Composite catalyst for manufacturing synthesis gas using carbon dioxide and methane and method for manufacturing synthesis gas using the same

Abstract

One embodiment of the present invention provides a composite catalyst for producing synthesis gas containing hydrogen and carbon monoxide, comprising: a porous support; a metal material impregnated on the surface or inside of the porous support; wherein the porous support is a thermoplastic plastic-based support synthesized by evaporation-induced self-assembly (EISA), and the metal material is a metal element, a metal oxide, or a combination thereof. The composite catalyst for synthesis gas production containing hydrogen and carbon monoxide described above exhibited high performance in methane reforming and can have excellent resistance to sintering and coking.

Description

Technology Field

[0001] The present invention relates to a composite catalyst for the production of synthesis gas containing hydrogen and carbon monoxide, and more specifically, to a catalyst in which nickel (Ni) is impregnated on a multifunctional and porous support for combined steam and dry reforming of methane (CSDRM). Background Technology

[0003] The U.S. National Oceanic and Atmospheric Administration (NOAA) reports that atmospheric carbon dioxide concentrations have risen from 280 ppm pre-industrial levels to 418 ppm by 2020 due to increased fossil fuel use. The increase in greenhouse gas concentrations accelerates climate change, leading to adverse effects such as rising global temperatures, droughts, and natural disasters like air pollution. The major greenhouse gases are carbon dioxide and methane, and many scientists have long studied Dry Reforming (DRM) of the methane process using catalysts to reduce the concentrations of these two gases in the atmosphere. DRM not only simultaneously reduces these two major greenhouse gases but also converts them into useful syngas, which is then used to produce high-value chemicals such as those produced in the Fischer-Tropsch (FT) process and methanol synthesis.

[0004] However, among the various entry barriers widely presented for dry reforming reactions, the most significant problem is the rapid deactivation of the catalyst by coke deposited on the catalyst during the reaction process. Furthermore, producing synthesis gas with an H2:CO ratio of 1:1 is not suitable for precise application in methanol synthesis and Fischer-Tropsch processes. For the precise supply and utilization of synthesis gas, maintaining a stable synthesis gas ratio for the FT process should be the primary focus. Therefore, combined steam and dry reforming of methane (CSDRM) is being considered as an effective alternative for adjusting synthesis gas selectivity under various feedstock conditions. CSDRM is regarded as a promising technology due to its ability to simultaneously reduce methane and carbon dioxide while generating a stable and flexible H2 / CO ratio.

[0005] Generally, since the CSDRM process is similar to the reforming process, there has been a lot of research on Ni-based catalysts that are economical and highly reactive. However, because the reforming process is carried out at high temperatures of 700 to 800°C or higher, it has the disadvantage that the sintering of nickel particles is easy or carbon deposits can easily form on the catalyst surface due to the influence of carbon generated during the reaction.

[0006] To compensate for these drawbacks, catalyst stability can be significantly improved by incorporating small amounts of precious metals, metal oxides, or promoters, along with the use of suitable support materials. Although Ni-Ru / MgAl2O4, Ni-Rh / MgAl2O4, and Co-Pt / Al2O3 have demonstrated excellent catalytic performance and remarkable resistance to carbon deposition as precious metal catalysts, their high cost and limited commercial availability present significant limitations. Furthermore, the incorporation of basic oxides or mixed oxides (Ni-Mg / Al2O3, Ni-Mg / SBA-15, K-Ni / MgAl2O4, Ni-Sn / Al2O3, Ni-CeO2 / Al2O3) into Ni-based catalysts generally contributes to improved catalyst stability. The incorporation of promoters significantly influences the physicochemical properties of the active metal, including reducing ability, basicity, and oxygen storage capacity.

[0007] Appropriate modification of the support can result in a high surface area and effectively disperse small metal particles, thereby improving the stability and activation of the catalyst and facilitating strong interactions with the active metal. Over the past decade, hierarchically aligned porous structures have been the subject of research in various fields due to their high surface area and low density. In porous structures characterized by meso-macro pores, the small pore configuration typically features a high surface area, which is advantageous for the efficient dispersion of metals, whereas the larger pore structure offers the advantage of facilitating efficient transport. Favorable mass transfer properties and a large surface area enable the stable deposition of active metal particles, effectively inhibiting metal aggregation and enhancing the stabilization and activation of Ni particles.

[0008] Conventional technology has stabilized Ni-Co alloy catalysts on bimodal mesoporous supports and improved resistance to carbon deposition, indicating that Ni nanoparticles are highly dispersed in the support in a hierarchically ordered macroporous alumina structure rather than a mesoporous structure. Furthermore, it has been shown that bimodal (macro-porous and meso-porous) supports prepared via the Evaporation-Induced Self-Assembly (EISA) method exhibit strong interactions with Ni particles, and that the effective diffusion coefficient of methane is higher in the bimodal pore structure than in the monomodal structure using chitosan as a template. Based on another conventional technology, it can be seen that the novel bimodal support possesses good dispersibility of Ni particles, demonstrates excellent hydrogen production from the steam reforming of vegetable oils, and shows significantly higher methanol selectivity for Cu-based catalysts with a bimodal pore structure compared to a mesoporous structure due to CO2 hydrogenation. In particular, Knudsen diffusion, as demonstrated in mathematical modeling, is considered the dominant transport mechanism in large pore networks of 50 nm or more, highlighting the advantageous properties of bimodal pore networks.

[0009] Bimodal porous structures are widely used in various fields and are recognized for their potential performance, making them a promising strategy for improving catalyst stability. However, research on their application to CSDRM is currently scarce, with the exception of a few studies on DRMs for catalysts with bimodal porous structures.

[0010] In the present invention, a bimodal porous structure prepared using polystyrene nanobeads as a template and the evaporation-induced self-assembly (EISA) method was used as a porous catalyst support. Ni metal was impregnated onto the support using incipient wetness impregnation (IWI), and pore formation was controlled by a polystyrene (PS) / aluminum (Al) weight ratio (0.5, 1.0, 1.5, 2.0). The effects of the catalyst impregnated with metal oxide on the porous and multifunctional support were analyzed using appropriate characterization techniques. The prepared catalyst was tested under various reaction conditions in a fixed-bed reactor. CH4 and CO2 conversion rates, H2 / CO ratios, yields, and production volumes were compared through the CSDRM reaction. To ensure stable process operation, conditions preventing carbon deposition were prioritized, and the stability of the metallic Ni particles was maintained. The problem to be solved

[0012] The present invention aims to solve the rapid deactivation of a catalyst caused by coke deposited on the catalyst in the dry reforming process (DRM) of a methane process.

[0013] The present invention aims to solve the disadvantage that nickel particles may be sintered or carbon deposits may easily form on the catalyst surface due to the influence of carbon generated during the reaction, as the combined steam and dry reforming of methane (CSDRM) reacts at a high temperature of 700 to 800°C or higher.

[0014] The technical problems that the present invention aims to solve are not limited to those mentioned above, and other unmentioned technical problems will be clearly understood by those skilled in the art to which the present invention belongs from the description below. means of solving the problem

[0016] As a technical means for achieving the aforementioned technical problem, one aspect of the present invention is,

[0017] A composite catalyst for producing synthesis gas containing hydrogen and carbon monoxide is provided, comprising: a porous support; and a metal material impregnated on the surface or inside of the porous support; wherein the porous support is a thermoplastic plastic-based support synthesized by evaporation-induced self-assembly (EISA), and the metal material is a metal element, a metal oxide, or a combination thereof.

[0018] The above thermoplastic plastic may be characterized as being polystyrene nanobeads formed by emulsion polymerization.

[0019] The porous support may be characterized as being a structure composed of at least one from the group consisting of alumina (Al2O3), methyl cellulose, carboxyhydrate, carboxylic methyl cellulose, polyvinyl alcohol, clay, silica (SiO2), thiofol (TiO2), and activated carbon.

[0020] The above porous support may be characterized by having meso-macro pores.

[0021] The above pores may be characterized by being determined by controlling the polystyrene (PS) / aluminum (Al) weight ratio.

[0022] The above metal material may be characterized as being an element, oxide, or combination thereof of one or more metals selected from the group consisting of nickel (Ni), cobalt (Co), iron (Fe), copper (Cu), zinc (Zn), manganese (Mn), chromium (Cr), vanadium (V), scandium (Sc), zirconium (Zr), and molybdenum (Mo).

[0023] It may be characterized by the fact that a metal material is impregnated into the surface or interior of the porous support using an incipient wetness impregnation (IWI) method.

[0024] The BET surface area of ​​the composite catalyst for producing synthesis gas containing hydrogen and carbon monoxide, measured by the Barrett-Joyner-Halenda (BJH) method, is 50 to 200 m² 2 It may be characterized by being / g.

[0025] The H2 consumption measured by the H2-TPR (Temperature-programmed reduction) of the composite catalyst for producing synthesis gas containing hydrogen and carbon monoxide may be characterized as being 0.5 to 2.0 mmol / g.

[0026] The pore diameter of the composite catalyst for producing synthesis gas containing hydrogen and carbon monoxide may be characterized as being 200 to 400 nm.

[0027] The H2 chemisortion dispersion of the composite catalyst for producing synthesis gas containing hydrogen and carbon monoxide may be characterized as being 1.5 to 3.5%.

[0028] The composite catalyst for producing synthesis gas containing hydrogen and carbon monoxide may be characterized by maintaining catalytic activity of 90% or more relative to the initial level for 5 hours or more and 100 hours or less.

[0029] The composite catalyst for producing synthesis gas containing hydrogen and carbon monoxide described above may be characterized by having a CH4 conversion rate of 80% or more and a CO2 conversion rate of 30% or more during the combined steam and dry reforming of methane (CSDRM) reaction, and may be characterized by having an H2 yield of 70% or more and a CO yield of 50% or more.

[0030] For the above-mentioned composite catalyst for synthesis gas production containing hydrogen and carbon monoxide, the turnover frequency (TOF) of CH4 during the combined steam and dry reforming of methane (CSDRM) reaction is 0.20s. -1 The anomaly and CO2 rotation frequency is 0.10s. -1 It is characterized by the above, and the above rotation frequency may be characterized by being calculated by the following chemical formula.

[0031] [Chemical Formula 10]

[0032]

[0033] The above CH4 or CO2 conversion, molar weight of silver and nickel, It represents the metallic dispersion of nickel.

[0035] Another aspect of the present invention provides a method for producing synthesis gas containing hydrogen and carbon monoxide, comprising the steps of: raising the temperature of a reactor; pre-mixing two or more reaction gases selected from the group consisting of methane (CH4), carbon dioxide (CO2), water (H2O), and nitrogen (N2); providing the catalyst of claim 1 inside the reactor and reducing the catalyst; introducing the pre-mixed reaction gas into the reactor to react with the reduced catalyst; and obtaining a synthesis gas containing hydrogen (H2) and carbon monoxide (CO) through the reaction. Effects of the invention

[0037] According to an embodiment of the present invention, a composite catalyst for producing synthesis gas containing hydrogen and carbon monoxide exhibited high performance in methane reforming and can have excellent resistance to sintering and coking.

[0038] In one embodiment of the present invention, Ni particles as impregnated metal oxide can act as a stable catalyst while maintaining an appropriate distance near the pores.

[0039] One embodiment of the present invention enables the production of synthesis gas with an appropriate H2:CO ratio and can exhibit stable catalytic performance after a long reaction.

[0040] The effects of the present invention are not limited to the effects described above, and should be understood to include all effects that can be inferred from the composition of the invention described in the description or claims of the present invention. Brief explanation of the drawing

[0042] Figure 1 shows the XRD patterns of calcined Ni / PS and Ni / MM-A (1-4) catalysts. Figure 2 shows (a) N2 physical adsorption-desorption isotherms and (b) pore size distribution of calcined Ni / PS and Ni / MM-A (1-4) catalysts. Figure 3 shows SEM images of the sintered supports. ((a) Polystyrene latex beads, (b) MM-A1, (c) MM-A2, (d) MM-A3, and (e) MM-A4) Figure 4 shows the H2-TPR profiles of calcined Ni / PS and Ni / MM-A (1-4) catalysts. Figure 5 shows the UV-vis-DRS (diffuse reflectance absorption) spectrum of the calcined Ni / MM-A (1-4) catalyst. The vertical dashed lines on the graph represent Ni in octahedral and tetrahedral coordination. 2+ It indicates the expected position of the absorption band for. Figure 6 shows the results of the CSDRM reaction catalyst evaluation under basic conditions using Ni / PS and Ni / MM-A (1-4) catalysts, representing (a) CH4 conversion, (b) CO2 conversion, (c) H2 / CO ratio, and (d) TGA curves of the catalyst after use, respectively. The red vertical dotted line in the graph indicates the three regions of weight loss with temperature. (Reaction conditions: catalyst = 0.3 g, T = 800℃, P = ambient pressure, CH4:CO2:H2O = 1:1:1 (molar ratio in sample), WHSV (weight hourly space velocity): 20,000 h⁻¹, TOS (time-on-stream) = 5 hours) Figure 7 shows the results of the CSDRM reaction catalyst evaluation for stable synthesis gas production using a Ni / MM-A3 catalyst, representing (a) CH4 and CO2 conversion rates, (b) H2 / CO ratio, and (c) yield and production volume of H2 and CO, respectively. (Reaction conditions: catalyst = 0.3 g, T = 800℃, P = ambient pressure, CH4:CO2:H2O = 1:0.4:0.8 (molar ratio in sample), WHSV (weight hourly space velocity): 20,000 h⁻¹, TOS (time-on-stream) = 5 hours) Figure 8 shows the catalytic performance and stability test data of the Ni / MM-A3 catalyst for the CSDRM reaction. (Reaction conditions: catalyst = 0.3 g, T = 800℃, P = ambient pressure, CH4:CO2:H2O = 1:0.4:0.8 (molar ratio in sample), WHSV (weight hourly space velocity): 20,000 h⁻¹, TOS (time-on-stream) = 5 hours) Figure 9 shows the XRD patterns of the catalyst after use following the CSDRM reaction (short-term catalyst 5 hours: STC-5 hours and long-term catalyst 100 hours: LTC-100 hours). Figure 10 shows (a) the N2 physical adsorption-desorption isotherm after the CSDRM reaction and (b) the pore size distribution of the catalyst (STC-5 h, LTC-100 h) after use. Figure 11 shows (a) TGA and (b) DSC profiles of the catalyst (STC-5h, LTC-100h) after use following the CSDRM reaction. Figure 12 shows SEM images of the catalyst after use following the CSDRM reaction ((a, b) STC-5 hours (c, d) LTC-100 hours). Figure 13 shows TEM images of catalysts after use following the CSDRM reaction (STC-5h sample; (a) TEM, (bc) HRTEM image, (d) HAADF-STEM image, LTC-100h sample; (ef) TEM, (g) HRTEM image and (h) HAADF-STEM image). Pore structures are indicated by red circles. Specific details for implementing the invention

[0043] The present invention will be described in more detail below. However, the present invention may be implemented in various different forms and is not limited by the embodiments described herein, and is defined only by the claims set forth below.

[0044] Additionally, the terms used in this invention are used merely to describe specific embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. Throughout the specification of this invention, the term 'comprising' any component means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0046] The first aspect of the present invention provides a composite catalyst for producing synthesis gas containing hydrogen and carbon monoxide, comprising: a porous support; a metal material impregnated on the surface or inside of the porous support; wherein the porous support is a thermoplastic plastic-based support synthesized by evaporation-induced self-assembly (EISA), and the metal material is a metal element, a metal oxide, or a combination thereof.

[0048] Hereinafter, a composite catalyst for producing synthesis gas containing hydrogen and carbon monoxide according to the first aspect of the present invention will be described in detail.

[0050] In one embodiment of the present invention, the most preferred thermoplastic plastic used in the composite catalyst for producing synthesis gas containing hydrogen and carbon monoxide is polystyrene nanobeads formed by an emulsion polymerization method without an emulsifier. At this time, the thermoplastic plastic used is not limited to polystyrene, and any plastic capable of exhibiting the performance and effect of the catalyst of the present invention may be used.

[0051] In one embodiment of the present invention, the porous support is a structure composed of at least one from the group consisting of alumina (Al2O3), methyl cellulose, carboxyhydrate, carboxylic methyl cellulose, polyvinyl alcohol, clay, silica (SiO2), thiofol (TiO2), and activated carbon, and most preferably, it may be an alumina (Al2O3) structure.

[0052] In one embodiment of the present invention, the porous support has meso-macro pores, and the degree of pore formation (etching) may vary depending on the amount of nitric acid added.

[0053] In one embodiment of the present invention, the polystyrene (PS) / aluminum (Al) weight ratio may be determined by controlling it. An increase in the PS / Al weight ratio may lead to more pronounced development of macropores, and a relatively ordered, dense support structure may exhibit strong interactions between the active metals. Therefore, the determination of the reduction temperature may depend on the pore structure. Accordingly, the metallic Ni reduction behavior in the formation of the catalyst's pore framework may vary depending on the Al precursor content.

[0054] In one embodiment of the present invention, the metal material may be an element, oxide, or combination thereof of one or more metals selected from the group consisting of nickel (Ni), cobalt (Co), iron (Fe), copper (Cu), zinc (Zn), manganese (Mn), chromium (Cr), vanadium (V), scandium (Sc), zirconium (Zr), and molybdenum (Mo), and most preferably, nickel (Ni) metal oxide may be used.

[0055] In one embodiment of the present invention, a metal material may be impregnated on the surface or inside of the porous support by incipient wetness impregnation (IWI).

[0056] In one embodiment of the present invention, the BET surface area of ​​the composite catalyst for producing synthesis gas containing hydrogen and carbon monoxide, measured by the Barrett-Joyner-Halenda (BJH) method, is 50 to 200 m² 2 / g, preferably 70 to 180m 2 / g, more preferably 80 to 160m 2 / g, more preferably 95 to 150m 2 It may be / g, and if it is below the above-mentioned range, it may be that sufficient metal material has not been impregnated, and if it exceeds the above-mentioned range, the surface area may become unnecessarily large compared to the size of the catalyst.

[0057] In one embodiment of the present invention, the H2 consumption measured by the H2-TPR (Temperature-programmed reduction) of the composite catalyst for producing synthesis gas containing hydrogen and carbon monoxide may be 0.5 to 2.0 mmol / g, preferably 0.7 to 1.9 mmol / g, more preferably 0.9 to 1.8 mmol / g, and even more preferably 1.1 to 1.85 mmol / g. If it exceeds the above-described range, an unnecessarily large amount of H2 may be consumed, and thus it may not have efficiency compared to conventional catalysts.

[0058] In one embodiment of the present invention, the pore diameter of the composite catalyst for producing synthesis gas containing hydrogen and carbon monoxide may be 200 to 400 nm, preferably 220 to 380 nm, more preferably 240 to 360 nm, and even more preferably 260 to 340 nm. If the diameter exceeds the above-described range, the pore diameter becomes too large, the stability of the catalyst decreases, and sufficient impregnation of the metal material may not occur.

[0059] In one embodiment of the present invention, the degree of H2 chemisortion dispersion of the composite catalyst for producing synthesis gas containing hydrogen and carbon monoxide may be 1.5 to 3.5%, preferably 1.8 to 3.3%, more preferably 2.0 to 3.1%, and even more preferably 2.2 to 3.0%, and it can be seen that when the above-described range is satisfied, the dispersion of metal particles is effectively well maintained.

[0060] In one embodiment of the present invention, the composite catalyst for producing synthesis gas containing hydrogen and carbon monoxide may maintain catalytic activity of 90% or more relative to the initial level for 5 hours or more and 100 hours or less.

[0061] In one embodiment of the present invention, the composite catalyst for producing synthesis gas containing hydrogen and carbon monoxide may have a CH4 conversion rate of 80% or more and a CO2 conversion rate of 30% or more during the combined steam and dry reforming of methane (CSDRM) reaction, preferably a CH4 conversion rate of 82% or more and a CO2 conversion rate of 33% or more, more preferably a CH4 conversion rate of 85% or more and a CO2 conversion rate of 37% or more.

[0062] In one embodiment of the present invention, for a Ni / PS catalyst with a poorly developed pore structure, low conversion rates of 40% for CH4 and 10.6% for CO2 were recorded. The Ni / PS catalyst showed a tendency for the conversion rate to decrease over time, which can be attributed to the sintering of Ni particles.

[0063] In one embodiment of the present invention, it can be seen that the composite catalyst for producing synthesis gas containing hydrogen and carbon monoxide of the present invention exhibits a significantly high overall conversion rate, and the Ni / MM-A3 catalyst of Example 3 showed the best performance by achieving CH4 and CO2 conversion rates of 92.2% and 42.4%, respectively.

[0064] In one embodiment of the present invention, the composite catalyst for producing synthesis gas containing hydrogen and carbon monoxide may have an H2 yield of 70% or more and a CO yield of 50% or more during the combined steam and dry reforming of methane (CSDRM) reaction, preferably an H2 yield of 72% or more and a CO yield of 55% or more.

[0065] In one embodiment of the present invention, the turnover frequency (TOF) of CH4 in the combined steam and dry reforming of methane (CSDRM) reaction of the composite catalyst for synthesis gas production containing hydrogen and carbon monoxide is 0.20s -1 The anomaly and CO2 rotation frequency is 0.10s. -1 Ideally, the rotation frequency of CH4 is 0.22s. -1 The anomaly and CO2 rotation frequency is 0.12s. -1 It may be above, and the above rotation frequency may be calculated by the following chemical formula. Here, CH4 or CO2 conversion, molar weight of silver and nickel, It represents the metallic dispersion of nickel.

[0066] [Chemical Formula 10]

[0067]

[0068] In one embodiment of the present invention, a method for producing a composite catalyst for producing synthesis gas containing hydrogen and carbon monoxide may be included, wherein the method comprises the steps of: preparing polystyrene nanobeads; manufacturing a porous support using the polystyrene nanobeads by an evaporation-induced self-assembly (EISA) method; impregnating a metal material onto the surface or interior of the porous support; drying the porous support impregnated with the metal material; calcining the dried porous support; and wherein the metal material is a metal element, a metal oxide, or a combination thereof.

[0070] A second aspect of the present invention provides a method for producing a synthesis gas containing hydrogen and carbon monoxide, comprising the steps of: raising the temperature of a reactor; pre-mixing two or more reaction gases selected from the group consisting of methane (CH4), carbon dioxide (CO2), water (H2O), and nitrogen (N2); providing the catalyst of claim 1 inside the reactor and reducing the catalyst; introducing the pre-mixed reaction gas into the reactor and reacting it with the reduced catalyst; and obtaining a synthesis gas containing hydrogen (H2) and carbon monoxide (CO) through the reaction.

[0072] Detailed explanations have been omitted for parts that overlap with the first aspect of the present invention; however, the content described in the first aspect of the present invention may be applied equally even if such explanations are omitted in the second aspect.

[0074] Hereinafter, a method for producing synthesis gas containing hydrogen and carbon monoxide according to the second aspect of the present invention will be described in detail.

[0076] In one embodiment of the present invention, in the step of raising the temperature of the reactor, the reactor is a fixed-bed continuous flow reactor, and a fixed-bed continuous flow reactor having an inner diameter of 10 to 14 mm and a length of 50 to 60 cm is used. The temperature may be controlled by installing a thermocouple in the center of the reactor, or by installing line heaters at the top and bottom of the reactor to raise the temperature to 150°C.

[0077] In one embodiment of the present invention, the reaction gas may be pre-mixed at a temperature of 200 to 300°C using a mixing chamber before being supplied into the reactor.

[0078] In one embodiment of the present invention, after the step of pre-mixing the reaction gas, a pressure sensor may be installed at the rear of the reactor to monitor the pressure drop.

[0079] In one embodiment of the present invention, the catalyst of claim 1 may be placed in the center of a reactor through a 1 mm quartz filter and then reduced at a flow rate of 50 mL / min for 1 to 3 hours at a temperature of 600 to 800°C under 10% H2 / N2 conditions.

[0080] In one embodiment of the present invention, in the step of introducing the pre-mixed reaction gas into the reactor to react with the reduced catalyst, the reaction gas may be supplied having a molar ratio of CH4:CO2:H2O:N2 of 1:0.3 to 1.1:0.8 to 1.4:0.8 to 1.6, and the total flow rate may be controlled by a mass flow controller (MFC) to be 80 to 120 mL / min. At this time, the N2 gas may be used as a balance gas during the pretreatment process and the reforming reaction.

[0081] In one embodiment of the present invention, the step of introducing the pre-mixed reaction gas into the reactor to react with the reduced catalyst comprises a temperature range of 700 to 900°C and a weight-hourly space velocity (WHSV) of 20,000 h -1 , it may be performed under atmospheric pressure, and subsequently obtain a synthesis gas containing hydrogen (H2) and carbon monoxide (CO).

[0083] Hereinafter, embodiments of the present invention are described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0085] Comparative Example 1: Ni / PS catalyst

[0086] Macropores were formed using polystyrene nanoparticles as templates. Synthesis was performed using an emulsion polymerization method without an emulsifier. To prepare spherical structures, 25 mL of styrene, 4.75 mL of divinylbenzene as a crosslinking agent, and 0.086 g of purified potassium persulfate as an initiator were added to 250 mL of deionized water. The synthesized solution was then continuously stirred at 200 rpm for 15 hours at 70°C under nitrogen conditions. The resulting white solution was dried in an oven at 60°C for 72 hours to obtain 450 nm polystyrene beads.

[0087] The above polystyrene beads were impregnated with nickel (Ni) as a metallic material.

[0088] The Ni / PS catalyst utilizes polystyrene (PS) without mesopores as a support material and exhibited a crystalline structure distinct from the other four catalysts.

[0090] Example 1: Ni / MM-A (No. 1)

[0091] Macropores were formed using polystyrene nanoparticles as templates. Synthesis was performed using an emulsion polymerization method without an emulsifier. To prepare spherical structures, 25 mL of styrene, 4.75 mL of divinylbenzene as a crosslinking agent, and 0.086 g of purified potassium persulfate as an initiator were added to 250 mL of deionized water. The synthesized solution was then continuously stirred at 200 rpm for 15 hours at 70°C under nitrogen conditions. The resulting white solution was dried in an oven at 60°C for 72 hours to obtain 450 nm polystyrene nanobeads.

[0092] Meso-macroporous alumina supports (MM-A) were synthesized by the evaporation-induced self-assembly (EISA) method. For the synthesis of the MM-A supports, 3 g of Pluronic P123 and 6 g of aluminum iso-propoxide were added to 50 mL of ethanol to ensure complete dissolution at room temperature. Next, 4 mL of nitric acid was added to the solution, and the mixture was vigorously stirred until the Al precursor was completely dissolved. The degree of etching (pore formation) varied depending on the amount of nitric acid added. Subsequently, 3 g of polystyrene beads were added to the solution and stirred for 1 hour. The sample was dried at 60°C for 4 days, causing the white solution to turn into a yellowish-orange solid. Finally, the obtained sample was slowly heated from room temperature to 700°C (1°C / min) and calcined in air at 700°C for 3 hours. Here, the weight of aluminum iso-propoxide was intended to control the bimodal pore framework, and these weights were synthesized by adjusting the PS / Al weight ratio to 0.5.

[0093] Nickel (Ni) was impregnated as a metallic material onto the above-prepared MM-A support using the incipient wetness impregnation (IWI) method. First, the synthesized MM-A support was dissolved in 100 mL of deionized water by stirring at room temperature. Then, a Ni(NO3)2-6H2O precursor containing 12 wt.% Ni was added and stirred for 5 hours. Subsequently, the deionized water was completely removed from the mixture using a rotary evaporator at 100 rpm and 60°C, and the sample was dried overnight in an oven at 60°C. The obtained sample was calcined in air at 700°C (5°C / min) for 3 hours and designated as Ni / MM-A (No. 1). Here, No. indicates the order of the synthesized PS / Al weight ratio.

[0095] Example 2: Ni / MM-A (No. 2)

[0096] The step of preparing the polystyrene nanobeads is the same as in Example 1.

[0097] The step of synthesizing a meso-macroporous alumina support (MM-A) by the evaporation-induced self-assembly (EISA) method involves aluminum iso- Pro The procedure is identical to Example 1 except for the addition of 3g of aluminum iso-propoxide. Here, the weight of aluminum iso-propoxide was intended to control the bimodal pore framework, and the synthesis was performed by adjusting the PS / Al weight ratio to 1.0.

[0098] The step of impregnating the above-prepared MM-A support with nickel (Ni) as a metallic material using the incipient wetness impregnation (IWI) method is the same as in Example 1. Here, No. indicates the order of the synthesized PS / Al weight ratio.

[0100] Example 3: Ni / MM-A (No.3)

[0101] The step of preparing the polystyrene nanobeads is the same as in Example 1.

[0102] The step of synthesizing a meso-macro porous alumina support (MM-A) by the evaporation-induced self-assembly (EISA) method is the same as in Example 1, except that 1.5 g of aluminum iso-propoxide is added. Here, the weight of aluminum iso-propoxide was intended to control the bimodal pore framework, and the synthesis was performed by adjusting the PS / Al weight ratio to 1.5.

[0103] The step of impregnating the above-prepared MM-A support with nickel (Ni) as a metallic material using the incipient wetness impregnation (IWI) method is the same as in Example 1. Here, No. indicates the order of the synthesized PS / Al weight ratio.

[0105] Example 4: Ni / MM-A (No. 4)

[0106] The step of preparing the polystyrene nanobeads is the same as in Example 1.

[0107] The step of synthesizing a meso-macro porous alumina support (MM-A) by the evaporation-induced self-assembly (EISA) method is the same as in Example 1, except for adding 1.5 g of aluminum iso-propoxide. Here, the weight of aluminum iso-propoxide was intended to control the bimodal pore framework, and the synthesis was performed by adjusting the PS / Al weight ratio to 2.0.

[0108] The step of impregnating the above-prepared MM-A support with nickel (Ni) as a metallic material using the incipient wetness impregnation (IWI) method is the same as in Example 1. Here, No. indicates the order of the synthesized PS / Al weight ratio.

[0110] Experimental Example 1: XRD Analysis

[0111] X-ray diffraction (XRD; Rigaku, Japan) was performed to determine the crystal structure and crystal size of the catalyst. The diffraction analyzer pattern was operated at 15 mA and 30 kV with Cu Kα radiation (λ = 1.5406 Å) over a 2θ scanning range from 10° to 80°. All comparative and exemplary examples were measured with a step size of 0.01° and a counting time of 1 second per step. The average crystal size d(NiO) on the NiO phase was calculated from Scherrer's equation as shown in Formula 1.

[0112]

[0114] Here, λ is the line wavelength of CuK (λ = 1.5406 Å), β is half the intensity of the highest linear expansion, and θ is the Brag diffraction angle. The size of the NiO metal crystal (nm) was estimated as the relative molar volumes of the NiO solid phase and the NiO solid phase as shown in Chemical Formula 2 below.

[0115]

[0117] Figure 1 shows the XRD patterns of the Ni / PS and Ni / MM-A (1-4) catalysts before the reaction, respectively. First, five sharp diffraction peaks were observed for the Ni / PS catalyst, and three peaks at 36°, 52°, and 77° can be attributed to the NiO phase, which is the main active site. The Ni / PS catalyst utilizes PS without mesopores as a support material and exhibited a crystalline structure distinct from the other four catalysts. The three first-order diffraction peaks observed for the Ni / MM-A (1-4) catalyst were at 36.5°, 46.2°, and 68.2°, indicating the presence of NiAl2O4 with a spinel structure. The peak shapes in the diffraction patterns did not show significant differences, and the NiAl2O4 structure matched well with the XRD patterns of the conventional method. The presence of the spinel structure can induce the redistribution of nickel ions between the octahedral and tetrahedral regions, which indicates the mobility of nickel within the framework. Furthermore, its excellent thermal stability imparted durability to the catalyst, contributing to overall stability. The three catalysts, including Ni / MM-A2, exhibited distinct diffraction peaks, indicating the presence of NiO as the primary active site. In particular, additional peaks were observed at 31° and 60° in the Ni / MM-A3 catalyst. This suggests that it possesses superior catalytic activity compared to the Ni / MM-A1 catalyst, as it has two main active sites. The Ni / MM-A4 catalyst showed the absence of a spinel structure; instead, a θ-Al2O3 structure was present. The observation of the theta phase in the support is considered to be due to a modification within the support structure. It appears that the amount of -OH groups decreased because a relatively small amount of aluminum isopropoxide, used as the Al precursor in the prepared catalyst, was added. Typically, the boehmite-to-gamma phase (γ-Al2O3) transition occurs at temperatures above approximately 400°. In contrast, the prepared Ni / MM-A catalyst was calcined at 700°C, but no peak corresponding to the theta phase was observed, while a gradual peak corresponding to the gamma phase was observed.This can be interpreted as being advantageous for the stabilization of metal particles due to the mesopore effect of hydroxyl-rich alumina. In conclusion, it was shown that while the spinel structure was not properly formed in catalysts with a relatively low Al precursor content, the spinel phase and NiO phase were observed in catalysts with a high or appropriate Al precursor content.

[0119] Experimental Example 2: N 2 - BET analysis

[0120] Surface characteristics were evaluated using a surface area analyzer (Microtrac, BELCAT II) for the nitrogen adsorption-desorption isotherms, specific surface area, and porosity of the samples. The comparative example and the example were degassed at 200°C for 2 hours under vacuum conditions prior to measurement. The specific surface area of ​​the comparative example and the example was measured by applying the BET (Brunauer-Emmett-Teller) equation. The pore size distribution of the catalyst was determined by applying the Barrett-Joyner-Halenda (BJH) method to the desorption portion of the isotherm.

[0121] Figure 2 was investigated through nitrogen isotherm adsorption-desorption studies of Ni / PS and Ni / MM-A (1-4) catalysts and summarized in Table 1. According to the IUPAC classification, the isotherms of all catalysts were observed to be unambiguous and typical Type IV hysteresis loops, and the size distribution of mesopores was determined by analyzing the desorption branching point of the ordinary isotherms. The bimodal pore catalysts prepared by the EISA method exhibit two stages at the desorption branching point.

[0122] First, large pores are found at higher pressures (P / P0 = 0.6 - 0.9), and smaller pores are revealed at lower pressures (P / P0 = 0.4 - 0.5). This was clearly evident in the nitrogen adsorption-desorption isotherm graphs. The sharp bends detected in these isotherm curves at relative pressures P / P0 of 0.6 - 0.9 indicate the presence of uniform mesopores. The tendency for sharp bends in the isotherms at relative pressures P / P0 > 0.9 indicates the presence of macropores. As expected, the polystyrene beads used as templates are removed in situ during high-temperature calcination and serve as macropores. Pore size distribution analysis measured by the Barrett-Joyner-Halenda (BJH) desorption method revealed that all catalysts exhibited relatively small pore sizes within the range of 3 to 8 nm. Furthermore, the pore size distribution curve showed the presence of macropores exceeding 60 nm, indicating that the polystyrene beads clearly act as a template.

[0123] All Ni / MM-A (1-4) catalysts, excluding the Ni / PS catalyst, were found to have well-developed bimodal pores, and there was no significant change in pore size despite varying amounts of Al precursor. The BET specific surface area and pore volume of the catalysts showed a gradual increase. This implies that the formation of the pore structure differed depending on the Al precursor content, which was judged to be better for growth into a bimodal structure. As Ni particles were impregnated, the specific surface area and pore volume decreased overall, which is inferred to be because the Ni particles partially blocked the mesopores. These observations confirm that the introduction of Ni particles led to changes in the physical properties of the bimodal pore support and the texture of the catalyst.

[0125] Experimental Example 3: SEM Analysis

[0126] Field Emission Scanning Electron Microscopy (FE-SEM; Hitachi, Regus 8220) analysis was performed to characterize the surface morphology and nickel particles of the catalyst before and after use. The catalyst was placed in carbon tape in powder form, and after osmium sputter coating, FE-SEM analysis was performed at an operating voltage range of 5.0 to 15 kV. The Ni particle content and distribution were determined by Energy-Dispersive X-ray Spectroscopy (EDS) and mapping analysis. The collected data were measured by comparing the resulting spectra with standard data stored in the system library.

[0127] Figure 3 investigates the surface morphology and particle size of catalysts prepared with different Al precursor contents by performing SEM measurements. Figure 3(a) shows a crystal image of highly ordered three-dimensional polystyrene beads with a size of 450 nm. As shown in Figure 3(bc), the pore structure of the MM-A1,2 support was non-uniform and not properly formed. It can be interpreted that the incorporation of a relatively large amount of Al precursor does not contribute to the formation of meso-macro pore frameworks. In contrast, Figure 3(de) shows a well-formed framework similar to cylindrical mesopores. In particular, the MM-A3 support appears to generate a highly organized and compact structure. Ultimately, it can be seen that an appropriate Al precursor content contributes favorably to the formation of a bimodal pore framework.

[0129] Experimental Example 4: TEM Analysis

[0130] To observe the nickel particle size and distribution on the catalyst surface with greater accuracy, a transmission electron microscope (TEM; JEOL, JEM-F200) operating at 200 kV was used. A small amount of powder sample was dispersed in ethanol and treated under ultrasonic vibration for 30 minutes. Subsequently, a drop of the suspension (0.1 mL) was placed onto a copper lattice layer (FCF-300-CU; 200 mesh) coated with a laced carbon film and dried. The particle size of Ni was statistically calculated by randomly measuring more than 50 particles from different regions. The presence of crystal planes within the solid and their characteristic reflections were analyzed using Fast Fourier Transform (FFT).

[0132] Experimental Example 5: H 2 - TPR Analysis

[0133] Temperature-programmed reduction (TPR; AutoChem II-2920) was investigated to evaluate the reduction temperature of the catalyst as well as metal-support interactions related to catalytic performance. Prior to measurements, 50 mg of comparative and example samples were loaded and mounted on the bottom of a straight quartz tube. The samples were then initially flushed at 100°C for 3 hours under a flow of high-purity He, and cooled and purged to 50°C. Reduction was performed from 50°C to 900°C under a 5% H2 / He flow at a heating rate of 5°C / min. H2 consumption was quantitatively measured by integrating the TPR profile over time using a thermal conductivity detector (TCD).

[0134] Since the reduction temperature of metallic Ni is closely related to the interaction between support materials, the reduction behavior of metallic Ni in calcined catalysts was investigated using the H2-TPR technique. As shown in Figure 4, the profiles of catalysts other than the Ni / PS catalyst exhibited two reduction peaks below 800°C, indicating the presence of two types of reducing Ni species. All reduction peaks observed in the analysis were attributed to the reduction of surface metal species coordinating with surface oxygen ions.

[0135] First, the Ni / PS catalyst exhibited NiO reduction at a significantly lower temperature (350°C) compared to other catalysts, indicating that the interaction between metallic Ni and the support was weaker. In contrast, the Ni / MM-A (1-3) catalyst showed broad peaks in two regions, reaching reduction temperatures below 600°C in the first region and below 800°C in the second region. The first region was attributed to the NiO species, and the second region was attributed to the NiAl2O4 spinel phase.

[0136] In the case of the Ni / MM-A (1-3) catalyst, which exhibits a distinct NiAl2O4 spinel phase, the reduction temperature exhibited a similar range, but a slight shift in position was observed. For the Ni / MM-A1 and 2 catalysts, the reduction temperature in the first region shifted to a lower temperature range than that of the Ni / MM-A1 catalyst, implying a gradual increase in bulk NiO species. The reduction temperature peak in the second region shifted to a higher temperature range. This suggested that an increase in the PS / Al weight ratio could lead to more pronounced development of macropores. In other words, the structure of a relatively ordered, dense support could exhibit strong interactions between the active metals. Therefore, the determination of the reduction temperature may depend on the pore structure. Consequently, the structure of the unencapsulated support exhibited not only weak interactions with Ni particles but also strong interactions with the NiAl2O4 spinel phase support. The NiAl2O4 spinel phase was formed through a solid-state reaction between Al2O3 and NiO, where NiO was incorporated into the crystal framework of Al2O3 under high temperature. Therefore, the metallic Ni reduction behavior during the formation of the catalyst's pore framework could vary depending on the Al precursor content.

[0137] The reduction temperature of the Ni / MM-A4 catalyst was observed to have shifted to a higher temperature range. This is presumed to be due to complex NiO reduction species in the gamma and theta-alumina phases as well as the NiAl2O4 spinel phase, indicating excessively strong interactions. Excessive strong interactions between the support and the catalyst can lead to degradation of catalytic performance, blocking of active sites, reduced reaction rates, and irreversibility. The observed results are consistent with the crystal structure trends of the comparative and examples, as indicated by XRD analysis.

[0139] Experimental Example 6: H 2 - Chemical adsorption analysis

[0140] H2-chemisorption (AutoChemisorption, AutoChem II 2920) was used to calculate the nickel surface area and metal dispersion of the catalyst using pulsed chemisorption and dynamic flow methods. A 50 mg sample was reduced under inert conditions at 800°C for 1 hour. Pulsed H2 chemisorption was performed at 40°C with a flow rate of 50 mL / min of a 5% H2 / Ar mixture. The Ni dispersion and surface area were determined by assuming the adsorption stoichiometry for H2 atoms as the moles of surface metal per 1 g of catalyst.

[0142] Experimental Example 7: TGA / DSC Analysis

[0143] Thermogravimetric analysis (TGA, TA instruments, SDT-Q600) was performed to quantify the coke deposited on the catalyst after use. 30 mg of the sample was placed in a ceramic crucible and dried at 100°C for 1 hour. The sample was heated from 100°C to 900°C at a constant heating rate of 5°C / min with an air flow rate of 50 mL / min. Differential scanning calorimetry (DSC, TA-DSC250) was performed to determine the enthalpy change of the catalyst after use. 5 mg of the sample was placed in a ceramic crucible, and a first scan was performed up to 520°C with an air flow rate to remove the thermal history. Subsequently, a second scan was performed within the same temperature range at a heating rate of 5°C / min, and the thermal analysis curve was measured using the scan.

[0145] Experimental Example 8: UV-VIS DRS Analysis

[0146] UV-Vis diffuse reflection spectrometer (UV-Vis DRS, SCINCO S-4100) analysis was performed to confirm the metallic state of the Ni species. The comparative example and the example were completely placed in a quartz holder, and spectra were acquired at room temperature in the wavelength range of 270–850 nm using a Varian CARY 3E dual-beam spectrophotometer and a PDA (Photo Diode Array) detector.

[0147] The optical properties of the coordination of the nickel (Ni) species used in the comparative examples and examples were investigated by DRS in the UV-Vis range of 300–850 nm. No absorption was observed in the support within the catalyst, which indicates that Ni 2+ It indicated only the sensitivity to the species. The Uv-Vis-DRS spectra of four catalysts with different Al precursor contents are shown in Fig. 5, and the spectra for all catalysts showed strong UV signals in three regions. Bands at 300–420 and 756 nm represent O in the octahedral coordination NiO lattice. 2- → Ni 2+ It was related to charge transfer and attributed to the dd transition. The appearance of the band in this region is Ni 2+ It depends on the state of coordination and aggregation, and is indirectly related to the interaction between Ni particles and the support.

[0148] On the other hand, the band in the 580–640 nm range represents tetrahedral coordination Ni 2+ It was related to species. Therefore, all Ni / MM-A(1-4) catalysts were assigned to the tetrahedral coordination of the NiAl2O4 spinel lattice and Ni 2+ The species are attributed to spin-allowed transitions. This indicated the diffusion of Ni ions into the support and their formation, where a transition occurred without a change in spin state. In the nickel aluminate lattice, specific bands exhibited absorption wavelengths in all samples, indicating diffusion into the spinel phase. In terms of relative absorption intensity, tetrahedral Ni 2+ The species is an octahedron Ni 2+ It showed stronger strength than the species.

[0149] In summary, the DRS spectrum confirmed the presence of nickel ions occupying both tetrahedral and octahedral sites following the formation of the spinel structure. The Ni / MM-A4 catalyst showed interesting observations regarding absorption capacity. The sample contained Ni located in the NiO lattice. 2+Differences were observed in the intensity of species-related bands. First, the 420 nm band shifted significantly to the left, and a new band appeared near the 341 nm wavelength. Additionally, the absorption band intensity of the peak near 756 nm showed a noticeably weakened intensity. This effectively suggests that the observed phenomenon can be attributed to the presence of Ni species contained in the θ-alumina support. Consequently, the results of XRD, H2-TPR, and DRS spectral analysis provided conclusive evidence that the dominant form of Ni species in all catalysts is the NiAl2O4 spinel phase.

[0150] catalyst N2 adsorption H2_TPR H2-chemisorbent (Chemisortion) SEM S BET (m 2 / g) V Por (cm 3 / g) D por (nm) H2 consumption (mmol / g) Dispersion (%) Pore ​​diameter (nm) Ni / PS 6.06 0.016 4.18 2.76 0.27 458.83 Ni / MMA-1 125.20 0.32 6.77 1.20 2.31 289.58 Ni / MMA-2 148.96 0.40 8.58 1.43 2.87 312.27 Ni / MMA-3 139.40 0.33 7.61 1.72 2.84 327.48 Ni / MMA-4 95.19 0.25 9.96 1.56 2.67 320.31

[0152] Experimental Example 9: Measurement of Catalyst Performance

[0153] The CSDRM reaction experiment was conducted in a fixed-bed continuous flow reactor with an inner diameter of 12 mm and a length of 55 cm. A thermocouple was installed in the center of the reactor to control the temperature, and line heaters were installed at the top and bottom of the reactor to maintain a temperature of 150°C. Pure gases (CH4, CO2, H2O, N2) were thoroughly mixed at 250°C using a mixing chamber before being supplied into the reactor. A pressure sensor was installed at the rear of the reactor to monitor pressure drop. 0.3 g of catalyst (60-80 mesh) was placed in the center of the reactor on a quartz filter made of 1 mm quartz wool. The catalyst was reduced for 2 hours at 700°C under 10% H2 / N2 conditions at a flow rate of 50 mL / min. The reaction feed was then controlled by a mass flow controller (MFC, Brooks 5850E) with a total flow rate of 100 mL / min, using CH4:CO2:H2O:N2 (1:1:1:1, 1:0.4:1.2:1.4 molar ratios). Water was supplied by a micro-syringe pump (pump, Eldex 5966), preheated to 250°C, and then fed into the mixing chamber at the top of the reactor. N2 was used as the balance gas during the pretreatment process and the reforming reaction. Catalytic experiments were conducted at a temperature range of 700 to 900°C, a weight-hourly space velocity (WHSV) of 20,000 h⁻¹, and atmospheric pressure. The resulting synthesis gas was used to separate unreacted vapor using a water condensation trap. The composition of the reacted gas effluent was analyzed using online gas chromatography (GC-7890B) with a TCD detector and a capillary column (HP-PLOT-Q).

[0154] To evaluate the performance of the sample in the CSDRM reaction, calculations were performed using the following chemical formulas 3 to 9. The conversion rates of methane and carbon dioxide were calculated based on the molar flow rates of the components at the inlet and outlet.

[0155]

[0156]

[0157]

[0158]

[0159]

[0160]

[0161]

[0162] Here, CH4, CO, and H2 represent molar flow rates, X represents the conversion, and Y represents the yield.

[0163]

[0164] Turnover frequency (TOF) is a quantitative measure representing the number of molecules converted at surface metal sites per unit of time. TOF was calculated using Formula 10, which set the gas hourly space velocity (GHSV) to 12,000 mL·h⁻¹·gcat⁻¹, taking into account the molecular residence time at the catalyst surface. Here, CH₄ or CO₂ conversion N(r), the molar weight of nickel (MNi), and metal dispersion (D) were considered. Metal dispersion was estimated by evaluating the amount of H₂ determined through H₂ chemical absorption.

[0166] Experimental Example 10: CSDRM Reaction Catalyst Performance Test

[0167] 1. Evaluation of Ni / MM-A Catalyst Activity

[0168] To investigate the activity of Examples 1 to 4 prepared according to Al precursor content, 20,000 h -1The CSDRM reaction was applied under WHSV and 800°C conditions. Considering the basic gas composition ratio, the constituent gases were composed in stoichiometric ratios (CH4:CO2:H2O = 1:1:1), and Figure 6 shows the CH4 and CO2 conversion rates, H2 / CO ratio, and TGA analysis results. The CO2 conversion rate in the CSDRM reaction is lower than the CH4 conversion rate and is in good agreement with conventional technology. Based on the thermodynamic data, the generation of CO2 is explained by the WGS (Water Transfer: CO + H2O → H2 + CO2) reaction.

[0169] Figure 6(ab) shows the CH4 and CO2 conversion rates, respectively. In the case of the Ni / PS catalyst with a poorly developed pore structure, it showed low conversion rates of 40% for CH4 and 10.6% for CO2. The Ni / PS catalyst showed a tendency for the conversion rate to decrease over time, which was attributed to the sintering of the Ni particles.

[0170] On the other hand, the Ni / MM-A catalyst showed a significantly high conversion rate overall. In this context, the Ni / MM-A3 catalyst demonstrated the best performance, achieving CH4 and CO2 conversion rates of 92.2% and 42.4%, respectively, and showed a significantly high conversion rate overall.

[0171] Therefore, it was inferred that the uniformly grown Ni / MM-A catalyst influences the activity of the CSDRM reaction. Catalytic activity increased in the order of Ni / PS > Ni / MM-A4 > Ni / MM-A1 > Ni / MM-A2 > Ni / MM-A3. Figure 6(c) shows the H2 / CO ratio produced after the CSDRM reaction. While no catalyst reached an H2 / CO ratio of 2, the Ni / MM-A3 catalyst exhibited the highest synthesis gas ratio (H2 / CO ratio 1.6). This indicates that the Ni / MM-A3 catalyst is attributable to its superior CH4 conversion performance compared to other catalysts.

[0172] The TOFs values, which represent the effect on the catalytic properties of the CSDRM reaction, were calculated. The Ni / MM-A3 catalyst exhibited the highest value of 0.26 s⁻¹, with the TOFs of CH₄ and CO₃ being 2.16 and 4.0 times higher, respectively, than those of the PS / Ni catalyst. The clearly balanced bimodal porous structure is presumed to be due to strong interactions with metallic Ni particles. Experimental results considering the basic gas composition are summarized in Table 2. During the CSDRM reaction, carbon deposition on the catalyst surface acts as a factor that degrades catalytic activity. Figure 6(d) presents the results of TGA analysis performed to determine the amount of carbon deposited on the catalyst surface after the reaction. Weight changes with temperature were divided into three regions. In the first region (50–250°C), weight loss was observed due to the evaporation of moisture and the oxidation of ash and amorphous carbon species. Subsequently, in the second region (250–500°C), weight increase was observed due to the NiO oxidation process.

[0173] Crystalline carbon in this region adheres to the surface of metallic Ni particles and becomes a major cause of catalyst deactivation. In the case of PS / Ni catalysts, this can be interpreted as significant oxidation of the metallic Ni particles. As confirmed by XRD and H2-TPR analysis results, this could be a result of weak metal-support interaction (WMSI). Under WMSI, the stability of catalyst particles may be reduced because the bond between the active metal and the support is relatively loose. Furthermore, the weak interaction between active metals under WMSI conditions can make it difficult to control the reaction.

[0174] Consequently, no significant weight loss was observed in any catalyst except for the Ni / PS catalyst, suggesting the absence of traces of carbon deposition on the catalyst surface. This is presumed to be due to the role of steam supplied in the CSDRM reaction (inhibition of carbon deposition, acceleration of gasification reaction; WGS reaction) or structural characteristics such as double-modal pores, contributing to the stability of the catalyst.

[0175] Since the Ni / MM-A3 catalyst has a well-developed pore structure and exhibits impressive performance in basic gas ratio tests, supplementary experiments were conducted to provide a synthesis gas composition suitable for optimal FT synthesis conditions. Accordingly, a stoichiometric ratio of CH4:CO2:H2O = 1:0.4:0.8 was established, which was consistent with theoretical simulations performed using HSC 7.1 Chemistry software as reported in the prior art. Figure 7 shows the CH4 and CO2 conversion rates, H2 / CO ratio, yield, and production volume after performing the CSDRM reaction.

[0176] Figure 7(a) shows the CH4 and CO2 conversion rates, recording 86.92% and 57.17%, respectively. Figure 7(b) shows the synthesis gas production after the CSDRM reaction; the H2 / CO ratio is approximately 1.99, which is close to 2, indicating suitability for FT synthesis. Figure 7(c) shows the yield and production volume, with H2 and CO yields of 72.51% and 70.89%, respectively, and production volumes of 1830.13 and 950.41. Naturally, as the synthesis gas ratio approached 2, the H2 production volume showed a difference of approximately twofold compared to the CO production volume. Consequently, it can be seen that the CO2 feed gas ratio must be lower than the basic gas composition ratio, and the steam ratio must be slightly higher than the CO2 feed gas ratio to ensure a complete forward reaction, a fact clearly demonstrated by the experimental results.

[0177] catalyst CH4 conversion rate (%) CO2 conversion rate (%) transference number(%) TOF(s -1 ) H2 / CO ratio (molar ratio) H2 CO CH4 CO2 Ni / PS 40.08 10.66 10.90 11.12 0.12 0.03 1.38 Ni / MMA-1 85.10 39.49 72.24 58.32 0.24 0.12 1.37 Ni / MMA-2 88.37 40.39 75.81 59.08 0.25 0.12 1.50 Ni / MMA-3 92.26 42.46 80.35 61.21 0.26 0.13 1.54 Ni / MMA-4 85.76 39.60 72.17 57.97 0.22 0.12 1.36

[0179] 2. Long-term catalyst test

[0180] The results of long-term experiments for stable synthesis gas production are shown in Fig. 8. The long-term experimental results showed that the gas composition changed over time, exhibiting an initial CH4 conversion rate of 86.5% and a sustained conversion rate of 83.7% at the end of the reaction, while CO2 showed an initial conversion rate of 53.4% ​​and a consistent conversion rate of 48.4%. The experimental results showed a slight decrease in the conversion rates of CH4 and CO2, which may be due to minute changes on the catalyst surface exposed to high temperatures over a long period. Nevertheless, the Ni / MM-A3 catalyst maintained high catalytic activity for 100 hours. Furthermore, it demonstrated stability in the reaction (without metal sintering or carbon deposition) and demonstrated competitive gas conversion rates, consistently generating an appropriate H2 / CO ratio of 2.

[0182] Experimental Example 11: Catalyst properties after use

[0183] Catalyst deactivation in CSDRM reactions is mainly caused by carbon deposition during the reaction. Consequently, using various analytical techniques, the characteristics of two used catalysts (short-term catalyst 5 hours: STC-5 hours and long-term catalyst 100 hours: LTC-100 hours) were compared and summarized in Table 3.

[0184] First, the XRD patterns of two used catalysts (STC-5 hours, LTC-100 hours) are shown in Fig. 9. The calcined catalysts exhibited three crystalline phases: γ2O3, NiAl2O4, and NiO, indicating that NiO was converted to the Ni metallic state in the active phase by reduction with H2. When observing the phase changes in the crystal structure of the two used catalysts (STC-5 hours, LTC-100 hours) after the CSDRM reaction, the reduction of the catalyst by H2 caused the original NiAl2O4 spinel peak to completely disappear and a metallic nickel peak to appear, implying that it can be completely reduced to NiO and Al2O3. Therefore, the NiO phase reduced by H2 exhibits an active state as NiO metal and shows distinct diffraction patterns at 45°, 54°, and 76°. Peaks assigned to graphite carbon species in the Ni-based catalyst were observed as diffraction peaks at 25° and 26°. As a result, both used catalysts (STC-5 hours and LTC-100 hours) exhibited intact NiO and Al2O3 phases without evidence of a graphite pattern, indicating the absence of carbon deposition. These findings were consistent with the TGA analysis performed in the previous section.

[0185] Nitrogen adsorption-desorption isotherm analysis was performed on two used catalysts (STC-5 h, LTC-100 h) to evaluate sample characteristics, porosity, isothermity, and BJH plots (Fig. 10). Similar to the calcined catalyst, the isotherms exhibited typical type IV hysteresis loops and showed similar trends at the desorption branching point due to relative pressure differences. However, slight deviations in the overall texture characteristics of the used catalysts were observed in the BJH measurements and BET results. Specifically, the pore sizes of the used catalysts, STC-5 h and LTC-100 h, were measured to have increased slightly from the initial size of 7.61 nm to 16.72 nm and 17.61 nm, respectively, and the BET results also indicated a slight decrease in specific surface area. This may be due to the phase change (NiAl2O4 → NiO, Al2O3) occurring as the initial catalyst is reduced by H2, as well as the prolonged exposure to high temperatures and the reaction. Considering the long-term test results of Experimental Example 10, it can be inferred that the decrease in CH4 and CO2 conversion rates may be attributed to changes in the texture characteristics of the catalyst.

[0186] To confirm the absence of carbon deposition, TGA analysis was performed on two used catalysts (STC-5 h, LTC-100 h) to quantitatively determine the carbon content, as shown in Fig. 11(a). Consistently, all regions showed the same trend, and no traces of carbon deposition were found. However, around the second region (250–500°C), a slight difference in weight loss was observed between the two used catalysts. DSC analysis was performed to evaluate the potential formation of nickel carbide intermediates, and the results are shown in Fig. 11(b). The DSC analysis revealed heat flow according to the temperature range, and no enthalpy change was observed in the second region below 350°C. It can be seen that in the CSDRM reaction, solid carbon provides various reaction pathways depending on selectivity and correlation as soon as it precipitates from the NiO layer. It is noteworthy that while the formation reaction of C(s) proceeds mainly through the highly endothermic decomposition of CH4, the resistance to carbon deposition is thermodynamically favorable at a temperature of 800°C. Therefore, this indicates that the CSDRM reaction mechanism occurred through the Ni active site rather than following the Ni3C pathway.

[0187] SEM and TEM analyses were performed to observe the behavior of metallic Ni particles, traces of carbon deposition, and the morphological structure of the metallic Ni particles in the used catalysts. The behavior of the metallic Ni particles during the CSDRM reaction could either maintain or reduce catalytic activity. In the Ni / PS catalyst, a thin oxide layer of NiO was observed in the metallic Ni particles rather than in an intact NiO state. As shown in the previous experimental examples, the decrease in the conversion rate of the Ni / PS catalyst was attributed to the sintering of metallic Ni particles during the CSDRM reaction, which was identified as a major cause of the reduced activity of the undeveloped porous catalyst. Figure 12 shows SEM images of two used catalysts (STC-5 h, LTC-100 h). As previously mentioned, the existing macropores underwent a reduction in size from the original diameter of 480 nm to less than 330 nm due to the shrinkage of the alumina framework during calcination. After the CSDRM reaction, slightly smaller pore diameters (from 327 nm to less than 130 nm) were observed in both used catalysts compared to the calcined catalyst. It can be seen that this is attributed to the phase change of NiAl2O4 and the shrinkage of the alumina framework at high temperatures. Despite some pore collapse, the macropores remained well preserved. The observed pore collapse showed a similar trend in nitrogen adsorption-desorption isotherm analysis. SEM images showed no evidence of crystalline carbon (nanowires, nanotubes, silk-like structures). Subsequently, Figure 13(ac) showed TEM images of the catalyst after use in STC-5 h. XRD analysis revealed that the pore structure of the catalyst particles (meso-macropority) was well preserved despite structural changes due to the phase change, and metallic NiO particles were also identified. In the TEM images, macropores were generally well identified, but mesopores were observed at the non-overlapping edge regions due to particle overlap (pore structures indicated by red circles).

[0188] To conduct a more comprehensive investigation into the composition and structure of the used catalyst, High Angle Annular Dark Field (HAADF) and High Resolution Transmission Electron Microscopy (HR-TEM) images were observed, and STEM-EDS mapping spectra were performed. Z-contrast analysis via HAADF-STEM provides a new perspective on the atomic structure by revealing atomic positions to facilitate sample interpretation. As shown in Fig. 13(d), the HAADF-STEM image displays a slightly sharper pore image due to the difference in contrast. Additionally, the EDS mapping spectrum confirmed a clear distinction between Al2O3 and metallic Ni particles. The metallic Ni particles did not exhibit sintering or clustering relative to the pores, and no traces of carbon deposition were observed. Fig. 13(eg) shows TEM images of the used catalyst randomly observed from the LTC-100 h sample, which underwent long-term testing. TEM analysis results confirmed that, similar to the STC-5 h sample, the macro and mesopore structures (non-overlapping edge regions) were well preserved and metallic Ni particles were identified. Figure 13(h) presents a clearer image from STEM-HAADF, and in the EDS mapping spectrum, it was observed that the metallic Ni particles were not sintered and maintained appropriate spacing near the pores. Additionally, TEM analysis was performed on two used catalysts to provide further insight into the size and distribution of the Ni particles. These observations led to the conclusion that the dispersion of the Ni particles was effectively well maintained. Consequently, the excellent stability of the metallic Ni particles was demonstrated in long-term test results, and no traces of carbon deposition were found in any of the used catalysts. It is evident that there is a difference in Z-contrast between Al2O3 and the metallic Ni particles, and the difference in contrast in the meso-macro pores was clearly distinguished by the distinct difference in mass-thickness contrast.

[0189] catalyst after use N2 adsorption XRD TGA SEM S BET (m 2 / g) V Por (cm 3 / g) D por (nm) D Ni (nm) Amount of coke (%) Pore ​​diameter (nm) STC-5 h 100.27 0.42 16.72 10.25 2.24 120.37 LTC-100 h 90.48 0.40 17.61 11.42 2.17 126.54

[0191] The foregoing description of the present invention is for illustrative purposes only, and those skilled in the art will understand that other specific forms can be easily modified without altering the technical spirit or essential features of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive. For example, each component described as a single unit may be implemented in a distributed manner, and components described as distributed may likewise be implemented in a combined form.

[0192] The scope of the present invention is defined by the claims set forth below, and all modifications or variations derived from the meaning and scope of the claims and equivalent concepts thereof should be interpreted as being included within the scope of the present invention.

Claims

Claim 1 A composite catalyst for producing synthesis gas containing hydrogen and carbon monoxide, comprising: an alumina (Al2O3) porous support having meso-macro bimodal pores; and nickel (Ni) impregnated on the surface or inside of the porous support; wherein the porous support is synthesized by evaporation-induced self-assembly (EISA) using polystyrene nanobeads with a diameter of 450 nm as a template, and wherein the porous support comprises macro pores having a diameter of 200 to 400 nm. Claim 2 A composite catalyst for producing synthesis gas containing hydrogen and carbon monoxide, characterized in that the polystyrene nanobeads in claim 1 are formed by emulsion polymerization. Claim 3 delete Claim 4 delete Claim 5 ◈Claim 5 was abandoned upon payment of the registration fee.◈ A composite catalyst for producing synthesis gas containing hydrogen and carbon monoxide, characterized in that the meso-macro pores according to Claim 1 are determined by controlling the polystyrene (PS) / aluminum (Al) weight ratio. Claim 6 delete Claim 7 A composite catalyst for producing synthesis gas containing hydrogen and carbon monoxide, characterized in that, in claim 1, a metal material is impregnated on the surface or inside of the porous support by an incipient wetness impregnation (IWI). Claim 8 In claim 1, the BET surface area of ​​the composite catalyst for producing synthesis gas containing hydrogen and carbon monoxide, measured by the Barrett-Joyner-Halenda (BJH) method, is 50 to 200 m² 2 A composite catalyst for producing synthesis gas containing hydrogen and carbon monoxide, characterized by having a content of / g. Claim 9 A composite catalyst for producing synthesis gas containing hydrogen and carbon monoxide according to claim 1, characterized in that the H2 consumption measured by the H2-TPR (Temperature-programmed reduction) of the composite catalyst for producing synthesis gas containing hydrogen and carbon monoxide is 0.5 to 2.0 mmol / g. Claim 10 delete Claim 11 A composite catalyst for producing synthesis gas containing hydrogen and carbon monoxide according to claim 1, characterized in that the degree of H2 chemisortion dispersion of the composite catalyst for producing synthesis gas containing hydrogen and carbon monoxide is 1.5 to 3.5%. Claim 12 A composite catalyst for producing synthesis gas containing hydrogen and carbon monoxide according to claim 1, characterized in that the composite catalyst for producing synthesis gas containing hydrogen and carbon monoxide maintains catalytic activity of 90% or more of the initial level for 5 hours or more and 100 hours or less. Claim 13 A composite catalyst for producing synthesis gas containing hydrogen and carbon monoxide according to claim 1, characterized in that, during the combined steam and dry reforming of methane (CSDRM) reaction of methane, the CH4 conversion rate is 80% or more and the CO2 conversion rate is 30% or more, and the H2 yield is 70% or more and the CO yield is 50% or more. Claim 14 In claim 1, for the composite catalyst for synthesis gas production containing hydrogen and carbon monoxide, the turnover frequency (TOF) of CH4 during the combined steam and dry reforming of methane (CSDRM) reaction is 0.20s -1 The anomaly and CO2 rotation frequency is 0.10s. -1 A composite catalyst for producing synthesis gas containing hydrogen and carbon monoxide, characterized by the above, wherein the rotation frequency is calculated by the following chemical formula. [Chemical Formula 10] The above CH4 or CO2 conversion, molar weight of silver and nickel, It represents the metallic dispersion of nickel. Claim 15 A method for producing synthesis gas containing hydrogen and carbon monoxide, comprising: a step of raising the temperature of a reactor; a step of pre-mixing two or more reaction gases selected from the group consisting of methane (CH4), carbon dioxide (CO2), water (H2O), and nitrogen (N2); a step of providing the catalyst of claim 1 inside the reactor and reducing the catalyst; a step of introducing the pre-mixed reaction gas into the reactor and reacting it with the reduced catalyst; and a step of obtaining synthesis gas containing hydrogen (H2) and carbon monoxide (CO) through the reaction.

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