Ultra-fast ammonia decomposition using an electrified tungsten wire lightbulb reactor

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Despite extensive efforts to develop active catalysts to address the reaction's slow kinetics, we introduce a tungsten wire lightbulb reactor that operates at unconventionally high temperatures with enhanced efficiency. Near the wire, temperature reaches up to 1,800 K, enabling ultra-fast ammonia decomposition with rate constants much higher than those of leading catalysts under typical reaction conditions. Concurrently, the sharp temperature decrease along the radial direction allows for low power inputs, thus enhancing energy efficiency. It also realized up to 99.995% conversion at enhanced power input without the use of membrane separation. We further discuss a scale-up reactor design that is two to three orders of magnitude smaller than current state-of-the-art reactors and highlight its potential applications within the emerging hydrogen economy. Physical sciences/Engineering/Chemical engineering Physical sciences/Energy science and technology/Renewable energy/Hydrogen energy Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Main As a lighting apparatus, quartz tungsten halogen lamps are often dismissed due to their low energy-to-light efficiency, discarding most of its input power as heat 1 . However, the extreme temperatures a tungsten wire reaches (> 3,000 K) with moderate power inputs may be advantageous for achieving ultra-fast rates in endothermic reactions, such as the ammonia decomposition reaction (ADR) for hydrogen production. Today, 87 million tonnes of hydrogen is produced globally per year, mainly via methods with high carbon footprints 2 , but this must shift to green hydrogen production and increase fourfold by 2050 if we are to achieve our industrial decarbonisation goals 3 . With the difficulty of compressing and transporting hydrogen, easily transportable and already widely distributed ammonia has emerged as a prime candidate for a carbon-free hydrogen carrier, making ADR a crucial reaction for future green industries 4 . Pure NH 3 -derived H 2 can be used as a feedstock for other chemical processes or fed to fuel cells (for vehicles or power generation, Fig. 1 a) 5 . Thermodynamically, ammonia should fully decompose (> 99%) at 660 K and above at atmospheric pressure 6 . However, the reaction is kinetically limited at these low temperatures due to the high N-H bond energy of 391 kJ/mol 7 . This results in a theoretical Gibbs free activation energy for the first N-H breaking step as high as 406 kJ/mol (Text S1). Small-scale commercial ADR reactors therefore often use Ni-based catalysts to lower the activation energy to around 100 kJ/mol 8 , but even then elevated operational temperatures of 973-1,173 K are needed 9 . These slow kinetics, which require a large amount of catalyst or bulky heating furnaces to overcome, would result in large reactor footprints that make it impractical for applications such as decentralised vehicle refuelling 10 , 11 . For example, available commercial crackers need a volume of 6–12 m 3 to refuel 100 cars a day 12 , which is an order of magnitude larger than the average size of a gasoline pumping station. Current research thus focuses on developing catalytic materials that further lower the activation energy until conversions close to the thermodynamic limit can be achieved at an operating temperature of 673–873 K 13 . In terms of activity, the most promising candidates are noble metal Ru-based ones 14 – 16 , although its high price and scarcity adds challenges for large-scale adoption. Following Ru, inexpensive transition metal catalysts such as those based on Ni or Co 17 have reached the lowest activation energy of 57 kJ/mol 18 . Based on the Arrhenius equation, switching from the commercial Ni catalyst to the best cheap metal catalyst at a typical temperature of 773 K can encouragingly increase the reaction rate constant by over 1000 times. Nonetheless, reaction rate is not only exponentially dependent on activation energy but also temperature. With the same commercial Ni catalyst, increasing temperature from 773 K to 1,673 K increases rate 5,000 times. Yet, almost all works on ADR catalytic reactors operate below 1,173 K 8 . Indeed, few industrial gas phase thermo-chemical processes are found to operate at temperatures above 1,173 K 19 , indicating that safe and energy efficient high temperature operation is a significant challenge in chemical reaction engineering. Maintaining such high temperatures in conventional packed-bed reactors is difficult due to low reactor efficiencies and the challenges of finding materials suitable for long-term operation in such harsh conditions 20 , 21 . To address this issue, we draw inspiration from recently developed high temperature joule heating processes, 22 – 25 as well as the commonplace tungsten lightbulb, which is able to emit high temperatures at relatively low energy input through Joule-heating of the very thin and resistive tungsten wire. After an extensive literature search, we do not yet see such a reactor concept applied to ADR. In this work, we report that an electrified tungsten wire lightbulb (TWL) reactor – essentially a quartz tungsten lamp with reactive gas flowing through – exhibits ultra-fast kinetic rates for ADR. Though tungsten is a relatively poor ADR catalyst 8 , 26 , its resistive properties allow for high temperatures to be reached at a low power input, which results in fast rates and high productivities (Fig. 1 b). We have examined the performance, heat and mass transfer phenomenon, and design parameters of this TWL reactor for ammonia decomposition through both experimental testing and computational fluid dynamics (CFD) modelling. We also propose a scaled-up design of the reactor that shows the potential of this technology in decarbonising essential industrial sectors. Results Experimental performance of a prototype lab-scale reactor The lab-scale TWL flow reactor consists of a tungsten wire (10 cm length, 0.1 mm diameter) connected to a DC power supply via copper rods (0.8 mm diameter) and encased in a gas-tight quartz tube (Fig. 2 a). Under a pure NH 3 flow at atmospheric pressure (10–180 mL/min flow rate i.e., 110-1,960 h − 1 space velocity), power was supplied and the tungsten wire heated. Both theoretical estimations (Text S2) and experimental measurement using an infrared camera show that the average tungsten wire temperature ranges from 1,230 K at 9 W to 1,690 K at 41 W (Fig S1 ), which was also reflected visually as the tungsten wire glows brighter with each power increment (Fig. 2 b). IR photographs show that these high temperature regions were primarily focused on the tungsten wire (Fig S2). Around 13% conversion was achieved at a power input of 9.5 W and space velocity of 220 h − 1 . At the same space velocity, 100% conversion was reached when the power input was increased to 25 W and above (Fig. 2 c). Conversion decreases from 100–62% when the space velocity was increased from 110 to 1,960 h − 1 (representing the lowest and highest possible space velocities that can be tested in our lab, respectively) at 25 W power input, while at 41 W input conversion only decreases from 100–89%. When the power input was increased to 60 W, an ultra-high conversion of 99.995% or 44 ppm residue NH 3 was achieved (Table S1 ). To the best of our knowledge, no other lab-scale ADR system has achieved such high purity without the aid of a membrane 13 , 27 . This shows the potential of the TWL reactor to be used directly for some high-purity applications with minimized purification. In addition to NH 3 conversion, the main process performance indicator in this work is energy efficiency, defined as the ratio of energy outflow in hydrogen to the input power and energy in ammonia consumed (Text S3) following the literature. 28 , 29 As conversion did not proportionally decrease with increasing space velocity, a peak efficiency of 60% was achieved under the highest space velocity of 1,960 h − 1 in lab setting at 24 W (Fig. 2 d), which is one of the highest reactor efficiencies found among other lab-scale catalytic ADR systems (Table S2). Performing the reaction over a period of 100 hours does not show a discernible change in conversion (Fig. 2 e), while SEM images show that the wire remains unchanged before and after this stability test (Fig S3). Given the average lifespan of a tungsten lightbulb of > 1,000 hours 30 and the stable performance over the first 100 hours, we expect the TWL reactor to have good durability. After experimentally determining reaction kinetic parameters (Fig S4), we calculated rate constants of the TWL reactor to compare to that of other recently reported lab-scale ADR reactors. Most conventional thermal reactors operate in the range of 723–873 K, much lower compared to our system. Systems with high activity catalysts have rate constants of 70–160 s − 1 at a temperature of 770 K 18 , 31 – 33 , while our reactor exhibits a value of 1,060 s − 1 at 41 W input and 210 s − 1 at 25 W input (Fig. 2 e) even using a poor catalyst like tungsten. As only a small amount of tungsten wire is necessary to achieve such high reaction rates, our system also achieves catalyst weight normalised hydrogen production rates 30 times higher than the average of other reactors. Energy utilisation of the lab-scale TWL reactor We elucidated the physical phenomenon occurring through a CFD model implemented in COMSOL Multiphysics. The reactor was modelled in a 2D axisymmetric geometry for ease of computational costs, with the middle of the reactor through the centre of the tungsten wire/rods being the symmetry axis (Fig. 3 a). The geometry consists of the copper rods, tungsten wire, quartz tube gas chamber, and quartz reactor wall, whose dimensions follow that of the experimental setup closely (see Computational Methods in SI for details). Mesh refinement was also performed to show that the model is mesh independent (Fig S5). The validity of the model was checked by comparing the model’s prediction of conversion and energy efficiency with the experimental data at the full range tested (Fig. 3 b). The average relative errors for conversion and energy efficiency, as well as temperature and power input (Fig S6), are all under 15% and thus deemed to be in a narrow enough range. We then used the model to estimate the performance at higher space velocities that are hard to achieve in our current lab setting (but possible in industrial settings). The main observation is that increasing space velocity continuously improves energy efficiency at the cost of decreased single pass conversion of ammonia. We also used the CFD model to investigate temperature distribution within the TWL reactor. At 25 W power input, the high temperature of the tungsten wire rapidly decreases across the radius (Fig. 3 c). Similar temperature profiles are observed at other power inputs (Fig S7), which concurs with the IR photographs that show a radial temperature decrease of up to 400 K by the dimensionless radial distance R = 0.05 (Fig S2). The majority of the reactor can thus be classified as a low temperature zone. This is in contrast to the typical temperature profile of a packed bed reactor for a fast endothermic reaction, which show little change radially but has large variations in the axial direction 34 , 35 . The maximum temperature at the high temperature region is higher than in the lower temperature zone by a staggering 870 K at 9 W, 1,214 K at 25 W, and 1,430 K at 41 W (Fig S8). Based on our estimation of non-catalytic ADR rate constants (Fig S9), there should be negligible activity in the gas-phase. Because reaction rates on tungsten surface are ultra-fast at high temperatures, the reactor is mass transport limited at our operating conditions. As shown in Fig. S10, conversion does not decrease proportionately with an increase in space velocity. Furthermore, due to the radial temperature variation, faster velocities are found at the low temperature zone around R = 0.5 (Fig S11) and viscosity varies radially as well (Fig S12). This leads to a gas flux that is up to five times faster in the low temperature zone than in the high temperature zone (Fig. 3 d & Fig S13). This is comparable to the H 2 flux through packed bed membrane reactors 36 , 37 , showing that the low temperature zone is beneficial for mass transport. Overall, having this sharp radial temperature gradient means that, in contrast to a conventional reactor where the entire packed bed must be kept at a high temperature to maximize catalyst utilisation 38 , the TWL reactor has less unutilised heat as the majority of the reactor temperature is kept low. Its radially non-isothermal nature contributes to the reactor’s high energy efficiency performance. We then performed energy balance calculations (Text S4) and present the key findings in a Sankey diagram for the condition with the highest energy efficiency as an example (Fig. 6 a). From every 66 W of energy brought into the system, including 24 W power input ( \(\:{P}_{in}\) ) and 42 W carried by NH 3 \(\:{(P}_{N{H}_{3,in}})\) , 30.6 W leaves the reactor as product gas ( \(\:{P}_{{H}_{2}})\) . This led to the observed energy efficiency of 60%, whilst considering the unutilised energy retained in the form of unreacted NH 3 ( \(\:{P}_{N{H}_{3},out}\) ). The major pathway for heat loss is via natural convection at the external quartz wall ( \(\:{P}_{conv}\) ). The rest of the energy is lost via radiation in the form of heat ( \(\:{P}_{rad}\) ). Increasing power input and thus temperature increases the proportion of energy transferred through radiative heat (Fig S14a), which is also evidenced by the increased radiative heat flux from the wire (Fig S15) and absorbed radiation (Fig S16). As space velocity and thus efficiency increases, in the externally mass transfer limited conditions our reactor operates in, the radiative heat loss decreases as more heat is consumed by the additional ammonia 39 (Fig S14b). Overall, 89% of the energy loss is contributed to convection and 11% to radiation. These losses need to be minimised for improved energy efficiency. To prevent radiative heat loss, reflectors are often used in radiative heating devices 40 . Thus, we constructed a TWL reactor that includes a silver-coated outer layer preserved under vacuum, which acts as a reflective wall around the gas flow chamber. This reactor glows more brightly compared to the original reactor at various power inputs, indicating that the radiation has been reflected inside (Fig S17). In another effort, we attempt to alleviate heat loss from natural convection on the outer reactor walls by covering it with a thick insulating layer of quartz wool followed by a layer of aluminium foil that should also act as a reflector. While no significant improvements in conversion were observed for both modified reactors (Fig S18), we see that there was an increase in the outlet gas temperature from 309 K to 334 K and 428 K, with the addition of reflector walls and insulator walls, respectively (Fig. 4 ). This indicates that the heat gained through reflectance or insulation is absorbed by NH 3 as internal energy and transferred to outlet N 2 and H 2 . In accordance with the energy balance, more heat is recovered by preventing convective heat loss rather than radiative heat loss. As many applications for NH 3 -derived H 2 require elevated temperatures (e.g., 370 K for PEMFCs), the use of reflectors and insulation present potential energy savings from downstream applications. Proposed scale-up design with enhanced productivity and efficiency We then evaluated the performance of the TWL reactor at industrially relevant production scales. Firstly, the reactor tube diameter was optimised and the reactor wall material changed from quartz to steel to reflect industry practices. Smaller tube radii can maintain higher conversions at higher space velocities (Fig S19a) due to less radial heat loss, and thus obtain peak efficiencies at higher space velocities (Fig S19b). However, smaller tubes would also lead to higher wall temperatures that are detrimental to the durability of the reactor wall material (Fig S19c). So, a reactor diameter of 0.3 cm was chosen as it showed a high efficiency while keeping the wall temperature well below the standard maximum for steel reactors at 1,173 K. The parameters for the best-case single-tube simulation were used in a multi-tubular model (Fig S20), as multiple tubes do not only increase hydrogen productivity but also energy efficiency due to decreased energy loss. This approach was inspired from our earlier discussion on external convection being a major heat loss contributor that may be reduced by packing multiple tubes closely together (Fig S21a). Different tube arrangements were simulated to obtain the optimal geometry (Table S3). Further improvement in ammonia decomposition activity was then found in the multi-tube model compared to a single tube, resulting in a maximum energy efficiency of 88% for partial cracking with 43% conversion, or 76% efficiency at 97% conversion (Fig S21b). Based on the simulation results, we propose a modular reactor design for easily increasing the production capacity to different application needs. In a single module of 3 L, 1,700 parallel tubes produce 100 kg H2 /day with 97% conversion and a 60 kW power input (Text S5). Alternatively, the same size module produces 150 kg H2 /day at 43% conversion, 52 kW power input, at a higher space velocity (Fig. 5 a). The reactor’s performance was compared to the most common method of making hydrogen today, steam methane reforming (SMR), and conventional thermal ADR (Fig. 5 b). A typical side-fired packed bed reactor used to make the same amount of hydrogen via steam methane reforming today would have a volume in the range of 1,000–2,280 m 3 41 – 44 , making the TWL reactor more compact by close to three orders of magnitude as it discards the bulky furnace and catalyst packing. Assuming the use of a carbon-free green ammonia feedstock and low-emissions renewable energy for power, the TWL reactor could emit up to 20 times less greenhouse gases compared to SMR 41 , similar to the emissions caused by conventional thermal ADR 10 . Due to the high costs of green ammonia (Fig S22), TWL is more costly than SMR today, but it is comparable with conventional thermal ADR. With the positive prognosis that the costs of renewable energy and green ammonia would decrease in the future 45 , 46 , and further improvements to the TWL reactor design to decrease its energy consumption, this technology would become more cost competitive. We finally performed back-of-the-envelope calculations to show its feasibility in various NH 3 to H 2 applications at different scales and requirements (Fig. 5 c). The total power input includes estimations of associated purification and compression steps (Text S6). For applications like decentralised vehicle refuelling, the compact reactor volume of the TWL reactor would be highly advantageous. Due to the low power requirements, renewable electricity could be supplied off-grid; for example, refuelling 100 vehicles a day in a sunny place like Singapore will require solar panels with an area just twice that of an average gas station. The reactor may also be applied for power generation. The electricity demand to fully crack NH 3 for a small stationary H 2 fuel cell is quite high. On the other hand, 30% of the electricity output is needed to partially crack NH 3 for use in a larger NH 3 /H 2 -blend-fulled turbine, which has better combustion properties than the use of pure NH 3 fuel 47 . As discussed above, 88% energy efficiency can be achieved in a reactor with 43% conversion, suggesting the TWL system may be more suitable for power generation via partial cracking. Nonetheless, the performance of the TWL, achieving full conversions at 76% energy efficiency, remains competitive for potential industrial application to produce high purity H 2 for fuel cell applications (Fig. 6 b-c). Thus, even without a fully optimised design, we see the potential for the TWL reactor to be applied in multiple scenarios of the ammonia/hydrogen economy. Discussion In this work, we have demonstrated the effectiveness of an electrified tungsten wire lightbulb reactor in decomposing ammonia into hydrogen. This reactor can overcome the sluggish ADR kinetics of the typical low-temperature system by operating in the range of 1,230 K to 1,690 K with high efficiency. The non-homogeneous temperature gradient in the reactor, where at low power inputs the tungsten catalyst has temperatures exceeding 1,400 K that achieves rates up to ten times higher than the best low-temperature ADR catalysts, enable high productivity. A peak energy efficiency of 60% is achieved experimentally, and a record high purity of only 44 ppm NH 3 in the product stream is obtained at higher power input. Modelling the performance at industrial scales show that the proposed reactor design would be much smaller and lower in energy consumption than existing conventional hydrogen production methods, and is feasible in multiple applications including power generation, H 2 vehicle refuelling, and for chemical feedstock supply. The use of Joule-heating is an advantage of the reactor, as it provides the opportunity for the process to be directly powered by renewable electricity in practice 22 , 42 , 48 – 52 , and has low barrier towards industrial adoption as the reactor design is more similar to traditionally heated furnaces 53 , 54 . High temperature Joule-heated reactors have been tested for reactions such as methane pyrolysis, but these are susceptible to coking whereas such issues do not exist in our ADR system 55 – 60 . Electrified tungsten for ADR has been reported decades earlier, but only a lower temperature range between 970 K and 1,073 K were explored to understand the kinetics of ammonia decomposition on the tungsten surface 19 , 20 . More recently, Joule-heating has been used to obtain uniform catalyst temperature distributions in ADR reactors, but once again these operate at low temperatures (up to 913 K) 29 , 61 . The TWL reactor is thus unique in its approach and efficacy for facilitating ADR. Regardless, steps shall be taken to improve the design of the reactor in future. A more robust model that considers the effects of the reflector should be constructed. Alternative configurations for the scaled-up reactor may also be studied, for example a modular parallel wire model 62 . Convective heat transfer within the reactor may be improved through the inclusion of baffles on the reactor walls 63 , which would allow the ammonia gas to recirculate into the centre of the reactor where temperatures are the highest, increasing contact time and therefore reaction extent. Given the intermittency of renewable sources that would be used to power such an electrified reactor, transient studies and modelling of the reactor should be performed. This will better inform the operational behaviour of the reactor, which together with the more detailed design would lead to improved accuracy of cost estimations. Nonetheless, the current design already shows promise of the TWL reactor in a variety of application scenarios, putting confidence in the potential application of this technology in decarbonising the future hydrogen economy. Methods Experimental Methods Lab-scale experiments were performed in a reactor consisting of a quartz tube (ID 1 cm, OD 1.27 cm) fitted with Swagelok UltraTorr fittings for gas-tightness. In either end of the tube, copper rods were inserted, with a thin tungsten wire (0.1 mm diameter) at a fixed length of 10 cm tied between the two ends of the rod inside the tube. A DC electric supply was connected onto the other ends of the copper rods that are protruding out the tube. Ammonia gas (Matheson, 99.9995%) was flowed through the inlet using mass flow controllers (Alicat), while the reactor outlet was connected to a GC equipped with a thermal conductivity detector (Agilent 7890B) for on-line product analysis. Space velocity was calculated based on the NH 3 flow rate and reactor quartz tube volume. Conversion was measured once the system has reached a stable state, and the reported values are the average of at least three GC injections (~ 30 mins on-stream). For measuring trace amounts of NH 3 , outlet gas was passed through 20 mL 10 mM H 2 SO 4 solution for 20 minutes, then the NH 4 + concentration of the solution was quantified using an ion chromatographer. Reaction kinetics were measured using tungsten mesh (150 mg) in a thermal-catalytic setup. Temperature of the tungsten filament was measured using the Optris PI 05M infrared camera equipped with an Optris ACPIXMO27 lens. Scanning electron microscopy (JEOL JSM-7610F Plus) and energy dispersive spectrometry (Oxford Instruments X-Max N ) were used to characterize the tungsten wire morphology and elemental composition before and after reactor testing. Computational Methods The CFD model consists of equations for electromagnetic heating, heat transfer, laminar flow, species transport, and radiation in a participating medium. The cylindrical lab-scale reactor was simulated as a 2D axisymmetric model at steady-state in COMSOL Multiphysics 5.6. Full details can be read in the Supplementary Information. Declarations Data availability All data supporting this investigation is available in the article and its Supplementary Information. Acknowledgments We thank the Singapore Low-Carbon Energy Research (LCER) Funding Initiative hosted under A*STAR for the financial support (Award No. U2102d2005) and the RIE2025 USS LCER Phase II Programme (Award No. U2305D4002). N. Yan acknowledges the support from National Research Foundation (NRF) Singapore under its NRF Investigatorship (NRFI07-2021-0015). Author contributions K.S.I. performed experiments, conducted simulations, analysed data, and wrote and revised the manuscript. S.S.W. performed experiments, conducted simulations, analysed data, and revised the manuscript. S.W. performed experiments and analysed data. D. X. analysed data and revised the manuscript. N.Y. conceived and supervised the entire study. 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Numerical modeling and experimental validation of focused surface heating using near-infrared rays with an elliptical reflector. Int. J. Heat Mass Transfer 78 , 240-250 (2014). https://doi.org/10.1016/j.ijheatmasstransfer.2014.06.073 IEAGHG. Techno-Economic Evaluation of SMR Based Standalone (Merchant) Plant with CCS. (IEA GHG, Gloucestershire, UK, 2017). Wismann, S. T. et al. Electrified methane reforming: A compact approach to greener industrial hydrogen production. Science 364 , 756-759 (2019). Yang, H. et al. Distributed electrified heating for efficient hydrogen production. Nat. Commun. 15 , 3868 (2024). https://doi.org/10.1038/s41467-024-47534-8 Bonaquist, D. Analysis of CO2 Emissions, Rductions, and Capture for Large-Scale Hydrogen Production Plants. (Praxair, 2010). IRENA & AEA. Innovation Outlook: Renewable Ammonia. (International Renewable Energy Agency, Ammonia Energy Association, Abu Dhabi, Brooklyn, 2022). Swearer, D. F., Knowles, N. R., Everitt, H. O. & Halas, N. J. Light-Driven Chemical Looping for Ammonia Synthesis. ACS Energy Lett. 4 , 1505-1512 (2019). https://doi.org/10.1021/acsenergylett.9b00860 Mei, B., Zhang, J., Shi, X., Xi, Z. & Li, Y. Enhancement of ammonia combustion with partial fuel cracking strategy: Laminar flame propagation and kinetic modeling investigation of NH3/H2/N2/air mixtures up to 10 atm. Combust. Flame 231 , 111472 (2021). https://doi.org/https://doi.org/10.1016/j.combustflame.2021.111472 Yu, K., Wang, C., Zheng, W. & Vlachos, D. G. Dynamic Electrification of Dry Reforming of Methane with In Situ Catalyst Regeneration. ACS Energy Lett. 8 , 1050-1057 (2023). https://doi.org/10.1021/acsenergylett.2c02666 Kim, Y. T., Lee, J.-J. & Lee, J. Electricity-driven reactors that promote thermochemical catalytic reactions via joule and induction heating. Chem. Eng. J. 470 (2023). https://doi.org/10.1016/j.cej.2023.144333 Wismann, S. T. et al. Electrified methane reforming: Elucidating transient phenomena. Chem. Eng. J. 425 (2021). https://doi.org/10.1016/j.cej.2021.131509 Mallapragada, D. S. et al. Decarbonization of the chemical industry through electrification: Barriers and opportunities. Joule 7 , 23-41 (2023). https://doi.org/https://doi.org/10.1016/j.joule.2022.12.008 Dong, Q. et al. Depolymerization of plastics by means of electrified spatiotemporal heating. Nature 616 , 488-494 (2023). https://doi.org/10.1038/s41586-023-05845-8 Zheng, L., Ambrosetti, M. & Tronconi, E. Joule-Heated Catalytic Reactors toward Decarbonization and Process Intensification: A Review. ACS Engineering Au 4 , 4-21 (2024). https://doi.org/10.1021/acsengineeringau.3c00045 Ma, Q. et al. Grave-to-cradle dry reforming of plastics via Joule heating. Nat. Commun. 15 , 8243 (2024). https://doi.org/10.1038/s41467-024-52515-y Shekunova, V. M., Aleksandrov, Y. A., Tsyganova, E. I. & Filofeev, S. V. Cracking of light hydrocarbons in the presence of electrically heated metal wires. Petroleum Chemistry 57 , 446-451 (2017). https://doi.org/10.1134/s0965544117050097 Porsin, A. V., Kulikov, A. V., Amosov, Y. I., Rogozhnikov, V. N. & Noskov, A. S. Acetylene synthesis by methane pyrolysis on a tungsten wire. Theor. Found. Chem. Eng. 48 , 397-403 (2014). https://doi.org/10.1134/s0040579514040241 Sun, Q., Tang, Y. & Gavalas, G. R. Methane Pyrolysis in a Hot Filament Reactor. Energy Fuels 14 , 490-494 (2000). https://doi.org/10.1021/ef9901995 Sigaeva, S. S., Likholobov, V. A. & Tsyrul’nikov, P. G. Pyrolysis of methane on a heat-treated FeCrAl coil heated with electric current. Kinet. Catal. 54 , 199-206 (2013). https://doi.org/10.1134/S0023158413010126 Osipov, A. R., Sidorchik, I. A., Borisov, V. A., Temerev, V. L. & Shlyapin, D. A. Conversions of Ethane and Ethylene with Methane on a Resistive Fechral Catalyst in the Presence of Hydrogen. Catalysis in Industry 13 , 258-262 (2021). https://doi.org/10.1134/S2070050421030090 Sigaeva, S. S., Temerev, V. L., Borisov, V. A. & Tsyrul’nikov, P. G. Pyrolysis of methane on fechral resistive catalyst with additions of hydrogen or oxygen to the reaction mixture. Catalysis in Industry 7 , 171-174 (2015). https://doi.org/10.1134/S2070050415030101 Cherif, A., Zarei, M., Lee, J.-S., Yoon, H.-J. & Lee, C.-J. Modeling and multi-objective optimization of electrified ammonia decomposition: Improvement of performance and thermal behavior. Fuel 358 (2024). https://doi.org/10.1016/j.fuel.2023.130243 Balakotaiah, V. & Ratnakar, R. R. Modular reactors with electrical resistance heating for hydrocarbon cracking and other endothermic reactions. AICHhE Journal 68 , e17542 (2022). https://doi.org/10.1002/aic.17542 Da Silva Miranda, B. M. & Anand, N. K. Convective Heat Transfer in a Channel with Porous Baffles. Numerical Heat Transfer, Part A: Applications 46 , 425-452 (2004). https://doi.org/10.1080/10407780490478515 Additional Declarations There is NO Competing Interest. Supplementary Files 250215SI.docx Cite Share Download PDF Status: Published Journal Publication published 21 Oct, 2025 Read the published version in Nature Chemical Engineering → Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6039914","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":417342041,"identity":"e8cc0abc-7be4-4aa5-b6e9-dc1f94e49885","order_by":0,"name":"Ning Yan","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA3klEQVRIiWNgGAWjYDACZijNj8olRotkA9FaYMDgALFazNl5D79gbLPLM77dY/yBocI6sYH/+AW8Wiyb+dIsGNuSi83unDGTYDiTntggkVOA3z2HecwMGNuYE7fdyDFjYGw7DNTCk0CMlvrEzTNyjD8w/gNq4T9DUIvxA5DhGyRyDCQYG4BaGNIPELSFIeHc8cQZN9LKJBKOpRu3SeTg1cFgcP6M8YcPZdWJ/TOSN3/4UGMt289//AF+PQwMbBKJbFAmyBNsDDwGhLQwf2D4gyLATtCWUTAKRsEoGFkAAIFIRRWEqoTMAAAAAElFTkSuQmCC","orcid":"https://orcid.org/0000-0002-1877-9206","institution":"National University of Singapore","correspondingAuthor":true,"prefix":"","firstName":"Ning","middleName":"","lastName":"Yan","suffix":""},{"id":417342042,"identity":"12ed2dfd-7b15-4c80-97ec-3668eb9ea3f3","order_by":1,"name":"Keshia Indriadi","email":"","orcid":"https://orcid.org/0009-0000-6938-2519","institution":"National University of Singapore","correspondingAuthor":false,"prefix":"","firstName":"Keshia","middleName":"","lastName":"Indriadi","suffix":""},{"id":417342043,"identity":"e2495f9d-2242-4ff3-ac15-c063c6817d16","order_by":2,"name":"Sie Shing Wong","email":"","orcid":"","institution":"National University of Singapore","correspondingAuthor":false,"prefix":"","firstName":"Sie","middleName":"Shing","lastName":"Wong","suffix":""},{"id":417342044,"identity":"45921f44-f40d-4ebf-bb7f-dfeede7130bb","order_by":3,"name":"Sikai Wang","email":"","orcid":"","institution":"National University of Singapore","correspondingAuthor":false,"prefix":"","firstName":"Sikai","middleName":"","lastName":"Wang","suffix":""},{"id":417342045,"identity":"b10c0ee3-7d88-4134-9f8d-1106a506d302","order_by":4,"name":"Di Xu","email":"","orcid":"","institution":"National University of Singapore","correspondingAuthor":false,"prefix":"","firstName":"Di","middleName":"","lastName":"Xu","suffix":""}],"badges":[],"createdAt":"2025-02-16 07:55:15","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6039914/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6039914/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s44286-025-00283-x","type":"published","date":"2025-10-21T04:00:00+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":76764166,"identity":"5048d089-e6cc-4b1b-8b0c-dd10582901d7","added_by":"auto","created_at":"2025-02-20 13:06:00","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":230041,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eIllustration of the tungsten wire lightbulb reactor concept. a \u003c/strong\u003eADR is a key reaction in the hydrogen economy that would be \u003cstrong\u003eb \u003c/strong\u003econventionally conducted in a fired catalytic packed-bed reactor, whereas the tungsten wire lightbulb (TWL) reactor has the potential to operate at a higher space time productivity. PBR: packed bed reactor.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-6039914/v1/3ccf8aaae4f9c01875fe2de1.png"},{"id":76764172,"identity":"3c335575-5c9d-4d74-9a98-d0a6207ca69a","added_by":"auto","created_at":"2025-02-20 13:06:00","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":477465,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eExperimental performance of lab-scale TWL reactor. a \u003c/strong\u003eExperimental setup. \u003cstrong\u003eb \u003c/strong\u003eAverage\u003cstrong\u003e \u003c/strong\u003etungsten wire temperature at various power inputs and 220 h\u003csup\u003e-1 \u003c/sup\u003eNH\u003csub\u003e3\u003c/sub\u003e flow as measured by an IR camera, and an IR image of a 3.4x0.5 mm portion of the tungsten wire at 40 W. The colour bar is temperature in Kelvins.\u0026nbsp; \u003cstrong\u003ec\u003c/strong\u003e NH\u003csub\u003e3\u003c/sub\u003e conversion and \u003cstrong\u003ed\u003c/strong\u003e energy efficiency at various power inputs and space velocities. \u003cstrong\u003ee \u003c/strong\u003eConversion and energy efficiency at 25 W input and 655 h\u003csup\u003e-1\u003c/sup\u003e space velocity over 100 h time-on-stream. \u003cstrong\u003ef \u003c/strong\u003eRate constant and hydrogen productivity of the TWL reactor compared to other catalytic ADR systems in literature (see Table S2 for details).\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-6039914/v1/c41bd398ce909b93ef7ec61b.png"},{"id":76765145,"identity":"fa68d147-2d19-429a-8aac-a0159318a853","added_by":"auto","created_at":"2025-02-20 13:14:00","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":257204,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eTemperatures and mass transport in the lab-scale TWL reactor based on CFD modelling. a \u003c/strong\u003eSchematic of the 2D axisymmetric model of our experimental setup built for CFD simulation.\u003cstrong\u003e b \u003c/strong\u003eValidation of simulation results with experimental data at three different power inputs and NH\u003csub\u003e3\u003c/sub\u003e space velocity of 100-2,000 h\u003csup\u003e-1\u003c/sup\u003e, and simulated results up to 17,461 h\u003csup\u003e-1\u003c/sup\u003e.\u003csup\u003e \u003c/sup\u003e\u003cstrong\u003ec \u003c/strong\u003eTemperature profile of the reactor at 25 W input and 220 h\u003csup\u003e-1 \u003c/sup\u003eNH\u003csub\u003e3\u003c/sub\u003e space velocity (left) and comparison of temperature across the reactor at different power inputs and 220 h\u003csup\u003e-1\u003c/sup\u003e NH\u003csub\u003e3\u003c/sub\u003e space velocity (right). \u003cstrong\u003ed\u003c/strong\u003e Flux of H\u003csub\u003e2\u003c/sub\u003e through the reactor at 1,960 h\u003csup\u003e-1\u003c/sup\u003e space velocity and 25 W power input.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-6039914/v1/fe1fa47ccc8ce90d93babbf6.png"},{"id":76765546,"identity":"23fda61a-aa07-4e8b-9d59-61398f32540a","added_by":"auto","created_at":"2025-02-20 13:22:00","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":102568,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eAttempts to reduce convective and radiative heat loss in lab scale reactor. \u003c/strong\u003eThe original reactor, reactor with insulator, and reactor with reflector are compared at 20 W input and 220 h\u003csup\u003e-1\u003c/sup\u003e NH\u003csub\u003e3\u003c/sub\u003e flow. The increase in temperature indicates that the energy gained is transferred to product internal energy (∆U).\u0026nbsp;\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-6039914/v1/517e1470fae19b40dd02ad78.png"},{"id":76764167,"identity":"b74d15ba-9021-454b-ba5c-f9bc151df222","added_by":"auto","created_at":"2025-02-20 13:06:00","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":406443,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eProposed scale-up applications of the TWL reactor. a \u003c/strong\u003eSchematic of a single TWL reactor module, producing either 97% or 43% NH\u003csub\u003e3\u003c/sub\u003e conversion at the same reactor size (drawings are not to scale). Multiple modules can be combined to increase the production capacity. \u003cstrong\u003eb \u003c/strong\u003eEstimation of reactor volume, global warming potential (GWP), and cost of the TWL reactor compared to thermal ammonia decomposition and steam methane reforming (SMR) at a scale of 200 ton\u003csub\u003eH2\u003c/sub\u003e/day production. \u003cstrong\u003ec\u003c/strong\u003e Viability of the TWL reactor system for various application scenarios.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-6039914/v1/38d864ceeb18d43088a346a7.png"},{"id":76765547,"identity":"b17176fd-dd39-499b-bea7-4b96d95b4836","added_by":"auto","created_at":"2025-02-20 13:22:00","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":254220,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eEnergy balance of the TWL reactor at different conditions and scales: a \u003c/strong\u003eLab-scale experimental at 24 W input and 1,960 h\u003csup\u003e-1\u003c/sup\u003e space velocity, \u003cstrong\u003eb \u003c/strong\u003esimulation for PEMFC vehicle refuelling scenario (low space velocity, high conversion), \u003cstrong\u003ec \u003c/strong\u003esimulation for partial cracking for power generation scenario (high space velocity, low conversion). The equation for energy efficiency (EE) is also shown. \u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-6039914/v1/7d95486bb301ab3178074d32.png"},{"id":94062433,"identity":"202e86f2-19f0-499b-afc4-92a557a33651","added_by":"auto","created_at":"2025-10-22 07:09:40","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2588798,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6039914/v1/a02aabe9-1dd7-49f8-940f-6737c0424b16.pdf"},{"id":76765548,"identity":"b09e3c33-a290-4976-ad6a-2992bfd77773","added_by":"auto","created_at":"2025-02-20 13:22:00","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":4295450,"visible":true,"origin":"","legend":"","description":"","filename":"250215SI.docx","url":"https://assets-eu.researchsquare.com/files/rs-6039914/v1/9eb468aadf3fc28ff3d107c8.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Ultra-fast ammonia decomposition using an electrified tungsten wire lightbulb reactor","fulltext":[{"header":"Main","content":"\u003cp\u003eAs a lighting apparatus, quartz tungsten halogen lamps are often dismissed due to their low energy-to-light efficiency, discarding most of its input power as heat\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e. However, the extreme temperatures a tungsten wire reaches (\u0026gt;\u0026thinsp;3,000 K) with moderate power inputs may be advantageous for achieving ultra-fast rates in endothermic reactions, such as the ammonia decomposition reaction (ADR) for hydrogen production.\u003c/p\u003e \u003cp\u003eToday, 87\u0026nbsp;million tonnes of hydrogen is produced globally per year, mainly via methods with high carbon footprints\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e, but this must shift to green hydrogen production and increase fourfold by 2050 if we are to achieve our industrial decarbonisation goals\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e. With the difficulty of compressing and transporting hydrogen, easily transportable and already widely distributed ammonia has emerged as a prime candidate for a carbon-free hydrogen carrier, making ADR a crucial reaction for future green industries\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e. Pure NH\u003csub\u003e3\u003c/sub\u003e-derived H\u003csub\u003e2\u003c/sub\u003e can be used as a feedstock for other chemical processes or fed to fuel cells (for vehicles or power generation, Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea)\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThermodynamically, ammonia should fully decompose (\u0026gt;\u0026thinsp;99%) at 660 K and above at atmospheric pressure\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e. However, the reaction is kinetically limited at these low temperatures due to the high N-H bond energy of 391 kJ/mol\u003csup\u003e7\u003c/sup\u003e. This results in a theoretical Gibbs free activation energy for the first N-H breaking step as high as 406 kJ/mol (Text S1). Small-scale commercial ADR reactors therefore often use Ni-based catalysts to lower the activation energy to around 100 kJ/mol\u003csup\u003e8\u003c/sup\u003e, but even then elevated operational temperatures of 973-1,173 K are needed\u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e. These slow kinetics, which require a large amount of catalyst or bulky heating furnaces to overcome, would result in large reactor footprints that make it impractical for applications such as decentralised vehicle refuelling\u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e,\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e. For example, available commercial crackers need a volume of 6\u0026ndash;12 m\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e to refuel 100 cars a day\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e, which is an order of magnitude larger than the average size of a gasoline pumping station.\u003c/p\u003e \u003cp\u003eCurrent research thus focuses on developing catalytic materials that further lower the activation energy until conversions close to the thermodynamic limit can be achieved at an operating temperature of 673\u0026ndash;873 K\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e. In terms of activity, the most promising candidates are noble metal Ru-based ones\u003csup\u003e\u003cspan additionalcitationids=\"CR15\" citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e, although its high price and scarcity adds challenges for large-scale adoption. Following Ru, inexpensive transition metal catalysts such as those based on Ni or Co\u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e have reached the lowest activation energy of 57 kJ/mol\u003csup\u003e18\u003c/sup\u003e. Based on the Arrhenius equation, switching from the commercial Ni catalyst to the best cheap metal catalyst at a typical temperature of 773 K can encouragingly increase the reaction rate constant by over 1000 times.\u003c/p\u003e \u003cp\u003eNonetheless, reaction rate is not only exponentially dependent on activation energy but also temperature. With the same commercial Ni catalyst, increasing temperature from 773 K to 1,673 K increases rate 5,000 times. Yet, almost all works on ADR catalytic reactors operate below 1,173 K\u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e. Indeed, few industrial gas phase thermo-chemical processes are found to operate at temperatures above 1,173 K\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e, indicating that safe and energy efficient high temperature operation is a significant challenge in chemical reaction engineering. Maintaining such high temperatures in conventional packed-bed reactors is difficult due to low reactor efficiencies and the challenges of finding materials suitable for long-term operation in such harsh conditions\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e,\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e. To address this issue, we draw inspiration from recently developed high temperature joule heating processes,\u003csup\u003e\u003cspan additionalcitationids=\"CR23 CR24\" citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e as well as the commonplace tungsten lightbulb, which is able to emit high temperatures at relatively low energy input through Joule-heating of the very thin and resistive tungsten wire. After an extensive literature search, we do not yet see such a reactor concept applied to ADR.\u003c/p\u003e \u003cp\u003eIn this work, we report that an electrified tungsten wire lightbulb (TWL) reactor \u0026ndash; essentially a quartz tungsten lamp with reactive gas flowing through \u0026ndash; exhibits ultra-fast kinetic rates for ADR. Though tungsten is a relatively poor ADR catalyst\u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e,\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e, its resistive properties allow for high temperatures to be reached at a low power input, which results in fast rates and high productivities (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). We have examined the performance, heat and mass transfer phenomenon, and design parameters of this TWL reactor for ammonia decomposition through both experimental testing and computational fluid dynamics (CFD) modelling. We also propose a scaled-up design of the reactor that shows the potential of this technology in decarbonising essential industrial sectors.\u003c/p\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eExperimental performance of a prototype lab-scale reactor\u003c/h2\u003e \u003cp\u003eThe lab-scale TWL flow reactor consists of a tungsten wire (10 cm length, 0.1 mm diameter) connected to a DC power supply via copper rods (0.8 mm diameter) and encased in a gas-tight quartz tube (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea). Under a pure NH\u003csub\u003e3\u003c/sub\u003e flow at atmospheric pressure (10\u0026ndash;180 mL/min flow rate i.e., 110-1,960 h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e space velocity), power was supplied and the tungsten wire heated. Both theoretical estimations (Text S2) and experimental measurement using an infrared camera show that the average tungsten wire temperature ranges from 1,230 K at 9 W to 1,690 K at 41 W (Fig \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e), which was also reflected visually as the tungsten wire glows brighter with each power increment (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb). IR photographs show that these high temperature regions were primarily focused on the tungsten wire (Fig S2).\u003c/p\u003e \u003cp\u003eAround 13% conversion was achieved at a power input of 9.5 W and space velocity of 220 h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. At the same space velocity, 100% conversion was reached when the power input was increased to 25 W and above (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec). Conversion decreases from 100\u0026ndash;62% when the space velocity was increased from 110 to 1,960 h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (representing the lowest and highest possible space velocities that can be tested in our lab, respectively) at 25 W power input, while at 41 W input conversion only decreases from 100\u0026ndash;89%. When the power input was increased to 60 W, an ultra-high conversion of 99.995% or 44 ppm residue NH\u003csub\u003e3\u003c/sub\u003e was achieved (Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e). To the best of our knowledge, no other lab-scale ADR system has achieved such high purity without the aid of a membrane\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e,\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e. This shows the potential of the TWL reactor to be used directly for some high-purity applications with minimized purification.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn addition to NH\u003csub\u003e3\u003c/sub\u003e conversion, the main process performance indicator in this work is energy efficiency, defined as the ratio of energy outflow in hydrogen to the input power and energy in ammonia consumed (Text S3) following the literature.\u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e,\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e As conversion did not proportionally decrease with increasing space velocity, a peak efficiency of 60% was achieved under the highest space velocity of 1,960 h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in lab setting at 24 W (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed), which is one of the highest reactor efficiencies found among other lab-scale catalytic ADR systems (Table S2). Performing the reaction over a period of 100 hours does not show a discernible change in conversion (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee), while SEM images show that the wire remains unchanged before and after this stability test (Fig S3). Given the average lifespan of a tungsten lightbulb of \u0026gt;\u0026thinsp;1,000 hours\u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e and the stable performance over the first 100 hours, we expect the TWL reactor to have good durability.\u003c/p\u003e \u003cp\u003eAfter experimentally determining reaction kinetic parameters (Fig S4), we calculated rate constants of the TWL reactor to compare to that of other recently reported lab-scale ADR reactors. Most conventional thermal reactors operate in the range of 723\u0026ndash;873 K, much lower compared to our system. Systems with high activity catalysts have rate constants of 70\u0026ndash;160 s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at a temperature of 770 K\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e,\u003cspan additionalcitationids=\"CR32\" citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e, while our reactor exhibits a value of 1,060 s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at 41 W input and 210 s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at 25 W input (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee) even using a poor catalyst like tungsten. As only a small amount of tungsten wire is necessary to achieve such high reaction rates, our system also achieves catalyst weight normalised hydrogen production rates 30 times higher than the average of other reactors.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eEnergy utilisation of the lab-scale TWL reactor\u003c/h3\u003e\n\u003cp\u003eWe elucidated the physical phenomenon occurring through a CFD model implemented in COMSOL Multiphysics. The reactor was modelled in a 2D axisymmetric geometry for ease of computational costs, with the middle of the reactor through the centre of the tungsten wire/rods being the symmetry axis (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea). The geometry consists of the copper rods, tungsten wire, quartz tube gas chamber, and quartz reactor wall, whose dimensions follow that of the experimental setup closely (see Computational Methods in SI for details). Mesh refinement was also performed to show that the model is mesh independent (Fig S5).\u003c/p\u003e \u003cp\u003eThe validity of the model was checked by comparing the model\u0026rsquo;s prediction of conversion and energy efficiency with the experimental data at the full range tested (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb). The average relative errors for conversion and energy efficiency, as well as temperature and power input (Fig S6), are all under 15% and thus deemed to be in a narrow enough range. We then used the model to estimate the performance at higher space velocities that are hard to achieve in our current lab setting (but possible in industrial settings). The main observation is that increasing space velocity continuously improves energy efficiency at the cost of decreased single pass conversion of ammonia.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eWe also used the CFD model to investigate temperature distribution within the TWL reactor. At 25 W power input, the high temperature of the tungsten wire rapidly decreases across the radius (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec). Similar temperature profiles are observed at other power inputs (Fig S7), which concurs with the IR photographs that show a radial temperature decrease of up to 400 K by the dimensionless radial distance R\u0026thinsp;=\u0026thinsp;0.05 (Fig S2). The majority of the reactor can thus be classified as a low temperature zone. This is in contrast to the typical temperature profile of a packed bed reactor for a fast endothermic reaction, which show little change radially but has large variations in the axial direction\u003csup\u003e\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e,\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u003c/sup\u003e. The maximum temperature at the high temperature region is higher than in the lower temperature zone by a staggering 870 K at 9 W, 1,214 K at 25 W, and 1,430 K at 41 W (Fig S8). Based on our estimation of non-catalytic ADR rate constants (Fig S9), there should be negligible activity in the gas-phase.\u003c/p\u003e \u003cp\u003eBecause reaction rates on tungsten surface are ultra-fast at high temperatures, the reactor is mass transport limited at our operating conditions. As shown in Fig. S10, conversion does not decrease proportionately with an increase in space velocity. Furthermore, due to the radial temperature variation, faster velocities are found at the low temperature zone around R\u0026thinsp;=\u0026thinsp;0.5 (Fig S11) and viscosity varies radially as well (Fig S12). This leads to a gas flux that is up to five times faster in the low temperature zone than in the high temperature zone (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed \u0026amp; Fig S13). This is comparable to the H\u003csub\u003e2\u003c/sub\u003e flux through packed bed membrane reactors\u003csup\u003e\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e,\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u003c/sup\u003e, showing that the low temperature zone is beneficial for mass transport. Overall, having this sharp radial temperature gradient means that, in contrast to a conventional reactor where the entire packed bed must be kept at a high temperature to maximize catalyst utilisation\u003csup\u003e\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e\u003c/sup\u003e, the TWL reactor has less unutilised heat as the majority of the reactor temperature is kept low. Its radially non-isothermal nature contributes to the reactor\u0026rsquo;s high energy efficiency performance.\u003c/p\u003e \u003cp\u003eWe then performed energy balance calculations (Text S4) and present the key findings in a Sankey diagram for the condition with the highest energy efficiency as an example (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea). From every 66 W of energy brought into the system, including 24 W power input (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{P}_{in}\\)\u003c/span\u003e\u003c/span\u003e) and 42 W carried by NH\u003csub\u003e3\u003c/sub\u003e \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{(P}_{N{H}_{3,in}})\\)\u003c/span\u003e\u003c/span\u003e, 30.6 W leaves the reactor as product gas (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{P}_{{H}_{2}})\\)\u003c/span\u003e\u003c/span\u003e. This led to the observed energy efficiency of 60%, whilst considering the unutilised energy retained in the form of unreacted NH\u003csub\u003e3\u003c/sub\u003e (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{P}_{N{H}_{3},out}\\)\u003c/span\u003e\u003c/span\u003e). The major pathway for heat loss is via natural convection at the external quartz wall (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{P}_{conv}\\)\u003c/span\u003e\u003c/span\u003e). The rest of the energy is lost via radiation in the form of heat (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{P}_{rad}\\)\u003c/span\u003e\u003c/span\u003e). Increasing power input and thus temperature increases the proportion of energy transferred through radiative heat (Fig S14a), which is also evidenced by the increased radiative heat flux from the wire (Fig S15) and absorbed radiation (Fig S16). As space velocity and thus efficiency increases, in the externally mass transfer limited conditions our reactor operates in, the radiative heat loss decreases as more heat is consumed by the additional ammonia\u003csup\u003e\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u003c/sup\u003e (Fig S14b).\u003c/p\u003e \u003cp\u003eOverall, 89% of the energy loss is contributed to convection and 11% to radiation. These losses need to be minimised for improved energy efficiency. To prevent radiative heat loss, reflectors are often used in radiative heating devices\u003csup\u003e\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u003c/sup\u003e. Thus, we constructed a TWL reactor that includes a silver-coated outer layer preserved under vacuum, which acts as a reflective wall around the gas flow chamber. This reactor glows more brightly compared to the original reactor at various power inputs, indicating that the radiation has been reflected inside (Fig S17). In another effort, we attempt to alleviate heat loss from natural convection on the outer reactor walls by covering it with a thick insulating layer of quartz wool followed by a layer of aluminium foil that should also act as a reflector. While no significant improvements in conversion were observed for both modified reactors (Fig S18), we see that there was an increase in the outlet gas temperature from 309 K to 334 K and 428 K, with the addition of reflector walls and insulator walls, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). This indicates that the heat gained through reflectance or insulation is absorbed by NH\u003csub\u003e3\u003c/sub\u003e as internal energy and transferred to outlet N\u003csub\u003e2\u003c/sub\u003e and H\u003csub\u003e2\u003c/sub\u003e. In accordance with the energy balance, more heat is recovered by preventing convective heat loss rather than radiative heat loss. As many applications for NH\u003csub\u003e3\u003c/sub\u003e-derived H\u003csub\u003e2\u003c/sub\u003e require elevated temperatures (e.g., 370 K for PEMFCs), the use of reflectors and insulation present potential energy savings from downstream applications.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eProposed scale-up design with enhanced productivity and efficiency\u003c/h3\u003e\n\u003cp\u003eWe then evaluated the performance of the TWL reactor at industrially relevant production scales. Firstly, the reactor tube diameter was optimised and the reactor wall material changed from quartz to steel to reflect industry practices. Smaller tube radii can maintain higher conversions at higher space velocities (Fig S19a) due to less radial heat loss, and thus obtain peak efficiencies at higher space velocities (Fig S19b). However, smaller tubes would also lead to higher wall temperatures that are detrimental to the durability of the reactor wall material (Fig S19c). So, a reactor diameter of 0.3 cm was chosen as it showed a high efficiency while keeping the wall temperature well below the standard maximum for steel reactors at 1,173 K. The parameters for the best-case single-tube simulation were used in a multi-tubular model (Fig S20), as multiple tubes do not only increase hydrogen productivity but also energy efficiency due to decreased energy loss. This approach was inspired from our earlier discussion on external convection being a major heat loss contributor that may be reduced by packing multiple tubes closely together (Fig S21a). Different tube arrangements were simulated to obtain the optimal geometry (Table S3). Further improvement in ammonia decomposition activity was then found in the multi-tube model compared to a single tube, resulting in a maximum energy efficiency of 88% for partial cracking with 43% conversion, or 76% efficiency at 97% conversion (Fig S21b). Based on the simulation results, we propose a modular reactor design for easily increasing the production capacity to different application needs. In a single module of 3 L, 1,700 parallel tubes produce 100 kg\u003csub\u003eH2\u003c/sub\u003e/day with 97% conversion and a 60 kW power input (Text S5). Alternatively, the same size module produces 150 kg\u003csub\u003eH2\u003c/sub\u003e/day at 43% conversion, 52 kW power input, at a higher space velocity (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe reactor\u0026rsquo;s performance was compared to the most common method of making hydrogen today, steam methane reforming (SMR), and conventional thermal ADR (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb). A typical side-fired packed bed reactor used to make the same amount of hydrogen via steam methane reforming today would have a volume in the range of 1,000\u0026ndash;2,280 m\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e \u003cspan additionalcitationids=\"CR42 CR43\" citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e\u003c/sup\u003e, making the TWL reactor more compact by close to three orders of magnitude as it discards the bulky furnace and catalyst packing. Assuming the use of a carbon-free green ammonia feedstock and low-emissions renewable energy for power, the TWL reactor could emit up to 20 times less greenhouse gases compared to SMR\u003csup\u003e\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e\u003c/sup\u003e, similar to the emissions caused by conventional thermal ADR\u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e. Due to the high costs of green ammonia (Fig S22), TWL is more costly than SMR today, but it is comparable with conventional thermal ADR. With the positive prognosis that the costs of renewable energy and green ammonia would decrease in the future\u003csup\u003e\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e,\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e\u003c/sup\u003e, and further improvements to the TWL reactor design to decrease its energy consumption, this technology would become more cost competitive.\u003c/p\u003e \u003cp\u003eWe finally performed back-of-the-envelope calculations to show its feasibility in various NH\u003csub\u003e3\u003c/sub\u003e to H\u003csub\u003e2\u003c/sub\u003e applications at different scales and requirements (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec). The total power input includes estimations of associated purification and compression steps (Text S6). For applications like decentralised vehicle refuelling, the compact reactor volume of the TWL reactor would be highly advantageous. Due to the low power requirements, renewable electricity could be supplied off-grid; for example, refuelling 100 vehicles a day in a sunny place like Singapore will require solar panels with an area just twice that of an average gas station. The reactor may also be applied for power generation. The electricity demand to fully crack NH\u003csub\u003e3\u003c/sub\u003e for a small stationary H\u003csub\u003e2\u003c/sub\u003e fuel cell is quite high. On the other hand, 30% of the electricity output is needed to partially crack NH\u003csub\u003e3\u003c/sub\u003e for use in a larger NH\u003csub\u003e3\u003c/sub\u003e/H\u003csub\u003e2\u003c/sub\u003e-blend-fulled turbine, which has better combustion properties than the use of pure NH\u003csub\u003e3\u003c/sub\u003e fuel\u003csup\u003e\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e\u003c/sup\u003e. As discussed above, 88% energy efficiency can be achieved in a reactor with 43% conversion, suggesting the TWL system may be more suitable for power generation via partial cracking. Nonetheless, the performance of the TWL, achieving full conversions at 76% energy efficiency, remains competitive for potential industrial application to produce high purity H\u003csub\u003e2\u003c/sub\u003e for fuel cell applications (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb-c). Thus, even without a fully optimised design, we see the potential for the TWL reactor to be applied in multiple scenarios of the ammonia/hydrogen economy.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eIn this work, we have demonstrated the effectiveness of an electrified tungsten wire lightbulb reactor in decomposing ammonia into hydrogen. This reactor can overcome the sluggish ADR kinetics of the typical low-temperature system by operating in the range of 1,230 K to 1,690 K with high efficiency. The non-homogeneous temperature gradient in the reactor, where at low power inputs the tungsten catalyst has temperatures exceeding 1,400 K that achieves rates up to ten times higher than the best low-temperature ADR catalysts, enable high productivity. A peak energy efficiency of 60% is achieved experimentally, and a record high purity of only 44 ppm NH\u003csub\u003e3\u003c/sub\u003e in the product stream is obtained at higher power input. Modelling the performance at industrial scales show that the proposed reactor design would be much smaller and lower in energy consumption than existing conventional hydrogen production methods, and is feasible in multiple applications including power generation, H\u003csub\u003e2\u003c/sub\u003e vehicle refuelling, and for chemical feedstock supply.\u003c/p\u003e \u003cp\u003eThe use of Joule-heating is an advantage of the reactor, as it provides the opportunity for the process to be directly powered by renewable electricity in practice\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e,\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e,\u003cspan additionalcitationids=\"CR49 CR50 CR51\" citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e\u003c/sup\u003e, and has low barrier towards industrial adoption as the reactor design is more similar to traditionally heated furnaces\u003csup\u003e\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e,\u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e\u003c/sup\u003e. High temperature Joule-heated reactors have been tested for reactions such as methane pyrolysis, but these are susceptible to coking whereas such issues do not exist in our ADR system\u003csup\u003e\u003cspan additionalcitationids=\"CR56 CR57 CR58 CR59\" citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e60\u003c/span\u003e\u003c/sup\u003e. Electrified tungsten for ADR has been reported decades earlier, but only a lower temperature range between 970 K and 1,073 K were explored to understand the kinetics of ammonia decomposition on the tungsten surface\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e,\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e. More recently, Joule-heating has been used to obtain uniform catalyst temperature distributions in ADR reactors, but once again these operate at low temperatures (up to 913 K)\u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e,\u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e61\u003c/span\u003e\u003c/sup\u003e. The TWL reactor is thus unique in its approach and efficacy for facilitating ADR.\u003c/p\u003e \u003cp\u003eRegardless, steps shall be taken to improve the design of the reactor in future. A more robust model that considers the effects of the reflector should be constructed. Alternative configurations for the scaled-up reactor may also be studied, for example a modular parallel wire model\u003csup\u003e\u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e62\u003c/span\u003e\u003c/sup\u003e. Convective heat transfer within the reactor may be improved through the inclusion of baffles on the reactor walls\u003csup\u003e\u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e63\u003c/span\u003e\u003c/sup\u003e, which would allow the ammonia gas to recirculate into the centre of the reactor where temperatures are the highest, increasing contact time and therefore reaction extent. Given the intermittency of renewable sources that would be used to power such an electrified reactor, transient studies and modelling of the reactor should be performed. This will better inform the operational behaviour of the reactor, which together with the more detailed design would lead to improved accuracy of cost estimations. Nonetheless, the current design already shows promise of the TWL reactor in a variety of application scenarios, putting confidence in the potential application of this technology in decarbonising the future hydrogen economy.\u003c/p\u003e"},{"header":"Methods","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eExperimental Methods\u003c/h2\u003e \u003cp\u003eLab-scale experiments were performed in a reactor consisting of a quartz tube (ID 1 cm, OD 1.27 cm) fitted with Swagelok UltraTorr fittings for gas-tightness. In either end of the tube, copper rods were inserted, with a thin tungsten wire (0.1 mm diameter) at a fixed length of 10 cm tied between the two ends of the rod inside the tube. A DC electric supply was connected onto the other ends of the copper rods that are protruding out the tube. Ammonia gas (Matheson, 99.9995%) was flowed through the inlet using mass flow controllers (Alicat), while the reactor outlet was connected to a GC equipped with a thermal conductivity detector (Agilent 7890B) for on-line product analysis. Space velocity was calculated based on the NH\u003csub\u003e3\u003c/sub\u003e flow rate and reactor quartz tube volume. Conversion was measured once the system has reached a stable state, and the reported values are the average of at least three GC injections (~\u0026thinsp;30 mins on-stream). For measuring trace amounts of NH\u003csub\u003e3\u003c/sub\u003e, outlet gas was passed through 20 mL 10 mM H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e solution for 20 minutes, then the NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e concentration of the solution was quantified using an ion chromatographer. Reaction kinetics were measured using tungsten mesh (150 mg) in a thermal-catalytic setup. Temperature of the tungsten filament was measured using the Optris PI 05M infrared camera equipped with an Optris ACPIXMO27 lens. Scanning electron microscopy (JEOL JSM-7610F Plus) and energy dispersive spectrometry (Oxford Instruments X-Max\u003csup\u003eN\u003c/sup\u003e) were used to characterize the tungsten wire morphology and elemental composition before and after reactor testing.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eComputational Methods\u003c/h3\u003e\n\u003cp\u003eThe CFD model consists of equations for electromagnetic heating, heat transfer, laminar flow, species transport, and radiation in a participating medium. The cylindrical lab-scale reactor was simulated as a 2D axisymmetric model at steady-state in COMSOL Multiphysics 5.6. Full details can be read in the Supplementary Information.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll data supporting this investigation is available in the article and its Supplementary Information.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe thank the Singapore Low-Carbon Energy Research (LCER) Funding Initiative hosted under A*STAR for the financial support (Award No. U2102d2005) and the RIE2025 USS LCER Phase II Programme (Award No. U2305D4002). N. Yan acknowledges the support from National Research Foundation (NRF) Singapore under its NRF Investigatorship (NRFI07-2021-0015).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eK.S.I. performed experiments, conducted simulations, analysed data, and wrote and revised the manuscript. S.S.W. performed experiments, conducted simulations, analysed data, and revised the manuscript. S.W. performed experiments and analysed data. D. X. analysed data and revised the manuscript. N.Y. conceived and supervised the entire study. All authors have discussed the results and given approval to the final version of the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u0026nbsp;\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eIlic, O.\u003cem\u003e et al.\u003c/em\u003e Tailoring high-temperature radiation and the resurrection of the incandescent source. \u003cem\u003eNat. Nanotechnol.\u003c/em\u003e \u003cstrong\u003e11\u003c/strong\u003e, 320-324 (2016). https://doi.org/10.1038/nnano.2015.309\u003c/li\u003e\n\u003cli\u003eKatebah, M., Al-Rawashdeh, M. m. \u0026amp; Linke, P. 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Convective Heat Transfer in a Channel with Porous Baffles. \u003cem\u003eNumerical Heat Transfer, Part A: Applications\u003c/em\u003e \u003cstrong\u003e46\u003c/strong\u003e, 425-452 (2004). https://doi.org/10.1080/10407780490478515\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-6039914/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6039914/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eAmmonia decomposition is a key reaction in the green hydrogen economy as ammonia is an important carbon-free hydrogen carrier. Despite extensive efforts to develop active catalysts to address the reaction's slow kinetics, we introduce a tungsten wire lightbulb reactor that operates at unconventionally high temperatures with enhanced efficiency. Near the wire, temperature reaches up to 1,800 K, enabling ultra-fast ammonia decomposition with rate constants much higher than those of leading catalysts under typical reaction conditions. Concurrently, the sharp temperature decrease along the radial direction allows for low power inputs, thus enhancing energy efficiency. It also realized up to 99.995% conversion at enhanced power input without the use of membrane separation. We further discuss a scale-up reactor design that is two to three orders of magnitude smaller than current state-of-the-art reactors and highlight its potential applications within the emerging hydrogen economy.\u003c/p\u003e","manuscriptTitle":"Ultra-fast ammonia decomposition using an electrified tungsten wire lightbulb reactor","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-02-20 13:05:55","doi":"10.21203/rs.3.rs-6039914/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-chemical-engineering","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"natchemeng","sideBox":"Learn more about [Nature Chemical Engineering](https://www.nature.com/natchemeng/)","snPcode":"44286","submissionUrl":"https://mts-natchemeng.nature.com/","title":"Nature Chemical Engineering","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"37e9f47a-2463-40c5-a36b-c1d9ce9a59e9","owner":[],"postedDate":"February 20th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":44492049,"name":"Physical sciences/Engineering/Chemical engineering"},{"id":44492050,"name":"Physical sciences/Energy science and technology/Renewable energy/Hydrogen energy"}],"tags":[],"updatedAt":"2025-10-22T07:09:34+00:00","versionOfRecord":{"articleIdentity":"rs-6039914","link":"https://doi.org/10.1038/s44286-025-00283-x","journal":{"identity":"nature-chemical-engineering","isVorOnly":false,"title":"Nature Chemical Engineering"},"publishedOn":"2025-10-21 04:00:00","publishedOnDateReadable":"October 21st, 2025"},"versionCreatedAt":"2025-02-20 13:05:55","video":"","vorDoi":"10.1038/s44286-025-00283-x","vorDoiUrl":"https://doi.org/10.1038/s44286-025-00283-x","workflowStages":[]},"version":"v1","identity":"rs-6039914","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6039914","identity":"rs-6039914","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}