A supported molten alloy catalyst for biomass gasification and a method of preparation and use

Abstract

The application discloses a supported molten alloy catalyst for biomass gasification and a preparation method and application thereof, and belongs to the technical field of biomass energy conversion and catalysts. The catalyst comprises a porous carrier and a molten alloy active component in the form of nano-droplets loaded on the surface and in the pores of the carrier. The molten alloy active component comprises a molten catalytic metal and a molten metal additive. The molten catalytic metal is selected from one or more of Ni, Mo and Cr, and the molten metal additive is Bi. During preparation, citric acid is added to a solution of metal salts corresponding to the molten catalytic metal and the molten metal additive, and the solution is stirred uniformly. An equal volume of the obtained precursor solution is loaded on a pretreated porous carrier by using an equal-volume impregnation method. Finally, the loaded catalyst is subjected to staged heating in a reducing atmosphere. The obtained supported molten alloy catalyst has a large specific surface area, can maintain a molten state at high temperatures, is highly dispersed, and has excellent carbon deposition resistance, sintering resistance and catalytic stability.

Description

Technical Field

[0001] This invention belongs to the field of biomass energy conversion and catalyst technology, specifically a supported molten alloy catalyst for biomass gasification, its preparation method, and its applications. Background Technology

[0002] Biomass gasification is a key technology for converting biomass into syngas (mainly composed of H2 and CO), which is of great significance for realizing renewable energy utilization and carbon cycling. Catalytic gasification can reduce reaction temperature, improve gasification efficiency, and regulate product composition. However, commonly used Ni-based and Fe-based solid metal catalysts face severe challenges in high-temperature biomass gasification environments: on the one hand, biomass-derived tar and solid soot easily deposit on the catalyst surface, forming an inert carbon layer that leads to rapid catalyst deactivation; on the other hand, active metal particles are prone to sintering and agglomeration under high-temperature conditions, reducing the active sites and decreasing thermal stability of the catalyst. The hydrocarbons in biomass gasification products are complex, including phenol, naphthalene, and aliphatic hydrocarbons. These high-molecular-weight species easily generate solid carbon deposits during catalytic surface cracking, causing traditional supported catalysts to rapidly decline in activity over long-term operation. Therefore, a novel catalyst system is needed to solve the problems of high carbon deposition and high-temperature sintering to achieve efficient and stable operation of biomass gasification.

[0003] As an emerging system, molten alloy catalysts possess a dynamically flowing active surface that significantly inhibits solid carbon deposition, exhibiting inherent anti-carbonization properties. Molten alloy catalysts have shown potential in methane pyrolysis and coal chemical industries: in these systems, the catalyst exists in liquid metal form, maintaining surface activity through flotation and carbon stripping. For example, reported Ni-Bi and Ni-Mo-Bi molten alloy catalysts exhibit low methane cracking activation energies and 100% hydrogen selectivity at medium to high temperatures, maintaining good stability even after long-term operation. However, current molten alloy catalysts are primarily designed for the cracking of pure hydrocarbon systems such as methane, and are mostly used in bulk liquid alloy (molten pool) form. These bulk molten alloys have extremely low specific surface areas, limiting their contact efficiency with gaseous reactants and hindering their application to complex biomass gasification scenarios. This presents significant technical challenges for using molten alloy catalysts to treat biomass cracking products containing impurities and tar.

[0004] Therefore, developing a catalyst system that combines the natural anti-carbon deposition and anti-sintering properties of molten metal with high dispersibility and large specific surface area is crucial for promoting the development of biomass catalytic gasification technology. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a supported molten alloy catalyst for biomass gasification, its preparation method, and its applications. A molten alloy is formed by combining a low-melting-point metal with an active metal, and then dispersed at the nanoscale on a high-temperature resistant support. This utilizes the advantage of the liquid alloy's flowing surface carrying away carbon deposits while also obtaining the large number of uniform active sites required by traditional supported catalysts. This results in a supported molten alloy catalyst with a large specific surface area, maintaining a molten state at high temperatures, and exhibiting high dispersion, excellent resistance to carbon deposition, sintering, and catalytic stability.

[0006] This invention is achieved through the following technical solution: A supported molten alloy catalyst for biomass gasification includes a porous support and a molten alloy active component loaded on its surface and within its pores in the form of nanodroplets. The molten alloy active component includes a molten catalytic metal and a molten metal promoter. The molten catalytic metal is selected from one or more of Ni, Mo, and Cr, and the molten metal promoter is Bi.

[0007] Preferably, the active component of the molten alloy comprises, by mass percentage, 1% to 10% of the total mass of the molten catalytic metal and 90% to 99% of the mass of the molten metal additive.

[0008] Preferably, the porous carrier is silicon carbide, partially stabilized zirconia, or corundum.

[0009] Preferably, the specific surface area of ​​the porous carrier is not less than 20 m² / g, and the pore size is 5-50 nm.

[0010] Preferably, the droplet size of the active component of the molten alloy is 2~20 nm.

[0011] A method for preparing a supported molten alloy catalyst for biomass gasification as described in any one of the above claims, comprising the following steps: Step 1: The porous support is acid-washed and then calcined to obtain a pretreated porous support; Step 2: Add citric acid to the corresponding metal salt solutions of molten catalytic metal and molten metal promoter and stir until homogeneous. The total molar ratio of citric acid to metal cation is (1.5~2.5):1 to obtain a precursor solution. Load the precursor solution onto a pretreated porous support using an equal-volume impregnation method, and then age and dry it sequentially to obtain the catalyst precursor. Step 3: After holding the catalyst precursor at 100-200℃, it is then held at 300-500℃ and 650-850℃ in a reducing atmosphere containing hydrogen, followed by cooling and passivation treatments to obtain a supported molten alloy catalyst for biomass gasification.

[0012] Preferably, in step 1, the porous support is refluxed in a 0.8-1.5 M acid solution for 6-8 hours, then washed until neutral and dried, and calcined at 500-700°C for 2-6 hours in air or oxygen atmosphere to obtain the pretreated porous support.

[0013] Preferably, in step 2, the corresponding metal salts of Ni, Mo, Cr, and Bi are Ni(NO3)2·6H2O, (NH4)6Mo7O, and (NH4)6Mo7O, respectively. 24 The metal salt solutions are 4H2O, Cr(NO3)3·9H2O and Bi(NO3)3·5H2O, and the solvents for the metal salt solutions are deionized water and ethylene glycol in a volume ratio of (1-3):(1-2). The aging process is carried out at room temperature for 6–12 hours, and the drying process is carried out under vacuum conditions at 50–80°C for 12–24 hours.

[0014] Preferably, in step 3, the catalyst precursor is heated to 100-200°C at a rate of 1-5°C / min under an inert atmosphere and held for 25-35 min. Then, it is heated to 300-500°C at a rate of 2-10°C / min under a reducing atmosphere containing 1-10% hydrogen and held for 45-75 min. Finally, it is heated to 650-850°C at a rate of 1-5°C / min under a reducing atmosphere containing 10-50% hydrogen and held for 1-6 h.

[0015] The use of any of the above-described supported molten alloy catalysts for biomass gasification in steam gasification and tar reforming reactions.

[0016] Compared with the prior art, the present invention has the following beneficial technical effects: This invention discloses a supported molten alloy catalyst for biomass gasification. Using a high-temperature resistant porous material as a support, the catalyst exhibits structural stability at high temperatures and good resistance to strong acids, alkalis, and high-temperature steam. A nanoscale molten alloy active component, composed of one or more molten catalytic metals selected from Ni, Mo, and Cr, and a molten metal promoter Bi, is loaded onto its surface and within its pores. The introduction of the low-melting-point molten metal promoter Bi to form a molten alloy system plays a crucial role in inhibiting carbon deposition, mitigating active site coverage, and maintaining long-term stable catalyst operation. The active component is highly dispersed in the form of nanodroplets. The nanoscale droplet size provides an ultra-high metal active surface area, and the capillary constraint of the support pore size inhibits droplet outflow or merging, significantly expanding the effective catalytic interface. During the gasification reaction, these droplets are suspended on the support. The continuous refresh of the liquid metal surface makes it difficult for carbon species to be immobilized, thereby effectively improving the catalyst's resistance to carbon deposition.

[0017] This invention discloses a method for preparing a supported molten alloy catalyst for biomass gasification. Acid washing removes residual impurities from the porous support surface and introduces hydroxyl active sites. Calcination removes organic residues, increases the specific surface area, and enhances the thermal stability of the support, thereby improving the bonding force between the support and subsequent metal active components. Through molecular-level complexation and equal-volume impregnation, a multi-metal salt is complexed with citric acid and loaded onto a pretreated support, achieving atomic-level uniform pre-dispersion of multiple metals (especially trace amounts of Cr) on the support. After graded heating in a reducing atmosphere, uniform molten alloy nanodroplets are formed in situ under the action of molten Bi, resulting in a uniform distribution of the multi-metal molten alloy within the microporous support. This catalyst remains liquid under biomass gasification conditions of 750–1000℃, exhibiting excellent anti-carbon deposition and anti-sintering properties. It effectively inhibits tar and carbon deposition, significantly improves syngas yield and operational stability, and provides a new approach for efficient and clean biomass gasification. This invention successfully constructs a composite catalytic system of a high-temperature resistant support and nano-molten alloy droplets. It combines the dynamic self-cleaning properties of molten metal with the high dispersion and high specific surface area advantages of a supported catalyst, significantly expanding the catalytic interface and promoting the adsorption and activation of reactant molecules on the catalyst surface. The molten active surface effectively inhibits the fixed growth and coverage of carbon deposits, while the liquid nature prevents the sintering of metal particles, enabling the catalyst to exhibit excellent stability and resistance to deactivation in the harsh biomass gasification environment. This invention achieves in-situ, controllable transformation from oxide precursors to homogeneous molten alloys through temperature-increasing reduction, ensuring the reliability of catalyst performance and providing a novel solution for efficient and stable biomass gasification. It can be used for the direct production of fuel gas or syngas, or integrated with downstream thermochemical processes (such as Fischer-Tropsch synthesis and methanol production). The catalyst's high resistance to carbon deposition significantly reduces equipment clogging and downtime cleaning frequency, improving the continuous operation time and economy of industrial processes. This is of great significance for promoting the development of clean energy technologies and achieving the goals of efficient utilization of biomass energy and carbon neutrality. Attached Figure Description

[0018] Figure 1 The graphs show the change in methane conversion rate over time during the catalytic cracking of methane to hydrogen in Examples 1-4 of this invention.

[0019] Figure 2 This is a scanning electron microscope (SEM) image of a solid, highly dispersed nanoalloy before the catalyst reaction in Example 4 of this invention, taken at 500 nm.

[0020] Figure 3 This is a scanning electron microscope (SEM) image of a solid, highly dispersed nano-alloy before the catalyst reaction in Example 4 of this invention, at a depth of 2 μm.

[0021] Figure 4The image shows the morphology of the molten droplets after the catalyst reaction and the anti-carbon deposition pattern at 500 nm in Example 4 of this invention.

[0022] Figure 5 The image shows the morphology of the molten droplets after the catalyst reaction and the anti-carbon deposition at 2 μm in Example 4 of this invention. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and not for limitation.

[0024] The first aspect of the present invention provides a supported molten alloy catalyst for biomass gasification, comprising a high-temperature resistant porous support and a molten alloy active component supported thereon, wherein the molten alloy active component comprises a molten catalytic metal and a molten metal promoter, wherein the molten catalytic metal is selected from one or more of Ni, Mo, and Cr, and the molten metal promoter is Bi.

[0025] In the active components of the molten alloy, the total mass percentage of molten catalytic metals (Ni, Mo, Cr) is 1%~10%, and the mass percentage of Bi is 90%~99%. This proportion range ensures that the alloy has a sufficiently low eutectic melting point within the biomass gasification temperature range of 750-1000℃, allowing it to remain completely in the molten state.

[0026] High-temperature resistant porous supports are selected from silicon carbide (SiC), partially stabilized zirconia (PSZ), or corundum (α-Al₂O₃), with a specific surface area of ​​not less than 20 m² / g and a pore size of 5-50 nm. These support materials exhibit structural stability at high temperatures and good resistance to strong acids, alkalis, and high-temperature steam. Among them, SiC has high thermal conductivity and chemical inertness, enabling rapid heat transfer and contributing to uniform temperature distribution; partially stabilized zirconia has excellent thermal shock resistance and mechanical strength; and corundum (α-Al₂O₃) has a mature preparation process and high-temperature creep resistance. Using supports with nanoporous structures can create a physical confinement effect on molten alloy droplets at the microscale, forcing the droplets to form within the channels and preventing them from leaking or agglomerating, thereby maintaining nanoscale dispersion.

[0027] The active component of the molten alloy exists as nanodroplets on the surface and within the pores of the support, with droplet sizes ranging from 2 to 20 nm. The nanoscale droplet size provides an extremely high active metal surface area, and the capillary confinement of the support pores inhibits droplet outflow or coalescence. By controlling the metal content and calcination reduction conditions in the synthesis method, a uniform droplet distribution with an average particle size of approximately 5–10 nm can be obtained. During the gasification reaction, these droplets remain suspended on the support, and the continuous refresh of the liquid metal surface makes it difficult for carbon species to be immobilized, thus effectively improving the catalyst's resistance to carbon deposition.

[0028] A second aspect of the present invention provides a method for preparing the above-mentioned supported molten alloy catalyst, comprising the following steps: S1. Vector pretreatment: The high-temperature resistant porous support is acid-washed with a dilute acid solution (0.8-1.5 M nitric acid solution) to remove residual impurities on the support surface and introduce hydroxyl active sites. The acid-washed support is then washed until neutral and dried, and then calcined at high temperature in air or oxygen atmosphere to remove organic residues, increase the specific surface area and enhance the thermal stability of the support, thereby improving the binding force between the support and subsequent metal active components.

[0029] Pickling is carried out by refluxing at 80°C for 6 to 8 hours, and calcination is carried out at 500 to 700°C for 2 to 6 hours.

[0030] S2. Preparation of precursor solution: Weigh out metal salts containing Ni, Mo, Cr and Bi elements according to the target molar ratio, dissolve the metal salts in a mixed solvent to obtain a homogeneous metal salt solution; add a complexing agent to the solution, and stir under a water bath at 40-80°C to fully complex the metal ions and form a stable metal complex precursor solution.

[0031] Metal salts include Ni(NO3)2·6H2O and (NH4)6Mo7O. 24 The solvents are 4H2O, Cr(NO3)3·9H2O, and Bi(NO3)3·5H2O. The mixed solvent is a mixture of deionized water and ethylene glycol, with a volume ratio of (1-3):(1-2), more preferably 2:1. The complexing agent is citric acid, with a total molar ratio of citric acid to metal cations of (1.5-2.5):1, more preferably 2:1. The ratio of metal salt to mixed solvent is (20-25) g:30 mL.

[0032] S3. Step-by-step loading and drying: The metal complex precursor solution obtained in step S2 was loaded onto a pretreated support using an equal-volume impregnation method, so that the precursor solution uniformly wetted the pores of the support. After impregnation, the solution was aged at room temperature for 6 to 12 hours, and then dried under vacuum at 50 to 80°C for 12 to 24 hours to obtain a catalyst precursor with uniformly distributed metal complexes.

[0033] S4. Programmed temperature reduction and in-situ alloying: The catalyst precursor obtained in step S3 is placed in a tube furnace and subjected to programmed temperature rise heat treatment under a reducing atmosphere to reduce the metal precursor and form molten alloy active components in situ within the carrier channels.

[0034] The reduction process includes the following stages: First, the temperature is raised to 100-200℃ at 1-5℃ / min under an inert atmosphere and held for 25-35 minutes to remove residual moisture and organic matter; then, the temperature is raised to 300-500℃ at 2-10℃ / min under a reducing atmosphere containing 1-10% hydrogen (volume ratio) and held for 45-75 minutes to carry out preliminary reduction of the metal oxide; finally, the temperature is raised to 650-850℃ at 1-5℃ / min under a reducing atmosphere containing 10-50% hydrogen (volume ratio) and held for 1-6 hours to completely reduce the metal oxide, promote interdiffusion of metal atoms, and undergo in-situ alloying under the promotion of low-melting-point metal additives, forming molten alloy nanodroplets in-situ on the carrier.

[0035] After reduction, the metal surface is cooled to room temperature under an inert atmosphere and then passivated with a low concentration of oxygen to stabilize it.

[0036] A third aspect of this invention provides the use of the above-described supported molten alloy catalyst in the catalytic production of syngas in biomass gasification reactions. It is particularly suitable for steam gasification and tar reforming reactions, wherein the temperature range is 750-1000°C.

[0037] In Examples 1-4 and the Comparative Examples, the numerical subscripts in the chemical formulas of the catalysts represent the mass fraction percentage (wt%) of the corresponding metal element in the active metal component of the catalyst, unless otherwise stated.

[0038] Example 1 This embodiment provides a specific method for molten alloy catalyst and biomass gasification, wherein the catalyst used is Ni0.1Bi0. 90 / SiC, the specific steps are as follows: 1. Preparation of Ni0.1Bi0. 90 / SiC catalyst (1) Place 10 grams of mesoporous silicon carbide (β-SiC, pore size ~15nm) in 1M nitric acid solution and reflux at 80°C for 6 hours. After washing until neutral, dry at 120°C and then calcine in air at 700°C for 4 hours. Cool for later use.

[0039] (2) Weigh 4.46 g Ni(NO3)2·6H2O and 18.79 g Bi(NO3)3·5H2O according to the mass fractions of Ni and Bi in the active metal component being 10 wt% and 90 wt%, respectively, and dissolve them in a mixture of 20 mL deionized water and 10 mL ethylene glycol; add 4.0 g citric acid (CA) as a complexing agent under stirring conditions, and stir for 4 hours under a water bath at 60 ℃ to obtain a uniform and clear metal complex precursor solution A.

[0040] (3) Using the equal volume impregnation method, solution A was slowly added dropwise to the pretreated SiC support, aged at room temperature for 10 hours, and then vacuum dried at 60°C for 24 hours.

[0041] (4) The dried sample was placed in a tubular furnace quartz boat. The temperature was increased to 150°C at 2°C / min under an Ar flow of 100 mL / min and held for 30 minutes. Then, the flow rate was switched to 5% H2 / Ar (a mixture of H2 and Ar, with a H2 volume concentration of 5%, 100 mL / min), and the temperature was increased to 450°C at 5°C / min and held for 1 hour. Finally, the flow rate was switched to 20% H2 / Ar (100 mL / min), and the temperature was increased to 750°C at 2°C / min, and the sample was reduced at this temperature for 4 hours. After reduction, the sample was cooled to below 50°C under Ar protection and then passivated with 1% O2 / Ar for 2 hours to obtain Ni0.1Bi0. 90 / SiC catalyst.

[0042] 2. Biomass steam gasification reaction Take 9g of Ni0 obtained in step 1. 05 Mo0. 05 Bi0. 90 The SiC catalyst was thoroughly and uniformly mixed with 10g of biomass feedstock to obtain the reaction material. The reaction material was placed in a ceramic boat and then moved to one end of a tube furnace. The power switch of the tube furnace was turned on; the gas line was connected, the airtightness of the device was checked, and the nitrogen flow rate was set to 0.5L / min. The air in the quartz tube was purged for 20min; the nitrogen flow rate was adjusted to 0.05L / min, the heating program of the tube furnace was set, and it was started; when the temperature rose to the vaporization temperature of 900℃, the peristaltic pump was turned on to deliver water, and the water flow rate (water vapor flow rate) and nitrogen flow rate were set to send the feedstock into the heating center. The biomass began to vaporize. After the reaction stabilized, the product was collected and passed into a gas chromatograph for online analysis of the contents of H2, CO, N2, CO2, CH4, C2H4, and C2H6 in the product.

[0043] Example 2 This embodiment provides a specific method for biomass gasification using a molten alloy catalyst, wherein the catalyst used is NiO. 05 Mo0. 05 Bi0. 90 / SiC, the specific steps are as follows: 1. Preparation of NiO. 05 Mo0. 05 Bi0. 90 / SiC catalyst (1) Place 10 grams of mesoporous silicon carbide (β-SiC, pore size ~15nm) in 1M nitric acid solution and reflux at 80°C for 6 hours. After washing until neutral, dry at 120°C and then calcine in air at 700°C for 4 hours. Cool for later use.

[0044] (2) Weigh out 2.23 g of Ni(NO3)2·6H2O and 0.83 g of (NH4)6Mo7O according to the mass fractions of Ni, Mo and Bi in the active metal components being 5 wt%, 5 wt% and 90 wt%, respectively. 24 ·4H2O and 18.79 g Bi(NO3)3·5H2O were dissolved in a mixture of 20 mL deionized water and 10 mL ethylene glycol; 4.0 g citric acid (CA) was added as a complexing agent under stirring, and the mixture was stirred for 4 hours in a 60 °C water bath to obtain a homogeneous and clear metal complex precursor solution A2.

[0045] (3) Using the equal volume impregnation method, solution B was slowly added dropwise to the pretreated SiC support, aged at room temperature for 10 hours, and then vacuum dried at 60°C for 24 hours.

[0046] (4) The dried sample was placed in a quartz boat in a tubular furnace. The temperature was increased to 150°C at 2°C / min under an Ar flow of 100 mL / min and held for 30 minutes. Then, the flow rate was switched to 5% H₂ / Ar (100 mL / min), and the temperature was increased to 450°C at 5°C / min, held for 1 hour. Finally, the flow rate was switched to 20% H₂ / Ar (100 mL / min), and the temperature was increased to 750°C at 2°C / min, and the sample was reduced at this temperature for 4 hours. After reduction, the sample was cooled to below 50°C under Ar protection, and then passivated with 1% O₂ / Ar for 2 hours to obtain Ni. 0.05 Mo 0.05 Bi 0.90 / SiC catalyst.

[0047] 2. Biomass steam gasification reaction The Ni obtained in step 1 (9g) 0.05 Mo 0.05 Bi 0.90The SiC catalyst was thoroughly and uniformly mixed with 10g of biomass feedstock to obtain the reaction mixture. The reaction mixture was placed in a ceramic boat and then moved to one end of a tube furnace. The tube furnace power switch was turned on; the gas line was connected, the airtightness of the device was checked, and the nitrogen flow rate was set to 0.5L / min. Air was purged from the quartz tube for 20 minutes; the nitrogen flow rate was adjusted to 0.05L / min, the tube furnace heating program was set, and the furnace was started; once the temperature reached the vaporization temperature, the peristaltic pump was turned on to deliver water, and the water flow rate and nitrogen flow rate were set to send the feedstock into the heating center. The biomass began to vaporize. After the reaction stabilized, the product was collected and passed into a gas chromatograph for online analysis of the contents of H2, CO, N2, CO2, CH4, C2H4, and C2H6.

[0048] Example 3 This embodiment provides a specific method for molten alloy catalyst and biomass gasification, wherein the catalyst used is: Ni 0.05 Cr 0.05 Bi 0.90 / SiC, the specific steps are as follows: 1. Preparation of Ni 0.05 Cr 0.05 Bi 0.90 / SiC catalyst (1) 10 grams of mesoporous silicon carbide (β-SiC, pore size ~15nm) was acid-washed, dried and calcined according to the method described in Example 1, and then cooled for later use.

[0049] (2) Weigh 2.23 g Ni(NO3)2·6H2O, 2.33 g Cr(NO3)3·9H2O and 18.79 g Bi(NO3)3·5H2O according to the mass fractions of Ni, Cr and Bi in the active metal component being 5 wt%, 5 wt% and 90 wt%, respectively, and dissolve them in a mixture of 20 mL deionized water and 10 mL ethylene glycol; add 4.0 g citric acid (CA), and stir for 4 hours in a water bath at 60 ℃ to obtain metal complex precursor solution A3.

[0050] (3) Using the equal volume impregnation method, solution C was slowly added dropwise to the pretreated SiC support, aged at room temperature for 10 hours, and then vacuum dried at 60℃ for 24 hours.

[0051] (4) The process was carried out under the same temperature reduction conditions as in Example 1. After reduction, the sample was cooled and passivated to obtain Ni. 0.05 Cr 0.05 Bi 0.90 / SiC catalyst.

[0052] 2. Biomass steam gasification reaction The biomass gasification reaction was carried out according to the method described in Example 1, and the composition of the products was analyzed online.

[0053] Example 4 This embodiment provides a specific method for molten alloy catalyst and biomass gasification, wherein the catalyst used is: Ni 0.03 Cr 0.01 Mo 0.01 Bi 0.95 / SiC, the specific steps are as follows: 1. Preparation of Ni 0.03 Cr 0.01 Mo 0.01 Bi 0.95 / SiC catalyst (1) 10 grams of mesoporous silicon carbide (β-SiC, pore size ~15nm) was pretreated according to the method described in Example 1 and cooled for later use.

[0054] (2) Weigh out 1.34 g Ni(NO3)2·6H2O, 0.47 g Cr(NO3)3·9H2O, and 0.17 g (NH4)6Mo7O according to the mass fractions of Ni, Cr, Mo, and Bi in the active metal components being 3 wt%, 1 wt%, 1 wt%, and 95 wt%, respectively. 24 ·4H2O and 19.84 g Bi(NO3)3·5H2O were dissolved in a mixture of 20 mL deionized water and 10 mL ethylene glycol; 4.0 g citric acid (CA) was added, and the mixture was stirred in a water bath at 60 °C for 4 hours to obtain metal complex precursor solution A4.

[0055] (3) Using the equal volume impregnation method, solution D was slowly added dropwise to the pretreated SiC support, aged at room temperature for 10 hours, and then vacuum dried at 60℃ for 24 hours.

[0056] (4) The process was carried out under the same temperature reduction conditions as in Example 1. After reduction, the sample was cooled and passivated to obtain Ni. 0.03 Cr 0.01 Mo 0.01 Bi 0.95 / SiC catalyst.

[0057] 2. Biomass steam gasification reaction The biomass gasification reaction was carried out according to the method described in Example 1, and the composition of the products was analyzed.

[0058] Example 5 This comparative example provides a method for biomass gasification, wherein the catalyst used is Ni. 0 .7 Bi 0 .3 / SiC, the specific steps are as follows: 1. Preparation of Ni 0 .7 Bi 0 .3 / SiC catalyst (1) Place 10 grams of mesoporous silicon carbide (β-SiC, pore size ~15nm) in 1M nitric acid solution and reflux at 80°C for 6 hours. After washing until neutral, dry at 120°C and then calcine in air at 700°C for 4 hours. Cool for later use.

[0059] (2) Weigh out 31.19 g of Ni(NO3)2·6H2O and 6.27 g of Bi(NO3)3·5H2O with mass fractions of 70 wt% and 30 wt% respectively. The remaining steps are the same as in Example 1.

[0060] (3) Using the equal volume impregnation method, the obtained solution F is slowly added dropwise to the pretreated SiC support, aged at room temperature for 10 hours, and then vacuum dried at 60℃ for 24 hours.

[0061] (4) The process was carried out under the same temperature reduction conditions as in Example 1. After reduction, the sample was cooled and passivated to obtain the comparative Ni. 0 .7 Bi 0 .3 / SiC catalyst.

[0062] 2. Biomass steam gasification reaction The Ni obtained in step 1 0 .7 Bi 0 .3 The SiC catalyst was thoroughly and uniformly mixed with 10g of biomass feedstock to obtain the reaction mixture. A gasification experiment was conducted according to the biomass gasification reaction conditions described in Example 1, and the composition of the products was analyzed online.

[0063] Comparative Example 1 This comparative example provides a method for biomass gasification, wherein the catalyst used is Ni. 0.40 Cr 0.60 / SiC, without low-melting-point metal additive Bi, the specific steps are as follows: 1. Preparation of Ni 0.40 Cr 0.60 / SiC catalyst (1) Place 10 grams of mesoporous silicon carbide (β-SiC, pore size ~15nm) in 1M nitric acid solution and reflux at 80°C for 6 hours. After washing until neutral, dry at 120°C and then calcine in air at 700°C for 4 hours. Cool for later use.

[0064] (2) Weigh 12.53 g Ni(NO3)2·6H2O and 22.89 g Cr(NO3)3·9H2O according to the mass fractions of Ni and Cr of 40 wt% and 60 wt%, respectively. The remaining preparation and gasification steps are the same as in Example 1.

[0065] (3) Using the equal volume impregnation method, the obtained solution E is slowly added dropwise to the pretreated SiC support, aged at room temperature for 10 hours, and then vacuum dried at 60℃ for 24 hours.

[0066] (4) The process was carried out under the same temperature reduction conditions as in Example 1. After reduction, the sample was cooled and passivated to obtain the comparative Ni. 0.40 Cr 0.60 / SiC catalyst.

[0067] 2. Biomass steam gasification reaction The Ni obtained in step 1 0.40 Cr 0.60 The SiC catalyst was thoroughly and uniformly mixed with 10g of biomass feedstock to obtain the reaction mixture. A gasification experiment was conducted according to the biomass gasification reaction conditions described in Example 1, and the composition of the products was analyzed online.

[0068] To further illustrate the feasibility of the present invention, a typical operating condition was selected, and the results of the calculations for the molten metal catalytic biomass gasification to syngas system in Example 4 were performed. Table 1 shows the basic operating parameters of the biomass steam gasification reaction in Example 1.

[0069] To demonstrate that the present invention can maintain high selectivity of syngas, Table 2 shows the main components of the reaction gas in the calculation results, Table 3 shows the main components of the gas produced in the calculation results, and Table 4 shows a comparative analysis of the optimal conditions for biomass gasification and the conditions without a catalyst in the calculation results.

[0070] Table 1 Basic parameters of the embodiment

[0071] Table 2 Main components of the reaction gas

[0072] Table 3 Main components of the produced gas

[0073] Table 4 Comparison of optimal conditions for biomass gasification with those without a catalyst.

[0074] Furthermore, Table 5 presents the main components of the reaction gas in the calculation results of Example 1, Table 6 presents the main components of the gas produced in the calculation results, and Table 7 presents a comparative analysis of the calculation results of biomass gasification and the catalyst-free method. Table 8 presents the main components of the reaction gas in the calculation results of Example 3, Table 9 presents the main components of the gas produced in the calculation results, and Table 10 presents a comparative analysis of the calculation results of biomass gasification and the catalyst-free method. Table 11 presents the main components of the reaction gas in the calculation results of Example 5, Table 12 presents the main components of the gas produced in the calculation results, and Table 13 presents a comparative analysis of the calculation results of biomass gasification and the catalyst-free method.

[0075] Table 5 Main components of the reaction gas

[0076] Table 6 Main components of the produced gas

[0077] Table 7 Comparative Analysis of Biomass Gasification and Catalyst-Free Gasification

[0078] Table 8 Main components of the reaction gas

[0079] Table 9 Main components of the produced gas

[0080] Table 10 Comparative Analysis of Biomass Gasification and Catalyst-Free Gasification

[0081] Table 11 Main components of the reaction gas

[0082] Table 12 Main components of the gas produced

[0083] Table 13 Comparative Analysis of Biomass Gasification and Catalyst-Free Gasification

[0084] The present invention also conducted stability experiments on the methods for producing syngas from biomass in Examples 1-4. Specifically, the biomass gasification reactions in Examples 1-4 were carried out in cycles, with the specific reaction conditions being the same as in Example 1. The carbon conversion rate of syngas produced from biomass in Examples 1-4 as a function of the number of catalyst cycles is shown in the curves below. Figure 1 As shown.

[0085] Depend on Figure 1It is clear that the molten metal catalyst for biomass gasification to syngas provided in this application has good stability, can be circulated in the reactor at least 20 times, has a carbon conversion rate of more than 75%, can be recycled, and the catalyst does not show deactivation and has a long service life.

[0086] As shown in Table 4, in Example 4, when the biomass gasification reaction was carried out under high temperature conditions, the syngas (H2 and CO) yield and carbon conversion rate remained at a high level. Meanwhile, the supported molten alloy catalysts used in each example exhibited good reaction stability, capable of continuous operation for a relatively long period without significant deactivation. Their stability changes are shown in Table 4. Figure 1 As shown. This indicates that, in the technical solution described in this invention, introducing a low-melting-point metal and forming a molten alloy system is beneficial for maintaining the continuous activity of the catalyst under high-temperature gasification conditions.

[0087] Figure 2 Example 4 (Ni) is shown 0.03 Cr 0.01 Mo 0.01 Bi 0.95 The initial state after the SiC catalyst preparation is completed. At a scale of 500 nm (20,000x magnification), densely and uniformly distributed 2–20 nm multi-element alloy particles are visible on the rough surface of the support. This indicates that, under the control of molecular-level complexation and stepwise reduction processes, the multi-element alloy active components are immobilized on the support with high nanoscale dispersion, without agglomeration or severe sintering. Figure 3 At a scale of 2μm (5000x magnification), it exhibits a hierarchical porous cauliflower-like skeletal structure. This rich network of mesopores and macropores not only provides channels for gasification mass transfer, but also provides physical space for anchoring liquid metal at high temperatures.

[0088] After the biomass gasification reaction was completed, the catalyst was removed from the reactor, allowed to cool naturally to room temperature and solidify, and then scanned by electron microscopy. At a scale bar of 500 nm (… Figure 4 The microstructure undergoes a dramatic change; the originally tiny nanoparticles completely disappear, transforming into extremely smooth spherical or hemispherical solidified droplets. This is because the bismuth-rich alloy completely transforms into flowing molten droplets at 900℃. Upon cooling, the droplets shrink and solidify into smooth shapes under surface tension. Most importantly, the droplet and carrier surfaces are extremely clean, without any filamentous carbon or amorphous carbon layers, directly demonstrating that the dynamic surface of the liquid metal fundamentally inhibits the adhesion and growth of tar deposits. At a scale of 2μm (… Figure 5In the macroscopic view, multiple independent catalyst particle aggregates appear, with nearly perfect, smooth, large spheres located slightly to the upper right, and the surface of the central particles covered with rounded, solidified droplets. This indicates that although some nanodroplets aggregated at the micrometer scale under prolonged high temperatures, the molten alloy remained firmly anchored by the strong physical confinement of the SiC support, preventing large-scale loss. Simultaneously, the clear boundaries between particles prove that the catalyst bed was not encapsulated or caked by carbon deposits, explaining why it can remain active after more than 20 cycles.

[0089] These four figures illustrate the microstructure evolution of the supported molten alloy catalyst before and after the reaction in the embodiments, demonstrating the phase transition process of the catalyst from solid, highly dispersed nanoparticles to molten droplets confined by a porous framework at high temperatures. The extremely clean surface after the reaction is the most powerful visual proof that this invention overcomes the problem of high-temperature carbon deposition and deactivation of traditional solid catalysts.

[0090] Further Example 3 (Ni) 0.05 Cr 0.05 Bi 0.90 / SiC) and Comparative Example 1 (Ni 0.40 Mo 0.60 As can be seen from the data ( / SiC), under the same biomass gasification reaction temperature, although Comparative Example 1 can achieve a certain degree of biomass conversion in the initial stage of the reaction, its catalyst system does not contain low-melting-point metal additives and has a high overall melting point. It cannot form a molten state at the gasification reaction temperature, leading to the easy adhesion and gradual deposition of coke and tar cracking products generated during biomass pyrolysis and gasification on the surface of the solid catalyst. As the reaction continues, the aforementioned carbon deposition covers the active sites on the catalyst surface, hindering effective contact between reactants and active components, thus causing a gradual decrease or even deactivation of the catalyst activity (see Table 14 below), making it difficult for the biomass gasification reaction to proceed continuously and stably for a long period. This indicates that, in the technical solution of this invention, introducing low-melting-point molten metal additives and forming a molten alloy system plays a crucial role in inhibiting carbon deposition, slowing down the coverage of active sites, and maintaining the long-term stable operation of the catalyst; without molten metal additives, the technical effects described in this application cannot be achieved.

[0091] Table 14 Comparison of gasification performance between Example 3 and Comparative Example 1

Claims

1. A supported molten alloy catalyst for biomass gasification, characterized in that, It includes a porous support and a molten alloy active component loaded on its surface and within its pores in the form of nanodroplets. The molten alloy active component includes a molten catalytic metal and a molten metal additive. The molten catalytic metal is selected from one or more of Ni, Mo, and Cr, and the molten metal additive is Bi.

2. The supported molten alloy catalyst for biomass gasification according to claim 1, characterized in that, The active component of the molten alloy, by mass percentage, comprises 1% to 10% of the total mass of the molten catalytic metal and 90% to 99% of the mass of the molten metal additive.

3. The supported molten alloy catalyst for biomass gasification according to claim 1, characterized in that, The porous carrier is silicon carbide, partially stabilized zirconia, or corundum.

4. The supported molten alloy catalyst for biomass gasification according to claim 1, characterized in that, The specific surface area of ​​the porous carrier is not less than 20 m² / g, and the pore size is 5-50 nm.

5. The supported molten alloy catalyst for biomass gasification according to claim 1, characterized in that, The droplet size of the active component of the molten alloy is 2~20 nm.

6. A method for preparing a supported molten alloy catalyst for biomass gasification as described in any one of claims 1 to 5, characterized in that, Includes the following steps: S1, the porous support is acid washed and then calcined to obtain a pretreated porous support; S2, add citric acid to the corresponding metal salt solutions of molten catalytic metal and molten metal promoter and stir evenly. The total molar ratio of citric acid to metal cation is (1.5~2.5):1 to obtain a precursor solution. The precursor solution is loaded onto a pretreated porous support by an equal volume impregnation method, and then aged and dried in sequence to obtain the catalyst precursor. S3. After the catalyst precursor is kept at 100-200℃, it is successively kept at 300-500℃ and 650-850℃ in a reducing atmosphere containing hydrogen, and then successively cooled and passivated to obtain a supported molten alloy catalyst for biomass gasification.

7. The method for preparing the supported molten alloy catalyst for biomass gasification according to claim 6, characterized in that, S1 The porous support is refluxed in a 0.8-1.5 M acid solution for 6-8 hours, then washed until neutral and dried, and calcined at 500-700℃ for 2-6 hours in air or oxygen atmosphere to obtain the pretreated porous support.

8. The method for preparing the supported molten alloy catalyst for biomass gasification according to claim 6, characterized in that, In S2, the corresponding metal salts of Ni, Mo, Cr and Bi are Ni(NO3)2·6H2O, (NH4)6Mo7O, and (NH4)6Mo7O, respectively. 24 The metal salt solutions are 4H2O, Cr(NO3)3·9H2O and Bi(NO3)3·5H2O, and the solvents for the metal salt solutions are deionized water and ethylene glycol in a volume ratio of (1-3):(1-2). The aging process is carried out at room temperature for 6–12 hours, and the drying process is carried out under vacuum conditions at 50–80°C for 12–24 hours.

9. The method for preparing the supported molten alloy catalyst for biomass gasification according to claim 6, characterized in that, S3 involves heating the catalyst precursor to 100–200°C at a rate of 1–5°C / min under an inert atmosphere and holding it at that temperature for 25–35 min. Then, it is heated to 300–500°C at a rate of 2–10°C / min under a reducing atmosphere containing 1–10% hydrogen and held at that temperature for 45–75 min. Finally, it is heated to 650–850°C at a rate of 1–5°C / min under a reducing atmosphere containing 10–50% hydrogen and held at that temperature for 1–6 h.

10. Use of the supported molten alloy catalyst for biomass gasification as described in any one of claims 1 to 5 in steam gasification and tar reforming reactions.

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