Emerging trends in research and development on earth abundant materials for ammonia degradation coupled with H2 generation

Ammonia, as an essential and economical fuel, is a key intermediate for the production of innumerable nitrogen-based compounds. Such compounds have found vast applications in the agricultural world, biological world (amino acids, proteins, and DNA), and various other chemical transformations. However, unlike other compounds, the decomposition of ammonia is widely recognized as an important step towards a safe and sustainable environment. Ammonia has been popularly recommended as a viable candidate for chemical storage because of its high hydrogen content. Although ruthenium (Ru) is considered an excellent catalyst for ammonia oxidation; however, its high cost and low abundance demand the utilization of cheaper, robust, and earth abundant catalyst. The present review article underlines the various ammonia decomposition methods with emphasis on the use of non-noble metals, such as iron, nickel, cobalt, molybdenum, and several other carbides as well as nitride species. In this review, we have highlighted various advances in ammonia decomposition catalysts. The major challenges that persist in designing such catalysts and the future developments in the production of efficient materials for ammonia decomposition are also discussed.

Recent Progress on Hydrogen Production from Ammonia Decomposition: Technical Roadmap and Catalytic Mechanism

Ammonia decomposition has attracted significant attention in recent years due to its ability to produce hydrogen without emitting carbon dioxide and the ease of ammonia storage. This paper reviews the recent developments in ammonia decomposition technologies for hydrogen production, focusing on the latest advances in catalytic materials and catalyst design, as well as the research progress in the catalytic reaction mechanism. Additionally, the paper discusses the advantages and disadvantages of each method and the importance of finding non-precious metals to reduce costs and improve efficiency. Overall, this paper provides a valuable reference for further research on ammonia decomposition for hydrogen production.

Catalysis of Alloys: Classification, Principles, and Design for a Variety of Materials and Reactions

Alloying has long been used as a promising methodology to improve the catalytic performance of metallic materials. In recent years, the field of alloy catalysis has made remarkable progress with the emergence of a variety of novel alloy materials and their functions. Therefore, a comprehensive disciplinary framework for catalytic chemistry of alloys that provides a cross-sectional understanding of the broad research field is in high demand. In this review, we provide a comprehensive classification of various alloy materials based on metallurgy, thermodynamics, and inorganic chemistry and summarize the roles of alloying in catalysis and its principles with a brief introduction of the historical background of this research field. Furthermore, we explain how each type of alloy can be used as a catalyst material and how to design a functional catalyst for the target reaction by introducing representative case studies. This review includes two approaches, namely, from materials and reactions, to provide a better understanding of the catalytic chemistry of alloys. Our review offers a perspective on this research field and can be used encyclopedically according to the readers' individual interests.

Recent Advances in Bimetallic Catalysts for Hydrogen Production from Ammonia

The emerging concept of the hydrogen economy is facing challenges associated with hydrogen storage and transport. The utilization of ammonia as an energy (hydrogen) carrier for the on-site generation of hydrogen via ammonia decomposition has gained attraction among the scientific community. Ruthenium-based catalysts are highly active but their high cost and less abundance are limitations for scale-up application. Therefore, combining ruthenium with cheaper transition metals such as nickel, cobalt, iron, molybdenum, etc., to generate metal-metal (bimetallic) surfaces suitable for ammonia decomposition has been investigated in recent years. Herein, the recent trends in developing bimetallic catalyst systems, the role of metal type, support materials, promoter, synthesis techniques, and the investigations of the reaction kinetics and mechanism for ammonia decomposition have been reviewed.

Hydrocracking optimization of palm oil to bio-gasoline and bio-aviation fuels using molybdenum nitride-bentonite catalyst

In this study, molybdenum nitride-bentonite was successfully employed for the reaction of hydrocracking of palm oil to produce a bio-gasoline and bio-aviation fuel. The prepared catalyst was characterized using XRD, FT-IR, and SEM-EDX. The acidity of the catalyst was determined using the pyridine gravimetric method. The result showed that the acidity of bentonite was increased after modification using molybdenum nitride. The hydrocracking study showed that the highest conversion and product fraction of bio-gasoline and bio-aviation fuel were exhibited by molybdenum nitride-bentonite 8 mEq g⁻¹. The catalyst was later used to optimize the hydrocracking process using RSM-CCD. The effects of the process variables such as temperature, contact time, and catalyst to feed ratio, on the response variables, such as conversion, oil, gas, and coke yield, were investigated. The analysis of variance showed that the proposed quadratic model was statistically significant with adequate precision to estimate the responses. The optimum conditions in the hydrocracking process were achieved at a temperature of 731.94 K, contact time of 0.12 h, and a catalyst to feed ratio of 0.12 w/v with a conversion of 78.33%, an oil yield of 50.32%, gas yield of 44.00% and coke yield of 5.73%. The RSM-CCD was demonstrated as a suitable method for estimating the hydrocracking process of palm oil using a MoN-bentonite catalyst due to its closeness to the optimal value of the expected yield. This study provided a potential catalyst of based on bentonite modified using molybdenum nitride for the hydrocracking of palm oil.

In this study, molybdenum nitride-bentonite was successfully employed for the reaction of hydrocracking of palm oil to produce a bio-gasoline and bio-aviation fuel.

Molybdenum nitrides from structures to industrial applications

Owing to their remarkable characteristics, refractory molybdenum nitride (MoN x )-based compounds have been deployed in a wide range of strategic industrial applications. This review reports the electronic and structural properties that render MoN x materials as potent catalytic surfaces for numerous chemical reactions and surveys the syntheses, procedures, and catalytic applications in pertinent industries such as the petroleum industry. In particular, hydrogenation, hydrodesulfurization, and hydrodeoxygenation are essential processes in the refinement of oil segments and their conversions into commodity fuels and platform chemicals. N-vacant sites over a catalyst’s surface are a significant driver of diverse chemical phenomena. Studies on various reaction routes have emphasized that the transfer of adsorbed hydrogen atoms from the N-vacant sites reduces the activation barriers for bond breaking at key structural linkages. Density functional theory has recently provided an atomic-level understanding of Mo–N systems as active ingredients in hydrotreating processes. These Mo–N systems are potentially extendible to the hydrogenation of more complex molecules, most notably, oxygenated aromatic compounds.

Co3Mo3N-An efficient multifunctional electrocatalyst

Efficient catalysts are required for both oxidative and reductive reactions of hydrogen and oxygen in sustainable energy conversion devices. However, current precious metal-based electrocatalysts do not perform well across the full range of reactions and reported multifunctional catalysts are all complex hybrids. Here, we show that single-phase porous Co₃Mo₃N prepared via a facile method is an efficient and reliable electrocatalyst for three essential energy conversion reactions; oxygen evolution reaction (OER), oxygen reduction reaction (ORR), and hydrogen evolution reaction (HER) in alkaline solutions. Co₃Mo₃N presents outstanding OER, ORR, and HER activity with high durability, comparable with the commercial catalysts RuO₂ for OER and Pt/C for ORR and HER. In practical demonstrations, Co₃Mo₃N gives high specific capacity (850 mA h g_Zn⁻¹ at 10 mA cm⁻²) as the cathode in a zinc-air battery, and a low potential (1.63 V at 10 mA cm⁻²) used in a water-splitting electrolyzer. Availability of Co and Mo d-states appear to result in high ORR and HER performance, while the OER properties result from a cobalt oxide-rich activation surface layer. Our findings will inspire further development of bimetallic nitrides as cost-effective and versatile multifunctional catalysts that will enable scalable usage of electrochemical energy devices.

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Porous Co₃Mo₃N can act as a multifunctional electrocatalyst for OER, ORR, and HER

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Co₃Mo₃N performs better than precious metal catalysts

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Cobalt oxide-rich activation surface layer is shown to aid OER activity

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Better ORR and HER performance of Co₃Mo₃N is due to Co and Mo d-states

Characteristics of High Surface Area Molybdenum Nitride and Its Activity for the Catalytic Decomposition of Ammonia

High surface area (>170 m2 g−1) molybdenum nitride was prepared by the temperature-programmed nitridation of α-MoO3 with pure ammonia. The process was optimized by adjusting the experimental variables: the reaction temperature, heating rate, and molar flow rate of ammonia. The physicochemical properties of the as-formed molybdenum nitride were characterized by X-ray diffraction, N2 sorption, transmission electron microscopy, temperature-programmed oxidation/reduction, and X-ray photoelectron spectroscopy. Of the experimental variables, the nitridation temperature was found to be the most critical parameter determining the surface area of the molybdenum nitride. When the prepared molybdenum nitride was exposed to air, the specific surface area rapidly decreased because of the partial oxidation of molybdenum nitride to molybdenum oxynitride. However, the surface area recovered to 90% the initial value after H2 treatment. The catalyst with the highest degree of nitridation showed the best catalytic activity, superior to that of unmodified α-MoO3, for the decomposition of ammonia because of its high surface area.

Building heterogeneous nanostructures for photocatalytic ammonia decomposition

Ammonia is an important chemical for human beings that is used in the synthesis of chemical fertilizers and products; meanwhile, it is also a hazardous compound which causes undesirable odors, several diseases, and environmental problems. Therefore, there is an urgent need to control and remove ammonia pollutants from water, air and soil. Hence, clean processes using photocatalysis to convert ammonia into H2 and N2 have been an important research topic in recent years. To date, only some metal-loaded common photocatalysts, such as TiO2, ZnO, C3N4, graphene and other carbon-based materials together with their hybrid materials, have been reported as active photocatalysts for the decomposition of aqueous ammonia solutions. In this review, we summarize the recent advances in heterogeneous nanostructures for photocatalytic ammonia decomposition. Particular emphasis is also given to metal-loading along with the resulting heterojunctions. Furthermore, the recent efforts toward the development of heterogeneous nanostructures for photocatalytic ammonia decomposition in this direction are discussed and appraised. Finally, perspectives and future opportunities regarding the challenges and future directions in the area of heterogeneous photocatalysts for ammonia decomposition are also provided.

Highly efficient decomposition of ammonia using high-entropy alloy catalysts

Ammonia represents a promising liquid fuel for hydrogen storage, but its large-scale application is limited by the need for precious metal ruthenium (Ru) as catalyst. Here we report on highly efficient ammonia decomposition using novel high-entropy alloy (HEA) catalysts made of earth abundant elements. Quinary CoMoFeNiCu nanoparticles are synthesized in a single solid-solution phase with robust control over the Co/Mo atomic ratio, including those ratios considered to be immiscible according to the Co-Mo bimetallic phase diagram. These HEA nanoparticles demonstrate substantially enhanced catalytic activity and stability for ammonia decomposition, with improvement factors achieving >20 versus Ru catalysts. Catalytic activity of HEA nanoparticles is robustly tunable by varying the Co/Mo ratio, allowing for the optimization of surface property to maximize the reactivity under different reaction conditions. Our work highlights the great potential of HEAs for catalyzing chemical transformation and energy conversion reactions.

Alloys are important materials for catalysis but are usually limited by miscibility gaps present in their phase diagrams. Here the authors break this limitation by developing high-entropy alloy catalysts made of five earth-abundant elements and demonstrate great catalytic enhancements for ammonia decomposition.

Catalytic Decomposition of Ammonia for Hydrogen Production over Carbon Nanofiber Supported Fe and Mo Catalysts in a Microwave Heated Reactor

Microwave heated reactor which was loaded with carbon fiber supported iron and molybdenum incorporated monometallic catalysts was used to produce COx free hydrogen from ammonia. Impregnation procedure was applied to synthesize the catalysts at different metal loading (4–14 wt % according to ICP-OES) using iron nitrate or ammonium molybdate and reaction tests were carried out under the flow of pure ammonia (GHSV: 36,000 ml/hgcat). Activities of molybdenum incorporated carbon fiber catalyts are found to be lower than that of the iron loaded ones in the conventional reaction system. The effect of metal loading was clealy seen in the activity of molybdenum incorporated catalyst, unlike iron incorporated catalyts, especially under high reaction temperature conditions. Catalysts showed greatly enhanced activities in microwave heated system in comparison to conventionally heated reactor system. Complete conversion of ammonia was achieved at 500 °C by using molybdenum incorporated catalysts and at 450 °C by using iron incorporated catalysts (with GHSV of 36,000 ml/hgcat) in microwave heated reactor system. Transfer of energy directly to the active species and formation of carbide species, Fe2C or Mo2C, during the reaction under microwave application could be considered as the major factors leading to a better ammonia conversion. Structural properties of carbon support materials, such as the surface area, could be effective on the activity of the catalysts via the distribution of active species, however, this would be more pronounced effect in conventional system.

Highly efficient COx-free hydrogen evolution activity on rod Fe2N catalysts for ammonia decomposition

The morphology of Fe₂O₃ precursors had a significant effect on the Fe₂N catalyst crystallite size, components and activity.

Ammonia decomposition over Ni catalysts supported on perovskite-type oxides for the on-site generation of hydrogen

Ammonia decomposition has attracted increasing attention as a promising process for the on-site generation of hydrogen. In this study, Ni catalysts supported on perovskite-type oxides (ABO3) were prepared and the activity for ammonia decomposition was examined. The Ni/ANbO3 (A = Na and K) and Ni/AEMnO3 (AE = Ca, Sr, and Ba) catalysts were less effective for this reaction. Meanwhile, the Ni/REAlO3 (RE = La, Sm, and Gd) catalysts exhibited relatively high activity. For Ni/AETiO3 and Ni/AEZrO3, the performance strongly depended on the A-site element of the perovskite-type oxides, and the Sr and Ba elements were more effective than the Ca one in the respective series. The catalytic activity for Ni/AEZrO3 was higher than Ni/AETiO3 in the case of the same alkaline earth element, and Ni/BaZrO3 was the most active among the samples investigated in this work. For these series, the order in the performance corresponded well with that in the basic property. The nitrogen desorption profiles revealed that the evolution of nitrogen atoms, which is one of the kinetically slow steps, effectively proceeded for Ni/SrZrO3 and Ni/BaZrO3 compared with the conventional Ni catalysts. This promotion effect would be ascribed to the strong basic properties of the SrZrO3 and BaZrO3 supports, resulting in the high activity of Ni/SrZrO3 and Ni/BaZrO3 for ammonia decomposition.

Bimetallic Ru-Co Clusters Derived from a Confined Alloying Process within Zeolite-Imidazolate Frameworks for Efficient NH3 Decomposition and Synthesis

Herein, a series of carbocatalysts containing Ru-based clusters have been prepared by the assistance of zeolite-imidazolate frameworks (ZIFs). The introduction of Ru is based on the adsorption of well-defined Ru₃(CO)₁₂ within the cavity of ZIFs following decomposition at 900 °C. Moreover, without breaking the skeleton and porosity of ZIFs, the as-generated Ru species would bond with the Co nodes in situ to form bimetallic Ru-Co clusters if the Co-bearing metal-organic frameworks were utilized as the host. Within the confined space of ZIFs, the assembly of Ru and Co could be rationally designed, and their structures could be sophisticatedly controlled at the atomic scale. Among these Ru-based compositions, the Ru-Co clusters@N-C exhibited remarkable catalytic activity for the NH₃ decomposition to H₂ and NH₃ synthesis versus Ru-Co NPs@N-C, Ru clusters@N-C, and Ru NPs@N-C. This study may open up a new routine to synthesize metallic clusters or other subnano structures by the confinement of ZIFs.

Cobalt-zinc nitride on nitrogen doped carbon black nanohybrids as a non-noble metal electrocatalyst for oxygen reduction reaction

Bimetallic nitrides are now being considered as one of the emerging advanced functional materials due to their characteristic features and remarkable physicochemical properties. Herein, we report a new crystalline bimetallic nitride (Co₃ZnN) that belongs to the cubic crystal phase, which was successfully synthesized through direct nitridation of metallic salts as precursors. Co₃ZnN nanoparticles were then supported on nitrogen-doped XC-72 carbon black (N-CB), and this typical Co₃ZnN/N-CB nanohybrid discovered can serve as an efficient non-noble metal electrocatalyst with a 4e^- reaction pathway for ORR, and demonstrated excellent electrocatalytic performance with high activity and stability.

COx-free hydrogen production via ammonia decomposition over molybdenum nitride-based catalysts

Co, Ni, and Fe-added Mo nitrides for ammonia decomposition facilitated the recombinative desorption of N atoms from the active components.

Porous cobalt–iron nitride nanowires as excellent bifunctional electrocatalysts for overall water splitting

Nanoparticle-stacked porous Co₃FeN_x nanowires as bifunctional electrocatalysts, exhibiting excellent OER and HER activity due to their unique structural advantages with grain boundaries, defects and dislocations.