Preparation method of organic ligand modified bimetallic nanosheet catalyst for upgrading waste plastics

Abstract

The invention belongs to the technical field of catalyst preparation, and relates to an organic ligand modified metal catalyst, in particular to a preparation method of an organic ligand modified PdMn catalyst for upgrading waste plastics. The preparation method comprises the following steps: uniformly mixing metal precursors of palladium and cobalt with an organic solvent n-caprylic acid by adopting a wet chemical method, carrying out an oil bath reaction for a period of time, separating precipitates, and sequentially washing and drying to obtain the nano flaky PdMn catalyst. The preparation method disclosed by the invention is simple, few in steps and simple to operate. The prepared organic ligand modified PdMn catalyst has more excellent catalytic activity than a monometal Pd catalyst in electrocatalytic oxidation in ethylene glycol in an alkaline environment, and can be converted into a high-value product under the condition of PET hydrolysate.

Description

[Technical field]

[0001] The invention belongs to the technical field of catalytic materials, and in particular relates to research on an organic ligand-modified bimetallic catalyst for upgrading waste plastics and oxidizing alcohols. [Background technology]

[0002] In recent years, due to the excessive dependence on plastic products in human life, a large amount of waste plastics has caused white pollution and endangered human health. Polyethylene terephthalate (PET) is one of the most consumed polyester plastics, with an annual output of more than 70 million tons, most of which are in landfills or natural environments, highlighting the urgency of recycling. Therefore, the degradation and recycling of PET plastic waste have been widely studied. PET can be hydrolyzed into terephthalic acid (TPA) and ethylene glycol (EG) monomers under alkaline conditions. Electrochemical EG oxidation reaction (EGOR) is an important link in the electrocatalytic upgrading and recycling of plastics, and it provides a sustainable and attractive way for direct upgrading to value-added fine chemicals, with potential driving effect.

[0003] Electrocatalysts modified with organic ligands have attracted widespread attention. They have been shown to change the electronic properties of metals, optimize the energy of adsorbed substances, and improve the transfer of charge and mass. The spatial configuration and coordination mode of the ligand can affect the formation of intermediates and transition state structures in the catalytic reaction, thereby regulating the reaction pathways and steps. By introducing organic ligands, coordination bonds are formed with the metal central atom to adjust the electronic structure. Two-dimensional nanomaterials, with huge specific surface area and low-coordinated metal atoms, show advantages such as good electrical conductivity and are considered to be a very promising choice for electrocatalysts in the current field of electrocatalysis. Some studies have found that adding a small amount of non-precious metals (such as Cu, Ni, In) to Pd-based materials to form bimetallic materials can effectively change their electronic structure and improve performance.

[0004] The present invention synthesizes a unique nanosheet PdMn (PdMn O-NS) bimetallic catalyst modified by an organic ligand. The successful introduction of the Mn element and the modification of the organic ligand can effectively adjust the electronic state of Pd, and the unique structure of the nanosheet exposes more active sites, which is beneficial to the transmission of electrons. The PdMn bimetallic catalyst can effectively convert the PET derivative EG into high-value formic acid and glycolic acid. [Summary of the invention]

[0005] [Technical issues to be solved]

[0006] In view of the deficiencies in the prior art, the present invention provides a method for preparing a nano-sheet organic ligand-modified PdMn catalyst.

[0007] One purpose of the present invention is to uniformly mix metal precursors of palladium and manganese with an organic solvent of n-octanoic acid by a wet chemical method, and then react in an oil bath for a period of time to obtain an organic ligand-modified PdMn nanosheet catalyst.

[0008] Technical solution:

[0009] A method for synthesizing a nanosheet organic ligand-modified PdMn catalyst comprises the following steps:

[0010] 1. Weigh two metal precursors, di(acetylacetonate)palladium(II) and di(acetylacetonate)manganese, add an organic solvent, n-octanoic acid, and stir for 30 minutes using a rotary mixer, wherein the mass ratio of the palladium to manganese precursors is 1:0-3; and the volume of the organic solution is 8-10 ml.

[0011] 2. Add all the above mixtures into a 30ml glass bottle, then place it in an oil bath and react at 90-100℃ for 2-3h. After the reaction is completed, take it out and cool it naturally. Wash it with ethanol and n-hexane by centrifugation, collect the precipitate and dry it for later use.

[0012] Preferably, the mass ratio of palladium to manganese precursor described in 1 is 3:1.

[0013] 1, the aliphatic acid is preferably n-octanoic acid, and the volume is 8 ml.

[0014] Another object of the present invention is to upgrade waste plastics using the prepared nanosheet organic ligand-modified PdMn catalyst.

[0015] Electrocatalytic performance methods

[0016] The prepared catalyst is weighed and ultrasonically dispersed in a Nafion mixed solution, then dripped onto a glassy carbon electrode, and dried at room temperature to form an electrode, wherein the Nafion mixed solution is prepared from ultrapure water, ethanol, and a Nafion (5wt%) solution. A three-electrode electrochemical test system is constructed with the sheet-shaped binary metal catalyst dripped onto the glassy carbon electrode as a working electrode, a platinum sheet electrode as a counter electrode, and a Hg / HgO electrode as a reference electrode; the cyclic voltammogram of the test catalyst in an alkaline solution is measured; the performance of the test catalyst is tested in a hydrolyzate containing ethylene glycol and PET, and the organic ligand-modified PdMn nanosheet catalyst has better performance than the commercial Pd / C catalyst.

[0017] Compared with the prior art, the advantages and beneficial effects of the present invention are:

[0018] The preparation method of the invention is a one-step wet chemical synthesis method with simple operation. The organic ligands such as octanoic acid and carboxylic acid ligands and their electron-rich functional groups are beneficial to increase the charge density and change the coordination environment of adjacent metal sites. The conductivity and charge transfer in the electrocatalytic reaction are promoted, and the electronic structure at the potential point will also significantly affect the adsorption / desorption energy of the reaction intermediates, thereby improving the catalytic activity of the catalyst; the organic ligand-modified PdMn nanosheet catalyst prepared by the invention has excellent activity for the electrocatalytic oxidation of ethylene glycol and PET hydrolyzate in an alkaline environment, and has good application prospects in the upgrading of waste plastics.

Brief Description of the Drawings

[0019] Figure 1 This is the TEM image of the organic ligand modified PdMn nanosheet catalyst described in Example 1.

[0020] Figure 2 XRD patterns of PdMn O-NS and Pd samples.

[0021] Figure 3 This is the infrared analysis (FTIR) diagram of PdMn O-NS before testing.

[0022] Figure 4 Cyclic voltammograms of PdMn O-NS, Pd and Pd black in 1 mol / L KOH solution containing 1 mol / L ethylene glycol.

[0023] Figure 5 LSV diagrams of PdMn O-NS, Pd and Pd black in PET hydrolyzate solution.

[0024] Figure 6 For PdMn O-NS 1 H NMR spectrum.

[0025] Figure 7 This is the infrared analysis (FTIR) diagram of PdMn O-NS after testing. [Specific implementation method]

[0026] Combined with Figure 1-7 The present invention is further described with reference to the following examples.

[0027] Example 1

[0028] 1. Preparation of organic ligand-modified PdMn catalysts

[0029] Dissolve 7.5mg Pd(acac)2, 2.5mg Mn(acac)2 and 10mg Mo(CO)6 in 8ml octanoic acid and add to a 30ml glass bottle, stir for 30min. Then place in an oil bath and react at 90℃ for 2h. After the reaction is completed, take out and cool naturally. Wash by centrifugation with ethanol and n-hexane, collect the precipitate and dry it. After dispersing the sample with the mixed solution, drop it on the glassy carbon electrode and dry it to make an electrode.

[0030] Figure 1 This is a transmission electron microscope image of the PdMn O-NS catalyst in Example 1 of the present invention, showing an ultra-thin and curled sheet structure.

[0031] 2. Study on electrocatalytic oxidation of ethanol in alkaline environment

[0032] A three-electrode electrochemical test system was constructed with the PdMn O-NS catalyst dripped on the polished glassy carbon electrode as the working electrode, the platinum electrode as the counter electrode, and the Hg / HgO electrode as the reference electrode. The cyclic voltammogram of the test catalyst in a 1 mol / L KOH solution containing 1 mol / L ethylene glycol was obtained with a potential window of -0.6-0.6 V and a scan rate of 50 mV / s.

[0033] Example 2

[0034] 1. Preparation of Pd flake catalyst

[0035] A three-electrode electrochemical test system was constructed with the PdMn O-NS catalyst dripped on the polished glassy carbon electrode as the working electrode, the platinum electrode as the counter electrode, and the Hg / HgO electrode as the reference electrode. The cyclic voltammogram of the test catalyst in a 1 mol / L KOH solution containing 1 mol / L ethylene glycol was obtained with a potential window of -0.6-0.6 V and a scan rate of 50 mV / s.

[0036] 2. Study on electrocatalytic oxidation of ethylene glycol in alkaline environment

[0037] A three-electrode electrochemical test system was constructed with the Pd catalyst dripped on the polished glassy carbon electrode as the working electrode, the platinum electrode as the counter electrode, and the Hg / HgO electrode as the reference electrode. The cyclic voltammogram of the test catalyst in a 1 mol / L KOH solution containing 1 mol / L ethylene glycol was obtained with a potential window of -0.6-0.6 V and a scan rate of 50 mV / s.

[0038] Figure 2 The XRD diagrams of the flaky PdMn catalyst and the Pd catalyst described in Examples 1 and 2 of the present invention show that the PdMn catalyst is shifted compared to the Pd catalyst, indicating that the Mn element is successfully introduced.

[0039] Figure 3 This is the infrared analysis of the PdMn catalyst before testing, proving the presence of PdMn O-NS n-octanoic acid. Located at 3436.73 cm -1 and 1619.40cm -1 The nearby peaks are attributed to the OH and C=O stretching vibrations of octanoic acid. 2928.88, 1357.62cm -1 The peaks at 1110.11cm correspond to the stretching and bending vibration modes of CH3 and CH2, respectively. -1 The peak at belongs to the bending vibration mode of CC and OH. n - at 720.62cm -1 Therefore, the presence of n-octanoic acid can be clearly confirmed.

[0040] Figure 4 The cyclic voltammograms of different catalysts in 1 mol / L KOH solution containing 1 mol / L ethylene glycol are shown in Figure 1. It can be seen that the prepared PdMn catalyst can effectively catalyze the oxidation of ethylene glycol in an alkaline environment, and the maximum peak current density provided is 2.38 A / mg.

[0041] Figure 5 The LSV curves of different catalysts in PET hydrolysate are compared, proving that the PdMn catalyst has excellent catalytic activity.

[0042] Figure 6 PdMn catalyst before and after reaction 1 The H NMR spectrum proves that the catalyst can effectively oxidize and upgrade PET hydrolyzate into high-value products such as formic acid and glycolic acid (GA).

[0043] Figure 7 This is the infrared analysis of the PdMn catalyst after testing. The catalyst PdMn O-NS can effectively convert EG into GA and formic acid, so there is no long chain -(CH2) n - exists. But Figure 7 There are long chains of -(CH2) n -The presence of octanoic acid proves the effect of octanoic acid.

Claims

1. A method for preparing a PdMn nanosheet catalyst modified by an organic ligand, comprising the following steps: (1) Add di(acetylacetonate)palladium(II) and di(acetylacetonate)manganese to a solution of organic solvent n-octanoic acid and stir with a rotor for 30 min; (2) Then, the reaction mixture is placed in an oil bath; (3) After the solution obtained in step (2) is allowed to stand and cool, the precipitate is separated and washed and dried in sequence to obtain the flaky PdMn catalyst.

2. The method for preparing organic ligand-modified PdMn according to claim 1, characterized in that: The organic solvent of step (1) is 8-10 mL of n-octanoic acid.

3. The method for preparing organic ligand-modified PdMn sheet according to claim 1, characterized in that: The mass ratio of di(acetylacetonate)palladium(II) to di(acetylacetonate)manganese in step (1) is 1:0-3.

4. The method for preparing the organic ligand-modified PdMn catalyst according to claim 1, characterized in that: The oil bath temperature in step (2) is 90-100°C.

5. The method for preparing the organic ligand-modified PdMn catalyst according to claim 1, characterized in that: The reaction time of step (3) is 2-3h.

6. The organic ligand-modified PdMn nanosheet catalyst prepared according to the method of any one of claims 1 to 5.

7. The organic ligand-modified PdMn nanosheet catalyst according to claim 6, characterized in that: It has excellent catalytic activity under ethylene glycol conditions, and the maximum peak current density it provides is 2.38A / mg, far exceeding the Pd / C catalyst on the market.

8. The organic ligand-modified PdMn nanosheet catalyst according to claim 6, characterized in that: Under the conditions of PET hydrolysis, it can be oxidized into high-value products such as formic acid and glycolic acid.

9. The organic ligand-modified PdMn nanosheet catalyst according to claim 6, characterized in that: Infrared analysis of functional group long chain -(CH2) before and after testing n -Prove the effect of caprylic acid.

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