Catalytic Ammonia Research Articles

New catalysts based on reduced graphene oxide for hydrogen production from ammonia decomposition

Promising and highly novel catalysts based on ruthenium (Ru) supported on reduced graphene oxide were synthesized, characterized and tested for COx-free hydrogen generation by catalytic ammonia decomposition. Metal loading and amount of a pre-reducing agent clearly affect the catalytic properties of the final catalysts. A Ru loading higher than 2.5 wt% resulted in Ru particles of size higher than 5 nm, which were agglomerated, thus decreasing the amount of the most active sites (B5 type-sites) and therefore the ammonia conversion. Additionally, a graphene oxide (GO) hydrothermal pre-reduction with 2-chloroethylamine hydrochloride, led materials with a more ordered structure which is associated with a good electronic conductivity and, higher basicity. Optimal catalytic activity is achieved using a reducing agent/GO ratio of 5/3 (wt/wt) and a Ru loading of 2.5 wt%. Thus, 2.5Ru/10C-rGO catalyst resulted in excellent hydrogen (H2) production from ammonia decomposition, with an ammonia conversion close to 96% and hydrogen production rate of 9.1 mmolH2 gcat−1 min−1 at 400 °C. Reduced graphene oxide proved to be a suitable support in the development of nanosized Ru catalysts being the optimal one highly active in COx-free hydrogen generation during more than 60 h of reaction, providing virtuous stability.

Facile Synthesis and High‐Value Utilization of Ammonia

Comprehensive SummaryAmmonia is a key component in fertilizer and the carbon‐free hydrogen carrier. Catalytic ammonia synthesis and utilization have played a central role in the development of chemical engineering. The industrial production of ammonia remains dependent on the energy‐ and carbon‐intensive Haber–Bosch process. A major effort has been devoted to developing robust and efficient catalysts, as well as alternative benign processes. Herein, we detail our endeavors that develop the ammonia synthesis and decomposition catalysts, and utilize the ammonia energy. We firstly discuss the catalysts for ammonia synthesis via dissociative and associative process, and the regulation of catalysts’ properties. Then, we review the burgeoning electrocatalytic nitrogen reduction process, focusing on the enhanced catalytic performances by the regulation of the catalysts and the electrode. Additionally, we provide a novel high‐value utilization of ammonia to achieve the “zero‐carbon” circular economy. The promising catalysts, reactors, and ammonia energy systems have been discussed in detail. We end this Account that offers future research directions and prospects of ammonia. What is the most favorite and original chemistry developed in your research group?Ammonia synthesis catalysts and ammonia energy.How do you get into this specific field? Could you please share some experiences with our readers?I have received my B.S. in 1997. After graduation from college, I have joined Prof. Kemei Wei's group at the National Engineering Research Center of Chemical Fertilizer Catalyst, Fuzhou University. Since 1972, our group has dedicated to the efficient industrial synthesis and high‐value utilization of ammonia. So, I have done much work in this field. I think that the research work should match with the major national demands and global challenges. The researcher should focus on cutting‐edge discoveries and creative work.How do you supervise your students?When the students come in our group, I teach them the norms andstandards of academic research and writing. After that, I would formulate the research project based on their motivations, aspirations, and academic background. If they have any problems during the project, I will help them overcome. We discuss termly on their research methods and evaluate their research results. I also encourage the students to prepare in advance for the next steps in their career or further study.What is the most important personality for scientific research?Research integrity.What are your hobbies? What's your favorite book(s)?I like playing badminton and table tennis. My favorite books are history and industry development plan.How do you keep the balance between research and family?The understanding and support from the family are very important. I have increased my efficiency and productivity, and tried alternative schedules.

Studies of a Highly Active Cobalt Atomic Cluster Catalyst for Ammonia Synthesis

Theoretical studies have demonstrated that metal atomic clusters are highly efficient in catalytic ammonia synthesis under mild conditions. However, activation of N2 over atomic clusters from an experimental viewpoint has not been systematically investigated. Here, for the first time, cobalt atomic dimers on a nitrogen–carbon support were synthesized for NH3 synthesis. It is disclosed that N2 activation over Co2 atomic clusters (Co2 ACCs) is entirely different from that over Co single-atom catalysts (Co SACs) or Co nanoparticles (Co NPs). A suite of in situ spectroscopy studies reveal that Co2 ACCs not only provide active sites to promote strong metal–support interactions but also initiate strong interclustering interactions, resulting in electron transfers from Co d-orbitals to antibonding orbitals of N2 molecules. As such, the activation energy of the Co2 ACC catalyst in NH3 synthesis is small. Consequently, the catalytic activity of the developed Ba-promoted Co2 ACC catalyst reached 19.42 mmolNH3 gcat–1 h–1 at 400 °C and 1 MPa, which is much superior than that of other Co-based catalysts under such mild conditions. More importantly, the synthesis strategy of Co2 ACCs has general applicability as demonstrated in the preparation of Fe2 and Mn2 atomic clusters.

Catalytic resonance of ammonia synthesis by simulated dynamic ruthenium crystal strain.

Ammonia affords dense storage for renewable energy as a fungible liquid fuel, provided it can be efficiently synthesized from hydrogen and nitrogen. In this work, the catalysis of ammonia synthesis was computationally explored beyond the Sabatier limit by dynamically straining a ruthenium crystal (±4%) at the resonant frequencies (102 to 105+ Hz) of N2 surface dissociation and hydrogenation. Density functional theory calculations at different strain conditions indicated that the energies of NHx surface intermediates and transition states scale linearly, allowing the description of ammonia synthesis at a continuum of strain conditions. A microkinetic model including multiple sites and surface diffusion between step and Ru(0001) terrace sites of varying ratios for nanoparticles of differing size revealed that dynamic strain yields catalytic ammonia synthesis conversion and turnover frequency comparable to industrial reactors (400°C, 200 atm) but at lower temperature (320°C) and an order of magnitude lower pressure (20 atm).

Synergistic Effect of Co–Ni Bimetal on Plasma Catalytic Ammonia Synthesis

Synergistic Effect of Co–Ni Bimetal on Plasma Catalytic Ammonia Synthesis

Porous Organic Cage Membranes for the Non-Thermal Plasma Catalytic Blue Ammonia Synthesis: The Protective Role of Porous Organic Cage Cc3

Porous Organic Cage Membranes for the Non-Thermal Plasma Catalytic Blue Ammonia Synthesis: The Protective Role of Porous Organic Cage Cc3

Decoration of Ru Nanoparticles on G-Alumina with Sub-Nanometer Ceria Species for Efficient Catalytic Ammonia Synthesis

Decoration of Ru Nanoparticles on G-Alumina with Sub-Nanometer Ceria Species for Efficient Catalytic Ammonia Synthesis

Catalytic ammonia reforming: alternative routes to net-zero-carbon hydrogen and fuel.

Ammonia is an energy-dense liquid hydrogen carrier and fuel whose accessible dissociation chemistries offer promising alternatives to hydrogen electrolysis, compression and dispensing at scale. Catalytic ammonia reforming has thus emerged as an area of renewed focus within the ammonia and hydrogen energy research & development communities. However, a majority of studies emphasize the discovery of new catalytic materials and their evaluation under idealized laboratory conditions. This Perspective highlights recent advances in ammonia reforming catalysts and their demonstrations in realistic application scenarios. Key knowledge gaps and technical needs for real reformer devices are emphasized and presented alongside enabling catalyst and reaction engineering fundamentals to spur future investigations into catalytic ammonia reforming.

Reaction Model Taking into Account the Catalyst Morphology and Its Active Specific Surface in the Process of Catalytic Ammonia Decomposition.

Iron catalysts for ammonia synthesis/nanocrystalline iron promoted with oxides of potassium, aluminum and calcium were characterized by studying the nitriding process with ammonia in kinetic area of the reaction at temperature of 475 °C. Using the equations proposed by Crank, it was found that the process rate is limited by diffusion through the interface, and the estimated value of the nitrogen diffusion coefficient through the boundary layer is 0.1 nm2/s. The reaction rate can be described by Fick’s first equation. It was confirmed that nanocrystallites undergo a phase transformation in their entire volume after reaching the critical concentration, depending on the active specific surface of the nanocrystallite. Nanocrystallites transform from the α-Fe(N) phase to γ’-Fe4N when the total chemical potential of nitrogen compensates for the transformation potential of the iron crystal lattice from α to γ; thus, the nanocrystallites are transformed from the smallest to the largest in reverse order to their active specific surface area. Based on the results of measurements of the nitriding rate obtained for the samples after overheating in hydrogen in the temperature range of 500–700 °C, the probabilities of the density of distributions of the specific active surfaces of iron nanocrystallites of the tested samples were determined. The determined distributions are bimodal and can be described by the sum of two Gaussian distribution functions, where the largest nanocrystallite does not change in the overheating process, and the size of the smallest nanocrystallites increases with increasing recrystallization temperature. Parallel to the nitriding reaction, catalytic decomposition of ammonia takes place in direct proportion to the active surface of the iron nanocrystallite. Based on the ratio of the active iron surface to the specific surface, the degree of coverage of the catalyst surface with the promoters was determined.

Progress on Noble Metal-Based Catalysts Dedicated to the Selective Catalytic Ammonia Oxidation into Nitrogen and Water Vapor (NH3-SCO).

A recent development for selective ammonia oxidation into nitrogen and water vapor (NH3-SCO) over noble metal-based catalysts is covered in the mini-review. As ammonia (NH3) can harm human health and the environment, it led to stringent regulations by environmental agencies around the world. With the enforcement of the Euro VI emission standards, in which a limitation for NH3 emissions is proposed, NH3 emissions are becoming more and more of a concern. Noble metal-based catalysts (i.e., in the metallic form, noble metals supported on metal oxides or ion-exchanged zeolites, etc.) were rapidly found to possess high catalytic activity for NH3 oxidation at low temperatures. Thus, a comprehensive discussion of property-activity correlations of the noble-based catalysts, including Pt-, Pd-, Ag- and Au-, Ru-based catalysts is given. Furthermore, due to the relatively narrow operating temperature window of full NH3 conversion, high selectivity to N2O and NOx as well as high costs of noble metal-based catalysts, recent developments are aimed at combining the advantages of noble metals and transition metals. Thus, also a brief overview is provided about the design of the bifunctional catalysts (i.e., as dual-layer catalysts, mixed form (mechanical mixture), hybrid catalysts having dual-layer and mixed catalysts, core-shell structure, etc.). Finally, the general conclusions together with a discussion of promising research directions are provided.

Importance of Hydrogen Migration in Catalytic Ammonia Synthesis over Yttrium-Doped Barium Zirconate-Supported Ruthenium Nanoparticles: Visualization of Proton Trap Sites

Importance of Hydrogen Migration in Catalytic Ammonia Synthesis over Yttrium-Doped Barium Zirconate-Supported Ruthenium Nanoparticles: Visualization of Proton Trap Sites

Advancement of Bismuth‐Based Materials for Electrocatalytic and Photo(electro)catalytic Ammonia Synthesis

AbstractAmmonia (NH3) plays a vital role in the fertilizer industry, nitrogen‐containing chemical production, and hydrogen storage. The development of electrocatalytic and photo(electro)catalytic nitrogen reduction reaction (NRR) to synthesize NH3 are desirable, which are more environmentally friendly than the conventional Haber–Bosch process. Due to the strong nonpolar bonding of the NN bond, the discovery of efficient catalysts is essential to overcome the high kinetic barrier. Here, bismuth‐based materials that show proven activities for NRR are highlighted. The fundamental knowledge, including thermodynamics, mechanisms, reaction systems, evaluation aspects of NRR, and product quantification, is introduced. Together with scientific reasoning and exhibited activities, the strategies for improving the performance are discussed in detail. Perspective and outlook, as well as the opportunities to further develop bismuth‐based materials for NH3 synthesis, are provided. This review aims to provide a comprehensive understanding of the advancement in this field and serves as a guide for the future design of highly efficient NRR catalysts.

Plasma-enhanced catalytic ammonia decomposition over ruthenium (Ru/Al2O3) and soda glass (SiO2) materials

Catalytic ammonia (NH3) decomposition has been identified as a COx-free, sustainable hydrogen production method for fuel cell applications. In this study, the performance of plasma–catalyst-based NH3 decomposition over ruthenium (Ru/Al2O3) and soda glass (SiO2) catalytic materials at atmospheric pressure and ambient temperature was investigated. NH3 decomposition reactions were conducted in a dielectric barrier discharge plasma plate-type reactor. NH3 was fed into the plate catalytic microreactor at flow rates of 0.1–1 L/min and plasma voltages of 12–18 kV. Compared to plasma NH3 decomposition without a catalyst, plasma–catalyst-based NH3 decomposition showed a significant enhancement of the hydrogen production rate and energy efficiency. Furthermore, the hydrogen concentration results obtained over the Ru/Al2O3 catalyst were higher than those over the SiO2 catalyst because Ru/Al2O3 possesses good electronic properties and exhibits high sensitivity to NH3 decomposition. In addition, the resulting plasma heat enhanced the activation of the catalytic material, subsequently leading to an increase in the hydrogen production rate from NH3. The maximum conversion rates were 85.65% and 84.39% for Ru/Al2O3 and SiO2, respectively. Moreover, the energy efficiency of NH3 decomposition over the Ru-based catalyst material was higher than that over the SiO2 material. The presence of the catalyst active sites and plasma enhanced the mean electron energy, which could enhance the dissociation of NH3. It can be concluded that the SiO2 material can be utilised as a catalyst and that its combination with plasma accelerates the decomposition process of NH3 and incurs a lower cost compared to Ru materials.

Synthesis, Structure, and Ammonia Oxidation Catalytic Activity of Ru-NH3 Complexes Containing Multidentate Polypyridyl Ligands.

Ammonia (electro)oxidation with molecular catalysts is a rapidly developing topic with wide practical applications ahead. We report here the catalytic ammonia oxidation reaction (AOR) activity using [Ru(tda-κ-N3O)(py)2], 2, (tda2- is 2,2':6',2''-terpyridine-6,6''-dicarboxylate; py is pyridine) as a catalyst precursor. Furthermore, we also describe the rich chemistry associated with the reaction of Ru-tda and Ru-tPa (tPa-4 is 2,2':6',2''-terpyridine-6,6''-diphosphonate) complexes with NH3 and N2H4 using [RuII(tda-κ-N3O)(dmso)Cl] (dmso is dimethyl sulfoxide) and [RuII(tPa-κ-N3O)(py)2], 8, as synthetic intermediates, respectively. All the new complexes obtained here were characterized spectroscopically by means of UV-vis and NMR. In addition, a crystal X-ray diffraction analysis was performed for complexes trans-[RuII(tda-κ-N3)(py)2(NH3)], 4, trans-[RuII(tda-κ-N3)(N-NH2)(py)2], 5, cis-[RuII(tda-κ-N3)(py)(NH3)2], 6 (30%), and cis-[RuII(tda-k-N3)(dmso)(NH3)2], 7 (70%). The AOR activity associated with 2 and 8 as catalyst precursors was studied in organic and aqueous media. For 2, turnover numbers of 7.5 were achieved under bulk electrolysis conditions at an Eapp = 1.4 V versus normal hydrogen electrode in acetonitrile. A catalytic cycle is proposed based on electrochemical and kinetic evidence.

Selective Catalytic Reduction System Ammonia Injection Control Based on Deep Deterministic Policy Reinforcement Learning

The control of flue gas emission in thermal power plants has been a topic of concern. Selective catalytic reduction technology has been widely used as an effective flue gas treatment technology. However, precisely controlling the amount of ammonia injected remains a challenge. Too much ammonia not only causes secondary pollution but also corrodes the reactor equipment, while too little ammonia does not effectively reduce the NOx content. In recent years, deep reinforcement learning has achieved better results than traditional methods in decision making and control, which provides new methods for better control of selective catalytic reduction systems. The purpose of this research is to design an intelligent controller using reinforcement learning technology, which can accurately control ammonia injection, and achieve higher denitrification effect and less secondary pollution. To train the deep reinforcement learning controller, a high-precision virtual denitration environment is first constructed. In order to make the virtual environment more realistic, this virtual environment was designed as a special structure with two decoders and a unique approach was used in fitting the virtual environment. A deep deterministic policy agent is used as an intelligent controller to control the amount of injected ammonia. To make the intelligent controller more stable, the actor-critic framework and the experience pool approach were adopted. The results show that the intelligent controller can control the emissions of nitrogen oxides and ammonia at the outlet of the reactor after training in virtual environment.

Modelling and simulation of catalytic ammonia decomposition over Ni-Ru deposited on 3D-printed CeO2

3D-printed ceria structures have been prepared by robocasting, without using any additive, and impregnated with different amounts of Ni and Ru, characterized and tested for the catalytic decomposition of ammonia in a fixed bed reactor. The best catalytic performance has been achieved with an active phase of 0.5Ni0.1Ru (w/w%). A kinetic expression has been obtained using a crushed catalytic structure, which has been employed in a 1D model to simulate the behaviour of the Ni-Ru impregnated 3D-printed ceria structures. The results have been compared with the experimental data to validate the proposed model. A series of simulations have been performed to determine the relationship between the geometric parameters of the 3D-printed structures and their catalytic performance in the ammonia decomposition, in order to optimize the catalytic structure with the aim of supplying the hydrogen produced to a PEM-type fuel cell.

Theoretical Investigation into Thermodynamics and Electronic Structure of an Ammonia-productive Molybdenum-centered Catalyst.

The N-N bond structure of the key intermediate in the reported catalytic ammonia production (Nature 2019, 568, 536-540) should be described as containing a N-N double bond, instead of containing a N-N triple bond. Two 3c-delocalized bonds are found in this fragment. The analysis of the oxidation states reveal that the N reduction is achieved mainly during the step of N-N bond cleavage; SmI2-ROH reduction steps reduce Mo atoms and add protons to N atoms without changing their oxidation states. The catalytic cycle is thermodynamically investigated using the DFT method, revealing that the rate-determining step is the reductive formation of the first N-H bond and the nitrogen reduction occurs mainly in the N-N cleavage step. In addition, linear relationships between vibrational stretching frequencies, effective nuclear charges (Z*), and bond dissociation energy (E0) of a Mo-N bond are also developed.

Microwave-enhanced catalytic ammonia synthesis under moderate pressure and temperature

In this study, an alternative approach based on microwave-enhanced ammonia synthesis for Haber-Bosch process was carried out under moderate pressure of 0.1–0.65 MPa and temperature range of 280–400 °C over a stable CsRu/CeO2 catalyst. The ammonia production rate is significantly improved under microwave conditions. At 0.65 MPa and 320 °C, maximum ammonia production rate was achieved at H2/N2 ratio of 1/1. Stable performance was obtained in a 6-cycles of startup-shutdown operation for cumulative on-line time of 80 h. The work demonstrates the potential of microwave catalytic technology for the distributed ammonia synthesis using renewable power having intermittent nature of energy supply.

Clean Conversion of Aqueous Ammonia Using a Solid Oxide Cell

Waste aqueous ammonia is produced in significant quantities as part of coke production processes required for steelmaking. In this work, the utilization of a simulated aqueous ammonia waste (ammonium hydroxide) was investigated using a commercially available anode-supported solid oxide cell. The electrical performance of the cell was characterized using I-V curves and the output gases from the anode were measured in real-time using quadrupole mass spectrometry. Upon delivery to the anode, there was total decomposition of ammonia to form hydrogen and nitrogen with no NO x formation observed. The cell operated more efficiently in fuel cell mode due to alleviation of OCV, activation, and concentration losses. In electrolysis mode, the cell produced H2 through a mixture of catalytic ammonia decomposition (48 vol%) and electrochemical H2O reduction (52 vol%) to yield output gas mixtures composed of 90-93 vol% H2 (voltage dependent) balanced only in N2.

Multiple N-H and C-H Hydrogen Atom Abstractions Through Coordination-Induced Bond Weakening at Fe-Amine Complexes.

We report the use of the reported Fe-phthalocyanine complex, PcFe (1; Pc = 1,4,8,11,15,18,22,25-octaethoxy-phthalocyanine), to generate PcFe-amine complexes 1-(NH3)2, 1-(MeNH2)2, and 1-(Me2NH)2. Treatment of 1 or 1-(NH3)2 to an excess of the stable aryloxide radical, 2,4,6-tritert-butylphenoxyl radical (tBuArO•), under NH3 resulted in catalytic H atom abstraction (HAA) and C-N coupling to generate the product 4-amino-2,4,6-tritert-butylcyclohexa-2,5-dien-1-one (2) and tBuArOH. Exposing 1-(NH3)2 to an excess of the trityl (CPh3) variant, 2,6-di-tert-butyl-4-tritylphenoxyl radical (TrArO•), under NH3 did not lead to catalytic ammonia oxidation as previously reported in a related Ru-porphyrin complex. However, pronounced coordination-induced bond weakening of both α N-H and β C-H in the alkylamine congeners, 1-(MeNH2)2 and 1-(Me2NH)2, led to multiple HAA events yielding the unsaturated cyanide complex, 1-(MeNH2)(CN), and imine complex, 1-(MeN═CH2)2, respectively. Subsequent C-N bond formation was also observed in the latter upon addition of a coordinating ligand. Detailed computational studies support an alternating mechanism involving sequential N-H and C-H HAA to generate these unsaturated products.