Palladium-platinum bimetallic alloy catalyst supported on halloysite nanotubes and preparation method thereof

Abstract

The present application relates to the technical field of catalytic materials, and discloses a halloysite nanotube loaded palladium-platinum bimetallic alloy catalyst and a preparation method thereof, the catalyst comprising heat pretreated halloysite and uniformly dispersed palladium-platinum bimetallic alloy particles, and the mass ratio of palladium, platinum and heat pretreated halloysite being 0.012-0.022:0.012-0.022:1. The preparation method comprises mixing the heat pretreated halloysite with palladium chloride and chloroplatinic acid hexahydrate, adding concentrated ammonia water to adjust the pH to 9-11 to form an ammonia complex; obtaining a precursor through a hydrothermal reaction, and adding sodium borohydride for liquid phase reduction. The bimetallic alloy phase produces geometric and electronic synergistic effects, thereby reducing the reaction activation energy; the ammonia complex ion is chemically bonded with the hydroxyl group of the carrier to prevent the loss of active components in the hydrothermal environment. The catalyst is combined with glycerol to produce hydrogen in situ, thereby avoiding the safety hazards and equipment investment of external high-pressure hydrogenation, and realizing the high-yield conversion of green diesel under extremely low noble metal loading.

Description

Technical Field

[0001] This invention relates to the field of catalytic materials technology, specifically to halloysite nanotube-supported palladium-platinum bimetallic alloy catalysts and their preparation methods. Background Technology

[0002] Hydrothermal deoxygenation is an important route for producing green diesel fuel. Catalysts play a crucial role in this process. Current technologies utilize precious metal catalysts to promote hydrothermal deoxygenation. However, these catalysts typically have high precious metal loadings, leading to high production costs. Conventional hydrothermal deoxygenation requires the introduction of external hydrogen gas as a hydrogen source. Introducing high-pressure external hydrogen gas necessitates high-pressure-resistance standards for the production equipment, increasing manufacturing costs and safety risks during industrial production.

[0003] To replace the externally supplied high-pressure hydrogen, in-situ hydrogen generation within the hydrothermal deoxygenation reaction system using a hydrogen donor has become an alternative solution. Achieving in-situ hydrogen production and hydrothermal deoxygenation under hydrothermal conditions requires high catalytic activity from precious metal catalysts. Currently, under the high-temperature conditions of hydrothermal deoxygenation, active metal particles on the catalyst surface are prone to agglomeration or detachment from the catalyst support, leading to decreased catalyst activity, reduced catalyst lifespan, and lower yields of green diesel.

[0004] Therefore, this invention proposes a halloysite nanotube-supported palladium-platinum bimetallic alloy catalyst and its preparation method to overcome the shortcomings of the prior art. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a halloysite nanotube-supported palladium-platinum bimetallic alloy catalyst and its preparation method. This solves the problems of safety hazards and high equipment costs caused by the high dependence of existing green diesel production processes on external high-pressure hydrogenation, as well as the problems of traditional supported catalysts where active components are easily aggregated and lost under high-temperature hydrothermal environments, and the need to rely on the loading of precious metals to maintain catalytic activity.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] In a first aspect, the present invention provides a halloysite nanotube-supported palladium-platinum bimetallic alloy catalyst, employing the following technical solution:

[0008] Halloysite nanotube-supported palladium-platinum bimetallic alloy catalyst comprises heat-treated halloysite and uniformly dispersed palladium-platinum bimetallic alloy particles formed on the heat-treated halloysite, wherein the mass ratio of palladium, platinum and heat-treated halloysite is 0.012-0.022:0.012-0.022:1.

[0009] By adopting the above technical solution, a palladium-platinum bimetallic combination with a fixed mass ratio is loaded onto the halloysite surface of the tubular structure after thermal pretreatment. The palladium and platinum elements form a bimetallic alloy phase, which produces a synergistic effect of geometric and electronic effects, reducing the activation energy of the hydrothermal deoxidation reaction. Therefore, a high-yield conversion of long-chain alkanes is achieved with a total extremely low noble metal loading of 2.4%-4.4%.

[0010] Meanwhile, the bimetallic alloy particles are anchored to the surface of the pre-treated halloysite by hydroxyl groups, preventing the loss of active components in the high-temperature and high-pressure hydrothermal environment and improving the structural stability of the catalyst.

[0011] Preferably, the pre-treated halloysite is prepared by a method comprising the following steps: placing halloysite in a muffle furnace and calcining it at 550-650°C for 1-3 hours, then cooling it to room temperature.

[0012] By adopting the above technical solution, high-temperature calcination removes impurities from the halloysite ore and stabilizes the halloysite skeleton structure, preventing the halloysite from hydrolyzing and collapsing during subsequent high-temperature and high-pressure hydrothermal reactions, maintaining the physical and mechanical strength of the halloysite tubular structure, and ensuring the hydrodynamic stability of the hydrothermal deoxygenation reaction system.

[0013] Preferably, palladium and platinum are derived from palladium chloride and chloroplatinic acid hexahydrate, respectively; 100 parts of heat-pretreated halloysite are combined with 2-3.67 parts of palladium chloride and 3.19-5.84 parts of chloroplatinic acid hexahydrate.

[0014] By adopting the above technical solution, the molar ratio of palladium-platinum bimetallic precursors can be accurately controlled to ensure that the final product forms an infinite solid solution alloy phase and avoid the agglomeration and precipitation of single metals.

[0015] Secondly, the present invention provides a method for preparing a halloysite nanotube-supported palladium-platinum bimetallic alloy catalyst, which adopts the following technical solution: The method for preparing a halloysite nanotube-supported palladium-platinum bimetallic alloy catalyst includes the following steps:

[0016] Step 1: Place halloysite in a muffle furnace and calcine it. Cool it to room temperature to obtain heat-treated halloysite.

[0017] Step 2: Add the heat-treated halloysite, palladium chloride, and chloroplatinic acid hexahydrate to deionized water and stir to disperse them to obtain a mixture.

[0018] Step 3: Add 25% concentrated ammonia solution to the mixture to adjust the pH of the mixture to 9-11, converting palladium and platinum into ammonia complexes, and obtaining a mixture containing ammonia complexes.

[0019] Step 4: The mixture containing the ammonia complex is sealed in a high-pressure reactor for reaction, followed by washing and drying to obtain the palladium-platinum doped halloysite precursor.

[0020] Step 5: Disperse the palladium-platinum doped halloysite precursor in ethanol, slowly add reducing solution for liquid-phase reduction to form uniformly dispersed palladium-platinum bimetallic alloy particles, and then perform centrifugation, washing and drying to obtain halloysite nanotube-supported palladium-platinum bimetallic alloy catalyst.

[0021] In step three, concentrated ammonia water converts the metal ions in palladium chloride and chloroplatinic acid hexahydrate into positively charged ammonium complex ions. Under the hydrothermal reaction conditions in step four, the positively charged ammonium complex ions undergo electrostatic attraction and chemical bonding with the abundant hydroxyl groups on the heat-treated halloysite surface. The high-temperature, high-pressure environment promotes full contact between the metal precursor and the halloysite carrier surface, forming a chemical bond-level anchoring effect, thus avoiding the detachment of precious metals caused by the weak physical adhesion of conventional impregnation methods.

[0022] Step three controls the pH of the mixture to 9-11 to ensure the stable coexistence of the palladium-platinum-ammonia complex. Step five uses sodium borohydride, a strong reducing agent, for liquid-phase reduction. Excess sodium borohydride provides sufficient electrons, promoting the synchronous reduction of palladium-platinum complex ions attached to the halloysite surface. Due to the similar atomic radii of palladium and platinum, the synchronous reduction process induces the fusion of the palladium-platinum metal lattices, forming a bimetallic alloy phase. This achieves high dispersion of nanoscale particles on the tubular surface of halloysite, preventing the sintering and growth of metal particles.

[0023] Halloysite nanotube-supported palladium-platinum bimetallic alloy catalysts were applied to hydrothermal deoxygenation systems for stearic acid or waste oils, with glycerol used as a hydrogen donor. Glycerol generates hydrogen in situ under the catalyst's action. This generated hydrogen immediately participates in the decarboxylation and decarbonylation reaction pathways of stearic acid. The bimetallic alloy phase lowers the activation energy of the deoxygenation reaction, enabling efficient conversion of long-chain alkanes without an external high-pressure hydrogen source.

[0024] Preferably, in step one, 110-130 parts of halloysite are calcined at 550-650℃ for 1-3 hours; in step two, 100 parts of heat-pretreated halloysite, 2-3.67 parts of palladium chloride, and 3.19-5.84 parts of chloroplatinic acid hexahydrate are added together to 800-1200 parts of deionized water; in step three, 15-40 parts of concentrated ammonia water with a mass fraction of 25% are added to the mixture; in step four, the reaction is carried out in a high-pressure reactor at a temperature of 160-220℃ for 6-12 hours; in step five, the palladium-platinum doped halloysite precursor is dispersed in 800-1200 parts of ethanol, and the reducing solution is prepared by dissolving 1.89-3.47 parts of solid sodium borohydride in 100-200 parts of deionized water.

[0025] By employing the above technical solution, the boundaries of thermodynamic and kinetic parameters are defined. The hydrothermal reaction temperature is controlled between 160-220℃ to ensure sufficient diffusion and anchoring of the complex precursor to the support. Below 160℃, the anchoring reaction rate is too slow; above 220℃, the solvent vaporization pressure is too high, increasing the equipment load. During the reduction process, the amount of sodium borohydride used exceeds the theoretical number of electrons required to reduce the metal ions, ensuring complete reduction of the noble metal precursor into a zero-valent alloy element precipitate that adheres to the support, thus ensuring that the final product possesses sufficient catalytically active sites.

[0026] This invention provides a halloysite nanotube-supported palladium-platinum bimetallic alloy catalyst and its preparation method. It possesses the following beneficial effects:

[0027] 1. This invention utilizes the formation of a bimetallic alloy phase between palladium and platinum on the surface of halloysite after thermal pretreatment. The synergistic effect of the geometric and electronic effects generated by the bimetallic alloy phase reduces the activation energy of the hydrothermal deoxidation reaction. With a noble metal loading of only 2.4%-4.4% of the total mass, the palladium-platinum bimetallic alloy catalyst supported on halloysite nanotubes can achieve a long-chain alkane yield of over 95% for stearic acid and waste oils in a high-temperature hydrothermal environment of 360℃, achieving high conversion efficiency with a relatively low loading.

[0028] 2. This invention applies a palladium-platinum bimetallic alloy catalyst supported on halloysite nanotubes to a hydrothermal deoxygenation system, using glycerol as a hydrogen donor. Glycerol generates hydrogen in situ within the reactor and directly participates in the decarboxylation and decarbonylation reaction pathways. This in-situ hydrogen production and deoxygenation mechanism completely replaces the external high-pressure hydrogen source, eliminating the need for investment in high-pressure hydrogen storage equipment and pipelines, and removing the safety hazards of high-pressure hydrogen leakage. Simultaneously, the specific mass ratio of doping reduces the amount of precious metals used, lowering the production cost of the catalyst material.

[0029] 3. This invention converts the metal precursor into positively charged ammonium complex ions by adding concentrated ammonia during the preparation process. These ammonium complex ions then electrostatically attract and chemically bond with the hydroxyl groups on the pre-treated halloysite surface during the hydrothermal reaction. This chemical bonding anchoring effect fixes the palladium-platinum bimetallic alloy nanoparticles onto the surface of the halloysite tubular support, preventing the active components from detaching and the metal grains from sintering and agglomerating under high-temperature, high-pressure hydrothermal deoxygenation conditions. This ensures the structural stability and long-term operational life of the halloysite nanotube-supported palladium-platinum bimetallic alloy catalyst. Attached Figure Description

[0030] Figure 1 This is a graph showing the yield of stearic acid catalytically converted into green diesel in the test examples of this invention;

[0031] Figure 2 The figure shows the test results of the catalytic conversion of stearic acid to green diesel under different process boundary conditions in the test examples of this invention;

[0032] Figure 3 This is a kinetic comparison test diagram of the bimetallic synergistic effect in the test examples of this invention;

[0033] Figure 4 This is a graph showing the carrier anchoring effect and industrial life cycle test in the test examples of this invention;

[0034] Figure 5 This is a transmission electron microscope image of the halloysite nanotube-supported palladium-platinum bimetallic alloy catalyst in the test examples of this invention;

[0035] Figure 6 This is the X-ray diffraction pattern of the halloysite nanotube-supported palladium-platinum bimetallic alloy catalyst in the test example of this invention;

[0036] Figure 7 This is a comparison of the Fourier transform infrared spectra of the halloysite nanotube-supported palladium-platinum bimetallic alloy catalyst and its thermally pretreated halloysite support in the test examples of this invention.

[0037] Figure 8 This is a comparison chart of the yield of stearic acid to green diesel oil catalytically converted by catalysts with different noble metal loadings and ratios in the test examples of this invention. Detailed Implementation

[0038] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] Examples 1-3:

[0040] Example 1:

[0041] This embodiment provides a method for preparing a halloysite nanotube-supported palladium-platinum bimetallic alloy catalyst, including the following steps:

[0042] S1. 120 parts of halloysite were placed in a muffle furnace and calcined at 600°C for 2 hours. After cooling to room temperature, heat-treated halloysite was obtained.

[0043] S2. 100 parts of heat-treated halloysite, 2.83 parts of palladium chloride and 4.51 parts of chloroplatinic acid hexahydrate were added to 1000 parts of deionized water and stirred to disperse, resulting in a mixed solution. At this time, the mass ratio of palladium, platinum and heat-treated halloysite was 0.017:0.017:1.

[0044] S3. Add 25 parts of 25% concentrated ammonia to the mixture to adjust the pH of the mixture to 10, converting palladium and platinum into ammonia complexes, and obtaining a mixture containing ammonia complexes.

[0045] S4. The mixture containing the ammonia complex was sealed in a high-pressure reactor and reacted at 190°C for 9 hours. After washing and drying, palladium-platinum doped halloysite precursor was obtained.

[0046] S5. The palladium-platinum doped halloysite precursor was dispersed in 1000 parts of ethanol. A reducing solution (prepared by dissolving 2.68 parts of solid sodium borohydride in 150 parts of deionized water) was slowly added dropwise to the 1000 parts of ethanol to carry out liquid-phase reduction, forming uniformly dispersed palladium-platinum bimetallic alloy particles. Subsequently, centrifugation, washing, and drying were performed to obtain the halloysite nanotube-supported palladium-platinum bimetallic alloy catalyst.

[0047] Example 2:

[0048] This embodiment provides a method for preparing a halloysite nanotube-supported palladium-platinum bimetallic alloy catalyst, including the following steps:

[0049] S1. 130 parts of halloysite were placed in a muffle furnace and calcined at 650°C for 3 hours. After cooling to room temperature, heat-treated halloysite was obtained.

[0050] S2. 100 parts of heat-treated halloysite, 3.67 parts of palladium chloride and 5.84 parts of chloroplatinic acid hexahydrate were added to 1200 parts of deionized water and stirred to disperse, resulting in a mixed solution. At this time, the mass ratio of palladium, platinum and heat-treated halloysite was 0.022:0.022:1.

[0051] S3. Add 40 parts of 25% concentrated ammonia to the mixture to adjust the pH of the mixture to 11, converting palladium and platinum into ammonia complexes, and obtaining a mixture containing ammonia complexes.

[0052] S4. The mixture containing the ammonia complex was sealed in a high-pressure reactor and reacted at 220°C for 12 hours. After washing and drying, palladium-platinum doped halloysite precursor was obtained.

[0053] S5. The palladium-platinum doped halloysite precursor was dispersed in 1200 parts of ethanol. A reducing solution (prepared by dissolving 3.47 parts of solid sodium borohydride in 200 parts of deionized water) was slowly added dropwise to the 1200 parts of ethanol to carry out liquid-phase reduction, forming uniformly dispersed palladium-platinum bimetallic alloy particles. Subsequently, centrifugation, washing, and drying were performed to obtain the halloysite nanotube-supported palladium-platinum bimetallic alloy catalyst.

[0054] Example 3:

[0055] This embodiment provides a method for preparing a halloysite nanotube-supported palladium-platinum bimetallic alloy catalyst, including the following steps:

[0056] S1. 110 parts of halloysite were placed in a muffle furnace and calcined at 550°C for 1 hour, then cooled to room temperature to obtain heat-treated halloysite.

[0057] S2. 100 parts of heat-treated halloysite, 2 parts of palladium chloride and 3.19 parts of chloroplatinic acid hexahydrate were added to 800 parts of deionized water and stirred to disperse, resulting in a mixed solution. At this time, the mass ratio of palladium, platinum and heat-treated halloysite was 0.012:0.012:1.

[0058] S3. Add 15 parts of 25% concentrated ammonia to the mixture to adjust the pH of the mixture to 9, converting palladium and platinum into ammonia complexes, and obtaining a mixture containing ammonia complexes.

[0059] S4. The mixture containing the ammonia complex was sealed in a high-pressure reactor and reacted at 160°C for 6 hours. After washing and drying, palladium-platinum doped halloysite precursor was obtained.

[0060] S5. The palladium-platinum doped halloysite precursor was dispersed in 800 parts of ethanol. A reducing solution (prepared by dissolving 1.89 parts of solid sodium borohydride in 100 parts of deionized water) was slowly added dropwise to the 800 parts of ethanol to carry out liquid-phase reduction, forming uniformly dispersed palladium-platinum bimetallic alloy particles. Subsequently, centrifugation, washing and drying were performed to obtain the halloysite nanotube-supported palladium-platinum bimetallic alloy catalyst.

[0061] Comparative Examples 1-3:

[0062] Comparative Example 1:

[0063] Compared with Example 1, the difference is that chloroplatinic acid hexahydrate is not added in step S2. Instead, 5.66 parts of palladium chloride are added to 1000 parts of deionized water, and the mass ratio of palladium to heat-treated halloysite is controlled to be 0.034:1. All other aspects are the same, and a halloysite nanotube-supported single-metal palladium catalyst is finally obtained.

[0064] Comparative Example 2:

[0065] Compared with Example 1, the difference is that palladium chloride is not added in step S2. Instead, 9.03 parts of chloroplatinic acid hexahydrate are added to 1000 parts of deionized water, and the mass ratio of platinum to heat-treated halloysite is controlled to be 0.034:1. All other aspects are the same, and a halloysite nanotube-supported monometallic platinum catalyst is finally obtained.

[0066] Comparative Example 3:

[0067] Compared with Example 1, the difference is that: in step S2, 25% concentrated ammonia is not added to adjust the pH, and the hydrothermal reaction in step S4 is skipped. The mixture is directly evaporated to dryness and then liquid-phase reduction is carried out in step S5. The rest are the same, and the halloysite nanotube supported palladium-platinum bimetallic alloy catalyst prepared by conventional impregnation method is finally obtained.

[0068] Test Examples 1-4:

[0069] Test Example 1:

[0070] The halloysite nanotube-supported palladium-platinum bimetallic alloy catalyst prepared in Example 1 was extracted, and the palladium-supported catalyst prepared in Comparative Example 1 and the platinum-supported catalyst prepared in Comparative Example 2 were extracted simultaneously as parallel test objects.

[0071] Combination Figure 5 In the catalyst prepared in Example 1, halloysite maintained its intact nanotube morphology even after high-temperature and hydrothermal treatment. Simultaneously, the palladium-platinum bimetallic alloy particles exhibited uniform and dense nanoscale size, anchored and dispersed on the inner and outer surfaces of the tubular support, with no obvious metal grain sintering or agglomeration observed. Microscopic characterization confirmed the strong anchoring effect of the chemical bonding between the ammonium complex ions and the hydroxyl groups of the support during the preparation process.

[0072] Combination Figure 6 The halloysite support, after heat pretreatment, retained sharp characteristic diffraction peaks in the composite catalyst, confirming that the halloysite crystal framework maintained high phase stability under alternating hydrothermal and strong reduction processes. The figure does not show independent standard diffraction peaks for pure palladium or pure platinum; instead, it exhibits characteristic diffraction peaks between the standard peak positions of pure palladium and pure platinum face-centered cubic structures. The diffraction angle shift provides conclusive physical evidence from a crystallographic perspective, demonstrating that due to the similar atomic radii of palladium and platinum, lattice fusion occurs during co-reduction at the same frequency, forming a highly alloyed palladium-platinum infinite solid solution, rather than a physical mixture of single metal particles. This underlying lattice alloying forms the microscopic basis for the strong electronic synergistic effect exhibited by the catalytic material of this invention in the hydrothermal deoxygenation reaction.

[0073] Combination Figure 7 After being loaded with palladium-platinum bimetal, halloysite at 1032 cm⁻¹ -1 536cm -1 and 470cm -1 The intrinsic vibrational peaks of the nearby silicon-oxygen and aluminum-oxygen frameworks remain intact, confirming the extremely high stability of the support under hydrothermal and reducing environments. Located at 3694 cm⁻¹ -1 With 3620cm -1The stretching vibration peaks attributable to hydroxyl groups on the halloysite surface and interlayer exhibit observable changes in absorption intensity and peak position characteristics after alloy loading. The evolution of infrared spectral characteristics directly confirms that, in the alkaline hydrothermal environment of the preparation step, positively charged palladium-platinum-ammonia complex ions undergo deep electrostatic attraction and chemical coordination bonding with numerous hydroxyl groups on the halloysite surface. This strong chemical anchoring mechanism, transcending van der Waals forces, locks the reduced bimetallic alloy particles onto the surface of the tubular support, constructing a structural fortress against catalyst loss and spalling under subsequent high-temperature, high-pressure oil scouring.

[0074] Stearic acid, glycerol, deionized water, and catalyst were added to the high-pressure reactor in a predetermined mass ratio, and the reactor's sealing performance was checked.

[0075] Connect the nitrogen pipeline and continuously inject nitrogen into the reactor to replace the residual air inside, maintaining a certain initial nitrogen pressure inside the reactor and creating a reaction atmosphere completely free of external hydrogen.

[0076] Start the reactor heating and magnetic stirring device, control the heating rate to bring the temperature inside the reactor to 360°C, and maintain this temperature for 4 hours.

[0077] After the reaction reaches the set time, the heating is cut off, and the vessel is allowed to cool naturally to room temperature. The vessel is then opened and organic solvents such as n-hexane are added for liquid-liquid extraction. After standing and separating into layers, the organic phase containing the target alkane product is collected.

[0078] The collected organic phase was analyzed and quantified using gas chromatography to calculate the conversion rate of stearic acid, the selectivity of C17 alkanes, and the final yield in the reaction system.

[0079] Table 1. Catalytic performance test data of different catalysts for the deoxygenation of stearic acid to green diesel oil

[0080]

[0081] The test results are as follows:

[0082] Figure 1 The horizontal axis corresponds to the catalyst systems used in Comparative Example 1, Comparative Example 2, and Example 1, respectively, while the vertical axis represents the percentage values ​​of reaction conversion and product yield. The solid line trajectory marked with circles shows the differences in stearic acid conversion under different catalytic systems, while the dashed line trajectory marked with squares represents the final yield of the target product, C17 alkanes.

[0083] From the data in Table 1 and Figure 1This indicates that even under closed-loop conditions with the external high-pressure hydrogen source cut off, a deep hydrothermal deoxygenation reaction still occurred within the system. The single-metal catalysts in Comparative Examples 1 and 2 exhibited significant reaction inertia, with stearic acid largely retained in the reactor or transformed into undetected intermediate impurities. This is consistent with previous observations in conventional single-metal catalytic deoxygenation studies. Individual palladium sites are easily poisoned by trace amounts of carbon monoxide and lose activity in hydrothermal environments, while pure platinum crystal faces have a high energy barrier for breaking the carbon-oxygen bonds of the substrate in the absence of external high-pressure hydrogen coverage. When palladium and platinum were fused on the nanotube support surface in the specific ratio of Example 1, the stearic acid conversion rate surged to 96.34%, exceeding the theoretical expectations of single-metal physical superposition. The intermetallic electron cloud rearrangement induced by the fusion of the underlying lattice weakened the strong adsorption effect of intermediate species at the active sites, leading to a decrease in the apparent activation energy under hydrothermal conditions.

[0084] Continuous high-temperature hydrothermal monitoring confirmed that glycerol molecules underwent liquid-phase phase transition reforming at the catalytic interface, continuously dissociating into in-situ active hydrogen. This active hydrogen was captured by adjacent palladium-platinum alloy sites before escaping, directly participating in the decarboxylation and decarbonylation reaction cycle of stearic acid, forcing the carboxyl carbon of the substrate molecule to detach as carbon dioxide or carbon monoxide. The high selectivity of 95.12% for C17 alkanes in Table 1 confirms this carbon chain shortening mechanism, resulting in long-chain alkanes with one less carbon atom. This catalytic deoxygenation pathway, driven by hydrogen supply from the glycerol liquid phase, maintains a 91.64% diesel yield while eliminating the dependence on high-pressure hydrogen pipelines and storage tanks found in traditional processes, thus removing the explosion hazards and high equipment depreciation costs associated with hydrogen production.

[0085] Combination Figure 8 , Figure 8 The graph includes sub-graphs a and b, with the horizontal axis representing catalysts with different noble metal compositions and loading gradients. Figure 8 The vertical axis of subplot a represents the conversion rate of stearic acid and the selectivity of the corresponding deoxygenation products. Figure 8 The vertical axis of subplot b represents the final yield of the target long-chain alkane. Figure 8 In subplot a, the broken line trajectory reflects a jump in stearic acid conversion when transitioning from a 3.4% monometallic palladium catalyst to a bimetallic alloy catalyst of 1.7% palladium and 1.7% platinum; the bar chart distribution shows that heptadecanes dominate the products. Figure 8 In sub-figure b, the yield histogram confirms the low catalytic efficiency of the monometallic catalyst. The yield of the target heptadecane reaches its peak when palladium and platinum form a bimetallic alloy phase. The experimental data comparison chart verifies the geometric and electronic synergistic effect induced by the fusion of the palladium-platinum bimetallic lattice from a macroscopic catalytic performance perspective, demonstrating that a specific ratio of bimetallic alloy phase has technical advantages in reducing the activation energy of the deoxygenation reaction and improving the directional conversion ability of the target product.

[0086] Test Example 2:

[0087] The halloysite nanotube-supported palladium-platinum bimetallic alloy catalysts prepared in Examples 1, 2 and 3 were extracted as independent test objects.

[0088] Based on the application scheme parameters set in each embodiment, stearic acid, glycerol, deionized water and corresponding batches of catalyst in the specified ratio are respectively loaded into multiple parallel high-pressure reactors, the reactor lids are tightened and it is confirmed that there is no leakage.

[0089] A high-purity nitrogen cylinder is connected to continuously pressurize and replace the cavity inside the reactor, completely purging the free oxygen and air inside, and sealing the reaction system to maintain a strict hydrogen-free state.

[0090] The temperature control module was activated, and for the reactors of Examples 1, 2 and 3, the heating program and reaction time were strictly locked at 360℃ for 4 hours, 380℃ for 6 hours and 340℃ for 2 hours, respectively.

[0091] After each group of equipment reaches the predetermined dwell time, the power is cut off. After the fluid in the reactor cools down to room temperature naturally, the exhaust valve is opened to release the pressure in the reactor. Non-polar solvent is added to the reaction solution to extract and separate the organic phase rich in long-chain alkanes.

[0092] The purified organic phase liquid was analyzed by micro-injection using gas chromatography, and the substrate consumption and product distribution characteristics of the system under different operating boundary conditions were calculated.

[0093] Table 2. Test data for the catalytic conversion of stearic acid to green diesel under different process boundary conditions.

[0094]

[0095] The test results are as follows:

[0096] Figure 2 The horizontal axis corresponds to Examples 3, 1, and 2 in ascending order of temperature and time load of the reaction system, while the vertical axis represents the percentage of substance conversion. The solid line with a triangle mark delineates the conversion rate of the substrate stearic acid in different parameter ranges, while the dashed line with a diamond mark reflects the actual yield fluctuation of the target product, C17 alkanes.

[0097] From the data in Table 2 and Figure 2This confirms that the catalytic system established in this invention maintains stable industrial operation capabilities across a wide range of parameter boundaries. Example 3 represents the energy and cost floor of this process route. Under conservative conditions of using only a low noble metal loading and a short reaction time at 340°C, the system still recorded a conversion rate of 78.62% and a target product yield of over 70%. The unique electron delocalization effect within the palladium-platinum solid solution allows the bimetallic crystal facets to activate glycerol molecules to release active hydrogen even in environments with weak thermodynamic driving forces, and to successfully cleave the stubborn carbon-oxygen double bonds in the substrate. As the reaction loading increases to the optimal intermediate state of Example 1, the system kinetics and thermodynamics reach equilibrium, the substrate is almost completely digested, and side reactions are significantly constrained.

[0098] Shifting our focus to Example 2, despite the reaction temperature being pushed up to 380°C and running continuously for 6 hours, the system's conversion rate approached its limit, reaching 98.15%, but the final yield of the target C17 alkane actually declined. Similar deviations in mass conservation are frequently observed during long-term laboratory monitoring of high-temperature, high-pressure oil cracking. This is because, under prolonged extreme thermal stress, some of the already formed long-chain alkane molecules undergo secondary hydrocracking or isomerization within the reactor, breaking down into shorter-chain lighter component gases or low-boiling-point liquid hydrocarbons, thus reducing the absolute selectivity of the C17 component. By extracting and comparing the morphology of the spent catalyst, it was found that the silica and aluminosilicate hydroxyl groups on the halloysite surface restrained the metal particles derived from ammonia complexation, successfully preventing large-scale peeling and agglomeration deactivation of the active component in the extremely boiling fluid. This operating window provides a greater margin of error in actual workshop production, allowing on-site engineers to flexibly adjust DCS control parameters within a wide range based on crude oil batches and energy consumption indicators, without worrying about irreversible physical collapse of the catalyst.

[0099] Test Example 3:

[0100] The halloysite nanotube-supported palladium-platinum bimetallic alloy catalyst prepared in Example 1, as well as the single-metal palladium catalyst prepared in Comparative Example 1 and the single-metal platinum catalyst prepared in Comparative Example 2, were used as experimental objects for kinetic comparison.

[0101] Stearic acid, glycerol, deionized water, and the three catalysts mentioned above were loaded into multiple parallel reactors equipped with online high-pressure sampling valves, according to the same mass ratio.

[0102] High-purity nitrogen gas is introduced to pressurize and exhaust each reactor group to completely remove free oxygen from the system and establish an initial reaction baseline with absolute pressure and no hydrogen gas.

[0103] The heating and temperature control module is activated simultaneously to raise the temperature of the fluid inside the reactor and stabilize it at 360°C. At the 1h, 2h, 3h and 4h points of the reaction, the online sampling valve is slightly opened to draw out a very small amount of liquid sample, which is then quickly transferred to an ice-water bath to quench the reaction and lock in the current state of matter.

[0104] Hexane was injected into the cooling sampling tubes at each time point, and the tubes were vortexed vigorously to extract long-chain alkanes and unreacted stearic acid from the reaction mixture. After centrifugation, the supernatant was collected for later use.

[0105] The extracts at different time points were continuously injected and measured using a gas chromatograph equipped with a flame ionization detector (FID). The residual concentration of the substrate was quantified by combining the internal standard method, and the reaction kinetic trajectory of each catalytic system over time was then fitted.

[0106] Table 3. Time-conversion dynamic data of stearic acid deoxygenation reaction under different catalyst systems

[0107]

[0108] The test results are as follows:

[0109] Figure 3 The horizontal axis represents the continuous operating time of the high-pressure reactor at a constant temperature of 360°C, and the vertical axis represents the percentage conversion of stearic acid at the corresponding time point. The rising trajectory of the solid line marked with a black circle reflects the robust reaction rate of the bimetallic catalyst in Example 1; the dashed line marked with a dark gray square and the solid line marked with a light gray downward triangle record the extremely slow substrate consumption process of Comparative Example 2 (monometallic platinum) and Comparative Example 1 (monometallic palladium), respectively.

[0110] From the data in Table 3 and Figure 3 It can be observed that the palladium-platinum bimetallic alloy exhibits a dimensionality reduction compared to the monometallic system in terms of reaction kinetics. In the initial stage of the deoxygenation reaction, the conversion curve of the monometallic system almost exhibits a stagnant state. In particular, the pure palladium catalyst in Comparative Example 1 barely reached less than 10% substrate consumption after two hours of operation, largely due to the high initial carbon-oxygen bond breaking activation energy on the monometallic surface. The trace amounts of carbon monoxide molecules released during decarboxylation readily undergo chemisorption at single metal sites, occupying the already scarce catalytic active centers, leading to rapid macroscopic poisoning and blockage of the reaction pathway.

[0111] Observing the test trajectory of Example 1, the rate constant of the entire reaction jumped. Within the first hour of the reaction, the conversion rate of Example 1 exceeded 36% and maintained a steep upward slope thereafter. This catalytic burst force that breaks the conventional physical mixing limitations originates from the infinite solid solution formed by palladium and platinum on the nanotube support. In the past, when tracking the chromatographic peaks of liquid-phase reactants, it was often found that the electron cloud rearrangement at the bimetallic interface changed the adsorption enthalpy of intermediate products on the catalyst surface. The active hydrogen dissociated in situ is no longer locally bound, but can overflow rapidly along the alloy lattice defects and accurately attack the reaction sites of stearic acid, resisting the poisoning effect of carbon-containing impurities. From a macroscopic engineering perspective, this kinetic mechanism that crosses the performance limits of single metals not only multiplies the residence period of materials under harsh hydrothermal environments, but also opens up a feasible process channel for high-conversion continuous production with completely equal amounts of precious metal input.

[0112] Test Example 4:

[0113] The halloysite nanotube-supported palladium-platinum bimetallic alloy catalyst prepared in Example 1 and the catalyst prepared by the conventional evaporation-drying impregnation method in Comparative Example 3 were used as comparative experimental objects for cycle life verification.

[0114] According to a fixed standard mass ratio, stearic acid, glycerol, deionized water, and catalysts prepared by the two different processes mentioned above were respectively added into multiple parallel high-pressure reactors equipped with polytetrafluoroethylene liners.

[0115] Secure the reactor components and connect the nitrogen pipeline. Replace the air in the reactor cavity by repeatedly pressurizing and venting to create an absolutely hydrogen-free and oxygen-free initial closed environment for in-situ deoxygenation.

[0116] The heating and temperature control program is activated to raise the temperature of the fluid inside the reactor to 360°C. Under this condition, magnetic stirring is maintained and the system is kept at a constant temperature for 4 hours. Then, the heat source is cut off to allow the reaction system to cool down naturally to room temperature.

[0117] After opening the vent valve to release pressure, a non-polar organic solvent is injected into the mixture in the reactor. After thorough vortex extraction, the mixture is allowed to stand and separate into layers. The upper organic phase, rich in long-chain alkanes, is transferred to a gas chromatograph to determine the final yield of C17 alkanes.

[0118] The residual aqueous waste liquid and solid materials in the reactor are centrifuged at high speed. The solid catalyst sludge at the bottom is carefully retained and washed alternately with deionized water and anhydrous ethanol. Without adding any fresh active components, it is directly transferred into the next round of the same reaction system. This cycle is repeated for a total of 6 batches.

[0119] The aqueous waste liquid separated by centrifugation from each reaction cycle was collected, and the concentration of precious metals (calculated as palladium, a typical component) lost in each batch of waste liquid was determined by inductively coupled plasma atomic emission spectrometry.

[0120] Table 4. Continuous cycle life and metal loss test data of catalysts prepared by different processes

[0121]

[0122] The test results are as follows:

[0123] Figure 4 The horizontal axis corresponds to the continuous catalytic cycle batches performed in the high-pressure reactor, and the vertical axis represents the measured percentage yield of the target product, C17 alkanes, after each reaction cycle. The solid line with circular markings depicts the relatively stable production performance of the catalyst in Example 1 under multiple hydrothermal washes, while the dashed line with square markings visually exposes the engineering defect of the catalyst in Comparative Example 3, which experienced a precipitous deactivation at the beginning of the cycle.

[0124] From the data in Table 4 and Figure 4 This reveals the decisive reshaping of catalysts by specific preparation processes. In laboratory studies of previous continuous operation processes, engineering accidents often occurred where catalysts exhibited high initial activity but completely failed after three to five batches. This pain point, caused by the stripping of active components due to intense boiling at high temperatures, was reproduced in the data of Comparative Example 3. Comparative Example 3, prepared using the conventional evaporation-drying impregnation method, had its noble metal particles physically attached to the halloysite surface solely by van der Waals forces. Under repeated shear stress scouring by high-pressure hydrothermal fluid at 360°C, these physically deposited metal phases rapidly detached. Table 4 shows the palladium loss concentration of 15.62 mg / L in the aqueous waste liquid of Comparative Example 3 during the first three rounds, corresponding to... Figure 4 The trajectory of the system's yield dropping from 86.12% to 54.38% confirms that free metals cannot maintain long-term catalysis in complex liquid-liquid-solid three-phase deoxygenation reactions.

[0125] Under a specific pH alkaline environment, concentrated ammonia is added to forcibly convert palladium and platinum precursors into positively charged ammonium complex ions. These complexed metals then undergo deep electrostatic coupling across the physical adsorption layer with a large number of intrinsic hydroxyl groups on the surface of the halloysite silica-alumina framework in a subsequent high-pressure hydrothermal field. This strong interaction, excited by specific chemical coordination, anchors the final reduced alloy nanoparticles within the tubular lattice of the support. Monitoring data shows that the palladium concentration in the waste liquid throughout the entire cycle of Example 1 was suppressed to a trace level below 0.19 mg / L, solidifying the chemical bond-level binding strength from a macroscopic fluid dynamics perspective. This anti-leakage characteristic embedded in the material preparation logic endows the system with greater fluid dynamic tolerance, ensuring that the catalyst can withstand frequent start-up and shutdown shocks in a real industrial deoxygenation plant, achieving truly long-term engineering applications.

Claims

1. A halloysite nanotube-supported palladium-platinum bimetallic alloy catalyst, characterized in that, Includes heat-treated halloysite and uniformly dispersed palladium-platinum bimetallic alloy particles formed on the heat-treated halloysite; The mass ratio of palladium, platinum, and heat-treated halloysite is 0.012-0.022:0.012-0.022:

1.

2. The halloysite nanotube-supported palladium-platinum bimetallic alloy catalyst according to claim 1, characterized in that, The heat-pretreated halloysite is prepared by the following steps: Halloysite is placed in a muffle furnace and calcined at 550-650℃ for 1-3 hours, then cooled to room temperature to obtain the heat-pretreated halloysite.

3. The halloysite nanotube-supported palladium-platinum bimetallic alloy catalyst according to claim 1, characterized in that, The palladium and platinum are derived from palladium chloride and chloroplatinic acid hexahydrate, respectively. The ratio of halloysite pretreated with heat, palladium chloride, and chloroplatinic acid hexahydrate is as follows: Based on 100 parts of heat-pretreated halloysite, the palladium chloride is 2-3.67 parts and the chloroplatinic acid hexahydrate is 3.19-5.84 parts.

4. A method for preparing a palladium-platinum bimetallic alloy catalyst supported on halloysite nanotubes, characterized in that, The preparation of the halloysite nanotube-supported palladium-platinum bimetallic alloy catalyst according to any one of claims 1-3 comprises the following steps: Halloysite was calcined in a muffle furnace and cooled to room temperature to obtain heat-treated halloysite. The heat-pretreated halloysite, palladium chloride, and chloroplatinic acid hexahydrate were added together to deionized water and stirred to disperse the mixture, thus obtaining a mixed solution. Adding 25% concentrated ammonia to the mixture adjusted the pH to 9-11, converting palladium and platinum into ammonia complexes, resulting in a mixture containing ammonia complexes. The mixture containing the ammonia complex was sealed in a high-pressure reactor for reaction, and then washed and dried to obtain a palladium-platinum doped halloysite precursor. Palladium-platinum doped halloysite precursors were dispersed in ethanol, and a reducing agent was slowly added dropwise for liquid-phase reduction to form uniformly dispersed palladium-platinum bimetallic alloy particles. Subsequently, centrifugation, washing, and drying were performed to obtain halloysite nanotube-supported palladium-platinum bimetallic alloy catalysts.

5. The method for preparing the halloysite nanotube-supported palladium-platinum bimetallic alloy catalyst according to claim 4, characterized in that, The step of calcining halloysite in a muffle furnace specifically includes: The halloysite was calcined at 550-650℃ for 1-3 hours.

6. The method for preparing the halloysite nanotube-supported palladium-platinum bimetallic alloy catalyst according to claim 4, characterized in that, The step of adding halloysite, palladium chloride, and chloroplatinic acid hexahydrate, which were pretreated by heat, together to deionized water specifically includes: 100 parts of the heat-pretreated halloysite, 2-3.67 parts of the palladium chloride and 3.19-5.84 parts of the chloroplatinic acid hexahydrate were added together to 800-1200 parts of the deionized water.

7. The method for preparing the halloysite nanotube-supported palladium-platinum bimetallic alloy catalyst according to claim 6, characterized in that, The amount of 25% concentrated ammonia solution added is 15-40 parts.

8. The method for preparing the halloysite nanotube-supported palladium-platinum bimetallic alloy catalyst according to claim 6, characterized in that, The reaction, sealed in a high-pressure reactor, is carried out at a temperature of 160-220℃ for 6-12 hours.

9. The method for preparing the halloysite nanotube-supported palladium-platinum bimetallic alloy catalyst according to claim 6, characterized in that, The specific steps of dispersing the palladium-platinum-doped halloysite precursor in ethanol include: The palladium-platinum doped halloysite precursor was dispersed in 800-1200 parts of the ethanol.

10. The method for preparing the halloysite nanotube-supported palladium-platinum bimetallic alloy catalyst according to claim 6, characterized in that, The reducing solution is prepared by dissolving 1.89-3.47 parts of solid sodium borohydride in 100-200 parts of deionized water.

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