Carbon-based catalyst, preparation method thereof and application of carbon-based catalyst in isomerization of glucose into fructose

Abstract

The invention discloses a carbon-based catalyst and a preparation method and application thereof to isomerization of glucose into fructose, the catalyst comprises an active component loaded on a carbon-based catalyst carrier and a chelating agent complexed with the active component, metal salts in the active component are Mg and K, the chelating agent is one or more of citric acid, triacetic acid, triethylamine ethylenediamine and potassium sodium tartrate. The chelating agent adjusts alkali active sites of a reaction system through acidic functional groups of the chelating agent, maintains an acid-base environment required by the reaction, and promotes an isomerization reaction from glucose to fructose. Meanwhile, the chelating agent and the metal ions form a stable complex to prevent metal salt from inactivation, and the metal ions are ensured to be uniformly distributed on the surface of the carrier and prevented from being agglomerated through the dispersity of the chelating agent, so that the activity and stability of the catalyst are improved. By controlling the dosage of the chelating agent and coordination of metal ions, the selectivity of the glucose isomerization reaction and the fructose yield are effectively improved, side reactions are inhibited, and the overall efficiency of the reaction is remarkably improved.

Description

Technical Field

[0001] The invention belongs to the field of biomass-based catalysis, and specifically relates to a carbon-based catalyst and a preparation method thereof, and application thereof in isomerizing glucose into fructose. Background Art

[0002] With the rapid development of social economy and science and technology, the global demand for sustainable energy and high value-added chemicals is growing. The use of renewable biomass to prepare key products has become an important issue that needs to be solved urgently. Fructose, as a chemical widely used in the food and pharmaceutical fields, has a high market demand. With the rapid growth of demand for fructose in the food and pharmaceutical industries, the market supply is gradually unable to meet the demand, resulting in fructose becoming an important strategic product. As the main product in the hydrolysis process of biomass, the technical research on the efficient isomerization of glucose into fructose has important industrial value. However, the current fructose production capacity cannot meet the market demand, and a large amount of unconverted glucose not only causes a waste of resources, but also limits the sustainable development of the biomass industry. Therefore, the efficient isomerization of glucose into fructose has become an urgent need at this stage.

[0003] The main methods for glucose isomerization include enzymatic decomposition and chemical catalysis (including homogeneous catalysis and heterogeneous catalysis). Glucose isomerase has the advantages of strong specificity and low reaction temperature, and is widely used in the industrial production of fructose. However, enzyme catalysis has some disadvantages, including low efficiency, high cost and short life. Homogeneous catalysts in chemical catalysis can efficiently isomerize glucose into fructose, but the separation and recovery of catalysts after the reaction limit its promotion and application. Relatively speaking, heterogeneous catalysts have greater application potential in glucose isomerization reactions due to their adjustable activity, high thermal stability and strong controllability. A variety of heterogeneous catalysts with Lewis acids and Bronsted bases such as aluminum oxide, lithium oxide and magnesium oxide have been used in glucose isomerization reactions. These catalysts are supported on carriers such as graphene, zeolite molecular sieves and MOF. Porous carbon is preferentially used as a carrier because of its adjustable pore structure, high specific surface area, rich functional groups and excellent chemical stability.

[0004] Although a variety of catalysts have been studied for glucose isomerization, the efficiency of existing catalysts is still insufficient, resulting in a low fructose yield. Acid catalysts, such as aluminum-based catalysts, have certain catalytic activity, but they mainly rely on surface acid sites and are prone to acid site decay, resulting in a decrease in catalytic efficiency, especially under high temperature or high concentration reaction conditions, the catalytic activity decreases significantly, affecting the fructose yield. Although alkaline catalysts increase the glucose conversion rate, due to their poor catalytic selectivity, they often cause glucose to decompose into by-products, reducing the fructose yield. Therefore, how to improve the selectivity, stability and yield of the catalyst is still an important challenge facing the glucose isomerization reaction.

[0005] The invention patent with the publication number CN116651435A discloses a tin-doped nano-silica material, its preparation method, and its application in catalyzing the isomerization of glucose into fructose. The preparation method of this Lewis acid functional catalyst is to dissolve amorphous silica nano-materials and 3-aminopropyltriethoxysilane in an alcohol solvent for reflux reaction. The obtained solid product is dried and then mixed and ground with a tetravalent tin salt. The obtained mixture is calcined to obtain the tin-doped nano-silica material. Then, this catalyst is applied to the reaction of preparing fructose by glucose isomerization. In the present invention, Sn4+ is uniformly doped in the amorphous silica nano-materials to form a tin-doped nano-silica material, which is rich in a large number of Lewis acid open Sn sites with high activity for glucose isomerization of proximal silanol groups. The catalyst is simple to prepare and has mild conditions. However, the excessive acidic sites of this catalyst lead to poor selectivity and require a longer reaction time.

[0006] The invention patent with the publication number CN116143849A discloses a method for preparing fructose by catalyzing glucose isomerization with a response surface optimized calcium-magnesium basic catalyst. This calcium-magnesium basic catalyst has a wide source and low cost. However, the fructose yield is low and the selectivity is poor. Summary of the Invention

[0007] The present invention provides a preparation method of a carbon-based catalyst. The carbon-based catalyst prepared by this preparation method can isomerize glucose into fructose, and the yield of fructose is relatively high and the selectivity is good.

[0008] The present invention provides a preparation method based on a carbon-based catalyst, including:

[0009] S1. Washing, drying, and carbonizing biomass residues to obtain a carbon-based catalyst support;

[0010] S2. Adding the carbon-based catalyst support, magnesium salt, potassium salt, and chelating agent to deionized water for impregnation, drying, and calcining to obtain a carbon-based catalyst. The calcination temperature is 600-900 °C, and the calcination time is 0.5-2 h.

[0011] Preferably, the mass ratio of the magnesium salt, potassium salt, and chelating agent is 1:10-30:10-40.

[0012] By controlling the content of the chelating agent, the present invention enables metal ions to undergo complexation reactions with a sufficient amount of the chelating agent, thereby achieving uniform dispersion on the carbon-based catalyst support, avoiding the agglomeration of metal ions. At the same time, it can also adjust the acidity and alkalinity, forming a large number of weak base and medium base sites on the carbon-based catalyst support, which is beneficial to improving the selectivity of the glucose isomerization reaction and achieving a relatively high fructose yield. It can avoid a large number of strong base sites and also prevent the generation of excessive acidic sites from neutralizing the basic sites, so that strong acidic sites are retained on the surface of the carbon-based catalyst, affecting the selectivity and efficiency of the reaction.

[0013] Further preferably, the mass ratio of the magnesium salt, potassium salt, and chelating agent is 1:10 - 30:20 - 40. By providing an appropriate amount of the chelating agent, its molecules wrap the metal ions through strong chelation, reducing the direct contact between metal ions, thereby inhibiting the agglomeration phenomenon. At the same time, the chelating agent molecules interact with the functional groups (such as hydroxyl groups, carboxyl groups, etc.) on the surface of the carbon material through their multiple coordination sites, regulating the adsorption behavior of metal ions on the material surface, and further promoting the uniform dispersion of metal ions in a smaller size on the surface of the carbon material, significantly enhancing the dispersion effect.

[0014] Preferably, the calcination temperature is 700 - 800 °C. In this temperature range, the catalytic effect of the chelating agent is relatively good mainly because in this temperature range, it can dissociate and release metal ions, and these metal ions have relatively high catalytic activity. In addition, in this temperature range, the interaction between the chelating agent, metal ions, and the surface of the support is closer, enhancing the stability and activity of the catalyst. The chelating agent has good thermal stability in this temperature range, can continuously participate in the catalytic reaction, and at the same time promote the activation of reactants, thereby improving the catalytic efficiency.

[0015] Preferably, the chelating agent is one or more of citric acid, triacetic acid, triethylamine ethylenediamine, and potassium sodium tartrate.

[0016] Preferably, the biomass residue is obtained by washing tea residues, followed by crushing and sieving.

[0017] Further preferably, a crusher is used to crush the tea residues, and the biomass residue is obtained by sieving through a 100 - 150 mesh sieve.

[0018] Further preferably, the tea residues are green tea residues or black tea residues.

[0019] Preferably, the drying temperature is 60 - 80 °C, and the drying time is 10 - 24 h.

[0020] Preferably, the mass ratio of the magnesium salt to the potassium salt is 1:10 - 30. By controlling the content of the potassium salt, the present invention can obtain sufficient basic sites to provide sufficient catalytic active sites. At the same time, it can avoid the reaction of excessive basic sites with the generated fructose, which may cause its re-isomerization, thereby reducing the glucose conversion rate.

[0021] Preferably, the mass ratio of the magnesium salt, potassium salt, chelating agent to the carbon-based catalyst support is 1:10 - 30:10 - 40:10 - 20.

[0022] An appropriate amount of carbon-based catalyst support can make the distribution of the chelating agent uniform, and then make the metal ions disperse sufficiently, which is beneficial to the activity and stability of the catalyst. It can avoid the over-dilution of the chelating agent, reduce the effectiveness of its coordination with metal ions, and then reduce the catalytic performance of the catalyst. At the same time, it can avoid the excessive carrier competing with the chelating agent for coordination sites, weakening its chelating effect and affecting the overall performance of the catalyst. Therefore, the dosage of the carbon-based catalyst support should be appropriately controlled to ensure that the chelating agent can be evenly distributed and exert its maximum efficiency, thereby optimizing the performance of the catalyst.

[0023] Preferably, the mass / volume ratio of the magnesium salt, potassium salt, chelating agent and carbon-based catalyst support to deionized water is 1:10 - 30:10 - 40:10 - 20:60 - 80 g / mL.

[0024] An appropriate amount of deionized water can make the solubility and dispersibility of the chelating agent better, thereby enhancing the binding efficiency of the chelating agent with metal ions, which is beneficial to the performance of the catalyst. It can avoid the concentration of the chelating agent becoming too low to effectively chelate with metal ions, resulting in uneven dispersion of metal ions and affecting the activity of the catalyst. It can also avoid diluting the reaction system and reducing the reaction rate. Therefore, the amount of deionized water needs to be appropriately controlled to ensure that the chelating agent can be effectively dissolved and fully react with metal ions.

[0025] On the other hand, the present invention also provides a carbon-based catalyst prepared by the preparation method of the carbon-based catalyst.

[0026] On the other hand, the present invention also provides the application of the carbon-based catalyst in the isomerization of glucose to fructose, including:

[0027] Weigh 0.05 - 0.15 g of glucose, 0.01 - 0.1 g of magnesium-potassium catalyst and 5 - 10 ml of deionized water and add them into a reaction kettle with a polytetrafluoroethylene liner. Stir magnetically at 80 - 100 °C at 100 - 200 rpm for 20 - 100 min to obtain fructose.

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] Since adding magnesium salts and potassium salts to deionized water results in strong alkalinity, which is not conducive to the isomerization of glucose to fructose, the present invention adjusts the pH by adding a chelating agent, enabling the prepared carbon-based catalyst to have a large number of weak base or medium basic sites, which can provide appropriate active sites in the catalytic reaction, improve the reaction selectivity and efficiency, and reduce the occurrence of side reactions, facilitating the isomerization of glucose to fructose.

[0030] The chelating agent provided by the present invention can form a stable complex with magnesium salts and potassium salts, avoiding the inactivation of metal salts, while improving the dispersion of metals, effectively improving the selectivity of the glucose isomerization reaction, increasing the yield of fructose, and inhibiting the occurrence of side reactions, thereby improving the overall efficiency of the reaction.

[0031] The present invention can ensure the full play of the role of the chelating agent in the catalyst preparation process by controlling the calcination temperature and time. Too low calcination temperature and time lead to insufficient coordination between the metal ions chelated by the chelating agent and the carrier, and uneven dispersion of metal ions, thus affecting the activity and stability of the catalyst. While too high calcination temperature and time result in excessive decomposition of the chelating agent, destroying the coordination structure between metal ions and the carrier, and even causing the desorption or aggregation of metal ions. Compared with the prior art, the present invention maintains the optimal structure of the catalyst and the dispersion of metal ions through appropriate calcination conditions, ensuring an efficient catalytic reaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is the temperature-programmed chemical adsorption analysis (NH 3 / CO 2 -TPD) of the catalysts prepared in Examples 1-3 and Comparative Examples 1-2 of the present invention;

[0033] Figure 2 It is the transmission electron microscope (TEM) of the catalysts prepared in Examples 1-3 and Comparative Examples 1-2 of the present invention;

[0034] Figure 3 It is the X-ray diffraction pattern (XRD) of the catalysts prepared in Examples 1-2 and Comparative Examples 1-2 of the present invention;

[0035] Figure 4 It is the infrared spectrum (FT-IR) of the catalysts prepared in Examples 1-2 and Comparative Examples 1-2 of the present invention;

[0036] Figure 5 It is the thermogravimetric analysis diagram (TG) of the catalysts prepared in Examples 1-2 and Comparative Examples 3-4 of the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0037] To further elaborate on the content of the present invention, the following will be described in conjunction with specific embodiments. These embodiments demonstrate the specific applications and operation steps of the technical solution of the present invention. The protection scope of the present invention is not limited to the content shown in these embodiments.

[0038] Example 1

[0039] (1) After washing the green tea residue, it is placed in an 80 °C oven and dried for 12 h. After drying, the tea residue is crushed with a pulverizer, placed in a crucible and put into a tubular furnace. Under a nitrogen atmosphere, it is heated from 20 °C to 900 °C at a heating rate of 5 °C / min and then carbonized for 2 h to obtain a carbon-based catalyst support.

[0040] (2) Take 1 g of the carbon-based catalyst support, 0.05 g of magnesium chloride, 1 g of potassium bicarbonate and 1 g of chelating agent, add them to 80 ml of deionized water, impregnate for 4 h, then place in an 80 °C oven and dry for 12 h. After grinding, it is placed in a crucible and put into a tubular furnace. Under a nitrogen atmosphere, it is heated from 20 °C to 800 °C at a heating rate of 10 °C / min and then calcined for 1 h to obtain a magnesium-potassium catalyst.

[0041] (3) Weigh 0.1 g of glucose, 0.05 g of the magnesium-potassium catalyst and 5 ml of deionized water and add them to a reaction kettle with a polytetrafluoroethylene liner. Subsequently, the reaction mixture is magnetically stirred at 100 rpm at 90 °C for 60 min. After the reaction, the reaction kettle is naturally cooled to room temperature. Finally, the content of fructose is detected by high performance liquid chromatography, and the conversion rate of glucose, the yield and selectivity of fructose are obtained by calculation. The detection results are shown in Table 1.

[0042] Example 2

[0043] (1) After washing the green tea residue, it is placed in an 80 °C oven and dried for 12 h. After drying, the tea residue is crushed with a pulverizer, placed in a crucible and put into a tubular furnace. Under a nitrogen atmosphere, it is heated from 20 °C to 900 °C at a heating rate of 5 °C / min and then carbonized for 2 h to obtain a carbon-based catalyst support.

[0044] (2) Take 1 g of the carbon-based catalyst support, 0.05 g of magnesium chloride, 1 g of potassium bicarbonate and 0.5 g of chelating agent, add them to 80 ml of deionized water, impregnate for 4 h, then place in an 80 °C oven and dry for 12 h. After grinding, it is placed in a crucible and put into a tubular furnace. Under a nitrogen atmosphere, it is heated from 20 °C to 800 °C at a heating rate of 10 °C / min and then calcined for 1 h to obtain a magnesium-potassium catalyst.

[0045] (3) Weigh 0.1 g of glucose, 0.05 g of magnesium-potassium catalyst and 5 ml of deionized water and add them to a reaction kettle with a PTFE inner lining. Subsequently, magnetically stir the reaction mixture at 100 rpm at 90 °C for 60 min. After the reaction, let the reaction kettle cool naturally to room temperature. Finally, use high-performance liquid chromatography to detect the content of fructose, and calculate the conversion rate of glucose, the yield and selectivity of fructose. The detection results are shown in Table 1.

[0046] Example 3

[0047] (1) After washing the green tea residue, place it in an oven at 80 °C and dry for 12 h. After drying, crush the tea residue with a pulverizer, put it into a crucible and place it in a tube furnace. Under a nitrogen atmosphere, heat it from 20 °C to 900 °C at a heating rate of 5 °C / min and carbonize for 2 h to obtain a carbon-based catalyst support.

[0048] (2) Take 1 g of carbon-based catalyst support, 0.05 g of magnesium chloride, 1 g of potassium bicarbonate and 1.5 g of chelating agent, add them to 80 ml of deionized water and impregnate for 4 h, then place it in an oven at 80 °C and dry for 12 h. After grinding, put it into a crucible and place it in a tube furnace. Under a nitrogen atmosphere, heat it from 20 °C to 800 °C at a heating rate of 10 °C / min and calcine for 1 h to obtain a magnesium-potassium catalyst.

[0049] (3) Weigh 0.1 g of glucose, 0.05 g of magnesium-potassium catalyst and 5 ml of deionized water and add them to a reaction kettle with a PTFE inner lining. Subsequently, magnetically stir the reaction mixture at 100 rpm at 90 °C for 60 min. After the reaction, let the reaction kettle cool naturally to room temperature. Finally, use high-performance liquid chromatography to detect the content of fructose, and calculate the conversion rate of glucose, the yield and selectivity of fructose. The detection results are shown in Table 1.

[0050] Comparative Example 1

[0051] (1) After washing the green tea residue, place it in an oven at 80 °C and dry for 12 h. After drying, crush the tea residue with a pulverizer, put it into a crucible and place it in a tube furnace. Under a nitrogen atmosphere, heat it from 20 °C to 900 °C at a heating rate of 5 °C / min and carbonize for 2 h to obtain a carbon-based catalyst support.

[0052] (2) Take 1 g of carbon-based catalyst support, 0.05 g of magnesium chloride and 1 g of potassium bicarbonate, add them to 80 ml of deionized water and impregnate for 4 h, then place it in an oven at 80 °C and dry for 12 h. After grinding, put it into a crucible and place it in a tube furnace. Under a nitrogen atmosphere, heat it from 20 °C to 800 °C at a heating rate of 10 °C / min and calcine for 1 h to obtain a magnesium-potassium catalyst.

[0053] (3) Weigh 0.1 g of glucose, 0.05 g of magnesium-potassium catalyst and 5 ml of deionized water and add them to a reaction kettle with a PTFE liner. Subsequently, magnetically stir the reaction mixture at 90 °C at 100 rpm for 60 min. After the reaction, naturally cool the reaction kettle to room temperature. Finally, detect the content of fructose by high performance liquid chromatography, and calculate the conversion rate of glucose, the yield and selectivity of fructose. The detection results are shown in Table 1.

[0054] Comparative Example 2

[0055] (1) Wash the green tea residue, then place it in an oven at 80 °C for drying for 12 h. After drying, crush the tea residue with a pulverizer, put it into a crucible and place it in a tube furnace. Under a nitrogen atmosphere, heat it from 20 °C to 900 °C at a heating rate of 5 °C / min and carbonize for 2 h to obtain a carbon-based catalyst support.

[0056] (2) Take 1 g of the carbon-based catalyst support, 0.05 g of magnesium chloride, 1 g of potassium bicarbonate and 2 g of chelating agent, add them to 80 ml of deionized water and impregnate for 4 h, then place it in an oven at 80 °C for drying for 12 h. After grinding, put it into a crucible and place it in a tube furnace. Under a nitrogen atmosphere, heat it from 20 °C to 800 °C at a heating rate of 10 °C / min and calcine for 1 h to obtain a magnesium-potassium catalyst.

[0057] (3) Weigh 0.1 g of glucose, 0.05 g of magnesium-potassium catalyst and 5 ml of deionized water and add them to a reaction kettle with a PTFE liner. Subsequently, magnetically stir the reaction mixture at 90 °C at 100 rpm for 60 min. After the reaction, naturally cool the reaction kettle to room temperature. Finally, detect the content of fructose by high performance liquid chromatography, and calculate the conversion rate of glucose, the yield and selectivity of fructose. The detection results are shown in Table 1.

[0058] Comparative Example 3

[0059] Differing from Example 1, the calcination temperature is 600 °C and the time is 2 h. Finally, detect the content of fructose by high performance liquid chromatography, and calculate the conversion rate of glucose, the yield and selectivity of fructose. The detection results are shown in Table 1.

[0060] Comparative Example 4

[0061] Differing from Example 1, the calcination temperature is 900 °C and the time is 0.5 h. Finally, detect the content of fructose by high performance liquid chromatography, and calculate the conversion rate of glucose, the yield and selectivity of fructose. The detection results are shown in Table 1.

[0062] Table 1 shows the performance evaluation results of glucose isomerization to fructose for each example and comparative example

[0063]

[0064] Performance analysis:

[0065] As can be seen from Table 1, the preparation method for efficiently isomerizing glucose into fructose provided by the present invention has high fructose yield and selectivity.

[0066] Figure 1 a is the temperature-programmed chemisorption analysis (NH 3 -TPD) of different examples and comparative examples of the present invention. The acidity change is reflected by the desorption behavior of ammonia at different temperatures. The catalyst of Example 1 exhibits more weak acid (<300 °C) and medium acid (300 - 500 °C) sites. These sites can effectively promote the glucose isomerization reaction, improve fructose selectivity and yield, and at the same time avoid triggering too many side reactions (such as formic acid, lactic acid, etc.); in contrast, the catalysts of Comparative Example 1 and Comparative Example 2 exhibit more strong acid sites (>500 °C). Although these strong acid sites have higher activity, they are prone to cause further isomerization or decomposition of fructose, reducing selectivity. Figure 1 b is the temperature-programmed chemisorption analysis (CO 2 -TPD) of different examples and comparative examples of the present invention. The catalyst of Example 1 exhibits more weak base (<300 °C) and medium base (300 - 500 °C) sites. These sites have moderate basic strength, which can improve the reaction selectivity and efficiency and reduce side reactions; while the catalysts of Comparative Example 1 and Comparative Example 2 exhibit more strong base sites (>500 °C). Although they have higher activity, they are prone to trigger side reactions and catalyst deactivation. Therefore, due to the advantages of weak acid, medium acid, weak base, and medium base sites, the catalyst of Example 1 exhibits better selectivity, efficiency, and stability in reactions such as glucose isomerization and CO 2 adsorption conversion.

[0067] This change in acidity and alkalinity is caused by the addition of a chelating agent. The chelating agent forms stable complexes with metal ions in the catalyst, changing the electronic environment and geometric structure of the metal active center, thereby regulating the distribution of acid-base sites on the catalyst surface. The chelating effect of the chelating agent reduces the number of strong acid-base sites, while increasing the proportion of weak acid / base and medium acid / base sites. This regulatory effect helps to optimize the acid-base distribution of the catalyst, making it more suitable for the isomerization reaction of glucose. The increase in weak acid / base and medium acid / base sites improves the reaction efficiency and fructose selectivity, while the decrease in strong acid / base sites inhibits the occurrence of side reactions. Therefore, the addition of the chelating agent significantly improves the performance of the Example 1 catalyst in the glucose isomerization reaction by regulating the acid-base distribution.

[0068] Figure 2The transmission electron microscope (TEM) results of different examples and comparative examples of the present invention show that in Example 2, due to the addition of a small amount of chelating agent, some metal particles are evenly distributed at the edge of the carrier, but there is still agglomeration; in Example 1, Example 3 and Comparative Example 2, due to the addition of an optimal or excessive amount of chelating agent, the metal particles are evenly distributed on the surface of the carrier, with small particle size and regular morphology, indicating that the chelating agent can effectively inhibit metal agglomeration and significantly improve the dispersion, but the excessive chelating agent does not further improve the dispersion morphology; in contrast, in Comparative Example 1, due to the absence of chelating agent, obvious agglomeration of metal particles appears, with uneven distribution and large size difference. Generally speaking, the use of chelating agent significantly enhances the dispersion of metal particles and optimizes the microstructure of the catalyst. This is because in the absence of chelating agent or insufficient amount of chelating agent, metal ions are easily agglomerated into larger particles due to electrostatic interaction or van der Waals force. With the increase of the amount of chelating agent, its molecules wrap the metal ions through strong chelation, reducing the direct contact between metal ions and inhibiting the agglomeration phenomenon; at the same time, the chelating agent molecules interact with the functional groups (such as hydroxyl groups, carboxyl groups, etc.) on the surface of the carbon material by virtue of multiple ligand sites, regulating the adsorption behavior of metal ions on the material surface, further promoting the uniform dispersion of metal ions in smaller sizes and significantly improving the dispersion effect.

[0069] Figure 3 The X-ray diffraction pattern (XRD) of the catalysts prepared from different examples and comparative examples of the present invention. The XRD pattern clearly shows the differences in crystal structures of different samples, and the crystal phases of potassium oxide (K 2 O), magnesium carbonate (MgCO 3 ) and magnesium oxide (MgO) are analyzed in combination with the PDF cards (PDF#77-2151, #08-0479 and #87-0653). In Comparative Example 1, without the addition of chelating agent, potassium bicarbonate mainly reacts with magnesium oxide to form magnesium carbonate, and its characteristic diffraction peaks at the (104) and (116) crystal planes are significant, while the diffraction peak of potassium oxide at (111) is weak, indicating that the crystallinity of potassium oxide crystals is poor or a small amount is loaded on the carbon-based catalyst carrier. In contrast, in Example 1, Example 2 and Comparative Example 2, due to the addition of chelating agent, the diffraction peak intensity of magnesium carbonate is significantly weakened, the characteristic diffraction peaks ((111), (200), (220)) of potassium oxide are significantly enhanced, and new diffraction peaks appear at the (311), (222), (420) crystal planes, which indicates that the chelating agent promotes the optimization of the crystal structure of potassium oxide or loads more active sites. The overall results show that the chelating agent plays a key role in inhibiting the generation of unstable active sites such as magnesium carbonate and improving the crystallinity of potassium oxide during the sample preparation process.

[0070] Figure 4 The Fourier transform infrared spectrum (FT-IR) of the catalysts prepared from different examples and comparative examples of the present invention. At 3438 cm -1The O-H stretching vibration peak observed at [X] cm⁻¹ indicates the presence of hydroxyl (-OH) groups on the material surface. 1627 cm⁻¹ -1 The peak at [X] cm⁻¹ is attributed to the stretching vibration of C=C in the aromatic ring. After adding the chelating agent, new diffraction peaks appear at 11461 cm⁻¹ in Comparative Example 4, Comparative Example 5, and the Example -1 These diffraction peaks correspond to the symmetric and antisymmetric stretching vibrations of the COO- groups derived from the chelating agent, confirming the formation of the chelating agent complex. 1393 cm⁻¹ -1 The peak at [X] cm⁻¹ is attributed to the bending vibration of aliphatic C-H. In addition, after adding the chelating agent, the peaks at 880 cm⁻¹ -1 and 705 cm⁻¹ -1 are significantly enhanced, corresponding to the stretching vibrations of the metal-ligand bonds respectively, indicating that K + and Mg 2+ have undergone chelation coordination with the N or O atoms in the chelating agent. These results show that the chelating agent has been successfully introduced into the material and has formed a stable complex with metal ions.

[0071] According to the analysis of the thermogravimetric curves ( Figure 5 ), the calcination temperatures of Example 1 and Example 2 are both 800 °C, and the calcination time is 1 hour. Therefore, their mass losses in the thermogravimetric curves are similar, mainly reflecting the evaporation of moisture and the decomposition of organic substances. The thermogravimetric curves of Comparative Example 3 and Comparative Example 4 show significant mass losses, which are closely related to different calcination temperatures and time conditions. The calcination temperature of Comparative Example 3 is 600 °C, and the calcination time is 2 hours. The relatively low calcination temperature results in the chelating agent being unable to effectively chelate metal ions onto the carrier, thus affecting the stability of the metal and the performance of the catalyst, and making the structural stability of the catalyst poor. The calcination temperature of Comparative Example 4 is 900 °C, and the calcination time is 0.5 hour. Under high-temperature conditions, the chelating agent and the metal decompose, resulting in the ineffective binding of metal ions and the chelating agent in the catalyst, causing significant mass loss, and the high temperature destroys the structure of the catalyst, affecting its catalytic performance. Therefore, the selection of the calcination temperature is crucial for the stability and performance of the catalyst.

Claims

1. A preparation method based on a carbon-based catalyst, characterized in that: include: S1, washing, drying and carbonizing the biomass residue to obtain a carbon-based catalyst carrier; S2. Add the carbon-based catalyst carrier, magnesium salt, potassium salt and chelating agent into deionized water for immersion, drying and calcination to obtain a carbon-based catalyst. The calcination temperature is 600-900° C. and the calcination time is 0.5-2 h.

2. The preparation method based on carbon-based catalyst according to claim 1, characterized in that: The mass ratio of the magnesium salt, potassium salt and chelating agent is 1:10-30:10-40.

3. The preparation method based on carbon-based catalyst according to claim 2, characterized in that: The mass ratio of the magnesium salt, potassium salt and chelating agent is 1:10-30:20-40.

4. The preparation method based on carbon-based catalyst according to claim 1, characterized in that: The calcination temperature is 700-800°C.

5. The preparation method based on carbon-based catalyst according to claim 1, characterized in that: The chelating agent is one or more of citric acid, triacetic acid, triethylamine ethylenediamine, and potassium sodium tartrate.

6. The preparation method based on carbon-based catalyst according to claim 1, characterized in that: The biomass residue is obtained by washing tea residue, crushing it and sieving it.

7. The method for preparing a carbon-based catalyst according to claim 1, characterized in that: The mass ratio of the magnesium salt to the potassium salt is 1:10-30.

8. The method for preparing a carbon-based catalyst according to claim 1, characterized in that: The mass ratio of the magnesium salt, potassium salt and chelating agent to the carbon-based catalyst carrier is 1:10-30:10-40:10-20.

9. A carbon-based catalyst, characterized in that: The catalyst is prepared by the carbon-based catalyst preparation method.

10. Use of the carbon-based catalyst according to claim 9 in isomerizing glucose to fructose, comprising: 0.05-0.15 g of glucose, 0.01-0.1 g of magnesium potassium catalyst and 5-10 ml of deionized water were weighed and added into a polytetrafluoroethylene-lined reactor, and reacted at 80-100° C. with magnetic stirring at 100-200 rpm for 20-100 min to obtain fructose.

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