Catalyst and reactor for intermediate-temperature catalytic methane splitting and methods thereof

Abstract

The disclosure describes a methane splitting reactor and catalyst, also known as methane decomposition or cracking, which transforms methane into hydrogen and solid carbon. Specifically, the present disclosure presents an intermediate-temperature catalytic methane splitting reactor – between 750 °C and 850 °C, for producing high-purity hydrogen and graphitic carbon. Solid catalyst apparatuses to be used in the reactor are also disclosed – supported nanoparticle composite catalyst bound to the macro-support. The catalyst comprehends catalytic metals or metal alloys – nickel, iron, cobalt, and any combination thereof, dispersed on a nanostructured oxide support. Stable reactor operation is described, by the implementation of periodic carbon shaving-off, using hydrogen, which separates carbon graphitic filaments from the active phase (selective methanation of the catalyst / carbon interface). The disclosed catalytic reactor allows the stable and continuous production of hydrogen and carbon, without carbon dioxide emissions.

Description

D E S C R I P T I O NCATALYST AND REACTOR FOR INTERMEDIATE-TEMPERATURE CATALYTIC METHANE SPLITTING AND METHODS THEREOFTechnical field

[0001] The present disclosure relates an intermediate-temperature catalytic methane splitting reactor, operating from 750 °C to 850 °C, for producing high-purity hydrogen and graphitic carbon.Background

[0002] Currently, most hydrogen produced worldwide comes from the reforming of natural gas and other hydrocarbons or coal gasification. These processes are gradually becoming environmentally and economically less appealing, due to extensive CO2 emissions. Among many alternatives, methane splitting, also known as methane decomposition, cracking, or pyrolysis, has particular potential to uproot the current status quo:CH4(g) 2H2(g) + C(s), AH0= 74.8 kJ mol1.

[0003] Catalytic methane splitting can seamlessly substitute reforming reactors in hydrogen production facilities, thanks to the similarities with hydrocarbon reforming processes. Methane splitting avoids any production of greenhouse gases, making it environmentally and economically more appealing.

[0004] Methane splitting systems can be operated at a variety of conditions, using a variety of catalytic materials. To work below high temperatures, <800 °C, supported Nickel (Ni) and Iron (Fe) nanoparticles and alloys thereof are widely accepted as the most efficient material.

[0005] Intermediate temperature catalytic methane splitting presents some issues that have slowed down its increase in economic relevance, namely: i) fast catalyst deactivation due to carbon growth over active sites; ii) catalyst destruction due to active metal detaching from the support; and iii) reactor clogging from uncontrolled carbon growth.

[0006] At intermediate temperatures, 750-850 °C, the deactivation of catalysts from coke formation over catalyst active sites is mostly associated with Ni nanoparticles. Ni is the most active metal, but it suffers from exceedingly high turnover frequencies of adsorbates in the active sites, compared to the carbon adatom diffusivity away from those same sites. This imbalance makes pure Ni catalysts very unstable at intermediate temperatures, as carbon swiftly accumulates around and on top of dehydrogenation sites.Adding Fe to the Ni-based materials is widely accepted to decrease the gas turnover frequency on the surface but increase the carbon diffusivity.

[0007] Two different carbon-growth mechanisms are known to those skilled in the technique for the methane splitting reaction proceeding on metal catalysts: i) base-growth mechanism; and ii) tip-growth mechanism.

[0008] The base-growth mechanism is characterized by carbon structures nucleating on the surface of static metal particles, gradually covering its surface, and generally forming tubular structures that grow away from the metal particle. In this case, the end of the carbon structure, opposite to the static metal particle where it grows, is free from metal.

[0009] The tip-growth mechanism is characterized by carbon nucleation at the interface between metal particles and the support on which they are dispersed, generally forming filamentous allotropes such as multi-walled carbon nanotubes or carbon nanofibers. In this case, the carbon structures entrain metal particles during their growth from the surface of the catalyst support material. Therefore, metal particles are effectively lifted from the support, bringing about a permanent physical disruption of the catalyst structure and disabling the reversion of catalyst deactivation.

[0010] Considering the technical implication of these two different carbon growth mechanisms for catalyst deactivation and online reactivation, the tip growth mechanism must be suppressed to enable the quasi-continuous (periodic) shaving-off of the catalyst and, therefore, long-term operation of a low- temperature methane splitting process, between 500 °C and 600 °C. The current background art does not report the effective suppression of the tip-growth mechanism under low-temperature methane splitting reaction conditions.

[0011] Reactor clogging due to carbon build-up is another under-addressed technical challenge, despite its eminent significance in ensuring long-term continuous process operation.

[0012] Document W02013004398A8 [1] explores the movement of carbon away from the reaction zone, by considering a mobile amorphous carbon bed, over which the methane-derived carbon grows. In this approach, a carbon stream is continuously fed to the reactor, which is then continuously removed from the reactor, together with the carbon product that has deposited in the course of the reactor pass.

[0013] Document WO2016 / 154666A1 [2] considers a similar system, in which iron ore is used as cheap catalytic material, being continuously fed and removed from the system, along with the carbon allotropes that form over it. These approaches solve issues associated with clogging of flow paths with carbon. However, this is achieved by complex reactor designs, including moving parts and the continuous discharge, and disposal, of catalytic materials, which provide low to no hydrogen productivity in a process of intermediate-temperature catalytic methane splitting at reaction temperatures <800 °C.

[0014] Current background art still lacks an effective intermediate temperature methane splitting system, which provides economically viable productivity, while avoiding carbon clogging of flow paths by solid carbon products. New and improved reactor designs must be considered to deal with the clogging of flow paths by carbon while attaining high hydrogen productivity, enabling the retention of the catalyst in the reactor, and providing means for removing carbon products online.

[0015] These facts are disclosed to illustrate the technical problem addressed by the present disclosure.General Description

[0016] The present disclosure relates to catalytic processes for methane splitting, focusing on intermediate-temperature reactors and catalysts. Specifically, it involves Ni:Fe-based nanoparticles supported on ceramic or metallic structures for producing hydrogen and solid carbon with high efficiency.

[0017] The present disclosure employs Ni:Fe-based nanoparticles embedded in a catalytic support, preferably a mesoporous support, ensuring exceptional stability during methane splitting. Operating at temperatures between 750 °C and 850 °C, and optimally between 750 °C and 800 °C, the reactor produces high-purity hydrogen and metal-free graphitic carbon nanofilaments. The catalyst, composed of catalytic metals or alloys such as nickel, iron, and cobalt on a nanostructured oxide support, is integrated into a macro-support or channel substrate to enhance performance.

[0018] To maintain stable operation, the system incorporates a periodic carbon shaving process using hydrogen to selectively target the catalyst / carbon interface, detaching carbon particles via methanation. This process enables continuous hydrogen production and solid carbon generation without carbon dioxide emissions, ensuring environmental sustainability. The disclosed reactor and catalyst system provide a cost-effective, scalable, and efficient solution for industrial hydrogen production, aligning with modern energy and environmental standards.

[0019] The integration of a periodic carbon shaving process using hydrogen to selectively detach carbon particles from the catalyst surface, enabling continuous, stable hydrogen production and carbon generation while eliminating carbon dioxide emissions, thus addressing key challenges in methane splitting technology.

[0020] In an embodiment, the supported catalyst comprises Ni:Fe-based nanoparticles enclosed within the pores of ceramic supports (catalytic support, mesoporous supports). This innovative configuration leverages two critical elements: nanoparticle entrapment, which stabilizes the catalyst structure at high operating temperatures; and Ni:Fe catalyst, which impedes carbon adatom diffusion to the metal-support interface, effectively suppressing destructive tip-growth mechanisms.

[0021] The substrates, also referred as macro-supports, for holding the catalyst, may include ceramic monoliths, plate-and-frame systems, honeycomb designs, or bundles of metal tubes. The supported catalyst is deposited on surfaces such as the inner walls of tubular holes, ensuring optimal reaction conditions. Bonding of the catalyst particles to the macro-support is achieved using either: sol-gel films, for example, silica or alumina ceramic films, which provide high thermal stability and maintain structural integrity at elevated temperatures; thermosetting polymer films, offering robust adhesion.

[0022] In an embodiment, the reactor of the present disclosure incorporates a metal honeycomb or tubebased reaction chamber, which presents numerous advantages compared to the state-of-the-art:Low cost and robust construction: Simple assembly and durable design;Efficient thermal management: Enables either electrical or thermal heating via a thermal fluid;Particle detachment: Allows easy removal of the carbon particles, denominated shaving-off;High thermal conductivity: Ensures uniform temperature distribution for consistent reaction performance.

[0023] In another embodiment, the present disclosure incorporates a parallelepipedal or cubical shaped reaction chamber comprising slots, wherein heated metal plates are placed (e.g., a stack of metal plates), which presents numerous advantages compared to the state-of-the-art:Low cost and robust construction: Simple assembly and durable design;Efficient thermal management: Enables either electrical or thermal heating via a thermal fluid.Particle detachment: Allows easy removal of the carbon particles, denominated shaving-off. Easy application of the supported catalyst: Allows the easy deposition and bonding of the supported catalyst;Specific catalytic surface area: Allows a high volumetric catalytic surface area;High thermal conductivity: Ensures uniform temperature distribution for consistent reaction performance.

[0024] In an embodiment, the reactor of the present disclosure comprises three main components: gas inlet for methane flow for a proper distribution through the reaction module channels, where the catalyst is attached to; a reaction chamber, where methane splitting reaction occurs; a conical collection chamber, designed to gather detached carbon particles efficiently.

[0025] The methane splitting reaction is 100 % selective under the described operating conditions, yielding only hydrogen and carbon as products. Novel aspects of the reactor include: the supported metal catalyst: The catalyst allows only base-growth of the carbon with no deactivation;carbon particle removal system: the so-called shaving-off mechanism allows the hydrogenation at the catalyst / carbon particle interface with consequent detachment of the carbon particle.

[0026] In an embodiment, the combination of the Ni:Fe-supported catalyst applied on a ceramic / metallic macro-support and the periodic shaving-off of the growing carbon particles enables an intermediatetemperature catalytic methane splitting process. Surprisingly, this unique setup is cost-effective, efficient, and scalable, offering high hydrogen yields and effective carbon management.

[0027] In an embodiment, mesoporous support refers to a material that contains pores with diameters in the range of 2 nm to 50 nm. Common mesoporous materials include silica-based ones, such as MCM- 41 and SBA-15, and mesoporous carbons.

[0028] In an embodiment, the nanostructured support is mesoporous silica, which are inorganic materials having porous structures where the catalyst can be placed or (entrapped), in particular, silica mesoporous SBA-15.

[0029] In an embodiment, for running the methane splitting reaction at intermediate temperatures, it is necessary to have a stable, active, and low-cost catalyst. Although the most active catalyst for this reaction is nickel, it deactivates very fast, normally remaining active for less than 100 hours on-stream. The present disclosure concerns the reactor, catalyst, and process for running the methane splitting reaction for producing hydrogen and tubular graphitic carbon, in a stable, high-power density, and energy-efficient way. The reactor enables periodic recovery of the carbon product without clogging gas flow pathways. The supported catalyst, when running at about 750-800 °C, does not deactivate due to the carbon growth. This disclosure also discloses an effective way for shaving -off the formed carbon particles to a given size to prevent carbon clogging.

[0030] The present disclosure relates to a reactor for production of hydrogen and carbon from methane splitting, comprising: a gas inlet for methane flow, a reaction chamber for methane splitting, a gas outlet comprising unreacted methane and hydrogen, a bottom outlet for carbon removal by gravity from the reaction chamber; wherein the reaction chamber comprises a plurality of gas flow channels with a macro-support; wherein the macro-support comprises a plurality of catalyst supports; wherein each catalyst support comprises a plurality of nickel and iron alloy active particles; wherein the alloy active particles are confined to the catalyst support for contacting with the methane flow for catalysing the methane splitting reaction.

[0031] In the present disclosure, the term macro-support refers to the substrate of the inner surface of each channel of the plurality of gas flow channels.

[0032] In an embodiment, the geometry of the reaction chamber is selected from a hexagonal shape, a honeycomb shape, a tubular shape, a cubical shape or a parallelepipedal shape.

[0033] In an embodiment, the geometry of the plurality of gas flow channels is selected from: tubular, hexagonal, rectangular, or combinations thereof.

[0034] In an embodiment, the reaction chamber and / or the plurality of gas flow channels comprises at least a heating device for controlling the temperature reaction, preferably an electrical heating resistance or a thermal fluid.

[0035] In an embodiment, the heating device is arranged in a tube or a plate.

[0036] In an embodiment, the reactor comprises a temperature transductor (i.e. temperature controller) arranged between the plurality of gas flow channels, preferably a thermocouple.

[0037] In an embodiment, the plurality of gas flow channels has an inner equivalent diameter from 0.25 cm to 2 cm; more preferably from 0.5 cm to 1 cm.

[0038] In an embodiment, each channel of the plurality of gas flow channels traverses the entire chamber, with a preferential length of the tubular channels from 1 cm to 20 m; more preferably from 30 cm to 3 m.

[0039] In an embodiment, the parallelepipedal shape of the reactor chamber contains slots between the rectangularly shaped plurality of gas flow channels, for heating device plate placement.

[0040] In an embodiment, the distance between consecutive aforementioned plates is from 1.5 mm to 10 mm, more preferably from 2 mm to 4 mm.

[0041] In an embodiment, the catalytic support has mesoporous with a size ranging from 10 nm to 50 nm; preferably from 10 nm to 30 nm; more preferably from 15 nm to 25 nm. Measurement of the mesopore size can be carried out by transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray diffraction (XRD), among others.

[0042] In an embodiment, the size of each particle of the plurality of nickel and iron alloy catalyst particles is from 8 nm to 40 nm; preferably from 10 nm to 20 nm; more preferably from 15 nm to 20 nm. Measurement of the mesopore size can be carried out by transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray diffraction (XRD), among others.

[0043] In an embodiment, the depth of the parallelepipedal shaped reactor module is from 5 cm to 10 m; more preferably from 20 cm to 1 m.

[0044] In an embodiment, the atomic amount of iron in each particle of the plurality of nickel and iron alloy catalysts particles is up to 20 % (wt.metai / wt.mesoPorous suPPort+metai); preferably from 5 % to 10 %(wt • metal / wt. mesoporous support+metal ) •

[0045] In an embodiment, the catalytic support has particles ranging from 0.1 pm to 100 pm; preferably from 0.5 pm to 100 pm; more preferably from 5 pm to 25 pm.

[0046] In an embodiment, the metal loading of the reactor ranges from 5 % to 60 % (w / w); preferably from 10 % to 50 % (w / w); more preferably from 30 % to 50 % (w / w).

[0047] In an embodiment, the reactor further comprises a second gas inlet for introducing a gas shaving- off flow, for removing the carbon deposition in the catalytic support, allowing the shaving-off of the plurality of nickel and iron alloy catalysts.

[0048] In an embodiment, the gas shaving-off stream is a hydrogen stream, preferably a pure hydrogen stream.

[0049] In an embodiment, the bottom of the reaction chamber is cone or funnel shaped.

[0050] In an embodiment, the reactor comprises a container arranged below a bottom of the reactor chamber, for carbon collection.

[0051] In an embodiment, the reactor comprises a third gas inlet to introduce a gas methane flow to the container, for protecting the produced carbon flacks.

[0052] In an embodiment, the macro-support is selected from a list consisting of: a metal, a ceramic, a carbon-based material, or combination thereof.

[0053] In an embodiment, the catalytic support material is selected from a list consisting of: an oxide of silicon, an oxide of aluminium, an oxide of zirconium, an oxide of titanium, an oxide of magnesium, or combinations thereof; preferably an oxide of silicon, an oxide of aluminium, an oxide of zirconium, or combinations thereof; more preferably oxide of silicon, oxide of aluminium or combinations thereof.

[0054] In an embodiment, the amount of active particles in the catalytic support ranges from 0.1 mgcataiyst cm-2to 2 mgcataiyst cm'2, preferably from 0.5 to 1 mgcataiyst cm-2.

[0055] It is also disclosed a process for continuous methane splitting using the reactor described in any of the previous claims, comprising: feeding the reactor with a methane rich flow, wherein the reactor comprises a gas inlet for methane flow, a reaction chamber for methane splitting, a gas outlet comprising unreacted methane and hydrogen, a bottom outlet for carbon removal by gravity from the reaction chamber; wherein the reaction chamber comprises a plurality of gas flow channels with a macro-support; wherein the macro-support comprises a plurality of catalyst supports;wherein each catalyst support comprises a plurality of nickel and iron alloy active particles; wherein the alloy catalysts particles are confined to the catalyst support for contacting with the methane flow for catalysing the methane splitting reaction; wherein the operation temperature ranges from about 750 °C to 850 °C; preferably from about 750 °C to 800 °C; adding a shaving-off stage to react at the catalyst interface with deposited carbon, for carbon detachment.

[0056] In an embodiment, the process further comprises a previous step of bonding the catalyst particles to the macro-support by an alumina ceramic, or a silica ceramic, or a thermosetting polymer.

[0057] In an embodiment, the alumina ceramic, or the silica ceramic, or the carbonized thermosetting polymer is stable at the operation temperature ranges.The following pertains to the reactor

[0058] In an embodiment, the reactor comprehends an upper chamber containing the reaction modules, placed vertically such that the released carbon particles freely fall to the bottom of the reactor. To facilitate the release of the carbon particles during the shaving-off stage, the reactor may be vibrated with the help of an external vibrating unit, preferably an axial vibration unit. The bottom of the reactor should be cone-shaped, designed to collect the produced carbon particles. After reaching its capacity, an evacuated or previously filled with methane-collecting container should be hermetically docked to the bottom of the reactor; then, a valve at the bottom of the reactor should be opened to allow the carbon particles to flow into this container. After this transfer process, the valve at the reactor's bottom should be closed again.The following pertains to the supported catalyst

[0059] In an embodiment, it was observed that, by confining Ni nanoparticles within the pores of mesoporous ceramic supports while retaining access to the dispersed metal close to the pore mouths, the formed carbon shows structures characteristic of the base-growth mechanism. This confinement may hinder the lifting of the metal particles. According to the disclosure, the support material shows pores with sizes in the mesopore range. According to the disclosure, the mesopore size is in the range from 10 nm to 50 nm, preferably from 10 nm to 30 nm, and more preferably from 15 nm to 25 nm. The catalytic activity of Ni is too high, and, to improve the morphological stability of the supported catalyst, Ni is alloyed with Fe. It is considered that both the lower gas turn-over frequency and the higher carbon diffusivity exhibited by Fe will reduce gas turn-over frequency and increase carbon diffusivity in the Ni-based alloys.

[0060] This effect may reduce the dehydrogenation rate of methane molecules, while increasing carbon allotrope nucleation / growth rate, avoiding the accumulation of carbon adatoms on the catalyst surface, which would result in the catalyst encapsulation and deactivation. The size of the Ni alloy particles mustrange from 8 nm to 40 nm, preferably from 10 nm to 20 nm, and more preferably from 15 nm to 20 nm. Smaller metal particles display minimum or no methane splitting catalytic activity, while larger particles display lower catalytic activities too. The atomic concentration of Fe in the metal alloy is up to 20 % (atomic), preferably from 1 % to 10 %. The methane splitting reaction occurs at the surface of the pore- confined metal nanoparticles, particularly those accessible at the pore mouths. The formed hydrogen easily evolves, while carbon forms mostly crystalline tubular structures such as multiwall carbon nanotubes and carbon nanofibers.

[0061] In an embodiment, the ceramic support material is preferably an oxide selected from those of silicon (Si), aluminium (Al), zirconium (Zr), titanium (Ti), magnesium (Mg), and combinations thereof, preferably an oxide selected from those of Si, Al, Zr, and combinations thereof, and more preferably is an oxide selected from silicon dioxide (SiCh), aluminium oxide (AI2O3) and combinations thereof. According to a preferred embodiment of the disclosure, the ceramic support material has primary particles ranging from 0.1 pm to 100 pm. Its primary particle size preferably is in the range from 0.5 pm to 100 pm, and, more preferably, from 5 pm to 25 pm.

[0062] In an embodiment, the catalyst shows a metal loading, defined as the mass of total metal, over the mass of the catalyst and expressed as a percentage, which is in the range from 5 % to 60 %, preferably from 10 % to 50 % and more preferably from 30 % to 50 %.The following pertains to the methane splitting reaction conditions

[0063] In an embodiment, the supported catalyst operates at a temperature from 750 °C to 850 °C, preferably from 750 °C to 800 °C. These reaction temperatures are required to attain favourable equilibrium conversion. Methane splitting is an endothermal, reversible reaction, and, as such, the methane conversion per reactor pass is limited by the thermodynamic equilibrium for the reaction at the reaction conditions. For example, at 1 x 105Pa (1 bar) total pressure and temperature of 650 °C, the equilibrium, i.e. maximum methane conversion is ca. 72 %, with an equilibrium hydrogen concentration of 84.4 %; at 1 x 105Pa (1 bar) total pressure and temperature of 750 °C, this maximum methane conversion is 88 %, with an equilibrium hydrogen concentration of 93.6 %; and at 1 x 105Pa (1 bar) total pressure and temperature of 800 °C this maximum methane conversion is 92.5 % with an equilibrium hydrogen concentration of 96.1 %. According to the present disclosure, the reactor produces hydrogenrich streams, which may be easily and cheaply purified downstream. The reactor of the present disclosure allows a quasi-continuous operation of the methane splitting process with periods for the carbon detachment: shaving-off the carbon particles.The following pertains to the substrate, also referred as macro-support, to hold the catalyst

[0064] In an embodiment, the supported catalyst should be applied to a macro-support, which, afterwards, should be inserted in the reactor chamber. The supported catalyst should ideally form a densemonolayer on the macro-support surface; this prevents the peeling-off of top catalyst layers, from carbon growth between layers. Also, the supported particles should be bounded to the macro-support using a gas-impermeable layer, or otherwise, the supported catalyst particles below the most external catalytic layer should be inactive, which prevents carbon particles from growing between the macro-support surface and the first layer of supported catalyst particles, making these particles detach from the macrosupport. Different approaches can be followed; using a sol-gel approach has, however, many advantages. It is a rheologic liquid when applied, which allows the capture of a monolayer of the supported catalyst particles and can be easily transformed into a solid binding underlayer after being calcinated. The calcinated layer should, however, display a high melting temperature, for example, >800 °C, to prevent atomic mobility at the operating temperatures and should be impermeable to methane, to prevent interfacial carbon growth, between the macro-support surface (i.e.; inner surface of the channels) and the supported catalyst layer. Materials such as silica or alumina are suitable for this application. An ink, made of a thermosetting polymer, can also be used as a binding underlayer. After being applied over the macro-support surface, it can easily capture a monolayer of the dry-sprayed supported catalyst. The layer should then be carbonized under an inert atmosphere at the maximum operating temperature of the reactor.

[0065] In an embodiment, the macro-support should comprehend a bundle of channels, or gaps, to host the supported catalyst on their inner surface. The macro-support can be made of metal tubes organized in a module, a honeycomb module, a plate-and-frame module, or a ceramic monolith. Since the methane splitting reaction is endothermic, either electrical resistances or a thermal fluid that will circulate are placed either: i) between the main channels of a ceramic monolith, or ii) inside the plates of the plate- and-frame module, or iii) in the gaps of the honeycomb module, or iv) in the shell side of the tubes of the ceramic monolith reaction chamber. The preferential implementation uses metal channels, with inner equivalent diameters from 0.25 cm to 2 cm, and, more preferably from 0.5 cm to 1 cm, or gaps from 0.25 cm to 2 cm, and, more preferably, from 0.5 cm to 1 cm. In the case of the plate-and-frame module - Figure 2, feature 2.4 - the distance between two consecutive plates should be from 1.5 mm to 10 mm, with a more preferential distance from 2 mm to 4 mm; the depth of the plate-and-frame module should be from 5 cm to 10 m, and more preferably from 20 cm to 1 m.The following pertains to the carbon detachment and recovery

[0066] In an embodiment, as the methane splitting reaction progresses, carbon allotropes grow progressively into longer filaments, organized in carbon particles. Consequently, the particles must be periodically removed, to avoid clogging gas passageways. The carbon detachment is performed by supplying back hydrogen, which at the catalyst surface, reacts with the attached carbon to selectively produce methane and allow the carbon particle to peel-off.

[0067] During the carbon detachment stage - shaving-off, pure hydrogen should be supplied to the top of the reaction channels / gaps, as indicated in Figure 4, feature 4.3. The directional valve - Figure 4, feature 4.4 - should be turned to link the hydrogen input to the channels of the reaction models, closing the production flow - Figure 4, feature 4.8. The methane spitting is an equilibrium-limited reaction, which displays higher equilibrium conversions for higher temperatures and lower pressures. When running above 700 °C, the hydrogen equilibrium concentration is already 90 % at 1 x 105Pa (1 bar), and the reverse reaction kinetics - the methanation reaction, when pure hydrogen is supplied, is slow. To increase the methanation reaction kinetics, the reactor's pressure should be increased up to 5 x 105Pa (5 bar) before the hydrogen inlet, using the methane inlet - Figure 4, feature 4.12. After the shaving-off stage, the reactor production flow is reopened, and the pressure returns to the normal reaction pressure of ca. 1 x 105Pa (1 bar). The shaving-off stage normally takes between 1 minute and 5 minutes, while the production stage normally takes between 1 and 24 hours. The production time interval should be set to control the size of the carbon particles, which depends on the production time. The reactor can be heated using the electrical resistances or a thermal fluid.

[0068] In an embodiment, the reaction pressure is 1 x 105Pa and the shaving-off pressure can go up to 5 x 105Pa.Brief Description of the Drawings

[0069] The following figures provide preferred embodiments for illustrating the disclosure and should not be seen as limiting the scope of invention.

[0070] Figure 1: Simplified representation of a porous ceramic support, in 3 stages of nanoparticle enclosure of the support pore: i) empty pores; ii) pores filled with precursor solution; and iii) nanoparticle enclosed in the pore; wherein:(1.1) Porous ceramic support;(1.2) Pores of the support;(1.3) Pores filled with saturated precursor solution;(1.4) Nanoparticle confined inside the pore.

[0071] Figure 2: Drawings of reaction chamber, for loading catalytic particles, wherein:(2.1) Ceramic monolith macro-support;(2.2) Metal tubular / honeycomb support;(2.3) Bundle of metal tubes;(2.4) Reaction module;(2.5) Plate-and-frame reaction module;(2.6) Inner wall of channel, for catalyst loading;(2.7) Inserted tube for passing thermal fluids or electrical resistances;(2.8) Inserted thermocouple for monitoring temperature;(2.9) Inserted tube for passing thermal fluids or electrical resistances;(2.10) Inserted electrical resistances for heating the reaction chamber.

[0072] Figure 3: Simplified schematic of the catalytic coating process, depicting the ceramic-supported catalyst embedded in a primary sol-gel coating, wherein:(3.1) macro-support;(3.2) Sol-gel layer;(3.3) Catalyst particles;(3.4) Calcinated / hardened sol-gel layer.

[0073] Figure 4: Simplified schematic of the intermediate temperature methane splitting reactor, consisting of a reaction module with a nanostructured catalyst loaded on a support; and a carbon collection container, which is periodically emptied using a valve placed at the bottom of the reactor, for the carbon removal, wherein:(4.1) Reaction compartment;(4.2) Reaction module;(4.3) Upper chamber;(4.4) Three-way valve, which should allow to connect from the top reaction chamber to i) the product outlet to the hydrogen separation process; and ii) the hydrogen inlet for the shaving-off stage;(4.5) Reaction product flow outlet;(4.6) Inlet of the hydrogen during the shaving-off stage;(4.7) Methane inlet to the methane splitting reactor;(4.8) Methane inlet valve;(4.9) The lower part of the reactor, where the produced carbon particles are dropped to;(4.10) On-off valve for withdrawing the carbon particles;(4.11) Docked container for collecting the carbon particles withdrawn for the reactor;(4.12) On-off valve for evacuating the container and filling it with methane, previous to dock to the reactor.

[0074] Figure 5: Continuous methane splitting profile, over a NiFe / SiOz catalyst.

[0075] Figure 6: Periodic methane splitting profile, using periodic shaving to remove carbon particles, over a NiFe / SiOz catalyst.

[0076] Figure 7: Periodic methane splitting profile, using periodic shaving to remove carbon particles, over a NiFe / SiC catalyst.

[0077] Figure 8: Transmission electron microscopy images of base-grown multiwalled carbon nanotubes, produced during periodic methane splitting, using periodic shaving to separate the carbon particles, over a NiFe / SiCh catalyst.Detailed Description

[0078] The present disclosure relates to a catalyst and reactor system for intermediate-temperature catalytic methane splitting. The catalyst comprises Ni:Fe-based nanoparticles within a mesoporous support, offering enhanced stability to the methane splitting reaction. The reactor ensures efficient hydrogen production and robust carbon particle removal, making the system cost-effective, scalable, and highly efficient for industrial hydrogen production.

[0079] The present disclosure describes a methane splitting reactor and catalyst system, also known as methane decomposition or cracking, designed to transform methane into hydrogen and solid carbon. Specifically, it is an intermediate-temperature catalytic methane splitting reactor operating at temperatures between 750 °C and 850 °C, and more preferably between 750 °C and 800 °C, capable of producing high-purity hydrogen and metal-free graphitic carbon nanofilaments.

[0080] The disclosed system includes solid catalyst configurations designed for use in the reactor, featuring a supported nanoparticle composite catalyst bound to a macro-support or macro-support. The catalyst comprises catalytic metals or metal alloys, such as nickel, iron, cobalt, or combinations thereof, dispersed on a nanostructured oxide support.

[0081] Stable reactor operation is achieved through the implementation of a period carbon shaving process using hydrogen, which detaches the carbon particles from the catalytic phase by selectively targeting the catalyst / carbon interface for methanation. This innovative approach ensures the continuous and stable production of hydrogen and solid carbon while eliminating carbon dioxide (CO2) emissions.The following pertains to supported-catalyst

[0082] In an embodiment, by confining nickel nanoparticles within the pores of mesoporous ceramic supports while retaining access to the dispersed metal close to the pore mouths, the formed carbon shows structures characteristic of the base growth mechanism. This confinement may hinder the dissolution of dehydrogenated carbon adatoms from dehydrogenation sites on the metal surface into the subsurface positions of the metal lattice and, thereby, the nucleation of carbon allotropes at the interface between the supported metal and the ceramic support material and the lifting of the metal particles. According to the disclosure, the ceramic support material shows pores with sizes exclusively in the mesopore range. According to the disclosure, the mesopore size is in the range from 10 nm to 50 nm, preferably from 10 nm to 30 nm, and more preferably from 15 nm to 25 nm. The catalytic activity of Ni is too high, and toimprove the morphological stability of the supported catalyst, Ni is alloyed with Fe. It is considered that both the lower gas turn-over frequency and the higher carbon diffusivity exhibited by iron will reduce gas turn-over frequency and increase carbon diffusivity in Ni-based alloys. This effect may reduce the dehydrogenation rate of methane molecules, while increasing carbon allotrope nucleation / growth rate, avoiding the accumulation of carbon adatoms on the catalyst surface, which would result in the catalyst encapsulation and deactivation. The size of the Ni alloy particles must be from 8 nm to 40 nm, preferably from 10 nm to 20 nm, and more preferably from 15 nm to 20 nm. Smaller metal particles display minimum or no methane splitting catalytic activity, while larger particles display lower catalytic activities too. The atomic concentration of Fe, in the metal alloy is from 1 % to 20 % (atomic), preferably from 5 % to 10%. The methane splitting reaction occurs at the surface of the pore-confined metal nanoparticles, particularly those accessible at the pore mouths. The formed hydrogen easily evolves, while carbon forms mostly crystalline tubular structures such as multiwall carbon nanotubes and carbon nanofibers. The formed carbon is mechanically prevented from diffusing through the side interfaces of the metal catalyst / support and reaching the bottom of the inclosing pore where the metal catalyst is inserted; thereby, the so-called tip growth is hampered.

[0083] In an embodiment, the ceramic support material is preferably an oxide selected from those of Si, Al, Zr, Ti, Mg, and combinations thereof, preferably an oxide selected from those of Si, Al, Zr, and combinations thereof, and more preferably is an oxide selected from SiCh, AI2O3 and combinations thereof. According to a preferred embodiment of the disclosure, the size of the ceramic support material ranges from 0.1 pm to 100 pm. Preferably from 0.5 pm to 100 pm; more preferably, from 5 pm to 25 pm.

[0084] In an embodiment, according to the disclosure, the catalyst shows a metal loading, defined as the mass of total metal, over the mass of the catalyst and expressed as a percentage, which is in the range from 5 % to 60 % (wt • meta l / wt • meso porous support+metai), preferably from 10 % to 50 % (wt.cataiyst / wt • mesoporous support+metai) and more preferably from 30 % to 50 % (wt.cataiyst / wt • mesoporous support+metai).

[0085] The following pertains to the inner surface of the channels and substrate, also referred to as macro-support.

[0086] In an embodiment, the substrate, also referred as macro-support, serves to hold the supported catalyst and should allow: i) the free drop of the formed carbon particles; ii) maximize the macro-surface per volume of the reactor; iii) minimize the construction costs; iv) minimize the hydrogen volume needed for the catalystshaving-off; and v) control the temperature, since the methane splitting reaction is endothermic. A preferential substrate design, which fulfils these requirements, considers using a ceramic monolith - Figure 2, feature 2.1, a metal honeycomb module - Figure 2, feature 2.2, a bundle of metal tubes - Figure 2, feature 2.3 - assembled as a module - Figure 2, feature 2.4, or a metallic, carbon-based or ceramic plate-and-frame module - Figure 2, feature 2.5. For simplicity, all types of substrates arereferred to as macro-support modules - Figure 2, features 2.1 to 2.5. A preferential implementation of the reaction chamber comprehends tubular channels that go through the entire module, with an inner equivalent diameter from 0.25 cm to 2 cm, and, more preferably, from 0.5 cm to 1 cm; larger diameters are required when the set size for the carbon particles is also large, or the length of the tubular channels are lengthy. The equivalent diameter is such that it should encompass at least four times the length of the carbon particles, to guarantee that no clogging of each channel, gap or tube occurs during carbon detachment. The preferential length of the tubular channels is from 1 cm to 20 m, and, more preferably, from 30 cm to 3 m. Longer tubular channels are prone to clogging with the produced carbon particles. The geometry of the tubular channels should facilitate the unimpeded growth of the carbon particles. Two preferential geometries are the cylindrical and the honeycomb - Figure 2, feature 2.2 and feature 2.3, where the honeycomb geometry displays a larger specific area and a higher power density of the catalytic module. In the case of the plate-and-frame reaction module - Figure 2, feature 2.5 - the distance between two consecutive plates should be from 1.5 mm to 10 mm, with a more preferential distance from 2 mm to 4 mm; the depth of the plate-and-frame macro-support should be from 5 cm to 10 m, and more preferably from 20 cm to 1 m.

[0087] In an embodiment, the supported catalyst should be applied over the bore surface side of the channels, as a monolayer - Figure 2, feature 2.6, or over both faces of each plate of the plat-and-frame module. For holding the supported catalyst to the catalyst support and preventing catalytic activity at the interface macro-support / supported catalyst, a thin, dense binding underlayer should be applied over the macro-support surface (or the inner surface of the channels) and the supported catalyst applied over as a monolayer - cf. Figure 3. This Figure illustrates the macro-support surface (the inner surface of the channels) - feature 3.1 - and a deposited binding under layer- feature 3.2. Figure 3, feature 3.3 illustrates a monolayer of supported catalyst particles over the binding underlayer, and Figure 3, feature 3.4, illustrates the underlayer loaded with a monolayer of supported catalyst already calcinated / carbonized.

[0088] In an embodiment, preferential implementations of this binding underlayer use a sol-gel approach, such as using tetraethoxysilane (TEOS) and 3-(trimethoxysilyl)propyl methacrylate (MAP) [4], to prepare a silica layer, or a sol-gel approach to produce an alumina layer [5], The sol-gel layer can be applied evenly [6] by suitable methods such as dip-coating, spraying, or slot-die. Another preferential implementation considers using a thermosetting polymer, such as a resin of resorcinol-formaldehyde, applied over the bore side surface of the catalytic module channels or both surfaces of each plate of the catalytic plate-and-frame module, normally as an ink formulation [7], The supported catalyst particles should be spread over the binding underlayer before being calcinated or carbonized, respectively, for the sol-gel or polymeric formulations; the adhesion displayed by the paste phase of this underlayer allows for holding the supported catalyst particles as a monolayer. After drying, the sol-gel layer should be calcinated at the maximum operating conditions of the reactor, between 750 °C and 850 °C, and the thermosettingpolymer coating should be carbonized at the maximum operating conditions of the reactor, between 750 °C and 850 °C, under an inert atmosphere. The binding underlayer should cover less than 50 % of the supported catalyst particles and more preferably ca. 25 %. During the drying process of the tubular substrate modules, they can be rotated horizontally to avoid inhomogeneities in thickness of the sol-gel or polymer layer. A preferential method for applying a homogeneous monolayer of the supported catalytic particles over the sol-gel or polymeric ink underlayer is dry flushing the particles down the tubular supports or over the plates. The sol-gel coating, or the polymeric ink, will capture the flowing down particles to a monolayer thickness; the excess particles should be reused. The macro-support after being loaded with the supported catalyst should be named the reaction module or catalytic module.

[0089] In an embodiment, since the methane splitting reaction is endothermic, reaction modules should allow local heating, either using electric resistances or thermal fluid. The heating power of these heating systems should be at least equal to the reaction enthalpy and preferably two to three times above, for assisting during the start-up of the reactor to heat it more quickly to the steady-state temperature. The reactor should have means to control the internal temperature to a maximum deviation of ± 50 °C, and, more preferably, to a maximum deviation of ± 15 °C. In a preferential implementation, the reaction modules may comprehend special holes for thermal controlling - e.g. inserting a thermocouple, or thermal heating - e.g., inserting a tube for circulating a thermal fluid or electrical heating resistances - Figure 2, feature 2.7. Figure 2, features 2.8 and 2.9 illustrate a preferential implementation of the thermal control and for thermal heating. A more preferential implementation of the heating resistances for the case of a plate-and-frame catalytic reaction module considers the use of electric conductive fibrous carbon plates (e.g. carbon paper) or folded metal foil plates, as sketched in Figure 2, feature 2.10. On the inner surface of the metal foil surface, it should be applied a thin foil of a thermostable electric insulating material, such as Thermiculite™. When folding the plate to the middle, wire-shaped electrical resistances should be placed inside. These resistances should then be connected to the plate-and-frame holders, where one should be the phase and the other the neutral - in the case if alternate current (AC) is used - or opposite potential signs if direct current (DC) is used. In the case of carbon-based plates, such as carbon paper, taking advantage of the electrical resistivity of these substrates, an electrical potential can be applied directly to the opposite ends of the reaction module, generating heat directly at the reaction module.The following pertains to the Reactor

[0090] A preferential implementation of the methane splitting reactor is sketched in Figure 4. Since it works between 750 °C and 850 °C, the reactor should be thermally insulated and electrically or thermally heated. The methane splitting reactor comprehends a top chamber - cf. Figure 4, feature 4.1, followed by the reaction module - cf. Figure 4, feature 4.2, and the cone for collecting the carbon particles - cf. Figure 4, feature 4.9. The reaction module or modules should fit into the reactor, leaving a chamberbetween the upper part of the reaction and the top of the reaction module - cf. Figure 4, feature 4.3; this chamber is named as the top reactor chamber. Moreover, the reaction module should fit into the reactor, such as if a gas feed enters through the top of the reactor, it can only reach its bottom if goes through the tubular channels / gaps of the reaction module. This top reactor chamber should comprehend a 3-way valve - cf. Figure 4, feature 4.4. During the production stage, this valve allows the reaction product stream to flow out of the reactor - cf. Figure 4, feature 4.5. During the carbon shaving-off stage, the 3-way valve closes the product stream and opens the inlet hydrogen flow - Figure 4, feature 4.6. The methane inlet should be fed to the bottom of the reactor - cf. Figure 4, feature 4.7; the inlet methane flowrate should be such that the methane conversion is at least 70 %. The reaction total pressure should be kept at a range from 1 x io5Pa to 5 x io5Pa (1 bar to 5 bar), during the production stage. When working at temperatures higher than 700 °C, the reaction equilibrium conversion is >82 %, and the hydrogen equilibrium concentration is >90 %, at atmospheric pressure. Increasing the operating pressure increases the kinetics of the methane spitting reaction but overloads the hydrogen separation process - normally a Pressure Swing Adsorption (PSA) unit or a carbon molecular sieve membrane module or modules - and the thermal energy recuperation from the product stream. The operating pressure should be tuned to minimize the production costs. During the shaving-off stage, the reactor's pressure should be set by the methane inlet stream- Figure 4, feature 4.8; then it should be closed, and the top 3-way valve turned to hydrogen feeding - Figure 4, feature 4.4. The inlet hydrogen enters through the top of the reaction module, filling up the reaction tubular channels or gaps and promoting the carbon particles peeling off and the recovery of the carbon product. The bottom of the reactor should be conical for collecting the carbon particles that fall, especially during the shaving-off stage - cf. Figure 4, feature 4.9. To promote a better detachment of the carbon particles, during this stage, the reactor may be made to vibrate. After filling up the conical bottom of the reactor, the carbon particles must be removed. This can be done by connecting this conical part, through a valve - cf. Figure 4, feature 4.10, to a container - cf. Figure 4, feature 4.11.

[0091] This container should be evacuated to prevent oxygen or inert gas from entering the reactor, or, preferably, it should be evacuated and filled with methane. In a preferential implementation, the carbon receiver container also has an on / off valve for venting the air and filling it with methane or just leaving it under vacuum - cf. Figure 4, feature 4.12. The dead volumes that may exist when coupling the reactor to the container, must be purged as well.The following pertains to shaving-off the carbon particles

[0092] During the carbon detachment stage - shaving-off, pure hydrogen should be supplied to the top of the reaction channels / gaps, as indicated in Figure 4, feature 4.3. The direction valve - Figure 4, feature 4.4 - should be turned to link the hydrogen input to the channels of the reaction models, closing theproduction flow - Figure 4, feature 4.5. The methane splitting is an equilibrium-limited reaction, which displays higher equilibrium conversions for higher temperatures and lower pressures. During the shaving- off stage, the reactor's pressure should be set, such that the methanation reaction kinetics is fast enough. For example, if the reactor is operated at 800 °C and 1 x 105Pa (1 bar), the reaction equilibrium conversion is ca. 92.5 %, and the hydrogen equilibrium concentration is ca. 96.1 %, while at 800 °C and 5 x 105Pa (5 bar), the reaction equilibrium conversion is co. 73 %, and the hydrogen equilibrium concentration is co. 84.4 %. If working at 800 °C, the shaving-off pressure should be co. 5 x 105Pa (5 bar) for a fast methanation and then for a fast shaving-off stage.The following pertains to General methods

[0093] In an embodiment, the specific surface area, pore volume, and mesopore mean diameter of the ceramic support materials, as described in this disclosure, were determined by IXh-physisorption at 77 K in a Micromeritics ASAP 2000 apparatus. In a standard experiment, the ceramic support material (co. 100 mg, 0.6-0.8 mm particle size) was dried at 523 K under a dynamic vacuum for 10 hours before recording the N2 physisorption isotherm. The total pore volume was determined from the total N2 uptake at a relative pressure (P / Po) of 0.95, where Po is the vapor pressure of nitrogen at 77 K. The specific surface area was determined by applying the Brunauer-Emmett-Teller (BET) method to the adsorption branch of the isotherm in the relative pressure (P / Po) range from 0.05 to 0.3. The average mesopore diameter was determined by applying the Barrett-Joyner-Halenda (BJH) formalism to the desorption branch of the isotherm.

[0094] In an embodiment, the metal loading on the catalysts was determined by Inductively-Coupled- Plasma Optical Emission Spectrometry (ICP-OES) in an iCAP™ PRO analyzer (Thermo Fisher Scientific) after disaggregating 30 mg of the solid sample in a HNO3:HF (1:3 vol ratio) solution at room temperature for 20 h. Quantification was based on calibration lines created by the analysis of certified standards (CertiPUR®) in the expected concentration ranges for each metal. Total metal loadings are expressed as the mass of metal over the mass of the catalyst and expressed as a percentage.

[0095] In an embodiment, the metal nanoparticle size on the catalysts was determined by Scanningtransmission electron microscopy ((S)TEM). The catalysts were first activated by a metal oxide reduction treatment by heating the sample from room temperature to 600 °C, using a heating ramp of 2 °C min1, and maintaining the temperature at 600 °C for 5 hours, under flow of 20 % l-h / He (vol). Next, catalysts, consisting of pore-confined Ni-Fe alloy nanoparticles, were embedded in a low-viscosity epoxy resin (Spurr, Merck) and cured at 343 K overnight. The embedded specimens were then cut into nm-thick sections (nominal thickness of co. 150 nm) using a Diatome 35" knife mounted on a Reichert-Jung Ultracut microtome, and the sections were collected on Cu TEM grids coated with a Formvar film and a carbon(300 mesh) overlay. For Co-based catalysts supported on non-porous ceramic supports, the powder catalyst was directly dry cast onto Cu TEM grids coated with a lacey carbon film. Microscopy experiments were performed in a JEOL JEM2100F microscope operating at 200 kV. Number-averaged particle diameters were determined by measuring at least 100 nanoparticles on different micrographs.

[0096] Methane conversion and hydrogen production rates were determined online, during methane splitting reaction tests utilizing a mass spectrometer Pfeiffer Vacuum ThermoStar GSD 301.Example 1

[0097] Particulate SiC (SiliaSphere silica Gel, 5 pm, Silicycle, CAS No. 112926-00-8) with spherical primary particles of 5 pm average diameter and 20 nm average pore size (narrow normal distribution) was dried at 150 °C under dynamic vacuum for 3 hours. Next, a solution of Ni NOah-SI- O, and Fe2(NO3)3-9H2O (Merck, CAS Nrs 13478-00-7 and 7782-61-8 respectively), with a Ni: Fe molar ratio of 80:20, in 0.1 M HNO3 was infiltrated into the porosity of the support under static vacuum. The overall metal concentration of the impregnating solution was adjusted to ca. 4 M. The volume of the impregnating solution applied was equivalent to 90 % of the total pore volume of the SiCh support material. Next, the impregnate was dried under dynamic vacuum (1 x 103Pa, which is 10 mbar) overnight and the dried solid (in powder form) was loaded into a packed-bed reactor, mounted in a vertically- oriented tubular oven and treated at 350 °C for 3 hours under flow of 2 % (vol) nitric oxide(NO) in He (Linde), using a heating rate of 2 °C min1from room temperature to decompose the pore-confined metal nitrate precursors into pore-confined metal oxide nanocrystals. The impregnation and calcination steps were repeated four times to attain a high cumulative degree of pore filling by the metal oxide nanocrystals and, thus, a high density of pore-confined metal at the pore mouths, i.e. close to the outer surface of the spherical primary SiC particles, which were not filled after the first calcination, due to the removed volume of water and nitrates. The overall metal loading was 43 wt.%.

[0098] In an embodiment, the supported catalyst material was loaded onto an 01-AI2O3 planar macroporous substrate through wet-spray deposition of a circular monolayer, corresponding to co. 0.5 mgcataiyst cm'2. The macroporous substrate was mounted into the reaction compartment of the reactor and the latter was sealed. To activate the catalyst, it was subjected to a thermal reduction treatment in the reactor, underflow of 50 % H2 in Ar, at 1 x 105Pa (1 bar) and heating to 750 °C at a heating rate of 1 °C min1to render the pore-confine metals into their active zerovalent alloy state. The catalyst was then exposed to a flow of pure methane, at 1 x 105Pa (1 bar) and 750 °C, promoting the methane splitting reaction. Figure 5 depicts the metal-normalized hydrogen production rate, expressed as grams of H2 produced, per unit of metal mass in the catalyst and per hour of operation. The catalyst was given space for carbon to grow continuously without requiring shaving-off. No deactivation is reported, throughout the catalytic process.Example 2

[0099] A set of 3 steel tubes with an internal diameter of 1.3 cm, 20 cm long, were taken. The bore-side of these tubes was coated, using a cylindrical paintbrush, with a layer of TEOS ca. 25 pm thick. The supported catalyst, prepared as described in Example 1, was applied using a turning brush initially loaded with the catalyst. The excess catalyst was then removed, making air circulate through the tube; a layer of ca. 0.8 mg / cm2of supported catalyst was obtained. Finally, the 3 tubes were inserted into an open-to-air oven, to convert the TEOS coating layer into silica, at 600 °C. The tubes were turned slowly, horizontally, inside the oven. At the end, the tubes were inspected to assess the quality of the catalyst layer.

[0100] On the shell side of the tubes, a heat flow of 40 W was applied from an electric resistance; a thermocouple attached to the external surface of a tube allowed to control the temperature. The catalytic tubes were then placed in a perforated steel plate; top and bottom perforated plates were applied. The set was held together using three threaded bars, see Figure 4; the interface between the plates and the tubes was made hermetic using vermiculite foil (e.g. Thermiculite™). The upper plate was fixed tight to the container; this allowed feeding of the bore side of all tubes through the top of the casing - Figure 4. The methane inlet was made through the side of the reactor casing at the bottom.

[0101] In an embodiment, the reactor was run for 200 hours at 750 °C, with hydrogen production stages of a duration of 360 min and carbon shaving-off stages of a duration of 20 min. Before cyclic carbon shaving-off, methane was continuously fed for 60 hours. After 6 shaving cycles, the catalyst was again continuously exposed to methane. The methane was fed at 1.1 x 105Pa (1.1 bar); the feed flowrate was set to 700 cm3min1, while the hydrogen flowrate was approximately 1 L min1. The hydrogen flowrate during the shaving-off stage was set to 500 cm3min1and the average operation pressure during the shaving-off stage was co. 2 x 105Pa (2 bar). Figure 6 shows the hydrogen concentration - mass spectrometer Pfeiffer Vacuum ThermoStar GSD 301 - at the product stream, during the production stage, and the produced flowrate.Example 3

[0102] A set of 3 steel tubes with an internal diameter of 1.3 cm, 20 cm long, were taken. The bore-side of these tubes was coated, using a cylindrical paintbrush, with a layer of TEOS co. 25 pm thick. The supported catalyst, prepared as described in Example 1, was applied using a turning brush initially loaded with the catalyst. Finally, the 3 tubes were inserted into an open-to-air oven, to convert the TEOS coating layer into silica, at 600 °C. The tubes were turned slowly, horizontally, inside the oven. At the end, the tubes were inspected to assess the quality of the catalyst layer.

[0103] On the shell side of the tubes, a heat flow of 40 W was applied from an electric resistance; a thermocouple attached to the external surface of a tube allowed to control the temperature. The tubes were then placed in a perforated steel plate; top and bottom perforated plates were applied. The set washeld together using three threaded bars, see Figure 4; the interface between the plates and the tubes was made hermetic using vermiculite (e.g. Thermiculite™). The upper plate was fixed tight to the container; this allowed feeding of the bore side of all tubes through the top of the casing - Figure 4. The methane inlet was made through the side of the reactor casing at the bottom.

[0104] This reactor was run for 18 hours at 700 °C, with hydrogen production stages of a duration of 60 min and catalyst shaving-off stages of a duration of 3 min. The methane was fed at 2.5 x 105Pa (2.5 bar); the feed flowrate was set to 1.2 L min1, while the hydrogen flowrate was approximately 1.7 L min1. The hydrogen flowrate during the shaving-off stage was set to 1 L min1and the average operation pressure during the shaving-off stage was ca. 5 x 105Pa (5 bar). Figure 7 shows the hydrogen concentration - mass spectrometer Pfeiffer Vacuum ThermoStar GSD 301 - at the product stream, during the production stage, and the produced flowrate. All the carbon particles formed during the process were multi-walled carbon nanotubes, produced by base-growth mechanism - Figure 8 displays transmission electron microscopy micrograms of carbon particles / filaments produced during the experiments used in this disclosure as examples.

[0105] The term "comprising" whenever used in this document is intended to indicate the presence of stated features, integers, steps, components, but not to preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[0106] The disclosure should not be seen in any way restricted to the embodiments described and a person with ordinary skill in the art will foresee many possibilities to modifications thereof. The abovedescribed embodiments are combinable.

[0107] The following dependent claims further set out particular embodiments of the disclosure.Example 4

[0108] A set of 3 steel tubes with an internal diameter of 1.3 cm, 20 cm long, were taken. The bore-side of these tubes was coated with an initial layer of boehmite by dip-coating, ca. 25 pm thick. The emulsion for dip-coating comprised 10 wt.% of solids, and ethylene glycol was used as the solvent. The solvent was evaporated at 200 °C. The supported catalyst, prepared as described in Example 1, was also applied using dip-coating with the same wt.% as the previous deposition. However, solids comprised both the supported catalyst and boehmite in a mass ratio of 5:1, respectively. A thermal treatment was then applied with a first stage at 200 °C to evaporate the solvent and then with a second stage at 700 °C to promote the phase transition of boehmite to y-ALOs, enabling it to act as a ceramic binder. During all drying stages, rotation of the tubes was applied to ensure layer uniformity.

[0109] On the shell side of the tubes, it was applied an electric resistance of 40 W; a thermocouple attached to the external surface of a tube allowed to control the temperature. The tubes were then placed in a perforated steel plate; top and bottom perforated plates were applied. The set was held togetherusing three threaded bars, see Figure 4; the interface between the plates and the tubes was made hermetic using vermiculite (e.g. Thermiculite). The upper plate was fixed tight to the container; this allowed feeding of the bore side of all tubes through the top of the casing - Figure 4. The methane inlet was made through the side of the reactor casing at the bottom.

[0110] This reactor was run for 18 hours at 700 °C, with hydrogen production stages of a duration of 60 min and catalyst shaving-off stages of a duration of 3 min. The methane was fed at 2.5 x 105Pa (2.5 bar); the feed flowrate was set to 1.2 L min1, while the hydrogen flowrate was ca. 1.7 L min1. The hydrogen flowrate during the shaving-off stage was set to 1 L min1and the average operation pressure during the shaving-off stage was co. 5 x 105Pa (5 bar). All the carbon particles formed during the process were multiwalled carbon nanotubes, produced by base-growth mechanism, as observed in the previous example (Figure 8).

[0111] This project has received funding from the European Commission through the European Union's Horizon 2020 programme - FET Proactive research and innovation action - under grant agreement No. 952219 (112CO2).

[0112] The term "comprising" whenever used in this document is intended to indicate the presence of stated features, integers, steps, components, but not to preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[0113] As used herein, the term "about" a number refers to that number plus or minus 10 % of that number. The term "about" a range refers to that range minus 10 % of its lowest value and plus 10 % of its greatest value.

[0114] Where ranges are given, endpoints are included. Furthermore, it is to be understood that unless otherwise indicated or otherwise evident from the context and / or the understanding of one of ordinary skill in the art, values that are expressed as ranges can assume any specific value within the stated ranges in different embodiments of the invention, to the tenth of the unit of the lower limit of the range, unless the context clearly dictates otherwise. It is also to be understood that unless otherwise indicated or otherwise evident from the context and / or the understanding of one of ordinary skill in the art, values expressed as ranges can assume any subrange within the given range, wherein the endpoints of the subrange are expressed to the same degree of accuracy as the tenth of the unit of the lower limit of the range.

[0115] The disclosure should not be seen in any way restricted to the embodiments described and a person with ordinary skill in the art will foresee many possibilities to modifications thereof.

[0116] The above described embodiments are combinable.

[0117] The following claims further set out particular embodiments of the disclosure.References[1] Method for parallel production of hydrogen and carbon-containing products. WO 2013 / 004398 A8, 2013.[2] Pocock G, Cornejo A, Chua HT. A process for producing hydrogen and graphitic carbon from hydrocarbons. WO 2016 / 154666 Al, 2016.[3] Magalhaes Mendes AM, Mateos Pedrero C, Dias Catarino M. Catalytic methane decomposition and catalyst regeneration, methods and uses thereof. WO 2020 / 12287 Al, 2020.[4] Longhi M, Casagrande RB, Kunst SR, Santos V dos, Ferreira JZ. Obtainment and Characterization of a Silicon alkoxides-based Coating Applied to a Substrate of Stainless Steel 316L for Use in Biomaterials. Mater Res 2019;22. https: / / doi.org / 10.1590 / 1980-5373-mr-2018-0514.[5] Hubert T, Schwarz J, Oertel B. Sol-gel alumina coatings on stainless steel for wear protection. J Sol-Gel Sci Technol 2006;38:179-84. https: / / doi.org / 10.1007 / sl0971-006-6470-7.[6] Innocenzi P, Abdirashid MO, Guglielmi M. Structure and properties of sol-gel coatings from methyltriethoxysilane and tetraethoxysilane. J Sol-Gel Sci Technol 1994;3:47-55. https: / / doi.org / 10.1007 / BF00490148.[7] Rodrigues SC, Whitley R, Mendes A. Preparation and characterization of carbon molecular sieve membranes based on resorcinol-formaldehyde resin. J Memb Sci 2014;459:207-16. https: / / doi.Org / 10.1016 / j.memsci.2014.02.013.

Claims

C L A I M S1. Reactor for production of hydrogen and carbon from methane splitting, comprising: a gas inlet for methane flow, a reaction chamber for methane splitting, a gas outlet comprising unreacted methane and hydrogen, a bottom outlet for carbon removal by gravity from the reaction chamber; wherein the reaction chamber; comprises a plurality of gas flow channels with a macro-support; wherein each macro-support comprises a plurality of catalyst supports; wherein each catalyst support comprises a plurality of nickel and iron alloy active particles as catalyst; wherein the alloy catalysts particles are confined in the catalyst support; wherein the alloy active particles are able to contact with the methane flow for catalysing the methane splitting reaction.

2. Reactor according to any of the previous claims, wherein the geometry of the reaction chamber is selected from a hexagonal shape, a honeycomb shape, a tubular shape, a cubical shape or a parallelepipedal shape.

3. Reactor according to any of the previous claims, wherein the geometry of the plurality of gas flow channels is selected from: tubular, hexagonal, rectangular, or combinations thereof.

4. Reactor according to any of the previous claims, wherein the reaction chamber and / or the plurality of gas flow channels comprises at least a heating device for controlling the temperature reaction, preferably an electrical heating resistance or a thermal fluid.

5. Reactor according to the previous claim, wherein the heating device is arranged in a tube or a plate.

6. Reactor according to any of the previous claims, further comprising a temperature transductor arranged between the plurality of gas flow channels, preferably a thermocouple.

7. Reactor according to any of the previous claims, wherein the plurality of gas flow channels has an inner equivalent diameter from 0.25 cm to 2 cm; more preferably from 0.5 cm to 1 cm.

8. Reactor according to the previous claims, wherein each channel of the plurality of gas flow channels traverses the entire chamber, with a preferential length of the tubular channels from 1 cm to 20 m; more preferably from 30 cm to 3 m.

9. Reactor according to the previous claims, wherein the parallelepipedal shape of the reactor chamber contains slots between the rectangularly shaped plurality of gas flow channels, for heating device plate placement.

10. Reactor according to the previous claims, wherein the distance between consecutive aforementioned plates is from 1.5 mm to 10 mm, more preferably from 2 mm to 4 mm.

11. Reactor according to the previous claims, wherein the catalytic support is porous; in particular the catalytic support is mesoporous.

12. Reactor according to the previous claims, wherein the size of the pores of the catalytic support ranges from 10 nm to 50 nm; preferably from 10 nm to 30 nm; more preferably from 15 nm to 25 nm.

13. Reactor according to the previous claim, wherein the size of each particle of the plurality of nickel and iron alloy active particles is from 8 nm to 40 nm; preferably from 10 nm to 20 nm; more preferably from 15 nm to 20 nm.

14. Reactor according to the previous claims, wherein the depth of the parallelepipedal shaped reactor module is from 5 cm to 10 m; more preferably from 20 cm to 1 m.

15. Reactor according to any of the previous claims, wherein the mass amount of iron in each particle of the plurality of nickel and iron alloy active particles is up to 20 % (wt.metai / wt.mesoporous support+metai); preferably from 5 % to 10 % (wt.metai / wt.mesoporous support+metai).

16. Reactor according to the previous claims, wherein the catalytic support has particles ranging from 0.1 pm to 100 pm; preferably from 0.5 pm to 100 pm; more preferably from 5 pm to 25 pm.

17. Reactor according to any of the previous claims, wherein the metal loading of the reactor ranges from 5 % to 60 % (w / w); preferably from 10 % to 50 % (w / w); more preferably from 30 % to 50 % (w / w).

18. Reactor according to any of previous claims, further comprising a second gas inlet for introducing a gas shaving-off flow, for removing the carbon deposition in the catalytic support, allowing the shaving-off of the plurality of nickel and iron alloy catalysts.

19. Reactor according to the previous claim, wherein the gas shaving-off stream is a hydrogen stream, preferably a pure hydrogen stream.

20. Reactor according to any of previous claims, wherein the bottom of the reaction chamber is cone or funnel shaped.

21. Reactor according to any of the previous claims, comprises a container arranged below a bottom of the reactor chamber, for carbon collection.

22. Reactor according to any of the previous claims, comprising a third gas inlet to introduce a gas methane flow to the container, for protecting the produced carbon flacks.

23. Reactor according to any of the previous claims, wherein the macro-support is selected from a list consisting of: a metal, a ceramic, a carbon-based material, or combination thereof.

24. Reactor according to any of the previous claims, wherein the catalytic support material is selected from a list consisting of: an oxide of silicon, an oxide of aluminium, an oxide of zirconium, an oxide of titanium, an oxide of magnesium, or combinations thereof; preferably an oxide of silicon, an oxide of aluminium, an oxide of zirconium, or combinations thereof; more preferably oxide of silicon, oxide of aluminium or combinations thereof.

25. Reactor according to any of the previous claims, wherein the amount of active particles in the macrosupport ranges from 0.1 mgcataiyst cm'2to 2 mgcataiyst cm'2, preferably from 0.5 to 1 mgcataiyst cm-2.

26. Process for continuous methane splitting using the reactor described in any of the previous claims, comprising: feeding the reactor with a methane rich flow, wherein the reactor comprises a gas inlet for methane flow, a reaction chamber for methane splitting, a gas outlet comprising unreacted methane and hydrogen, a bottom outlet for carbon removal by gravity from the reaction chamber; wherein the reaction chamber comprises a plurality of gas flow channels with a macro-support; wherein the macro-support comprises a plurality of catalyst supports; wherein each catalyst support comprises a plurality of nickel and iron alloy active particles; wherein the alloy active particles are partially confined in the catalyst support; wherein the alloy catalysts particles are able to contact with the methane flow for catalysing the methane splitting reaction; wherein the operation temperature ranges from about 750 °C to 850 °C; preferably from about 750 °C to 800 °C; optionally adding a shaving-off stage to react at the catalyst interface with deposited carbon, for carbon detachment.

27. Process according to the previous claim, comprising a further previous step of bonding the catalyst particles to the macro-support by an alumina ceramic, or a silica ceramic, or a thermosetting polymer.

28. Process according to the previous claim, wherein the alumina ceramic, or the silica ceramic, or the carbonized thermosetting polymer is stable at the operation temperature ranges.

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