Palladium-based graphene catalyst, preparation method and application of palladium-based graphene catalyst in production of dimethyl carbonate

Abstract

The invention discloses a palladium-based graphene catalyst, a preparation method and application of the palladium-based graphene catalyst in production of dimethyl carbonate. The palladium-based graphene catalyst comprises a graphene carrier and loaded palladium nanoparticles, and nano tracks are distributed on the surface of the graphene carrier. The preparation method comprises the following steps: etching a nano track on a graphene sheet through a cyclic voltammetry method, and then depositing palladium nano particles through electrochemistry, so that nano palladium can be uniformly distributed in the track, and the palladium-based graphene catalyst is prepared. The palladium-based graphene catalyst can be used in a method for producing dimethyl carbonate (DMC) by catalyzing a gas-phase carbonylation reaction. According to the method, palladium-based graphene catalysis is used for replacing original PbCl2 catalysis for producing dimethyl carbonate.

Description

Technical Field

[0001] The invention relates to a palladium-based graphene catalyst and a preparation method thereof, and a method for producing dimethyl carbonate by catalyzing a gas-phase carbonylation reaction using the palladium-based graphene catalyst, belonging to an indirect gas-phase carbonylation preparation method of dimethyl carbonate. Background Art

[0002] There are many methods for preparing dimethyl carbonate, which is mainly prepared by indirect gas-phase carbonylation reaction, in which methanol and nitrogen oxides generate methyl nitrite, and methyl nitrite reacts with carbon monoxide to generate dimethyl carbonate. The traditional indirect gas-phase carbonylation reaction usually uses palladium chloride as a catalyst, which has many defects. For example, the "Progress in the Synthesis Technology of Dimethyl Carbonate" of Guangdong Chemical Industry in the 11th issue of 2023 pointed out: (1) The reaction conversion rate is low, less than 50%, and PbCl2 is easily reduced and deactivated by CO, so the product selectivity is not high, about 85%; (2) In order to prevent the situation (1), HCl is used as a protective agent for PbCl2, which has the risk of personnel poisoning; (3) The catalyst stability is poor, and the loss rate is as high as 20%. Summary of the invention

[0003] In view of the above problems existing in the prior art, one of the purposes of the present invention is to provide a palladium-based graphene catalyst and a preparation method, wherein nano-tracks are etched on a graphene sheet by cyclic voltammetry, and palladium nanoparticles are electrochemically deposited so that nano-palladium can be evenly distributed in the track to obtain a palladium-based graphene catalyst.

[0004] The second object of the present invention is to provide a method for producing dimethyl carbonate (DMC) by catalyzing a gas-phase carbonylation reaction using the above-mentioned palladium-based graphene catalyst, wherein the method uses palladium-based graphene catalysis to replace the original PbCl2 catalysis to produce dimethyl carbonate.

[0005] In order to achieve the above-mentioned invention object, the present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides a palladium-based graphene catalyst, wherein the palladium-based graphene catalyst comprises a graphene carrier and supported palladium nanoparticles, and nanotracks are distributed on the surface of the graphene carrier.

[0007] In a specific embodiment, based on the total mass of the palladium-based graphene catalyst, the content of the palladium nanoparticles is 15.8-27.2 wt %.

[0008] In a specific embodiment, the palladium nanoparticles are distributed in nanotracks etched on the surface of the graphene carrier; preferably, the palladium nanoparticles are loaded in the nanotracks distributed on the surface of the graphene carrier by electrochemical deposition.

[0009] In a specific embodiment, the particle size of the palladium nanoparticles is between 3 and 10 nm, and the average particle size is between 6 and 8 nm.

[0010] In a specific embodiment, the nanotracks on the surface of the graphene carrier have a track width of 8 to 13 nm and a track depth of 8 to 10 nm;

[0011] Preferably, the nanotracks distributed on the surface of the graphene carrier are obtained by etching using cyclic voltammetry.

[0012] In a second aspect, the present invention provides a method for preparing the palladium-based graphene catalyst, comprising the steps of:

[0013] 1) Etching nanotracks on the surface of graphene support by cyclic voltammetry;

[0014] 2) Using a solution containing a palladium source as an electrolyte, converting the palladium source into palladium nanoparticles by an electrochemical deposition method and loading the palladium nanoparticles on a graphene carrier to obtain the palladium-based graphene catalyst.

[0015] In a specific embodiment, the graphene carrier in step 1) is a graphene flake with a size of 2cm*2cm to 0.5cm*0.5cm and a thickness of 0.4 to 0.1mm.

[0016] In a specific embodiment, the cyclic voltammetry method in step 1) is performed in a three-electrode system using an electrochemical workstation;

[0017] The voltage range of the cyclic voltammetry is -0.05 to 0.4 V, the scan rate is 1 to 100 mV / s, and the number of cycles is 1 to 15;

[0018] Etching the substrate material by cyclic voltammetry in a three-electrode system is a method disclosed in the prior art, and the relevant conditions in the operation process are defined above. For other operation and process conditions in the cyclic voltammetry of the present invention, and the devices used, all can be selected according to the corresponding conventional methods in the art, and there is no special restriction on this; for example, in a specific application, the operation described in step 1) is to etch nanotracks on the surface of the graphene sheet by cyclic voltammetry after establishing a three-electrode system with the aid of an electrochemical workstation, with a voltage of 0.1V, a scanning speed of 25mV / s, and a scanning number of 11 circles as the best substrate. The morphology of the nanotracks etched on the surface of the graphene sheet can also be observed with the aid of an atomic force microscope (AFM).

[0019] In a specific embodiment, the solution containing a palladium source in step 2) has a palladium source concentration of 10.4 to 15.6 wt %, and the remaining component is water (such as ultrapure water);

[0020] Wherein, the palladium source is selected from soluble salts of palladium, preferably palladium chloride.

[0021] In a specific embodiment, the electrochemical deposition in step 2) is performed in a cyclic voltammetry mode, with a voltage range of -0.05 to -0.4 V, a scan rate of 1 to 100 mV / s, and a cycle number of 1 to 15;

[0022] Preferably, the electrochemical workstation used for electrochemical deposition is a Shanghai Chenhua electrochemical workstation; the process of loading active components on a carrier by electrochemical deposition is known in the art, and some relevant conditions in the operation process are defined above. For other operating and process conditions, and the devices used, technicians can obtain them by conventional selection based on existing technologies; in a specific application, the operation described in step 2) is to use a graphite carrier as a working electrode, Pt as a counter electrode, and Pb / Pb 2+ As a reference electrode, a solution containing a palladium source is used as an electrolyte, and an electrochemical workstation is used to perform electrochemical deposition on the working electrode. The palladium source is converted into palladium nanoparticles with a particle size distribution between 3 and 10 nm and an average particle size of 6 to 8 nm. The particles are loaded in the nanotracks of the graphene carrier without obvious agglomeration.

[0023] In a third aspect, the present invention provides applications of the palladium-based graphene catalyst.

[0024] The palladium-based graphene catalyst described in the present invention is the palladium-based graphene catalyst described above, or the palladium-based graphene catalyst prepared by the method described above, which can be used as a carbonylation reaction catalyst, a hydrogenation reaction catalyst, a photosynthetic reaction catalyst, etc., and is particularly suitable for catalyzing gas-phase carbonylation reaction to produce dimethyl carbonate (DMC). This method uses the palladium-based graphene catalyst of the present invention to replace the original PbCl2 to catalyze the production of dimethyl carbonate.

[0025] The above-mentioned method for preparing dimethyl carbonate by gas phase carbonylation can adopt existing technology and carry out ammoxidation reaction through a conventional reactor in the art. For example, the reactor used can be a fluidized bed reactor or a fixed bed reactor.

[0026] Specifically, a method for producing dimethyl carbonate by gas phase carbonylation reaction, the method using the palladium-based graphene catalyst of the present invention, the steps comprising:

[0027] A palladium-based graphene catalyst is added to the reactor, and then carbon monoxide and methyl nitrite are added for gas phase carbonylation reaction to produce dimethyl carbonate. The feed volume ratio of the raw material carbon monoxide to methyl nitrite is 1:2.5-6.9 (unit: Nm 3 / h);

[0028] The carbonylation reaction temperature is 105-115°C, and the reaction pressure is 0.7-0.8MPaG;

[0029] In the above method, the methyl nitrite (MN) raw material is prepared by the MN generation system using nitric oxide as the starting raw material, specifically, oxygen and NO react in an oxygen mixer to produce nitrogen oxides, which then react with methanol gas to produce MN. This process is a known process in the prior art and the present invention has no special requirements for this.

[0030] In the above method, after the gas phase carbonylation reaction is completed, a liquid phase separation operation is further included, specifically, a mixed solution of methanol and dimethyl oxalate is used to absorb the gas phase product to obtain a mixed solution containing dimethyl carbonate (DMC);

[0031] Preferably, in the mixed solution of methanol and dimethyl oxalate, the mixing mass ratio of the two is 1:1-6.

[0032] In the above method, after the completion of the gas phase carbonylation reaction, a catalyst separation operation is also included, which is a conventional solid-liquid separation operation in the field. For example, the solid catalyst can be separated by immersing it in ultrapure water for 24 hours using a precipitation method. The separated catalyst of the present invention can be directly recycled.

[0033] In the present invention, ultra-sensitive gas flow measurement and Raman spectroscopy were used for verification, and it was found that the etched nano-track pattern palladium-based graphene catalyst had a positive effect on the gas-phase carbonylation chemical reaction. After the catalyst was reused three times in a row, it still maintained a high catalytic activity without obvious reduction.

[0034] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0035] Nano-tracks are etched on the graphene surface by cyclic voltammetry, and palladium nanoparticles are then electrochemically deposited so that nano-palladium can be evenly distributed in the tracks to produce a palladium-based graphene catalyst.

[0036] The catalyst is used to directional catalyze the gas-phase carbonylation reaction to produce DMC, which can improve the reaction conversion rate and product selectivity; the method no longer requires HCl as a catalyst protective agent, which can reduce the risk of personnel poisoning; it has the advantages of improved stability, not easy to lose activity, and extended service life; it is suitable for batch reactions and can be used repeatedly. DETAILED DESCRIPTION

[0037] The present invention is further described below in conjunction with embodiments, but the present invention is not limited to the listed embodiments, and should also include equivalent improvements and modifications of the technical solutions defined in the claims attached to the present application.

[0038] Unless otherwise specified, the reagents, materials and instruments used in the following examples are conventional reagents, conventional materials and conventional instruments in the art and can be obtained commercially. The reagents involved can also be synthesized by conventional methods in the art.

[0039] Reagents:

[0040] Graphene carrier: 0.4 mm thick, 99% pure, purchased from Hefei Microcrystalline Material Technology Co., Ltd.

[0041] Methyl nitrite (MN): prepared by MN generation system, 1.2 Nm 3 / h oxygen and 8.3Nm 3 / h of NO reacts in the oxygen mixer to produce nitrogen oxides which are then introduced into the MN generating tower. 15 kg / h of methanol is introduced from the top of the tower to react with the gas phase to produce MN for standby use.

[0042] instrument:

[0043] Ocean Optics QE 65Pro Raman spectrometer, B&W TEK laser probe, Ruhai Optoelectronics laser, Shanghai Chenhua electrochemical workstation (C HI660E 413489c);

[0044] Atomic force microscopy (AFM) was used to scan the nano-track morphology on the surface of graphene sheets to determine their size.

[0045] Example 1

[0046] Preparation of palladium-based graphene catalyst:

[0047] 1) A three-electrode system was established in an electrochemical workstation, and nanotracks were etched on the surface of a 2cm*2cm*0.4mm graphene sheet using cyclic voltammetry at a voltage of -0.1V, a scanning speed of 25mV / s, and 11 scanning circles;

[0048] 2) Using graphite flakes as working electrodes, Pt as counter electrodes, and Pb / Pb 2+ As a reference electrode, a solution of 9wt% palladium chloride and ultrapure water was used as the electrolyte, and an electrochemical workstation was used to perform electrochemical deposition on the working electrode. The mode was cyclic voltammetry. The voltage range used was -0.1V, the scanning rate was 25mV / s, and the number of cycles was 11. The palladium nanoparticles were loaded on the surface of the graphene carrier without obvious agglomeration, thereby obtaining a palladium-based graphene catalyst.

[0049] The palladium-based graphene catalyst prepared in this embodiment has a palladium nanoparticle content of 27.2 wt %, a particle size between 3 and 10 nm, and an average particle size of 6 nm.

[0050] The nanotracks on the surface of the graphene carrier have a track width of 8-11nm and a track depth of 8-10nm.

[0051] Example 2

[0052] Preparation of palladium-based graphene catalyst:

[0053] 1) A three-electrode system was established in an electrochemical workstation, and cyclic voltammetry was used to etch nanotracks on the surface of a 1 cm*1 cm*0.4 mm graphene sheet at a voltage of -0.05 V, a scanning speed of 50 mV / s, and a scanning number of 1 circle;

[0054] 2) Using graphite flakes as working electrodes, Pt as counter electrodes, and Pb / Pb 2+ As a reference electrode, a solution of 9wt% palladium chloride and ultrapure water was used as the electrolyte, and an electrochemical workstation was used to perform electrochemical deposition on the working electrode. The mode was cyclic voltammetry. The voltage range used was -0.05V, the scanning rate was 50mV / s, and the number of cycles was 1. The palladium nanoparticles were loaded on the surface of the graphene carrier without obvious agglomeration, thereby obtaining a palladium-based graphene catalyst.

[0055] The palladium-based graphene catalyst prepared in this embodiment has a palladium nanoparticle content of 24.4 wt %, a particle size of 3 to 10 nm, and an average particle size of 7 nm. The nanotracks on the surface of the graphene carrier have a track width of 8 to 13 nm and a track depth of 9 to 10 nm.

[0056] Example 3

[0057] Preparation of palladium-based graphene catalyst:

[0058] 1) A three-electrode system was established in an electrochemical workstation, and cyclic voltammetry was used to etch nanotracks on the surface of a 5 mm*5 mm*0.1 mm graphene sheet at a voltage of -0.4 V, a scanning speed of 100 mV / s, and 15 scanning circles;

[0059] 2) Using graphite flakes as working electrodes, Pt as counter electrodes, and Pb / Pb 2+ As a reference electrode, a solution of 9wt% palladium chloride and ultrapure water was used as the electrolyte, and an electrochemical workstation was used to perform electrochemical deposition on the working electrode. The mode was cyclic voltammetry. The voltage range used was -0.4V, the scanning rate was 100mV / s, and the number of cycles was 15. The palladium nanoparticles were loaded on the surface of the graphene carrier without obvious agglomeration, thereby obtaining a palladium-based graphene catalyst.

[0060] The palladium-based graphene catalyst prepared in this embodiment has a palladium nanoparticle content of 20.2 wt %, a particle size of 3 to 10 nm, and an average particle size of 8 nm. The nanotracks on the surface of the graphene carrier have a track width of 8-11 nm and a track depth of 8-10 nm.

[0061] Example 4

[0062] Preparation of dimethyl carbonate by gas phase carbonylation reaction:

[0063] Weigh 5 kg of palladium-based graphene catalyst (prepared in Example 1) and place it in a closed reactor. Replace with nitrogen and keep the pressure in the reactor at 0.7 MPa. Raise the temperature to 110 ± 5 °C and introduce 10 Nm 3 / h MN generating tower gas and 2.2Nm 3 / h of CO was used for carbonylation reaction. Samples were taken for testing after 4 hours. The conversion rate was 92.2% and the selectivity was 85.7%.

[0064] The gaseous product was absorbed by a methanol and dimethyl oxalate solution in a mass ratio of 1:1 to obtain a mixed solution containing dimethyl carbonate, wherein the DMC content was 94.2 wt%.

[0065] The reaction was terminated after a total of 14 hours of operation, and the catalyst was separated and reused in the gas-phase carbonylation reaction to prepare dimethyl carbonate. After repeating the above operation three times, sampling was performed for testing, and the conversion rate was 89.7% and the selectivity was 85.2%. The mixed solution containing dimethyl carbonate had a DMC content of 95.2%.

[0066] Example 5

[0067] Preparation of dimethyl carbonate by gas phase carbonylation reaction:

[0068] 10 kg of palladium-based graphene catalyst (prepared in Example 2) was weighed and placed in a closed reactor. The reactor was replaced with nitrogen to maintain the pressure at 0.7 MPa. The temperature was raised to 110 ± 5 °C and 20 Nm 3 / h MN generating tower gas and 8Nm 3 / h of CO was used for carbonylation reaction. Samples were taken for testing after 4 hours. The conversion rate was 97.4% and the selectivity was 96.2%.

[0069] The gas product was absorbed by using a methanol and dimethyl oxalate solution with a mass ratio of 1:1 to obtain a mixed solution containing dimethyl carbonate, wherein the DMC content was 95.4 wt%.

[0070] The reaction was terminated after a total of 14 hours of operation, and the catalyst was separated and reused in the gas-phase carbonylation reaction to prepare dimethyl carbonate. After repeating the above operation three times, sampling was performed for testing, and the conversion rate was 96.5% and the selectivity was 93.2%. The mixed solution containing dimethyl carbonate had a DMC content of 92.4%.

[0071] Example 6

[0072] Preparation of dimethyl carbonate by gas phase carbonylation reaction:

[0073] 15 kg of palladium-based graphene catalyst (prepared in Example 3) was weighed and placed in a closed reactor. The reactor was replaced with nitrogen to maintain the pressure at 0.7 MPa. The temperature was raised to 110 ± 5 °C and 30 Nm 3 / h MN generating tower gas and 10Nm 3 / h of CO was used for carbonylation reaction. Samples were taken for testing after 4 hours. The conversion rate was 96.2% and the selectivity was 98.3%.

[0074] The gas product was absorbed by using a methanol and dimethyl oxalate solution with a mass ratio of 1:1 to obtain a mixed solution containing dimethyl carbonate, wherein the DMC content was 95.2 wt%.

[0075] The reaction was terminated after a total of 14 hours of operation, and the catalyst was separated and reused in the gas-phase carbonylation reaction to prepare dimethyl carbonate. After repeating the above operation three times, sampling was performed for testing, and the conversion rate was 95.4% and the selectivity was 97.1%. The mixed solution containing dimethyl carbonate had a DMC content of 94.8%.

[0076] Comparative Example 1

[0077] (1) Weigh 5 kg of palladium chloride catalyst and place it in a closed reactor, replace it with nitrogen to 99.9% and the pressure is 0.7 MPa;

[0078] (2) After step (1), the preheater is put into the reactor to raise the temperature of the reactor to 110±5°C, and the reactor is automatically heated;

[0079] (3) After step (2), add 10 Nm 3 / h MN generating tower gas and 2.2Nm 3 / h of CO, and introduce 0.022Nm 3 / h HCl was used as the protective gas for the catalyst PbCl2 to carry out carbonylation reaction; after 4 hours, the sample was taken for testing, and the conversion rate was 50.1% and the selectivity was 87.2%;

[0080] (4) After step (3), the generated mixed gas is dissolved in a 1:1 methanol and dimethyl oxalate solution to obtain a mixed solution containing dimethyl carbonate, wherein the DMC content is 43.8%.

[0081] The reaction was terminated after a total of 14 hours of operation, and the catalyst was separated and reused in the gas-phase carbonylation reaction to prepare dimethyl carbonate. After repeating the above operation three times, sampling was performed for testing, and the conversion rate was 62.1% and the selectivity was 82.9%. The mixed solution containing dimethyl carbonate had a DMC content of 45.6%.

[0082] Comparative Example 2

[0083] In the method of Example 1, step 1) etching nanotracks by cyclic voltammetry is omitted, and the untreated graphene sheet is directly used in step 2) electrochemical deposition of palladium nanoparticles to prepare a catalyst.

[0084] The catalyst prepared in this comparative example was used as the catalyst in Example 4, and other operations remained unchanged. After 4 hours, sampling was performed and the conversion rate was 10.3% and the selectivity was 20.2%. A mixed solution containing dimethyl carbonate was obtained, in which the DMC content was 4.2%.

[0085] After the catalyst was reused three times, samples were taken for testing, and the conversion rate was 11.6%, and the selectivity was 18.7%; the mixed solution contained dimethyl carbonate, in which the DMC content was 5.6%.

[0086] Comparative Example 3

[0087] The catalyst was prepared by referring to the method of Example 1, except that the graphene sheet was replaced by a silver sheet of the same size and other operations remained unchanged.

[0088] The catalyst prepared in this comparative example was used as the catalyst in Example 4, and other operations remained unchanged. After 4 hours, sampling was performed and the conversion rate was 14.7% and the selectivity was 20.4%. A mixed solution containing dimethyl carbonate was obtained, in which the DMC content was 23.8%.

[0089] After the catalyst was reused three times, sampling was performed and the conversion rate was 15.8% and the selectivity was 27.1%. The mixed solution contained dimethyl carbonate, in which the DMC content was 25.6%.

Claims

1. A palladium-based graphene catalyst, characterized in that: The palladium-based graphene catalyst comprises a graphene carrier and supported palladium nanoparticles, and nano-tracks are distributed on the surface of the graphene carrier; Preferably, based on the total mass of the palladium-based graphene catalyst, the content of the palladium nanoparticles is 15.8-27.2 wt %.

2. The palladium-based graphene catalyst according to claim 1, characterized in that The palladium nanoparticles are distributed in nanotracks on the surface of the graphene support; Preferably, the palladium nanoparticles are loaded in nanotracks distributed on the surface of the graphene carrier by electrochemical deposition; and / or The particle size of the palladium nanoparticles is between 3 and 10 nm, and the average particle size is between 6 and 8 nm.

3. The palladium-based graphene catalyst according to claim 1 or 2, characterized in that The nano-tracks on the surface of the graphene carrier have a track width of 8 to 11 nm and a track depth of 8 to 10 nm; and / or The nano-tracks distributed on the surface of the graphene carrier are obtained by etching through cyclic voltammetry.

4. A method for preparing a palladium-based graphene catalyst according to any one of claims 1 to 3, characterized in that the steps include: 1) Etching nanotracks on the surface of graphene support by cyclic voltammetry; 2) Using a solution containing a palladium source as an electrolyte, converting the palladium source into palladium nanoparticles by an electrochemical deposition method and loading the palladium nanoparticles on a graphene carrier to obtain the palladium-based graphene catalyst.

5. The preparation method according to claim 4, characterized in that: Step 1) The graphene carrier is a graphene sheet with a size of 2cm*2cm to 0.5cm*0.5cm and a thickness of 0.4 to 0.1mm; and / or The cyclic voltammetry in step 1) is performed in a three-electrode system using an electrochemical workstation; Preferably, the voltage range of the cyclic voltammetry is -0.05 to 0.4 V, the scan rate is 1 to 100 mV / s, and the number of cycles is 1 to 15.

6. The preparation method according to claim 4, characterized in that: Step 2) the solution containing a palladium source, wherein the palladium source concentration is 10.4-15.6 wt %, and the remaining component is water; Preferably, the palladium source is selected from a soluble salt of palladium, more preferably palladium chloride; and / or In step 2), the electrochemical deposition is carried out in a cyclic voltammetry mode, with a voltage range of -0.05 to -0.4 V, a scan rate of 1 to 100 mV / s, and a cycle number of 1 to 15 circles.

7. The palladium-based graphene catalyst according to any one of claims 1 to 3, or the palladium-based graphene catalyst prepared by the method according to any one of claims 4 to 6, is used as a carbonylation reaction catalyst, a hydrogenation reaction catalyst, or a photosynthetic reaction catalyst, and is particularly suitable for catalyzing gas-phase carbonylation reaction to produce dimethyl carbonate.

8. A method for producing dimethyl carbonate by gas phase carbonylation reaction, characterized in that: The method uses the palladium-based graphene catalyst according to any one of claims 1 to 3, or the palladium-based graphene catalyst prepared by the method according to any one of claims 4 to 6, and the steps include: A palladium-based graphene catalyst is added into the reactor, and then carbon monoxide and methyl nitrite are added to carry out a gas-phase carbonylation reaction to obtain dimethyl carbonate.

9. The method according to claim 8, characterized in that The feed volume ratio of carbon monoxide to methyl nitrite is 1:2.5-6.9; and / or The carbonylation reaction has a temperature of 105-115°C and a reaction pressure of 0.7-0.8 MPaG.

10. The method according to claim 8, characterized in that After the gas phase carbonylation reaction is completed, a liquid phase separation operation is performed, specifically, a mixed solution of methanol and dimethyl oxalate is used to absorb the gas phase product to obtain a mixed solution containing dimethyl carbonate; Preferably, in the mixed solution of methanol and dimethyl oxalate, the mixing mass ratio of the two is 1:1-6.