Composite catalyst for preparing graphite-like carbon by cracking carbon-rich natural gas and application method of composite catalyst

Abstract

The invention discloses a composite catalyst for preparing graphite-like carbon by cracking carbon-rich natural gas and an application method of the composite catalyst, and belongs to the technical field of catalyst materials. The composite catalyst is composed of a metal matrix, a catalytic induction phase and an interface regulation phase. The catalytic induction phase is a reversible valence metal compound, and the interface regulation and control phase is selected from at least one of metal halide salt or metal carbonate. The preparation method comprises the following steps: heating a metal matrix in an inert atmosphere until the metal matrix is molten, adding a catalytic induction phase, uniformly dispersing, adding an interface regulation phase, uniformly mixing, and cooling to obtain the composite catalyst. The application method comprises the following steps: arranging a high-temperature-resistant sealed reaction section at a target production layer of a shaft, and filling the reaction section with a composite catalyst; heating to convert the composite catalyst into a molten state, and then introducing the carbon-rich natural gas into a reaction section, so that the carbon-rich natural gas is in full contact with the molten catalyst to generate cracking reaction. The composite catalyst provided by the invention overcomes the problems of easy inactivation, uncontrollable carbon structure, many side reactions and the like of the traditional catalyst.

Description

Technical Field

[0001] This invention relates to the field of catalyst materials technology, and in particular to a composite catalyst for preparing graphite-like carbon by cracking carbon-rich natural gas and its application method. Background Technology

[0002] With the large-scale development of unconventional and deep oil and gas resources, wellbore environments are increasingly characterized by complex features such as high temperature, high pressure, high carbon content, and high sulfur content. Traditional centralized surface processing methods have limitations in terms of energy efficiency, cost, and safety, necessitating the development of in-situ conversion and resource utilization technologies adapted to the extreme wellbore environment. Directly cracking carbon-rich natural gas into hydrogen and carbonaceous materials within the wellbore can reduce the surface processing load and achieve efficient on-site resource utilization, thus attracting significant attention.

[0003] This technology aims to achieve efficient separation and synergistic utilization of hydrocarbon resources. Hydrogen can be used as a clean energy source or to power downhole equipment, while solid carbon can be deposited, stored, or utilized in situ. Among these, graphite-like carbon possesses both ordered layered structure and defect characteristics, exhibiting excellent electrical conductivity, temperature resistance, corrosion resistance, and stability, making it highly valuable in energy storage, composite materials, and other fields. Directional preparation of graphite-like carbon under in-situ wellbore conditions is of great significance for improving the economics of the pyrolysis process and increasing the added value of the products.

[0004] Existing carbon production technologies primarily employ solid-state catalysts made of transition metals such as Ni, Fe, and Co. These traditional catalysts are prone to sintering and carbon deposition under high temperature and pressure, leading to deactivation and difficulty in long-term stable operation. Furthermore, traditional catalytic systems have limited ability to regulate carbon structure, resulting in products that are mostly disordered carbons such as carbon black and fibrous carbon. It is difficult to effectively control the preparation of graphite-like carbon structures and morphologies, limiting the added value of the products. Moreover, they are susceptible to poisoning in sulfur-containing, strongly reducing wellbore environments and lack adaptability.

[0005] Molten metal catalytic cracking technology has emerged in recent years. Utilizing liquid metal or alloys as the reaction medium, it can alleviate the problems of sintering and deactivation due to carbon deposition in traditional catalysts, and possesses good heat transfer and self-renewal characteristics, making it more suitable for the high-temperature and high-heat-flux environment of wellbores. However, existing molten systems mostly focus on single or binary alloys, with relatively limited functions, primarily concerned with hydrogen production rate. Research on the structural control of carbon materials is insufficient, and there are many organic byproducts, making it difficult to achieve controllable preparation of graphite-like carbon. Furthermore, single systems struggle to balance cracking activity, sulfur toxicity resistance, and carbon structure induction capabilities, still exhibiting insufficient selectivity and uncontrollable product structures in complex wellbore atmospheres. In addition, traditional molten metal cracking catalysts for methane are prone to catalyst oxidation deactivation, carbon product oxidation, and the generation of numerous organic byproducts after the introduction of carbon dioxide. Therefore, there is an urgent need to develop a catalytic system capable of achieving multiphase synergy, multi-active-center coupling, and controllable preparation of graphite-like carbon through carbon structure-induced growth in the molten state, while also catalyzing carbon dioxide cracking. Summary of the Invention

[0006] To address the problems of existing catalysts used in carbon-rich natural gas cracking technologies, which cannot controllably prepare graphite-like carbon and are prone to catalytic deactivation, this invention provides a composite catalyst for preparing graphite-like carbon from carbon-rich natural gas. This catalyst is suitable for in-situ cracking of natural gas in wellbore environments to prepare graphite-like carbon materials.

[0007] The composite catalyst for preparing graphite-like carbon by cracking carbon-rich natural gas provided by this invention is a multiphase synergistic catalyst composed of a low-melting-point metal matrix as the continuous phase, a reversible valence state metal compound as the catalytic induction phase, and a metal halide or metal carbonate as the interface regulating phase.

[0008] The metal matrix comprises at least two low-melting-point metals (melting point below 400°C) that remain stable in a liquid state at 400–1000°C. Preferably, the metal matrix is ​​selected from at least two of Sn, Bi, Ga, and In. The molten metal matrix has low carbon solubility and low metal-graphite wettability, making it difficult to form stable metal carbides, thereby facilitating the surface migration of carbon atoms and the formation of graphite-like structures.

[0009] The catalytically induced phase is a reversible valence metal compound with a particle size of 50 nm to 5 μm, preferably 100 nm to 2 μm. Specifically, the catalytically induced phase is selected from at least one oxide or sulfide of iron, cerium, tungsten, cobalt, or molybdenum. Fe occurs during the cracking reaction. 3+ / Fe 2+ Ce 3+ / Ce 4+ Co 3+ / Co 2+ Or Mo 6+ / Mo 4+ The reversible valence state transition. Preferably, the catalytic inducing phase is a binary complex of CeO2 and MoO3, or a binary complex of CeO2 and WO3, or a ternary complex of CeO2, MoO3, and WO3, added in an amount of 0.5% to 10% of the total catalyst mass. CeO2 is used to provide the reversible CeO2 valence state transition. 3+ / Ce 4+ Redox pairs, MoO3 and / or WO3 have layered lattice structures, which are used to induce sp 2 The formation of carbon structures.

[0010] The interface regulating phase is selected from at least one of metal halide or metal carbonate. Preferably, the interface regulating phase is selected from at least one of NaCl, KCl, LaCl3, MgCl2, Li2CO3, and Na2CO3, and the amount added is 0.1-5 wt% of the total catalyst mass. During the cracking reaction, the interface regulating phase forms an intermediate ionic layer between the molten metal matrix and the generated graphite-like carbon, which reduces the interfacial binding energy and improves the performance of the catalyst. 2 The orientational growth of carbon sheets has an inductive effect, promoting the continuous growth and automatic peeling of graphite-like carbon sheets.

[0011] The preparation method of the composite catalyst is as follows: The metal matrix is ​​heated to complete melting under an inert atmosphere to form a molten metal matrix. Then, a catalytic induction phase is added to uniformly disperse it in the molten metal matrix. Next, an interface control phase is added, and after mixing evenly and cooling, the target composite catalyst is obtained.

[0012] The catalytically induced phase is uniformly dispersed in a molten metal matrix at the micron or nanoscale, remaining in a suspended or semi-wetted state during the reaction. This catalytically induced phase activates the CH and CO bonds in carbon-rich natural gas molecules and induces the ordered arrangement of carbon atoms along a two-dimensional direction through its crystal structure and electronic properties, thereby promoting the formation of graphite-like carbon. Furthermore, the efficient breaking of CH and CO bonds reduces the formation of organic matter and the occurrence of side reactions. The composite catalyst maintains structural stability at temperatures ranging from 400 to 950°C.

[0013] This invention also provides a method for applying the aforementioned composite catalyst. The main steps involve placing the composite catalyst in a wellbore and performing in-situ cracking of carbon-rich natural gas at 400-950°C to produce hydrogen and graphite-like carbon. During the in-situ cracking of carbon-rich natural gas in the wellbore, the composite catalyst induces carbon to form a graphite-like carbon structure through the synergistic effects of the electron conduction capacity of the molten metal matrix, the valence state cycling of the reversible valence state metal compound, and the phase regulation effect. Simultaneously, the composite catalyst can construct microscale electrochemical reaction conditions in the wellbore environment to reduce the apparent activation energy of methane and carbon dioxide cracking.

[0014] The specific steps of the application method are as follows: (1) Arrange a high-temperature resistant sealed reaction section at the target production layer location in the wellbore of the oil and gas well, and fill the reaction section with a composite catalyst; (2) Heating is carried out by using formation temperature, wellbore auxiliary heating or a combination of both to heat the composite catalyst into a molten state and form a continuous liquid reaction environment; (3) The carbon-rich natural gas extracted from the wellbore is introduced into the reaction section so that the carbon-rich natural gas can fully contact the molten catalyst. The reaction temperature is controlled at 400-950℃ so that the methane and carbon dioxide in the natural gas can be cracked to generate hydrogen and graphite-like carbon. The graphite-like carbon is deposited or enriched in the wellbore reaction section.

[0015] To further improve the orderliness and structural controllability of carbon materials during in-situ cracking of natural gas in the wellbore, composite catalysts can be organically integrated with electrochemical regulation mechanisms to form a downhole molten multiphase synergistic catalyst system with adaptive adjustment capabilities. That is, during the cracking process in step (3), the natural potential difference formed between the wellbore casing and the formation, or an additional DC bias, is used to construct a micro-electrochemical reaction environment in the molten catalyst.

[0016] The synergistic catalytic and regulatory mechanism of the composite catalyst of the present invention is as follows: During in-situ cracking in the wellbore, the continuous phase of the molten metal matrix not only acts as a heat carrier but also constructs a micro-electrochemical environment in a localized area through the natural potential difference between the wellbore casing and the formation, or through an applied low-intensity DC bias. Methane and carbon dioxide molecules in the natural gas are adsorbed and activated at the interface between the molten metal matrix and the reversible valence metal compound. The breaking of CH bonds and CO is accompanied by electron transfer, thereby reducing the apparent activation energy of the cracking reaction. Simultaneously, the reversible valence metal compound in Fe... 3+ / Fe 2+ Mo 6+ / Mo 4+ or Co 3+ / Co 2+ The cyclical transformation between equivalent states dynamically regulates the nucleation and rearrangement of carbon atoms, suppressing the formation of amorphous carbon and promoting the formation of disordered layered graphite-like structures through carbon stacking along two-dimensional directions. The interface-regulating phase creates a highly polar ionic environment at the gas-liquid interface, which influences the formation of sp... 2 The orientational growth of carbon sheets generates an interface-induced effect, which further improves the orderliness of the resulting graphite-like carbon.

[0017] Compared with the prior art, the advantages of the present invention are: (1) The composite catalyst of the present invention constructs a multiphase synergistic system consisting of a continuous molten metal phase, a multivalent layered composite metal oxide induced phase, and a halide ion interface-regulated phase. These phases do not simply coexist during the reaction; instead, they form a dynamic synergistic relationship through interface reconstruction and functional complementarity. This enables efficient cracking of carbon-rich natural gas under high-temperature wellbore conditions and the directional reaction to generate graphite-like carbon materials. This achieves efficient utilization of carbon-rich natural gas in the wellbore and overcomes the problems of easy deactivation, uncontrollable carbon structure, and numerous side reactions inherent in traditional catalysts. The graphite-like carbon prepared has a crystallite size of 2–5 nm, and the intensity ratio (ID / IG) of the D peak to the G peak in the Raman spectrum of the graphite-like carbon is 0.68–0.95.

[0018] (2) This invention achieves effective control over the direction of graphite-like carbon generation by introducing multivalent composite metal oxides with layered lattice characteristics as carbon structure inducing phases, breaking through the traditional method that relies solely on the direct catalytic graphitization of transition metals.

[0019] (3) The halide ion-regulated phase introduced in this invention forms a stable ion interface layer in situ under high temperature conditions. This interface layer is not a simple flux or heat transfer medium, but rather reduces the interfacial bonding energy between graphite-like carbon and molten metal, causing the graphite-like carbon sheets to spontaneously peel off during the formation process, thus solving the problem of carbon covering the active interface in the molten system from the material level.

[0020] (4) The composite catalyst of the present invention can maintain structural and functional stability under high temperature, high pressure and complex atmosphere conditions in the wellbore, and realize the continuous generation of graphite-like carbon, providing a new material technology route for in-situ resource conversion and high value-added carbon material preparation in oil and gas fields.

[0021] (5) The composite catalyst of the present invention overcomes the problems of multiple side reactions, insufficient cracking and multiple organic products caused by traditional catalysts. It has high hydrogen selectivity and high carbon yield, and is suitable for oil and gas field development and application such as oil and gas well production enhancement, wellbore sealing enhancement, sand control or conductive function modification.

[0022] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0023] Figure 1 These are Raman spectra of carbon materials prepared using the catalysts of Examples 1, 2, and Comparative Example 1.

[0024] Figure 2 These are Raman spectra of carbon materials prepared using the catalysts of Examples 3 and Comparative Examples 2-6.

[0025] Figure 3These are SEM images of the carbon materials prepared in Examples 1, 2, and 3, where a, b, and c represent Examples 1, 2, and 3, respectively.

[0026] Figure 4 These are XRD patterns of the carbon materials prepared in Examples 1, 2, and 3. Detailed Implementation

[0027] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0028] Example 1 A composite catalyst for preparing graphite-like carbon from carbon-rich natural gas is prepared by the following method: Metal raw materials were weighed according to the following atomic fractions: Sn 65 at%, Bi 20 at%, Ga 10 at%, In 5 at%. The mixture was heated to complete melting under an argon atmosphere to form a molten metal matrix. CeO2, MoO3, and WO3 powders with a particle size of approximately 500 nm were then added and uniformly dispersed within the molten metal matrix. LaCl3 and KCl were then added, mixed thoroughly, and cooled to obtain a multiphase composite catalyst. The metal matrix accounted for 95% of the catalyst mass, the total amount of CeO2, MoO3, and WO3 powders accounted for 4% of the catalyst mass, and the total amount of LaCl3 and KCl accounted for 1% of the catalyst mass. The molar ratio of CeO2, MoO3, and WO3 was 2:1:1; the molar ratio of LaCl3 to KCl was 1:3.

[0029] Example 2 Based on Example 1, WO3 powder was removed while all other conditions remained the same, resulting in a composite catalyst.

[0030] Comparative Example 1 Based on Example 1, CeO2, MoO3 and WO3 powders were removed, while other conditions remained the same, resulting in a composite catalyst without a catalytic induction phase.

[0031] The composite catalysts prepared in Examples 1, 2, and Comparative Example 1 were used in natural gas cracking experiments. The three catalysts were placed in simulated wellbores, and wellbore-assisted heating was used to heat the catalysts to a molten state, creating a continuous liquid reaction environment. Then, carbon-rich natural gas was introduced under high-temperature conditions (900°C) to carry out the cracking reaction. After the reaction, the resulting carbon material was collected and its structure was characterized. Raman spectroscopy results are shown below. Figure 1As shown, the intensity ratios (ID / IG) of the D peak to the G peak of the carbon materials obtained from the catalysts of Examples 1 and 2 are 0.73 and 0.85, respectively, which are significantly lower than those of the catalyst without a catalytic induction phase in Comparative Example 1. The carbon materials obtained from the catalysts of Examples 1 and 2 are mainly graphitic carbon, but the degree of graphitization in Example 2 is lower than that in Example 1. The carbon material obtained from the catalyst of Comparative Example 1 is mainly amorphous carbon, with a significant reduction in graphitic structures, a significant decrease in carbon product yield, and the generation of a large amount of oily organic matter. This indicates that the multiphase composite catalyst of the present invention has a significant promoting effect on the directional formation of graphitic carbon and can suppress the occurrence of side reactions.

[0032] Example 3 A composite catalyst for preparing graphite-like carbon by cracking carbon-rich natural gas comprises a metal matrix accounting for 95% of the catalyst mass, Fe3O4 powder accounting for 4% of the catalyst mass, and KCl accounting for 1% of the catalyst mass. The metal matrix is ​​composed of Sn and Ga, with an atomic fraction of Sn 80 at% and Ga 20 at%. The metal matrix is ​​heated to complete melting under an argon atmosphere to form a molten metal matrix; then Fe3O4 powder with a particle size of approximately 500 nm is added and uniformly dispersed in the molten metal matrix; finally, KCl is added, and after thorough mixing and cooling, a multiphase composite catalyst is obtained.

[0033] The composite catalyst prepared in Example 3 was used in a natural gas cracking experiment. The catalyst was placed in a simulated wellbore, and wellbore-assisted heating was used to heat the catalyst to a molten state, creating a continuous liquid reaction environment. Then, carbon-rich natural gas was introduced under high-temperature conditions (900°C) to carry out the cracking reaction. During the cracking process, an additional DC bias was applied for electrochemical regulation. Specifically, during the cracking reaction, high-temperature resistant conductive electrodes were placed at the upper and lower ends of the reaction section, and a DC bias voltage of 1.0 V was applied to the molten composite catalyst system through an external DC regulated power supply at the wellhead, corresponding to a current density of approximately 5 mA·cm⁻¹. -2 Under these conditions, the molten metal matrix acts as a continuous conductive phase, forming a stable micro-electrochemical environment within the reaction zone, thereby promoting Fe... 3+ / Fe 2+ Valence cycling and two-dimensional rearrangement of carbon atoms significantly improve the order of graphite-like carbon. The resulting carbon material was collected after the reaction. Raman spectroscopy results of the carbon material are shown below. Figure 2 As shown.

[0034] The SEM test results of the carbon materials prepared in Examples 1, 2, and 3 are shown in the figure. Figure 3Where a, b, and c represent Examples 1, 2, and 3, respectively. It can be seen that all three carbon materials exhibit the layered structure characteristic of graphitic carbon. Furthermore, the XRD test results of the carbon materials prepared in Examples 1, 2, and 3 are shown below. Figure 4 XRD tests of the carbon materials obtained by the catalysts in the three examples were performed at 2 A broadened diffraction peak appeared at approximately 26°, indicating that the obtained carbon material possesses typical graphitic disordered layer structure characteristics, and there was no significant accumulation of organic matter in the reaction apparatus and carbon products. The carbon materials obtained in the three examples were all predominantly graphitic carbon, but Example 3 showed the highest degree of graphitization, followed by Example 1, and the lowest was Example 2. This demonstrates that the composite catalyst of the present invention can controllably prepare graphitic carbon materials. Moreover, the synergistic effect of this composite catalyst and electrochemical regulation can further promote the formation of graphitic structures and increase the degree of graphitization.

[0035] Comparative Example 2: Single Molten Metal Catalyst The simulated wellbore reaction section is filled only with a metal matrix, the composition of which is the same as in Example 3, without introducing a catalytically induced phase or an interface-controlled phase.

[0036] The carbon-rich natural gas was introduced under the same pyrolysis reaction conditions as in Example 3 to carry out the pyrolysis reaction. The Raman spectral results of the carbon materials are as follows: Figure 2 As shown in the figure. The results indicate that most of the solid carbon products generated in the wellbore during the pyrolysis process are disordered carbon deposits, and the resulting carbon material exhibits amorphous characteristics. The intensity ratio of the D peak to the G peak in the Raman spectrum, ID / IG, is greater than 1.4, and no obvious graphite-like microcrystalline structure was observed. The pyrolysis of methane and carbon dioxide is incomplete, resulting in a large amount of organic matter and low hydrogen yield.

[0037] Comparative Example 3: Molten metal + metal oxide with fixed valence state (no interface control phase) The composition of the metal matrix is ​​the same as that of Comparative Example 2. The metal matrix is ​​heated to complete melting under an argon atmosphere to form a molten metal matrix. Then, MgO is added at an amount of 4 wt% of the total mass of the catalyst to uniformly disperse it in the molten metal matrix. After cooling, the catalyst is obtained.

[0038] The carbon-rich natural gas was introduced under the same pyrolysis reaction conditions as in Example 3 to carry out the pyrolysis reaction. The Raman spectral results of the carbon materials are as follows: Figure 2 As shown in the figure. The results indicate that although the cracking rate of methane and carbon dioxide is higher than that of Comparative Example 2, the resulting carbon material is still mainly characterized by disordered stacking, with limited carbon atom rearrangement ability, and the graphitization degree of the obtained carbon material is low.

[0039] Comparative Example 4: Molten metal + reversible valence state metal compound (without interface control phase) The composition of the metal matrix is ​​the same as that of Comparative Example 2. The metal matrix is ​​heated to complete melting under an argon atmosphere to form a molten metal matrix. Then, Fe3O4 is added at an amount of 4 wt% of the total mass of the catalyst to uniformly disperse it in the molten metal matrix. After cooling, the catalyst is obtained.

[0040] The carbon-rich natural gas was introduced under the same pyrolysis reaction conditions as in Example 3 to carry out the pyrolysis reaction. The Raman spectral results of the carbon materials are as follows: Figure 2 As shown in the figure. The results indicate that the carbon nucleation process during the pyrolysis reaction was regulated to a certain extent, and local graphite-like microcrystals appeared in the generated carbon material. However, their orientation was poor, the proportion of graphite-like structures was limited, and the overall orderliness was significantly lower than that of Example 3.

[0041] Comparative Example 5: Molten metal + interface-controlled phase (without catalytically induced phase) The composition of the metal matrix is ​​the same as that of Comparative Example 2. The metal matrix is ​​heated to complete melting under an argon atmosphere to form a molten metal matrix. Then, KCl is added at an amount of 1 wt% of the total mass of the catalyst to uniformly disperse it in the molten metal matrix. After cooling, the catalyst is obtained.

[0042] The carbon-rich natural gas was introduced under the same pyrolysis reaction conditions as in Example 3 to carry out the pyrolysis reaction. The Raman spectral results of the carbon materials are as follows: Figure 2 As shown in the figure. The results indicate that KCl has a certain influence on the gas-liquid interface, but due to the lack of effective regulation of carbon nucleation and electron transfer processes, the generated carbon materials are still dominated by disordered carbon, with a low proportion of graphite-like structures. Compared with Comparative Example 2, the presence of the interface-regulated phase can reduce the generation of organic matter.

[0043] Comparative Example 6: The same composite catalyst as in Example 3 was used, but no additional DC bias was applied during the pyrolysis process.

[0044] Raman spectral test results of carbon materials are as follows Figure 2 As shown in the figure. The results indicate that the composite catalyst can still generate a certain proportion of graphite-like carbon, but the degree of order of the carbon material, the size of the graphite crystallites, and the Raman parameter are all lower than those in Example 3. This shows that electrochemical regulation has a significant promoting effect on improving the graphite-like structure, and the hydrogen selectivity is higher.

[0045] As can be seen from the above examples and comparative examples, the heterogeneous composite catalyst prepared by the present invention and its application method have significant and irreplaceable technical effects in the preparation of graphite-like carbon, specifically reflected in the following aspects: (1) As shown in Comparative Example 2, when only a single molten metal is used as a catalyst, disordered carbon deposition easily occurs during the cracking of methane and carbon dioxide. Carbon atoms lack an effective rearrangement mechanism, making it difficult to form a graphite-like structure. Moreover, the cracking mode of methane plus carbon dioxide produces more organic matter and side reactions compared to the traditional pure methane cracking. However, this invention, by introducing reversible valence state metal compounds and metal salt interface control phases, significantly improves the nucleation and growth pathway of carbon and suppresses the generation of side reactions, thereby generating more carbon products and hydrogen.

[0046] (2) As can be seen from Comparative Example 3, although simply introducing a fixed-valence metal oxide can improve the pyrolysis activity, it cannot substantially regulate the evolution of carbon structure. The reversible valence metal compound used in this invention participates in electron transfer and valence cycling during the pyrolysis process, effectively promoting the two-dimensional rearrangement of carbon atoms and the formation of graphite-like microcrystals.

[0047] (3) As can be seen from Comparative Examples 4 and 5, relying solely on reversible valence metal compounds or metal salt interface regulation phases is insufficient to obtain highly ordered graphite-like carbon. This invention significantly improves the proportion of graphite-like structures by coupling carbon nucleation regulation and interface orientation induction through multiphase synergy.

[0048] (4) As can be seen from Comparative Example 6, under the condition of lack of electrochemical regulation, the composite catalyst of the present invention can still generate a certain proportion of graphite-like carbon, but its degree of order and crystallite size are significantly lower than those of Example 3. This shows that the microscale electrochemical environment plays an important role in reducing the apparent activation energy of methane and carbon dioxide cracking and promoting the improvement of graphite-like structure.

[0049] In summary, this invention enhances pyrolysis activity, improves resistance to deactivation, and induces controllable growth of graphite-like carbon through the synergistic effect of a molten metal conductive continuous phase, a reversible valence state metal compound, a metal salt interface-controlled phase, and electrochemical control conditions. It also achieves high efficiency in carbon dioxide pyrolysis and carbon production while suppressing carbon dioxide oxidation and side reactions, successfully preparing a highly ordered disordered layered graphite-like carbon material. These technical effects are not simply the sum of individual technical features, but rather a comprehensive effect resulting from the synergistic effect of these features, thus fully demonstrating the significant inventiveness and substantial progress of this invention. This invention breaks through the bottlenecks of existing technologies and has significant engineering value and application prospects for promoting in-situ resource utilization in wellbore systems.

[0050] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A composite catalyst for preparing graphite-like carbon by cracking carbon-rich natural gas, characterized in that, It is composed of a metal matrix, a catalytic induction phase, and an interface regulating phase. The metal matrix includes at least two metals with melting points below 400°C. The catalytic induction phase is a reversible valence metal compound. The interface regulating phase is selected from at least one of metal halide or metal carbonate.

2. The composite catalyst for preparing graphite-like carbon by cracking carbon-rich natural gas as described in claim 1, characterized in that, The metal matrix is ​​heated to complete melting under an inert atmosphere to form a molten metal matrix. Then, a catalytic induction phase is added to uniformly disperse it in the molten metal matrix. Next, an interface control phase is added, and after mixing evenly and cooling, the target composite catalyst is obtained.

3. The composite catalyst for preparing graphite-like carbon by cracking carbon-rich natural gas as described in claim 2, characterized in that, The catalytically induced phase is selected from at least one of oxides or sulfides of iron, cerium, tungsten, cobalt, or molybdenum.

4. The composite catalyst for preparing graphite-like carbon by cracking carbon-rich natural gas as described in claim 3, characterized in that, The catalytic induction phase is a binary complex of CeO2 and MoO3, or a binary complex of CeO2 and WO3, or a ternary complex of CeO2, MoO3 and WO3, and the amount added is 0.5% to 10% of the total mass of the catalyst.

5. The composite catalyst for preparing graphite-like carbon by cracking carbon-rich natural gas as described in claim 2, characterized in that, The interface control phase is selected from at least one of NaCl, KCl, LaCl3, MgCl2, Li2CO3, and Na2CO3, and the amount added is 0.1 to 5 wt% of the total mass of the catalyst.

6. The composite catalyst for preparing graphite-like carbon by cracking carbon-rich natural gas as described in claim 2, characterized in that, The metal matrix is ​​selected from at least two of Sn, Bi, Ga, In, and Pb.

7. A method for applying the composite catalyst as described in any one of claims 1-6, characterized in that, By placing the composite catalyst in the wellbore and performing in-situ cracking of carbon-rich natural gas at 400–950°C, hydrogen and graphite-like carbon were produced.

8. The method of applying the composite catalyst as described in claim 7, characterized in that, Includes the following steps: (1) Arrange a high-temperature resistant sealed reaction section at the target production layer location in the wellbore of the oil and gas well, and fill the reaction section with a composite catalyst; (2) Heating is carried out by using formation temperature, wellbore auxiliary heating or a combination of both to heat the composite catalyst into a molten state and form a continuous liquid reaction environment; (3) The carbon-rich natural gas extracted from the wellbore is introduced into the reaction section so that the carbon-rich natural gas can fully contact the molten catalyst. The reaction temperature is controlled at 400-950℃ so that the methane and carbon dioxide in the natural gas can be cracked to generate hydrogen and graphite-like carbon. The graphite-like carbon is deposited or enriched in the wellbore reaction section.

9. The method of applying the composite catalyst as described in claim 8, characterized in that, Step (3) involves using the natural potential difference between the well casing and the formation during the pyrolysis process, or by applying an additional DC bias, to construct a micro-electrochemical reaction environment in the molten catalyst.

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