High-activity pd-la / k it-6 catalyst, preparation method and application thereof

Abstract

The application belongs to the technical field of catalysts, and particularly relates to a high-activity Pd-La / KIT-6 catalyst and a preparation method and application thereof. The carrier of the catalyst is a mesoporous silica material KIT-6; a nitrogen-doped KIT-6 material is prepared by using urea; the active component of the catalyst is Pd metal, the loading amount of Pd is 0.1-2 wt%; and the assistant of the catalyst is La, the loading amount is 1-5 wt%. The catalyst is prepared by using a chemical vapor deposition-spraying method, the active component of the catalyst is highly dispersed, the loading amount of Pd is low, and the catalyst has high activity. In a toluene catalytic oxidation reaction, the raw material gas space velocity is 10000-60000 mL.g ‑1 ·h ‑1 -1.h-1, the toluene concentration is 1000-4000 ppm, and the toluene conversion rate can reach 99% and above at 160-175 DEG C.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, specifically relating to a highly active Pd-La / KIT-6 catalyst, its preparation method, and its application. Background Technology

[0002] Noble metal catalysts are widely used in chemical, pharmaceutical, environmental protection, and new energy fields due to their high activity, high temperature resistance, and corrosion resistance. Among them, Pd catalysts are one of the most widely used industrial noble metal catalysts. Impregnation is an industrial method for preparing noble metal catalysts, but the dispersion of noble metal centers within the catalyst is difficult to control; especially during pretreatment processes such as catalyst calcination and activation, local aggregation of noble metals occurs, reducing catalyst activity. To improve the activity of industrial catalysts, the loading of noble metals needs to be increased. For example, in typical Pd-activated carbon catalysts, the Pd loading is as high as 5-10%, and noble metals account for 80-90% of the total catalyst cost, resulting in high catalyst costs. Therefore, there is an urgent need to develop new high-performance noble metal catalyst materials to reduce the amount of noble metals used in catalysts and improve the utilization efficiency of noble metal resources.

[0003] By employing suitable supports, adding promoters, and improving catalyst preparation methods, the bulk and surface structures of catalysts can be effectively adjusted, thereby enhancing their catalytic activity, product selectivity, and stability. SiO2, due to its acid resistance, heat resistance, wear resistance, and low surface acidity, is commonly used as a catalyst support. KIT-6 is a SiO2 with a cubic Ia3d mesoporous structure. Its unique three-dimensional cross-linked pore structure facilitates the high dispersion of active species on the support surface, while allowing reactants and products to migrate rapidly within the pores, preventing blockage caused by typical pore structures. Adding promoters to catalysts can improve their lifespan, mechanical strength, and thermal stability. Rare earth elements such as La and Ce possess certain basicity, redox properties, and electron-donating capabilities, which can alter the surface properties of catalysts and adjust the acidity / basicity of the support. Therefore, adding them as promoters can improve catalyst activity and selectivity. Furthermore, nitrogen doping can generate strong electron feedback interactions with noble metals in the catalyst, resulting in an electron-rich state on the surface of noble metal nanoparticles, which is beneficial for their activation and adsorption of reactants. Therefore, it is of great significance to develop and utilize nitrogen-doped KIT-6 as an active metal support and rare earth elements as promoters to prepare noble metal catalysts with high activity, high selectivity and low loading. Summary of the Invention

[0004] To address the issues of high loading and low catalytic activity in existing precious metal catalysts, this invention provides a highly active Pd-La / KIT-6 catalyst, its preparation method, and its application.

[0005] To achieve the above object, the present application is implemented by the following technical solutions:

[0006] In a first aspect, the present application provides a preparation method of high-activity Pd-La / KIT-6 catalyst, which comprises the following steps:

[0007] (1) Preparation of nitrogen-doped KIT-6: KIT-6 and urea are added to anhydrous ethanol, heated to reflux, aged, dried, ground, calcined to obtain a nitrogen-doped KIT-6 carrier;

[0008] (2) Preparation of La / KIT-6: after ultrasonic treatment of the nitrogen-doped KIT-6 carrier, it is placed in the reaction chamber of a chemical vapor deposition device, and a lanthanum-containing solution is introduced into the reaction chamber by nitrogen bubbling to perform chemical vapor deposition; after the chemical vapor deposition is completed, it is naturally cooled, washed, and dried to obtain a La / KIT-6 material;

[0009] (3) Preparation of Pd-La / KIT-6: La / KIT-6 is immersed in a palladium-containing impregnation solution by spray impregnation, after the immersion is completed, it is dried and calcined to obtain a Pd-La / KIT-6 catalyst.

[0010] Preferably, in the step (1), the mass ratio of KIT-6 to urea is 1:0.5-3.0, and the solid-liquid ratio is 1:10-20.

[0011] Preferably, in the step (1), the heating reflux temperature is 50-60℃, the heating reflux time is 3-6h; the aging temperature is room temperature, and the aging time is 12-24h; the calcination temperature is 500-600℃, and the calcination time is 2-4h.

[0012] Preferably, in the step (2), the conditions of chemical vapor deposition are as follows: the temperature of the lanthanum-containing solution is 60-80℃, the deposition temperature is 800-1000℃, the deposition pressure is 2-5kPa, and the deposition time is 6-10h.

[0013] Preferably, in the step (2), the lanthanum-containing solution is at least one of lanthanum nitrate, lanthanum acetate, and lanthanum chloride.

[0014] Preferably, in the step (3), the impregnation solution is at least one of palladium nitrate, palladium chloride, and palladium sulfate solution.

[0015] Preferably, in the step (3), the impregnation temperature is 30-40℃, the impregnation time is 2-4h; the calcination temperature is 300-450℃, and the calcination time is 1-2h.

[0016] In a second aspect, the present application provides a Pd-La / KIT-6 catalyst prepared by the above method, wherein the catalyst has a nitrogen-doped mesoporous silica material KIT-6 as a carrier, Pd as an active component, and La as an additive, and the Pd and La particles are uniformly dispersed on the surface of the carrier; the content of Pd is 0.1-2 wt% of the total weight of the catalyst, and the content of La is 1-5 wt% of the total weight of the catalyst.

[0017] In a third aspect, the present application provides an application of the above Pd-La / KIT-6 catalyst in a catalytic oxidation reaction of toluene.

[0018] Preferably, the catalyst is reduced in a H2 / Ar mixed gas at 300-500 ℃ for 1-3 h before use, and the catalytic oxidation reaction of toluene is carried out in a micro fixed-bed reactor, and the reaction conditions are as follows: the size of the catalyst is 20-40 mesh, the loading amount of the catalyst is 0.2 g, the toluene gas space velocity is 10000-60000 mL·g -1 ·h -1 , the toluene gas concentration is 1000-4000 ppm, the reaction is carried out at normal pressure, and the reaction temperature is 90-200 ℃.

[0019] Compared with the prior art, the present application has the following beneficial effects:

[0020] (1) The catalyst prepared by the present application has high dispersion of active components and high catalytic activity;

[0021] (2) The interaction between the active metal and the carrier in the catalyst prepared by the traditional impregnation method is Van der Waals force, electrostatic adsorption and weak covalent bond, and the dispersion and stability of the active metal center of the catalyst are poor. The catalyst prepared by the present application has high stability by preparing KIT-6 through nitrogen doping and taking it as a carrier;

[0022] (3) Compared with the impregnated catalyst, the catalyst prepared by the present application can greatly reduce the economic cost under the same loading amount, and has good industrial application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 It is a transmission electron microscope picture of the 0.5Pd-5La / KIT-6 catalyst prepared in Example 1 of the present application.

[0024] Figure 2 It is a N2-physical adsorption / desorption curve and pore size distribution graph of the 0.5Pd-5La / KIT-6 catalyst prepared in Example 1 of the present application.

[0025] Figure 3 It is an XRD spectrum of the 0.5Pd-5La / KIT-6 catalyst prepared in Example 1 of the present application.

[0026] Figure 4 Toluene conversion curves for the catalytic oxidation reaction of Pd-based catalysts prepared for Examples 1 to 3 and Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0027] For the purposes of promoting an understanding of the principles of the application, the application will be described below in greater detail. It will be appreciated, however, that the application can be practiced in many different forms and should not be considered limited to the embodiments set forth in the following description. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the application to those skilled in the art.

[0028] Example 1

[0029] 1. Preparation of nitrogen-doped KIT-6

[0030] KIT-6 and urea were added to anhydrous ethanol in a mass ratio of 1:2 (solid-liquid ratio of 1:20), refluxed at 50°C for 4 h, aged at room temperature for 18 h, and then vacuum dried until the ethanol was completely volatilized. After being ground, the product was placed in a high-temperature tube furnace and calcined at 500°C in a nitrogen atmosphere for 2 h to obtain a nitrogen-doped KIT-6 carrier.

[0031] 2. Preparation of La / KIT-6

[0032] 5 g of the nitrogen-doped KIT-6 carrier was tabletted and used as a chemical vapor deposition substrate. The substrate was ultrasonically treated in anhydrous ethanol for 15 min, dried at 100°C for 1 h, and then placed in the reaction chamber of a chemical vapor deposition vertical reactor. 0.78 g of lanthanum nitrate hexahydrate was weighed out, dissolved in 10 mL of water, and the lanthanum nitrate solution was kept at a constant temperature (60°C). The deposition temperature of the reaction chamber was kept constant (800°C), the deposition pressure was kept constant (3 kPa), and the constant temperature was maintained for 8 h. After natural cooling to room temperature, the sample was removed, washed with anhydrous ethanol several times, and dried at 60°C for 6 h to obtain 5La / KIT-6. The La loading was 5 wt%.

[0033] 3. Preparation of Pd-La / KIT-6

[0034] The 5La / KIT-6 was added to an impregnation tank. 0.625 mL of a palladium nitrate solution (concentration of Pd 4-5% w / w (cont. Pd)) was diluted to 10 mL with 0.1% dilute nitric acid. The diluted solution was added to the impregnation tank through a spraying device, impregnated in a microwave reactor for 2 h, and the impregnation temperature was kept at 40°C. After the impregnation was completed, the product was dried at 60°C for 8 h and calcined in a muffle furnace at 400°C for 2 h to obtain a 0.5Pd-5La / KIT-6 catalyst. The Pd loading was 0.5 wt%.

[0035] 4. Evaluation of catalytic activity

[0036] The 0.5Pd-5La / KIT-6 catalyst prepared by the above method was applied to catalytic oxidation of toluene, and the catalyst was reduced in H2 / Ar mixed gas at 450 ℃ for 2 h before use. The catalytic oxidation of toluene was carried out under the following conditions: the loading amount of the catalyst (20-40 mesh) in the micro fixed bed reactor was 0.2 g, the toluene gas space velocity was 20000 mL·g -1 ·h -1

[0037] The results show that when the reaction temperature is 175 ℃, the conversion rate of toluene reaches 99%, and the catalytic activity does not decrease significantly after the catalyst runs for 40 h.

[0038] Example 2

[0039] 1. Preparation of nitrogen-doped KIT-6

[0040] KIT-6 and urea were added to anhydrous ethanol (solid-liquid ratio 1:15) at a mass ratio of 1:1, refluxed at 50 ℃ for 5 h, aged at room temperature for 15 h, and then vacuum dried until the ethanol was completely volatilized. After grinding, the product was placed in a high-temperature tube furnace and calcined at 550 ℃ in a nitrogen atmosphere for 4 h to obtain a nitrogen-doped KIT-6 carrier.

[0041] 2. Preparation of La / KIT-6

[0042] 5 g of the nitrogen-doped KIT-6 carrier was pressed into a tablet as a chemical vapor deposition matrix. The matrix was ultrasonically treated in anhydrous ethanol for 15 min, dried at 100 ℃ for 1 h, and then placed in the reaction chamber of a chemical vapor deposition vertical reaction furnace. 0.27 g of lanthanum chloride was dissolved in 10 mL of water, and the lanthanum chloride solution was kept at a constant temperature (80 ℃). The deposition temperature of the reaction chamber was kept constant (900 ℃), the deposition pressure was kept constant (5 kPa), and the constant temperature was maintained for 6 h. After natural cooling to room temperature, the sample was removed, washed with anhydrous ethanol several times, and dried at 60 ℃ for 8 h to obtain 3La / KIT-6. The La loading was 3 wt%.

[0043] 3. Preparation of Pd-La / KIT-6

[0044] The 3La / KIT-6 was added to an impregnation tank. 0.08 g of palladium chloride was dissolved in 10 mL of water. The solution was added to the impregnation tank through a spraying device, and impregnated in a microwave reactor for 3 h at an impregnation temperature of 40 ℃. After impregnation, the sample was dried at 80 ℃ for 4 h and then calcined in a muffle furnace at 300 ℃ for 2 h to obtain a 1Pd-3La / KIT-6 catalyst. The Pd loading was 1 wt%.

[0045] 4. Catalytic activity evaluation ​

[0046] The 1Pd-3La / KIT-6 catalyst prepared by the above method was applied to the catalytic oxidation of toluene. The catalyst was reduced in a H2 / Ar mixed gas at 500 ℃ for 1 h before use. The catalytic oxidation of toluene was carried out under the following conditions: the loading amount of the catalyst (20-40 mesh) in the micro fixed bed reactor was 0.2 g, the toluene gas space velocity was 20000 mL·g -1 ·h -1 , the toluene gas concentration was 2000 ppm, the reaction was carried out at normal pressure, and the reaction temperature was 90-200 ℃.

[0047] The results show that when the reaction temperature is 168 ℃, the conversion rate of toluene reaches 99%, and the catalytic activity does not decrease significantly after the catalyst is operated for 40 h.

[0048] Example 3

[0049] 1. Preparation of nitrogen-doped KIT-6

[0050] KIT-6 and urea were added to anhydrous ethanol (solid-liquid ratio 1:10) at a mass ratio of 1:1.5, refluxed at 60 ℃ for 3 h, aged at room temperature for 18 h, and then vacuum dried until the ethanol was completely volatilized. After grinding, the product was placed in a high-temperature tube furnace and calcined at 600 ℃ in a nitrogen atmosphere for 2 h to obtain a nitrogen-doped KIT-6 carrier.

[0051] 2. Preparation of La / KIT-6

[0052] 5 g of the nitrogen-doped KIT-6 carrier was pressed into a tablet as a chemical vapor deposition matrix. The matrix was ultrasonically treated in anhydrous ethanol for 20 min, dried at 90 ℃ for 2 h, and then placed in the reaction chamber of a chemical vapor deposition vertical reaction furnace. 0.23 g of lanthanum acetate was dissolved in 10 mL of water, and the lanthanum nitrate solution was kept at a constant temperature (60 ℃). The deposition temperature of the reaction chamber was kept constant (1000 ℃), the deposition pressure was kept constant (4 kPa), and the constant temperature was kept for 8 h. After natural cooling to room temperature, the sample was taken out, washed with anhydrous ethanol several times, and dried at 60 ℃ for 8 h to obtain 2La / KIT-6. The La loading amount was 2 wt%.

[0053] 3. Preparation of Pd-La / KIT-6

[0054] The 2La / KIT-6 was added to an impregnation tank. 0.18 g of palladium sulfate was dissolved in 10 mL of water. The solution was added to the impregnation tank through a spraying device, impregnated in a microwave reactor for 2 h, and the impregnation temperature was kept at 40 ℃. After impregnation, the product was dried at 70 ℃ for 5 h and calcined in a muffle furnace at 450 ℃ for 2 h to obtain a 1.5Pd-2La / KIT-6 catalyst. The Pd loading amount was 1.5 wt%.

[0055] 4. Evaluation of catalytic activity

[0056] The 1.5Pd-2La / KIT-6 catalyst prepared by the above method was applied to the catalytic oxidation of toluene. Before use, the catalyst was reduced in a H2 / Ar mixture at 450℃ for 2 hours. The conditions for the toluene catalytic oxidation reaction were as follows: the catalyst (20-40 mesh) loading in the micro-fixed-bed reactor was 0.2 g, and the toluene gas hourly space velocity was 20000 mL·g⁻¹. -1 ·h -1 The toluene gas concentration was 2000 ppm, the pressure was normal, and the reaction temperature was 90–200 °C.

[0057] The results showed that the conversion rate of toluene reached 99% at a reaction temperature of 160℃, and the catalytic activity did not decrease significantly after 40 hours of operation.

[0058] Comparative Example 1

[0059] 1. Preparation of Pd-La / KIT-6 catalyst by traditional impregnation method.

[0060] Weigh 0.04 g palladium chloride and 0.44 g lanthanum chloride, dissolve them in 12.5 mL of ultrapure water, shake well, add 5 g KIT-6 support to the solution, mix well, impregnate at room temperature for 12 h, dry at 60 °C for 24 h, calcine at 500 °C in air atmosphere for 2 h, and reduce in H2 / Ar mixed gas at 300 °C for 2 h to obtain a catalyst with a Pd loading of 0.5 wt% and a La loading of 5 wt%, compared with the conventional impregnated 0.5Pd-5La / KIT-6 catalyst.

[0061] 2. Evaluation of catalytic activity

[0062] The 0.5Pd-5La / KIT-6 impregnated catalyst prepared by the above method was used for the catalytic oxidation of toluene. The conditions for the catalytic oxidation of toluene were as follows: the amount of catalyst (20-40 mesh) loaded in the micro fixed-bed reactor was 0.2 g, and the toluene gas hourly space velocity was 20000 mL·g. -1 ·h -1 The toluene gas concentration was 2000 ppm, the pressure was normal, and the reaction temperature was 90–200 °C.

[0063] The results showed that the conversion rate of toluene was 99% at a reaction temperature of 181℃, and the catalytic activity decreased significantly after 18 hours of operation.

[0064] The above results show that, compared with the Pd-La / KIT-6 catalyst prepared by the traditional impregnation method, the catalyst prepared by the chemical vapor deposition-spray method has significantly improved the activity and stability of the catalyst and has high industrial application value.

[0065] Further, referring to Table 1, the catalytic activity of the 0.5Pd-5La / KIT-6 catalyst prepared in Example 1 and the 1.5Pd-2La / KIT-6 catalyst prepared in Example 3 were compared with catalysts prepared in existing literature. Compared with catalysts with a Pd loading of 0.5 wt%, the 0.5Pd-5La / KIT-6 catalyst prepared in Example 1 exhibited higher catalytic activity, achieving 90% conversion of toluene at 165 °C. 90 The temperature drop is 20°C lower than that of the 0.5% Pd / Mn3Ce2-300 catalyst and 65°C lower than that of the 0.5% Pd / MCM-41 catalyst. Compared to the 0.5% Au-0.27% Pd / CeO2 / GC catalyst, the T6 of the 0.5Pd-5La / KIT-6 catalyst is also lower. 90 Reduce by 10℃. Compared to a 0.92% Pd / InO3 with a higher Pd loading. x @CoO x Compared to other catalysts, the 0.5Pd-5La / KIT-6 catalyst exhibits higher activity and T. 90 The temperature was reduced by 88°C. The 1.5Pd-2La / KIT-6 catalyst prepared in Example 3 with a Pd loading of 1.5 wt% was... 90 Lowering the temperature to 150°C further enhances the catalytic activity.

[0066] Table 1 Comparison of the catalyst of this invention with existing literature

[0067]

[0068] The embodiments described above are merely specific examples of the present invention, and while the descriptions are detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing a highly active Pd-La / KIT-6 catalyst, characterized in that, Includes the following steps: (1) Preparation of nitrogen-doped KIT-6: KIT-6 and urea were added to anhydrous ethanol, heated under reflux, aged, dried, ground and calcined to obtain nitrogen-doped KIT-6 support; (2) Preparation of La / KIT-6: After ultrasonic treatment, the nitrogen-doped KIT-6 support was placed in the reaction chamber of the chemical vapor deposition equipment, and the lanthanum-containing solution was introduced into the reaction chamber by nitrogen bubbling for chemical vapor deposition; after chemical vapor deposition, the material was cooled naturally, washed, and dried to obtain the La / KIT-6 material. (3) Preparation of Pd-La / KIT-6: La / KIT-6 was impregnated in a palladium-containing impregnation solution by spray impregnation method. After impregnation, it was dried and calcined to obtain Pd-La / KIT-6 catalyst; In step (1), the mass ratio of KIT-6 to urea is 1:0.5~3.0, and the solid-liquid ratio is 1:10~20; In step (2), the chemical vapor deposition conditions are as follows: the temperature of the lanthanum-containing solution is 60~80℃, the deposition temperature is 800~1000℃, the deposition pressure is 2~5 kPa, and the deposition time is 6~10 h; In step (3), the impregnation temperature is 30~40℃ and the impregnation time is 2~4 h; the calcination temperature is 300~450℃ and the calcination time is 1~2 h. The Pd content accounts for 0.1 to 2 wt% of the total catalyst weight, and the La content accounts for 1 to 5 wt% of the total catalyst weight.

2. The method for preparing a highly active Pd-La / KIT-6 catalyst according to claim 1, characterized in that, In step (1), the heating reflux temperature is 50~60℃ and the heating reflux time is 3~6 h; the aging temperature is room temperature and the aging time is 12~24 h; the calcination temperature is 500~600℃ and the calcination time is 2~4 h.

3. The method for preparing a highly active Pd-La / KIT-6 catalyst according to claim 1, characterized in that, In step (2), the lanthanum-containing solution is at least one of lanthanum nitrate, lanthanum acetate, and lanthanum chloride.

4. The method for preparing a highly active Pd-La / KIT-6 catalyst according to claim 1, characterized in that, In step (3), the impregnation solution is at least one of palladium nitrate, palladium chloride, and palladium sulfate solution.

5. A Pd-La / KIT-6 catalyst prepared by the method according to any one of claims 1-4, characterized in that, The nitrogen-doped mesoporous silica material KIT-6 is used as a support, Pd is the active component and La is the auxiliary agent. Pd and La particles are uniformly dispersed on the surface of the support. The Pd content accounts for 0.1~2 wt% of the total weight of the catalyst and the La content accounts for 1~5 wt% of the total weight of the catalyst.

6. The application of the Pd-La / KIT-6 catalyst according to claim 5 in the catalytic oxidation of toluene.

7. The application of the Pd-La / KIT-6 catalyst according to claim 6 in the catalytic oxidation of toluene, characterized in that, Before use, the catalyst was reduced in a H2 / Ar mixture at 300-500℃ for 1-3 hours. The catalytic oxidation of toluene was carried out in a micro fixed-bed reactor under the following conditions: catalyst size 20-40 mesh, catalyst loading 0.2 g, and toluene gas hourly space velocity 10000-60000 mL·g. -1 ·h -1 The toluene gas concentration is 1000~4000 ppm, the pressure is normal, and the reaction temperature is 90~200℃.

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