Copper-based catalyst, preparation method thereof and application of copper-based catalyst in preparation of 2-methyltetrahydrofuran through furfural hydrogenation

Abstract

The invention discloses a copper-based catalyst, a preparation method thereof and application of the copper-based catalyst in preparation of 2-methyltetrahydrofuran through furfural hydrogenation, and the copper-based catalyst comprises an alumina carrier and a copper element and a zinc element which are loaded on the carrier. According to the application, in the hydrogen atmosphere, a furfural solution is fed at a certain weight hourly space velocity and passes through the copper-based catalyst and the Pd-loaded g-C3N4 catalyst in sequence after being vaporized. Zn is introduced into the copper-based catalyst, so that the effects of regulating and controlling the local coordination structure, the electronic environment and the acid distribution of Cu, remarkably improving the dispersity of Cu, improving the surface property of Cu and inhibiting carbon deposition are achieved, and the activity and the stability of the Cu-based catalyst are improved. The copper-based catalyst and Pd / g-C3N4 with extremely low noble metal Pd loading capacity are subjected to cascade reaction, so that the complete conversion of furfural and the yield of 97.1% of 2-methyltetrahydrofuran are realized.

Description

Technical Field

[0001] This invention relates to a copper-based catalyst, its preparation method, and its application in the hydrogenation of furfural to 2-methyltetrahydrofuran, belonging to the field of catalytic hydrogenation technology. Background Technology

[0002] Fossil fuels are non-renewable resources. To address the energy crisis and environmental pollution caused by excessive fossil fuel consumption, biomass energy has received widespread attention in recent years due to its renewable and low-carbon characteristics. Furfural (FF) is the only commercially produced biomass-based platform chemical, and its high reactivity makes it an ideal precursor for preparing high-value-added chemicals. Among them, 2-methyltetrahydrofuran (2-MeTHF) is a biomass platform molecule and green solvent with significant application value. It can not only serve as an excellent biofuel additive, increasing the octane number and oxygen content of gasoline without affecting engine performance, but also as an environmentally friendly polar aprotic solvent in the pharmaceutical and fine chemical industries, and has important application prospects in Grignard reactions and lithium-ion battery electrolytes. Therefore, developing efficient and green synthetic routes for 2-methyltetrahydrofuran is of significant industrial importance.

[0003] The synthesis of 2-MeTHF from FF is a multi-step process involving hydrogenation and dehydration: hydrogenation and deoxygenation (-H₂O), namely the hydrogenation and deoxygenation of the aldehyde group (C=O) and the hydrogenation of the furan ring (C=C). Transition metals such as chromium (Cr), copper (Cu), and nickel (Ni) are commonly used as active metals in dehydration catalysts, often for the first step of hydrogenation of the aldehyde group (C=O) to obtain the intermediate products furfuryl alcohol (FA) or 2-methylfuran (2-MF); Cu has a higher η compared to other metals. 1 The adsorption model of -(O)-aldehydes best fits the route of hydrogenolysis of FF to prepare 2-MF. Furthermore, due to the partial overlap and mutual repulsion between the antiorbital bonds of FF and the furan ring, the formation of byproducts and ring-opening products during FF hydrogenation is avoided. Platinum group metals (such as palladium (Pd), platinum (Pt), and ruthenium (Ru)) are commonly used as active metals in hydrogenation catalysts for the hydrogenation of furan rings (C=C) to obtain the final hydrogenation product 2-MeTHF. Among them, Pd-based catalysts have been proven to have the highest activity and excellent selectivity for the hydrogenation of furan rings; however, as a noble metal, the amount of Pd metal used has always limited the development of Pd-based catalysts. Summary of the Invention

[0004] The purpose of this invention is to provide a copper-based catalyst, its preparation method, and its application in the hydrogenation of furfural to 2-methyltetrahydrofuran. By introducing Zn into the copper-based catalyst, the local structure of Cu is stabilized and its electronic environment is regulated. At the same time, the introduction of Zn also facilitates the adsorption and activation of furfural and the desorption of 2-MF, thereby improving the catalytic cycle efficiency and effectively inhibiting carbon deposition.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A copper-based catalyst includes a support and copper and zinc elements supported on the support; the support is alumina, and the loading amounts of copper and zinc elements are 3-15 wt% and 1-5 wt%, respectively.

[0006] The above-mentioned method for preparing copper-based catalysts involves preparing a Cu- and Zn-containing solution and an alumina support solution, mixing the Cu- and Zn-containing solution with the alumina support solution, removing the solvent by evaporation, drying the resulting solid, and then calcining it.

[0007] Preferably, the solution contains Cu and Zn, with Cu sourced from Cu(NO3)2·3H2O and Zn sourced from Zn(NO3)2·3H2O, and the support is γ-Al2O3; the mixing time between the Cu and Zn solution and the alumina support solution is 8-15 h.

[0008] Preferably, the drying conditions are: 70-90℃, 10-15 h.

[0009] Preferably, the calcination conditions are: 480-550℃, 3-5 h, and heating rate of 3-8℃ / min.

[0010] The application of the aforementioned copper-based catalyst in the hydrogenation of furfural to prepare 2-methyltetrahydrofuran involves hydrogenating the furfural solution under a hydrogen atmosphere for 0.2-0.45 h. -1 The material is fed in at a gravity time space velocity and vaporized at 170-220℃, then passes through a copper-based catalyst and a Pd-supported g-C3N4 catalyst.

[0011] Preferably, in the Pd-supported carbon nitride catalyst, the loading of Pd element is 0.25-1 wt%, and the carbon nitride is porous graphitic carbon nitride (g-C3N4); the mass ratio of copper-based catalyst to Pd-supported carbon nitride catalyst is 7:(2-5).

[0012] Preferably, the preparation method of Pd-supported carbon nitride catalyst is as follows: prepare a Pd-containing solution and a g-C3N4 support solution, mix the Pd-containing solution and the g-C3N4 support solution, evaporate the solvent, dry the resulting solid, calcine it, and then reduce it in situ.

[0013] Preferably, the conditions for in-situ reduction are: under a hydrogen atmosphere, 250-300℃, 0.5-2 h, and a heating rate of 3-8℃ / min.

[0014] Preferably, the preparation method of g-C3N4 carrier is to mix melamine and NH4Cl in a mass ratio of 1:(0.2-1), and then heat the mixture to 520-580℃ at a heating rate of 1-5℃ / min and hold it at that temperature for 3-5 h.

[0015] Preferably, the weight hourly space velocity is 0.32 h. -1 The vaporization temperature is 200℃; in the copper-based catalyst, the loading of copper and zinc elements is 5 wt% and 3 wt%, respectively; in the Pd-supported g-C3N4 catalyst, the loading of Pd element is 0.5 wt%; the mass ratio of copper-based catalyst to Pd-supported carbon nitride catalyst is 7:3; in the preparation of g-C3N4 support, the mass ratio of melamine to NH4Cl is 1:0.5.

[0016] The beneficial effects of this invention are as follows: By adding Zn to the copper-based catalyst, the local coordination structure, electronic environment, and acidity distribution of Cu are regulated, significantly improving the dispersibility of Cu, enhancing its surface properties, and inhibiting carbon deposition, thereby improving the activity and stability of the Cu-based catalyst. Furthermore, by coupling a Pd / g-C3N4 catalyst and controlling the catalyst ratio of the cascade reaction, the reaction pathway of the target product is controlled, enabling the efficient conversion of furfural to 2-MeTHF. This was carried out in a fixed-bed reactor under mild conditions (200℃, atmospheric pressure), using a CuZnAl catalyst in series with a 0.5Pd / g-C3N4 catalyst with a very low Pd loading, achieving complete furfural conversion and a 97.1% yield of 2-methyltetrafuran. Attached Figure Description

[0017] Figure 1 Experimental apparatus for hydrogenation of furfural; Figure 2 Results for different reaction conditions: (a) different reaction temperatures, (b) different Cu metal loadings, (c) different weight hourly space velocities (WHSV), (d) different Zn metal loadings, (e) different bimetallic loadings, and (f) different Cu-Pd catalyst cascade ratios. Figure 3 Discussion of the stabilization time in continuous experiments with different catalysts; Figure 4 (a) XRD test results of Cu-based catalyst before and after reduction, (b) XRD test results of Pd-based catalyst with different melamine:NH4Cl ratios; Figure 5 XANES and XPS test results for CuZnAl catalyst; Figure 6 (a) H2-TPR test results for different catalysts, (b) NH3-TPD test results, and (c) pyridine infrared test results; Figure 7 TEM test results and particle size analysis of different Cu-based catalysts; Figure 8 The results show the carbon deposition content after using different Cu-based catalysts. Detailed Implementation

[0019] Catalyst preparation.

[0020] The catalyst was prepared by wet impregnation. Cu(NO3)2·3H2O and Zn(NO3)2·3H2O were used as metal precursors, and γ-Al2O3 was used as the support. The preparation process is as follows: A certain amount of Cu and Zn precursors were dissolved in 10 mL of deionized water to obtain a homogeneous solution A; at the same time, γ-Al2O3 was dispersed in 20 mL of deionized water to form a suspension B. Solution A was slowly added dropwise to solution B under stirring, and the mixture was stirred at room temperature for 12 h to ensure sufficient impregnation. The mixture was then heated in a water bath and stirred until dry until no free water remained. The resulting solid was then dried overnight at 80 °C. The dried sample was calcined at 500 °C for 4 h at a rate of 5 °C / min to obtain the supported catalyst xCuyZn / γ-Al2O3, where x and y are the mass percentages of Cu and Zn, respectively.

[0021] g-C3N4 is synthesized through the thermal polycondensation reaction of melamine. The specific steps are as follows: 10g of melamine is uniformly mixed with a certain proportion of NH4Cl and placed in a covered ceramic crucible. Subsequently, the crucible is transferred to a muffle furnace and heated at 3℃·min in an air atmosphere. -1 The heating rate was increased from room temperature to 550°C and maintained at that temperature for 4 hours. During this heat treatment, melamine underwent pyrolysis, and NH4Cl decomposed to produce gas. The gas escaped from the polymer matrix, thereby inducing the formation of porous graphitic carbon nitride (g-C3N4).

[0022] Pd / g-C3N4 catalyst was prepared by a wet impregnation method. First, an appropriate amount of Pd(NO3)2·2H2O was dissolved in 20 mL of ultrapure water and ultrasonically treated to obtain a homogeneous solution. Then, the synthesized g-C3N4 support was added to this solution, and the mixture was stirred continuously for 12 h. Afterward, the mixture was stirred in a 70 °C water bath until completely dry, and the resulting solid was dried in an 80 °C oven for 12 h. The dried sample was then placed in a muffle furnace and dried at 2 °C·min⁻¹. -1 The temperature was increased to 350℃ at a rate of [missing information], and calcined for 3 hours. Finally, the calcined sample was reduced in situ in a fixed-bed reactor under the following conditions: [missing information] at 60 mL / min [missing information]. -1 In an H2 atmosphere, at 5℃·min -1The temperature was raised to 270℃ and held for 1 hour to obtain the Pd / g-C3N4-NH4Cl catalyst.

[0023] Catalyst performance testing.

[0024] The gas-phase hydrogenation reaction of furfural (FF) was carried out in a 1 / 4-inch stainless steel fixed-bed reactor under atmospheric pressure. For each experiment, the catalyst was crushed and sieved to 40-60 mesh, then uniformly mixed with silica sand at a mass ratio of 1:2. The mixture was packed into the isothermal zone of the reactor, secured at both ends with silica wool, and the reaction temperature was precisely controlled by a three-stage temperature control system. The catalytic experimental setup is as follows: Figure 1 As shown. Before the reaction, the catalyst was first subjected to in-situ hydrogen reduction treatment for 1 hour. After the reduction was completed, the system was cooled to the preset reaction temperature. Then, the catalyst was pumped at 3.87 mL / h using an HPLC pump. -1 The system was injected with a CPME solution containing 5 vol.% FF at a rate of [missing value], while simultaneously purging with 10 mL / min [missing value]. -1 Hydrogen was used as both the carrier gas and the reactant gas. The reactants were thoroughly mixed and vaporized in a preheated vaporization chamber before entering the reactor. The products were collected by a condenser. Product analysis was performed using a Fuli GC9270Plus gas chromatograph equipped with a flame ionization detector (FID) and a DB-5 capillary column for quantitative analysis of the reactant FF and the gas-phase hydrogenation products. The reactant conversion and product yields were calculated using the following formulas:

[0025] Among them, C i S represents the conversion rate of different raw materials. j and Y j These represent the selectivity and yield of different products, both in percentage (%). i and j These correspond to raw materials and finished products, respectively. i0 and n i1 n represents the amount of the raw material before and after the reaction, respectively. j The values ​​represent the amount of substance of the product, all in mol.

[0026] Catalytic performance.

[0027] In a fixed-bed reactor, key reaction parameters were systematically controlled using furfural as a feedstock, including hydrogenation temperature (170-220℃), Cu and Zn loadings, and weight hourly space velocity (WHSV). Figure 2 (middle ad region). The results showed that 200℃ was the optimal temperature for the hydrogenation of furfural to 2-MF, under which the highest yield of 2-MF of 64.4% could be obtained. Compared with 200℃, excessively high reaction temperatures would significantly promote the formation of byproducts (such as furfuryl alcohol).

[0028] Regarding Cu loading ( Figure 2 The influence of region b) was investigated, and experimental results showed that the furfural conversion rate of the pure Cu catalyst was only 11.7%; after introducing 1 wt% Cu into Al2O3, the conversion rate increased to 24.5%, indicating that the support can effectively improve the distribution and exposure of active sites. When the Cu loading was increased to 5 wt%, both furfural conversion and FA formation were further improved, and the number of Cu active centers was within a suitable range. However, when the Cu loading exceeded 5 wt%, the catalytic performance decreased, which was consistent with the XRD results (…). Figure 4 The consistent Cu grain growth trend shown in region a indicates that excessive loading leads to Cu particle agglomeration, reducing the utilization rate of active sites. Further investigation was conducted on the effect of WHSV. With decreasing WHSV, the residence time of reactants in the catalyst bed increased, the yield of 2-MF significantly increased, while the amount of FA formed decreased, demonstrating a cascade reaction pathway of FF→FA→2-MF. These results provide direct process evidence for the reaction mechanism.

[0029] Further investigation was conducted into the effect of different second metals on catalytic performance. Figure 2 The results (in the e-region) showed that Zn had a better promoting effect than Re, Ni, and Pd. Ni readily initiated ring-breaking to generate byproducts such as 1,4-pentadiene, while Pd and Re had stronger hydrogenation capabilities, readily promoting the deep hydrogenation of 2-MF to 2-MeTHF. The optimal Zn loading was 3 wt%, at which the 2-MF yield reached 92.5 mol%, with complete furfural conversion. When the Zn loading increased to 5 wt%, the 2-MF yield decreased and 3.6% FA was generated, consistent with the aggregation of Cu species (confirmed by the increase in XRD grain size to 15.1 nm).

[0030] To further improve the overall conversion efficiency of FF to 2-MeTHF, the 5Cu3Zn-Al catalyst and the Pd / g-C3N4 catalyst were used in series. Figure 2 (Middle f region). The results show that when 0.5 wt% Pd / g-C3N4 and 5Cu3Zn-Al are combined at a mass ratio of 0.3:0.7, a 2-MeTHF yield of 97.1 mol% can be obtained, which is significantly better than the results obtained by using either catalyst alone. In contrast, when using a 3 wt% Pd / C commercial catalyst, the Pd utilization efficiency is actually lower, and the performance only approaches that of 0.5 wt% Pd / g-C3N4 after the mass ratio is increased to 0.2:0.7. This is related to the fact that the lower-loaded Pd is easier to maintain good dispersion.

[0031] Reaction pathway.

[0032] Figure 3The long-term catalytic performance of 5Cu-Al, 5Cu3Zn-Al, and tandem catalytic systems was demonstrated. The hydrogenation of furfural to 2-MeTHF involves multiple sequential reaction steps, with FA and 2-MF as the main intermediates. The results show that, regardless of the single Cu-based catalyst system, 2-MF can be prepared from FF. Figure 3 In the middle a region), 2-MeTHF was prepared from FF in a tandem system consisting of a Cu-based catalyst and Pd / g-C3N4. Figure 3 In the middle b region, the 5Cu-Al catalyst required approximately 10 hours to reach a stable reaction state; however, the 5Cu3Zn-Al catalyst with Zn introduced only required about 4 hours to enter the stable region, exhibiting faster reaction stability. All systems generated a certain amount of 1,4-pentadiene byproduct before reaching a stable state. Figure 3 (Central C region).

[0033] In contrast, when 2-MeTHF is prepared from 2-MF, the tandem system reaches a stable state in only about 3 hours. Figure 3 (Middle d region). The above results collectively indicate that the hydrogenation process of FF→2-MF is the rate-controlling step in the entire FF→2-MeTHF hydrogenation pathway.

[0034] To further clarify the two key steps of FF→FA and FA→2-MF, FA was used as the raw material at different WHSVs (0.32-1.12h). -1 The reaction equilibrium time and product distribution were tested under these conditions. Figure 3 (midef region). The results showed that at a WHSV of 0.45h... -1 At that time, the 2-MF yield reached 93.0%, which is comparable to that of FF as a raw material at a WHSV of 0.32h. -1 The results obtained were similar, further verifying that FA is a key intermediate in the hydrogenation of FF to 2-MF. Furthermore, the stabilization time of the FA→2-MF conversion was approximately 4 hours, consistent with the stabilization time of FF→2-MF, again indicating that both follow the same tandem hydrogenation pathway.

[0035] The role of Zn adjuvants.

[0036] To investigate the regulatory effect of Zn on the structure and performance of Cu-based catalysts, the catalysts were characterized using multiple methods including XANES, EXAFS, XRD, H2-TPR, TEM, NH3-TPD, Py-FTIR, and N2 adsorption-desorption. Figure 4-6 (Table 1-2). The results show that Zn mainly exists in the form of ZnO in the 5Cu3Zn-Al catalyst ( Figure 5 The c region did not undergo a change in valence state before and after the reaction, indicating that Zn itself is difficult to be reduced by hydrogen and is not considered a metal active site that directly participates in the reaction.

[0037] Table 1 Physicochemical properties of different catalysts

[0038] a Calculated using Scherrer's formula; b The determination was made by NH3-TPD (ammonia temperature-programmed desorption). c The ratio of Brønsted acid to Lewis acid was determined by pyridine adsorption Fourier transform infrared spectroscopy. d BET specific surface area; micropore area using eT-plot method; f Under the condition of p / p°=0.295328652, the total pore volume of single-point adsorption is less than 190.2244 nm; g The 4V / A value calculated using the BET method.

[0039] Table 2. Coordination layer structure parameters fitted by EXAFS for Cu K-edge in different catalysts

[0040] H2-TPR analysis ( Figure 6 The region (a) shows that the 5Cu-Al catalyst exhibits two reduction peaks at approximately 176.4 °C and 450.2 °C, attributed to the reduction of small-sized CuO and large-sized CuO, respectively. The introduction of Zn caused the high-temperature reduction peak to disappear, while the low-temperature peak shifted to 166.5 °C, indicating that Zn promoted the reducibility of CuO. To verify whether the difference in reaction stability time was related to insufficient pre-reduction, the reduction time was extended to 3 h. The results showed that its stability time was the same as that of the sample reduced for 1 h, and XRD also showed that the two had identical structures. Figure 4 The presence of region b indicates that 1 hour of pre-reduction is sufficient to complete the reduction of Cu. Therefore, the difference in stabilization time between 5Cu-Al and 5Cu3Zn-Al is mainly caused by the differences in their microstructure and surface properties.

[0041] The N2 adsorption-desorption results (Table 1) show that the specific surface area of ​​pure Al2O3 is 188.0 m² / g and the pore size is 19.7 nm. After loading with 5Cu-Al, the specific surface area decreases to 128.4 m² / g and the pore size shrinks to 7.8 nm, indicating that Cu enters the pores of the support and occupies part of the pore volume. After further introducing Zn (1-5 wt%), there is no significant change in the specific surface area and pore volume, indicating that Zn has good dispersibility in the pore structure of the support.

[0042] XRD Figure 4 The middle region (a) shows that the 5Cu-Al catalyst contains obvious metallic Cu. 0The diffraction peaks were observed, while the Cu peak intensity in 5Cu3Zn-Al decreased significantly. Calculations showed that the Cu grain size decreased from 17.6 nm to 9.6 nm (Table 1), and TEM (…)… Figure 7 This directly confirmed that Cu clusters decreased from about 17 nm to about 9 nm, indicating that Zn can effectively inhibit Cu aggregation and improve its dispersibility.

[0043] In terms of electronic structure, XANES and XPS ( Figure 5 The ab region indicates that the average valence state of Cu in both catalysts is close to that of Cu. + However, the introduction of Zn slightly shifts the valence state of Cu upwards, indicating an electronic interaction between Zn and Cu. (EXAFS) Figure 5 Table 2 further shows that the introduction of Zn leads to an adjustment in the coordination environment of the first Cu-O coordination layer, with a decrease in the coordination number of short Cu-O bonds and an increase in the coordination number of longer Cu-O bonds. The coordination number of the second coordination layer, Cu-O-Cu, decreases, indicating that Zn partially replaces local Cu sites. In the post-reaction 5Cu3Zn-Al, Cu-O coordination further increases, while the Cu-Cu distance shortens to approximately 2.5 nm, demonstrating that the presence of Zn can stabilize the local structure of Cu and regulate its electronic environment.

[0044] Acid characterization (NH3-TPD and Py-FTIR, Figure 6 The presence of Zn in the bc region showed that the concentration of moderately strong acid centers decreased from 0.77 mmol / g to 0.67 mmol / g, and the Brønsted / Lewis acid ratio (B / L) decreased from 0.18 to 0.10. This indicates that Zn can partially neutralize Brønsted acids and enhance Lewis acids, thereby benefiting the adsorption and activation of furfural. Simultaneously, the regulation of acidity helps promote the desorption of 2-MF, improving the catalytic cycle efficiency.

[0045] Furthermore, the introduction of Zn significantly inhibited catalyst coking. After the reaction, the specific surface area of ​​5Cu-Al decreased from 128.4 to 96.45 m² / g, and the pore size decreased from 7.8 to 5.8 nm; while the changes in 5Cu3Zn-Al were smaller (specific surface area decreased from 123.1 to 105.9 m² / g, and pore size decreased from 7.7 to 6.2 nm). TG analysis showed that the coking content of 5Cu-Al was 19.5%, while that after Zn modification decreased to 10.9%. Figure 8 (Region a); and the peak temperature of carbon deposition oxidation decreased from 285℃ to 260℃ after Zn modification, indicating that the catalyst without Zn is more likely to form highly stable "hard carbon," while the carbon deposits after Zn modification tend to be more easily removed "soft carbon." TEM ( Figure 8Further analysis in the middle bc region shows that the 5Cu-Al surface is covered with a dense amorphous carbon layer (approximately 24.3 wt%), while the carbon deposition on 5Cu3Zn-Al is significantly reduced (approximately 10.8 wt%).

[0046] In summary, although the introduction of Zn does not directly participate in the hydrogenation reaction, it can significantly improve the dispersibility of Cu, enhance its surface properties, and inhibit carbon deposition by regulating the local coordination structure, electronic environment, and acidity distribution of Cu, thereby improving the activity and stability of Cu-based catalysts.

[0047] Physicochemical properties of Pd-based catalysts.

[0048] The dispersion state of active metal Pd was investigated by optimizing the support structure. XRD results of different catalysts ( Figure 4 As shown in region c), the diffraction peaks at 2θ of 12.9° and 27.5° can be attributed to the (100) and (002) crystal planes of g-C3N4 (PDF50-1512). Meanwhile, in the spectrum of the 0.5Pd / g-C3N4 catalyst without NH4Cl modification, a weak diffraction peak at approximately 33.8° 2θ can be clearly observed, which is attributed to the PdO (101) crystal plane (PDF41-1107). However, in the 0.5Pd / g-C3N4(NH4Cl) catalyst, this PdO characteristic peak completely disappears. This phenomenon strongly indicates that the porous g-C3N4 support, with its significantly increased specific surface area and abundant surface anchoring sites, greatly promotes the dispersion of the Pd precursor and effectively inhibits its migration and sintering during heat treatment, ultimately forming smaller, highly dispersed Pd species.

[0049] To systematically investigate the effect of NH4Cl pore-forming modification on the physicochemical properties of the g-C3N4 support and the performance of its supported Pd catalyst, the physical structure of the support was systematically characterized. The N2 physical adsorption-desorption test results (Table 3) show that the specific surface area of ​​the porous g-C3N4 prepared using NH4Cl as a dynamic template agent was significantly increased from 13.5 m² / g by the traditional method to 40.1 m² / g, and the total pore volume increased from 0.0868 cm³ / g to 0.2606 cm³ / g. These results confirm that the dynamic template effect and pore-forming effect generated by NH4Cl during pyrolysis successfully constructed a more developed pore system in the g-C3N4 matrix, while simultaneously improving the efficient mass transfer of reactant molecules and maximizing the utilization of active sites.

[0050] Table 3. BET test results for different melamine:NH4Cl (mass ratio) g-C3N4 carriers

[0051] Table 4 shows the experimental results of 2-MF catalysts with different NH4Cl:melamine (mass ratio) ratios.

[0052] In summary, the synthesis strategy using NH4Cl as a template agent significantly increased the specific surface area, pore volume, and pore size. This not only provided more abundant and uniform anchoring sites for the noble metal Pd, promoting the efficient dispersion and stable immobilization of the active components, but also maintained the catalyst's high level of activity and long-term stability while reducing the amount of Pd metal used and improving atom economy (Table 4).

Claims

1. A copper-based catalyst, characterized in that, It includes a support and copper and zinc elements loaded on the support; the support is alumina, and the loading of copper and zinc elements is 3-15 wt% and 1-5 wt%, respectively.

2. The method for preparing the copper-based catalyst according to claim 1, characterized in that, The process involves preparing a Cu- and Zn-containing solution and an alumina-supported solution, mixing the Cu- and Zn-containing solution with the alumina-supported solution, removing the solvent by evaporation, and then drying and calcining the resulting solid.

3. The method for preparing the copper-based catalyst according to claim 2, characterized in that, The drying conditions are: 70-90℃, 10-15 h.

4. The method for preparing the copper-based catalyst according to claim 2, characterized in that, The calcination conditions are: 480-550℃, 3-5 h, heating rate 3-8℃ / min.

5. The application of the copper-based catalyst according to claim 1 in the hydrogenation of furfural to prepare 2-methyltetrahydrofuran, characterized in that, Under a hydrogen atmosphere, the furfural solution was incubated for 0.2-0.45 h. -1 The material is fed in at a gravity time space velocity and vaporized at 170-220℃, then passes through a copper-based catalyst and a Pd-supported g-C3N4 catalyst.

6. The application of the copper-based catalyst according to claim 5 in the hydrogenation of furfural to prepare 2-methyltetrahydrofuran, characterized in that, In the Pd-supported carbon nitride catalyst, the loading of Pd element is 0.25-1 wt%; the mass ratio of copper-based catalyst to Pd-supported carbon nitride catalyst is 7:(2-5).

7. The application of the copper-based catalyst according to claim 6 in the hydrogenation of furfural to prepare 2-methyltetrahydrofuran, characterized in that, The preparation method of Pd-supported carbon nitride catalyst is as follows: prepare a Pd-containing solution and a g-C3N4 support solution, mix the Pd-containing solution and the g-C3N4 support solution, evaporate the solvent, dry the resulting solid, calcine it and then reduce it in situ.

8. The application of the copper-based catalyst according to claim 7 in the hydrogenation of furfural to prepare 2-methyltetrahydrofuran, characterized in that, The conditions for in-situ reduction are: under a hydrogen atmosphere, 250-300℃, 0.5-2 h, and a heating rate of 3-8℃ / min.

9. The application of the copper-based catalyst according to claim 6 in the hydrogenation of furfural to prepare 2-methyltetrahydrofuran, characterized in that, The g-C3N4 carrier is prepared by mixing melamine and NH4Cl in a mass ratio of 1:(0.2-1), heating the mixture to 520-580℃ at a heating rate of 1-5℃ / min, and holding it at that temperature for 3-5 h.

10. The application of the copper-based catalyst according to claim 9 in the hydrogenation of furfural to prepare 2-methyltetrahydrofuran, characterized in that, The weight hourly space velocity is 0.32 h. -1 The vaporization temperature is 200℃; in the copper-based catalyst, the loading of copper and zinc elements is 5 wt% and 3 wt%, respectively; in the Pd-supported g-C3N4 catalyst, the loading of Pd element is 0.5 wt%; the mass ratio of copper-based catalyst to Pd-supported carbon nitride catalyst is 7:3; in the preparation of g-C3N4 support, the mass ratio of melamine to NH4Cl is 1:0.5.

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