NH3 Decomposition Research Articles

Catalyst Coatings for Ammonia Decomposition in Microchannels at High Temperature and Elevated Pressure for Use in Decentralized and Mobile Hydrogen Generation

We report an investigation of catalyst performance for the decomposition of ammonia under industrially relevant conditions (high temperatures of up to 800 °C and an elevated pressure of 5 bar) with further emphasis on their stability at high reaction temperatures. The catalysts were applied and tested as coatings in 500 µm wide channels of microreactors. Nickel-based catalysts were studied and compared to a ruthenium-based catalyst supported on SiO2. The effect of the support on the catalytic performance was investigated, and CeO2-supported nickel catalysts were found to exhibit the highest activity. Promoters were applied to increase the NH3 decomposition activity of the Ni/CeO2 catalysts. The addition of cesium led to a slight reduction in activity, while lanthanum, calcium, and barium doping resulted in increased activity. In particular, the barium-doped Ni/CeO2 catalyst showed very high ammonia conversion and closed the activity gap with respect to ruthenium catalysts at reactor temperatures of 650 °C and higher. The hydrogen production rates achieved in this work were compared to values in the literature and were shown to exceed values found earlier for both nickel- and ruthenium-based catalysts. Furthermore, the ruthenium-based catalysts under investigation were rapidly deactivated at 700 °C, while the nickel-based catalysts did not show deactivation after 220 h on time on stream at 700 °C.

Adsorption and dehydrogenation of ammonia on Ru55, Cu55 and Ru@Cu54 nanoclusters: role of single atom alloy catalyst.

Hydrogen production by the catalytic decomposition of ammonia (NH3) is an important process for several important applications, which include energy production and environment-related issues. The role of single Ru-atom substitution in a Cu55 nanocluster (NC) has been illustrated using the NH3 decomposition reaction as a model system. The structural stability of Ru@Cu54 NC has been evaluated using Ru55 and Cu55 NCs for comparison. Ru@Cu54 prefers an icosahedron structure (Ih), like Ru55 and Cu55 NCs, with almost comparable average binding energies of -5.55 eV per atom. The adsorption of NHx (x = 0-3) on different adsorption sites of the icosahedron Ru@Cu54 NC has also been studied and the corresponding adsorption energies have been estimated. The site-preference investigation suggested that NH3 prefers to adsorb vertically to the Ru@Cu54. The stable geometries of the N and H atoms on the high symmetry adsorption sites of Ru@Cu54 NC have been studied. Although the N atom favours top and hollow sites, the H atom prefers to stay in the Ru-Cu bridge site along with the hollow sites. The adsorption energy of N on the Ru@Cu54 NC fcc site is found to be -5.42 eV, which is very close to the optimal value (-5.81 eV) of the ammonia decomposition volcano curve. The reaction energies for stepwise H atom elimination from an adsorbed NH3 molecule have been estimated. Finally, NH3 adsorption and decomposition on Ru@Cu54 have been illustrated in terms of electronic structure analysis. The energetics calculations for the dehydrogenation of NH3 suggest that Ru@Cu54 NC can be a suitable catalyst.

Hydrogen production by NH3 decomposition at low temperatures assisted by surface protonics.

Ammonia, which can be decomposed on-site to produce CO2-free H2, is regarded as a promising hydrogen carrier because of its high hydrogen density, wide availability, and ease of transport. Unfortunately, ammonia decomposition requires high temperatures (>773 K) to achieve complete conversion, thereby hindering its practical applicability. Here, we demonstrate that high conversion can be achieved at markedly lower temperatures using an applied electric field along with a highly active and readily producible Ru/CeO2 catalyst. Applying an electric field lowers the apparent activation energies, promotes low-temperature conversion, and even surpasses equilibrium conversion at 398 K, thereby providing a feasible route to economically attractive hydrogen production. Experimentally obtained results and neural network potential studies revealed that this reaction proceeds via HN-NH intermediate formation by virtue of surface protonics.

Clean hydrogen production from ammonia decomposition over zeolite 13X-supported Ni catalysts

Ni/zeolite 13X catalyst synthesized by deposition–precipitation exhibits improved low-temperature performance for NH3 decomposition owing to high dispersion and uniform deposition of active Ni on the surface and in the pores of the zeolite support.

Ammonia Decomposition over Low-loading Ruthenium Catalyst Achieved through “Adiabatic” Plasma Reactor

Electrified catalytic processes for ammonia (NH3) decomposition have been considered as essential technologies for distributed COx-free hydrogen production. Here we show that efficient NH3 decomposition can be achieved over low-loading...

Effect of Equivalence Ratio on Pollutant Formation in CH4O/H2/NH3 Blend Combustion.

This paper investigates the effect of equivalence ratio on pollutant formation characteristics of CH4O/H2/NH3 ternary fuel combustion and analyzes the pollutant formation mechanisms of CO, CO2, and NOX at the molecular level. It was found that lowering the equivalence ratio accelerates the decomposition of CH4O, H2, and NH3 in general. The fastest rate of consumption of each fuel was found at φ = 0.33, while the rates of CH4O and NH3 decomposition were similar for the φ = 0.66 and φ = 0.4. CO shows an inverted U-shaped trend with time, and peaks at φ = 0.5. The rate and amount of CO2 formation are inversely proportional to the equivalence ratio. The effect of equivalence ratio on CO2 is obvious when φ > 0.5. NO2 is the main component of NOX. When φ < 0.66, NOX shows a continuous increasing trend, while when φ ≥ 0.66, NOX shows an increasing and then stabilizing trend. Reaction path analysis showed that intermediates such as CH3 and CH4 were added to the CH4O to CH2O conversion stage as the equivalence ratio decreased with φ ≥ 0.5. New pathways, CH4O→CH3→CH2O and CH4O→CH3→CH4→CH2O, were added. At φ ≤ 0.5, new intermediates CHO2 and CH2O2 were added to the CH2O to CO2 conversion stage, and new pathways are added: CH2O→CO→CHO2→CO2, CH2O→CO→CO2, CH2O→CHO→CO→CHO2→CO2, and CH2O→CH2O2→CO2. The reduction in the number of radical reactions required for the conversion of NH3 to NO from five to two directly contributes to the large amount of NOX formation. Equivalent ratios from 1 to 0.33 corresponded to 12%, 21.4%, 34%, 46.95%, and 48.86% of NO2 remaining, respectively. This is due to the fact that as the equivalence ratio decreases, more O2 collides to form OH and some of the O2 is directly involved in the reaction forming NO2.

Decarbonizing the energy supply chain: Ammonia as an energy carrier for renewable power systems

Growing global awareness of global warming has led to a focus on reducing greenhouse gas emissions and promoting renewable energy. Energy storage is essential for ensuring a reliable power supply due to the intermittent nature of renewables. While green hydrogen (H2) is considered a clean energy carrier, it faces challenges such as high cost, safety concerns, and low volumetric energy density. In contrast, safer and cost-effective ammonia (NH3) offers higher volumetric energy density for storage. The study explores the Electricity-H2-NH3-H2-Electricity system, a promising low-carbon global renewable electricity transportation avenue. It involves an Aspen Plus process simulation, encompassing air separation, NH3 synthesis, and H2 generation from the NH3 decomposition process. We analyze renewable energy sources, NH3 transportation, process mass balance, and energy consumption and conduct economic and CO2 analyses. Three scenarios (current, near future, sustainable future) with varying technology levels and costs are presented. The findings reveal that 11.044–9.349 MWh of renewable electricity in exporting countries generates 1 tonne of NH3, then split, with 0.17 tonnes combusted to provide heat for the decomposition process and the remaining 0.83 tonnes converted to produce 0.145 tonnes of H2. This H2 is sent to fuel cells, yielding 1.711–2.436 MWh of imported electricity to the grid, with 575–141 USD/MWh cost. Additionally, the imported NH3 and H2 incur costs of 0.719–0.289 USD/kg and 5.993–2.362 USD/kg, respectively. Considering the heat integration of the fuel cells and NH3 decomposition process, an additional 23 % of H2 production is achieved (0.178 tonnes), and a 34 % increase in imported electricity is sent to the grid (2.370–3.259 MWh). This leads to a 27 % decrease in imported renewable energy costs (432–103 USD/MWh) and a 29 % reduction in H2 costs (4.087–1.666 USD/kg); the ultimate CO2 emission of the system is 318–36 kg/MWh.

Spherical mesoporous silica-supported Ru nanoparticles for ammonia decomposition

To synthesize highly dispersed Ru nanoparticles (NPs) with desired particle size for NH3 decomposition, an appropriate support is crucial. Herein, spherical mesoporous silica (SMS) NPs with ∼3 nm pores are synthesized by a microwave-assisted evaporation-induced self-assembly method and used as support of Ru NPs for NH3 decomposition. Characterization shows that compared to Ru NPs supported on SBA-15 and fumed SiO2, Ru NPs supported on SMS (Ru@SMS) exhibit superior NH3 decomposition performance, achieving a hydrogen generation rate of 31.4 mmol·g-1 cat·min−1 at 500 °C, which is one of the highest reported values for supported Ru catalysts in NH3 decomposition. The excellent NH3 decomposition performance observed on Ru@SMS should be attributed to effective dispersion and appropriate particle size (2.22 ± 0.29 nm) of Ru NPs. This work highlights the potential of SMS as support of Ru catalyst in NH3 decomposition.

Efficient Ni/Y2O3 catalyst prepared by sol-gel self-combustion method for ammonia decomposition to hydrogen

Ammonia has sparked a lot of interest as a promising hydrogen carrier for the development of renewable energy and as a workable method to produce COx-free hydrogen for fuel cells through its on-site decomposition. The catalysts, composed of nickel as an active metal supported on the Y2O3, were synthesized by the sol-gel self-combustion method conveniently, in which the active metals are uniformly dispersed. 700–1.25Ni1Y1Oα exhibits the best catalytic activity and has the most active metal dispersion (6.15 %). The ammonia conversion can reach 96 % at 550 °C and 12000 ml·gcat−1·h−1 gas hourly space velocities (GHSVs) as well as 100 % at 600 °C and the same GHSVs. Temperature-programmed reduction, temperature-programmed desorption, and X-ray photoelectron spectroscopy were used to characterize the catalysts. It was found that 700–1.25Ni1Y1Oα has the best capacity for hydrogen desorption resulting in weakening the inhibitory effect of hydrogen to the reaction and enhancing the reactivity of the catalyst. The electron transfer from Y in Y–O–Ni structure increases gradually as the Ni to Y ratio becomes appropriate, enhancing the alkalinity of the catalyst and electron density around the Ni, which is beneficial to NH3 decomposition.

The effects of Al (111) and Al2O3/Al (111) surfaces on the decomposition of ammonium perchlorate: A DFT-D study

Ammonium perchlorate (AP) is a crucial oxidizing agent in composite solid propellants, where aluminum (Al) is used as an additive to increase the energy density of composite solid propellants. The interaction between AP and Al significantly improves the ignition and combustion performance of propellants, but the mechanism of their interactions still lacks essential understanding, especially the interaction between AP and Al, as well as the Al surface containing aluminum oxide (Al2O3). To solve this problem, the adsorption and decomposition processes of AP and its decomposition products such as perchloric acid (HClO4) and ammonia (NH3) on the pure-Al (111) and Al2O3/Al (111) surfaces were studied by using the density functional theory (DFT). The effects of temperature and pressure on the adsorption and reactions were discussed. AP tends to adsorb on the pure-Al (111) surface with O-termination, while under the influence of Al2O3, AP is more inclined to adsorb on the surface of Al2O3/Al (111). At the low-temperature stage, the Al2O3 molecules on the surface of Al (111) promote the disengagement H of AP decomposition and the adsorption and decomposition of NH3, while at the high-temperature stage, the pure Al surface is more conducive to the AP disengagement H and NH3 decomposition. The increase in the pressure is in favor of NH3 adsorption, but the effect gradually decreases. HClO4 cannot adsorb on the pure-Al (111) and AP (001) surfaces, but it can adsorb on the surface of Al2O3/Al (111). In the gas phase, the decomposition of HClO4 priors to NH3. At the high temperature and pressure, the pure-Al (111) surface can contribute significantly to the adsorption and activation of NH3. The findings are very valuable for regulating the combustion of solid propellants.

Ammonia cracking for hydrogen production using a microwave argon plasma jet

Ammonia (NH3) is a promising hydrogen carrier that effectively connects producers of blue hydrogen with consumers, giving rapid conversion of ammonia to hydrogen a critical role in utilizing hydrogen at the endpoints of application in an ammonia-hydrogen economy. Because conventional thermal cracking of NH3 is an energy intensive process, requiring a relatively longer cold start duration, plasma technology is being considered as an assisting tool—or an alternative. Here we detail how an NH3 cracking process, using a microwave plasma jet (MWPJ) under atmospheric pressure, was governed by thermal decomposition reactions. We found that a delivered MW energy density (ED) captured the conversion of NH3 well, showing a full conversion for ED > 6 kJ l−1 with 0.5-% v/v NH3 in an argon flow. The hydrogen production rate displayed a linear increase with MW power and the NH3 content, being almost independent of a total flow rate. A simplified one-dimensional numerical model, adopting a thermal NH3 decomposition mechanism, predicted the experimental data well, indicating the importance of thermal decomposition in the plasma chemistry. We believe that such a prompt thermal reaction, caused by MW plasma, will facilitate a mobile and/or non-steady application. A process combined with the conventional catalytic method should also effectively solve a cold start issue.

NH3 decomposition for H2 production by thermal and plasma catalysis using bimetallic catalysts

Plasma catalysis has emerged as a promising approach for driving thermodynamically unfavorable chemical reactions. Nevertheless, comprehending the mechanisms involved remains a challenge, leading to uncertainty about whether the optimal catalyst in plasma catalysis aligns with that in thermal catalysis. In this research, we explore this question by studying monometallic catalysts (Fe, Co, Ni and Mo) and bimetallic catalysts (Fe-Co, Mo-Co, Fe-Ni and Mo-Ni) in both thermal catalytic and plasma catalytic NH3 decomposition. Our findings reveal that the Fe-Co bimetallic catalyst exhibits the highest activity in thermal catalysis, the Fe-Ni bimetallic catalyst outperforms others in plasma catalysis, indicating a discrepancy between the optimal catalysts for the two catalytic modes in NH3 decomposition. Comprehensive catalyst characterization, kinetic analysis, temperature program surface reaction experiments and plasma diagnosis are employed to discuss the key factors influencing NH3 decomposition performance.

Ultrasmall nickel boride nanoparticles supported on reduced graphene oxide as a high-performance catalyst for hydrazine electrooxidation

The direct hydrazine fuel cell is an attractive power generation technology for automotive applications. However, existing anode electrocatalysts generally suffer from low stability and problematic selectivity towards the non-Faradaic hydrazine (N2H4) decomposition. Herein, we report the fabrication of reduced graphene oxide (rGO)-supported nickel boride (Ni2B) nanocatalyst with a narrow size distribution around 1.5 nm by an ice-melting controlled NaBH4 reduction of Ni salt and graphene oxide. The chemical combination of Ni with B improves the intrinsic activity for N2H4 electrooxidation while suppressing the non-Faradaic N2H4 decomposition concurrently. Furthermore, Ni2B/rGO exhibits excellent stability with 91.4 % activity retention after 3000 cycles and a potential increment of only 13 mV after 50 h of constant-current measurement at 100 mA cm–2. Such stable performance is unprecedented for HzOR electrocatalysts. Our study presents the prospect of transition metal borides as high-performance HzOR electrocatalysts and may encourage further studies to explore their electrocatalytic applications.

Achieving equilibrium conversions for low-temperature NH3 decomposition: Synergy between catalyst and electric field effects

In the advent of an energy shift towards renewable energy sources, ammonia is considered a promising energy carrier for convenient hydrogen storage and transport. However, ammonia decomposition requires temperatures higher than 500 °C to achieve 100% conversion. Here, we present the facile synthesis and use of nanocluster RuCeO2 catalysts for the low-temperature electric field-assisted ammonia decomposition reaction. The catalysts obtained desirable properties and achieved high conversions for ammonia decomposition under conventional conditions. Interestingly, catalyst activities significantly increased upon exposure to an electric field, achieving 100% conversion at 450 °C and obtaining exceptional conversions of up to 34% at a low temperature of 200 °C and a high GHSV of 30,000 mLNH3/gcath. Optimization of reaction parameters effectively increased NH3 conversions, allowed highly stable long-term activities, and enabled the catalyst to achieve equilibrium conversions at remarkably lower temperatures. Further studies reveal that the electric field essentially reduces apparent activation energies and boosts the ammonia decomposition reaction by promoting the recombinative desorption of N2 and H2, thereby alleviating the rate-determining step and preventing deactivation due to H2 poisoning. The occurrence of surface protonics as a result of N-H bond scission and transport of H+ species to the support, along with increased NH3 activation and oxygen vacancy migration improves charge transfer between the support and the Ru active sites, thereby resulting in increased desorption of N2 and H2 products. Thus, an energy-efficient route toward economical hydrogen production is achieved by combining electric field effects with a highly active RuCeO2 catalyst.

Systematic in situ Investigation of the Formation of NH3 Cracking Catalysts from Precursor Perovskites ABO3 (A=La,Ca,Sr and B=Fe,Co,Ni) and their Catalytic Performance

AbstractThis work addresses the formation of ammonia (NH3) decomposition catalysts derived from perovskites ABO3 (A=La, Ca, Sr, and B=Fe, Co, Ni) precursors via operando synchrotron X‐ray diffraction experiments. During the reaction in NH3, the perovskite precursors are decomposed and the transition metals are reduced. Depending on their reduction properties, active metallic catalysts are formed in situ on La2O3 as support. The reduction behavior of the perovskites, formation of intermediate phases during activation, and catalytic performance was studied in detail. In addition, microstructure properties such as crystallite sizes and particle morphology were analyzed. Co‐/Ni‐based perovskites decomposed completely during activation to Co0/Ni0 supported on La2O3 while Fe‐based perovskites were fully stable but inactive in catalysis. This difference is due to varying electronic properties of the transition metals, e. g., decreasing electronegativity from Ni to Fe. With decreasing reducibility, the intermediate phases during activation formed more distinct. La3+ was partially substituted by Ca2+/Sr2+ in LaCoO3 to test for advantageous effects in NH3 decomposition. The best performance was observed using the precatalyst La0.8Sr0.2CoO3 with a conversion of 86 % (100 % NH3, 15000 mL g−1 h−1) at 550 °C.

Ce0.5Zr0.5O2 solid solutions supported Co-Ni catalyst for ammonia oxidative decomposition to hydrogen

A series of CexZr1-xO2 catalysts with different Ce content (x = 1, 0.80, 0.75, 0.50, 0.33) were synthesized by co-precipitation method. The partial doping of Zr in CeO2 framework was observed to enhance the surface area and increase oxygen vacancy of the catalyst, which resulted in promoting of both NH3 oxidation and dehydrogenation in the NH3 oxidative decomposition process. The structural property of the catalysts were characterized by various methods, including XRD, BET, TEM, NH3-TPD, H2-TPR and XPS. It appears that the 5 wt% Co − 5 wt% Ni/Ce0.5Zr0.5O2 (CNCZ-55) catalyst demonstrates excellent activity in the given experimental conditions. The results indicate that when NH3 / O2 = 1:0.25, the conversion rates of both ammonia and oxygen reach 97% and 100%, respectively. Additionally, the hydrogen production achieved a notable efficiency of 63%. Moreover, the stability and repeatability of the CNCZ-55 catalyst have been obtained over 5 cycles and a total experimental duration of 100 h. This suggests that the catalyst exhibits good durability and can consistently perform well in the given reaction conditions. This design concept of improving the performance by optimizing the catalyst carrier may be broadly applicable to catalysts for a wide range of NH3 decomposition and H2 production reaction.

Catalytic ammonia decomposition to produce hydrogen: A mini-review

Hydrogen (H2) is considered one of the most promising alternative energy resources instead of fossil fuels, serving as a clean energy carrier. Ammonia (NH3) is regarded as a high percentage hydrogen carrier and utilized as an initial material for H2 production. As for the H2 production through NH3 decomposition, there are various catalytic processes particularly using Ru- and Pd-based catalysts. The Ru- and Ni-based NH3 decomposition catalysts have been studied due to synergetic effect of active metal phase in stabilizing unstable nitrogen intermediate species during NH3 decomposition reaction. The Pd catalyst-based membrane reactors were developed to enhance H2 separation from the product stream of NH3 decomposition. Integrated systems combining Ru catalyst and Pd-based membrane were also explored to achieve a high yield of H2 from NH3. This review summarizes recent literatures on catalytic NH3 decomposition to produce H2. It probably provides useful insights into designing large-scale H2 production processes.

Effects of bipolar plate flow channel configuration on thermal-electric performance of direct ammonia solid oxide fuel cell: Part I - Numerical study of channel section geometry

Direct ammonia SOFCs (DA-SOFCs) are numerical studied to investigate the effects of bipolar plate flow channel configuration on thermal-electric performance. This study establishes a planar DA-SOFC model and investigates triangular, quadrangular, and oval flow channel configurations’ impact using numerical simulations. Results reveal oval cross-section channels outperform trapezoidal and triangular ones, achieving power density increases of 15.6%, 16.1%, and 18.6%, respectively, compared to rectangular channels at 0.6V. The oval channel displays superior velocity and vorticity, enhancing mass transfer between the main flow and reaction zone. Increasing channel width reduces rib width, promoting O2 distribution, temperature improvement via exothermic reactions, NH3 decomposition into H2, and improved cell performance. Rib width increase shortens diffusion and reduces concentration polarization, but increases ion transport and ohmic polarization. A theoretical formula for optimal rib width (Wrib0) to minimize polarization loss is provided. These findings offer a comprehensive reference for optimizing DA-SOFC design.

Self-Construction of Efficient Interfaces Ensures High-Performance Direct Ammonia Protonic Ceramic Fuel Cells.

Direct ammonia protonic ceramic fuel cells (PCFCs) are highly efficient energy conversion devices since ammonia as a carbon-neutral hydrogen-rich carrier shows great potential for storage and long-distance transportation when compared with hydrogen fuel. However, traditional Ni-based anodes readily suffer from severe structural destruction and dramatic deactivation after long-time exposure to ammonia. Here a Sr2 Fe1.35 Mo0.45 Cu0.2 O6-δ (SFMC) anode catalytic layer (ACL) painted onto a Ni-BaZr0.1 Ce0.7 Y0.1 Yb0.1 O3- δ (BZCYYb) anode with enhanced catalytic activity and durability toward the direct utilization of ammonia is reported. A tubular Ni-BZCYYb anode-supported cells with the SFMC ACL show excellent peak power densities of 1.77 W cm-2 in wet H2 (3% H2 O) and 1.02 W cm-2 in NH3 at 650 °C. A relatively stable operation of the cells is obtained at 650 °C for 200 h in ammonia fuel. Such achieved improvements in the activity and durability are attributed to the self-constructed interfaces with the phases of NiCu or/and NiFe for efficient NH3 decomposition, resulting in a strong NH3 adsorption strength of the SFMC, as confirmed by NH3 thermal conversion and NH3 -temperature programmed desorption. This research offers a valuable strategy of applying an internal catalytic layer for highly active and durable ammonia PCFCs.

A highly efficient Ni/3DOM-La2O2CO3 catalyst with ordered macroporous structure for CO2 methanation

The global focus on new energy sources and energy storage methods has prompted significant research interest. Ni-based catalysts for CO2 methanation have the potential for industrialization, but face challenges such as high-temperature sintering, carbon deposition, and unstable catalytic activity; of which similar problems exist in NH3 decomposition reactions. A 10%Ni/3DOM-La2O2CO3 catalyst, featuring a three-dimensional ordered macroporous (3DOM) structure, demonstrated competitive low-temperature catalytic performance in CO2 methanation through formate intermediates. Comprehensive characterizations revealed improved Ni dispersion and carbon deposition prevention due to the 3DOM structure, enhancing catalytic activity. This structural advantage also translated to improved performance in ammonia decomposition.