Hydrogen generation by ammonia decomposition using Co/MgO–La2O3 catalyst: Influence of support calcination atmosphere

Chemical Bonds Containing Hydrogen: Choices for Hydrogen Carriers and Catalysts

Compounds containing B─H, C─H, N─H, or O─H bonds with high hydrogen content have been extensively studied as potential hydrogen carriers. Their hydrogen storage performance is largely determined by the nature of these bonds, decomposition pathways, and the properties of the dehydrogenation products. Among these compounds, methanol, cyclohexane, and ammonia stand out due to their low costs and established infrastructure, making them promising hydrogen carriers for large-scale storage and transport. They offer viable pathways for decarbonizing society by enabling hydrogen to serve as a clean energy source. However, several challenges persist, including the high temperatures required for (de)hydrogenation, slow kinetics, and the reliance on costly catalysts. To address these issues, strategies such as chemical modification and catalyst development are being pursued to improve hydrogen cycling performance. This review highlights recent progress in hydrogen carriers with B─H, C─H, N─H, or O─H bonds. It examines the fundamental characteristics of these bonds and carriers, as well as advances in catalyst development. Our objective is to offer a comprehensive understanding of current state of hydrogen carriers and identify future research directions, such as molecular modification and system optimization. Innovations in these areas are crucial to advance hydrogen storage technologies for a large-scale hydrogen deployment.

The Hydrolysis of Ball-Milled Aluminum–Bismuth–Nickel Composites for On-Demand Hydrogen Generation

The hydrolysis of aluminum (Al) is a promising method for on-demand hydrogen generation for low-power proton exchange membrane fuel cell (PEMFC) applications. In this study, Al composites were mechanochemically activated using bismuth (Bi) and nickel (Ni) as activation compounds. The main objective was to determine the effects of Bi and Ni on Al particles during mechanochemical processing, and the hydrolysis activity of the Al-Bi-Ni composites. Successfully formulated ternary Al-Bi-Ni composites were hydrolyzed with de-ionized water under standard ambient conditions to determine the reactivity of the composite (extent of hydrogen production). Scanning electron microscopy (SEM) showed that Bi and Ni were distributed relatively uniformly throughout the Al particles, resulting in numerous micro-galvanic interactions between the anodic Al and cathodic Bi/Ni during hydrolysis reaction. The addition of >1 wt% Ni resulted in incomplete activation of Al, and such composites were non-reactive. All successfully prepared composites had near-complete hydrogen yields. X-ray diffraction (XRD) showed that no mineralogical interaction occurred between Al, Bi, and/or Ni. The main phases detected were Al, Bi, and minute traces of Ni (ascribed to low Ni content). In addition, the effect of the mass ratio (mass Al:mass water) and water quality were also determined.

A high performance barium-promoted cobalt catalyst supported on magnesium-lanthanum mixed oxide for ammonia synthesis

Ammonia synthesis was performed over a barium-promoted cobalt catalyst supported on magnesium-lanthanum mixed oxide. The rate of NH3 formation over this catalyst was about 3.5 times higher than that over the unpromoted catalyst at 9 MPa and 400 °C. Furthermore, no sign of thermal deactivation was observed during long-term overheating at 600 °C for 360 h. The results of physicochemical studies, including XRPD, DRIFTS, H2-TPD, CO2-TPD, Nads + H2 TPSR and kinetic analysis, revealed that the addition of Ba promoter increased the surface basicity of the catalyst and modified the adsorption properties of the Co surface towards H2 and NH3. The decreased adsorption strength of the corresponding sites towards hydrogen and ammonia resulted in greater availability of active sites in the Ba-promoted cobalt catalyst. These characteristics are considered to have a profound effect on the performance of this catalyst in NH3 synthesis.

Development of a Ba–CoCe catalyst for the efficient and stable decomposition of ammonia

CO_x-free hydrogen production; cobalt-based catalysts for ammonia decomposition; cerium–barium promoter in cobalt catalysts.

Metal–support interaction-modulated catalytic activity of Ru nanoparticles on Sm2O3 for efficient ammonia decomposition

The activity of Ru/Sm₂O₃ catalyst for ammonia decomposition can be greatly improved by modulating the metal–support interaction of the catalyst.

Applications of rare earth oxides in catalytic ammonia synthesis and decomposition

Due to their unique structural and electronic properties, rare earth oxides have been widely applied as supports and promoters in catalytic ammonia synthesis and decomposition.

Material Discovery and High Throughput Exploration of Ru Based Catalysts for Low Temperature Ammonia Decomposition

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 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.

Cobalt nanoparticles embedded in a porous carbon matrix as an efficient catalyst for ammonia decomposition

A metallic Co nanoparticle catalyst embedded in a carbon matrix catalyst was synthesized through a facile solvothermal method and subsequent thermal treatment.

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.