A highly dispersed Pd / HY molecular sieve catalyst with ultra-low loading, and its preparation method and application

Abstract

The invention discloses a highly dispersed Pd / HY molecular sieve catalyst with ultra-low loading, and a preparation method and application thereof. After a Pd precursor, a HY carrier and a solvent are uniformly mixed, the pH value of the solution is regulated, the solution is fully stirred and dried overnight, and a molecular sieve-loaded highly dispersed Pd catalyst is synthesized by an electrostatic adsorption method. The preparation method of the invention is simple, and different pre-treatment methods improve the utilization rate of precious metals, which can greatly reduce the amount of Pd and the cost of the catalyst. The catalyst of the invention is applied to the naphthalene hydrogenation reaction, exhibiting excellent catalytic hydrogenation activity and deep hydrogenation performance, and can convert naphthalene into high-value-added decahydronaphthalene by saturated hydrogenation at low temperature, and has good application prospects.

Description

Technical Field

[0001] The invention relates to the technical field of catalytic hydrogenation of condensed ring aromatics, and in particular to an ultra-low-loaded highly dispersed Pd / HY molecular sieve catalyst and a preparation method and application thereof. Background Art

[0002] Using coal tar as the starting material, coal-based high-density fuels are prepared through processes such as enrichment of polycyclic aromatic hydrocarbons, catalytic hydrogenation and product separation and purification, which can achieve effective utilization of coal tar by classification and quality. The core link is to develop highly active and highly selective hydrogenation catalysts. The catalysts used in the traditional coal tar hydrogenation process are mainly transition metal (Co-Mo and Ni-Mo) sulfides. Although they are low in cost and have good stability, they have limited hydrogenation saturation capacity and require high reaction temperatures (>320℃). Higher temperatures will lead to increased cracking depth and reduced polycyclic alkane selectivity. In contrast, precious metal catalysts are considered to be ideal catalysts for deep hydrogenation of coal tar under mild conditions (<250℃) due to their excellent low-temperature hydrogen dissociation and aromatic activation capabilities, which can minimize the thermodynamic limitations of the reaction. However, their high price further restricts their application. In order to give full play to the advantages of precious metal catalysts in the hydrogenation reaction of polycyclic aromatic hydrocarbons, the preparation of catalysts with ultra-low loading, high dispersion and high metal utilization has become a key issue to be solved. Summary of the invention

[0003] One of the purposes of the present invention is to provide a method for preparing a highly dispersed Pd / HY molecular sieve catalyst with ultra-low loading, which has simple steps and can significantly reduce the amount of Pd used and the catalyst cost.

[0004] The second object of the present invention is to provide an ultra-low loading highly dispersed Pd / HY molecular sieve catalyst prepared by the above preparation method, wherein the highly dispersed Pd is uniformly and stably on the surface of the HY molecular sieve and has excellent catalytic hydrogenation activity and deep hydrogenation performance.

[0005] The third object of the present invention is to provide the application of the above-mentioned ultra-low loading highly dispersed Pd / HY molecular sieve catalyst.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] The first aspect of the present invention provides a method for preparing a highly dispersed Pd / HY molecular sieve catalyst with an ultra-low loading, comprising the following steps:

[0008] (1) weighing a Pd precursor and ethylenediamine (EN), adding them into deionized water and ultrasonicating them at room temperature for 5-10 minutes to obtain a first mixture;

[0009] (2) adjusting the pH of the first mixture in step (1) to 11-12, then adding the pretreated HY carrier powder, and stirring for 2 h to obtain a second mixture;

[0010] (3) Centrifuge the second mixture obtained in step (2) to separate the Pd 2+ Drying the solid mixture to obtain a first solid;

[0011] (4) Grinding the first solid obtained in step (3) into powder, then calcining it in a muffle furnace for 4 hours, and cooling it to room temperature to obtain a second solid, namely, HY molecular sieve supported palladium catalyst, recorded as Pd / HY-SEA catalyst (SEA represents electrostatic adsorption method).

[0012] Preferably, the Pd precursor in step (1) is palladium chloride. Palladium chloride is slightly soluble in water at room temperature, and ethylenediamine is added to fully dissolve it. Ethylenediamine can react with Pd 2+ Chelation to form a stable metal complex precursor (Pd(en) 2 ), which is easily soluble in water. The molar ratio of n(Pd) / n(en) is controlled to be 1 / 10 to ensure the full complexation of the precious metal.

[0013] Preferably, the pretreated HY carrier in step (2) is calcined in a muffle furnace to remove impurities and templates.

[0014] More preferably, in step (2), the calcination temperature of the HY carrier pretreatment is 550° C., the heating rate is 2.5° C. / min, and the calcination time is 4 h.

[0015] Preferably, the HY carrier in step (2) is HY-10 molecular sieve.

[0016] Preferably, the drying temperature in step (3) is 80° C. and the drying time is 12 h.

[0017] Preferably, the calcination heating rate in step (4) is 1°C / min, and the calcination temperature is 350°C-650°C.

[0018] Preferably, the palladium loading in the HY molecular sieve-supported palladium catalyst in step (4) is 0.1 wt.%-0.5 wt.%.

[0019] The second aspect of the present invention provides an ultra-low loading highly dispersed Pd / HY molecular sieve catalyst prepared by the above preparation method.

[0020] The Pd metal in the Pd / HY molecular sieve catalyst is evenly distributed on the carrier HY molecular sieve, with an average particle size of 2.29-4.23 nm, and remains highly dispersed after high-temperature calcination.

[0021] The third aspect of the present invention provides the application of a highly dispersed Pd / HY molecular sieve catalyst with an ultra-low loading, which is used as a catalyst for the saturated hydrogenation reaction of condensed aromatic hydrocarbon naphthalene to improve its reaction activity, product selectivity and product yield.

[0022] The specific application steps include: placing substrate naphthalene, Pd / HY-SEA catalyst and n-hexane solvent into a reactor, sealing it and introducing hydrogen three times to remove residual air; then, pressurizing the reactor to 0.1-2.0 MPa with hydrogen at room temperature, then heating it to 180-220° C. and maintaining it at a stirring speed of 800 rpm for 30-60 minutes. After the experiment, the reaction system is naturally cooled to room temperature and the pressure is released; filtering the reaction mixture to remove the catalyst, and obtaining an organic phase by gas chromatography-mass spectrometry and gas phase analysis.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. In the Pd / HY-10-SEA-550C catalyst of the present invention, metal Pd is uniformly distributed on the carrier, and the average size of metal particles in the catalyst is small, which is 2.29nm. Relative to the catalyst prepared by other pre-treatment methods, the Pd / HY-10-SEA-550C catalyst shows excellent catalytic activity and decahydronaphthalene selectivity in naphthalene catalytic hydrogenation. It can be seen from Examples 1-4 that the catalyst (0.5wt%Pd / HY-10-SEA, 0.5wt%PdHY-10-SEA-R) not subjected to calcination treatment, the naphthalene conversion rate is only 63.9% at the highest, and the decahydronaphthalene yield is <3.0%. And the 0.5wt%Pd / HY-10-SEA-550C catalyst after calcination treatment, the naphthalene conversion rate is 100%, and the decahydronaphthalene yield can reach 56.39%.

[0025] 2. The present invention uses HY as a carrier, loads Pd onto the carrier surface by strong electrostatic adsorption, adjusts the calcination / reduction pretreatment method, changes the acidity of the catalyst, the metal dispersion and the interaction between the metal and the carrier, which is beneficial to H 2 Dissociation, overflow and adsorption of substrate naphthalene, ultimately achieving high catalytic activity with ultra-low Pd loading. By comparing Example 1 with Comparative Example 1, the activity and selectivity of Pd metal catalyst loaded on HY molecular sieve by impregnation method are significantly lower than those by electrostatic adsorption method. It can be seen from Example 1 and Example 8 that the naphthalene hydrogenation conversion rate is as high as 74.7% at only 0.1wt% Pd loading.

[0026] 3. The strong electrostatic adsorption method of the present invention is not limited to loading Pd noble metal on HY molecular sieve. By comparing Example 1 with Comparative Example 2, loading Pd noble metal on HZSM-5 molecular sieve is also applicable. In the naphthalene hydrogenation reaction under the same reaction conditions, the naphthalene conversion rate of the Pd / HZSM-5-SEA catalyst reaches 68.7%. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a TEM image of the catalyst obtained in Example 1.

[0028] Figure 2 It is the FT-IR chart of the catalyst obtained in Example 1-4.

[0029] Figure 3 This is a TEM image of the catalyst obtained in Example 5.

[0030] Figure 4 This is a TEM image of the catalyst obtained in Example 6.

[0031] Figure 5 This is a TEM image of the catalyst obtained in Example 7. DETAILED DESCRIPTION

[0032] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] The HY molecular sieves used in the following examples were all pretreated, and the pretreatment process was as follows: the HY carrier was placed in a muffle furnace and calcined, and heated to 550° C. at a heating rate of 2.5° C. / min, preferably kept for 4 hours to remove impurities and templates.

[0034] Examples 1-4 vary the catalyst calcination (C) and reduction (R) pre-treatment methods.

[0035] Example 1: Synthesis of 0.5 wt.% Pd / HY-10-SEA-550C (calcined + not reduced) catalyst by strong electrostatic adsorption method.

[0036] The 0.5wt.% Pd / HY-10-SEA catalyst was synthesized by strong electrostatic adsorption. 0.0083g palladium chloride and 0.0282g ethylenediamine were weighed into a beaker, 50mL deionized water was added, and the solution was dissolved by ultrasonic for 5min; the pH of the solution was adjusted to 11.5 with dilute hydrochloric acid and ammonia water, 0.995g calcined HY-10 powder was added, stirred for 2h and centrifuged, and the obtained solid was dried in a vacuum oven at 80℃ for 12h; the dried solid was ground into powder and placed in a muffle furnace, heated to 550℃ at a heating rate of 1℃ / min, maintained for 4h, and the solid powder was collected after cooling to obtain the target catalyst 0.5wt.% Pd / HY-10-SEA-550C.

[0037] Example 2: Synthesis of 0.5 wt.% Pd / HY-10-SEA-550C-R (calcination + reduction) catalyst by strong electrostatic adsorption method.

[0038] The specific implementation conditions are the same as those in Example 1, but the calcined solid is further reduced: the solid powder is placed in an atmosphere furnace and heated to 400°C at a heating rate of 15°C / min in an Ar atmosphere with a flow rate of 70 mL / min, and then replaced with H at the same flow rate. 2 The mixture was reduced under an Ar atmosphere for 2 h. Finally, the mixture was replaced with an Ar atmosphere and cooled to room temperature to obtain the target catalyst 0.5 wt. % Pd / HY-10-SEA-550C-R.

[0039] Example 3: Synthesis of 0.5 wt.% Pd / HY-10-SEA (no calcination + no reduction) catalyst by strong electrostatic adsorption method.

[0040] The specific implementation conditions are similar to those of Example 1, but the calcination process is removed to obtain the target catalyst 0.5 wt. % Pd / HY-10-SEA.

[0041] Example 4: Synthesis of 0.5 wt.% Pd / HY-10-SEA-R (without calcination + reduction) catalyst by strong electrostatic adsorption method.

[0042] The specific implementation conditions are similar to those of Example 2, but the calcination process is removed to obtain the target catalyst 0.5 wt. % Pd / HY-10-SEA-R.

[0043] The TEM image of the catalyst prepared in Example 1 is as follows: Figure 1 As shown; the Fourier transform infrared spectra of Examples 1-4 are as shown Figure 2 As shown, they all show typical silicon dioxide structures, among which 1100cm -1 and 1300cm -1 The peaks near this point are attributed to Si-O-Si vibration peaks. Among them, Example 3 without high temperature treatment has a peak at 3600 cm -1 The peak intensity near is the highest, which indicates that the strong acid-stabilized Pd single atom has weak hydrogen activation ability and is almost inactive in the hydrogenation reaction. Example 1 has a suitable acid amount and metal dispersion, which is conducive to the occurrence of naphthalene deep hydrogenation reaction.

[0044] Example 5-7: Based on Example 1, the catalyst pre-calcination treatment temperature was adjusted.

[0045] Wherein, in Example 5, the calcination temperature was 350° C., and a 0.5 wt. % Pd / HY-10-SEA-350C (calcination + no reduction) catalyst was synthesized;

[0046] Wherein, in Example 6, the calcination temperature was 450° C., and a 0.5 wt. % Pd / HY-10-SEA-450C (calcination + no reduction) catalyst was synthesized;

[0047] Wherein, in Example 7, the calcination temperature was 650° C., and a 0.5 wt. % Pd / HY-10-SEA-650C (calcination + no reduction) catalyst was synthesized;

[0048] The TEM images of the catalysts prepared in Examples 5-7 are as follows: Figure 3-5 As shown. Figure 1 It was found that the size of Pd metal particles can be adjusted at different calcination temperatures. When the calcination temperature is 550°C, the average particle size of Pd metal with the same loading amount is the smallest, only 2.29nm, indicating that the metal is most evenly dispersed on the support surface at this temperature. At the same time, small Pd particles show the best naphthalene hydrogenation activity and decahydronaphthalene selectivity, achieving high utilization of Pd metal at ultra-low loading.

[0049] Example 8: Synthesis of 0.1 wt.% Pd / HY-10-SEA-550C (calcination + no reduction) catalyst by strong electrostatic adsorption method.

[0050] The specific implementation conditions are similar to those in Example 1, but the weighed Pd precursor palladium chloride is 0.0022 g, the complex ethylenediamine is 0.0056 g, and the HY-10 carrier is 0.999 g, to obtain the target catalyst 0.1 wt.% Pd / HY-10-SEA-550C.

[0051] Comparative Example 1: Preparation of 0.5 wt. % Pd / HY-10 catalyst by impregnation method.

[0052] 0.5wt.% Pd / HY-10 catalyst was synthesized by impregnation method as comparative example 1. 0.0105g palladium acetate and 25mL dichloromethane were added to a beaker to obtain a uniform mixed solution; 0.995g HY-10 molecules after calcination (550°C, 4h, 2.5°C / min) were weighed and added to the solution, stirred at room temperature for 3h, and then allowed to stand for 24h; the beaker was placed in a blast oven and dried at 120°C for 12h; the dried solid was ground into powder and placed in a muffle furnace, heated to 550°C at a heating rate of 1°C / min, and maintained for 4h to obtain a solid powder; then it was placed in an atmosphere furnace, heated to 400°C at a heating rate of 15°C / min under Ar atmosphere, and replaced with H with the same flow rate. 2 The mixture was reduced under an Ar atmosphere for 2 h. Finally, the mixture was replaced with an Ar atmosphere and cooled to room temperature to obtain the target catalyst 0.5 wt. % Pd / HY-100.

[0053] Comparative Examples 2-3 changed the carrier type and structure based on Example 1.

[0054] Comparative Example 2: Synthesis of 0.5wt.% Pd / HZSM5-50-SEA-550C (calcination + no reduction) catalyst by strong electrostatic adsorption method.

[0055] The specific implementation conditions are similar to those of Example 1, but the carrier is changed to HZSM5-50 (0.995 g) to obtain the target catalyst 0.5 wt. % Pd / HZSM5-50-SEA-550C.

[0056] Comparative Example 3: Synthesis of 0.5 wt.% Pd / HY-40-SEA-550C (calcination + no reduction) catalyst by strong electrostatic adsorption method.

[0057] The specific implementation conditions are similar to those of Example 1, but the carrier is changed to HY-40 (0.995 g) to obtain the target catalyst 0.5 wt. % Pd / HY-400-SEA-550C.

[0058] Examples 9-13: Application of the above catalyst in the catalytic hydrogenation reaction of naphthalene.

[0059] Example 9: The catalysts obtained in Examples 1, 2, 3 and 4 were applied to the hydrogenation reaction of naphthalene. The palladium loading in the catalyst was 0.5 wt.%. All catalytic reactions were carried out in a 100 mL stainless steel autoclave. In a typical experiment, 100 mg of naphthalene, 50 mg of catalyst and 20 mL of n-hexane solvent were placed in the reactor. After sealing, H was introduced 3 times. 2 The remaining air was removed. Subsequently, the 2 The reactor was pressurized to the initial reaction pressure (2 MPa), the temperature was raised to the reaction temperature (200°C), and the reaction was carried out for 60 min at a vigorous stirring speed of 800 rpm. After the experiment, the reaction system was naturally cooled to room temperature and the pressure was released. The reaction mixture was filtered to remove the catalyst, and the organic phase product was analyzed by gas chromatography-mass spectrometry (GC-MS) and gas chromatography (GC).

[0060] The reaction results of naphthalene hydrogenation catalyzed by catalysts with different calcination and reduction pre-treatment methods are shown in Table 1. Under the same reaction conditions, the 0.5wt% Pd / HY-10-SEA catalyst has no naphthalene hydrogenation activity, but the 0.5wt% Pd / HY-10-SEA-R catalyst after reduction treatment is added, and the conversion rate of naphthalene is increased to 63.9%, of which the selectivity for tetralin is 97.02%. On this basis, the 0.5wt% Pd / HY-10-SEA-550C-R catalyst after calcination treatment is added, and the naphthalene conversion rate is increased to 83.2%, and the selectivity for decahydronaphthalene is slightly improved. However, the naphthalene conversion rate of the 0.5wt% Pd / HY-10-SEA-550C catalyst that has only been calcined and not reduced is as high as 100%, and the selectivity of the saturated hydrogenation product decahydronaphthalene is greatly increased to 56.4%. Since the calcination process enhances the metal-support interaction, the metal particles are smaller and more dispersed; at the same time, the 0.5wt% Pd / HY-10-SEA-550C catalyst has both self-reduction and catalytic naphthalene hydrogenation conversion during the naphthalene hydrogenation reaction, which directly promotes the deep hydrogenation of naphthalene to decahydronaphthalene. The experimental results show that compared with four different treatment methods, the catalytic activity of the catalyst 0.5wt.% Pd / HY-10-SEA-550C prepared by combining calcination and non-reduction is better than that of the catalysts prepared by the other three pre-treatment methods, and the decahydronaphthalene selectivity is more prominent.

[0061] Table 1 Product analysis of naphthalene hydrogenation reaction under different pretreatment catalysts

[0062]

[0063] Example 10: The catalysts obtained in Examples 1, 5, 6 and 7 are applied to the hydrogenation reaction of naphthalene. The specific implementation conditions are the same as those in Example 9.

[0064] The reaction results of naphthalene hydrogenation catalyzed by catalysts with different calcination temperatures are shown in Table 2. When the calcination temperature gradually increases from 350℃ to 650℃, the naphthalene hydrogenation activity reaches 100%, but the selectivity of decahydronaphthalene shows a volcano-shaped distribution. When the calcination temperature is 550℃, the selectivity of decahydronaphthalene is the highest, which is 56.4%. The results show that the appropriate calcination temperature can effectively improve the catalytic performance, thereby improving the conversion rate of naphthalene and the selectivity of decahydronaphthalene.

[0065] Table 2 Product analysis of naphthalene hydrogenation reaction under catalysts at different calcination temperatures

[0066]

[0067] Example 11: The catalysts obtained in Examples 1 and 8 were applied to the hydrogenation reaction of naphthalene. The specific implementation conditions were the same as those in Example 9.

[0068] The reaction results of naphthalene hydrogenation catalyzed by catalysts with different Pd loadings are shown in Table 3. For the catalyst of Example 8 (0.1wt.%Pd / HY-10-SEA-550C), the conversion rate of naphthalene reached 74.7%, and its unit mass Pd hydrogenation activity was much higher than that of the catalyst with 0.5wt.%Pd / HY-10-SEA-550C with 5 times the loading. The results show that at an ultra-low loading of 0.1wt.%Pd, the catalyst activity after adjusting the calcination temperature by electrostatic adsorption method is greatly improved.

[0069] Table 3 Product analysis of naphthalene hydrogenation reaction under catalysts with different metal loadings

[0070]

[0071] Example 12: The catalysts obtained in Example 1 and Comparative Example 1 were applied to the hydrogenation reaction of naphthalene. The specific implementation conditions were the same as those in Example 9.

[0072] The reaction results of naphthalene hydrogenation catalyzed by catalysts prepared by different methods are shown in Table 4. The palladium source in the palladium-based supported catalyst also has an impact on the catalytic activity. According to the different chemical properties of the palladium precursor, the 0.5wt.%Pd / HY-10-SEA-550C catalyst prepared by the strong electrostatic adsorption method in Example 1 and the 0.5wt.%Pd / HY-10 catalyst prepared by the impregnation method in Comparative Example 1. For the naphthalene hydrogenation reaction under the same reaction conditions, the catalytic activities of the two are quite different. The 0.5wt.%Pd / HY-10-SEA-550C catalyst prepared by palladium chloride as the palladium source has higher catalytic performance and higher decahydronaphthalene selectivity, while the 0.5wt.%Pd / HY-10 catalyst prepared by the impregnation method using palladium acetate as the palladium source, the conversion rate of naphthalene is only 42.1%, and the hydrogenation product is all tetralin.

[0073] Table 4 Product analysis of naphthalene hydrogenation reaction carried out by catalysts prepared by different methods

[0074]

[0075] Example 13: The catalysts obtained in Example 1 and Comparative Examples 2 and 3 were applied to the hydrogenation reaction of naphthalene. The specific implementation conditions were the same as those in Example 9.

[0076] The reaction results of naphthalene hydrogenation catalyzed by catalysts with different supports are shown in Table 5. Among the different supports, the catalyst prepared by using HY zeolite as a support has a higher conversion rate of naphthalene than that prepared by using HZSM5 as a support, but the 0.5wt.%Pd / HY-10-SEA-550C catalyst makes decahydronaphthalene more selective, and the 0.5wt.%Pd / HY-40-SEA-550C catalyst makes tetrahydronaphthalene more selective.

[0077] Table 5 Product analysis of naphthalene hydrogenation reaction under catalysts with different supports

[0078]

[0079]

[0080] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with the technical field within the technical scope disclosed by the present invention and within the spirit and principle of the present invention should be covered by the protection scope of the present invention.

Claims

1. Application of ultra-low-loaded highly dispersed Pd / HY molecular sieve catalyst in naphthalene hydrogenation reaction, characterized in that: The ultra-low-loaded highly dispersed Pd / HY molecular sieve catalyst is prepared by the following steps: (1) weighing a Pd precursor and ethylenediamine, adding them to deionized water and ultrasonicating them at room temperature for 5-10 minutes to obtain a first mixture; the Pd precursor is palladium chloride; (2) adjusting the pH of the first mixture in step (1) to 11-12, then adding the pretreated HY carrier powder, and stirring for 2 hours to obtain a second mixture; the HY carrier is HY-10 molecular sieve; (3) Centrifuge the second mixture obtained in step (2) to separate the Pd 2+ Drying the solid mixture to obtain a first solid; (4) Grinding the first solid obtained in step (3) into powder, and then calcining it in a muffle furnace to obtain 1 o C / min heating rate to 550 o C, keep warm for 4 hours, and cool to room temperature to obtain a second solid, i.e., HY molecular sieve supported palladium catalyst, recorded as Pd / HY-SEA catalyst, wherein the loading amount of palladium is 0.5wt.%.

2. The use according to claim 1, characterized in that: The pretreated HY carrier in step (2) is placed in a muffle furnace and calcined to remove impurities and templates.

3. The use according to claim 2, characterized in that: The HY carrier pretreatment calcination temperature in step (2) is 550 o C, heating rate is 2.5 o C / min, and the calcination time is 4h.

4. The use according to claim 1, characterized in that: The specific application steps include: placing the substrate naphthalene, Pd / HY-SEA catalyst and n-hexane solvent into a reactor, sealing it and introducing hydrogen to remove the residual air; then, pressurizing the reactor with hydrogen to 0.1-2.0 MPa at room temperature, and then heating it to 180-220 o C, and maintained at a stirring speed of 800 rpm for 30-60 min. After the experiment, the reaction system was naturally cooled to room temperature and the pressure was released; the reaction mixture was filtered to remove the catalyst, and the organic phase was obtained by gas chromatography-mass spectrometry and gas phase analysis.

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