Pt-Ni bimetallic core-shell catalyst and application thereof in synthesis of bio-based tetrahydrofuran

Abstract

The invention relates to a preparation method of a Pt-Ni bimetallic core-shell catalyst. The preparation method comprises the following steps: step 1, preparing spherical ZSM-5; step 2, adding CTAB (cetyltrimethyl ammonium bromide), spherical ZSM-5, TEOS (tetraethyl orthosilicate) and ammonia water into an ethanol water solution, maintaining the pH value at 10.0 + / -0.2, stirring and reacting at 45 + / -5 DEG C for 4-8 hours, and roasting at 500-650 DEG C for 4-8 hours to obtain ZSM-5-mSiO; step 3, carrying out phosphoric acid post-treatment on the carrier ZSM-5 (at) mSiO; 4, mixing the carrier obtained in the step 3 with a magnesium nitrate solution, performing vacuum impregnation, curing at room temperature for 12-24 hours, drying, and roasting at 500-650 DEG C for 4-8 hours; and step 5, mixing an ethanol water solution of platinum salt and a nickel salt water solution, adjusting the pH value to 3.5 + / -0.2, then dropwise adding the solution to the carrier obtained in the step 4, sealing at room temperature, standing and curing in a dark place for 10-20 hours, drying, and roasting and activating at 500-600 DEG C for 4-6 hours to obtain the catalyst. The catalyst can be used for efficiently preparing tetrahydrofuran (THF) from furfural by a one-step method, realizes efficient and continuous conversion of furfural, and is suitable for industrial production.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of biological-based chemical catalysis technology, and particularly relates to a Pt-Ni bimetallic core-shell catalyst and its application in the synthesis of biological-based tetrahydrofuran. BACKGROUND

[0002] Tetrahydrofuran (THF) is a key raw material in the fields of polyurethane, medicine, solvent, etc. The traditional petroleum-based process relies on the route of 1,4-butanediol from propylene, and then dehydrating and cyclizing, which has the problems of high carbon emission and residual aromatic impurities. The biological-based route takes furfural as the raw material, generates furan by decarboxylation, and then generates THF by hydrogenation, which has the advantage of low carbon emission. However, the existing technology also has some defects as follows: 1) Complex two-step process: furfural is first decarboxylated to furan (Pt / Al2O3-TiO2 catalyst is needed), and then hydrogenated to THF (Pd / C catalyst is needed), and the total yield is less than 80%; 2) Low efficiency of one-step catalyst: Pd / Al2O3 catalyst is prone to furan ring-opening side reactions, and the selectivity of THF is only 70% to 75%.

[0003] Therefore, developing a catalyst with high stability, low noble metal consumption, and controllable product selectivity is the key to breaking through the bottleneck.

[0004] Based on this, the present application is developed. SUMMARY

[0005] The application aims to overcome the defects of the prior art and provide a Pt-Ni bimetallic core-shell catalyst. The catalyst is a core-shell catalyst with Pt-Ni bimetallic as active component, MgO as additive, and phosphoric acid modified ZSM-5@mesoporous SiO2 as carrier, which can be used for efficient preparation of tetrahydrofuran (THF) from furfural by one-step method, realizes efficient continuous conversion of furfural, and is suitable for industrial production.

[0006] The application also provides a preparation method of the above-mentioned Pt-Ni bimetallic core-shell catalyst and its application in the synthesis of biological-based tetrahydrofuran.

[0007] To achieve the above-mentioned purpose, the application adopts the following technical solutions: A preparation method of a Pt-Ni bimetallic core-shell catalyst (Pt-Ni / MgO@ZSM-5@mSiO2) includes the following steps: Step 1: preparing a spherical ZSM-5 core; Step 2: ZSM-5@mSiO2 (CTAB template method) is prepared by coating a mesoporous SiO2 shell; CTAB, spherical ZSM-5 and TEOS are added to an aqueous ethanol solution, and ammonia water is added to maintain the pH of the system at 10.0±0.2, and the reaction is stirred at 45±5°C for 4-8 h. After the reaction is completed, it is calcined at 500-650°C for 4-8 h to obtain ZSM-5@mSiO2. Step 3: Post-treatment of the carrier with phosphoric acid; The carrier ZSM-5@mSiO2 is mixed with phosphoric acid in a certain proportion, then refluxed and stirred at 80-90°C for 4-6 h, then washed with deionized water until neutral, and then calcined at 300-400°C for 3-4 h; Step 4: Load MgO additive; The carrier obtained in step 3 is mixed with a magnesium nitrate solution, then vacuum impregnated, then aged at room temperature for 12-24 h, then dried, and then calcined at 500-650°C for 4-8 h; Step 5: Load active components Pt-Ni; An aqueous ethanol solution of platinum salt is mixed with an aqueous nickel salt solution, the pH is adjusted to 3.5±0.2, then the solution is added dropwise to the carrier obtained in step 4, and then aged at room temperature for 10-20 h after the dropwise addition is completed, then dried to obtain a precursor catalyst; the precursor catalyst is calcined in static air at 500-600°C for 4-6 h to obtain the catalyst.

[0008] Specifically, the spherical ZSM-5 prepared in step 1 is prepared as follows: under stirring, first mix the template agent with deionized water (stir at 40-50°C for 10-20 min), then add the aluminum source and hydrolyze for 30-60 min, then slowly add the silicon source, the dropwise addition time is 2-4 h, and the stirring speed is maintained at 400-600 rpm throughout the stirring process. After the mixing is completed, the mixed solution is transferred to a reaction kettle and hydrothermally crystallized at 160-220°C for 24-36 h; after the crystallization is completed, the solid-liquid separation is performed, the product is washed to neutral (pH=7), and finally calcined at 500-650°C for 4-8 h, with the temperature rising rate controlled at 1-3°C / min, to obtain the spherical ZSM-5.

[0009] Further, in step 1, the template agent is tetrapropylammonium hydroxide TPAOH, the aluminum source is aluminum isopropoxide, and the silicon source is ethyl silicate TEOS; the mass ratio of aluminum isopropoxide to TEOS is 1:0.008-0.02, and the molar ratio of TEOS to TPAOH is 1-5:1, and the TPAOH is prepared as a 20-30% TPAOH aqueous solution.

[0010] Specifically, in the system of step 2, the CTAB concentration is 0.004-0.02 g / ml, the concentration of spherical ZSM-5 is 0.1-2 g / ml, and the ratio of TEOS to spherical ZSM-5 is 1-3 mL / g; the ethanol aqueous solution is composed of ethanol and water mixed at a volume ratio of 3-5:1. In step 2, first prepare the ethanol aqueous solution, and then add CTAB, ZSM-5, TEOS, and ammonia water in sequence. After the reaction is completed, the carrier ZSM-5@mSiO2 is obtained by calcination. Further, the specific operation process is as follows: first prepare the ethanol aqueous solution, add CTAB, and stir until completely dissolved. Then add ZSM-5, and ultrasonic dispersion for 10-20 min. Next, add TEOS according to the corresponding proportion, and the dropwise addition time is 15-30 min. At the same time of adding TEOS, 20-35 wt% ammonia water is added synchronously to maintain the pH of the reaction system at 10.0±0.2. The whole reaction is carried out at 45℃, and after the dropwise addition is completed, continue to stir for 4-8 h, and the stirring rate is maintained at 350-450 rpm. After the reaction is completed, calcination is carried out at 500-650 ℃ for 4-8 h, and the temperature rising rate is controlled at 1-2 ℃ / min to obtain ZSM-5@mSiO2.

[0011] Specifically, in step 3, the addition ratio of phosphoric acid to the carrier ZSM-5@mSiO2 is 5-20 mL / g, and the concentration of phosphoric acid is 0.5-0.7 mol / L.

[0012] Specifically, in step 4, magnesium nitrate (Mg(NO3)2·6H2O) is added to the ethanol aqueous solution to prepare a magnesium nitrate solution with a concentration of 2.0-3.0 mol / L, and the ethanol aqueous solution is composed of ethanol and water mixed at a volume ratio of 0.5-2:1; the mass ratio of the carrier obtained in step 3 to solid magnesium nitrate hexahydrate is 1-4:1; during vacuum impregnation, the vacuum degree is -0.05 to -0.1 MPa, and the impregnation time is 2-4 h. After impregnation and maturation are completed, drying is carried out, and the drying is gradient drying, which is carried out at 40-50℃ for 2-5 h, at 80-90 ℃ for 2-5 h, and at 120-140 ℃ for 4-6 h in sequence.

[0013] Specifically, in step 5, the platinum salt can be one or more of platinum chlorate (H2PtCl6), potassium chloroplatinate (K2PtCl6), and platinum nitrate (Pt(NO3)2); the nickel salt can be one or more of nickel nitrate Ni(NO3)2·6H2O, nickel acetate (CH3COO)2Ni·4H2O, and nickel chloride (NiCl2·6H2O); the platinum loading is 0.05-0.5 wt%; and the nickel loading is 0.1-5.0 wt%.

[0014] Further, the platinum salt is dissolved in an aqueous ethanol solution (the volume ratio of ethanol to water is preferably 1-3:1), the nickel salt is dissolved in water, the two solutions are mixed, and 0.1-0.3 mol / L nitric acid is used to adjust the pH of the mixed solution to 3.5±0.2 to inhibit the hydrolysis of metal ions. Further, the prepared mixed solution is added dropwise to the carrier obtained in step 4, the dropwise addition time is 20-60 min, and a 40 kHz ultrasonic wave is turned on at the same time to promote the uniform dispersion of metal ions on the carrier. After the dropwise addition is completed, the carrier is sealed and light-shielded at room temperature (25±5 ℃) for 10-20 h, and is manually shaken every 2 h to ensure that the precursor is fully adsorbed on the carrier. After the aging is completed, gradient drying is performed, and the carrier is sequentially dried at 40-50 ℃ for 2-5 h, at 80-90 ℃ for 2-5 h, and at 120-140 ℃ for 4-6 h, to obtain a precursor catalyst. The precursor catalyst is calcined and activated in static air, the temperature is set to 500-600 ℃, the time is 4-6 h, and the temperature rising rate is 1-3 ℃ / min, to obtain a Pt-Ni bimetallic core-shell catalyst (Pt-Ni / MgO@ZSM-5@mSiO2), and the particle size of the catalyst is 2.8±0.3 nm.

[0015] The application provides a Pt-Ni bimetallic core-shell catalyst prepared by the preparation method.

[0016] The application also provides application of the Pt-Ni bimetallic core-shell catalyst in the synthesis of bio-based tetrahydrofuran.

[0017] Compared with the prior art, the application has the following advantages and beneficial effects: The application improves the existing catalysts, and provides a novel bimetallic catalyst (Pt-Ni / MgO@ZSM-5@mSiO2) with a core-shell structure. The Pt-Ni bimetallic alloy structure promotes the decarbonylation reaction, the Ni strengthens the hydrogenation activity, the amount of noble metal is reduced, the MgO additive provides surface basic sites, the furan ring-opening side reaction is inhibited, and the THF selectivity is improved. The strong interaction between the core and the shell improves the hydrothermal stability of the carrier. The application solves the problems and defects of the prior art through the above advantages, and also provides application of the catalyst in the one-step preparation of tetrahydrofuran from furfural. Test verification shows that the catalyst has good catalytic performance, and the conversion rate of tetrahydrofuran is relatively high, and is higher than 90%. DETAILED DESCRIPTION

[0018] In order to make the technical purposes, technical solutions and beneficial effects of the application clearer, the technical solutions of the application will be further described below in combination with specific embodiments, and the described embodiments are intended to explain the application, and cannot be understood as a limitation of the application.

[0019] In the present application, the raw materials used are all ordinary commercially available products or can be prepared by using conventional techniques in the art.

[0020] Example 1: A preparation method of a Pt-Ni bimetallic core-shell catalyst (Pt-Ni / MgO@ZSM-5@mSiO2), which specifically comprises the following steps: Carrier preparation: ①Accurately weigh 30 g of TPAOH and 90 g of deionized water, stir at 40℃ for 10 minutes, then add 2.04 g of aluminum isopropoxide, hydrolyze for 30 minutes, then slowly add 152 g of TEOS, the dropwise adding time is 2.5 h, and the stirring rate is kept at 500 rpm during the whole stirring process. After the mixing is completed, the mixed solution is transferred to a reaction kettle, and hydrothermal crystallization is carried out at 180℃ for 24 h. After the crystallization is completed, the product is washed to neutral (pH=7) by centrifugal washing, and finally calcined at 550℃ for 5 h, with the temperature rising rate controlled at 2℃ / min, to obtain spherical ZSM-5.

[0021] ②Accurately weigh 200 mL of ethanol and 50 mL of water, mix uniformly at 45℃. Add 1.125 g of CTAB to the solvent system, stir until completely dissolved. Then add 25 g of ZSM-5, ultrasonic dispersion for 15 minutes. Then add 45 mL of TEOS, dropwise adding is completed in 20 min, while adding TEOS, 28 wt% ammonia water is added synchronously to maintain the pH of the reaction system at about 10.0, after the dropwise adding is completed, continue to stir for 5 h, and the stirring rate is kept at 400 rpm. After the reaction is completed, calcine at 550℃ for 5 h to obtain ZSM-5@mSiO2.

[0022] ③Take 30 g of the above ZSM-5@mSiO2 carrier, add 300 mL of 0.6 mol / L phosphoric acid, and reflux stir at 80℃ for 4 h. After the treatment is completed, wash the carrier to neutral with deionized water. Finally, calcine at 350℃ for 3 h.

[0023] ④Mix the above obtained carrier with a magnesium nitrate solution (obtained by adding 20.48 g of Mg(NO3)2·6H2O to 40 mL of 50% ethanol aqueous solution), vacuum impregnate at a pressure of -0.1 MPa for 2 h, then mature at 25℃ for 12 h, and then sequentially dry at 40℃ for 3 h, at 80℃ for 3 h, and at 130℃ for 4 h, and finally calcine at 550℃ for 6 h.

[0024] Catalyst preparation: ①H2PtCl6 ethanol aqueous solution (ethanol and water volume ratio 1:1) was mixed with Ni(NO3)·6H2O aqueous solution (2 wt% of Ni loading) according to 0.1 wt% of Pt loading, and 0.2 mol / L nitric acid was used to adjust the pH of the mixed solution to 3.5. Then the solution was added dropwise to the above-mentioned carrier while the ultrasonic was turned on at 40 kHz, the dropwise time was 30 min, and after the dropwise was completed, it was sealed and light-proof at 25℃ for 12 h, and manually shaken every 2 h. After the maturation was completed, gradient drying was carried out, and the drying was carried out at 40℃ for 3 h, 80℃ for 3 h, and 130℃ for 4 h in sequence, and then the obtained precursor catalyst was calcined at 550℃ in static air for 5 h, to obtain a Pt-Ni / MgO@ZSM-5@mSiO2 bimetallic catalyst, and the particle size was 2.8±0.3 nm.

[0025] Examples 2-6 The loadings were 0.05 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, and 0.5 wt% respectively according to Pt loading.

[0026] Examples 7-11 The loadings were 0.1 wt%, 0.5 wt%, 1.0 wt%, 3.0 wt%, 4.0 wt%, and 5.0 wt% respectively according to Ni loading.

[0027] Catalytic performance test The above examples are the preparation process of the catalyst, and the performance evaluation method of all the catalysts is the same, that is, the performance of the catalyst is tested by using the furfural gas phase continuous decarbonylation method to prepare tetrahydrofuran in one step. The specific reaction conditions are: temperature 270℃, pressure 1.0 MPa, furfural feed rate 15 g / h, molar ratio of hydrogen to furfural 40:1, and catalyst loading 25 g. The specific operation is as follows: The catalyst was loaded into the reaction tube of the fixed bed reactor, the air was replaced by nitrogen, and after the leakage test was qualified, the temperature was increased to 270℃, the hydrogen amount was gradually increased, the catalyst was activated, and after no water was produced, pure hydrogen was used for continuous activation for 2 h, then furfural was fed, the reaction products were collected after condensation, and the composition and relative content of each component were analyzed by gas chromatography. The results are shown in Tables 1 and 2.

[0028] Table 1 Catalytic performance of the catalysts prepared in Examples 1-6 As can be seen from Table 1, when the loading of platinum is 0.1% or more, the conversion rate of furfural is significantly increased, but when it is higher than 0.1%, the conversion rate is not significantly improved.

[0029] Table 2: Catalytic performance of the catalysts prepared in Examples 1 and 7 to 12 As can be seen from Table 2, when the loading of nickel is below 2.0%, the residual amount of furan is relatively large and the selectivity of tetrahydrofuran is poor; when the loading of nickel is 2.0% or above, the residual amount of furan gradually decreases with the increase of the loading of nickel, and the selectivity of tetrahydrofuran does not obviously increase when the loading of nickel is above 2.0%, so it is determined that 0.1% / Pt / 2.0%Ni is the optimal loading.

[0030] The above is a detailed description of the present application in combination with specific embodiments, but the present application should not be limited to the above. For those skilled in the art to which the present application belongs, any modification or replacement within the scope of the present application without departing from the concept of the present application is considered to be within the protection scope of the present application.

Claims

1. A method for preparing a Pt-Ni bimetallic core-shell catalyst, characterized by, The method comprises the following steps: Step 1: preparing spherical ZSM-5; Step 2: coating the ZSM-5 with a mesoporous SiO2 shell to prepare ZSM-5@mSiO2; CTAB, spherical ZSM-5 and TEOS are added into an ethanol aqueous solution, and ammonia water is added to maintain the pH of the system at 10.0±0.2; the system is stirred at 45±5 ℃ for 4-8 h; after the reaction is completed, the system is calcined at 500-650 ℃ for 4-8 h to obtain ZSM-5@mSiO2; Step 3: post-treating the carrier with phosphoric acid; The carrier ZSM-5@mSiO2 is mixed with phosphoric acid, and the mixture is refluxed and stirred at 80-90 ℃ for 4-6 h; then the mixture is washed to neutral, and then calcined at 300-400 ℃ for 3-4 h; Step 4: loading MgO as an additive; The carrier obtained in step 3 is mixed with a magnesium nitrate solution, and then vacuum impregnation is performed; then the mixture is aged at room temperature for 12-24 h; after drying, the mixture is calcined at 500-650 ℃ for 4-8 h; Step 5: loading an active component Pt-Ni; An ethanol aqueous solution of a platinum salt is mixed with a nickel salt aqueous solution, and the pH is adjusted to 3.5±0.2; then the solution is added dropwise to the carrier obtained in step 4; after the dropwise addition is completed, the mixture is aged at room temperature for 10-20 h in a sealed container in the dark; after drying, a precursor catalyst is obtained; the precursor catalyst is calcined in static air at 500-600 ℃ for 4-6 h, and then a catalyst is obtained.

2. The method of claim 1, wherein the Pt-Ni bimetallic core-shell catalyst is prepared by the steps of: In step 1, the spherical ZSM-5 is prepared as follows: under stirring, a template agent is first mixed with deionized water, then an aluminum source is hydrolyzed for 30-60 min, and then a silicon source is added dropwise, and the dropwise addition is performed for 2-4 h; after the mixing is completed, the mixture is hydrothermally crystallized at 160-220 ℃ for 24-36 h; after the crystallization is completed, the mixture is subjected to solid-liquid separation, and then washed to neutral; and then the mixture is calcined at 500-650 ℃ for 4-8 h to obtain the spherical ZSM-5.

3. The method of claim 2, wherein the Pt-Ni bimetallic core-shell catalyst is prepared by the steps of: In step 1, the template agent is tetrapropylammonium hydroxide (TPAOH), the aluminum source is aluminum isopropoxide, and the silicon source is tetraethyl orthosilicate (TEOS); the mass ratio of the aluminum isopropoxide to the TEOS is 1:0.008-0.02, and the molar ratio of the TEOS to the TPAOH is 1-5:1; the TPAOH is prepared into a 20-30% TPAOH aqueous solution.

4. The method of claim 1, wherein the Pt-Ni bimetallic core-shell catalyst is prepared by the steps of: In the system in step 2, the concentration of the CTAB is 0.004-0.02 g / ml, the concentration of the spherical ZSM-5 is 0.1-2 g / ml, and the ratio of the TEOS to the spherical ZSM-5 is 1-3 mL / g; the ethanol aqueous solution is composed of ethanol and water in a volume ratio of 3-5:

1.

5. The method of claim 1, wherein the Pt-Ni bimetallic core-shell catalyst is prepared by the steps of: In step 3, the addition ratio of the phosphoric acid to the carrier ZSM-5@mSiO2 is 5-20 mL / g, and the concentration of the phosphoric acid is 0.5-0.7 mol / L.

6. The method of claim 1, wherein the Pt-Ni bimetallic core-shell catalyst is prepared by the steps of: In step 4, the magnesium nitrate hexahydrate is added into an ethanol aqueous solution to prepare a magnesium nitrate solution with a concentration of 2.0-3.0 mol / L, and the ethanol aqueous solution is prepared by mixing ethanol and water at a volume ratio of 0.5-2:1; the mass ratio of the carrier obtained in step 3 to the magnesium nitrate hexahydrate is 1-4:1; the vacuum degree is -0.05 to -0.1 MPa during vacuum impregnation, and the impregnation time is 2-4 h; and the drying is gradient drying, i.e., drying at 40-50 ℃ for 2-5 h, drying at 80-90 ℃ for 2-5 h, and drying at 120-140 ℃ for 4-6 h.

7. The method for preparing the Pt-Ni bimetallic core-shell catalyst as described in claim 1, characterized in that, In step 5, the platinum salt is one or more of platinum chlorate, potassium chloroplatinate and platinum nitrate; the nickel salt is one or more of nickel nitrate, nickel acetate and nickel chloride; the platinum loading is 0.05-0.5 wt%; and the nickel loading is 0.1-5.0 wt%.

8. The method of claim 7, wherein the Pt-Ni bimetallic core-shell catalyst is prepared by the steps of: In step 5, the drying is gradient drying, i.e., drying at 40-50 ℃ for 2-5 h, drying at 80-90 ℃ for 2-5 h, and drying at 120-140 ℃ for 4-6 h.

9. A Pt-Ni bimetallic core-shell catalyst prepared by the preparation method of any one of claims 1 to 8.

10. Use of the Pt-Ni bimetallic core-shell catalyst of claim 9 in the synthesis of bio-based tetrahydrofuran.

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