[0037] Example 1:
[0038] 1. Oxygen-deficient rod-like core-shell structure 650℃-Au/2L-ZrO 2 Preparation of @HNTs catalysts.
[0039] (1) Weigh 40g of HNTs into a three-necked flask, measure 250mL of HNO with a graduated cylinder 3 The solution was placed in a three-necked flask. Then it was placed in an oil bath and a reflux condensing device was installed, and stirred at 75° C. for 12 h. After the reaction was completed, the obtained reaction mixture was washed with deionized water until neutral, and then collected by centrifugation. The obtained samples were dried in a vacuum drying oven at 60 °C for 12 h. The obtained solid was then ground into powder, placed in a tube furnace under an air atmosphere, and calcined at 200° C. for 2 h.
[0040] (2) Weigh 0.23 g of pretreated HNTs and 0.01 g of HPC, disperse them in 20 mL of ethanol, dropwise add 0.1 mL of deionized water, and disperse by ultrasonic to make the samples evenly mixed. The flask was then placed in a 25°C water bath and stirred for 30 min. Measure 0.6 mL of ZBOT solution into 4.5 mL of ethanol solution (5.1 mL of hydrolyzed zirconium salt solution), and after mixing evenly, slowly add it dropwise to the reaction solution for 20 h. After the reaction was completed, the obtained solution was washed with ethanol, the precipitate was collected by centrifugation, and dried in an oven at 60 °C for 12 h to obtain a sample loaded with amorphous zirconia 1L-ZrO 2 @HNTs.
[0041] (3) Weigh 0.23g of 1L-ZrO obtained in the previous step 2 @HNTs and 0.01 g HPC were redispersed into 20 mL of ethanol and stirred for 30 min. Then measure 0.6 mL of ZBOT, disperse it in 4.5 mL of ethanol (5.1 mL of hydrolyzed zirconium salt solution), and add it dropwise to the reaction system after mixing evenly. After the reaction system was reacted at 25 °C for 20 h, the obtained product was washed 3-4 times with ethanol, collected by centrifugation, and dried in an oven at 60 °C for 12 h. Then, the dried sample powder was placed in a tube furnace, calcined at 650 °C for 2 h in an air atmosphere, and the heating rate was 5 °C/min to obtain a mixed crystal (monoclinic phase ZrO) supported on the surface of HNTs. 2 and tetragonal ZrO 2 ) of the two-layer zirconia product 650℃-2L-ZrO 2 @HNTs.
[0042] (4) Measure 75ml of 1wt% PVA aqueous solution, add 0.8mL of 1wt% HAuCl 4 ·3H 2 O solution was added to it, stirred in a water bath at 25 °C for 5 min, and then 1 mL of 0.1 M NaBH was added dropwise 4 solution. After stirring uniformly, 0.4 mL of HCl was added to the reaction system to make the pH of the reaction system 7. Then weigh 0.2g of 650℃-2L-ZrO 2 @HNTs was added to the reaction system and stirred for 2h. After the reaction, the obtained product was washed 4-5 times with deionized water, collected by centrifugation, and vacuum-dried at 60 °C for 24 h to obtain a rod-shaped core-shell catalyst for catalyzing HMF oxidation to prepare FDCA. 650 °C-Au/2L- ZrO 2 @HNTs.
[0043] Depend on figure 1 The SEM images (a) and TEM images (d) show that the HNTs are hollow rod-like structures. According to the SEM images (b) and (c), it can be seen that 1L-ZrO 2 @HNTs and 2L-ZrO 2 The @HNTs still showed a rod-like structure. In addition, it can be observed from TEM images (e) and (f) that zirconia was successfully loaded onto the surface of HNTs. It is 93nm, and the transmission electron microscope image further proves that the prepared sample is a rod-like core-shell structure.
[0044] Depend on figure 2 TEM image (a) shows that Au nanoparticles were successfully loaded to 650℃-2L-ZrO 2 @HNTs surface, and it was observed after lattice measurement from the captured high-resolution images that ZrO calcined at 650 °C 2 It is a mixed crystal form (monoclinic m-ZrO 2 Phase and tetragonal t-ZrO 2 ). From the particle size distribution diagram (b), it can be observed that the particle size of the supported Au is small, and its average size is about 2.25 nm. The smaller the particle size of Au, the more active sites the catalyst provides for the reaction. The better the catalytic performance.
[0045] Depend on image 3 , the X-ray diffraction pattern shows that the prepared rod-like core-shell catalyst 650℃-Au/2L-ZrO 2 @HNTs show different crystal forms of ZrO 2 Characteristic peaks. The peaks at 28.2° and 31.5° correspond to the monoclinic phase ZrO, respectively 2 (m-ZrO 2 ) of the (-111) and (111) planes, while 30.2°, 35.3°, 50.4° and 59.7° correspond to the tetragonal phase ZrO, respectively 2 (t-ZrO 2) of the (111), (200), (220) and (311) crystal planes, which indicate that the zirconia obtained by calcination at 650 °C is a mixed crystal form (monoclinic and tetragonal). The characteristic peaks of Au should appear at 38.3°, 44.4° and 64.5°, but the characteristic peaks of Au are not observed in the spectrum. Combined with the results observed in the transmission electron microscope, it is speculated that this is because the Au nanoparticles are uniformly distributed On the support and small in size, below the limit of X-ray diffraction detection.
[0046] Depend on Figure 4 , 650℃-Au/2L-ZrO 2 The electron paramagnetic resonance spectrum of @HNTs can be observed to have a peak with g value of 2.003, which corresponds to the characteristic peak of oxygen deficiency, which indicates that the as-prepared catalyst 650℃-Au/2L-ZrO 2 @HNTs have oxygen vacancies.
[0047] Depend on Figure 5 , HNTs and 650℃-Au/2L-ZrO 2 NH of @HNTs 3 Temperature-programmed desorption diagrams show that there are hardly any acidic sites on the surface of HNTs, while the as-prepared catalyst 650℃-Au/2L-ZrO 2 There are strong acid sites on the surface of @HNTs, and the total amount of strong acid in the catalyst is 5.1057 mmol g after quantitative analysis of the curve integral. -1.
[0048] Depend on Image 6 The pyridine infrared spectrum shows that the prepared rod-like core-shell catalyst 650℃-Au/2L-ZrO 2 @HNTs also presented Bronsted acid (1542cm -1 ) and Lewis acid (1447cm -1 ) characteristic band of active site, 1490cm -1 The characteristic bands at are assigned to Bronsted and Lewis acid sites. Quantitative analysis of the curve integral shows that the Lewis acid sites on the surface of the prepared catalyst are 0.0556 mmol g -1. Among them, the Lewis acid site is conducive to the adsorption of the intermediate product by the catalyst, thereby improving the catalytic reaction activity.
[0049] Depend on Figure 7 Medium 650℃-2L-ZrO 2 @HNTs and the as-prepared rod-like core-shell catalyst 650℃-Au/2L-ZrO 2 The XPS full spectrum of @HNTs (a) shows the appearance of Zr 3d and Au 4f signal peaks, which proves that zirconia and Au nanoparticles have been successfully loaded onto HNTs. From Figure (b) Au/HNTs and 650℃-Au/2L-ZrO 2 The high-resolution spectra of the Au 4f region of @HNTs can be observed that compared with the binding energy of Au 4f of Au/HNTs, the catalyst 650°C-Au/2L-ZrO 2 The Au 4f binding energies of @HNTs are shifted towards lower. This shows that ZrO 2 The charge on the (mixed crystal form) carrier is transferred to the Au nanoparticles, so that the Au nanoparticles are in a negatively charged state, and there is charge transfer between the carrier and the metal. From Figure (c), it can be observed that 650℃-Au/2L-ZrO 2 The binding energies of Zr 3d in @HNTs shift towards an elevated direction, which indicates that the charge of Zr ions is transported to the Au nanoparticles. Figure (d) is the high-resolution spectrum of the O1s region, for the catalyst 650℃-Au/2L-ZrO 2 For @HNTs, the peak at 531.60 eV is attributed to the surface adsorbed oxygen (O ads ), and the surface adsorbed oxygen is closely related to oxygen vacancies, so this result indicates that the as-prepared ZrO has a mixed crystal form 2 The catalyst surface contains oxygen vacancies. In addition, it can be observed that the binding energy of O1s after the sample is loaded with Au moves to a lower direction, which further indicates that there is an interaction between the support and the metal.
[0050] 2. Catalytic activity test:
[0051] Weigh 0.05g HMF, 0.06g NaOH and 0.05g 650℃-Au/2L-ZrO 2 @HNTs, disperse it in 40mL deionized water, then fill the autoclave with O 2 , the pressure was 2MPa, the reaction system was reacted at 100°C for 3h, and the rotational speed was 600rpm. The liquid product obtained by the reaction was detected by a high performance liquid chromatograph (HPLC) equipped with an ultraviolet detector and a hydrogen column. The obtained liquid product was diluted 80 times with deionized water, and then the liquid was filtered with a 0.2 μm polytetrafluoroethylene filter membrane. The detection conditions are: the column temperature is 65°C; the mobile phase is 0.01M H 2 SO 4; The flow rate was 0.4 mL/min; the injection volume was 20 μL. The standard curve of FDCA sample is y=352.03x-81.042 (y represents the corresponding concentration of FDCA, the unit is mg/L, and x represents the peak area). According to the standard curve, the concentration of FDCA can be calculated and converted into molar concentration. Product yield is calculated as Y (molar yield)=n 1 /n 0 ×100, n 1 represents the molar amount of FDCA obtained, n 0 represents the molar amount of reaction substrate HMF. The calculation results show that the product FDCA can reach a higher yield, and the FDCA yield of the reaction for 3h is 99.36%.
[0052] 3. Regeneration performance test
[0053] In the present invention, the prepared rod-shaped core-shell structure catalyst 650°C-Au/2L-ZrO 2 @HNTs can be obtained by centrifugation, separation, and drying. The recovered catalyst was put back into the above-mentioned catalytic experiment to test its catalytic effect; four regeneration experiments were carried out in this way. The detection method and experimental conditions of the obtained liquid products are the same as the above-mentioned catalytic experiments. The results showed that the loss of catalyst activity during the regeneration process was relatively low, and the yields of FDCA were 95.04%, 89.02%, 88.40%, and 87.68% during the one to four regeneration experiments.
