Encapsulation of (NH4)3Cr(OH)6Mo6O 18 Y-type molecular sieve compounds and their use

Abstract

The application discloses a Y-type molecular sieve compound encapsulating (NH4)3Cr(OH)6Mo6O 18 and application thereof. The compound is obtained by encapsulating Anderson heteropoly acid synthesized from sodium molybdate dihydrate and chromium nitrate nonahydrate into a Y-type molecular sieve supercage. The compound is applied as a catalyst in an oxidation desulfurization reaction. The application overcomes the shortcoming that the heteropoly acid is easy to dissolve and difficult to recover, and has high stability, high cyclic activity and wide application prospect.

Description

Technical Field

[0001] This invention belongs to the field of heterogeneous catalysis technology and relates to an encapsulated (NH4)3Cr(OH)6Mo6O 18 Y-type molecular sieve compounds and their applications. Background Technology

[0002] In today's era, the slogan of green development has been put forward, and green and clean energy is bound to become the mainstream of future energy. Although the development and utilization of green and clean energy is proceeding in an orderly manner in today's society, recent social development still relies heavily on fossil fuels for energy. Diesel, due to its high calorific value and low consumption rate, is widely used in the power of various large vehicles and machinery engines. The incomplete combustion of sulfur compounds in diesel fuel leads to increased carbon deposits in the combustion chamber, resulting in accelerated vehicle wear and significantly reduced engine life. Therefore, countries around the world have strictly regulated the sulfur content in diesel fuel through legislation. Hydrodesulfurization (HDS) technology is the most widely used technology in industry, but for sulfur compounds containing benzene rings, it generally requires relatively harsh desulfurization conditions, and needs to be carried out under high temperature and high pressure conditions, placing high demands on equipment. Oxidative desulfurization (ODS) is an alternative to HDS deep desulfurization, and has attracted widespread attention due to its mild reaction conditions, high efficiency, and ability to effectively remove thiophene compounds. In the reaction process, oxygen is used as an oxidant, which is environmentally friendly, but it is not easily activated under mild conditions, requiring the addition of sacrificial agents to obtain high oxidation performance. (NH4)3Cr(OH)6Mo6O 18 Under mild conditions, it exhibits excellent desulfurization performance without the addition of sacrificial agents, and due to its unique polymetallic oxygen clusters, it possesses high catalytic activity. However, its high solubility in water and organic solutions, and its dissolution into the liquid phase, makes catalyst recovery difficult. Y-type molecular sieves have a unique bottle-shaped supercage structure with a pore diameter of 0.74 nm and an internal spherical cavity diameter of 1.3 nm. Although its structure is unique, its small pore size prevents compounds with molecular structures larger than its pore size from binding, thus limiting its application scenarios. Summary of the Invention

[0003] The purpose of this invention is to provide an encapsulated (NH4)3Cr(OH)6Mo6O 18 Y-type molecular sieve compounds and their applications.

[0004] The technical solution of the present invention includes the following specific steps: Encapsulation (NH4)3Cr(OH)6Mo6O 18 (CrMo6) Y-type molecular sieve compounds, the preparation method of said compounds is as follows: 1) Mix Na2MoO4·2H2O and Y molecular sieve at a mass ratio of 1:50-200, dissolve in excess deionized water, stir and sonicate at 25-50 ℃ until completely dispersed to obtain solution 1; 2) Dissolve Cr(NO3)3·9H2O in deionized water and stir until completely dissolved to obtain solution 2, wherein the mass ratio of Na2MoO4·2H2O to Cr(NO3)3·9H2O is 1:3~10; 3) Place the solution 1 prepared in step 1) in an oil bath at 100~150 ℃, while adding solution 2 dropwise until the addition is complete. Then reflux for 5~20 min, stir, and cool to room temperature to obtain solution 3 containing the target product. 4) Filter solution 3, wash the target product with deionized water, and dry it at 30~70 ℃ to obtain the final product.

[0005] Encapsulation (NH4)3Cr(OH)6Mo6O 18 The application of Y-type molecular sieve compounds as catalysts for oxidative desulfurization reactions.

[0006] The compounds of this invention encapsulate heteropolyacids within Y-type molecular sieve supercages, enabling their application in oxidative desulfurization reactions using oxygen as the oxidant. This invention overcomes the drawbacks of heteropolyacids, such as easy solubility and difficulty in separation. (NH4)3Cr(OH)6Mo6O 18 (CrMo6) has a planar hexagonal structure with a diameter of approximately 0.9 nm and a thickness of approximately 0.3 nm. Its dimensions exceed the pore size of Y-type molecular sieves (0.74 nm), making it impossible to directly confine it within the small-pore Y-type molecular sieve. The design concept of this invention is as follows: Figure 5 As shown, the innovation of this invention lies in the fact that the above design concept enables the encapsulation of large molecular structure Anderson-type heteropoly compounds within a small-pore Y-type molecular sieve supercage. This not only achieves the multiphase existence of Anderson-type heteropoly compounds and solves the problem of the difficulty in recycling Anderson-type heteropoly compounds, but also provides effective desulfurization of various sulfides and significantly improves the desulfurization effect.

[0007] The beneficial effects of this invention are: This invention achieves a heterogeneous catalytic effect in the oxidative desulfurization reaction, exhibits excellent catalytic performance, high stability, and high cycle activity, and has broad application prospects.

[0008] The innovation of this invention lies in the preparation of an encapsulated (NH4)3Cr(OH)6Mo6O 18The Y-type molecular sieve compound of (CrMo6) can effectively overcome the disadvantages of high solubility and difficult recovery of heteropoly acids as a catalyst for oxidative desulfurization reaction. In other words, the eutectic agent and Anderson-type heteropoly compound cannot be separated and recovered in the oxidative desulfurization system. This invention achieves effective separation of eutectic agent and Anderson-type heteropoly compound. Furthermore, the Y-type molecular sieve encapsulated heteropoly acid catalyst of this invention has high stability, thereby realizing the reuse of the catalyst of this invention.

[0009] Furthermore, the Y-type molecular sieve-encapsulated heteropolyacid catalyst of the present invention can achieve excellent desulfurization effects for various sulfides, such as benzothiophene dissolved in decahydronaphthalene, dibenzothiophene dissolved in decahydronaphthalene, and 4,6-dimethyldibenzothiophene dissolved in decahydronaphthalene, etc., and has high catalytic activity in the oxidative desulfurization reaction of low eutectic flux and Anderson-type heteropoly compound system.

[0010] The CrMo6@Y of this invention is a multifunctional catalyst with both acidic and redox properties, which is easily separated from the reaction system (separated from the eutectic solvent) and is environmentally friendly. Attached Figure Description

[0011] Figure 1 XRD patterns of catalysts with different loadings.

[0012] Figure 2 The images show the FT-IR spectra of catalysts with different loadings.

[0013] Figure 3 Oxidative desulfurization of model diesel fuel with catalysts of different CrMo6 loadings.

[0014] Figure 4 The figure shows the removal performance of the catalyst for different sulfides.

[0015] Figure 5 This is the technical route for CrMo6@Y in this invention. Implementation

[0016] The principles and features of the present invention are described below. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0017] Example 1: Encapsulation of (NH4)3Cr(OH)6Mo6O 18 Y-type molecular sieve compounds (CrMo6@Y) 1) Add 0.0196 g Na2MoO4·2H2O and 2.5 g Y molecular sieve to 25 mL of deionized water, stir for 5 min, sonicate for 30 min, and then stir at 40 ℃ for 24 h.

[0018] 2) Dissolve 0.0054 g Cr(NO3)3·9H2O in 1 mL H2O and stir until completely dissolved.

[0019] 3) Transfer the solution from step 1) to an oil bath at 120 °C. Add the liquid from step 2) dropwise to the solution from step 1). After the addition is complete, reflux for 10 min, then stir and cool to room temperature, and stir for another 24 h.

[0020] 4) Filter the solution prepared in step 3), wash the filtered powder with deionized water, and dry it at 60 °C for 12 h to obtain the heteropolyacid catalyst CrMo6@Y (1%).

[0021] The XRD and FT-IR characterization results are as follows: Figure 1 , Figure 2 As shown. Figure 1 The original Y-type molecular sieve exhibited representative diffraction peaks at 6.0, 10.0, 11.8, 15.6, 20.3, and 23.6°. The catalyst, after encapsulation with the heteropolyacid, displayed clear Y-type molecular sieve diffraction peaks, indicating that encapsulation with the heteropolyacid does not disrupt the structure of the Y-type molecular sieve. Figure 2 The results showed that, compared with pure Y-type molecular sieves, encapsulation of heteropolyacids resulted in the appearance of characteristic peaks of CrMo6. (891 cm⁻¹) -1 The peaks at 632 and 547 cm⁻¹ represent the stretching vibrations of the terminal oxygen Mo=O bond in heteropolyacids. -1 The peak belongs to Mo-O-Mo and is 412 cm -1 These are characteristic peaks belonging to the Mo-O-Cr group. The appearance of these peaks indicates that the heteropolyacid has been encapsulated within the Y-type molecular sieve.

[0022] CrMo6@Y catalysts with CrMo6 loadings (3%, 5%, 10%) can be prepared using the same method as described above. Only the corresponding weight ratios of Na2MoO4·2H2O, Cr(NO3)3·9H2O, and Y molecular sieve need to be adjusted.

[0023] Moreover, such as Figure 1-2 The results show that, with the heteropolyacid (NH4)3Cr(OH)6Mo6O 18 With the increase of (CrMo6) loading, the intensity of the characteristic peaks of heteropoly acids increased, but the structure of the Y-type molecular sieve was not destroyed, indicating that the heteropoly acids were successfully encapsulated in the Y-type molecular sieve.

[0024] Example 2: Oxidative desulfurization of diesel fuel (CrMo6@Y and eutectic solvent system) Among them, the application of CrMo6@Y catalysts with CrMo6 loading (1%, 3%, 5%, 10%) in oxidative desulfurization of model diesel.

[0025] Preparation of eutectic solvent: Mix p-toluenesulfonic acid and polyethylene glycol 4000 in a molar ratio of 1:2, and heat to 80°C. o C. Stir vigorously and react for 1 h to obtain a eutectic solvent.

[0026] Diesel fuel desulfurization: Add 4 g of eutectic solvent and 20 mL of model diesel fuel (dibenzothiophene dissolved in decahydronaphthalene, S: 500 ppm) to a 100 mL three-necked round-bottom flask, place it in an oil bath, and set the temperature to 90 °C. o C. After stirring and extraction for 30 min, 20 mg of catalyst with different CrMo6 loadings (1%, 3%, 5%, 10%) was added to a round-bottom flask. Oxygen was introduced at a flow rate of 60 mL / min, and the reaction was started with stirring and timing. Stirring was stopped after 8 h. 1.0 mL of the upper model oil phase was taken and placed in a sample bottle. The sulfur content was determined by GC-FPD, and the results are as follows. Figure 3 .

[0027] Figure 3 The results showed that the desulfurization activity first increased and then decreased with the increase of the loading, and the desulfurization rate of CrMo6@Y with four different CrMo6 loadings reached 100% after 8 h of reaction.

[0028] Recovery of CrMo6@Y (1%): After the reaction is completed, the three-necked round-bottom flask loaded with 1% CrMo6@Y is allowed to stand at room temperature. The upper clear oil phase is separated and decanted. The mixture of the lower eutectic solvent and CrMo6@Y is transferred to a centrifuge tube, acetonitrile is added, centrifuged, and washed to obtain CrMo6@Y.

[0029] After drying CrMo6@Y at 60 ℃ for 12 h, the diesel desulfurization process was repeated according to the above experiment, and the sulfur content was determined by GC-FPD. The results showed that after 5 cycles, the desulfurization rate could reach more than 90%.

[0030] Example 3: Application of CrMo6@Y (1%) in the removal of different sulfides (CrMo6@Y with eutectic solvent system) Preparation of eutectic solvent: Mix p-toluenesulfonic acid and polyethylene glycol 4000 in a molar ratio of 1:2, and heat to 80°C. o C. Stir vigorously and react for 1 h to obtain a eutectic solvent.

[0031] Oxidative desulfurization: Add 4 g of eutectic solvent and 20 mL of model diesel fuel (benzothiophene dissolved in decahydronaphthalene, S: 500 ppm, dibenzothiophene dissolved in decahydronaphthalene, S: 500 ppm, 4,6-dimethyldibenzothiophene dissolved in decahydronaphthalene, S: 500 ppm) to three 100 mL three-necked round-bottom flasks respectively. Place them in an oil bath and set the temperature to 90 °C.o C. Stir and extract for 30 min, add 10 mg of catalyst CrMo6@Y (1%) to a round-bottom flask, introduce oxygen at a flow rate of 60 mL / min, stir and start timing to begin the reaction, stop stirring after 8 h, take 1.0 mL of sample from the upper oil phase into a sample bottle. Determine its removal rate using GC-FPD.

[0032] The results show that CrMo6@Y of the present invention has good removal effects on different sulfides. Removal performance is as follows: Figure 4 As shown, CrMo6@Y has a removal rate of 50% for benzothiophene, a removal rate of 90% for dibenzothiophene, and a removal rate of 100% for 4,6-dimethyldibenzothiophene.

[0033] The above demonstrates that the present invention successfully synthesized encapsulated (NH4)3Cr(OH)6Mo6O 18 The Y-type molecular sieve compound of (CrMo6) is used as a catalyst in the oxidative desulfurization system of eutectic flux and Anderson-type heteropoly compounds. This not only effectively overcomes the drawbacks of high solubility and difficult recovery of heteropoly acids, achieving efficient separation of the eutectic flux and Anderson-type heteropoly compounds, but also demonstrates high stability in the Y-type molecular sieve-encapsulated heteropoly acid catalyst, thus enabling its reuse. Furthermore, the Y-type molecular sieve-encapsulated heteropoly acid catalyst exhibits excellent desulfurization effects for various sulfides, such as benzothiophene dissolved in decahydronaphthalene, dibenzothiophene dissolved in decahydronaphthalene, and 4,6-dimethyldibenzothiophene dissolved in decahydronaphthalene, and possesses high catalytic activity in the oxidative desulfurization reaction of the eutectic flux and Anderson-type heteropoly compound system.

[0034] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. Encapsulation of (NH4)3Cr(OH)6Mo6O 18 The Y-type molecular sieve compound is prepared by the following steps: 1) Mix Na2MoO4·2H2O and Y molecular sieve at a mass ratio of 1:50-200, dissolve in excess deionized water, stir and sonicate at 25-50 ℃ until completely dispersed to obtain solution 1; 2) Dissolve Cr(NO3)3·9H2O in deionized water and stir until completely dissolved to obtain solution 2, in which, The mass ratio of Na2MoO4·2H2O to Cr(NO3)3·9H2O is 1:3~10; 3) Place the solution 1 prepared in step 1) in an oil bath at 100~150 ℃, while adding solution 2 dropwise until the addition is complete. Then reflux for 5~20 min, stir, and cool to room temperature to obtain solution 3 containing the target product. 4) Filter solution 3, wash the target product with deionized water, and dry it at 30~70 ℃ to obtain the final product.

2. The encapsulation method described in claim 1 for (NH4)3Cr(OH)6Mo6O 18 The application of Y-type molecular sieve compounds as catalysts for oxidative desulfurization reactions.

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