Preparation of iridium catalyst and its catalytic activity over hydrazine hydrate decomposition for hydrogen production and storage

An Effective Strategy to Boost Formic Acid Dehydrogenation over Pd/AC-NH2 Catalyst through Pd Size Control

Formic acid (FA, HCOOH) is regarded as one of the most promising carriers for hydrogen storage. However, the catalyst design for FA dehydrogenation into H2 with high efficiency is not clear. Here, we elucidate the rationale of size effect over the most commonly used Pd-based catalyst through supporting different Pd species, including single atoms, nanoclusters, and nanoparticles, on amine-functionalized active carbon (Pd/AC-NH2). The activity test presents that Pd/AC-NH2 with Pd nanoclusters exhibits the best turnover frequency (TOF) value of 40856 h-1 for 1 M FA at 328 K and even 1504 h-1 for neat FA at 308 K, which is comparable to the homogeneous catalysts and has been the first heterogeneous catalyst used in neat FA dehydrogenation under mild conditions. The comprehensive characterizations reveal that the size of Pd species affects the ratios of Pd0/Pd2+ and hydrogen spillover effect, which is crucial for the C-H cleavage and H2 desorption. Besides, the influences of amine groups on catalytic performance were further examined. This work provided an ingenious guideline to design efficient and practical catalysts for hydrogen storage under ambient conditions.

Characteristics of ignition delay of hypergolic ionic liquids combined with 1-amino-4-methylpiperazine

The ignition delay time of the hypergolic ionic liquids, 1-ethyl-3-methylimidazolium dicyanamide [EMIM][C₂N₃] and 1,3-dimethyl imidazolium dicyandiamide [DMIM][C₂N₃], can be controlled to approximately 20 ms by adding 1-amino-4-methylpiperazine while keeping the vapor pressure below 1 torr at 298 K.

Enhanced stability of sub-nanometric iridium decorated graphitic carbon nitride for H2 production upon hydrous hydrazine decomposition

Stabilizing metal nanoparticles is vital for large scale implementations of supported metal catalysts, particularly for a sustainable transition to clean energy, e.g., H₂ production. In this work, iridium sub-nanometric particles were deposited on commercial graphite and on graphitic carbon nitride by a wet impregnation method to investigate the metal-support interaction during the hydrous hydrazine decomposition reaction. To establish a structure-activity relationship, samples were characterized by transmission electron microscopy and X-ray photoelectron spectroscopy. The catalytic performance of the synthesized materials was evaluated under mild reaction conditions, i.e. 323 K and ambient pressure. The results showed that graphitic carbon nitride (GCN) enhances the stability of Ir nanoparticles compared to graphite, while maintaining remarkable activity and selectivity. Simulation techniques including Genetic Algorithm geometry screening and electronic structure analyses were employed to provide a valuable atomic level understanding of the metal-support interactions. N anchoring sites of GCN were found to minimise the thermodynamic driving force of coalescence, thus improving the catalyst stability, as well as to lead charge redistributions in the cluster improving the resistance to poisoning by decomposition intermediates.

Selective decomposition of hydrazine over metal free carbonaceous materials

Herein we report a combined experimental and computational investigation unravelling the hydrazine hydrate decomposition reaction on metal-free catalysts. The study focuses on commercial graphite and two different carbon nanofibers, pyrolytically stripped (CNF-PS) and high heat-treated (CNF-HHT), respectively, treated at 700 and 3000 °C to increase their intrinsic defects. Raman spectroscopy demonstrated a correlation between the initial catalytic activity and the intrinsic defectiveness of carbonaceous materials. CNF-PS with higher defectivity (I_D/I_G = 1.54) was found to be the best performing metal-free catalyst, showing a hydrazine conversion of 94% after 6 hours of reaction and a selectivity to H₂ of 89%. In addition, to unveil the role of NaOH, CNF-PS was also tested in the absence of alkaline solution, showing a decrease in the reaction rate and selectivity to H₂. Density functional theory (DFT) demonstrated that the single vacancies (SV) present on the graphitic layer are the only active sites promoting hydrazine decomposition, whereas other defects such as double vacancy (DV) and Stone-Wales (SW) defects are unable to adsorb hydrazine fragments. Two symmetrical and one asymmetrical dehydrogenation pathways were found, in addition to an incomplete decomposition pathway forming N₂ and NH₃. On the most stable hydrogen production pathway, the effect of the alkaline medium was elucidated through calculations concerning the diffusion and recombination of atomic hydrogen. Indeed, the presence of NaOH helps the extraction of H species without additional energetic barriers, as opposed to the calculations performed in a polarizable continuum medium. Considering the initial hydrazine dissociative adsorption, the first step of the dehydrogenation pathway is more favourable than the scission of the N-N bond, which leads to NH₃ as the product. This first reaction step is crucial to define the reaction mechanisms and the computational results are in agreement with the experimental ones. Moreover, comparing two different hydrogen production pathways (with and without diffusion and recombination), we confirmed that the presence of sodium hydroxide in the experimental reaction environment can modify the energy gap between the two pathways, leading to an increased reaction rate and selectivity to H₂.

Hydrous Hydrazine Decomposition for Hydrogen Production Using of Ir/CeO2: Effect of Reaction Parameters on the Activity

In the present work, an Ir/CeO₂ catalyst was prepared by the deposition-precipitation method and tested in the decomposition of hydrazine hydrate to hydrogen, which is very important in the development of hydrogen storage materials for fuel cells. The catalyst was characterised using different techniques, i.e., X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), scanning electron microscopy (SEM) equipped with X-ray detector (EDX) and inductively coupled plasma-mass spectroscopy (ICP-MS). The effect of reaction conditions on the activity and selectivity of the material was evaluated in this study, modifying parameters such as temperature, the mass of the catalyst, stirring speed and concentration of base in order to find the optimal conditions of reaction, which allow performing the test in a kinetically limited regime.

Bimetallic NiIr nanoparticles supported on lanthanum oxy-carbonate as highly efficient catalysts for hydrogen evolution from hydrazine borane and hydrazine

La₂O₂CO₃-supported NiIr nanoparticles (NPs) have been facilely synthesized via a sodium–hydroxide-assisted reduction approach and used as highly efficient catalysts for hydrogen generation from hydrazine borane and hydrous hydrazine.

Bimetallic nickel-iridium nanocatalysts for hydrogen generation by decomposition of hydrous hydrazine

Alloying Ni with Ir leads to the formation of highly active catalysts for complete decomposition of hydrous hydrazine with 100% H(2) selectivity at room temperature. Use of surfactants enhances the activity by suppressing the agglomeration of nanoparticles, but does not affect the bimetallic compositions of the nanoparticles.