CN117342572B - Preparation method and application of magnetic cobalt phosphate molecular sieve - Google Patents

Abstract

The invention provides a preparation method and application of a magnetic cobalt phosphate molecular sieve, wherein the preparation method comprises the following steps: dissolving a soluble cobalt source in water, adding phosphoric acid, stirring uniformly, adding a template agent, continuously stirring uniformly, and regulating the pH to be weak acid by using ammonia water; transferring the material to a crystallization kettle, aging, crystallizing, washing, drying and roasting to obtain the magnetic cobalt phosphate molecular sieve; the template agent is a compound of long-chain alkyl quaternary ammonium salt and 3, 8-diazabicyclo [3.2.1] octane according to a molar ratio of 3-5:1; the mole ratio of the soluble cobalt source, phosphoric acid, the template agent and water is 1:2.5-3:2-2.4:200-300, wherein the mole number of the soluble cobalt source is calculated as metal Co. The cobalt phosphate molecular sieve provided by the invention can exert excellent catalytic activity in benzyl alcohol oxidation reaction and benzyl alcohol esterification reaction, and can realize recycling through a magnetic field, so that the recycling rate is high.

Description

Preparation method and application of magnetic cobalt phosphate molecular sieve

Technical field

The invention belongs to the field of catalysts, and specifically relates to a preparation method and application of magnetic cobalt phosphate molecular sieve.

Background technique

Metal phosphate is a new type of molecular sieve with mesoporous structure, which has attracted widespread attention in recent years due to its excellent catalytic performance. Phosphate molecular sieves such as aluminum phosphate, vanadium phosphate, iron phosphate, zirconium phosphate, tin phosphate, etc. have been synthesized one after another, and their structures and properties have been studied. Han Shuyun of Jilin University synthesized a large single crystal of CoAPO-5 molecular sieve ("Synthesis, Structure and Properties of Cobalt Aluminum Phosphate (CoAPO-5) Molecular Sieve", Journal of Advanced Chemistry, 1988, 9(8): 274-276). After that, CoAPSO-11 molecular sieve was synthesized one after another ("Structure and Properties of Cobalt Aluminum Silicon Phosphate Molecular Sieve (CoAPSO-11)", Applied Chemistry, 1992, 9(2): 28-32). There are also reports on the use of ion thermal synthesis of cobalt phosphate molecular sieve GIS with micropores. Wu Huimin used di-n-butylamine as a template to synthesize silicoaluminophosphate SAPO-31 molecular sieve by changing the silicon source and aluminum source. On this basis, Pd-doped SAPO-31 (metallic acid) was prepared by an equal-volume impregnation method. /The influence of the metal type and acidity of SAPO-31 molecular sieve on the performance of n-alkanes isomerization reaction). As people's research on various types of metal phosphate molecular sieves becomes more and more in-depth, porous phosphate molecular sieves with different properties and unique structures will continue to be synthesized. Phosphate molecular sieves have become the mainstay in the field of inorganic synthesis and materials. Research hotspots. However, the catalytic performance of the cobalt phosphate molecular sieve synthesized by the above method is not ideal enough and cannot meet the requirements of industrial catalysts. It is speculated that the reason may be that the pore structure, specific surface area, acidic center, and thermal stability cannot be matched with each other to form a molecular sieve with optimal catalytic activity. structure.

In addition, there are few reports on magnetic metal phosphate molecular sieves among many studies. Magnetic metal phosphate molecular sieves can react in most organic solvents to achieve reaction uniformity, and produce very little waste during the preparation process. The use of an external magnetic field can effectively improve the separation and recovery efficiency of the catalyst. It is an environmentally friendly new catalyst and can be widely used as a catalyst in redox, acid catalysis and other reactions. With the enhancement of people's environmental awareness and the development of green chemistry, more and more attention has been paid to the research of environmentally friendly catalysts or molecular sieve carriers. Generally, people achieve efficiency improvement through effective control of the pore structure of molecular sieves and regulation of the number and type of active sites. Although some introduce magnetic materials, they hope that by applying an external magnetic field to them, the catalyst can be effectively separated and used for subsequent cycle reactions, so that it has the dual functions of catalytic activity and magnetic separation performance. But most of them are realized by loading or coating on a specific carrier. Although this will achieve the purpose of magnetic separation, it may affect the surface structure of the catalyst and thus affect some aspects of its performance.

Contents of the invention

In order to solve the problem that the catalytic performance of the existing cobalt phosphate molecular sieve catalyst needs to be improved and the magnetic and catalytic properties cannot be taken into account, the present invention proposes a magnetic cobalt phosphate molecular sieve and its preparation method and application. The present invention uses a compound of long-chain alkyl quaternary ammonium salt and 3,8-diazabicyclo[3.2.1]octane as a template agent to optimize and screen the conditions for preparing cobalt phosphate molecular sieves, and finally obtains a cobalt phosphate molecular sieve with excellent comprehensive properties. Magnetic cobalt phosphate molecular sieve has good catalytic activity and is magnetic, making it easy to recycle and utilize, and has industrial convenience and advantages. The present invention achieves the above objects through the following technical solutions:

A preparation method of magnetic cobalt phosphate molecular sieve, including the following steps:

Dissolve the soluble cobalt source in water, add phosphoric acid, stir evenly, add template agent, continue stirring evenly, and adjust the pH to weak acidity with ammonia water; transfer the material to the crystallization kettle for aging, crystallization, washing, drying, and roasting. Obtain magnetic cobalt phosphate molecular sieve; the template agent is a compound of long-chain alkyl quaternary ammonium salt and 3,8-diazabicyclo[3.2.1]octane according to the molar ratio of 3-5:1; soluble cobalt source, The molar ratio of phosphoric acid, template agent, and water is 1:2.5-3:2-2.4:200-300, in which the number of moles of soluble cobalt source is calculated as metal Co.

Preferably, the molar ratio of soluble cobalt source, phosphoric acid, template agent, and water is 1:2.8:2.1:228.

Further, the long-chain alkyl quaternary ammonium salt is dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, cetyltrimethylammonium bromide, dodecyltrimethylammonium bromide, At least one of trimethylammonium chloride, tetradecyltrimethylammonium chloride, and cetyltrimethylammonium chloride.

Unexpectedly, the inventor found that the cobalt phosphate molecular sieve finally obtained by using the above compound template agent had good catalytic activity, and the yield and selectivity of the catalytic oxidation of benzyl alcohol to benzaldehyde were significantly improved at the same time. It is possible that the macromolecular surfactant of long-chain alkyl quaternary ammonium salts and the diazabicyclo with a bicyclic stereostructure have a synergistic effect, and the interface assembly process with inorganic species can better serve as a space filler to support the skeleton. , suitable as a catalytic reaction for benzyl alcohol compounds.

Further, the soluble cobalt source is selected from at least one of cobalt acetate, cobalt nitrate, and cobalt chloride, preferably cobalt acetate. Cobalt acetate is used because the final product is relatively more crystalline and has better order. The possible reason is that different soluble cobalt sources have different dissolution speeds, and the pH adjustment speed and dosage are different, which in turn affects the crystal growth process.

Further, the phosphoric acid is not particularly limited, and industrial phosphoric acid can be used.

Further, ammonia water is used to adjust the pH to 4-7, preferably 4.5-5.

Further, the aging is left to stand for 5-10 hours.

Further, the crystallization is performed at 140-180°C, and the crystallization time is 24-72h, preferably 36-48h.

Further, the washing and drying are not particularly limited and are well known to those skilled in the art. For example, washing uses deionized water and ethanol alternately; drying involves oven drying or vacuum drying.

Further, the roasting is carried out by raising the temperature to 450-600°C at a heating rate of 1-2°C/min, and maintaining the temperature for 10-20 hours.

The second object of the present invention is to provide magnetic cobalt phosphate molecular sieves prepared by the above preparation method.

The third object of the present invention is to provide the use of the magnetic cobalt phosphate molecular sieve prepared by the above preparation method in catalyzing organic reactions.

Further, the organic reaction is an oxidation reaction or an esterification reaction; further, the organic reaction is a reaction in which benzyl alcohol is oxidized to benzaldehyde, or a reaction in which benzyl alcohol is esterified into benzyl alcohol ester; further, the The esterification reaction is an esterification reaction between benzyl alcohol and glacial acetic acid to prepare benzyl acetate.

The magnetic cobalt phosphate molecular sieve prepared by the present invention can exert excellent catalytic activity in benzyl alcohol oxidation reaction and benzyl alcohol esterification reaction, and has high conversion rate and selectivity. Moreover, the magnetic cobalt phosphate molecular sieve of the present invention has strong paramagnetic properties, and its recycling can be realized by simply applying an external magnetic field, and the reuse rate is high.

Compared with the existing technology, the magnetic cobalt phosphate molecular sieve of the present invention has achieved the following beneficial effects:

1. The magnetic cobalt phosphate molecular sieve of the present invention has a larger pore size than general phosphate molecular sieves and good thermal stability, and is suitable for some reactions at high temperatures; it uses a compound template agent, and the resulting catalyst has high catalytic activity and good stability. The conversion rate and selectivity of benzaldehyde produced by catalytic oxidation of benzyl alcohol are improved.

2. The magnetic cobalt phosphate molecular sieve of the present invention has paramagnetic properties with moderate strength, and can be easily recycled by applying an external magnetic field. The reuse rate is high and the cost as a catalyst in industry is reduced.

3. The preparation method of the magnetic cobalt phosphate molecular sieve of the present invention is simple, green and environmentally friendly, and is suitable for industrial production.

4. The magnetic cobalt phosphate molecular sieve of the present invention can be used for a variety of organic reactions, such as the oxidation of alcohol and the esterification of alcohol, especially the oxidation reaction and esterification reaction of benzyl alcohol.

Description of the drawings

Figure 1 is an SEM image of the magnetic cobalt phosphate molecular sieve obtained in Preparation Example 1;

Figure 2 is an XRD pattern of the magnetic cobalt phosphate molecular sieve obtained in Preparation Example 1-3;

Figure 3 is an XRD pattern of the magnetic cobalt phosphate molecular sieve obtained in Preparation Example 1, Comparative Preparation Example 1, Comparative Preparation Example 2, and Comparative Preparation Example 3;

Figure 4 is the Fourier transform infrared spectrum (FT-IR) of samples with different roasting temperatures;

Figure 5 is a NH ₃ temperature-programmed desorption spectrum of the cobalt phosphate molecular sieve prepared in Preparation Example 1.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and specific examples, so that those skilled in the art can better understand and implement the present invention, but the examples are not intended to limit the present invention.

Preparation Example 1

Dissolve cobalt acetate in water, add phosphoric acid, stir evenly, and add a mixture of cetyltrimethylammonium bromide and 3,8-diazabicyclo[3.2.1]octane in a molar ratio of 3:1 as a template. agent, continue to stir evenly and adjust the pH to 4.5 with ammonia water, where the molar ratio of cobalt acetate, phosphoric acid, template agent, and water is 1:2.8:2.1:228; transfer to the crystallization kettle, age for 5 hours, and crystallize at 180°C After drying, the solid obtained was heated to 450°C at a heating rate of 2°C/min in a muffle furnace and roasted for 10h to obtain magnetic cobalt phosphate molecular sieves.

Preparation Example 2

Other conditions are the same as Preparation Example 1, except that the molar ratio of cobalt acetate, phosphoric acid, template agent, and water is 1:2.5:2:300.

Preparation Example 3

Other conditions are the same as Preparation Example 1, except that the molar ratio of cobalt acetate, phosphoric acid, template agent, and water is 1:3:2.4:200.

Preparation Example 4

Other conditions are the same as Preparation Example 1, except that the template agent is a mixture of cetyltrimethylammonium bromide and 3,8-diazabicyclo[3.2.1]octane at a molar ratio of 5:1.

Comparative Preparation Example 1

Other conditions are the same as Preparation Example 1, except that the template agent is cetyltrimethylammonium bromide.

Comparative Preparation Example 2

Other conditions are the same as Preparation Example 1, except that the template agent is 3,8-diazabicyclo[3.2.1]octane.

Comparative Preparation Example 3

Other conditions are the same as Preparation Example 1, except that the template agent is a mixture of cetyltrimethylammonium bromide and amantadine at a molar ratio of 3:1.

Figure 1 is an SEM image of the magnetic cobalt phosphate molecular sieve obtained in Preparation Example 1. It can be seen that the obtained molecular sieve is a massive solid of about 1 micron with uniform morphology.

Figure 2 is an XRD pattern of the magnetic cobalt phosphate molecular sieve obtained in Preparation Examples 1-3, where a is Preparation Example 2, b is Preparation Example 3, and c is Preparation Example 1. It can be seen that the molecular sieves obtained in Preparation Examples 1-3 are all cobalt phosphates, but the crystal forms are different. Among them, the (011) and (210) peak shapes of the cobalt phosphate molecular sieve obtained in Preparation Example 1 are sharper, indicating that its crystallinity is higher. , higher orderliness. It also means that its catalytic activity is better.

Figure 3 is the XRD pattern of the magnetic cobalt phosphate molecular sieve obtained in Preparation Example 1, Comparative Preparation Example 1, Comparative Preparation Example 2, and Comparative Preparation Example 3, where a is Comparative Preparation Example 3, b is Comparative Preparation Example 1, and c is Comparative Preparation Example 2, d is Preparation Example 1. It can be seen that when the template agent is changed, the crystalline morphology of the obtained cobalt phosphate molecular sieve is also affected. Using a compound of cetyltrimethylammonium bromide and 3,8-diazabicyclo[3.2.1]octane as a template agent, the crystallization form of the obtained cobalt phosphate molecular sieve is better. Moreover, the inventor also found that replacing 3,8-diazabicyclo[3.2.1]octane with amantadine, which also has a cyclic structure, cannot achieve the same effect.

Table 1 is the specific surface area and pore characteristics data of the cobalt phosphate molecular sieves obtained in Preparation Example 1 and Comparative Preparation Examples 1-3. Combined with the XRD data, it is believed that the cobalt phosphate molecular sieve prepared in Preparation Example 1 has the greatest potential for use as a catalyst.

Table 1 Specific surface area and pore characteristics data of cobalt phosphate molecular sieves

.

We also adjusted the roasting temperature conditions, roasting at 300°C, 350°C, 400°C, 450°C, 500°C, and 550°C, and obtained the Fourier transform infrared spectra (FT-IR) of samples with different roasting temperatures. As shown in Figure 4. The vibration peaks appearing in the range of 1200~1000cm ^-1 are attributed to the asymmetric stretching vibration peaks of the PO ₄ tetrahedron, so the two peaks appearing at 1020cm ^-1 and 1110 cm ^-1 in the figure are the asymmetry of the PO ₄ tetrahedron. Stretching vibration peak; the peak appearing in the range of 700~400cm ^-1 is the bending vibration peak of the O-P-O bond, so the vibration peak at 571 cm ^-1 in the figure is the bending vibration peak of the O-P-O bond ; Below 1000 cm ^-1 corresponds to the Co-O stretching vibration peak and the Co-OH bending vibration peak, so the peak appearing at 694 cm ^-1 is not the O-P-O bond bending vibration peak but should belong to [ Vibration band of Co―(OH) ₄ ] ^{2 -} tetrahedron; the absorption vibration peak at 796cm ^-1 is attributed to the N―H out-of-plane bending vibration absorption peak; the source of N―H should be in the template agent As a space filler of the inorganic skeleton, N is formed by combining with H in water molecules when supporting the skeleton; 2955cm ^-1 is the NH stretching vibration absorption peak, in which N―H also comes from the formed skeleton structure. ; The hydroxyl vibration absorption peak of crystal water appears at 1650cm ^-1 and 3420cm ^-1 . Among them, the absorption vibration peaks of N-H bonds and water gradually weaken as the temperature increases, indicating that they are gradually removed as the roasting temperature increases. As the temperature increases, the hydroxyl vibration absorption peak of crystal water gradually weakens, and weakens significantly at 400°C. This shows that the product changes from Co ₃ (OH) ₂ (PO ₃ OH) ₂ to Co ₃ (PO ₄ ) ₂ . The vibration band of [Co―(OH) ₄ ] ² tetrahedron appearing at 694 cm ^-1 is transformed into the vibration band of Co―O ₄ tetrahedron that moves to 611 cm ^-1 ; the O― at 571 cm-1 The bending vibration peak of the P-O bond has moved to 539 cm ^-1 ; the asymmetric stretching vibration peaks of the PO ₄ tetrahedron at 1020 cm ^-1 and 1110 cm ^-1 are only left with a single peak at 1054 cm ^-1 . It shows that Co replaces P and is incorporated into the framework, and divalent cobalt exists in the form of four coordinations.

Figure 5 is a NH ₃ temperature-programmed desorption spectrum of the cobalt phosphate molecular sieve prepared in Preparation Example 1. It can be seen that desorption peaks were generated at 78°C, 269°C, 452°C, 514°C and 605°C respectively, among which the peaks at 78°C and 269°C were stronger. There are two adsorption states of _NH3 during the desorption process: physical adsorption and chemical adsorption. According to the surface adsorption theory of the catalyst, the broad and less obvious peak at the lower temperature of 78°C is NH ₃ removed by physical adsorption; the strong peak appearing in the range of 200~400°C is due to the acidic sites in the catalyst and Alkaline gas NH ₃ is chemically bound to NH ₃ and then broken off. The higher the desorption peak temperature, the greater the intensity of the acid center, and the peak area is proportional to the acid concentration. As shown in Table 3, the desorption peak at the temperature of 78°C is sharp but the area is not large enough, accounting for 39.3% of the total area, which indicates the existence of a weak acid center with a certain acid concentration; the desorption peak at the temperature of 269°C The maximum area is 55.8% of the total area, indicating that there is an acid center whose acid strength and acid concentration are both greater than the former; the peak area at the remaining temperature is smaller, indicating that there is a small amount of strong acid center. In later reaction applications, it was also proven that its effect was obvious after being added as a catalyst, and the conversion rate of reactants was significantly improved.

Table 2 TPD data of cobalt phosphate molecular sieves

.

Vibrating sample magnetometer magnetic analysis (VSM) was performed on the cobalt phosphate molecular sieve in Preparation Example 1. The magnetic susceptibility was 2.83×10 ^-6 , which can meet the requirements of catalyst separation through an external magnetic field.

Application examples

The cobalt phosphate molecular sieves prepared in the above examples and comparative examples were used as catalysts in the oxidation of benzyl alcohol to prepare benzaldehyde, and the catalyst performance in the reaction of benzyl alcohol and glacial acetic acid to prepare benzyl acetate. Specifically, benzyl alcohol, hydrogen peroxide (or glacial acetic acid), and cobalt phosphate molecular sieve are added to the reaction vessel, and the reaction is carried out under heating, stirring, condensation and reflux conditions. After the reaction is completed, the magnetic molecular sieve is magnetically separated by a magnet, washed, and dried before continued use.

The reaction conditions for the oxidation of benzyl alcohol to prepare benzaldehyde are a reaction temperature of 70°C, a reaction time of 4 hours, a molar ratio of benzyl alcohol and hydrogen peroxide of 1:1.5, hydrogen peroxide is slowly added dropwise, and the dropwise humidity is controlled to be completed within 3 hours. The catalyst phosphoric acid Cobalt molecular sieve is 0.15wt% of the mass of benzyl alcohol. The reaction conversion rate and benzaldehyde selectivity are shown in Table 3.

Table 3 Reaction results of benzyl alcohol oxidation to prepare benzaldehyde

.

The reaction conditions for the reaction of benzyl alcohol and glacial acetic acid to prepare benzyl acetate are a reaction temperature of 110°C, a reaction time of 3 hours, the molar ratio of benzyl alcohol and glacial acetic acid is 1:1.2, and the catalyst cobalt phosphate molecular sieve is 0.1wt% of the mass of benzyl alcohol. The reaction conversion rate and benzyl acetate selectivity are shown in Table 4.

Table 4 Reaction results of benzyl alcohol esterification to prepare benzyl acetate

.

The magnetic cobalt phosphate molecular sieve obtained in Preparation Example 1 is recycled. Specifically, after the reaction is completed, the molecular sieve is recovered through an externally reinforced magnet. The recovered molecular sieve is washed with deionized water and ethanol, dried and reused in the reaction. Table 5 shows the conversion rate and selectivity of the magnetic cobalt phosphate molecular sieve prepared in Preparation Example 1 after 20 cycles.

Table 5 Catalyst cycle times

.

It can be seen from the data in Table 3-5 that the magnetic cobalt phosphate molecular sieve prepared by the present invention has good catalytic activity for the oxidation and esterification reaction of benzyl alcohol, and has good conversion rate and selectivity. Moreover, it can be easily recycled through magnetism. After recycling 20 times, it still has good catalytic activity and selectivity, which can meet the needs of industrialization.

Claims (6)

1. The use of a magnetic cobalt phosphate molecular sieve in catalyzing organic reactions, characterized in that the organic reaction is a reaction in which benzyl alcohol is oxidized to benzaldehyde, or a reaction in which benzyl alcohol is esterified into benzyl alcohol ester; the magnetic phosphoric acid The preparation method of cobalt molecular sieve includes the following steps: dissolve the soluble cobalt source in water, add phosphoric acid, stir evenly, add template agent, continue stirring evenly and adjust the pH to weak acidity with ammonia water; transfer the material to the crystallization kettle for aging, Crystallize, wash, dry, and roast to obtain magnetic cobalt phosphate molecular sieve; the template agent is a long-chain alkyl quaternary ammonium salt and 3,8-diazabicyclo[3.2.1]octane according to a molar ratio of 3-5: The compound of 1; the molar ratio of soluble cobalt source, phosphoric acid, template agent and water is 1:2.5-3:2-2.4:200-300, where the mole number of soluble cobalt source is calculated as metal Co; the long-chain alkyl group The quaternary ammonium salts are dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, cetyltrimethylammonium bromide, dodecyltrimethylammonium chloride, tetradecyltrimethylammonium bromide, At least one of alkyltrimethylammonium chloride and cetyltrimethylammonium chloride. 2. The use according to claim 1, characterized in that the molar ratio of soluble cobalt source, phosphoric acid, template agent and water is 1:2.8:2.1:228. 3. The use according to claim 1, characterized in that the soluble cobalt source is selected from at least one of cobalt acetate, cobalt nitrate, and cobalt chloride. 4. The use according to claim 1, characterized in that ammonia water adjusts the pH to 4-7. 5. The use according to claim 4, characterized in that ammonia water adjusts the pH to 4.5-5. 6. The use according to claim 1, characterized in that the aging is left standing for 5-10h; the crystallization is carried out at 140-180°C, and the crystallization time is 36-48h; the roasting is Raise the temperature to 450-600℃ at a heating rate of 1-2℃/min, and keep roasting for 10-20h.