Ammonia Borane Research Articles

NiPdMo nanoparticles reduced by Cs[closo-B6H7] as high-performance catalysts for hydrogen generation from hydrolysis of ammonia borane

The synthesis of efficient catalysts for the hydrolysis of ammonia borane (NH3BH3, AB) is a matter of critical importance and immediate necessity, as it is currently considered a promising approach for the production of hydrogen. The synergy of interactions between different metals has been widely applied in the hydrolysis of AB. In this work, we first applied Cs [closo-B6H7] as the reductant to prepare a series of NixPdyMoz NPs catalysts using a simple in-situ reduction method. The structural and physical chemical properties of the as-prepared catalysts are investigated employing a multitude of various characterizations. Utilizing the optimal catalyst Ni0·3Pd0·7Mo0.2 NPs, AB hydrolysis can be completed at room temperature in just 21 s. This catalyst exhibits a lower activation energy (Ea = 52.3 kJ mol−1) and relatively higher activity (TOF = 252.7 mmolH2·mmolmetal−1min−1), which greatly outperforms many previously reported similar or corresponding catalysts. The enhancement in catalytic activity is ascribed to the moderate reducibility of Cs [closo-B6H7] and the synergistic interaction among Ni, Pd, and Mo. These results suggest the promise of multi-metal catalysts derived from Cs [closo-B6H7] for the hydrolytic dehydrogenation of hydrogen storage materials.

Desirable performance and mechanism of RuPd nanoalloys in catalyzing hydrolytic dehydrogenation of NH3BH3

The dehydrogenation of liquid-phase chemical hydrogen storage materials (such as ammonia borane, AB, NH3BH3) is a promising strategy to develop the promising hydrogen economy. Considering that the self-hydrolysis of AB is nearly impossible at room temperature, it is very worthwhile to search a robust catalyst for this hydrolytic reaction and clarify the catalytic mechanism. In this work, a glucose-derived N/O co-doped and multi-level porous carbon (marked as g-pC, SBET = 1356 m2 g−1, Vtotal = 0.762 cm3 g−1, Smicro = 1079 m2 g−1, Vmicro = 0.427 cm3 g−1) is prepared for confining RuPd alloys. Benefitting from the positive effect of g-pC (such as the particular anchoring and geometric effects on highly and tightly confining RuPd nanoparticles, as well as enhanced hydrophilicity) and the exceptional metal alloy effect, the obtained bimetallic catalysts unveil drastically enhanced catalytic activity in AB hydrolysis compared to the monometallic counterparts. Especially, catalyzed by the optimal Ru0.25Pd0.75@g-pC with a mean alloy size of 1.5 nm (10 mg), the dehydrogenation of 1.00 mmol AB can be finished within 1 min at 303 K in NaOH solution (1.5 M). The corresponding turnover frequency and hydrogen generation rate are calculated to be 541.09 min−1 and 145,950 mL min−1 g−1, respectively. Moreover, about 62% of the initial catalytic activity is still retained even in the 18th cyclic experiment, suggesting the extraordinarily long durability. In addition, the isotopic analyses present a kinetic isotope effect (KIE) of 3.38, further confirming that the scission of an O-H bond in H2O is the rate-controlling step in this hydrolytic reaction. Our work offers a competitive metal alloy catalyst for generating hydrogen from AB aqueous solution and promote the development and safety utilization of hydrogen energy.

Halloysite nanotubes supported Co2P bridged by carbon dots for enhanced hydrogen evolution from ammonia borane

Rational design of efficient, low-cost and eco-friendly catalysts for hydrogen generation from solid-state hydrogen storage material ammonia borane (AB) is identified as an ideal approach for solving the problems of energy crisis and environmental pollution. Herein, we construct a robust and low-cost composite catalyst with the combination of non-noble metal cobalt phosphide (Co2P), carbon dots (CDs) and halloysite nanotubes (HNTs), in which CDs serve as the bridge and conductive mediator to link Co2P and HNTs for facilitating electron transfer. Attributing to the synergistic effects among Co2P, CDs and HNTs, the high conductivity of CDs and the dispersion/supporting of HNTs, the as-prepared Co2P-CDs/mHNTs composite catalyst displays a considerably high hydrogen evolution rate with TOF of 178.02 molH2 molco2P−1 min−1, which is much higher than Co2P/HNTs, Co2P/CDs and other non-noble metals-based catalysts. This work provides a new insight and bridging strategy for the design of low-cost composite catalysts with excellent performance toward AB hydrolysis.

Phase Diagram Analysis of High-Pressure/High-Temperature Polymorphs of Ammonia Borane.

Ammonia borane (NH3BH3) is a promising hydrogen-storage material because of its high hydrogen density. It is employed as a hydrogen source when synthesizing superconducting polyhydrides under high pressure. Additionally, NH3BH3 is a crystallographically interesting compound that features protonic hydrogen (Hδ+) and hydridic hydrogen (Hδ-), and it forms a dihydrogen bond, which explains its stable existence as a solid. Herein, X-ray diffraction experiments were performed at high pressures (HPs) and high temperatures (HTs) of up to 30 GPa and 300 °C, respectively, to investigate the HP/HT phase diagram of NH3BH3. A new HP/HT phase (HPHT2) was identified above 9 GPa and 150 °C. Crystal-structure analysis using the Rietveld method and stability verification using density functional theory calculations revealed that HPHT2 has a P21/n (Z = 4) structure, similar to that of a previously reported HP/HT phase (HPHT) that appears at a lower pressure. HPHT2 is denser than the HP phases that appear at room temperature (HP1 and HP2) at the same pressure (up to ∼17 GPa). In the phase diagram, the phase-boundary line between HPHT and HP1 is a downward convex curve. These unconventional phenomena in the density and phase boundary can be attributed to the influence of dihydrogen bonding on the crystal structure and phase diagram.

Gamma-ray-irradiated preparation and performance of magnetothermally responsive hybrid materials towards the tandem hydrogenation of halonitrobenzenes

Novel magneto-thermo dual responsive organic-inorganic hybrid materials (PdCu/Fe3O4@SiO2@PNIPAM) were successfully prepared under γ-ray irradiation in this work. The γ-ray irradiation simultaneously induced the grafting of the polymer PNIPAM, and the in-situ anchoring of metallic Pd and Cu via an irradiation reduction. The catalytic performance of the prepared PdCu/Fe3O4@SiO2@PNIPAM hybrid material (abbr. PdCu/FSP) was investigated for the dehydrogenation of ammonia borane (AB) and the tandem hydrogenation of halonitrobenzenes. The results showed that the as-prepared PdCu/FSP exhibited more excellent catalytic performance in the tandem hydrogenation reaction of halonitrobenzenes in comparison with a controlled sample by a traditional preparation method. Furthermore, the PdCu/FSP catalyst prepared at a radiation dose of 25 kGy achieved excess 99 % yield of m-chloroaniline (m-CAN) at room temperature within 5 min. The PdCu/FSP hybrid material could be easily recycled by simple magnetic separation, and increasing temperature led to obvious time-shortening behavior for facile magnetic separation. Owing to lack of the intrinsic drawbacks of conventional chemical reductants and radical initiators, the gamma-ray irradiation method provides an available strategy for the construction of hybrid catalytic materials towards the hydrogenated reduction of halonitrobenzenes.

Controlled synthesis of reduced graphene oxide-supported bimetallic Pt–Au nanoparticles for enhanced electrooxidation of methanol

Controlled construction of bimetallic interfaces on conductive carbon supports is extremely important for achieving better synergistic effect required for electrooxidation of small organic molecules for energy applications. Herein, controlled synthesis of reduced graphene oxide (RGO)-supported bimetallic Pt–Au nanoparticles (Pt–Au/RGO) for electrooxidation of methanol using a facile and practical approach was described. By carefully adapting sequential and simultaneous reduction steps H2PtCl6 and AuCl3were reduced on RGO support using ammonia borane (AB) and ascorbic acid (AA) as reducing agents. Three types of Pt–Au/RGO catalysts were prepared and labeled as PtAu/RGO-AB1, PtAu/RGO-AB, and PtAu/RGO-AA. The reduction process was carried at ambient conditions, without the use of surfactants, and the catalysts obtained were analyzed through various techniques, including X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), selected area electron diffraction (SAED), and energy dispersive X-ray spectroscopy (EDS). The PtAu/RGO-AB1 catalyst showed remarkable uniformity on the RGO sheets, with an average particle size of 2–3 nm. The electrochemical behavior of Pt–Au catalysts supported on reduced graphene oxide (RGO) for methanol oxidation was systematically investigated via cyclic voltammetry and chronoamperometry techniques. Among the studied catalysts, PtAu/RGO-AB1 exhibited high electrochemical active surface area (ECSA) of 92.47 m2/g, along with the highest mass and ECSA-normalized activities for the electrooxidation of methanol. PtAu/RGO-AB1 manifested exceptional resistance to accumulated CO-like species, as evidenced by its higher forward peak current density to reverse peak current density ratio (If/Ib) of 2.20. The facile and effective synthesis strategy described here provides a promising method for fabricating well-defined multi-component nanostructured electrocatalysts with potential applications for various fuel cell reactions.

Amorphous Nickel Nanofilms for Efficient Hydrogen Generation from ammonia borane

AbstractClean and sustainable hydrogen production through liquid hydrogen storage material requires highly active and stable earth‐abundant non‐noble metal to replace expensive and rare noble metals. Herein, nickel nanofilms (Ni/NiO‐NFs) were prepared by the ionic liquid/water interface route. The cationic carbon chain length of the ionic liquid affects the phase composition of the nickel nanofilm, and the ionic liquid with [OMIm][PF6] as the anion has good thermal stability during the synthesis process. The efficiency of Ni/NiO‐NFs catalysts was tested by comparative kinetic analysis of the AB hydrolysis for hydrogen production. The as‐prepared Ni/NiO‐NFs catalyst exhibits excellent hydrogen generation performances, including a hydrogen production rate (2917 ml min−1 gNi−1), and a low activation energy (48.1 kJ/mol). The transition of nickel oxide to metallic nickel and the destruction of the catalyst structure is responsible for the decreased durability. This work highlights the significance of amorphous nanofilms catalysts via the ionic interface method on the regulation of activity for AB hydrolysis.

P-bridged Fe-X-Co coupled sites in hollow carbon spheres for efficient hydrogen generation

Non-precious metals have shown attractive catalytic prospects in hydrogen production from ammonia borane hydrolysis. However, the sluggish reaction kinetics in the hydrolysis process remains a challenge. Herein, P-bridged Fe-X-Co coupled sites in hollow carbon spheres (Fe-CoP@C) has been synthesized through in situ template solvothermal and subsequent surface-phosphorization. Benefiting from the optimized electronic structure induced by Fe doping to enhance the specific activity of Co sites, bimetallic synergy and hollow structure, the as-prepared Fe-CoP@C exhibits superior performances with a turnover frequency (TOF) of 183.5 min−1, and stability of over 5 cycles for ammonia borane hydrolysis, comparable to noble metal catalysts. Theoretical calculations reveal that the P-bridged Fe-X-Co coupled sites on the Fe-CoP@C catalyst surfaces is beneficial to adsorb reactant molecules and reduce their reaction barrier. This strategy of constructing hollow P-bridged bimetallic coupled sites may open new avenues for non-precious metal catalysis.

A Theoretical Perspective on the Photochemistry of Boron-Nitrogen Lewis Adducts.

Boron-Nitrogen (B-N) Lewis adducts form a versatile family of compounds with numerous applications in functional molecules. Despite the growing interest in this family of compounds for optoelectronic applications, little is currently known about their photophysics and photochemistry. Even the electronic absorption spectrum of ammonia borane, the textbook example of a B-N Lewis adduct, is unavailable. Given the versatility of the light-induced processes exhibited by these molecules, we propose in this work a detailed theoretical study of the photochemistry and photophysics of simple B-N Lewis adducts. We used advanced techniques in computational photochemistry to identify and characterize the possible photochemical pathways followed by ammonia borane and extended this knowledge to the substituted B-N Lewis adducts pyridine-borane and pyridine-boric acid. The photochemistry observed for this series of molecules allows us to extract qualitative rules to rationalize the light-induced behavior of more complex B-N-containing molecules.

Development of a microwave chemical cell coupled with post-wall waveguide for in situ/operando soft x-ray absorbance spectroscopy under microwave irradiation

In this study, we developed a microwave chemical cell for total electron yield soft x-ray absorption spectroscopy (XAS) using synchrotron radiation under microwave irradiation. In addition, in situ XAS measurements of ammonia borane were performed using the device developed. The device comprises a post-wall waveguide housing a sample holder formed within it. Electrons emitted from the sample during soft x-ray irradiation pass through the metal plates of the waveguide and are measured using a picoammeter. Integration of the microwave irradiation structure into a synchrotron radiation beamline, which is a challenge in soft x-ray analysis requiring measurements in a high-vacuum atmosphere, was achieved by miniaturizing the device using 24.125 GHz ISM band microwaves, instead of the typical 2.45 GHz microwaves. Performance of the device was thoroughly assessed through temperature distribution simulation, temperature measurement of water, and evaluation of frequency characteristics. When the sample holder was filled with water and irradiated with 3 W microwaves, the temperature increased to 97 °C, which is close to the boiling point. The in situ XAS measurements performed using this device with ammonia borane/graphite (2:1) powder at the B-K edge during microwave irradiation showed that peaks associated with hydrogen desorption intensified with prolonged microwave exposure. This result indicates that microwave heating in a vacuum and soft x-ray analysis during microwave heating were achieved. The developed microwave chemical cell emerges as a powerful tool, facilitating advancements in our understanding of elementary chemical processes and elucidating microwave-specific effects such as local heating during microwave irradiation.

RuCo@P Core-Shell Nanoparticles Filled with Carbon Nanotubes for Highly Effective Catalytic Hydrolysis of Ammonia Borane

The doping of nonmetals in multiphase metal catalysts can effectively improve the catalytic performance and reduce the catalyst cost. In this study, we synthesized transition metal phosphide (RuCo@P/CNT) catalysts loaded on carbon nanotubes (CNT) using sodium borohydride (NaBH4) as the reducing agent. The microstructure and phase composition of RuCo@P/CNT nanoparticles were investigated using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), transmission electron microscopy (TEM), and BET. RuCo@P/CNT nanoparticles show superior catalytic activity and cycle stability in the catalytic ammonia borane hydrolysis process compared to Ru/CNT and RuCo/CNT nanoparticles, retaining 65.74% of their initial catalytic activity after 5 reaction cycles. The test yielded values for turnover frequency and activation energy of 327.33 min-1 and 36.77 kJ·mol-1, respectively. Additionally, a kinetic isotope effect value of 2.61 for H2O/D2O showed that O-H bond breaking in proportional acceptor water is the decisive step in the dehydrogenation of ammonia borane, and based on this discovery, a specific mechanism for the catalytic hydrolysis of AB by RuCo@P NPs is postulated.

Dual catalytic activity of a cucurbit[7]uril-functionalized metal alloy nanocomposite for sustained hydrogen generation: hydrolysis of ammonia borane and electrocatalysts for the hydrogen evolution reaction.

H2 is one of the most attractive fuel alternatives to the existing fossil fuels that cause detrimental environmental issues. Thus, there has been an upsurge in the research on the production of green hydrogen. In this view, cucurbit[7]uril (CB7)-functionalized Co:Ni alloy nanocomposites with different compositions, reported here for the first time, were synthesized to synergise the catalytic activities of a nanoalloy and CB7 and screened for hydrogen generation via hydrolysis of ammonia borane (AB). The (Co85:Ni15)50:(CB7)50 nanocomposite exhibited enhanced catalytic performance for AB hydrolysis even at room temperature as compared to the nanoalloy without CB7. Efficient release of ammonia-free green H2 is ensured by the retention of NH3 by the surface functionalized CB7 macrocycles. For sustained release, a novel and cost-effective procedure was used to regenerate AB from the by-product, and the H2 release activity was verified to be on par with commercial AB. The used nanocomposite magnetically separated from the by-product solution was shown to be an efficient electrochemical catalyst for the hydrogen evolution reaction (HER). The cucurbit[7]uril-functionalized Co:Ni nanocomposite demonstrates remarkable dual catalytic performance to generate clean hydrogen from both the hydrolysis of AB at room temperature and the electrochemical HER, thus opening new avenues in supramolecular chemistry for developing noble metal-free catalysts with high activity and long-term stability.

Solvent- and catalyst-free reduction of CO2 with ammonia borane

The catalyst-free CO2 reduction with ammonia borane in the solid state is reported. Close to 40 mmol of CO2 per gram of ammonia borane can be reduced at 0.5 MPa and 60 °C to formamide in high yield, achieving a highly atom-economical process.

TiCl4-mediated deoxygenative reduction of aromatic ketones to alkylarenes with ammonia borane.

A rapid and mild protocol for the exhaustive deoxygenation of various aromatic ketones to corresponding alkanes was described, which was mediated by TiCl4 and used ammonia borane (AB) as the reductant. This reduction protocol applies to a wide range of substrates in moderate to excellent yields at room temperature. The gram-scale reaction and syntheses of some key building blocks for SGLT2 inhibitors demonstrated the practicability of this methodology. Preliminary mechanistic studies revealed that the ketone is first converted into an alcohol, which then undergoes a carbocation to give the alkane via hydrogenolysis.

Selective dehydrogenation of ammonia borane to borazine and derivatives by rhodium olefin complexes.

This report presents a selective synthetic approach towards borazine from ammonia borane using a dinuclear rhodium olefin homogeneous catalyst. The synthesis and spectroscopic characterization of a dirhodium ammonia borane complex as an intermediate provides insight into a possible mode of activation.

Manganese catalysed reduction of nitriles with amine boranes.

The room temperature reduction of various nitriles using amine boranes (ABs) catalysed by a manganese(i) alkyl complex is described. Based on experimental findings, a plausible mechanistic scenario is presented. This includes the presence of two catalytic cycles, one for productive reduction of nitriles and one for hydrogen evolution.

Reduction of CO2 with ammonia borane and selective formylation of amines in the presence of imidazolium halides

The addition of the imidazolium halide ionic liquids increases the efficiency of N-methylaniline formylation with CO2 and NH3·BH3. This effect is illustrated by an increase in the 3a/2a ratio from 1.7 to approximately 10.

Near-infrared driven photocatalytic hydrogen production from ammonia borane hydrolysis using heterostructure-upconverted nanoparticles

This study presents a novel approach to hydrogen evolution through ammonia borane dehydrogenation, utilizing the unique properties of upconverted nanoparticles (UCNPs) and safe, abundant near-infrared (NIR) light. By converting low-energy...

A boron nitride – carbon composite derived from ammonia borane and ZIF-8 with promises for the adsorption of carbon dioxide

In the present study, we report the synthesis, characterization and assessment of the carbon dioxide adsorption capacity of a composite made of boron nitride and carbon. The material is obtained...

Nanoparticle-enabled integration of air capture and conversion of CO2.

Integrating air capture and conversion of CO2 is key to realizing energy sustainability. However, current integration approaches require high temperature and pressure, making them energy intensive. Here, we demonstrate a nanoparticle (NP) catalysis approach for the hydrogenation of alkyl carbonate, an intermediate obtained from the CO2 capture process, to formate, achieving one-pot air capture and conversion of CO2 under ambient conditions. The capture is realized in an ethylene glycol (EG) solution of KOH (EG-KOH) at room temperature, where CO2 is selectively converted into HO-CH2CH2-O-COOK (∼100% conversion). This carbonate is then hydrogenated using ammonia borane (under ambient pressure and at 50 °C) to formate (HCOOK) (>90% yield) in the presence of a stable Pd NP catalyst with EG being regenerated. Atomistic simulations suggest that the CO2 absorption process in the EG-KOH solution is energetically stable, and the catalyst surface provides the reaction site to break the C-O bond in the -O-COOK structure, enabling the hydrogenation of the alkyl carbonate to formate and the regeneration of EG. Our study provides a promising NP-catalysis approach for air capture and conversion of CO2 into value-added chemicals/fuels under ambient conditions.