A carbon nitride supported noble metal catalyst, its preparation method and application

Abstract

This invention discloses a carbon nitride-supported noble metal catalyst, its preparation method, and its application, belonging to the technical field of preparation and application of supported noble metal catalysts. Using melamine as a precursor, graphitic carbon nitride (g-C3N4) support is obtained through high-temperature calcination and ultrasonic exfoliation. Noble metal palladium nanoparticles are then loaded onto the surface of g-C3N4 via an impregnation-reduction method to obtain a Pd / g-C3N4 catalyst. In the prepared catalyst, palladium nanoparticles are uniformly dispersed on the support surface, with an average particle size of approximately 3.2 nm, and the mesoporous structure of the support remains intact before and after loading. This invention features a simple preparation method, low noble metal usage, and high catalyst activity, exhibiting excellent catalytic performance in the hydrogenation of 5-hydroxymethylfurfural to 2,5-dimethylfuran. Under reaction conditions of 150 °C, 1.5 MPa H2, and formic acid as the hydrogen donor, a 1% Pd / g-C3N4 catalyst can achieve complete HMF conversion, with a DMF selectivity of 95% and a conversion frequency of 362 h⁻¹. ‑1 Even after five cycles of use, it still maintains a conversion rate of 93% and a selectivity of 83%, showing good prospects for industrial application.

Description

Technical Field

[0001] This invention relates to a method for preparing a carbon nitride-supported nano-noble metal catalyst, and also to the application of the invented catalyst in the selective hydrogenation of 5-hydroxymethylfurfural to prepare 2,5-dimethylfuran, belonging to the technical field of preparation and application of supported noble metal catalysts. Background Technology

[0002] The deepening of global carbon emission reduction policies and the accelerated transformation to a green energy system have brought biomass, as an important renewable resource, into the spotlight. Biomass can not only be used to produce fuels but also be converted into a variety of high-value-added chemicals, playing a vital role in promoting sustainable industrial development. Among numerous biomass derivatives, 5-hydroxymethylfurfural (HMF), due to the presence of three functional groups in its molecular structure—aldehyde (-CHO), hydroxymethyl (-CH2OH), and furan ring—possesses rich chemical reactivity and can be converted into various high-value-added compounds through reaction pathways such as hydrogenation reduction, oxidation, esterification, and ring-opening. Among these, 2,5-dimethylfuran (DMF), with its low volatility, high octane number, high energy density, and immiscibility with water, is considered a promising alternative to fossil-based fuels.

[0003] In the research field of HMF-catalyzed DMF production, palladium-based noble metal catalysts are a core class of catalytic materials. Existing studies have shown that the catalytic performance of palladium-based catalysts is mainly influenced by the combined effects of palladium particle size, support properties, and palladium-support interactions. Therefore, screening suitable supports to achieve stable dispersion of small-sized palladium species and effectively regulating the microchemical environment of palladium active sites are key approaches to optimizing the catalytic activity of palladium-based catalysts.

[0004] Two-dimensional graphitic carbon nitride (g-C3N4) has attracted widespread attention as a palladium-based catalyst support due to its low cost, excellent thermochemical stability, and nitrogen-rich framework structure. The nitrogen species in its framework are believed to anchor metal particles and modulate their microchemical environment, thereby improving the overall performance of the catalyst. However, existing research on the application of Pd / g-C3N4 catalysts in the selective hydrogenation of HMF to DMF remains limited. In particular, no breakthrough has been achieved in constructing highly active catalytic systems under low palladium loading conditions. Furthermore, existing reports have encountered problems such as low DMF yields and high palladium loadings, limiting its widespread industrial application.

[0005] Invention patent CN202511714643.7 describes the preparation of a CuPd / C bimetallic catalyst using a continuous flow method. This catalyst catalyzes the hydrogenation of HMF to DMF at 130 °C and 2 MPa H2, achieving a conversion rate of 100% and a selectivity of 97.5%. However, this patent does not explore the regulatory mechanism of the electronic structure of the active center, and the use of a bimetallic system makes the catalyst preparation process relatively complex, with the utilization rate of precious metals needing improvement.

[0006] Invention patent CN202511285929.8 uses a metal-organic coordination porous polymer (MOF) as a carrier. Non-precious metal active components such as Cu, Ni, and Co are impregnated and anchored, and a supported catalyst is obtained through calcination in an air atmosphere. This catalyst catalyzes the hydrogenation of HMF to DMF at 150 °C and 1.5 MPa H2, achieving a conversion rate of 100% and a selectivity of 99.60%. While this patent utilizes the pore structure of MOF materials to restrict metal particle aggregation and achieve high dispersion of the active components, it does not address the intrinsic activity evaluation of the catalyst (such as the TOF value) or explore the mechanism by which the electronic structure of the active center regulates catalytic performance. Furthermore, the catalyst preparation process involves multi-step solvent system control, making the process relatively complex.

[0007] Invention patent CN202510431441.5 describes a bimetallic catalyst for the hydrogenation of HMF to DMF, prepared by sequentially loading non-precious metals (Co, Fe, Ni, or Mo) and precious metal Pt via a stepwise impregnation method using humic acid-based carbon materials as a carrier. The catalyst achieves a conversion rate of 100% and a selectivity of 81.4% to 92.0%. This patent employs a bimetallic system with a high Pt loading (0.1 wt% to 10 wt%), and the preparation process involves two metal loading steps, multiple calcinations, and hydrogen reduction, resulting in a complex process with high energy consumption. Furthermore, the reaction conditions are relatively harsh (200 °C, 3.0 MPa H2), which is not conducive to industrial-scale application.

[0008] The 1% Pd / g-C3N4 catalyst prepared in this invention achieves 100% conversion of HMF to DMF under reaction conditions of 1.5 MPa H2 and 423 K, with a DMF selectivity of 95% and a TOF of 362 h⁻¹. -1 The literature reports that the TOF of the Pd / NMC (nitrogen-doped porous carbon) catalyst is 150 h under the conditions of 0.5 MPa H2 and 433 K. -1 The DMF selectivity was 97% (Angew. Chem. Int. Ed. 2021, 60, 6807-6815); the Pd / MOF-808 (Zr-based metal-organic framework) catalyst had a TOF of 152 h under conditions of 1.0 MPa H2 and 373 K. -1The DMF selectivity was 99% (ACS Sustainable Chem. Eng. 2022, 10, 10286-10293); the TOF of the Pd-GVL (γ-valerolactone) / C catalyst was 246 h under the conditions of 2.0 MPa H2 and 353 K. -1 The DMF selectivity was 95.6% (ACS Sustainable Chem. Eng. 2019, 7, 5711-5716). In contrast, the 5Pd-M-600 catalyst, although exhibiting a high TOF of 524.46 h⁻¹, showed a different result. -1 However, its DMF selectivity is less than 10% (Catal. Today 2025, 457, 115353). In comparison, the catalyst of this invention achieves a synergistic balance between high conversion and high selectivity under mild reaction conditions, and with a noble metal loading of only 1 wt%, it still maintains a conversion rate of 93% and a DMF selectivity of 83% after five cycles. It combines excellent catalytic activity, selectivity and stability, showing significant prospects for industrial application. Summary of the Invention

[0009] This invention addresses the problems of low activity, poor selectivity, and complex preparation processes of existing noble metal catalysts in biomass hydrogenation reactions. It provides a carbon nitride-supported noble metal catalyst, its preparation method, and its applications. This catalyst uses graphitic carbon nitride (g-C3N4) as a support and loads palladium nanoparticles. It offers advantages such as simple preparation method, high catalytic activity, good selectivity, and recyclability, and is particularly suitable for the hydrogenation of 5-hydroxymethylfurfural to 2,5-dimethylfuran.

[0010] To achieve the above objectives, the technical solution provided by the present invention is as follows:

[0011] In a first aspect, the present invention provides a carbon nitride-supported noble metal catalyst.

[0012] The catalyst is supported by graphitic carbon nitride, and the active component is palladium nanoparticles.

[0013] Secondly, the present invention provides a method for preparing the carbon nitride-supported noble metal catalyst.

[0014] The method includes the following steps:

[0015] 0.1 g g-C3N4 support was dispersed in 20 mL of deionized water, followed by the addition of 5-20 mL of H2PdCl4 solution. The mixture was ultrasonically dispersed and then stirred in an ice bath. NaOH solution (0.1 mol / L) was added dropwise to adjust the pH of the system to 10, and stirring was continued for 3 h. The resulting product was dried at 60 °C overnight, thoroughly ground, and then reduced at 200-350 °C for 2-4 h under a high-purity hydrogen atmosphere to obtain the Pd / g-C3N4 catalyst.

[0016] Furthermore, the g-C3N4 support is preferably prepared via the following steps:

[0017] 5 g of melamine was weighed and placed in a corundum crucible. The crucible was heated to 550 °C for 2 h under a nitrogen atmosphere at a heating rate of 5 °C / min to obtain bulk carbon nitride (bulk-C3N4). The obtained bulk-C3N4 was thoroughly ground and dispersed in 150 mL of ethanol-water solution (volume ratio 1:2). The mixture was ultrasonically treated for 2 h and then washed with ethanol and water in sequence. The washed product was vacuum dried at 60 °C overnight and then ground to obtain g-C3N4 support.

[0018] Thirdly, the present invention provides the application of the carbon nitride-supported noble metal catalyst in the hydrogenation of 5-hydroxymethylfurfural to prepare 2,5-dimethylfuran.

[0019] The specific application method includes the following steps:

[0020] Mix 50 mg of the catalyst, 0.5 mmol of 5-hydroxymethylfurfural, and 8.87 mL of tetrahydrofuran (THF), and add 0.5–1.5 mL of formic acid (FA). Purge the reactor with hydrogen to a pressure of 1.1–1.6 MPa, and heat to 120–170 °C under stirring for 1.5–6 h. After the reaction is complete, separate the catalyst to obtain 2,5-dimethylfuran.

[0021] Preferably, the amount of formic acid used is 1.0 mL.

[0022] Preferably, the reaction temperature is 150 °C.

[0023] Preferably, the hydrogen pressure is 1.5 MPa.

[0024] Preferably, the reaction time is 4 hours.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) The catalyst exhibits high activity and excellent selectivity. Under mild reaction conditions (150 °C, 1.5 MPa H2, 4 h), the 1% Pd / g-C3N4 catalyst prepared in this invention achieves 100% HMF conversion, 95% DMF selectivity, and a high TOF (transformation frequency) of 362 h when catalyzing the hydrogenation of 5-hydroxymethylfurfural to 2,5-dimethylfuran. -1 Its overall performance is superior to that of similar palladium-based catalysts.

[0027] (2) The catalyst has low noble metal loading and good atom economy. The palladium loading in the catalyst of this invention is only 1 wt%, which is much lower than that in some bimetallic or multi-step impregnation systems in the prior art. While ensuring high catalytic activity, it significantly reduces the amount of noble metal used and has good economy.

[0028] (3) The catalyst has good stability and can be recycled. After five cycles, the HMF conversion rate of 1% Pd / g-C3N4 catalyst remains at 93% and the DMF selectivity remains at 83%, showing excellent catalytic stability and recyclability, and has the potential for industrial application.

[0029] (4) The preparation process is simple and the conditions are mild. The present invention uses a one-step impregnation-reduction method to prepare the catalyst, without the need for complex solvent control or multi-step calcination process; the reaction conditions are mild (150 ℃, 1.5 MPa H2), which is more advantageous for industrial promotion.

[0030] (5) The support structure is stable and the metal is uniformly dispersed. The g-C3N4 support has a nitrogen-rich framework structure. Pd nanoparticles (average particle size of about 3.2 nm) are uniformly dispersed on the support surface. The mesoporous structure of the support is well maintained before and after loading, which ensures the mass transfer efficiency of the catalytic reaction. Attached Figure Description

[0031] Figure 1 The infrared spectra of Embodiment 1 and Comparative Examples 1 and 2 of the present invention are shown.

[0032] Figure 2 The X-ray diffraction patterns are those of Example 1, Comparative Example 1, and Comparative Example 2 of the present invention.

[0033] Figure 3 Transmission electron microscopy (TEM) images and corresponding Pd particle size distributions of the catalysts in Comparative Example 2 (0.5% Pd / g-C3N4, a, b, c), Example 1 (1% Pd / g-C3N4, d, e, f), and Comparative Example 2 (2% Pd / g-C3N4, g, h, i) of this invention.

[0034] Figure 4 (a) Transmission electron microscope image and fast Fourier transform spectrum of palladium nanoparticles in Example 1 of the present invention; (b) EDS elemental distribution map.

[0035] Figure 5 The following are the N2 adsorption-desorption isotherms and pore size distribution curves of Example 1 and Comparative Example 1 of the present invention: (a) N2 adsorption-desorption isotherms and (b) pore size distribution curves.

[0036] Figure 6 The following are the (a) C 1s XPS spectra, (b) Pd 3d XPS spectra, and (c) N 1s XPS spectra of Example 1 (1% Pd / g-C3N4), Comparative Example 1 (g-C3N4), and Comparative Example 2 (0.5% Pd / g-C3N4, 2% Pd / g-C3N4) of the present invention.

[0037] Figure 7 The catalytic performance of Example 1 (1% Pd / g-C3N4) and Comparative Example 2 with different Pd loadings of Pd / g-C3N4 in this invention was evaluated (reaction conditions: 0.5 mmol HMF, 8.87 mL THF, 1 mL FA, 50 mg catalyst, 150 °C, 1.5 MPa H2, reaction time 4 h).

[0038] Figure 8 This invention provides the catalytic performance of 1%Pd / g-C3N4 catalysts at different hydrogen reduction temperatures and times in Example 1 (1%Pd / g-C3N4, 250 °C for 3 h) and Comparative Example 3 (reaction conditions: 0.5 mmol HMF, 8.87 mL THF, 1 mL FA, 50 mg catalyst, 150 °C, H2 1.5 MPa, reaction 4 h).

[0039] Figure 9 The catalytic performance of the 1%Pd / g-C3N4 catalyst in Example 1 (1%Pd / g-C3N4, hydrogen donor is 1 mL FA) and Comparative Example 4 is evaluated when the hydrogen donors are formic acid 1 mL + N2 1.5 MPa, methanol 1 mL + H2 1.5 MPa, ethanol 1 mL + H2 1.5 MPa, and isopropanol 1 mL + H2 1.5 MPa, respectively (reaction conditions: 0.5 mmol HMF, 8.87 mL THF, 1 mL FA, 50 mg catalyst, 150 ℃, H2 1.5 MPa, reaction 4 h).

[0040] Figure 10 This invention describes the catalytic performance of the 1%Pd / g-C3N4 catalyst in Example 1 (1%Pd / g-C3N4, hydrogen donor is 1 mL FA) and Comparative Example 5 with different amounts of FA (reaction conditions: 0.5 mmol HMF, 8.87 mL THF, 1 mL FA, 50 mg catalyst, 150 °C, H2 1.5 MPa, reaction 4 h).

[0041] Figure 11 This invention compares the catalytic performance of 1% Pd / g-C3N4 catalyst in Example 1 (1% Pd / g-C3N4, reaction temperature 150 °C, pressure 1.5 MPa, time 4 h) and Comparative Example 6 with only the reaction temperature adjusted (reaction conditions: 0.5 mmol HMF, 8.87 mL THF, 1 mL FA, 50 mg catalyst, H2 1.5 MPa, reaction 4 h).

[0042] Figure 12 The catalytic performance of the 1%Pd / g-C3N4 catalyst in Example 1 of the present invention (1%Pd / g-C3N4, reaction temperature 150 ℃, pressure 1.5 MPa, time 4 h) and Comparative Example 7 was compared by adjusting only the reaction pressure (reaction conditions: 0.5 mmol HMF, 8.87 mL THF, 1 mL FA, 50 mg catalyst, 150 ℃, reaction 4 h).

[0043] Figure 13 The catalytic performance of the 1%Pd / g-C3N4 catalyst in Example 1 of the present invention (1%Pd / g-C3N4, reaction temperature 150 ℃, pressure 1.5 MPa, time 4 h) and Comparative Example 8 was compared by adjusting only the reaction time (reaction conditions: 0.5 mmol HMF, 8.87 mL THF, 1 mL FA, 50 mg catalyst, pressure 1.5 MPa, 150 ℃).

[0044] Figure 14 The recycling performance of Example 1 of the present invention (reaction conditions: 0.5 mmol HMF, 8.87 mL THF, 1 mL FA, 50 mg catalyst, 150 °C, H2 1.5 MPa, reaction 4 h). Detailed Implementation

[0045] The present invention will be further explained below with reference to specific embodiments and accompanying drawings:

[0046] Example 1:

[0047] 5 g of melamine was weighed and placed in a corundum crucible. The crucible was heated to 550 °C for 2 h under a nitrogen atmosphere at a heating rate of 5 °C / min to obtain bulk carbon nitride (bulk-C3N4). The obtained bulk-C3N4 was thoroughly ground and dispersed in 150 mL of ethanol-water solution (volume ratio 1:2). The mixture was ultrasonically treated for 2 h and then washed with ethanol and water in sequence. The washed product was vacuum dried at 60 °C overnight and then ground to obtain g-C3N4 support.

[0048] 0.1 g g-C3N4 support was dispersed in 20 mL of deionized water, followed by the addition of 10 mL of H2PdCl4 (0.1 g g). Pd / L) solution; after ultrasonic dispersion of the mixture, it was placed in an ice bath and stirred, and NaOH solution (0.1 mol / L) was added dropwise to adjust the pH value of the system to 10, and stirring was continued for 3 h; the obtained product was dried at 60 ℃ overnight, and after thorough grinding, it was reduced at 250 ℃ for 3 h in a high-purity hydrogen atmosphere to obtain the Pd / g-C3N4 catalyst.

[0049] 50 mg of the catalyst, 0.5 mmol of 5-hydroxymethylfurfural (HMF), and 8.87 mL of tetrahydrofuran were mixed, and 1.0 mL of formic acid (FA) was added. Hydrogen gas was introduced into the reactor to a pressure of 1.5 MPa, and the temperature was raised to 150 °C for 4 h under stirring. After the reaction was completed, the catalyst was separated to obtain 2,5-dimethylfuran (DMF).

[0050] HMF conversion rate 100%, DMF selectivity 95%, conversion frequency (TOF) 362 h. -1 .

[0051] Comparative Example 1: Comparison with only g-C3N4 carrier prepared according to Example 1.

[0052] Comparative Example 2: Catalysts were prepared according to Example 1 (1% Pd / g-C3N4), with only the volume of tetrachloropalladium acid (H2PdCl4) solution added adjusted accordingly. During the adjustment process, the amount of deionized water was changed simultaneously to ensure that the total volume of the mixture of tetrachloropalladium acid solution and deionized water remained constant at 30 mL. Catalysts of 0.1% Pd / g-C3N4, 0.5% Pd / g-C3N4, 0.7% Pd / g-C3N4, 1.5% Pd / g-C3N4, and 2% Pd / g-C3N4 were prepared as comparisons.

[0053] Figure 1 Fourier transform infrared spectra of the prepared Comparative Example 1 g-C3N4 support and the catalysts of Examples 1 and 2 are shown. The range is 1200–1650 cm⁻¹. -1 The series of characteristic peaks appearing within the interval correspond to the stretching vibrations of aromatic CN bonds; 808 cm⁻¹ -1 The peak at 3000-3300 cm⁻¹ is attributed to the characteristic absorption peak of the triazine ring; while the peak at 3000-3300 cm⁻¹ is attributed to the characteristic absorption peak of the triazine ring. -1 The broad peaks within the range originate from the stretching vibration of the NH bond. The presence of these characteristic peaks confirms the successful synthesis of the g-C3N4 support. After loading with the noble metal Pd, the characteristic peaks did not change significantly, indicating that low Pd loading did not alter the support's skeletal structure. Figure 2X-ray diffraction patterns of the prepared g-C3N4 support (Comparative Example 1) and catalysts (Examples 1 and 2) are shown. All samples exhibit two distinct diffraction peaks at 2θ = 13.8° and 27.8°, corresponding to the (100) and (002) crystal planes of g-C3N4, respectively. Furthermore, the diffraction patterns of each catalyst show three characteristic peaks at 2θ = 40.1°, 46.6°, and 68.0°, attributed to the (111), (200), and (220) crystal planes of metallic Pd, respectively, confirming that Pd has been successfully loaded onto the g-C3N4 surface. Moreover, the intensity of the Pd-related diffraction peaks gradually increases with increasing Pd loading.

[0054] Figure 3 Transmission electron microscopy (TEM) images and corresponding Pd particle size distributions of the catalysts in Comparative Example 2 (0.5% Pd / g-C3N4, a, b, c), Example 1 (1% Pd / g-C3N4, d, e, f), and Comparative Example 2 (2% Pd / g-C3N4, g, h, i) of this invention are shown. The results indicate that spherical Pd nanoparticles are uniformly dispersed on the surface of the g-C3N4 support. Particle size distribution analysis shows that the average particle sizes of the three catalysts are 3.0 nm, 3.2 nm, and 3.5 nm, respectively, indicating that the particle size increases slightly with increasing Pd loading. Figure 4 The images show the transmission electron microscope (TEM) image and EDS elemental distribution map of Embodiment 1 of the present invention. The Pd (111) lattice fringes with a spacing of 0.23 nm are clearly visible in the images. The corresponding Fast Fourier Transform (FFT) spectrum confirms that the lattice belongs to the (111) crystal plane of metallic Pd. Combined with the elemental distribution map, this provides direct evidence for the successful loading of Pd particles.

[0055] Figure 5 The N2 adsorption-desorption isotherms and pore size distribution curves for Example 1 and Comparative Example 1 of this invention are shown. All these samples exhibit type IV adsorption isotherms, demonstrating that the samples before and after palladium loading have similar mesoporous structures and essentially consistent pore distributions. Table 1 lists the specific surface area, pore volume, and pore size data. Comparison reveals that after loading Pd onto g-C3N4, 1% Pd / g-C3N4 (18.4 m³) results in a higher specific surface area, pore volume, and pore size. 2 The specific surface area of ​​g-C3N4 (19.2 m² / g) is only slightly lower than that of g-C3N4 (19.2 m² / g). 2 / g), while the pore volume and average pore size also decreased slightly, which may be due to the Pd NPs being loaded on the pores and the carrier surface, occupying a certain volume.

[0056]

[0057] Figure 6The following are the (a) C 1s XPS spectra, (b) Pd 3d XPS spectra, and (c) N 1s XPS spectra of Example 1 (1% Pd / g-C3N4), Comparative Example 1 (g-C3N4), and Comparative Example 2 (0.5% Pd / g-C3N4, 2% Pd / g-C3N4) of the present invention. Figure 6 The C1s spectrum contains three characteristic peaks, corresponding to CC, CNH, and NC=N, respectively. Figure 6 The C=NN, N-C3, and CNH structures in the cN1s spectrum correspond to each other, confirming the successful synthesis of the g-C3N4 support. (Pd 3d spectrum) Figure 6 b) There are two main species, namely Pd 0 and Pd 2+ Among them, the catalysts are 0.5% Pd / g-C3N4, 1% Pd / g-C3N4, and 2% Pd / g-C3N4, which contain Pd 3d 5 / 2 The binding energies are 335.6 eV, 335.8 eV, and 335.5 eV, respectively, shifting towards higher binding energies compared to the standard binding energy of metallic Pd; the Pd binding energies of the three catalysts... 2+ 3D 5 / 2 The binding energy also shifted towards higher binding energies, reaching 337.9 eV, 337.4 eV, and 337.7 eV respectively. This change signifies an alteration in the electronic state of the metal surface, resulting in a depletion of electrons on the Pd surface, implying some interaction between Pd particles and the carrier. Table 2 shows the proportions of Pd species in 0.5%Pd / g-C3N4, 1%Pd / g-C3N4, and 2%Pd / g-C3N4. For 0.5%Pd / g-C3N4, Pd... 2+ / Pd 0 The ratio is 1.4. However, for 1% Pd / g-C3N4, the ratio is 0.68, and when the Pd loading continues to increase, the ratio of this catalyst with 2% Pd / g-C3N4 increases to 0.82, indicating that the interaction between the support and the metal varies with the Pd content. At lower loadings, Pd is highly dispersed on the surface of g-C3N4, forming strong coordination with nitrogen atoms in the support (such as –NH or –N= groups), which easily leads to Pd formation. 2+ Species, therefore Pd 2+ The proportion was relatively high (58.4%); as the amount of Pd increased, some Pd began to aggregate or was more easily reduced (especially during H2 reduction), forming more Pd. 0 At this time, Pd 2+ The proportion decreased (28.0%); as the loading further increased (2% Pd), the surface Pd... 2+ It may originate from incompletely reduced PdO or Pd at the Pd-carrier interface.2+ Therefore, Pd 2+ The proportion increased again (45.1%). Therefore, this invention can adjust the electronic structure of active species by regulating the loading of active metals, thereby affecting catalytic performance.

[0058]

[0059] Figure 7 This invention presents the catalytic performance of Example 1 (1% Pd / g-C3N4) and Comparative Example 2 with different Pd loadings in Pd / g-C3N4. Under the same evaluation conditions, the pure g-C3N4 support without Pd showed no significant catalytic activity for the hydrogenation of HMF (conversion rate <5%). However, with the introduction of trace amounts of Pd, even at a loading of only 0.5%, a 98% HMF conversion and a 76% DMF selectivity were achieved, confirming the core catalytic role of Pd nanoparticles in the HMF hydrogenation reaction. At this low Pd loading, intermediate products, including 5-methylfurfural (5%), 2,5-furandimethylethanol (BHMF) (1%), and other byproducts (18%), were still detectable in the system. As the Pd loading increased, the HMF conversion gradually improved; when the Pd loading was 1%, HMF was completely converted, and the DMF selectivity reached its maximum value of 95%. Beyond this optimal loading level, further increasing the Pd loading leads to a decrease in DMF selectivity, dropping to 82% at a loading of 2%. Therefore, the catalytic performance is optimal in this system when the Pd loading is 1%. Figure 6 The XPS data in Table 2 show the changes in active Pd with varying loading. 2+ and Pd 0 The ratio of Pd to other components is controlled, ultimately affecting the adsorption, activation, and desorption of the feedstock, and consequently, the catalytic performance. The activity is most excellent when the Pd loading is 1%.

[0060] Comparative Example 3: A catalyst was prepared according to Example 1 (1% Pd / g-C3N4, hydrogen reduction at 250 °C for 3 h), with only the temperature and time of H2 reduction adjusted. 1% Pd / g-C3N4 catalysts were prepared for hydrogen reduction at 200 °C for 3 h, 300 °C for 3 h, 350 °C for 3 h, 250 °C for 2 h, and 250 °C for 4 h as controls.

[0061] Figure 8This paper presents the catalytic performance of the 1% Pd / g-C3N4 catalyst at different hydrogen reduction temperatures and times in Examples 1 and 3 of this invention. When the hydrogen reduction time is fixed at 3 h, the HMF conversion rates at different reduction temperatures (200, 250, 300, and 350 °C) are 94%, 100%, 100%, and 100%, respectively, with corresponding DMF selectivities of 86%, 95%, 87%, and 78%. When the reduction temperature is controlled at 250 °C, the HMF conversion rates at reduction times of 2, 3, and 4 h are 96%, 100%, and 100%, respectively, with corresponding DMF selectivities of 84%, 95%, and 75%. Therefore, complete HMF conversion can be achieved at 250 °C for 3 h under an H2 atmosphere, while obtaining the highest DMF selectivity.

[0062] Comparative Example 4: Catalysts were prepared according to Example 1, except that formic acid was replaced with methanol, ethanol, or isopropanol in the catalytic process, or hydrogen was replaced with nitrogen (in Example 1, H2 1.5 MPa + formic acid 1 mL), namely formic acid 1 mL + N2 1.5 MPa, methanol 1 mL + H2 1.5 MPa, ethanol 1 mL + H2 1.5 MPa, and isopropanol 1 mL + H2 1.5 MPa, respectively, as comparisons.

[0063] Figure 9 This paper presents the catalytic performance of the 1% Pd / g-C3N4 catalyst with different hydrogen donors in Examples 1 and 4 of this invention. The formation of the target product DMF is extremely challenging in the absence of formic acid and under mild conditions. When using the H2 + formic acid system, the selectivity for DMF reaches 95%. However, under the same H2 conditions, replacing other hydrogen donors yields almost no DMF. Systems using methanol or ethanol as hydrogen donors produce only trace amounts of the intermediate product MF, with the remainder being byproducts. In the isopropanol system, 64% BHMF was obtained, along with small amounts of MF, 5-methyl-2-furanethanol (MFA), and other byproducts, while the HMF conversion was only 73%. Notably, even in the N2 + formic acid system without external H2, the H2 produced by formic acid decomposition still promotes the formation of 20% DMF and 56% MF, but the HMF conversion is relatively low, at only 72%. Comparative analysis of these five systems shows that formic acid can enhance deoxygenation capacity, thereby promoting the conversion of intermediate species to DMF. This result highlights the crucial role of formic acid in guiding the reaction pathway toward the formation of the target product under optimized reaction conditions.

[0064] Comparative Example 5: The catalyst was prepared according to Example 1, but the amount of formic acid (FA) used in the catalytic process was adjusted (the amount used in Example 1 was 1 mL). The amount of formic acid used in the reaction process was adjusted to 0 mL, 0.5 mL, 0.8 mL, 1.2 mL and 1.5 mL respectively as a comparison.

[0065] Figure 10 This study examines the catalytic performance of the 1% Pd / g-C3N4 catalyst in Example 1 (1% Pd / g-C3N4, with 1 mL formic acid as the hydrogen donor) and Comparative Example 5 at different formic acid dosages. Without formic acid, only trace amounts of DMF are generated. As the formic acid content increases, the tendency for intermediate products to convert to DMF strengthens, and its concentration gradually decreases. When the formic acid dosage is 1 mL, the DMF selectivity reaches its maximum value of 95%. Exceeding this dosage leads to a decrease in selectivity and an increase in byproduct formation. Therefore, the optimal formic acid dosage is determined to be 1 mL.

[0066] Comparative Example 6: The catalyst was prepared according to Example 1, but the temperature of the catalytic reaction during the catalytic process was adjusted (150 °C in Example 1). The reaction temperature was adjusted to 60 °C, 90 °C, 120 °C, 130 °C, 140 °C, 160 °C, and 170 °C respectively as a comparison.

[0067] Figure 11 This invention presents the catalytic performance of the 1% Pd / g-C3N4 catalyst in Examples 1 and 6 of the present invention, with only the reaction temperature adjusted. As the reaction temperature increased from 60 °C to 170 °C, the conversion of HMF reached 100% at 120 °C, while the yield of DMF reached a maximum of 95% at 150 °C. Further increasing the temperature did not change the HMF conversion to 100%, but the selectivity of DMF decreased to 92%, while the selectivity of other products increased to 8%. Therefore, the optimal reaction temperature for HMF in the 1% Pd / g-C3N4 catalytic reaction system is 150 °C.

[0068] Comparative Example 7: The catalyst was prepared according to Example 1, but the H2 pressure during the catalytic reaction was adjusted only (1.50 MPa in Example 1). The H2 pressure during the reaction was adjusted to 0.5 MPa, 1.1 MPa, 1.2 MPa, 1.3 MPa, 1.4 MPa and 1.6 MPa respectively as a comparison.

[0069] Figure 12 This invention provides the catalytic performance of the 1% Pd / g-C3N4 catalyst in Example 1 and Comparative Example 7 when only the reaction pressure was adjusted. Figure 12The results show that H2 pressure has little effect on the conversion of HMF; at a hydrogen pressure of 0.5 MPa, the HMF conversion rate reaches 88%, and as the pressure gradually increases, HMF is completely converted. However, considering the selectivity of DMF, the results show a significant difference depending on the H2 pressure. At low pressure (0.5 MPa), the contents of MF and other products are high, at 53% and 34%, respectively. When the pressure is increased to 1.1 MPa, DMF begins to become the main product, and the selectivity continues to increase with the pressure, reaching a maximum of 95% at 1.5 MPa. Therefore, the optimal reaction pressure should be 1.5 MPa.

[0070] Comparative Example 8: The catalyst was prepared according to Example 1, but the reaction time during the catalytic process was adjusted (4 h in Example 1). The reaction time was adjusted to 0.5 h, 0.75 h, 1 h, 1.5 h, 2 h, 3 h, 5 h, and 6 h respectively as a comparison.

[0071] Figure 13 This invention demonstrates the catalytic performance of the 1% Pd / g-C3N4 catalyst in Example 1 and Comparative Example 8, with only the reaction time adjusted. At a reaction time of 0.5 h, the conversion rate of HMF reached 82%, and 100% conversion was achieved when the reaction time was extended to 1.5 h. For the target product DMF, the selectivity was only 19% at 0.5 h, with intermediates MF, BHMF, and other byproducts accounting for 41%, 17%, and 22%, respectively, with MF comprising the majority. As time increased, the selectivity of these intermediates and byproducts decreased, while the selectivity of DMF gradually increased, reaching a maximum of 95% at a reaction time of 4 h. Further extending the time resulted in a decrease in the selectivity of the target product, while the selectivity of other byproducts slightly increased, indicating that a longer reaction time is unfavorable for the hydrogenation of HMF to DMF under these reaction conditions. Therefore, a reaction time of 4 h is the optimal reaction time for this catalytic system.

[0072] Figure 14 This is a cycle stability test of the catalyst in Example 1 of the present invention. The 1%Pd / g-C3N4 catalyst maintained high conversion and DMF selectivity (93% and 83%, respectively) after five cycles, indicating that the catalyst of the present invention has excellent recyclability and potential for industrial application.

[0073] Example 2:

[0074] 5 g of melamine was weighed and placed in a corundum crucible. The crucible was heated to 550 °C for 2 h under a nitrogen atmosphere at a heating rate of 5 °C / min to obtain bulk carbon nitride (bulk-C3N4). The obtained bulk-C3N4 was thoroughly ground and dispersed in 150 mL of ethanol-water solution (volume ratio 1:2). The mixture was ultrasonically treated for 2 h and then washed with ethanol and water in sequence. The washed product was vacuum dried at 60 °C overnight and then ground to obtain g-C3N4 support.

[0075] 0.1 g g-C3N4 support was dispersed in 20 mL of deionized water, followed by the addition of 5 mL H2PdCl4 (0.1 g g). Pd / L) solution; after ultrasonic dispersion of the mixture, it was placed in an ice bath and stirred, and NaOH solution (0.1 mol / L) was added dropwise to adjust the pH of the system to 10, and stirring was continued for 3 h; the obtained product was dried at 60 ℃ overnight, and after thorough grinding, it was reduced at 300 ℃ for 2 h in a high-purity hydrogen atmosphere to obtain 0.5% Pd / g-C3N4 catalyst.

[0076] Mix 50 mg of the catalyst, 0.5 mmol of 5-hydroxymethylfurfural, and 8.87 mL of tetrahydrofuran, and add 1.0 mL of formic acid; purge the reactor with hydrogen to a pressure of 1.5 MPa, and heat to 150 °C for 4 h under stirring; after the reaction is complete, separate the catalyst to obtain 2,5-dimethylfuran.

[0077] HMF conversion rate 92%, DMF selectivity 80%, TOF 227 h -1 .

[0078] Example 3:

[0079] 5 g of melamine was weighed and placed in a corundum crucible. The crucible was heated to 550 °C for 2 h under a nitrogen atmosphere at a heating rate of 5 °C / min to obtain bulk carbon nitride (bulk-C3N4). The obtained bulk-C3N4 was thoroughly ground and dispersed in 150 mL of ethanol-water solution (volume ratio 1:2). The mixture was ultrasonically treated for 2 h and then washed with ethanol and water in sequence. The washed product was vacuum dried at 60 °C overnight and then ground to obtain g-C3N4 support.

[0080] 0.1 g g-C3N4 support was dispersed in 20 mL of deionized water, followed by the addition of 20 mL of H2PdCl4 (0.1 g g). Pd / L) solution; after ultrasonic dispersion of the mixture, it was placed in an ice bath and stirred, and NaOH solution (0.1 mol / L) was added dropwise to adjust the pH of the system to 10, and stirring was continued for 3 h; the obtained product was dried at 60 ℃ overnight, and after thorough grinding, it was reduced at 250 ℃ for 4 h in a high-purity hydrogen atmosphere to obtain 2%Pd / g-C3N4 catalyst.

[0081] Mix 50 mg of the catalyst, 0.5 mmol of 5-hydroxymethylfurfural, and 8.87 mL of tetrahydrofuran, and add 1.0 mL of formic acid; purge the reactor with hydrogen to a pressure of 1.5 MPa, and heat to 150 °C for 4 h under stirring; after the reaction is complete, separate the catalyst to obtain 2,5-dimethylfuran.

[0082] HMF conversion rate 100%, DMF selectivity 82%; TOF 203 h. -1 .

Claims

1. A carbon nitride-supported noble metal catalyst and its preparation method, characterized in that: The support for the nano-noble metal catalyst is graphitic carbon nitride (g-C3N4), and the noble metal is palladium nanoparticles. The preparation method of the carbon nitride-supported noble metal catalyst is as follows: 0.1 g g-C3N4 support is dispersed in 20 mL of deionized water, followed by the addition of 5-20 mL of H2PdCl4 solution. After ultrasonic dispersion, the mixture is placed in an ice bath and stirred. NaOH solution (0.1 mol / L) is added dropwise to adjust the pH of the system to 10, and stirring is continued for 3 h. The resulting product is dried at 60 ℃ overnight, thoroughly ground, and then reduced at 200-350 ℃ for 2-4 h under a high-purity hydrogen atmosphere to obtain the Pd / g-C3N4 catalyst.

2. The carbon nitride-supported noble metal catalyst and its preparation method according to claim 1, characterized in that: The g-C3N4 support was prepared according to the following steps: 5 g of melamine was weighed and placed in a corundum crucible, and calcined at 550 °C for 2 h under a nitrogen atmosphere at a heating rate of 5 °C / min to obtain bulk carbon nitride (bulk-C3N4); the obtained bulk carbon nitride was thoroughly ground and dispersed in 150 mL of ethanol-water solution (volume ratio 1:2), and the mixture was ultrasonically treated for 2 h, followed by washing with ethanol and water in sequence; the washed product was vacuum dried at 60 °C overnight, and then ground to obtain the g-C3N4 support.

3. The application of the catalyst according to claim 1 in the hydrogenation of 5-hydroxymethylfurfural to prepare 2,5-dimethylfuran, characterized in that, Includes the following steps: Mix 50 mg of the catalyst, 0.5 mmol of 5-hydroxymethylfurfural, and 8.87 mL of tetrahydrofuran. Add 0.5–1.5 mL of formic acid. Purge the reactor with hydrogen to a pressure of 1.1–1.6 MPa. Heat the reactor to 120–170 °C under stirring and react for 1.5–6 h. After the reaction is complete, separate the catalyst to obtain 2,5-dimethylfuran.

4. The application according to claim 3, characterized in that: The amount of formic acid used is 1.0 mL, the reaction temperature is 150 °C, the hydrogen pressure is 1.5 MPa, and the reaction time is 4 h.

Images