A method for preparing a Pd catalyst supported by MgO carrier and application thereof

Abstract

The application belongs to the field of catalytic science and technology, and specifically discloses a preparation method of a Pd catalyst supported by a MgO carrier and application thereof. x The Pd / MO x The Pd / MO x The preparation method of the Pd / MO x -MgO catalyst can be used for selective hydrogenation of acetylene, and at 100 DEG C, 100% acetylene conversion rate and 98% ethylene selectivity can be simultaneously achieved, and the catalyst shows high stability, which is superior to most existing catalysts, indicating that the Pd / MO x The preparation method of the Pd / MO x The preparation method of the Pd / MO x The preparation method of the Pd / MO x The preparation method of the Pd / MO x The preparation method of the Pd / MO x The preparation method of the Pd / MO x The preparation method of the Pd / MO x The preparation method of the Pd / MO x The preparation method of the Pd / MO x

Description

Technical Field

[0001] This invention belongs to the field of catalysis science and technology, specifically relating to a method for preparing a Pd catalyst supported on an MgO support and its application. Background Technology

[0002] Selective hydrogenation of acetylene plays a crucial role in the petrochemical industry. Industrially, ethylene is primarily produced through the steam cracking of petroleum hydrocarbons, but this process inevitably generates acetylene impurities at a volume fraction of approximately 0.5-2.0 vol.%. These trace amounts of acetylene severely poison the Ziegler-Natta catalyst used in ethylene polymerization, not only reducing catalyst activity and lifespan but also affecting the quality of polyethylene. Therefore, it is essential to reduce the acetylene content to below 5 ppm. Selective hydrogenation of acetylene is considered one of the most effective methods for removing acetylene impurities. This process converts harmful acetylene into ethylene and offers advantages such as simplicity, low energy consumption, and minimal ethylene loss.

[0003] In acetylene hydrogenation catalysts, the properties of the support have a significant impact on reaction performance, with acidic supports posing a particularly serious threat. First, the acidic sites on the support catalyze side reactions such as polymerization and cracking of acetylene. Acetylene molecules readily aggregate at acidic sites, generating large-molecule liquid hydrocarbons, commonly known as "green oil." This "green oil" covers the active sites of the catalyst, hindering contact between reactant molecules and the active sites, leading to rapid catalyst deactivation. Studies have shown a direct relationship between the catalyst deactivation rate and the density of acidic groups on the support. Second, carbon deposits generated by polymerization further clog the catalyst's pores, reducing not only the diffusion and adsorption efficiency of acetylene but also exacerbating localized overheating in the bed. Since acetylene hydrogenation is a strongly exothermic reaction, the combined effects of carbon deposits caused by acidic supports and poor heat transfer make the catalyst highly susceptible to sintering and irreversible deactivation. Therefore, in industrial catalyst design, precise control of the acidity of the support surface is typically required, or the use of low-acidity inert α-Al₂O₃ materials as supports is employed to suppress side reactions, extend catalyst life, and ensure high selectivity for ethylene. Summary of the Invention

[0004] Therefore, the purpose of this invention is to provide a method for preparing a Pd catalyst supported on alkaline MgO and its application. By modifying the surface of the alkaline MgO support with an atomically highly dispersed metal oxide layer, the dispersion of metal Pd is facilitated, which can effectively reduce the amount of noble metal Pd in ​​the catalyst for selective hydrogenation of acetylene, inhibit the occurrence of side reactions, and improve the service life of the catalyst.

[0005] According to a first aspect of the present invention, a method for preparing a Pd catalyst supported on an MgO support is provided, comprising the following steps: S1, dissolve metal M salt in water to form M salt solution, add carrier until completely wetted, stir evenly, freeze dry to obtain product A; S2, product A is impregnated with a diluted Pd salt solution, freeze-dried to obtain product B, which is then calcined and reduced to obtain Pd / MO. x -MgO catalyst, where x is 0.5~2; The metal M in the metal M salt is selected from at least one of La, Ce, Ga, In, and Sn; The carrier is a Mg-containing compound.

[0006] Based on the above technical solution, the metal M salt in step S1 is selected from at least one of La(NO3)3·xH2O, Ce(NO3)3·6H2O, Ga(NO3)3·xH2O, In(NO3)3·H2O, and SnCl2·2H2O. The Mg-containing compound mentioned in step S1 is selected from one of MgO, Mg(OH)2, MgC2O4, Mg3(PO4)2, and MgCO3.

[0007] Based on the above technical solution, the concentration of salt M in step S1 is 0.1~100 mg / mL; In step S1, the mass ratio of the carrier added to the volume of the M salt solution is 0.5~2g:0.5~1mL.

[0008] Based on the above technical solution, the freeze-drying conditions described in steps S1 and S2 are as follows: The freeze-drying temperature is -30~-80℃; The freeze-drying time is 4 to 12 hours.

[0009] Based on the above technical solution, the Pd salt in step S2 is selected from at least one of Na2PdCl4, PdCl2·2H2O, Pd(NO3)2·2H2O, PdSO4·2H2O, Pd(OCOCH3)2, and Pd(C5H7O2)2. The specific method for diluting the Pd salt solution is as follows: take 50~200μL of Pd salt solution with a concentration of 0.1~1g / L and mix it with 0.5~2mL of ultrapure water to obtain the diluted Pd salt solution; The volume ratio of the diluted Pd salt solution to the mass ratio of product A is 0.5~2 ml : 0.5~4 g.

[0010] Based on the above technical solution, the calcination in step S2 is specifically as follows: in an air atmosphere, the temperature is increased to 300-700 ℃ at a heating rate of 2-10℃ / min for 1-5 h.

[0011] Based on the above technical solution, the Pd / MOx The content of metal M in the MgO catalyst is 0.1~10 wt%.

[0012] Based on the above technical solution, the Pd / MO x The Pd content in the MgO catalyst is 0.01~0.5 wt%; The Pd / MO x In the MgO catalyst, M atoms form a densely packed sub-monolayer structure on the MgO support, accompanied by sparsely and randomly distributed isolated M atoms, while Pd exists in the form of single atoms or clusters of few atoms.

[0013] According to a second aspect of the invention, a Pd / MO is provided. x The application of MgO catalysts in the selective hydrogenation of acetylene includes the following steps: Pd / MO x - The MgO catalyst is reduced in an H2 atmosphere, and the H2 is switched to feed gas to carry out the catalytic reaction in a fixed-bed reactor.

[0014] Based on the above technical solution, the reduction specifically involves reducing at 300~600℃ for 1~5 hours; The conditions for the catalytic reaction are as follows: The temperature of the catalytic reaction is 30~200℃, preferably 50~110℃.

[0015] Beneficial effects The technical solution disclosed in this invention uses basic MgO as a support. A sub-monolayer oxide layer is formed through the strong interaction between the metal oxide and the basic sites of MgO, which helps the noble metal Pd to be highly dispersed on the support surface, effectively reducing the Pd loading. Simultaneously, the oxide layer transfers electrons to Pd, improving the activity and selectivity of the acetylene selective hydrogenation reaction. Furthermore, the basic surface of the MgO support can inhibit the formation of "green oil" and carbon deposits, improving the stability of the catalyst. Attached Figure Description

[0016] To more clearly illustrate the embodiments of the present invention, the accompanying drawings involved in the embodiments will be briefly described below.

[0017] Figure 1 The Pd / LaO of Embodiment 1 of the present invention x -Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy and elemental imaging of MgO catalyst; Figure 2 Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy image and elemental imaging of the Pd / MgO catalyst of Comparative Example 1 of this invention. Figure 3The graphs show the selective hydrogenation performance of the catalysts obtained in Example 1, Comparative Example 1, and Comparative Example 2 of this invention. Figure 4 The series of Pd / LaO with different La contents obtained in Example 3 of this invention x XRD pattern of MgO catalyst; Figure 5 The Pd / 5LaO obtained in Example 3 of this invention x -Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy image of MgO catalyst; Figure 6 The Pd / 10LaO obtained in Example 3 of this invention x -Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy image of MgO catalyst; Figure 7 The series of Pd / LaO with different La contents obtained in Example 3 of this invention x Performance diagram of selective hydrogenation reaction of acetylene with MgO catalyst; Figure 8 The Pd / 5LaO obtained in Example 3 of this invention x -Stability evaluation diagram of MgO catalyst in selective hydrogenation of acetylene; Figure 9 Pd / CeO in Embodiment 6 of the present invention x -Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy image of MgO catalyst; Figure 10 The Pd / GaO of Embodiment 7 of the present invention x -Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy image of MgO catalyst; Figure 11 Pd / InO of Embodiment 8 of the present invention x -Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy image of MgO catalyst; Figure 12 PdSnO of Embodiment 9 of the present invention x -Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy image of MgO catalyst; Figure 13 The Pd / LaO in Comparative Example 3 of this invention x -MgO, Pd / MgO and Pd / LaO x Comparison of ethylene selectivity of -α-Al2O3 during complete acetylene conversion. Detailed Implementation

[0018] To make the objectives and technical solutions of this invention clearer, the following embodiments are provided for further explanation. However, the scope of protection of this invention is not limited to these embodiments; the embodiments are merely for illustrative purposes. Those skilled in the art should understand that any changes or equivalent substitutions that do not depart from the concept of this invention are included within the scope of protection of this invention.

[0019] Unless otherwise specified, all reagents and raw materials used in this invention are obtained through purchase.

[0020] Example 1 First, 31 mg of La(NO3)3·xH2O was dissolved in 0.75 mL of ultrapure water to prepare a solution. 1 g of MgCO3 support was added to the solution to just completely wet the solution, and the mixture was stirred thoroughly. The mixture was then freeze-dried at -50°C for 8 h to obtain product A. Subsequently, 535 μL of a 0.937 g / L Na2PdCl4 solution was mixed with 0.8 mL of ultrapure water and used to impregnate product A. The mixture was then freeze-dried again at -50°C for 8 h to obtain product B. The product B was calcined in air at 500°C (heating rate: 5°C / min) for 3 h, and the resulting product was designated as Pd / LaO. x -MgO (La content is 1.5wt%, Pd content is 0.1wt%, MgO content is 98.4wt%).

[0021] Pd / LaO x In the aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (SEM) image of MgO, dense and sparse bright spots are clearly visible. Combined with the EDS elemental distribution map, these bright spots are confirmed to be La atoms. Careful image analysis reveals that most La atoms tend to form a close-packed submonolayer structure on the MgO support, accompanied by sparse, randomly distributed isolated La atoms (see...). Figure 1 ).

[0022] Comparative Example 1 The process and conditions were the same as in Example 1, except that La(NO3)3·xH2O was not added. Instead, 535 μL of a 0.937 g / L Na2PdCl4 solution was mixed with 0.75 mL of ultrapure water to prepare a Na2PdCl4 solution, and 1 g of MgCO3 support was impregnated with this solution. The mixture was freeze-dried at -50 °C for 8 h and then calcined in air at 500 °C (heating rate: 5 °C / min) for 3 h. The resulting product was denoted as Pd / MgO (MgO content was 99.9 wt%, and Pd content was 0.1 wt%).

[0023] Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy images of Pd / MgO reveal a large number of Pd nanoparticles with an average size of approximately 3 nm (see...). Figure 2 Therefore, it can be seen that LaO x The presence of [something] can significantly enhance the interaction between the carrier and the Pd species, which is beneficial to the dispersal of the Pd species.

[0024] Comparative Example 2 The process and conditions were the same as in Example 2, except that the MgCO3 support was replaced with a La2O3 support, and the corresponding aqueous solution volume was changed to 0.4 mL. Specifically, 535 μL of a 0.937 g / L Na2PdCl4 solution was mixed with 0.4 mL of ultrapure water to prepare a Na2PdCl4 solution, and 1 g of La2O3 support was impregnated with this solution. The mixture was freeze-dried at -50 °C for 8 h and then calcined in air at 500 °C (heating rate: 5 °C / min) for 3 h. The resulting product was denoted as Pd / La2O3 (La2O3 content was 99.9 wt%, and Pd content was 0.1 wt%).

[0025] Example 2 The Pd / LaO obtained in Example 1 and Comparative Examples 1-2 x The selective hydrogenation performance of acetylene was evaluated using MgO, Pd / MgO, and Pd / La2O3 as catalysts. Before the reaction, 50 mg of each catalyst was diluted with 500 mg of quartz sand and reduced in H2 at 400 °C for 1 h. After cooling to the reaction temperature, the reaction gas was introduced into the reaction tube to begin testing the reaction performance. The reaction and testing conditions were as follows: The selective hydrogenation performance evaluation of acetylene was conducted in a fixed-bed microreactor with an inner diameter of 8 mm. The reaction atmosphere composition simulated the feed gas for pre- and post-hydrogenation reactions in industrial processes. Specifically, the pre-hydrogenation composition (by 100% of total volume) consisted of: CO 0.06%, H2 22.74%, C2H2 0.6%, C2H4 40%, C2H6 10%, CH4 15%, C3H 81%, C3H6 10%, and a mixture of propadiene and propyne (with a volume ratio of 1:1) 0.6%. The gaseous products of the reaction were analyzed online using a gas chromatograph (Agilent, 7890B) equipped with an HP-PLOT AL2O3M capillary column to determine the conversion of acetylene and the selectivity for ethylene.

[0026] Evaluation results as follows Figure 3 As shown, the catalytic activity order is Pd / La₂O₃ > Pd / MgO > Pd / LaO xAll three catalysts (Pd / La₂O₃, Pd / MgO, and Pd / MgO) achieved 100% acetylene conversion at 100℃. The order of ethylene selectivity was the reverse of the acetylene conversion order. When the acetylene conversion was below 60%, the ethylene selectivity remained at 100%; however, when acetylene was completely converted, the ethylene selectivity on the Pd / La₂O₃ and Pd / MgO catalysts decreased to 77% and 84%, respectively. This contrasts sharply with the Pd / La₂O₃ catalyst. x -MgO catalysts maintain almost 100% ethylene selectivity throughout the entire experimental temperature range (60-100℃), demonstrating a significant advantage in overcoming the activity-selectivity "seesaw" effect.

[0027] Example 3 The process and conditions were the same as in Example 1, except that the amount of La(NO3)3 added was changed to 20.6 mg, 41.2 mg, 103.3 mg, and 206.6 mg, respectively. The mass fractions of La in the resulting catalysts were 1 wt%, 2 wt%, 5 wt%, and 10 wt%, respectively, denoted as Pd / 1LaO. x -MgO, Pd / 2LaO x -MgO, Pd / 5LaO x -MgO and Pd / 10LaO x -MgO.

[0028] When the La content is below 5 wt%, only diffraction peaks belonging to the MgO support are observed in the XRD pattern, with no signals related to the La species. When the La content increases to 10 wt%, characteristic diffraction peaks belonging to the bulk La2O3 begin to appear in the XRD pattern, indicating that the La species have transformed from a monolayer dispersion to a bulk crystalline state (see...). Figure 4 ).

[0029] Pd / 5LaO x Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy images of the MgO catalyst show that La is still distributed in a highly dispersed sub-monolayer state on the MgO support (see...). Figure 5 In stark contrast, Pd / 10LaO x Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy images of the MgO catalyst show that excess La aggregates, resulting in rod-shaped La₂O₃ particles exceeding 100 nm in length (see...). Figure 6 ).

[0030] Example 4 The process and conditions are the same as in Example 2, and the series of Pd / LaO obtained in Example 3 are also described. xThe performance of MgO catalyst (50 mg) in the selective hydrogenation reaction of acetylene was evaluated and compared with that of the Pd / La2O3 catalyst obtained in Comparative Example 2.

[0031] from Figure 7 As shown in Figure A, when the La content increases from 1 wt% to 5 wt%, the acetylene conversion rate at the same temperature gradually increases. However, when the La content is further increased to 10 wt%, the acetylene conversion rate decreases. This indicates that with the increase of La content, the Pd / LaO ratio... x The selective hydrogenation activity of acetylene catalysts exhibits a volcano-shaped curve. Ethylene selectivity, however, is almost unaffected by La content; the ethylene selectivity on catalysts with varying La contents does not decrease with increasing acetylene conversion. Figure 7 B). However, on the Pd / La₂O₃ catalyst, it was clearly observed that as the acetylene conversion increased to near complete conversion, the ethylene selectivity decreased significantly. These results indicate that the highly dispersed La₂O₃ modified on MgO is fundamentally different from the bulk-supported La₂O₃.

[0032] Example 5 The process and conditions were the same as in Example 2, with the reaction temperature controlled within the range of 80~86 °C for the Pd / 5LaO obtained in Example 3. x The stability of the MgO catalyst in the selective hydrogenation of acetylene was evaluated. For example... Figure 8 As shown, after 400 h of continuous reaction, Pd / 5LaO x The conversion rate of acetylene and the selectivity of ethylene on MgO are both greater than 90%, demonstrating extremely high reaction stability.

[0033] Example 6 The process and conditions are the same as in Example 1, except that La(NO3)3·xH2O is replaced with Ce(NO3)3·6H2O, i.e., 31 mg of Ce(NO3)3·6H2O is added. The resulting catalyst is denoted as Pd / CeO. x -MgO (Ce content 2wt%, Pd content 0.1wt%, MgO content 97.9wt%), its aberration-corrected high-angle annular dark-field scanning transmission electron micrograph is shown below. Figure 9 As shown.

[0034] Example 7 The process and conditions are the same as in Example 1, except that La(NO3)3·xH2O is replaced with Ga(NO3)3·xH2O, i.e., 31 mg of Ga(NO3)3·xH2O is added. The resulting catalyst is denoted as Pd / GaO. x-MgO (Ga content 1.2wt%, Pd content 0.1wt%, MgO content 98.7wt%), its aberration-corrected high-angle annular dark-field scanning transmission electron micrograph is shown below. Figure 10 As shown.

[0035] Example 8 The process and conditions are the same as in Example 1, except that La(NO3)3·xH2O is replaced with In(NO3)3·H2O, i.e., 31 mg of In(NO3)3·H2O is added. The resulting catalyst is denoted as Pd / InO. x -MgO (In content 2.4wt%, Pd content 0.1wt%, MgO content 97.5wt%), its aberration-corrected high-angle annular dark-field scanning transmission electron micrograph is shown below. Figure 11 As shown.

[0036] Example 9 The process and conditions are the same as in Example 1, except that La(NO3)3·xH2O is replaced with SnCl2·2H2O, i.e., 31 mg of SnCl2·2H2O is added. The resulting catalyst is denoted as Pd / SnO. x -MgO (Sn 3.3wt%, Pd 0.1wt%, MgO 96.6wt%), its aberration-corrected high-angle annular dark-field scanning transmission electron micrograph is shown below. Figure 12 As shown.

[0037] Comparative Example 3 The difference from Example 1 is that the MgCO3 support is changed to α-Al2O3 to prepare Pd / LaO x The α-Al₂O₃ catalyst was prepared under the same conditions as in Example 1, and the testing conditions were the same as in Example 2. Test results showed that when acetylene was nearly completely converted, the Pd / LaO₃ ratio... x -MgO, Pd / MgO and Pd / LaO x The ethylene selectivity of -α-Al₂O₃ was 99%, 84%, and 75%, respectively, indicating that in Pd / LaO₂... x - The alkalinity of MgO in MgO and LaO x The modification layer helps to achieve uniform dispersion of Pd atoms, which plays an important role in improving the selective hydrogenation performance of acetylene (see...). Figure 13 ).

[0038] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for preparing a Pd catalyst supported on an MgO support, characterized in that, Includes the following steps: S1, dissolve metal M salt in water to form M salt solution, add carrier until completely wetted, stir evenly, freeze dry to obtain product A; S2, product A is impregnated with a diluted Pd salt solution, freeze-dried to obtain product B, which is then calcined and reduced to obtain Pd / MO. x -MgO catalyst, where x is 0.5~2; The metal M in the metal M salt is selected from at least one of La, Ce, Ga, In, and Sn; The carrier is a Mg-containing compound.

2. The preparation method according to claim 1, characterized in that, The metal M salt mentioned in step S1 is selected from at least one of La(NO3)3·xH2O, Ce(NO3)3·6H2O, Ga(NO3)3·xH2O, In(NO3)3·H2O, and SnCl2·2H2O; The Mg-containing compound mentioned in step S1 is selected from one of MgO, Mg(OH)2, MgC2O4, Mg3(PO4)2, and MgCO3.

3. The preparation method according to claim 1, characterized in that, The concentration of salt M in step S1 is 0.1~100 mg / mL; In step S1, the mass ratio of the carrier added to the volume of the M salt solution is 0.5~2g:0.5~1mL.

4. The preparation method according to claim 1, characterized in that, The freeze-drying conditions described in steps S1 and S2 are as follows: The freeze-drying temperature is -30~-80℃; The freeze-drying time is 4 to 12 hours.

5. The preparation method according to claim 1, characterized in that, The Pd salt in step S2 is selected from at least one of Na2PdCl4, PdCl2·2H2O, Pd(NO3)2·2H2O, PdSO4·2H2O, Pd(OCOCH3)2, and Pd(C5H7O2)2; The specific method for diluting the Pd salt solution is as follows: take 50~200μL of Pd salt solution with a concentration of 0.1~1g / L and mix it with 0.5~2mL of ultrapure water to obtain the diluted Pd salt solution; The volume ratio of the diluted Pd salt solution to the mass ratio of product A is 0.5~2 ml : 0.5~4 g.

6. The preparation method according to claim 1, characterized in that, The roasting described in step S2 specifically involves roasting the food in an air atmosphere at a heating rate of 2-10°C / min to 300-700°C for 1-5 hours.

7. The preparation method according to claim 1, characterized in that, The Pd / MO x The content of metal M in the MgO catalyst is 0.1~10 wt%.

8. The preparation method according to claim 1, characterized in that, The Pd / MO x The Pd content in the MgO catalyst is 0.01~0.5 wt%.

9. Pd / MO prepared by the preparation method according to any one of claims 1 to 8 x The application of MgO catalyst in the selective hydrogenation of acetylene is characterized by, The steps include: Pd / MO x - The MgO catalyst is reduced in an H2 atmosphere, and the H2 is switched to feed gas to carry out the catalytic reaction in a fixed-bed reactor.

10. The application according to the annual requirement 9, characterized in that, The reduction process specifically involves reducing at 300-600℃ for 1-5 hours. The conditions for the catalytic reaction are as follows: The temperature of the catalytic reaction is 30~200℃, preferably 50~110℃.

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