Ammonia Decomposition Research Articles

In Situ Exsolved CoFeRu Alloy Decorated Perovskite as An Anode Catalyst Layer for High‐Performance Direct‐Ammonia Protonic Ceramic Fuel Cells

AbstractDirect‐ammonia proton ceramic fuel cell (DA‐PCFC) is a promising clean energy technology because ammonia (NH3) is easier to store, transport, and handle than hydrogen. However, NH3 decomposition efficiency is unsatisfactory, and the anti‐sintering resistance of conventional Ni‐based ceramic anodes has limited the large‐scale application of DA‐PCFC technology. Herein, Pr0.6Sr0.4(Co0.2Fe0.8)0.85Ru0.15O3‐δ (PSCFR15), a novel anode catalyst layer (ACL) material is developed. PSCFR15 is treated under a reducing atmosphere to form a composite with CoFeRu alloy nanoparticles. Density functional theory simulations reveal that Ru modification in the CoFe alloy promotes nitrogen desorption during ammonia decomposition reaction, thereby boosting ammonia decomposition efficiency. As a result, DA‐PCFC with PSCFR15 ACL can achieve superior peak power density compared to bare DA‐PCFC operated with H2 and NH3 fuels. Furthermore, the ACL also reduces the direct contact between the Ni‐based ceramic anode and the NH3 fuel, then suppressing Ni sintering, and enhancing the durability of the DA‐PCFC.

Efficient solar-driven ammonia decomposition using economical K-Co3Mo3N catalyst at low temperatures

Solar-driven ammonia decomposition suffers from either using expensive ruthenium catalysts or requiring a high operating temperature (>550 °C). Here, we report that this limitation can be overcome by using a K-modified Co3Mo3N catalyst constructed by a single-step nitridation of CoMoO4 and plentiful K2CO3. The optimal 0.864 %K-Co3Mo3N catalyst presents a conversion of 86.5 % and a hydrogen production rate of 347.5 mmol gcat−1⋅h−1 under conditions of 500 °C and a gas hourly space velocity of 6000 mL gcat−1⋅h−1, which is comparable to most of the reported Ru-based catalysts. Based on the results from density functional theory calculations, the step of desorbed N2 is with the highest energy barrier. The overall energy barrier computed is 0.54 eV, which is consistent with the experimentally measured activation energy. Further, a remarkable solar-to-fuel efficiency of 14.4 % is achieved. This work highlights the enhancement effect of K on Co3Mo3N for efficient solar-driven NH3 decomposition at low temperatures.

Catalytic properties of trivalent rare-earth oxides with intrinsic surface oxygen vacancy

Oxygen vacancy (Ov) is an anionic defect widely existed in metal oxide lattice, as exemplified by CeO2, TiO2, and ZnO. As Ov can modify the band structure of solid, it improves the physicochemical properties such as the semiconducting performance and catalytic behaviours. We report here a new type of Ov as an intrinsic part of a perfect crystalline surface. Such non-defect Ov stems from the irregular hexagonal sawtooth-shaped structure in the (111) plane of trivalent rare earth oxides (RE2O3). The materials with such intrinsic Ov structure exhibit excellent performance in ammonia decomposition reaction with surface Ru active sites. Extremely high H2 formation rate has been achieved at ~1 wt% of Ru loading over Sm2O3, Y2O3 and Gd2O3 surface, which is 1.5–20 times higher than reported values in the literature. The discovery of intrinsic Ov suggests great potentials of applying RE oxides in heterogeneous catalysis and surface chemistry.

Decarbonizing hydrogen supply chain via electrifying endothermic processes

Chemical/manufacturing industries are significant source of CO2 emissions. Despite the ongoing development of renewable pathways, there remains a substantial gap in enabling these resources for industrial applications while enhancing the thermal efficiency. Hydrogen has been proposed as a useful energy vector, however, its large-scale storage/transportation is still a challenge. Alternatively, ammonia has been proposed as a hydrogen carrier, since it is more readily transported and stored. But the hydrogen recovery from ammonia requires a high endothermic heat and may cause significant emissions when the traditionally fossil-fuel-based heating is used. In this work, we describe the electrified reactor configurations that can enable the integration of renewable powers with the manufacturing processes to provide the endothermic heat. In particular, we demonstrate the technical feasibility of the proposed reactor configurations for ammonia decomposition, enabling the storage and transportation of hydrogen while decarbonizing its production and retaining the mechanical/process integrity through a programmed heating.

Exploration of Alkali Metal-Induced Effects on Promoting Ammonia Decomposition Performance

Exploration of Alkali Metal-Induced Effects on Promoting Ammonia Decomposition Performance

Ammonia decomposition over La-doped Al2O3 supported Co catalyst

As the hydrogen source of carbon-free fuel cells, the key to realize the green and low-energy decomposition hydrogen production process is to select materials with excellent catalytic performance for ammonia dehydrogenation. In this study, the rare earth element lanthanum (La) was doped onto the surface of Al2O3 by the impregnation method. The aforementioned material was subsequently used as a new material for the synthesis of single metal Co catalysts that catalyzed ammonia decomposition. Various characterization techniques (XRD, HRTEM, N2 physical adsorption-desorption, ICP, XPS, SEM, H2-TPR) were employed to investigate the relationship between the structure and performance of Co/La–Al2O3 catalysts. The findings indicated that the 10Co/La(5)-Al2O3 catalyst was the most active. Under the conditions of 550 °C and 9000 mL h−1·gcat−1, the conversion of ammonia reached 90 %, and the yield of hydrogen reached 8.9 mmol·gcat−1·min−1. A perovskite-type metal oxide layer of LaAlO3 was generated on the surface of Al2O3 support after doping the appropriate amount of lanthanum (5 %), which directly affects the catalytic performance of the catalyst. The small amount of LaAlO3 optimized the strong interaction between the metal Co and the supports, thereby enhancing catalytic performance. While stabilizing the active component Co, XPS and H2-TPR also implied that the presence of La could enhance the electron transfer between the support and Co, as well as facilitate the desorption of nitrogen and hydrogen products, therefore, the low temperature activity of Co/La–Al2O3 catalyst can be improved. The ammonia decomposition efficiency of the catalyst doped with 5 % wt La was much higher than that of the catalyst without La incorporation. The simple modified support developed by us, which loads a monoatomic Co catalyst, provides a new approach for the development of high-activity transition metal catalysts.

Kinetic modelling of non-equilibrium plasma enhanced catalytic ammonia decomposition

It is important for the usage of ammonia as energy carrier to achieve ammonia decomposition at low temperature. In the present study, a reactor model of plasma catalytic ammonia decomposition over Fe catalyst at atmospheric pressure is developed in the aspect of plasma and chemical synergies kinetics. The plasma catalytic model accounted for multiple physical mechanisms in electronic and vibrational plasma kinetics and detailed ammonia decomposition mechanisms on the catalyst surface. In addition, a novel view that identify the surface chemisorption enhancement by plasma attributed to charge transfer via EMSI (electronic metal-support interaction) effect is highlighted. The result shows that the synergetic effect of plasma and thermal-catalyst is much greater than that of plasma or catalyst alone on ammonia decomposition, especially at low temperature. It is revealed that the surface desorption of nitrogen is still the rate-limiting step. Moreover, the numerical results also indicate that Langmuir-Hinshelwood reaction via 2 N(s)=>N2 is more likely to dominate the surface desorption of nitrogen in the presence of plasma rather than Eley-Rideal reaction via N + N(s)=>N2. At low electric field, there are infrequent free radicals (NH2, NH and N) and few vibrational ammonia (NH3(v)) generated by the plasma, thus considering that the adsorbed ammonia only undergoes a three-step dehydrogenation reaction. As a consequence, the rate of surface nitrogen desorption with plasma is greater than that with catalyst alone since plasma promotes the chemisorption process of ammonia. This work provides new fundamental insights into the synergistic effect of plasma and catalyst, as well as the direction for the ammonia decomposition catalyst design in plasma.

Insight into the impact of rare earth metals in modified Ni/MgO on promoting ammonia decomposition to hydrogen

The lack of detailed functions of different REMs in NH3 decomposition to H2 makes the efficient modified catalysts not rationally be designed though many REMs-modified catalysts have been reported. In this work, the 10Ni/A1Mg4Oα (A = La, Ce, and Y) and 10Ni/MgO, in which supports were synthesized by the sol–gel method and Ni was loaded by the wet-impregnate method, were comparatively investigated to reveal the effect of REMs against NH3 decomposition reaction. The presence of REMs enhanced the activity of 10Ni/A1Mg4Oα and decreased the activation energy as greatly as by half compared to 10Ni/MgO. The produced H2 in situ has little impact on the activity of 10Ni/A1Mg4Oα, among which Ce has the most excellent H2 desorption ability. The intrinsic activity of catalysts was improved better by Ce and Y than La and the best Ni particle size is around 6 nm according to TOF, though the Ni particle is the smallest (4.9 nm) in 10Ni/La1Mg4Oα. The surface structure of catalysts was tuned by doping REMs, forming a solid solution and some defects (oxygen vacancies), which enhanced the interaction between active metal and support with obvious electron transfer from support to Ni obtaining a better Ni dispersion and making NiO easier to be reduced. Additionally, the catalysts doped by La or Ce possess more oxygen vacancy due to the changes of La2O2CO3 and the valence of Ce, exhibiting stronger basic sites and better N2 desorption capacity. The study offers a promising strategy for utilizing appropriate or multiple REMs to synthesize effective catalysts effectively for catalyzing NH3 decomposition in the future.

Catalytic activity of Co/γ-Al2O3 catalysts for decomposition of ammonia to produce hydrogen

This paper aims to study the performance of Co/meso-Al2O3 catalysts for ammonia decomposition to produce hydrogen. High-performance Co/meso-Al2O3 catalysts were prepared using a sequential metal loading approach. The synthesized catalysts were analyzed by several techniques including X-ray diffraction (XRD), N2 physisorption analysis, temperature-programmed reduction (H2-TPR), temperature-programmed desorption (NH3-TPD) and transmission electron microscope (TEM). The effect of metal loading, decomposition temperature and weight hourly space velocity (WHSV) on the catalyst activity were studied. Temperature-programmed desorption (NH3-TPD) analysis showed the coexistence of weak acidic sites and strong acidic sites in the synthesized catalysts, indicative of weak metal–support interaction. The reaction activation energy of the catalysts followed the order of 26Co-CAT(A) < 9Co-CAT(A) < 16Co-CAT(A) < 5Co-CAT(A) < CAT(A). Particularly, 26 Co-CAT(A) exhibited significantly lower activation energy compared to the other catalyst, which was in line with its catalytic activity. This observation indicated that the cobalt loading in 26 Co-CAT(A) resulted in relatively weaker metal-support interactions, leading to lower desorption energy and thus allowing higher NH3 conversion at lower temperatures. These findings offer valuable insights for the development and optimization of advanced Co-based catalysts, facilitating the sustainable and efficient application of ammonia decomposition.

CeO2/Ni Inverse Catalyst as a Highly Active and Stable Ru-free Catalyst for Ammonia Decomposition

CeO₂/Ni Inverse Catalyst as a Highly Active and Stable Ru-free Catalyst for Ammonia Decomposition

Thermal Kinetics and Nitriding Effect of Ammonia-Based Direct Reduction of Iron Oxides.

Ammonia is a promising alternative hydrogen carrier that can be utilized for the solid-state reduction of iron oxides for sustainable ironmaking due to its easy transportation and high energy density. The main challenge for its utilization on an industrial scale is to understand the reaction kinetics under different process conditions and the associated nitrogen incorporation in the reduced material that originates from ammonia decomposition. In this work, the effect of temperature on the reduction efficiency and nitride formation is investigated through phase, local chemistry, and gas evolution analysis. The effects of inherent reactions and diffusion on phase formation and chemistry evolution are discussed in relation to the reduction temperature. The work also discusses nitrogen incorporation into the material through both spontaneous and in-process nitriding, which fundamentally affects the structure and chemistry of the reduced material. Finally, the effect of nitrogen incorporation on the reoxidation tendency of the ammonia-based reduced material is investigated and compared with that of the hydrogen-based reduced counterpart. The results provide a fundamental understanding of the reduction and nitriding for iron oxides exposed to ammonia at temperatures from 500 to 800 °C, serving as a basis for exploitation and upscaling of ammonia-based direct reduction for future green steel production.

Development of an ammonia decomposition reactor, afterburner and post-decomposition reactor for 1 kW solid oxide fuel cells using ammonia

Solid oxide fuel cells can overcome the poor flammability of ammonia by directly converting the chemical energy of ammonia into electricity. However, thermal stress by internal decomposition, nitriding at the solid oxide fuel cells stack and nitrogen oxides emissions must be considered when using ammonia in solid oxide fuel cells. In this study, an ammonia fuel processor was developed for stable operation and low emissions of solid oxide fuel cells using ammonia. The ammonia fuel processor consisting of an ammonia decomposition reactor, an afterburner and a post-decomposition reactor was tested using simulated off-gases of solid oxide fuel cells using ammonia. The ammonia conversion of the decomposition reactor varied from 32 % to 84 % with off-gas temperatures from 360 °C to 670 °C. When ammonia conversion after the solid oxide fuel cell stack was 99.70 %, nitrogen oxides emissions of the afterburner was 1.05 g/kWh, which is higher than the regulatory limit of 0.26 g/kWh. High fuel utilization and excess air ratio made nitrogen oxides emission even worse. The regulatory limit was successfully satisfied by using the post-decomposition reactor even when ammonia conversion after the solid oxide fuel cell stack was 99.10 %. The developed ammonia fuel processor could supply fuel at the optimal hydrogen-to-ammonia ratio and prevent nitrogen oxides emissions in solid oxide fuel cells using ammonia.

Optimized global reaction mechanism for H2+NH3+N2 mixtures

Hydrogen and ammonia are playing an increasingly vital role in combustion technologies. Recently, some detailed reaction mechanisms (DRMs) can predict reliable laminar burning velocities (LBVs). Meanwhile, despite their broad applicability in practical combustion engineering, global reaction mechanisms (GRMs) suitable for ammonia and its mixtures with hydrogen or nitrogen have yet to be reported. This study aims to address this gap by investigating new GRMs. Five DRMs were used to calculate the LBVs, and their average values were employed as a reference. First, a single-step GRM was developed for hydrogen (H2 + 0.5O2 → H2O), and another single-step GRM was developed for ammonia (NH3 + 0.75O2 → 0.5N2 + 1.5H2O). However, their combined GRM did not provide reasonable predictions of LBVs for the H2+NH3 mixtures. Therefore, a 4-step GRM was developed consisting of the single-step hydrogen and three additional reactions, i.e., an endothermic ammonia decomposition (NH3 + 0.5O2 → NO + 3H), an exothermic NO reduction (NO + 2H → 0.5N2 + H2O), and an exothermic H recombination (H + H → H2). In conclusion, this 4-step GRM and its revisions could predict reasonable LBVs, flame temperatures, and primary product compositions for mixtures of hydrogen, ammonia, and cracked ammonia gas over a wide range of temperatures (300–600 K) and pressures (1–5 atm).

Insight into the complex ammonia decomposition/oxidation kinetics in ammonia protonic ceramic fuel cells via elementary modeling

AbstractThe protonic ceramic fuel cells (PCFCs) can convert the chemical energy of fuel directly into electric power, with the advantages of high efficiency and alternative fuel range at intermediate temperatures. Ammonia has been regarded as a promising fuel for PCFCs due to its carbon‐free and hydrogen‐rich properties, high volumetric energy density and easy storage/transportation. However, the performance of ammonia PCFCs (NH3‐PCFCs) is far inferior to the hydrogen PCFCs (H2‐PCFCs) because of the sluggish and complex kinetics at anodes. In this study, we established an elementary reaction kinetic model for NH3‐PCFCs, investigated the effect of reaction parameters, anode components and reaction partition, and explored the coupling mechanism between the ammonia decomposition and electrochemical reaction. Importantly, the ammonia decomposition and electrochemical reaction can be flexibly regulated by adjusting anode parameters, then affecting the performance ratio of NH3‐PCFCs and H2‐PCFCs. The detailed rate‐determining steps were further identified by experimental and model analysis. Thus, the ammonia/hydrogen performance ratio of the cell can exceed 95% at 550°C after accelerating the ammonia decomposition reaction. Our work provides insights into the kinetics in NH3‐PCFCs for improving their performance with optimization.

Ru nanoparticles embedded in Ru/SiO2@N-CS for boosting hydrogen production via ammonia decomposition with robust lifespan

Ammonia decomposition for onsite hydrogen production has been regarded as an important reaction which links to efficient hydrogen storage, transport and utilization. However, it still remains challenging to develop efficient catalysts with robust stability for ammonia decomposition. Herein, an integrated strategy was employed to synthesize Ru/SiO2@N-CS via wrapping a thin layer of N-doped carbon onto the SiO2 sphere, following the anchor of Ru nanoparticles (NPs) onto the support. The obtained Ru/SiO2@N-CS (Ru loading: 1 wt%) shows a promising performance for ammonia decomposition, reaching 94.5 % at 550 °C with a gas hourly space velocity (GHSV) of 30 000 mL gcat-1h−1. The combination of the SiO2 as the core prevents the degradation of N-doped carbon layers and then enhance the durability of the catalysts, remaining stable after 50 h at evaluated temperatures. Adequate characterizations were used to illustrate the effect of microchemical environment on ammonia decomposition activity of Ru/SiO2@N-CS catalyst under different calcination atmosphere and the correlation between structure and performance.

Highly efficient dual-phase hydrogen-transporting membranes for NH3 decomposition coupling with CO2 reduction

Hydrogen-transporting membrane reactors play active roles in ammonia (NH3) decomposition and carbon dioxide (CO2) reduction by combining reaction and separation in one unit, simplifying the processes and reactor design and therefore saving the cost. These important reactions normally occur at high temperatures and in reducing and acidic atmosphere, thus posing great challenges on the membrane stability. Previous effort was devoted to thin Pd membranes, which however, suffer the shortcomings of hydrogen embrittlement, CO poisoning and high costs. Herein, we develop a H2-COx-tolerant and non-noble metal-ceramic dual-phase hydrogen permeable membrane reactors with a nominal composition of 60 vol% Ni-40 vol% La5.5WO11.25-δ (Ni-LWO). NH3 decomposition and hydrogen permeation was observed via the developed mixed protonic and electronic conducting membrane. A considerable production of CO in the sweep (CO2) side could also be achieved from CO2 reduction when the membrane was coupled by NH3 decomposition where the permeated hydrogen can consume the produced oxygen from favorable CO2 decomposition. Furthermore, we systematically investigated the performance of NiO–CeO2 catalyst coated Ni-LWO membrane reactor for CO2 reduction. Noteworthy that the CO generation rate obtained from Ni-LWO membrane reactor was increased in the presence of NiO–CeO2 catalysts. Hydrogen separation process coupled with surface reactions is jointly controlled by hydrogen surface exchange and bulk diffusion kinetics. These findings reveal a vital step towards the development of efficient hydrogen-transporting membrane reactor for the integration of chemical reactions and separation processes.

Microwave-assisted ammonia decomposition over metal nitride catalysts at low temperatures

The negative environmental impact of fossil fuel-based energy systems has unveiled the need to develop a COx-free sustainable hydrogen (H2) economy. Employing a microwave-assisted route, a ternary metal nitride catalyst (i.e., Co2Mo3N), and a low-temperature-pressure NH3 decomposition process, this study investigated the possibility of developing a distributed H2 production process. This study not only explored lower cost-based catalyst systems but also the use of a microwave reactor to increase the energy efficiency of the process. Results from catalytic NH3 decomposition experiments, performed in microwave reactors on Co2Mo3N catalyst, demonstrated the peak energy efficiency (of ∼0.006 kgH2/kWh) at 400 °C in ambient pressure (with an NH3 conversion >90%) which was around ninety times (∼90 x) more efficient than a conventional system. Activation energy calculation also displayed a 20% less energy requirement for the microwave-based process (∼31 kJ mol−1) than the conventional system (∼37 kJ mol−1), indicating the advantage of the microwave-based process. Further microwave-assisted catalytic measurements and characterization of the Co2Mo3N catalyst, using x-ray diffraction (XRD) technique and scanning electron microscopic (SEM) images, revealed the excellent stability of this material at its peak performance (at 400 °C) and illustrated the potential of using this catalyst for a sustainable, economic, and energy-efficient approach for producing COx-free H2.

Hydrogen and NH3 co-adsorption on Pd–Ag membranes

Ammonia (NH3) represents a carbon-free hydrogen carrier that can be used as a zero-emission fuel in the maritime and heavy transport sector with hydrogen fuel cells. To use ammonia as feedstock, the hydrogen must be recovered through NH3 decomposition into H2 and N2. Ammonia decomposition by a membrane-enhanced reactor would inherently produce high-purity H2 through the membrane avoiding the need for a costly hydrogen separation/purification unit. Pd-based membrane reactors can obtain full ammonia decomposition and show significantly higher conversion than conventional reactors. However, the H2 permeability is found to be inhibited in the presence of NH3. A further fundamental understanding of the long-term stability and performance of the Pd-based membranes under exposure to NH3 is therefore required. In the current work, the adsorbate-adsorbate interactions during co-adsorption, the influence the presence of NH3 has on the hydrogen dissociation kinetics, and surface segregation effects in the presence of NH3 and/or hydrogen on the surface of Pd and Pd3Ag are investigated in detail using density functional theory calculations. We find that both the hydrogen surface coverage and dissociation kinetics are hindered by the presence of NH3 on the surface, and possible segregation of Ag towards the surface in the presence of NH3, which could explain the reduced hydrogen permeation in NH3.

Influence of trapezoidal channel design on volume power density of ammonia-hydrogen fuel cells

Proton exchange membrane fuel cells based on ammonia decomposition gas (ammonia-hydrogen fuel cells) contain about 25% nitrogen at the anode, resulting in lower power density. In this paper, the volume power density enhancement effect of trapezoid channel with different upper edge length is studied. Research shows that the volume power density of trapezoid 0.1, 0.2, 0.4, 0.6 is increased by 53.5%, 62.0%, 81.9% and 108.3% compared with the conventional rectangular channel, respectively, and it is increased by 5.5%, 11.4%, 25.4% and 43.6% respectively, compared with the triangular channel. However, as the upper edge of the trapezoidal flow channel increases, the anode and cathode of the trapezoidal flow channel appear hydrogen hunger with a zero domain of up to 45% and the phenomenon of the horn mouth gradually moving forward respectively. Moreover, longer flow channels have lower fuel utilization efficiency, as low as 76%.

Performance of solid-oxide fuel cells operating with different sustainable fuel reformates

Solid oxide fuel cells (SOFCs) are recognized for their outstanding fuel flexibility and high efficiency in converting chemical energy into electrical energy. This research presents experiments on SOFCs fed with humidified hydrogen and hydrogen-rich gaseous reformates derived from methanol and ammonia: methanol steam reforming (MSR), methanol decomposition (MD), and ammonia decomposition (AD), at 700–850 °C. Results of SOFCs operating with MD reformate on different types of SOFCs, which to the best of our knowledge aren't available in the literature, are presented and compared with other reformate types for the first time. MD-reformate yielded the highest cell performance, with the least disparity in power density from humidified hydrogen, followed by AD-, and MSR-reformates. The study compares the direct internal reforming method, and the innovative Combined Electro-Thermo-Chemical cycle's potential. Introducing the concept of critical power density, the research evaluates fuel utilization across SOFC types. Scanning Electron Microscopy imaging and Energy-Dispersive X-ray Spectroscopy analyses confirm the viability of CO as a fuel, with no carbon deposits on the anodes when using MD-reformate. The findings demonstrate the suitability of using methanol- and ammonia-decomposition products in SOFCs and their compatibility with hybrid power generation cycles.