Highly dispersed ruthenium atomic-cluster adjacent to CeO2 oxygen vacancy as an active catalyst for ammonia decomposition

Solid Acid Electrochemical Cell for the Production of Hydrogen from Ammonia

Hydrogen has been proposed as a clean energy source to replace fossil fuels. The hydrogen economy encompasses the production, storage, transport, and use of hydrogen. Among the various potential hydrogen carriers, ammonia is considered an efficient and economical option due to its established infrastructure for production, storage, and transport. In this ammonia value chain, ammonia decomposition enables the efficient and sustainable production of carbon‐free hydrogen. Recently, Co has gained attention as an active metal for thermal ammonia decomposition due to its excellent catalytic performance and cost‐effectiveness. This review presents current developments in supported and unsupported Co‐based catalysts for ammonia decomposition. Key strategies to enhance the hydrogen formation rate include optimizing the Co precursor and synthesis methods, incorporating a second active metal and promoters, tuning the physical properties of the catalyst, and doping heteroatoms into the support. Practical considerations for the preparation of Co‐based catalysts are also outlined. This review provides valuable insights into the development of advanced Co‐based catalysts for ammonia decomposition, with the aim of guiding future research toward highly efficient, cost‐effective, and scalable hydrogen production solutions.

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

High throughput experimentation has the capability to generate massive, multidimensional datasets, allowing for the discovery of novel catalytic materials. Here, we show the synthesis and catalytic screening of over 100 unique Ru-Metal-K based bimetallic catalysts for low temperature ammonia decomposition, with a Ru loading between 1–3 wt% Ru and a fixed K loading of 12 wt% K, supported on γ-Al2O3. Bimetallic catalysts containing Sc, Sr, Hf, Y, Mg, Zr, Ta, or Ca in addition to Ru were found to have excellent ammonia decomposition activity when compared to state-of-the-art catalysts in literature. Furthermore, the Ru content could be reduced to 1 wt% Ru, a factor of four decrease, with the addition of Sr, Y, Zr, or Hf, where these secondary metals have not been previously explored for ammonia decomposition. The bimetallic interactions between Ru and the secondary metal, specifically RuSrK and RuFeK, were investigated in detail to elucidate the reaction kinetics and surface properties of both high and low performing catalysts. The RuSrK catalyst had a turnover frequency of 1.78 s−1, while RuFeK had a turnover frequency of only 0.28 s−1 under identical operating conditions. Based on their apparent activation energies and number of surface sites, the RuSrK had a factor of two lower activation energy than the RuFeK, while also possessing an equivalent number of surface sites, which suggests that the Sr promotes ammonia decomposition in the presence of Ru by modifying the active sites of Ru.

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

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

Ru-Ba/ANF catalysts for ammonia decomposition: Support carbonization influence

Elucidating the effect of Ce with abundant surface oxygen vacancies on MgAl2O4-supported Ru-based catalysts for ammonia decomposition

Co–Al nanocomposite materials as active and stable catalysts for ammonia decomposition have been synthesized by a one-pot evaporation-induced self-assembly method. The catalysts were characterized by various techniques including powder X-ray diffraction (XRD), X-ray absorption fine structure (XAFS), X-ray photoelectron spectroscopy (XPS), N2 adsorption/desorption, and transmission/scanning electron microscopy (TEM/SEM). Especially, in situ XRD under catalytic reaction conditions was performed, and metallic Co with a cubic structure was identified to be most probably the active crystalline phase for the decomposition of ammonia; also, contribution of CoO to the catalytic activity cannot be excluded. Most importantly, the introduction of alumina can significantly suppress the agglomeration of the active metallic Co phase and thus maintain the high activity of the cobalt catalyst.

Research progress of ruthenium-based catalysts for hydrogen production from ammonia decomposition

A cheap and disposal catalyst will be required for the decomposition of ammonia in the presence of sulfur compounds. The possibility of iron ore and red mud as the ammonia decomposition catalyst was investigated using pure or diluted ammonia containing hydrogen sulfide as a reactant. Among the catalysts tested, red mud had the highest catalytic activity for the ammonia decomposition in the presence of hydrogen sulfide. On the other hand, a relatively low conversion of ammonia was observed using a nickel-based commercial catalyst for the ammonia decomposition. The deactivation behavior of an iron ore catalyst caused by sulfur poisoning depended on the pretreatment atmosphere before the reaction; namely, the deactivation was observed for the H2 pretreatment, while the high level of ammonia conversion remained constant for the CO pretreatment. From the X-ray diffraction pattern of the catalysts, the used iron ore catalyst pretreated in the CO atmosphere included FeCx, which was also included in the red mud that was active for the ammonia decomposition. FeCx may be responsible to the sulfur poisoning resistance.

Mesoporous multimetal oxide microspheres (Ni–Ce–Al–O) with tuned and uniformly distributed composition are prepared through an aerosol-assisted self-assembly approach and further used as catalysts for ammonia decomposition. The as-prepared and spent materials are characterized by various techniques including ex situ/in situ X-ray diffraction (XRD), X-ray absorption fine structure (XAFS), scanning electron microscope (SEM)/transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), and N2-adsorption. The tricomponent Ni–Ce–Al–O catalysts show great superiority over pure NiO or bicomponent catalysts (Ni–Ce–O and Ni–Al–O) in both catalytic activity and durability. By using H2-TPR combined with in situ XRD, we have identified metallic Ni0 as the active crystalline phase and further confirmed the strong interaction between alumina and other components. This strong interaction helps suppress the growth of both metallic Ni0 as active site and ceria as promoter under the harsh catalytic condit...

Highly monodisperse sub-nanometer and nanometer Ru particles confined in alkali-exchanged zeolite Y for ammonia decomposition

Since ammonia (NH3) decomposition catalysts for on-site hydrogen fueling stations must possess at least 10 years of durability, an activity/durability evaluation technique that can estimate catalyst activity after several thousands of hours was developed based on short-term durability tests in the laboratory. It consists of a series of repetitive activity/durability tests: (a) thermal treatments in NH3 at a predetermined endurance temperature for a given time, followed by (b) activity measurements at a reaction temperature of 500 °C. The technique was utilized for accelerated-deterioration durability evaluation of a Ru/MgO catalyst. It was discovered that the NH3 conversion decreases almost linearly, as a function of the endurance time at all endurance temperatures. Furthermore, the Arrhenius equation was employed to explore the relationship between the deterioration rate and endurance temperature. This technique can be considered a crucial tool for predicting the durability of NH3 decomposition catalysts employed in H2 fueling stations.

Efficient hydrogen storage and transportation are crucial for the sustainable development of human society. Ammonia, with a hydrogen storage density of up to 17.6 wt%, is considered an ideal energy carrier for large-scale hydrogen storage and has great potential for development and application in the "hydrogen economy". However, achieving ammonia decomposition to hydrogen under mild conditions is challenging, and therefore, the development of suitable catalysts is essential. Metal oxide-based catalysts are commonly used in the industry. This paper presents a comprehensive review of single and composite metal oxide catalysts for ammonia decomposition catalysis. The focus is on analyzing the conformational relationships and interactions between metal oxide carriers and active metal sites. The aim is to develop new and efficient metal oxide-based catalysts for large-scale green ammonia decomposition.