Zeolite confined ptco monatomic alloy catalyst, preparation method and application thereof in preparation of naphthenes

Abstract

This invention belongs to the field of high-value utilization of biomass resources and catalytic hydrodeoxygenation technology, specifically involving a zeolite-confined PtCo single-atom alloy catalyst, its preparation method, and its application in the catalytic production of cycloalkanes from lignin. The catalyst comprises a zeolite molecular sieve support and PtCo single-atom alloy particles confined within the pores, cages, and / or intracrystalline mesoporous structures of the zeolite molecular sieve. Co serves as the main metal phase, and Pt is dispersed as isolated atoms on the surface, subsurface, or near-surface sites of the Co metal particles, forming a Pt-Co coordination structure. Lignin-derived phenolic compounds, lignin oil, or pre-depolymerized lignin oil can be directionally converted into C6-C18 cycloalkanes, with a cycloalkane carbon yield exceeding 85%. This invention provides a highly efficient catalytic system for the production of sustainable aviation fuels and high-energy-density cycloalkane fuel components from lignin.

Description

Technical Field

[0001] This invention belongs to the field of high-value utilization of biomass resources and catalytic hydrogenation and deoxygenation technology, specifically involving a zeolite-confined PtCo single-atom alloy catalyst, its preparation method, and its application in the preparation of cycloalkanes. Background Technology

[0002] Lignin is the most abundant aromatic renewable polymer resource in nature. Its structure contains a large number of phenylpropane units, linked by C–O bonds such as β-O-4, α-O-4, and 4-O-5, as well as C–C bonds. Unlike cellulose and hemicellulose, which mainly provide sugar platform compounds, lignin is naturally rich in aromatic ring structures, and is therefore considered an important renewable carbon source for the preparation of aromatic hydrocarbons, cycloalkanes, and high-energy-density fuel components.

[0003] Lignin, after pyrolysis, solvent depolymerization, catalytic hydrogenolysis, or oxidative depolymerization, yields lignin oils, represented by guaiacol, eugenol, alkylphenols, methoxyphenols, phenoxyphenols, and polyphenols. However, these products typically contain numerous oxygen-containing functional groups such as hydroxyl, methoxy, ether bonds, and carbonyl groups, exhibiting problems such as high oxygen content, poor stability, low calorific value, and strong corrosiveness, making them unsuitable for direct use as fuel. Therefore, it is necessary to remove oxygen-containing functional groups through hydrodeoxygenation reactions and selectively hydrogenate aromatic rings to obtain hydrocarbon fuel components.

[0004] Cycloalkanes possess high volumetric calorific value, good low-temperature fluidity, and excellent combustion performance, making them an important component of aviation fuels, bio-based diesel, and high-energy-density fuels. Converting lignin into cycloalkanes can not only improve the utilization efficiency of lignin resources but also provide a renewable carbon source for sustainable aviation fuels.

[0005] Currently, the hydrodeoxygenation of lignin and its derived phenolic compounds to cycloalkanes mostly employs metal / acid bifunctional catalysts. In these catalysts, the metal sites are responsible for H2 activation, aromatic ring hydrogenation, and partial C–O bond hydrogenolysis, while the acidic sites promote demethoxylation, dehydroxylation, dehydration, and further deoxygenation. Previous studies have shown that Pt / zeolite, Ru / zeolite, Ni / zeolite, and Ni-Co bimetallic catalysts can all be used for the hydrodeoxygenation of lignin phenolic compounds to cycloalkanes. For example, a hollow ZSM-5 supported Pt catalyst has been used for the highly selective hydrodeoxygenation of guaiacol to cycloalkanes (Nanomaterials, 2019, 9, 3, 362); Zhao and Lercher used a Pd / C combined with HZSM-5 catalytic system to achieve the selective hydrodeoxygenation conversion of lignin-derived phenolic monomers and dimers to cycloalkanes (ChemCatChem, 2012, 4, 1, 64). Ru / HZSM-5 catalyst can convert lignin phenol monomers and dimers into cycloalkanes (ACS Sustainable Chem. Eng., 2014, 2, 4, 683); in addition, Ni–Co / NbO x Non-noble metal bifunctional catalysts have also been used for the hydrodeoxygenation of lignin phenolic compounds to prepare cycloalkanes, such as Ni–Co alloys with oxyphilic NbO. x Synergistic effects among species can promote the removal of oxygen-containing functional groups and achieve high cycloalkane selectivity in the hydrodeoxygenation of guaiacol (Appl. Energy, 2022, 328, 120199.).

[0006] However, existing systems still have the following problems: First, the amount of precious metals Pt or Ru is relatively high, resulting in insufficient utilization of metal atoms and high catalyst costs; Second, conventional supported metal particles are prone to sintering, loss, or carbon deposition in high-temperature, high-pressure hydrogen and complex lignin oil systems; Third, a single metal site cannot simultaneously handle H2 activation, aromatic ring hydrogenation, and C–O bond breaking processes; Fourth, the complex structure of oxygen-containing aromatic molecules in lignin oil leads to insufficient spatial matching of conventional metal / acid sites, resulting in incomplete deoxygenation of oxygen-containing intermediates and limited carbon yield of cycloalkanes; Fifth, existing Pt / zeolite or Ru / zeolite systems are mostly concentrated on model compounds, and further improvements are needed for high carbon yield conversion of real lignin oil or pre-depolymerized lignin oil.

[0007] Single-atom alloy catalysts are a special type of alloy catalyst formed by a small number of noble metal atoms isolated and dispersed on or near the surface of a host metal. Compared with ordinary bimetallic alloy nanoparticles, single-atom alloys can maintain high atom utilization of noble metals while simultaneously regulating H2 activation, adsorption configuration, and bond breaking processes through electronic synergy between the isolated noble metal sites and the host metal. Introducing Pt into the Co host metal in the form of isolated atoms is expected to simultaneously leverage Pt's excellent H2 activation ability and Co's role in aromatic ring hydrogenation and C–O bond conversion, thereby constructing a catalytic interface that combines high hydrogenation activity, high deoxygenation capacity, and low noble metal content.

[0008] Meanwhile, zeolite molecular sieves possess a regular pore structure, tunable acidic sites, and good thermal stability. Confining PtCo single-atom alloy particles within zeolite channels, cages, or intracrystalline mesoporous structures can suppress Pt single-atom aggregation and Co particle sintering, and shorten the spatial distance between metal sites and acidic sites. This promotes the continuous occurrence of aromatic ring hydrogenation, C–O bond breaking, demethoxylation, dehydroxylation, and hydrodeoxylation reactions in lignin-derived oxygen-containing aromatic compounds.

[0009] Therefore, developing a zeolite-confined PtCo single-atom alloy catalyst and using it for high-carbon-yield conversion of lignin or lignin oil to prepare cycloalkanes is of great significance for improving the utilization efficiency of lignin resources and developing sustainable fuels. Summary of the Invention

[0010] The purpose of this invention is to provide a zeolite-confined PtCo single-atom alloy catalyst to solve problems such as high noble metal usage, easy sintering of metal particles, insufficient metal-acid synergy, incomplete deoxygenation of oxygen-containing intermediates, and low carbon yield of cycloalkanes in existing lignin hydrodeoxygenation processes. Another objective of this invention is to provide a method for preparing the aforementioned zeolite-confined PtCo single-atom alloy catalyst and to apply it to the directed conversion of lignin, lignin oil, lignin depolymerization oil, lignin-derived phenolic model compounds, and / or lignin-derived phenolic compounds to prepare cycloalkanes.

[0011] According to a first aspect of the present invention, a zeolite-confined PtCo single-atom alloy catalyst is provided, the catalyst comprising a zeolite molecular sieve support and PtCo single-atom alloy particles confined in the zeolite molecular sieve channels, cages, intracrystalline defect sites and / or intracrystalline mesoporous structures.

[0012] The PtCo single-atom alloy particles are mainly composed of Co metal particles, with Pt dispersed in the form of isolated atoms on the surface, subsurface and / or near-surface of the Co metal particles, forming Pt-Co coordination structures with coordination numbers of 1 to 12 and Pt-Pt coordination structures with coordination numbers of 0 to 3.

[0013] In this invention, "PtCo single-atom alloy" refers to Pt atoms existing in an isolated or highly dispersed state on the surface, subsurface or near-surface structure of Co main metal, where Pt atoms do not form a continuous Pt-Pt metal aggregate structure, or where the Pt-Pt coordination number is significantly lower than that of ordinary Pt nanoparticles, while Pt-Co coordination is clearly present.

[0014] Based on the above technical solution, the average particle size of the PtCo single-atom alloy particles is 0.5-20nm, preferably 1-10nm, and more preferably 2-6nm; The molar ratio of Pt to Co in the PtCo single-atom alloy particles is 1:5-1:500, preferably 1:10-1:200, and more preferably 1:20-1:100.

[0015] Based on the above technical solution, the Pt loading in the catalyst is 0.001-1.0 wt%, preferably 0.005-0.5 wt%, and more preferably 0.01-0.2 wt%. The catalyst has a Co loading of 0.5-40 wt%, preferably 2-25 wt%, and more preferably 5-15 wt%.

[0016] Based on the above technical solution, the zeolite molecules are screened from one or more of Beta, USY, Y, ZSM-5, MOR, MCM-22, ZSM-11, ZSM-22, SAPO-34, and SSZ-13, preferably Beta, USY, Y, or ZSM-5, and more preferably hierarchical porous Beta or hierarchical porous USY zeolite with a microporous-mesoporous composite structure, wherein micropores account for 30-80% and mesopores account for 20-70%, based on a total pore volume of 100%.

[0017] Catalyst design principle: Zeolite molecular sieves possess Brønsted and Lewis acidic sites. Brønsted acidic sites promote the dehydration, demethoxylation, and dehydroxylation of oxygen-containing intermediates, while Lewis acidic sites promote the adsorption and activation of oxygen-containing functional groups such as ether bonds, methoxy groups, and phenolic hydroxyl groups. The PtCo single-atom alloy sites and the zeolite acidic sites form a spatially adjacent synergistic catalytic interface, jointly promoting the conversion of lignin-derived oxygen-containing aromatic compounds into cycloalkanes.

[0018] According to a second aspect of the present invention, a method for preparing a zeolite-confined PtCo single-atom alloy catalyst is provided, comprising the following steps: Step 1: Pretreatment of zeolite molecular sieves to obtain zeolite support with acidic sites and confined pore structure; Step 2, Preparation of zeolite-confined Co metal particles: The zeolite support prepared in Step 1 is contacted with a Co precursor solution to allow the Co precursor to enter the zeolite channels, cages, intracrystalline defect sites and / or intracrystalline mesoporous structures. After drying, calcination and reduction treatment, zeolite-confined Co metal particles are obtained. Step 3, Preparation of zeolite-confined PtCo single-atom alloy catalyst: The zeolite-confined Co metal particles prepared in Step 2 are contacted with a Pt precursor solution, so that the Pt precursor is selectively deposited, adsorbed or replaced on the surface, subsurface and / or near-surface sites of the Co metal particles. After drying and reduction treatment, the zeolite-confined PtCo single-atom alloy catalyst is obtained.

[0019] Based on the above technical solution, the zeolite molecular sieve pretreatment in step 1 includes one or more of the following: ammonium exchange, acid treatment, alkali treatment, steam treatment, dealumination treatment, desilication treatment, or template agent-assisted treatment.

[0020] Based on the above technical solution, the zeolite molecular sieve pretreatment in step 1 includes alkali treatment and ammonium exchange treatment. Specifically, the zeolite molecular sieve is added to an alkaline solvent for alkali treatment, which selectively dissolves some silicon species in the zeolite crystals, thereby introducing a mesoporous structure while retaining the microporous framework structure of the zeolite. After the treatment, the mixture is rapidly cooled to room temperature, filtered, and washed with deionized water until the filtrate is close to neutral. Subsequently, the washed solid is added to an ammonium salt solution for ammonium exchange, with the number of exchanges being 1 to 4 times, preferably 2 to 3 times. After washing, drying, and calcination, a zeolite carrier with acidic sites and a microporous-mesoporous composite confined pore structure is obtained.

[0021] Based on the above technical solution, the alkaline solvent is selected from one or more of sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, sodium carbonate aqueous solution, and ammonia water; preferably, it is a sodium hydroxide aqueous solution with a concentration of 0.05-1.0 mol / L, and more preferably, it is a sodium hydroxide aqueous solution with a concentration of 0.1-0.5 mol / L.

[0022] Based on the above technical solution, the stirring conditions for the alkali treatment are: the treatment temperature is 25-90℃, preferably 40-80℃; the treatment time is 10-180min, preferably 20-90min.

[0023] Based on the above technical solution, the ammonium salt solution is selected from one or more of ammonium nitrate aqueous solution, ammonium chloride aqueous solution, ammonium sulfate aqueous solution, and ammonium acetate aqueous solution; preferably, it is an ammonium nitrate aqueous solution with a concentration of 0.1 to 2.0 mol / L, and more preferably, it is an ammonium nitrate aqueous solution with a concentration of 0.3 to 1.0 mol / L.

[0024] Based on the above technical solution, the temperature of the ammonium exchange is 50-100℃, preferably 70-90℃; the time for each ammonium exchange is 1-8 h, preferably 2-6 h.

[0025] Based on the above technical solution, the calcination conditions in the zeolite molecular sieve pretreatment in step 1 are as follows: in an air atmosphere, at a heating rate of 1-10℃ / min, preferably 1-5℃ / min, the temperature is raised to 450-650℃, preferably 500-600℃, and calcined for 2-8 hours, preferably 3-6 hours.

[0026] The zeolite carrier has a microporous-mesoporous composite structure, wherein mesoporous pores account for 20-70% and microporous pores account for 30-80%, based on a total pore volume of 100%; preferably, mesoporous pores account for 30-60% and microporous pores account for 40-70%, based on a total pore volume of 100%.

[0027] Based on the above technical solution, the Co precursor in the Co precursor solution in step 2 is selected from one or more of cobalt nitrate, cobalt chloride, cobalt acetate, cobalt acetylacetone, cobalt oxalate, and cobalt carbonate, with a concentration of 0.05 to 0.5 mol / L; In step 2, the mass ratio of the precursor solution to the zeolite carrier is 0.1–20:1; In step 2, the Co precursor is introduced into the zeolite channels or intracrystalline mesoporous structures through ion exchange, impregnation, dual solvent method, deposition precipitation, in-situ crystallization encapsulation, or ligand-assisted confinement. The roasting in step 2 specifically involves roasting at 250-650℃ for 1-8 hours; The reduction in step 2 is specifically carried out in a nitrogen atmosphere containing 1-100% hydrogen by volume, at 300-700℃ for 0.5-8 hours.

[0028] Based on the above technical solution, the Pt precursor in the Pt precursor solution in step 3 is selected from one or more of chloroplatinic acid, ammonium chloroplatinate, tetraammineplatinum nitrate, tetraammineplatinum chloride, and platinum acetylacetonate, and the concentration is 0.001-10 mmol / L, preferably 0.005-2 mmol / L, and more preferably 0.01-1 mmol / L; In step 3, the mass ratio of the zeolite-confined Co metal particles to the Pt precursor solution is 1:0.5 to 1:100. The reduction conditions in step 3 are as follows: reduction at 150-500℃ for 0.5-6h in a nitrogen atmosphere containing 1-100% hydrogen by volume, preferably 200-400℃.

[0029] According to a third aspect of the present invention, a method for the directional conversion of lignin to prepare cycloalkanes is provided, wherein lignin, lignin oil, lignin depolymerization oil, lignin-derived phenolic model compounds and / or lignin-derived phenolic compounds are used as raw materials, and are contacted with a zeolite-confined PtCo single-atom alloy catalyst, and a hydrodeoxygenation reaction is carried out in a hydrogen atmosphere and in the presence of a solvent to obtain a liquid product containing C6–C18 cycloalkanes.

[0030] Based on the above technical solution, the lignin is selected from one or more of alkali lignin, organic solvent lignin, enzymatic hydrolyzed lignin, sulfate lignin, lignin sulfonate, bamboo lignin, birch lignin, poplar lignin, pine lignin, corn straw lignin, and wheat straw lignin. The lignin-derived phenolic compounds are selected from one or more of guaiacol, alkylguaiacol, syringol, alkylsyringol, phenol, alkylphenol, methoxyphenol, dimethoxyphenol, phenoxyphenol, diphenyl ether, and phenethylphenyl ether.

[0031] Based on the above technical solution, the hydrogenation deoxygenation reaction is specifically carried out in the presence of a solvent, wherein the solvent is selected from one or more of dodecane, hexadecane, cyclohexane, methylcyclohexane, decahydronaphthalene, tetrahydronaphthalene, n-hexane, n-heptane, isopropanol, ethanol, water, dioxane, and tetrahydrofuran, and reacted at 180-380°C under a hydrogen pressure of 1-10 MPa for 0.5-24 h, preferably at 220-330°C under a hydrogen pressure of 2-8 MPa for 1-12 h, and more preferably at 240-310°C under a hydrogen pressure of 3-6 MPa for 2-8 h.

[0032] Based on the above technical solution, in the hydrodeoxygenation reaction, the mass ratio of raw material to catalyst is 1:0.02-2.0, preferably 1:0.05-1.0, and more preferably 1:0.1-0.6; the mass-volume ratio of raw material to solvent is 1g:5-100mL, preferably 1g:10-60mL, and more preferably 1g:20-50mL.

[0033] Based on the above technical solution, the raw material is a lignin-derived phenolic model compound, a mixture of lignin-derived phenols, lignin depolymerization oil, lignin oil, or a combination thereof; when the raw material is a lignin-derived phenolic model compound or a mixture of lignin-derived phenols, the amount of raw material used is 0.05–5.0 g, preferably 0.1–2.0 g; the amount of catalyst used is 0.01–2.0 g, preferably 0.05–1.0 g; and the amount of solvent used is 2–100 mL, preferably 5–50 mL; when the raw material is lignin depolymerization oil or lignin oil, the amount of raw material used is 0.05–5.0 g, preferably 0.1–2.0 g; the amount of catalyst used is 0.02–3.0 g, preferably 0.05–1.5 g; and the amount of solvent used is 2–100 mL, preferably 5–50 mL.

[0034] The reaction is carried out in a closed high-pressure reactor with a volume of 10-500 mL, preferably 25-200 mL; the total volume of the liquid phase after the addition of reactants, catalyst and solvent accounts for 10-80% of the effective volume of the reactor, preferably 20-60%.

[0035] Beneficial effects (1) The present invention adopts a PtCo single-atom alloy structure, which disperses Pt in the form of isolated atoms on the surface, subsurface or near-surface of Co main metal particles, thereby improving the utilization rate of Pt atoms and significantly reducing the amount of precious metals used.

[0036] (2) Pt single atoms form Pt-Co coordination and electronic interaction with the Co host metal. Pt sites can enhance H2 activation and hydrogen spillover ability, while Co sites can promote the hydrogenation of aromatic rings and the hydrogenolysis of CO bonds, thereby improving the conversion efficiency of lignin-derived oxygen-containing aromatic compounds.

[0037] (3) The zeolite confined structure can suppress the aggregation of Pt single atoms and the sintering of Co particles, thereby improving the stability of the catalyst in high temperature, high pressure hydrogen and complex lignin oil systems.

[0038] (4) The Brønsted and Lewis acid sites of zeolite can promote the demethoxylation, dehydroxylation, dehydration and hydrodeoxylation processes, forming a spatially adjacent metal-acid synergistic catalytic interface with the PtCo single-atom alloy sites.

[0039] (5) The catalyst of the present invention is applicable to a variety of raw materials such as lignin-derived phenolic compounds, lignin oil, pre-depolymerized lignin oil and real lignin, and can achieve a carbon yield of more than 85% for C6-C18 cycloalkanes under preferred conditions. Attached Figure Description

[0040] Figure 1SEM images of the Pt1Co@Beta catalyst prepared in Example 3 (left: magnification of 20,000x, right: magnification of 80,000x). Figure 2 The image shows the XRD pattern of the Pt1Co@Beta catalyst prepared in Example 3. Detailed Implementation

[0041] To make the objectives and technical solutions of this invention clearer, the following embodiments are provided for further explanation. However, the scope of protection of this invention is not limited to these embodiments; the embodiments are merely for illustrative purposes. Those skilled in the art should understand that any changes or equivalent substitutions that do not depart from the concept of this invention are included within the scope of protection of this invention.

[0042] Unless otherwise specified, all reagents and raw materials used in this invention are obtained through purchase.

[0043] Example 1: Weigh 5.0 g of commercial H-Beta zeolite molecular sieve and add it to 250 mL of 0.2 mol / L NaOH aqueous solution. Stir at 60 °C for 30 min. After treatment, quickly cool to room temperature, filter, and wash with deionized water until the filtrate is nearly neutral.

[0044] 4.3 g of washed, nearly neutral solid was added to 100 ml of 0.5 mol / L NH4NO3 aqueous solution and ion-exchanged at 80 °C for 4 h, with the exchange process repeated twice. The mixture was then filtered, washed, dried, and calcined in air at 550 °C at a rate of 2 °C / min for 4 h to obtain hierarchical porous H-Beta zeolite (45% micropores and 55% mesopores).

[0045] Example 2: Weigh 2.0 g of the hierarchical H-Beta zeolite prepared in Example 1 and add it to 10 mL of a 0.34 mol / L cobalt nitrate aqueous solution to achieve a theoretical Co loading of 10 wt%. Stir the suspension at room temperature for 6 h to allow the Co precursor to fully enter the zeolite channels, cages, and intracrystalline mesoporous structure.

[0046] The system was then evaporated to dryness at 80 °C and dried at 110 °C for 12 h. The resulting solid was calcined in air at a rate of 2 °C / min to 400 °C for 4 h. The calcined sample was then reduced in a 10 vol% H2 / N2 atmosphere at a rate of 2 °C / min to 500 °C for 3 h to obtain the Co@Beta catalyst.

[0047] Example 3: 1.0 g of the Co@Beta catalyst prepared in Example 2 was weighed and added to 100 mL of a low-concentration chloroplatinic acid aqueous solution (0.0256 mmol / L) under N2 atmosphere protection, so that the theoretical Pt loading was 0.05 wt%. The mixture was stirred at room temperature for 4 h to allow the Pt precursor to selectively adsorb, deposit, or displace on the surface, subsurface, or near-surface sites of the Co metal particles. After the reaction was complete, the mixture was filtered and washed with deionized water. The resulting solid was vacuum dried at 80 °C for 12 h, and then reduced at 300 °C for 2 h under a 5 vol% H2 / N2 atmosphere at a rate of 2 °C / min to obtain a zeolite-confined PtCo single-atom alloy catalyst, designated as Pt1Co@Beta catalyst. The SEM and XRD characterization results of the Pt1Co@Beta catalyst are shown below. Figure 1 , 2 .

[0048] Example 4: Weigh 2.0 g of USY zeolite, exchange it with 100 ml of 0.5 mol / L NH4NO3 solution at 80 °C for 4 h, repeat the exchange twice, wash, dry and calcine to obtain H-USY zeolite.

[0049] 2.0 g of H-USY zeolite was impregnated with 2.0 ml of a 1.36 mol / L cobalt nitrate solution using an equal-volume impregnation method to achieve a theoretical Co loading of 8 wt%. The sample was dried, calcined at 400 °C for 4 h, and reduced with hydrogen at 500 °C for 3 h (10 vol% H₂ / N₂ atmosphere) to obtain Co@USY. Subsequently, 1.0 g of Co@USY was added with 100 ml of a 0.0154 mmol / L chloroplatinic acid solution (using a low-concentration chloroplatinic acid solution to introduce Pt) to achieve a theoretical Pt loading of 0.03 wt%. After vacuum drying at 80 °C for 12 h, the sample was reduced with hydrogen at 300 °C for 2 h in a 5 vol% H₂ / N₂ atmosphere to obtain the Pt1Co@USY catalyst (Pt-Co coordination number 3–9, Pt-Pt coordination number 0–0.5).

[0050] Example 5: 0.20 g of guaiacol, 0.05 g of the Pt1Co@Beta catalyst prepared in Example 3, and 10 mL of dodecane were added to a 25 mL stainless steel high-pressure reactor. After sealing the reactor, it was purged with H2 three times, and then H2 was introduced to 5 MPa.

[0051] The reaction system was heated to 250℃ and stirred for 3 hours. After the reaction was completed, it was cooled to room temperature, the gas was released, the catalyst was separated by centrifugation, and the liquid product was collected. The liquid product was analyzed by GC-MS and GC-FID.

[0052] The results showed that the conversion rate of guaiacol was 100%, with cyclohexane and a small amount of methylcyclohexane as the main products. Based on the carbon content of guaiacol, the carbon yield of C6–C7 cycloalkanes was 90.3%.

[0053] Example 6: 0.20 g of 4-propylguaiacol, 0.05 g of the Pt1Co@Beta catalyst prepared in Example 3, and 10 mL of dodecane were added to a 25 mL high-pressure reactor. After purging the reactor with H2, H2 was introduced to 5 MPa, and the reaction was carried out at 260 °C for 4 h.

[0054] After the reaction was completed, GC-MS and GC-FID analysis showed that the main product was propylcyclohexane, and the byproducts included small amounts of propylbenzene, propylcyclohexanol, and propylphenol. Based on the carbon content of 4-propylguaiacol, the carbon yield of propylcyclohexane was 88.7%.

[0055] These results demonstrate that the Pt1Co@Beta catalyst can effectively promote the removal of methoxy groups, phenolic hydroxyl groups, and aromatic ring hydrogenation, achieving efficient conversion of G-type lignin monomers to cycloalkanes.

[0056] Example 7: 0.20 g of 4-propyleugenol, 0.06 g of the Pt1Co@Beta catalyst prepared in Example 3, and 10 mL of dodecane were added to a 25 mL high-pressure reactor. After purging the reactor with H2 three times, H2 was introduced to a pressure of 6 MPa, and the reaction was carried out at 280 °C for 5 h.

[0057] The main liquid products after the reaction were propylcyclohexane, methyl-substituted cyclohexane, and dimethyl-substituted cyclohexane. Based on the carbon content of 4-propyleugenol, the carbon yield of C8–C10 cycloalkanes was 86.2%.

[0058] The results indicate that the catalyst of the present invention is applicable not only to G-type lignin monomers, but also to S-type lignin monomers containing a dimethoxy structure.

[0059] Example 8: Prepare a 0.50 g mixture of lignin-derived phenols, wherein the mixture comprises guaiacol, 4-methylguaiacol, 4-ethylguaiacol, 4-propylguaiacol, syringol and 4-propylsyringol (guaiacol accounts for 10 wt%, 4-methylguaiacol 15 wt%, 4-ethylguaiacol 15 wt%, 4-propylguaiacol 30 wt%, and syringol and 4-propylsyringol together account for 30 wt%).

[0060] The above mixture, 0.15 g of the Pt1Co@Beta catalyst prepared in Example 3, and 20 mL of dodecane were added to a 50 mL high-pressure reactor. After sealing, the reactor was purged with H2 three times, and then H2 was introduced to a pressure of 5 MPa. The reactor was then reacted at 270 °C for 4 h.

[0061] After the reaction, the liquid product mainly contained cyclohexane, methylcyclohexane, ethylcyclohexane, propylcyclohexane, dimethylcyclohexane, and trimethylcyclohexane. Based on the total carbon content of the feedstock, the carbon yield of C6–C10 cycloalkanes was 87.6%.

[0062] Example 9: 2.0 g of lignin was dissolved in 40 ml of an ethanol / water mixture and pyrolyzed at 250 °C for 4 h to obtain lignin oil. After removing solid residue, the lignin oil was used as a feedstock for hydrodeoxygenation. The lignin oil mainly contains alkyl guaiacol, alkyl eugenol, phenols, methoxyphenols, and a small amount of lignin dimers.

[0063] 0.50 g of lignin oil, 0.25 g of the Pt1Co@Beta catalyst prepared in Example 3, and 20 mL of decahydronaphthalene were added to a 50 mL high-pressure reactor. After sealing, the reactor was purged with H2 three times, and the pressure was increased to 6 MPa. The reactor was then reacted at 300 °C for 6 h.

[0064] After the reaction, the liquid products were analyzed by GC-MS, GC-FID, and elemental analysis. The results showed that the products were mainly C6–C18 monocyclic, bicyclic, and polycyclic cycloalkanes, including cyclohexane, alkylcyclohexane, bicyclohexane, alkylbicyclohexane, and polycyclic cycloalkanes. Based on detectable organic carbon in lignin oil, the carbon yield of C6–C18 cycloalkanes was 85.4%.

[0065] Example 10: 1.0 g of organic solvent lignin, 0.50 g of the Pt1Co@Beta catalyst prepared in Example 3, and 30 mL of decahydronaphthalene were added to a 100 mL high-pressure reactor. After sealing, the reactor was purged with H2 three times, and the pressure was increased to 6 MPa. The reactor was then reacted at 320 °C for 8 h. The lignin prepared by the organic solvent method was organosolvlignin obtained from lignocellulose raw materials using an ethanol / water mixed solvent. The lignin was dispersed or suspended in decahydronaphthalene, forming a lignin suspension with a solid content of approximately 33.3 g / L.

[0066] After the reaction was completed, the mixture was cooled to room temperature, and the solid catalyst and residue were separated by centrifugation. The liquid product was collected. GC-MS, GC-FID, and elemental analysis showed that the liquid product mainly contained C6–C18 cycloalkanes, a small amount of aromatics, and a small amount of incompletely deoxygenated cycloalcohol intermediates. Based on the total carbon content in the lignin feedstock, the carbon yield of C6–C18 cycloalkanes was 72.8%.

[0067] Example 11: Following the reaction conditions of Example 8, a catalyst cycling test was conducted using a mixture of lignin-derived phenols as raw material. After each reaction, the Pt1Co@Beta catalyst was recovered by centrifugation, washed sequentially with ethanol and dodecane, and dried at 80°C for 12 h before being used in the next reaction.

[0068] After five consecutive cycles, the mixed phenolic substrate remained essentially completely converted, with the C6–C10 cycloalkane carbon yield remaining above 82.5%. Post-reaction catalyst characterization by HAADF-STEM and EXAFS showed that Pt remained in isolated atom form, with no significant Pt nanoparticle aggregation observed, and the Co particle size showed minimal change, indicating that the zeolite confinement structure effectively stabilized the PtCo single-atom alloying sites.

[0069] Comparative Example 1: The Co@Beta catalyst prepared in Example 2 was used without introducing Pt single atoms. The hydrodeoxygenation reaction of the lignin-derived phenolic mixture was carried out according to the method of Example 8.

[0070] The results showed that the substrate conversion rate was 82.4%, and the product still contained a large amount of cyclohexanol, alkylcyclohexanol and incompletely deoxygenated alkylphenol intermediates. The C6–C10 cycloalkane carbon yield was 54.3%.

[0071] Comparative Example 2: The Pt@Beta catalyst was prepared using an equal-volume impregnation method. 2.0 g of the hierarchical porous H-Beta zeolite prepared in Example 1 was weighed and added to 2.0 mL of a 25.6 mmol / L chloroplatinic acid aqueous solution to achieve a theoretical Pt loading of 0.5 wt%. The concentration of the chloroplatinic acid aqueous solution is based on Pt elemental content, and the theoretical Pt loading is based on the mass of Pt elemental content relative to the mass of the hierarchical porous H-Beta zeolite.

[0072] The obtained sample was thoroughly mixed and allowed to stand for 6 hours to allow the Pt precursor to be fully dispersed. The system was then evaporated to dryness at 80 °C and dried at 110 °C for 12 hours. The resulting solid was calcined in air at a rate of 2 °C / min to 400 °C for 4 hours. The calcined sample was then reduced in a 5 vol% H₂ / N₂ atmosphere at a rate of 2 °C / min to 300 °C for 2 hours to obtain the Pt@Beta catalyst, denoted as 0.5Pt@Beta.

[0073] The results showed that the substrate could be largely converted, but the product contained a large number of cyclic alcohols and some aromatic intermediates, with a C6–C10 cycloalkane carbon yield of 65.8%.

[0074] Comparative Example 3: A common PtCo / Beta catalyst was prepared by simultaneously loading Pt and Co onto the surface of H-Beta zeolite using a co-impregnation method. Specifically, 2.0 g of the hierarchical porous H-Beta zeolite prepared in Example 1 was weighed. Separately, 0.99 g of Co(NO3)2·6H2O and 2.65 mg of H2PtCl6·6H2O were dissolved in deionized water and diluted to 10 mL to obtain a mixed precursor solution containing Co and Pt, wherein the concentration of Co was approximately 0.34 mol / L and the concentration of Pt was approximately 0.513 mmol / L.

[0075] The hierarchical H-Beta zeolite was added to the Pt-Co mixed precursor solution and stirred at room temperature for 6 h, allowing the Pt and Co precursors to be simultaneously adsorbed or deposited on the surface, channels, and mesoporous structure within the H-Beta zeolite. The system was then evaporated to dryness at 80 °C and dried at 110 °C for 12 h. The resulting solid was calcined in air at a rate of 2 °C / min to 400 °C for 4 h. The calcined sample was then reduced in a 10 vol% H₂ / N₂ atmosphere at a rate of 2 °C / min to 500 °C for 3 h to obtain a conventional PtCo / Beta catalyst.

[0076] Characterization results showed that the catalyst contained some PtCo alloy particles, but also a small amount of Pt aggregates or Pt-rich regions. Following the method of Example 8, the C6–C10 cycloalkane carbon yield was 72.4%.

[0077] Comparative Example 4: Pt1Co / Beta catalysts were prepared using untreated H-Beta zeolite via a conventional impregnation method. Due to the metal's predominantly distributed outer surface of the zeolite, the confinement effect was weak.

[0078] The reaction was carried out according to the method of Example 8. In the initial reaction, the carbon yield of C6–C10 cycloalkanes was 76.1%. After 5 cycles, the carbon yield of cycloalkanes decreased to 58.7%. TEM characterization showed that the metal particles grew significantly.

[0079] Comparative Example 5: A commercial Pt / C catalyst was physically mixed with the hierarchical porous H-Beta zeolite prepared in Example 1 at a mass ratio of 1:9, and then ground until homogeneous to obtain a Pt / C+H-Beta physically mixed catalyst. The commercial Pt / C catalyst contained 5 wt% Pt.

[0080] The results showed that the substrate could undergo partial hydrogenation and deoxygenation, but the C6–C10 cycloalkane carbon yield was only 48.9%. The product contained a significant amount of cyclohexanol, alkylphenol, and methoxycyclohexanol.

[0081] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A zeolite-confined PtCo single-atom alloy catalyst, characterized in that, The catalyst includes a zeolite molecular sieve support and PtCo single-atom alloy particles confined in the zeolite molecular sieve channels, cages, intracrystalline defect sites and / or intracrystalline mesoporous structures. The PtCo single-atom alloy particles are mainly composed of Co metal particles, with Pt dispersed in the form of isolated atoms on the surface, subsurface and / or near-surface of the Co metal particles, forming Pt-Co coordination structures with coordination numbers of 1 to 12 and Pt-Pt coordination structures with coordination numbers of 0 to 3.

2. The zeolite-confined PtCo single-atom alloy catalyst according to claim 1, characterized in that, The average particle size of the PtCo single-atom alloy particles is 0.5-20 nm, preferably 1-10 nm, and more preferably 2-6 nm; The molar ratio of Pt to Co in the PtCo single-atom alloy particles is 1:5-1:500, preferably 1:10-1:200, and more preferably 1:20-1:100; The Pt loading in the catalyst is 0.001-1.0 wt%, preferably 0.005-0.5 wt%, and more preferably 0.01-0.2 wt%. The catalyst has a Co loading of 0.5-40 wt%, preferably 2-25 wt%, and more preferably 5-15 wt%.

3. The zeolite-confined PtCo single-atom alloy catalyst according to claim 1, characterized in that, The zeolite molecules are selected from one or more of Beta, USY, Y, ZSM-5, MOR, MCM-22, ZSM-11, ZSM-22, SAPO-34, and SSZ-13, preferably Beta, USY, Y, or ZSM-5, and more preferably hierarchical porous Beta or hierarchical porous USY zeolite with a microporous-mesoporous composite structure, wherein micropores account for 30-80% and mesopores account for 20-70%, based on a total pore volume of 100%.

4. A method for preparing a zeolite-confined PtCo single-atom alloy catalyst, characterized in that, Includes the following steps: Step 1: Pretreatment of zeolite molecular sieves to obtain zeolite support with acidic sites and confined pore structure; Step 2, Preparation of zeolite-confined Co metal particles: The zeolite support prepared in Step 1 is contacted with a Co precursor solution to allow the Co precursor to enter the zeolite channels, cages, intracrystalline defect sites and / or intracrystalline mesoporous structures. After drying, calcination and reduction treatment, zeolite-confined Co metal particles are obtained. Step 3, Preparation of zeolite-confined PtCo single-atom alloy catalyst: The zeolite-confined Co metal particles prepared in Step 2 are contacted with a Pt precursor solution, so that the Pt precursor is selectively deposited, adsorbed or replaced on the surface, subsurface and / or near-surface sites of the Co metal particles. After drying and reduction treatment, the zeolite-confined PtCo single-atom alloy catalyst is obtained.

5. The preparation method according to claim 4, characterized in that, The zeolite molecular sieve pretreatment in step 1 includes ammonium exchange, acid treatment, alkali treatment, steam treatment, dealumination treatment, desilication treatment, or template agent-assisted treatment.

6. The preparation method according to claim 4, characterized in that, The Co precursor in the Co precursor solution mentioned in step 2 is selected from one or more of cobalt nitrate, cobalt chloride, cobalt acetate, cobalt acetylacetone, cobalt oxalate, and cobalt carbonate, with a concentration of 0.05-0.5 mol / L; In step 2, the mass ratio of the precursor solution to the zeolite carrier is 0.1-20:1; In step 2, the Co precursor is introduced into the zeolite channels or intracrystalline mesoporous structures through ion exchange, impregnation, dual solvent method, deposition precipitation, in-situ crystallization encapsulation, or ligand-assisted confinement. The roasting in step 2 specifically involves roasting at 250-650℃ for 1-8 hours; The reduction in step 2 is specifically carried out at 300-700℃ for 0.5-8 hours in a nitrogen atmosphere containing 1-100% hydrogen by volume.

7. The preparation method according to claim 4, characterized in that, In step 3, the Pt precursor in the Pt precursor solution is selected from one or more of chloroplatinic acid, ammonium chloroplatinate, tetraammineplatinum nitrate, tetraammineplatinum chloride, and platinum acetylacetonate, and the concentration is 0.001-10 mmol / L, preferably 0.005-2 mmol / L, and more preferably 0.01-1 mmol / L; In step 3, the mass ratio of the zeolite-confined Co metal particles to the Pt precursor solution is 1:0.5 to 1:

100. The reduction process in step 3 specifically involves reducing the hydrogen in a nitrogen atmosphere containing 1-100% hydrogen by volume at 150-500°C for 0.5-6 hours, preferably at 200-400°C.

8. A method for the directional conversion of lignin to prepare cycloalkanes, characterized in that, Using lignin, lignin oil, lignin depolymerization oil, lignin-derived phenolic model compounds and / or lignin-derived phenolic compounds as raw materials, they are contacted with a zeolite-confined PtCo single-atom alloy catalyst and subjected to a hydrodeoxygenation reaction under a hydrogen atmosphere to obtain a liquid product containing C6–C18 cycloalkanes.

9. The method according to claim 8, characterized in that, The lignin is selected from one or more of the following: alkali lignin, organic solvent lignin, enzymatic hydrolyzed lignin, sulfate lignin, lignin sulfonate, bamboo lignin, birch lignin, poplar lignin, pine lignin, corn straw lignin, and wheat straw lignin. The lignin-derived phenolic compounds are selected from one or more of guaiacol, alkylguaiacol, syringol, alkylsyringol, phenol, alkylphenol, methoxyphenol, dimethoxyphenol, phenoxyphenol, diphenyl ether, and phenethylphenyl ether.

10. The method according to claim 8, characterized in that, The hydrogenation deoxygenation reaction is specifically carried out in the presence of a solvent selected from one or more of dodecane, hexadecane, cyclohexane, methylcyclohexane, decahydronaphthalene, tetrahydronaphthalene, n-hexane, n-heptane, isopropanol, ethanol, water, dioxane, and tetrahydrofuran. The reaction is carried out at 180-380°C under a hydrogen pressure of 1-10 MPa for 0.5-24 h, preferably at 220-330°C under a hydrogen pressure of 2-8 MPa for 1-12 h, and more preferably at 240-310°C under a hydrogen pressure of 3-6 MPa for 2-8 h.

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