Thermocatalytic Decomposition of Methane Using Catalyst System Design and Operating Parameters to Control the Yield and Properties of Products

Abstract

Disclosed herein are aspects of a method of contacting a methane composition with a catalyst system to produce H2 and carbon co-products. In some aspects, the catalyst system comprises (i) a Ni-Cu alloy catalyst comprising Ni and Cu and (ii) a support. In some additional aspects, Ni and Cu are present in a Ni:Cu mass ratio in the range of 0 to 4.5. Also disclosed herein are aspects of a method for manufacturing the disclosed catalyst system.

Description

Cross - reference to related applications

[0001] This application claims the benefit and the priority of the filing date of U.S. Provisional Application No. 63 / 345,603, filed May 25, 2022, which is hereby incorporated by reference in its entirety.

[0002] 〔Acknowledgment of government support〕 This invention was made with government support under Contract No. DE - AC05 - 76RL01830 awarded by the U.S. Department of Energy. The government has certain rights in this invention.

Technical Field

[0003] Disclosed is a method of using a catalyst system to convert a methane composition to produce H2 and carbon co - products, which method utilizes operating parameters and tuning of the catalyst system to control the yield and form of the H2 and / or carbon co - products. Also disclosed is a method of manufacturing the catalyst system used in the method embodiments herein.

[0004] 〔Parties to a joint research agreement〕 This invention was made based on a CRADA (CRADA401) between C4 - MCP, LLC and the Pacific Northwest National Laboratory operated for the U.S. Department of Energy.

Background Art

[0005] Thermal catalytic decomposition (TCD) of methane (CH4) provides a way to produce H2 without generating CO2. Catalyst systems conventionally used in such methods often deactivate at the high temperatures typically desired for good yields using TCD. To enable widespread application of TCD, there is a need in the art for methods to produce and use catalyst systems that are stable and active at relatively high operating temperatures. Commercialization of the TCD process would also benefit from the ability to recover and sell the carbon by - products produced by the TCD process; thus, there is also a need in the art for methods to produce suitable carbon by - products of high quality and purity.

Summary of the Invention

Problems to be Solved by the Invention

[0006] Disclosed herein are embodiments of a method that includes contacting a methane composition with a catalyst system at a reaction temperature in the range of 500 °C to 700 °C to produce H2 and carbon co-products. In some embodiments, the catalyst system includes (i) a Ni-Cu alloy catalyst containing Ni and Cu, and (ii) a support, wherein the Ni and Cu are present in a mass ratio of Ni:Cu in the range of greater than zero to 4.5.

[0007] Also disclosed are embodiments of a method for manufacturing a catalyst system, which includes: i) contacting a solution containing a first metal with a support material to impregnate the support material with the first metal, thereby forming an impregnated support; ii) heating the impregnated support using a ramp temperature protocol to provide a pre-catalyst system, the ramp temperature protocol including increasing the temperature to which the impregnated support is exposed by 5 °C per minute until a final temperature of 350 °C is reached; iii) contacting the pre-catalyst system with a second metal to form a bimetal-impregnated support; and iv) heating the bimetal-impregnated support using the ramp temperature protocol to provide the catalyst system. In some embodiments, the first metal and the second metal are different from each other and are independently selected from Ni and Cu, and the first metal and the second metal provide a Ni:Cu mass ratio in the range of greater than 0 to 4.5.

[0008] The above and other objects, features, and advantages of the present disclosure will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.

Brief Description of the Drawings

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[0010] ​ Glossary of Terms The following explanations of terms and abbreviations are provided to better explain the present disclosure and to guide those skilled in the art in the implementation of the present disclosure. As used herein, "comprising" means "including", and the singular forms "a", "an", or "the" include plural references unless the context clearly dictates otherwise. The term "or" refers to a single element of the recited alternative elements or a combination of two or more elements unless the context clearly indicates otherwise.

[0011] Unless otherwise explained, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. In the practice or testing of the present disclosure, methods and materials similar or equivalent to those described herein can be used, but suitable methods and materials are described below. The materials, methods, and examples are illustrative only and not intended to be limiting. Other features of the present disclosure will be apparent from the following detailed description and the claims.

[0012] The disclosure of a numerical range should be understood to refer to each discrete point within the range including the endpoints, unless otherwise indicated. Unless otherwise indicated, all numerical values representing amounts of components, molecular weights, percentages, temperatures, times, etc. used in this specification or the claims should be understood to be modified by the term "about". Accordingly, unless implicitly or explicitly indicated otherwise, or unless the context is appropriately understood by one of ordinary skill in the art to have a more definitive configuration, the recited numerical parameters are approximations that may depend on the desired properties and / or detection limits required under standard test conditions / methods known to one of ordinary skill in the art. When distinguishing embodiments directly and explicitly from the prior art discussed, the numbers of the embodiments are not approximations unless the word "about" is recited.

[0013] Furthermore, the following description is merely exemplary in nature and is not intended to limit the scope, applicability, or configuration of the present disclosure. Various changes can be made to the described embodiments without departing from the preset scope of the present disclosure in terms of the functions and arrangements of the elements described herein. Additionally, the descriptions and disclosures provided in connection with one particular embodiment are not limited to that embodiment and can be applied to any disclosed embodiment. Further, the terms "coupled" and "associated" generally mean being coupled or connected fluidly, electrically, and / or physically (e.g., mechanically or chemically), and do not exclude the existence of intermediate elements between the coupled or associated items unless a specific contrary statement is made.

[0014] The operations of exemplary aspects of the disclosed methods and / or systems may be described in a particular, sequential order for convenience of presentation, but it should be understood that the disclosed aspects of the present disclosure may encompass orders of operations other than the particular, sequential order disclosed, unless the context clearly indicates otherwise. For example, the operations described sequentially may, in some cases, be rearranged or performed simultaneously. Additionally, the descriptions and disclosures provided in connection with one particular embodiment are not limited to that embodiment and can be applied to any disclosed embodiment.

[0015] To facilitate the consideration of various aspects of the present disclosure, the following explanations are provided for certain terms.

[0016] Carbon co-product: A solid carbonaceous product produced by the thermal catalytic decomposition (TCD) of methane (CH4) using the method according to the present disclosure.

[0017] CH4 conversion rate: CH4 conversion rate X CH4 is calculated based on the amount of CH4 reacted in the method according to the present disclosure and can be calculated using Equation (1):

Number

[0018] Carbon yield: The carbon yield Y C (t) is calculated as the cumulative weight of carbon produced per unit mass of the catalyst based on the conversion rate of CH4.

[0019] Carbon deposition rate: The carbon deposition rate is calculated as the cumulative weight of carbon produced per unit mass of the catalyst based on the conversion rate of CH4 over a specific period.

[0020] Carbon nanotube (CNT): A carbon nanotube is a cylindrical structure made of carbon atoms. Carbon nanotubes typically have diameters measured in nanometers. As used herein, this term includes single-walled CNTs (SWCNTs), double-walled CNTs (DWCNTs), multi-walled CNTs (MWCNTs), and other forms of CNTs.

[0021] Carbon nanomaterial: A carbon-based material having at least one dimension on the nanometer scale (e.g., 1 nm to 1000 nm). Examples of carbon nanomaterials include, but are not limited to, nanoparticles, fullerenes, carbon filaments, carbon nanotubes (CNTs), carbon nanofibers (CNFs), and various graphene-based materials.

[0022] CO x Free: A method described herein that does not produce measurable amounts of carbon dioxide (here, x = 2), carbon monoxide (here, x = 1), or related compounds as by-products. In some embodiments, the processes and methods disclosed herein are CO x free, CO2 free, or both. In further embodiments, CO xFree and CO2-free processes are environmentally friendly because they do not emit excessive greenhouse gases into the atmosphere.

[0023] Official weight: The amount of metal (e.g., Cu or Ni) normally present in the alloy catalysts disclosed in this specification. In some embodiments, the official weight of the metal in the alloy catalyst may be different from the measured amount of the alloy catalyst, but usually it is not an amount that will have a harmful effect on the properties of the alloy catalyst. The values of the mass ratios in this disclosure are based on the official weights unless otherwise specified.

[0024] Sequential impregnation: A process of sequentially applying different metal species to a support material (e.g., the surface of the support material). This process includes sequentially depositing one or more layers of a first metal species on the support material, followed by depositing one or more layers of a second metal species. As used in this specification, sequential impregnation is different from the solvothermal method (ST).

[0025] I D / I G Ratio: The ratio of the intensity of the D band (I D )(1340 cm -1 ) measured using Raman spectroscopy to the intensity of the G band (I G )(1580 cm -1 ).

[0026] I G’ / I G Ratio: The ratio of the intensity of the G' band (I G’ )(2700 cm -1 ) measured using Raman spectroscopy to the intensity of the G band (I G )(1580 cm -1 ).

[0027] II. Introduction The thermal catalytic decomposition (TCD) of methane (CH4) produces hydrogen (H2) and forms solid carbon as a by-product. TCD provides a way to produce H2 without generating CO2. Therefore, fossil fuel (methane) can be converted to H2 and utilized without increasing greenhouse gas emissions. Catalytic systems for the TCD reaction have been studied; however, deactivation of the catalytic system remains an issue for methane TCD because conventional catalytic systems often deactivate at temperatures desirable for optimal TCD yields (e.g., above 600 °C). For example, conventional nickel-based catalytic systems deactivate because the active sites are blocked by undesirable graphite-like carbon. Bimetallic catalytic systems such as NiPd have been used for TCD, but due to the expensive nature of the Pd component, they cannot be used in commercial / large-scale operations. Also, conventional TCD methods have not been able to produce by-products suitable for other applications, such as carbon-based by-products that could potentially be used as materials for methods other than the TCD process.

[0028] The present disclosure is directed to a method of using a catalytic system tailored for TCD that enables the continuous production of CO2-free H2 and further produces carbon co-products with tunable properties. The catalytic system used in the disclosed method includes a Ni-Cu bimetallic catalyst specially designed to have an appropriate Ni:Cu ratio to improve the TCD yield at high temperatures. The disclosed method further provides the ability to utilize the catalytic system and operating parameters to control the production and morphology of isolable carbon co-products generated during TCD. Additionally, the methods described herein utilize controlled metal particle sizes and / or operating temperatures to affect the TCD yield and / or the properties of the carbon co-products.

[0029] In certain aspects of the present disclosure, the relationship between catalyst system deactivation, sintering of metal particles, increase in Ni:Cu ratio, and / or selection of operating temperature is described and can be used to improve the output of the process (e.g., increase in H2 and / or carbon co-product yield, and / or control / adjustment of the form and / or identity of the carbon co-product). For example, a single-metal Ni / CNT catalyst system rapidly deactivates at an operating temperature >550 °C; however, the inventors of the present disclosure have found that increasing the amount of Cu added to the Ni catalyst system increases the stability of the catalyst system. Further, the Ni catalyst system having the Cu loading amount described herein promotes the stability of the catalyst system at high operating temperatures (e.g., >650 °C).

[0030] Also, as described herein, by selecting a specific Ni:Cu ratio and / or operating temperature, the quality of the carbon co-product can be adjusted. The carbon co-product is mainly composed of multi-walled carbon nanotubes (MWCNTs). The inventors have found a way to control parameters such as the amount of Cu added and the operating temperature to positively affect the quality of the carbon co-product and the stability of the catalyst system.

[0031] III. Method of Using the Catalyst System Disclosed herein is a method of using a catalyst system to convert a methane composition to produce H2 and a carbon co-product, and adjusting the product yield and / or the form / quality of the carbon co-product using operating parameters and / or the catalyst system composition. The method includes contacting the methane composition with the catalyst system at a reaction temperature described herein to produce H2 and a carbon co-product. In some aspects, the catalyst system includes an alloy catalyst and a support. In a further aspect, the methane composition is converted to H2 at a specific CH4 conversion rate, and in such an aspect, a carbon co-product is produced. In a specific aspect, the catalyst system includes a Ni-Cu alloy catalyst including Ni, Cu, and a support, and Ni and Cu are present at a Ni:Cu mass ratio controlled to improve the product yield and / or the form / quality of the carbon co-product. In a further aspect, the reaction temperature can be in the range of 500 °C to 700 °C.

[0032] In some embodiments, the catalyst system comprises a bimetallic catalyst. In one embodiment, the catalyst system comprises Ni and Cu. In a further embodiment, the catalyst system further comprises a support. In certain embodiments, Ni and Cu are present in an amount that provides a Ni:Cu mass ratio of greater than zero to 25, such as greater than zero to 24.5, or greater than zero to 20, or greater than zero to 15, or greater than zero to 10, or greater than zero to 6, or greater than zero to less than 5, or greater than zero to 4.5, or greater than zero to 2, or greater than zero to 1, or 0.01 to 1, 0.05 to 1, or 0.1 to 1, or 0.2 to 1, or 0.3 to 1, or 0.4 to 1, or 0.5 to 1. In one embodiment, Ni and Cu are present in an amount that provides a Ni:Cu mass ratio of 2:3 (Ni:Cu). In an independent embodiment, Ni and Cu are not present in an amount that provides a Ni:Cu mass ratio of 5 (i.e., 5:1, Ni:Cu), 10 (i.e., 10:1, Ni:Cu), or 15 (i.e., 15:1, Ni:Cu).

[0033] In an exemplary embodiment, Ni and Cu are present in an amount that provides a Ni:Cu mass ratio in the range of greater than zero to 2, such as 0.01 to 1, or 0.1 to 0.15, or 0.2 to 0.3, or 0.6 to 0.7. In one embodiment, Ni and Cu are present in an amount that provides a Ni:Cu mass ratio in the range of 0.1 to 2.

[0034] The total metal loading can range from greater than 0 wt.% to 95 wt.%, such as greater than 0 wt.% to 90 wt.%, or greater than 0 wt.% to 80 wt.%, or greater than 0 wt.% to 70 wt.%, or greater than 0 wt.% to 60 wt.%.

[0035] In some embodiments, Ni and Cu are present at a mass ratio of Ni:Cu of 2, and the total metal weight loading may range from 1 wt.% to 60 wt.%, and representative amounts include, but are not limited to, 1.5 wt.%, 3 wt.%, 7.5 wt.%, 15 wt.%, 16.5 wt.%, 18 wt.%, 24 wt.%, 30 wt.%, 45 wt.% or 60 wt.%. In one embodiment, Ni and Cu are present as 1 wt.% of Ni and 0.5 wt.% of Cu, 2 wt.% of Ni and 1 wt.% of Cu, 5 wt.% of Ni and 2.5 wt.% of Cu, 10 wt.% of Ni and 5 wt.% of Cu, 11 wt.% of Ni and 5.5 wt.% of Cu, 12 wt.% of Ni and 6 wt.% of Cu, 16 wt.% of Ni and 8 wt.% of Cu, 20 wt.% of Ni and 10 wt.% of Cu, 30 wt.% of Ni and 15 wt.% of Cu, 40 wt.% of Ni and 20 wt.% of Cu. In one embodiment, Ni and Cu are present as 10 wt.% of Ni and 5 wt.% of Cu.

[0036] In some embodiments, Ni and Cu are present at a mass ratio of Ni:Cu of 1, and the total metal weight loading can range from 1 wt.% to 60 wt.%, and representative amounts include, but are not limited to, 2 wt.%, 10 wt.%, 20 wt.%, 30 wt.%, 40 wt.%, 50 wt.% or 60 wt.%. In one embodiment, Ni and Cu are present as 1 wt.% of Ni and 1 wt.% of Cu, 5 wt.% of Ni and 5 wt.% of Cu, 10 wt.% of Ni and 10 wt.% of Cu, 15 wt.% of Ni and 15 wt.% of Cu, 20 wt.% of Ni and 20 wt.% of Cu, 25 wt.% of Ni and 25 wt.% of Cu, 30 wt.% of Ni and 30 wt.% of Cu. In one embodiment, Ni and Cu are present as 10 wt.% of Ni and 10 wt.% of Cu.

[0037] In some embodiments, Ni and Cu are present at a mass ratio of Ni:Cu of 0.67, and the total metal weight loading can range from 1 wt.% to 60 wt.%. Representative amounts include, but are not limited to, 2.5 wt.%, 5 wt.%, 7.5 wt.%, 10 wt.%, 12.5 wt.%, 15 wt.%, 17.5 wt.%, 20 wt.%, 22.5 wt.%, 25 wt.%, 30 wt.%, 40 wt.%, 50 wt.% or 60 wt.%. In one embodiment, Ni and Cu are present as 1 wt.% Ni and 1.5 wt.% Cu, 2 wt.% Ni and 3 wt.% Cu, 3 wt.% Ni and 4.5 wt.% Cu, 4 wt.% Ni and 6 wt.% Cu, 5 wt.% Ni and 7.5 wt.% Cu, 6 wt.% Ni and 9 wt.% Cu, 7 wt. Ni and 10.5 wt.% Cu, 8 wt.% Ni and 12 wt.% Cu, 9 wt.% Ni and 13.5 wt.% Cu, 10 wt.% Ni and 15 wt.% Cu, 12 wt.% Ni and 18 wt.% Cu, 16 wt.% Ni and 24 wt.% Cu, 20 wt.% Ni and 30 wt.% Cu, 24 wt.% Ni and 36 wt.% Cu. In one embodiment, Ni and Cu are present as 10 wt.% Ni and 15 wt.% Cu.

[0038] In an independent embodiment, Ni and Cu are present in an amount that provides a mass ratio of Ni:Cu of 10, and the total metal weight loading can range from 1 wt.% to 60 wt.%, such as 5.5 wt.%, 11 wt.%, 22 wt.% or 44 wt.%. In one embodiment, Ni and Cu are present as 5 wt.% Ni and 0.5 wt.% Cu, 10 wt.% Ni and 1 wt.% Cu, 20 wt.% Ni and 2 wt.% Cu or 40 wt.% Ni and 4 wt.% Cu. In one embodiment, Ni and Cu are present as 10 wt.% Ni and 1 wt.% Cu.

[0039] In an independent aspect, Ni and Cu are present in an amount providing a Ni:Cu mass ratio of 5. The total metal loading can be in the range of 1 wt.% to 60 wt.%, such as 1.2 wt.%, 6 wt.%, 12 wt.%, 18 wt.%, 24 wt.%, 30 wt.%, 36 wt.%, 42 wt.%, 48 wt.%, 54 wt.%, 60 wt.%. In some aspects, Ni and Cu are present as 1 wt.% Ni and 0.2 wt.% Cu, 5 wt.% Ni and 1 wt.% Cu, 10 wt.% Ni and 2 wt.% Cu, 15 wt.% Ni and 3 wt.% Cu, 20 wt.% Ni and 4 wt. Cu, 25 wt.% Ni and 5 wt.% Cu, 30 wt.% Ni and 6 wt.% Cu, 35 wt.% Ni and 7 wt.% Cu, 40 wt.% Ni and 8 wt.% Cu, 45 wt.% Ni and 9 wt.% Cu, 50 wt.% Ni and 10 wt.% Cu. In one aspect, Ni and Cu are present as 10 wt.% Ni and 2 wt.% Cu.

[0040] In some aspects, the Ni of the Ni-Cu alloy catalyst is provided by using nickel-containing precursors such as Ni(NO3)2-6H2O, Ni(NO3)2.6H2O, NiCl2, NiCl2.6H2O, NiBr2, NiF2, NiBr2.xH2O, NiBr2.3H2O. In one aspect, the nickel-containing precursor is Ni(NO3)2·6H2O. In some aspects, the Cu of the Ni-Cu alloy catalyst is provided by using copper-containing precursors such as Cu(NO3)2·2.5H2O, CuSO4, CuCl2, Cu(NO3)2, Cu(NO3)2.3H2O, CuO, Cu(CH3COO)2, Cu3(PO4)2, Cu(ClO4)2, CuO2,Cu(hfac)2, CuO3Si, Cu(CO2CH3), Cu(NH3)4, Cu(SCN)2, Cu(NH3)4SO4·H2O, Cu(OH)2, CuBr2. In one aspect, the copper-containing precursor is Cu(NO3)2·2.5H2O.

[0041] In some embodiments, the catalyst system includes a Ni-Cu alloy catalyst containing nanoparticles having an average particle size in the range of greater than 0 nm to 10 nm before the reaction in the TCD. Since such an embodiment of the catalyst system has not yet been exposed to the TCD cycle, it can be referred to herein as a "before use" catalyst system. In certain embodiments, the "before use" catalyst system (referred to in an example and / or figure herein) is a catalyst system that has not been heated at a reaction temperature above 450°C. In some embodiments, the "used" catalyst system is a catalyst system that has undergone at least one TCD cycle. In one embodiment, the "used" catalyst system is a catalyst system that has been heated at a reaction temperature above 450°C.

[0042] In one embodiment, the Ni-Cu alloy catalyst before use contains nanoparticles having an average particle size in the range of greater than 0 nm to 10 nm, such as 1 nm to 9 nm or 2 nm to 9 nm or 3 nm to 9 nm or 4 nm to 9 nm or 5 nm to 9 nm or 6 nm to 9 nm or 7 nm to 9 nm or 7 nm to 8 nm or 8 nm to 9 nm. In one embodiment, the Ni-Cu alloy catalyst contains nanoparticles having an average particle size in the range of 7.3 nm to 8.6 nm.

[0043] In one embodiment, the catalyst system before use includes a Ni-Cu alloy catalyst having a Ni:Cu mass ratio in the range of greater than zero to less than 5, and such a Ni-Cu alloy catalyst contains nanoparticles having an average particle size in the range of 1 nm to 10 nm before the reaction in the TCD. In one embodiment, the catalyst system includes a Ni-Cu alloy catalyst having a Ni:Cu mass ratio in the range of greater than zero to 2, and such a Ni-Cu alloy catalyst contains nanoparticles having an average particle size in the range of 7 nm to 9 nm.

[0044] In some embodiments, the Ni-Cu alloy catalyst contains nanoparticles that show a change in average particle size after being used in the TCD process, particularly after being exposed to a temperature of 600°C or higher. In some such embodiments, the nanoparticles may show an increase in average particle size of 5% to 150%, such as 5% to 120% or 6% to 110% or 40% to 110% after the reaction.

[0045] In some specific embodiments, the Ni-Cu alloy catalyst contains Ni and Cu in an amount providing a mass ratio in the range of 0.8 to 1.2, and may exhibit an average particle size increase of 5% to 10% after reaction at 600 °C or higher. In one embodiment, the Ni-Cu alloy catalyst contains Ni and Cu in an amount providing a mass ratio of 1, the reaction temperature is 600 °C, and the nanoparticles have a size change in the range of 6% to 7% after the reaction.

[0046] In some other embodiments, the Ni-Cu alloy catalyst contains Ni and Cu in an amount providing a mass ratio in the range of 1.5 to 2.5, and may exhibit an average particle size increase of 40% to 50% after reaction at 600 °C or higher. In one embodiment, the Ni-Cu alloy catalyst contains Ni and Cu in an amount providing a mass ratio in the range of 1.9 to 2.1, the reaction temperature is 600 °C, and the nanoparticles have a size change in the range of 45% to 46% after the reaction.

[0047] In still other embodiments, the Ni-Cu alloy catalyst contains Ni and Cu in an amount providing a mass ratio in the range of 0.5 to 0.75, and may exhibit an average particle size increase of 80% to 120% after reaction at 600 °C or higher. In one embodiment, the Ni-Cu alloy catalyst contains Ni and Cu in an amount providing a mass ratio in the range of 0.65 to 0.7, the reaction temperature is 600 °C, and the nanoparticles have a size change in the range of 95% to 110% after the reaction.

[0048] In some embodiments, the Ni-Cu alloy catalyst contains Ni and Cu in an amount providing a mass ratio in the range of 0.5 to 0.75, and the nanoparticles have the same particle size after being reacted at a reaction temperature of 550 °C, 600 °C, 650 °C or higher. In one embodiment, the nanoparticles may exhibit a size change of less than 30% after being reacted at a reaction temperature of 550 °C, 600 °C, 650 °C or higher. In one embodiment, the nanoparticles may exhibit a size change of less than 25% after being reacted at a reaction temperature of 550 °C, 600 °C, 650 °C or higher.

[0049] As described herein, the catalyst system can further include a carrier. Carrier components for use in the catalyst system are described herein.

[0050] The methane composition used in the methods described herein can be obtained from industrial sources that produce methane as a by-product, such as fossil fuel production (coal, oil, and / or natural gas industries) and / or industries that produce food waste and / or green waste. In some embodiments, the methane composition comprises CH4 in an amount ranging from 1 vol% to 100 vol%, such as 5 vol% to 90 vol%, 10 vol% to 80 vol%, 15 vol% to 70 vol%, 20 vol% to 60 vol%, 25 vol% to 50 vol%, 25 vol% to 40 vol%, or 25 vol% to 35 vol%. The methane composition can further comprise an inert gas selected from inert gases such as N2 and Ar. In one embodiment, the methane composition comprises at least 30 vol% CH4 in N2. In some other embodiments, the methane composition comprises 100 vol% CH4. The methane composition can be utilized at an appropriate flow rate. In some embodiments, the flow rate is 5 cm 3 / min to 120 cm 3 / min, such as 10 cm 3 / min to 100 cm 3 / min or 15 cm 3 / min to 100 cm 3 / min or 20 cm 3 / min to 100 cm 3 / min or 30 cm 3 / min to 100 cm 3 / min and can range. In some embodiments, the flow rate is at least 30 cm 3 / min. In one embodiment, the methane composition comprises 30 vol% CH4, which is utilized in the method at a flow rate of 30 cm 3 / min. In a further embodiment, the methane composition comprises 30 vol% CH4 in N2, which is utilized in the method at a flow rate of 30 cm 3 / g / h to maintain a constant space velocity of 9,000 cm 3 / min. In one embodiment, the methane composition comprises 100 vol% CH4, which is at 30 cm3 / min to 120 cm 3 a flow rate in the range of / min, for example 30 cm 3 / min, 60 cm 3 / min or 120 cm 3 is used at / min.

[0051] In some embodiments, the reaction temperature used in the disclosed method ranges from 400 °C to 900 °C, for example in the range of at least 500 °C to 800 °C or 500 °C to 700 °C or 550 °C to 700 °C or 550 °C to 700 °C or 600 °C to 700 °C or 650 °C to 700 °C. In one embodiment, the reaction temperature ranges from 600 °C to 650 °C or 640 °C to 660 °C or 670 °C to 700 °C. In certain embodiments, the reaction temperature may be 550 °C, 600 °C, 650 °C or 700 °C. In one embodiment, the reaction temperature is 600 °C or 650 °C. In some embodiments, at least the reactor in which the methane composition-catalyst system contact step is carried out can be heated by any practical means such as, for example, an electric tube furnace.

[0052] In some embodiments, the method is carried out over a reaction time in the range of greater than 0 hours to several days, for example in the range of 1 hour to 5 days or 1 hour to 4 days or 1 hour to 3 days or 1 hour to 48 hours or 1 hour to 24 hours or 1 hour to 20 hours or 1 hour to 14 hours or 1 hour to 10 hours or 1 hour to 8 hours or 1 hour to 7 hours or 1 hour to 6 hours or 1 hour to 5 hours or 1 hour to 4 hours. In one embodiment, the method is carried out over a reaction time in the range of 3 hours to 5 hours. In one embodiment, the reaction time is 4 hours. At least certain steps of the method can be carried out in a fixed bed reactor, a continuous flow reactor or other suitable reactors operable under batch and / or continuous flow conduction. In some embodiments, the reactor is any reactor suitable for bench scale work and evaluation and / or industrial scale processes.

[0053] The catalyst system described in this specification can exhibit good stability under TCD conditions even at high temperatures (e.g., temperatures above 500 °C, such as temperatures above 550 °C or above 600 °C). In some embodiments, the catalyst system contains selected amounts of nickel and copper that provide a mass ratio that promotes the stability of the catalyst such that the catalyst system can be stable over multiple TCD cycles. In some embodiments, the catalyst system is stable for at least 1.5 hours, such as at least 2 hours, at least 3 hours, or at least 4 hours. In some embodiments, the catalyst system has Ni and Cu in amounts that provide a mass ratio in the range of greater than zero to less than 5 or greater than zero to 4.5, and is stable for at least 1.5 hours, such as at least 2 hours, at least 3 hours, or at least 4 hours when exposed to a reaction temperature of at least 500 °C, such as 500 °C to 700 °C, or 550 °C to 700 °C, or 550 °C to 600 °C, or 600 °C to 650 °C; or 650 °C to 700 °C, or 600 °C to 700 °C, or 650 °C to 700 °C, and includes a Ni-Cu alloy catalyst.

[0054] In certain embodiments, the catalyst system contains a Ni-Cu alloy catalyst that has Ni and Cu in amounts that provide a mass ratio in the range of greater than zero to 4.5 and is stable for at least 4 hours when exposed to a reaction temperature in the range of 600 °C to 650 °C. In one embodiment, the Ni-Cu alloy catalyst has Ni and Cu in amounts that provide a mass ratio in the range of 0.5 to 1 and is stable for at least 4 hours when exposed to a reaction temperature in the range of 600 °C to 650 °C.

[0055] In some other embodiments, the catalyst system comprises a Ni-Cu alloy catalyst having Ni and Cu in an amount providing a mass ratio in the range of greater than zero to 4.5, and being stable for at least 2 hours when exposed to a reaction temperature in the range of 660°C to 700°C. In one embodiment, the Ni-Cu alloy catalyst has Ni and Cu in an amount providing a mass ratio in the range of 0.5 to 1, and is stable for at least 2 hours when exposed to a reaction temperature in the range of 660°C to 700°C. In one aspect, the Ni-Cu alloy catalyst has Ni and Cu in a mass ratio in the range of 0.5 to 1, and is stable for at least 1.5 hours when exposed to a reaction temperature in the range of 690°C to 710°C.

[0056] In one embodiment, the catalyst system comprises an alloy catalyst having Ni and Cu in an amount providing a mass ratio in the range of greater than zero to 4.5, the reaction temperature is at least 550°C, and the methane composition is converted to H2 with a CH4 conversion rate of at least 25% in at least 4 hours. In one embodiment, the catalyst system comprises an alloy catalyst having Ni and Cu in an amount providing a mass ratio in the range of greater than zero to 2, the reaction temperature is in the range of 550°C to 600°C, and the methane composition is converted to H2 with a CH4 conversion rate of at least 25% in at least 4 hours. In one aspect, the catalyst system comprises an alloy catalyst having Ni and Cu in an amount providing a mass ratio in the range of 0.5 to 1, the reaction temperature is in the range of 550°C to 600°C, and the methane composition is converted to H2 with a CH4 conversion rate of at least 25% in at least 4 hours.

[0057] In one aspect, the catalyst system includes an alloy catalyst having Ni and Cu in an amount providing a mass ratio in the range of greater than zero to 4.5, the reaction temperature is at least 600 °C, and the methane composition is converted to H2 with at least a 25% CH4 conversion rate in at least 4 hours. In one aspect, the catalyst system includes an alloy catalyst having Ni and Cu in an amount providing a mass ratio in the range of greater than zero to 2, the reaction temperature is in the range of 600 °C to 650 °C, and the methane composition is converted to H2 with at least a 25% CH4 conversion rate in at least 4 hours. In one aspect, the catalyst system includes an alloy catalyst having Ni and Cu in an amount providing a mass ratio in the range of 0.5 to 1, the reaction temperature is in the range of 600 °C to 650 °C, and the methane composition is converted to H2 with at least a 30% CH4 conversion rate in at least 4 hours.

[0058] In some aspects, the catalyst system includes an alloy catalyst having Ni and Cu in an amount providing a mass ratio in the range of greater than zero to 4.5, the reaction temperature is at least 640 °C, and the methane composition is converted to H2 with at least a 40% CH4 conversion rate in at least 4 hours. In one aspect, the catalyst system includes an alloy catalyst having Ni and Cu in an amount providing a mass ratio in the range of greater than zero to 2, the reaction temperature is in the range of 640 °C to 690 °C, and the methane composition is converted to H2 with at least a 45% CH4 conversion rate in at least 4 hours. In one aspect, the catalyst system includes an alloy catalyst having Ni and Cu in an amount providing a mass ratio in the range of 0.5 to 1, the reaction temperature is in the range of 640 °C to 660 °C, and the methane composition is converted to H2 with at least a 40% CH4 conversion rate in at least 4 hours.

[0059] In still other embodiments, the catalyst system includes an alloy catalyst having Ni and Cu in an amount providing a mass ratio in the range of greater than zero to 4.5, the reaction temperature is at least 670 °C, and the methane composition is converted to H2 with a CH4 conversion rate of at least 10% in at least 1.5 hours. In certain embodiments, the catalyst system includes an alloy catalyst having Ni and Cu in an amount providing a mass ratio in the range of greater than zero to 2, the reaction temperature is in the range of 670 °C to 710 °C, and the methane composition is converted to H2 with a CH4 conversion rate of at least 10% in at least 1.5 hours. In one embodiment, the catalyst system includes an alloy catalyst having Ni and Cu in an amount providing a mass ratio in the range of 0.5 to 1, the reaction temperature is in the range of 670 °C to 700 °C, and the methane composition is converted to H2 with a CH4 conversion rate of at least 10% in at least 1.5 hours.

[0060] In some representative embodiments of the present disclosure, the reaction temperature is at least 500 °C, the methane composition contains CH4 in an amount in the range of 10 vol% to 50 vol%, and H2 is produced at a ratio in the range of 0.5 g H2 / (g metal·h) to 15 g H2 / (g metal·h). In some other embodiments, the reaction temperature is in the range of 550 °C to 700 °C, the methane composition contains CH4 in an amount in the range of 20 vol% to 40 vol%, and H2 is produced at a ratio in the range of 0.5 g H2 / (g metal·h) to 15 g H2 / (g metal·h). In one embodiment, the reaction temperature is 600 °C, the methane composition contains 30 vol% CH4, and H2 is produced at a ratio in the range of 0.5 g H2 / (g metal·h) to 4 g H2 / (g metal·h). In any or all of the above embodiments, the catalyst may contain Ni:Cu in an amount sufficient to provide a Ni:Cu mass ratio in the range of greater than zero to 4.5 or less, such as 0.67, 1, 2, or 4.5 or less.

[0061] Also, this specification also describes carbon co-products produced by the methods of the present disclosure. The carbon co-products disclosed herein can be controlled in terms of morphology and yield by utilizing the operating parameters described herein and / or by varying the metal content and / or ratio in the catalyst system. In some embodiments, the carbon co-products include carbon nanomaterials such as carbon nanotubes (including single-walled CNTs, double-walled CNTs, and multi-walled CNTs). In some embodiments, the carbon co-products can be controlled to be provided in the form of carbon nanomaterials or in the form of graphene or graphite. In certain embodiments, the operating and / or catalyst system parameters are changed to provide different forms of carbon nanomaterials such as SWCNTs, DWCNTs, or MWCNTs. In some embodiments, the carbon co-products can include 50% to 100% multi-walled CNTs, such as 60% to 100% or 70% to 100% or 80% to 100%.

[0062] In one embodiment, the carbon co-product can be MWCNTs having a diameter in the range of 3 nm to 40 nm, such as 4 nm to 35 nm or 5 nm to 30 nm or 10 nm to 25 nm or 15 nm to 30 nm. In one embodiment, the carbon co-product includes MWCNTs having a diameter in the range of 20 nm to 30 nm. In some specific embodiments, the carbon co-product can be MWCNTs having an outer diameter in the range of 3 nm to 40 nm, such as 4 nm to 35 nm or 5 nm to 30 nm or 10 nm to 25 nm or 15 nm to 30 nm. In one embodiment, the carbon co-product includes MWCNTs having an outer diameter in the range of 20 nm to 30 nm. In some such embodiments, the carrier and the carbon co-product can be the same material.

[0063] In some embodiments, Raman spectroscopy is used to evaluate the morphology, diameter, and / or identity of the carbon co-products. In some such embodiments, three main bands in the Raman spectrum of the sample are analyzed to determine the amount of "constructed" versus "unconstructed" carbon co-products. These three bands include the following: i) the D band (1340 cm-1 such as 1300 cm -1 ~1400 cm -1 in the wavenumber range of (ii) the G band (1580 cm -1 such as 1500 cm -1 ~1600 cm -1 in the wavenumber range of; (iii) the G’ band (or two-dimensional band) (2700 cm -1 such as 2600 cm -1 ~2800 cm -1 in the wavenumber range of). I D / I G The ratio represents the ratio of the intensity of the D band (I G ) to the intensity of the G band (I D ), as discussed herein. I G’ / I G The ratio represents the ratio of the intensity of the G’ band (I G ) to the intensity of the G band (I G’ ), as discussed herein. In some embodiments, the I D / I G ratio can be in the range of 1 to 2, such as 1.1 to 1.9 or 1.1 to 1.6; the I G’ / I G ratio can be in the range of 0.3 to 1.3, such as 0.4 to 1.2 or 0.5 to 1. In some embodiments where the catalyst contains Ni and Cu in an amount providing a Ni:Cu mass ratio in the range of greater than zero to 4.5, the I D / I G ratio can be in the range of 1.1 to 1.81, and the I G’ / I G ratio can be in the range of 0.407 to 1.11. In still other embodiments, the I D / I G ratio can be in the range of 1.1 to 1.6, and the I G’ / I G ratio can be in the range of 0.55 to 0.95.

[0064] In some specific embodiments, the reaction temperature ranges from 500°C to 700°C, such as 550°C, 600°C, 650°C or 700°C, the catalyst contains Ni and Cu in an amount providing a Ni:Cu mass ratio in the range of greater than zero to 4.5, and the carbon co-product has an I ratio in the range of 1 to 2, such as 1.2 to 2 or 1.4 to 2 or 1.6 to 2 or 1.8 to 2; and an I ratio of less than 0.90. In one embodiment, the reaction temperature is 600°C, the catalyst contains Ni and Cu in an amount providing a mass ratio in the range of greater than zero to 4.5, and the carbon co-product has an I ratio in the range of 1.5 to 2 and an I ratio of less than 0.70. D / I G ratio; and an I ratio of less than 0.90. G’ / I G In one embodiment, the reaction temperature is 600°C, the catalyst contains Ni and Cu in an amount providing a mass ratio in the range of greater than zero to 4.5, and the carbon co-product has an I ratio in the range of 1.5 to 2 and an I ratio of less than 0.70. D / I G ratio; and an I ratio of less than 0.70. G’ / I G ratio.

[0065] In some embodiments, the catalyst contains Ni and Cu in a Ni to Cu mass ratio in the range of greater than zero to 1, such as 0.1 to 0.9 or greater than 0.5 to 0.8 or greater than 0.6 to 0.7, the reaction temperature ranges from 500°C to 700°C, such as 550°C, 600°C, 650°C or 700°C, and the carbon co-product has an I ratio in the range of 1 to 2 and an I ratio of less than 1.2. D / I G ratio; and an I ratio of less than 1.2. G’ / I G In one embodiment, the reaction temperature is 550°C, the carbon co-product has an I ratio in the range of 1.7 to 1.8 and an I ratio in the range of 0.6 to 0.7. D / I G ratio; and an I ratio in the range of 0.6 to 0.7. G’ / I G ratio. In another embodiment, the reaction temperature is 600°C, the carbon co-product has an I ratio in the range of 1.8 to 1.9 and an I ratio in the range of 0.4 to 0.5. D / I G ratio; and an I ratio in the range of 0.4 to 0.5. G’ / I G ratio. In yet another embodiment, the reaction temperature is 650°C, the carbon co-product has an I ratio in the range of 1.7 to 1.8 and an I ratio in the range of 0.7 to 0.8. D / I G ratio; and an I ratio in the range of 0.7 to 0.8. G’ / I Ghas a ratio. In another embodiment, the reaction temperature is 700 ° C, and the carbon co-product has an I D / I G ratio of 1.0 to 1.1 and an I G’ / I G ratio in the range of 1.1 to 1.2.

[0066] In the method described herein, the CH4 conversion rate X CH4 is calculated based on the amount of CH4 reacted as shown in Equation (1):

Number

[0067] The carbon yield Y C (t) and the carbon deposition rate are calculated as the cumulative weight of carbon per mass of catalyst based on the CH4 conversion rate. In some embodiments, the method is carried out for a reaction time sufficient to provide a total carbon yield of at least 3.5 g 炭素 / g 触媒 or until at least 80% of the carbon present in the support used with the catalyst system (e.g., 80% of the amount of carbon present in the used catalyst system) corresponds to the amount of carbon co-product produced by the method. In such embodiments, such an accumulation rate facilitates the use of the used catalyst system rather than the starting amount of carbon present in the catalyst system before use as an indicator for determining the amount of carbon co-product produced.

[0068] In some embodiments, the molar balance is in the range of 95 - 100% and can be calculated using Equation 2:

Number

[0069] To roughly quantify catalyst deactivation, first, assume that the carbon θ accumulated over the reaction elapsed time, as assumed in catalytic decomposition, increases to a small power, i.e., C ∝ θ 0.5 Second, assume that the catalyst deactivation is represented by a poisoning coefficient Φ multiplied by the initial conversion rate Χ0:

Number

[0070] Assume that Φ(C) is a decaying exponential function that depends on the accumulated carbon:

Number

[0071] The CH4 conversion is fitted as a function of the reaction elapsed time using a functional form with two coefficients, the initial conversion coefficient Χ0 and the deactivation rate parameter k.

[0072]

Number

[0073] The mass of carbon C(θ) at any reaction elapsed time is estimated by integrating Equation 5 and multiplying by the mass flow rate of carbon per hour at the carbon inlet C 供給 and the initial fitting conversion rate Χ0.

[0074]

Number

[0075]

Number

[0076] In some embodiments, the predicted amount of accumulated carbon co-product (carbon yield) is related to the actually measured amount of carbon. The predicted carbon yield is the extrapolation of the accumulated amount of carbon co-product up to θ = ∞ normalized by the catalyst weight: [Number] In the formula, C f is the carbon supply rate, X0 is the initial conversion rate, K is the deactivation constant, and θ is the reaction time.

[0077] As confirmed in Equation 8, the disclosed method can be expected to result in a high carbon yield. For example, in some embodiments including (i) a catalyst system containing Ni and Cu in an amount providing a mass ratio in the range of greater than zero to 4.5, and (ii) a reaction temperature in the range of 550 °C to 650 °C, a predicted carbon yield in the range of 0 g carbon / g catalyst to 6150 g carbon / g catalyst can be obtained. In yet another embodiment including (i) a catalyst system containing Ni and Cu in an amount providing a mass ratio of 0.67, and (ii) a reaction temperature of 650 °C, a predicted carbon yield in the range of 0 g carbon / g catalyst to 6150 g carbon / g catalyst can be obtained.

[0078] In some embodiments including (i) a catalyst system, (ii) a reaction temperature in the range of 550 °C to 700 °C, and (iii) a methane composition containing 100 vol% CH4, the carbon co-product can be produced at a carbon deposition rate in the range of 5 to 50 g carbon / (g metal·h).

[0079] In some embodiments including (i) a catalyst system containing Ni and Cu in an amount providing a mass ratio in the range of greater than zero to 4.5, and (ii) a reaction temperature in the range of 550 °C to 700 °C, the carbon co-product can be produced at a carbon deposition rate in the range of 1 g carbon / (g metal·h) to 4 g carbon / (g metal·h). In one embodiment, the reaction temperature is 650 °C, and the carbon co-product can be produced at a carbon deposition rate in the range of 2 g carbon / (g metal·h) to 3 g carbon / (g metal·h). In another embodiment, the reaction temperature is 600 °C, and the carbon co-product can be produced at a carbon deposition rate in the range of 1 g carbon / (g metal·h) to 2 g carbon / (g metal·h). In yet another embodiment, the reaction temperature is 550 °C, and the carbon co-product can be produced at a carbon deposition rate in the range of 1 g carbon / (g metal·h) to 2 g carbon / (g metal·h).

[0080] In some embodiments, including a catalyst system containing Ni and Cu in amounts providing a mass ratio in the range of zero to 4.5, and a reaction temperature in the range of 550 °C to 700 °C, after contacting the methane composition with the catalyst system for 5 hours, a carbon yield of at least 5 g carbon / g catalyst can be obtained. In one embodiment, the reaction temperature is 550 °C, and after contacting the methane composition with the catalyst system for 5 hours, a carbon yield in the range of 5 g carbon / g catalyst to 7 g carbon / g catalyst can be obtained. In another embodiment, the reaction temperature is 600 °C, and after contacting the methane composition with the catalyst system for 5 hours, a carbon yield in the range of 7 g carbon / g catalyst to 10 g carbon / g catalyst can be obtained. In yet another embodiment, the reaction temperature is 650 °C, and after contacting the methane composition with the catalyst system for 5 hours, a carbon yield in the range of 10 g carbon / g catalyst to 15 g carbon / g catalyst can be obtained.

[0081] In some embodiments, the disclosed method further includes separating the catalyst system from the carbon co-product. In one embodiment, separating the catalyst system from the carbon co-product comprises contacting the catalyst system and the carbon co-product with an acid to form a suspension, the suspension comprising (i) the carbon co-product (in solid form) and (ii) a liquid solution; and separating the carbon co-product from the liquid solution. In some embodiments, the acid can be selected from nitric acid (HNO3) or other suitable acids. In one embodiment, the liquid solution contains metal salts, such as metal nitrates (e.g., as Ni(NO3)2 and / or Cu(NO3)2). In one embodiment, the carbon co-product is separated from the liquid solution using filtration.

[0082] In embodiments where the carbon co-product is separated from the catalyst system, it can be reused in the method. In such embodiments of the present disclosure, the method can further include a regeneration step, which includes using the carbon co-product as a carrier component of the catalyst system. In some such embodiments, the TCD reaction of the method can be repeated in multiple cycles, and one or more reaction cycles include separating the carbon co-product from the catalyst system. In certain embodiments, repeating the reaction in multiple cycles includes repeating 4 to 100 cycles, such as 2, 3, 4, 5, or 6 times.

[0083] In some embodiments, a method of using a catalyst system involves performing at least two reaction cycles, such as two reaction cycles, three reaction cycles, four reaction cycles, or five reaction cycles. In one embodiment, a method of using a catalyst system involves performing at least four reaction cycles. A reaction cycle typically involves (i) contacting a methane composition with the catalyst system; (ii) treating the catalyst system with an acid treatment (after reaction with methane); (iii) separating a carbon co-product from a liquid solution containing a metal salt; (iv) regenerating a metal precursor by concentrating and / or crystallizing the metal salt; and (vi) combining the metal precursor with at least a portion of the separated carbon co-product.

[0084] In some embodiments, repeating the reaction for multiple cycles involves using a carbon co-product generated from a previous reaction cycle as a carrier in a subsequent reaction cycle. In such embodiments, the steps of the disclosed method are repeated over at least two cycles, where a methane composition is contacted with a catalyst system comprising a Ni-Cu alloy catalyst and a carrier at a reaction temperature to produce H2 and a carbon co-product; the catalyst system is separated from the carbon co-product; a metal precursor is regenerated for use in a regenerated catalyst system used in a subsequent cycle; the carbon co-product is isolated; the methane composition is contacted with the regenerated catalyst system to produce H2 and an additional amount of carbon co-product, and the carrier used in the regenerated catalyst system is the carbon co-product produced and isolated from a previous reaction cycle. In a further embodiment, repeating the reaction for multiple cycles involves repeating the cycle at least two times, such as two times, three times, four times, five times, or six times.

[0085] The carbon co-product can be mixed with a spent catalyst containing metal nanoparticles. In some embodiments, the carbon co-product is oxidized at a temperature of at least 300 °C in the presence of metal nanoparticles. In one embodiment, the carbon co-product is a CNT, and the carbon co-product is oxidized at a temperature of 300 °C to 500 °C. In one embodiment, the carbon co-product is a CNT, and the carbon co-product is oxidized at a temperature of 400 °C to 450 °C.

[0086] IV. Catalyst Manufacturing Method Also disclosed herein is a method for manufacturing the catalyst systems described herein. In some embodiments, the method may include sequential impregnation (SI) techniques, solvothermal (ST) techniques, incipient wetness (IW) techniques, or co-impregnation (CI) techniques. In certain embodiments, the method includes the SI technique.

[0087] Disclosed herein is a method for manufacturing a catalyst system by sequential impregnation, where substances are applied to a support material or the surface of a support material in sequential order. This process involves depositing different layers of substances on the support material. Each layer is applied successively in a continuous order.

[0088] In some embodiments, the method includes: i) contacting a solution containing a first metal with a support material to impregnate the support material with the first metal, thereby forming an impregnated support; ii) heating the impregnated support using a ramp temperature protocol to provide a pre-catalyst system; (iii) contacting the pre-catalyst system with a second metal to form a bimetal-impregnated support; and (iv) heating the bimetal-impregnated support using a ramp temperature protocol to provide a catalyst system. In some embodiments, the method may further include performing a preheating step before executing the ramp temperature protocol.

[0089] In some embodiments, the support material may be a non-carbonaceous support such as a silica support. In an independent embodiment, the support material and / or the catalyst system do not contain alumina. In some other embodiments, the support material is a carbonaceous support. In one embodiment, the support material includes a carbon material such as a carbon nanomaterial (e.g., single-walled CNT, double-walled CNT, and multi-walled CNT). In one embodiment, the support material includes multi-walled CNT. The support material may be a carbon co-product generated from one or more previous reaction cycles.

[0090] The carrier can be treated with an acid to functionalize its surface. In some embodiments, the carrier is treated with an acid to produce a carrier that has been acid-washed, and then the acid-washed carrier is combined with an alloy catalyst. In one embodiment, the acid contains nitric acid (HNO3). In some embodiments, the carrier is a carbon co-product generated from a previous reaction, and the acid-washed carrier is an acid-washed generated carbon co-product. In one embodiment, the carrier is a CNT, and the acid-washed carrier is an acid-washed CNT. In one embodiment, the carrier is a CNT, the acid is nitric acid (HNO3), and the acid-washed carrier is an acid-washed CNT (HCNT).

[0091] In some embodiments, the ramp temperature protocol includes increasing the temperature to which the impregnated carrier is exposed at a rate of 2 °C / min to 10 °C / min, such as 3 °C / min to 9 °C / min or 4 °C / min to 8 °C / min or 4 °C / min to 7 °C / min or 4 °C / min to 6 °C / min. In one embodiment, the temperature is increased by 5 °C / min.

[0092] In some embodiments, the final temperature of the ramp temperature protocol ranges from 300 °C to 400 °C, such as 310 °C to 390 °C or 320 °C to 380 °C or 330 °C to 370 °C or 340 °C to 360 °C. In one embodiment, the final temperature ranges from 345 °C to 355 °C. In one embodiment, the final temperature is 350 °C.

[0093] In some embodiments, the first metal and the second metal are Ni and Cu. In one embodiment, the first metal is Ni and the second metal is Cu. In another embodiment, the first metal is Cu and the second metal is Ni.

[0094] In a further aspect, the preheating step is carried out before executing the ramp temperature protocol. In such an aspect, the preheating step includes heating the impregnated carrier at a temperature in the range of 130°C to 200°C for a time in the range of 6 hours to 10 hours. In some aspects, the temperature in the pre-step is in the range of 100°C to 200°C, such as 110°C to 170°C, 120°C to 160°C, 120°C to 150°C, and 130°C to 150°C. In one aspect, the temperature is in the range of 130°C to 150°C. In one aspect, the temperature is 140°C.

[0095] In some aspects, the time of the pre-step is in the range of 6 hours to 10 hours, such as 7 hours to 10 hours, 7 hours to 9 hours. In one aspect, the time is in the range of 7.5 hours to 8.5 hours. In one aspect, the time is 8 hours. In one aspect, the temperature of the pre-step is 140°C and the time of the pre-step is 8 hours.

[0096] In some independent aspects, the catalyst system is prepared by ST precipitation. In this process, the catalyst precursor is dissolved in a solvent and reacted to form the catalyst. In one aspect, the catalyst system contains Ni and Cu, and the precursors of Ni and Cu are dissolved in a solvent to form a solution, the carrier material is added to the solution to form a mixture, and the mixture is heated and dried to form the catalyst system.

[0097] In some independent aspects, the catalyst system is prepared by IW impregnation. In one aspect, the catalyst system contains Ni and Cu, and the catalyst synthesized by incipient wetness impregnation (IW) can be prepared by slowly adding a concentrated aqueous solution of Ni and Cu to the carrier material to just moisten the carrier and create a slurry. Then, this slurry is dried and heated to prepare the catalyst system.

[0098] In some independent embodiments, the catalyst system is prepared by wet impregnation. In one embodiment, the catalyst system comprises Ni and Cu, and the catalyst synthesized by wet impregnation is prepared by mixing an aqueous solution containing Ni and Cu with a support material to form a mixture. This mixture may be dried and heated to prepare the catalyst system.

[0099] V. Overview of Some Embodiments Disclosed herein are embodiments of a method comprising contacting a methane composition with a catalyst system at a reaction temperature in the range of 500 °C to 700 °C to produce H2 and carbon co-products; wherein the catalyst system comprises (i) a Ni-Cu alloy catalyst containing Ni and Cu, and (ii) a support, and Ni and Cu are present in a mass ratio of Ni:Cu in the range greater than zero to 4.5.

[0100] In any or all of the above embodiments, the method further comprises separating the catalyst system from the carbon co-products.

[0101] In any or all of the above embodiments, separating the catalyst system from the carbon co-products comprises: contacting the catalyst system and the carbon co-products with an acid to form a suspension comprising (i) the carbon co-products and (ii) a liquid solution; and separating the carbon co-products from the liquid solution.

[0102] In any or all of the above embodiments, the carbon co-products are used as a support for the Ni-Cu alloy catalyst.

[0103] In any or all of the above embodiments, the carbon co-products are treated with an acid before combining the carbon co-products with Ni and Cu.

[0104] In any or all of the above embodiments, the reaction temperature is 600 °C and the carbon co-products have an I / I ratio in the range of 1 to 2 and / or an I / I ratio less than 0.70. D / I G ratio and / or an I G’ / I G ratio less than 0.70.

[0105] In any one or all of the above aspects, the reaction temperature ranges from 550°C to 700°C, the methane composition contains 30 vol% of CH4, and H2 is generated at a ratio in the range of 0.5 to 15 g H2 / (g metal·h).

[0106] In any one or all of the above aspects, the reaction temperature ranges from 550°C to 700°C, and the carbon co-product is generated at a carbon precipitation rate in the range of 1 to 4 g carbon / (g metal·h).

[0107] In any one or all of the above aspects, the reaction temperature ranges from 600°C to 650°C, and the methane composition is converted to H2 at a CH4 conversion rate of at least 25% for at least 4 hours.

[0108] In any one or all of the above aspects, the reaction temperature ranges from 670°C to 700°C, and the methane composition is converted to H2 at a CH4 conversion rate of at least 10% for at least 1.5 hours.

[0109] In any one or all of the above aspects, the Ni-Cu alloy catalyst contains nanoparticles having an average particle size in the range of greater than 0 nm to 10 nm before the Ni-Cu alloy catalyst contacts the methane composition.

[0110] In any one or all of the above aspects, the nanoparticles show a change in particle size after contacting the methane composition at a reaction temperature of 600°C, and the Ni-Cu alloy catalyst contains nanoparticles showing a particle size change in the range of 40% to 110% after the reaction.

[0111] In any one or all of the above aspects, Ni and Cu are present in a mass ratio of Ni:Cu in the range of greater than 0 to 2.

[0112] In any one or all of the above aspects, Ni and Cu are present in a mass ratio of Ni:Cu in the range of 0.6 to 0.7.

[0113] In any or all of the above aspects, Ni and Cu are present in a mass ratio of Ni:Cu in the range of 0.1 to 2; the reaction temperature is in the range of 550 °C to 700 °C.

[0114] Also disclosed are aspects of a method that includes contacting a methane composition with a catalyst system at a reaction temperature in the range of 600 °C to 650 °C to produce H2 and carbon nanotubes, where the catalyst system includes (i) a Ni-Cu alloy catalyst containing Ni and Cu, and (ii) a carbonaceous support, and Ni and Cu are present in a mass ratio of Ni:Cu in the range of 0.6 to 0.7.

[0115] Also disclosed are aspects of a method for manufacturing a catalyst system, the method including: i) contacting a solution containing a first metal with a support material to impregnate the support material with the first metal, thereby forming an impregnated support; ii) heating the impregnated support using a ramp temperature protocol to provide a pre-catalyst system, the ramp temperature protocol including increasing the temperature to which the impregnated support is exposed by 5 °C per minute until a final temperature of 350 °C is reached; iii) contacting the pre-catalyst system with a second metal to form a bimetal-impregnated support; and iv) heating the bimetal-impregnated support using a ramp temperature protocol to provide a catalyst system, where the first metal and the second metal are different from each other and are independently selected from Ni and Cu, and the first metal and the second metal provide a mass ratio of Ni:Cu in the range greater than 0 to 4.5.

[0116] In any or all of the above aspects, the method further includes performing a preheating step before performing the ramp temperature protocol, the preheating step including heating the impregnated support at a temperature in the range of 130 °C to 200 °C for a time in the range of 6 hours to 10 hours.

Examples

[0117] VI. Examples Example 1 Materials and Catalyst Synthesis Nickel nitrate hexahydrate (Ni(NO3)2·6H2O), copper nitrate hemipentahydrate (Cu(NO3)2·2.5H2O), acetone, and concentrated HNO3 were purchased from Sigma Aldrich (St. Louis, MO). Multi-walled CNTs with an outer diameter of 20 - 30 nm were purchased from Cheap Tubes (Catalog No. 030104) (Grafton, VT).

[0118] Preparation of Ni-Cu / CNT Catalyst System by Solvothermal (ST) Method

[0119] A series of Ni-Cu / CNT catalyst systems were prepared at different total metal loadings (nominal 5.5 wt.%, 11 wt.%, 22 wt.%, and 44 wt.%) according to the ST method. The mass ratio of Ni to Cu was kept constant at 10. For a typical ST synthesis of 10 wt% Ni - 1 wt% Cu in CNT [10Ni-1Cu / CNT(ST)], first, 0.347 g of Ni(NO3)2·6H2O and 0.0154 g of Cu(NO3)2·2.5H2O were dissolved in 60 mL of acetone and sonicated for 30 minutes. As-received CNT (0.626 g) was added to the acetone solution and sonicated for an additional 30 minutes. Then, the mixture was transferred to a 100 mL Teflon-lined Parr reactor, sealed, and stirred for 30 minutes. The Parr reactor was heated to 120 °C over 1 hour and this temperature was maintained for 12 hours under static conditions. After cooling to room temperature, the solution was recovered from the Parr reactor, placed in a glass container, and evaporated overnight at room temperature and atmospheric pressure in a hood. The dried solid was placed in a furnace with air stagnation at 80 °C overnight. Then, the dried solid was ground, sieved (>100 mesh), and stored in a glass vial.

[0120] Preparation of Ni-Cu / CNT Catalyst System by Incipient Wetness (IW) Impregnation

[0121] A series of Ni-Cu / CNT catalyst systems with different total metal loadings (11 wt.%, 22 wt.%, 44 wt.%) were prepared according to the incipient wetness impregnation method. The mass ratio of Ni to Cu was kept constant at 10. In a typical incipient wetness synthesis of 10 wt% Ni-1 wt% Cu in CNT [10Ni-1Cu / CNT(IW)], an aqueous solution of Ni(NO3)2·6H2O (0.595 g) and Cu(NO3)2·2.5H2O (0.0439 g) (0.635 mL) was slowly added to as-received CNT (1.068 g) using a pre-determined liquid volume (0.595 mL / g) to just moisten the support. Subsequently, the slurry was dried in a furnace under stagnant air at 80 °C overnight. After drying, the solid was heated in air at 140 °C for 8 h and then a 500 mg aliquot was heated at 350 °C for 3 h in flowing N2 (30 cm 3 / min). The temperature ramp rate was 5 °C / min. The solid was cooled to room temperature and stored in a glass vial.

[0122] Example 2 The catalyst systems were characterized before (before use) and after (after use) the reaction to determine their stability and to clarify the relationships between activity, stability, and surface properties. The catalyst system before use (500 mg) was reduced at 400 °C for 4 h in 5 vol.% H2 in N2 at 30 cm 3 / min and then heated to the reaction temperature (usually 600 °C) in N2 at 30 cm 3 / min. After the sample was cooled to room temperature, it was passivated by flowing 1.0 vol.% O2 in N2 overnight (30 cm 3 / min). The used catalyst system was characterized in the state recovered from the TCD reactor.

[0123] Physical adsorption of nitrogen (N2) at 77 K was measured for the catalyst systems before use and after use using a Quantachrome Instruments Quadrasorb EVO / SI Gas Sorption System. The samples were degassed at 150 °C under vacuum for 12 h. The surface area was determined using the five-point Brunauer-Emmett-Teller method from the adsorption data in the relative pressure range of 0.05 - 0.3. The metal loadings (Table 1) were measured by inductively coupled plasma optical emission spectrometry.

[0124]

Table 1

[0125] X-ray diffraction (XRD) patterns were collected using a Rigaku SmartLab SE Bragg-Brentano diffractometer equipped with a fixed Cu anode operating at 40 kV and 44 mA and a D / Tex Ultra250 one-dimensional detector. The patterns were collected with a variable divergence slit at 0.01° intervals between 2° < 2θ < 100°. The composition, lattice constant, and crystallite size of the crystalline components were determined by Rietveld fitting between 30° < 2θ < 100° using Topas v6 (Bruker AXS), as discussed elsewhere. It has been recognized that the crystallite size may be underestimated by this method due to the presence of Ni-Cu alloys with various compositions. The composition of the metal phase (Table 2) was estimated from the refined cubic lattice constant by linear interpolation between Ni (a = 3.5238 Å) and Cu (a = 3.615 Å). The XRD patterns are shown in Figures 1 and 2. The Raman pattern is shown in Figure 3.

[0126]

Table 2-1

Table 2-2

[0127] Temperature-programmed oxidation (TPO) was performed using a Micromeritics AutoChem2920 instrument. The sample (about 50 mg) was first loaded and pretreated at 120 °C for 120 minutes under helium, and then heated to 800 °C at a ramp rate of 5 °C / min in helium flowing at 30 cm 3 / min in 5 vol.% O2. -1

[0128] The Raman spectra were excited with a 10 mW laser (532 nm) and recorded using a Renishaw InVia Raman microscope. Each spectrum was averaged over 3 scans to characterize the solid carbon co-produced by the TCD of CH4.

[0129] The FEI Titan80-300 high-resolution transmission electron microscope was operated at 300 kV to measure the morphology, metal particle size, and elemental distribution of the solid carbon co-products before and after the reaction. This microscope was equipped with a double hexapole aberration corrector for the probe-forming lens and an energy-dispersive X-ray spectroscopy detector from CEOS GmbH. The size and composition distribution of the metal particles were calculated from the images by sampling an average of 100 particles.

[0130] Also, the morphology of the carbon co-products was evaluated at an acceleration voltage of 2 kV using a JEOL 7001F field emission gun scanning electron microscope (SEM) equipped with two Bruker X-Flash|60EDS detectors. Imaging and X-ray spectroscopy detection were performed in high-vacuum mode at an acceleration voltage of 15 kV.

[0131] Fourier transform infrared (FTIR) spectra of samples embedded in potassium bromide (KBr) pellets were obtained using a Bruker Vertex70 spectrometer. The KBr pellets were prepared by mixing and grinding 0.3 mg of the sample and 300 mg of KBr using a mortar and pestle. The mixture was then compressed for 3 minutes using a hydraulic press and a 12 mm diameter mold (10,000 lb / in 2 ). Each FTIR result was obtained by accumulating 128 scans at a resolution of 2 cm -1 .

[0132] Example 3 In this example, a fixed-bed, continuous-flow, vertical stainless-steel reactor was used for the TCD reaction at atmospheric pressure. The as-synthesized catalyst system (0.2 g, density ≈ 0.33 g / cm 3) was filled between two plugs of quartz wool. N2 gas was used as the carrier gas and the internal standard for product analysis (online gas chromatography). Before each test, a 0.2 g catalyst system sample was reduced in situ at 400 °C for 4 hours at a ramp rate of 3 °C / min under 10 vol.% H2 in N2 at 70 cm 3 / min. Subsequently, the reactor was heated to the reaction temperature (e.g., 550 - 700 °C) under N2 at 70 cm 3 / min. Before the reaction, H2 was completely purged from the system (monitored by an online gas chromatograph). Subsequently, the feed was switched to 30 vol.% CH4 in N2 at 30 cm 3 / min, and a constant space velocity of 9,000 cm 3 / g / h was maintained (≒3000 h -1 ) at the assumed density of the bed. The outlet gas flow rate was measured with a digital flow meter (DryCal). The composition of the outlet gas was analyzed with a two-channel Inficon MicroGC Fusion equipped with a molecular sieve 5A, a PLOT U column, and a TCD detector. At the end of the test, the reactor system was cooled to room temperature under N2 at 30 cm 3 / min, and the used catalyst system (including solid carbon co-products) was recovered from the reactor for analysis. The gaseous reaction products were only hydrogen; no CO2 and carbon monoxide were detected.

[0133] The CH4 conversion rate, carbon yield, and carbon deposition rate were monitored as a function of the time on stream (TOS). Typically, the reaction was carried out for more than 14 hours to achieve a minimum total carbon yield of at least 3.56 g 炭素 / g 触媒 (e.g., ≒80% of the carbon in the used catalyst system was freshly accumulated carbon co-products). Usually, it took 7 - 8 hours for the 10Ni-1Cu / CNT catalyst system (see Figures 4A - 4D). Due to this accumulation, the characteristics of the used catalyst system came to represent the carbon co-products rather than the starting carbon support. The material balance was in the range of 95% - 100%.

[0134] After the spent catalyst system was recovered from the reactor, it was crushed and sieved through a >100 mesh sieve. The crushed solid was mixed with a 5M HNO3 solution (in deionized water) at a volume ratio of the acid solution to the crushed solid mass of 50. In a typical treatment, 5 g of the spent catalyst was treated with 250 mL of the solution placed in a 500 mL round-bottom flask. The flask was immersed in an oil bath connected to a condenser cooled to 5 °C. The top of the condenser was connected to house N2 at atmospheric pressure to reduce loss of the solution. The oil bath was heated to 120 °C and maintained at that temperature for 24 hours. After the suspension was cooled to room temperature, it was sieved using 100, 200, and 480 mesh sieves to separate and retain the aggregates. Each fraction was rinsed with deionized water until the pH of the water passing through the carbon was 5.5 - 6. Since there were small carbon particles that were not recovered by the mesh, the recovered solution was initially black. As the carbon particles settled, the color of the solution became slightly green due to the presence of dissolved Cu. The solid collected on the mesh was placed in a drying oven at 80 °C under stagnant air for 12 hours. Then, the dried solid was cooled to room temperature, weighed, and stored in a glass vial. The total mass of the metals originally contained in 5 g of the spent catalyst was 122 mg (e.g., a pre-used catalyst system of 1.11 g containing 11 wt.% metals). It was suggested that 250 - 450 mg was lost in the acid washing step for the dried recovered solid, and 90.8 - 94.9% of the carbon co-products were recovered (=(5,000 mg - 122 mg - 450 mg) / (5,000 mg - 122 mg)).

[0135] Example 4 In this example, a series of Ni - Cu catalyst systems prepared by the ST technique (the metal loading varies in an 8-fold range, but the Ni:Cu weight ratio is constant at 10:1) were used at 600 °C in 30 vol.% CH4 in N2 at 30 cm 3 / min and 30 - 120 cm 3The influence of CH4 concentration and CH4 residence time on the performance of the catalyst system was investigated by testing at below 1 / 100 vol.%. As a result, the CH4 conversion rate, carbon deposition rate, and H2 production rate were summarized in Figs. 6A - 6B. The performance of the catalyst system as a function of TOS in 100 vol.% operation is shown in Figs. 7A - 7B.

[0136] Among the catalyst systems tested under the same reaction conditions, when operating with a 30 vol% CH4 feed composition, there was <20% variation in the average initial CH4 conversion rate during the first 20 minutes of TOS regardless of the total metal loading (Fig. 6A), indicating that the catalyst system is not operating in a kinetically limited region. When the thermodynamic equilibrium conversion rate of CH4 was calculated as a function of the temperature of 30 vol.% CH4 in an N2 stream (Fig. 8), it was similar to the experimentally obtained conversion rate, confirming that the system is operating near equilibrium. However, the stability (such as lifetime) of the catalyst system is greatly affected by the metal weight loading even if the catalyst systems have the same Ni:Cu composition (Table 1). For example, 5Ni - 0.5Cu / CNT deactivated after 1 hour of reaction start; other ST catalyst systems maintained their activity throughout the experimental period even with the same Ni:Cu composition. If the deactivation of the catalyst system only depended on the composition of the catalyst system, proportional deactivation of the catalyst system between low - metal - loading and high - metal - loading catalyst systems would have been expected (e.g., the 10Ni - 1Cu catalyst system and 20Ni - 2Cu catalyst system would take 2 times and 4 times longer to deactivate compared to the 5Ni - 0.5Cu catalyst system); this trend was not observed, suggesting that the deactivation in this example might be controlled by other parameters such as metal particle size or the location of metal particles (e.g., macropores vs. micropores). The 10Ni - 1Cu(ST) formulation had similar activity and lifetime to the 20Ni - 2Cu and 40Ni - 4Cu(ST) formulations, and as a result, the carbon yield normalized by the mass of the catalyst (e.g., g C / g Cat ) was similar; since the 10Ni - 1Cu(ST) formulation had a lower metal loading and similar stability compared to the 20Ni - 2Cu and 40Ni - 4Cu(ST) formulations, the carbon yield normalized by the metal mass (e.g., g C / g 金属) was the highest. Therefore, the 10Ni-1Cu(ST) formulation was selected as the catalyst system for the cycling experiment and TEA.

[0137] Table 2 summarizes the XRD analysis of the catalyst system before use and the used catalyst system, and it can be seen that there are differences in the metal crystallite size between the catalyst system before use and the used catalyst system. In the catalyst system before use, the crystallite sizes of the ST catalyst systems (20Ni-2Cu and 40Ni-4Cu) with more stable TCD performance were the largest (18.8 and 26.9 nm respectively), and the crystallite sizes of the catalyst systems with low stability (5Ni-0.5Cu and 10Ni-1Cu) were small (11.4 and 11 nm respectively). During the reaction experiment, changes in the crystallite sites and Ni:Cu composition were observed. After the reaction, the most stable ST catalyst systems (20Ni-2Cu and 40Ni-4Cu) had larger metal crystallite sizes (23.7 and 29.2 nm respectively) compared to the less stable catalyst systems (5Ni-0.5Cu and 10Ni-1Cu) with small crystallite sizes (11.8 and 9.4 nm respectively). Regardless of the metal loading, a decrease in the Ni:Cu ratio of the metal crystallites (such as loss of Ni) was observed in all used catalyst systems, suggesting that Ni was selectively lost during the reaction. The metal particle size distribution was evaluated by the SEM images shown in Figures 9A-9L, and a similar trend in metal particle size as identified by XRD was observed. That is, the average metal particle size increases with the metal loading. In this example, it is speculated that the decrease in particle size is the main cause of catalyst system deactivation; however, changes in the Ni:Cu composition may also affect the life of TCD. In this example, Cu-rich metal particles are not active for TCD under the reaction conditions, and Ni-rich particles are required for TCD.

[0138] Therefore, in this example, Ni-deficient particles may be formed due to the continuous loss of Ni from the active metal particles during the reaction, and the catalyst system may be deactivated. The effect of the particle size on the catalyst system synthesized by IW was investigated by varying the metal weight loading (the mass ratio of Ni:Cu to Cu was constant at 10). As shown in FIGS. 10A and 10B, 10Ni-1Cu / CNT (IW) was deactivated within 2 h; however, when the total nominal metal loading was increased to 22 wt.% and 44 wt.%, the TCD activity and stability (such as lifetime) were improved, similar to the TCD performance observed for the ST catalyst system.

[0139] When the fresh and used catalyst systems were evaluated using XRD, the average crystallite size (e.g., particle size) of the IW catalyst system was consistently smaller than that obtained by ST for both the fresh catalyst system (7.9 nm - 9.31 nm) and the used catalyst system (9.60 nm - 14.5 nm) (Table 2). In this example, the smaller the crystallite size, the faster the catalyst deactivation. When the metal particle size of the used catalyst system was evaluated by SEM, it was observed that 10Ni-1Cu / CNT (IW) was mainly composed of particles <20 nm (FIGS. 11A - 11L). However, the 20Ni-2Cu / CNT (IW) and 40Ni-4Cu / CNT (IW) catalyst systems were mainly composed of particles >55 nm and were stable for the TCD reaction. Therefore, the difference in performance between the IW- and ST-synthesized 10Ni-1Cu / CNT formulations in this example was mainly caused by the difference in metal particle size. That is, smaller crystallites were generated by IW than by ST, resulting in faster inactivation of the catalyst system. The IW and ST catalyst systems of 20Ni-2Cu and 40Ni-4Cu had similar particle size distributions (mainly composed of metal particles >55 nm), and thus had equivalent performance and no observed deactivation. The Ni:Cu molar ratio was similar for all fresh IW and ST catalyst systems (9.25 and 12.7, respectively), but the used stable-type (20Ni-2Cu and 40Ni-2Cu) IW catalyst systems had higher Ni:Cu ratios (37.0 and 303, respectively) than the ST catalyst systems (24.3 and 13.5, respectively). In this example, the results emphasize how the size of the crystallites and particles determines the activity and lifetime of the catalyst system.

[0140] Example 5 In this example, the TCD performance (constant Ni:Cu ratio and temperature) was also evaluated by changing the composition of CH4 and the space velocity (Figure 6B). In all the Ni-Cu catalyst systems tested, it was observed that by changing the composition of CH4 from 30 to 100 vol.% CH4, the carbon deposition rate and the amount of H2 produced almost doubled. Furthermore, when the space velocity was increased from 30 to 120 cm 3 / min, the TCD performance doubled further. At 60 and 120 cm / min, an increase in the conversion rate with the metal loading began to be shown (Figure 7A-7B), suggesting that the system was not operating under mass transport and / or equilibrium limitations at high space velocities. In this example, these results indicate that the TCD activity and stability can be improved by almost an order of magnitude by controlling the feed and the composition of the catalyst system.

[0141] Example 6 In this example, the used catalyst system was analyzed by XRD, TPO, SEM, and Raman spectroscopy to characterize the properties and morphology of the carbon co-products. XRD analysis (Figure 1A-1D) shows that after reaction with a 30 vol.% CH4 feed, the metal features (44° and 52°) decrease while the graphite-like carbon features (26° and 43°) increase, qualitatively indicating that carbon was deposited during the reaction. The decrease in the metal features and the increase in the graphite-like carbon features are prominent when operating with 100 vol.% CH4, which is consistent with the increase in the carbon deposition rate described in the previous section. TPO of the used catalyst system revealed that the graphite-like carbon was indeed graphite at oxidation temperatures >400 °C (see Figure 5A-5D). A ≈50 °C shift in the oxidation temperature was observed between different samples; this was speculated to be due to the heat generation associated with the difference in carbon loading and the variation in the position of the internal thermocouple. SEM analysis revealed that the used ST catalyst system was composed of CNTs regardless of the composition of the catalyst system (see Figure 9A-9H). In this example, the diameter of the imaged CNTs was >100 nm, suggesting that the Ni-Cu metal particles responsible for their growth were of a similar size. The presence of metal particles >100 nm at the tip of the CNTs was confirmed using backscattered SEM imaging (Figure 12A and 12B).

[0142] Figures 13A - 13D are images showing elemental mapping of 10Ni - 1Cu / CNT synthesized by the solvothermal method after reacting at 600 °C under 30 vol.% CH4 in N2. The Ni:Cu compositions of different analyzed particles are given in Table 3.

[0143] [Table 3]

[0144] As shown in Figures 9A - 9L, by analyzing the metal particle sizes of the used catalyst systems, it was found that the particle size distributions and averages of the stable catalyst systems were larger than those of the inactive ones for both the ST and IW catalyst systems, further confirming the relationship between metal particle size and catalyst system activity. For example, both 5Ni - 0.5Cu / CNT (ST) and 10Ni - 1Cu / CNT (IW) had an average metal particle size smaller than 40 nm and deactivated within 2 hours. However, when the nominal metal loading was increased to more than 11 wt.% for the ST catalyst system and more than 22 wt.% for the IW catalyst system, the average crystallite size increased to 62 nm and stable performance was obtained. When using the highest nominal weight loading evaluated, the particle size distributions of the catalyst systems prepared using both the ST and IW methods were almost the same, explaining that the TCD performances were similar. The difference between the average crystallite size observed by XRD and the metal particles observed by SEM analysis is presumably indicative of a wide metal particle size distribution in the catalyst system, which is supported by the fact that backscattering imaging revealed the presence of smaller metal nanoparticles (<50 nm) associated with smaller CNTs. In this example, elemental mapping of the used materials revealed that Ni and Cu were well alloyed in all particles; the Ni:Cu compositions varied from pure Ni to a Ni:Cu ratio of 3.16 (Table 4). The presence of Ni - rich particles and Ni - deficient particles explains the change in the Ni:Cu ratio from the crystallites overly observed by XRD (Table 2). That is, Ni moves out of the crystallites (e.g., loss of Ni) to form separate Ni - rich particles.

[0145]

Table 4

[0146] In this example, by monitoring the D band, G band, and G’ band, the quality of the carbon co-product can be evaluated using Raman spectroscopy. From FIGS. 14A-14B, I D / I G ratio (related to the presence of defects) and I G’ / I G ratio (related to the number of layers) were found to have little effect on the metal loading and feed composition. The Raman spectrum is shown in FIG. 3.

[0147] FIGS. 14A-14B show a) I D / I G (FIG. 14A) and b) I G’ / I G ratio (FIG. 14B) obtained from Raman spectroscopy as a function of the carbon deposition rate of the Ni-Cu catalyst system synthesized by the ST method. The white pentagons are 5Ni-0.5Cu-CNT, △ is 10Ni-1Cu-CNT, □ is 20Ni-2Cu-CNT, and ○ is 40Ni-4Cu-CNT. 5Cu-CNT, △ is 10Ni-1Cu-CNT, □ is 20Ni-2Cu-CNT, and ○ is 40Ni-4Cu / CNT. The reaction conditions were 600 °C under 30 vol.% CH4 (hollow symbols) and 100 vol.% CH4 (solid line symbols) in N2. The Raman spectrum is shown in FIG. 3.

[0148] FIGS. 14A-14B compare the I D / I G and I G’ / I G ratios of the used catalyst systems at the same Raman excitation wavelength of 532 nm as the literature values of different MWCNTs (MWCNTI and MWCNTII), SWCNT, and graphite. Also, FIGS. 14A-14B show that in this example, the I D / I G and I G’ / I GThe ratio is consistent with the literature-reported value of MWCNT and is of the same order regardless of the composition of the catalyst system, the carbon deposition rate, and the feed composition. For example, the 5Ni-0.5Cu / CNT catalyst system has the same ratio as the MWCNT support and I D :I G and I G’ :I G but this is because the catalyst deactivates quickly (low carbon deposition amount). In a stable catalyst system, the increase in the I D / I G ratio (from 1.0 to >1.23) and the decrease in the I G’ / I G ratio (from 0.982 to <0.937) were consistent with the growth of MWCNT with a high defect density. In the most stable catalyst systems (20Ni-2Cu / CNT and 40Ni-4Cu / CNT), the I D / I G ratio was high (1.38 and 1.36 respectively), and the I G’ / I G ratio was low (0.824 and 0.888 respectively). Therefore, it was speculated that the change in this ratio might be correlated with multiple factors affecting the properties of MWCN, such as 1) metal particle size (and related MWCNT diameter, number of layers, defect density) and 2) change in Ni:Cu molar ratio. When the CH4 concentration in the feed was increased (from 30 vol.% to 100 vol.%), the I D / I G ratio increased in all catalyst systems, and the I G’ / I G ratio decreased, which was consistent with the formation of CNTs with a higher defect density and a higher number of layers. For example, in 40Ni-4Cu / CNT, the I D / I G ratio increased from 1.36 to 1.56, and the I G’ / I G ratio decreased from 1.56 to 0.544. These changes in the I D / I G and I G’ / I G ratios were due to the formation of MWCNT with a higher defect density during operation under 100 vol.% CH4 (compared to 30 vol.% CH4), which was caused by the increase in the carbon deposition rate observed.

[0149] When Raman spectroscopy was performed on the spent catalyst system synthesized by the IW method, a similar trend to the ST catalyst system was observed (Figure 3 and Table 2). In this example, although the composition and performance of the catalyst systems synthesized by both methods were almost the same, the I D / I G and I G’ / I G ratios were slightly better than those of the ST catalyst system (for example, the I D / I G ratio was low and the I G’ / I G ratio was high). In this example, XRD analysis of the spent catalyst system revealed that the crystallite sites of the IW system (Table 2) were consistently smaller than those of the ST catalyst system. Figures 11A - 11L show SEM images of the spent 20Ni - 2Cu and 40Ni - 4Cu synthesized by IW, and these were also found to be composed of large (>50 nm) Ni - Cu particles and CNTs as well as small (<20 nm) metal particles and CNTs. In this example, the results indicated that the differences in I D / I G , I G’ / I G and TCD performance may be related to changes in the metal particle size (and distribution). Therefore, in this example, the main carbon co - product formed during the TCD of CH4 was MWCNT, and the results indicated that the metal particle size, its composition and growth rate (such as the carbon deposition rate) control the properties of MWCNT and the lifetime of the catalyst system.

[0150] Example 7 The 10Ni-1Cu / CNT complex had the highest carbon deposition rate, carbon yield, and lifespan among all the ST and IW catalyst systems evaluated in this example, and was thus used for the collection of MWCNTs and demonstration of the catalyst system regeneration cycle. The reactivity tests were carried out using a larger catalyst bed (800 mg) to produce a sufficient amount of the used catalyst system (3.5 - 4.0 g) that enabled the collection and regeneration cycle and the characterization of the products. The reproducibility of the experimental performance is shown in Figure 2. The initial deactivation observed in the large reactor was due to the endothermic nature of the reaction and heat transfer when the temperature dropped by nearly 30 °C. That is, during the reaction, the catalyst bed temperature decreased, resulting in a decrease in catalyst activity and equilibrium conversion. In this example, since this catalyst system composition was stable only for TCD at temperatures below 600 °C, compensating excessively for the temperature loss was not a viable mitigation strategy. When the reaction temperature approached 650 °C, the catalyst system deactivated. Figure 15 shows the change in the CH4 conversion rate and the I D / I G and I G’ / I G ratio as a function of the cycle for three different cycles, indicating that the conversion rates were comparable (within the range of reproducibility error) in all the tests. The conversion rate as a function of TOS is in Figure 2.

[0151] The influence of the quality of carbon and the presence of metals on the cycles (especially the pickling step) was evaluated. As shown in Figure 2, in all the cycles evaluated, the metallic features (44 and 52°) decreased after the reaction and disappeared after the pickling treatment. From the TPO profiles of the samples, it was shown that the oxidation temperature remained >500 °C regardless of the cycle step, indicating that the MWCNT product was not substantially modified during recycling. In this example, while the metal concentrations before and after the reaction were 11 wt.% and 3.7 wt.% (11,000 ppm and 3,700 ppm) respectively, the metal concentration was <50 ppm (ICP detection limit), suggesting that >99% of the metal was removed from the used catalyst system. When the recovered pickling solution (≈750 mL) was analyzed by ICP, it was revealed that >95% (240 ppm) of the metal in the used catalyst system was in the solution. Therefore, in this example, this result indicates that pickling is a feasible method for removing metals from carbon products.

[0152] Raman spectroscopy showed minor changes in the carbon co-product MWCNT as a function of the cycle (see Figures 14A - 14B). The I D / I G and I G / I G ratios of the carbon co-product were higher (I D / I G >1.41) and the I G’ / I G ratio was lower (<0.705) compared to those of the MWCNT support (1.2 and 1.0 respectively), which is consistent with the formation of MWCNT. Slight changes in the ratios were observed during different cycles, which may be due to sample handling. Figure 3 shows the I D / I G and I G’ / I GThe ratio indicates that it was not affected by the acid washing step, suggesting that the MWCNT collection and purification methods (such as acid washing) and the catalyst system regeneration cycle do not affect the quality of the MWCNT produced. According to the SEM analysis of selected samples during the regeneration cycle, CNTs are produced in all cycles, and it can be seen that the CNTs remain intact even in the acid washing step (Figures 16A - 16P), which is consistent with the results of Raman spectroscopy. Elemental mapping shows that Ni and Cu were successfully removed from the acid-washed samples, as already depicted by ICP (Figures 16A - 16P). According to SEM imaging, it can be seen that carbon co-products form large clusters of CNTs, which appear to be even denser with each cycle. In this example, it is thought to be due to the repeated growth of CNT co-products inside the pore structure of the catalyst support. That is, with each cycle, new metal particles are deposited inside the pore structure of the catalyst system, and CNTs grow continuously within the restricted space. Furthermore, since the reaction was carried out in a packed bed reactor (with a fixed catalyst bed volume), in contrast to the expansion of the catalyst bed (as expected in a fluidized bed reactor), CNT growth may have been forced inside the void volume of the catalyst system (for example, the void space between CNT clusters and particles). However, since a comparable surface area was maintained as a function of the cycle, it was suggested that the surface area of the product was not affected and the microporous structure was maintained to a similar extent (Table 4).

[0153] FTIR measurements were performed on the acid-washed MWCNT co-products produced after each cycle and compared with a commercially available (raw) MWCNT material used as a support. As shown in Figures 17A - 17E, the characteristics of the MWCNTs produced in this example are similar to those of commercially available MWCNTs and are consistent with previously acid-washed MWCNTs. The carbon yield obtained in this example was >5g 炭素 / g catConsidering this (Figs. 4 and 5), the ratio of carbon co-products in the pickled sample after the first pickling step was >80% (Table 5). At the end of the cycle experiment (4th pickling), the ratio of carbon co-products in the final sample was >99%, suggesting that the sample subjected to the 4th pickling was representative of the reaction co-products. Thus, in this example, it was demonstrated that the carbon co-products synthesized by TCD have properties similar to those of commercially available MWCNTs with a selling price of $700 - $10,000 / kg. The XRD patterns are shown in Figs. 1A - 1D and 2. The Raman pattern is shown in Fig. 3.

[0154]

Table 5

[0155] Example 8 To evaluate the commercial viability of the TCD process, a process model of the process to produce carbon co-products and CO2-free H2 was developed using Aspen Plus V10, and then a preliminary techno-economic analysis (TEA) was performed.

[0156] In the preliminary TEA analysis, in the main reaction system and the TCD reaction, natural gas (NG) was converted to H2 and carbon co-products at 600 °C and 2.5 bar over a heterogeneous catalyst system (i.e., 10Ni-1Pd / CNT and 10Ni-1Cu / CNT). The gaseous products were compressed and subjected to pressure swing adsorption (PSA) to separate H2 from the unconverted natural gas. A portion of the off-gas from the PSA (mainly unconverted NG) was recycled to the main reactor, and the remainder was used to supply heat required for the TCD reactor and other unit operations. The solid products from the main reactor were sent to the acid washing and carbon recovery section, where the metal catalyst was dissolved in a concentrated HNO3 solution at 120 °C. Subsequently, the carbon co-products were separated from the solution by filtration and dried. The metal nitrate solution (Ni(NO3)2 / Pd(NO3)2 or Ni(NO3)2 / Cu(NO3)2) solution was sent to the catalyst system regeneration section that generates the unused catalyst system by impregnation, calcination, and reduction, together with a portion of the carbon co-products from the acid washing section. A small amount of H2 produced in the main reactor was used for the reduction of the catalyst system. Considerable amounts of nitrogen oxides were generated during acid washing and calcination, mixed with air, compressed, and sent to the HNO3 recovery unit, where they were converted to HNO3 by water absorption at 11 bar, a technology developed as part of the Ostwald process.

[0157] In this analysis, the single-pass NG conversion rate in the TCD reactor was assumed to be 43% based on the reaction equilibrium calculated by minimizing the Gibbs free energy, as shown in Figure 18. The carbon yield obtained in the fixed-bed reactor using 10Ni-1Cu / CNT > 3.5 g C / g cat (Figures 4 and 5) was assumed to be achievable similarly in the fluidized-bed reactor. Based on the above assumptions, material and energy balances were calculated using Aspen Plus V10. The capital costs of the main TCD reactor, PSA unit, and catalyst system regeneration section were estimated based on data available in the open literature, and for the remaining standard equipment, the databases available in Aspen Process Economic Analyzer V10 were used for estimation.

[0158] To demonstrate a distributed hydrogen refueling system, a large-scale (100,000 kg for centralized H2 generation) H2 / day) and small-scale (1,500 kg H2 A TEA for an operational scale of 10000 MW (10 ...

[0159] The CO2 emissions from the TCD process are 1.67 and 9.6-11.5 kg / kg, respectively, compared to the emissions from the conventional SMR process. CO2 / kg H2 ) and emissions from the SMR+CCS process (2.98 kg CO2 / kg H2 ) and 61% lower than the emissions from conventional pyrolysis processes. The CO2 emissions were not zero because part of the NG was used to provide the heat required for the endothermic TCD reaction. However, they can be reduced to near zero by using H2 as the heat source, but at the expense of higher costs (e.g., higher NG consumption per kilogram of H2 produced). The power consumption of the TCD process was up to five times higher than that of the SMR process, even with on-site power generation from waste heat. This is mainly due to the large pressure difference required for the H2 purification unit. A relatively large compressor was required between the reactor and the PSA unit, since the reactor had to be operated at a relatively low pressure due to the equilibrium constraints shown in Figure 18. However, the power consumption of the TCD process was 18 times lower than that of electrolysis (3.13 and 55.5 kWh / kgH2, respectively), making it 24% more energy efficient. These results suggest that TCD is a more energy-efficient and less energy-intensive process for H2 production than electrolysis.

[0160] In the proposed TCD process for CH4, four cases were evaluated for two catalyst system compositions (Ni-Pd and Ni-Cu) and two types of metal losses considering metals not recovered from the carbon co-products. In cases NiPd0.1L and NiCu0.1L, metal loss in the pickling section was assumed to be 0.1%. In cases NiPd5L and NiCu5L, 5% metal loss was assumed. The disclosed method has the potential to produce H2 economically, whether on a small or large scale, provided sufficient value can be obtained from the carbon co-products (e.g., MWCNT). By replacing the expensive Ni-Pd catalyst with an inexpensive Ni-Cu catalyst, MCSP and MH2SP can be significantly reduced. Since the cost of Pd is high, when using the expensive Ni-Pd catalyst, both MCSP and MH2SP are susceptible to the influence of the metal loss rate.

[0161] The method described herein is a more environmentally friendly approach for H2 production from NG because the overall CO2 emissions are 85% and 45% lower than those of SMR and SMR+CCS, respectively. The proposed technology has the potential to produce H2 economically, whether on a small or large scale, provided sufficient value can be obtained from the carbon co-products.

[0162] Examples 1-8 show that in this example, a cyclic CH4 TCD process for generating H2 with a low to zero CO2 emission using a CNT-supported Ni-Cu alloy catalyst and recoverable carbon nanomaterials was investigated. In this example, the stability of the Ni-Cu catalyst system depends on the metal particle size, which can be adjusted by the metal weight loading and the synthesis method of the catalyst system. In this example, a catalyst system with an average metal particle size > 45 nm exhibits stable TCD performance regardless of the total metal loading and the synthesis method (ST or IW). In this example, by optimizing the reaction conditions and the catalyst system composition, the process performance (e.g., carbon deposition rate and H2 generation rate) was improved by almost an order of magnitude. In this example, the characterization of the carbon co-products by SEM, Raman, and FTIR analysis revealed that the characteristics of the generated carbon co-products are representative of MWCNT. In this example, the characteristics of MWCNT did not vary significantly depending on the composition of the catalyst system and the synthesis method of the catalyst system. In this example, the cyclic process of the catalyst system was demonstrated by collecting the carbon co-products and resynthesizing the catalyst system in four cycles, and the performance of the resynthesized catalyst system was similar to the characteristics of the MWCNT generated after each cycle. In this example, the characterization of the used catalyst system and the carbon co-products after pickling in four different cycles showed that the characteristics of the generated MWCNT do not change as a function of the cycle and are similar to commercially available MWCNT.

[0163] Example 9 Synthesis of Materials and Catalyst System Nickel nitrate hexahydrate (Ni(NO3)2·6H2O), copper nitrate hemipentahydrate (Cu(NO3)2·2.5H2O), acetone, and concentrated nitric acid (HNO3) were purchased from Sigma Aldrich. Multi-walled CNTs with an outer diameter of 20-30 nm were provided by Cheap Tubes Inc. (www.cheaptubes.com, catalog number 030104).

[0164] Preparation of NiCux / CNT Catalyst System by Solvothermal (ST) Method

[0165] A series of NiCux / CNT catalyst systems were prepared according to the solvothermal (ST) method. Here, x represents the target Cu weight loading. The Ni loading was kept constant at about 10 wt%, and the wt% loading of Cu was varied from 0 to 15 wt%. In a typical ST synthesis (NiCu1 / CNT(ST)) with 10 wt% Ni - 1 wt% Cu supported on CNT, first, 0.347 g of Ni(NO3)2·6H2O and 0.0154 g of Cu(NO3)2·2.5H2O were dissolved in 60 mL of acetone and sonicated for 30 minutes. As-received CNT (0.626 g) was added to the acetone solution and sonicated for an additional 30 minutes. Then, the mixture was transferred to a 100 mL Teflon-lined Parr reactor, sealed, and stirred for 30 minutes. The Parr reactor was heated to 120 °C and left at this temperature for 12 hours. After cooling to room temperature, the solution was removed from the Parr reactor, placed in a glass container, and evaporated overnight at room temperature and atmospheric pressure in a hood. The dried solid was placed in a furnace with air stagnation at 80 °C overnight. Next, the dried solid was pulverized, sieved (100 mesh), and stored in a glass vial.

[0166] Preparation of acid-treated CNT (HCNT) as a support material

[0167] The CNTs were acid-treated to functionalize their surfaces so that the metals would be better distributed during impregnation. In a typical acid treatment, 3 g of as-received CNTs were suspended in 150 mL of 10 M HNO3 solution and sonicated for 30 minutes. Then, the solution was placed in a reflux apparatus heated in an oil bath set at 100 °C for 14 hours. After cooling the system to room temperature, the solution was filtered to recover the solid, which was washed with a large amount of distilled water until the pH of the filtrate was about 7. The acid-washed product was dried in a furnace with air stagnation at 60 °C for 12 hours. The dried acid-washed CNT (HCNT) was cooled and stored in a glass vial.

[0168] Preparation of catalyst systems by co-impregnation (CI) and sequential impregnation (SI)

[0169] A catalyst system was prepared by the co-impregnation method by mixing 46 mL of an aqueous solution containing Ni(NO3)2·6H2O (0.7331 g) and Cu(NO3)2·2.5H2O (0.0570 g) with 1.3 g of HCNT. The mixture was sonicated for 30 minutes and stirred at room temperature for 2 hours. Then, the solvent was evaporated under ambient conditions in a fume hood. After drying, the solid was heat-treated: first, dried at 140 °C in air for 8 hours, then 1.72 g was heated to 350 °C at a ramp rate of 5 °C / min in N2 and held at 350 °C for 3 hours. After cooling to room temperature, the treated solid was stored in a glass vial with a cap. The catalyst system synthesized by this method was designated as NiCu1 / HCNT(CI).

[0170] The sequentially impregnated catalyst system followed the same protocol as the co-impregnated catalyst system (0.771 g Ni(NO3)2·6H2O, 0.0570 g Cu(NO3)2·2.5H2O), but impregnated one metal at a time and performed heat treatment after each impregnation. This catalyst system was first impregnated with Ni and then with Cu, and was designated as Cu1Ni / HCNT(SI).

[0171] Preparation of the incipient wetness catalyst system NiCu1 / HCNT(IW)

[0172] The catalyst system synthesized by incipient wetness impregnation (IW) was prepared by slowly adding a concentrated aqueous solution of Ni(NO3)2·6H2O (0.595 g) and Cu(NO3)2·2.5H2O (0.0439 g) to HCNT (1.068 g) using a predetermined liquid volume (0.595 mL / g) to just wet the support. Next, this slurry was dried in a furnace under stagnant air at 80 °C overnight. After drying, the solid was heated at 140 °C in air for 8 hours, and subsequently 500 mg was heated in flowing N2 (30 cm 3 / min) at 350 °C for 3 hours. The ramp rate was 5 °C / min. After cooling to room temperature, the solid was stored in a glass vial with a cap. The catalyst system with a nominal 10 wt% Ni and 1 wt% Cu prepared by IW was designated as NiCu1 / HCNT(IW).

[0173] Example 10 To determine the stability of the catalyst system and devise the relationship between activity, stability, and surface characteristics, the catalyst system before (before use) and after (used) the reaction was characterized. 500 mg of the catalyst system before use was reduced at 400 °C for 4 hours under 5 vol% H2 in N2 at 30 cm 3 / min, and then heated to the reaction temperature (usually 600 °C) in N2 at 30 cm 3 / min. After cooling to room temperature, the sample was passivated by flowing 1 vol% O2 in N2 overnight (30 cm 3 / min). The used catalyst system was characterized in the state recovered from the TCD reactor.

[0174] The nitrogen (N2) physisorption of the catalyst system before and after use was performed at 77 K using a Quadrasorb EVO / SI Gas Sorption System from Quantachrome Instruments. The surface area was determined using the five-point Brunauer–Emmett–Teller (BET) method from the adsorption data in the relative pressure range of 0.05 - 0.3. The metal loading was measured by inductively coupled plasma optical emission spectrometry (ICP-OES).

[0175] XRD patterns were collected using a Rigaku SmartLab SE Bragg-Brentano diffractometer equipped with a fixed Cu anode operating at 40 kV and 44 mA and a D / Tex Ultra250 one-dimensional detector. Patterns were collected at 0.01° intervals with a variable divergence slit from 2 to 100° (2θ). The phase composition, lattice constant, and crystallite size of the crystalline components were determined by Rietveld fitting between 30° and 100° (2θ) using Topas v6 (Bruker AXS), as discussed elsewhere. Since there are NiCu alloys with various compositions, the crystallite size may be underestimated by this method. The composition of the metal phase was estimated from the refined cubic lattice parameter by linear interpolation between Ni (a = 3.5238 Å) and Cu (a = 3.615 Å).

[0176] Temperature-programmed oxidation (TPO) was carried out using a Micromeritics AutoChem 2920 instrument. The sample was first loaded and pretreated at 120 °C for 120 minutes under He, and then heated to 800 °C at a ramp rate of 5 °C / min under 5 vol% O2 in He.

[0177] Raman spectra were recorded on a Renishaw InVia Raman microscope at an excitation wavelength of 532 nm and a laser power of 10 mW. Each spectrum was averaged over 3 scans to characterize the solid carbon co-produced by the TCD of CH4.

[0178] A FEI Titan 80-300 high-resolution transmission electron microscope (HRTEM) operated at 300 kV and equipped with a double hexapole aberration corrector for the probe-forming lens and an energy-dispersive X-ray (EDX) spectroscopic detector from CEOS GmbH was used to measure the morphology, metal particle size, and elemental distribution of the solid carbon co-products before and after the reaction. The metal particle size and composition distribution were calculated from HRTEM images by sampling an average of 100 particles.

[0179] Figures 19A - 19C show the XRD patterns of a) Ni / CNT, b) NiCu1 / CNT, and c) NiCu15 prepared by solvothermal synthesis under 30 vol.% CH4 in N2 at 30 cm 3 / min at different reaction temperatures.

[0180] Example 11 For the TCD reaction of CH4 at ambient pressure, a fixed-bed, continuous-flow, vertical stainless-steel reactor was used. The as-synthesized catalyst system (0.2 g, density = 0.33 g / cm 3 assuming) was packed between two plugs of quartz wool. N2 gas was used as the carrier gas and the internal standard for product analysis using on-line gas chromatography (GC). Before each test, a 0.2 g sample of the catalyst system was reduced in situ at 400 °C for 4 hours at a ramp rate of 3 °C / min under 10 vol% H2 in N2 at 70 cm 3 / min. Then, the reactor was at 70 cm 3Heated to a reaction temperature (e.g., 550 - 700 °C) under N₂ at a rate of N₂ / min. Before the reaction, H₂ was completely purged from the system (monitored by on-line GC). Then, the feed was switched to 30 vol% CH₄ in N₂ at a rate of 30 cm 3 / min, and a constant space velocity of 9,000 cm 3 / g / h was maintained (≈3000 h at the assumed density of the bed -1 ). The outlet gas flow rate was measured with a digital flow meter (DryCal). The composition of the outlet gas was analyzed with a 4-channel Agilent Micro GC equipped with molecular sieve 5A, PLOT U, alumina, and OV-1 columns and a TCD detector for each column. At the end of the test, the reactor system was cooled to room temperature under N₂ at a rate of 30 cm 3 / min, and the used catalyst system (including solid carbon co-products) was recovered from the reactor for analysis. The gaseous reaction products were only hydrogen, and no CO₂ or carbon monoxide was detected.

[0181] CH₄ conversion, X CH4 Carbon yield Y C (t) and the carbon deposition rate were calculated as described herein.

[0182] Example 12

[0183]

Table 6

[0184] In this example, a series of NiCu catalyst systems synthesized by the solvothermal method (ST) while keeping the Ni loading at 10 wt% constant were used under N₂ at a rate of 30 cm 3It was tested at 600 °C under 30 vol% CH4 in N2 at a flow rate of N2 of N2. The Cu loading was varied from 0 wt% to 15 wt% to explore the effect of Cu on the TCD activity and the form of carbon co-products. The characteristics of the catalyst system, such as the metal content derived from BET and ICP, are summarized in Table 6. The addition of Cu to Ni affects the initial TCD activity and stability (Figure 20). In the case of high loadings (e.g., nominal Cu loadings of 0 wt%, 0.6 wt%, 1.0 wt%), the initial measured values of the CH4 conversion remain at a level similar to that of pure Ni (e.g., 60%), but the stability of the catalyst system improves with increasing Cu. In catalyst systems with a high molar fraction of copper (e.g., nominal copper loadings of 2 wt%, 5 wt%, 10 wt%, 15 wt%), the initial TCD activity is low, but the deactivation is very slow.

[0185] Figure 20 shows the CH4 conversion as a function of reaction time for the NiCux / CNT (x = 0, 0.6, 1, 2, 5, 10, 15) catalyst systems at a reaction temperature of 600 °C, 30 cm 3 / min of N2 under 30 vol% CH4 in N2 for catalyst systems prepared by the solvothermal method. The background activity of the CNT support was a CH4 conversion of <0.2%. The time functions of the carbon yield and the carbon deposition rate are shown in Figures 21A - 21D. The lines represent a decay exponential fit, and the fitting parameters are shown in Table 7.

[0186] Approximate quantification can be performed using Equations (3) - (5) described herein.

[0187] The curves corresponding to the fitting parameters shown in Table 7 were overlaid on the data shown in Figures 20 and 22.

[0188]

Table 7

[0189] The characteristics of Ni and Cu metals contained in the freshly reduced catalyst system were examined by XRD (Figs. 23A - 23B), the role of Cu in the TCD performance was understood, and the results were summarized in Table 8. The freshly reduced NiCu catalyst system is mainly composed of reduced NiCu alloy nanoparticles. The catalyst system with a Ni:Cu mass ratio >5 had larger nanoparticles (e.g., 11 - 14 nm) compared to the catalyst system with a Ni:Cu mass ratio <2 (e.g., 7.3 - 8.6 nm). In other examples, it has been shown that the crystallite size of single - metal Ni nanoparticles is the dominant factor in TCD activity, which is also consistent with the activity trend discussed in this example. That is, in the catalyst system with a high Ni:Cu mass ratio (e.g., >5), metal nanoparticles with large particle sizes and high TCD activity are obtained. On the other hand, in the catalyst system with a low Ni:Cu mass ratio (e.g., <2), metal nanoparticles with small particle sizes and low TCD activity are obtained. This relationship between TCD activity and NiCu crystallite size is also consistent with a previous report by Pinilla et al. The Ni:Cu ratio obtained from XRD is different from that obtained by ICP, especially when the Ni:Cu ratio is high (e.g., >5); it is speculated that this may be because the XRD analysis excludes some particles from the analysis or the metal composition is underestimated. However, it was speculated that the improvement in TCD stability in the catalyst system with a Ni:Cu ratio <2 was directly due to the high Cu loading used in the catalyst system.

[0190] To elucidate the role of copper in the stability of the catalyst system, the used catalyst system was analyzed by XRD, and the results are shown in Table 8. Overall, changes in crystallite size and redistribution of the metal composition were observed. In all catalyst systems except one, loss of Ni on the alloy (e.g., decrease in Ni:Cu ratio) was seen, which is thought to be due to selective Ni migration from the metal particles to the carbon co-products. The segregation of Cu and Ni from different Ni:Cu alloy nanoparticles at the reaction temperature is consistent with the solubility gap region of the NiCu phase diagram. Among the seven different Ni:Cu catalyst systems evaluated, only NiCu1 showed particle fragmentation, as evident from a 15% decrease in the average crystallite diameter. The other six catalyst systems underwent metal sintering, as evident from an increase in the average crystallite diameter of 7% to 100% (Table 8). Therefore, the change in TCD catalyst performance shown in Figure 20 is presumed to be the result of changes in both the Ni:Cu ratio and the average crystallite diameter of the active sites.

[0191] Figure 22 shows the activity of NiCu1 / CNT prepared by different synthesis methods as a function of reaction elapsed time under 30 vol% CH4 in N2 at a reaction temperature of 600 °C and 30 cm 3 / min. GHSV ≈ 3000 h -1 . The background activity of the raw CNT was a CH4 conversion rate of <0.2%. In Figures 21A - 21D, the carbon yield and carbon deposition rate as a function of reaction elapsed time can be found. The lines represent decay exponential fits, and the fitting parameters are shown in Table 7.

[0192] Figures 24A - 24F show the carbon deposition rate and carbon yield of Ni / CNT, NiCu1 / CNT, and NiCu15 / CNT at different reaction temperatures (550 °C to 700 °C) as a function of reaction elapsed time (SOT) under 30 vol.% CH4 in N2 at 30 cm 3 / min.

[0193] Example 13 In this example, to investigate the effects on metal particle size, Ni:Cu composition, and catalytic performance, catalysts containing 10 wt% Ni and 1 wt% Cu with the same nominal weight loading were prepared using different synthesis methods (solvothermal deposition (ST), incipient wetness impregnation (IW), co-impregnation (CI), and sequential impregnation (SI)). The synthesis method affected the CH4 conversion rate and the stability of the catalyst system (Figure 22). The catalyst systems synthesized by both the ST and SI methods had the highest activity and stability compared to the catalyst systems synthesized by IW and CI. Table 9 summarizes the characterization of the catalyst systems before use, showing that all catalyst systems had a similar Ni:Cu ratio, but the weight loading varied up to 47% for the ST catalyst system. Figures 21A - 21D show that considering the differences in metal content, the catalyst system synthesized by the ST method had the highest TCD activity (such as carbon deposition rate and carbon yield). As a result of ICP, the Ni:Cu ratio of all catalyst systems was similar (10.7 - 11.8); XRD analysis showed that the Ni:Cu ratio on the metal particles was 13.0 - 24.3, and the metal particle size was similar at 8.0 nm - 11 nm. These results suggest that the synthesis method of the freshly reduced samples mainly affects the distribution of Ni and Cu on the metal nanoparticles and does not affect the metal particles.

[0194] In the XRD analysis of the used catalyst systems, a much larger variation (19 - 49) in the Ni:Cu ratio was revealed. The Ni:Cu ratios of the catalyst systems synthesized by the ST method and the SI method were the lowest at 19 (each), while the Ni:Cu ratios of the catalyst systems prepared by IW and CI were significantly higher at 32 and 49 (Table 9). The ST catalyst system and the SI catalyst system also had the smallest deactivation rate constants of 0.42 and 0.08. In contrast, the catalyst systems prepared by IW and CI showed high deactivation rate constants of 0.76 and 1.2 (Table 7). Thus, the catalyst systems composed of bimetallic NiCu metal nanoparticles with a significantly high Cu content (low Ni:Cu ratio) were more stable. Furthermore, XRD analysis showed that the metal particle size increased after the reaction in 3 out of the 4 catalyst systems, but the catalyst system prepared by SI had the largest particle size (15.1 nm) and the greatest growth (8.4 nm -). The combination of a large particle size and a low Ni:Cu ratio compared to other catalyst systems is considered to explain its excellent stability. In summary, XRD analysis of the used catalyst systems revealed that the particle size and the Ni:Cu ratio varied depending on the synthesis method, and this could directly explain the differences in catalyst stability.

[0195]

Table 8

[0196] Example 14 In this example, the performance of three types of catalyst systems [Ni / CNT(ST), NiCu1 / CNT(ST), and NiCu15 / CNT(ST)] was evaluated as a function of reaction temperature (550 °C - 700 °C). Figures 25A - 25C show how different Ni:Cu compositions affect the TCD activity and stability at different reaction temperatures. For example, at 550 °C, the pure Ni catalyst system showed the highest CH4 conversion rate compared to NiCu1 and NiCu15 and slowly deactivated over 4 hours. When the reaction temperature of the pure Ni system was raised to 600 °C, the catalyst system almost completely deactivated within 1 hour. However, the catalyst systems containing 1 wt% and 15 wt% Cu remained stable at 600 °C, even though the CH4 conversion rate was inversely proportional to the Cu content. At 650 °C, both the pure Ni / CNT and NiCu1 / CNT catalyst systems deactivated within 1 hour, but NiCu15 remained stable for >4 hours. At 700 °C, both Ni and NiCu1 deactivated within 15 minutes after the reaction, but NiCu15 deactivated slowly and lasted nearly 2 hours. Therefore, these results suggest that Cu addition is harmful to TCD catalyst activity at operating temperatures <550 °C, while it is beneficial at temperatures ≥600 °C.

[0197] Figures 25A - 25C show the activity of Ni / CNT(ST), NiCu1 / CNT(ST), and NiCu15 / CNT(ST) as a function of reaction elapsed time at reaction temperatures of 550 °C - 700 °C under 30 vol% CH4 in N2 at 30 cm 3 / min. The background activity of the as-received CNT was <0.2% CH4 conversion and was ignored in the curve fitting. The fitting parameters are in Table 10.

[0198]

Table 9

[0199] Given the assumed functional form of the deactivation function, the mass of carbon C(θ) at any reaction elapsed time can be estimated using Equations 5 - 7 as described herein.

[0200] The predicted amount of carbon co-product accumulation (e.g., carbon yield) is almost identical to the actual amount of carbon measured in the reactor (Figure 26 Error! Reference source not found), enhancing the credibility of the selected functional form. Based on appropriate fitting of both the instantaneous conversion rate and the integral conversion rate, the predicted carbon yield by extrapolating the accumulation of carbon co-products up to θ = ∞ normalized by the weight of the catalyst was calculated using Equation 8 described herein.

[0201] These values show the maximum values that depend on both the operating temperature and the composition of the catalyst system represented by the mol fraction of Cu (Error! Reference source not found. 27). In this example, it was shown that there is an optimal Ni:Cu ratio at each operating temperature due to carbon accumulation.

[0202] Figure 26 shows a parity plot in which the carbon yield calculated as the predicted or actual cumulative carbon co-product amount is normalized by the catalyst weight used at the reaction time points shown in Table 0.

[0203] Figure 27 shows the predicted carbon yield calculated as the predicted carbon co-product accumulation amount at infinite residence time divided by the catalyst weight used according to Equation (8) for the catalyst system prepared by the solvothermal (ST) method as a function of the catalyst system composition and the operating temperature.

[0204] The spent catalyst system was analyzed by XRD to clarify the role of copper in the stability of the catalyst system. As a result, it was shown that metal particle reconstruction might have caused the deactivation of the catalyst system at different reaction temperatures. For example, as shown in Table 9, the metal particles in Ni / CNT remained as small as 9.2 nm when operated at 550 °C, but sintered to a large metal particle size (14.6 nm - 19.4 nm) as the reaction temperature increased, suggesting that the cause of deactivation was metal sintering. NiCu1 / CNT maintained a small metal particle size and TCD activity even at 550 °C and 600 °C. This was consistent with the small changes in metal particle size and Ni:Cu ratio observed for the pre-used material. However, NiCu1 deactivated in less than 1 hour at 650 °C, and the metal particles sintered and segregated Cu to a secondary Cu-rich alloy. At 700 °C, NiCu1 showed no activity towards TCD, and the composition and particle size were the same as those of the pre-used catalyst system, suggesting that the catalyst system deactivated before metal reconstruction occurred.

[0205] Deactivation at high temperatures was speculated to be due to the selective formation of graphitic carbon and subsequent blockage of active sites. Interestingly, the NiCu15 / CNT catalyst system showed similar metal particle sizes (17.2 - 21.4 nm) at 550 °C, 600 °C, and 650 °C where the catalyst system was active and stable; however, the Ni:Cu ratio of the metal particles changed with the reaction conditions. From these results, it was suggested that at 550 °C, Ni was preferentially segregated from the metal particles due to the change in the Ni:Cu ratio with respect to the catalyst system before use (0.133 and 0.790, respectively). At 600 °C and 650 °C, the Ni:Cu ratio increased (0.254 and 0.418), suggesting that the higher the reaction temperature, the less Ni segregation. At 700 °C, the Ni:Cu ratio of the metal particles was similar to that of the catalyst system before use (0.676 and 0.790), further confirming that Ni segregation is less at high temperatures. However, the metal particle size only stabilized at 10.4 nm (8.60 nm in the catalyst system before use), in contrast to the larger metal particle sizes observed at the lowest temperature. The slow deactivation at 700 °C was speculated to be due to the poisoning of active sites before they were stabilized in a preferential particle morphology (e.g., Ni:Cu ratio < 0.254, > 17 nm). In this example, these results suggest that the role of Cu is to stabilize large metal particles (> 17 nm); however, as the reaction temperature increases, the metal migrates and the Ni:Cu ratio changes to less than the value required to stabilize large metal particles. The properties of the carbon co-products may also be involved in the stability of the catalyst system, which will be explained in the next section.

[0206] Example 15 As shown in FIGS. 23A-23B, from the XRD of the catalyst system operated at 600 °C, as the characteristics of Ni and NiCu alloy metals decreased, the characteristics of graphitic carbon increased, indicating that carbon deposition is supported. From the TPO of the used sample operated at 600 °C, the deposited carbon co-product is mainly composed of crystalline carbon, and the oxidation temperature is between 400 °C and 500 °C, which is in contrast to amorphous carbon that generally oxidizes at 200 °C - 350 °C (see FIGS. 31A-31D). The oxidation temperature of commercially available (raw) MWCNT decreases from 500 °C - 550 °C to 200 °C - 250 °C when NiCu bimetallic metal nanoparticles (e.g., NiCux / CNT before use) are added, suggesting that the bimetallic particles catalyze the oxidation reaction. However, the used NiCux / CNT material shows an oxidation temperature of 400 °C - 450 °C (in the presence of bimetallic nanoparticles), suggesting that the CNTs formed during the TCD reaction have higher thermal stability than the commercially available CNTs used as carriers in this example. The presence of 10 wt% of monometallic Ni decreased the oxidation temperature of the used material by ≒50 °C for raw MWCNT, but when up to 15 wt% of Cu was added to 10 wt% Ni, the oxidation temperature further decreased by ≒50 °C. This was presumably due to an increase in the metal content that can catalyze the oxidation reaction at a lower temperature, in contrast to the change in the composition of the carbon co-product.

[0207] FIGS. 28A-28F are at 600 °C, 30 cm 3High-angle annular dark field (HAADF) imaging using scanning transmission electron microscopy (STEM) of selected catalyst systems before (before use) and after (after use) reaction under 30 vol% CH4 in N2 / min is shown. The related elemental maps obtained by energy-dispersive spectroscopy (EDS) are in Figures 29A - 29N and Figures 30A - 30I. Figures 28A - 28F show STEM images of selected samples after reaction at 600 °C, revealing that CNTs are selectively formed as carbon co-products and the morphology and size of the metal particles. Overall, all pre-used catalyst systems are composed of a wide range of metal particles with a width of 10 nm - 20 nm, as suggested by XRD; the used catalyst systems are composed of larger >50 nm (also <20 nm) particles with three different compositions, suggesting that metal sintering occurred during the TCD reaction. Metal particle sintering was also seen in the XRD analysis summarized in Table 8, but the formation of larger metal nanoparticles was not captured. The large metal nanoparticles observed by STEM are presumed to be domains of multiple small crystals, explaining why they could not be fully captured by XRD analysis. It was found that Ni and Cu remained in the metal particles regardless of the metal particle size; as revealed by XRD analysis, there is a change in the Ni:Cu ratio of the used materials, and Ni-rich particles and Cu-rich particles seem to be formed. More importantly, it was also revealed from the HAADF STEM micrographs of the used catalyst systems that CNTs are selectively formed as the main solid co-product on the large metal nanoparticles. Figures 32A - 32H show the differences in the morphology of CNTs produced by different catalyst systems, highlighting the role played by the Ni:Cu ratio. Figures 32A - 32H show a - c) 600 °C and d) 700 °C, 30 cm 3 Scanning transmission electron microscopy (STEM) image of a selected catalyst system after reaction (after use) under 30 vol% CH4 in N2 / min. Additional STEM images are in Figures 33A - 33F and Figures 34A - 34H.

[0208] When 1 wt% of Cu was added (e.g., NiCu1 / CNT), multi-layer CNT carbon co-products with a layer diameter ≈ 5 nm were formed. When the Cu loading was further increased, larger Ni:Cu metal particles were formed and larger CNTs with a layer thickness > 10 nm were produced. Figures 33A - 33F further show STEM images of used NiCu15 / CNT at 600 °C. The change in the morphology of the carbon co-products depicted in this example as a function of the metal particle size is consistent with previous reports.

[0209] Figures 35A - 35D show a) used solvothermal (ST) catalyst systems with different Ni:Cu ratios operated at 600 °C, and Raman spectra of b) Ni / CNT, c) NiCu1 / CNT, and d) NiCu15 / CNT operated at different temperatures under 30 vol% CH4 in N2 at 30 cm 3 / min. The spectra were collected using a 10 mW laser at an excitation wavelength of 532 nm. Except for Ni / CNT operated at > 600 °C, all other catalyst systems and the CNT support operated at 700 °C, > 80% of the mass of the catalyst system was composed of carbon co-products formed in the TCD.

[0210] Using Raman spectroscopy, the quality of carbon can be evaluated using three main bands: a) the D band (1340 cm -1 ) related to defects in the graphite lattice, 2) the G band (1580 cm -1 ) related to regular carbon, and 3) the G'-band (or 2D band, 2700 cm -1 ) related to the interaction between stacked graphene layers that can be used to distinguish single-layer CNT (SWCNT) and multi-layer CNT (MWCNT). Figures 35A - 35D show the I D / I G and I G’ / I G ratios of the used catalyst systems compared to the untreated support (MWCNT support), the untreated support operated under reaction conditions, and the pre-used catalyst system. As a result, it was revealed that there is a direct correlation between the Ni:Cu ratio and the I D / I G and I G’ / I G ratios of the produced CNTs. For example, ID / I G The ratio was comparable to that of MWCNT (0.993) after exposure to the received MWCNT (1.11) and the catalyst system before use (1.05 - 1.0); however, for the used catalyst system, I D / I G due to the different ratios, it was suggested that the CNTs generated in the TCD had characteristics different from those of the starting carrier. The rest of the catalyst systems except for Ni / CNT(ST) and NiCu1 / HCNT(CI) had comparable final carbon deposition amounts per gram of catalyst (>4g 炭素共生成物 / g 炭素担体 ); therefore, in this example, I D / I G and I G’ / I G ratio changes were considered to be due to changes in the form of the precipitated carbon co-products. Ni / CNT was only active at 600 °C for 1 hour and little carbon was precipitated (~1g 炭素共生成物 / g 炭素担体 ), so the Raman characteristics were similar to those of the CNT carrier. As the Ni:Cu ratio decreased (e.g., as the Cu loading increased), the I D / I G ratio increased, suggesting a higher defect density of the generated carbon co-products, which may be due to the larger diameter and layer thickness of the CNT co-products. The I G’ / I G ratio decreased with increasing Cu loading (e.g., decreasing Ni:Cu ratio), which is consistent with the presence of multi-wall CNTs with a large number of layers. The Raman observation results were consistent with the formation of multi-layer CNTs with larger diameters (and layer thicknesses) (HAADF) STEM images (Figs. 28A - 28F and Figs. 32A - 32H). The multi-layer CNTs with larger diameters were formed due to the reconstruction of the metal into larger domains and crystallites, which is also consistent with the XRD analysis.

[0211] Therefore, the amount of Cu added to Ni is directly correlated with the stability of the catalyst system and the quality of the carbon proven by Raman spectroscopy. Fig. 36 shows the I D / IG The deactivation rate after reaction at 600 °C is compared as a function of the Cu molar fraction. When the Cu molar fraction is slightly increased (e.g., 0.081; NiCu1 / CNT), the deactivation rate constant decreases significantly from 2.77 to 0.42 h -0.5 (85% decrease), while the I D / I G ratio increases from 1.00 to 1.23 (23% increase). However, even when the Cu loading is further increased, the effect on the deactivation rate with respect to the I D / I G ratio is small. For example, even when the Cu molar fraction is almost doubled from 0.081 to 0.142, there is little change in the deactivation rate (0.48 vs. 0.42). However, the I D / I G ratio increases from 1.23 to 1.41. The I D / Ig ratio reached a plateau of ~1.9 between a Cu molar fraction of 0.35 and 0.55.

[0212] Figure 36 shows the deactivation rate constants of NiCux / CNT (x = 0, 0.6, 1, 2, 5, 10, 15) catalyst systems prepared by the solvothermal method under 30 vol% CH4 in N2 at 600 °C and 30 cm 3 / min, as well as the Raman I D / I G ratio of the resulting carbon products. The deactivation rate constants and the I D / I G ratio were cited from Table 7 and Figures 35A - 35D, respectively.

[0213] Example 16 As shown in Figures 35A - 35D, both the I D / I G and I G’ / I G ratios change with the reaction temperature, similar to the Ni:Cu ratio. Ni / CNT operated at 550 °C has an I D / I GThe ratio was slightly higher compared to the CNT support (1.23 and 1.11 respectively), suggesting that the properties of the generated CNT co-products were similar to those of the CNT support. The Raman spectra collected at high reaction temperatures using 10Ni / CNT were the same as those of the CNT support. This is because the carbon yield (at 600 °C) of the catalyst system was low or the deactivation was rapid and it was inactive (650 and 700 °C). NiCu1 / CNT at 550 °C showed TCD performance comparable to that of 10Ni / CNT, but the I D / I G ratio was high (1.79 and 1.23 respectively), highlighting the influence of the Ni:Cu ratio on the morphology of the carbon co-products. At 600 °C, the TCD performance of NiCu1 was similar to that at 550 °C, but the I D / I G ratio decreased from 1.79 to 1.23. This is presumably partly due to the formation of CNTs with different diameters and layer thicknesses due to changes in the metal particle size caused by metal sintering (Table 10). At 650 °C and 700 °C, the I D / I G ratio of NiCu1 / CNT further decreased to approximately 1.0 due to less carbon deposition, and the I D / I G ratio became almost the same as that of the CNT support. NiCu15 / CNT at 550 °C had TCD performance similar to that of NiCu1 / CNT, and regardless of the difference in the initial metal particle size and Ni:Cu composition, the I D / I G (1.78 and 1.79 respectively) and the I G’ / I G (both 0.690) were the same. In this example, this result suggests the possibility that both catalyst systems generate similar active sites (e.g., larger metal particles) under the reaction conditions, leading to similar CNT morphologies. At 600 °C and 650 °C, NiCu15 / CNT maintained activity and stability towards TCD, and the resulting carbon co-products were the I D / I GSince the ratios were comparable (1.81 and 1.77 respectively), it was suggested that the stabilized activity was comparable to 550 °C. As shown in Table 11, the crystallite sizes obtained from the XRD of the used NiCu15 / CNT catalyst system remained comparable regardless of the reaction temperature (17.2 - 21.4 nm), suggesting that the crystallite size is the main factor determining the form of the carbon co-product. At 700 °C, NiCu15 / CNT was the most active and stable test catalyst system, but it deactivated within 2 hours after the reaction and the overall carbon deposition amount decreased. Therefore, as can be seen from the fact that the obtained Raman signals had almost the same ratios of I D / I G and I G’ / I G , most of them were obtained from the CNT support.

[0214]

Table 10-1

Table 10-2

[0215] As shown in Table 11, the crystallite sizes (10.4 nm and 8.6 nm) and Ni:Cu molar ratios (0.676 and 0.790) of the used NiCu15 / CNT remained comparable to those of the catalyst system before use, suggesting that some of the metal nanoparticles were deactivated before being reconstructed into larger crystallites necessary to catalyze a stable TCD reaction. From the HAADF-STEM images of the NiCu15 / CNT catalyst system operated at 700 °C, it was confirmed that intact ≈10 nm NiCu metal particle portions remained in the used catalyst system (Figs. 30A - 30I). In other examples, it has been shown that >15 nm particles are required for the catalysis of the TCD reaction and selective CNT formation; metal particles ≤10 nm are deactivated because graphene layers (and occlusion of metal particles) are preferentially formed as opposed to CNTs. In Figs. 32A - 32H and Figs. 30A - 30I, it was confirmed that >50 nm nanoparticles were also formed at 700 °C, explaining the initial TCD. From the STEM images at 700 °C of the used NiCu15 / CNT, it became clear that the carbon co-products formed on the >50 nm metal particles were mainly multi-walled CNTs with a layer thickness >14 nm. That is, Cu plays a dual role in the TCD reaction; 1) changing the morphology of the carbon co-products to multi-walled CNTs, and 2) reconstructing the metal particles into larger metal particles that are more stable towards TCD at high temperatures and selective towards the formation of multi-walled CNTs.

[0216] In Examples 9 - 16, the role of Cu in the TCD performance of the Ni - Cu / CNT catalyst system was investigated. In this example, it was shown that the crystallite size, Ni:Cu ratio, and operating temperature are important factors for TCD activity, stability, and the morphology of the carbon co-products. NiCu catalyst systems synthesized with different Ni:Cu ratios showed different advantages as a function of the reaction temperature. At 550 °C, an adverse effect on the TCD activity due to Cu addition was observed; however, the properties of the resulting carbon co-products were different. At 600 °C, Cu addition improved the TCD activity and stability, and the properties of the carbon co-products changed. At >650 °C, only the catalyst systems with a high Cu loading maintained the activity and stability towards TCD.

[0217] From the characterization of the catalyst system after the reaction, it was revealed that adding Cu to Ni stabilizes larger metal nanoparticles, making them more stable against TCD and more selective for CNT growth even at high reaction temperatures. In the absence of Cu, bamboo-like CNTs are the predominantly observed morphology, and the addition of Cu changes the CNT morphology to multi-walled CNTs. In all cases, preferential segregation of Cu from the NiCu alloy (e.g., an increase in the Ni:Cu ratio) and reconstruction of the active sites due to changes in the metal particle size were observed. When the Cu loading was low (e.g., high Ni:Cu ratio), the catalyst system deactivated at reaction temperatures >600 °C. This is because the metal active sites were encapsulated before reconstruction and Cu was lost. When the Cu loading was high (e.g., low Ni:Cu ratio), at reaction temperatures of 550 - 650 °C, the metal particles were reconstructed into <17 nm particles with a higher Ni:Cu loading compared to the catalyst system before use, and as a result, multi-walled CNTs were preferentially formed. At operation at 700 °C, the metal particles were encapsulated before they could be reconstructed, and the catalyst system became inactive. These examples highlight how the composition and operating conditions of the catalyst system can be used to optimize the stability of the catalyst system and obtain different carbon co-product morphologies produced during methane TCD.

[0218] Considering the many possible embodiments to which the principles of the present disclosure can be applied, it should be recognized that the illustrated embodiments are merely preferred examples and should not be construed as limiting the scope of the present disclosure. Rather, its scope is defined by the following claims. Accordingly, we claim as the invention all that falls within the scope of these claims and the gist thereof.

Claims

1. The methane composition is brought into contact with a thermal catalyst system at a reaction temperature in the range of 500°C to 700°C, H ２ The process involves generating carbon co-products, wherein the thermal catalyst system includes a Ni-Cu alloy catalyst and a support; The thermal catalyst system is separated from the carbon co-products; The carbon co-product is brought into contact with a solution containing a first metal, which is Ni or Cu, to impregnate the carbon co-product with the first metal, thereby forming an impregnated carrier; A pre-catalyst system is provided by heating the impregnated carrier using a gradient temperature protocol, wherein the gradient temperature protocol includes increasing the temperature to which the impregnated carrier is exposed by 5°C per minute until a final temperature of 350°C is reached; The pre-catalyst system is brought into contact with a solution containing a second metal, which is Ni or Cu, to reshape the thermal catalyst system; The aforementioned thermal catalyst system is reused to produce an additional amount of H₂ and carbon co-products. Includes, The first metal and the second metal are different from each other. method.

2. Separating the aforementioned thermal catalyst system from the carbon co-products is: The thermal catalyst system and the carbon co-product are brought into contact with an acid to produce (i) a suspension containing the carbon co-product and (ii) a liquid solution; The method according to claim 1, comprising separating the carbon co-product from the liquid solution.

3. The method according to claim 1, wherein the carbon co-product is treated with an acid before contacting the carbon co-product with the first metal.

4. The reaction temperature is 600°C, and the carbon coproduct is in the range of 1 to 2. Ｄ / I Ｇ Ratio and / or I less than 0.70 Ｇ’ / I Ｇ The method according to claim 1, wherein the ratio is present.

5. The reaction temperature is in the range of 550°C to 700°C, and the methane composition is 30 vol% CH ４ Including the above H ２ 0.5 to 15 g of H ２ The method according to claim 1, wherein the product is produced in a ratio within the range of / (g metal・h).

6. The method according to claim 1, wherein the reaction temperature is in the range of 550°C to 700°C, and the carbon co-product is produced with a carbon deposition rate in the range of 1 to 4 g carbon / (g metal·h).

7. The reaction temperature is in the range of 600°C to 650°C, and the methane composition is at least 25% of CH ４ converted to H ２ at a conversion rate in at least 4 hours, the method according to claim 1.

8. The reaction temperature is in the range of 670°C to 700°C, and the methane composition contains at least 10% CH4 in at least 1.5 hours. ４ H at conversion rate ２ The method according to claim 1, which is converted to the following.

9. The method according to claim 1, wherein the Ni-Cu alloy catalyst includes nanoparticles having an average particle size in the range of more than 0 nm to 10 nm before the methane composition comes into contact with the thermal catalyst system.

10. The method according to claim 9, wherein the nanoparticles exhibit a change in particle size after the methane composition comes into contact with the thermal catalyst system at a reaction temperature of 600°C, and the Ni-Cu alloy catalyst includes nanoparticles that exhibit a change in diameter in the range of 40% to 110% after the reaction.

11. The method according to claim 1, wherein the Ni and Cu in the Ni-Cu alloy catalyst are present in a Ni:Cu mass ratio in the range of greater than 0 to 4.

5.

12. The method according to claim 1, wherein the Ni and Cu in the Ni-Cu alloy catalyst are present in a Ni:Cu mass ratio in the range of 0.6 to 0.

7.

13. The Ni and Cu in the Ni-Cu alloy catalyst are present in a Ni:Cu mass ratio in the range of 0.1 to 2; The method according to claim 1, wherein the reaction temperature is in the range of 550°C to 700°C.

14. The methane composition is brought into contact with the thermal catalyst system at a reaction temperature in the range of 600°C to 650°C. ２ The process involves generating carbon nanotubes, wherein the thermal catalyst system includes a Ni-Cu alloy catalyst and a carbonaceous support; Separating the thermal catalyst system from the carbon nanotubes; The carbon nanotubes are brought into contact with a solution containing a first metal, which is Ni or Cu, to impregnate the carbon nanotubes with the first metal, thereby forming impregnated nanotubes; A pre-catalyst system is provided by heating the impregnated nanotubes using a gradient temperature protocol, wherein the gradient temperature protocol includes increasing the temperature to which the impregnated nanotubes are exposed by 5°C per minute until a final temperature of 350°C is reached; The pre-catalyst system is brought into contact with a solution containing a second metal, which is Ni or Cu, to reshape the thermal catalyst system; The aforementioned thermal catalyst system is reused to generate additional H₂ and carbon nanotubes. Includes, The first metal and the second metal are different from each other. method.

15. A method for manufacturing a thermal catalyst system, i) bringing a solution containing a first metal into contact with a carrier material to impregnate the carrier material with the first metal, thereby forming an impregnated carrier; ii) A pre-catalyst system is provided by heating the impregnated carrier using a gradient temperature protocol, wherein the gradient temperature protocol includes increasing the temperature to which the impregnated carrier is exposed by 5°C per minute until a final temperature of 350°C is reached; iii) The pre-catalyst system is brought into contact with a second metal to form a bimetallic impregnated carrier; (iv) Heating the bimetal-impregnated carrier using the gradient temperature protocol to provide the thermal catalyst system, A method wherein the first metal and the second metal are different from each other and independently selected from Ni and Cu.

16. The method according to claim 15, further comprising performing a preheating step before performing the gradient temperature protocol, wherein the preheating step includes heating the impregnated carrier at a temperature in the range of 130°C to 200°C for a time in the range of 6 to 10 hours.

17. To separate the carbon product from a mixture containing the carbon product and a catalyst system, and to provide a certain amount of isolated carbon product; A portion of the aforementioned certain amount of isolated carbon product is brought into contact with a solution containing a first metal, which is Ni or Cu, to impregnate the isolated carbon product with the first metal, thereby forming an impregnated carrier; A pre-catalyst system is provided by heating the impregnated carrier using a gradient temperature protocol, wherein the gradient temperature protocol includes increasing the temperature to which the impregnated carrier is exposed by 5°C per minute until a final temperature of 350°C is reached; The aforementioned pre-catalyst system is brought into contact with a solution containing a second metal, which is Ni or Cu, to form a regenerated catalyst system. Includes, The first metal and the second metal are different from each other. method.

18. The method according to claim 17, further comprising producing H₂ and carbon coproducts from methane using the regenerative catalyst system.

19. The first metal and the second metal are Ni(NO 3 ) 2 .6H 2 O, NiCl 2 , NiCl 2 .6H 2 O, NiBr 2 , NiF 2 , NiBr 2 .3H 2 O, Cu(NO 3 ) 2 .2.5H 2 O, CuSO 4 , CuCl 2 , Cu(NO 3 ) 2 , Cu(NO 3 ) 2 .3H 2 O, CuO, Cu(CH 3 COO) 2 , Cu 3 (PO 4 ) 2 , Cu(ClO 4 ) 2 , CuO 2 , Cu(hfac) 2 , CuO 3 Si, Cu (CO 2 CH 3 ), Cu (NH 3 The method according to claim 17, provided by using a metal precursor selected from 4, Cu(SCN)2, Cu(NH3)4SO4・H2O, Cu(OH)2, and CuBr2.

20. The first metal and the second metal are Ni(NO 3 ) 2 .6H 2 O, NiCl 2 , NiCl 2 .6H 2 O, NiBr 2 , NiF 2 , NiBr 2 .3H 2 O, Cu(NO 3 ) 2 .2.5H 2 O, CuSO 4 , CuCl 2 , Cu(NO 3 ) 2 , Cu(NO 3 ) 2 .3H 2 O, CuO, Cu(CH 3 COO) 2 , Cu 3 (PO 4 ) 2 , Cu(ClO 4 ) 2 , CuO 2 , Cu(hfac) 2 , CuO 3 Si, Cu (CO 2 CH 3 ), Cu (NH 3 The method according to claim 15, provided by using a metal precursor selected from 4, Cu(SCN)2, Cu(NH3)4SO4・H2O, Cu(OH)2, and CuBr2.

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