Ammonia Decomposition Activity Research Articles

Discovery of Alloy Catalysts for Ammonia Decomposition by Machine Learning-Based Prediction of Adsorption Energies

Ammonia decomposition has gained significant attention as an eco-friendly method for hydrogen production because it creates no carbon dioxide emissions. While Ru catalysts are known for their high activity in ammonia decomposition, their high cost makes them uneconomical for commercial use. Therefore, it is essential to explore novel alloy catalysts composed of inexpensive elements with high catalytic performance. Nitrogen adsorption energies serve as key descriptors indicating the catalytic performance for ammonia decomposition, and first-principle calculations can compute these energies. However, the screening of numerous alloy catalyst candidates through extensive first-principle calculations and experimental validations remains time-consuming due to the vast number of potential candidates. To address this, artificial intelligence and machine learning models are being developed to quickly predict catalyst performance, efficiently searching for promising catalyst candidates. In this study, we developed a machine-learning-based method to rapidly predict nitrogen adsorption energies using a graph-based artificial neural network, thereby efficiently searching for novel catalysts for ammonia decomposition. Our training dataset included the nitrogen adsorption energies of 30 pure transition metal catalyst candidates, as well as binary alloy catalyst candidates, including core-shell and intermetallic compounds. As a result, we successfully identified 12 catalyst candidates composed of inexpensive elements that are likely to exhibit catalytic performance comparable to Ru catalysts.

Effects of nitrogen vacancy sites of oxynitride support on the catalytic activity for ammonia decomposition

Nitrogen-containing compounds such as imides and amides have been reported as efficient materials that promote ammonia decomposition over nonnoble metal catalysts. However, these compounds decompose in an air atmosphere and become inactive, which leads to difficulty in handling. Here, we focused on perovskite oxynitrides as air-stable and efficient supports for ammonia decomposition catalysts. Ni-loaded oxynitrides exhibited 2.5–18 times greater catalytic activity than did the corresponding oxide-supported Ni catalysts, even without noticeable differences in the Ni particle size and surface area of the supports. The catalytic performance of the Ni-loaded oxynitrides is well correlated with the nitrogen desorption temperature during N2 temperature-programmed desorption, which suggests that the lattice nitrogen in the oxynitride support rather than the Ni surface is the active site for ammonia decomposition. Furthermore, NH3 temperature-programmed surface reactions and density functional theory (DFT) calculations revealed that NH3 molecules are preferentially adsorbed on the nitrogen vacancy sites on the support surface rather than on the Ni surface. Thus, the ammonia decomposition reaction is facilitated by a vacancy-mediated reaction mechanism.

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.

Preparation of silicon carbide supported nickel catalyst with enhanced catalytic activity for ammonia decomposition

Preparation of silicon carbide supported nickel catalyst with enhanced catalytic activity for ammonia decomposition

Supported highly dispersed molybdenum nitride derived from molybdate-intercalated Mg‒Al hydrotalcite-like compounds as a catalyst for ammonia decomposition

Molybdate-intercalated magnesium–aluminum hydrotalcite-like compounds (HTlc) were synthesized by anion-exchange and used as precursor to prepare supported molybdenum nitride catalyst for ammonia decomposition. The as-synthesized precursors and the derived mixed metal oxides and nitride catalysts were characterized by ICP, XRD, Raman spectroscopy, XPS, H2-TPR, and HAADF-STEM-EDX. The characterizations indicated that molybdate was well intercalated into the HTlc interlayer as MoO42– and the Mo content was tunable by altering the intercalation degree of molybdate. Upon calcination, molybdena was dominantly presented as isolated tetrahedrally coordinated MoOx species. Upon nitridation with ammonia at 700 ºC, highly dispersed and composition-uniform molybdenum nitride (Mo2±xN) was formed. The Mo0.5Mg3Al nitride catalyst showed good activity for ammonia decomposition, providing nearly full conversion of ammonia at 625 ºC under a space velocity of 5,000 mL gcat–1 h–1. The optimal catalyst also exhibited high catalytic stability during 100 h operation at 625 ºC, and no obvious aggregation took place, attributable to the strong metal–support interaction between molybdenum nitride and Mg–Al mixed oxide. It is suggested that the hydrotalcite-derived Mg–Al mixed oxide supported highly dispersed Mo2±xN species was active and stable for ammonia decomposition.

Preparation of Co/SiC catalyst and its catalytic activity for ammonia decomposition to produce hydrogen

SiC was first synthesized using the sol-gel method and subsequent carbothermal reduction method, then xCo/SiC-700 and 30%Co/SiC-T catalysts were prepared by hydrothermal method and thermal treatment. The structure of the catalysts was characterized by XRD, SEM/TEM, XPS, H2-TPR, CO2-TPD, etc. Their catalytic activities for ammonia decomposition to produce hydrogen were investigated in a fixed-bed reactor. The results showed that the synthesized SiC had a high specific surface area and could evenly disperse Co3O4 nanoparticles, which increased the exposure of active sites and improved the adsorption capacity on the catalyst surface. N2-TPD indicates that 30%Co/SiC-700 has a high N2 adsorption capacity, effectively preventing hydrogen reduction of Co3O4 nanoparticles in the catalyst during ammonia decomposition. CO-TPD shows that Co has the best dispersion on 30%Co/SiC-700 catalyst. CO2-TPD shows the higher the catalyst's basicity, the stronger ammonia's decomposition ability. Among the synthesized catalysts, 30% Co/SiC-700 showed the best catalytic activity for ammonia decomposition, with the ammonia conversion of 78.3% and hydrogen production of 25.0 mmol H2 gcat−1 min−1 at 550 °C under 30,000 mL gcat−1 h−1.

A High-Performance and Durable Direct-Ammonia Symmetrical Solid Oxide Fuel Cell with Nano La0.6Sr0.4Fe0.7Ni0.2Mo0.1O3-δ-Decorated Doped Ceria Electrode.

Solid oxide fuel cells (SOFCs) offer a significant advantage over other fuel cells in terms of flexibility in the choice of fuel. Ammonia stands out as an excellent fuel choice for SOFCs due to its easy transportation and storage, carbon-free nature and mature synthesis technology. For direct-ammonia SOFCs (DA-SOFCs), the development of anode catalysts that have efficient catalytic activity for both NH3 decomposition and H2 oxidation reactions is of great significance. Herein, we develop a Mo-doped La0.6Sr0.4Fe0.8Ni0.2O3-δ (La0.6Sr0.4Fe0.7Ni0.2Mo0.1O3-δ, LSFNM) material, and explore its potential as a symmetrical electrode for DA-SOFCs. After reduction, the main cubic perovskite phase of LSFNM remained unchanged, but some FeNi3 alloy nanoparticles and a small amount of SrLaFeO4 oxide phase were generated. Such reduced LSFNM exhibits excellent catalytic activity for ammonia decomposition due to the presence of FeNi3 alloy nanoparticles, ensuring that it can be used as an anode for DA-SOFCs. In addition, LSFNM shows high oxygen reduction reactivity, indicating that it can also be a cathode for DA-SOFCs. Consequently, a direct-ammonia symmetrical SOFC (DA-SSOFC) with the LSFNM-infiltrated doped ceria (LSFNM-SDCi) electrode delivers a superior peak power density (PPD) of 487 mW cm-2 at 800 °C when NH3 fuel is utilised. More importantly, because Mo doping greatly enhances the reduction stability of the material, the DA-SSOFC with the LSFN-MSDCi electrode exhibits strong operational stability without significant degradation for over 400 h at 700 °C.

Ni2Mo3N: crystal structure, thermal properties, and catalytic activity for ammonia decomposition

Abstract Ni2Mo3N was synthesized by ammonolysis of NiMoO4, prepared by a sol-gel-based modified Pechini route. X-ray powder diffraction measurements confirmed that Ni2Mo3N crystallizes in a filled β-Mn type (cubic space group P4132) with a lattice parameter of a = 6.6338 Å. Group theoretical methods were applied to elucidate the relation between the crystal structure of Ni2Mo3N and that of the rock salt type. The high-temperature behavior was investigated in-situ by X-ray diffraction measurements in flowing ammonia gas at temperatures up to 875 °C. Ni2Mo3N exhibits significant catalytical activity for ammonia decomposition, which is critically discussed in comparison to literature.

Nickel perovskite catalysts for ammonia decomposition: DFT calculations and microreaction kinetics

Combining policy guidance, catalyzing ammonia decomposition to produce hydrogen is a new concept for hydrogen energy supply. Alkaline carriers can effectively improve the ammonia decomposition activity on the catalyst by adjusting the dispersion of nickel (Ni) and controlling the size of Ni. However, the activity of Ni-based perovskite catalysts does not seem to be entirely affected by the above factors. Exploring the mechanism of Ni and perovskite alkaline carrier surfaces through theoretical calculations provides deeper theoretical guidance for ammonia (NH3) decomposition. This study uses periodic density functional theory calculation methods to investigate the reaction paths and energy distribution of monomeric ammonia and dimeric ammonia on a nickel-doped barium zirconate (Ni/BaZrO3) catalyst. Molecular dynamics simulations, Bader charge analysis, and density of states assist in understanding the adsorption states of NH3 and the catalytic decomposition mechanism. The energy barriers for N-H bond breaking and nitrogen generation reactions of Ni clusters loaded on the BaZrO3 surface (Ni4/BaZrO3) were compared and analyzed. The results show that Ni/BaZrO3 is more conducive to ammonia decomposition, with a maximum reaction barrier of 0.90 eV. The catalytic activity of the catalyst under oxygen vacancy conditions was further examined. By comparing the mechanisms of dimeric ammonia decomposition on the clean catalyst surface and the oxygen vacancy catalyst surface, it was found that the presence of oxygen vacancies facilitates ammonia decomposition, but Ni doping provides more effective assistance for N-H bond breaking. The rate constant for ammonia decomposition was calculated using transition state theory. This work not only provides theoretical references for the decomposition mechanism of NH3 in Ni-based perovskite materials but also provides kinetic data for the kinetic modeling of NH3 decomposition.

Preparation of nickel aluminate supported Ni nanocatalyst and its catalytic activity for ammonia decomposition to produce hydrogen

In this work, nickel aluminate (NiAl2O4) was synthesized through the co-precipitation, and then the Ni/NiAl2O4 catalysts were prepared by impregnation and the catalytic activity of the catalyst was evaluated. The results indicated that the synthesized NiAl2O4 had a large specific surface area, promoting the dispersion of Ni species and thus exposing more active sites. The strong metal-support interaction between Ni species and NiAl2O4 contributed significantly to the catalysts' high catalytic activity. Meanwhile, the strong basicity of catalyst could adjust the bond energy of Ni–N, which were conducive to desorption of the recombinant N2 from the metal surface. The Ni/NiAl2O4 catalyst with Ni loading of 50 wt% and calcination temperature of 700 oC exhibited the best catalytic activity with ammonia conversion of 95.3% at 550 oC under 30000 mL∙gcat-1∙h-1. This study offers a potential approach to developing a cost-effective and highly efficient catalyst for decomposing ammonia.

Industrial waste-based Ni-catalysts for ammonia decomposition to produce clean hydrogen

The high mineral containing solid waste materials generated during aluminum production currently lacks any practical application. In this work, the potential of solid waste with/without additional nickel loading (10 to 20 wt%) was investigated as an active catalyst for low temperature ammonia decomposition to produce high purity hydrogen. The X-ray diffraction (XRD) analysis of the samples reveals that iron oxide was the primary component of solid waste with the ability to catalyze the ammonia decomposition reaction. The reducibility, metal support interaction and catalytic activity of the solid waste supported Ni-based catalysts were correlated by the reduction kinetics of the catalysts using temperature-programmed reduction (H2-TPR) data and nucleation/nuclei growth models. Based on the statistical indicators, it was concluded that the random nucleation model describes catalyst reduction adequately. The estimated activation energy for the reduction of the solid waste itself was significantly higher (108.5 kJ/mol) than that of solid waste supported catalyst containing 10 wt% Ni (86.6 kJ/mol). The increase in nickel loading also slightly decreased the activation energy of catalyst reduction, indicating an improvement in the reducibility of the nickel-containing catalysts. These reduction behaviors were also reflected in the ammonia decomposition reaction in a flow reactor. The addition of nickel onto the solid waste resulted in the creation of additional active nickel sites. Consequently, the nickel loaded solid waste supported catalysts exhibited significant improvements in ammonia decomposition activity. Among the three solid waste supported Ni-based catalysts, the catalyst containing 15 wt% Ni displayed the highest activity, that also remained unchanged over extended period, indicating the catalyst stability.

Boosting hydrogen production of ammonia decomposition via the construction of metal-oxide interfaces

The ammonia decomposition for the production of carbon-free hydrogen has triggered great attention yet still remains challenging due to its sluggish kinetics, posting the importance of precise design of efficient catalysts for ammonia decomposition under low temperatures. Constructing the metal-support interaction and interface is one of the most important strategies for promoting catalysts. In this work, by coating ceria onto the Ni nanoparticles (NPs), we discover that the Ni–CeO2 interfaces create an exceptional effect to enhance the catalytic decomposition of ammonia by over 10 folds, compared with the pristine Ni. The kinetic analysis demonstrates that the recombinative N2 desorption is the rate-determining step (RDS) and the Ni–CeO2 interface greatly increases the RDS. Based on these understandings, a strategy to fabricate the Ni/CeO2 catalyst with abundant Ni–Ce–O interfaces via one-pot sol-gel method was employed (hereafter denoted to s–Ni/CeO2). The s–Ni/CeO2 catalyst shows a high activity for ammonia decomposition, achieving a H2 formation rate of 10.5 mmol gcat−1 min−1 at 550 °C. Combined with a series of characterizations, the relationship between the catalyst structure and the performance was investigated for further understanding the effect of metal-oxide interfaces.

Highly active internal catalyst promoting the efficient ammonia decomposition and durability of protonic ceramic fuel cells

Direct ammonia protonic ceramic fuel cells (DA-PCFCs) have attracted extensive attention by virtue of their high hydrogen content, superior energy density, and zero carbon emissions. However, the practical application of DA-PCFCs is impeded by their unsatisfactory catalytic activity and limited durability. This study aims to evaluate the feasibility of utilizing ammonia solution as a fuel for PCFCs. In the hope of enhancing performance and reducing costs, a low-cost iron catalyst layer was proposed and fabricated within cells, with a structure of NiO–BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb)| NiO-BZCYYb| BZCYYb| PrBa0.5Sr0.5Co1.5Fe0.5O5+δ (PBSCF)-BZCYYb. The introduction of the iron catalyst layer yields promising results, achieving a remarkable increase (from 165 mW/cm2 to 300 mW/cm2 by 81.8 %) in maximum power density at 600 °C and a significant lengthening of durability. The enhanced electrochemical performance and durability can be attributed to the presence of the iron catalyst layer, which improves the catalytic activity for ammonia decomposition while preventing the formation of nitride.

Ammonia decomposition for carbon-free hydrogen production over Ni/Al-Ce catalysts: Synergistic effect between Al and Ce

To deeply understand the synergistic effect between Al and Ce in the composite support of Ni-based catalysts for ammonia decomposition, a series of Ni/Al-Ce catalysts with 10 wt% Ni loading were prepared combining coprecipitation and impregnation methods. The activity test results showed that the Ni/Al0.1Ce0.9Ox catalyst exhibited significantly improved activity for ammonia decomposition in the temperature range of 450–600 ℃ compared with Ni/Al2O3, Ni/CeO2, and other Ni/Al-Ce catalysts. Systematic characterization results showed that appropriate ratio of Al and Ce formed an Al-Ce-O solid solution and increased the number of oxygen vacancies on the surface, which induced synergistic effect and played a vital role in the improved activity. Such synergistic effect not only promoted the dispersion of Ni species, facilitated the activation of NH3, but also enhanced the interaction between metal and support. This work provided a new strategy for designing efficient Ni-based catalysts for ammonia decomposition and deepened the understanding of the synergistic effect between Al and Ce in the composite support.

The effect of acidic–basic structural modification of nickel-based catalyst for ammonia decomposition for hydrogen generation

The utilization of non-precious nickel-based catalyst in increasing ammonia dissociation for COx-free hydrogen production was investigated. Typically, Co, La and basic metal oxides (Na, K, Ba) promoters were synthesized with nickel over acidic gamma alumina support. The main objective of the study was to modify the acid-base surface of catalyst structure thereby increasing ammonia dissociation activity. The catalytic activity for ammonia decomposition was strongly influenced by the addition of Na and K oxide promoters over 15 %Ni/Al2O3 resulting in moderate-stronger basic sites suitable for ammonia conversion. The addition of Na and K oxides showed a clear trend in tuning the trimetallic catalyst and significantly reducing the amount of strongly adsorbed hydrogen on the catalyst surface. This results in higher ammonia conversion which increased as a function of temperature to 32.4 %, 67.5 % and 95.3 % at 430 ᵒC, 485 ᵒC, and 533 ᵒC, respectively. Ammonia conversion using promoters was stable with no degradation of performance and the conversion increased with the decrease in WHSV. The catalytic reactivity over trimetallic catalysts was systematically influenced by their basic-acidic property that promoted ammonia dehydrogenation on the surface of nickel oxide-based catalyst.

Ammonia Decomposition over Water‐Durable Hexagonal BaTiO3−xNy‐Supported Ni Catalysts

AbstractNickel is a promising candidate as an alternative to ruthenium for an ammonia decomposition catalyst. However, the performance of Ni‐based catalysts for ammonia decomposition is still not sufficient to achieve a good hydrogen production rate under low‐temperature because the weak nitrogen affinity of Ni reduces the frequency of the ammonia decomposition reaction. Here, it is reported that Ni supported on barium titanium oxynitride (Ni/h‐BaTiO3−xNy) with a hexagonal structure acts as a highly active and water‐durable catalyst for ammonia decomposition. The operation temperature is reduced by over 140 °C when N3− ions are substituted onto the O2− sites of the BaTiO3 lattice, and the Ni/h‐BaTiO3−xNy catalyst significantly outperforms conventional oxide‐supported Ni catalysts for ammonia decomposition. Furthermore, the activity of Ni/h‐BaTiO3−xNy remains unchanged after exposure to water. The 15NH3 decomposition reaction and Fourier transform‐infrared spectroscopy (FT‐IR) measurements reveal that lattice nitrogen vacancy sites on h‐BaTiO3−xNy function as the active sites for ammonia decomposition. The ammonia decomposition activity of Ni/h‐BaTiO3−xNy is also higher than that of the Ni/h‐BaTiO3−xHy oxyhydride catalyst, making a contrast to the activity trend in ammonia synthesis.

Exsolved Nanoparticles Decorated Double Perovskites as High-Performance Anodes for Direct-Ammonia Solid Oxide Fuel Cells

Due to the high energy density, mature production technology, ease of storage and transportation, and the no carbon/sulfur nature of ammonia fuel, direct-ammonia solid oxide fuel cells (DA-SOFCs) have received rapidly increasing attention, showing distinct advantages over H2-fueled SOFCs and low-temperature fuel cells. However, DA-SOFCs with conventional Ni-based cermet anodes still suffer from several drawbacks, including serious sintering and inferior activity for ammonia decomposition, strongly limiting the large-scale applications. To tackle the above-mentioned issues, exsolved NiCo nanoparticles decorated double perovskite oxides are fabricated and employed as high-performance anodes for DA-SOFCs in this work. By optimizing the Ni doping amount in Sr2CoMo1−xNixO6−δ (x = 0.1, 0.2 and 0.3), the reduced Sr2CoMo0.8Ni0.2O6−δ (r-SCMN2) anode exhibits superb catalytic activity for ammonia cracking reaction and high anti-sintering capability. More specifically, the electrolyte-supported single cell with r-SCMN2 nanocomposite anode delivers superior power outputs and operational durability in ammonia fuel as compared with other r-SCMN anodes owing to the significantly promoted nanoparticle exsolution and stronger interaction between alloy nanoparticles and the support. In summary, this study presents an effective strategy for the design of efficient and stable nanocomposite anodes for DA-SOFCs.

Enhanced ammonia decomposition activity over unsupported Co3O4: Unravelling the promotion effect of alkali metal

To deeply understand the effect of alkali metals on the structure-activity relationship of cobalt-based catalysts for ammonia decomposition, unsupported Co3O4 was fabricated as catalyst model. It was found that alkali metals (Na and K) enhanced the NH3 decomposition performance of Co3O4 significantly, with NH3 conversion even higher than supported ones. As indicated by characterizations, appropriate amount of Na doping generated more reducible Co3+, which induced strong interaction with NH3 during reaction. As a result, it was easier for NH3 as well as -NH2 intermediate to dehydrogenate at low temperature. Therefore, the intrinsic activity of Co3O4 for NH3 decomposition was increased. This study not only provided a novel strategy in the practical use of cobalt-based catalysts for NH3 decomposition, but also gave deep insight into the promotion effect of alkali metal.

Ammonia Decomposition Over Cobalt-Based Silica-Supported Fischer-Tropsch Synthesis Catalysts

Decomposition of ammonia over silica-supported cobalt catalysts for Fischer–Tropsch synthesis has been studied at a pressure of 0.1 MPa, a gas hourly space velocity range of 1000–6000 h–1 and a temperature range of 400–650°C in a tubular fixed bed reactor in a flow-through mode. It was found that silica-supported cobalt catalysts for hydrocarbons synthesis via the Fischer–Tropsch protocol also exhibit high activity in ammonia decomposition. Both activity and hydrogen productivity decrease in the series: Co–Ru/SiO2 Co–Al2O3/SiO2 Ru/SiO2 Co–Al2O3/SiO2(35%)/ZSM-5(30%)/Al2O3(35%). The relatively low values of effective activation energies estimated for all catalysts indicate that the reaction can proceed with a high conversion at moderate temperatures.

Switching on/off molybdenum nitride catalytic activity in ammonia synthesis through modulating metal-support interaction.

Modulating the interaction between Mo nanoparticles and their support is an elegant approach to finely tune the structural, physico-chemical, redox and electronic properties of the active site. In this work, a series of molybdenum nitride catalysts supported on TiO2, and SBA-15 has been prepared and fully characterized. The results of characterization confirmed the high dispersion of Mo and the formation of small molybdenum nanoparticles in both the 10-Mo-N/SBA-15 and 10-Mo-N/TiO2 catalysts. In this context, we have shown that the catalytic activity of Mo species was strongly impacted by the nature of the catalytic support. Amongst the studied supports, SBA-15 was found to be the most appropriate for Mo dispersion. In comparison, when supported on a reducible oxide (TiO2), Mo species showed poor catalytic activity in both ammonia synthesis and decomposition and were prone to quick deactivation in the ammonia synthesis reaction. Evidence of charge transfer from the reducible support to the active phase, indicative of possible SMSI behaviour, has been observed by XPS and EPR. Differences in the oxidation states, redox behaviours, and electronic properties have been further studied by means of EPR, H2-TPR and H2-TPD.