Acid-metal bifunctional catalyst for catalyzing cellulose to prepare isosorbide as well as preparation method and application of acid-metal bifunctional catalyst

Abstract

The invention discloses an acid-metal bifunctional catalyst for catalyzing cellulose to prepare isosorbide as well as a preparation method and application of the acid-metal bifunctional catalyst, the catalyst takes an acid-functionalized porous organic polymer as a carrier to load metal nanoparticles, the chemical general formula of the catalyst is M-PPh3-SO3H (at) POPs, and M is Ru, Pt, Pd or Ni. According to the catalyst, an acid active center is provided through a sulfonic acid group and used for cellulose hydrolysis and sorbitol dehydration, meanwhile, a hydrogenation center is provided through metal nanoparticles and used for glucose hydrogenation, and synergistic catalysis of acid-metal double active centers is achieved. The invention also provides a preparation method of the catalyst. The preparation method comprises the steps of carrier synthesis, acid functionalization and metal loading. The catalyst is applied to a reaction for directly preparing isosorbide from cellulose, the technological process can be remarkably simplified, the yield of isosorbide can reach 85% or above under the optimal condition, the catalyst is good in stability, and the activity retention rate exceeds 90% after the catalyst is repeatedly used five times.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, and particularly relates to an acid-metal bifunctional catalyst for the catalytic preparation of isosorbide from cellulose, its preparation method and application. Background Technology

[0002] Isosorbide is an important biomass-based platform compound, widely used in pharmaceuticals, polymer monomers, and fuel additives due to its two chiral centers and rigid structure. Particularly in the synthesis of high-performance bio-based polymers such as polycarbonates and polyesters, isosorbide can serve as a green alternative monomer, replacing traditional petroleum-based bisphenol A, demonstrating good environmental friendliness and promising application prospects.

[0003] Traditionally, the preparation of isosorbide from cellulose is a multi-step, sequential reaction process, typically involving three key steps: cellulose hydrolysis to glucose, glucose hydrogenation to sorbitol, and sorbitol dehydration to isosorbide. In existing technologies, these reaction steps are often carried out separately in different reactors, using different monofunctional catalysts. For example, the cellulose hydrolysis stage usually uses homogeneous acids (such as sulfuric acid) or heterogeneous solid acid catalysts; the glucose hydrogenation step requires metal catalysts (such as supported Ru / C, Ni, etc.); and the sorbitol dehydration step requires switching back to an acid catalyst. This multi-step, separate reaction process leads to problems such as high equipment investment, long process flow, high energy consumption, cumbersome operation, and low overall efficiency.

[0004] More importantly, because monofunctional catalysts (such as single acid catalysts or single metal catalysts) cannot simultaneously provide the multiple active sites required for hydrolysis, hydrogenation, and dehydration in the same reaction environment, it is difficult to achieve a one-pot direct conversion from cellulose to isosorbide. Even when attempting to physically mix two or more monofunctional catalysts, poor catalytic synergy often results in ineffective coupling of the reaction pathway due to factors such as excessive spatial distance between different active sites, low mass transfer efficiency, or mutual interference and shielding of active sites. This leads to a low overall yield of isosorbide, a slow reaction rate, and the potential for increased side reactions due to the accumulation of intermediate products, resulting in decreased selectivity for the target product.

[0005] Furthermore, existing catalysts, especially hydrolysis catalysts used in strong acid environments, are prone to problems such as loss of active components, collapse of pore structure, or carbon deposition covering of active sites under high-temperature hydrothermal reaction conditions. This leads to rapid deactivation of the catalyst, poor stability, and difficulty in meeting the requirements of long-term continuous operation in industrial applications.

[0006] Therefore, developing a bifunctional or multifunctional catalyst that integrates multiple catalytic functions, has a suitable pore structure to promote mass transfer between reactants and products, and exhibits high stability under hydrothermal conditions to achieve efficient, highly selective, one-step catalytic conversion of cellulose to isosorbide has become a key technical problem that urgently needs to be solved in this field, and also has significant industrial application value. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention proposes an acid-metal bifunctional catalyst for the catalytic preparation of isosorbide from cellulose, along with its preparation method and application. This catalyst, through its unique structural design, can synergistically catalyze the three-step tandem reaction of cellulose hydrolysis, hydrogenation, and dehydration in the same reaction system, achieving a one-pot conversion of cellulose to isosorbide with high selectivity and high yield, and possesses excellent reusability.

[0008] To achieve the above objectives, the present invention provides an acid-metal bifunctional catalyst for the catalytic preparation of isosorbide from cellulose. The catalyst uses an acid-functionalized porous organic polymer as a support on which metal nanoparticles are loaded. The acid-functionalized porous organic polymer provides acid active sites through sulfonic acid groups, and the metal nanoparticles provide metal active sites. The general chemical formula of the catalyst is M-PPh3-SO3H@POPs, where M is a metal element in the metal nanoparticles.

[0009] Furthermore, the metallic element M is selected from any one of Ru, Pt, Pd, and Ni.

[0010] Furthermore, the specific surface area of ​​the acid-functionalized porous organic polymer support is 400-600 m². 2 / g, with a pore size of 2-10 nm.

[0011] Furthermore, the acidity of the sulfonic acid group is 0.8-2.5 mmol / g.

[0012] Furthermore, the loading of the metal nanoparticles is 0.5-5.0 wt% based on the mass of the metal element.

[0013] This invention also provides a method for preparing the acid-metal bifunctional catalyst as described above, comprising the following steps: a) Provide porous organic polymer carriers; b) The porous organic polymer support is acid-functionalized by introducing sulfonic acid groups to obtain an acid-functionalized porous organic polymer support. c) Metal nanoparticles are loaded onto the acid-functionalized porous organic polymer support and then post-treated to obtain the acid-metal bifunctional catalyst.

[0014] Further, in step a), the porous organic polymer support is prepared by a solvothermal method using phenylphosphine as a monomer; and / or, In step b), the acid functionalization is performed using chlorosulfonic acid; and / or, In step c), the metal nanoparticles are loaded using an impregnation method combined with a reduction method, wherein the reduction method is a chemical reduction method or a hydrogen thermal reduction method.

[0015] The present invention also provides the application of the acid-metal bifunctional catalyst as described above in the catalytic preparation of isosorbide from cellulose.

[0016] Furthermore, the process conditions for the reaction are: reaction temperature 180-220℃, hydrogen pressure 2-4 MPa, and reaction time 2-6 hours.

[0017] The present invention also provides a method for catalytically preparing isosorbide from cellulose, wherein cellulose, hydrogen and an acid-metal bifunctional catalyst as described above are reacted in water under the reaction conditions described above.

[0018] Compared with the prior art, the present invention has the following advantages and technical effects: This invention provides an acid-metal bifunctional catalyst for the catalytic preparation of isosorbide from cellulose. The catalyst uses an acid-functionalized porous organic polymer as a support to load metal nanoparticles, with the general chemical formula M-PPh3-SO3H@POPs. This catalyst achieves the direct conversion of cellulose to isosorbide through the synergistic effect of sulfonic acid groups and metal nanoparticles.

[0019] Thanks to the aforementioned structural design, the catalyst of this invention exhibits significant technical advantages. The close synergy between its acid and metal centers at the nanoscale effectively promotes the tandem reaction pathway of hydrolysis-hydrogenation-dehydration, significantly increasing the isosorbide yield to over 85%, far exceeding that of traditional monofunctional catalysts. Simultaneously, the catalyst demonstrates excellent stability, retaining over 90% of its activity even after five reuses, showcasing promising potential for industrial applications. Furthermore, this technology simplifies the traditional multi-step reaction into a single step, significantly reducing equipment investment and energy consumption, and simplifying the process flow. By adjusting parameters such as the support structure, acid content, and metal loading, the catalyst performance can be further optimized to meet diverse application requirements. Detailed Implementation

[0020] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0021] All raw materials used in this invention are not particularly limited in their source; they can be purchased from the market or prepared using conventional methods known to those skilled in the art.

[0022] There are no particular restrictions on the purity of any of the raw materials used in this invention. However, this invention preferably uses raw materials of analytical grade or purity commonly used in the field of chemical synthesis.

[0023] Example 1: Preparation of Ru-PPh3-SO3H@POPs catalyst and its application in the preparation of isosorbide from cellulose First, the acid-metal bifunctional catalyst Ru-PPh3-SO3H@POPs was prepared. The specific steps are as follows: (1) A porous organic polymer (POPs) support was synthesized using phenylphosphine as a monomer via a solvothermal method. The synthesis was carried out in a reactor using N,N-dimethylformamide as the solvent at 150°C for 24 hours. After the reaction, the POPs support was obtained by filtration, washing, and vacuum drying, resulting in a POPs support with a high specific surface area. Characterization by nitrogen adsorption-desorption testing showed a BET specific surface area of ​​500 m². 2 / g, the pore size distribution is mainly concentrated in the range of 2-10 nm, exhibiting a good mesoporous structure.

[0024] (2) Acid functionalization of the above POPs carrier. 1 g of dried POPs carrier was dispersed in 50 mL of anhydrous dichloromethane. Under ice-water bath and nitrogen protection, 20 mL of dichloromethane solution containing 0.01 mol chlorosulfonic acid was slowly added dropwise. After the addition was complete, the reaction mixture was slowly raised to room temperature and stirred continuously for 12 hours. After the reaction was completed, the solid product was collected by filtration and washed thoroughly with anhydrous dichloromethane and deionized water until the filtrate was neutral. Finally, it was vacuum dried at 80°C for 12 hours to obtain the acid-functionalized carrier, labeled as PPh3-SO3H@POPs. The acidity of its sulfonic acid group was determined to be 1.5 mmol / g by acid-base titration.

[0025] (3) Ruthenium (Ru) nanoparticles were loaded using an impregnation-reduction method. 0.5 g of the acid-functionalized support was added to 20 mL of a 10 mg / mL RuCl3·xH2O aqueous solution, and the mixture was stirred and impregnated at room temperature for 12 hours to ensure sufficient adsorption of the metal precursor. Subsequently, an excess of freshly prepared NaBH4 aqueous solution (0.1 M) was slowly added dropwise under stirring for reduction, and the mixture was stirred continuously for 2 hours. After the reaction was complete, the catalyst was separated by filtration and thoroughly washed with deionized water to remove chloride ions and other impurities until no white precipitate was detected in the filtrate using silver nitrate solution. The resulting solid was dried in a vacuum drying oven at 100°C for 12 hours to obtain the final catalyst Ru-PPh3-SO3H@POPs. The Ru loading was determined to be 2.0 wt% by ICP-OES.

[0026] The catalyst was applied to the direct preparation of isosorbide from cellulose. In a 100 mL high-pressure reactor, 1 g of microcrystalline cellulose, 0.1 g of the prepared Ru-PPh3-SO3H@POPs catalyst, and 50 mL of deionized water were added sequentially. The reactor was sealed, and the air inside was purged three times with hydrogen, then hydrogen was introduced until the initial pressure reached 3 MPa. The reaction temperature was set at 200°C, the stirring speed at 600 rpm, and the reaction time at 4 hours. After the reaction was completed, the reactor was rapidly cooled, and the reaction solution was collected. After centrifuging to separate the catalyst, the reaction solution was filtered through a 0.22 μm filter membrane, and the filtrate was analyzed by high-performance liquid chromatography (HPLC).

[0027] HPLC analysis showed that the yield of isosorbide reached 85%, with a formation rate of 0.5 g isosorbide / (g catalyst·h). The catalyst was recovered after the reaction, washed with deionized water, dried, and then reusable under the same reaction conditions. After five reuses, the isosorbide yield remained above 88%, indicating that the catalyst has excellent stability.

[0028] Example 2: Preparation and performance of Pt-PPh3-SO3H@POPs catalyst Following the preparation method of Example 1, the metal precursor was changed to chloroplatinic acid (H2PtCl6·6H2O), and the sulfonation conditions were adjusted to prepare the Pt-PPh3-SO3H@POPs catalyst. Specifically, in the acid functionalization step, the amount of chlorosulfonic acid was controlled to adjust the acidity of the sulfonic acid groups in the final catalyst to 2.0 mmol / g. In the metal loading step, the loading of Pt was controlled to be 1.0 wt%.

[0029] Cellulose conversion was carried out under the same reaction conditions as in Example 1. HPLC analysis showed that the yield of isosorbide was 80%, with a formation rate of 0.45 g isosorbide / (g catalyst·h). This result indicates that a highly efficient acid-metal bifunctional catalytic system can also be constructed using the noble metal Pt.

[0030] Example 3: Preparation and performance of Ni-PPh3-SO3H@POPs catalyst To investigate the application of non-precious metals, a Ni-based bifunctional catalyst was prepared in this embodiment. The specific steps are as follows: Nickel nitrate (Ni(NO3)2·6H2O) was used as the metal precursor. The support preparation and acid functionalization steps were the same as in Example 1, with an acid content of 1.5 mmol / g. In the metal loading step, after impregnation, reduction was carried out in a tube furnace at 400°C under a hydrogen atmosphere (5% H2 / Ar) for 2 hours to obtain the Ni-PPh3-SO3H@POPs catalyst, wherein the Ni loading was 5.0 wt%.

[0031] Catalytic testing was conducted under the same reaction conditions as in Example 1. The results showed that the yield of isosorbide reached 70%, with a formation rate of 0.35 g isosorbide / (g catalyst·h). This example demonstrates that non-noble metal Ni also possesses good catalytic potential in bifunctional catalyst systems, which helps to reduce catalyst costs.

[0032] Example 4: Effect of different acid amounts on catalytic performance To investigate the effect of acidity on catalytic performance, following the preparation method in Example 1, a series of Ru-PPh3-SO3H@POPs catalysts with different acidities were prepared by changing the amount of chlorosulfonic acid used in the sulfonation process. The acidities were 0.8 mmol / g, 1.5 mmol / g (same as in Example 1), and 2.5 mmol / g, respectively, and the Ru loading was controlled at 2.0 wt%.

[0033] Catalytic evaluation was conducted under the same reaction conditions (200°C, 3 MPa H2, 4 h), and the results are shown in the table below:

[0034] The results showed that the acid content had a significant impact on the reaction performance. When the acid content was too low (0.8 mmol / g), the cellulose hydrolysis and sorbitol dehydration steps were limited, resulting in a decrease in yield. When the acid content was moderate (1.5 mmol / g), the bifunctional synergistic effect was optimal, and the yield was the highest. When the acid content was too high (2.5 mmol / g), it may lead to an aggravation of side reactions or pore blockage, resulting in a slight decrease in yield.

[0035] Comparative Example 1: Monofunctional Acid Catalyst Using only the unsupported metal-functionalized acid support PPh3-SO3H@POPs (acidity 1.5 mmol / g) prepared in Example 1 as a catalyst, the test was conducted under the exact same reaction conditions as in Example 1. The results showed that the yield of isosorbide was only 30%, with a formation rate of 0.15 g / (gcat·h). The main products were glucose and a portion of sorbitol, indicating a lack of metal hydrogenation centers, which prevented the efficient completion of the complete pathway from glucose to sorbitol, and subsequently dehydration to isosorbide.

[0036] Comparative Example 2: Monofunctional Metal Catalysts A commercially available supported ruthenium-carbon catalyst (5% Ru / C) without acid sites was used as the catalyst. Tests were conducted under the same reaction conditions as in Example 1. The results showed an extremely low yield of isosorbide, only 15%, at a formation rate of 0.08 g / (gcat·h). The accumulation of sorbitol was predominantly detected in the reaction system, demonstrating that the lack of acid sites hinders the effective catalysis of cellulose hydrolysis and sorbitol dehydration.

[0037] Comparative Example 3: Physically Mixed Catalysts The monofunctional acid catalyst PPh3-SO3H@POPs (acid content 1.5 mmol / g) was physically mixed with the monofunctional metal catalyst Ru / C (5% Ru), wherein the mass ratio of PPh3-SO3H@POPs to Ru / C was 1:1 (the total loading based on metal Ru was similar to that in Example 1), and the reaction was tested under the same conditions as in Example 1. The results showed that the yield of isosorbide was 55%, and the formation rate was 0.28 g / (gcat·h). Although this yield was higher than that of the monofunctional catalyst, it was significantly lower than that of the bifunctional catalyst (85%) designed in this invention. This indicates that the acid and metal sites are spatially separated under the physical mixing mode, resulting in limited synergistic effect and low mass transfer efficiency.

[0038] Comparative Example 4: Different carriers (non-porous structure) To illustrate the importance of the support's pore structure, non-porous silica (SiO2) was used for comparison. First, the non-porous SiO2 was sulfonated to obtain SO3H-SiO2 with an acid content of 1.4 mmol / g. Then, 2.0 wt% Ru was loaded onto it to prepare the Ru-SO3H-SiO2 catalyst. Under the same reaction conditions as in Example 1, the isosorbide yield was only 45%. This indicates that the lack of a suitable pore structure hinders the diffusion and contact of macromolecular cellulose and its reaction intermediates, severely limiting the catalytic efficiency.

[0039] In summary, the acid-metal bifunctional catalyst provided by this invention integrates acid and metal active centers onto a porous organic polymer support with a suitable pore structure, achieving close synergy and spatial proximity effects among the active sites. This results in significantly superior catalytic activity, selectivity, and stability compared to monofunctional catalysts or physically mixed catalysts in the one-pot direct preparation of isosorbide from cellulose. Furthermore, by adjusting parameters such as the amount of acid, the type of metal, and the loading, its catalytic performance can be further optimized to meet diverse application requirements.

[0040] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. An acid-metal bifunctional catalyst for catalyzing the preparation of isosorbide from cellulose, characterized in that, The catalyst uses an acid-functionalized porous organic polymer as a support, on which metal nanoparticles are loaded; the acid-functionalized porous organic polymer provides acid active sites through sulfonic acid groups, and the metal nanoparticles provide metal active sites; the general chemical formula of the catalyst is M-PPh3-SO3H@POPs, where M is a metal element in the metal nanoparticles.

2. The acid-metal bifunctional catalyst according to claim 1, wherein The metallic element M is selected from any one of Ru, Pt, Pd, and Ni.

3. The acid-metal bifunctional catalyst according to claim 1 or 2, characterized in that, The acid-functionalized porous organic polymer support has a specific surface area of 400-600 m 2 / g and a pore size of 2-10 nm.

4. The acid-metal bifunctional catalyst according to claim 1 or 2, characterized in that, The acidity of the sulfonic acid group is 0.8-2.5 mmol / g.

5. The acid-metal bifunctional catalyst according to claim 1 or 2, characterized in that, The loading of the metal nanoparticles is 0.5-5.0 wt% based on the mass of the metal element.

6. A method for preparing an acid-metal bifunctional catalyst as described in any one of claims 1-5, characterized in that, Includes the following steps: a) Provide porous organic polymer carriers; b) The porous organic polymer support is acid-functionalized by introducing sulfonic acid groups to obtain an acid-functionalized porous organic polymer support. c) Metal nanoparticles are loaded onto the acid-functionalized porous organic polymer support and then post-treated to obtain the acid-metal bifunctional catalyst.

7. The preparation method according to claim 6, characterized in that, In step a), the porous organic polymer support is prepared by a solvothermal method using phenylphosphine as a monomer; and / or, In step b), the acid functionalization is performed using chlorosulfonic acid; and / or, In step c), the metal nanoparticles are loaded using an impregnation method combined with a reduction method, wherein the reduction method is a chemical reduction method or a hydrogen thermal reduction method.

8. The application of an acid-metal bifunctional catalyst as described in any one of claims 1-5 in the catalytic preparation of isosorbide from cellulose.

9. The application according to claim 8, characterized in that, The reaction process conditions are: reaction temperature 180-220℃, hydrogen pressure 2-4 MPa, and reaction time 2-6 hours.

10. A method for catalytically preparing isosorbide from cellulose, characterized in that, Under the reaction conditions described in claim 9, cellulose, hydrogen, and the acid-metal bifunctional catalyst as described in any one of claims 1-5 are brought into contact with water for reaction.

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