Preparation method and application of ruthenium-loaded reconstructed cobalt-magnesium-aluminum hydrotalcite catalyst

Abstract

The invention discloses a preparation method and application of a ruthenium-loaded reconstructed cobalt-magnesium-aluminum hydrotalcite catalyst, and belongs to the technical field of catalyst preparation and application. The preparation method comprises the following steps: doping Co in MgAl hydrotalcite by adopting a hydrothermal method to prepare CoMgAl-LDH, then calcining and rehydrating the hydrotalcite, and loading ruthenium nanoparticles by adopting an impregnation reduction method to prepare the Ru / CoMgAl-RLDH catalyst. The hydrotalcite is calcined and hydrated, so that the reconstructed hydrotalcite enriches alkaline sites on the surface of the catalyst, the specific surface area of the catalyst is increased, and the catalytic activity is improved by doping a proper amount of cobalt. The preparation method of the catalyst is simple, the 5-hydroxymethylfurfural is efficiently and selectively oxidized under the mild condition without adding liquid caustic soda, the conversion rate of the 5-hydroxymethylfurfural reaches 100%, the yield of the 2, 5-furandicarboxylic acid is 87.6%, and the catalyst has potential application value for large-scale production of the 2, 5-furandicarboxylic acid.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalyst preparation and application, and particularly relates to a preparation method and application of a ruthenium-loaded reconstructed cobalt-magnesium-aluminum hydrotalcite catalyst. Background Art

[0002] In recent years, the selective oxidation of biomass-derived platform chemicals into valuable commodity chemicals has attracted a great deal of attention in the catalytic community. 5-Hydroxymethylfurfural can be synthesized by dehydration of C6 carbohydrates, and many excellent compounds can be produced using 5-hydroxymethylfurfural. One of the downstream products formed by the oxidation of 5-hydroxymethylfurfural, 2,5-furandicarboxylic acid, is a key monomer for the production of bio-based polyethylene furandicarboxylate (PEF), and is an emerging ideal alternative to traditional petroleum-based polyethylene terephthalate (PET).

[0003] As is well known, the synthesis of 2,5-furandicarboxylic acid by the selective oxidation of 5-hydroxymethylfurfural requires multiple consecutive steps, including the oxidation of the hydroxyl group and the aldehyde group in 5-hydroxymethylfurfural, which poses high requirements for the design and performance of the catalyst. In the reaction of catalytic oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid with the addition of a base, the addition of liquid base can improve the yield of 2,5-furandicarboxylic acid. However, from an industrial perspective, the addition of excessive base may lead to the degradation of 5-hydroxymethylfurfural and increase the cost of the separation step. Therefore, the design of a solid base catalyst to replace liquid base is of great significance for the selective oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid.

[0004] Hydrotalcite is a common solid base catalyst, which is a type of anionic clay mineral with layered hydroxides (LDHs), consisting of a positively charged main layer with metal hydroxides and an exchangeable interlayer region with compensating anions and solvated molecules. The general formula of layered hydroxides can be written as where M 2+ and M 3 + represent divalent and trivalent metal cations, A n- is the interlayer anion, x represents the proportion of trivalent metal cations (usually 0.2 < x < 0.33), and m is defined as the number of solvated molecules (usually water). The base strength of hydrotalcite can be controlled by adjusting the properties of metal ions and the preparation method. The metal elements in its lamellar structure are adjustable, and the interlayer anions are exchangeable. The tunability of this structure gives it flexibility in a variety of catalytic reactions and enables optimization according to different reaction requirements.

[0005] It is reported that Li et al. synthesized the catalyst AuPd / LaCaMgAl-LDH by loading Au and Pd on La-doped CaMgAl layered hydroxide as the carrier. Under the reaction conditions of a temperature of 120 °C, a time of 6 h, and 0.5 MPa O2, the conversion rate of 5-hydroxymethylfurfural was 100%, and the selectivity to 2,5-furandicarboxylic acid reached 99%. The synergistic effect of bimetallic Au and Pd nanoparticles and the alkalinity on the surface of the LaCaMgAl-LDH carrier both play important roles in improving the catalytic performance. Gorbanev et al. prepared a Ru(OH) 2 / g Ru(OH) x / HT catalyst for the oxidation of 5-hydroxymethylfurfural. At 1 bar O2 and 140 °C for about 37 h, the yield of 2,5-furandicarboxylic acid was higher than 90%. However, HT was slightly dissolved during the reaction and reacted with 2,5-furandicarboxylic acid, and the stability of the catalyst needs to be improved. Xia et al. loaded a series of bimetallic Pd-Au nanoparticles with different ratios on the reconstructed MgAl hydrotalcite to prepare the catalyst Pd-Au / HT. When Au / Pd = 4, the O2 flow rate was 60 mL / min, and the reaction was carried out at 60 °C for 6 h. The conversion rate of 5-hydroxymethylfurfural was 100%, and the yield of 2,5-furandicarboxylic acid could reach over 90%. The reaction conditions involved the simultaneous addition of liquid base and solid base, which not only increased the cost but also increased the difficulty of separating the subsequent 2,5-furandicarboxylic acid product. The calcination temperature of this hydrotalcite was 550 °C. During the reconstruction process of the hydrotalcite, too high a calcination temperature affected the restoration of the hydrotalcite to the layered structure.

[0006] Problems existing in the reported reaction system for the oxidation of 5-hydroxymethylfurfural to synthesize 2,5-furandicarboxylic acid include the addition of liquid base, high price of active components, and the need to improve the stability of the catalyst. Therefore, there is an urgent need for a new technical solution in the prior art to solve this problem. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a preparation method and application of a ruthenium-loaded reconstructed cobalt magnesium aluminum hydrotalcite catalyst to solve the technical problems such as the addition of liquid base, high price of active components, and the need to improve the stability of the catalyst in the reaction system for the oxidation of 5-hydroxymethylfurfural to synthesize 2,5-furandicarboxylic acid in the prior art.

[0008] The technical solution adopted by the present invention is a preparation method of a ruthenium-loaded reconstructed cobalt magnesium aluminum hydrotalcite catalyst, which includes the following steps:

[0009] Step A1: Preparation of CoMgAl-LDH

[0010] Prepare CoMgAl-LDH hydrotalcite by hydrothermal method. Under stirring conditions, add urea dropwise to the mixed metal salt solution of Co(NO3)2·6H2O, Mg(NO3)2·6H2O and Al(NO3)3·9H2O. After the hydrothermal reaction of the mixture in the reaction kettle is completed, let it cool naturally to room temperature. After centrifugal filtration and repeated washing with water, the obtained precipitate is dried to obtain CoMgAl-LDH hydrotalcite;

[0011] Step A2: Preparation of CoMgAl-LDO

[0012] Calcine the prepared CoMgAl-LDH hydrotalcite and then grind it to obtain cobalt-magnesium-aluminum mixed oxide CoMgAl-LDO;

[0013] Step A3: Loading of active components

[0014] Use the impregnation-reduction method to load ruthenium nanoparticles as active components on the prepared CoMgAl-LDO support, and at the same time carry out rehydration. Specifically:

[0015] Disperse the cobalt-magnesium-aluminum mixed oxide CoMgAl-LDO support by impregnation under stirring in an aqueous solution of RuCl3·3H2O, place it in an ice-water bath, and dropwise add an aqueous solution of NaBH4 containing NaOH to the dispersion of ruthenium trichloride and the support, continue stirring and reducing for a certain time, filter by suction and wash until neutral, and obtain the rehydrated ruthenium-loaded reconstructed cobalt-magnesium-aluminum hydrotalcite catalyst after vacuum drying.

[0016] In the step A1, the molar ratio of Co(NO3)2·6H2O, Mg(NO3)2·6H2O, and Al(NO3)3·9H2O is 0.5:2.5:1 or 1:2:1 or 1.5:1.5:1 or 2:1:1 or 2.5:0.5:1.

[0017] In the step A1, take a total of 12 mmol of Co(NO3)2·6H2O, Mg(NO3)2·6H2O, and Al(NO3)3·9H2O, and dissolve them in 30 mL of deionized water to obtain a mixed salt solution;

[0018] The urea is obtained by dissolving 24 mmol of urea in 30 mL of deionized water to obtain a urea solution, and then adding all the urea solution dropwise to the mixed salt solution;

[0019] For the reaction kettle, the hydrothermal temperature is 120 °C to 180 °C, and the hydrothermal time is 20 h to 24 h.

[0020] In the step A2, the calcination temperature is 300 °C to 500 °C, and the calcination time is 3 h to 6 h.

[0021] In the step A3, the loading amount of ruthenium Ru accounts for 1 wt% to 5 wt% of the carrier. The catalysts with different ruthenium Ru loading amounts are denoted as Ru z / CoMgAl-RLDH, where z represents the mass percentage of the Ru loading amount in the carrier, and z = 1, 2, 3, 4, 5.

[0022] In the step A3, the impregnation and dispersion time is 10 h to 24 h; the molar ratio of Ru in RuCl3·3H2O 3+ to BH4ˉ in NaBH4 is 1:15 to 1:25; the concentration of NaBH4 is 1 mol / L to 2 mol / L, the concentration of the NaOH aqueous solution is 0.3 wt% to 0.7 wt%, and the reduction time is 10 h to 24 h.

[0023] Application of a ruthenium-loaded reconstructed cobalt-magnesium-aluminum hydrotalcite catalyst prepared by the above method in the selective oxidation of 5-hydroxymethylfurfural to synthesize 2,5-furandicarboxylic acid.

[0024] The selective oxidation of 5-hydroxymethylfurfural to synthesize 2,5-furandicarboxylic acid includes the following steps:

[0025] Add 5-hydroxymethylfurfural, deionized water, and a ruthenium-loaded reconstructed cobalt-magnesium-aluminum hydrotalcite catalyst to the reaction kettle, then charge oxygen into it, and carry out the reaction under the conditions of heating and stirring. After the reaction, cool to room temperature, open the air release valve to discharge the gas, and filter out the catalyst; the obtained reaction solution is diluted with pure water, and the diluted reaction solution is analyzed by high performance liquid chromatography, so as to calculate the conversion rate of the raw material 5-hydroxymethylfurfural and the yield of the target product 2,5-furandicarboxylic acid.

[0026] The usage amounts of the 5-hydroxymethylfurfural, deionized water, and the ruthenium-loaded reconstructed cobalt-magnesium-aluminum hydrotalcite catalyst are as follows: dissolve 25.2 mg of 5-hydroxymethylfurfural in 5 mL of deionized water, and the ruthenium-loaded reconstructed cobalt-magnesium-aluminum hydrotalcite catalyst is 0.04 g to 0.12 g, the oxygen pressure is 0 MPa to 1 MPa, the reaction temperature is 90 °C to 140 °C, and the reaction time is 8 h to 24 h.

[0027] Through the above design scheme, the present invention can bring the following beneficial effects:

[0028] (1) In the present invention, Co is doped into MgAl hydrotalcite to prepare CoMgAl-LDH as a precursor. The original hydrotalcite is calcined and rehydrated by using the "memory effect" of the hydrotalcite. While rehydrating, ruthenium nanoparticles are loaded by the impregnation reduction method to prepare the catalyst Ru / CoMgAl-RLDH. The hydrotalcite can significantly improve the thermal stability of the catalyst after being calcined and then rehydrated, and at the same time significantly increase the specific surface area of the catalyst, and doping an appropriate amount of cobalt is beneficial to improving the catalytic activity.

[0029] (2) Conventional hydrotalcites in the prior art generally only have weak basic sites. In the present invention, the hydrotalcite is calcined and then rehydrated, so that the reconstructed hydrotalcite has both weak basic sites and medium-strong basic sites, enriching the basic sites on the catalyst surface. By changing the preparation conditions, the basic sites of the catalyst can be adjusted. Using the Ru / CoMgAl-RLDH catalyst in the reaction process can avoid adding liquid alkali to the system. Oxidize 5-hydroxymethylfurfural under the condition of no liquid alkali. Charge 1.0 MPa O2 into the reaction kettle and react at 110 °C for 10 h. The conversion rate of 5-hydroxymethylfurfural is 100%, and the yield of 2,5-furandicarboxylic acid can reach 87.6%. This provides an idea for the selective oxidation reaction of reconstructed hydrotalcite in an alkali-free system and has potential application value for the large-scale production of 2,5-furandicarboxylic acid. The catalyst preparation process in the present invention is simple and has good stability, and has good industrial application prospects. Description of the Drawings

[0030] Figure 1 SEM image of the Ru4 / Co1Mg2Al1-RLDH catalyst prepared in Example 2 of the preparation method and application of a ruthenium-loaded reconstructed cobalt-magnesium-aluminum hydrotalcite catalyst of the present invention;

[0031] Figure 2 Thermogravimetric comparison chart of the reconstructed hydrotalcite Ru4 / Co1Mg2Al1-RLDH after calcination and rehydration and the uncalcined hydrotalcite Ru4 / Co1Mg2Al1-LDH in the preparation method and application of a ruthenium-loaded reconstructed cobalt-magnesium-aluminum hydrotalcite catalyst of the present invention. Detailed Embodiments

[0032] The present invention will be further described below in conjunction with the drawings and specific embodiments:

[0033] Example 1:

[0034] Example 1 of the present invention discloses a preparation method of a ruthenium-loaded reconstructed cobalt-magnesium-aluminum hydrotalcite catalyst, and the specific steps are as follows:

[0035] Co 0.5 Mg 2.5Preparation of Al1-LDH: A total of 12 mmol of Co(NO3)2·6H2O, Mg(NO3)2·6H2O, and Al(NO3)3·9H2O were dissolved in 30 mL of deionized water to obtain a mixed salt solution according to the molar ratio of Co(NO3)2·6H2O, Mg(NO3)2·6H2O, and Al(NO3)3·9H2O of 0.5:2.5:1. At the same time, 24 mmol of urea was dissolved in 30 mL of deionized water. The urea solution was slowly added dropwise to the mixed salt solution under stirring. The reaction kettle containing the mixture was hydrothermally treated at 120 °C for 24 h. After the hydrothermal treatment, it was allowed to cool naturally to room temperature, centrifuged and filtered, and then the obtained precipitate was dried at 80 °C for 12 h to obtain a hydrotalcite named Co 0.5 Mg 2.5 Al1-LDH.

[0036] Co 0.5 Mg 2.5 Preparation of Al1-LDO: The hydrotalcite Co 0.5 Mg 2.5 Al1-LDH was placed in a muffle furnace and calcined at 400 °C for 4 h, and then ground to obtain a cobalt-magnesium-aluminum mixed oxide, named Co 0.5 Mg 2.5 Al1-LDO.

[0037] Loading of active components: A certain amount of RuCl3·3H2O was weighed according to the Ru loading of 4 wt% of the support Co 0.5 Mg 2.5 Al1-LDO, added to 12.5 mL of deionized water, and fully dissolved. 0.5 g of the catalyst support Co 0.5 Mg 2.5 Al1-LDO was dispersed therein, and impregnated and dispersed under stirring in a cold water bath for 12 h. According to the molar ratio of BH4 - in NaBH4 to Ru 3+ in RuCl3·3H2O of 20:1, NaBH4 was weighed and dissolved in a 0.5 wt% NaOH aqueous solution to satisfy the NaBH4 concentration of 1.5 mol / L. Then, the NaBH4 aqueous solution containing NaOH was added dropwise to the dispersion of ruthenium trichloride and the support under stirring in an ice water bath and continued to stir and reduce for 12 h. The solid powder was filtered, washed until the filtrate was neutral, and dried in vacuo at 60 °C for 12 h to obtain a ruthenium-loaded reconstructed cobalt-magnesium-aluminum hydrotalcite catalyst, named Ru4 / Co 0.5 Mg 2.5 Al1-RLDH.

[0038] Example 2:

[0039] Example 2 of the present invention discloses a preparation method of a ruthenium-loaded reconstructed cobalt-magnesium-aluminum hydrotalcite catalyst, and the specific steps are as follows:

[0040] Preparation of Co1Mg2Al1-LDH: A total of 12 mmol of Co(NO3)2·6H2O, Mg(NO3)2·6H2O, and Al(NO3)3·9H2O were dissolved in 30 mL of deionized water according to the molar ratio of Co(NO3)2·6H2O, Mg(NO3)2·6H2O, and Al(NO3)3·9H2O of 1:2:1 to obtain a mixed salt solution. At the same time, 24 mmol of urea was dissolved in 30 mL of deionized water. The urea solution was slowly added dropwise to the mixed salt solution under stirring conditions. The reaction kettle containing the mixture was hydrothermally treated at 120 °C for 24 h. After the hydrothermal treatment, when it was naturally cooled to room temperature, the obtained precipitate was centrifuged, filtered, washed repeatedly with water, and then dried at 80 °C for 12 h to obtain a hydrotalcite named Co1Mg2Al1-LDH.

[0041] Preparation of Co1Mg2Al1-LDO: The hydrotalcite Co1Mg2Al1-LDH was placed in a muffle furnace and calcined at 400 °C for 4 h, and then ground to obtain a cobalt-magnesium-aluminum mixed oxide, named Co1Mg2Al1-LDO.

[0042] Loading of the active component: A certain amount of RuCl3·3H2O was weighed according to the ruthenium loading of 4 wt% of the support Co1Mg2Al1-LDO, added to 12.5 mL of deionized water, and fully dissolved. 0.5 g of the catalyst support Co1Mg2Al1-LDO was dispersed therein, and impregnated and dispersed under stirring in a cold water bath for 12 h. According to the molar ratio of BH4 in NaBH4 - to Ru in RuCl3·3H2O 3+ of 20:1, NaBH4 was weighed and dissolved in a 0.5 wt% NaOH aqueous solution to satisfy a NaBH4 concentration of 1.5 mol / L. Then, the NaBH4 aqueous solution containing NaOH was slowly added dropwise to the dispersion of ruthenium trichloride and the support under stirring in an ice-water bath and continued to stir and reduce for 12 h. The solid powder was filtered, washed until the filtrate was neutral, and dried in vacuo at 60 °C for 12 h to obtain a ruthenium-loaded reconstructed cobalt-magnesium-aluminum hydrotalcite catalyst, named Ru4 / Co1Mg2Al1-RLDH.

[0043] In this example, the SEM image of Ru4 / Co1Mg2Al1-RLDH is shown in Figure 1 .

[0044] Example 3:

[0045] Example 3 of the present invention discloses a preparation method of an uncalcined ruthenium-loaded cobalt-magnesium-aluminum hydrotalcite catalyst, and the specific steps are as follows:

[0046] Preparation of Co1Mg2Al1-LDH: A total of 12 mmol of Co(NO3)2·6H2O, Mg(NO3)2·6H2O, and Al(NO3)3·9H2O were dissolved in 30 mL of deionized water according to the molar ratio of Co(NO3)2·6H2O, Mg(NO3)2·6H2O, and Al(NO3)3·9H2O of 1:2:1 to obtain a mixed salt solution. At the same time, 24 mmol of urea was dissolved in 30 mL of deionized water. The urea solution was slowly added dropwise to the mixed salt solution under stirring conditions. The reaction kettle containing the mixture was hydrothermally treated at 120 °C for 24 h. After the hydrothermal treatment, when it was naturally cooled to room temperature, it was centrifuged, filtered, washed repeatedly with water, and the obtained precipitate was dried at 80 °C for 12 h to obtain a hydrotalcite named Co1Mg2Al1-LDH.

[0047] Loading of active components: A certain amount of RuCl3·3H2O was weighed according to the Ru loading of 4 wt% of the support Co1Mg2Al1-LDH, added to 12.5 mL of deionized water, and fully dissolved. 0.5 g of the catalyst support Co1Mg2Al1-LDH was dispersed therein, and impregnated and dispersed under stirring in a cold water bath for 12 h. According to the molar ratio of BH4 in NaBH4 - to Ru in RuCl3·3H2O 3+ of 20:1, NaBH4 was weighed and dissolved in a 0.5 wt% NaOH aqueous solution to satisfy the concentration of NaBH4 of 1.5 mol / L. Then, the NaBH4 aqueous solution containing NaOH was gradually added dropwise to the dispersion of ruthenium trichloride and the support under stirring in an ice-water bath and continued to stir and reduce for 12 h. The solid powder was filtered, washed until the filtrate was neutral, and dried in vacuo at 60 °C for 12 h to obtain an uncalcined ruthenium-loaded cobalt-magnesium-aluminum hydrotalcite catalyst, named Ru4 / Co1Mg2Al1-LDH.

[0048] Example 4:

[0049] Each catalyst was used in the reaction of oxidizing 5-hydroxymethylfurfural to synthesize 2,5-furandicarboxylic acid. The specific steps were as follows:

[0050] Oxidation of 5-hydroxymethylfurfural: 25.2 mg of 5-hydroxymethylfurfural, 5 mL of deionized water, and 0.1 g of the catalyst were added to the reaction kettle, and then 1.0 MPa of oxygen was charged into it. The reaction was carried out at 120 °C with heating and stirring for 12 h. After the reaction, it was cooled to room temperature, the gas release valve was opened to discharge the gas, and the catalyst was filtered out. The obtained reaction solution was diluted with pure water, and the diluted reaction solution was analyzed by high performance liquid chromatography to calculate the conversion rate of the raw material 5-hydroxymethylfurfural and the yield of the target product 2,5-furandicarboxylic acid.

[0051] Liquid phase test conditions: UV detector, Poroshell 120 (3.0 mm × 150 mm, 2.7 μm) C18 chromatographic column was selected as the chromatographic column, 0.1 wt% formic acid aqueous solution: acetonitrile = 95:5 was used as the mobile phase. The mobile phase started to change at 0.5 min and reached 0.1 wt% formic acid aqueous solution: acetonitrile = 60:40 until 4.5 min. The column temperature was 30 °C, the injection volume was 5 μL, the peak position and peak area were recorded, and external standard method was used for quantitative analysis.

[0052] Examples 5, 6, 7, 8, 9, 10, 11:

[0053] The Hammett indicator titration method was used to qualitatively and quantitatively analyze the basic properties of hydrotalcite. Bromothymol blue was used to confirm the total number of basic sites. The total basic sites were divided into strong bases and weak bases. In order to analyze medium-strong basic sites and strong basic sites, phenolphthalein indicator and Orange G indicator were used respectively, and the number of weak base sites was calculated by subtracting the number of strong base sites from the total number of basic sites. The base amount results of the catalysts are shown in Table 1.

[0054] Table 1 Determination of the base amount of the catalyst

[0055]

[0056]

[0057] As shown in Table 1, the total surface basic amount of the Co1Mg2Al1-LDH catalyst was 0.25 mmol / g, and all were weak basic sites. The total surface base amount of the uncalcined Ru4 / Co1Mg2Al1-LDH catalyst was 0.24 mmol / g, and all were weak basic sites. The total surface base amount of the Ru4 / Co1Mg2Al1-RLDH catalyst obtained after calcination and rehydration was 0.37 mmol / g, among which the weak base amount was 0.21 mmol / g and the medium-strong base amount was 0.16 mmol / g. It can be seen that the original hydrotalcite generally only has weak basic sites, but after the hydrotalcite is calcined and rehydrated, it has both weak basic sites and medium-strong basic sites, providing richer basic sites for the reaction. The catalysts constructed with different cobalt-magnesium-aluminum molar ratios in the reconstructed hydrotalcite have different base amounts on the surface. Among them, the total surface basic amount of the Ru4 / Co 0.5 Mg 2.5 Al1-RLDH catalyst reached 0.41 mmol / g, which was much larger than the surface base amounts of other catalysts; when the Co content continued to increase, the base amount on the surface of the catalyst also decreased accordingly. When the Co:Mg:Al ratio was 2.5:0.5:1, Ru4 / Co 2.5 Mg 0.5The total basic amount on the surface of the Al1-RLDH catalyst decreased to 0.18 mmol / g.

[0058] Examples 12, 13, 14, 15, 16, 17, 18:

[0059] Table 2 Specific surface area of the catalyst

[0060]

[0061] As shown in Table 2, the specific surface area of Co1Mg2Al1-LDH is 9.2 m 2 / g. The specific surface area of the hydrotalcite that was directly rehydrated without calcination, Ru4 / Co1Mg2Al1-LDH, is 8.6 m 2 / g. When the hydrotalcite was calcined and then rehydrated to obtain Ru4 / Co1Mg2Al1-RLDH, the specific surface area of the catalyst was 130.0 m 2 / g. The specific surface area of the hydrotalcite that was calcined and then rehydrated is higher than that of the original hydrotalcite. The specific surface area of Ru4 / Co 0.5 Mg 2.5 Al1-RLDH is 118.5 m 2 / g. As the Co content in the catalyst increases, the specific surface area gradually increases. When the Co:Mg:Al ratio is 2.5:0.5:1, the specific surface area of the catalyst Ru4 / Co 2.5 Mg 0.5 Al1-RLDH increases to 152.6 m 2 / g.

[0062] Examples 19, 20, 21, 22 and 23:

[0063] Under the same reaction conditions as in Example 4, catalytic reactions were carried out on the reconstructed cobalt-magnesium-aluminum hydrotalcite catalysts loaded with ruthenium with different cobalt-magnesium-aluminum molar ratios, and the reaction results are shown in Table 3.

[0064] Table 3 Influence of different cobalt-magnesium-aluminum molar ratios on catalytic performance

[0065]

[0066] Table 3 shows the catalytic results for different cobalt-magnesium-aluminum molar ratios. It can be seen that Ru4 / Co1Mg2Al1-RLDH with a cobalt-magnesium-aluminum molar ratio of 1:2:1 has the best catalytic effect as a catalyst, with an HMF conversion rate of 100%, an FDCA yield of 65.1%, a by-product HFCA yield of 1.5%, and an FFCA yield of 6.5%. This shows that doping an appropriate amount of cobalt is beneficial to the selective oxidation of HMF to FDCA.

[0067] Among them, HMF represents 5-hydroxymethylfurfural, FDCA represents 2,5-furandicarboxylic acid, HFCA represents 5-hydroxymethyl-2-furoic acid, and FFCA represents 5-formyl-2-furoic acid.

[0068] Examples 24 and 25:

[0069] Under the same reaction conditions as in Example 20, the Ru4 / Co1Mg2Al1-RLDH catalyst was used for the catalytic reaction. When the calcination temperature of the support was different, the reaction results are shown in Table 4.

[0070] Table 4 Influence of the support calcination temperature on the catalytic performance

[0071]

[0072]

[0073] Table 4 shows the catalytic results at different calcination temperatures of the support. When the calcination temperature of the support was 300 °C, HMF was completely converted, and the yield of FDCA was 57.6%. When the calcination temperature of the support was 400 °C, HMF was completely converted, and the highest yield of FDCA was 65.1%. As the calcination temperature of the support continued to increase, the yield of FDCA also decreased. When the calcination temperature of the support was 500 °C, the catalyst activity decreased, and the yield of FDCA decreased to 50.9%.

[0074] Examples 26, 27, 28, 29, and 30:

[0075] Under the same reaction conditions as in Example 20, the Ru4 / Co1Mg2Al1-RLDH catalyst was used for the reaction under different reaction temperature conditions. The reaction results are shown in Table 5.

[0076] Table 5 Influence of the reaction temperature on the catalytic performance

[0077]

[0078] Table 5 shows the catalytic results at different reaction temperatures. When the reaction temperature was 90 °C, the conversion rate of HMF was 85.2%. When the reaction temperature was 100 °C, the conversion rate of HMF was 100%. HMF could be completely converted between 100 °C and 140 °C. As the temperature increased, the yield of FDCA showed a trend of first increasing and then decreasing. When the temperature was 110 °C, the yield of FDCA was the highest, reaching 75.6%. At this time, the yield of the by-product HFCA was 1.1%, and the yield of FFCA was 1.4%.

[0079] Examples 31, 32, 33, 34, 35, and 36:

[0080] The reaction conditions were the same as those in Example 28, and the reaction was carried out using the Ru4 / Co1Mg2Al1-RLDH catalyst under different reaction time conditions. The reaction results are shown in Table 6.

[0081] Table 6 Influence of reaction time on catalytic performance

[0082]

[0083]

[0084] Table 6 shows the catalytic results at different reaction times. As the reaction time increased, the conversion rate of HMF continuously increased. When the reaction time was 8 h, HMF was completely converted, and the yield of FDCA was 72.3%. When the reaction time was 10 h, the yield of FDCA was 82.5%, and at this time, the yield of by-product HFCA was 1.3% and the yield of FFCA was 1.9%. When the reaction time continued to extend, the yield of FDCA decreased.

[0085] Examples 37, 38, 39:

[0086] The reaction conditions were the same as those in Example 35, and an oxidation reaction was carried out using the Ru4 / Co1Mg2Al1-RLDH catalyst. When the catalyst dosage was different, the reaction results are shown in Table 7.

[0087] Table 7 Influence of catalyst dosage on catalytic performance

[0088]

[0089] Table 7 shows the catalytic results at different catalyst dosages. When 0.06 g of catalyst was added to the reaction system, HMF could be completely converted, and at this time, the yield of FDCA was 75.4%. When 0.08 g of catalyst was added to the reaction system, an 87.6% FDCA yield was obtained, and at this time, the yield of by-product HFCA was 1.7% and the yield of FFCA was 2.4%. When the catalyst dosage was continuously increased, the yield of FDCA gradually decreased. When the catalyst dosage was 0.12 g, the FDCA yield decreased to 70.9%.

[0090] The implementation manners of the present invention are not limited by the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement manners and are all included in the protection scope of the present invention.

Claims

1. A preparation method of a ruthenium-loaded reconstructed cobalt-magnesium-aluminum hydrotalcite catalyst, characterized in that: It includes the following steps: Step A1: Preparation of CoMgAl-LDH Prepare CoMgAl-LDH hydrotalcite by hydrothermal method. Under stirring conditions, drop urea into the mixed metal salt solution of Co(NO3)2·6H2O, Mg(NO3)2·6H2O and Al(NO3)3·9H2O. After the hydrothermal reaction of the reaction kettle containing the mixture is completed, let it cool naturally to room temperature. After centrifugation, filtration and repeated washing with water, the obtained precipitate is dried to obtain CoMgAl-LDH hydrotalcite; Step A2: Preparation of CoMgAl-LDO The prepared CoMgAl-LDH hydrotalcite is calcined and ground to obtain cobalt-magnesium-aluminum mixed oxide CoMgAl-LDO; Step A3: Loading of active components Use the impregnation-reduction method to load ruthenium nanoparticles as active components on the prepared CoMgAl-LDO support, and at the same time carry out rehydration. Specifically: Under stirring conditions, immerse and disperse the cobalt-magnesium-aluminum mixed oxide CoMgAl-LDO support in the RuCl3·3H2O aqueous solution, place it in an ice-water bath, and drop the NaBH4 aqueous solution containing NaOH into the dispersion of ruthenium trichloride and the support drop by drop. Continue to stir and reduce for a certain time, filter and wash until neutral, and obtain the rehydrated ruthenium-loaded reconstructed cobalt-magnesium-aluminum hydrotalcite catalyst after vacuum drying.

2. The preparation method of a ruthenium-loaded reconstructed cobalt-magnesium-aluminum hydrotalcite catalyst according to claim 1, characterized in that: In the said step A1, the molar ratio of Co(NO3)2·6H2O, Mg(NO3)2·6H2O, Al(NO3)3·9H2O is 0.5:2.5:1 or 1:2:1 or 1.5:1.5:1 or 2:1:1 or 2.5:0.5:

1.

3. The preparation method of a ruthenium-loaded reconstructed cobalt-magnesium-aluminum hydrotalcite catalyst according to claim 2, characterized in that: In the said step A1, a total of 12 mmol of Co(NO3)2·6H2O, Mg(NO3)2·6H2O, Al(NO3)3·9H2O are taken and dissolved in 30 mL of deionized water to obtain a mixed salt solution; The urea is obtained by dissolving 24 mmol of urea in 30 mL of deionized water to obtain a urea solution, and the urea solution is all dropped into the mixed salt solution; For the said reaction kettle, the hydrothermal temperature is 120°C to 180°C, and the hydrothermal time is 20 h to 24 h.

4. The preparation method of a ruthenium-loaded reconstructed cobalt-magnesium-aluminum hydrotalcite catalyst according to claim 1, characterized in that: In the said step A2, the calcination temperature is 300°C to 500°C, and the calcination time is 3 h to 6 h.

5. The preparation method of a ruthenium-loaded reconstructed cobalt-magnesium-aluminum hydrotalcite catalyst according to claim 1, characterized in that: In the said step A3, the loading amount of ruthenium Ru accounts for 1 wt% to 5 wt% of the carrier. The catalysts with different ruthenium Ru loading amounts are denoted as Ru z / CoMgAl-RLDH, where z represents the mass percentage of the ruthenium Ru loading amount in the carrier, and z = 1, 2, 3, 4, 5.

6. The preparation method of a ruthenium-loaded reconstructed cobalt-magnesium-aluminum hydrotalcite catalyst according to claim 1, characterized in that: In the step A3, the impregnation and dispersion time is 10 h to 24 h; the molar ratio of Ru in RuCl3·3H2O 3+ to BH4ˉ in NaBH4 is 1:15 to 1:25; the concentration of NaBH4 is 1 mol / L to 2 mol / L, the concentration of the NaOH aqueous solution is 0.3 wt% to 0.7 wt%, and the reduction time is 10 h to 24 h.

7. Use of a ruthenium-loaded reconstructed cobalt-magnesium-aluminum hydrotalcite catalyst prepared by the method according to claim 1, characterized in that: It is applied to the selective oxidation of 5-hydroxymethylfurfural to synthesize 2,5-furandicarboxylic acid.

8. Use of a ruthenium-loaded reconstructed cobalt-magnesium-aluminum hydrotalcite catalyst according to claim 7, characterized in that: The selective oxidation of 5-hydroxymethylfurfural to synthesize 2,5-furandicarboxylic acid includes the following steps: Add 5-hydroxymethylfurfural, deionized water, and ruthenium-loaded reconstructed cobalt-magnesium-aluminum hydrotalcite catalyst into the reaction kettle, and then charge oxygen into it. React under the conditions of heating and stirring. After the reaction, cool to room temperature, open the air release valve to discharge the gas, and filter out the catalyst; the obtained reaction solution is diluted with pure water, and the diluted reaction solution is analyzed by high performance liquid chromatography, so as to calculate the conversion rate of the raw material 5-hydroxymethylfurfural and the yield of the target product 2,5-furandicarboxylic acid.

9. Use of a ruthenium-loaded reconstructed cobalt-magnesium-aluminum hydrotalcite catalyst according to claim 8, characterized in that: The usage amounts of the 5-hydroxymethylfurfural, deionized water, and the ruthenium-loaded reconstructed cobalt-magnesium-aluminum hydrotalcite catalyst are as follows: 25.2 mg of 5-hydroxymethylfurfural is dissolved in 5 mL of deionized water, and the ruthenium-loaded reconstructed cobalt-magnesium-aluminum hydrotalcite catalyst is 0.04 g to 0.12 g, the oxygen pressure is 0 MPa to 1 MPa, the reaction temperature is 90 °C to 140 °C, and the reaction time is 8 h to 24 h.

Images