A sulfur-tolerant high-dispersion Pd@HZSM5 molecular sieve catalyst, a preparation method and application thereof

Abstract

This invention discloses a sulfur-resistant, highly dispersed Pd@HZSM5 molecular sieve catalyst, its preparation method, and its application. A Pd precursor, silicon source, aluminum source, template agent, and water are mixed uniformly and thoroughly stirred. The resulting HZSM5 molecular sieve-encapsulated Pd-based catalyst is then synthesized using an in-situ encapsulation method. Pd metal is immobilized within the micropores or cages of the molecular sieve. Due to the size effect, molecules with diameters larger than the pore size have difficulty diffusing into the molecular sieve and contacting the Pd metal. The active metal has a particle size of 2.28–3.75 nm and a content of 0.1–0.5 wt%. The Pd@HZSM5 molecular sieve catalyst prepared by this invention exhibits excellent catalytic hydrogenation activity and sulfur-resistant hydrogenation effect in the hydrogenation system of polycyclic aromatic hydrocarbons (PAHs) containing macromolecular organic sulfur, showing promising application prospects.

Description

Technical Field

[0001] This invention relates to a palladium-based molecular sieve catalyst, specifically a sulfur-resistant, highly dispersed Pd@HZSM5 molecular sieve catalyst, its preparation method, and its application, belonging to the fields of catalyst preparation technology and catalytic hydrogenation technology of polycyclic aromatic hydrocarbons. Background Technology

[0002] Coal, as my country's primary energy source, produces a massive amount of coal tar through gasification, dry distillation, and pyrolysis. Coal tar retains the unique macromolecular aromatic ring structure of coal, exhibiting high energy density and good thermal oxidation stability. Therefore, using coal tar as a starting material to synthesize high-density fuels through enrichment of polycyclic aromatic hydrocarbons and catalytic hydrogenation to alleviate the oil crisis has become an inevitable trend in the future development of aerospace jet fuels, holding significant strategic importance for national defense. Noble metal catalysts, due to their excellent low-temperature hydrogen dissociation and aromatic hydrocarbon activation capabilities, are considered ideal catalysts for deep hydrogenation of coal tar under mild conditions (<250℃). However, noble metal catalysts are highly susceptible to poisoning by sulfur-containing compounds (ppm level), leading to a significant reduction in activity and stability. In industrial production, coal tar typically requires deep desulfurization before hydrogenation, which undoubtedly increases energy consumption and production costs significantly. Therefore, enhancing the sulfur resistance of noble metal catalysts is crucial for simultaneously ensuring high catalyst activity and high stability in deep hydrogenation, and this is the primary challenge that must be addressed in the production of high-density fuels from coal tar.

[0003] Currently, precious metal catalysts are mostly used in supported forms; therefore, adjusting the acidity of the support has a significant impact on the catalyst's sulfur resistance. Utilizing the surface of the support... The interaction between acid sites and neighboring noble metals can promote the migration of metal charges to acid centers, thereby improving the sulfur resistance of catalysts by increasing the electronic defects of noble metal clusters. However, catalysts synthesized by simple impregnation have limited sulfur resistance. It is particularly important to develop encapsulated catalysts that prevent direct contact between large sulfur-containing organic molecules and the active sites of noble metals through physical coating methods. This invention addresses the above-mentioned problems. Summary of the Invention

[0004] One of the objectives of this invention is to provide a method for preparing a sulfur-resistant, highly dispersed Pd@HZSM5 molecular sieve catalyst. The synthesis steps are simple and can achieve uniform and stable encapsulation of highly dispersed Pd noble metal into the pores of HZSM5 molecular sieve.

[0005] A second objective of this invention is to provide a sulfur-resistant, highly dispersed Pd@HZSM5 molecular sieve catalyst prepared by the above-described method.

[0006] The third objective of this invention is to provide the application of the above-mentioned sulfur-resistant, highly dispersed Pd@HZSM5 molecular sieve catalyst, which, when used in a sulfur-containing naphthalene hydrogenation system, exhibits excellent catalytic hydrogenation activity and hydrogenation anti-sulfur effect.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] The first aspect of this invention provides a method for preparing a sulfur-resistant, highly dispersed Pd@HZSM5 molecular sieve catalyst, comprising the following steps:

[0009] (1) Weigh tetraethyl orthosilicate (TEOS) and tetrapropylammonium hydroxide (TPAOH), stir and mix at 80-120℃ for 18-24h to form a gel, then add a mixed solution of aluminum nitrate nonahydrate (Al(NO3)3·9H2O) and sodium hydroxide (NaOH), and continue stirring at room temperature for 3-5h to obtain the first mixture;

[0010] (2) Add a mixed solution of ethylenediamine containing palladium precursor to the first mixture obtained in step (1), and continue stirring for 1-2 hours to obtain a second mixture;

[0011] (3) The second mixture obtained in step (2) is transferred to a hydrothermal reactor and crystallized at 150-200℃ for 36-48h. After cooling to room temperature, it is centrifuged, dried, and the dried solid is ground into powder and then calcined in a muffle furnace for 6h to obtain the first solid.

[0012] (4) The first solid obtained in step (3) undergoes three consecutive ion exchanges, and then is dried. The dried solid is ground into powder and then calcined in a muffle furnace for 6 hours to obtain the second solid.

[0013] (5) The second solid obtained in step (4) is placed in a tube furnace and heated to 300-400°C in an argon atmosphere. Then, the atmosphere is switched to hydrogen and reduced for 2 hours. The atmosphere is then replaced with argon and cooled to room temperature to obtain the HZSM5 molecular sieve encapsulated palladium catalyst, denoted as Pd@HZSM5 catalyst.

[0014] Preferably, the palladium precursor in step (2) is palladium chloride. Palladium chloride is slightly soluble in water at room temperature. Adding ethylenediamine allows it to dissolve completely. Ethylenediamine can react with Pd... 2+ A stable metal complex precursor (Pd(en)2) is formed through chelation, which is readily soluble in water. The molar ratio of n(Pd) / n(en) is controlled at 1 / 10 to ensure sufficient complexation of the noble metal.

[0015] Preferably, the purpose of calcination in steps (3) and (4) is to remove impurities and template agents, and the calcination temperature is 450-650℃, with a heating rate of 1.5℃ / min.

[0016] Preferably, the specific operation of ion exchange in step (4) is to stir the sample powder with 0.8M NH4Cl solution at 80-100℃ for 1-3 hours.

[0017] Preferably, in step (5), the heating rate is 10-15℃ / min, and the flow rates of Ar and H2 are both 70-100mL / min.

[0018] Preferably, the n(SiO2 / Al2O3) of the HZSM5 support in the Pd@HZSM5 catalyst in step (5) is 50.

[0019] Preferably, the palladium loading in the Pd@HZSM5 catalyst in step (5) is 0.1 wt.% - 0.5 wt.%.

[0020] A second aspect of this invention provides a sulfur-resistant, highly dispersed Pd@HZSM5 molecular sieve catalyst prepared by the above-described method. In the Pd@HZSM5 molecular sieve catalyst, Pd metal is uniformly distributed within the HZSM5 molecular sieve support, with an average particle size of 2.28-3.75 nm, and maintains a highly dispersed state even after high-temperature calcination.

[0021] The third aspect of this invention provides the application of the above-mentioned sulfur-resistant, highly dispersed Pd@HZSM5 molecular sieve catalyst as a catalyst for the hydrogenation reaction of sulfur-containing naphthalene. Compared with impregnated catalysts, it can improve the reaction activity, product selectivity and product yield.

[0022] The specific application steps include: placing the substrate naphthalene (or containing dibenzothiophene), Pd@HZSM5 catalyst, and n-hexane solvent in a reaction vessel. The hydrogenation reaction temperature is 200-260℃, and the initial hydrogenation reaction pressure is 2.0-2.5 MPa.

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

[0024] 1. The present invention selects materials with a surface A highly dispersed Pd@HZSM5 molecular sieve catalyst was prepared via in-situ synthesis using an acidic HZSM5 support. This catalyst exhibits typical ZSM5 diffraction peaks. Examples and comparative studies show that the catalyst prepared using the weakly acidic pure silica S-1 molecular sieve as the support achieved a maximum naphthalene conversion of only 3.61%, while the catalyst prepared using the acidic HZSM5 support achieved a naphthalene conversion exceeding 60%. These results indicate a synergistic hydrogen spillover effect between the noble metal Pd nanoparticles and the acidic sites of the support, increasing the accessibility of the metal sites to reactant molecules, ultimately leading to enhanced catalyst activity and product selectivity.

[0025] 2. This invention employs an in-situ encapsulation method to synthesize encapsulated noble metal catalysts, where metallic Pd is confined within the internal channels of HZSM5 molecular sieves. Due to the pore size limitation, large organic sulfur molecules cannot directly contact naphthalene, thus protecting the encapsulated metallic Pd from sulfur poisoning. Simultaneously, the hydrogen overflow effect at acidic sites on the surface of the HZSM5 molecular sieve support is utilized to transfer active hydrogen to the support surface, thereby achieving the hydrogenation reaction of naphthalene. Attached Figure Description

[0026] Figure 1 These are the XRD patterns of the catalysts obtained in Examples 1 and 2.

[0027] Figure 2 This is a TEM image of the catalyst obtained in Example 1.

[0028] Figure 3 This is a particle size distribution diagram of Pd metal particles in the catalyst obtained in Example 1.

[0029] Figure 4 This is a TEM image of the catalyst obtained in Example 2.

[0030] Figure 5 This is a particle size distribution diagram of the Pd metal particles in the catalyst obtained in Example 2.

[0031] Figure 6 This is the XPS image of the catalyst obtained in Example 1.

[0032] Figure 7 This is the XPS image of the catalyst obtained in Example 2.

[0033] Figure 8 The conversion rate of dibenzothiophene in the hydrogenation reaction of naphthalene (containing dibenzothiophene) catalyzed by the catalysts obtained in Examples 1 and 2 is shown. Detailed Implementation

[0034] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0035] Examples 1-2 altered the binding mode and position of Pd metal with the HZSM5 molecular sieve support.

[0036] Example 1: Synthesis of 0.5 wt.% Pd@HZSM5-50 catalyst by in-situ encapsulation method.

[0037] A 0.5 wt.% Pd@HZSM5-50 catalyst was synthesized using an in-situ encapsulation method. 22.2169 g of tetraethyl orthosilicate (TEOS) and 21.6882 g of tetrapropylammonium hydroxide (TPAOH) were weighed and mixed in a beaker, and stirred at 80 °C for 24 h to form a transparent gel. Then, a mixed solution of 1.6002 g of aluminum nitrate nonahydrate (Al(NO3)3·9H2O) and 0.7401 g of sodium hydroxide (NaOH) was added, and stirring continued at room temperature for 4.5 h. Next, a metal ligand solution was added, specifically 0.0529 g of PdCl2 dissolved in 2 mL of ethylenediamine in 6 mL of water. After adding the metal ligand solution, stirring was continued for 1 h. This mixture was then added to the solution that had been stirred for 4.5 h, and stirring continued for another h. Then, stirring was stopped, and the final mixture was transferred to a 100 mL polytetrafluoroethylene hydrothermal reactor and crystallized in a 170 °C oven for 48 h. After cooling to room temperature, the mixture was washed with deionized water until neutral, and the resulting solid was dried in a 100 °C oven for 12 h. The dried solid was ground into powder and placed in a muffle furnace, heated to 550 °C at a heating rate of 1.5 °C / min, and held for 6 h. After cooling, the solid powder was collected. The powder was subjected to ion exchange by stirring with 0.8 M NH4Cl solution at 80 °C for 3 h, and the exchange was repeated three times. The solid was then dried in a 100 °C oven for 12 h. Subsequently, the solid was ground into powder and calcined in a muffle furnace for 6 h. After cooling to room temperature, it was placed in a tube furnace and heated to 400 °C under an argon atmosphere. The atmosphere was then switched to hydrogen, and the solid was reduced for 2 h. After reduction, the atmosphere was switched back to argon and cooled to room temperature. The solid powder was collected to obtain the target catalyst 0.5 wt.% Pd@HZSM5-50.

[0038] The XRD pattern of the catalyst prepared in Example 1 is shown below. Figure 1 As shown, the TEM image is as follows Figure 2 As shown in the figure, the particle size distribution of Pd metal particles is as follows: Figure 3 As shown, XPS Figure 6 As shown. From Figure 1 It can be seen that the catalyst of Example 1 prepared by the in-situ encapsulation method exhibits typical ZSM5 molecular sieve crystal diffraction peaks, and there are no diffraction peaks of metal Pd or metal oxide PdO, indicating that the metal particles are small and relatively uniformly dispersed. Figure 2 As can be seen, the in-situ synthesized HZSM5 molecular sieve has a regular morphology. From... Figure 3 As can be seen, the average particle size of Pd metal is small, only 2.28 nm, indicating that the metal is uniformly dispersed on the carrier surface. Figure 6 No obvious Pd metal diffraction peaks were observed. Since XPS, a surface technology, is difficult to detect metals encapsulated inside molecular sieves, this indicates that Pd metal was successfully encapsulated in HZSM5 molecular sieve.

[0039] Example 2: Synthesis of 0.5 wt.% Pd / HZSM5-50 catalyst by impregnation method.

[0040] The HZSM5-50 support was synthesized using a method similar to that in Example 1, but without the addition of any palladium-related substances. Then, a 0.5 wt.% Pd / HZSM5-50 catalyst was prepared using a conventional impregnation method, the specific steps of which are as follows:

[0041] 0.0105 g of palladium acetate and 20 mL of dichloromethane were added to a beaker to obtain a homogeneous solution. 0.995 g of calcined HZSM5-50 molecular sieve was weighed and added to the solution. The mixture was stirred at room temperature for 3 h and then allowed to stand for 24 h. The beaker was placed in a forced-air drying oven and dried at 120 °C for 12 h. The resulting solid was ground into powder and placed in a muffle furnace. The powder was heated to 550 °C at a heating rate of 2.5 °C / min and held for 4 h to obtain a solid powder. This powder was then placed in an atmosphere furnace and heated to 400 °C at a heating rate of 15 °C / min under an Ar atmosphere. The temperature was then changed to an H2 atmosphere with the same flow rate for 2 h of reduction. Finally, the temperature was changed back to an Ar atmosphere and cooled to room temperature to obtain the target catalyst 0.5 wt.% Pd / HZSM5-50.

[0042] The XRD pattern of the catalyst prepared in Example 2 is shown below. Figure 1 As shown, the TEM image is as follows Figure 4 As shown in the figure, the particle size distribution of Pd metal particles is as follows: Figure 5 As shown, XPS Figure 7 As shown. From Figure 1 It can be seen that the molecular sieve crystal structure of the catalyst in Example 2, prepared by a combination of hydrothermal and impregnation methods, is very similar to that in Example 1, both exhibiting obvious ZSM5 crystal diffraction peaks. Figure 5 As can be seen, the average size of the Pd metal particles loaded by the impregnation method is slightly larger than that in Example 1, at 3.75 nm, and the metal dispersion is slightly worse. Figure 7 As can be seen, significantly different from Example 1, the intensity of the Pd metal diffraction peaks is significantly enhanced. Specifically, the Pd 3d energy spectrum exhibits two sets of double peaks, corresponding to the Pd 3d5 / 2 and Pd 3d3 / 2 orbitals, respectively. 2+ The presence may be unreduced PdO and Pd 0 It is caused by oxidation upon contact with air.

[0043] Comparative Example 1 changed the type of carrier based on Example 1.

[0044] Comparative Example 1: Synthesis of 0.5 wt.% Pd@S-1 catalyst by in-situ encapsulation method.

[0045] 6.5 g of TPAOH solution was added to deionized water under stirring, followed by dropwise addition of 4.16 g of TEOS, stirring for 6 hours until the solution became clear and the TEOS was completely hydrolyzed. Then, 0.0177 g of PdCl2 and 0.0395 g of ethylenediamine were dissolved in 3 ml of water and stirred for half an hour. The solution was transferred to a 100 mL container with a PTFE liner in a stainless steel crystallization vessel and kept in an oven at 170°C for 96 hours. After cooling, the sample was washed with deionized water and ethanol by centrifugation to remove excess template agent. It was then dried in a 100°C oven for 12 hours. The dried sample was calcined in a muffle furnace at 550°C for 6 hours, then heated to 400°C under an Ar atmosphere at a heating rate of 15°C / min, and reduced for 2 hours under the same flow rate of H2. Finally, the atmosphere was changed back to Ar and cooled to room temperature. The powder was collected to obtain the target catalyst 0.5 wt.% Pd@S-1.

[0046] Comparative Examples 2-4 modified the acidity of the HZSM5 carrier based on Example 2.

[0047] Comparative Example 2: Synthesis of 0.5 wt.% Pd / HZSM5-20 catalyst by impregnation method.

[0048] The specific implementation conditions are similar to those in Example 2, except that Al(NO3)3·9H2O is changed to 4.0005g to obtain the target catalyst 0.5wt.% Pd / HZSM5-20.

[0049] Comparative Example 3: 0.5 wt.% Pd / HZSM5-100 catalyst was synthesized by a combination of hydrothermal and impregnation methods.

[0050] The specific implementation conditions are similar to those in Example 2, except that Al(NO3)3·9H2O is changed to 0.8001g to obtain the target catalyst 0.5wt.% Pd / HZSM5-100.

[0051] Comparative Example 4: Synthesis of 0.5 wt.% Pd / S-1 catalyst by impregnation method.

[0052] The S-1 support was synthesized using a method similar to that in Example 3, but without the addition of any palladium-related substances. After the S-1 support was prepared, a 0.5 wt.% Pd / S-1 catalyst was prepared using a conventional impregnation method similar to that in Example 2, but with the support changed to S-1, to obtain the target catalyst of 0.5 wt.% Pd / S-1.

[0053] Examples 3-8: The above catalyst was applied to the catalytic hydrogenation reaction of naphthalene (or containing dibenzothiophene).

[0054] Example 3: The catalysts obtained in Example 2, Comparative Example 2, and Comparative Example 3 were applied to the naphthalene hydrogenation reaction.

[0055] In a typical experiment, 100 mg of naphthalene, 50 mg of catalyst, and 20 mL of n-hexane solvent were placed in a reaction vessel. After sealing, residual air was purged three times with H2, and the vessel's seal was checked. Subsequently, the reaction vessel was pressurized to 2 MPa with H2 at room temperature, the temperature was raised to 220 °C, and the reaction was vigorously stirred at 800 rpm / min for 60 min. The hydrogenation products were qualitatively and quantitatively analyzed using GC-MS and GC-FID.

[0056] The results of using catalysts with different acidic HZSM5 supports for naphthalene hydrogenation are shown in Table 1. By comparing the catalytic performance of different acidic HZSM5 supports for naphthalene hydrogenation, it was found that catalysts prepared using HZSM5-50 molecular sieve as the support exhibited significantly higher activity for naphthalene hydrogenation than those prepared using HZSM5-20 and HZSM5-100 supports. For 0.5 wt% Pd / HZSM5-20 and 0.5 wt% Pd / HZSM5-10, the naphthalene conversion was only 33.81% and 70.41%, respectively, but the 0.5 wt% Pd / HZSM5-50 catalyst increased the naphthalene conversion to 75.18%, and also improved the yields of tetrahydronaphthalene and decahydronaphthalene products. The results indicate that the acidity of the support significantly affects the catalytic performance of the catalyst, and the HZSM5-50 support provides a more suitable acidic site, which can further promote the hydrogenation conversion of naphthalene.

[0057] Table 1. Results of naphthalene hydrogenation reaction using catalysts with different acidic HZSM5 supports.

[0058]

[0059] Example 4: The catalysts obtained in Examples 1, 2, 1, and 4 were applied to the hydrogenation reaction of naphthalene. The specific implementation conditions were the same as in Example 3.

[0060] The results of using catalysts prepared by different methods for the hydrogenation of naphthalene are shown in Table 2. Under the same reaction conditions, 0.5 wt% Pd@S-1 showed almost no activity, indicating that naphthalene molecules could not enter the molecular sieve. The hydrogenation conversion rate of naphthalene catalyzed by 0.5 wt% Pd / S-1 was only 3.61%, indicating low hydrogenation activity at a single metal site. The hydrogenation conversion rates of 0.5 wt% Pd@HZSM5-50 and 0.5 wt% Pd / HZSM5-50 were significantly improved, reaching 60.38% and 75.18%, respectively, with the latter slightly higher than the former. This is because the Pd catalyst encapsulated in the silica-alumina molecular sieve (Pd@HZSM-5) synthesized in situ using ethylenediamine complexation only exhibits hydrogenation at acidic sites assisted by hydrogen overflow. However, the Pd catalyst supported on the silica-alumina molecular sieve (Pd / HZSM-5) synthesized by impregnation method exhibits both metal and acidic hydrogenation activities, thus slightly improving the hydrogenation activity.

[0061] Table 2 Results of naphthalene hydrogenation reaction using catalysts prepared and synthesized from different methods.

[0062]

[0063]

[0064] Example 5: The catalysts obtained in Examples 1 and 2 were applied to the hydrogenation reaction of naphthalene. The specific implementation conditions were similar to those in Example 3. However, in typical experiments, the reaction temperature involved was 220-260°C.

[0065] The results of using the catalysts obtained in Examples 1 and 2 for the hydrogenation of naphthalene at different temperatures are shown in Table 3. The results indicate that reaction temperature is a crucial factor affecting the hydrogenation of naphthalene. The optimal reaction temperature for the 0.5 wt% Pd@HZSM5-50 catalyst is 220 °C, which is relatively close to the other two higher reaction temperatures. With the 0.5 wt% Pd / HZSM5-50 catalyst, the hydrogenation activity of the catalyst increases significantly with increasing reaction temperature. At a reaction temperature of 260 °C, naphthalene can be completely converted, and the yield of decahydronaphthalene is 62.70%, with a selectivity of up to 71.30% for trans-decahydronaphthalene.

[0066] Table 3 Results of naphthalene hydrogenation reaction at different reaction temperatures using different catalysts

[0067]

[0068] Example 6: The catalysts obtained in Examples 1 and 2 were applied to the hydrogenation reaction of naphthalene. The specific implementation conditions were similar to those in Example 3. However, in a typical experiment, the reaction temperature involved was 200-240°C, and the initial pressure was increased to 2.5 MPa.

[0069] The catalysts obtained in Examples 1 and 2 were used to catalyze the hydrogenation of naphthalene at the same pressure but different reaction temperatures, and the results are shown in Table 4. At an initial pressure of 2.5 MPa, the catalytic performance of the catalyst was slightly enhanced when the pressure increased from 2 MPa (Table 1) to 2.5 MPa (Table 4). At 240 °C, the 0.5 wt% Pd@HZSM5-50 catalyst increased the conversion rate of naphthalene by approximately 6%; at 220 °C, the 0.5 wt% Pd / HZSM5-50 catalyst increased the conversion rate of naphthalene by 11.52%. The hydrogenation reaction of naphthalene is a reversible exothermic process, and increasing the pressure favors the forward reaction. However, excess hydrogen during the reaction has little effect on the reaction, which is the main reason why increasing the pressure only slightly increases the catalyst activity.

[0070] Table 4. Results of naphthalene hydrogenation reaction of catalyst at the same pressure but different reaction temperatures.

[0071]

[0072] Example 7: The catalysts obtained in Examples 1 and 2 were applied to the hydrogenation reaction of naphthalene (containing dibenzothiophene). The specific implementation conditions were similar to those in Example 3, but in a typical experiment, 50 ppm of dibenzothiophene was added to the reactor.

[0073] The results of the hydrogenation of naphthalene (containing 50 ppm dibenzothiophene) in a sulfur-containing system using catalysts prepared by in-situ encapsulation and impregnation methods are shown in Table 5. The results indicate that after adding 50 ppm dibenzothiophene to the naphthalene hydrogenation catalytic reaction system, the Pd noble metal on the surface of the 0.5 wt% Pd / HZSM5-50 catalyst in Example 2 directly contacts the macromolecular organic sulfur dibenzothiophene, leading to a significant decrease in catalyst activity from 75.18% to 13.73%. However, the activity of the 0.5 wt% Pd@HZSM5-50 catalyst in Example 1 also decreased, with the naphthalene hydrogenation conversion rate decreasing from 60.38% to 24.36%, but the yield of tetrahydronaphthalene remained at 20.70%, indicating that the catalyst has good resistance to the poisoning of macromolecular sulfur-containing organic compounds. Figure 8 The conversion rate of dibenzothiophene in the hydrogenation reaction of naphthalene (containing dibenzothiophene) catalyzed by the catalysts obtained in Examples 1 and 2 is shown. Due to the good hydrogen overflow capacity of Pd metal in the channels, dibenzothiophene molecules undergo hydrogenation and desulfurization to generate small molecule H2S. Some of the H2S enters the molecular sieve channels in the closed reactor, causing Pd metal poisoning and thus reducing the catalytic activity.

[0074] Table 5 Results of hydrogenation reaction of naphthalene (containing 50 ppm dibenzothiophene) with encapsulated and impregnated catalysts

[0075]

[0076] Example 8: The catalysts prepared in Examples 1 and 2 were applied to the hydrogenation reaction of naphthalene (containing dibenzothiophene). The specific implementation conditions were similar to those in Example 3, but in a typical experiment, 100 ppm of dibenzothiophene was added to the reactor for co-reaction.

[0077] The catalytic results of the hydrogenation of naphthalene (containing 100 ppm dibenzothiophene) in a sulfur-containing system using catalysts prepared by in-situ encapsulation and impregnation methods are shown in Table 6. With the increase of macromolecular organic sulfur-containing substances, the catalytic activity of the catalysts prepared in Examples 1 and 2 further decreased, but the activity of the 0.5 wt% Pd@HZSM5-50 catalyst was still significantly higher than that of the 0.5 wt% Pd / HZSM5-50 catalyst, demonstrating that the 0.5 wt% Pd@HZSM5-50 catalyst also exhibits certain sulfur-resistant activity in high-sulfur systems.

[0078] Table 6 Results of hydrogenation reaction of naphthalene (containing 100 ppm dibenzothiophene) with encapsulated and impregnated catalysts

[0079]

[0080] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a sulfur-resistant, highly dispersed Pd@HZSM5 molecular sieve catalyst, characterized in that, Includes the following steps: (1) Weigh out tetraethyl orthosilicate and tetrapropylammonium hydroxide, and heat at 80-120 °C. o Stirring at C for 18-24 hours to form a gel, then add a mixed solution of aluminum nitrate nonahydrate and sodium hydroxide, and continue stirring at room temperature for 3-5 hours to obtain the first mixture; (2) Add a mixed solution of ethylenediamine containing palladium precursor to the first mixture obtained in step (1), and continue stirring for 1-2 hours to obtain the second mixture; (3) Transfer the second mixture obtained in step (2) to a hydrothermal reactor and heat it at 150-200 °C. o Crystallize at C for 36-48 hours, cool to room temperature, centrifuge, dry, grind the dried solid into powder, and calcine in a muffle furnace for 6 hours to obtain the first solid. (4) The first solid obtained in step (3) undergoes three consecutive ion exchanges, and then is dried. The dried solid is ground into powder and then calcined in a muffle furnace for 6 hours to obtain the second solid. (5) Place the second solid obtained in step (4) in a tube furnace and heat it to 300-400°C under an argon atmosphere. o C, then switch to hydrogen atmosphere, reduce for 2 hours, then replace with argon atmosphere and cool to room temperature to obtain HZSM5 molecular sieve encapsulated palladium catalyst, denoted as Pd@HZSM5 catalyst, in which the palladium loading is 0.1wt.%-0.5wt.% and the n(SiO2 / Al2O3) of HZSM5 support is 50.

2. The preparation method of a sulfur-resistant, highly dispersed Pd@HZSM5 molecular sieve catalyst according to claim 1, characterized in that, The palladium precursor mentioned in step (2) is palladium chloride, and the molar ratio of n(Pd) / n(ethylenediamine) is controlled to be 1 / 10.

3. The preparation method of a sulfur-resistant, highly dispersed Pd@HZSM5 molecular sieve catalyst according to claim 1, characterized in that, The calcination temperature in steps (3) and (4) is 450-650°C. o C, heating rate is 1.5 o C / min.

4. The preparation method of a sulfur-resistant, highly dispersed Pd@HZSM5 molecular sieve catalyst according to claim 1, characterized in that, The specific operation of ion exchange in step (4) is to react the first solid with 0.8M NH4Cl solution at 80-100°C. o Stir at temperature C for 1-3 hours.

5. The preparation method of a sulfur-resistant, highly dispersed Pd@HZSM5 molecular sieve catalyst according to claim 1, characterized in that, The heating rate in step (5) is 10⁻¹⁵. o C / min, Ar and H2 flow rates are both 70-100 mL / min.

6. The sulfur-resistant, highly dispersed Pd@HZSM5 molecular sieve catalyst is prepared by the preparation method according to any one of claims 1 to 5.

7. The application of the sulfur-resistant, highly dispersed Pd@HZSM5 molecular sieve catalyst according to claim 6 in the hydrogenation reaction of naphthalene and sulfur-containing systems.

8. The application according to claim 7, characterized in that, The specific application steps include: placing the substrate naphthalene or naphthalene containing dibenzothiophene, Pd@HZSM5 catalyst, and n-hexane solvent in a reaction vessel, and performing a hydrogenation reaction at a temperature of 200-260°C. o C, hydrogenation reaction pressure 2.0-2.5 MPa.

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