Catalytic Decomposition Of Ammonia Research Articles

Synergistic Effect of Co and Ni Co-Existence on Catalytic Decomposition of Ammonia to Hydrogen—Effect of Catalytic Support and Mg-Al Oxide Matrix

Hydrotalcite-derived mixed metal oxides containing Co and Ni and containing these metals supported on MgO and Al2O3 were prepared and tested as catalysts for the decomposition of ammonia to hydrogen and nitrogen. The obtained samples were characterised in terms of chemical composition (ICP-OES), structure (XRD), textural parameters (low-temperature N2 adsorption–desorption, SEM), form and aggregation of transition-metal species (UV-Vis DRS), reducibility (H2-TPR) and surface acidity (NH3-TPD). The catalytic efficiency of the tested systems strongly depends on the support used. Generally, the alumina-based catalyst operated at lower temperatures compared to transition metals deposited on MgO. For both series of catalysts, a synergistic effect of the co-existence of cobalt and nickel on the catalytic efficiency was observed. The best catalytic results were obtained for hydrotalcite-derived catalysts; however, in the case of these catalysts, an increase in the Al/Mg ratio resulted in a further increase in catalytic activity in the decomposition of ammonia.

Role of cation in catalytic decomposition of ammonia over Ni supported zeolite Y catalysts

A series of nickel (Ni) catalysts were prepared using zeolites Y with different cation types (Na, Mg, Ca, Sr, Ba, Ce, and La) as supports and characterized by using XRD, BET, ICP-OES, XPS, and TEM, as well as NH3-TPD, CO2-TPD, and H2-TPR techniques. Their catalytic performances in decomposition of ammonia (NH3) to hydrogen (H2) were evaluated with a fixed-bed flow reactor system. The catalytic activities of the prepared catalysts for NH3 decomposition decreased in the order of Ni/SrY > Ni/BaY > Ni/LaY > Ni/CaY > Ni/NaY > Ni/MgY > Ni/CeY. The high activity of Ni/SrY catalyst may be attributed to its small Ni nanoparticle size, high basicity and strong interaction between highly dispersed Ni nanoparticles and SrY support. At 600 °C and GHSV of 9000 mLNH3·gcat−1·h−1, 98.0 % NH3 conversion with about 105.2 mmol min−1·gNi−1 H2 formation rate can be accomplished over Ni/SrY catalyst.

Metallic nickel exsolved from a two-dimensional MWW-type zeolitic nickel silicate: An effective catalyst for ammonia decomposition

Exsolution of active species from metal oxide materials is an effective strategy for preparing a highly active and stable catalyst. Here, we prepared two-dimensional nickel (Ni) silicate material with delaminated MWW layers (Ni-DMLs) by hydrothermal treatment of borosilicate MWW precursor (B-MWW(P)) with Ni nitrate solutions and applied on the catalytic decomposition of ammonia (NH3) via exsolution. The layered B-MWW(P) was transformed to a three-dimensional (3D) tectosilicate MWW, a two-dimensional (2D) Ni-DML, and a 2D phyllosilicate structures at temperature regions of 100–120 °C, 140–160 °C, and 170–180 °C, respectively. Meanwhile, the Ni contents on the samples increased from 3.6 to 37.6 wt.% as the hydrothermal temperature increased from 100 to 180 °C, owing to the substitution of framework B by Ni. The chemical state of Ni on each sample was characterized by various analytical tools and correlated with their catalytic properties of NH3 decomposition over the exsolved metallic Ni species. The NH3 decomposition over Ni-DMLs was evaluated in the temperature range of 300–600 °C, and the apparent activation energies were compared. The Ni-DML-160 exhibited the best catalytic activity, achieving an NH3 conversion of 70% at 500 °C and maintained 90% to initial conversion during 100 h on stream at 550 °C. The synergistic effect of the strong interaction between the exsolved metallic Ni and the zeolite support and the 2D nature of Ni-DMLs relieved the catalytic deactivation by sintering and coking, respectively.

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.

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.

A review of multiscale modelling approaches for understanding catalytic ammonia synthesis and decomposition

Ammonia plays a crucial role in our lives as it is widely used, for example, in the synthesis of fertilizers, the production of carbon-free hydrogen for fuel cells, or electricity generation. However, the conventional Haber-Bosch process for ammonia synthesis has several drawbacks, such as requiring high temperatures and pressures, consuming 1–2% of the world's energy supply. While significant progress has been made in performing the reaction under milder conditions, the subject has experienced a second renaissance with the advent of multiscale modeling and improvements in computational capabilities.Multiscale modeling at various levels, including density functional theory (DFT), transition state theory (TST), kinetic Monte Carlo method (KMC), microkinetic modeling, molecular dynamics (MD), and computational fluid dynamics (CFD), allows us to describe the reaction system at all levels simultaneously. In this review, we focus on the treatment of ammonia synthesis, decomposition, or oxidation using multiscale models, ranging from the study of quantum-level interactions to the optimization of reactor design.Recently, significant progress has been made in modeling. Current modeling tools, while well developed, still have weaknesses in their linkage. DFT /TST is often coupled with KMC and MD or microkinetic data are fed into CFD while a comprehensive model is lacking. The potential for further progress through the use of multiscale models is enormous, which could lead to more efficient catalyst and process design.

Plasma-Promoted Ammonia Decomposition over Supported Ruthenium Catalysts for COx -Free H2 Production.

The efficient decomposition of ammonia to produce COx -free hydrogen at low temperatures has been extensively investigated as a potential method for supplying hydrogen to mobile devices based on fuel cells. In this study, we employed dielectric barrier discharge (DBD) plasma, a non-thermal plasma, to enhance the catalytic ammonia decomposition over supported Ru catalysts (Ru/Y2 O3 , Ru/La2 O3 , Ru/CeO2 and Ru/SiO2 ). The plasma-catalytic reactivity of Ru/La2 O3 was found to be superior to that of the other three catalysts. It was observed that both the physicochemical properties of the catalyst (such as support acidity) and the plasma discharge behaviours exerted significant influence on plasma-catalytic reactivity. Combining plasma with a Ru catalyst significantly enhanced ammonia conversion at low temperatures, achieving near complete NH3 conversion over the 1.5 %-Ru/La2 O3 catalyst at temperatures as low as 380 °C. Under a weight gas hourly space velocity of 2400 mL gcat -1 h-1 and an AC supply power of 20 W, the H2 formation rate and energy efficiency achieved were 10.7 mol gRu -1 h-1 and 535 mol gRu -1 (kWh)-1 , respectively, using a 1.5 %-Ru/La2 O3 catalyst.

Influence of CaCe ratio on the hydrogen production from ammonia over CaO-CeO2 supported Co catalysts

Hydrogen (H2) fuel has the potential to replace fossil fuel for generating electricity, clean energy and generating power. Ammonia (NH3) has the potential to overcome the challenges associated with storage, transportation, and use of hydrogen fuel. The catalytic decomposition of ammonia into hydrogen is studied over cobalt catalysts supported on CaO-CeO2 mixed oxide. The influence of the Ca/Ce ratio in the support composition on catalytic activity was investigated. The CaO-CeO2 mixed oxide support materials prepared with different Ca/Ce ratios (1:1, 2:1 and 3:1). The overall basicity of catalyst varied with the increase of Ca to CaO-CeO2 mixed oxide and showed maximum at Ca/Ce = 2. The cobalt catalysts are prepared with a nominal 5 wt% Co over CaO-CeO2 mixed oxide support with various Ca/Ce ratios. Among all prepared catalysts 5CoCaCe-21 (5 wt%Co on CaO-CeO2 mixed oxide with Ca/Ce = 2) showed highest activity. Surface area, X-ray diffraction (XRD), Temperature Program Reduction (TPR), Scanning Electron Microscopy (SEM), and CO2 Temperature Program Desorption (TPD) methods were used to characterize the synthesized materials. The high performance of 5CoCaCe-21 catalyst is due to high basicity, suitable metal support interactions, high surface area and easy reducibility of Co species resulting from its support favorable properties. The effect of cobalt loadings also studied on CaCe-21 support. The 10 wt%Co on CaCe-21 (10CoCaCe-21) showed highest activity among all other cobalt loadings. The 10CoCaCe-21 catalyst showed excellent stability for H2 production from NH3 during 70 h of time on study with different GHSVs.

Hydrogen production by the catalytic decomposition of ammonia over a Ru/SiCeOx catalyst: The synergistic effect of Si addition

Controlling active metal–support interaction is critical in the catalytic decomposition of ammonia (NH3). In this study, we investigated the generation of oxygen vacancies in the SiCeOx support by Si addition and the increase in catalytic performance for the decomposition of NH3 by their interaction with Ru. The Si content in the Ru/SiCeOx catalysts was controlled by glassware elution during the precipitation of Ce(NO3)3 at a high pH level (10.5) by applying different aging temperatures and times. The formation of oxygen vacancies by the insertion of Si4+ into the CeO2 lattice was characterized by O2-pulse experiments as well as Raman and X-ray photoelectron spectroscopy analyses. The effect of oxygen vacancies on the adsorption strengths of hydrogen and nitrogen on Ru was characterized by H2-temperature-programmed reduction and NH3-temperature-programmed desorption. The correlation between NH3 conversion, oxygen vacancy content, and nitrogen desorption temperature was experimentally proven.

H2 production from ammonia decomposition with Mo2N catalyst driven by dielectric barrier discharge plasma

Dielectric barrier discharge (DBD) plasma-assisted ammonia decomposition reaction was investigated to produce carbon-free hydrogen for fuel cell applications. Mo2N catalyst was synthesized and applied for catalytic ammonia decomposition in different reaction modes. The synergistic effect of using Mo2N catalyst in combination with DBD plasma resulted in near complete conversion of NH3 decomposition at specific energy input (SEI) of 39.6 kJ L−1, giving an energy efficiency of 6.1 mol·kWh−1 for H2 production. The particle size of Mo2N catalyst was discovered to affect the plasma-catalytic performance for NH3 decomposition, with Mo2N-powder catalyst showing higher reactivity compared with Mo2N-particle catalyst. The plasma diagnostic results showed that, compared to the filamentary discharge with Mo2N-particle catalyst, the Mo2N-powder catalyst packing lead to a predominant surface discharge; such localized surface discharges might contribute to a facile transportation of reactive species from the plasma phase to the catalyst surface, thus leading to higher plasma-catalytic performance.

Enhancement of the Catalytic Activity of Lithium Amide towards Ammonia Decomposition by Addition of Transition Metals

The catalytic decomposition of ammonia to hydrogen is a vital process in the use of ammonia as a zero-carbon energy store. However, the viability of current catalyst systems in terms of operating conditions, versatility, and cost efficiency has proven an issue. Catalytic and gravimetric studies were conducted considering mechanistic uncertainty surrounding the enhanced catalytic activity reported for lithium amide and imide composited with transition metals (Cr, Mn, Fe). Gas flow in excess of ammonia decomposition was quantified and used to differentiate the extent of formation of non-stoichiometric lithium imide amide from other competing processes. This analysis showed the initial compositional transition from lithium amide to an imide-rich phase was reduced in temperature by compositing with Mn and Cr, but not with Fe. The system is, therefore, best considered as promoted lithium imide, with Cr and Mn acting to reduce the formation temperature of the active imide-rich phase such that the catalytic activity is enhanced.

Non-Noble FeCrOx Bimetallic Nanoparticles for Efficient NH3 Decomposition

Ammonia has the advantages of being easy to liquefy, easy to store, and having a high hydrogen content of 17.3 wt%, which can be produced without COx through an ammonia decomposition using an appropriate catalyst. In this paper, a series of FeCr bimetallic oxide nanocatalysts with a uniform morphology and regulated composition were synthesized by the urea two-step hydrolysis method, which exhibited the high-performance decomposition of ammonia. The effects of different FeCr metal ratios on the catalyst particle size, morphology, and crystal phase were investigated. The Fe0.75Cr0.25 sample exhibited the highest catalytic activity, with an ammonia conversion of nearly 100% at 650 °C. The dual metal catalysts clearly outperformed the single metal samples in terms of their catalytic performance. Besides XRD, XPS, and SEM being used as the means of the conventional characterization, the local structural changes of the FeCr metal oxide catalysts in the catalytic ammonia decomposition were investigated by XAFS. It was determined that the Fe metal and FeNx of the bcc structure were the active species of the ammonia-decomposing catalyst. The addition of Cr successfully prevented the Fe from sintering at high temperatures, which is more favorable for the formation of stable metal nitrides, promoting the continuous decomposition of ammonia and improving the decomposition activity of the ammonia. This work reveals the internal relationship between the phase and structural changes and their catalytic activity, identifies the active catalytic phase, thus guiding the design and synthesis of catalysts for ammonia decomposition, and excavates the application value of transition-metal-based nanocomposites in industrial catalysis.

Sintering-free catalytic ammonia cracking by vertically standing 2D porous framework supported Ru nanocatalysts

Catalytic ammonia decomposition enables ammonia to be a hydrogen gas carrier for a carbon-free fuel economy. The challenge is to obtain high conversion yields and rates at low temperatures for a prolonged time. A promising approach is to engineer a catalyst support to minimize deleterious effects like sintering. Here, we compared a conventional 2D planar porous framework support with a vertically standing 2D structure to ascertain the effects of support geometry on the catalytic performance. The catalysts were made by loading ruthenium (Ru) nanoparticles onto the structures, and the catalytic activities were monitored by varying the ammonia (NH3) feeding rate and reaction temperature. Unlike the planar version, the vertically standing 2D support prevented nanoparticle aggregation, retained the original nanoparticle size, and showed an excellent hydrogen production rate (95.17 mmol gRu−1 min−1) at a high flow rate of 32,000 mL gcat−1 h−1 at a temperature of 450 °C.

Plasma-assisted low temperature ammonia decomposition on 3d transition metal (Fe, Co and Ni) doped CeO2 catalysts: Synergetic effect of morphology and co-doping

Catalytic ammonia decomposition generating zero‑carbon and high-energy-density hydrogen over low-cost catalysts has been a hot topic. In this study, ceria support with three morphologies including nanocubes (CeO2-C), nanorods (CeO2-R) and nanospheres (CeO2-S) doped 3d transition metal (Fe, Co and Ni) catalysts have been prepared, characterized and used in ammonia decomposition reaction (ADR). With enhanced metal-support interaction, the co-doped bimetal enriches oxygen vacancies and raised [Ce3+] concentrations, facilitating the electrons transfer from the CeO2 support to active metals. The FeCo/CeO2-S catalyst exhibits excellent thermal stability over continues 48 h. In the non-thermal plasma (NTP) assisted-catalysis in ADR, the FeCo/CeO2-S catalyst showed the highest ammonia conversion with a GHSV of 36,000 mL/gcat/h, which achieves 100% conversion at 550 °C and shows the highest hydrogen generation rate of 29.3 mmol/min·gcat at 500 °C. Our work adopts a novel strategy to improve reaction efficiency of ADR through synergistic promotion of plasma and inexpensive ceria-based catalysts.

In-situ catalytic decomposition of emitted ammonia from municipal solid waste gasification by Ni–M bimetallic catalysts supported on sewage sludge-derived biochar

In-situ catalytic decomposition of emitted ammonia from municipal solid waste gasification by Ni–M bimetallic catalysts supported on sewage sludge-derived biochar

Dispersed surface Ru ensembles on MgO(111) for catalytic ammonia decomposition

Ammonia is regarded as an energy vector for hydrogen storage, transport and utilization, which links to usage of renewable energies. However, efficient catalysts for ammonia decomposition and their underlying mechanism yet remain obscure. Here we report that atomically-dispersed Ru atoms on MgO support on its polar (111) facets {denoted as MgO(111)} show the highest rate of ammonia decomposition, as far as we are aware, than all catalysts reported in literature due to the strong metal-support interaction and efficient surface coupling reaction. We have carefully investigated the loading effect of Ru from atomic form to cluster/nanoparticle on MgO(111). Progressive increase of surface Ru concentration, correlated with increase in specific activity per metal site, clearly indicates synergistic metal sites in close proximity, akin to those bimetallic N2 complexes in solution are required for the stepwise dehydrogenation of ammonia to N2/H2, as also supported by DFT modelling. Whereas, beyond surface doping, the specific activity drops substantially upon the formation of Ru cluster/nanoparticle, which challenges the classical view of allegorically higher activity of coordinated Ru atoms in cluster form (B5 sites) than isolated sites.

Bimetallic NixCo10-x/CeO2 as highly active catalysts to enhance mid-temperature ammonia decomposition: Kinetics and synergies

Catalytic ammonia decomposition is an attractive method to generate hydrogen at mid-temperatures (<700 °C) but must incorporate precious metals (Pd, Ru, etc.) to ensure high reactivity. Developing Ni-based catalysts to decompose ammonia can enhance its prospect for hydrogen generation. However, the catalytic activity of Ni is hardly satisfactory at mid-temperatures. In this work, we show the bimetallic NixCo10-x/CeO2 towards mid-temperature NH3 decomposition, with the metal loading of Ni and Co tuned. Kinetics study demonstrates that the NH3 decomposition reaction follows the Temkin Pyzhev mechanism and the synergy between Ni and Co can decrease the reaction orders regarding NH3 and increase the reaction orders regarding H2. Mechanistic results indicate that the recombinative N desorption limits the reaction rate. The synergy between Ni and Co can simultaneously decrease the energy barriers of the recombinative N desorption and mitigate the H2 poisoning effect. Therefore, Ni7.5Co2.5/CeO2 displays both high ammonia conversion (96.96%) and hydrogen formation rate (1947.9 mmol/(gcat.h)) at 650 °C. We hope the mechanism in this work can be used to guide the design of inexpensive catalysts to decompose ammonia at mid-temperatures.

Catalytic ammonia decomposition to COx-free hydrogen over ruthenium catalyst supported on alkali silicates

• The oxygen vacancies (Vo) would appear in Ru/Ru/A 2 SiO 3 (A=Li, Na and K) after H 2 reduction. • The formation Vo would induce the production of EMSI effect and higher Ru dispersion. • A 2 SiO 3 (A=Li, Na and K) can transfer their electron to Ru particle through EMSI effect. • K 2 SiO 3 is firstly reported to be an effective support as Ru catalyst for NH 3 decomposition. A series of alkali metal silicates A 2 SiO 3 (A = Li, Na and K) were synthesized by a sol–gel method route and employed as support for Ru nanoparticles to catalyze NH 3 decomposition. The NH 3 conversion can be ranked as the order of Ru/K 2 SiO 3 > Ru/Na 2 SiO 3 > Ru/Li 2 SiO 3 > Ru/SiO 2 at the same conditions, and Ru/K 2 SiO 3 displays the highest NH 3 conversion of 60.5% with the TOF H2 of 2.03 s −1 under the weight hourly space velocity (GHSV) of 30,000 mL.g cat -1 .h −1 at 450 o C. The combination results of different characterization indicate that the formation of alkali metal silicates can increase the strength and number of basic sites, and the strong electronic metal-support interaction (EMSI) would appear between Ru particles and oxygen vacancies in A 2 SiO 3 structure at reduction conditions. The presence of EMSI can result in the higher Ru dispersion and enhanced electronic density of Ru particles over A 2 SiO 3 , greatly facilitating the decomposition of NH 3 to CO x -free hydrogen.

Self-combustion Ni and Co-based perovskites as catalyst precursors for ammonia decomposition. Effect of Ce and Mg doping

LaCo1-xNixO3 perovskites have been synthesized by self-combustion, characterized, and examined as catalyst precursors for the COx-free hydrogen production from catalytic ammonia decomposition at low temperatures. The influence of the cobalt content as well as the addition of two dopant in different amount was studied and optimized. Small Ni crystallite size and high total basic sites were found to remarkably enhance the catalytic activity. Moreover, bimetallic perovskites generated cobalt/nickel in higher size, higher impurities and lower active sites than pure nickel perovskite, which decreased the ammonia conversion. On the other hand, the addition of dopant in adequate amount over pure Ni perovskite (La0.1A0.9NiO3; A = Ce or Mg) generated catalyst with low nickel crystallite size and high basicity delivering superior catalytic performance. Catalysts were demonstrated to be stable for at least 40 h. In fact, 96 % and 98 % ammonia conversion were achieved at low temperature (400 °C), when La0.1Ce0.9NiO3 and La0.1Mg0.9NiO3 were employed, resulting from the synergic effect between La-Ce and Ni-Mg-La. Presenting the Mg-doped perovskite the highest catalytic activity at the mild temperature of 350 °C.This study provides new insight in designing diverse catalyst precursors to develop economic and efficient catalysts to achieve high ammonia conversion (high hydrogen production) at low temperature and enhance the ammonia perspective as hydrogen carrier toward the ‘hydrogen economy’.

Electrification of Catalytic Ammonia Production and Decomposition Reactions: From Resistance, Induction, and Dielectric Reactor Heating to Electrolysis

The conventional method for synthesizing ammonia is a power-hungry process that requires high operating temperatures (400–500 °C) in addition to elevated pressures (150–300 bar). The reaction is normally catalyzed by magnetite-based particles, and occurs between a single mole of nitrogen and three moles of hydrogen to form two moles of ammonia. The original Haber–Bosch process was developed and patented in 1916 by Fritz Haber and Carl Bosch. Since then, it has been extensively upgraded and optimized, with many improvements in the area of catalysis. Iron- and ruthenium-based catalysts are commonly used, where the active metal is deposited onto an appropriate support material. However, this method remains rather costly for the mass production of ammonia. The pursuit of a high-efficiency production process combined with the desirable use of renewables has driven the development of alternative, stand-alone methods (such as electrolysis, plasma- and microwave-mediated synthesis, various photochemical pathways, and catalysis aided by magnetic heating) as well as completely separate reactant-production procedures coupled with the traditional Haber–Bosch reactors. This review aims to highlight and critically evaluate recent developments in the electrification of ammonia production and decomposition.