NH3 Decomposition Research Articles

Linear scaling relations for N2H4 decomposition over transition metal catalysts

Catalytic decomposition of hydrazine monohydrate (N2H4·H2O) represents a promising hydrogen storage/production technology. Nowadays, the development of N2H4 decomposition catalysts is sluggish due primarily to a lack of universal screening rules. Herein, with the aid of first-principles calculations, we identify a reliable descriptor, N2H4 adsorption energy, to properly address N2H4 decomposition kinetics on TM catalysts. Particularly, we extract linear scaling relations between the adsorption energetics of key intermediates, H (and N2H3) vs. NH2 that exert a fundamental limitation on the H2 selectivity of N2H4 decomposition over elementary transition metal catalysts. We propose that catalysts with optimum H2 selectivity may be achieved by independently stabilizing and destabilizing adsorption of H (or N2H3, or both) and NH2, respectively. The disclosed dissociation behaviors of N2H4 and their physical origins are expected to advance the rational design of advanced catalysts for selectively promoting H2 production from N2H4.

Ammonia decomposition over SiO2-supported Ni–Co bimetallic catalyst for COx-free hydrogen generation

NH3 decomposition over non-noble catalyst to generate COx-free H2 has attracted great attention in recent years. In this work, fumed SiO2-supported Ni, Co and Ni–Co bimetallic catalysts are synthesized by using a co-impregnation method and evaluated for NH3 decomposition, which shows that the bimetallic catalysts exhibit better catalytic activity than the monometallic ones. This enhanced activity observed on bimetallic catalyst can be largely attributed to the more appropriate catalyst metal-N binding energy resulting from the synergistic effect between Ni and Co in the formed Ni–Co alloy. Among the synthesized catalysts, Ni5Co5/SiO2 synthesized with the Ni/Co molar ratio of 5:5 achieves 76.8% NH3 conversion under a GHSV of 30,000 mL h−1 g−1cat at 550 °C and shows the best catalytic activity, which can be further improved by doping with K (78.1% NH3 conversion at 30,000 mL h−1 g−1cat), and the obtained Ni5Co5/SiO2–K also shows excellent catalytic stability.

Intrinsic thermal decomposition pathways of lead halide perovskites APbX3

We present a systematic study on intrinsic thermal stability of a series of complex lead halides APbX3, used as absorber materials in perovskite solar cells. Mechanistically, the perovskites APbX3 were shown to decompose under thermal stress conditions initially to form PbX2 and AX salts. Thermolysis of the latter yields multiple volatile products, which were analyzed by mass spectrometry. We reconfirmed the CH3I + NH3 decomposition route for MAPbI3 and observed for the first time CH4, ethylene and HI (formed from CH3I). In case of FAPbI3, the formation of 2-aminomalononitrile (not 1,3,5-triazine as reported recently) was revealed along with NH4I and HCN. Importantly, the stability of the lead halide perovskites shows a good correlation with the volatility of univalent cation halides (or their decomposition products) incorporated in their structure. In particular, MAPbX3 have the lowest stability since they incorporate the most volatile (or easy to decompose) methylammonium halides MAX. On the contrary, all-inorganic CsPbX3 show remarkable compositional stability since CsBr and CsI are non-volatile under the solar cell operation conditions. The established relationship and material decomposition pathways provide important guidelines for rational design of novel absorber materials for perovskite solar cells with improved thermal stability suitable for terrestrial and space applications.

Monodispersed bimetallic nanoparticles anchored on TiO2-decorated titanium carbide MXene for efficient hydrogen production from hydrazine in aqueous solution

Selective catalytic decomposition of hydrazine (N2H4) to provide a clean energy carrier hydrogen (H2) is a promising alternative to fossil fuels for the future energy economy. NiPt nanoparticles (NPs) dispersed on delamination of TiO2-decorated Ti3C2Tx (denoted as DT-Ti3C2Tx) nanosheets are prepared via a simple wet chemical reduction method and applied as an efficient catalyst for dehydrogenation of N2H4 in aqueous solution. The rich oxygen-containing functional groups on the surface of DT-Ti3C2Tx not only facilitate the formation and immobilization of monodisperse NiPt NPs but also enhance the synergistic effect between metal NPs and MXene support. Among all of the tested samples, the optimized Ni0.8Pt0.2/DT-Ti3C2Tx nanocatalyst exhibits the 100% H2 selectivity and best catalytic performance with a TOF value of 1220 h−1 for the selective decomposition of N2H4 at 323 K. In addition, this catalyst also shows excellent catalytic performance for hydrogen production from hydrazine borane (N2H4BH3) via the hydrolysis of borane group and selective decomposition of hydrazine moiety. The TiO2-decorated Ti3C2Tx MXene can be applied as an excellent support to obtain well-dispersed and ultrafine metal NPs for various applications.

Recent Advances in Plasmonic Nanostructures for Enhanced Photocatalysis and Electrocatalysis.

Plasmonic nanomaterials coupled with catalytically active surfaces can provide unique opportunities for various catalysis applications, where surface plasmons produced upon proper light excitation can be adopted to drive and/or facilitate various chemical reactions. A brief introduction to the localized surface plasmon resonance and recent design and fabrication of highly efficient plasmonic nanostructures, including plasmonic metal nanostructures and metal/semiconductor heterostructures is given. Taking advantage of these plasmonic nanostructures, the following highlights summarize recent advances in plasmon-driven photochemical reactions (coupling reactions, O2 dissociation and oxidation reactions, H2 dissociation and hydrogenation reactions, N2 fixation and NH3 decomposition, and CO2 reduction) and plasmon-enhanced electrocatalytic reactions (hydrogen evolution reaction, oxygen reduction reaction, oxygen evolution reaction, alcohol oxidation reaction, and CO2 reduction). Theoretical and experimental approaches for understanding the underlying mechanism of surface plasmon are discussed. A proper discussion and perspective of the remaining challenges and future opportunities for plasmonic nanomaterials and plasmon-related chemistry in the field of energy conversion and storage is given in conclusion.

Nickel-induced structure transformation in hydrocalumite for enhanced ammonia decomposition

Modifying the material structure of catalysts and determining how the structure controls their catalytic activities are critical topics in heterogeneous catalysis research. Herein we report that the structure of hydrocalumite-layered double hydroxides (CaAl-LDHs) can be tuned by gradually introducting Ni2+. It was revealed that the gradual introduction of Ni2+ in hydrocalumite led to a structure-transformation process, which introduced hydrombobomkulite and eventually evolved into takovite. Compared with the case without structure-transformation process, the structure-transformation catalysts showed excellent NH3 decomposition activity after high-temperature reduction. Moreover, the obtained catalysts showed a relatively high conversion per Ni weight compared with other reported oxide-supported Ni catalysts. This study demonstrates the feasibility of preparing LDHs-based heterogeneous catalysts by modulating the material structure through induced structure-transformation process.

Computationally aided, entropy-driven synthesis of highly efficient and durable multi-elemental alloy catalysts.

Multi-elemental alloy nanoparticles (MEA-NPs) hold great promise for catalyst discovery in a virtually unlimited compositional space. However, rational and controllable synthesize of these intrinsically complex structures remains a challenge. Here, we report the computationally aided, entropy-driven design and synthesis of highly efficient and durable catalyst MEA-NPs. The computational strategy includes prescreening of millions of compositions, prediction of alloy formation by density functional theory calculations, and examination of structural stability by a hybrid Monte Carlo and molecular dynamics method. Selected compositions can be efficiently and rapidly synthesized at high temperature (e.g., 1500 K, 0.5 s) with excellent thermal stability. We applied these MEA-NPs for catalytic NH3 decomposition and observed outstanding performance due to the synergistic effect of multi-elemental mixing, their small size, and the alloy phase. We anticipate that the computationally aided rational design and rapid synthesis of MEA-NPs are broadly applicable for various catalytic reactions and will accelerate material discovery.

The role of cobalt oxide or magnesium oxide in ozonation of ammonia nitrogen in water

In this study, the reaction mechanisms for ozonation of ammonia nitrogen in the presence of Co3O4 or MgO were investigated. For the reaction over Co3O4, Cl– in the reaction solution was indispensable and ClO– was formed by a non-catalytic oxidation of Cl–. Co3O4 promoted the reaction of NH4+ with ClO– to give the products including NO3–, chloramines and gaseous products. In contrast, Cl– was unnecessary for the reaction with MgO. pH of the reaction solution was maintained at around 9 throughout the reaction owing to partial dissolution of MgO. Ammonia nitrogen was decomposed to mainly NO3– by non-catalytic radical reaction involving OH·, which was formed by the reaction of OH– with O3 in weakly basic solution. To keep the reaction solution weakly basic, H+ formed with the decomposition of NH4+ was neutralized. As a result, about the same amount of Mg2+ as that of decomposed ammonia nitrogen was dissolved.

Mechanism on reduction and nitridation of micrometer‐sized titania with ammonia gas

AbstractAmmonia gas can be simultaneously used as a reductant and nitrogen source to prepare TiN from titania. In this work, the mechanisms on reduction and nitridation of micrometer‐sized anatase with ammonia gas have been investigated, using both thermodynamic and experimental studies. The thermodynamic analysis indicated that reduction and nitridation of TiO2 by NH3 was feasible. Anatase will undergo different paths to form TiN, depending on the reaction temperature. Upon heating, NH3 was seen to partially decompose into N2 and H2, although the actual NH3 decomposition ratio was less than the theoretical value. The experimental results indicated that the obtained titanium nitride was non‐stoichiometric (TiNxO1−x, x ≤ 1), as it contained a certain amount of oxygen. Based on the phase transformation and X‐ray photoelectron spectroscopy analysis, the reduction and nitridation routes were deduced: TiO2 reacted with NH3 to form TiNxO1−x directly, at lower temperatures, and followed the path TiO2 → TinO2n−1 → TiNxO1−x, at higher temperatures. TinO2n−1 was determined to be Ti4O7 and Ti3O5 at 1100°C and 1200°C, respectively. Reaction temperature and time significantly affected the oxygen and nitrogen contents in TiNxO1−x, with the lattice parameter of roasted products gradually increasing—approaching those of pure TiN—with an increase in reaction temperature and holding time. At the same time, the content of oxygen in TiNxO1−x decreased, and its nitrogen content correspondingly increased.

High performance stainless-steel supported Pd membranes with a finger-like and gap structure and its application in NH3 decomposition membrane reactor

Pd composite membranes show great potential in several important fields, such as H2 production for fuel cell or pre-combustion applications. This study presents a facile and effective approach to develop high performance stainless-steel supported Pd composite membranes with a finger-like and gap structure by coating the finger-like porous stainless-steel support (PSS) with MnCO3 particles, which forms a small gap of ca. 1 µm during subsequent thermal treatment. The stability of this novel configuration was demonstrated under 20–50 fast heating up/cooling down cycles at a maximum ramp rate of 10 K/min, under near practical fuel cell application conditions. Such a structure imitates semi-free-standing bulk Pd membranes, which not only avoids the direct contact between Pd layer and PSS and ensures a high H2 permeance, but also avoids the shear stresses between the metal membrane and module. The membrane with a finger-like and gap structure was applied in NH3 decomposition membrane reactor, which achieved nearly complete NH3 conversion at a relatively low temperature of 673 K and remained stable for 200 h, exhibiting potential in future applications.

IR and NMR Studies of the Status of Al and Acid Sites in Desilicated Zeolite Y.

The desilication of zeolite Y (of Si/Al = 31) that was previously dealuminated by steaming and acid treatment was studied. Desilication of zeolites of high Si/Al module in alkali solutions extracts both Si and Al from zeolite crystals, but while Si remains in solution, Al is reinserted into the zeolite grain. The main goal of our study was to follow the status of Al reinserted into zeolite during the desilication procedure, and its role in the formation of acid sites of the Brønsted and Lewis types. The properties of Al were followed by 27Al MAS NMR spectroscopy (for parent samples and zeolites treated either with NaOH or NaOH/tetrabutylammonium hydroxide), whereas the acid sites generated in the final stages were studied by IR spectroscopy with NH3 and CO as probe molecules. In non-desilicated zeolite, most of the Al was in a typically zeolitic tetrahedral coordination, while both NMR and quantitative IR studies of NH3 sorption evidenced that Al that was extracted by desilication and was subsequently reinserted had a tetrahedral coordination similar to amorphous aluminosilicates and showed an ion exchange ability. After the exchange of Na+ to NH4+ and decomposition of NH4+ ions, reinserted Al forms generated protonic sites from which some condensed at higher temperatures producing Lewis acid sites (with stoichiometry typical for zeolites i.e., the condensation of two protonic sites produces one Lewis site) but some other kept their character.

Promising zirconia-mixed Al-based nitrogen carriers for chemical looping of NH3: Reduced NH3 decomposition and improved NH3 yield

The chemical looping ammonia generation (CLAG) of N-sorption/desorption reactions via Al-based N-carriers for producing ammonia (NH3) (a non-carbon fuel) is thought to be an important alternative to the conventional Haber–Bosh NH3 synthesis technology. However, the low yield of NH3, because of significant NH3 decomposition at the required N-desorption temperature, inhibits the development of CLAG. Accordingly, ZrO2 mixed AlN was designed in this study to investigate the NH3 generation characteristics of AlN during the N-desorption process in a stationary bed reactor. The results showed that ZrO2 can improve the formation of NH3 because the molecular adsorption of NH3 occurred on the ZrO2 surface, thus preventing NH3 from decomposing. The ZrO2 loadings and steam concentrations in the atmosphere positively affect the yield and generation efficiency of NH3, while increasing the reaction temperature increased the NH3 yield from 1.2 to 3.3 mmol, but reduced the NH3 generation efficiency from 91.7% to 60.3%.

Energy characteristics of a supersonic continuous-wave chemical HF laser using hydrazine decomposition products

We report the results of calculations and experimental studies of specific energy characteristics of a supersonic cw chemical HF laser with a flat nozzle block corresponding to the nozzle – nozzle reagent mixing scheme, in which catalytic decomposition products of hydrazine N2H4 (H2 + N2 + NH3) are used as a secondary fuel. As a result of experiments with cold (300 K) model mixtures, the specific energy extraction of the laser is found to decrease in this case by 43 % compared with the laser utilising pure hydrogen. The calculations show that the main reason for a decrease in the specific energy of the laser is an increase in the temperature in the mixing zone of the oxidising gas and secondary fuel jets. A strong effect of ammonia is revealed. Taking into account the actual heating of the products (up to 1000 K) during the catalytic decomposition of N2H4 allows the level of specific energy extraction from the laser to approach that of energy extraction from the laser operated on pure hydrogen by 13 %, which will lead to a decrease in the specific energy extraction by only 30 % in the absence of NH3 decomposition products.

Surface phosphorization of hierarchically nanostructured nickel molybdenum oxide derived electrocatalyst for direct hydrazine fuel cell

Non-faradaic catalytic decomposition of hydrazine (N2H4) is a vital but underappreciated problem for direct hydrazine fuel cell (DHFC). Herein, a careful study of a nickel molybdenum oxide derived catalyst for N2H4 electrooxidation is reported, with special focus on the method for effectively suppressing non-faradaic decomposition of hydrazine as well as the underlying mechanism. A hierarchically nanostructured catalyst consisting of tiny Ni10Mo alloy nanoparticles dispersed on porous NiMoO nanosheets is synthesized using a simple hydrothermal method followed by reductive annealing treatment. Thus-prepared catalyst shows high activity towards N2H4 electrooxidation, but is entangled with the problematic selectivity towards non-faradaic decomposition of N2H4. Our study find that this problem can be circumvented by a controlled phosphorization method. The resultant catalyst (Ni2P@Ni10Mo/Ni-Mo-O/NF) exhibits exceptionally high activity, excellent durability and nearly 100 % selectivity towards N2H4 electrooxidation. A detailed structural characterization and density functional theory calculations are conducted to understand the phosphorization-induced modification of catalytic property.

Effect of BaNH, CaNH, Mg3N2 on the activity of Co in NH3 decomposition catalysis

Abstract Development of active and non-noble metal-based catalyst for H2 production via NH3 decomposition is crucial for the implementation of NH3 as a H2 carrier. Co-based catalysts have received increasing attention because of its high intrinsic activity and moderate cost. In this work, we examined the effect of BaNH, CaNH and Mg3N2 on the catalytic activity of Co in the NH3 decomposition reaction. The H2 formation rate ranks the order as Co-BaNH > Co-CaNH > Co-Mg3N2 ≈ Co/CNTs within a reaction temperature range of 300–550 °C. It is worth pointing out that the H2 formation rate of Co-BaNH at 500 °C reaches 20 mmolH2 gcat–1 min–1, which is comparable to those of the active Ru/Al2O3 (ca. 17 mmolH2 gcat–1 min–1) and Ru/AC (21 mmolH2 gcat–1 min–1) catalysts under the similar reaction conditions. In-depth research shows that Co-BaNH exhibits an obviously higher intrinsic activity and much lower Ea (46.2 kJ mol–1) than other Co-based catalysts, suggesting that BaNH may play a different role from CaNH, Mg3N2 and CNTs during the catalytic process. Combined results of XRD, Ar-TPD and XAS show that a [Co–N–Ba]-like intermediate species is likely formed at the interface of Co metal and BaNH, which may lead to a more energy-efficient reaction pathway than that of neat Co metal for NH3 decomposition.

Effect of Magnetic Inducement in Preparation of Ni/Ce‐doped Al2O3 for Ammonia Decomposition

AbstractCatalytic activity of Ni catalysts for NH3 decomposition can be enhanced by using Ce‐doped Al2O3 support. Magnetic inducement during sol‐gel preparation of supports was studied to enhance the Ce dispersion in Al2O3 framework. In this study, the same poles and different pole of magnetic arrangement were applied during the sol‐gel preparation. Ni catalysts over the supports were investigated for the NH3 decomposition activity along with catalyst and support properties, including Ce dispersion in Al2O3 framework, Ni dispersion, acidic sites, basic sites, and reaction kinetics. The magnetic inducement can control the Ce composition and uniformity in the Al2O3 framework. The Ni/Ce‐doped Al2O3 prepared under the same poles of magnetic inducement show significant improvements in Ni dispersion, and yield highest catalytic activity due to a high Ce composition and uniformity in the framework, as well as the high Lewis basic sites which enhance the limiting step of NH3 decomposition. Thus, combination of the partial doping with magnetic inducement provides a novel approach with low cost to improve the activity of Ni catalyst without changing the reaction mechanism.

Hydrogen production via catalytic decomposition of NH3 using promoted MgO-supported ruthenium catalysts

Catalytic decomposition of NH3 to high purity hydrogen offers a promising strategy for fuel cells, but presents challenges for high hydrogen yields at comparatively low temperatures due to the lack of efficient catalysts. Here, we report the facile preparation of ultra-fine ruthenium (Ru) species dispersed on MgO, which show excellent activity and high temperature stability for NH3 decomposition reaction. The hydrogen yield of the prepared Ru/MgO catalysts reaches ca. 2,092 mmol H2 gRu–1 min–1 at 450 °C, far exceeding that of the previously reported most reactive Ru-based catalysts and the same chemical composition samples prepared by other approaches. Various characterization techniques containing X-ray absorption fine structure (XAFS), in-situ diffuse reflectance infrared Fourier transform spectroscopy ( in-situ DRTFTS) and temperature-programmed reduction/desorption (TPR/TPD) were carried out to explore the structure-function relation of the prepared Ru/MgO catalysts. We found that the Ru species interact strongly with the MgO support, which can efficiently protect the Ru species and MgO support from agglomerating during NH3 decomposition test, maintaining the stability of the catalysts.

Preparation of Nb-doped TiO2 nanopowder by liquid-feed spray pyrolysis followed by ammonia annealing for tunable visible-light absorption and inhibition of photocatalytic activity

Visible-light absorbing TiO2 with color tunability and negligible photocatalytic activity was developed by synthesizing Nb-doped TiO2 using liquid-feed flame spray pyrolysis (LF-FSP) followed by NH3 annealing. Nb-doped TiO2 nanopowders with selected Nb contents were synthesized by changing ratios of metalloorganic precursors. By using Ti and Nb precursors whose thermal decomposition behavior is very similar, the maximum Nb doping concentration was improved compared to Nb-doped TiO2 prepared by flame spray pyrolysis (FSP) in previous reports. As-synthesized Nb-doped TiO2 nanopowders were white regardless of the Nb content, while all became colored after NH3 annealing. In addition, the color of Nb-doped TiO2 after NH3 annealing varied from yellow to dark green depending on the Nb content. Light absorption characterization indicates that the color variation is attributable to the localized levels formed by interstitial N-doping and Nb-doping-induced Ti3+ formation resulting from reduction by H2, formed as a result of NH3 decomposition.

Beyond the Thermal Equilibrium Limit of Ammonia Synthesis with Dual Temperature Zone Catalyst Powered by Solar Light

Summary Artificial ammonia synthesis (Haber-Bosch process) is a prototypical exothermic reaction of maximum catalytic yield restricted by the unbreakable equilibrium law. This is because bottlenecked N2 dissociation necessitates high temperature, but high temperature reversely shifts the thermal equilibrium toward NH3 decomposition. To surmount this equilibrium limit, here, we propose a new scenario of dual-temperature-zone catalysis. Powered by sunlight, the apparent temperature of TiO2-xHy/Fe hybrid reaches 495°C but with local temperature difference up to 137°C between the hot zone (Fe) and “cooling” zone (TiO2-xHy) owing to the plasmonic local heating effect. The hot Fe bearing hot carriers efficiently dissociates N2, while working-in-tandem TiO2-xHy well accommodates spilled-over N from Fe via successive hydrogenation, prominently mitigating the reverse equilibrium shift and thus delivering record NH3 concentrations of 1,939 (1 atm) and 19,620 ppm (10 atm) at 495°C, 1.55 and 1.57 times the theoretical equilibrium limits of 1,249 and 12,459 ppm, respectively.

Verification on Possibility of Nitrogen Diffusion into Steel by High Temperature N-Quench

N-Quench, which is a new surface heat treatment to infiltrate nitrogen into steel parts followed by quenching to achieve hardening, is gathering attention in the nitriding field as it affords low distortion while maintaining a higher effective case depth (ECD) compared with conventional nitriding. N-Quench is conducted mainly between 680°C and 800°C, where the two-phase region of ferrite and austenite exists in the Fe-N phase diagram. However, a few studies have reported on nitriding at temperatures higher than 800°C due to decomposition of NH3, which is a key source of nitrogen infiltration. Our results revealed that in a conventional furnace such as resistance heating furnace, no nitrogen infiltrated the specimen at 930°C, which is the general carburizing temperature. On the other hand, in the infrared heating furnace, nitrogen infiltrated the specimen at 930°C successfully with lesser NH3introduction than that required by the conventional furnace. Therefore, in this study, the limit of NH3decomposition is assessed and possibility of extending the applicability of N-Quench, especially increasing the ECD while maintaining a low distortion, is examined.