Catalyst for synthesizing nitrite ester and preparation method thereof
By loading the catalyst of precious metals and rare earth metal oxides and p-toluenesulfonic acid on the modified mesoporous molecular sieve, the equipment corrosion and catalyst deactivation problems in nitrite synthesis are solved, and efficient and stable nitrite synthesis is achieved.
Patent Information
- Application Number
- CN202510551262.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-29
- Publication Date
- 2025-08-05
AI Technical Summary
In the prior art, the synthesis method of nitrite has problems such as serious equipment corrosion, difficulty in separation of products, and inability to recycle the catalyst, and traditional solid acid catalysts have low activity and are prone to inactivation.
A noble metal catalyst supported on the modified mesoporous molecular sieve is used, supplemented with rare earth metal oxides and p-toluenesulfonic acid as co-catalysts to form a highly active and highly stable heterogeneous catalyst, and the synthesis of nitrite is promoted through protonation and activation of reactants.
The catalytic activity is increased by more than 30%, the reaction time is shortened to 2-4 hours. The activity remains above 90% after the catalyst can be recycled for 5 times, and the product selectivity reaches more than 98%, without the need for complex purification steps.
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Abstract
Description
Technical Field
[0001] The present invention relates to a catalyst and a preparation method thereof, in particular to a catalyst for synthesizing nitrite and a preparation method thereof, belonging to the technical field of catalysts. Background Art
[0002] Nitrite esters (such as methyl nitrite and ethyl nitrite) are important chemical intermediates and are widely used in the fields of medicine, pesticides and fuel additives. Traditional synthesis methods usually use liquid acids such as concentrated sulfuric acid as catalysts, which have problems such as severe equipment corrosion, difficulty in product separation, and inability to recycle catalysts. In recent years, although solid acid catalysts (such as molecular sieves and metal oxides) have been used, they still have defects such as low activity and easy deactivation. Therefore, the development of highly active, highly stable and recyclable catalysts is a problem to be solved in this field. Summary of the Invention
[0003] In order to solve the shortcomings of the above technology, the present invention provides a catalyst for synthesizing nitrite and a preparation method thereof.
[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is: a catalyst for synthesizing nitrite, the catalyst consisting of the following components:
[0005] The main active component loaded on the carrier is a noble metal: the loading amount is 0.5% to 5wt% of the carrier mass;
[0006] The carrier is a modified mesoporous molecular sieve, and the loading amount is 40% to 60% of the carrier mass;
[0007] The co-catalyst is a rare earth metal oxide, and the loading amount is 5% to 15% of the carrier mass;
[0008] The acid catalyst is p-toluenesulfonic acid, and the loading amount is 0.3% to 1.5% of the carrier mass.
[0009] The sulfonic acid group (-SO3H) of p-toluenesulfonic acid can release a proton (H + ), protonating the functional groups (such as hydroxyl and amino groups) in the reactants and enhancing the reaction activity. In the reaction of synthesizing nitrites, p-toluenesulfonic acid mainly plays a role through the following mechanisms:
[0010] 1. Provide a strong acidic environment: p-Toluenesulfonic acid is a strong organic acid. Its acidity is significantly stronger than benzoic acid and close to that of inorganic strong acid. It can release protons (H + ), forming an acidic reaction medium. This acidic environment can promote the activation of nitrous acid (HNO2) or its derivatives (such as nitrite), while protonating the alcohol substrate and enhancing its nucleophilicity.
[0011] 2. Catalytic protonation and activation of intermediates: H + Combined with the oxygen atom in the reactant, such as the oxygen of protonated nitrous acid or the hydroxyl oxygen of alcohol, thereby increasing the electrophilicity of the carbonyl or related group, promoting the attack of nucleophiles (such as alcohols or nitrites), and forming an intermediate transition state (such as a tetrahedral intermediate). In the synthesis of nitrite esters, this step may involve a nucleophilic substitution reaction between nitrite and protonated alcohol, ultimately forming nitrite and releasing a water molecule.
[0012] Preferably, the noble metal is at least one of Pd, Pt, and Rh.
[0013] Preferably, the pore size of the modified mesoporous molecular sieve is 2 to 10 nm, and the specific surface area of the carrier is 200 to 350 m 2 / g, modified by ion exchange with 0.5-2 mol / L ammonium nitrate solution.
[0014] Preferably, the rare earth metal oxide is selected from La2O3 or CeO2 or a mixture of the two.
[0015] A method for preparing a catalyst for synthesizing nitrites, the preparation process of the catalyst comprising the following steps:
[0016] (1) Carrier pretreatment, including the following processes:
[0017] Acid washing treatment: immerse the modified mesoporous molecular sieve support in a nitric acid or hydrochloric acid solution with a concentration of 0.5-2 mol / L and stir for 2-4 hours to remove surface impurities;
[0018] Washing and drying: washing with deionized water until neutral, and then drying at 80-120°C for 6-12h to obtain a high-purity modified mesoporous molecular sieve carrier;
[0019] (2) Preparation of the impregnation solution, including the following steps:
[0020] Dissolving the precious metal salt: dissolving the precious metal precursor in deionized water or ethanol to prepare an impregnation solution with a concentration of 0.02% to 2.5%;
[0021] Control the loading amount: by adjusting the volume of the impregnation solution and the mass ratio of the carrier, ensure that the total loading amount of the precious metal is 0.02% to 2.5% of the total mass of the catalyst;
[0022] (3) Impregnation and loading, including the following processes:
[0023] Impregnation operation: immerse the pretreated modified mesoporous molecular sieve into the impregnation solution, disperse it with ultrasound assistance for 30 to 60 minutes, and then let it stand for 12 to 24 hours to allow the precious metal to be evenly adsorbed;
[0024] Prepare a solution containing 0.3-1.5% p-toluenesulfonic acid, immerse in equal volumes, let stand for 6 hours and then dry;
[0025] Drying treatment: Dry the impregnated carrier at 80-100°C for 6-8 hours to remove the solvent;
[0026] (4) Calcination and reduction, including the following processes:
[0027] High-temperature calcination: Under the protection of inert gas nitrogen, heat the temperature to 300-500°C at a rate of 2-5°C / min and calcine for 2-4 hours to convert the noble metal salt into oxide;
[0028] Hydrogen reduction: under H2 atmosphere, at a flow rate of 50-100 mL / min, at 200-400°C for 2-3 h to obtain the catalyst;
[0029] (5) Catalyst post-treatment, including the following processes:
[0030] Passivation and storage: The reduced catalyst is purged with nitrogen and cooled to room temperature, then sealed and stored in a dry environment to avoid oxidation.
[0031] Preferably, the noble metal precursor is one of PdCl2, H2PtCl6 or RhCl3.
[0032] Preferably, the volume ratio of the impregnation liquid to the mass ratio of the carrier is 1:5 to 1:10.
[0033] The invention discloses an application of a catalyst in the reaction of synthesizing nitrite esters from alcohols and nitrites.
[0034] Preferably, the catalyst needs to be activated before use. The activation method is to introduce a hydrogen-nitrogen mixed gas (N2 volume content 50% to 100%) or a carbon monoxide-nitrogen mixed gas (N2 volume content 50% to 100%) at 250 to 550° C. for 3 to 7 hours. After the catalyst is activated, it is used in the synthesis of nitrites.
[0035] Preferably, a fixed bed reactor is used, the raw materials for the nitrite synthesis reaction are diluted with nitrogen, and the reaction temperature is 90-150°C.
[0036] The beneficial effects of the present invention are: a multiphase catalyst with high catalytic activity, good stability and reusability. In the esterification reaction of alcohol and nitrite, the catalyst activity is increased by more than 30%, and the reaction time is shortened to 2 to 4 hours; the catalytic activity is still maintained at more than 90% after being recycled for 5 times; the product selectivity reaches more than 98%, and no complicated purification steps are required. DETAILED DESCRIPTION
[0037] The present invention will be further described in detail below with reference to specific embodiments.
[0038] Example 1: Preparation of Pd-La2O3 / modified molecular sieve catalyst
[0039] Support pretreatment: The mesoporous molecular sieve (SBA-15) was immersed in a 1.5 mol / L ammonium nitrate solution, stirred at 60°C for 4 h, filtered and dried at 120°C for 6 h to obtain an ion exchange modified molecular sieve support.
[0040] Precious metal loading: PdCl2 (0.8 g) was dissolved in 50 mL of deionized water, 1.2 g of citric acid was added as a complexing agent, and the mixture was stirred until completely dissolved to prepare an impregnation solution.
[0041] The modified molecular sieve support (20 g) was immersed in the above solution, ultrasonically dispersed for 40 min, allowed to stand for 12 h, and then dried at 100° C. for 8 h.
[0042] Prepare a 0.3% p-toluenesulfonic acid solution, immerse in equal volumes, let stand for 6 hours and then dry;
[0043] Calcination and Reduction: Under nitrogen, the temperature was increased to 450°C at a rate of 3°C / min for 3 h to convert PdCl2 to Pd. The mixture was then reduced to a hydrogen atmosphere (80 mL / min) at 300°C for 2 h to obtain a catalyst precursor containing dispersed Pd nanoparticles.
[0044] Co-catalyst loading: Lanthanum nitrate (1.5 g) was dissolved in ethanol and sprayed onto the surface of the above catalyst. After drying at 80°C, it was activated in an air atmosphere at 400°C for 2 h to form a La2O3 co-catalyst layer.
[0045] Performance testing:
[0046] In the reaction of methanol and sodium nitrite (molar ratio 1:1.2, 70°C), the yield of methyl nitrite reached 95.3%, and the yield remained at 92.1% after being recycled five times.
[0047] Example 2: Preparation of bimetallic Pd-Rh / activated carbon catalyst
[0048] Carrier acid treatment: Activated carbon (specific surface area ≥ 1000m 2 / g) were immersed in 0.8 mol / L nitric acid solution, refluxed at 80°C for 3 h, washed with deionized water until neutral, and dried at 120°C for 12 h.
[0049] Bimetallic impregnation: Pd(NO3)2 and RhCl3 were weighed at a Pd:Rh molar ratio of 3:1 and dissolved in an ethanol-water mixed solvent (volume ratio 1:1) to prepare an impregnation solution with a total metal concentration of 1.2%.
[0050] The solution was loaded onto activated carbon using the equal volume impregnation method, ultrasonically treated for 30 min, allowed to stand for 24 h, and dried at 80 °C for 6 h.
[0051] Prepare a 1.5% p-toluenesulfonic acid solution, immerse in equal volumes, let stand for 6 hours and then dry;
[0052] Reduction and passivation: In a H2 atmosphere (flow rate 100 mL / min), reduction was carried out at 350 °C for 3 h, and then nitrogen was introduced to cool to room temperature to form a passivation layer on the surface.
[0053] Performance testing:
[0054] Used in the reaction of isoamyl alcohol and potassium nitrite (110°C), the selectivity of isoamyl nitrite reaches 98.5%, and the catalyst stability exceeds 200h.
[0055] Example 3: Preparation of Fe-CeO2 composite oxide catalyst
[0056] Synthesis by co-precipitation method: Fe(NO3)3·9H2O (10.1 g) and Ce(NO3)3·6H2O (4.3 g) were dissolved in 200 mL of deionized water, and ammonia water was added dropwise with stirring until the pH was 9 to form a precipitate.
[0057] The precipitate was centrifuged, washed, dried at 100°C for 12 h, and calcined at 500°C for 4 h to obtain Fe2O3-CeO2 composite oxide.
[0058] Acid site modification: The composite oxide was immersed in 0.5 mol / L sulfuric acid solution and treated at 60°C for 2 h to enhance the surface acid site density. After drying, the composite oxide was ground to 200 mesh.
[0059] Performance testing:
[0060] The catalytic reaction of ethanol and sodium nitrite in concentrated sulfuric acid medium achieved a nitric acid conversion rate of 91.2% and reduced by-product generation by 40%.
[0061]
[0062] Example 4: Preparation of Pt / Al2O3 bifunctional catalyst
[0063] Carrier pretreatment: γ-Al2O3 (specific surface area ≥ 200m 2 The carrier was immersed in a 1.0 mol / L nitric acid solution at 80°C for 2 hours to remove surface impurities and enhance the pore structure. After washing and drying, it was calcined in air at 550°C for 4 hours to improve the thermal stability of the carrier.
[0064] Precious metal loading: H2PtCl6 (0.5 g) and ammonium citrate (1.2 g) were dissolved in an ethanol-water mixture (volume ratio 1:1) to prepare an impregnation solution with a Pt concentration of 0.6%.
[0065] The material was loaded on the Al2O3 support by the equal volume impregnation method, ultrasonically treated for 40 min, left to stand for 24 h, and dried at 100 °C for 6 h.
[0066] Reduction and activation: In a H2 atmosphere (flow rate 120 mL / min), reduction was performed at 400 °C for 3 h to form Pt nanoparticles with a particle size of ≤3 nm.
[0067] NH3-TPD characterization showed that the density of acidic sites on the catalyst surface increased to 0.8 mmol / g.
[0068] Performance testing:
[0069] Used in the reaction of n-butanol and sodium nitrite (molar ratio 1:1.2, 90°C), the yield of butyl nitrite reaches 97.8%, and the residual n-butanol content is ≤1.9%.
[0070] Example 5: Preparation of Rh / ZSM-5 molecular sieve catalyst
[0071] Molecular sieve modification: ZSM-5 molecular sieve (SiO2 / Al2O3=50) was immersed in 0.5 mol / L NH4Cl solution and ion exchanged twice at 80°C for 4 h each time to convert it into H-type molecular sieve.
[0072] After calcination at 600℃, the BET specific surface area of the molecular sieve reaches 380m 2 / g.
[0073] Metal loading: RhCl3 (0.3 g) was coordinated and dissolved with ethylenediaminetetraacetic acid (EDTA, 0.8 g) to form a Rh-EDTA complex solution.
[0074] The molecular sieves were loaded by vacuum impregnation method, the solvent was removed by rotary evaporation at 60°C, and the mixture was dried at 80°C for 12 h.
[0075] Optimization of reduction conditions: In a H2 / N2 mixed gas (H2 accounts for 30%), reduction was carried out at 250℃ for 4h, and the Rh dispersion reached 65%.
[0076] Performance testing:
[0077] In the synthesis of aromatic sulfides, tert-butyl nitrite was used as the nitrosating agent, and the selectivity of C-N bond construction reached 98.5%, and the reaction time was shortened to 2 hours.
[0078] Example 6: Preparation of Pd-Fe / activated carbon bimetallic catalyst
[0079] Activated carbon pretreatment: Coconut shell activated carbon (pore size 2-5 nm) was treated with 0.8 mol / L HNO3 for 3 h, and the surface oxygen-containing functional group density was increased to 1.2 mmol / g.
[0080] Bimetallic co-impregnation: a mixed solution of Pd(NO3)2 and Fe(NO3)3 was prepared at a Pd:Fe molar ratio of 1:2, with a total metal loading of 1.5%.
[0081] The loading was carried out by the excess impregnation method, the volume of the impregnation liquid was 1.5 times of the pore volume of the carrier, and the particles were dried after standing for 48 hours.
[0082] Stepwise calcination: first increase the temperature to 300°C at 2°C / min and maintain for 2h, then increase the temperature to 500°C at 5°C / min and calcine for 1h to form a Pd-Fe alloy phase.
[0083] Performance testing:
[0084] In the reaction of isoamyl alcohol and potassium nitrite (110°C), the space-time yield of isoamyl nitrite reached 2.8 g / (g·h), and the amount of by-products generated was reduced by 35%.
[0085]
[0086] Carrier adaptability: Optimize the surface properties of the carrier through acid washing, ion exchange and other means. For example, the acidity control of ZSM-5 molecular sieve can inhibit side reactions.
[0087] Metal dispersion control: Complexing agents (EDTA, ammonium citrate) and a step-by-step calcination strategy are used to achieve high dispersion of precious metal nanoparticles.
[0088] Bimetallic synergy: The Pd-Fe alloy phase enhances electron transfer efficiency and increases the rate of nitrite synthesis. The above examples cover single-component noble metal, bimetallic, and molecular sieve support systems, which can adapt to the synthesis of nitrites from C1 to C5 alcohols.
[0089] The above embodiments are not limitations of the present invention, and the present invention is not limited to the above examples. Any changes, modifications, additions or substitutions made by technicians in this technical field within the scope of the technical solution of the present invention also fall within the scope of protection of the present invention.
Claims
1. A catalyst for synthesizing nitrite, characterized in that: The catalyst is composed of the following components: The main active component loaded on the carrier is a noble metal: the loading amount is 0.5% to 5wt% of the carrier mass; The carrier is a modified mesoporous molecular sieve, and the loading amount is 40% to 60% of the carrier mass; The co-catalyst is a rare earth metal oxide, and the loading amount is 5% to 15% of the carrier mass; The acid catalyst is p-toluenesulfonic acid, and the loading amount is 0.3% to 1.5% of the carrier mass.
2. The catalyst for synthesizing nitrite according to claim 1, wherein: The noble metal is at least one of Pd, Pt, and Rh.
3. The catalyst for synthesizing nitrite according to claim 1, wherein: The pore size of the modified mesoporous molecular sieve is 2 to 10 nm, and the specific surface area of the carrier is 200 to 350 m 2 / g, modified by ion exchange with 0.5-2 mol / L ammonium nitrate solution.
4. The catalyst for synthesizing nitrite according to claim 1, wherein: The rare earth metal oxide is selected from La2O3 or CeO2 or a mixture of the two.
5. A method for preparing a catalyst for synthesizing nitrite according to claim 1, characterized in that: The preparation process of the catalyst comprises the following steps: (1) Carrier pretreatment, including the following processes: Acid washing treatment: immerse the modified mesoporous molecular sieve support in a nitric acid or hydrochloric acid solution with a concentration of 0.5-2 mol / L and stir for 2-4 hours to remove surface impurities; Washing and drying: washing with deionized water until neutral, and then drying at 80-120°C for 6-12h to obtain a high-purity modified mesoporous molecular sieve carrier; (2) Preparation of the impregnation solution, including the following steps: Dissolving the precious metal salt: dissolving the precious metal precursor in deionized water or ethanol to prepare an impregnation solution with a concentration of 0.02% to 2.5%; Control the loading amount: by adjusting the volume of the impregnation solution and the mass ratio of the carrier, ensure that the total loading amount of the precious metal is 0.02% to 2.5% of the total mass of the catalyst; (3) Impregnation and loading, including the following processes: Impregnation operation: immerse the pretreated modified mesoporous molecular sieve into the impregnation solution, disperse it with ultrasound assistance for 30 to 60 minutes, and then let it stand for 12 to 24 hours to allow the precious metal to be evenly adsorbed; Prepare a solution containing 0.3-1.5% p-toluenesulfonic acid, immerse in equal volumes, let stand for 6 hours and then dry; Drying treatment: Dry the impregnated carrier at 80-100°C for 6-8 hours to remove the solvent; (4) Calcination and reduction, including the following processes: High-temperature calcination: Under the protection of inert gas nitrogen, heat the temperature to 300-500°C at a rate of 2-5°C / min and calcine for 2-4 hours to convert the noble metal salt into oxide; Hydrogen reduction: under H2 atmosphere, at a flow rate of 50-100 mL / min, at 200-400°C for 2-3 h to obtain the catalyst; (5) Catalyst post-treatment, including the following processes: Passivation and storage: The reduced catalyst is purged with nitrogen and cooled to room temperature, then sealed and stored in a dry environment to avoid oxidation.
6. The method for preparing a catalyst for synthesizing nitrite according to claim 5, wherein: The noble metal precursor is one of PdCl2, H2PtCl6 or RhCl3.
7. The method for preparing a catalyst for synthesizing nitrite according to claim 5, wherein: The volume ratio of the impregnation liquid to the carrier mass is 1:5 to 1:
10.
8. Use of the catalyst as claimed in claim 1 in the reaction of synthesizing nitrites from alcohols and nitrites.
9. Use of the catalyst according to claim 8 in the reaction of synthesizing nitrites from alcohols and nitrites, characterized in that: The catalyst needs to be activated before use. The activation method is to introduce a hydrogen-nitrogen mixture (N2 volume content 50% to 100%) or a carbon monoxide-nitrogen mixture (N2 volume content 50% to 100%) at 250-550°C for 3-7 hours. After activation, the catalyst is used in the synthesis of nitrites.
10. Use of the catalyst according to claim 8 in the reaction of synthesizing nitrites from alcohols and nitrites, characterized in that: A fixed bed reactor is used to dilute the raw materials for the nitrite synthesis reaction with nitrogen, and the reaction temperature is 90-150°C.