Cobalt-reduced graphene oxide Co/rGO catalyst and preparation method and application thereof
阅读说明：本技术 一种钴-还原氧化石墨烯Co/rGO催化剂及其制备方法与应用 (Cobalt-reduced graphene oxide Co/rGO catalyst and preparation method and application thereof ) 是由 周锦霞 郭启昌 毛璟博 李慎敏 尹静梅 于 2021-09-28 设计创作，主要内容包括：本发明涉及一种钴-还原氧化石墨烯Co/rGO催化剂及其制备方法与应用,该催化剂以廉价的过渡金属Co为加氢活性组分,以还原氧化石墨烯rGO为载体,所制备的催化剂无需经过高温预还原处理,可用于催化加氢愈创木酚制备环己醇的反应。该催化剂在正十二烷溶液中于1MPa氢气压力和200℃的条件下反应2h,可将愈创木酚完全转化,环己醇收率95％。无需还原预处理的Co/rGO催化剂比Ni/rGO、Fe/rGO催化剂以及Co/Al-(2)O-(3)、Co/HY、Co/AC催化剂具有更高的催化活性和选择性,比Pt、Pd等贵金属类催化剂廉价,具有工业应用价值。(The invention relates to a cobalt-reduced graphene oxide Co/rGO catalyst and a preparation method and application thereof. The catalyst reacts in n-dodecane solution for 2 hours under the conditions of 1MPa of hydrogen pressure and 200 ℃, guaiacol can be completely converted, and the yield of cyclohexanol is 95%. Co/rGO catalyst ratios Ni/rGO, Fe/rGO and Co/Al without reduction pretreatment 2 O 3 Co/HY and Co/AC catalysts have higher catalytic activity and selectivity, are cheaper than noble metal catalysts such as Pt, Pd and the like, and have industrial application value.)
1. A preparation method of a cobalt-reduced graphene oxide Co/rGO catalyst is characterized by comprising the following specific steps:
(1) preparing a graphene carrier: 230mL of concentrated sulfuric acid and 5.0g of NaNO are taken3Adding 10g of natural flake graphite powder with stirring, adding 30g of KMnO after stirring for 2.5h4Transferring the mixture into a 35 ℃ constant temperature water bath for reaction for 2H, adding 460mL of deionized water, stirring the mixture in an oil bath at 98 ℃ for 15min, finally adding 1.4L of deionized water to stop the reaction, and simultaneously adding 25mL of 30% H2O2Cooling to room temperature, centrifugally washing with deionized water, washing to be neutral, dispersing the prepared GO paste with the dry basis content of 1g in 1000mL of deionized water, carrying out ultrasonic treatment for 30min, standing, aging, adding 25mL of 30% ammonia water and 6mL of 80% hydrazine hydrate, refluxing in an oil bath at 95 ℃ for 3h, adding 4mL of 80% hydrazine hydrate, reacting for 30min, adding 4% hydrochloric acid solution, carrying out suction filtration while hot, and carrying out freeze drying to obtain an rGO carrier for later use;
(2) preparation of salt solution: taking Co (NO)3)2·6H2Putting the O into a beaker, dissolving the O with deionized water to prepare a salt solution, adding absolute ethyl alcohol, and shaking up for later use;
(3) dipping: weighing the rGO carrier prepared in the step (1), adding the rGO carrier into the beaker in the step (2), continuously stirring the rGO carrier by using a glass rod, and standing the sample at room temperature;
(4) and (3) drying: placing the sample after standing in the step (3) in a vacuum drying oven for drying for 12h at 50 ℃, and grinding the sample by using an agate mortar until the sample becomes powder;
(5) roasting: and (3) putting the powdery sample prepared in the step (4) into a quartz tube, putting the quartz tube into a tube furnace, raising the temperature from room temperature to 500 ℃ by a program of 10 ℃/min in the atmosphere of nitrogen, roasting the quartz tube at the constant temperature of 500 ℃ for 1 to 4 hours, taking out the sample when the temperature is reduced to the room temperature, and sealing and storing the sample.
2. The method for preparing a cobalt-reduced graphene oxide Co/rGO catalyst according to claim 1, wherein the sample in step (3) is left to stand at room temperature for 2-5 h.
3. The method of claim 1, wherein the sample obtained in step (4) is in the form of 80-100 mesh powder.
4. The method for preparing a Co-reduced graphene oxide Co/rGO catalyst according to claim 1, wherein Co (NO) in the step (2) and the step (3)3)2·6H2The proportion relationship between O and the carrier rGO is 0.5-3.0 mmol/g; the volume ratio of the water to the ethanol is 10: 1-5: 5; the salt solution prepared in step (2) can just be absorbed by the rGO weighed in step (3).
5. A cobalt-reduced graphene oxide Co/rGO catalyst, characterised in that it is prepared according to the process of claims 1-4.
6. The application of the cobalt-reduced graphene oxide Co/rGO catalyst is characterized in that the catalyst is used for preparing cyclohexanol by catalyzing and hydrogenating guaiacol, and the specific steps are as follows: taking n-dodecane as a solvent, and reacting guaiacol with H under the action of a Co/rGO catalyst2And (4) carrying out reaction to obtain cyclohexanol.
7. The use of the Co-reduced graphene oxide Co/rGO catalyst according to claim 6, wherein the reaction temperature for preparing cyclohexanol by catalytic hydrogenation of guaiacol is 180-220 ℃, the hydrogen pressure is 1-4 MPa, and the reaction time is 0.25-3 h.
Technical Field
The invention belongs to the field of cyclohexanol preparation, and particularly relates to a cobalt-reduced graphene oxide Co/rGO catalyst, and a preparation method and application thereof.
Background
With the continuous development of society, the great consumption of energy sources brings great pressure to the natural environment, and the search for new energy sources which can replace fossil fuels and reduce the environmental pollution is urgent. As a novel renewable clean energy source, the biomass energy is similar to the composition of fossil fuel, mainly comprises C, H, O and other elements, is expected to become a traditional fossil fuel substitute, and has been widely concerned by various scholars all the time. Wherein, the lignin accounts for 30 to 40 percent of the mass of the biomass, is an adequate renewable raw material, and in recent years, the chemical conversion reaction of lignin biomass energy is widely concerned by scholars at home and abroad.
Guaiacol (Guaiacol, GUA for short) is one of the simplest model compounds of lignin, and on one hand, the chemical structure of the Guaiacol contains hydroxyl and methoxy, and the two functional groups are widely present in lignin polymers. Therefore, the majority of researchers usually choose the lignin as a model compound of lignin to conduct hydrodeoxygenation reaction research. In the presence of a catalyst, guaiacol can be subjected to Hydrodeoxygenation (HDO) to obtain Cyclohexanol (Cyclohexanol). Cyclohexanol is colorless viscous liquid at normal temperature and pressure, can be used as industrial raw material with wide application, can be used as synthetic raw material for producing adipic acid and caprolactam, and can obtain important chemical intermediate (nylon-66) in industrial production, so that cyclohexanol has wide application. Currently, the catalysts used in the art include primarily noble metal catalysts (Ru/C, Pd/C, Pt/C) and non-noble metal catalysts, such as cobalt-based catalysts (Co/rGO, NiCo/gamma-Al)2O3) Nickel-based catalyst (Ni/Al)2O3Ni/C), molybdenum-based catalyst (Mo)2C/CNT、MoS2and/C), etc. Although some precious metal catalysts can achieve good catalytic effect, the precious metal catalysts are expensive, so that the large-scale use is limited. Some researchers have focused on non-noble metal catalysts. R.Olcese, M.M.Bettahar, B.Malaman, J.Ghanbaja, L.Tibavizco, D.Petitjean and dA.Dufour, appl.Catal.B,2013,129,528 and jar 538. Studies on SiO.C.2And an Activated Carbon (AC) supported iron-based catalyst for HDO reaction of guaiacol model compounds. At 400 deg.C and 1bar with Fe/SiO2Conversion of guaiacol as catalyst74% is achieved and the yield of aromatics and other aromatic oxygenates (i.e. phenol, anisole and cresol) is 38%, the product being virtually free of cyclohexanol. I.T.Ghampson, C.Sep lveda, R.Garcia, B.G.Frederick, M.C.Wheeler, N.Escalona and W.J.Desista, appl.Catal.A,2012,413-2N and CoMoNx catalysts. These nitrides can be used to directly cleave benzene ring-OCH in guaiacol3Bond, form phenol, but then during HDO at 300 ℃ and 50bar H2Under pressure, benzene ring-OH bond cleavage occurs to form cyclohexene and cyclohexane. In addition, non-noble metal catalysts reported in the literature typically require a reductive pretreatment prior to being charged to the reaction system. The catalyst needs pre-reduction treatment, which not only makes the preparation and maintenance process of the catalyst complicated and increases energy consumption, but also some reduced catalysts may lose activity due to oxidation.
Disclosure of Invention
In order to overcome the defects and shortcomings of the prior art, the invention provides a cobalt-reduced graphene oxide Co/rGO catalyst and a preparation method and application thereof.
The purpose of the invention is realized by the following technical scheme:
a preparation method of a cobalt-reduced graphene oxide Co/rGO catalyst comprises the following specific steps:
(1) preparing a graphene carrier: 230mL of concentrated sulfuric acid and 5.0g of NaNO are taken3Adding 10g of natural flake graphite powder with stirring, adding 30g of KMnO after stirring for 2.5h4Transferring the mixture into a 35 ℃ constant temperature water bath for reaction for 2H, adding 460mL of deionized water, stirring the mixture in an oil bath at 98 ℃ for 15min, finally adding 1.4L of deionized water to stop the reaction, and simultaneously adding 25mL of 30% H2O2Cooling to room temperature, centrifugally washing with deionized water, washing to be neutral, dispersing the prepared GO paste with the dry basis content of 1g in 1000mL of deionized water, carrying out ultrasonic treatment for 30min, standing, aging, adding 25mL of 30% ammonia water and 6mL of 80% hydrazine hydrate, refluxing in an oil bath at 95 ℃ for 3h, adding 4mL of 80% hydrazine hydrate, reacting for 30min, adding 4% hydrochloric acid solution, carrying out suction filtration while hot, and carrying out freeze drying to obtain an rGO carrier for later use;
(2) preparation of salt solution: getCo(NO3)2·6H2Putting the O into a beaker, dissolving the O with deionized water to prepare a salt solution, adding absolute ethyl alcohol, and shaking up for later use;
(3) dipping: weighing the rGO carrier prepared in the step (1), adding the rGO carrier into the beaker in the step (2), continuously stirring the rGO carrier by using a glass rod, and standing the sample at room temperature;
(4) and (3) drying: placing the sample after standing in the step (3) in a vacuum drying oven for drying for 12h at 50 ℃, and grinding the sample by using an agate mortar until the sample becomes powder;
(5) roasting: and (3) putting the powdery sample prepared in the step (4) into a quartz tube, putting the quartz tube into a tube furnace, raising the temperature from room temperature to 500 ℃ by a program of 10 ℃/min in the atmosphere of nitrogen, roasting the quartz tube at the constant temperature of 500 ℃ for 1 to 4 hours, taking out the sample when the temperature is reduced to the room temperature, and sealing and storing the sample.
Further, standing the sample in the step (3) at room temperature for 2-5 h.
Further, the sample in the step (4) becomes 80-100 mesh powder.
Further, Co (NO) in the step (2) and the step (3)3)2·6H2The proportion relationship between O and the carrier rGO is 0.5-3.0 mmol/g; the volume ratio of the water to the ethanol is 10: 1-5: 5; the salt solution prepared in step (2) can just be absorbed by the rGO weighed in step (3).
An application of a cobalt-reduced graphene oxide Co/rGO catalyst in preparing cyclohexanol by catalyzing and hydrogenating guaiacol comprises the following specific steps: taking n-dodecane as a solvent, and reacting guaiacol with H under the action of a Co/rGO catalyst2And (4) carrying out reaction to obtain cyclohexanol.
Further, the reaction temperature for preparing cyclohexanol by catalytically hydrogenating guaiacol is 180-220 ℃, the hydrogen pressure is 1-4 MPa, and the reaction time is 0.25-3 h.
Compared with the prior art, the invention has the following advantages and effects:
(1) co is non-noble metal, the cost is low, and in addition, the Co/rGO catalyst does not need to be subjected to high-temperature pre-reduction treatment and can not be inactivated due to oxidation. Furthermore, the Co/rGO catalyst does not precipitate out the active metal component in the reaction.
(2) The Co/rGO catalyst is prepared by adopting an impregnation-roasting method, and the preparation method is simple and suitable for large-scale industrial preparation. Co/rGO catalyst does not cause cyclohexanol decomposition and has a H value of 1MPa at 200 DEG C2And under the condition of 2h, the yield of the cyclohexanol can reach 95%, and high selectivity to the cyclohexanol is reflected.
In conclusion, the Co/rGO catalyst has the characteristics of high reaction activity, high selectivity and the like when catalyzing guaiacol hydrogenation reaction, the conversion rate of the guaiacol hydrogenation reaction catalyzed by the Co/rGO catalyst can reach 100%, the cyclohexanol selectivity can reach 95%, metal components are not separated out, the catalyst does not need to be subjected to high-temperature pre-reduction in the reaction process, and the preparation method is suitable for industrial mass preparation and has obvious advantages and industrial application values.
Detailed Description
The present invention will be described in further detail with reference to examples, but the embodiments of the present invention are not limited thereto. Unless otherwise specified, the experimental methods adopted by the invention are all conventional methods, and experimental equipment, materials, reagents and the like used in the experimental method can be purchased from chemical companies.
Graphene (Graphene) is a planar film of carbon atoms in a hexagonal honeycomb lattice with sp2 hybridized orbitals, a two-dimensional material only one carbon atom thick. The graphene has a plurality of unique physical and chemical properties, such as high specific surface area, high conductivity, high mechanical strength and easy modification, can be produced in a large scale by using graphite, and has high application value in the field of catalysis. The graphene serving as a carrier not only can provide a large specific surface area, but also can form a strong electronic synergistic effect with active components such as loaded metal and metal oxide, so that the electronic characteristics of the metal active components are modulated to generate excellent catalytic performance.
The invention has the following inventive concept: the catalyst takes low-cost transition metal Co as a hydrogenation active component and reduced graphene oxide rGO as a carrier, and the prepared catalyst does not need high-temperature pre-reduction treatment and can be used for catalyzing the reaction of preparing cyclohexanol by hydrogenating guaiacol. The catalyst reacts in n-dodecane solution for 2 hours under the conditions of 1MPa of hydrogen pressure and 200 ℃, guaiacol can be completely converted, and the yield of cyclohexanol is 95%. The graphene with the two-dimensional plane structure not only plays a role in dispersing and carrying Co active components, but also further enhances the catalytic function through the electronic synergistic effect of Co and graphene. The synthesized catalyst does not need reduction pretreatment, generates higher catalytic activity and product selectivity under mild conditions, and provides a novel high-efficiency catalyst for preparing cyclohexanol by selective hydrogenation of guaiacol.
Examples 1-3 batch reactions at different reaction temperatures
1. Preparing a catalyst: the method for preparing the Co/rGO catalyst by adopting a dipping-roasting method comprises the following specific steps:
(1) preparing a graphene carrier: 230mL of concentrated sulfuric acid and 5.0g of NaNO are taken3Adding 10g of natural flake graphite powder with stirring, adding KMnO after stirring for 2.5h4Transferring the mixture into a 35 ℃ constant temperature water bath for reaction for 2H, adding 460mL of deionized water, stirring the mixture in an oil bath at 98 ℃ for 15min, finally adding 1.4L of deionized water to stop the reaction, and simultaneously adding 25mL of 30% H2O2Cooling to room temperature, centrifugally washing with deionized water, washing to neutrality, dispersing the prepared GO paste with a dry basis of 1g in 1000mL of deionized water, carrying out ultrasonic treatment for 30min, standing, aging, adding 25mL of 30% ammonia water and 6mL of 80% hydrazine hydrate, refluxing in an oil bath at 95 ℃ for 3h, adding 4mL of 80% hydrazine hydrate, reacting for 30min, adding 4% hydrochloric acid solution, carrying out suction filtration while hot, and carrying out freeze drying to obtain the rGO carrier for later use.
(2) Preparation of salt solution: taking 72.8mg of Co (NO)3)2·6H2Dissolving the O in 0.82mL of deionized water to prepare a salt solution;
(3) dipping: 0.2mL of absolute ethyl alcohol is added into the prepared salt solution, and the mixture is shaken up for standby. 100mg of rGO was weighed into a beaker and stirred continuously with a glass rod. Standing the sample at room temperature for 3 h;
(4) and (3) drying: placing the sample after standing in the step (3) in a vacuum drying oven for drying for 12h at 50 ℃, and grinding the sample by using an agate mortar until the sample becomes powder;
(5) roasting: putting the powdery sample prepared in the step (4) into a quartz tube, putting the quartz tube into a tube furnace, raising the temperature from room temperature to 500 ℃ by a program of 10 ℃/min in the atmosphere of nitrogen, roasting the quartz tube at the constant temperature of 500 ℃ for 2 hours, taking out the sample when the temperature is reduced to the room temperature, and sealing and storing the sample;
2. reaction test: the performance of a Co/rGO catalyst in catalyzing guaiacol hydrogenation reaction is tested by adopting an intermittent reaction, and the method comprises the following specific steps:
(1) taking a mechanical stirring high-pressure reaction kettle, adding 300.0mg of guaiacol, 10ml of n-decane, 120mg of internal standard substance tetradecane and 30mg of Co/rGO catalyst into the mechanical stirring high-pressure reaction kettle, screwing the reaction kettle, checking the air tightness of the device, and introducing 1MPa of H after ensuring that the device is airtight2700rpm stirring rate, set the specified temperature, react for 2 h.
(2) After the reaction was completed, the liquid phase product was collected and analyzed by gas chromatography. The catalyst was recovered by centrifugation.
Wherein: the conversion of guaiacol was (amount of guaiacol substance at the start of reaction-amount of guaiacol substance at the end of reaction)/amount of guaiacol substance at the start of reaction × 100%
The yield of cyclohexanol was defined as the amount of cyclohexanol material at the end of the reaction/the amount of guaiacol material at the beginning of the reaction × 100%
The selectivity of cyclohexanol was defined as the yield of cyclohexanol/conversion of guaiacol × 100%
The chromatographic analysis conditions were: a hydrogen flame detector FID is adopted, hydrogen is used as carrier gas, an internal standard method is adopted, and tetradecane is used as an internal standard substance.
3. The reaction results are shown in Table 1
TABLE 1 results for different reaction temperatures
Examples 1-3 show that guaiacol is also converted at 180 c, but the reaction rate is lower, and that guaiacol achieves 100% conversion and 95% cyclohexanol yield when the reaction temperature reaches 200 c. When the temperature is higher than 220 ℃, the cyclohexanol selectivity is slightly reduced, which indicates that the catalyst will continue to decompose at high temperature.
Examples 2 and 4-6 batch reactions at different reaction pressures
1. Preparing a catalyst: the same procedure was used to prepare the catalysts of examples 1-3.
2. Reaction test: the operation procedure was the same as the reaction test procedure in examples 1 to 3, and the specific reaction conditions were set as follows: ensuring that the device is not leaked and then is introduced with different specified pressures H2700rpm stirring rate, set temperature 200 ℃ for 2 h.
3. The reaction results are shown in Table 2.
TABLE 2 results of different reaction pressures
As can be seen from examples 2 and 4-6, the conversion rate of guaiacol can reach 100% when the reaction is carried out for 2 hours under the conditions of 1MPa-4 MPa and 200 ℃. When H is present2The catalyst has better catalytic activity when the pressure is 1.0MPa, and the yield of cyclohexanol can reach 95 percent; when the pressure was increased to 2.0MPa, the cyclohexanol yield was slightly decreased. Continuously increase H2The pressure caused the yield of cyclohexanol to continue to decrease, indicating a H of 1.0MPa in the reaction system2The reaction of guaiacol to cyclohexanol can be promoted over a Co/rGO catalyst. Too high a pressure will rapidly convert guaiacol to 1-methyl-1, 2-cyclohexanediol.
Examples 2 and 7-11 batch reactions with different reaction times
1. Preparing a catalyst: the same procedure was used to prepare the catalysts of examples 1-3.
2. Reaction test: the operation procedure was the same as that of the reaction test procedure in examples 1 to 3, and the specific reaction conditions were as follows: after ensuring the device is airtight, 1MPaH is introduced2700rpm stirring rate, set temperature 200 ℃ and reaction times specified.
3. The reaction results are shown in Table 3.
TABLE 3 results for different reaction times
Example 2And 7-11, at 200 ℃ and 1MPa H2When the reaction time is 1h, the guaiacol is converted to 95%, the yield of cyclohexanol is 81%, after the reaction time reaches 2h, the yield of cyclohexanol reaches 95%, and the reaction time is continuously prolonged, the yield of cyclohexanol is not reduced, which shows that the catalyst is catalytically inert to cyclohexanol at 200 ℃, and excessive hydrogenation products and ring-opening products for breaking benzene ring rings are not generated.
Comparative example 1 batch reaction of Ni/rGO catalyst
1. Preparing a catalyst: preparing a Ni/rGO catalyst by adopting an impregnation-roasting method, and specifically, removing the preparation of the salt solution in the step (2): 72.8mg of Ni (NO)3)2·6H2Dissolving the mixture into deionized water to prepare a salt solution;
the remaining preparation steps were as in examples 1-3.
2. Reaction test: the performance of the Ni/rGO catalyst in catalyzing the guaiacol hydrogenation reaction is tested by adopting an intermittent reaction, and the specific steps are the same as those in example 2.
The reaction result shows that the conversion rate of guaiacol is 90% and the selectivity of cyclohexanol is 58% under the action of the catalyst. Under the condition of the same proportion, the Co/rGO catalyst can completely convert guaiacol, and the yield of cyclohexanol reaches 95%.
Comparative example 2 batch reaction of Fe/rGO catalyst
1. Preparing a catalyst: preparing the Fe/rGO catalyst by adopting an impregnation-roasting method, and specifically, removing the preparation of the salt solution in the step (2): 101mg of Fe (NO)3)3·9H2Dissolving the mixture into deionized water to prepare a salt solution;
the remaining preparation steps were as in examples 1-3.
2. Reaction test: the performance of the Fe/rGO catalyst in catalyzing the guaiacol hydrogenation reaction was tested by using the batch reaction, which was the same as example 2.
The reaction result shows that the conversion rate of guaiacol is 4.5% and the selectivity of cyclohexanol is 12% under the action of the catalyst. Under the condition of the same proportion, the Co/rGO catalyst can completely convert guaiacol, and the yield of cyclohexanol reaches 95%.
Comparative examples 3-5 batch reaction of different supported catalysts
1. Preparing a catalyst: preparation of Co/Al by dipping-roasting method2O3Co/HY and Co/AC catalyst, and comprises the following specific steps except the step (3) of impregnation: the prepared salt solution was placed in a beaker. 100mgAl is weighed respectively2O3HY, AC, added to the beaker and stirred continuously with a glass rod. Standing the sample at room temperature for 3 h;
the remaining preparation steps were as in examples 1-3.
2. Reaction test: testing of Co/Al Using batch reaction2O3The specific steps of the performance of the Co/HY and Co/AC catalysts for catalyzing the guaiacol hydrogenation reaction are the same as those in example 2.
3. The reaction results are shown in Table 4.
TABLE 4 results for different supported catalysts
As can be seen from comparative examples 3 to 5, the load is in Al2O3、HY、SiO2Co on the carrier can not obtain good catalytic activity without reduction pretreatment. So transition metal catalysis in the literature usually requires reductive pretreatment. The pretreatment process not only complicates the catalyst preparation and maintenance process and increases energy consumption, but also some reduced catalysts may lose activity due to oxidation. The Co/rGO catalyst of the invention is in N2The calcined product is used directly and is directly operated in air atmosphere. Therefore, the catalyst disclosed by the invention is energy-saving and efficient and has the characteristic of oxidation resistance and inactivation.
The above description is only for the purpose of creating a preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can substitute or change the technical solution and the inventive concept of the present invention within the technical scope of the present invention.