In-situ crystal transformation preparation method and catalytic application of Nd-modified ANA molecular sieve

Abstract

The invention relates to the technical field of chemical engineering and industrial catalysis, and discloses an in-situ crystal transformation preparation method of an Nd-modified ANA molecular sieve, which comprises the following steps: S1, proportioning: dissolving an alkali source in deionized water, stirring until the alkali source is fully dissolved, adding a USY molecular sieve, and fully stirring to form gel; adding a neodymium (Nd)-containing metal source into the gel, and continuously stirring and uniformly mixing; s2, crystal transformation: putting the mixed gel obtained in the step S1 into a reaction kettle, and carrying out hydrothermal crystallization reaction to generate the Nd modified ANA molecular sieve. According to the in-situ crystal transformation preparation method and catalytic application of the Nd-modified ANA molecular sieve, acidic sites of the ANA molecular sieve are accurately regulated and controlled through specific modification of Nd. Experiments prove that under various acid catalytic reaction conditions, the Nd modified ANA molecular sieve shows catalytic activity far higher than that of unmodified and other rare earth element (such as La and Sm) modified molecular sieves.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of chemical engineering and industrial catalysis technology, in particular to a method for in-situ crystal transformation of Nd-modified ANA molecular sieve and catalytic application. BACKGROUND

[0002] In chemical production, acid-catalyzed reactions are crucial, but traditional homogeneous catalysts (such as concentrated sulfuric acid) have inherent defects. For example, Chinese patent CN108148020B discloses a method for preparing tetrahydrofuran by using concentrated sulfuric acid to catalyze the dehydration of 1,4-butanediol. Although this method is effective, the strong corrosive nature of sulfuric acid leads to severe equipment wear and tear, generates a large amount of acid-containing wastewater after the reaction, and has high treatment costs and causes significant environmental pollution. In addition, it is prone to cause side reactions, affecting the selectivity of the product.

[0003] Molecular sieves, as an environmentally friendly solid acid catalyst, are an ideal alternative. Among them, ANA-type molecular sieves have attracted attention due to their unique pore structure. However, traditional ANA molecular sieves have poor acid adjustability and insufficient hydrothermal stability, which limits their catalytic efficiency and lifespan under harsh reaction conditions. Although there have been studies on the modification of molecular sieves in the prior art, it is still a technical problem to be solved in the field how to use a simple, economical and efficient method to directionally synthesize a specific modified ANA molecular sieve with high activity, high selectivity and excellent stability. SUMMARY

[0004] To solve the problems raised in the background art, the present application provides the following technical solution: a method for in-situ crystal transformation of Nd-modified ANA molecular sieve, comprising the following steps: S1, batching Dissolve the alkali source in deionized water, stir until fully dissolved, then add USY molecular sieve, and stir thoroughly to form a gel. Then add a metal source containing neodymium (Nd) to the gel, and continue to stir until well mixed. S2, crystal transformation Place the mixed gel obtained in step S1 in a reaction kettle and perform a hydrothermal crystallization reaction to produce Nd-modified ANA molecular sieve. S3, post-treatment The product obtained in step S2 is sequentially subjected to suction filtration, washing, drying, grinding and calcination to obtain the final Nd@ANA molecular sieve catalyst.

[0005] Preferably, in step S1, the alkali source is sodium hydroxide.

[0006] Preferably, in step S1, the metal source containing neodymium is neodymium nitrate, and the doping amount of neodymium element is 1% to 7% of the mass of USY molecular sieve.

[0007] Preferably, the doping amount of the neodymium element is 4% to 5%.

[0008] Preferably, in the step S1, the stirring process for forming the gel is performed at a rotation speed of 800-1000 r / min, and the stirring time is 2-6 hours.

[0009] Preferably, in the step S2, the temperature of the hydrothermal crystallization reaction is 130-180℃, and the time is 24-72 hours.

[0010] Preferably, the temperature of the hydrothermal crystallization reaction is 150℃, and the time is 36-60 hours.

[0011] An Nd-modified ANA molecular sieve catalyst prepared by the preparation method.

[0012] Application of the Nd-modified ANA molecular sieve catalyst in acid-catalyzed reactions for replacing concentrated sulfuric acid catalysts.

[0013] Compared with the prior art, the present application provides an in-situ crystal transformation preparation method and catalytic application of an Nd-modified ANA molecular sieve, which has the following beneficial effects: The in-situ crystal transformation preparation method and catalytic application of the Nd-modified ANA molecular sieve precisely control the acid sites of the ANA molecular sieve through specific modification of Nd³⁺. Experiments have proved that the Nd-modified ANA molecular sieve exhibits much higher catalytic activity than unmodified and other rare earth element (such as La, Sm) modified molecular sieves under various acid catalytic reaction conditions.

[0014] The in-situ crystal transformation preparation method and catalytic application of the Nd-modified ANA molecular sieve prepare a solid acid catalyst, which fundamentally avoids the problems of equipment corrosion and waste liquid treatment caused by the use of concentrated sulfuric acid and other liquid strong acids, meets the development requirements of green chemical industry, and has remarkable environmental benefits.

[0015] The in-situ crystal transformation preparation method and catalytic application of the Nd-modified ANA molecular sieve use inexpensive and readily available USY molecular sieves as raw materials, do not need to use expensive organic template agents, have a simple process flow, mild conditions, good reproducibility, and greatly reduced production costs, and are conducive to large-scale industrial production.

[0016] The in-situ crystal transformation preparation method and catalytic application of the Nd-modified ANA molecular sieve enhance the structural stability and hydrothermal stability of the ANA molecular sieve framework by introducing Nd, so that the catalyst is easy to separate and recycle, and can be used repeatedly, thereby reducing the operating cost of continuous production. The in-situ crystal transformation preparation method and catalytic application of the Nd-modified ANA molecular sieve avoid the use of strong corrosive and high-risk chemicals in the entire preparation and application process, and the production safety and operation safety are greatly improved.BRIEF DESCRIPTION OF DRAWINGS BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 Schematic diagram of the material morphology of the present application; Figure 2 XRD pattern of Nd@ANA prepared by taking neodymium nitrate as raw material in the present application; Figure 3 XRD pattern of Sm@ANA prepared by taking samarium nitrate as raw material in the present application; Figure 4 XRD pattern of Ce@ANA prepared by taking cerium nitrate as raw material in the present application; Figure 5 Ammonia TPD graph of the catalyst prepared by different rare earth elements in the present application; Figure 6 Test result graph of different catalysts in the present application DETAILED DESCRIPTION

[0018] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0019] Please refer to Figures 1-6 The present application provides the following solutions: Embodiment 1: Preparation of Nd@ANA molecular sieve with Nd doping amount of 5% S1, batching Accurately weigh 0.9 g of sodium hydroxide (NaOH) and place it in a beaker, add 60 ml of deionized water, and stir with a magnetic stirrer for 30 minutes until it is completely dissolved. Then, 2.0 g of USY molecular sieve (commercially purchased, SiO2 / Al2O3 molar ratio about 5.5) is added to the alkali solution, and stirring is continued at a stirring speed of 800 r / min for 4 hours to form a uniform initial gel. Then, neodymium nitrate hexahydrate (Nd(NO3)3·6H2O) corresponding to 5% of the mass of the USY molecular sieve is weighed, and added to the above gel, and stirring is continued at 800 r / min for 90 minutes to ensure that the neodymium species is fully dispersed and uniformly mixed, to obtain a final reaction gel.

[0020] S2, crystal transformation The reaction gel obtained in step S1 is completely transferred to a polytetrafluoroethylene-lined stainless steel high-pressure reaction kettle, and after sealing, it is placed in a forced air drying oven. The temperature of the drying oven is set to 150℃, and the hydrothermal crystallization reaction is carried out, and the reaction time lasts for 48 hours. After the reaction is completed, it is naturally cooled to room temperature.

[0021] S3, post-treatment The reactor was opened and the solid product was filtered and washed repeatedly with deionized water until the filtrate was neutral (pH ≈ 7). The filter cake was dried in an oven at 80 °C for 12 hours. The dried sample was ground into fine powder and then placed in a muffle furnace, and heated from room temperature to 550 °C at a heating rate of 2 °C / min under air atmosphere, and calcined at 550 °C for 4 hours to remove the possible residual template and stabilize the structure of the molecular sieve. The final Nd-modified ANA molecular sieve catalyst was obtained as a white powder, denoted as Nd@ANA-1.

[0022] Example 2: Changing the crystallization time (36 hours) The preparation method was exactly the same as Example 1, except that the hydrothermal crystallization time in step S2 was changed from 48 hours to 36 hours. The final catalyst was denoted as Nd@ANA-2.

[0023] Example 3: Changing the crystallization time (60 hours) The preparation method was exactly the same as Example 1, except that the hydrothermal crystallization time in step S2 was changed from 48 hours to 60 hours. The final catalyst was denoted as Nd@ANA-3.

[0024] Example 4: Changing the Nd doping amount (4%) The preparation method was exactly the same as Example 1, except that the amount of neodymium nitrate in step S1 was adjusted to be equivalent to 4% of the mass of the USY molecular sieve. The final catalyst was denoted as Nd@ANA-4.

[0025] Example 5: Changing the Nd doping amount (7%) and the crystallization temperature The preparation method was basically the same as Example 1, but with two adjustments: the amount of neodymium nitrate in step S1 was adjusted to be equivalent to 7% of the mass of the USY molecular sieve; and the hydrothermal crystallization temperature in step S2 was adjusted to 130 °C, with a time of 48 hours. The final catalyst was denoted as Nd@ANA-5.

[0026] Comparative Example 1: Preparation of La-modified ANA molecular sieve The preparation method was exactly the same as Example 1, except that the neodymium metal source (neodymium nitrate hexahydrate) in step S1 was replaced with lanthanum nitrate hexahydrate (La(NO3)3·6H2O) of the same metal molar amount (i.e., the mass of La metal was also 5% of the mass of the USY molecular sieve). The final catalyst was denoted as La@ANA.

[0027] Comparative Example 2: Preparation of Sm-modified ANA molecular sieve The preparation method is basically the same as that in Example 1, but the neodymium metal source in step S1 is replaced with samarium nitrate hexahydrate (Sm(NO3)3·6H2O) of equal metal molar quantity (i.e., the mass of Sm metal is also 5% of the mass of the USY molecular sieve). The final obtained catalyst is recorded as Sm@ANA.

[0028] Preparation of unmodified ANA molecular sieve The preparation method is basically the same as that in Example 1, but the step of adding neodymium nitrate in step S1 is omitted, i.e., no rare earth metal is introduced for modification. The final obtained sample is recorded as ANA.

[0029] Comparison of catalytic performance To verify the excellent performance of the Nd@ANA catalyst prepared in the application in acid catalytic reactions, it is compared with La@ANA, Sm@ANA and unmodified ANA molecular sieve in the comparative examples. The esterification reaction of acrylic acid and methanol is used as a model reaction, and the reaction equation is as follows: CH2=CH-COOH + CH3OH ⇌ CH2=CH-COOCH3 + H2O.

[0030] The specific test method is as follows: 1. Catalyst preparation: Nd@ANA-1 prepared in Example 1, La@ANA prepared in Comparative Example 1, Sm@ANA prepared in Comparative Example 2 and unmodified ANA molecular sieve prepared in Comparative Example 3 are respectively taken, and all are calcined at 550 ℃ for 2 hours before use to activate the acid sites. 0.1285 g of each catalyst is accurately weighed for standby.

[0031] 2. Reactants and reagents: Methanol: 1.39 g (0.0434 mol) Acrylic acid: 1.18 g (0.0164 mol) Polymerization inhibitor: hydroquinone monomethyl ether (MEHQ), added when the reaction temperature is ≥130°C, 0.00064 g (the addition amount is 0.05% of the total mass of the reactants).

[0032] 3. Equipment and instruments: A high-pressure kettle with a polytetrafluoroethylene lining, a heating magnetic stirrer, a precision balance (one ten-thousandth), a micro-syringe and a gas chromatograph are used.

[0033] 4. Experimental steps: Place a clean magnetic stir bar inside the PTFE liner of the autoclave. Add the solid catalyst and methanol (and hydroquinone monomethyl ether if necessary), stirring until dissolved. Then add acrylic acid and gently shake to mix. Tighten the lid to ensure a seal, and purge the autoclave with nitrogen to a pressure of 0.5 MPa. Place the autoclave on a heated stirrer and turn on the stirrer (set to 1000 rpm). Increase the temperature to the target temperature (e.g., 110°C or 130°C) at a programmed rate of 3-5 °C / min and start timing for a specific reaction time (e.g., 2 hours or 6 hours). After the reaction is complete, turn off the heating and allow the autoclave to cool to room temperature. Transfer the entire reaction mixture to centrifuge tubes and centrifuge (10000 rpm, 10 min). Collect the supernatant for later use.

[0034] 5. Product analysis and conversion rate calculation: The supernatant after the reaction was analyzed using gas chromatography (GC). The conversion rate of acrylic acid was calculated using the following formula: Conversion rate (%) = (1 - Molar amount of acrylic acid after reaction / Molar amount of initial acrylic acid) × 100% 6. Test Results: The performance of each catalyst was systematically compared under different reaction conditions (including but not limited to 110°C / 2h and 130°C / 6h). Detailed conversion data are attached. Figure 6 .

[0035] Representative data are as follows: Under harsh reaction conditions of 130°C, 6h, and ~1 MPa, the acrylic acid conversion rate of the Nd@ANA-1 catalyst can reach 93.41%, which is significantly higher than that of La@ANA, Sm@ANA and unmodified ANA molecular sieve catalysts under the same conditions.

[0036] 7. Conclusion: As attached Figure 6 As shown, under all tested reaction conditions, the Nd-modified ANA molecular sieve catalyst (Nd@ANA-1) prepared in this invention exhibited the highest catalytic activity, with its conversion rate consistently superior to that of other rare earth element (La, Sm) modified ANA molecular sieves and unmodified ANA molecular sieves. This fully demonstrates the universality, specificity, and superiority of Nd modification in improving the catalytic performance of ANA molecular sieves, strongly supporting the inventiveness of this invention.

[0037] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An in-situ crystal transformation preparation method of an Nd-modified ANA molecular sieve, characterized in that, The method comprises the following steps: S1, batching The alkali source is dissolved in deionized water, and after stirring until fully dissolved, the USY molecular sieve is added, and the gel is fully stirred to form; then the metal source containing neodymium (Nd) is added to the above gel, and the stirring is continued until the mixture is uniform; S2, crystal transformation The mixed gel obtained in step S1 is placed in a reaction kettle, and a hydrothermal crystallization reaction is carried out to generate Nd-modified ANA molecular sieve; S3, post-treatment The product obtained in step S2 is sequentially subjected to suction filtration, washing, drying, grinding and calcination to obtain the final Nd@ANA molecular sieve catalyst.

2. The in situ crystallization conversion process according to claim 1, wherein, In step S1, the alkali source is sodium hydroxide.

3. The in situ crystallization conversion process according to claim 1, wherein In step S1, the metal source containing neodymium is neodymium nitrate, and the doping amount of neodymium element is 1% to 7% of the mass of the USY molecular sieve.

4. The in situ crystallization conversion process according to claim 3, wherein The doping amount of the neodymium element is 4% to 5%.

5. The in situ crystallization conversion process according to claim 1, wherein In step S1, the process of stirring to form a gel is carried out at a rotation speed of 800-1000 r / min, and the stirring time is 2-6 hours.

6. The in situ crystallization conversion process according to claim 1, wherein In step S2, the temperature of the hydrothermal crystallization reaction is 130-180℃, and the time is 24-72 hours.

7. The in situ crystallization conversion process according to claim 6, wherein The temperature of the hydrothermal crystallization reaction is 150℃, and the time is 36-60 hours.

8. The Nd-modified ANA molecular sieve catalyst prepared by the preparation method of any one of claims 1 to 7.

9. The use of the Nd-modified ANA molecular sieve catalyst of claim 8 in acid-catalyzed reactions to replace concentrated sulfuric acid catalysts.

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