Highly active dry reforming catalyst and method for producing same

Abstract

A dry reforming catalyst with high activity and long-term stability and a method for producing the dry reforming catalyst are disclosed. A sol-gel reaction takes place at the interface of a micelle-shaped sol-gel reaction catalyst, forming silica particles with pores. In addition, nickel or nickel oxide catalyst particles are formed in the gaps or pores of the silica by utilizing the difference in solubility in the gel state of silica.

Description

[Technical Field]

[0001] The present invention relates to a dry reforming catalyst and a method for producing the same, and more particularly to a highly active dry reforming catalyst that ensures long-term stability and a method for producing the same. [Background technology]

[0002] As the concentration of carbon dioxide in the atmosphere increases, various problems arise, and research into converting carbon dioxide into other substances is being actively conducted. Among these, the dry reforming of methane is a reaction in which carbon dioxide and methane are reacted at high temperatures in the presence of a catalyst to produce hydrogen and carbon monoxide. The synthesis gas produced by this reaction is known to have great added value, as it can be applied to reactions to synthesize various chemicals and hydrocarbons. However, the dry reforming of methane has not been put to practical use due to the instability and low activity of the catalyst.

[0003] The catalyst becomes unstable in the dry reforming reaction because it vaporizes and disappears during the reaction at high temperatures of 600°C or higher. Furthermore, the activity of catalysts decreases over time due to accelerated deactivation caused by agglomeration of catalytic metals at high temperatures, carbon deposition on the catalyst, or poisoning by other poisons that reduces the number of active sites on the catalyst.

[0004] In the case of Ni catalysts that are commercially available or under consideration for commercialization, a process has been developed to block at least a portion of the active sites on the Ni surface with sulfur to prevent carbon deposition, but this requires a complex process that requires separate, expensive metal precursors and other additives. Nevertheless, Ni catalysts used in dry reforming reactions suffer from low activity and long-term stability. Summary of the Invention [Problem to be solved by the invention]

[0005] The first technical problem to be achieved by the present invention is to provide a dry reforming catalyst in which catalyst particles are immobilized in a three-dimensional silica matrix through metal oxide bonds. The second technical object of the present invention is to provide a method for producing a dry reforming catalyst for achieving the first technical object. [Means for solving the problem]

[0006] To achieve the first technical objective, the present invention provides a dry reforming catalyst comprising: silica having a three-dimensional network structure with pores formed therein; and catalyst particles for methane reforming formed in the pores with a diameter smaller than the pores.

[0007] In order to achieve the second technical object, the present invention provides a method for preparing a dry reforming catalyst, the method comprising the steps of: mixing a sol-gel catalyst, a nickel precursor, and water to prepare a first precursor solution in which the sol-gel catalyst is suspended in droplets or micelles; adding a silane precursor solution to the first precursor solution to form a silica solution in which network-structured silica particles are formed; removing water from the silica solution to form silica gel; and adding a second precursor solution to the silica gel to form a nickel-silica solution in which nickel particles are formed within the network-structured silica particles. [Effects of the Invention]

[0008] According to the present invention, catalyst particles for dry reforming of methane are formed. The catalyst particles are formed inside silica and within nano-sized pores. Nickel atoms supplied from a precursor are covalently bonded to oxygen atoms of silica produced by a sol-gel reaction during the synthesis process. Furthermore, in a subsequent process, nickel precipitates at the nickel-oxygen covalent bond sites due to differences in solubility. Furthermore, as the sintering process progresses, nickel metal may be partially oxidized on the surface, forming nickel or nickel oxide catalyst particles. The catalyst particles formed within the pores of silica, which has a relatively high density and a consistent pore size, ensure long-term stability and maintain a high conversion rate during the dry reforming reaction of methane. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a flow chart illustrating the method for producing a dry reforming catalyst of the present invention. [Figure 2] FIG. 2 is an image showing the dry reforming catalyst according to Preparation Example 1 of the present invention. [Figure 3] FIG. 3 shows a TEM image and an EDX image of the dry reforming catalyst according to Preparation Example 1 of the present invention. [Figure 4] FIG. 4 is a distribution diagram showing the size of nickel or nickel oxide in the dry reforming catalyst shown in FIG. [Figure 5] FIG. 5 is an image showing the powder phase of Comparative Production Example 1. [Figure 6] FIG. 6 is a graph showing XRD patterns of the dry reforming catalysts according to Preparation Example 1 of the present invention and Comparative Preparation Example 1. [Figure 7] FIG. 7 is an image showing the powder phase of Comparative Production Example 2. [Figure 8] FIG. 8 is an image showing the powder phase of Comparative Production Example 3. [Figure 9] FIG. 9 is a graph showing the size distribution of nickel or nickel oxide in the powder phase shown in FIG. [Figure 10] FIG. 10 is an image showing the powder phase of Comparative Production Example 4. [Figure 11] FIG. 11 is a graph showing the conversion rates of Preparation Example 1 and Comparative Preparation Example 1 measured by Measurement Example 1 of the present invention. [Figure 12] FIG. 12 is a graph showing the results of a long-term stability test of a dry reforming catalyst according to Measurement Example 2 of the present invention. [Figure 13] FIG. 13 is a TEM image showing the results of a long-term stability test of a dry reforming catalyst according to Measurement Example 2 of the present invention. [Figure 14] FIG. 14 is a graph showing the results of thermogravimetric analysis of the dry reforming catalyst according to Measurement Example 3 of the present invention. BEST MODE FOR CARRYING OUT THE INVENTION

[0010] The present invention can be modified in various ways and can have various forms, and specific embodiments are illustrated in the drawings and described in detail herein. However, this is not intended to limit the present invention to the specific disclosed form, and it should be understood that the present invention includes all modifications, equivalents, and alternatives within the spirit and technical scope of the present invention. Like reference numerals are used to refer to like elements throughout the drawings.

[0011] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Terms as defined in commonly used dictionaries should be understood to have a meaning consistent with the meaning they have in the relevant art, and should not be understood as idealized or overly formal unless expressly defined in this application.

[0012] Preferred embodiments of the present invention will now be described in more detail with reference to the accompanying drawings. Embodiment FIG. 1 is a flow chart illustrating the method for producing a dry reforming catalyst of the present invention.

[0013] 1, a first precursor solution is prepared by mixing a sol-gel catalyst, a nickel precursor, and water (S100). The first precursor solution is a nanoemulsion or microemulsion in which the sol-gel catalyst exists in the form of droplets or micelles in water. However, the nickel precursor may be dispersed within the droplets of the sol-gel catalyst or may be dispersed within the water.

[0014] The sol-gel reaction catalyst preferably has hydrophobic properties and the physical properties of a silicate sol-gel reaction catalyst. Furthermore, the sol-gel reaction catalyst is more preferably a substance that can be used as an organic ligand that can control the crystal growth of metal. For example, oleic acid can be used as the sol-gel reaction catalyst.

[0015] Furthermore, it is preferable to use Ni(NO3)2·6H2O as the nickel precursor, and it is preferable that the water be deionized water. First, a sol-gel catalyst and a nickel precursor are mixed and stirred at 150-250°C for 1-3 minutes to prepare a preliminary precursor solution. If the temperature during mixing is below 150°C, the nickel precursor will not be uniformly dispersed in the sol-gel catalyst, or Ni ions will not be sufficiently formed. Furthermore, if the temperature during mixing exceeds 250°C, the high temperature can increase the amount of volatilization of the sol-gel catalyst.

[0016] The container containing the preliminary precursor solution is placed in a water bath at 60°C to 90°C, and water is added to the preliminary precursor solution. The water is preferably deionized water. The water is preferably added while the preliminary precursor solution is being stirred. Through this, the hydrophobic sol-gel reaction catalyst is suspended in the water in the form of fine droplets or micelles, forming a first precursor solution. The fine droplets or micelles are composed of the hydrophobic sol-gel reaction catalyst, and nickel ions or nickel precursors are dispersed within the micelles. Nickel ions or nickel precursors may also be dispersed within the water in a nanoemulsion or microemulsion.

[0017] Next, a silane precursor solution is added to the first precursor solution to form silica having a three-dimensional network structure, thereby producing a silica solution in which silica particles having a three-dimensional network structure are formed in a solution containing water (S200). The three-dimensional network structure silica is formed by a sol-gel reaction, and a silane precursor solution is prepared in advance for the sol-gel reaction.

[0018] The silane precursor solution contains a silane precursor and a silane coupling agent. The silane precursor primarily forms a three-dimensional network structure of silica through a sol-gel reaction. To achieve this, the silane precursor must have silicon (Si) as the central metal and an alkoxy group OR (R is an alkyl group) that forms a covalent bond with silicon. The silane precursor may be tetraethyl orthosilicate (TEOS), methyltrimethoxysilane (MTMS), or tetramethyl orthosilicate (TMOS), with TEOS being preferred.

[0019] The silane coupling agent must have silicon as the central metal, an alkoxy group that forms a covalent bond with silicon, and a structure that can bond with metals or organic molecules via other reactive groups that bond to the central metal. The silane coupling agent chemically bonds with nickel metal, improves compatibility with silane precursors, and chemically bonds with the silane precursors.

[0020] Therefore, the silane precursor may have a relatively uniform distribution by the silane coupling agent, and may form a three-dimensional network structure of silica. As the silane coupling agent, APTES (amonipropyl triethoxysilane) is preferred.

[0021] When the silane precursor solution is introduced into the first precursor solution, a sol-gel reaction occurs at the interface of the sol-gel catalyst, which can be explained as a hydrolysis reaction and a condensation polymerization reaction.

[0022] When the silane precursor or silane coupling agent in the silane precursor solution comes into contact with the interface of the sol-gel reaction catalyst, the following hydrolysis reaction and condensation polymerization reaction occur: Since the silane precursor or silane coupling agent has an alkoxysilyl group Si-OR (R is an alkyl group), the sol-gel reaction occurs according to the following reaction formula:

[0023] [Reaction Scheme 1] -Si-OR+H2O → -Si-OH+ROH [Reaction Scheme 2] -Si-OR+HO-Si-→-Si-O-Si-+ROH [Reaction Scheme 3] -Si-OH+HO-Si→-Si-O-Si-+HO The reaction formula 1 is a hydrolysis reaction, and the reaction formulas 2 and 3 are condensation polymerization reactions.

[0024] Due to the compatibility of the silane coupling agent, the three-dimensional network structure formed by the sol-gel reaction has voids with a relatively uniform distribution, and the silica particles formed by the micelle-form sol-gel reaction catalyst have a micron size.

[0025] In addition, the silanol group Si-OH of the silane precursor or silane coupling agent generated by the hydrolysis of Reaction Scheme 1 can bond with nickel ions or nickel precursors in the first precursor solution to form a Si-O-Ni structure. The bond between oxygen and nickel is understood to be a covalent bond, and the nickel metal bonded to oxygen can act as a seed in the subsequent precipitation and growth process of nickel metal.

[0026] Therefore, in the formed silica solution, silica particles with a three-dimensional network structure are formed, and minute voids are formed within the micro-sized silica particles. When the silica solution is maintained at 80°C for about 12 hours, water is removed and silica gel is formed (S300). Within the silica gel, nickel can be bonded to Si-O-Ni and can be randomly distributed within the silica network.

[0027] Next, a second precursor solution is added dropwise to the silica gel to form a nickel-silica solution (S400). The second precursor solution has a higher concentration of nickel precursor than the first precursor solution. The second precursor solution uses water as a solvent and Ni(NO3)2·6H2O as the nickel precursor. In particular, the second precursor solution may have a higher concentration of nickel than that distributed within the silica gel, and nickel ions migrate into the silica gel.

[0028] The addition of the second precursor solution converts the silica gel into a sol state, and nickel metal aggregates and precipitates within the nickel-silica solution due to the difference in solubility. That is, the nickel ions distributed within the silica gel are converted from a gel state to a sol state when the second precursor solution, which has a higher nickel concentration, is added. To maintain uniform nickel solubility within the sol, the nickel within the silica gel precipitates as particles within the silica. However, the aggregation and precipitation occur within the voids or pores within the three-dimensional network structure of the silica particles, which can bond with the silanol groups (Si-OH) of the silane precursor or silane coupling agent to form Si-O-Ni bonds. These aggregate or precipitate on the Si-O-Ni bonds already formed in the silica solution, forming single or polycrystalline nickel metal.

[0029] However, since silanol groups and the like may remain in the precursor solution, oxygen atoms may bond to the nickel metal that aggregates or precipitates, and Ni-O bonds may be formed internally.

[0030] In addition, during the deposition of nickel metal, oleic acid, a catalyst for the sol-gel reaction, acts as a regulator that controls the growth of the deposited nickel metal. Therefore, the size of the deposited nickel metal can be controlled by adjusting the concentration or amount of oleic acid.

[0031] Through the above process, nickel nanoparticles are formed that are chemically bonded, such as by covalent bonding, within the silica of a three-dimensional network structure. Next, water used as a solvent is evaporated or dried from the nickel-silica solution to obtain a powder phase, which is then calcined in an air atmosphere at 600-900°C to obtain a dry reforming catalyst (S500). The resulting dry reforming catalyst is in a powder phase, and within the silica particles with a three-dimensional network structure, nickel atoms of the nickel nanoparticles or nickel atoms of the nickel oxide nanoparticles form covalent bonds with oxygen atoms of the silica particles. Furthermore, during the calcination in an air atmosphere, some of the nickel particles may be oxidized to form nickel oxide. This is a variable that can be changed depending on the time of the calcination process and the type of atmospheric gas, so the catalyst particles produced in the present invention correspond to nickel or nickel oxide.

[0032] Manufacturing Example 1 A preliminary precursor solution is formed by mixing 2 mmol of oleic acid, a catalyst for the sol-gel reaction, with 0.2094 g (0.7 mmol) of the nickel precursor, Ni(NO)3)2·6H2O. The preliminary precursor solution is stirred at 200°C for 2 minutes to dissolve the nickel precursor. Next, 70 ml of deionized water is added to the preliminary precursor solution and stirred for 3 minutes. While adding deionized water and stirring, the preliminary precursor solution is heated to 80°C in a water bath. This forms a first precursor solution. The first precursor solution is in the form of green fine droplets or micelles dispersed in deionized water. Nickel ions or nickel precursors are dispersed within the micelles.

[0033] Next, a silane precursor solution was prepared using 7.35 g (35 mmol) of TEOS as the silane precursor and 1.341 g (6 mmol) of APTES as the silane coupling agent. The resulting silane precursor solution was added to the first precursor solution to form a silica solution. The synthesis of pale white silica with a network structure was observed from the silica solution. The silica solution was stirred in a water bath at 80°C for 12 hours to form silica gel.

[0034] Next, the second precursor solution is added dropwise to the silica gel. The second precursor solution is prepared by mixing 0.419 g (1.4 mmol) of Ni(NO)3)2·6H2O with 6 ml of deionized water. The mixture is stirred in a water bath at 80°C for 12 hours while the second precursor solution is added dropwise. A powder phase is then obtained through a drying process. The powder phase is then calcined at 800°C to produce the dry reforming catalyst.

[0035] Comparative Manufacturing Example 1 Commercially available fumed silica was purchased. 2.4 g of the silica was then immersed in a Ni(NO)3)2·6H2O solution, adjusting the amount of the precursor solution to correspond to 10 wt% nickel. After immersion, the silica was calcined at 800°C to coat the silica network with nickel or nickel oxide.

[0036] Comparative Manufacturing Example 2 The powder phase was formed using the same process as in Preparation Example 1, but oleic acid, which is a catalyst for the sol-gel reaction, was not added.

[0037] Comparative Manufacturing Example 3 The powder phase was formed using the same steps as in Preparation Example 1, but the addition of TEOS, a silane precursor, was omitted.

[0038] Comparative Manufacturing Example 4 The powder phase was formed using the same steps as in Production Example 1, but the addition of the silane coupling agent APTES was omitted.

[0039] FIG. 2 is an image showing the dry reforming catalyst according to Preparation Example 1 of the present invention. Referring to Figure 2, the image using a 200 nm scale bar confirms the formation of a three-dimensional network structure of silica. It also confirms the formation of nickel or nickel oxide in the voids within the silica network. The dark spherical images represent nickel or nickel oxide formed within the three-dimensional network structure, and do not appear as clear images due to their formation within the silica. However, the image using a 10 nm scale bar confirms the formation of nickel or nickel oxide within the voids of the three-dimensional network structure of silica. It can be seen that the formed nickel or nickel oxide has an approximately spherical shape and is uniformly distributed within the silica.

[0040] FIG. 3 shows a TEM image and an EDX image of the dry reforming catalyst according to Preparation Example 1 of the present invention. Referring to Figure 3, the presence of nickel, oxygen, and silicon in the dry reforming catalyst is confirmed. In particular, oxygen and silicon are distributed in large amounts, which can be seen to form silica. The distribution of nickel and oxygen also indicates that nickel exists as metal or in the form of nickel oxide.

[0041] FIG. 4 is a distribution diagram showing the size of nickel or nickel oxide in the dry reforming catalyst shown in FIG. 4, the average size of the spherical nickel or nickel oxide is 2 nm, and the size distribution is 0.8 nm to 3.6 nm. The distribution curve resembles a normal distribution.

[0042] FIG. 5 is an image showing the powder phase of Comparative Production Example 1. 5, it can be seen that large crystals of nickel or nickel oxide were formed on the surface of the silica, i.e., precipitates with a size of 10 nm or more appeared as a coating on the surface of the silica.

[0043] Comparing this with FIG. 2, it can be seen that the dry reforming catalyst of the present invention is uniformly distributed within the silica network structure and is formed in a form that fills the voids within the network structure, whereas the dry reforming catalyst of FIG. 5 exists in a planar form on the surface of the silica.

[0044] FIG. 6 is a graph showing XRD patterns of the dry reforming catalysts according to Preparation Example 1 of the present invention and Comparative Preparation Example 1. Referring to Figure 6, the dry reforming catalyst of Preparation Example 1 is represented by NiES, and the dry reforming catalyst of Comparative Preparation Example 1 is represented by IMP. It can be seen that the peak intensity corresponding to nickel oxide in the catalyst of Preparation Example 1 is lower than that in Comparative Preparation Example 1. This is believed to be due to the uniform distribution of nickel oxide within the silica. It is also presumed that nickel metal is not visible in the XRD graph due to its very small size.

[0045] FIG. 7 is an image showing the powder phase of Comparative Production Example 2. 7, in the powder phase where oleic acid is not added, no silica synthesis is observed, and unknown objects with needle-like shapes are confirmed. This is because oleic acid acts as a catalyst for the sol-gel reaction to form silica, and the sol-gel reaction is not smoothly induced when oleic acid is not added.

[0046] FIG. 8 is an image showing the powder phase of Comparative Production Example 3. Referring to Figure 8, in the powder phase without the silica precursor TEOS, no silica network structure is observed. Also, some silica is formed at a very low concentration or density, and nickel or nickel oxide is formed in an irregular plate-like shape. The plate-like particles formed are relatively large.

[0047] FIG. 9 is a graph showing the size distribution of nickel or nickel oxide in the powder phase shown in FIG. Referring to Figure 9, the particle size distribution does not show a normal distribution but rather an irregular pattern. In particular, the average particle size is significantly increased compared to Figure 4, with the average particle size distributed at 25 nm and 80 nm. In other words, more than two normal distributions appear irregularly. This means that a network-like silica structure cannot be formed using only a silane coupling agent without the use of a silica precursor. However, the alkoxy groups of the silane coupling agent can form some incomplete silica, resulting in the formation of particles with a wide size range that are not dense inside or on the surface of the silica.

[0048] FIG. 10 is an image showing the powder phase of Comparative Production Example 4. 10, in the powder without the silane coupling agent APTES, the silica itself has a very irregular appearance. Furthermore, the distribution of pores within the silica or pores within the network structure is also non-uniform. Therefore, the shape and size of the nickel or nickel oxide formed on the silica are also irregular.

[0049] This is because the compatibility of silica synthesized in the absence of a silane coupling agent is reduced, and the covalent bond between the oxygen element of silica and the nickel metal does not occur smoothly. Measurement example 1 The gas reforming performance of the dry reforming catalyst prepared according to Preparation Example 1 of the present invention and the dry reforming catalyst prepared according to Comparative Preparation Example 1 was investigated. The feed gases were CO2 and CH4, and the process temperature was 500°C to 850°C. The process temperature was increased by 10°C per minute and analyzed for 1.5 hours. The conversion rate at each temperature was measured. The gas hourly space velocity (GHSV) of the feed gas was 250 L g cat h -1 is.

[0050] FIG. 11 is a graph showing the conversion rates of Preparation Example 1 and Comparative Preparation Example 1 measured by Measurement Example 1 of the present invention. Referring to FIG. 11, IMP indicates the use of the dry reforming catalyst of Comparative Preparation Example 1, and NiES indicates the use of the dry reforming catalyst of Preparation Example 1.

[0051] In Comparative Preparation Example 1, the conversion rate increases as the process temperature increases. However, when the temperature rises to 850°C, the maximum conversion rate is less than 60%. In addition, the CO2 conversion rate exceeds that of CH4. The dry reforming reaction of methane is explained in Reaction Scheme 4 below.

[0052] [Reaction Scheme 4] CH4+CO2→2H2+2CO In Reaction 4, the conversion rates of CO2 and CH4 should be the same in a normal reaction, but when IMP is used as a dry reforming catalyst, CO2 is rapidly converted from the feed gas. This is presumably due to unexplained side reactions, where a significant amount of CO2 is lost in other reactions without going through Reaction 4.

[0053] When NiES of Preparation Example 1 is used as a dry reforming catalyst, the conversion rate increases as the process temperature increases. It exhibits a much higher conversion rate than IMP, with CO2 and CH4 showing a conversion rate of over 80% at 750°C and above. This is a value that is more than 30% higher than IMP. Furthermore, CO2 and CH4 show almost the same conversion rate. This indicates that with the NiES dry reforming catalyst, Reaction 4 proceeds with other side reactions minimized. In particular, it was confirmed that the difference in conversion rate between CO2 and CH4 is less than 10% at temperatures above 700°C.

[0054] Measurement example 2 FIG. 12 is a graph showing the results of a long-term stability test of a dry reforming catalyst according to Measurement Example 2 of the present invention.

[0055] Referring to Figure 12, the long-term stability of the dry reforming catalyst prepared according to Preparation Example 1 of the present invention and the dry reforming catalyst prepared according to Comparative Preparation Example 1 was tested. The feed gases were CO2 and CH4, and the process temperature was 800°C. The gas hourly space velocity (GHSV) of the feed gas was 250 L g cat h -1 Under the above conditions, the conversion rate and the ratio of CO and H2 products are measured up to 500 hours.

[0056] First, in graph (a) of Figure 12, blue indicates the CO2 conversion rate, and red indicates the CH4 conversion rate. The dry reforming catalyst of the present invention maintains a conversion rate of over 90% even after 500 hours. However, the IMP dry reforming catalyst of Comparative Preparation Example 1 exhibits a higher CO2 conversion rate than CH4 conversion rate, and as time passes, it loses catalytic performance and enters an inactive state due to catalyst poisoning, etc. In particular, after about 50 hours, no CO2 or CH4 was converted or reformed at all.

[0057] 12(b), the molar ratio of CO to H2 was measured. The NiES dry reforming catalyst of the present invention maintained a H2 / CO ratio of over 0.95 up to 500 hours, close to 1. However, the IMP dry reforming catalyst, in which nickel or nickel oxide is coated on silica, showed a decrease in H2 / CO over time, and no reforming activity was observed after 50 hours.

[0058] FIG. 13 is a TEM image showing the results of a long-term stability test of a dry reforming catalyst according to Measurement Example 2 of the present invention. Referring to image (a) of Figure 13, the IMP dry reforming catalyst is shown to have nickel or nickel oxide coated in plate form on the silica structure before being introduced into the reforming process. After 31 hours of dry reforming of methane (DRM) under the conditions of Figure 12, nickel or nickel oxide particles migrated to the silica surface and agglomerated, increasing particle size. The rightmost image shows that carbon was deposited on the catalyst particles during the high-temperature process at 800°C, blocking the active sites of the catalyst. This suggests that the active sites of a conventional IMP dry reforming catalyst are blocked by prolonged reforming, and the area of ​​the active sites is reduced due to the agglomeration of catalyst particles.

[0059] 13 (b), it can be seen that catalyst nanoparticles are uniformly dispersed within the internal space of the silica network structure in the dry reforming catalyst of the present invention prepared in Preparation Example 1. Furthermore, the image after the methane reforming reaction was carried out at 800°C for 500 hours confirms that despite the high temperature process, no aggregation of catalyst particles due to particle diffusion or aggregation occurred, and that catalyst deactivation due to carbon deposition did not occur.

[0060] The above effect is due to the fact that the catalyst nanoparticles of the present invention form covalent bonds between oxygen and nickel within the silica having a three-dimensional network structure, and are formed within the internal pores or cavities. Measurement example 3 FIG. 14 is a graph showing the results of thermogravimetric analysis of the dry reforming catalyst according to Measurement Example 3 of the present invention.

[0061] 14, the dry reforming catalyst NiES of Preparation Example 1 did not lose weight even when heated up to 800°C. This indicates that the catalyst particles did not separate from the silica or decompose during the agglomeration process even at high process temperatures. Furthermore, no thermal decomposition due to carbon deposition was observed.

[0062] However, for the dry reforming catalyst IMP of Comparative Preparation Example 1, sustained weight loss was observed at process temperatures above 500°C. It is believed that nickel or nickel oxide did not evaporate or thermally decompose at this temperature. Despite this, weight loss occurred because the catalyst particles formed on the silica surface coarsened, leading to their detachment or removal from the silica surface. Furthermore, no further weight loss occurred at process temperatures above approximately 720°C. This is due to the completion of coarsening due to aggregation of the catalyst particles on the silica surface, followed by carbon deposition on the catalyst particle surface, forming stabilized inactive sites where no active sites exist.

[0063] The above measurement examples confirm that the dry reforming catalyst of the present invention has nickel or nickel oxide catalyst particles formed within the pores of silica with a three-dimensional network structure. The nickel atoms of the catalyst particles form covalent bonds with the oxygen atoms of the silica, allowing the catalyst particles to form within the pores within the silica and migrate to other pores, preventing coarsening of the catalyst particles. In particular, the silica with a network structure formed by the manufacturing method of the present invention has pores of uniform size and uniform distribution within the silica. This is due to the fact that the catalyst for the sol-gel reaction is formed as fine droplets or micelles in the first precursor solution. That is, because the catalyst for the sol-gel reaction is separated into micelles and has a relatively uniform size, the sol-gel reaction to form silica also occurs uniformly around the micelles. Therefore, the catalyst particles formed within the pores of the network structure can be uniformly distributed throughout the silica, ensuring long-term stability during the reforming reaction without catalyst particle aggregation or poisoning.

[0064] Table 1 below shows the measured values ​​of the surface area, pore volume and average pore diameter of the silica provided in Preparation Example 1 and Comparative Preparation Example.

[0065] [Table 1]

[0066] In Table 1, the silica of Comparative Preparation Example 4 exhibits a very high surface area. This is because the silica does not contain a silane coupling agent, and the compatibility between the silane precursor and the sol-gel catalyst during the sol-gel reaction of silica is reduced, resulting in a lack of uniform mixing and a sol-gel reaction occurring solely with the silane precursor. Therefore, the silica of Comparative Preparation Example 4 also exhibits the largest average pore diameter.

[0067] The pore volume is the largest in Comparative Preparation Example 2. In Comparative Preparation Example 2, a sol-gel reaction catalyst is not used, so a network-like silica structure to accommodate the catalyst is not properly formed. Therefore, a dense silica structure is not observed, and silica with a very large pore volume appears.

[0068] The silica of the present invention has a nano-sized average pore diameter and a very small pore volume. That is, because nano-sized pores are formed and the pore volume is small, the catalyst particles formed in the pores are prevented from diffusing or agglomerating at high temperatures. In addition, the large surface area creates a large number of nano-sized active sites, ensuring the performance and long-term stability of the catalyst.

[0069] Furthermore, the catalyst particles of the present invention have been confirmed to have an average diameter smaller than the pores because they are formed inside the pores. This is due to the intervention of oleic acid, which controls the size of nickel metal during nickel metal deposition, or due to the shrinkage of nickel metal during the final sintering process. In particular, oleic acid, which is a catalyst for the sol-gel reaction and acts as a growth regulator for nickel metal, can control the size of nickel metal during nickel metal deposition depending on the amount or concentration added. Therefore, as needed, catalyst particles can fill the silica pores and be formed inside the pores with a diameter smaller than the pores. In particular, catalyst particles formed with a diameter smaller than the pores increase the contact area with the feed gas required for conversion inside the pores, ensuring long-term stability.

[0070] The present invention discloses a nickel or nickel oxide catalyst for use in the dry reforming of methane. The catalyst particles are formed within silica, even within nano-sized pores. Nickel atoms supplied from a precursor are covalently bonded to oxygen atoms in silica produced by a sol-gel reaction during the synthesis process. In a subsequent process, nickel precipitates at the nickel-oxygen covalent bond sites due to differences in solubility. During the sintering process, nickel metal may be partially oxidized on the surface, forming nickel or nickel oxide catalyst particles. The catalyst particles are formed within silica, which has a relatively high density and a consistent pore size. Because the formed catalyst particles are smaller than the pores, a consistent spacing is formed between the pores and the catalyst particles. This increases the contact area between methane gas and the catalyst particles, ensuring long-term stability and maintaining a high conversion rate during the dry reforming of methane.

Claims

1. preparing a first precursor solution by mixing a sol-gel reaction catalyst, a nickel precursor, and water, in which the sol-gel reaction catalyst, oleic acid, is suspended in water in the form of droplets or micelles; adding a silane precursor solution containing a silane precursor and a silane coupling agent to the first precursor solution to form a silica solution in which silica particles having a network structure are formed; removing water from the silica solution to form silica gel; adding dropwise to the silica gel a second precursor solution having a nickel concentration higher than that of the first precursor solution to form a nickel-silica solution in which nickel particles are formed within the reticulated silica particles; A method for producing a dry reforming catalyst comprising:

2. 2. The method for producing a dry reforming catalyst according to claim 1, wherein the nickel particles are formed by precipitation using nickel-oxygen covalent bonds as seeds for growth.

3. 2. The method for preparing a dry reforming catalyst according to claim 1, wherein the particle size of the nickel particles is adjusted by the oleic acid.

4. The step of preparing the first precursor solution includes: mixing the sol-gel reaction catalyst and the nickel precursor to form a pre-precursor solution; mixing the water with the pre-precursor solution to form droplets or micelles of the catalyst for the sol-gel reaction suspended in the water; 2. The method for producing a dry reforming catalyst according to claim 1, comprising:

5. 2. The method of claim 1, wherein the silane precursor or the silane coupling agent forms the network-structured silica particles through a sol-gel reaction at the interface of the micelle-type sol-gel reaction catalyst.

6. 6. The method for producing a dry reforming catalyst according to claim 5, wherein silanol groups generated by hydrolysis of the silane precursor or the silane coupling agent bond with nickel ions or nickel precursors in the first precursor solution to form a Si—O—Ni structure, and the covalent bond between oxygen and nickel acts as a seed for the growth of the nickel particles.

7. The method for producing a dry reforming catalyst according to claim 1, wherein the second precursor solution is a solution of the nickel precursor in water.

8. 2. The method for preparing a dry reforming catalyst according to claim 1, wherein the catalyst for the sol-gel reaction adjusts the size of the nickel particles when the nickel particles are formed.

9. After forming the nickel-silica solution, evaporating the water from the nickel-silica solution to dry it and obtain a powder; The method for preparing a dry reforming catalyst according to claim 1, further comprising: calcining the powder at 600 to 900° C. in an air atmosphere.

10. The method for preparing a dry reforming catalyst according to claim 9, wherein at least a portion of the nickel particles are converted into nickel oxide through the calcination.

Images