Twin palladium catalysts, their preparation methods and applications, and hydrogenation methods for carboxybenzaldehyde.

Abstract

This invention relates to the field of catalyst technology, specifically to a twinned palladium catalyst, its preparation method and application, and a method for hydrogenating carboxybenzaldehyde. The twinned palladium catalyst contains palladium and carbon and has a spherical morphology. The spherical shape of the twinned palladium catalyst not only provides abundant surface reaction sites for the hydrogenation reaction, but the synergistic electronic effect caused by the twinned interface also significantly improves the catalyst's activity and stability. When used for the hydrogenation of carboxybenzaldehyde (e.g., p-carboxybenzaldehyde), it has the advantages of high substrate conversion and high catalyst stability.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, specifically to a twinned palladium catalyst, its preparation method and application, and a method for hydrogenating carboxybenzaldehyde. Background Technology

[0002] Terephthalic acid (PTA) is an important organic dicarboxylic acid, mainly used industrially in polymerization reactions with ethylene glycol to produce polyester fibers, polyester chips, and polyester films, with downstream applications in chemical fibers and packaging materials. The main impurity in crude terephthalic acid is p-carboxybenzaldehyde (4-CBA), which severely affects the polymerization performance of PTA and must be removed. Industrially, 4-CBA is mainly converted into other more water-soluble products through hydrogenation purification, followed by crystallization and purification to obtain high-purity terephthalic acid. Currently, palladium-on-carbon catalysts are the most commonly used hydrogenation purification catalysts in industrial plants. However, existing palladium-on-carbon catalysts suffer from high palladium loading, low activity, and poor stability. Developing efficient and stable palladium catalysts remains a significant challenge for researchers.

[0003] The hydrogenation activity of supported palladium catalysts is closely related to their surface structure and exposed active sites. Controlling the synthesis of metal nanocatalysts with specific sizes or morphologies has always been a challenging problem in heterogeneous catalyst research. A scientific paper (Rare Metal Materials and Engineering, 2017, 46(8):2065-2069.) used palladium chloride as a metal precursor and a simple visible light-assisted method to prepare palladium nanoparticles with single-crystal and multi-twinned structures. The results showed that the multi-twinned palladium nanoparticles exhibited good electrocatalytic activity and anti-poisoning ability for ethanol.

[0004] CN107175338B uses polyvinylpyrrolidone as a reducing agent and dispersant, nitrate particles as an oxidizing etchant, and iodide ions as an adsorption stabilizer to prepare trigonal bipyramidal palladium single twins. This material can be used as a catalyst or in fields such as optics and electronics. To date, the synthesis of polyhedral palladium catalysts is not only very difficult and complex, but research on the microstructure of palladium in the hydrogenation conversion of carboxybenzaldehyde is also scarce. Therefore, this work has significant academic and industrial value for the controllable synthesis of palladium-based catalysts in terms of morphology and crystal structure. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of low hydrogenation activity and poor stability of existing catalysts, and to provide a twinned palladium catalyst, its preparation method and application, and a method for hydrogenating carboxybenzaldehyde. This twinned palladium catalyst has a spherical structure and is used for hydrogenation reactions, especially for the hydrogenation of carboxybenzaldehyde, with the advantages of high substrate conversion and high catalyst stability.

[0006] To achieve the above objectives, the present invention provides a twinned palladium catalyst containing palladium and carbon, and having a spherical morphology.

[0007] A second aspect of the present invention provides a method for preparing the twinned palladium catalyst of the present invention, the method comprising:

[0008] (1) Dissolve zinc salt and organic ligand in solvent to obtain a dispersion containing Zn-MOFs;

[0009] (2) Add palladium source and complexing agent to dispersion, and adjust pH to 9-10 to obtain mixed solution;

[0010] (3) The mixed solution undergoes a reduction reaction under a reducing gas atmosphere to separate the solid, and the solid is then calcined under an inert gas atmosphere.

[0011] A third aspect of this invention provides the application of the twinned palladium catalyst described herein in hydrogenation.

[0012] A fourth aspect of the present invention provides a method for hydrogenating carboxybenzaldehyde, the method comprising:

[0013] Carboxybenzaldehyde is hydrogenated in the presence of a hydrogenation catalyst and hydrogen, wherein the hydrogenation catalyst contains the twinned palladium catalyst described in this invention.

[0014] Through the above technical solution, the twinned palladium catalyst provided by the present invention has a spherical morphology; the twinned structure in the twinned palladium catalyst not only provides abundant surface reaction sites for hydrogenation reaction, but also the synergistic electronic effect caused by the twinned interface significantly improves the activity and stability of the catalyst.

[0015] This invention obtains the twinned palladium catalyst described in this invention by introducing a palladium source and a complexing agent onto a metal-organic framework (MOF) material, adjusting the pH, and then reducing and calcining it.

[0016] The twinned palladium catalyst described in this invention is used for hydrogenation reactions such as the hydrogenation of carboxybenzaldehyde (e.g., p-carboxybenzaldehyde), and has the advantages of high substrate conversion and high catalyst stability. Attached Figure Description

[0017] Figure 1 This is a transmission electron microscope image of the palladium catalyst prepared in Example 1;

[0018] Figure 2 This is a transmission electron microscope image of the palladium catalyst prepared in Comparative Example 1;

[0019] Figure 3This is a transmission electron microscope (TEM) image of the palladium catalyst prepared in Comparative Example 2. Detailed Implementation

[0020] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0021] The first aspect of the present invention provides a twinned palladium catalyst, which contains palladium and carbon and has a spherical morphology.

[0022] In this invention, in the palladium catalyst forming a spherical twin structure, the two palladium crystals with hemispherical structures are aligned in a mirror-symmetric manner along a common crystal plane.

[0023] According to a preferred embodiment of the present invention, the palladium content in the twinned palladium catalyst is 0.1-0.5 wt%.

[0024] According to a preferred embodiment of the present invention, the carbon content in the twinned palladium catalyst is 99.9-99.5 wt%.

[0025] According to a preferred embodiment of the present invention, the twinned palladium catalyst has a particle size of 4-8 nm.

[0026] In this invention, all twinned palladium catalysts possessing the aforementioned characteristics can achieve the objectives of this invention. This invention does not particularly limit the preparation method of the twinned palladium catalyst. According to a preferred embodiment of this invention, this invention provides a method for preparing the twinned palladium catalyst. This invention obtains the twinned palladium catalyst by introducing a palladium source and a complexing agent onto a metal-organic framework (MOF), adjusting the pH, and then reducing and calcining. The preparation method of the twinned palladium catalyst includes:

[0027] (1) Dissolve zinc salt and organic ligand in solvent to obtain a dispersion containing Zn-MOFs;

[0028] (2) Add palladium source and complexing agent to dispersion, and adjust pH to 9-10 to obtain mixed solution;

[0029] (3) The mixed solution undergoes a reduction reaction under a reducing gas atmosphere to separate the solid, and the solid is calcined at a temperature of not less than 850°C under an inert gas atmosphere.

[0030] In step (1) of this invention, as long as Zn-MOFs can be obtained, Zn 2+ The range of selectable ratios of Zn to organic ligands is relatively wide. According to a preferred embodiment of the present invention, Zn 2+ The molar ratio with the organic ligand is 1:5 to 1:10.

[0031] In step (1) of this invention, the amount of solvent can be selected from a wide range. According to a preferred embodiment of this invention, the amount of solvent used is such that the Zn concentration in the dispersion is... 2+ The concentration is 0.02-0.7 mol / L.

[0032] In this invention, the amount of palladium source can be selected from a wide range. According to a preferred embodiment of this invention, the amount of palladium source is 0.06wt%-0.21wt% of the mass of zinc source.

[0033] In this invention, the range of selectable complexing agent dosage is relatively wide. According to a preferred embodiment of this invention, the amount of complexing agent is 12wt%-26.7wt% of the zinc source mass.

[0034] In this invention, the reduction conditions are not particularly limited and can be conventional reduction conditions in the art. According to a preferred embodiment of the present invention, the reduction reaction conditions include: pressure of 1-2 MPa; temperature of 50-120°C; the reduction time can be reasonably adjusted according to the temperature and pressure, preferably, the reduction time is 2-4 hours.

[0035] In this invention, the roasting conditions are not particularly limited and can be conventional roasting conditions in the art. According to a preferred embodiment of the invention, the roasting conditions include: a temperature of 850-1000℃, and a roasting time adjusted according to the roasting temperature and actual needs. Preferably, the roasting time is 0.5-4 hours.

[0036] In this invention, there is no particular limitation on the type of zinc salt, as long as it can be dissolved in a solvent. For example, it can be a soluble salt of zinc. Preferably, the zinc salt is selected from at least one of zinc nitrate and zinc chloride.

[0037] In this invention, there is no particular limitation on the type of organic ligand, as long as it can form a metal-organic framework material with zinc. Preferably, the organic ligand is selected from at least one of dimethylimidazole and imidazole, and more preferably dimethylimidazole.

[0038] In this invention, there is no particular limitation on the type of solvent, as long as it can dissolve zinc and organic ligands. Preferably, the solvent is selected from at least one of water and methanol, more preferably a mixed solution of water and methanol, such as a mixed solution of water and methanol with a mass ratio of 1:0.1-10.

[0039] In this invention, there is no particular limitation on the type of palladium source, as long as it can form a complex in aqueous solution or has good water solubility. According to a preferred embodiment of the present invention, the palladium source is selected from at least one of palladium nitrate and palladium chloride.

[0040] In this invention, there is no particular limitation on the type of complexing agent, as long as it can control the selective growth rate of the palladium crystal face. According to a preferred embodiment of the present invention, the complexing agent is selected from at least one of hexadecyltrimethylammonium halide and octadecyltrimethylammonium chloride, preferably hexadecyltrimethylammonium halide, preferably hexadecyltrimethylammonium bromide and / or hexadecyltrimethylammonium chloride.

[0041] In this invention, there are no particular limitations on the substances used to adjust the pH to 9-10, as long as they are alkaline salts that can be decomposed at high temperatures. Preferably, at least one of ammonium carbonate and ammonium bicarbonate is used to adjust the pH.

[0042] In this invention, there is no particular limitation on the type of reducing gas, as long as it can reduce Pd to Pd. Preferably, the reducing gas is selected from at least one of hydrogen and hydrogen / nitrogen mixture, and hydrogen is preferred.

[0043] In this invention, there is no particular limitation on the type of inert gas, which can be a conventional inert gas in the art, such as nitrogen or rare gas, preferably nitrogen.

[0044] A third aspect of this invention provides the application of the twinned palladium catalyst described herein in hydrogenation. The twinned palladium catalyst provided by this invention has a spherical morphology; the twinned structure in the twinned palladium catalyst not only provides abundant surface reaction sites for the hydrogenation reaction, but the synergistic electronic effect caused by the twinned interface also significantly improves the activity and stability of the catalyst.

[0045] A fourth aspect of the present invention provides a method for hydrogenating carboxybenzaldehyde, the method comprising:

[0046] Carboxybenzaldehyde is hydrogenated in the presence of a hydrogenation catalyst and hydrogen gas. The hydrogenation catalyst contains the twinned palladium catalyst described in this invention. The twinned palladium catalyst, used for the hydrogenation of carboxybenzaldehyde, has the advantages of high substrate conversion and high catalyst stability.

[0047] In this invention, there is no particular limitation on the hydrogenation reaction conditions, which can be conventional hydrogenation conditions in the art. According to a preferred embodiment of the present invention, the hydrogenation reaction conditions include: hydrogen pressure of 0.5-2 MPa; reaction temperature of 60-110°C; and time of 1-5 h.

[0048] According to a preferred embodiment of the present invention, the mass ratio of hydrogenation catalyst to carboxybenzaldehyde is 1:6 to 1:10.

[0049] According to a preferred embodiment of the present invention, the hydrogenation reaction is carried out in the presence of a diluent liquid phase material, preferably, the mass ratio of carboxybenzaldehyde to the diluent liquid phase material is 1:50-180.

[0050] According to a preferred embodiment of the present invention, the dilutive liquid phase material is selected from water.

[0051] To more clearly illustrate the technical solution of the present invention, the present invention will be described in detail below through embodiments.

[0052] In the following examples, TEM and HRTEM images were obtained by AC-S / TEM (aberration-corrected transmission electron microscopy), which also allowed for the measurement of palladium particle size; the palladium content was obtained by ICP-OES testing and analyzed using an Agilent 725ES instrument.

[0053] Example 1

[0054] (1) Dissolve 1.5g zinc nitrate and 3.3g dimethylimidazole in 40ml methanol and 20ml water;

[0055] (2) Add 1.51 g of 2 mg / g palladium nitrate solution and 0.29 g of cetyltrimethylammonium bromide, and adjust the pH to 9 with 1.0 mol / L ammonium carbonate;

[0056] (3) The mixed solution described in step (2) was reacted at 80°C for 3 hours under a hydrogen pressure of 2 MPa. After washing and drying with methanol, the resulting solid powder was calcined at 900°C for 1 hour under a nitrogen atmosphere to obtain a palladium catalyst with a palladium content of 0.45 wt% and a palladium particle size of 4-8 nm.

[0057] The obtained palladium catalyst was characterized by transmission electron microscopy, and the results are shown in the figure. Figure 1 As shown, it can be clearly seen that the obtained palladium catalyst has a typical twinned structure and a spherical morphology.

[0058] Catalyst evaluation: The palladium catalyst was used in the hydrogenation reaction of p-carboxybenzaldehyde (4-CBA) in a 100 mL high-pressure reactor under the following conditions: 0.3 g 4-CBA, 50 mL water, 50 mg catalyst, hydrogen pressure 1 MPa, and reaction at 90 °C for 4 h. The resulting product was quantitatively analyzed by liquid chromatography.

[0059] Example 2

[0060] The method is the same as in Example 1, except that the amount of hexadecyltrimethylammonium bromide used in step (2) is 0.18 g, and the other conditions are the same as in Example 1.

[0061] The obtained palladium catalyst has a typical twinned structure and a spherical morphology; the palladium content in the palladium catalyst is 0.46%, and the palladium particle size is 4-8 nm.

[0062] The catalyst evaluation conditions were the same as in Example 1, and the test results are shown in Table 1.

[0063] Example 3

[0064] The method is the same as in Example 1, except that the amount of hexadecyltrimethylammonium bromide used in step (2) is 0.4g, and the other conditions are the same as in Example 1.

[0065] The obtained palladium catalyst exhibits a typical twinned structure and a spherical morphology; the palladium content in the catalyst is 0.46%, and the palladium particle size is 4-8 nm. The catalyst evaluation conditions are the same as in Example 1, and the test results are shown in Table 1.

[0066] Example 4

[0067] (1) Dissolve 1.5g zinc nitrate and 6.0g dimethylimidazole in 40ml methanol and 20ml water;

[0068] (2) Add 0.7g and 0.29g of 2mg / g palladium nitrate solution and adjust the pH to 10 with 1.0mol / L ammonium carbonate;

[0069] (3) The mixed solution described in step (2) was reacted at 120°C for 4 hours under 1 MPa hydrogen pressure. After washing and drying with methanol, the resulting solid powder was calcined at 1000°C for 1 hour under nitrogen atmosphere to obtain a palladium catalyst with a palladium content of 0.12 wt% and a palladium particle size of 4-8 nm.

[0070] Palladium catalysts exhibit a typical twinned structure and a spherical morphology.

[0071] Catalyst evaluation: The palladium catalyst was used in the hydrogenation reaction of p-carboxybenzaldehyde (4-CBA) in a 100 mL high-pressure reactor under the following conditions: 0.3 g 4-CBA, 50 mL water, 50 mg catalyst, hydrogen pressure 0.5 MPa, and reaction at 110 °C for 4 h. The resulting product was quantitatively analyzed by liquid chromatography. The test results are shown in Table 1.

[0072] Example 5

[0073] (1) Dissolve 1.5g zinc nitrate and 4.6g imidazole in 40ml methanol and 20ml water;

[0074] (2) Add 1.51 g of 2 mg / g palladium nitrate solution and 0.26 g of cetyltrimethylammonium chloride, and adjust the pH to 9.5 with 1.0 mol / L ammonium carbonate;

[0075] (3) The mixed solution described in step (2) was reacted at 60°C for 4 hours under a hydrogen pressure of 1.5 MPa. After washing and drying with methanol, the resulting solid powder was calcined at 950°C for 2 hours under a nitrogen atmosphere to obtain a palladium catalyst with a palladium content of 0.3 wt% and a palladium particle size of 4-8 nm.

[0076] Palladium catalysts exhibit a typical twinned structure and a spherical morphology.

[0077] Catalyst evaluation: The palladium catalyst was used in the hydrogenation reaction of p-carboxybenzaldehyde (4-CBA) in a 100 mL high-pressure reactor under the following conditions: 0.3 g 4-CBA, 50 mL water, 50 mg catalyst, hydrogen pressure 1.2 MPa, and reaction at 60 °C for 5 h. The resulting product was quantitatively analyzed by liquid chromatography. The test results are shown in Table 1.

[0078] Example 6

[0079] The method of Example 1 is the same as in Example 1, except that in step (2), the palladium salt is palladium chloride, specifically, 1.15g of 2mg / g palladium chloride solution is added; the other conditions are the same as in Example 1.

[0080] The obtained palladium catalyst exhibits a typical twinned structure and a spherical morphology; the palladium content in the catalyst is 0.46%, and the palladium particle size is 4-8 nm. The catalyst evaluation conditions are the same as in Example 1, and the test results are shown in Table 1.

[0081] Comparative Example 1

[0082] The palladium catalyst was prepared using the same method as in Example 1, except that cetyltrimethylammonium bromide was not added in step (2). The catalyst evaluation conditions were the same as in Example 1, and the test results are shown in Table 1.

[0083] The obtained palladium catalyst was characterized by transmission electron microscopy, and the results are shown in the figure. Figure 2 As shown, the palladium catalyst exhibits Pd(111) lattice fringes and does not have a twinned structure.

[0084] Comparative Example 2

[0085] The method of Example 1 is different except that in step (3), the reaction is carried out at 80°C for 3 hours under a nitrogen atmosphere of 2 MPa. After washing and drying with methanol, the resulting solid powder is calcined at 900°C for 1 hour under a nitrogen atmosphere to obtain a palladium catalyst.

[0086] The obtained palladium catalyst was characterized by transmission electron microscopy, and the results are shown in the figure. Figure 3 As shown, the palladium catalyst exhibits Pd(111) lattice fringes and does not possess a twinned structure. Furthermore, the palladium catalyst obtained by this method has a smaller palladium particle size compared to Comparative Example 1.

[0087] The catalyst evaluation conditions were the same as in Example 1, and the test results are shown in Table 1.

[0088] Comparative Example 3

[0089] The commercially available 0.5% Pd / C catalyst obtained from Shanghai Petrochemical Company was used to evaluate the hydrogenation reaction of carboxybenzaldehyde. The reaction evaluation and product analysis conditions were the same as in Example 1, and the results are shown in Table 1.

[0090] Comparative Example 4

[0091] The method was followed in Example 1, except that in step (2), the pH was adjusted to 8.5 with 1.0 mol / L ammonium carbonate; the other conditions were the same as in Example 1. This palladium catalyst exhibited Pd(111) lattice fringes and did not have a twinned structure.

[0092] The catalyst evaluation conditions were the same as in Example 1, and the test results are shown in Table 1.

[0093] Table 1

[0094]

[0095]

[0096] The catalysts evaluated in Example 1 and Comparative Examples 1-4 were collected, cleaned with ethanol, and their stability was evaluated according to the evaluation conditions of Example 1. The results are shown in Table 2.

[0097] Table 2

[0098]

[0099] As shown in Table 2, compared with commercially available palladium-on-carbon catalysts, the hydrogenation conversion rate of 4-CBA did not decrease significantly after three cycles of recycling, remaining at 98.8%. Therefore, compared with traditional palladium-on-carbon catalysts, the palladium catalyst with a twinned structure provided by this invention achieves better technical performance.

[0100] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A palladium catalyst with a twinned structure, characterized in that, The twinned palladium catalyst contains palladium and carbon and has a spherical morphology; the preparation method of the twinned palladium catalyst includes: (1) dissolving zinc salt and organic ligand in a solvent to obtain a dispersion containing Zn-MOFs; (2) Add palladium source and complexing agent to dispersion, and adjust pH to 9-10 to obtain mixed solution; (3) The mixed solution is subjected to a reduction reaction under a reducing gas atmosphere to obtain a solid, and the solid is calcined at a temperature of not less than 850°C under an inert gas atmosphere; the complexing agent is selected from hexadecyltrimethylammonium halide; the organic ligand is selected from at least one of dimethylimidazolium and imidazolium.

2. The catalyst according to claim 1, wherein, The palladium content is 0.1-0.5 wt%; and / or the carbon content is 99.9-99.5 wt%.

3. The catalyst according to claim 1 or 2, wherein, The twinned palladium catalyst has a particle size of 4-8 nm.

4. The catalyst according to claim 1, wherein, In step (1), Zn 2+ a molar ratio to the organic ligand of 1 : 5-10; and / or In the dispersion, Zn 2+ at a concentration of 0.02-0.7 mol / L; and / or In step (2), The amount of palladium source used is 0.06wt%-0.21wt% of the zinc source mass; and / or The amount of complexing agent used is 12wt%-26.7wt% of the zinc source mass.

5. The catalyst according to claim 1 or 4, wherein, The reduction reaction conditions include: pressure of 1-2 MPa; temperature of 50-120℃; time of 2-4 h; and / or The roasting conditions include: a temperature of 850-1000℃; and / or a time of 0.5-4 h.

6. The catalyst according to claim 1 or 4, wherein, The zinc salt is selected from at least one of zinc nitrate and zinc chloride; and / or The solvent is selected from at least one of water and methanol; and / or The palladium source is selected from at least one of palladium nitrate and palladium chloride; and / or The complexing agent is hexadecyltrimethylammonium bromide and / or hexadecyltrimethylammonium chloride; and / or pH is adjusted using ammonium carbonate and / or ammonium bicarbonate.

7. The use of the catalyst according to any one of claims 1-6 in hydrogenation.

8. A method for hydrogenating carboxybenzaldehyde, characterized in that, The method includes: Carboxybenzaldehyde is hydrogenated in the presence of a hydrogenation catalyst and hydrogen, wherein the hydrogenation catalyst comprises the catalyst according to any one of claims 1-6.

9. The hydrogenation method according to claim 8, wherein, The hydrogenation reaction conditions include: hydrogen pressure 0.5-2 MPa; reaction temperature 60-110℃; reaction time 1-5 h; and / or The mass ratio of hydrogenation catalyst to carboxybenzaldehyde is 1:6 to 1:

10.

10. The hydrogenation method according to claim 9, wherein, The hydrogenation reaction is carried out in the presence of a diluent liquid material, wherein the mass ratio of carboxybenzaldehyde to the diluent liquid material is 1:50-180.

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