Preparation method of iron-cobalt oxide and Beta molecular sieve composite catalyst and application of iron-cobalt oxide and Beta molecular sieve composite catalyst in demethoxylation of lignin derivative vanillic acid

Abstract

The invention relates to the technical field of catalysts, in particular to a preparation method of an iron-cobalt oxide and Beta molecular sieve composite catalyst and application of the iron-cobalt oxide and Beta molecular sieve composite catalyst to demethoxylation of lignin derivative vanillic acid. Meanwhile, due to the interaction of iron and cobalt species, the acid site of the catalyst is enhanced, and adsorption and activation of a substrate are facilitated; the iron-cobalt oxide is combined with the Beta molecular sieve, and the reaction activity of demethoxylation is improved through cooperation of metal / zeolite; the Co0 / Fe0. 04Co0. 96O-Beta composite catalyst is used for a vanillic acid demethoxylation catalytic reaction, the reaction is performed for 2 hours under the condition of 0.4 MPa H2 and 0.4 MPa CO2, the substrate conversion rate reaches 96.07%, the p-hydroxybenzoic acid selectivity reaches 86.96%, and the target product yield is 83.54%.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, specifically to a method for preparing a composite catalyst of iron cobalt oxide and Beta molecular sieve and its application in the demethoxylation of vanillic acid, a lignin derivative. Background Technology

[0002] In the context of dual carbon, biomass, as the only renewable carbon source in nature, can effectively address energy shortages and environmental pollution. Therefore, utilizing renewable biomass resources to replace traditional fossil fuels in the production of high-value-added chemicals is of great significance. A series of derivatives obtained from lignin depolymerization contain varying numbers of methoxy groups, requiring catalytic hydrogenation and demethoxylation to prepare single chemicals. This invention focuses on the selective demethoxylation of lignin-derived vanillic acid to prepare p-hydroxybenzoic acid, an important fine chemical raw material widely used in food, cosmetic preservatives, and medical antibacterial applications. Problems in the catalytic demethoxylation reaction of vanillic acid include excessive hydrogenation activity leading to side reactions such as benzene ring hydrogenation and phenolic hydroxyl group removal, and decarboxylation under high-temperature catalytic conditions. Therefore, it is necessary to develop a highly efficient and selective demethoxylation catalytic system capable of selectively removing methoxy groups under relatively mild conditions, while avoiding excessive benzene ring hydrogenation, phenolic hydroxyl group removal, and decarboxylation side reactions, thereby achieving high-value utilization of lignin derivatives.

[0003] Currently, demethoxylation catalysts are mainly classified into noble metal catalysts, transition metal catalysts, and molybdenum-based catalysts. Noble metals Au and Ag exhibit relatively weak hydrogenation activity, but can reduce the formation of benzene ring hydrogenation byproducts while simultaneously demethoxylating; however, their cost is high. Transition metals Fe and Co, on the other hand, have oxophilic properties that facilitate the adsorption and activation of methoxy groups, and they are abundant and inexpensive. While molybdenum-based catalysts exhibit good demethoxylation performance, the reaction conditions typically require high hydrogen pressure, and excessively strong catalyst acidity can easily lead to catalyst deactivation. Liu et al. [Journal of Catalysis. 2019, 369, 396−404] studied the catalytic demethoxylation of guaiacol by Ag / TiO2 catalyst at 300℃ and 3MPa hydrogen conditions, achieving a phenol yield of approximately 45% and a total phenol yield of approximately 64%. Li et al. [ACSCatal. 2020, 10, 14624–14639] prepared a FeOx / CeO2 catalyst for the demethoxylation reaction of guaiacol. Using a fixed-bed reaction at 400 °C and 0.1 MPa hydrogen, they achieved a phenol yield of 56% and a phenolic compound yield of 87%. Bai et al. [ACSCatal. 2016, 6, 6141–6145] used a MoWBOx / AC catalyst to demethoxylate vanillic acid and syringic acid, achieving a 71.6% yield of p-hydroxybenzoic acid at 400 °C under a H2 / CO2 atmosphere. Therefore, for vanillic acid derived from lignin oxidative depolymerization, it is necessary to develop a catalyst system that can selectively remove methoxy groups under relatively mild conditions while retaining the benzene ring and other functional groups. Summary of the Invention

[0004] Technical problems to be solved To address the aforementioned shortcomings of existing technologies, this invention provides a method for preparing a composite catalyst of iron-cobalt oxide and Beta molecular sieve and its application in the demethoxylation of vanillic acid, a lignin derivative. The aim is to enable the prepared composite catalyst of iron-cobalt oxide and Beta molecular sieve to selectively demethoxylate vanillic acid under relatively mild conditions, while avoiding excessive hydrogenation of the benzene ring, removal of phenolic hydroxyl groups, and decarboxylation side reactions, thereby achieving high-value utilization of lignin derivatives.

[0005] Technical solution To achieve the above objectives, the present invention provides the following technical solution: A method for preparing a composite catalyst of iron cobalt oxide and Beta molecular sieve, wherein the preparation method comprises: S1. Dissolve iron salt and cobalt salt in deionized water, add citric acid solution dropwise, stir evenly, and heat to evaporate to dryness until a foamy gel is formed. S2. The foamed gel prepared in S1 was placed in a muffle furnace and calcined in air to obtain black iron-cobalt oxide Fe. XCo 1-X O (x represents the molar percentage of iron doping: x = mol(Fe) / [mol(Fe) + mol(Co)]); S3, Fe iron-cobalt oxide X Co 1-X O and Beta molecular sieves are dispersed in deionized water and stirred evenly. After drying and calcination in air, they are reduced in a hydrogen-argon mixed atmosphere to obtain the composite catalyst of iron cobalt oxide and Beta molecular sieve.

[0006] Furthermore, the iron salt and cobalt salt in S1 are ferric nitrate nonahydrate and cobalt nitrate hexahydrate, respectively. The total concentration of the iron salt and cobalt salt is 0.67 mol / L, the concentrations of both the iron salt and cobalt salt are less than 0.67 mol / L and greater than 0.67 mol / L. The molar ratio of iron to cobalt is 1:(1~32), more preferably 1:(9~32), and most preferably 1:(19~32).

[0007] Furthermore, the citric acid in S1 is citric acid monohydrate, the concentration of the citric acid solution is 70~280g / L, the molar amount of the citric acid is 0.5~2 times the total molar amount of iron and cobalt, more preferably 1 time, and the dropping rate of the citric acid solution is 2~4mL / min.

[0008] Furthermore, the temperature for heating and evaporation in S1 to form a foamed gel is 60~140℃, and the time is 2~6h.

[0009] Furthermore, the calcination treatment in S1 is carried out at a temperature of 300~550℃ for 2~5h, and the heating rate of the calcination treatment is 3~10℃ / min. More preferably, the calcination temperature is 400℃ and the time is 3h.

[0010] Furthermore, in S3, the iron-cobalt oxide Fe X Co 1-X The weight of O accounts for 5-30% of the total weight of the composite catalyst of iron cobalt oxide and Beta molecular sieve, more preferably 20%; the silicon-to-aluminum ratio of the Beta molecular sieve is (25-50):1, more preferably 30:1; the stirring time for uniform stirring is 6-24h, more preferably 12h; the drying method is to dry at a temperature of 50-80℃ for 6-12h.

[0011] Furthermore, in S3, grinding is performed before reduction treatment, the hydrogen volume ratio of the hydrogen-argon mixed atmosphere is 8%, the gas flow rate of the hydrogen-argon mixed atmosphere is 40~150mL / min, more preferably 100mL / min; the temperature of the reduction treatment is 200~400℃, the reduction treatment time is 2~4h, more preferably the reduction temperature is 300℃ and the time is 3h; the heating rate of the reduction treatment is 3~10℃ / min.

[0012] An application of a composite catalyst prepared by an iron-cobalt oxide and Beta molecular sieve in the demethoxylation of vanillic acid, a lignin derivative, is disclosed. The method for application is as follows: In a high-pressure batch reactor, using a solvent as the reaction medium, and under conditions of 200~250℃ and an initial pressure of 0~1.2MPa, more preferably an initial pressure of 0.8MPa, the lignin derivative vanillic acid undergoes a demethoxylation reaction under the catalytic action of the iron-cobalt oxide and Beta molecular sieve composite catalyst.

[0013] Furthermore, the solvent is methanol, the ratio of the solvent to the lignin derivative vanillic acid is 20:(0.05~0.3) mL / g, and the weight ratio of the lignin derivative vanillic acid to the iron-cobalt oxide to the Beta molecular sieve composite catalyst is (0.05~0.30):(0.05~0.30), more preferably 0.15:0.05.

[0014] Furthermore, the initial hydrogen pressure is 0~0.6MPa, the initial carbon dioxide pressure is 0~0.6MPa, more preferably the initial hydrogen pressure is 0.4MPa, the initial carbon dioxide pressure is 0.4MPa, and the volume ratio of initial hydrogen to initial carbon dioxide is 1:1; the catalytic time of the catalyst is 1~4h, and the catalytic temperature of the catalyst is 220℃.

[0015] Beneficial effects Compared with known public technologies, the technical solution provided by this invention has the following beneficial effects: 1. The preparation method of the iron-cobalt oxide and Beta molecular sieve composite catalyst in this invention uses non-precious metal nitrate, citric acid and molecular sieve as raw materials. It achieves low-cost and simplified catalyst preparation through a sol-gel method combined with a composite process. Citric acid, as a complexing agent, can promote the uniform dispersion of iron-cobalt species, reduce particle size, increase specific surface area and pore structure, and enhance the adsorption and activation ability of methoxy groups.

[0016] 2. The combination of iron-cobalt oxide and Beta molecular sieve forms a metal / zeolite synergistic catalytic system. The reduction degree of cobalt species is regulated by iron species, generating zero-valent cobalt active sites, which effectively activate hydrogen species. This synergistic effect solves the technical problems of insufficient acid sites, poor substrate adsorption and activation, and difficulty in suppressing the side reaction of benzene ring hydrogenation in traditional catalysts. Secondly, under the optimal ratio and specific reaction conditions, the vanillic acid demethoxylation reaction conversion rate reaches 96.07%, the selectivity of p-hydroxybenzoic acid is 86.96%, and the target product yield is 83.54%, which is significantly better than existing similar catalysts.

[0017] 3. For the first time, a mixed atmosphere of hydrogen and carbon dioxide was established as the exclusive reaction atmosphere for vanillic acid demethoxylation. By combining the synergistic regulation of acidic sites and metal / zeolite dual active centers by iron and cobalt species, directional demethoxylation was achieved and the side reaction of benzene ring hydrogenation was suppressed, while the integrity of the aromatic ring structure was preserved. This revealed the core catalytic mechanism of "acidic site regulation + synergistic dual active center", providing theoretical support for the design of similar aromatic acid demethoxylation reaction systems.

[0018] 4. The iron-cobalt oxide and Beta molecular sieve composite catalyst prepared by this invention can promote the technological development of lignin biomass route for the preparation of specific chemicals, and provide a new route for the biomass conversion of high-value-added fine chemicals such as p-hydroxybenzoic acid, with significant industrial application potential and economic value. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0020] Figure 1 To prepare Fe with different iron doping amounts for this invention X Co 1-X Scanning electron microscopy (SEM) images of O were used to characterize the morphology of iron-cobalt oxides with different proportions. (a) shows Fe. 0.04 Co 0.96 O, (b) is Fe 0.20 Co 0.8 When the iron doping ratio is low, iron and cobalt are oxidized into irregular particles, which is beneficial to increasing the number of catalytic active sites. As the iron doping ratio increases, the particle size decreases and they exhibit an aggregated state. Figure 2 To prepare Fe with different iron doping amounts for this invention X Co 1-X XRD patterns of O were obtained by using X-ray diffraction (XRD) to analyze Fe oxides with different proportions.X Co 1-X The structure of O was characterized. In the unreduced state, the iron-cobalt oxide with a low iron doping content still maintains the crystal structure of Co3O4. As the iron doping content increases, the intensity of the diffraction peak of Co3O4 decreases and the peak position shifts to the left, indicating that excessive iron doping may affect its crystal structure. Figure 3 For different iron doping amounts of Fe X Co 1-X XRD patterns of the O-Beta composite catalyst showed that iron incorporation inhibited the reduction process of cobalt species, while Fe alone... 0.04 Co 0.96 After O reduction, there is a lack of active metal Co. 0 This leads to a decrease in catalytic performance, while the Co obtained after reduction... 0 / Fe 0.04 Co 0.96 O-Beta composite catalyst contains Co 0 And CoO, Co 0 The coexistence of CoO and CoO is beneficial to improving the reactivity and the adsorption capacity of acidic sites for substrates, thereby enhancing the catalytic hydrogenation and demethoxylation ability. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0022] The present invention will be further described below with reference to embodiments.

[0023] Example 1 In this embodiment, Co 0 / Fe 0.04 Co 0.96 The preparation method of O-Beta composite catalyst is as follows: S1. Weigh 0.3232 g of iron salt and 5.5878 g of cobalt salt at room temperature and dissolve them in a beaker containing 30 mL of deionized water. Stir in an oil bath until fully dissolved to prepare a nitrate mixed solution. Weigh 4.2028 g of citric acid monohydrate and dissolve it in a beaker containing 30 mL of deionized water to prepare a citric acid solution. Then, add the citric acid solution dropwise to the nitrate mixed solution at a rate of 2 mL / min. Heat and stir at 80 °C for 2 h, then raise the temperature to 120 °C and continue heating and stirring until the water evaporates to form a foamed gel. Transfer the gel to a muffle furnace for calcination. The calcination procedure is as follows: raise the temperature to 400 °C at a rate of 5 °C / min and hold for 3 h. After calcination, allow it to cool naturally to room temperature to obtain iron-cobalt oxide Fe. 0.04 Co 0.96 O; S2. Weigh 0.1g of iron-cobalt oxide (Fe) at room temperature. 0.04 Co 0.96 O and 0.4 g of Beta molecular sieve were dissolved in a beaker containing 30 mL of deionized water. After stirring for 12 h, the solution was evaporated to dryness at 80 °C, ground, and placed in a tube furnace. Under a mixed atmosphere of 8% H2 / Ar with a gas flow rate of 100 mL / min, the temperature was increased to 300 °C at a rate of 5 °C / min and held for 3 h. After the reduction treatment, the solution was allowed to cool naturally to room temperature to obtain Co. 0 / Fe 0.04 Co 0.96 O-Beta composite catalyst.

[0024] Co 0 / Fe 0.04 Co 0.96 Application test of O-Beta composite catalyst in the demethoxylation of lignin derivative vanillic acid: Add 0.15g vanillic acid and 0.05g Fe to the reaction vessel. 0.04 Co 0.96 The O-Beta composite catalyst and 20 mL of methanol were introduced, followed by purging with hydrogen gas and then venting the atmosphere. This process was repeated three times. Finally, the reactor was purged with 0.4 MPa of hydrogen gas and 0.4 MPa of carbon dioxide gas. The reaction was carried out at 220 °C and a stirring speed of 400 r / min for 2 h. After the reaction was completed, the reactor was cooled to room temperature, and 20 μL of n-decane was added. The liquid product was then separated by filtration through a 0.22 μm organic filter membrane and samples were taken for analysis. The reaction products were qualitatively analyzed by gas chromatography-mass spectrometry (GC-MS) and quantitatively analyzed by gas chromatography (GC).

[0025] Example 2 In this embodiment, Co 0 / Fe 0.02 Co 0.98 The preparation method of O-Beta composite catalyst is as follows: S1. Weigh 0.1616 g of iron salt and 5.7041 g of cobalt salt at room temperature and dissolve them in a beaker containing 30 mL of deionized water. Stir in an oil bath until fully dissolved to prepare a nitrate mixed solution. Weigh 4.2028 g of citric acid monohydrate and dissolve it in a beaker containing 30 mL of deionized water to prepare a citric acid solution. Then, add the citric acid solution dropwise to the nitrate mixed solution at a rate of 2 mL / min. Heat and stir at 80 °C for 2 h, then raise the temperature to 120 °C and continue heating and stirring until the water evaporates to form a foamed gel. Transfer the gel to a muffle furnace for calcination. The calcination procedure is as follows: raise the temperature to 400 °C at a rate of 5 °C / min and hold for 3 h. After calcination, allow it to cool naturally to room temperature to obtain iron-cobalt oxide Fe. 0.02 Co 0.98 O; S2. Weigh 0.1g of iron-cobalt oxide (Fe) at room temperature. 0.02 Co 0.98 O and 0.4 g of Beta molecular sieve were dissolved in a beaker containing 30 mL of deionized water. After stirring for 12 h, the solution was evaporated to dryness at 80 °C, ground, and placed in a tube furnace. Under a mixed atmosphere of 8% H2 / Ar with a gas flow rate of 100 mL / min, the temperature was increased to 300 °C at a rate of 5 °C / min and held for 3 h. After the reduction treatment, the solution was allowed to cool naturally to room temperature to obtain Co. 0 / Fe 0.02 Co 0.98 O-Beta composite catalyst.

[0026] Co 0 / Fe 0.02 Co 0.98 Application test of O-Beta composite catalyst in the demethoxylation of lignin derivative vanillic acid: The application test method is consistent with that in Example 1.

[0027] Example 3 In this embodiment, Fe 0.10 Co 0.90 The preparation method of O-Beta composite catalyst is as follows: S1. Weigh 0.8080 g of iron salt and 5.2385 g of cobalt salt at room temperature and dissolve them in a beaker containing 30 mL of deionized water. Stir in an oil bath until fully dissolved to prepare a nitrate mixed solution. Weigh 4.2028 g of citric acid monohydrate and dissolve it in a beaker containing 30 mL of deionized water to prepare a citric acid solution. Then, add the citric acid solution dropwise to the nitrate mixed solution at a rate of 2 mL / min. Heat and stir at 80°C for 2 hours, then raise the temperature to 120°C and continue heating and stirring until the water evaporates to form a foamed gel. Transfer the gel to a muffle furnace for calcination. The calcination procedure is as follows: raise the temperature to 400°C at a rate of 5°C / min and hold for 3 hours. After calcination, allow it to cool naturally to room temperature to obtain iron-cobalt oxide Fe.0.10 Co 0.90 O; S2. Weigh 0.1g of iron-cobalt oxide (Fe) at room temperature. 0.10 Co 0.90 O and 0.4 g of Beta molecular sieve were dissolved in a beaker containing 30 mL of deionized water and stirred for 12 h. The solution was then evaporated to dryness at 80 °C, ground, and placed in a tube furnace. Under an 8% H₂ / Ar mixed atmosphere with a gas flow rate of 100 mL / min, the temperature was increased to 300 °C at a rate of 5 °C / min and maintained for 3 h. After reduction treatment, the solution was allowed to cool naturally to room temperature to obtain Fe. 0.10 Co 0.90 O-Beta composite catalyst.

[0028] Fe 0.10 Co 0.90 Application test of O-Beta composite catalyst in the demethoxylation of lignin derivative vanillic acid: The application test method is consistent with that in Example 1.

[0029] Example 4 In this embodiment, Fe 0.04 Co 0.96 The preparation method of the O-Beta composite catalyst is the same as in Example 1, except that the hydrogen reduction treatment temperature is 250℃ during the catalyst preparation process.

[0030] Fe 0.04 Co 0.96 Application test of O-Beta composite catalyst in the demethoxylation of lignin derivative vanillic acid: The application test method is consistent with that in Example 1.

[0031] Example 5 In this embodiment, Fe 0.04 Co 0.96 The preparation method of the O-Beta composite catalyst is the same as in Example 1, except that the hydrogen reduction treatment temperature is 350℃ during the catalyst preparation process.

[0032] Fe 0.04 Co 0.96 Application test of O-Beta composite catalyst in the demethoxylation of lignin derivative vanillic acid: The application test method is consistent with that in Example 1.

[0033] Example 6 In this embodiment, Fe 0.04 Co 0.96 The preparation method of the O-Beta composite catalyst is the same as in Example 1.

[0034] Fe 0.04 Co 0.96Application test of O-Beta composite catalyst in demethoxylation of lignin derivative vanillic acid: The application test method is the same as that in Example 1, except that the cycle stability test is performed 5 times, that is, the catalyst is recovered after each performance test for the next performance test.

[0035] Comparative Example 1 In this comparative example, Co 0 The preparation method of the / CoO-Beta composite catalyst is as follows: S1. Weigh 5.8026 g of cobalt salt at room temperature and dissolve it in a beaker containing 30 mL of deionized water. Stir the solution in an oil bath until fully dissolved to obtain a nitrate mixed solution. Weigh 4.2028 g of citric acid monohydrate and dissolve it in a beaker containing 30 mL of deionized water to prepare a citric acid solution. Then, add the citric acid solution dropwise to the nitrate mixed solution at a rate of 2 mL / min. Heat and stir at 80°C for 2 hours, then raise the temperature to 120°C and continue heating and stirring until the water evaporates to form a foamed gel. Transfer the gel to a muffle furnace for calcination. The calcination procedure is as follows: raise the temperature to 400°C at a rate of 5°C / min and hold for 3 hours. After calcination, allow it to cool naturally to room temperature to obtain cobalt oxide Co3O4. S2. Weigh 0.1g of cobalt oxide (Co3O4) and 0.4g of Beta molecular sieve at room temperature and dissolve them in a beaker containing 30mL of deionized water. After stirring for 12 hours, evaporate to dryness at 80℃, grind, and place in a tube furnace. Under an 8% H2 / Ar mixed atmosphere with a gas flow rate of 100mL / min, heat to 300℃ at a rate of 5℃ / min and maintain for 3 hours. After the reduction treatment, allow to cool naturally to room temperature to obtain Co. 0 / CoO-Beta composite catalyst.

[0036] Co 0 Application test of / CoO-Beta composite catalyst in the demethoxylation of lignin derivative vanillic acid: The application test method is consistent with that in Example 1.

[0037] Comparative Example 2 In this comparative example, Co 0 / Fe 0.04 Co 0.96 The preparation method of the O-Beta composite catalyst is the same as in Example 1.

[0038] Co 0 / Fe 0.04 Co 0.96 Application test of O-Beta composite catalyst in the demethoxylation of lignin derivative vanillic acid: The application test method is the same as that in Example 1, except that only 0.4 MPa of hydrogen gas is introduced into the reaction system, and carbon dioxide is not introduced.

[0039] Comparative Example 3 In this comparative example, Fe 0.04 Co 0.96 The preparation method of the O-Beta composite catalyst is the same as in Example 1, except that Fe... 0.04 Co 0.96 No hydrogen reduction treatment was performed during the preparation of the O-Beta composite catalyst.

[0040] Fe 0.04 Co 0.96 Application test of O-Beta composite catalyst in the demethoxylation of lignin derivative vanillic acid: The application test method is consistent with that in Example 1.

[0041] Performance testing 1. The results of the demethoxylation reaction performance of Examples 1-6 and Comparative Examples 1-3 were summarized and the data are recorded in Table 1; 2. The specific surface area and pore structure of different catalysts were characterized using low-temperature nitrogen adsorption-desorption tests of BET and BJH. The test objects here were the composite catalysts prepared in Example 1 and Comparative Example 1, and also included the iron-cobalt oxide Fe in Example 1. 0.04 Co 0.96 O and Beta molecular sieves, the data obtained are recorded in Table 2; Table 1 Results of vanillic acid catalytic demethoxylation reaction. catalyst hydrogen reduction temperature Reaction pressure Conversion rate Yield Example 1 <![CDATA[Co 0 / Fe 0.04 Co 0.96 O-Beta]]> 300℃ <![CDATA[0.4MPaH2+0.4MPaCO2]]> 96.07% 83.54% Example 2 <![CDATA[Co 0 / Fe 0.02 Co 0.98 O-Beta]]> 300℃ <![CDATA[0.4MPaH2+0.4MPaCO2]]> 94.45% 76.79% Example 3 <![CDATA[Fe 0.10 What 0.90 O-Beta]]> 300℃ <![CDATA[0.4MPaH2+0.4MPaCO2]]> 86.70% 70.07% Example 4 <![CDATA[Co 0 / Fe 0.04 Co 0.96 O-Beta]]> 250℃ <![CDATA[0.4MPaH2+0.4MPaCO2]]> 82.16% 67.14% Example 5 <![CDATA[Co 0 / Fe 0.04 Co 0.96 O-Beta]]> 350℃ <![CDATA[0.4MPaH2+0.4MPaCO2]]> 86.99% 61.00% Implementation 6-1 <![CDATA[Co 0 / Fe 0.04 Co 0.96 O-Beta]]> 300℃ <![CDATA[0.4MPaH2+0.4MPaCO2]]> 96.07% 83.54% Implementation 6-2 <![CDATA[Co 0 / Fe 0.04 Co 0.96 O-Beta]]> 300℃ <![CDATA[0.4MPaH2+0.4MPaCO2]]> 96.10% 82.83% Implementation 6-3 <![CDATA[Co 0 / Fe 0.04 Co 0.96 O-Beta]]> 300℃ <![CDATA[0.4MPaH2+0.4MPaCO2]]> 96.00% 83.04% Implementation 6-4 <![CDATA[Co 0 / Fe 0.04 Co 0.96 O-Beta]]> 300℃ <![CDATA[0.4MPaH2+0.4MPaCO2]]> 90.50% 77.92% Implementation 6-5 <![CDATA[Co 0 / Fe 0.04 Co 0.96 O-Beta]]> 300℃ <![CDATA[0.4MPaH2+0.4MPaCO2]]> 85.00% 73.10% Comparative Example 1 <![CDATA[Co 0 / CoO-Beta]]> 300℃ <![CDATA[0.4MPaH2+0.4MPaCO2]]> 95.74% 52.45% Comparative Example 2 <![CDATA[Co 0 / Fe 0.04 Co 0.96 O-Beta]]> 300℃ <![CDATA[0.4MPaH2]]> 86.26% 24.51% Comparative Example 3 <![CDATA[Fe 0.04 What 0.96 O-Beta]]> Not restored <![CDATA[0.4MPaH2+0.4MPaCO2]]> 67.95% 53.49% Table 2. Specific surface area and pore structure properties data. catalyst <![CDATA[Specific surface area / (m 2 ∙g -1 )]]> <![CDATA[Porosity / (cm 3 ∙g -1 )]]> Average pore size (nm) <![CDATA[Co 0 / Fe 0.04 Co 0.96 O-Beta]]> 323.19 0.2072 13.45 <![CDATA[Co 0 / CoO-Beta]]> 340.42 0.1876 11.82 <![CDATA[Fe 0.04 What 0.96 About]]> 41.52 0.1997 19.13 Beta 613.30 0.1729 7.27 As shown in Table 1, based on the substrate conversion rate and product yield as performance indicators, the preferred catalyst is Fe. 0.04 Co 0.96 O-Beta molecular sieve, in which Fe 0.04 Co 0.96 With an O content of 20 wt%, Fe was prepared. 0.04 Co 0.96 The molar ratio of citric acid to metal in O is 1:1. The preferred catalyst reduction temperature is 300℃, the preferred initial reaction pressure is 0.4MPaH2+0.4MPaCO2, and the preferred reaction temperature is 220℃. After 2 hours of reaction, the vanillic acid conversion rate reaches 96.07%, and the yield of the demethoxylated product p-hydroxybenzoic acid reaches 83.54%.

[0042] As can be seen from the data in Table 2, Co 0 / Fe 0.04 Co 0.96 The O-Beta composite catalyst incorporates Fe 0.04 Co 0.96The advantages of both O and Beta molecular sieves are that they have a higher specific surface area and a richer pore structure, making them a microporous + mesoporous composite material, which is beneficial for the dispersion of active metals and improves the catalytic reaction activity.

[0043] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a composite catalyst of iron-cobalt oxide and Beta molecular sieve, characterized in that, The preparation method is as follows: S1. Dissolve iron salt and cobalt salt in deionized water, add citric acid solution dropwise, stir evenly, and heat to evaporate to dryness until a foamy gel is formed. S2. The foamed gel prepared in S1 was placed in a muffle furnace and calcined in air to obtain black iron-cobalt oxide Fe. X Co 1-X O; S3, Fe iron-cobalt oxide X Co 1-X O and Beta molecular sieves are dispersed in deionized water and stirred evenly. After drying and calcination in air, they are reduced in a hydrogen-argon mixed atmosphere to obtain the composite catalyst of iron cobalt oxide and Beta molecular sieve.

2. The method for preparing a composite catalyst of iron-cobalt oxide and Beta molecular sieve according to claim 1, characterized in that, The iron and cobalt salts in S1 are ferric nitrate nonahydrate and cobalt nitrate hexahydrate, respectively. The total concentration of the iron and cobalt salts is 0.67 mol / L. The concentrations of both iron and cobalt salts are less than 0.67 mol / L and greater than 0.67 mol / L. The molar ratio of iron to cobalt is 1:(1~32).

3. The method for preparing a composite catalyst of iron-cobalt oxide and Beta molecular sieve according to claim 1, characterized in that, The citric acid in S1 is citric acid monohydrate, the concentration of the citric acid solution is 70~280g / L, the molar amount of the citric acid is 0.5~2 times the total molar amount of iron and cobalt, and the dropping rate of the citric acid solution is 2~4mL / min.

4. The method for preparing a composite catalyst of iron-cobalt oxide and Beta molecular sieve according to claim 1, characterized in that, The temperature for heating and evaporating S1 to form a foamed gel is 60~140℃, and the time is 2~6h.

5. The method for preparing a composite catalyst of iron-cobalt oxide and Beta molecular sieve according to claim 1, characterized in that, The calcination treatment in S1 is carried out at a temperature of 300~550℃ for 2~5h, and the heating rate of the calcination treatment is 3~10℃ / min.

6. The method for preparing a composite catalyst of iron-cobalt oxide and Beta molecular sieve according to claim 1, characterized in that, In S3, the iron-cobalt oxide Fe X Co 1-X The weight of O accounts for 5-30% of the total weight of the composite catalyst of iron cobalt oxide and Beta molecular sieve. The silicon-to-aluminum ratio of the Beta molecular sieve is (25-50):

1. The stirring time for uniform stirring is 6-24 hours. The drying method is to dry at a temperature of 50-80°C for 6-12 hours.

7. The method for preparing a composite catalyst of iron-cobalt oxide and Beta molecular sieve according to claim 1, characterized in that, In S3, grinding is performed before reduction treatment. The hydrogen volume ratio of the hydrogen-argon mixed atmosphere is 8%, the gas flow rate of the hydrogen-argon mixed atmosphere is 40~150mL / min, the temperature of the reduction treatment is 200~400℃, the reduction treatment time is 2~4h, and the heating rate of the reduction treatment is 3~10℃ / min.

8. The application of the iron-cobalt oxide and Beta molecular sieve composite catalyst prepared by the method according to any one of claims 1-7 in the demethoxylation of lignin derivative vanillic acid, characterized in that, The method of application is as follows: In a high-pressure batch reactor, using solvent as the reaction medium, and under the conditions of a temperature of 200~250℃ and an initial pressure of 0~1.2MPa, the lignin derivative vanillic acid undergoes a demethoxylation reaction under the catalytic action of the iron-cobalt oxide and Beta molecular sieve composite catalyst.

9. The application of the iron-cobalt oxide and Beta molecular sieve composite catalyst according to claim 8 in the demethoxylation of lignin derivative vanillic acid, characterized in that, The solvent is methanol, and the ratio of the solvent to the lignin derivative vanillic acid is 20:(0.05~0.3) mL / g. The weight ratio of the lignin derivative vanillic acid to the iron-cobalt oxide to the Beta molecular sieve composite catalyst is (0.05~0.30):(0.05~0.30).

10. The application of the iron-cobalt oxide and Beta molecular sieve composite catalyst according to claim 8 in the demethoxylation of lignin derivative vanillic acid, characterized in that, The initial hydrogen pressure is 0 ~ 0.6 MPa, the initial carbon dioxide pressure is 0 ~ 0.6 MPa, the catalytic time of the catalyst is 1 ~ 4 h, and the catalytic temperature of the catalyst is 220 °C.

Images