Selective hydrogenation catalyst for acetylene and preparation method and application thereof

Abstract

The present application relates to a kind of acetylene selective hydrogenation catalyst, it is characterized in that, carrier is alpha-Al2O3, active component is Pd-Zn single-atom alloy, adjuvant is rare earth element, the nano-particle of the Pd-Zn single-atom alloy is dispersed on the surface of carrier, and average particle size is less than 5 nanometers, the specific surface area of the carrier is 1 ~ 10 m 2 / g.The present application also relates to a kind of acetylene selective hydrogenation catalyst preparation method and application.The acetylene selective hydrogenation catalyst provided by the present application has the characteristics of high acetylene conversion rate, high ethylene selectivity, long catalyst life, etc.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of selective hydrogenation catalysts, and particularly relates to a selective acetylene hydrogenation catalyst and a preparation method and application thereof. BACKGROUND

[0002] Selective hydrogenation of acetylene is an important reaction in industry. In the field of petroleum chemical industry, ethylene is a monomer for preparing polymers, which can be prepared from steam cracking of naphtha. The ethylene fraction in the cracking separation section contains 0.1-2% of acetylene, which is a poison for the catalyst in the further polymerization of ethylene, and affects the normal progress of the polymerization reaction, and therefore must be removed. In industry, catalytic hydrogenation is usually used to selectively hydrogenate acetylene into ethylene, and the selective hydrogenation catalysts usually use Pd as the active component. However, due to the lack of control over the microstructure of the Pd catalyst, different structures of Pd aggregates often exist at the same time, resulting in the over-hydrogenation of acetylene and the hydrogenation of ethylene in the raw material gas into ethane, causing waste of the raw material gas; or through hydrogenation dimerization to generate unsaturated C4 hydrocarbons, which continue to react to generate some polymers, commonly known as green oil, causing deactivation of the catalyst.

[0003] Generally, in order to avoid the occurrence of over-hydrogenation reaction and the generation of green oil as much as possible, the support of the hydrogenation catalyst is selected to be α-Al2O3, the main active component is mainly Pd, and different promoters are added, such as Ag (US5648576), Li (US3325556), Cu (US66275798), Bi (US6459008), K (CN1151908A), Cr (US4577047), Fe and Co (US3900526) and the like. These promoters mainly adjust the geometric or electronic structure of the main active component to achieve the purpose of inhibiting the occurrence of side reactions. In addition to α-Al2O3, the support of the selective hydrogenation catalyst also includes TiO2(US4839329), CaCO3(US4906800), SiO2(US5856262), ZnO(CN1317367A, CN104689816A) and the like. CN110876930A provides a supported metal catalyst and a preparation method thereof, but the preparation process is relatively complex, the catalyst precursor needs to be subjected to ionizing radiation or laser pretreatment, which is not conducive to large-scale production and application; in addition, the invention uses a support with a specific surface area of 10-500m 2 / g. Although the above-mentioned acetylene selective hydrogenation catalysts can achieve the purposes of improving the selectivity of ethylene and reducing the generation of green oil, the ethylene selectivity of the catalysts prepared by most of the methods is still low at high acetylene conversion. The reason is that due to the lack of control over the microstructure of the Pd catalyst, different structures of Pd aggregates exist at the same time, and a single structure of isolated Pd monomers cannot be formed, thereby causing the occurrence of over-hydrogenation and polymerization and the like.

[0004] CN106607024A provides a catalyst for CO gas phase synthesis of oxalate and its preparation method, although the activity of the catalyst is improved by doping with appropriate rare earth metals, and the active component is impregnated and loaded on the surface of the carrier by using a metal precursor solution, but the preparation method does not undergo reduction treatment, and the prepared active component is still mainly dispersed in the form of nanoparticles on the surface of the carrier, and does not form a single atom form. CN104588006A provides a palladium-containing alloy single atom catalyst for selective hydrogenation of alkyne, although Pd single atoms are formed, but the catalyst uses silica modified with organic reagents as the carrier, the preparation process is too complicated and the reaction temperature is too high, and at the same time, the selectivity of ethylene sharply decreases when the conversion rate of acetylene is high, which cannot meet the industrial requirements.

[0005] The catalyst preparation processes disclosed in CN110560086A, CN110560156A, CN110560157A, CN110560158A, CN110508277A, CN110508278A, CN110508290A and the like are complex, and high activity and high selectivity cannot be obtained simultaneously for carbon dioxide after hydrogenation reaction, and the generation of green oil also cannot be avoided, which affects the service life of the catalyst. The selective hydrogenation catalyst widely used in the industry at present has high catalytic activity, but the selectivity is still unsatisfactory, and the reason is mainly that the catalyst structure is not a single Pd atom. Only the single and isolated Pd single atom can inhibit the excessive hydrogenation of acetylene, improve the selectivity of ethylene, and inhibit the generation of green oil to improve the stability of the catalyst.

[0006] Therefore, it is of great significance to seek a relatively simple method to prepare a Pd single atom-containing alloy catalyst and to study its application in acetylene selective hydrogenation reaction. SUMMARY

[0007] Based on the above, the main purpose of the present application is to provide an acetylene selective hydrogenation catalyst and a preparation method thereof. The acetylene selective hydrogenation catalyst provided by the present application has the characteristics of high acetylene conversion rate, high ethylene selectivity, long catalyst life and the like.

[0008] In order to achieve the above purpose, the present application provides an acetylene selective hydrogenation catalyst, the carrier is α-Al2O3, the active component is Pd-Zn single atom alloy, the promoter is rare earth element, the nanoparticles of the Pd-Zn single atom alloy are dispersed on the surface of the carrier, and the average particle size is less than 5 nanometers, the specific surface area of the carrier is 1-10 m 2 / g.

[0009] In order to obtain a catalyst with good activity, selectivity and stability, the selective hydrogenation catalyst, wherein preferably, the content of Pd and Zn in the active component is 0.02-0.1% and 0.1-10% respectively in terms of element mass based on the mass of the carrier α-Al2O3, and the content of the additive is 0.1-1.0% in terms of the mass of the rare earth element.

[0010] The selective hydrogenation catalyst, wherein preferably, the mass ratio of Pd to Zn is 0.005-0.3:1.

[0011] The selective hydrogenation catalyst, wherein preferably, the rare earth element is selected from lanthanum and / or cerium.

[0012] In order to achieve the above-mentioned purpose, the application further provides a preparation method of the selective hydrogenation catalyst, comprising the following steps:

[0013] (1) α-Al2O3 carrier is added to a rare earth precursor solution for impregnation for 2-8 hours (temperature is 10-30°C), and then dried and calcined to obtain a catalyst intermediate;

[0014] (2) the catalyst intermediate is added to a Zn precursor solution for impregnation for 2-8 hours, dried and calcined, and then added to a Pd precursor solution for impregnation for 2-8 hours, dried and calcined to obtain a catalyst precursor;

[0015] (3) the catalyst precursor is reduced by a reducing gas to obtain a catalyst.

[0016] The preparation method of the selective hydrogenation catalyst, the concentration of the rare earth precursor solution, the Zn precursor solution and the Pd precursor solution is not limited and can meet the implementation of the scheme. Preferably, the concentration of the rare earth precursor solution is 2-25 mg / ml, the concentration of the Zn precursor solution is 3-400 mg / ml, and the concentration of Pd in the Pd precursor solution is 0.1-1.0 mg / ml.

[0017] The preparation method of the selective hydrogenation catalyst, wherein preferably, the drying conditions are: temperature 60-120°C, time 3-15 hours.

[0018] The preparation method of the selective hydrogenation catalyst, wherein preferably, the calcination conditions in step (1) are: temperature 400-600°C, time 1-3 hours; and the calcination conditions in step (2) are: temperature 400-600°C, time 1-3 hours.

[0019] The preparation method of the selective hydrogenation catalyst, wherein preferably, the reducing gas is pure hydrogen.

[0020] The preparation method of the selective hydrogenation catalyst, wherein preferably, the reduction conditions are: temperature 300-400℃, pressure 0.1-1.0MPa, time 0.5-5h.

[0021] The preparation method of the selective hydrogenation catalyst, wherein preferably, the Pd precursor solution is selected from one or more of the following: palladium chloride, palladium nitrate, palladium acetate, palladium acetylacetonate; the Zn precursor solution is selected from one or more of the following: zinc chloride, zinc nitrate, zinc acetate; the rare earth precursor solution contains lanthanum source and / or cerium source, and further preferably, the lanthanum source is selected from one or more of the following: lanthanum nitrate, lanthanum chloride, lanthanum acetate, and the cerium source is selected from one or more of the following: cerium nitrate, cerium chloride, cerium acetate.

[0022] To achieve the above-mentioned purpose, the application further provides a method for preparing ethylene by selective hydrogenation of acetylene, wherein the composition of the raw material gas in the reaction for preparing ethylene by selective hydrogenation of acetylene is: 0-0.1v% CO, 0.3-3.0v% C2H2, 1-25v% H2, 0-1.0v% MAPD (mixture of propyne and allene), and the balance is one or more of CH4, C2H6, C2H4, C3H8, C3H6 gas, and helium is the balance gas; the reaction temperature is 30-100℃, the reaction pressure is 0.5-4.0MPa, the gas space velocity is 3000-15000h-1, the acetylene conversion rate is 60-100%, and the ethylene selectivity is 60-100%. -1

[0023] Specifically, the application provides a preparation method of a selective hydrogenation catalyst, and the specific preparation process is as follows:

[0024] 1) The rare earth elements in the rare earth precursor solution are impregnated on the α-Al2O3 carrier by wet impregnation for 2-8h (at room temperature or room temperature), dried in an oven at 60-120℃ for 3-15h, calcined at 400-600℃ in a muffle furnace for 1-3h, to obtain a rare earth metal-alumina catalyst, denoted as M-Al2O3;

[0025] 2) The M-Al2O3 catalyst is impregnated in a precursor solution containing component Zn for 2-8h, dried in an oven at 60-120℃ for 3-15h, calcined at 400-600℃ in a muffle furnace for 1-3h, and then impregnated in a precursor solution containing component Pd for 2-8h, dried in an oven at 60-120℃ for 3-15h, calcined at 400-600℃ in a muffle furnace for 1-3h;

[0026] ​3) The catalyst obtained above is reduced by pure hydrogen, the reduction temperature is 300-400℃, the reduction pressure is 0.1-1.0MPa, and the reduction time is 0.5-5 hours, to obtain a PdZn / M-Al2O3 single-atom alloy catalyst.

[0027] Compared with the prior art, the present application has the following advantages:

[0028] (1) The selective hydrogenation catalyst provided by the present application has Pd completely in the form of single-atom alloy in the active component, and Pd-Zn alloy nanoparticles are highly dispersed on the surface of the carrier with an average particle size less than 5nm. Due to the existence of Pd-Zn single-atom alloy structure, the occurrence of side reactions is greatly inhibited, and the stability of the catalyst is improved.

[0029] (2) The selective hydrogenation catalyst provided by the present application adopts a carrier with a specific surface area of 1-10m 2 / g, while the carrier in the prior art has a specific surface area of 10-500m 2 / g, which indicates that the active component of the present application has better dispersion performance.

[0030] (3) The selective hydrogenation catalyst provided by the present application has high acetylene conversion rate and high ethylene selectivity at both low and high temperatures. That is, the catalyst has a wide operating temperature range and certain adaptability to different process conditions, which is beneficial to the stable operation of the hydrogenation device in industry.

[0031] (4) The selective hydrogenation catalyst provided by the present application is particularly suitable for the reaction of removing acetylene from petroleum cracking gas directly under the condition of a large amount of ethylene, low acetylene content, and large hydrogen-acetylene ratio. Under the premise of ensuring high hydrogenation activity and ethylene selectivity of the reaction, the cumbersome step of removing hydrogen in the post-treatment process of cracking gas is reduced, thus bringing significant economic benefits.

[0032] (5) The preparation method of the selective hydrogenation catalyst provided by the present application has the advantages of simple operation and easy industrial amplification. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 The infrared DRIFTS spectrum of the catalyst prepared in Example 1-3.

[0034] Figure 2-A The high-resolution spherical aberration correction electron microscope spectrum of the 0.02Pd-0.1Zn / 0.5La2O3-Al2O3 catalyst prepared in Example 1.

[0035] Figure 2-B The HRTEM graph of PdZn particles in the 0.02Pd-0.1Zn / 0.5La2O3-Al2O3 catalyst prepared in Example 1.

[0036] Figure 2-C STEM image of PdZn particles in the 0.02Pd-0.1Zn / 0.5La2O3-Al2O3 catalyst prepared in Example 1.

[0037] Figure 3 High resolution spherical aberration-corrected electron microscopy image of Pd particles catalyst prepared in Comparative Example 4. DETAILED DESCRIPTION

[0038] The following detailed description of the embodiments of the present application is made on the premise of the technical solutions of the present application, and detailed implementation manners and processes are given, but the protection scope of the present application is not limited to the following examples, and the experimental methods not specified in the following examples are usually carried out according to the conventional conditions.

[0039] The chemical reagents used in the examples of the present application are all of chemical purity and can be freely purchased in the market. The conversion rate and selectivity in the examples are calculated according to the following formulae:

[0040] Acetylene conversion rate (%) = 100 x △acetylene / inlet acetylene content

[0041] Ethylene selectivity (%) = 100 x △ethylene / △acetylene

[0042] Example 1

[0043] 0.02Pd-0.1Zn / 0.5La2O3-Al2O3 catalyst

[0044] 0.031 g of lanthanum nitrate solution was measured and diluted with water to 2.5 mL, and after stirring uniformly, 2.0 g of α-Al2O3 carrier (specific surface area 6.5 m 2 / g), impregnated at room temperature for 8 h, dried in an oven at 120 °C for 15 h, calcined at 400 °C in a muffle furnace for 3 h, to obtain a La2O3-Al2O3 catalyst (i.e., catalyst intermediate); the obtained La2O3-Al2O3 catalyst was dispersed into a 2.5 mL aqueous solution prepared from 0.0091 g of zinc chloride solution, impregnated at room temperature for 8 h, dried in an oven at 120 °C for 15 h, calcined at 400 °C in a muffle furnace for 3 h; the obtained catalyst precursor was dispersed again into a 2.5 mL aqueous solution prepared from 0.214 mL (1.874 mg Pd / mL) of palladium nitrate solution, impregnated at room temperature for 8 h, dried in an oven at 120 °C for 15 h, calcined at 400 °C in a muffle furnace for 3 h; the obtained catalyst precursor was reduced with 100% H2, at a reduction temperature of 400 °C, a reduction pressure of 0.1 MPa, and a reduction time of 1 h, to obtain a Pd-Zn / La-Al2O3 single-atom alloy catalyst. The theoretical loading of Pd was 0.02% (wt), the theoretical loading of Zn was 0.1% (wt), and the theoretical loading of La was 0.5% (wt), based on the mass of the a-Al2O3 support.

[0045] Example 2

[0046] 0.02Pd-0.1Zn / 0.2La2O3-Al2O3 catalyst

[0047] A 0.0124 g lanthanum nitrate solution was measured and water was added to 2.5 mL. After stirring until uniform, 2.0 g of a-Al2O3 support (specific surface area 6.5 m 2 / g), impregnated at room temperature for 8 h, dried in an oven at 120 °C for 15 h, calcined at 500 °C in a muffle furnace for 3 h; the obtained La2O3-Al2O3 catalyst was dispersed into a 2.5 mL aqueous solution prepared from 0.0091 g of zinc chloride solution, impregnated at room temperature for 8 h, dried in an oven at 120 °C for 15 h, calcined at 400 °C in a muffle furnace for 3 h; the obtained catalyst precursor was dispersed again into a 2.5 mL aqueous solution prepared from 0.214 mL (1.874 mg Pd / mL) of palladium nitrate solution, impregnated at room temperature for 8 h, dried in an oven at 120 °C for 15 h, calcined at 400 °C in a muffle furnace for 3 h; the obtained catalyst was reduced with 100% H2, at a reduction temperature of 400 °C, a reduction pressure of 0.1 MPa, and a reduction time of 1 h, to obtain a Pd-Zn / La-Al2O3 single-atom alloy catalyst. The theoretical loading of Pd was 0.02% (wt), the theoretical loading of Zn was 0.1% (wt), and the theoretical loading of La was 0.2% (wt), based on the mass of the a-Al2O3 support.

[0048] Example 3

[0049] 0.02Pd-0.1Zn / 0.1La2O3-Al2O3 catalyst

[0050] Measure 0.0062 g of lanthanum nitrate solution and add water to a final volume of 2.5 mL. After stirring thoroughly, add 2.0 g of α-Al₂O₃ support (specific surface area 6.5 m²). 2 The La2O3-Al2O3 catalyst was impregnated at room temperature for 8 hours, dried in an oven at 120°C for 15 hours, and calcined in a muffle furnace at 500°C for 3 hours. The resulting La2O3-Al2O3 catalyst was dispersed in a 2.5 mL aqueous solution prepared from 0.0091 g zinc chloride solution, impregnated at room temperature for 8 hours, dried in an oven at 120°C for 15 hours, and calcined in a muffle furnace at 400°C for 3 hours. The resulting catalyst precursor was then further dispersed in a 0.214 mL (1.874 mg) aqueous solution. Pd The catalyst was impregnated in a 2.5 mL aqueous solution of palladium nitrate ( / mL) at room temperature for 8 h, dried in an oven at 120 °C for 15 h, and calcined in a muffle furnace at 400 °C for 3 h. The resulting catalyst was then reduced with 100% H₂ at 400 °C, 0.1 MPa, and for 1 h to obtain a Pd-Zn / La-Al₂O₃ single-atom alloy catalyst. Based on the mass of the α-Al₂O₃ support, the theoretical loading of Pd was 0.02% (wt), the theoretical loading of Zn was 0.1% (wt), and the theoretical loading of La was 0.1% (wt).

[0051] Example 4

[0052] 0.02Pd-3Zn / 0.1La2O3-Al2O3 catalyst

[0053] Measure 0.0062 g of lanthanum nitrate solution and add water to a final volume of 2.5 mL. After stirring thoroughly, add 2.0 g of α-Al₂O₃ support (specific surface area 6.5 m²). 2 The La2O3-Al2O3 catalyst was impregnated at room temperature for 8 hours, dried in an oven at 120°C for 15 hours, and calcined in a muffle furnace at 500°C for 3 hours. The resulting La2O3-Al2O3 catalyst was dispersed in a 2.5 mL aqueous solution prepared from 0.273 g of zinc chloride solution, impregnated at room temperature for 8 hours, dried in an oven at 120°C for 15 hours, and calcined in a muffle furnace at 400°C for 3 hours. The resulting catalyst precursor was then further dispersed in a 0.214 mL (1.874 mg) aqueous solution. PdThe catalyst was impregnated in a 2.5 mL aqueous solution of palladium nitrate ( / mL) at room temperature for 8 h, dried in an oven at 120 °C for 15 h, and calcined in a muffle furnace at 400 °C for 3 h. The resulting catalyst was then reduced with 100% H₂ at 400 °C, 0.1 MPa, and for 1 h to obtain a Pd-Zn / La-Al₂O₃ single-atom alloy catalyst. Based on the mass of the α-Al₂O₃ support, the theoretical loading of Pd was 0.02% (wt), the theoretical loading of Zn was 3% (wt), and the theoretical loading of La was 0.1% (wt).

[0054] Example 5

[0055] 0.03Pd-0.1Zn / 0.5La2O3-Al2O3 catalyst

[0056] Measure 0.031 g of lanthanum nitrate solution and add water to a final volume of 2.5 mL. After stirring thoroughly, add 2.0 g of α-Al₂O₃ support (specific surface area 6.5 m²). 2 The La2O3-Al2O3 catalyst was impregnated at room temperature for 8 hours, dried in an oven at 50°C for 15 hours, and calcined in a muffle furnace at 500°C for 3 hours. The resulting La2O3-Al2O3 catalyst was dispersed in a 2.5 mL aqueous solution prepared from 0.0091 g of zinc chloride solution, impregnated at room temperature for 8 hours, dried in an oven at 90°C for 8 hours, and calcined in a muffle furnace at 400°C for 3 hours. The resulting catalyst precursor was then further dispersed in a 0.321 mL (1.874 mg) aqueous solution. Pd The catalyst was impregnated in a 2.5 mL aqueous solution of palladium nitrate ( / mL) at room temperature for 8 h, dried in an oven at 120 °C for 5 h, and calcined in a muffle furnace at 400 °C for 3 h. The resulting catalyst was then reduced with 100% H₂ at 400 °C, 0.1 MPa, and for 1 h to obtain a Pd-Zn / La-Al₂O₃ single-atom alloy catalyst. Based on the mass of the α-Al₂O₃ support, the theoretical loading of Pd was 0.03% (wt), the theoretical loading of Zn was 0.1% (wt), and the theoretical loading of La was 0.5% (wt).

[0057] Example 6

[0058] 0.02Pd-0.1Zn / 0.5La2O3-Al2O3 catalyst

[0059] Measure 0.031 g of lanthanum nitrate solution and add water to a final volume of 2.5 mL. After stirring thoroughly, add 2.0 g of α-Al₂O₃ support (specific surface area 6.5 m²). 2Pd / mL) palladium nitrate solution, impregnated at room temperature for 6 h, dried in an oven at 120 °C for 15 h, and calcined at 400 °C in a muffle furnace for 3 h; the resulting catalyst precursor was dispersed again into 2.5 mL of an aqueous solution prepared from 0.214 mL (1.874 mg 2 / mL) of palladium nitrate solution, impregnated at room temperature for 6 h, dried in an oven at 120 °C for 15 h, and calcined at 400 °C in a muffle furnace for 3 h; the resulting catalyst was reduced with 100% H2at a reduction temperature of 400 °C, a reduction pressure of 1 MPa, and a reduction time of 1 h to obtain a Pd-Zn / La-Al2O3 monatomic alloy catalyst. The theoretical loading of Pd was 0.02% by weight, the theoretical loading of Zn was 0.1% by weight, and the theoretical loading of La was 0.5% by weight, based on the mass of the a-Al2O3 support.

[0060] Example 7

[0061] 0.02Pd-0.1Zn / 0.1CeO2-Al2O3 catalyst

[0062] A 0.0053 g cerium nitrate solution was measured into 2.5 mL of water, and after stirring until uniform, 2.0 g of a-Al2O3 support (specific surface area 6.5 m 2 / g) was added, impregnated at room temperature for 8 h, dried in an oven at 120 °C for 15 h, and calcined at 500 °C in a muffle furnace for 3 h; the resulting La2O3-Al2O3 catalyst was dispersed into a 2.5 mL aqueous solution prepared from 0.0091 g of zinc chloride solution, impregnated at room temperature for 8 h, dried in an oven at 120 °C for 15 h, and calcined at 400 °C in a muffle furnace for 3 h; the resulting catalyst precursor was dispersed again into a 2.5 mL aqueous solution prepared from 0.214 mL (1.874 mg Pd / mL) of palladium nitrate solution, impregnated at room temperature for 8 h, dried in an oven at 120 °C for 15 h, and calcined at 400 °C in a muffle furnace for 3 h; the resulting catalyst was reduced with 100% H2at a reduction temperature of 400 °C, a reduction pressure of 0.1 MPa, and a reduction time of 1 h to obtain a Pd-Zn / Ce-Al2O3 monatomic alloy catalyst. The theoretical loading of Pd was 0.02% by weight, the theoretical loading of Zn was 0.1% by weight, and the theoretical loading of Ce was 0.1% by weight, based on the mass of the a-Al2O3 support.

[0063] Example 8

[0064] 0.1Pd-10Zn / 1La2O3-Al2O3 catalyst

[0065] Measure 0.0620 g of lanthanum nitrate solution, add water to a final volume of 2.5 mL, stir well, and then add 2.0 g of α-Al₂O₃ support (specific surface area 6.5 m²). 2 The La2O3-Al2O3 catalyst was impregnated at room temperature for 2 hours, dried in an oven at 60°C for 3 hours, and calcined in a muffle furnace at 600°C for 1 hour. The obtained La2O3-Al2O3 catalyst was dispersed in a 2.5 mL aqueous solution prepared from 0.9100 g of zinc chloride solution, impregnated at room temperature for 2 hours, dried in an oven at 60°C for 3 hours, and calcined in a muffle furnace at 600°C for 1 hour. The obtained catalyst precursor was again dispersed in a 2.5 mL aqueous solution prepared from 1.07 mL (1.874 mg Pd / mL) of palladium nitrate solution, impregnated at room temperature for 2 hours, dried in an oven at 60°C for 3 hours, and calcined in a muffle furnace at 600°C for 1 hour. The catalyst obtained above was reduced with 100% H2 at a reduction temperature of 400°C, a reduction pressure of 0.1 MPa, and a reduction time of 0.5 h to obtain a Pd-Zn / La-Al2O3 single-atom alloy catalyst. Based on the mass of the α-Al2O3 support, the theoretical loading of Pd is 0.1% (by weight), the theoretical loading of Zn is 10% (by weight), and the theoretical loading of La is 1% (by weight).

[0066] Comparative Example 1

[0067] 0.02Pd / Al2O3 catalyst

[0068] Measure 0.214 mL (1.874 mg) Pd A 2.5 mL aqueous solution prepared from palladium nitrate solution (6.5 mL / mL) was stirred until homogeneous, and then 2.0 g of α-Al₂O₃ support (specific surface area 6.5 m² / mL) was added. 2 The catalyst was impregnated at room temperature for 8 hours, dried in an oven at 120°C for 15 hours, and calcined in a muffle furnace at 400°C for 3 hours. The resulting catalyst was then reduced with 100% H₂ at 400°C, a reduction pressure of 0.1 MPa, and a reduction time of 1 hour to obtain the Pd / Al₂O₃ catalyst. The theoretical Pd loading, based on the mass of the α-Al₂O₃ support, was 0.02%.

[0069] Comparative Example 2

[0070] 0.02Pd-0.1Zn / Al2O3 catalyst

[0071] Measure 0.0091 g of zinc chloride solution to prepare a 2.5 mL aqueous solution, stir well, and then add 2.0 g of α-Al₂O₃ support (specific surface area 6.5 m²). 2 / g), impregnated at room temperature for 8 h, dried in an oven at 120 °C for 15 h, and calcined in a muffle furnace at 400 °C for 3 h; the obtained catalyst precursor was redispersed in 0.214 mL (1.874 mg) Pd The catalyst was impregnated in a 2.5 mL aqueous solution of palladium nitrate ( / mL) at room temperature for 8 h, dried in an oven at 120 °C for 15 h, and calcined in a muffle furnace at 400 °C for 3 h. The resulting catalyst was then reduced with 100% H₂ at 400 °C, 0.1 MPa, and for 1 h to obtain a PdZn / Al₂O₃ single-atom alloy catalyst. Based on the mass of the α-Al₂O₃ support, the theoretical loading of Pd was 0.02%, and the theoretical loading of Zn was 0.1%.

[0072] Comparative Example 3

[0073] 0.03Pd-0.1Zn / Al2O3 catalyst

[0074] Measure 0.0091 g of zinc chloride solution to prepare a 2.5 mL aqueous solution, stir well, and then add 2.0 g of α-Al₂O₃ support (specific surface area 6.5 m²). 2 / g), impregnated at room temperature, dried in an oven at 120℃ for 15h, and calcined in a muffle furnace at 400℃ for 3h; the obtained catalyst precursor was redispersed in 0.321mL (1.874mg) Pd The catalyst was impregnated in a 2.5 mL aqueous solution of palladium nitrate ( / mL) at room temperature for 8 h, dried in an oven at 120 °C for 15 h, and calcined in a muffle furnace at 400 °C for 3 h. The resulting catalyst was then reduced with 100% H₂ at 400 °C, 0.1 MPa, and for 1 h to obtain a PdZn / Al₂O₃ single-atom alloy catalyst. Based on the mass of the α-Al₂O₃ support, the theoretical loading of Pd was 0.03%, and the theoretical loading of Zn was 0.1%.

[0075] Comparative Example 4

[0076] 0.02Pd-0.1Zn / Al2O3 laser pretreated catalyst

[0077] Measure 0.0091g ​​of zinc chloride solution to prepare 2.5mL of aqueous solution, stir well, and then add 2.0g of a solution with a specific surface area of ​​100m². 2 / g Al2O3 support, impregnated at room temperature, and dried in an oven at 120℃ for 15h; the obtained catalyst precursor was redispersed in 0.214mL (1.874mg) of Al2O3 support. PdThe catalyst precursor was impregnated in a 2.5 mL aqueous solution prepared with palladium nitrate ( / mL) at room temperature and dried in an oven at 120 °C for 15 h. The precursor was then thermally treated with a laser at 2 mm / s and 80 W for 28 s. It was then reduced with 1 mg / mL, 500 mL, 30 °C oxalic acid solution for 1 h. After washing and drying, a Pd-Zn / Al₂O₃ single-atom alloy catalyst was obtained. The theoretical loading of Pd was 0.02%, and the theoretical loading of Zn was 0.1%.

[0078] Comparative Example 5

[0079] 0.02Pd-0.1Zn / 0.5La2O3-Al2O3 catalyst

[0080] Measure 0.031 g of lanthanum nitrate solution, add water to a final volume of 2.5 mL, stir well, and then add 2.0 g of a solution with a specific surface area of ​​100 m². 2 A La2O3-Al2O3 catalyst was obtained by impregnating a 0.0091 g zinc chloride solution on an Al2O3 support at room temperature for 8 h, drying it in an oven at 120 °C for 15 h, and calcining it in a muffle furnace at 400 °C for 3 h. The La2O3-Al2O3 catalyst was dispersed in a 2.5 mL aqueous solution prepared with 0.214 mL (1.874 mg Pd / mL) palladium nitrate solution, impregnated at room temperature for 8 h, dried in an oven at 120 °C for 15 h, and calcined in a muffle furnace at 400 °C for 3 h. The catalyst precursor was then dispersed again in a 2.5 mL aqueous solution prepared with 0.214 mL (1.874 mg Pd / mL) palladium nitrate solution, impregnated at room temperature for 8 h, dried in an oven at 120 °C for 15 h, and calcined in a muffle furnace at 400 °C for 3 h. The catalyst precursor obtained above was reduced with 100% H2 at a reduction temperature of 400 °C, a reduction pressure of 0.1 MPa, and a reduction time of 1 h to obtain a Pd-Zn / La-Al2O3 catalyst. Based on the mass of the α-Al2O3 support, the theoretical loading of Pd is 0.02% (by weight), the theoretical loading of Zn is 0.1% (by weight), and the theoretical loading of La is 0.5% (by weight).

[0081] Experimental Example 1

[0082] Activity evaluation of Examples 1-8 and Comparative Examples 1-5

[0083] The reaction was carried out in a fixed-bed microreactor. The reaction feed gas composition was 0.1% CO, 1.0% C2H2, 25% H2, 1.0% MAPD, and the balance was 1% each of CH4, C2H6, C2H4, C3H8, and C3H6. Helium was used as the balance gas.

[0084] Table 1

[0085]

[0086] Figure 1The image shows the infrared DRIFTS spectra of the Pd-Zn / La2O3-Al2O3 catalysts prepared in Examples 1-3. The spectra can be used to determine the form of Pd. Generally, there are two CO adsorption modes: bridge adsorption (1950 cm⁻¹). -1 The left and right positions indicate the presence of Pd-Pd bonding, and linear adsorption (2069 cm⁻¹) -1 The left and right positions indicate that Pd exists in a single-atom form. Each Pd-Zn / La2O3-Al2O3 catalyst exhibits only one adsorption form, namely linear adsorption, indicating that Pd exists entirely in a single-atom form within the catalyst. Figure 2-A Here is a high-resolution aberration-corrected electron micrograph of the Pd-Zn single-atom alloy catalyst (prepared in Example 1), from... Figure 2-A Measurements revealed that the lattice spacing of the Pd-Zn nanoparticles was 0.219 nm, which matches the (111) plane spacing of the tetragonal Pd-Zn alloy; from Figure 2-B and Figure 2-C It can be seen that the Pd-Zn alloy has a uniform particle size distribution, with an average particle size of less than 5.0 nm.

[0087] Based on the above figures and the data in Table 1, it can be found that in Comparative Examples 1-5, the single Pd / Al2O3 catalyst, the Pd-Zn / Al2O3 catalyst without rare earth metal addition, or the support with a specific surface area not exceeding 1-10 m², all exhibit these characteristics. 2 Catalysts prepared within the / g range exhibited low catalytic activity; even with increased Pd loading, the acetylene conversion was only around 60%. However, for the single-atom alloy catalysts of Examples 1-7, comparisons under the same Pd loading and reaction conditions revealed that the formation of the Pd-Zn single-atom alloy and the doping of rare earth metals significantly improved the catalyst's hydrogenation activity and selectivity for ethylene. Furthermore, Comparative Example 4 used catalysts with a specific surface area of ​​100 m² / g. 2 / g Al2O3 support, and the catalyst precursor was treated with laser thermal treatment. The results show (see appendix) Figure 3 The Pd-Zn particles obtained by this preparation method are not single-atom alloys, but Pd nanoparticles with an average particle size greater than 5 nm; in addition, a surface area with a large specific area (100 m²) is used. 2 The Al2O3 support (g) exhibits low catalytic activity and poor selectivity, possibly due to excessive hydrogenation caused by its high specific surface area.

[0088] 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 selective hydrogenation catalyst for acetylene, characterized in that, The support is α-Al₂O₃, the active component is a Pd-Zn single-atom alloy, and the additives are rare earth elements. The average particle size of the Pd-Zn single-atom alloy is less than 5 nanometers, and the specific surface area of ​​the support is 1–10 m². 2 / g; The acetylene selective hydrogenation catalyst is used for the selective hydrogenation of acetylene to prepare ethylene at a reaction temperature of 30-100℃. The catalyst comprises 100% α-Al₂O₃ as the support, and the active components contain 0.02-0.1% and 0.1-10% Pd and Zn by mass, respectively, and the auxiliary agent by mass is 0.1-1.0%. The rare earth elements are selected from one or more of lanthanum and cerium.

2. The selective hydrogenation catalyst according to claim 1, characterized in that, The mass ratio of Pd to Zn is 0.005-0.3 :

1.

3. A method for preparing the acetylene selective hydrogenation catalyst according to claim 1 or 2, characterized in that, Includes the following steps: (1) The α-Al2O3 support was impregnated in a rare earth precursor solution, then dried and calcined to obtain a catalyst intermediate; (2) The catalyst intermediate was impregnated in a Zn precursor solution, dried and calcined, and then impregnated in a Pd precursor solution, dried and calcined to obtain the catalyst precursor; (3) The catalyst precursor is reduced by reducing gas to obtain the catalyst.

4. The method for preparing the selective hydrogenation catalyst according to claim 3, characterized in that, The drying conditions are: temperature 60-120℃, time 3-15 hours; the calcination conditions in step (1) are: temperature 400-600℃, time 1-3 hours; the calcination conditions in step (2) are: temperature 400-600℃, time 1-3 hours.

5. The method for preparing the selective hydrogenation catalyst according to claim 3, characterized in that, The reducing gas is pure hydrogen.

6. The method for preparing the selective hydrogenation catalyst according to claim 3, characterized in that, The reduction conditions are: temperature 300-400℃, pressure 0.1MPa-1.0MPa, and time 0.5-5h.

7. The method for preparing the selective hydrogenation catalyst according to claim 3, characterized in that, The Pd source in the Pd precursor solution is selected from one or more of palladium chloride, palladium nitrate, palladium acetate, and palladium acetylacetonate; the zinc source in the Zn precursor solution is selected from one or more of zinc chloride, zinc nitrate, and zinc acetate; the rare earth precursor solution contains a lanthanum source and / or a cerium source, wherein the lanthanum source is selected from one or more of lanthanum nitrate, lanthanum chloride, and lanthanum acetate, and the cerium source is selected from one or more of cerium nitrate, cerium chloride, and cerium acetate.

8. A method for selective hydrogenation of acetylene to prepare ethylene, characterized in that, In the selective hydrogenation of acetylene to ethylene reaction, the selective hydrogenation catalyst of claim 1 or 2 is used. The composition of the reactant gas is: 0-0.1 v% CO, 0.3-3.0 v% C2H2, 1-25 v% H2, 0-1.0 v% MAPD, and the balance is one or more of CH4, C2H6, C2H4, C3H8, and C3H6 gases, with helium as the balance gas; the reaction temperature is 30-100℃, the reaction pressure is 0.5-4.0 MPa, and the gas space velocity is 3000-15000 h⁻¹. -1 Acetylene conversion rate 60-100%, ethylene selectivity 60-100%.

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