CN106582763A - Catalyst, preparation method thereof and application in preparation of oxalate - Google Patents

Abstract

The invention discloses a catalyst, a preparation method thereof and application in preparation of oxalate. The catalyst comprises a carrier and an active ingredient, and is characterized in that the carrier comprises nitrogen doped graphene nano-sheets, and the active ingredient comprises nano-palladium. The content of the active ingredient palladium in the catalyst is 0.03-2wt%, and the defects of high loading capacity of precious metals, low space time yield of oxalate and the like in production of an oxalate catalyst through CO coupling in the prior art are overcome when the catalyst is used in a CO coupling oxalate production technology.

Description

A kind of catalyst, its preparation method and the application in preparation oxalate

technical field

The application relates to a catalyst, its preparation method and its application in the preparation of oxalate, belonging to the field of chemistry and chemical industry.

Background technique

Oxalate is an important organic chemical raw material and is widely used in the preparation of various important chemical products, such as hydrolysis of oxalate to obtain oxalic acid, ammoniation to obtain oxamide, and hydrogenation to prepare ethylene glycol. CO gas-phase oxidative coupling to oxalate (2CO+2RONO→(COOR)2+2NO) is a key step in "coal to ethylene glycol" and has important industrial application value. In addition, this process also has important application prospects in industrial tail gas treatment. Many industrial tail gases contain a large amount of CO, which is currently mainly treated by combustion. If the CO in the tail gas is collected and converted into oxalate with high added value, it can not only achieve energy saving and emission reduction, but also make full use of resources and solve environmental problems.

Ethylene glycol is an important organic chemical raw material and strategic material, mainly used in the production of polyester, fiber, explosives, and can be used as antifreeze, plasticizer and solvent, etc. Wide range of uses. The world's annual demand for ethylene glycol is more than 25 million tons. The traditional ethylene glycol production method is mainly the petroleum route. The cost of ethylene glycol produced by this technical route is relatively high, mainly due to the high oil price and the lack of oil resources. my country's relatively rich coal resources and lack of oil and gas determine that the technical route and industrial application of coal-to-ethylene glycol have important strategic significance and economic value. Coupling of CO to oxalate is a key step in the conversion of inorganic C1 to organic C2 in coal-to-ethylene glycol technology. The process has the advantages of atom economy, mild reaction conditions, low energy consumption, environmental friendliness, low equipment investment and good product quality. Palladium-based catalysts have proven to be active catalysts for this process. Most of the catalysts reported so far use α-A1 ₂ O ₃ or other metal oxides as supports, while highly efficient palladium-based catalysts prepared on carbon material supports are seldom reported. The industrially used catalyst Pd/α-Al ₂ O ₃ has a relatively high loading of Pd (about 2 wt%), which greatly increases the cost of the catalyst for the production of ethylene glycol.

Therefore, using a carrier with a larger specific surface area, enhancing the interaction between the carrier and the catalyst, improving the performance of the catalyst, and reducing the loading of noble metals are of great significance for improving the production efficiency of oxalate and reducing the cost of coal-to-ethylene glycol.

Contents of the invention

According to one aspect of the present application, a nitrogen-doped graphene nanosheet-supported palladium high-efficiency catalyst is provided, the content of the active component palladium in the catalyst is 0.03-2wt%, and it is used in the CO coupling production process of oxalate, CO The conversion rate per pass is as high as 68%, the selectivity of oxalate is 97%, and the space-time yield of oxalate is 1.46g·g ^-1 (cat)·h ^-1 (space velocity is 3L·g ^-1 ·h ^-1 ) It overcomes the disadvantages of high noble metal loading and low space-time yield of oxalate when the catalyst used in the CO coupling production process of oxalate in the prior art uses α-alumina as a carrier.

The catalyst includes a carrier and an active component, wherein the carrier includes nitrogen-doped graphene nanosheets, and the active component includes nano-palladium.

Preferably, the mass percentage of the nano-palladium in the catalyst is 0.03-2wt%. Further preferably, the mass percentage of the nano-palladium in the catalyst is 0.18-0.71wt%.

Preferably, the average particle diameter of the nano-palladium is 1-9 nm. Further preferably, the average particle diameter of the nano-palladium is 1-5 nm.

Preferably, the atomic percent content of nitrogen in the nitrogen-doped graphene nanosheets is 1-7 at%. Further preferably, the atomic percentage of nitrogen in the nitrogen-doped graphene nanosheets is 2-7 at%.

Preferably, the nitrogen-doped graphene nanosheets have a thickness of 0.8-30 nm.

According to another aspect of the present application, there is provided a method for preparing any of the above-mentioned catalysts, at least comprising the following steps:

a) placing the graphene nanosheets in an _NH3 atmosphere and keeping them at 400-800° C. for no less than 3 hours to obtain nitrogen-doped graphene nanosheets;

b) Place the nitrogen-doped graphene nanosheets obtained in step a) in a solution containing palladium, and after ultrasonic treatment, separate to obtain a solid phase;

c) After the solid phase obtained in step b) is washed, dried and calcined, it is placed in an atmosphere containing a reducing gas and reduced for at least 2 hours at a reducing temperature of 150 to 450° C. At room temperature, the catalyst is obtained.

The graphene nanosheets in step a) can be purchased from commercial sources, or can be prepared by electrochemical methods.

As an embodiment, the graphene nanosheets are prepared by an electrochemical method. Preferably, said preparation of graphene nanosheets by electrochemical method at least comprises the following steps:

With the graphite source as the cathode and anode, sulfuric acid and/or sulfate solution as the electrolyte, the graphite source as the electrode is electrochemically ground by applying a voltage of 5 to 60V in square wave, AC and DC modes, and further ultrasonicated, filtered, washing and vacuum drying to obtain graphene nanosheets.

As an embodiment, the graphite source is selected from graphite rods and/or graphite papers.

As a preferred embodiment, the sulfate is selected from at least one of lithium sulfate, sodium sulfate, and ammonium sulfate.

As a preferred embodiment, the preparation of graphene nanosheets by electrochemical method at least includes the following steps:

(1) A two-electrode system is adopted, with high-purity graphite paper as the anode and cathode, followed by cleaning with 0.1mol/L hydrochloric acid, acetone, ethanol, ultrapure water, etc.

(2) Use 0.5-3mol/L ammonium sulfate solution as the electrolyte.

(3) Using the square wave potential method, the upper limit is 5～60V, the lower limit is -60～-5V, and the frequency is 0.1～50Hz, the graphite paper used as the electrode is electrolyzed, and the graphene nanosheet suspension is obtained by sulfate radical intercalation expansion and stripping.

(4) The graphene nanosheet suspension is further ultrasonicated, filtered, washed, and vacuum dried to obtain the graphene nanosheet.

Preferably, in step a), the graphene nanosheets are placed in a tube furnace, and kept in an NH ₃ atmosphere at 400-800° C. for 3-5 hours to obtain nitrogen-doped graphene nanosheets.

Preferably, the ultrasonic treatment in step b) is stirring in ultrasonic for 2-18 hours.

Preferably, the solution containing palladium in step b) is obtained by dissolving a palladium source in a solvent. Further preferably, the palladium source is selected from palladium chloride, palladium acetate, potassium chloropalladate, sodium chloropalladate, potassium chloropalladate, dichlorodiammine palladium, dichlorotetraammine palladium, palladium nitrate, acetyl At least one of palladium acetone. Still further preferably, the solvent is at least one selected from water, acetone, methylene chloride, chloroform, methanol, ethanol, cyclohexane, dimethylformamide, benzene, and toluene.

Preferably, step c) is that the solid phase obtained in step b) is washed, dried, and calcined, and then placed in an atmosphere containing reducing gas at a reducing temperature of 150-450°C for 2-8 hours, and then the solid phase containing reducing gas The catalyst is obtained by cooling down to room temperature in a gas atmosphere.

Preferably, the atmosphere containing the reducing gas in step c) is selected from hydrogen, a mixture of hydrogen and an inert gas. Further preferably, the inert gas is nitrogen and/or argon.

According to another aspect of the present application, there is provided a method for preparing oxalate, characterized in that, using at least one of the above-mentioned arbitrary catalysts and/or at least one of the catalysts prepared according to the above-mentioned arbitrary methods, through carbon monoxide Gas-phase oxidative coupling to produce oxalate.

Preferably, the gas-phase oxidative coupling of carbon monoxide to produce oxalate is in a fixed-bed reactor, the raw material gas containing carbon monoxide and nitrite is contacted with the catalyst, and the reaction pressure is normal pressure and the reaction temperature is 90-150 Under the condition of ℃, gas phase reaction prepares oxalate ester;

In the raw material gas, the volume ratio of carbon monoxide to nitrite is 1.1-1.8;

The gas phase space velocity of the raw material gas is 2-5 L·g ^-1 ·h ^-1 .

Preferably, the nitrite is methyl nitrite and/or ethyl nitrite; the oxalate is dimethyl oxalate and/or diethyl oxalate.

The beneficial effects of this application include but are not limited to:

1. The catalyst provided by this application uses electrochemically exfoliated and nitrogen-doped graphene nanosheets as a carrier. The carrier has the advantages of large specific surface area and good thermal conductivity; in addition, the modification of nitrogen changes the graphene nanosheets. The electronic structure enhances the basicity of graphene nanosheets, enhances the interaction between the carrier and the active component, and improves the performance of the supported catalyst.

2. The palladium loading of the noble metal in the catalyst provided by this application is as low as 0.03-2wt%, usually lower than 0.8wt% of the mass of the carrier, which can save a lot of precious metals and significantly reduce the cost of the catalyst.

3. The preparation method of the catalyst provided by this application does not need to use any surfactant. The surface of the active component palladium nanoparticles in the catalyst is clean, the size is small, the particle size distribution is uniform, and it is highly dispersed on the surface of the carrier graphene nanosheets, significantly Enhanced CO oxidative coupling catalytic performance.

4. The method for preparing oxalate provided by this application uses the catalyst described in this application to produce oxalate through gas-phase oxidation coupling of carbon monoxide; the single-pass conversion rate of CO is as high as 68%, and the selectivity of oxalate is 97%. The space-time yield of the ester is 1.46g·g ^-1 (cat)·h ^-1 (space velocity is 3L·g ^-1 ·h ^-1 ).

Description of drawings

Figure 1 is a scanning electron microscope image of graphene nanosheet GNP.

Fig. 2 is a transmission electron microscope image of the catalyst sample CAT-1.

3 is a transmission electron microscope image of the Pd/GNP catalyst prepared in Comparative Example 1.

detailed description

The present application will be described in detail below in conjunction with the embodiments and drawings, but the present application is not limited to these embodiments.

In the embodiment, the scanning electron microscope photos were taken with JEOL-6700F instrument of Hitachi Corporation.

In the embodiment, the transmission electron microscope is taken with a TECNAI F20 instrument of FEI Company of the United States.

In an embodiment, the N content in the sample adopts the ESCA-LAB type X-ray photoelectron spectroscopy (abbreviated as XPS) of British VG Scienta Company to measure; the Pd content adopts the Ultima2 type inductively coupled plasma emission spectrum (abbreviated as ICP ) determination.

In the examples, graphite paper was purchased from Jixing Sheng'an Industry and Trade Co., Ltd.

In the embodiment, the evaluation of the catalyst is carried out on a GC2014 gas chromatograph of Shimadzu Corporation of Japan by monitoring and analyzing the feed gas and product on-line gas chromatograph.

Unless otherwise specified, the reagents used in the examples were purchased commercially without any treatment; the instrument parameters were set according to the manufacturer’s recommendations.

Embodiment 1 Catalyst sample preparation

Preparation of graphene nanosheets

A two-electrode system is adopted, with high-purity graphite paper as the anode and cathode, followed by cleaning with 0.1mol/L hydrochloric acid, acetone, ethanol, and ultrapure water; 1mol/L ammonium sulfate solution as the electrolyte. Using the square wave potentiometric method, the upper limit is 9V, the lower limit is -9V, and the frequency is 10 Hz, the graphite electrode is electrolyzed, and the graphene nanosheet suspension is obtained through sulfate radical intercalation expansion and stripping, and the graphene nanosheet suspension is ultrasonically filtered, washed, After vacuum drying, graphene nanosheets are obtained, which are denoted as GNPs.

Preparation of nitrogen-doped graphene nanosheets

The graphene nanosheet GNP obtained above is placed in a tube furnace, and at nitrogen doping temperature, feeds ammonia gas for a period of time (nitrogen doping time ₎ , and then is cooled to room temperature under N atmosphere, to obtain Nitrogen-doped graphene nanosheets, denoted as N-GNPs.

The relationship between the sample number and the doping temperature of the obtained nitrogen-doped graphene nanosheets is shown in Table 1.

Table 1

Catalyst sample preparation

When the solvent is an organic solvent in the solution containing palladium: Weigh 1 g of the above-prepared nitrogen-doped graphene nanosheets as a carrier and impregnate them into the solution containing palladium, disperse ultrasonically for a period of time, then heat and ultrasonically at 50°C Until the solvent evaporates to dryness, a solid phase is obtained. Further calcining at 400° C. for 3 h in a N ₂ atmosphere, and finally reducing at a reducing temperature for a period of time in an atmosphere containing a reducing gas, the catalyst sample is prepared.

When the solution containing palladium contains water in the solvent: Weigh 1g of the above-prepared nitrogen-doped graphene nanosheets as a carrier and immerse them in the solution containing palladium, ultrasonically disperse for a period of time, stir for 8h, and centrifuge to obtain a solid phase , washed three times with deionized water, and dried in vacuum at 80°C for 8 hours. Further calcining at 400° C. for 3 h in a N ₂ atmosphere, and finally reducing at a reducing temperature for a period of time in an atmosphere containing a reducing gas, the catalyst sample is prepared.

The relationship between the number of the obtained catalyst sample and the sample number of the selected nitrogen-doped graphene nanosheets, the solution containing palladium, the ultrasonic dispersion time, the composition of the atmosphere containing the reducing gas, the reduction temperature, and the reduction time is shown in Table 2.

Table 2

Comparative example 1

Preparation of catalyst Pd/GNP: Weigh 1 g of the GNP carrier prepared according to Example 1 and immerse it in a solution made of 23.4 mg of palladium acetate and 20 mL of acetone, ultrasonically disperse for 2 hours, then heat and ultrasonicate at 50°C until the acetone evaporates to dryness. A solid mixture was obtained. It was further calcined at 400°C for 3h in N ₂ atmosphere, and finally reduced with hydrogen at 300°C for 2h to prepare the catalyst Pd/GNP. The palladium loading was determined to be 0.62 wt% by ICP.

Example 2 Sample Characterization

The nitrogen doping amount in the nitrogen-doped graphene nanosheet samples N-GNP-1-N-GNP-3 was measured by XPS, and the results are shown in Table 1.

The loading capacity of palladium in the catalyst samples CAT-1 to CAT-7 was measured by ICP, and the results are shown in Table 2.

The scanning electron microscope photo of the graphene nanosheet GNP is shown in Figure 1; it can be seen from the figure that the GNP is a nanosheet with a thickness of 0.8-30 nm and a size of 1-15 μm.

Catalyst samples CAT-1~CAT-7 were characterized by transmission electron microscopy. The results showed that nitrogen doping greatly improved the dispersion of active component palladium. Taking sample CAT-1 as a typical representative, its transmission electron microscope photo is shown in Figure 2. It can be seen from Figure 2 that palladium nanoparticles are highly dispersed on the surface of nitrogen-doped graphene nanosheets, and the particle size distribution of Pd particles is uniform and average. The particle size is 3.6nm.

The comparison sample Pd/GNP was characterized by transmission electron microscopy, and the results are shown in FIG. 3 . It can be seen from the figure that the Pd nanoparticles are highly dispersed on the surface of the carrier. Compared with the sample CAT-1, the size of the nanoparticles is larger (average particle diameter 6.2nm), and the particle size distribution is less uniform.

Embodiment 3 catalyst sample is used for the reaction evaluation of preparing oxalic acid ester

The catalyst samples CAT-1~CAT-7 and the comparative sample Pd/GNP were respectively placed in a fixed-bed reactor and applied to the gas-phase oxidative coupling of CO to prepare oxalate. The raw material gas included CO and methyl nitrite. The flow volume ratio of CO and methyl nitrite is 1.4, the gas phase space velocity of the raw material gas is 3L·g ^-1 ·h ^-1 , the reaction temperature is 130°C, and the reaction pressure is 0.1Mpa. The raw material gas and products are separated by online gas chromatography Monitoring and analysis, the reaction results are shown in Table 3.

table 3

As can be seen from the data in Table 3, compared with the catalyst sample provided by the technical solution of the present application, when the palladium loading is similar (compared with CAT-4), the comparative example sample has a single-pass conversion rate of CO far lower than that of CAT -4, even lower than CAT-3 with only 0.18wt% Pd loading. It can be seen that the catalyst prepared according to the technical scheme of the present application can greatly increase the single-pass conversion rate of CO and the yield of oxalate while saving the amount of precious metal palladium.

The above are only a few embodiments of the application, and do not limit the application in any form. Although the application is disclosed as above with preferred embodiments, it is not intended to limit the application. Any skilled person familiar with this field, Without departing from the scope of the technical solution of the present application, any changes or modifications made using the technical content disclosed above are equivalent to equivalent implementation cases, and all belong to the scope of the technical solution.

Claims (10)

1. A catalyst comprising a carrier and an active component, characterized in that the carrier comprises nitrogen-doped graphene nanosheets, and the active component comprises nano-palladium. 2. The catalyst according to claim 1, characterized in that, the mass percentage of the nano-palladium in the catalyst is 0.03-2wt%. 3. The catalyst according to claim 1, characterized in that, the average particle diameter of the nano-palladium is 1-9 nm. 4 . The catalyst according to claim 1 , characterized in that the atomic percent content of nitrogen in the nitrogen-doped graphene nanosheets is 1 to 7 at%. 5. The method according to claim 4, characterized in that the thickness of the nitrogen-doped graphene nanosheets is 0.8-30 nm. 6. The method for preparing the catalyst described in any one of claims 1 to 5, at least comprising the following steps: a) placing the graphene nanosheets in an _NH3 atmosphere and keeping them at 400-800° C. for no less than 3 hours to obtain nitrogen-doped graphene nanosheets; b) Place the nitrogen-doped graphene nanosheets obtained in step a) in a solution containing palladium, and after ultrasonic treatment, separate to obtain a solid phase; c) After the solid phase obtained in step b) is washed, dried and calcined, it is placed in an atmosphere containing a reducing gas and reduced for at least 2 hours at a reducing temperature of 150 to 450° C. At room temperature, the catalyst is obtained. 7. The method according to claim 4, characterized in that, the graphene nanosheets are prepared by an electrochemical method. 8. The method according to claim 4, characterized in that, the solution containing palladium element is obtained by dissolving the palladium source in a solvent; The palladium source is selected from palladium chloride, palladium acetate, potassium chloropalladate, sodium chloropalladate, potassium chloropalladate, palladium dichlorodiammine, palladium dichlorotetraammine, palladium nitrate, palladium acetylacetonate at least one; The solvent is at least one selected from water, acetone, methylene chloride, chloroform, methanol, ethanol, cyclohexane, dimethylformamide, benzene, and toluene. 9. A method for preparing oxalate, characterized in that, adopt at least one of the catalysts described in any one of claims 1 to 5 and/or prepare according to the method described in any one of claims 6 to 8 At least one of the catalysts is used to produce oxalate by carbon monoxide gas-phase oxidative coupling. 10. method according to claim 9, is characterized in that, described carbon monoxide gas-phase oxidative coupling produces oxalic acid ester as in fixed-bed reactor, the raw material gas that contains carbon monoxide and nitrite contacts with described catalyzer, in The reaction pressure is normal pressure, and the reaction temperature is 90～150 ℃ under the conditions of gas phase reaction to prepare oxalate ester; In the raw material gas, the volume ratio of carbon monoxide to nitrite is 1.1-1.8; The gas phase space velocity of the raw material gas is 2-5 L·g ^-1 ·h ^-1 .