Preparation method of nanoscale Ti-Co-beta molecular sieve

Abstract

The application discloses a preparation method of nanoscale Ti-Co-beta molecular sieve, which comprises the following steps: taking tetraethyl orthosilicate or silica sol as a silicon source, titanium tetrachloride or titanium isopropoxide as a titanium source, cobalt chloride hexahydrate as a cobalt source, sodium hydroxide as an alkali source, tetraethylammonium hydroxide as a template agent, and sodium acetate or sodium benzoate as a mineralizer; after one-step hydrothermal treatment, drying and calcination, Na type Ti-Co-beta molecular sieve is obtained; and after ion exchange treatment, sodium ions are removed, and nanoscale Ti-Co-beta molecular sieve is obtained. The method has the advantages of no need of adding fluoride, simple operation, good repeatability, low cost, easy industrialization, and the like, and the prepared Ti-Co-beta molecular sieve has the advantages of nanoscale, good crystallinity, uniform distribution of Ti and Co in the zeolite framework of the beta molecular sieve, large specific surface area and rich metal active sites, and the like, and is suitable for a toluene hydroxylation reaction and has very good catalytic activity, high toluene conversion rate and phenol selectivity.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterials technology, specifically relating to a method for preparing a dual heteroatom nanoscale Ti-Co-β molecular sieve. Background Technology

[0002] Beta zeolites are high-silica molecular sieves with unique three-dimensional twelve-membered channels and good hydrothermal stability. They are currently widely used as catalytic materials in the chemical industry. Introducing heteroatoms into the beta zeolite framework using appropriate methods is an effective method for modifying molecular sieves. In particular, partially replacing Al or Si atoms in the zeolite structure with transition metal ions achieves a highly dispersed state of transition metal ions in the crystal structure. This allows for the control of the acidity and pore properties of the molecular sieve, endowing it with some new catalytic functions and expanding the application fields of beta zeolites.

[0003] Currently, common heteroatom β-zeolites mainly include Ti-β, Mn-β, Fe-β, and Sn-β. By doping another metal ion into a heteroatom β-zeolite, a dual-active-center metal heteroatom β-zeolite is formed. Utilizing the respective properties of the two heteroatoms, complementary catalytic performance can be achieved, leading to the construction of novel catalytic materials. A previous study (Journal of Natural Science of Hunan Normal University, April 2014, Vol. 37, No. 2) introduced Ti and Co into the zeolite framework of a β-zeolite through a hydrothermal reaction with the addition of the mineralizer NH4F, obtaining a dual-heteroatom Ti-Co-β-zeolite. However, this method uses fluorides, which causes significant environmental pollution and is unsuitable for industrial application. Summary of the Invention

[0004] The purpose of this invention is to provide a simple one-step hydrothermal method for preparing bimetallic Ti-Co-β molecular sieves without the need for adding fluorides or aluminum sources. Ti and Co exhibit good dispersibility, and the prepared molecular sieve particles are in the nanometer scale. It demonstrates very high activity in the catalytic hydroxylation of toluene.

[0005] To achieve the above objectives, the technical solution adopted by the present invention consists of the following steps:

[0006] Step 1: At room temperature, mix tetraethylammonium hydroxide, deionized water, sodium hydroxide, cobalt chloride hexahydrate, titanium tetrachloride or titanium isopropoxide evenly to obtain a clear solution A;

[0007] Step 2: At room temperature, add the mineralizing agent to solution A and mix well to obtain a clear solution B; the mineralizing agent mentioned above is sodium acetate or sodium benzoate;

[0008] Step 3: Under stirring conditions, add silica sol or tetraethyl orthosilicate to solution B obtained in step 2, stir evenly to obtain a crystallized gel. The molar ratio of each component in the crystallized gel is NaOH:SiO2:TiO2:CoO:TEAOH:R:H2O = 0.2~0.6:1:0.005~0.04:0.005~0.04:0.10~0.50:0.2~0.8:15~60, where TEAOH represents tetraethylammonium hydroxide and R is a mineralizing agent.

[0009] Step 4: Place the crystallized gel obtained in Step 3 in a reaction vessel and hydrothermally react at 140-170℃ for 36-72 hours. Wash and dry the obtained product, and then calcine it in a muffle furnace at 530-570℃ for 4-10 hours to obtain Na-type Ti-Co-β molecular sieve.

[0010] Step 5: Add the Na-type Ti-Co-β molecular sieve obtained in Step 4 to a 0.5 mol / L NH4Cl aqueous solution or a 0.5 mol / L ammonium nitrate aqueous solution, heat to 60-80℃ for ion exchange to remove sodium ions, then filter, wash, and dry, and calcine in a muffle furnace at 530-570℃ for 3-6 hours to obtain nano-sized Ti-Co-β molecular sieve.

[0011] In step 3 above, the preferred molar ratio of each component in the crystallized gel is NaOH:SiO2:TiO2:CoO:TEAOH:R:H2O = 0.2~0.3:1:0.02~0.04:0.01~0.03:0.20~0.40:0.2~0.4:30~50.

[0012] In step 4 above, it is preferable to place the crystallized gel obtained in step 3 in a reaction vessel and perform a hydrothermal reaction at 145–160°C for 36–60 hours.

[0013] In step 5 above, the preferred solid-liquid ratio of the Na-type Ti-Co-β molecular sieve to 0.5 mol / L NH4Cl aqueous solution or 0.5 mol / L ammonium nitrate aqueous solution is 1 g: 8-12 mL, the heating reaction time is 3-6 hours, and the ion exchange process is repeated 2-3 times.

[0014] The beneficial effects of this invention are as follows:

[0015] 1. This invention uses titanium tetrachloride or titanium isopropoxide as the titanium source, cobalt chloride hexahydrate as the cobalt source, tetraethyl orthosilicate or silica sol as the silicon source, and tetraethylammonium hydroxide as the template agent. Sodium acetate or sodium benzoate is added as a mineralizing agent. This mineralizing agent can form complexes with Ti and Co heteroatoms, thereby introducing Ti and Co into the zeolite framework. After the hydrothermal reaction, the product is filtered, washed, dried, ground, and calcined, followed by ion exchange to obtain a Na-removed Ti-Co-β molecular sieve. This method does not require the addition of fluorides, is simple to operate, has good reproducibility, and is low in cost, making it suitable for large-scale industrial production and application.

[0016] 2. The dual heteroatom Ti-Co-β molecular sieve prepared by the method of this invention has good crystallinity, with Ti and Co uniformly distributed in the zeolite framework of the β molecular sieve, and almost no non-framework Ti and Co. Moreover, the particle size is in the nanoscale, with good dispersibility and no obvious agglomeration. It has rapid mass transfer capability, large specific surface area and abundant metal active sites, making it suitable for toluene hydroxylation reaction, and exhibiting high toluene conversion rate and phenol selectivity. Attached Figure Description

[0017] Figure 1 This is the XRD pattern of sample S1 prepared in Example 1.

[0018] Figure 2 This is a SEM image of sample S1 prepared in Example 1.

[0019] Figure 3 This is the XRD pattern of sample S2 prepared in Example 2.

[0020] Figure 4 This is an SEM image of sample S2 prepared in Example 2.

[0021] Figure 5 This is the XRD pattern of sample S3 prepared in Example 3.

[0022] Figure 6 This is an SEM image of sample S3 prepared in Example 3. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments, but the scope of protection of the present invention is not limited to these embodiments.

[0024] Example 1

[0025] Step 1: At room temperature, add 19.8695g (0.0472mol) of 35wt% tetraethylammonium hydroxide aqueous solution and 142.9646g (8.6600mol) of deionized water to a 500mL beaker, then add 2.388g (0.0597mol) of NaOH and 0.9041g (0.0038mol) of cobalt chloride hexahydrate, stir to dissolve, then slowly add 1.0930g (0.0058mol) of titanium tetrachloride, stir for 1 hour to obtain solution A.

[0026] Step 2: At room temperature, add 3.7951g (0.0462mol) sodium acetate to solution A obtained in step 1, stir for 30 minutes, and obtain a clear solution B.

[0027] Step 3: Under stirring conditions, 56.3930 g (0.2134 mol) of tetraethyl orthosilicate was slowly added to solution B obtained in Step 2. After stirring for 1 hour, a crystallized gel was obtained. The molar ratio of each component in the obtained crystallized gel was NaOH:SiO2:TiO2:CoO:TEAOH:R:H2O = 0.28:1:0.0270:0.0180:0.2213:0.2168:40.5810, where R represents sodium acetate.

[0028] Step 4: Place the crystallized gel obtained in Step 3 in a 100mL stainless steel reactor and hydrothermally react at 145℃ for 56 hours. Then, allow it to cool naturally to room temperature. Filter the resulting white suspension, wash it three times with deionized water, and dry it at 120℃ for 10 hours. Grind the resulting solid and place it in a porcelain boat. Place the boat in a muffle furnace and calcine it at a heating rate of 3℃ / min to 550℃ for 4 hours to obtain Na-type Ti-Co-β molecular sieve.

[0029] Step 5: The Na-type Ti-Co-β molecular sieve obtained in Step 4 was added to a 0.5 mol / L NH4Cl aqueous solution at a solid-liquid ratio of 1 g:10 mL. The solution was heated to 70 °C for ion exchange to remove sodium ions for 4 hours. This process was repeated twice. The mixture was then filtered, washed three times with deionized water, dried at 120 °C for 10 hours, and then calcined in a muffle furnace at a heating rate of 3 °C / min to 550 °C for 4 hours to obtain nano-sized Ti-Co-β molecular sieve (denoted as S1). Figure 1 It is evident that the sample exhibits a β-zeolite crystal structure, good crystallinity, high purity, and the absence of impurity peaks. Figure 2 It can be seen that the sample particles are 80-100 nm in size, with good particle dispersion and no obvious agglomeration.

[0030] Example 2

[0031] Step 1: At room temperature, add 22.7151g (0.0540mol) of 35wt% tetraethylammonium hydroxide aqueous solution and 88.8442g (5.7559mol) of deionized water to a 500mL beaker, then add 1.8105g (0.0453mol) of NaOH and 0.7406g (0.0031mol) of cobalt chloride hexahydrate, stir to dissolve, then slowly add 1.0591g (0.0056mol) of titanium tetrachloride, stir for 1 hour to obtain solution A.

[0032] Step 2: At room temperature, add 8.5885g (0.0596mol) sodium benzoate to solution A obtained in step 1, stir for 30 minutes, and obtain a clear solution B.

[0033] Step 3: Under stirring conditions, 49.82 g (0.1886 mol) of tetraethyl orthosilicate was slowly added to solution B obtained in Step 2. After stirring for 1 hour, a crystallized gel was obtained. The molar ratio of each component in the obtained crystallized gel was NaOH:SiO2:TiO2:CoO:TEAOH:R:H2O = 0.24:1:0.0296:0.0165:0.2862:0.3158:30.5190, where R represents sodium benzoate.

[0034] Step 4: Place the crystallized gel obtained in Step 3 in a 100mL stainless steel reactor and hydrothermally react at 155℃ for 48 hours. Then, allow it to cool naturally to room temperature. Filter the resulting white suspension, wash it three times with deionized water, and dry it at 120℃ for 10 hours. Grind the resulting solid and place it in a porcelain boat. Place the boat in a muffle furnace and calcine it at a heating rate of 3℃ / min to 550℃ for 6 hours to obtain Na-type Ti-Co-β molecular sieve.

[0035] Step 5: Add the Na-type Ti-Co-β molecular sieve obtained in Step 4 to a 0.5 mol / L NH4Cl aqueous solution at a solid-liquid ratio of 1 g:10 mL. Heat to 60 °C for ion exchange to remove sodium ions for 5 hours. Repeat this process three times. Then filter, wash three times with deionized water, dry at 120 °C for 10 hours, and calcine in a muffle furnace at a heating rate of 3 °C / min to 550 °C for 4 hours to obtain the Ti-Co-β molecular sieve (denoted as S2). Figure 3 It is evident that the sample exhibits a β-zeolite crystal structure, good crystallinity, high purity, and the absence of impurity peaks. Figure 4 It can be seen that the sample particles have a size of 60-80 nm, good particle dispersion, and no obvious agglomeration.

[0036] Example 3

[0037] Step 1: At room temperature, add 37.0486 g (0.0880 mol) of 35 wt% tetraethylammonium hydroxide aqueous solution and 188.9039 g (14.0126 mol) of deionized water to a 500 mL beaker, then add 3.3588 g (0.0840 mol) of NaOH and 1.6050 g (0.0067 mol) of cobalt chloride hexahydrate, stir to dissolve, then slowly add 2.2317 g (0.0088 mol) of titanium isopropoxide, stir for 1 hour to obtain solution A.

[0038] Step 2: At room temperature, add 8.8282g (0.1076mol) sodium acetate to solution A obtained in step 1, stir for 30 minutes, and obtain a clear solution B.

[0039] Step 3: Under stirring conditions, 56.06 g (0.2799 mol) of silica sol with a mass concentration of 30% was slowly added to solution B obtained in Step 2. After stirring for 0.5 hours, a crystallized gel was obtained. The molar ratio of each component in the obtained crystallized gel was NaOH:SiO2:TiO2:CoO:TEAOH:R:H2O = 0.30:1:0.0315:0.0241:0.3146:0.3845:50.0628, where R is sodium acetate.

[0040] Step 4: Place the crystallized gel obtained in Step 3 in a 100mL stainless steel reactor and hydrothermally react at 160℃ for 36 hours. Then, allow it to cool naturally to room temperature. Filter the resulting white suspension, wash it three times with deionized water, and dry it at 120℃ for 10 hours. Grind the resulting solid and place it in a porcelain boat. Place the boat in a muffle furnace and calcine it at a heating rate of 3℃ / min to 550℃ for 8 hours to obtain Na-type Ti-Co-β molecular sieve.

[0041] Step 5: The Na-type Ti-Co-β molecular sieve obtained in Step 4 was added to a 0.5 mol / L ammonium nitrate aqueous solution at a solid-liquid ratio of 1 g:10 mL. The mixture was heated to 70 °C for ion exchange to remove sodium ions for 4 hours. This process was repeated twice. The mixture was then filtered, washed three times with deionized water, dried at 120 °C for 10 hours, and then calcined in a muffle furnace at a heating rate of 3 °C / min to 550 °C for 4 hours to obtain the Ti-Co-β molecular sieve (denoted as S3). Figure 5 It is evident that the sample exhibits a β-zeolite crystal structure, good crystallinity, high purity, and the absence of impurity peaks. Figure 6 It can be seen that the sample particles have a size of 70-90 nm, good particle dispersion, and no obvious agglomeration.

[0042] Comparative Example 1

[0043] In step 2 of Example 1, sodium acetate was replaced with an equimolar amount of sodium hydroxide, and the other steps were the same as in Example 1, to obtain Ti-Co-β molecular sieve (denoted as P1).

[0044] The Ti-Co-β molecular sieves obtained in Examples 1-3 and Comparative Example 1 were used to carry out the catalytic oxidation reaction of toluene hydroxylation with hydrogen peroxide as oxidant. The specific method was as follows: 1.8 mmol of toluene and 24 mL of deionized water were added to a 100 mL round-bottom flask, and then 0.4 g of Ti-Co-β molecular sieve was added. The mixture was stirred evenly, and then 31.36 mmol of hydrogen peroxide (30 wt%) was slowly added. The reaction was carried out for 2 hours under continuous magnetic stirring and reflux at 70 °C. The sample was then taken, and the conversion rate of toluene and the selectivity of phenol formation were detected by gas chromatography (GC, Bruker 450-GC). The detection results are shown in Table 1.

[0045] Table 1. Selectivity and conversion rate of toluene to phenol catalyzed by Ti-Co-β molecular sieve.

[0046]

[0047]

[0048] As can be seen from Table 1, the Ti-Co-β molecular sieve prepared by the method of the present invention has high catalytic oxidation activity, indicating that the sodium acetate or sodium benzoate mineralizer used in the present invention has advantages over other mineralizers.

Claims

1. A method for preparing nanoscale Ti-Co-β molecular sieves, characterized in that... It comprises the following steps: Step 1: at room temperature, mix tetraethylammonium hydroxide, deionized water, sodium hydroxide, cobalt chloride hexahydrate, titanium tetrachloride or titanium isopropoxide evenly to obtain a clear solution A; Step 2: at room temperature, add a mineralizer to solution A and mix evenly to obtain a clear solution B; the mineralizer is sodium acetate or sodium benzoate; Step 3: under stirring, add silica sol or tetraethyl orthosilicate to solution B obtained in step 2 and stir evenly to obtain a crystallization gel, wherein the molar ratio of components in the crystallization gel is NaOH:SiO2:TiO2:CoO:TEAOH:R:H2O=0.2-0.6:1:0.005-0.04:0.005-0.04:0.10-0.50:0.2-0.8:15-60, wherein TEAOH represents tetraethylammonium hydroxide and R is the mineralizer; Step 4: place the crystallization gel obtained in step 3 in a reaction kettle and hydrothermally react at 140-170°C for 36-72 hours, then wash and dry the obtained product and calcine it in a muffle furnace at 530-570°C for 4-10 hours to obtain Na-type Ti-Co-β molecular sieve; Step 5: add the Na-type Ti-Co-β molecular sieve obtained in step 4 to 0.5 mol / L NH4Cl aqueous solution or 0.5 mol / L ammonium nitrate aqueous solution, heat to 60-80°C to remove sodium ions by ion exchange, then filter, wash and dry, and calcine in a muffle furnace at 530-570°C for 3-6 hours to obtain nanoscale Ti-Co-β molecular sieve. 2.The method for preparing nanosized Ti-Co-β molecular sieve according to claim 1, characterized in that: In step 3, the molar ratio of components in the crystallization gel is NaOH:SiO2:TiO2:CoO:TEAOH:R:H2O=0.2-0.3:1:0.02-0.04:0.01-0.03:0.20-0.40:0.2-0.4:30-50. 3.The method for preparing nanosized Ti-Co-β molecular sieve according to claim 1, characterized in that: In step 4, place the crystallization gel obtained in step 3 in a reaction kettle and hydrothermally react at 145-160°C for 36-60 hours. 4.The method for preparing nanosized Ti-Co-β molecular sieve according to claim 1, characterized in that: In step 5, the solid-liquid ratio of the Na-type Ti-Co-β molecular sieve to 0.5 mol / L NH4Cl aqueous solution or 0.5 mol / L ammonium nitrate aqueous solution is 1g:8-12mL, the heating reaction time is 3-6 hours, and the ion exchange process is repeated 2-3 times.

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