Preparation method and application of nitrogen-doped carbon supported palladium catalyst

Abstract

The invention provides a preparation method and application of a nitrogen-doped carbon-loaded palladium catalyst, specifically, the nitrogen-doped carbon-loaded palladium catalyst is prepared by an impregnation method, and can efficiently catalyze ketene and carbonyl compounds to generate a gas phase [2 + 2] reaction to simply and efficiently prepare a series of beta-propiolactone derivatives. Firstly, the structure and the preparation method of the nitrogen-doped carbon-loaded palladium catalyst are novel, an assistant metal salt, palladium and assistant metal are introduced for concerted catalysis, ketene and carbonyl compound gas phase [2 + 2] reaction can be efficiently catalyzed, and the nitrogen-doped carbon-loaded palladium catalyst has good potential application value; secondly, the gas phase [2 + 2] cycloaddition reaction is adopted, the defects that an existing liquid phase process is large in solvent dosage, high in cost and the like are overcome, the preparation cost of the beta-propiolactone can be reduced, and wide application prospects are achieved.

Description

Technical Field

[0001] The present invention belongs to the field of fine chemical engineering, and particularly relates to a preparation method of a palladium catalyst supported on nitrogen-doped carbon, and an application of the catalyst in the synthesis of lactone compounds. Background Art

[0002] β-Propiolactone compounds have a four-membered ring structure with relatively large ring strain, and their chemical properties are active and very prone to ring-opening reactions with nucleophiles. Therefore, they are very important synthetic intermediates and fine chemical products. For example, the simplest member of this type of compound, β-propiolactone, also known as 2-oxetanone, is a colorless viscous liquid at room temperature and can directly act on the DNA or RNA of viruses, changing their nucleic acid structure, so it has a strong virus inactivation effect. At present, β-propiolactone has been widely used in the inactivation of various vaccines abroad. Not only is the inactivation time short, which can shorten the vaccine production cycle, but β-propiolactone is also extremely easy to hydrolyze, and its hydrolysis product is 3-hydroxypropionic acid, which can be quickly metabolized and absorbed by the human body without toxic side effects. In addition to β-propiolactone, some other 4-membered lactone compounds such as β-butyrolactone and β-valerolactone can be used to synthesize liquid crystals, biodegradable plastics, spices and other products, and have a wide range of uses in production and life.

[0003] At present, the main synthesis methods of β-propiolactone are the ring-closing method of β-haloacid and the [2+2] addition method of ketene. The ring-closing method of β-haloacid (Equation 1) uses β-haloacid as the raw material, and under the action of alkalis such as sodium hydroxide, sodium carbonate, and potassium carbonate, β-propiolactone is obtained by removing hydrogen halide while closing the ring. The amount of alkali used in this method is generally 1 equivalent and should not be excessive; the temperature should not be too high, generally not exceeding 50°C; since the product β-propiolactone is prone to hydrolysis into β-hydroxy acid by-products under alkaline and high-temperature conditions, the yield of the product β-propiolactone will be reduced. Due to the relatively high synthesis cost of β-haloacid, at present, the preparation of β-propiolactone by this method is mostly used in laboratories, and there are almost no reports on its large-scale production application.

[0004]

[0005] Another commonly used process for preparing β-propiolactone is the [2+2] cycloaddition process of ketene and carbonyl compounds (Formula 2). This method utilizes the highly reactive chemical activity of ketene and can easily undergo a [2+2] cycloaddition reaction with carbonyl compounds under the action of a catalyst to obtain a series of β-propiolactone derivatives in one step. Lewis acids or Lewis bases can generally be used to catalyze this reaction. It should be noted that due to the four-membered ring structure of the product β-propiolactone with a large ring strain, its chemical properties are also very active. Under the catalysis of Lewis acids or Lewis bases, side reactions such as ring-opening polymerization, elimination, and dehydration are likely to occur. Therefore, the above [2+2] cycloaddition reaction generally needs to be carried out at a very low concentration, and a large amount of solvent is required to dilute the reaction substrates, resulting in relatively high production costs.

[0006]

[0007] In summary, the current synthesis methods of β-propiolactone mainly include the ring-closure method of β-haloacid and the [2+2] addition method of ketene. Among them, the [2+2] addition method of ketene has relatively low-cost raw materials and can obtain β-propiolactone in one step with almost no by-products, which is a relatively promising synthesis route for β-propiolactone. However, since the current [2+2] cycloaddition of ketene and carbonyl generally occurs in solution, a large amount of solvent is required to dilute the two raw materials, resulting in high costs, a large reactor, and low production efficiency. In view of the importance of β-propiolactone compounds, in order to prepare this type of intermediate more economically and efficiently, it is urgent to develop new catalysts and reaction systems to overcome the disadvantages of the current liquid-phase [2+2] cycloaddition process of ketene and carbonyl compounds. Summary of the Invention

[0008] The purpose of the present invention is to provide a preparation method of a palladium catalyst supported on nitrogen-doped carbon and its application in the catalytic [2+2] cycloaddition of ketene and carbonyl compounds to prepare lactones. The catalyst of this method has a novel structure, mild preparation conditions, and simple operation. The catalyst can efficiently catalyze the gas-phase [2+2] reaction of ketene compounds and carbonyl compounds to simply and efficiently prepare a series of β-propiolactone derivatives.

[0009] To achieve the above purpose and technical effects, the present invention adopts the following technical solutions:

[0010] In the first aspect, the present invention provides a preparation method of a palladium catalyst supported on nitrogen-doped carbon. This catalyst is prepared by an impregnation method and specifically includes the following steps:

[0011] (1) Activate the carbon material with a strong acid to obtain an activated carbon material as the catalyst support;

[0012] (2) Prepare an aqueous solution of palladium salt, metal salt promoter, alkali promoter, and imidazolium salt, mix it with the activated carbon material, stir and impregnate, and dry to obtain a catalyst precursor;

[0013] (3) The catalyst precursor is subjected to high-temperature calcination treatment to obtain a palladium catalyst supported on nitrogen-doped carbon.

[0014] In the present invention, the carbon material in the step (1) is coconut shell carbon, walnut shell carbon, petroleum coke, etc., preferably coconut shell carbon and walnut shell carbon. Preferably, the diameter of the carbon material is 1.5 - 2.0 mm, and the length is 3 - 5 mm.

[0015] In the present invention, the strong acid in the step (1) is one or more of nitric acid, sulfuric acid, hydrochloric acid, perchloric acid, phosphoric acid, etc. The acid concentration is preferably 0.5 - 3.0 M, and activation treatment can be carried out under stirring at room temperature. The treatment time is preferably 6 - 12 h.

[0016] In the present invention, the palladium salt in the step (2) is one or more of palladium chloride, palladium acetate, palladium nitrate, ammonium tetrachloropalladate, palladium acetylacetonate, etc.; the metal salt promoter is one or more of zinc salt, copper salt, molybdenum salt, cadmium salt, lithium salt, etc., such as copper nitrate, zinc nitrate, ammonium molybdate, cadmium acetate, etc.; the alkali promoter is one or more of sodium carbonate, potassium carbonate, cesium carbonate, calcium carbonate, etc.; the imidazolium salt is one or more of 1-ethyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium methanesulfonate, 1,3-diethylimidazolium acetate, (1-butyl-3-methylimidazolium) chloride, etc.

[0017] In the present invention, in the step (2), the mass ratio of the palladium salt, metal salt promoter, alkali promoter, imidazolium salt, and activated carbon material is 0.01 - 0.05:0.001 - 0.005:0.001 - 0.005:0.1 - 0.3:1; the impregnation time is 3 - 6 h; the impregnation temperature is 15°C - 50°C, preferably at room temperature.

[0018] In the present invention, operations such as stirring and drying in the step (2) can be conventionally adjusted by those skilled in the art.

[0019] In the present invention, in the step (3), the high-temperature calcination temperature is 400 - 600°C, and the time is 2 - 8 h; preferably, calcination is carried out in a carbon dioxide atmosphere. More preferably, it is heated to 400 - 600°C at a rate of 1 - 3°C / min, held for calcination for 2 - 8 h, and then cooled to 100 - 200°C at a rate of 1 - 3°C / min. After cooling to room temperature, a palladium catalyst supported on nitrogen-doped carbon is obtained.

[0020] Second, the palladium catalyst supported on nitrogen-doped carbon prepared by the impregnation method of the present invention is used in the [2 + 2] gas-phase cycloaddition reaction of ketene compounds and carbonyl compounds to prepare a series of β-propiolactone derivatives in high yield.

[0021] The specific reaction route is shown as follows:

[0022]

[0023] In the present invention, in the [2+2] cycloaddition reaction, the ketene compound is a compound containing a vinyl ketone structure, preferably one or more of ketene, methyl vinyl ketone, dimethyl vinyl ketone, diketene, etc.; the carbonyl compound may include one or more of formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, acetone, butanone, 2-pentanone, methyl isopropyl ketone, etc.

[0024] In the present invention, the [2+2] cycloaddition reaction is carried out in the gas phase. The reaction temperature is preferably 20-300 °C, and the molar ratio of the ketene compound to the carbonyl compound in the feed is 1.0-1.5:1, preferably with a slight excess of the ketene compound; the reaction pressure is preferably atmospheric pressure, and the total gas hourly space velocity of the raw materials and the carrier gas in the reactor is preferably 800-1500 h -1 .

[0025] In the present invention, the gas-phase [2+2] cycloaddition reaction preferably uses a tubular reactor. The two raw materials are vaporized and then fed in a mixed manner. After the reaction, it is rapidly cooled to 0 °C and then introduced into toluene to achieve gas-liquid separation, and the product in toluene is collected to obtain the target product.

[0026] In the present invention, in the [2+2] cycloaddition reaction, after the two raw materials (ketene compound, carbonyl compound) are vaporized, inert gases such as nitrogen and argon are used as the carrier gas to drive the two raw materials into the reactor. The flow rate of the carrier gas is preferably 80-300 mL / min / g (total of raw materials).

[0027] In the present invention, unless otherwise specified, the pressure is gauge pressure.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. The nitrogen-doped carbon-supported palladium catalyst described in this method has a novel structure and a simple preparation process. An additional promoter metal salt is introduced, and palladium and the promoter metal synergistically catalyze to obtain β-propiolactone derivatives in high yield.

[0030] 2. This method uses nitrogen-doped carbon as the carrier. The nitrogen element has basic and coordination complexing functions, which can moderate the Lewis acidity of palladium metal, and at the same time can play a good role in fixing and loading palladium metal and stabilizing the catalyst.

[0031] 3. The gas-phase method is used for the [2+2] cycloaddition reaction of ketene compounds and carbonyl compounds, and nitrogen is used to dilute the raw materials and products to avoid side reactions such as ring-opening polymerization of the products under the action of the catalyst. Specific Embodiments

[0032] The present invention will be described in detail below through examples, but the present invention is not limited to the following examples.

[0033] The information of the main raw materials is as follows:

[0034] Diketene, isobutyric anhydride, paraformaldehyde, AR, Aladdin reagent; palladium nitrate, copper nitrate, potassium nitrate, J&K reagent, purity 98 - 99%; coconut shell charcoal, walnut shell charcoal (diameter 1.5 - 2.0 mm, length 3 - 5 mm); nitric acid, hydrochloric acid, sulfuric acid, perchloric acid, Macklin, 98%; phosphoric acid, AR, J&K; 1,3 - diethylimidazolium acetate, 1 - ethyl - 3 - methylimidazolium acetate, 1 - butyl - 3 - methylimidazolium chloride, Energy Chemical reagent; zinc nitrate, sodium carbonate, ammonium molybdate, magnesium nitrate, Sinopharm reagent; palladium acetylacetonate, cadmium acetate, calcium carbonate, potassium carbonate, Alfa reagent.

[0035] Acetaldehyde, propionaldehyde, 99%, Energy Chemical reagent; acetone, chromatographic pure, Sinopharm reagent;

[0036] Cerium nitrate, 99%, Xilong reagent; sodium hydroxide, quartz sand, Sinopharm reagent.

[0037] The gas chromatography test conditions of the present invention are as follows:

[0038] Instrument model: Agilent 7890B; chromatographic column: capillary column HP - DB - 3 (30 m × 0.30 mm × 0.25 μm); initial temperature 60°C, rising to 120°C at a rate of 5°C / min; then rising to 220°C at a rate of 10°C / min and holding for 5 min. Carrier gas high - purity nitrogen, split ratio 40:1, split flow rate 45 mL / min. Carrier gas saving: 20 mL / min, start waiting time 2 min. Injection temperature 240°C, detector FID, detector temperature 280°C, air flow rate 350 mL / min, hydrogen flow rate 35 mL / min, tail gas purge flow rate 30 mL / min, injection volume 0.2 μL.

[0039] Example 1

[0040] Preparation of nitrogen - doped carbon - supported palladium catalyst Pd(CuK) / NBC

[0041] Weigh 3.7 g of coconut shell charcoal at room temperature, add it to a 20 mL mixed solution (volume ratio 1:1) of hydrochloric acid (3.0 M) and nitric acid (2.0 M), stir at room temperature for 8 h, then filter the obtained suspension to remove the acid solution. The filter cake is washed thoroughly with deionized water (15 mL × 4), and the washing is stopped when the pH of the washing water > 6 to obtain the activated carbon support. Next, put the obtained carbon support into 15 mL of impregnating solution. The impregnating solution uses water as the solvent and dissolves palladium nitrate (0.037 g), copper nitrate (0.004 g), potassium carbonate (0.004 g), and 1,3 - diethylimidazolium acetate (0.74 g). After stirring and impregnating at room temperature for 10 h, evaporate the water to obtain the catalyst precursor. Put the obtained catalyst precursor into a tubular muffle furnace, heat it to 500 °C at a heating rate of 3 °C / min under the protection of a carbon dioxide atmosphere, calcine for 4 h, then cool it to 200 °C at a rate of 3 °C / min, and finally turn off the power supply. The muffle furnace naturally cools to room temperature to obtain the nitrogen - doped carbon - supported palladium catalyst Pd(CuK) / NBC with a mass of 3.84 g and a palladium loading of approximately 0.44 wt%.

[0042] Example 2

[0043] Preparation of nitrogen - doped carbon - supported palladium catalyst Pd(ZnNa) / NBC

[0044] Weigh 3.5 g of coconut shell charcoal at room temperature, add it to a 20 mL mixed solution (volume ratio 1:1) of perchloric acid (3.0 M) and nitric acid (2.0 M), stir at room temperature for 12 h, then filter the obtained suspension to remove the acid solution. The filter cake is washed thoroughly with deionized water (15 mL × 4), and the washing is stopped when the pH of the washing water > 6 to obtain the activated carbon support. Next, put the obtained carbon support into 15 mL of impregnating solution. The impregnating solution uses water as the solvent and dissolves palladium nitrate (0.175 g), zinc nitrate (0.018 g), sodium carbonate (0.018 g), and 1,3 - diethylimidazolium acetate (1.05 g). After stirring and impregnating at room temperature for 10 h, evaporate the water to obtain the catalyst precursor. Put the obtained catalyst precursor into a tubular muffle furnace, heat it to 600 °C at a heating rate of 3 °C / min under the protection of a carbon dioxide atmosphere, calcine for 2 h, then cool it to 200 °C at a rate of 3 °C / min, and finally turn off the power supply. The muffle furnace naturally cools to room temperature to obtain the nitrogen - doped carbon - supported palladium catalyst Pd(ZnNa) / NBC with a mass of 3.75 g and a palladium loading of approximately 2.1 wt%.

[0045] Example 3

[0046] Preparation of nitrogen - doped carbon - supported palladium catalyst Pd(MoK) / NBC

[0047] Weigh 4.1 g of coconut shell charcoal at room temperature, add it to nitric acid (2.0 M), stir at room temperature for 8 h, then filter the obtained suspension to remove the acid solution. The filter cake is washed thoroughly with deionized water (15 mL * 4). Stop washing when the pH of the washing water is > 6 to obtain the activated carbon support. Next, put the obtained carbon support into 15 mL of impregnating solution. The impregnating solution uses water as the solvent and dissolves palladium acetate (0.090 g), ammonium molybdate (0.008 g), potassium carbonate (0.012 g), and 1-butyl-3-methylimidazolium chloride (0.41 g). After stirring and impregnating at room temperature for 10 h, evaporate the water to obtain the catalyst precursor. Put the obtained catalyst precursor into a tubular muffle furnace, heat it to 400 °C at a heating rate of 3 °C / min under the protection of a carbon dioxide atmosphere, keep it warm for 8 h, then cool it to 200 °C at a rate of 3 °C / min, and finally turn off the power. The muffle furnace naturally cools to room temperature to obtain the nitrogen-doped carbon-supported palladium catalyst Pd(MoK) / NBC, with a mass of 4.21 g and a palladium loading of about 1.0 wt%.

[0048] Example 4

[0049] Preparation of nitrogen-doped carbon-supported palladium catalyst Pd(CdCa) / NBC

[0050] Weigh 5.6 g of walnut shell charcoal at room temperature, add it to a 20 mL mixture of phosphoric acid (3.0 M) and nitric acid (2.0 M) (volume ratio 1:1), stir at room temperature for 8 h, then filter the obtained suspension to remove the acid solution. The filter cake is washed thoroughly with deionized water (15 mL * 4). Stop washing when the pH of the washing water is > 6 to obtain the activated carbon support. Next, put the obtained carbon support into 15 mL of impregnating solution. The impregnating solution uses water as the solvent and dissolves palladium acetylacetonate (0.2524 g), cadmium acetate (0.028 g), calcium carbonate (0.028 g), and 1,3-diethylimidazolium acetate (1.56 g). After stirring and impregnating at room temperature for 10 h, evaporate the water to obtain the catalyst precursor. Put the obtained catalyst precursor into a tubular muffle furnace, heat it to 500 °C at a heating rate of 3 °C / min under the protection of a carbon dioxide atmosphere, calcine for 4 h, then cool it to 200 °C at a rate of 3 °C / min, and finally turn off the power. The muffle furnace naturally cools to room temperature to obtain the nitrogen-doped carbon-supported palladium catalyst Pd(CdCa) / NBC, with a mass of 5.91 g and a palladium loading of about 1.49 wt%.

[0051] Example 5

[0052] The nitrogen-doped carbon-supported palladium catalyst is used to catalyze the [2 + 2] cycloaddition of ketene and formaldehyde to prepare propiolactone.

[0053] The experiment was carried out using a double-tube fixed bed. Reaction tube 1 was used to prepare the ketene raw material, and reaction tube 2 was used for the gas-phase [2+2] cycloaddition reaction of ketene and formaldehyde. At room temperature, diketene was added to feed tank 1, and paraformaldehyde powder was added to feed tank 2. Feed tank 1 and feed tank 2 were connected to reaction tube 1 and tube 2 respectively. The lengths of both reaction tubes 1 and 2 were 30 cm, and the inner diameter was 2 cm. Reaction tube 1 was filled with glass spring packing (φ4 mm, length 10 mm), and the middle part of reaction tube 2 was filled with palladium catalyst supported on nitrogen-doped carbon (5 cm, volume 15.7 mL). Both the upper and lower parts of the catalyst layer were filled with quartz sand to fix the catalyst. When performing the [2+2] cycloaddition experiment, first turn on the power of the device, start the preheater and the reaction tube heater, and start the nitrogen carrier gas (40 mL / min). When the temperature of reaction tube 1 stabilizes at 550 °C, start the diketene feeding (0.42 g / min). After the diketene is vaporized by the preheater, it enters reaction tube 1 under the drive of the nitrogen carrier gas and undergoes a cracking reaction to generate ketene (yield 54%, 0.23 g / min). The high-temperature reaction gas coming out of reaction tube 1 is cooled to 20 °C, and after gas-liquid separation, it enters reaction tube 2 (20 °C). At the same time, formaldehyde gas (0.15 g / min), obtained by vaporizing paraformaldehyde, also enters reaction tube 2, and the carrier gas is nitrogen (40 mL / min). The gas hourly space velocity of the raw materials and the carrier gas is 1188 h -1 . The [2+2] cycloaddition reaction of ketene and formaldehyde occurs in the catalyst layer to obtain the lactone product, which is obtained as the target product after rapid cooling and absorption with toluene solution. The conversion rate of raw material formaldehyde and the selectivity of the target product β-propiolactone are shown in the following table.

[0054] Number Catalyst Formaldehyde conversion rate % Selectivity % 1 Pd(CuK) / NBC 98％ 96％ 2 Pd(ZnNa) / NBC 97％ 95％ 3 Pd(MoK) / NBC 99％ 97％ 4 Pd(CdCa) / NBC 97％ 96％

[0055] Example 6

[0056] The palladium catalyst supported on nitrogen-doped carbon Pd(MoK) / NBC catalyzes the [2+2] cycloaddition of ketene and acetaldehyde to prepare butyrolactone.

[0057] An experimental study was carried out using a double-tube fixed bed. The reaction tube had a length of 30 cm and an inner diameter of 2 cm. The middle part of the reaction tube was filled with a palladium catalyst supported on nitrogen-doped carbon (5 cm, volume 15.7 mL), and both the upper and lower parts were filled with quartz sand to fix the catalyst. When conducting the [2+2] cycloaddition experiment, first turn on the power of the device, start the preheater and the pyrolysis tube heater, and start nitrogen (40 mL / min). When the temperature of the pyrolysis tube stabilizes at 550 °C, start the feeding of diketene (0.42 g / min). After the diketene is vaporized by the preheater, it enters the pyrolysis tube under the drive of the nitrogen carrier gas and undergoes a pyrolysis reaction to generate ketene (yield 54%, 0.23 g / min). The high-temperature reaction gas coming out of the pyrolysis tube is cooled to 30 °C, and after gas-liquid separation, it enters the reaction tube (30 °C). At the same time, acetaldehyde gas (0.22 g / min) and nitrogen carrier (30 mL / min) also enter the reaction tube. The space velocity of the mixed gas in the reactor is 1150 h -1 . Ketene and acetaldehyde undergo a [2+2] cycloaddition reaction in the catalyst layer, and the β-butyrolactone product is obtained after rapid cooling and absorption with toluene solution. The conversion rate of acetaldehyde is 99%, and the selectivity of the target product β-butyrolactone is 98%.

[0058] Example 7

[0059] The [2+2] cycloaddition of ketene and propionaldehyde catalyzed by palladium catalyst supported on nitrogen-doped carbon Pd(MoK) / NBC

[0060] An experimental study was carried out using a double-tube fixed bed. The reaction tube had a length of 30 cm and an inner diameter of 2 cm. The middle part of the reaction tube was filled with a palladium catalyst supported on nitrogen-doped carbon (5 cm, volume 15.7 mL), and both the upper and lower parts were filled with quartz sand to fix the catalyst. When conducting the [2+2] cycloaddition experiment, first turn on the power of the device, start the preheater and the pyrolysis tube heater, and start nitrogen (30 mL / min). When the temperature of the pyrolysis tube stabilizes at 550 °C, start the feeding of diketene (0.56 g / min). After the diketene is vaporized by the preheater, it enters the pyrolysis tube under the drive of the nitrogen carrier gas and undergoes a pyrolysis reaction to generate ketene (yield 56%, 0.31 g / min). The high-temperature reaction gas coming out of the pyrolysis tube is cooled to 30 °C, and after gas-liquid separation, it enters the reaction tube (60 °C). At the same time, propionaldehyde gas (0.36 g / min) and nitrogen carrier (30 mL / min) also enter the reaction tube. The space velocity of the mixed gas in the reactor is 1400 h -1 .. Ketene and propionaldehyde undergo a [2+2] cycloaddition reaction in the catalyst layer, and the target product is obtained after rapid cooling and absorption with toluene solution. The conversion rate of propionaldehyde is 99%, and the selectivity of the target product β-valerolactone is 98%.

[0061] Example 8

[0062] Pd(MoK) / NBC Catalyzed [2+2] Cycloaddition of Ketenes and Acetone over Nitrogen-Doped Carbon-Supported Palladium Catalysts

[0063] The experiment was carried out in a double-tube fixed bed. The reaction tube was 30 cm in length and 2 cm in inner diameter. The middle part of the reaction tube was filled with a nitrogen-doped carbon-supported palladium catalyst (5 cm, volume 15.7 mL), and both the upper and lower parts were filled with quartz sand to fix the catalyst. When performing the [2+2] cycloaddition experiment, first turn on the power of the device, start the preheater and the cracking tube heater, and start nitrogen (30 mL / min). When the temperature of the cracking tube stabilizes at 550 °C, start feeding diketene (0.46 g / min). After the diketene is vaporized by the preheater, it enters the cracking tube under the drive of the nitrogen carrier gas and undergoes a cracking reaction to generate ketene (yield 58%, 0.27 g / min). The high-temperature reaction gas coming out of the cracking tube is cooled to 30 °C, and after gas-liquid separation, it enters the reaction tube (70 °C). At the same time, acetone gas (0.37 g / min) and nitrogen carrier (30 mL / min) also enter the reaction tube. The space velocity of the mixed gas in the reactor is 1321 h -1 .. The [2+2] cycloaddition reaction of ketene and acetone occurs in the catalyst layer, and the target product is obtained after rapid cooling and absorption with toluene solution. The conversion rate of acetone is 80%, and the selectivity of the target product β-dimethyl-β-propiolactone is 94%.

[0064] Example 9

[0065] Pd(MoK) / NBC Catalyzed [2+2] Cycloaddition of Dimethylketene and Formaldehyde

[0066] The experiment was carried out in a double-tube fixed bed. The reaction tube was 30 cm in length and 2 cm in inner diameter. The middle part of the reaction tube was filled with a nitrogen-doped carbon-supported palladium catalyst (5 cm, volume 15.7 mL), and both the upper and lower parts were filled with quartz sand to fix the catalyst. When performing the [2+2] cycloaddition experiment, first turn on the power of the device, start the preheater and the cracking tube heater, and start nitrogen (40 mL / min). When the temperature of the cracking tube stabilizes at 550 °C, start feeding isobutyric anhydride (1.08 g / min). After the isobutyric anhydride is vaporized by the preheater, it enters the cracking tube under the drive of the nitrogen carrier gas and undergoes a cracking reaction to generate dimethylketene (yield 68%, 0.325 g / min). The high-temperature reaction gas coming out of the cracking tube is cooled to 30 °C, and after gas-liquid separation, it enters the reaction tube (80 °C). At the same time, formaldehyde gas (0.13 g / min) and nitrogen carrier (40 mL / min) also enter the reaction tube. The space velocity of the mixed gas in the reactor is 1065 h -1. The [2+2] cycloaddition reaction of dimethylketene and formaldehyde occurs in the catalyst layer, and the target product is obtained after rapid quenching and absorption with toluene solution. The conversion rate of formaldehyde is 99%, and the selectivity of the target product α-dimethyl-β-propiolactone is 98%.

Claims

1. A preparation method of a palladium catalyst supported on nitrogen-doped carbon, characterized in that, It includes the following steps: (1) Activate the carbon material with strong acid to obtain the activated carbon material; (2) Prepare an aqueous solution of palladium salt, metal salt promoter, alkali promoter, and imidazole salt, mix it with the activated carbon material, stir, impregnate, and dry to obtain the catalyst precursor; (3) The catalyst precursor is subjected to high-temperature calcination treatment to obtain a nitrogen-doped carbon-supported palladium catalyst.

2. The method according to claim 1, characterized in that, In the step (1), the carbon material is selected from one or more of coconut shell carbon, walnut shell carbon, and petroleum coke. Preferably, the diameter of the carbon material is 1.5 - 2.0 mm, and the length is 3 - 5 mm.

3. The method according to claim 1, characterized in that, In the step (1), the strong acid is selected from one or more of nitric acid, sulfuric acid, hydrochloric acid, perchloric acid, and phosphoric acid. The acid concentration is preferably 0.5 - 3.0 M, and the activation treatment time is preferably 6 - 12 h.

4. The method according to claim 1, wherein In the step (2), the palladium salt is selected from one or more of palladium chloride, palladium acetate, palladium nitrate, ammonium tetrachloropalladate, and palladium acetylacetonate; the metal salt promoter is one or more of zinc salt, copper salt, molybdenum salt, cadmium salt, and lithium salt, preferably one or more of copper nitrate, zinc nitrate, ammonium molybdate, and cadmium acetate; the alkali promoter is selected from one or more of sodium carbonate, potassium carbonate, cesium carbonate, and calcium carbonate; the imidazole salt is selected from one or more of 1-ethyl-3-methylimidazole acetate, 1-ethyl-3-methylimidazole methanesulfonate, 1,3-diethylimidazole acetate, and 1-butyl-3-methylimidazolium chloride.

5. The method according to claim 1, wherein In the step (2), the impregnation time is 3 - 6 h; the impregnation temperature is 15°C - 50°C.

6. The method according to any one of claims 1-5, characterized in that In the step (2), the mass ratio of the palladium salt, metal salt promoter, alkali promoter, imidazole salt, and activated carbon material is 0.01 - 0.05:0.001 - 0.005:0.001 - 0.005:0.1 - 0.3:

1.

7. The method according to claim 1, characterized in that In the step (3), the temperature of the high-temperature calcination is 400 - 600°C, and the time is 2 - 8 h.

8. A method for the gas-phase [2+2] cycloaddition reaction of a ketene compound and a carbonyl compound, characterized in that, The nitrogen-doped carbon-supported palladium catalyst prepared by the method according to any one of claims 1 - 7, the ketene compound is a compound containing a vinyl ketone structure, preferably selected from one or more of ketene, methyl vinyl ketone, dimethyl vinyl ketone, and diketene; the carbonyl compound is selected from one or more of formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, acetone, butanone, 2-pentanone, and methyl isopropyl ketone.

9. The method according to claim 8, characterized in that, The [2+2] gas-phase cycloaddition reaction is carried out in the gas phase, the reaction temperature is 20 - 300°C, and the feed ratio of the ketene compound and the carbonyl compound is 1.0 - 1.5:

1.

10. The method according to claim 8 or 9, characterized in that, In the [2+2] gas-phase cycloaddition reaction, the ketene compound and the carbonyl compound are vaporized and then mixed for feeding, and enter the reactor with an inert gas as the carrier gas; preferably, the inert gas includes nitrogen or argon; preferably, the flow rate of the carrier gas is 80 - 300 mL / min / g of raw material.

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