Palladium-cobalt bimetallic catalyst as well as preparation method and application thereof

Abstract

The invention discloses a palladium-cobalt bimetallic catalyst and a preparation method and application thereof, and the preparation method comprises the following steps: dissolving a zinc salt and a cobalt salt in an organic solvent to obtain a metal solution, dissolving a ligand in the organic solvent to obtain a ligand solution, and mixing the metal solution and the ligand solution for reaction to obtain Co-ZIF-8; the method comprises the following steps: dissolving Co-ZIF-8 in an organic solvent, adding a palladium salt solution, and reacting to obtain Pd / Co-ZIF-8; the Pd / Co-ZIF-8 is subjected to calcination treatment, and the palladium-cobalt bimetallic catalyst is obtained. According to the palladium-cobalt bimetallic catalyst provided by the invention, the cobalt-containing metal organic framework is adopted to load palladium nanoparticles, and after calcination, the catalyst has relatively strong magnetism and can be well separated after reaction; compared with a single-palladium catalyst, the catalyst has the advantages of higher catalytic activity, better selectivity and lower loading capacity, and can be used for synthesizing glycerol carbonate.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts, and in particular to a palladium-cobalt bimetallic catalyst and a preparation method and application thereof. Background Art

[0002] Biodiesel is an important renewable energy source extracted from biomass resources such as vegetable oil, animal fat and waste cooking oil, and plays a vital role in the fields of environment, agriculture and energy. However, how to deal with the large amount of waste glycerol generated during the production process has become an obstacle to its development. Therefore, how to effectively utilize glycerol has become the focus of researchers. Glycerol carbonate is an important derivative of glycerol. It has attracted widespread attention due to its high solubility, low toxicity and good biodegradability. It has a wide range of applications in electrolytes, pharmaceuticals, polymer synthesis and other fields.

[0003] The processes for synthesizing glycerol carbonate from glycerol include the phosgene method and the transesterification method. The phosgene used in the phosgene method is not only highly corrosive, but also highly toxic; the transesterification method cannot be used on a large scale due to its high production cost and difficulty in separating the products. The carbonylation method is not only environmentally friendly and in line with the concept of sustainable development, but also has only water as a by-product, so it has become a good research hotspot. The existing technology uses copper-palladium bimetallic catalysis to synthesize glycerol carbonate. The carbonization quality of the copper-palladium bimetallic catalyst decreases significantly after calcination, and the loading amount needs to be greater than 5%, resulting in high costs and inconvenience in recovery. Summary of the invention

[0004] In order to solve the technical problems of low yield, difficult recovery and high cost caused by high loading amount in the process of synthesizing glycerol carbonate from glycerol in the prior art, the purpose of the present invention is to provide a palladium-cobalt bimetallic catalyst and its preparation method and application.

[0005] The present invention is achieved through the following technical solutions:

[0006] The first object of the present invention is to provide a method for preparing a palladium-cobalt bimetallic catalyst, comprising the following steps:

[0007] S1. dissolving a zinc salt and a cobalt salt in an organic solvent to obtain a metal solution, dissolving a ligand in an organic solvent to obtain a ligand solution, mixing the metal solution and the ligand solution to react, and obtaining Co-ZIF-8;

[0008] S2. dissolving the Co-ZIF-8 obtained in step S1 in an organic solvent, adding a solution of a palladium salt, and reacting to obtain Pd / Co-ZIF-8;

[0009] S3. calcining the Pd / Co-ZIF-8 obtained in step S2 to obtain the palladium-cobalt bimetallic catalyst Pd / Co-ZIF-8-N.

[0010] The palladium-cobalt bimetallic catalyst provided by the present invention uses a cobalt-containing metal organic framework to load palladium nanoparticles. After calcination, the catalyst has strong magnetism and can be well separated after the reaction. Compared with a single palladium catalyst, it has higher catalytic activity, better selectivity, and lower loading.

[0011] Furthermore, in step S1, the zinc salt is selected from Zn(NO 3 ) 2 6H 2 O、ZnSO 4 and ZnCl 2 One or more of; the cobalt salt is selected from Co(NO 3 ) 2 6H 2 O. CoSO 4 and CoCl 2 One or more of the .

[0012] Furthermore, in step S1, the ligand is selected from one or more of imidazole, benzimidazole, 2-methylimidazole and dimethylimidazole.

[0013] Furthermore, in step S1, the organic solvent is selected from one or more of methanol, ethanol and N,N-dimethylformamide (DMF).

[0014] Furthermore, in step S1, the mass ratio of the cobalt salt to the zinc salt is (0.01-2):1, preferably (0.03-1):1, and more preferably (0.06-0.24):1.

[0015] Furthermore, in step S1, the ratio of the total mass of the zinc salt and the cobalt salt to the volume of the organic solvent is (1-2) g:(40-150) mL.

[0016] Furthermore, in step S1, the ratio of the mass of the ligand to the volume of the organic solvent is (7-15) g:(80-160) mL.

[0017] Furthermore, in step S1, the volume ratio of the metal solution to the ligand solution is 1:(0.5-1.5).

[0018] Furthermore, in step S1, the reaction conditions are: reacting at 25-60° C. for 10-30 hours, and the Co-ZIF-8 obtained by the reaction is used as a catalyst carrier.

[0019] Furthermore, in step S2, the ratio of the mass of the Co-ZIF-8 to the volume of the organic solvent is (0.1-0.4) g: (40-50) mL.

[0020] Furthermore, in step S2, the mass ratio of palladium element in the palladium salt to Co-ZIF-8 is (0.25-3):100, that is, the loading amount of palladium element relative to the carrier Co-ZIF-8 is 0.25%-3%, preferably 0.25%-2%, and more preferably 0.25%-1.25%.

[0021] Furthermore, in step S2, the palladium salt is palladium acetate.

[0022] In a specific embodiment, in step S2, Co-ZIF-8 is dissolved in an organic solvent, a solution of palladium salt is added, mixed and stirred, and the mixture is centrifuged and dried to obtain Pd / Co-ZIF-8.

[0023] Furthermore, in step S2, the solution of palladium salt is a methanol solution of palladium salt.

[0024] Furthermore, in step S2, the concentration of palladium salt in the methanol solution of palladium salt is 0.4-1.5 g / L.

[0025] Furthermore, in step S2, the ratio of the mass of the Co-ZIF-8 to the volume of the methanol solution of the palladium salt is (0.1-0.4) g:(1-5) mL.

[0026] Furthermore, in step S2, the stirring time is 10-24 hours.

[0027] Furthermore, in step S3, the calcination temperature is 600-950° C., and the calcination time is 2-6 hours.

[0028] Furthermore, in step S3, calcination treatment is performed under an inert gas environment, such as under nitrogen conditions.

[0029] The second object of the present invention is to provide a palladium-cobalt bimetallic catalyst prepared by the above method.

[0030] The third object of the present invention is to provide an application of the above-mentioned palladium-cobalt bimetallic catalyst in the production of oils and fats in the fields of medicine, agriculture, and chemical industry, such as in the field of oil chemical industry, plastics or cosmetics production, mainly for the synthesis of glycerol carbonate.

[0031] Beneficial effects of the present invention:

[0032] 1. The preparation method of the palladium-cobalt bimetallic catalyst provided by the present invention is under normal pressure conditions and is simple to operate. Its precursor is Co-ZIF-8 material, so the catalyst inherits the high specific surface area and uniform porous structure of Cu-ZIF-8. In addition, under the conditions, the only by-product of the reaction is water, and the reaction process is green and environmentally friendly.

[0033] 2. Compared with the prior art, the present invention has the advantages that Co metal can stably form a framework under calcination at 400-600°C compared with transition metals such as Cu and Zn, and because of its weak acidity, it can better promote glycerol carbonylation, and because of its own magnetism, it is easier to separate. In addition, the palladium-cobalt bimetallic catalyst provided by the present invention not only has magnetism, but also has a lower loading (according to inductively coupled plasma optical emission spectroscopy (ICP-OES) analysis, it can be 1.1%, and the previous bimetallic or other framework catalysts are almost all around 2.5%), and can obtain extremely high yield (92.97%) and selectivity (96.37%) during the reaction process. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 2. The XRD patterns of Co-ZIF-8, Pd / Co-ZIF-8 and Pd / Co-ZIF-8-N in Example 1.

[0035] Figure 2 The Fourier transform infrared spectra of the catalysts prepared in Example 1 and Comparative Examples 1-5 are shown. DETAILED DESCRIPTION

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0037] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0038] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods, and the materials, reagents, etc. used are all available from commercial sources unless otherwise specified.

[0039] Example 1

[0040] A method for preparing a palladium-cobalt bimetallic catalyst (Pd / Co-ZIF-8-N) comprises the following steps:

[0041] S1. 1.5 g Zn(NO 3 ) 2 6H 2 O and 0.1g Co(NO 3 ) 2 6H 2 O was placed in a 100 mL beaker (Co(NO3 ) 2 6H 2 O and Zn(NO 3 ) 2 6H 2 O mass ratio is 0.06:1), 45mL methanol is added, and a metal solution is obtained after dissolving; 6.6g 2-methylimidazole is placed in a 50mL beaker, 45mL methanol is added, and a 2-methylimidazole solution is obtained after dissolving. The metal solution and the 2-methylimidazole solution are mixed at room temperature to react for 24h, and the retained solid is washed with methanol 3 times after filtration, and then dried at 80°C for 24h to obtain cobalt-doped ZIF-8 (Co-ZIF-8).

[0042] S2. Place 0.4 g Co-ZIF-8 in a 250 mL beaker, add 45 mL methanol for dispersion, add 5 mL of methanol solution of palladium acetate (1 g / L), the loading amount of palladium element in palladium acetate relative to the carrier Co-ZIF-8 is 0.25%, stir for 24 h, filter, and dry at 80 ° C for 24 h to obtain Pd / Co-ZIF-8.

[0043] S3. Pd / Co-ZIF-8 was calcined in a tubular furnace at 800°C for 2 h under nitrogen conditions to obtain Pd / Co-ZIF-8-N.

[0044] Example 2

[0045] A method for preparing a palladium-cobalt bimetallic catalyst (Pd / Co-ZIF-8-N) is basically the same as the preparation method in Example 1, except that in step S2, the loading amount of palladium element in palladium acetate relative to carrier Co-ZIF-8 is 0.5%.

[0046] Example 3

[0047] A method for preparing a palladium-cobalt bimetallic catalyst (Pd / Co-ZIF-8-N) is basically the same as the preparation method of Example 1, except that in step S2, the loading amount of palladium element in palladium acetate relative to carrier Co-ZIF-8 is 1.25%.

[0048] Example 4

[0049] A method for preparing a palladium-cobalt bimetallic catalyst (Pd / Co-ZIF-8-N) is basically the same as the preparation method in Example 1, except that in step S2, the loading amount of the palladium element in palladium acetate relative to the carrier Co-ZIF-8 is 2%.

[0050] Example 5

[0051] A method for preparing a palladium-cobalt bimetallic catalyst (Pd / Co-ZIF-8-N) is basically the same as the preparation method of Example 1, except that in step S2, the loading amount of palladium element in palladium acetate relative to carrier Co-ZIF-8 is 2.5%.

[0052] Example 6

[0053] A method for preparing a palladium-cobalt bimetallic catalyst (Pd / Co-ZIF-8-N) is basically the same as the preparation method of Example 1, except that in step S2, the loading amount of palladium element in palladium acetate relative to carrier Co-ZIF-8 is 3%.

[0054] Example 7

[0055] A preparation method of a palladium-cobalt bimetallic catalyst (Pd / Co-ZIF-8-N) is basically the same as the preparation method of Example 1, except that: in step S1, Co(NO 3 ) 2 6H 2 O and Zn(NO 3 ) 2 6H 2 The mass ratio of O is 0.03:1.

[0056] Example 8

[0057] A preparation method of a palladium-cobalt bimetallic catalyst (Pd / Co-ZIF-8-N) is basically the same as the preparation method of Example 1, except that: in step S1, Co(NO 3 ) 2 6H 2 O and Zn(NO 3 ) 2 6H 2 The mass ratio of O is 0.12:1.

[0058] Example 9

[0059] A preparation method of a palladium-cobalt bimetallic catalyst (Pd / Co-ZIF-8-N) is basically the same as the preparation method of Example 1, except that: in step S1, Co(NO 3 ) 2 6H 2 O and Zn(NO 3 ) 2 6H 2 The mass ratio of O is 0.24:1.

[0060] Example 10

[0061] A preparation method of a palladium-cobalt bimetallic catalyst (Pd / Co-ZIF-8-N) is basically the same as the preparation method of Example 1, except that: in step S1, Co(NO 3 ) 2 6H 2 O and Zn(NO 3 ) 2 6H 2 The mass ratio of O is 0.48:1.

[0062] Embodiment 11

[0063] A preparation method of a palladium-cobalt bimetallic catalyst (Pd / Co-ZIF-8-N) is basically the same as the preparation method of Example 1, except that: in step S1, Co(NO 3 ) 2 6H 2 O and Zn(NO 3 ) 2 6H 2 The mass ratio of O is 1:1.

[0064] Comparative Example 1

[0065] A method for preparing a copper-palladium bimetallic catalyst (Pd / Cu-ZIF-67-N) is substantially the same as the method for preparing Example 1, except that in step S1, Zn(NO 3 ) 2 6H 2 O is replaced by Cu(NO 3 ) 2 6H 2 O, the carrier obtained in step S1 is Cu-ZIF-67, and Pd / Cu-ZIF-67-N is finally obtained after calcination in step S3.

[0066] Comparative Example 2

[0067] A method for preparing a copper-palladium bimetallic catalyst (Pd / Cu-ZIF-8-N) is substantially the same as the method for preparing Example 1, except that in step S1, Co(NO 3 ) 2 6H 2 O is replaced by Cu(NO 3 ) 2 6H 2 O, the carrier obtained in step S1 is Cu-ZIF-8, and Pd / Cu-ZIF-8-N is finally obtained after calcination in step S3.

[0068] Comparative Example 3

[0069] A method for preparing a catalyst (Pd-ZIF-8-N) is basically the same as the method for preparing Example 1, except that in step S1, no Zn(NO 3 ) 2 6H 2 O, only Co(NO 3 ) 2 6H 2 O, the carrier obtained in step S1 is ZIF-8, and Pd-ZIF-8-N is finally obtained after calcination in step S3.

[0070] Comparative Example 4

[0071] A method for preparing a catalyst (Pd-ZIF-67-N) is basically the same as the method for preparing Example 1, except that in step S1, only Zn(NO 3 ) 2 6H 2 O, without adding Co(NO 3 ) 2 6H 2 O, the carrier obtained in step S1 is ZIF-67, and Pd-ZIF-67-N is finally obtained after calcination in step S3.

[0072] Comparative Example 5

[0073] A method for preparing a catalyst (Pd / Cu-MOF-N) is basically the same as the method for preparing Example 1, except that in step S1, no Zn(NO 3 ) 2 6H 2 O and Co(NO 3 ) 2 6H 2 O, only Cu(NO 3 ) 2 6H 2 O, the support obtained in step S1 is Cu-MOF, and Pd / Cu-MOF-N is finally obtained after calcination in step S3.

[0074] Figure 1 The X-ray diffraction (XRD) patterns of Co-ZIF-8, Pd / Co-ZIF-8 and Pd / Co-ZIF-8-N in Example 1 are shown in Table 1. Figure 1It can be seen that after palladium acetate is loaded, no extra diffraction peaks are shown, indicating that the loading amount of divalent palladium is low and relatively dispersed. After calcination, the catalyst precursor shows obvious diffraction peaks of carbon materials. The bun peak at 25° is C(100), and 44.27 and 51.61° represent the (111)(200) crystal plane of Co (PDF#15-0806). This is because Co is reduced after doping and calcination. This figure shows the successful synthesis of the catalyst.

[0075] Figure 2 The Fourier transform infrared spectra of the catalysts prepared in Example 1 and Comparative Examples 1-5 are shown in FIG. Figure 2 It can be seen that all catalysts perfectly inherit the basic functional groups that the metal-organic framework should have.

[0076] The ICP-OES test results of the palladium content in the palladium-cobalt bimetallic catalyst (Pd / Co-ZIF-8-N) prepared in Example 1 are shown in Table 1:

[0077] Table 1

[0078]

[0079] Table 1 shows that the palladium loading of the catalyst is only 1.11%, which is much lower than that of the reported bimetallic or other framework catalysts.

[0080] Test Example 1

[0081] The catalytic activity of the catalysts prepared in Example 1 and Comparative Examples 1-5 for synthesizing glycerol carbonate was tested by adding 1.446 g of glycerol, 0.015 g of catalyst and 0.018 g of KI to a 50 mL polytetrafluoroethylene-lined reactor, stirring evenly, and mixing with O 2 Purge three times, then fill with O 2 and CO(O 2 :CO=1.3:2.7, pressure ratio), react at 140℃ for 2h.

[0082] The test results are shown in Table 2:

[0083] Table 2

[0084]

[0085] Comparing the catalytic performance of bimetallic catalysts prepared with Cu, Co and Zn, it can be seen from Table 2 that the Pd / Co-ZIF-8-N prepared in Example 1 has the best catalytic effect.

[0086] Test Example 2

[0087] The catalytic activity of the palladium-cobalt bimetallic catalyst prepared in Example 2-6 for synthesizing glycerol carbonate was tested by adding 1.446 g of glycerol, 0.015 g of catalyst and 0.018 g of KI to a 50 mL polytetrafluoroethylene-lined reactor, stirring evenly, and stirring with O 2 Purge three times, then fill with O 2 and CO(O 2 :CO=1.3:2.7, pressure ratio), react at 140℃ for 2h.

[0088] The test results are shown in Table 3:

[0089] Table 3

[0090]

[0091]

[0092] It can be seen from Table 3 that, considering the catalyst cost and the precious metal loading, the catalytic activity of the palladium-cobalt bimetallic catalyst is better when the loading is 1.25%.

[0093] Test Example 3

[0094] The catalytic activity of the palladium-cobalt bimetallic catalysts prepared in Example 1 and Examples 7-11 for synthesizing glycerol carbonate was tested by adding 1.446 g of glycerol, 0.015 g of catalyst and 0.018 g of KI to a 50 mL polytetrafluoroethylene-lined reactor, stirring evenly, and stirring with O 2 Purge three times, then fill with O 2 and CO(O 2 :CO=1.3:2.7, pressure ratio), react at 140℃ for 2h.

[0095] The test results are shown in Table 4:

[0096] Table 4

[0097]

[0098] It can be seen from Table 4 that when the mass ratio is 0.06, the catalytic activity of the palladium-cobalt bimetallic catalyst for synthesizing glycerol carbonate is the best.

[0099] Test Example 4

[0100] The reproducibility of the palladium-cobalt bimetallic catalyst prepared in Example 1 for synthesizing glycerol carbonate was tested by adding 1.446 g of glycerol, 0.015 g of catalyst and 0.018 g of KI to a 50 mL polytetrafluoroethylene-lined reactor, stirring evenly, and stirring with O 2 Purge three times, then fill with O 2and CO(O 2 :CO=1.3:2.7, pressure ratio), react at 140℃ for 2h, and repeat 3 times.

[0101] The test results are shown in Table 5:

[0102] Table 5

[0103]

[0104] As can be seen from Table 5, the palladium-cobalt bimetallic catalyst prepared in Example 1 has good reproducibility for synthesizing glycerol carbonate. After repeating the process three times, the yield of the product was 90.10%, the selectivity was 95.50%, the average yield was 92.97%, and the average selectivity was 96.37%.

[0105] Obviously, the above embodiments of the present invention are only examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Those skilled in the art should understand that other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A method for preparing a palladium-cobalt bimetallic catalyst, characterized in that: The following steps are involved: S1. dissolving a zinc salt and a cobalt salt in an organic solvent to obtain a metal solution, dissolving a ligand in an organic solvent to obtain a ligand solution, mixing the metal solution and the ligand solution to react, and obtaining Co-ZIF-8; S2. dissolving the Co-ZIF-8 obtained in step S1 in an organic solvent, adding a solution of a palladium salt, and reacting to obtain Pd / Co-ZIF-8; S3. calcining the Pd / Co-ZIF-8 obtained in step S2 to obtain the palladium-cobalt bimetallic catalyst.

2. The preparation method according to claim 1, characterized in that: In step S1, the zinc salt is selected from one or more of Zn(NO3)2·6H2O, ZnSO4 and ZnCl2; the cobalt salt is selected from one or more of Co(NO3)2·6H2O, CoSO4 and CoCl2.

3. The preparation method according to claim 1, characterized in that: In step S1, the mass ratio of the cobalt salt to the zinc salt is (0.01-2):1, and the ratio of the total mass of the zinc salt and the cobalt salt to the volume of the organic solvent is (1-2) g:(40-150) mL.

4. The preparation method according to claim 1, characterized in that: In step S1, the ratio of the mass of the ligand to the volume of the organic solvent is (7-15) g: (80-160) mL.

5. The preparation method according to claim 1, characterized in that: In step S1, the volume ratio of the metal solution to the ligand solution is 1:(0.5-1.5).

6. The preparation method according to claim 1, characterized in that: In step S2, the ratio of the mass of the Co-ZIF-8 to the volume of the organic solvent is (0.1-0.4) g: (40-50) mL.

7. The preparation method according to claim 1, characterized in that: In step S2, the mass ratio of the palladium element in the palladium salt to Co-ZIF-8 is (0.25-3):

100.

8. The preparation method according to claim 1, characterized in that: In step S3, the calcination temperature is 600-950°C, and the calcination time is 2-6 hours.

9. A palladium-cobalt bimetallic catalyst prepared by the method according to any one of claims 1 to 8.

10. Use of the palladium-cobalt bimetallic catalyst according to claim 9 in the production of oils and fats in the fields of medicine, agriculture and chemical industry.

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