Preparation method of glycerol hydrogenolysis catalyst

Abstract

The invention discloses a preparation method of a glycerol hydrogenolysis catalyst, and belongs to the field of glycerol hydrogenolysis. Ammonium metatungstate is used as a tungsten source, acid sites and oxygen hole content on the surface of a WO3 carrier are further improved by doping metal, and hollow mesoporous carrier spheres are synthesized by using mesoporous hollow silicon dioxide spheres as a hard template agent; active metal copper and nickel are loaded in an atomic layer deposition mode, and the glycerol hydrogenolysis catalyst is obtained. The catalyst is small in metal particle, high in dispersity, excellent in catalytic activity and rich in oxygen holes and acid sites, anchoring and mass transfer of active metal are facilitated, and the reaction activity can be effectively improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of glycerol hydrocracking, and particularly relates to a preparation method of a glycerol hydrocracking catalyst. Background Art

[0002] With the increasing maturity of biodiesel technology, biodiesel has been vigorously developed worldwide, resulting in a growing content of its by-product glycerol. In this process, approximately 0.1 kg of glycerol is by-produced for every 1 kg of fatty acid methyl ester produced, leading to an oversupply of glycerol in the world market.

[0003] Using glycerol to prepare 1,3-propanediol can not only alleviate the surplus of glycerol, but also 1,3-propanediol is an important commercial product widely used in the food, cosmetics, and pharmaceutical industries. Among them, the most promising is the synthesis of polytrimethylene terephthalate (PTT), with a consumption ratio reaching 80%. This polyester can be used to produce PTT fibers and is applied in industries such as clothing and carpets. However, in the existing technology, the activity of the catalyst for glycerol hydrocracking to 1,3-propanediol needs to be improved, and the selectivity of the catalyst to 1,3-propanediol is relatively low, resulting in more by-products and increasing the cost of separation and purification.

[0004] The Chinese patent invention document with the publication number CN111036206A discloses a glycerol hydrocracking catalyst and its preparation method. By impregnation, dual active components are loaded onto an alumina support, and its active components are precious metals such as platinum and rhodium, which are expensive. At the same time, the impregnation method of loading leads to a low dispersion of active metals, a small exposed active specific surface area, and is not conducive to the progress of the reaction.

[0005] The Chinese patent invention document with the publication number CN102728380A discloses a catalyst for preparing 1,3-propanediol by glycerol hydrocracking, with mesoporous tungsten oxide as the support and metal platinum or other precious metals as the active components. Its support specific surface area is small and insufficient to disperse the active metal. In the reaction of preparing 1,3-propanediol, the conversion rate of glycerol is less than 25%. Summary of the Invention

[0006] The purpose of the present invention is to provide a preparation method of a glycerol hydrocracking catalyst. By designing a tungsten oxide support with a hollow mesoporous structure, introducing oxygen vacancies and acidic sites, and using atomic layer deposition technology to load dual metal active components, the activity of the catalyst is significantly improved. The prepared glycerol hydrocracking catalyst has a higher glycerol conversion rate and 1,3-propanediol selectivity, low preparation cost, and broad application prospects.

[0007] To solve the above problems, the present invention provides the following technical solutions: (1) Dissolve bicarbonate and cationic surfactant in an alcohol solvent, add an organosilicon source, stir at a constant temperature of 30 - 50 °C, and centrifuge to obtain silica hollow mesoporous spheres; (2) Dissolve a metal precursor and a tungsten source in a mixed solution of alcohol and deionized water with a volume ratio of 1:1 - 3, add the silica hollow mesoporous spheres obtained in step (1) thereto, and stir at room temperature to obtain a SiO 2 solid coated with a tungsten source and a metal precursor; (3) Calcinate the SiO 2 solid coated with a tungsten source and a metal precursor to obtain MO 2 WO 3 @SiO 2 ; (4) Add MO 2 WO 3 @SiO 2 to an alkaline solution, stir, separate the solid and liquid, and dry the solid to obtain MO 2 WO 3 hollow mesoporous spheres.

[0008] (5) Use the MO 2 WO 3 hollow mesoporous spheres as a carrier, use β-diketone copper complex and nickelocene as a copper source and a nickel source respectively, use ozone as an oxygen source, and adopt an atomic layer deposition device to deposit nickel oxide and copper oxide layers on the surface of the MO 2 WO 3 hollow mesoporous spheres, and then calcine and reduce the product with hydrogen to obtain a glycerol hydrogenolysis catalyst.

[0009] Preferably, in step (1), the alcohol solvent is one of methanol, ethanol, and propanol; the bicarbonate is sodium bicarbonate or ammonium bicarbonate; the cationic surfactant is one of octadecyltrimethylammonium chloride, cetyltrimethylammonium bromide, and cetyl dimethylammonium chloride; the organosilicon source is tetraethyl orthosilicate or tetramethyl orthosilicate; the volume-mass ratio of the alcohol solvent, bicarbonate, cationic surfactant, and organosilicon source is 5 - 10 mL:0.5 - 1 g:0.1 - 0.5 g:1 - 3 mL, and the constant temperature stirring time is 12 - 24 h.

[0010] Preferably, in step (2), the metal precursor is one of cerium nitrate, ammonium molybdate, and zirconium nitrate; the tungsten source is ammonium metatungstate or ammonium paratungstate; the molar ratio of the metal precursor to the tungsten source is 0.05:0.5 - 1; the mass ratio of the tungsten source to the silica hollow mesoporous spheres is 1:0.5 - 2.

[0011] Preferably, in step (3), the calcination temperature is 400 - 600 °C and the time is 1 - 3 h.

[0012] Preferably, in step (4), the alkaline solution is a potassium hydroxide or sodium hydroxide solution; MO 2 WO 3 @SiO 2 The molar ratio to the alkaline solution is 1:2 - 4; the stirring time is 6 - 12 h.

[0013] Preferably, in step (5), for the copper source and nickel source, the molar ratio of copper to nickel is 1:1 - 5; the atomic layer deposition temperature is 180 - 250 °C, the deposition cycle is 5 - 20 cycles; the hydrogen flow rate for hydrogen calcination reduction is 80 - 120 ml / min, the calcination reduction temperature is 400 - 550 °C, and the time is 1 - 3 h.

[0014] Compared with the prior art, the present invention has the following beneficial effects: (1) The technical solution provided by the present invention uses the hard template method to prepare tungsten oxide hollow spheres as catalyst carriers. Tungsten oxide not only contains Bronsted acid sites. When used for glycerol hydrogenolysis, glycerol dehydrates to form 3-hydroxypropenol intermediates under the action of Bronsted acid sites, and then hydrogenates to form 1,3-propanediol under the action of active metals. Moreover, during the catalyst preparation process, after reduction, tungsten oxide is partially reduced to form oxygen vacancies. The oxygen vacancies in tungsten oxide promote the adsorption of hydrogen, which is beneficial to the activation of hydrogen. At the same time, the oxygen vacancies are conducive to the anchoring of active components, enhancing the interaction force between the active metal and the carrier, and thus will not migrate during the reaction process, maintaining a high dispersion degree, which is beneficial to the progress of the reaction. At the same time, in the process of preparing the catalyst carrier in the present invention, different metals such as cerium, molybdenum or zirconium are doped, and the second metal is introduced into the lattice, which helps the formation of oxygen vacancies and promotes the formation of more strong acid sites, further improving the catalytic efficiency.

[0015] (2) The present invention uses atomic layer deposition to load active metals, which can precisely realize the construction of catalytic species on the surface of the carrier. Compared with the traditional method of preparing catalysts by impregnation, using the atomic layer deposition method, the obtained metal particles are smaller and have a higher dispersion degree, significantly improving the catalytic activity.

[0016] (3) The technical solution provided by the present invention not only has a relatively high specific surface area (252 m 2 / g), which helps the dispersion of active components and improves the catalytic activity; but also the reactants can enter the interior of the hollow spheres through the pores. While increasing the reaction contact area, the hollow sphere structure also creates a reaction microenvironment for the reaction, and the pore structure can accelerate mass transfer and improve the reaction efficiency. The conversion rate of glycerol can reach 68.5%, and the selectivity of 1,3-propanediol is 58.3%. Compared with the prior art, the conversion rate and selectivity of this catalyst have been significantly improved, and there are fewer by-products, reducing the cost of separation and purification.

[0017] (4)The technical solution provided by the present invention uses copper-nickel bimetal as the active component, and the two have a synergistic effect; copper is more conducive to hydrogen dissociation and overflow to the support, and nickel effectively adsorbs reactants and transfers products. Compared with the prior art that uses platinum as the active component to catalyze glycerol hydrogenolysis to prepare 1,3-propanediol, it has the advantages of low cost, high activity and high selectivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present invention will be further described below with reference to the drawings and embodiments: Figure 1 XRD pattern of the catalyst prepared in Example 1; Figure 2 TEM image of the catalyst prepared in Example 1; Figure 3 TEM image of the catalyst prepared in Comparative Example 1; Figure 4 TEM image of the catalyst prepared in Comparative Example 2; Figure 5 For the NiCuCeO prepared in Example 1 2 WO x Catalyst, NiCuWO prepared in Comparative Example 3 x Catalyst NH 3 -TPD comparison spectrum. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] To make the purpose, technical solution and effects of the present invention clearer, the technical solution of the present invention will be described in detail below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work belong to the scope protected by the present invention. The atomic layer deposition equipment used in the embodiments of the present invention is the MNT f-150-212 type thermal atomic layer deposition equipment. Example 1

[0020] (1) Add 0.5 g of ammonium bicarbonate and 0.3 g of cetyltrimethylammonium bromide to 5 mL of ethanol, stir until dissolved, add 2 mL of tetraethyl orthosilicate, stir at a constant temperature of 40 °C for 18 h, and centrifuge to obtain silica hollow mesoporous spheres; (2) Dissolve cerium nitrate and ammonium metatungstate in a solution with a volume ratio of ethanol to deionized water of 1:1. The molar ratio of cerium nitrate to ammonium metatungstate is 0.05:0.8. Add silica hollow mesoporous spheres, and the mass ratio of ammonium metatungstate to silica hollow mesoporous spheres is 1:1. Continue to stir at room temperature for 3 h to obtain ammonium metatungstate and cerium nitrate @SiO 2 ; (3) Transfer ammonium metatungstate and cerium nitrate @SiO 2 to a muffle furnace, heat up to 500 °C and keep it at a constant temperature for 2 h, then calcine to obtain CeO 2 WO 3 @SiO 2 ; (4) Add CeO 2 WO 3 @SiO 2 to a sodium hydroxide solution, stir to remove the ordered mesoporous silica. The molar ratio of CeO 2 WO 3 @SiO 2 to sodium hydroxide is 1:2, stir for 9 h, perform solid-liquid separation and drying to obtain CeO 2 WO 3 hollow mesoporous spheres.

[0021] (5) Use CeO 2 WO 3 hollow mesoporous spheres as carriers, use β-diketone copper complex and nickelocene as copper source and nickel source respectively, use ozone as the oxygen source, and deposit nickel oxide and copper oxide layers on the surface of the hollow mesoporous spheres by atomic layer deposition equipment. The molar ratio of copper to nickel is 1:3, the deposition temperature is 220 °C, and the deposition cycle is 15 laps. The obtained sample is placed in a tube furnace, hydrogen is introduced at a flow rate of 120 ml / min, heated up to 500 °C and reduced for 2 h to obtain NiCuCeO 2 WO x catalyst, and the nickel loading is 2.25%. Example 2

[0022] (1) Add 1 g of sodium bicarbonate and 0.5 g of octadecyltrimethylammonium chloride to 10 mL of methanol, stir until dissolved, add 3 ml of methyl orthosilicate, stir at a constant temperature of 30 °C for 12 h, and centrifuge to obtain silica hollow mesoporous spheres; (2) Dissolve zirconium nitrate and ammonium paratungstate in a solution with a volume ratio of ethanol to deionized water of 1:2. The molar ratio of zirconium nitrate to ammonium paratungstate is 0.05:1. Add silica hollow mesoporous spheres. The mass ratio of ammonium paratungstate to silica hollow mesoporous spheres is 1:0.5, and continue to stir at room temperature for 5 h to obtain ammonium paratungstate and zirconium nitrate @SiO 2 ; (3) Transfer ammonium paratungstate and zirconium nitrate @SiO 2 to a muffle furnace, heat up to 400 °C and keep it at a constant temperature for 3 h, then calcine to obtain ZrO 2 WO 3 @SiO 2 ; (4) Add ZrO 2 WO 3 @SiO 2Add it to the potassium hydroxide solution and stir to remove the ordered mesoporous silica, ZrO 2 WO 3 @SiO 2 The molar ratio to sodium hydroxide is 1:3. Stir for 6 h, perform solid-liquid separation and drying to obtain ZrO 2 WO 3 hollow mesoporous spheres.

[0023] (5)Using the ZrO 2 WO 3 hollow mesoporous spheres as the carrier, using β-diketone copper complex and nickelocene as the copper source and nickel source respectively, and ozone as the oxygen source, deposit nickel oxide and copper oxide layers on the surface of the hollow mesoporous spheres by atomic layer deposition equipment. The molar ratio of copper to nickel is 1:5, the deposition temperature is 250 °C, and the deposition cycle is 5 circles. Place the obtained sample in a tubular furnace, introduce hydrogen at a flow rate of 100 ml / min, heat up to 400 °C and reduce for 3 h to obtain NiCuZrO 2 WO x catalyst, and the nickel loading is 0.75%. Example 3

[0024] (1)Add 0.8 g of sodium bicarbonate and 0.1 g of cetyl dimethyl ammonium chloride to 7 mL of propanol and stir until dissolved. Add 1 ml of tetraethyl orthosilicate and stir at a constant temperature of 50 °C for 24 h, then centrifuge to obtain silica hollow mesoporous spheres; (2)Dissolve ammonium molybdate and ammonium metatungstate in a solution with a volume ratio of ethanol to deionized water of 1:3. The molar ratio of ammonium molybdate to ammonium metatungstate is 0.05:0.5. Add the silica hollow mesoporous spheres, and the mass ratio of ammonium metatungstate to the silica hollow mesoporous spheres is 1:2. Continue to stir at room temperature for 6 h to obtain ammonium metatungstate and ammonium molybdate @SiO 2 ; (3)Transfer the ammonium metatungstate and ammonium molybdate @SiO 2 to a muffle furnace, heat up to 600 °C and keep it at a constant temperature for 1 h, and calcine to obtain MoO 2 WO 3 @SiO 2 ; (4)Add the MoO 2 WO 3 @SiO 2 to the sodium hydroxide solution, stir to remove the ordered mesoporous silica, and the molar ratio of MoO 2 WO 3 @SiO 2 to sodium hydroxide is 1:4. Stir for 12 h, perform solid-liquid separation and drying to obtain MoO 2 WO 3 hollow mesoporous spheres.

[0025] (5) Using MoO 2 WO 3 hollow mesoporous spheres as the carrier, using copper β-diketone complex and nickelocene as the copper source and nickel source respectively, using ozone as the oxygen source, depositing nickel oxide and copper oxide layers on the surface of the hollow mesoporous spheres by atomic layer deposition equipment, with the molar ratio of copper to nickel being 1:1, the deposition temperature being 180 °C, and the deposition cycle being 20 cycles. The obtained sample is placed in a tube furnace, and hydrogen is introduced at a flow rate of 80 ml / min, and the temperature is raised to 550 °C and reduced for 1 h to obtain NiCuMoO 2 WO x catalyst, and the nickel loading is 3%. Comparative Example 1

[0026] In step (2), cerium nitrate and ammonium metatungstate are dissolved in a solution prepared by mixing ethanol and deionized water in a volume ratio of 1:1. The molar ratio of cerium nitrate to ammonium metatungstate is 0.05:0.8. Silica hollow mesoporous spheres are added, and the mass ratio of ammonium metatungstate to silica hollow mesoporous spheres is 1:0.2. Stirring is continued at room temperature for 3 h to obtain ammonium metatungstate and cerium nitrate@SiO 2 . Other conditions are the same as those in Example 1. Comparative Example 2

[0027] In step (5), CeO 2 WO x hollow mesoporous spheres are used as the carrier, and nickel oxide and copper oxide are loaded by the impregnation method, and the nickel loading is 2.25%. Other conditions are the same as those in Example 1. Other conditions are the same as those in Example 1. Comparative Example 3

[0028] In step (2), ammonium metatungstate is dissolved in a solution prepared by mixing ethanol and deionized water in a volume ratio of 1:1. Silica hollow mesoporous spheres are added, and the mass ratio of ammonium metatungstate to silica hollow mesoporous spheres is 1:1. Stirring is continued at room temperature for 3 h to obtain ammonium metatungstate@SiO 2 ; other conditions are the same as those in Example 1.

[0029] Figure 1 is the X-ray diffraction (XRD) pattern of the catalyst prepared in Example 1. As can be seen from Figure 1 , in the figure, in addition to the diffraction peaks of WO x , no diffraction peaks of CeO 2 appear, indicating that CeO 2 enters the interior of WO 3 in the form of a lattice, which helps to form oxygen vacancies, is more conducive to hydrogen dissociation and spillover, and promotes the formation of more Brønsted acid sites. At the same time, no diffraction peaks of copper and nickel are seen, indicating that the active metals are loaded by atomic layer deposition, making their dispersion highly uniform. The NiCuCeO 2 WOx The catalyst is applied to the glycerol hydrocracking reaction, and the conversion rate of glycerol is as high as 68.3%, and the selectivity of 1,3-propanediol can reach 58.3%.

[0030] Figure 2 It is the transmission electron microscopy (TEM) image of the catalyst prepared in Example 1. Figure 1 It can be seen that the catalyst presents a complete hollow sphere structure with uniform size and thickness, indicating that CeO 2 WO 3 hollow mesoporous spheres are successfully synthesized by using silica hollow mesoporous spheres as hard templates, which mainly benefits from the control of the ratio of ammonium metatungstate to silica hollow mesoporous spheres (1:0.5 - 2) and the loading of active metals by atomic layer deposition.

[0031] Figure 3 It is the transmission electron microscopy (TEM) image of the catalyst prepared in Comparative Example 1. During the preparation process, the mass ratio of ammonium metatungstate to silica hollow mesoporous spheres is greater than 1:0.5, and the obtained NiCuCeO 2 WO x in the catalyst has too thick CeO 2 WO 3 layer, resulting in the internal substances being unable to contact the reactants and reducing their utilization rate. Therefore, when it is applied to the glycerol hydrocracking reaction, the conversion rate of glycerol is as low as 40.8%, and the selectivity of 1,3-propanediol is only 41.5%.

[0032] Figure 4 It is the transmission electron microscopy (TEM) image of the catalyst prepared in Comparative Example 2. Figure 4 It can be seen that, compared with Example 1, the surface thickness of the catalyst formed in Comparative Example 2 is uneven. This is because during the preparation of the catalyst by the impregnation method, the precursors of copper and nickel are unevenly attached to the surface of CeO 2 WO 3 surface. After calcination and reduction, some of the support CeO 2 WO 3 has too thick copper and nickel loaded on the surface, and the internal metals cannot contact the reactants, resulting in reduced catalytic activity; for another part of CeO 2 WO 3 surface, no copper and nickel are loaded, lacking active metals, which is not conducive to the catalytic activation of glycerol.

[0033] The catalyst is measured by a chemisorption instrument for temperature-programmed desorption experiment of NH 3 (NH 3 -TPD) to determine the amount of NH 3In the case where the ammonia adsorption capacity is larger, it indicates that there are more acidic sites in the sample. First, the sample is loaded into a U-shaped quartz tube, the program is set, carrier gas and hydrogen are introduced for reduction. After the reduction is completed, hydrogen is turned off and the carrier gas is used for purging. Then ammonia is introduced for adsorption. After the adsorption is completed, ammonia is turned off, and the signal is recorded during the programmed temperature rise.

[0034] Figure 5 The NiCuCeO prepared in Example 1 2 WO x catalyst, the NiCuWO prepared in Comparative Example 3 x catalyst NH 3 -TPD comparison spectra. From Figure 5 It can be seen that as the temperature increases, two signal peaks appear in the NH 3 -TPD spectra of the catalysts in Example 1 and Comparative Example 3. However, the signal peak area of Example 1 is significantly larger than that of the catalyst in Comparative Example 3, indicating that the former has a larger ammonia adsorption capacity, and thus it shows that the catalyst in Example 1 contains more acidic sites. This is because the introduction of the second metal cerium into the lattice of tungsten trioxide helps the formation of oxygen vacancies, is more conducive to hydrogen dissociation and spillover, forms more acidic sites, and thus improves the catalytic activity.

[0035] The catalysts prepared in Examples 1 to 3 and Comparative Examples 1 to 3 are respectively applied to the glycerol hydrogenolysis reaction, and the glycerol hydrogenolysis belongs to the scope of the prior art. The results are listed in Table 1.

[0036]

Claims

1. A method for preparing a glycerol hydrogenolysis catalyst, characterized in that: The steps include: (1) dissolving bicarbonate and cationic surfactant in an alcohol solvent, adding an organic silicon source, stirring at a constant temperature of 30 to 50° C., and centrifuging to obtain hollow mesoporous silica spheres; (2) dissolving the metal precursor and the tungsten source in a mixed solution of alcohol and deionized water in a volume ratio of 1:1 to 3, adding the hollow mesoporous silica spheres obtained in step (1), and stirring at room temperature for 3 to 6 hours to obtain a SiO2 solid coated with the tungsten source and the metal precursor; (3) calcining the SiO2 solid coated with the tungsten source and the metal precursor obtained in step (2) to obtain MO2WO3@SiO2; (4) Adding MO2WO3@SiO2 to an alkaline solution, stirring, separating, and drying the solid to obtain MO2WO3 hollow mesoporous spheres; (5) Using MO2WO3 hollow mesoporous spheres as carriers, β-diketone copper complex and nickelocene as copper source and nickel source, respectively, and ozone as oxygen source, an atomic layer deposition device was used to deposit nickel oxide and copper oxide layers on the surface of MO2WO3 hollow mesoporous spheres. The product was then calcined and reduced with hydrogen to obtain a glycerol hydrogenolysis catalyst.

2. The method for preparing a glycerol hydrogenolysis catalyst according to claim 1, wherein In the step (1), the alcohol solvent is one of methanol, ethanol and propanol; the bicarbonate is sodium bicarbonate or ammonium bicarbonate; the cationic surfactant is one of octadecyltrimethylammonium chloride, hexadecyltrimethylammonium bromide and hexadecyldimethylammonium chloride; the organosilicon source is ethyl orthosilicate or methyl orthosilicate; the volume mass ratio of the alcohol solvent, the bicarbonate, the cationic surfactant and the organosilicon source is 5-10 mL: 0.5-1 g: 0.1-0.5 g: 1-3 mL, and the constant temperature stirring time is 12-24 h.

3. The method for preparing a glycerol hydrogenolysis catalyst according to claim 1, characterized in that: In the step (2), the metal precursor is one of cerium nitrate, ammonium molybdate, and zirconium nitrate; the tungsten source is ammonium metatungstate or ammonium paratungstate; the molar ratio of the metal precursor to the tungsten source is 0.05:0.5-1; and the mass ratio of the tungsten source to the hollow mesoporous silica spheres is 1:0.5-2.

4. The method for preparing a glycerol hydrogenolysis catalyst according to claim 1, characterized in that: In the step (3), the calcination temperature is 400-600° C. and the calcination time is 1-3 hours.

5. The method for preparing a glycerol hydrogenolysis catalyst according to claim 1, characterized in that: In the step (4), the alkaline solution is a potassium hydroxide solution or a sodium hydroxide solution; the molar ratio of MO2WO3@SiO2 to the alkaline solution is 1:2-4; and the stirring time is 6-12 hours.

6. The method for preparing a glycerol hydrogenolysis catalyst according to claim 1, characterized in that: In the step (5), the molar ratio of copper to nickel is 1:1-5; the atomic layer deposition temperature is 180-250°C, and the deposition cycle is 5-20 cycles; the hydrogen flow rate of the hydrogen calcination reduction is 80-120 ml / min, the calcination reduction temperature is 400-550°C, and the time is 1-3 hours.

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