application of the reversed-phase catalyst described in this invention in the catalytic hydrogenation of cyclic lactones to prepare diols.

[0013] The reaction of hydrogenating the cyclic lactone to prepare a diol can be carried out in a batch or continuous reactor. During the reaction, the H2 pressure is 1–8 MPa and the reaction temperature is 140–220 °C. The reaction system can be a solvent system or a solvent-free system; if a solvent system is used, the solvent can be selected from 1,4-dioxane, methanol, ethanol, isopropanol, or tetrahydrofuran. Attached Figure Description

[0014] Figure 1 This is a transmission electron microscope (TEM) image of the reversed ZnO / Cu catalyst prepared in Example 11 of the present invention.

[0015] Figure (a) shows a low-magnification transmission electron microscope (TEM) image of the reversed ZnO / Cu catalyst.

[0016] Figure (b) shows a high-resolution transmission electron microscope (HRTEM) image of the reversed ZnO / Cu catalyst.

[0017] Figures (c) to (e) show the energy dispersive spectroscopy (EDS) diagrams of the reversed ZnO / Cu catalyst. Detailed Implementation

[0018] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; unless otherwise specified, the reagents and materials are commercially available.

[0019] Example 1

[0020] Preparation of reversed-phase ZnO / Cu catalyst (Cu / Zn molar ratio of 95:5):

[0021] 5.07 g of copper nitrate trihydrate was dissolved in 40 mL of ethanol. Under vigorous stirring, 33 mL of ethanol solution containing 1.99 g of oxalic acid was added. After stirring for 4 h, the mixture was centrifuged, dried at 100 °C for 12 h, and ground to obtain copper oxalate solid powder. 5 g of copper oxalate was dispersed in 300 mL of ethanol. Under vigorous stirring, 40 mL of ethanol solution containing 0.52 g of zinc nitrate and ethanol solution containing 0.16 g of oxalic acid were simultaneously added dropwise using a syringe pump at a rate of 1 mL / min. Stirring was continued for 4 h. After the reaction was completed, the mixture was centrifuged, dried at 100 °C for 12 h, and then calcined in air at 380 °C for 4 h at a rate of 5 °C / min. The calcined product was placed in a quartz tube and subjected to in-situ reduction in an atmosphere furnace. A 10 vol% H2 / Ar mixed gas was introduced, and reduction was carried out at 280 °C for 3 h to obtain a ZnO / Cu reverse-phase catalyst, which was directly used in the hydrogenation reaction.

[0022] Example 2

[0023] The reaction was carried out using the reversed-phase ZnO / Cu catalyst prepared in Example 1: γ-butyrolactone was dissolved in 1,4-dioxane to prepare a 5% mixed solution. 0.4 g of the reduced catalyst and 20 g of the mixed solution were added to a 100 mL stainless steel high-pressure batch reactor. The reactor was sealed, and the gas inside was replaced with hydrogen 3-4 times. Before the reaction, the reactor was purged with 3 MPa of hydrogen at room temperature. The reactor was heated to 200 °C and the reaction was started. After 3 hours of reaction, the reactor was cooled to room temperature and discharged. After centrifugation, the liquid was analyzed online by a gas chromatograph equipped with a flame ionization detector (FID). The results are shown in Table 1.

[0024] Example 3

[0025] Preparation of ZnO / Cu reverse catalyst (Cu / Zn molar ratio 90:10): Except for using an ethanol solution containing 1.09 g zinc nitrate and an ethanol solution containing 0.346 g oxalic acid, the other operations are the same as in Example 1.

[0026] Example 4

[0027] The catalyst prepared and reduced in Example 3 was used for the hydrogenation reaction of γ-butyrolactone, and the procedure was the same as in Example 2. The results are shown in Table 1.

[0028] Example 5

[0029] The catalyst was prepared in the same manner as in Example 3, except that the reduction temperature was changed to 300°C, while the other conditions remained the same.

[0030] Example 6

[0031] The hydrogenation reaction of γ-butyrolactone was carried out using the catalyst of Example 5, and the procedure was the same as in Example 4. The results are shown in Table 1.

[0032] Example 7

[0033] Preparation of ZnO / Cu reverse catalyst (Cu / Zn molar ratio 80:20): Except for using an ethanol solution containing 2.45g zinc nitrate and an ethanol solution containing 0.779g oxalic acid, the other operations are the same as in Example 1.

[0034] Example 8

[0035] The catalyst prepared and reduced in Example 7 was used for the hydrogenation reaction of γ-butyrolactone, and the procedure was the same as in Example 2. The results are shown in Table 1.

[0036] Example 9

[0037] The γ-butyrolactone hydrogenation reaction was carried out using the catalyst of Example 7, except that the hydrogen pressure was 5 MPa, and the other operations were the same as in Example 8. The results are shown in Table 1.

[0038] Example 10

[0039] Preparation of ZnO / Cu reverse catalyst (Cu / Zn molar ratio 75:25): 5g of copper oxalate was dispersed in 250mL of ethanol. Except for using an ethanol solution containing 3.27g of zinc nitrate and an ethanol solution containing 1.04g of oxalic acid, the other operations were the same as in Example 1.

[0040] Example 11

[0041] The γ-butyrolactone hydrogenation reaction was carried out using the catalyst prepared and reduced in Example 10, following the same procedure as in Example 2. The results are shown in Table 1.

[0042] Example 12

[0043] The hydrogenation reaction of γ-butyrolactone was carried out using the catalyst of Example 10, and the operation was the same as in Example 11 except that the reaction temperature was 180°C. The results are shown in Table 1.

[0044] Example 13

[0045] The hydrogenation reaction of γ-butyrolactone was carried out using the catalyst of Example 10, except that the reaction temperature was 220°C, and the other operations were the same as in Example 11. The results are shown in Table 1.

[0046] Example 14

[0047] The hydrogenation reaction of γ-valerol was carried out using the catalyst of Example 10, except that the substrate was replaced with γ-valerol, and the other operations were the same as in Example 11. The results are shown in Table 1.

[0048] Comparative Example 1

[0049] Preparation of normal-phase catalyst (Cu / Zn molar ratio 90:10): The normal-phase copper-zinc catalyst was prepared by oxalic acid precipitation method, with the following specific steps: 4.57 g of copper nitrate trihydrate and 0.63 g of zinc nitrate hexahydrate were dissolved in 40 mL of ethanol to obtain metal salt solution A; 1.99 g of oxalic acid was dissolved in 33 mL of ethanol to obtain precipitant solution B. Under vigorous stirring, precipitant solution B was rapidly added to metal salt solution A, and the reaction was stirred for 6 h. After the reaction was completed, the mixture was centrifuged, dried at 100 °C for 12 h, and then ground into powder. The powder was placed in a muffle furnace and calcined at 380 °C at a heating rate of 5 °C / min for 4 h. The calcined product was packed into a quartz tube and placed in an atmosphere furnace for in-situ reduction. A mixed gas of 10 vol% H2 / Ar was introduced, and the reduction was carried out at 280 °C for 3 h to obtain the normal-phase Cu / ZnO catalyst.

[0050] Comparative Example 2

[0051] Preparation of normal-phase catalyst (Cu / Zn molar ratio 90:10): A normal-phase copper-zinc catalyst was prepared by ball milling, with the following specific steps: 5.07 g of copper nitrate trihydrate was dissolved in 40 mL of ethanol to obtain metal salt solution A; 1.99 g of oxalic acid was dissolved in 33 mL of ethanol to obtain precipitant solution B; under vigorous stirring, solution B was rapidly added to solution A, and the reaction was stirred for 6 h. After the reaction, the solution was centrifuged, dried at 100 °C for 12 h, and ground to obtain copper oxalate solid powder. 6.25 g of zinc nitrate hexahydrate was dissolved in 40 mL of ethanol to obtain metal salt solution C; 1.99 g of oxalic acid was dissolved in 33 mL of ethanol to obtain precipitant solution D; under vigorous stirring, solution D was rapidly added to solution C, and the reaction was stirred for 6 h. After the reaction, the solution was centrifuged, dried at 100 °C for 12 h, and obtained zinc oxalate solid powder. Take 5g of copper oxalate and 0.69g of zinc oxalate, add an appropriate amount of ethanol, and ball mill in a ball mill for 2 hours (600 r / min). After ball milling, dry the product in a 100℃ oven for 12 hours, then place it in a muffle furnace and calcine it to 380℃ at a heating rate of 5℃ / min for 4 hours. Take the calcined product, put it in a quartz tube, and place it in an atmosphere furnace for in-situ reduction. Pass a 10 vol% H2 / Ar mixed gas through the tube and reduce it at 280℃ for 3 hours. After reduction, a normal-phase Cu / ZnO catalyst is obtained.

[0052] Comparative Example 3

[0053] The hydrogenation reaction of γ-butyrolactone was carried out using the normal-phase Cu / ZnO catalysts prepared in Comparative Example 1 and Comparative Example 2, respectively, under the same reaction conditions as in Example 4. The reaction results corresponding to the catalyst prepared in Comparative Example 1 are denoted as Comparative Example 3a, and the reaction results corresponding to the catalyst prepared in Comparative Example 2 are denoted as Comparative Example 3b. Specific results are shown in Table 1.

[0054] Table 1. Analysis results of cyclic lactone products catalyzed by reversed-phase catalyst and normal-phase catalyst.

[0055]

[0056]

Claims

1. A reverse-phase ZnO / Cu catalyst having a nano-oxide / metal reverse-phase interface structure, characterized in that, Metal oxide ZnO is used as a supported phase on metal Cu species.

2. The reversed ZnO / Cu catalyst as described in claim 1, characterized in that, The molar ratio of ZnO to Cu is the molar ratio of Zn to Cu elements, and the range of this molar ratio is 10:90 to 95:

5.

3. A method for preparing the reversed ZnO / Cu catalyst as described in claim 1, characterized in that, Includes the following steps: (1) Dissolve and disperse the Cu precursor salt in a solvent, add an appropriate proportion of precipitant solution to form a dispersed Cu precipitate solution. (2) Under the condition of stirring speed of 200-1000 r / min, the Zn precursor solution and the precipitant solution are added to the Cu precipitate solution formed in (1) at the same volume flow rate of 0.5-2 mL / min by an injection pump. After the injection is completed, stirring is continued for 3-6 h. (3) After stirring, the CuZn precipitate solution is centrifuged and dried at 80-120℃ for 12-24 hours; (4) The dried sample is heated to 300-380℃ in air at a heating rate of 2-5℃ / min and calcined for 4-6h. Then it is reduced in hydrogen atmosphere at 220-300℃ for 2-6h to obtain reverse ZnO / Cu catalyst, wherein the hydrogen gas integral in the reducing atmosphere is not less than 10%.

4. The method for preparing the reversed-phase catalyst as described in claim 3, characterized in that, The Cu precursor is one or more of copper nitrate, copper acetate, copper chloride, and copper sulfate, and the Zn precursor is one or more of zinc nitrate, zinc acetate, zinc chloride, and zinc sulfate.

5. The method for preparing the reversed-phase catalyst as described in claim 3, characterized in that, The solvents used for the Cu precursor solution and Zn precursor solution are one or more of water, ethanol, isopropanol, and n-butanol, and the precipitant solution is one or more of oxalic acid aqueous solution, oxalic acid ethanol solution, oxalic acid isopropanol solution, and oxalic acid n-butanol solution. The molar ratio of metal ions to precipitant in the process is 1:1.0–1.

1.

6. The application of the reversed-phase catalyst as described in claim 1 in the catalytic hydrogenation reaction of cyclic lactones, characterized in that, This reversed catalyst is used in the hydrogenation of cyclic lactones to prepare diols.

7. The application of the reversed-phase catalyst as described in claim 6 in the catalytic hydrogenation of cyclic lactones to prepare diols, characterized in that, The reaction for the hydrogenation of the cyclic lactone to prepare a diol can be carried out in a batch or continuous reactor. During the reaction, the H2 pressure is 1–8 MPa and the reaction temperature is 140–220 °C. The reaction system can be a solvent system or a solvent-free system. If a solvent system is used, the solvent can be selected from 1,4-dioxane, methanol, ethanol, isopropanol, or tetrahydrofuran.

8. The application of the ZnO / Cu reverse-phase catalyst according to claim 6 in the hydrogenation reaction of cyclic lactones, characterized in that, During the application of this catalyst, the selectivity of the target diol can reach over 90%.

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