Nickel-indium co-doped X-type molecular sieve as well as preparation method and application thereof

Abstract

The invention discloses a nickel-indium co-doped X-type molecular sieve and a preparation method and application thereof, and relates to the technical field of molecular sieve preparation, the preparation method comprises the following steps: mixing an X-type molecular sieve and a nickel-containing organic complex, adding a solvent, heating and stirring, drying, dipping in an indium nitrate-containing ethanol water solution, and carrying out ultrasonic cavitation to obtain a mixed solution; injecting a mixed solution of ammonia water and ethylene glycol into the mixed solution, and performing dynamic pressure treatment to obtain a post-treated mixed solution; roasting the post-treatment mixed solution in a reducing gas atmosphere, finally dipping the post-treatment mixed solution in an ethanol solution containing a silane coupling agent, and drying to obtain the nickel-indium co-doped X-type molecular sieve. In combination with dynamic pressure fluctuation, gradient of metal distribution and accurate regulation and control of lattice sites are realized; metal oxide reduction and skeleton stabilization are synchronously completed, and pore channel collapse caused by traditional high-temperature oxidizing roasting is avoided; the problems of metal leaching and acid site inactivation are solved, and the catalyst is suitable for catalytic reaction in a high-temperature environment.

Description

Technical Field

[0001] The present invention relates to a nickel-indium co-doped X-type molecular sieve, a preparation method thereof, and an application thereof, belonging to the technical field of molecular sieve preparation. Background Art

[0002] Due to its regular pore structure and high specific surface area, X-type molecular sieves are widely used in fields such as adsorption, separation, and catalysis. However, traditional X-type molecular sieves are prone to framework collapse in acidic environments or high-temperature conditions, and single metal doping often has problems such as uneven distribution and insufficient active sites.

[0003] In recent years, bimetal-doped molecular sieves have received extensive attention due to their synergistic effects. However, in existing technologies, metal doping methods are mostly static ion exchange or impregnation methods, which have defects such as uneven metal distribution and poor lattice stability. In addition, traditional calcination processes are prone to pore collapse, limiting their application in high-temperature environments. Therefore, it is of great significance to develop an efficient and stable method for modifying bimetal-doped X-type molecular sieves. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a nickel-indium co-doped X-type molecular sieve, a preparation method thereof, and an application thereof. By combining dynamic pressure fluctuations, gradient metal distribution and precise regulation of lattice sites are achieved; introducing reduction atmosphere calcination to simultaneously complete the reduction of metal oxides and framework stabilization, avoiding pore collapse caused by traditional high-temperature oxidation calcination; combining hydrophobic treatment and carbon layer confinement to solve the problems of metal leaching and inactivation of acidic sites, and being applicable to catalytic reactions in high-temperature environments.

[0005] To achieve the above object, the present invention is implemented by the following technical solutions: In the first aspect, the present invention provides a preparation method of a nickel-indium co-doped X-type molecular sieve, including: Mixing an X-type molecular sieve and a nickel-containing organic complex, adding a solvent and then heating and stirring, and drying to obtain a Ni 2+ -doped intermediate; Impregnating the Ni 2+ -doped intermediate in an ethanol aqueous solution containing indium nitrate, and performing ultrasonic cavitation to obtain a mixed solution; Injecting a mixed solution of ammonia water and ethylene glycol into the mixed solution, and performing dynamic pressure treatment to obtain a post-treatment mixed solution; Calcining the post-treatment mixed solution in a reducing gas atmosphere to obtain a molecular sieve precursor; Impregnating the molecular sieve precursor in an ethanol solution containing a silane coupling agent, and drying to obtain a nickel-indium co-doped X-type molecular sieve.

[0006] Further, the nickel-containing organic complex is nickel acetylacetonate; and / or, the mass ratio of the X-type molecular sieve to the nickel-containing organic complex is 1:0.05-1; and / or, the solvent is ethanol or water.

[0007] Further, in the ethanol aqueous solution containing indium nitrate, the mass fraction of indium nitrate is 5-8%, and the volume ratio of ethanol to water is 1:3.

[0008] Further, the ultrasonic cavitation is carried out by ultrasonic treatment at 40-60 kHz for 1-2 h; and / or, the pH range is 4-5.

[0009] Further, in the mixed solution of ammonia water and ethylene glycol, the volume ratio of ammonia water to ethylene glycol is 1:2-4.

[0010] Further, the dynamic pressure treatment includes dynamic treatment at an apparent pressure of 0.5-1.2 MPa and a temperature of 150-200 °C for 6-12 h, and the fluctuation range of the apparent pressure during the process is ±0.2 Mpa.

[0011] Further, in the ethanol solution containing silane coupling agent, the mass fraction of silane coupling agent is 0.5-1%, wherein the silane coupling agent is KH-550.

[0012] Further, at least one of the following conditions is satisfied: The condition parameters of the heating and stirring include heating and stirring at 50-80 °C for 2-6 h; The drying time is 6-12 h, and the drying temperature is 60-80 °C; The reducing gas atmosphere is nitrogen and hydrogen, and the volume ratio of nitrogen to hydrogen is 9:1; The calcination temperature range is 400-500 °C.

[0013] In a second aspect, the present invention also provides a nickel-indium co-doped X-type molecular sieve, which is prepared by the preparation method of the nickel-indium co-doped X-type molecular sieve according to any one of the above.

[0014] In a third aspect, the present invention also provides an application of the above-mentioned nickel-indium co-doped X-type molecular sieve, including as a catalyst for the catalytic hydrogenation of carbon dioxide to prepare methane.

[0015] Compared with the prior art, the beneficial effects achieved by the present invention are: In the present invention, the X-type molecular sieve and the nickel-containing organic complex are mixed in a solvent system, and the solvent is used to promote the decomposition of the nickel-containing organic complex and the release of Ni 2+ to obtain a Ni 2+ doped intermediate, and Ni 2+The doped intermediate is impregnated in an ethanol-aqueous solution containing indium nitrate. Through ultrasonic cavitation, indium ions are assisted to migrate to specific lattice sites of the molecular sieve, forming a Ni-In bimetallic distribution gradient. The pH is adjusted to inhibit the hydrolysis of indium ions, while promoting the bonding of metals to the molecular sieve framework, realizing step-by-step metal doping. Subsequently, dynamic pressure treatment is used to promote lattice reconstruction to form stable Ni-O-Si and In-O-Al bonds. After calcination, part of the metal oxides are reduced to the elemental state, and the reducing atmosphere can avoid the collapse of the framework. Finally, surface passivation and pore modification of the molecular sieve are carried out, and a carbon nanolayer (thickness < 2 nm) is introduced into the pores to form a confined space, improving the catalytic selectivity; The preparation method of the present invention is different from the traditional static ion exchange. It adopts ultrasonic-assisted step-by-step doping, combined with dynamic pressure fluctuations, to realize the gradient of metal distribution and precise regulation of lattice sites; introducing a reducing atmosphere for calcination to synchronously complete the reduction of metal oxides and the stabilization of the framework, avoiding the pore collapse caused by traditional high-temperature oxidation calcination; combining hydrophobic treatment (drying Ni 2+ doped intermediate) with carbon layer confinement (impregnated in an ethanol-aqueous solution containing indium nitrate) to solve the problems of metal leaching and inactivation of acidic sites, and is applicable to catalytic reactions under high-temperature environments; The nickel-indium co-doped molecular sieve prepared by the present invention has the characteristics of uniform metal distribution, high lattice stability, excellent catalytic performance, etc., and is applicable to industrial production. Description of the Drawings

[0016] Figure 1 It is a schematic diagram of the comparison of the X-ray diffraction patterns of the nickel-indium co-doped X-type molecular sieve prepared in Example 1 of the present invention and the commercial X-type molecular sieve of Comparative Example 3. Detailed Embodiments

[0017] The present invention will be further described below with reference to the drawings. The following examples are only used to more clearly illustrate the technical solutions of the present invention and cannot be used to limit the protection scope of the present invention. Example 1

[0018] The embodiment of the present invention provides a preparation method of a nickel-indium co-doped X-type molecular sieve, including the following steps: 10 g of X-type molecular sieve and 4 g of nickel acetylacetonate are mixed in 50 mL of 95% ethanol solution. In this example, the X-type molecular sieve is selected as 13X type. The mixture is transferred to a 100 mL ordinary reaction kettle and heated and stirred at 60 °C for 4 hours. The reaction mixture is centrifuged 3 times with deionized water as the detergent. It is dried at 80 °C for 12 h to obtain Ni 2+ doped intermediate.

[0019] Secondly, immerse the above intermediate in 16 mL of an ethanol-water mixed solution (volume ratio 1:3) containing 5% indium nitrate, perform ultrasonic cavitation (frequency 40 kHz) for 2 h, and add citric acid to adjust the pH of the solution to 4 to obtain a mixed solution.

[0020] Place the mixed solution in a 100 mL high-pressure reactor, inject 20 mL of a mixed solution of ammonia water and ethylene glycol (volume ratio 1:3), and perform dynamic treatment for 12 hours under the conditions of an apparent pressure of 1.2 MPa and a temperature of 150 °C. The periodic pressure change is ±0.2 Mpa to obtain a post-treatment mixed solution.

[0021] In a nitrogen-hydrogen mixed gas (volume ratio 9:1), perform calcination on the post-treatment mixed solution at a programmed heating rate (2 °C / min) to 450 °C for 3 - 5 hours to obtain a molecular sieve precursor.

[0022] Finally, immerse the molecular sieve precursor in 20 mL of a KH-550 ethanol solution with a mass fraction of 0.5%, stir at 25 °C for 4 h, and then dry at 80 °C to obtain the final product, nickel-indium co-doped X-type molecular sieve. Example 2

[0023] The embodiment of the present invention provides a method for preparing a nickel-indium co-doped X-type molecular sieve, which includes the following steps: Mix 20 g of X-type molecular sieve (13X type) and 8 g of nickel acetylacetonate in 100 mL of 95% ethanol solution. In this example, the 13X type of X-type molecular sieve is selected. Transfer the mixture to a 200 mL ordinary reactor and heat and stir at 70 °C for 6 hours. Wash the reacted mixture 3 times by centrifugation using deionized water as the detergent. Dry at 80 °C for 12 h to obtain a Ni 2+ -doped intermediate.

[0024] Secondly, immerse the above intermediate in 32 mL of an ethanol-water mixed solution (volume ratio 1:3) containing 5% indium nitrate, perform ultrasonic cavitation (frequency 40 kHz) for 4 h, and add citric acid to adjust the pH of the solution to 4 to obtain a mixed solution.

[0025] Place the mixed solution in a 200 mL high-pressure reactor, inject 40 mL of a mixed solution of ammonia water and ethylene glycol (volume ratio 1:3), and perform dynamic treatment for 12 hours under the conditions of an apparent pressure of 1.2 MPa and a temperature of 150 °C. The periodic pressure change is ±0.2 MPa.

[0026] In a nitrogen-hydrogen mixed gas (volume ratio 9:1), perform calcination at a programmed heating rate (2 °C / min) to 450 °C for 3 - 5 hours to obtain a molecular sieve precursor.

[0027] Finally, immerse the zeolite precursor in 40 mL of a 0.5% KH-550 ethanol solution, stir at 25 °C for 6 h, and then dry at 80 °C to obtain the final product, nickel-indium co-doped X-type zeolite (Ni:In = 1:1). Example 3

[0028] The embodiment of the present invention provides a method for preparing nickel-indium co-doped X-type zeolite, including the following steps: Mix 5 g of X-type zeolite with 5 g of nickel acetylacetonate in 25 mL of 95% ethanol solution. In this example, 13X-type zeolite is selected as the X-type zeolite. Transfer the mixture to a 50 mL ordinary reaction kettle, heat and stir at 50 °C for 4 hours. Wash the reacted mixture 3 times by centrifugation using deionized water as the detergent. Dry at 80 °C for 12 h to obtain the Ni 2+ -doped intermediate.

[0029] Secondly, immerse the above intermediate in 20 mL of an ethanol-water mixed solution (volume ratio 1:3) containing 5% indium nitrate, perform ultrasonic cavitation (frequency 40 kHz) for 2 h, and adjust the pH of the solution to 4 by adding citric acid to obtain a mixed solution.

[0030] Place the mixed solution in a 50 mL autoclave, inject 10 mL of a mixed solution of ammonia water and ethylene glycol (volume ratio 1:3), and perform dynamic treatment at an apparent pressure of 1.2 MPa and a temperature of 150 °C for 12 hours, with a periodic pressure change of ±0.2 MPa.

[0031] In a nitrogen-hydrogen mixed gas (volume ratio 9:1), calcine at a programmed heating rate (2 °C / min) to 450 °C for 3 - 5 hours to obtain the zeolite precursor. Finally, immerse the zeolite precursor in 10 mL of a 0.5% KH-550 ethanol solution, stir at 25 °C for 6 h, and then dry at 80 °C to obtain the final product, nickel-indium co-doped X-type zeolite (Ni:In = 1:1).

[0032] Comparative Example 1: This comparative example provides a method for preparing X-type zeolite loaded with nickel-indium bimetal by the equal-volume impregnation method, specifically including the following steps: Calcine 10 g of X-type zeolite (13X-type) at 550 °C for 4 hours to remove surface adsorbed water and impurities to obtain activated zeolite. Immerse the solution containing nickel nitrate and indium nitrate with a nickel-indium ratio of 1:1 in the zeolite in an equal volume, and stir at 80 °C for 6 h. Dry the impregnated sample at 100 °C for 12 h, then put it into a muffle furnace, calcine in an air atmosphere, heat at 2 °C / min to 400 °C, keep the temperature constant for 4 hours, and finally grind and sieve.

[0033] Comparative Example 2: This comparative example provides a method for preparing X-type molecular sieve loaded with nickel-indium bimetal by static ion exchange method, which specifically includes the following steps: 10 g of X-type molecular sieve (13X type) was calcined at 550 °C for 4 hours to remove surface adsorbed water and impurities, obtaining activated molecular sieve. Weigh 1.16 g of nickel nitrate and 1.42 g of indium nitrate, and dissolve them in 200 mL of deionized water (solid-liquid ratio 1:20). Adjust the pH of the solution to 3.5 with 0.1M HNO3 to avoid In 3+ hydrolysis. Add 10 g of molecular sieve into the exchange solution, and stir in a constant temperature water bath at 80 °C for 8 hours. After centrifugal separation, replace the fresh exchange solution and repeat the exchange 2 times (3 times in total). After washing thoroughly, dry at 80 °C for 12 h, and then put it into a muffle furnace and calcine in air atmosphere, heat up to 350 °C at 2 °C / min and keep the temperature constant for 4 hours.

[0034] Comparative Example 3: This comparative example provides a 13X type molecular sieve, purchased from Tianjin Nanhua Catalyst Co., Ltd., denoted as commercial X-type molecular sieve.

[0035] Next, performance analysis and comparison were carried out on the nickel-indium co-doped X-type molecular sieves prepared in Examples 1 to 3 and the X-type molecular sieves loaded with nickel-indium bimetal prepared in Comparative Examples 1 and 2.

[0036] First, the X-ray diffraction patterns of the molecular sieves in Example 1 and Comparative Example 3 are as Figure 1 shown. It can be seen from the figure that in contrast, the nickel-indium co-doped X-type molecular sieve prepared in Example 1 has the characteristics of uniform metal distribution, high dispersion degree and good lattice stability.

[0037] Then, the nickel-indium co-doped X-type molecular sieves prepared in Examples 1 to 3 and the X-type molecular sieves loaded with nickel-indium bimetal prepared in Comparative Examples 1 and 2 were used to catalyze the hydrogenation of carbon dioxide to prepare methane reaction for catalytic testing. The testing method is as follows: For the catalytic evaluation of the product, weigh 0.25 g of the product powder into a sample tube, and introduce a mixed gas of carbon dioxide and nitrogen (CO2:N2 = 2:8) with a flow rate of 40 mL / min. After adsorption saturation, introduce hydrogen with a flow rate of 40 mL / min. After the hydrogen fills the reactor, close the outlet valve, heat up, and continue to inject and pressurize for reaction. When the catalytic temperature is 400 °C, the catalytic pressure is 300 kPa, and the catalytic time is 30 min, the catalytic reaction evaluation is shown in Table 1.

[0038] Table 1: Catalytic reaction evaluation results of the products prepared in Examples 1 to 3 and Comparative Examples 1 and 2

[0039] As can be seen from Table 1, compared with the comparative examples, the nickel-indium co-doped X-type molecular sieve prepared in the examples of the present invention has better catalytic performance, and it improves the CO2 conversion rate while maintaining a high CH4 selectivity. Among them, the reason for the slight difference in the CO2 conversion rate and CH4 selectivity in Examples 1 to 3 is that the loading amounts of nickel and indium are affected by the dynamic pressure treatment (although the dynamic pressure treatment is the same in the three examples, there are uncertainties in hydrodynamics in itself, and this kind of uncertainty is likely to cause slight differences in the loading amounts of nickel-indium co-doping, non-uniform morphology, and different catalytic effects). Although stable Ni-O-Si and In-O-Al bonds are formed in the molecular sieve lattice as a whole, due to the influence of pressure fluctuations, there are still a very small number of indefinite defects in the molecular sieve, which affect the loading effect of nickel and indium, thereby affecting the catalytic reaction results.

[0040] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and deformations can be made, and these improvements and deformations should also be regarded as the protection scope of the present invention.

Claims

1. Preparation method of nickel and indium co-doped X-type molecular sieve, characterized in that, Comprising: Mix the X-type molecular sieve and the nickel-containing organic complex, add a solvent, heat and stir, and obtain the Ni 2+ -doped intermediate after drying; Impregnate the Ni 2+ doped intermediate in an aqueous ethanol solution containing indium nitrate, and adjust the pH to acidic after ultrasonic cavitation to obtain a mixed solution; Injecting a mixed solution of ammonia water and ethylene glycol into the mixed solution, and obtaining a post-treatment mixed solution after dynamic pressure treatment; Roasting the post-treatment mixed solution in a reducing gas atmosphere to obtain a molecular sieve precursor; Impregnating the molecular sieve precursor in an ethanol solution containing a silane coupling agent, and drying to obtain a nickel-indium co-doped X-type molecular sieve.

2. The preparation method of the nickel and indium co-doped X-type molecular sieve according to claim 1, characterized in that, The nickel-containing organic complex is nickel acetylacetonate; and / or, the mass ratio of the X-type molecular sieve to the nickel-containing organic complex is 1:0.05-1; and / or, the solvent is ethanol or water.

3. The preparation method of the nickel and indium co-doped X-type molecular sieve according to claim 1, wherein In the ethanol aqueous solution containing indium nitrate, the mass fraction of indium nitrate is 5-8%, and the volume ratio of ethanol to water is 1:

3.

4. The preparation method of the nickel-indium co-doped X-type molecular sieve according to claim 1, characterized in that, The ultrasonic cavitation is ultrasonic treatment at 40-60 kHz for 1-2 h; and / or, the pH range is 4-5.

5. The preparation method of the nickel-indium co-doped X-type molecular sieve according to claim 1, characterized in that, In the mixed solution of ammonia water and ethylene glycol, the volume ratio of ammonia water to ethylene glycol is 1:2-4.

6. The preparation method of the nickel and indium co-doped X-type molecular sieve according to claim 1, wherein, The dynamic pressure treatment includes dynamic treatment for 6-12 h under the conditions of an apparent pressure of 0.5-1.2 MPa and a temperature of 150-200 °C, and the fluctuation range of the apparent pressure during the process is ±0.2 Mpa.

7. The preparation method of the nickel-indium co-doped X-type molecular sieve according to claim 1, wherein In the ethanol solution containing a silane coupling agent, the mass fraction of the silane coupling agent is 0.5-1%, wherein the silane coupling agent is KH-550.

8. The preparation method of the nickel-indium co-doped X-type molecular sieve according to claim 1, characterized in that, At least one of the following conditions is satisfied: The condition parameters of the heating and stirring include heating and stirring at 50-80 °C for 2-6 h; The drying time is 6-12 h, and the drying temperature is 60-80 °C; The reducing gas atmosphere is nitrogen and hydrogen, and the volume ratio of nitrogen to hydrogen is 9:1; The roasting temperature range is 400-500 °C.

9. A nickel-indium co-doped X-type molecular sieve, characterized in that, Prepared by the preparation method of the nickel-indium co-doped X-type molecular sieve according to any one of claims 1-8.

10. Use of the nickel and indium co-doped X-type molecular sieve according to claim 9, characterized in that, Including being used as a catalyst for the reaction of catalytic hydrogenation of carbon dioxide to prepare methane.

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