Catalyst for selective hydrogenation of acetylene and its preparation method and application

Abstract

The present application relates to a kind of catalyst for the selective hydrogenation of acetylene, main active component is palladium, carrier is phosphorus-doped carbon material, palladium is dispersed on carrier at atomic level;Palladium content is 0.005~0.5wt% of the total mass of catalyst.The present application also relates to a kind of preparation method for the catalyst for the selective hydrogenation of acetylene, and a kind of method for preparing ethylene by the selective hydrogenation of acetylene.The catalyst provided by the present application is dispersed on carrier at atomic level, and the catalyst has higher activity, selectivity and stability for the selective hydrogenation of acetylene;The preparation method provided by the present application is environmentally friendly, and easy to operate.

Description

Technical Field

[0001] This invention relates to the field of selective hydrogenation of acetylene, and more particularly to a Pd-PC single-atom catalyst for selective hydrogenation of acetylene, its preparation method, and its application in the selective hydrogenation of acetylene to ethylene. Background Technology

[0002] Polyethylene, obtained by polymerizing the important monomer ethylene, is a widely used polymer material. Its raw material, ethylene monomer, is mainly obtained through methods such as high-temperature hydrocarbon cracking, methanol-to-olefins (MTO), and ethanol-to-ethylene (ETO). However, the ethylene gas obtained from these methods typically contains a small amount of acetylene (0.5–2%). The presence of even trace amounts of acetylene can quickly poison and deactivate the Ziegler-Natta catalyst used in ethylene polymerization, resulting in poor polymerization degree of polyethylene and thus affecting material properties. Therefore, it is essential to reduce the acetylene content in the ethylene feedstock gas to the ppm level before using it for polymerization.

[0003] Currently, selective hydrogenation of acetylene to polymer-grade ethylene is the most effective method for removing acetylene and further utilizing it, with Pd being the preferred catalyst as the active component. While industrially used Pd and Ag catalysts exhibit high activity, the α-Al₂O₃ support used is difficult to dissolve, and the introduction of doped metals makes it difficult to separate and recover the noble metal component Pd. CN101433842B discloses a hydrogenation catalyst using a bimetallic mixture of Pd and Ag as the active components. Its characteristic feature is that the catalyst support has both micropores with a most probable radius of 2–50 nm and macropores with a most probable radius of 100–500 nm. This support has low surface acidity, effectively reducing side reactions during acetylene hydrogenation and extending the catalyst's service life. CN108147938B discloses a method for the selective hydrogenation of acetylene to ethylene, using Pd as the catalyst. x M y Pd was obtained by high-temperature calcination using silica as a precursor and silicon dioxide as a carrier. x M / SiO2 catalyst, where M is one of Ag, Au, Cu, Ni, and Pd; CN101862653B discloses an acetylene selective hydrogenation catalyst and its preparation method, using Pd as the main metal component and adding Bi, Sb, Pb, and other metals as promoters. The prepared catalyst Pd exists in elemental form after ionization radiation treatment. Compared with Pd catalysts prepared by traditional methods, this catalyst has higher activity and selectivity. Although the catalyst mentioned above improves the activity and selectivity of the catalyst to a certain extent, the use of promoters makes the catalyst preparation process cumbersome, and the addition of promoters makes the subsequent recovery and separation of the precious metal Pd difficult.

[0004] Although Pd-based catalysts are considered the mainstream research focus for acetylene selective hydrogenation, the process still faces several challenges: 1) the use of large amounts of promoters makes catalyst recovery and reuse difficult; 2) catalyst coking leads to deactivation of Pd-based catalysts. Therefore, developing a novel single-atom palladium catalyst that is resistant to coking and requires no promoters for the selective hydrogenation of acetylene under conditions involving large amounts of ethylene and hydrogen is of great significance. Summary of the Invention

[0005] Based on the above, the main objective of this invention is to provide a catalyst for the selective hydrogenation of acetylene and its preparation method, wherein palladium is dispersed at the atomic level on a support, and the catalyst exhibits high activity, selectivity, and stability for the selective hydrogenation reaction of acetylene; the preparation method is environmentally friendly and simple to operate.

[0006] To achieve the above objectives, the present invention provides a catalyst for the selective hydrogenation of acetylene, wherein the main active component is palladium, the support is a phosphorus-doped carbon material, and the palladium is dispersed at the atomic level on the support; the palladium content is 0.005 to 0.5 wt% of the total mass of the catalyst.

[0007] The catalyst for selective hydrogenation of acetylene described in this invention preferably involves the following preparation process: dissolving a phosphorus-containing compound and a carbohydrate in water by thorough stirring (the amount of water used is sufficient to ensure complete dissolution of the phosphorus-containing compound and carbohydrate; excessive water will increase the energy consumption of subsequent calcination but will not affect the performance of the catalyst), followed by calcination under an inert atmosphere; more preferably, the stirring time is 30–120 min and the temperature is 10–30 °C; more preferably, the calcination conditions are: a heating rate of 1–10 °C / min, a calcination temperature of 600–1000 °C, and a calcination time of 1–5 h.

[0008] The catalyst for selective hydrogenation of acetylene according to the present invention preferably comprises a phosphorus-containing compound selected from one or two of phosphoric acid and phytic acid, and a carbohydrate selected from one or two of glucose and sucrose; more preferably, the molar ratio of the phosphorus-containing compound to the carbohydrate is 0.0001 to 1000, and even more preferably 0.001 to 10.

[0009] To achieve the above objectives, the present invention also provides a method for preparing the above-mentioned catalyst for selective hydrogenation of acetylene, comprising the following steps:

[0010] S1. Add the support to the palladium precursor solution (the concentration of the precursor solution is not limited, as long as it can be ensured that the precursor is completely dissolved in the solution, which will not affect the performance of the final catalyst), stir evenly, place it in liquid nitrogen for rapid freezing, and then irradiate it under ultraviolet xenon lamp.

[0011] S2. The solution obtained in step S1 is freeze-dried and then calcined under an inert atmosphere to obtain the catalyst for selective hydrogenation of acetylene.

[0012] The method for preparing the catalyst for selective hydrogenation of acetylene according to the present invention preferably includes the following steps: the stirring temperature in step S1 is 10–30°C, the irradiation time of the ultraviolet xenon lamp is 0.5–5 h, and the lamp intensity is 0.5–5.0 mW / cm². 2 .

[0013] The method for preparing the catalyst for selective hydrogenation of acetylene according to the present invention preferably includes the following calcination conditions in step S2: heating rate of 2-5 °C / min, temperature of 300-500 °C, and time of 0.5-5 h.

[0014] The method for preparing the catalyst for selective hydrogenation of acetylene according to the present invention uses an inert atmosphere of one or more of He, N2 and Ar.

[0015] The method for preparing the catalyst for selective hydrogenation of acetylene according to the present invention preferably includes a palladium precursor solution selected from one or more of palladium chloride, palladium nitrate, palladium acetate, and palladium acetylacetonate.

[0016] To achieve the above objectives, the present invention also provides a method for selective hydrogenation of acetylene to prepare ethylene, wherein the reaction atmosphere is an acetylene atmosphere in the presence of a large amount of ethylene and hydrogen, wherein, by volume, C2H2 accounts for 0.5-3%, C2H4 accounts for 50-90%, H2 accounts for 5-20%, and the remainder is an inert gas; the amount of the catalyst is 10-100 mg, the selective hydrogenation reaction temperature of acetylene is 60-200 °C, the gas flow rate of the reaction atmosphere is 0.1-60 ml / min, and the space velocity is 10000-30000 ml / g·h.

[0017] The method for selective hydrogenation of acetylene to prepare ethylene according to the present invention preferably further includes the following steps: before using the catalyst, it is reduced in a reducing gas; more preferably, the reducing gas is composed of hydrogen and an inert gas, wherein the volume percentage of H2 in the reducing gas is 1%-100%, and the inert gas is selected from one or more of He, N2 and Ar; the reduction conditions are: temperature 50-300℃, more preferably 100-200℃, pressure 0.1MPa-1.0MPa, more preferably 0.5MPa-1.0MPa, time 0.5-10h, and space velocity 10000-50000ml / g·h.

[0018] Specifically, the preparation method of the catalyst for selective hydrogenation of acetylene provided by the present invention includes the following steps:

[0019] 1) Preparation of phosphorus-doped carbon material carrier: At room temperature (10-30℃), phosphorus-containing compounds and carbohydrates are thoroughly dissolved in water by stirring for 30-120 min; then dried to remove moisture, and calcined at 600-1000℃ for 1-5 h under an inert atmosphere at a heating rate of 1-10℃ / min.

[0020] 2) Preparation of single-atom catalyst: Weigh the phosphorus-doped carbon material support obtained in step (1) and add it to the palladium precursor aqueous solution. After stirring evenly at room temperature, place it in liquid nitrogen for rapid freezing, and then place it under light intensity of 0.5-5.0 mW / cm. 2 Irradiate under ultraviolet xenon lamp for 0.5–5 hours;

[0021] 3) Freeze-dry the solution obtained in step (2) for 2 to 7 hours, and then calcine it at 300-500℃ for 0.5 to 5 hours under an inert atmosphere at a rate of 2 to 5℃ / min.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] (1) The catalyst provided by the present invention uses phosphorus-doped carbon material as a carrier and employs photoreduction to disperse palladium in a single-atom state rather than forming nanoparticles or sub-nano clusters.

[0024] (2) The catalyst provided by the present invention can achieve an ethylene selectivity of 95% when the acetylene conversion rate is above 95% in the selective hydrogenation reaction of acetylene.

[0025] (3) The catalyst provided by the present invention has no deactivation phenomenon after running stably for 100 hours in the selective hydrogenation reaction of acetylene. Attached Figure Description

[0026] Figure 1 The image shows the aberration-corrected electron micrograph of the catalyst prepared in Example 4.

[0027] Figure 2 The image shows the aberration-corrected electron micrograph of the catalyst prepared in Example 3 after reaction.

[0028] Figure 3 The stability test results are shown for the Pd-PC catalyst prepared in Example 3 and the Pd-NC catalyst prepared in Comparative Example 2. Detailed Implementation

[0029] The following provides a detailed description of the embodiments of the present invention: These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and processes. However, the scope of protection of the present invention is not limited to the following embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions.

[0030] All chemical reagents used in the embodiments of this invention are chemically pure and readily available on the market. The conversion rate and selectivity in the embodiments are calculated using the following formula:

[0031] Acetylene conversion rate (%) = 100 × Δacetylene / inlet acetylene content

[0032] Ethylene selectivity (%) = 100 × Δethylene / Δacetylene

[0033] The catalyst activity testing method is as follows:

[0034] Selective hydrogenation of acetylene to ethylene in the presence of large amounts of ethylene and hydrogen: The reactor is a fixed bed; before use, the catalyst is reduced with a mixture of H2 and He containing 1%–100% hydrogen by volume, the reduction temperature range is 50–300℃, preferably 100–200℃; the reduction pressure is 0.1 MPa–1.0 MPa, preferably 0.5 MPa–1.0 MPa; the reduction time is 0.5–10 h; the catalytic hydrogenation reaction atmosphere is an acetylene atmosphere in the presence of large amounts of ethylene and hydrogen, by volume, of which C2H2 accounts for 0.5–3%, C2H4 accounts for 50–90%, H2 accounts for 5–20%, and the remainder is inert gas He; the amount of Pd-PC single-atom catalyst is 10–100 mg, the selective hydrogenation reaction temperature of acetylene is 60–200℃, the gas flow rate of the reaction atmosphere is 0.1–60 ml / min, and the space velocity is 10000–30000 ml / g·h.

[0035] Example 1

[0036] Preparation of phosphorus-doped carbon support: First, 1g of phytic acid and 12g of sucrose were dissolved in 50ml of aqueous solution and stirred at room temperature for 2h until dissolved. The resulting solution was dried in an oven at 100℃ for 12h, and then heated to 160℃ for 12h. The solution was ground into powder, placed in a quartz boat in a tubular furnace, and N2 was introduced at 100ml / min. The temperature was increased to 900℃ at 2℃ / min and maintained for 3h.

[0037] Example 2

[0038] Preparation of single-atom catalysts:

[0039] At room temperature (~25℃), measure 0.5 mL of 1 mg. Pd A 1.0 g sample of phosphorus-doped carbon support prepared according to the method in Example 1 was added to a 1 mL Pd(NO3)2 aqueous solution. After stirring for 30 min, the mixture was rapidly frozen in liquid nitrogen and then subjected to light intensity of 0.89 mW / cm². 2 The solution was irradiated with ultraviolet xenon lamp for 3 hours; then freeze-dried for 7 hours, and placed in a quartz boat in a tubular furnace. N2 was introduced at a rate of 100 ml / min, and the temperature was raised to 350°C at a rate of 2°C / min and maintained for 3 hours to obtain a single-atom palladium catalyst with a loading of 0.05 wt%.

[0040] Example 3

[0041] At room temperature (~25℃), measure 1 mL of 1 mg Pd A 1.0 g sample of phosphorus-doped carbon support prepared according to the method in Example 1 was added to a 1 mL Pd(NO3)2 aqueous solution. After stirring for 30 min, the mixture was rapidly frozen in liquid nitrogen and then subjected to light intensity of 0.89 mW / cm². 2 The solution was irradiated with ultraviolet xenon lamp for 3 hours; then freeze-dried for 7 hours, and placed in a quartz boat in a tubular furnace. N2 was introduced at a rate of 100 ml / min, and the temperature was raised to 300℃ at a rate of 2℃ / min and maintained for 3 hours to obtain a single-atom palladium catalyst with a loading of 0.1 wt%.

[0042] Example 4

[0043] At room temperature (~25℃), measure 5 mL of 1 mg Pd A 1.0 g sample of phosphorus-doped carbon support prepared according to the method in Example 1 was added to a 1 mL Pd(NO3)2 aqueous solution. After stirring for 30 min, the mixture was rapidly frozen in liquid nitrogen and then subjected to light intensity of 1.5 mW / cm². 2 The solution was irradiated with a xenon lamp for 3 hours; then freeze-dried for 7 hours, and placed in a quartz boat in a tubular furnace. N2 was introduced at a rate of 100 ml / min, and the temperature was increased to 350°C at a rate of 2°C / min and maintained for 3 hours. A single-atom palladium catalyst with a loading of 0.5 wt% was obtained.

[0044] Example 5

[0045] Activity evaluation of the single-atom palladium catalyst 0.05wt% Pd-PC prepared in Example 2:

[0046] Pretreatment conditions: 150℃, 15% (v / v) H2 and He mixture, space velocity 40000 mL·h -1 ·g -1 The reduction pressure is 1 MPa, and the reduction time is 2 hours.

[0047] Catalytic reaction conditions: Fixed-bed microreactor, feed gas composition (volume content) of 2.18% C2H2, 80.53% C2H4, 8.73% H2, He as balance gas, gas flow rate of 20 ml / min, space velocity of 24000 ml / g·h;

[0048] Reaction temperature range: 50℃~150℃.

[0049] Example 6

[0050] Activity evaluation of the single-atom palladium catalyst 0.1wt% Pd-PC prepared in Example 3: under the same conditions as in Example 5.

[0051] Example 7

[0052] Activity evaluation of the single-atom palladium catalyst 0.5wt% Pd-PC prepared in Example 4: under the same conditions as in Example 5.

[0053] Example 8

[0054] Activity evaluation of the single-atom palladium catalyst 0.05wt% Pd-PC prepared in Example 2:

[0055] Pretreatment conditions: 250℃, 15% (v / v) H2 and He mixture, space velocity 40000 mL·h -1 ·g -1 The reduction pressure is 1 MPa, and the reduction time is 2 hours.

[0056] Catalytic reaction conditions: Fixed-bed microreactor, feed gas composition (volume content) of 2.18% C2H2, 80.53% C2H4, 8.73% H2, He as balance gas, gas flow rate of 20 ml / min, space velocity of 24000 ml / g·h.

[0057] Reaction temperature range: 50℃~150℃.

[0058] Example 9

[0059] Activity evaluation of the single-atom palladium catalyst 0.5wt% Pd-PC prepared in Example 4: under the same conditions as in Example 8.

[0060] Example 10

[0061] Preparation of phosphorus-doped carbon support: First, 0.07 g phytic acid and 18 g sucrose were dissolved in 150 ml of aqueous solution and stirred at room temperature for 2 h until dissolved. The obtained solution was placed in an oven at 100 °C for 12 h and then heated to 160 °C for 12 h. The solution was ground into powder, placed in a quartz boat in a tubular furnace, and N2 was introduced at 100 ml / min. The temperature was increased to 600 °C at 10 °C / min and maintained for 5 h.

[0062] Example 11

[0063] Preparation of phosphorus-doped carbon support: First, 35g of phytic acid and 0.02g of sucrose were dissolved in 150ml of aqueous solution and stirred at room temperature for 2h. The resulting solution was then dried in an oven at 100℃ for 12h, and then heated to 160℃ for another 12h. The solution was then ground into powder, placed in a quartz boat in a tubular furnace, and N2 was introduced at 100ml / min. The temperature was increased to 600℃ at 10℃ / min and maintained for 5h.

[0064] Example 12

[0065] Preparation of phosphorus-doped carbon support: First, 0.01 g phytic acid and 18 g sucrose were dissolved in 150 ml of aqueous solution and stirred at room temperature for 2 h. The resulting solution was then dried in an oven at 100 ℃ for 12 h, and then heated to 160 ℃ for another 12 h. The solution was then ground into powder, placed in a quartz boat in a tubular furnace, and N2 was introduced at 100 ml / min. The temperature was increased to 600 ℃ at 10 ℃ / min and maintained for 5 h.

[0066] Example 13

[0067] Preparation of phosphorus-doped carbon support: First, 33g of phytic acid and 1g of sucrose were dissolved in 150ml of aqueous solution and stirred at room temperature for 2h. The resulting solution was then dried in an oven at 100℃ for 12h, and then heated to 160℃ for another 12h. The solution was then ground into powder, placed in a quartz boat in a tubular furnace, and N2 was introduced at 100ml / min. The temperature was increased to 600℃ at 10℃ / min and maintained for 5h.

[0068] Example 14

[0069] Preparation of single-atom catalysts:

[0070] At room temperature (~25℃), measure 0.5 mL of 1 mg. Pd A 1.0 g sample of phosphorus-doped carbon support prepared according to the method in Example 10 was added to a 1 mL Pd(NO3)2 aqueous solution. After stirring for 30 min, the mixture was rapidly frozen in liquid nitrogen and then subjected to a light intensity of 5.0 mW / cm². 2The solution was irradiated with ultraviolet xenon lamp for 3 hours; then freeze-dried for 7 hours, and placed in a quartz boat in a tubular furnace. N2 was introduced at a rate of 100 ml / min, and the temperature was raised to 500℃ at a rate of 5℃ / min and maintained for 3 hours to obtain a single-atom palladium catalyst with a loading of 0.05 wt%.

[0071] Example 15

[0072] Preparation of single-atom catalysts:

[0073] At room temperature (~25℃), measure 0.5 mL of 1 mg. Pd A 1.0 g sample of phosphorus-doped carbon support prepared according to the method in Example 11 was added to a 1 mL Pd(NO3)2 aqueous solution. After stirring for 30 min, the mixture was rapidly frozen in liquid nitrogen and then subjected to a light intensity of 5.0 mW / cm². 2 The solution was irradiated with ultraviolet xenon lamp for 3 hours; then freeze-dried for 7 hours, and placed in a quartz boat in a tubular furnace. N2 was introduced at a rate of 100 ml / min, and the temperature was raised to 500℃ at a rate of 5℃ / min and maintained for 3 hours to obtain a single-atom palladium catalyst with a loading of 0.05 wt%.

[0074] Example 16

[0075] Preparation of single-atom catalysts:

[0076] At room temperature (~25℃), measure 0.5 mL of 1 mg. Pd A 1.0 g sample of phosphorus-doped carbon support prepared according to the method in Example 12 was added to a 1 mL Pd(NO3)2 aqueous solution. After stirring for 30 min, the mixture was rapidly frozen in liquid nitrogen and then subjected to light intensity of 5.0 mW / cm². 2 The solution was irradiated with ultraviolet xenon lamp for 3 hours; then freeze-dried for 7 hours, and placed in a quartz boat in a tubular furnace. N2 was introduced at a rate of 100 ml / min, and the temperature was raised to 500℃ at a rate of 5℃ / min and maintained for 3 hours to obtain a single-atom palladium catalyst with a loading of 0.05 wt%.

[0077] Example 17

[0078] Preparation of single-atom catalysts:

[0079] At room temperature (~25℃), measure 0.5 mL of 1 mg. Pd A 1.0 g sample of phosphorus-doped carbon support prepared according to the method in Example 13 was added to a 1 mL Pd(NO3)2 aqueous solution. After stirring for 30 min, the mixture was rapidly frozen in liquid nitrogen and then subjected to a light intensity of 5.0 mW / cm². 2The solution was irradiated with ultraviolet xenon lamp for 3 hours; then freeze-dried for 7 hours, and placed in a quartz boat in a tubular furnace. N2 was introduced at a rate of 100 ml / min, and the temperature was raised to 500℃ at a rate of 5℃ / min and maintained for 3 hours to obtain a single-atom palladium catalyst with a loading of 0.05 wt%.

[0080] Example 18

[0081] Activity evaluation of the single-atom palladium catalyst 0.05 wt% Pd-PC prepared in Example 14:

[0082] Pretreatment conditions: 300℃, 50% (v / v) H2 and Ar mixture, space velocity 40000 mL·h -1 ·g -1 The reduction pressure was 0.1 MPa, and the reduction time was 10 hours.

[0083] Catalytic reaction conditions: Fixed-bed microreactor, feed gas composition (volume content) of 2.18% C2H2, 80.53% C2H4, 8.73% H2, He as balance gas, gas flow rate of 25 ml / min, space velocity of 30000 ml / g·h;

[0084] Example 19

[0085] Activity evaluation of the single-atom palladium catalyst 0.05wt% Pd-PC prepared in Example 15: under the same conditions as in Example 18.

[0086] Example 20

[0087] Activity evaluation of the single-atom palladium catalyst 0.05wt% Pd-PC prepared in Example 16: under the same conditions as in Example 18.

[0088] Example 21

[0089] Activity evaluation of the single-atom palladium catalyst 0.05wt% Pd-PC prepared in Example 17: under the same conditions as in Example 18.

[0090] Comparative Example 1

[0091] Preparation of nitrogen-doped carbon support: First, 1 gram of cysteine ​​and 12 g of sucrose were dissolved in 50 ml of aqueous solution and stirred at room temperature for 2 h. The resulting solution was then dried in an oven at 100 ℃ for 12 h, and then heated to 160 ℃ for another 12 h. The solution was then ground into powder, placed in a quartz boat in a tubular furnace, and N2 was introduced at 100 ml / min. The temperature was increased to 900 ℃ at 2 ℃ / min and maintained for 3 h.

[0092] Catalyst preparation: At room temperature (~25℃), measure 1 mL of 1 mg catalyst. PdAdd 1.0 g of nitrogen-doped carbon support to a 1 mL Pd(NO3)2 aqueous solution, continue stirring for 30 min, then rapidly freeze in liquid nitrogen, and finally freeze under light intensity of 0.89 mW / cm². 2 The solution was irradiated with ultraviolet xenon lamp for 3 hours; then freeze-dried for 7 hours, and placed in a tubular furnace quartz boat. N2 was introduced at a rate of 100 ml / min, and the temperature was raised to 300℃ at a rate of 2℃ / min and maintained for 3 hours to obtain a Pd-NC catalyst with a loading of 0.1 wt%.

[0093] Comparative Example 2

[0094] Activity evaluation of the 0.1 wt% Pd-NC catalyst prepared in Comparative Example 1: under the same conditions as in Example 5.

[0095] Comparative Example 3

[0096] Activity evaluation of the 0.1 wt% Pd-NC catalyst prepared in Comparative Example 1: under the same conditions as in Example 8.

[0097] Comparative Example 4

[0098] Carbon carrier preparation: First, 12g of sucrose was dissolved in 50ml of aqueous solution and stirred at room temperature for 2h. The resulting solution was then dried in an oven at 100℃ for 12h, and then heated to 160℃ for another 12h. The solution was then ground into powder, placed in a quartz boat in a tubular furnace, and N2 was introduced at 100ml / min. The temperature was increased to 900℃ at 2℃ / min and maintained for 3h.

[0099] Catalyst preparation: At room temperature (~25℃), 1 mL of 1 mg catalyst was measured. Pd Add 1.0 g of carbon support to a 1 mL Pd(NO3)2 aqueous solution, stir for 30 min, then rapidly freeze in liquid nitrogen, and finally freeze under light intensity of 0.89 mW / cm². 2 The solution was irradiated with ultraviolet xenon lamp for 3 hours; then freeze-dried for 7 hours, and placed in a quartz boat in a tubular furnace. N2 was introduced at a rate of 100 ml / min, and the temperature was raised to 300℃ at a rate of 2℃ / min and maintained for 3 hours to obtain a Pd / C catalyst with a loading of 0.1 wt%.

[0100] Comparative Example 5

[0101] Activity evaluation of the 0.1 wt% Pd / C catalyst prepared in Comparative Example 4: under the same conditions as in Example 5.

[0102] Comparative Example 6

[0103] Activity evaluation of the 0.1 wt% Pd / C catalyst prepared in Comparative Example 4: under the same conditions as in Example 8.

[0104] Comparative Example 7

[0105] At room temperature (~25℃), measure 10 mL of 1 mg. Pd A 1.0 g sample of phosphorus-doped carbon support prepared according to the method in Example 1 was added to a 1 mL Pd(NO3)2 aqueous solution. After stirring for 30 min, the mixture was rapidly frozen in liquid nitrogen and then subjected to light intensity of 0.89 mW / cm². 2 The solution was irradiated with ultraviolet xenon lamp for 3 hours; then freeze-dried for 7 hours, and placed in a quartz boat in a tubular furnace. N2 was introduced at a rate of 100 ml / min, and the temperature was raised to 300℃ at a rate of 2℃ / min and maintained for 3 hours to obtain a single-atom palladium catalyst with a loading of 1.0 wt%.

[0106] The activity evaluation of the above-mentioned single-atom palladium catalyst 1.0 wt% Pd-PC was conducted under the same conditions as in Example 5.

[0107] The corresponding conversion rates and selectivity results are shown in Table 1 below:

[0108] Table 1

[0109]

[0110] Experimental Example 1

[0111] The 0.1 wt% Pd-PC catalyst prepared in Example 3 and the 0.1 wt% Pd-NC catalyst prepared in Comparative Example 2 were evaluated for their acetylene hydrogenation performance in a fixed-bed microreactor. 100 mg of catalyst was mixed with 100 mg of alumina and reduced at 150 °C for 2 h in an atmosphere with a volume content of 15% H2 / He at a reduction pressure of 1 MPa. The temperature was then lowered to 70 °C for acetylene hydrogenation. The feed gas composition (volume content) was 2.18% C2H2, 80.53% C2H4, and 8.73% H2, with He as the equilibrium gas. The gas flow rate was 20 ml / min, and the space velocity was 24000 ml / g·h. The catalytic activity and stability of the Pd-PC and Pd-NC catalysts were investigated. Analysis of the feed gas and products was performed using Agilent gas chromatography with a flame ionization detector. The reaction results are shown in [Figure number missing]. Figure 3 .

[0112] Figure 1 Aberration-corrected electron microscopy (EM) spectra of the 0.5 wt% Pd-PC catalyst prepared in Example 4 are presented. At a loading of 0.5 wt%, Pd exists in the Pd-PC catalyst in a single-atom form, indicating that Pd also exists in a single-atom form under lower loading conditions. Figure 2 Aberration-corrected electron microscopy (EM) spectra of the 0.1 wt% Pd-PC catalyst prepared in Example 3 after the reaction are presented to preliminarily determine the morphology of Pd before and after the reaction. Figure 2 This indicates that Pd in ​​the Pd-PC catalyst also exists in a completely single-atom form after the reaction. Figure 1Combination Figure 2 It can be seen that Pd exists in a completely single-atom form both before and after the reaction in the Pd-PC catalyst.

[0113] Figure 3 Stability test graphs are provided for the 0.1 wt% Pd-PC catalyst prepared in Example 3 and the 0.1 wt% Pd-NC catalyst prepared in Comparative Example 2. Figure 3 It can be seen that the activity and selectivity of the 0.1wt% Pd-PC catalyst remain relatively stable after 100 hours of operation; while the activity of the 0.1wt% Pd-NC catalyst begins to decline rapidly in a short period of time, but the selectivity is not significantly affected, indicating that the Pd-NC catalyst has severe coking.

[0114] As shown in the attached figures and Table 1, the undoped palladium-based catalysts in Comparative Examples 5 and 6 exhibited low acetylene conversion and selectivity under milder pretreatment conditions. While increasing the pretreatment conditions improved acetylene conversion, the selectivity remained negative, indicating extremely poor performance. Furthermore, comparing Example 5 with Comparative Examples 2 and 5 reveals that, under the same reaction conditions, using a phosphorus-doped carbon support yields higher selectivity than using a non-phosphorus-doped carbon support. The results of Comparative Example 7 show that excessively high Pd content actually hinders optimal reaction performance. Therefore, the Pd content should be controlled between 0.005% and 0.5% of the total catalyst weight; within this range, the Pd dispersion in the catalyst is optimal.

[0115] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the present invention.

Claims

1. A method for selective hydrogenation of acetylene to prepare ethylene, characterized in that, The catalyst used has palladium as its main active component, and the support is phosphorus-doped carbon material. The palladium is dispersed at the atomic level on the support; the palladium content is 0.005 wt% to 0.5 wt% of the total catalyst mass. The method for preparing the catalyst includes the following steps: S1. Add the carrier to the palladium precursor solution, stir evenly, place it in liquid nitrogen for rapid freezing, and then irradiate it under a UV xenon lamp. S2. The solution obtained in step S1 is freeze-dried and then calcined under an inert atmosphere to obtain the catalyst.

2. The method for selective hydrogenation of acetylene to prepare ethylene according to claim 1, characterized in that, The preparation process of the phosphorus-doped carbon material includes the following steps: dissolving phosphorus-containing compounds and carbohydrates in water by thorough stirring, and then calcining under an inert atmosphere.

3. The method for selective hydrogenation of acetylene to prepare ethylene according to claim 2, characterized in that, The phosphorus-containing compound is selected from one or both of phosphoric acid and phytic acid, and the carbohydrate is selected from one or both of glucose and sucrose.

4. The method for selective hydrogenation of acetylene to prepare ethylene according to claim 1, characterized in that, In step S1, the stirring temperature is 10–30°C; the irradiation time of the ultraviolet xenon lamp is 0.5–5 hours, and the irradiation intensity is 0.5–5.0 mW / cm². 2 .

5. The method for selective hydrogenation of acetylene to prepare ethylene according to claim 1, characterized in that, The calcination conditions described in step S2 are: a heating rate of 2-5℃ / min, a temperature of 300-500℃, and a time of 0.5-5h.

6. The method for selective hydrogenation of acetylene to prepare ethylene according to claim 1, characterized in that, The palladium precursor solution is selected from one or more of palladium chloride, palladium nitrate, palladium acetate, and palladium acetylacetonate.

7. The method for selective hydrogenation of acetylene to prepare ethylene according to claim 1, characterized in that, The inert atmosphere is one or more of He, N2, and Ar.

8. The method for selective hydrogenation of acetylene to prepare ethylene according to claim 1, characterized in that, The reaction atmosphere for the selective hydrogenation of acetylene to prepare ethylene is an acetylene atmosphere in the presence of ethylene and hydrogen, wherein, by volume, C2H2 accounts for 0.5-3%, C2H4 accounts for 50-90%, H2 accounts for 5-20%, and the remainder is an inert gas; the amount of catalyst is 10-100 mg, the reaction temperature for the selective hydrogenation of acetylene is 60-200 °C, the gas flow rate of the reaction atmosphere is 0.1-60 ml / min, and the space velocity is 10000-30000 ml / g·h.

9. The method for selective hydrogenation of acetylene to prepare ethylene according to claim 8, characterized in that, The method for selective hydrogenation of acetylene to prepare ethylene further includes the following steps: before using the catalyst, it is first reduced in a reducing gas; the reduction conditions are: temperature 50-300℃, pressure 0.1MPa-1.0MPa, and time 0.5-10h.

10. The method for selective hydrogenation of acetylene to prepare ethylene according to claim 2, characterized in that, During the preparation of the phosphorus-doped carbon material, the stirring time is 30-120 min and the temperature is 10-30℃.

11. The method for selective hydrogenation of acetylene to prepare ethylene according to claim 2, characterized in that, In the preparation process of the phosphorus-doped carbon material, the calcination conditions are as follows: heating rate of 1-10℃ / min, calcination temperature of 600-1000℃, and time of 1-5h.

12. The method for selective hydrogenation of acetylene to prepare ethylene according to claim 3, characterized in that, The molar ratio of the phosphorus-containing compound to the carbohydrate is 0.0001 to 1000.

13. The method for selective hydrogenation of acetylene to prepare ethylene according to claim 12, characterized in that, The molar ratio of the phosphorus-containing compound to the carbohydrate is 0.001 to 10.

14. The method for selective hydrogenation of acetylene to prepare ethylene according to claim 9, characterized in that, The reducing gas is composed of hydrogen and an inert gas, wherein the volume percentage of H2 in the reducing gas is 1% to 100%, and the value is not 100%, and the inert gas is selected from He and / or Ar.

15. The method for selective hydrogenation of acetylene to prepare ethylene according to claim 9, characterized in that, The reduction temperature is 100–200°C.

16. The method for selective hydrogenation of acetylene to prepare ethylene according to claim 9, characterized in that, The reduction pressure is 0.5 MPa to 1.0 MPa.

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