Preparation method of high-selectivity semi-hydrogenation MOF (Metal Organic Framework) supported palladium catalyst for catalyzing acetylene

Abstract

The invention provides a preparation method of a high-selectivity semi-hydrogenation MOF (Metal Organic Framework) supported palladium catalyst for catalyzing acetylene. According to the invention, 2-methylimidazole is used as a ligand, Zn < 2 + > is used as a metal node, water is used as a solvent, and a ZIF-8-dia carrier is synthesized at room temperature by controlling the molar ratio of Zn < 2 + > to 2-methylimidazole; and depositing Pd < 2 + > on the ZIF-8-dia carrier by using a reducing agent to synthesize the MOF supported palladium catalyst. Strong electron interaction is formed between Pd nano-particles and a carrier loaded in the MOF loaded palladium catalyst, a rich Pd-N structure is constructed on the interface of the Pd nano-particles and the carrier, formation of Pd0 species is inhibited, the hydrogen activation capacity of the Pd nano-particles is reduced, excessive hydrogenation of acetylene is inhibited, and therefore the selectivity of ethylene is improved; the catalyst shows excellent catalytic performance in acetylene hydrogenation reaction, at 160 DEG C, the acetylene conversion rate reaches 100%, the ethylene selectivity is 85%, and the catalyst has excellent durability and stability.

Description

Technical Field

[0001] The invention belongs to the field of catalyst preparation, and in particular relates to a method for preparing a MOF-supported palladium catalyst for catalyzing highly selective semi-hydrogenation of acetylene. Background Art

[0002] Ethylene, an important chemical raw material, is mainly derived from petroleum cracking. Because of the presence of impurities such as acetylene, it will not only poison the Ziegler-Natta catalyst of the ethylene polymerization reaction, but also form acetylene salts with metal catalysts, causing certain safety hazards in production. Therefore, before feeding the ethylene polymerization reaction, the ethylene raw material needs to be purified so that the acetylene impurity content is less than 5ppm. At present, ethylene is mainly purified through various methods such as solvent extraction, cryogenic distillation and adsorption, and selective hydrogenation. Relatively speaking, the selective hydrogenation conversion of acetylene can effectively remove acetylene impurities and utilize acetylene at the same time, and has a relatively important application prospect. However, the selective hydrogenation of catalytic acetylene is usually accompanied by a variety of side reactions to generate by-products such as ethane and oligomers, which may introduce new impurities and generate oligomers such as green oil, resulting in catalyst deactivation.

[0003] Pd catalysts are widely used in industrial hydrogenation reactions such as acetylene hydrogenation due to their excellent hydrogen cracking ability and excellent catalytic hydrogenation activity. However, due to the high hydrogenation activity that is difficult to control and the easy occurrence of over-hydrogenation of acetylene to produce ethane, there are still great limitations in the application of acetylene selective hydrogenation. Therefore, the development of highly catalytically active and selective Pd catalysts for highly selective hydrogenation of acetylene and the regulation of the degree of catalytic hydrogenation are the key to efficient catalytic selective hydrogenation of acetylene to reduce the acetylene impurity content in ethylene feedstock.

[0004] In the currently widely used metal oxide carrier-supported Pd nanocatalysts, the surface oxygen of the oxide carrier is easily reduced and eliminated under the hydrogen-rich conditions of acetylene hydrogenation reaction, thereby weakening the interaction between the carrier and the metal catalyst, making the Pd nanoparticle catalyst in the Pd 0 The electron-rich state easily produces highly active hydrogen, which leads to excessive hydrogenation of ethylene, thereby reducing the ethylene selectivity.

[0005] In view of this, the present invention proposes a supported Pd nanoparticle catalyst (Pd / ZIF-8-dia) with strong carrier-metal electronic interaction, which is synthesized by using a metal-organic framework (MOF) material ZIF-8-dia as a carrier and an in situ replacement growth strategy. Summary of the invention

[0006] In view of the technical problems in the background technology, the object of the present invention is to provide a method for preparing a MOF-supported palladium catalyst for catalyzing highly selective semi-hydrogenation of acetylene.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] The first aspect of the present invention provides a method for preparing a MOF-supported palladium catalyst for catalyzing highly selective semi-hydrogenation of acetylene, comprising the following steps:

[0009] S1. Add a soluble zinc salt to a 2-methylimidazole aqueous solution, stir and react, and obtain a ZIF-8-dia carrier; wherein the molar ratio of the metallic zinc in the soluble zinc salt to the 2-methylimidazole is 1:5.

[0010] S2, dispersing the ZIF-8-dia carrier in deionized water to obtain dispersion liquid I, and then adding the palladium precursor to the dispersion liquid I, stirring, to obtain dispersion liquid II;

[0011] S3. Add the reducing agent solution to the dispersion II, stir and react to obtain a MOF-supported palladium catalyst, recorded as Pd / ZIF-8-dia.

[0012] Preferably, in step S1, the stirring reaction temperature is room temperature, and the stirring time is 2 to 5 hours.

[0013] Preferably, the soluble zinc salt is added in the form of a soluble zinc salt aqueous solution, the mass volume concentration of the soluble zinc salt aqueous solution is 0.03-0.1 g / mL; the soluble zinc salt is zinc acetate.

[0014] Preferably, in step S2, the dosage ratio of the ZIF-8-dia carrier to deionized water is 50 mg: 2-5 mL.

[0015] Preferably, in step S2, the mass ratio of the ZIF-8-dia carrier to the palladium precursor is 500:1-10.

[0016] Preferably, in step S2, the stirring time is 20 to 40 minutes.

[0017] Preferably, the molar ratio of palladium in the palladium precursor to the reducing agent in the reducing agent aqueous solution is 1 to 10:1.

[0018] Preferably, in step S3, the stirring reaction time is 20 to 50 minutes.

[0019] Preferably, the palladium precursor is added in the form of a palladium precursor solution, and the concentration of the palladium precursor solution is 3-8 mg / mL.

[0020] Preferably, the concentration of the reducing agent in the reducing agent aqueous solution is 5 to 50 mg / mL.

[0021] Preferably, the palladium precursor is any one of PdCl2, palladium acetate or palladium nitrate.

[0022] Preferably, the reducing agent in the reducing agent solution is KBH4 or NaBH4.

[0023] Preferably, step S1 and step S3 further include purification treatment, specifically including: centrifuging the reaction product, washing the obtained centrifuged product with deionized water and anhydrous ethanol, and finally drying; the drying temperature is 70-80° C., and the drying time is 1-3 hours.

[0024] The second aspect of the present invention provides a MOF-supported palladium catalyst prepared by the above preparation method.

[0025] The third aspect of the present invention provides the use of the above MOF-supported palladium catalyst in catalyzing the selective semi-hydrogenation of acetylene to produce ethylene.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) In the present invention, 2-methylimidazole is first used as a ligand, Zn 2+ As a metal node, water as a solvent, by controlling the Zn 2+ and 2-methylimidazole at a molar ratio, and a metal-organo-framework (MOF) material, specifically a ZIF-8-dia carrier, was quickly synthesized at room temperature; then a reducing agent (such as KBH4) was used to transfer Pd 2+ The MOF-supported palladium catalyst was deposited on the ZIF-8-dia carrier. The Pd nanoparticles in the MOF-supported palladium catalyst formed a strong electronic interaction between the carrier and the metal, and a rich Pd-N structure was constructed at the interface between the Pd nanoparticles and the carrier, which inhibited the Pd 0 The formation of species reduces the ability of Pd nanoparticles to activate hydrogen and inhibits the over-hydrogenation of acetylene to ethane, thereby improving the selectivity of ethylene.

[0028] (2) The present invention utilizes the low symmetric coordination and Zn nodes in ZIF to achieve precise regulation of strong carrier-metal strong electronic interactions, changing the electronic structure of Pd NPs, forming more Pd-N, and reducing the Pd 0 The proportion of NPs limits its ability to activate hydrogen. The experimental results show that the prepared Pd / ZIF-8-dia exhibits excellent catalytic performance in acetylene hydrogenation reaction as a catalyst. When the temperature reaches 80°C, it exhibits catalytic acetylene hydrogenation activity. At 160°C, the acetylene conversion rate can reach 100%, and the ethylene selectivity increases with the increase of reaction temperature. At 80°C, the ethylene selectivity is 75%, and at 160°C it can reach 85%, and it has excellent durable stability.

[0029] (3) In addition, the preparation method of the present invention is simple to operate, has mild reaction conditions, and has the advantages of being green, efficient, environmentally friendly, and having low energy consumption, and is therefore suitable for large-scale promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0031] Figure 1 SEM images: (a) Pd / ZIF-8; (b) Pd / ZIF-8-dia;

[0032] Figure 2 TEM images: (a) and (b) are Pd / ZIF-8; (d) and (e) are Pd / ZIF-8-dia;

[0033] Figure 3 This is the EDS spectrum of Pd / ZIF-8-dia catalyst material;

[0034] Figure 4 XPS spectra and DRIFTS spectra of Pd / ZIF-8 and Pd / ZIF-8-dia:

[0035] (a) Full XPS spectrum; (b) C 1s XPS spectrum; (c) N 1s XPS spectrum; (d) Zn 2p XPS spectrum; (e) High-resolution Pd 3d XPS spectrum;

[0036] Figure 5 The following are: (a) XRD spectra of ZIF-67 and Pd / ZIF-67; (b) SEM image of Pd / ZIF-67; (c) XRD spectra of ZIF-L(Co) and Pd / ZIF-L(Co); (d) SEM image of Pd / ZIF-L(Co);

[0037] Figure 6 The following are: (a) catalytic activity of ZIFs support; (b) acetylene conversion of acetylene hydrogenation catalyzed by Pd / ZIF-8 and Pd / ZIF-8-dia at different temperatures; (c) ethylene selectivity; (d) ethane selectivity;

[0038] Figure 7 The following are: (a) catalytic performance of Pd / ZIF-67 as a catalyst at different temperatures; (b) catalytic performance of Pd / ZIF-L(Co) as a catalyst at different temperatures;

[0039] Figure 8 The selectivity diagram of ethylene product in acetylene hydrogenation reaction catalyzed by Pd / ZIF-8-dia at 160℃;

[0040] Fig. 9 Comparison results of Pd / ZIF-8-dia before and after stability test: (a) XRD spectrum; (b) SEM image; (c) FTIR spectrum; (d) TG results;

[0041] Fig.10 Schematic diagram of the synthesis route of Pd / ZIF-8 and Pd / ZIF-8-dia. DETAILED DESCRIPTION

[0042] In the following description, for the purpose of illustration rather than limitation, specific details such as specific system structures and technologies are provided to provide a thorough understanding of the embodiments of the present invention. However, it should be clear to those skilled in the art that the present invention may also be implemented in other embodiments without these specific details.

[0043] Example 1

[0044] Reference Fig.10 , a method for preparing a MOF-supported palladium catalyst for catalyzing highly selective semi-hydrogenation of acetylene, the specific steps are as follows:

[0045] (1) Weigh 1.5 g of ZnAc2·2H2O and dissolve it in 25 mL of deionized water, and stir to dissolve it at room temperature to obtain a ZnAc2 solution; weigh 2.8 g of 2-methylimidazole and dissolve it in 35 mL of deionized water to obtain a 2-methylimidazole aqueous solution;

[0046] (2) adding 2-methylimidazole aqueous solution to ZnAc2 solution, stirring continuously for 3 h, then collecting the resulting crystals by centrifugation, washing with deionized water and anhydrous ethanol three times, and drying in an oven at 80 °C for 2 h to obtain a ZIF-8-dia carrier;

[0047] (3) Weigh 500.0 mg of ZIF-8-dia carrier and disperse it in 20 mL of deionized water to obtain dispersion I; add 200 μL of 5 mg / mL PdCl2 solution to dispersion I and continue stirring for 30 min to obtain dispersion II;

[0048] (4) 10 mL of KBH4 aqueous solution (5.4 mg / mL) was added dropwise to the obtained dispersion II, and stirring was continued for 30 min. After that, the solid catalyst sample was collected by centrifugation, washed with deionized water and anhydrous ethanol three times each, and dried in an oven at 80 °C for 1 h to obtain a MOF-supported palladium catalyst, which was recorded as Pd / ZIF-8-dia.

[0049] Example 2

[0050] (1) Weigh 1.5 g of ZnAc2·2H2O and dissolve it in 25 mL of deionized water, and stir to dissolve it at room temperature to obtain a ZnAc2 solution; weigh 2.8 g of 2-methylimidazole and dissolve it in 35 mL of deionized water to obtain a 2-methylimidazole aqueous solution;

[0051] (2) adding 2-methylimidazole aqueous solution to ZnAc2 solution, stirring continuously for 3 h, then collecting the resulting crystals by centrifugation, washing with deionized water and anhydrous ethanol three times, and drying in an oven at 80 °C for 2 h to obtain a ZIF-8-dia carrier;

[0052] (3) Weigh 500.0 mg of ZIF-8-dia carrier and disperse it in 50 mL of deionized water to obtain dispersion I; add 400 μL of 5 mg / mL PdCl2 solution to dispersion I and continue stirring for 40 min to obtain dispersion II;

[0053] (4) 30 mL of KBH4 aqueous solution (5.4 mg / mL) was added dropwise to the obtained dispersion II, and stirring was continued for 20 min. After that, the solid catalyst sample was collected by centrifugation, washed with deionized water and anhydrous ethanol three times each, and dried in an oven at 70 °C for 3 h to obtain a MOF-supported palladium catalyst.

[0054] Example 3

[0055] (1) Weigh 1.5 g of ZnAc2·2H2O and dissolve it in 25 mL of deionized water, and stir to dissolve it at room temperature to obtain a ZnAc2 solution; weigh 2.8 g of 2-methylimidazole and dissolve it in 35 mL of deionized water to obtain a 2-methylimidazole aqueous solution;

[0056] (2) adding 2-methylimidazole aqueous solution to ZnAc2 solution, stirring continuously for 3 h, then collecting the resulting crystals by centrifugation, washing with deionized water and anhydrous ethanol three times, and drying in an oven at 80 °C for 2 h to obtain a ZIF-8-dia carrier;

[0057] (3) Weigh 500.0 mg of ZIF-8-dia carrier and disperse it in 20 mL of deionized water to obtain dispersion I; add 500 μL of 5 mg / mL PdCl2 solution to dispersion I and continue stirring for 40 min to obtain dispersion II;

[0058] (4) 20 mL of KBH4 aqueous solution (5.4 mg / mL) was added dropwise to the obtained dispersion II, and stirring was continued for 50 min. After that, the solid catalyst sample was collected by centrifugation, washed with deionized water and anhydrous ethanol for 3 times each, and dried in an oven at 80 °C for 1 h to obtain a MOF-supported palladium catalyst.

[0059] Comparative Example 1

[0060] The method is basically the same as Example 1, except that "2.8 g 2-methylimidazole" in Example 1 is replaced by "5.6 g 2-methylimidazole solution" to obtain a MOF-supported palladium catalyst, which is recorded as Pd / ZIF-8.

[0061] Comparative Example 2

[0062] The method is basically the same as Example 1, except that the "2.8 g 2-methylimidazole" and "1.5 g ZnAc2·2H2O" in Example 1 are replaced by "1.7 g CoAc2·4H2O" and "5.6 g 2-methylimidazole solution" respectively to obtain a MOF-supported palladium catalyst, which is recorded as Pd / ZIF-67.

[0063] Comparative Example 3

[0064] It is basically the same as Example 1, except that the "2.8 g 2-methylimidazole" and "1.5 g ZnAc2·2H2O" in Example 1 are replaced by "2.0 g Co(NO3)2·6H2O" and "5.6 g 2-methylimidazole", respectively, to obtain a MOF-supported palladium catalyst, which is recorded as Pd / ZIF-L(Co).

[0065] The Pd / ZIF-8-dia and Pd / ZIF-8 prepared in Example 1 and Comparative Example 1 were characterized. The results of SEM, TEM, EDS and XPS are shown in Figure 1-4 .

[0066] Depend on Figure 1 The results show that the Pd / ZIF-8-dia prepared in Example 1 exhibits an irregular nanosheet morphology ( Figure 1 (a)); while the Pd / ZIF-8 prepared in Comparative Example 1 exhibits a regular dodecahedral morphology ( Figure 1 (b)).

[0067] Depend on Figure 2 The results show that Pd / ZIF-8 exhibits a dodecahedral morphology ( Figure 2 (a)), the lattice spacing is 0.224nm ( Figure 2 (b) Inset) corresponds to the (111) plane of metallic Pd in ​​Pd / ZIF-8, while Pd / ZIF-8-dia exhibits an irregular nanosheet morphology ( Figure 2 (d)), and no obvious lattice fringes of metallic Pd or Pd oxide were observed in Pd / ZIF-8-dia, indicating that the crystallinity of Pd NPs in Pd / ZIF-8-dia was significantly reduced.

[0068] Depend on Figure 3The results show that Pd nanoparticles are uniformly loaded on the surface of the ZIF-8-dia carrier, which also confirms the successful loading of Pd on the ZIF-8-dia carrier, that is, Pd / ZIF-8-dia is successfully prepared.

[0069] Depend on Figure 4 The results show that the full XPS spectrum proves the presence of C, N, Zn and Pd elements in Pd / ZIFs (specifically Pd / ZIF-8 and Pd / ZIF-8-dia) Figure 4 (a)).

[0070] like Figure 4 As shown in (b), in Pd / ZIFs (specifically Pd / ZIF-8 and Pd / ZIF-8-dia), C 1s can be fitted into three peaks, and the peaks with binding energies of 284.8, 286.1, and 288.3 eV are attributed to CC, CN, and C=N, respectively. The proportion of C=N in Pd / ZIF-8 is higher than that in Pd / ZIF-8-dia, indicating that there are more weakly connected 2-methylimidazoles on Pd / ZIF-8.

[0071] In the N1s high-resolution XPS spectrum ( Figure 4 (c)), the peaks with binding energies of 399.0 and 400.7 eV are attributed to CN and C=N in 2-methylimidazole, respectively.

[0072] Compared with Pd / ZIF-8, the binding energy of N(CN) in Pd / ZIF-8-dia shifts downfield by 0.19 eV, and the binding energy of Zn 2p shifts downfield by 0.1 eV ( Figure 4 (d)).

[0073] In the Pd 3d XPS spectrum ( Figure 4 (e)), the peaks with binding energies of 335.3 and 340.7 eV are attributed to Pd 0 (3d 5 / 2 ) and Pd 0 (3d 3 / 2 ), the peaks with binding energies of 338.1 and 343.2 eV are attributed to ionized Pd species, which is due to the charge transfer between Pd 4d orbital and N 2p orbital, reducing the electron density of Pd species, indicating that there is EMSI between Pd species and ZIF carrier, and constructing Pd-N pairs, in which the proportion of Pd-N in Pd / ZIF-8-dia is higher than that in Pd / ZIF-8, and the increase of N(CN) electron density indicates that there is a stronger metal-support electronic interaction (EMSI) between ZIF-8-dia and Pd in ​​Pd / ZIF-8-dia. Most of the Pd species on the catalytic surface of Pd / ZIF-8-dia exist in the form of Pd-N, and Pd0 The low content of species indicates that a Pd-N bond structure is generated at the interface of the loaded Pd nanoparticles and the ZIF-8-dia support, which greatly reduces the Pd 0 Species content.

[0074] The results of the in situ DRIFTS study on CO adsorption are as follows: Figure 4 As shown in (f), the signal peak of CO on Pd / ZIF-8-dia is blue-shifted compared with the signal peak of CO on Pd / ZIF-8, indicating that there is a more significant charge transfer effect from Pd to the ZIF carrier in Pd / ZIF-8-dia, which is consistent with the XPS results.

[0075] From the above results, it can be seen that in Pd / ZIF-8-dia, there is a strong electronic interaction between the ZIF-8-dia carrier and the loaded Pd nanoparticles, resulting in the loaded Pd nanoparticles showing lower crystallinity.

[0076] Depend on Figure 5 The results show that the structures of ZIF-67 and ZIF-L(Co) prepared in Comparative Examples 2 and 3 are consistent with those reported in the literature. Pd / ZIF-67 has a dodecahedral morphology, and Pd / ZIF-L(Co) has a blade-like morphology. In the high-resolution XPS spectra, the C1s peaks of Pd / ZIF-67 and Pd / ZIF-L(Co) are assigned to the same, and the peaks with binding energies of 284.8, 286.1, and 288.3 eV are assigned to CC, CN, and C=N, respectively. In the Pd 3d XPS spectra, Pd 0 and Pd-N, and Pd 0 The high ratio indicates that there is no strong EMSI between Pd and ZIF support in Pd / ZIF-67 and Pd / ZIF-L(Co). Although there is low-symmetry coordination between Co(II) and 2-methylimidazole in ZIF-L(Co), the EMSI between Pd and ZIF support in Pd / ZIF-L(Co) is weak due to the difference in metal nodes, indicating that Zn node also plays an important role in strong EMSI. The above results show that to achieve strong EMSI between Pd and ZIF, ZIF needs to meet the two conditions of low-symmetry coordination between metal and 2-methylimidazole and Zn node.

[0077] Test Example 1

[0078] The MOF-supported palladium catalysts (Pd / ZIF-8-dia, Pd / ZIF-8, ZIF-67 and ZIF-L(Co)) prepared in Example 1 and Comparative Examples 1-3 were used as catalysts to catalyze the selective semi-hydrogenation of acetylene to explore the effect of the EMSI strength in the catalyst on the catalytic performance. The amount of catalyst used was 20 mg, the reaction gas composition was 1 vol% C2H2, 16 vol% H2 and 83 vol% Ar, the air velocity was 120000 mL / (gh), and the data was collected by online gas chromatography after 1 hour of reaction. The test was repeated three times to complete the error analysis of the data. The results are shown in Figure 6-10 .

[0079] Depend on Figure 6 The results show that Figure 6 (a) shows the acetylene conversion rates of ZIF-8 and ZIF-8-dia supports at different temperatures. Within the tested temperature range, the acetylene conversion rates are all 0, indicating that the supports are inert and have no hydrogenation activity.

[0080] Figure 6 (b) shows the acetylene conversion rate of Pd / ZIF-8 and Pd / ZIF-8-dia as catalysts at different temperatures. It can be observed that in the range of 60℃ to 200℃, Pd / ZIF-8 always maintains 100% acetylene conversion rate, while Pd / ZIF-8-dia has an acetylene conversion rate of 0 at 60℃. When the temperature rises to 100℃, it has an acetylene conversion rate similar to that of Pd / ZIF-8, and reaches its maximum conversion rate of 100% at 160℃. It is difficult for Pd / ZIF-8-dia catalyst to achieve acetylene conversion at low temperatures, indicating that the activation of hydrogen by Pd / ZIF-8-dia is inhibited at low temperatures.

[0081] Figure 6 (c) shows the ethylene selectivity of Pd / ZIF-8 and Pd / ZIF-8-dia as catalysts at different temperatures. It can be observed that the ethylene selectivity of Pd / ZIF-8 is 57% at 60°C, and the ethylene selectivity decreases significantly with the increase of the test temperature. The ethylene selectivity of Pd / ZIF-8-dia is higher than that of Pd / ZIF-8 in the entire test temperature range. When the temperature is increased to 160°C, the ethylene selectivity of Pd / ZIF-8-dia can reach 85%.

[0082] Figure 6 (d) shows that the ethane selectivity of Pd / ZIF-8 increases with increasing temperature, indicating that ethane is produced by over-hydrogenation of acetylene on Pd / ZIF-8. However, the ethane selectivity of Pd / ZIF-8-dia does not exceed 5% over the entire temperature range, indicating that over-hydrogenation of acetylene on Pd / ZIF-8-dia is suppressed, resulting in higher ethylene selectivity and extremely low ethane selectivity.

[0083] Figure 7 The catalytic performance of Pd / ZIF-67 and Pd / ZIF-L(Co) as catalysts at different temperatures was shown. It can be observed that the catalytic performance of acetylene hydrogenation reaction of Pd / ZIF-67 and Pd / ZIF-L(Co) as catalysts shows similar rules in the test temperature range. In the whole temperature range, the acetylene conversion rate of Pd / ZIF-67 and Pd / ZIF-L(Co) remains at 100%, the ethylene selectivity is less than 50%, and the ethane selectivity is high, which indicates that acetylene is easily over-hydrogenated to produce ethane on Pd / ZIF-67 and Pd / ZIF-L(Co). In addition, with the increase of temperature, the ethylene selectivity of the two gradually decreases, and the ethane selectivity gradually increases, indicating that the over-hydrogenation of acetylene is more serious at high temperature.

[0084] Depend on Figure 8 The results show that Pd / ZIF-8-dia exhibits stable catalytic performance in the acetylene hydrogenation reaction at 160°C within 60h of reaction time, with the acetylene conversion rate remaining at 100% and no significant decrease in ethylene selectivity.

[0085] Depend on Fig. 9 The results show that the structure and morphology of Pd / ZIF-8-dia as a catalyst have not changed significantly after long-term testing ( Fig. 9 (a) and Fig. 9 (b)); No absorption peaks related to other by-products were observed in the FTIR spectrum ( Fig. 9 (c)); In the TG results, there is no significant difference in the weight loss curves of Pd / ZIF-8-dia after stability test and freshly prepared Pd / ZIF-8-dia in air ( Fig. 9 (d)). These results indicate that no carbon deposits were formed on the catalyst surface during the stability test of Pd / ZIF-8-dia, so Pd / ZIF-8-dia can exhibit excellent durability and stability in acetylene hydrogenation reaction.

[0086] In summary, the present invention precisely regulates the strong EMSI between Pd and the ZIF carrier through the low symmetric coordination between the metal and 2-methylimidazole in ZIF and the Zn node, and explores the structure-activity relationship in the acetylene hydrogenation reaction. The Pd / ZIF-8-dia prepared by the present invention exhibits excellent catalytic performance as a catalyst in the acetylene hydrogenation reaction. At 160°C, the acetylene conversion rate is 100%, the ethylene selectivity is 85%, and it has excellent durable stability. Combined with the in situ DRIFTS spectrum, the improvement of ethylene selectivity in Pd / ZIFs mainly depends on the activation ability of the active sites to hydrogen. The coordination structure between Zn(II) and 2-methylimidazole in ZIF-8-dia is low-symmetry, and the Zn-N bond is unstable, which is more conducive to the interaction between Pd and the ZIF carrier, thereby producing more Pd-N pairs and reducing the ability of Pd nanoparticles to activate hydrogen. Therefore, when Pd / ZIF-8-dia is used as a catalyst in the acetylene hydrogenation reaction, a higher temperature is required to achieve complete conversion of acetylene. However, due to the low coverage of active hydrogen on the active sites, excessive hydrogenation of acetylene to ethane is inhibited, thereby improving ethylene selectivity.

[0087] The present invention is not limited to the above-mentioned specific implementation modes. Various changes made by ordinary technicians in this field based on the above-mentioned concepts without creative work are all within the protection scope of the present invention.

Claims

1. A method for preparing a MOF-supported palladium catalyst for catalyzing highly selective semi-hydrogenation of acetylene, characterized in that: The following steps are involved: S1. Add a soluble zinc salt to a 2-methylimidazole aqueous solution, stir and react, and obtain a ZIF-8-dia carrier; wherein the molar ratio of the metallic zinc in the soluble zinc salt to the 2-methylimidazole is 1:

5. S2, dispersing the ZIF-8-dia carrier in deionized water to obtain dispersion liquid I, and then adding the palladium precursor to the dispersion liquid I, stirring, to obtain dispersion liquid II; S3. Add the reducing agent solution to the dispersion II, stir and react to obtain a MOF-supported palladium catalyst.

2. The preparation method of the MOF-supported palladium catalyst for catalytic acetylene highly selective semi-hydrogenation according to claim 1, characterized in that: In step S1, the temperature of the stirring reaction is room temperature, and the stirring time is 2 to 5 hours; the soluble zinc salt is added in the form of a soluble zinc salt aqueous solution, and the mass volume concentration of the soluble zinc salt aqueous solution is 0.03 to 0.1 g / mL; the soluble zinc salt is zinc acetate.

3. The preparation method of the MOF-supported palladium catalyst for catalytic acetylene highly selective semi-hydrogenation according to claim 1, characterized in that: In step S2, the stirring time is 20 to 40 minutes; the dosage ratio of the ZIF-8-dia carrier to deionized water is 50 mg: 2 to 5 mL; the mass ratio of the ZIF-8-dia carrier to the palladium precursor is 500: 1 to 10.

4. The preparation method of the MOF-supported palladium catalyst for catalytic acetylene highly selective semi-hydrogenation according to claim 1, characterized in that: In step S3, the stirring reaction time is 20 to 50 minutes; the molar ratio of palladium in the palladium precursor to the reducing agent in the reducing agent aqueous solution is 1 to 10:

1.

5. The preparation method of the MOF-supported palladium catalyst for catalytic acetylene highly selective semi-hydrogenation according to claim 1, characterized in that: The palladium precursor is added in the form of a palladium precursor solution, the concentration of the palladium precursor solution is 3-8 mg / mL; the concentration of the reducing agent in the reducing agent aqueous solution is 5-50 mg / mL.

6. The method for preparing a MOF-supported palladium catalyst for catalyzing highly selective semi-hydrogenation of acetylene according to claim 1, characterized in that: The palladium precursor is any one of PdCl2, palladium acetate or palladium nitrate; the reducing agent in the reducing agent solution is KBH4 or NaBH4.

7. A MOF-supported palladium catalyst prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the MOF-supported palladium catalyst as claimed in claim 7 in catalyzing the highly selective semi-hydrogenation of ethane to produce ethylene olefins.

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