Dehydrogenation of Ammonia Borane by Metal Nanoparticle Catalysts

Single-Atom Ce-Doped Metal Hydrides with High Phosphatase-like Activity Amplify Oxidative Stress-Induced Tumor Apoptosis

Phosphates within tumors function as key biomolecules, playing a significant role in sustaining the viability of tumors. To disturb the homeostasis of cancer cells, regulating phosphate within the organism proves to be an effective strategy. Herein, we report single-atom Ce-doped Pt hydrides (Ce/Pt-H) with high phosphatase-like activity for phosphate hydrolysis. The resultant Ce/Pt-H exhibits a 26.90- and 6.25-fold increase in phosphatase-like activity in comparison to Ce/Pt and Pt-H, respectively. Mechanism investigations elucidate that the Ce Lewis acid site facilitates the coordination with phosphate groups, while the surface hydrides enhance the electron density of Pt for promoting catalytic ability in H2O cleavage and subsequent nucleophilic attack of hydroxyl groups. Finally, by leveraging its phosphatase-like activity, Ce/Pt-H can effectively regulate intracellular phosphates to disrupt redox homeostasis and amplify oxidative stress within cancer cells, ultimately leading to tumor apoptosis. This work provides fresh insights into noble-metal-based phosphatase mimics for inducing tumor apoptosis.

Recent Progress on Nanomedicine-Mediated Repolarization of Tumor-Associated Macrophages for Cancer Immunotherapy

Tumor-associated macrophages (TAMs) constitute the largest number of immune cells in the tumor microenvironment (TME). They play an essential role in promoting tumor progression and metastasis, which makes them a potential therapeutic target for cancer treatment. TAMs are usually divided into two categories: pro-tumoral M2-like TAMs and antitumoral M1 phenotypes at either extreme. The reprogramming of M2-like TAMs toward a tumoricidal M1 phenotype is of particular interest for the restoration of antitumor immunity in cancer immunotherapy. Notably, nanomedicines have shown great potential for cancer therapy due to their unique structures and properties. This review will briefly describe the biological features and roles of TAMs in tumor, and then discuss recent advances in nanomedicine-mediated repolarization of TAMs for cancer immunotherapy. Finally, perspectives on nanomedicine-mediated repolarization of TAMs for effective cancer immunotherapy are also presented.

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.

Insights into the hydrogen generation and catalytic mechanism on Co-based nanocomposites derived from pyrolysis of organic metal precursor

Hydrogen generation from boron hydride is important for the development of hydrogen economy. Cobalt (Co) element has been widely used in the hydrolysis of boron hydride. Pyrolysis is a common method for materials synthesis in catalytic fields. Herein, Co-based nanocomposites derived from the pyrolysis of organic metal precursors and used for hydrolysis of boron hydride are summarized and discussed. The different precursors consisting of MOF, supported, metal, and metal phosphide precursors are summarized. The catalytic mechanism consisting of dissociation mechanism based on oxidative addition-reduction elimination, pre-activation mechanism, SN2 mechanism, four-membered ring mechanism, and acid-base mechanism is intensively discussed. Finally, conclusions and outlooks are conveyed from the design of high-efficiency catalysts, the characterization of catalyst structure, the enhancement of catalytic activities, the investigation of the catalytic mechanism, and the catalytic stability of active structure. This review can provide guidance for designing high-efficiency catalysts and boosting development of hydrogen economy.

Engineering a hollow bowl-like porous carbon-confined Ru-MgO hetero-structured nanopair as a high-performance catalyst for ammonia borane hydrolysis

Exploration of high-performance catalysts holds great importance for on-demand H2 production from ammonia borane (AB) hydrolysis. In this work, a hollow bowl-like porous carbon-anchored Ru-MgO hetero-structured nano-pair with high-intensity interfaces is made, using a tailored design approach. Consequently, the optimized catalyst shows AB hydrolysis activity with a turnover frequency value of 784 min-1 in aqueous media and 1971 min-1 in alkaline solvent. Robust durability is also achieved, with slight deactivation after a ten-cycle test. Combined experimental and theoretical calculations validate the positive function of the interface between Ru and MgO for facilitating H transfer and boosting water activation, thus leading to improved AB hydrolysis performance. This study could be valuable in guiding the upgradation of Ru catalytic systems, to advance their practical applications.

Nanomaterials-Involved Tumor-Associated Macrophages' Reprogramming for Antitumor Therapy

Tumor-associated macrophages (TAMs) play pivotal roles in tumor development. As primary contents of tumor environment (TME), TAMs secrete inflammation-related substances to regulate tumoral occurrence and development. There are two kinds of TAMs: the tumoricidal M1-like TAMs and protumoral M2-like TAMs. Reprogramming TAMs from immunosuppressive M2 to immunocompetent M1 phenotype is considered a feasible way to improve immunotherapeutic efficiency. Notably, nanomaterials show great potential for biomedical fields due to their controllable structures and properties. There are many types of nanomaterials that exhibit great regulatory activities for TAMs' reprogramming. In this review, the recent progress of nanomaterials-involved TAMs' reprogramming is comprehensively discussed. The various nanomaterials for TAMs' reprogramming and the reprogramming strategies are summarized and introduced. Additionally, the challenges and perspectives of TAMs' reprogramming for efficient therapy are discussed, aiming to provide inspiration for TAMs' regulator design and promote the development of TAMs-mediated immunotherapy.

Two active species from a single metal halide precursor: a case study of highly productive Mn-catalyzed dehydrogenation of amine-boranes via intermolecular bimetallic cooperation

Metal-metal cooperation for inert bond activation is a ubiquitous concept in coordination chemistry and catalysis. While the great majority of such transformations proceed via intramolecular mode in binuclear complexes, to date only a few examples of intermolecular small molecule activation using usually bimetallic frustrated Lewis pairs (Mδ+⋯M'δ-) have been reported. We introduce herein an alternative approach for the intermolecular bimetallic cooperativity observed in the catalytic dehydrogenation of amine-boranes, in which the concomitant activation of N-H and B-H bonds of the substrate via the synergetic action of Lewis acidic (M+) and basic hydride (M-H) metal species derived from the same mononuclear complex (M-Br). It was also demonstrated that this system generated in situ from the air-stable Mn(i) complex fac-[(CO)3(bis(NHC))MnBr] and NaBPh4 shows high activity for H2 production from several substrates (Me2NHBH3, tBuNH2BH3, MeNH2BH3, NH3BH3) at low catalyst loading (0.1% to 50 ppm), providing outstanding efficiency for Me2NHBH3 (TON up to 18 200) that is largely superior to all known 3d-, s-, p-, f-block metal derivatives and frustrated Lewis pairs (FLPs). These results represent a step forward towards more extensive use of intermolecular bimetallic cooperation concepts in modern homogeneous catalysis.

Surface Chemical Engineering of a Metal 3D-Printed Flow Reactor Using a Metal-Organic Framework for Liquid-Phase Catalytic H2 Production from Hydrogen Storage Materials

The accurate positioning of metal-organic frameworks (MOFs) on the surface of other materials has opened up new possibilities for the development of multifunctional devices. We propose here a postfunctionalization approach for three-dimensional (3D)-printed metallic catalytic flow reactors based on MOFs. The Cu-based reactors were immersed into an acid solution containing an organic linker for the synthesis of MOFs, where Cu2+ ions dissolved in situ were assembled to form MOF crystals on the surface of the reactor. The resultant MOF layer served as a promising interface that enabled the deposition of catalytically active metal nanoparticles (NPs). It also acted as an efficient platform to provide carbonous layers via simple pyrolysis under inert gas conditions, which further enabled functionalization with organic modifiers and metal NPs. Cylindrical-shaped catalytic flow reactors with four different cell densities were used to investigate the effect of the structure of the reactors on the catalytic production of H2 from a liquid-phase hydrogen storage material. The activity increased with an increasing internal surface area but decreased in the reactor with the smallest cell size despite its high internal surface area. The results of fluid dynamics studies indicated that the effect of pressure loss becomes more pronounced as the pore size decreases.

Highly electron-deficient ultrathin Co nanosheets supported on mesoporous Cr2O3 for catalytic hydrogen evolution from ammonia borane

The hydrolysis of ammonia borane (NH3BH3) on metal-based heterogeneous catalysts under light irradiation has been considered as an efficient technique for hydrogen (H2) generation, in which the activity of the catalyst can be improved by increasing the electron density of the active metal. However, studies focused on reducing the electron density of the active metal are rare. Here, we report an electron density manipulation strategy to prepare highly electron-deficient ultrathin Co nanosheets via transferring nanosheets to support mesoporous Cr2O3 by simple one-step in situ reduction (denoted as Co/Cr2O3). X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge structure (XANES) spectra confirm the formation of electron-deficient Co nanosheets and the Co-O-Cr bond due to electron transfer from the nanosheets to mesoporous Cr2O3. Importantly, the Co-O-Cr bond can work as a bridge to accelerate the electron transfer under light irradiation and then improve the electron-deficiency degree of Co nanosheets. As a result, the optimal Co/Cr2O3 exhibits a high intrinsic catalytic performance with the turnover frequency (TOF) value of 106.8 min-1 and significantly reduces the activation energy (Ea) to 16.8 kJ mol-1 under visible light irradiation, which make it among the best ever recorded monometallic Co-based catalyst with enriched electrons. The density functional theory (DFT) calculation results suggest that the electron-deficient Co nanosheets are responsible for the greatly decreased H2O activation and dissociation energy barriers and then the acceleration of the evolution of H2. The work provides a new perspective for designing high efficiency catalysts for H2 production, which is beneficial for relative energy conversion and storage catalysis.

Ir-Catalyzed B(3)-Amination of o-Carboranes with Amines via Acceptorless Dehydrogenative BH/NH Cross-Coupling

An efficient and convenient strategy for Ir-catalyzed selective B(3)-amination of o-carboranes with amines via acceptorless BH/NH dehydrocoupling was developed, affording a series of B(3)-aminated-o-carboranes in moderate to high isolated yields with H2 gas as a sole by-product. Such an oxidant-free system endues the protocol sustainability, atom-economy and environmental friendliness. A reaction mechanism via an Ir(I)-Ir(III)-Ir(I) catalytic cycle involving oxidative addition, dehydrogenation and reductive elimination was proposed.

Reducible tungsten(VI) oxide-supported ruthenium(0) nanoparticles: highly active catalyst for hydrolytic dehydrogenation of ammonia borane

Reducible WO3 powder with a mean diameter of 100 nm is used as support to stabilize ruthenium(0) nanoparticles. Ruthenium(0) nanoparticles are obtained by NaBH4 reduction of ruthenium(III) precursor on the surface of WO3 support at room temperature. Ruthenium(0) nanoparticles are uniformly dispersed on the surface of tungsten(VI) oxide. The obtained Ru0/WO3 nanoparticles are found to be active catalysts in hydrolytic dehydrogenation of ammonia borane. The turnover frequency (TOF) values of the Ru0/WO3 nanocatalysts with the metal loading of 1.0%, 2.0%, and 3.0% wt. Ru are 122, 106, and 83 min-1, respectively, in releasing hydrogen gas from the hydrolysis of ammonia borane at 25.0 °C. As the Ru0/WO3 (1.0% wt. Ru) nanocatalyst with an average particle size of 2.6 nm provides the highest activity among them, it is extensively investigated. Although the Ru0/WO3 (1.0% wt. Ru) nanocatalyst is not magnetically separable, it has extremely high reusability in the hydrolysis reaction as it preserves 100% of initial catalytic activity even after the 5th run of hydrolysis. The high activity and reusability of Ru0/WO3 (1.0% wt. Ru) nanocatalyst are attributed to the favorable metal-support interaction between the ruthenium(0) nanoparticles and the reducible tungsten(VI) oxide. The high catalytic activity and high stability of Ru0/WO3 nanoparticles increase the catalytic efficiency of precious ruthenium in hydrolytic dehydrogenation of ammonia borane.

Facile construction of robust Ru-Co3O4 Mott-Schottky catalyst enabling efficient dehydrogenation of ammonia borane for hydrogen generation

Developing efficient catalysts for the dehydrogenation of ammonia borane (AB) is important for the safe storage and controlled release of hydrogen, but it is a challenging task. In this study, we designed a robust Ru-Co₃O₄ catalyst using the Mott-Schottky effect to induce favorable charge rearrangement. The self-created electron-rich Co₃O₄ and electron-deficient Ru sites at heterointerfaces are indispensable for the activation of the B-H bond in NH₃BH₃ and the OH bond in H₂O, respectively. The synergistic electronic interaction between the electron-rich Co₃O₄ and electron-deficient Ru sites at the heterointerfaces resulted in an optimal Ru-Co₃O₄ heterostructure that exhibited outstanding catalytic activity for the hydrolysis of AB in the presence of NaOH. The heterostructure had an extremely high hydrogen generation rate (HGR) of 12238 mL min^-1 g_cat^-1 and an expected high turnover frequency (TOF) of 755 mol_H2 mol_Ru^-1 min^-1 at 298 K. The activation energy needed for the hydrolysis was low (36.65 kJ mol^-1). This study opens up a new avenue for the rational design of high-performance catalysts for AB dehydrogenation based on the Mott-Schottky effect.

Water State-Driven Catalytic Hydrolysis of Ammonia Borane on Cu3P-Carbon Dot-Cu Composite

Hydrogen production from ammonia borane (AB) is usually governed by water activation, which is not only energy-intensive but also requires expensive and complicated catalysts. We here propose an integrated photocatalytic-photothermal system that dramatically improves water activation and lowers the transport resistance of H₂ by means of intermediate state water evaporation. This system is constructed by covering nanocomposites (Cu₃P-carbon dots-Cu) upon vertically aligned acetate fibers (VAAFs). As a result of superior hydration effect of VAAFs and local photothermal heating for rapid water evaporation, its hydrogen production efficiency from AB hydrolysis reaches over 10 times the particulate suspension system under solar irradiation. Mechanism analysis reveals that the rapid vaporization of intermediate water promotes the cleavages of O-H bonds in bound water and the adsorption reaction of AB and water molecules at active sites. Therefore, this work provides a novel approach to optimize catalytic reaction in thermodynamics and kinetics for the hydrolysis of AB.

Rapid nanocatalytic reaction using antibody-conjugated gold nanoparticles for simple and sensitive detection of parathyroid hormone

Biomolecule-conjugated metal nanoparticles (NPs) have been primarily used as colorimetric labels in affinity-based bioassays for point-of-care testing. A facile electrochemical detection scheme using a rapid nanocatalytic reaction of a metal NP label is required to achieve more quantitative and sensitive point-of-care testing. Moreover, all the involved components should be stable in their dried form and solution. This study developed a stable component set that allows for rapid and simple nanocatalytic reactions combined with electrochemical detection and applied it for the sensitive detection of parathyroid hormone (PTH). The component set consists of an indium-tin oxide (ITO) electrode, ferrocenemethanol (FcMeOH), antibody-conjugated Au NPs, and ammonia borane (AB). Despite being a strong reducing agent, AB is selected because it is stable in its dried form and solution. The slow direct reaction between FcMeOH⁺ and AB provides a low electrochemical background, and the rapid nanocatalytic reaction allows for a high electrochemical signal. Under optimal conditions, PTH could be quantified in a wide range of concentrations in artificial serum, with a detection limit of ~0.5 pg/mL. Clinical validation of the developed PTH immunosensor using real serum samples indicates that this novel electrochemical detection scheme is promising for quantitative and sensitive immunoassays for point-of-care testing.

Light-Induced Selective Hydrogenation over PdAg Nanocages in Hollow MOF Microenvironment

Selective hydrogenation with high efficiency under ambient conditions remains a long-standing challenge. Here, a yolk-shell nanostructured catalyst, PdAg@ZIF-8, featuring plasmonic PdAg nanocages encompassed by a metal-organic framework (MOF, namely, ZIF-8) shell, has been rationally fabricated. PdAg@ZIF-8 achieves selective (97.5%) hydrogenation of nitrostyrene to vinylaniline with complete conversion at ambient temperature under visible light irradiation. The photothermal effect of Ag, together with the substrate enrichment effect of the catalyst, improves the Pd activity. The near-field enhancement effect from plasmonic Ag and optimized Pd electronic state by Ag alloying promote selective adsorption of the -NO₂ group and therefore catalytic selectivity. Remarkably, the unique yolk-shell nanostructure not only facilitates access to PdAg cores and protects them from aggregation but also benefits substrate enrichment and preferential -NO₂ adsorption under light irradiation, the latter two of which surpass the core-shell counterpart, giving rise to enhanced activity, selectivity, and recyclability.

Porous aromatic frameworks with high Pd nanoparticles loading as efficient catalysts for the Suzuki coupling reaction

The development of efficient and recyclable heterogeneous Pd catalysts is an area of continuing attention due to their critical applications in organic synthesis and pharmaceutical production. In this study, two novel heterogeneous catalysts Pd@PAF-182 and Pd@PAF-183 were prepared by the immobilization/NaBH₄ reduction of PdCl₄^2- on hydrophilic cationic porous aromatic frameworks (PAF-182 and PAF-183), which were synthesized via a Yamamoto-type Ullmann coupling reaction from the corresponding aryl quaternary phosphonium salt monomer. Characterization by powder X-ray diffraction (PXRD), solid-state Cross-Polarization Magic-Angle-Spinning Nuclear Magnetic Resonance (CP/MAS NMR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) established the structures of the as-prepared catalysts. Inductively coupled plasma atomic emission spectrometry (ICP-AES) detection showed that the loading of Pd nanoparticles (Pd NPs) were 29.4 wt% for Pd@PAF-182 and 37.5 wt% for Pd@PAF-183, much higher than those of similar porous materials. Evaluation of the catalytic activity of the Pd@PAFs using Suzuki coupling as the model reaction demonstrated that as little as 0.12 mol% of Pd NPs could catalyze the Suzuki coupling with high efficiency, achieving yields up to 99% at 80 °C in 8 h. Recycling experiments also suggested that Pd@PAF-182 and Pd@PAF-183 maintained high catalytic activity with negligible leaching of Pd NPs after five cycles.

Synthesis, Formation Mechanism, and Structure of K[BH3S(CH3)BH3] and Its Application in Preparation of KB3H8

The design, synthesis, and applications of new boranes are eternal topics in boron chemistry. A new bis(borane)alkanethiolate salt, K[BH₃S(CH₃)BH₃], was synthesized in high yield by the reaction of K with (CH₃)₂S·BH₃ at room temperature. The formation mechanism was elucidated based on experimental and theoretical studies. The single-crystal structure of the K[BH₃S(CH₃)BH₃]·18-crown-6 adduct was determined in which the B-S-B bonding information of K[BH₃S(CH₃)BH₃] was illustrated for the first time. Using K[BH₃S(CH₃)BH₃] as a starting material, KB₃H₈ was successfully synthesized.

Broadband Plasmonic NbN Photocatalysts for Enhanced Hydrogen Generation from Ammonia Borane under Visible-Near-Infrared Illumination

The superior light-harvesting ability of plasmonic metallic nanostructures makes them uniquely suitable for applications in the light-driven chemical transformations relevant to renewable fuels. Here we demonstrate the use of niobium nitride (NbN) nanostructures as a nonprecious plasmonic photocatalyst for the highly efficient H₂ generation from the hydrolytic decomposition of ammonia borane (AB). Porous nanostructured NbN with a hierarchical flower-like nanoarchitecture was synthesized to achieve strong broadband plasmonic absorption in the visible and near-infrared (NIR) regions. The plasmonic NbN absorbers, when loaded with an optimized amount (∼2 wt %) of nanoparticulate Ni as the catalytic centers, show notably enhanced activity toward AB decomposition for H₂ evolution under both visible and NIR illumination, with the reaction rates being 4.6 (>420 nm) and 2.7 (>780 nm) times higher than that of the dark reaction. Further kinetic measurements and mechanistic investigations reveal that the photocatalytic activity originates from the plasmonic hot-carrier contributions.

Cu2O nanoparticle-catalyzed tandem reactions for the synthesis of robust polybenzoxazole

We report the synthesis of Cu₂O nanoparticles (NPs) by controlled oxidation of Cu NPs and the study of these NPs as a robust catalyst for ammonia borane dehydrogenation, nitroarene hydrogenation, and amine/aldehyde condensation into Schiff-base compounds. Upon investigation of the size-dependent catalysis for ammonia borane dehydrogenation and nitroarene hydrogenation using 8-18 nm Cu₂O NPs, we found 13 nm Cu₂O NPs to be especially active with quantitative conversion of nitro groups to amines. The 13 nm Cu₂O NPs also efficiently catalyze tandem reactions of ammonia borane, diisopropoxy-dinitrobenzene, and terephthalaldehyde, leading to a controlled polymerization and the facile synthesis of polybenzoxazole (PBO). The highly pure PBO (M_w = 19 kDa) shows much enhanced chemical stability than the commercial PBO against hydrolysis in boiling water or simulated seawater, demonstrating a great potential of using noble metal-free catalysts for green chemistry synthesis of PBO as a robust lightweight structural material for thermally and mechanically demanding applications.

Molecular Cavity for Catalysis and Formation of Metal Nanoparticles for Use in Catalysis

The employment of weak intermolecular interactions in supramolecular chemistry offers an alternative approach to project artificial chemical environments like the active sites of enzymes. Discrete molecular architectures with defined shapes and geometries have become a revolutionary field of research in recent years because of their intrinsic porosity and ease of synthesis using dynamic non-covalent/covalent interactions. Several porous molecular cages have been constructed from simple building blocks by self-assembly, which undergoes many self-correction processes to form the final architecture. These supramolecular systems have been developed to demonstrate numerous applications, such as guest stabilization, drug delivery, catalysis, smart materials, and many other related fields. In this respect, catalysis in confined nanospaces using such supramolecular cages has seen significant growth over the years. These porous discrete cages contain suitable apertures for easy intake of substrates and smooth release of products to exhibit exceptional catalytic efficacy. This review highlights recent advancements in catalytic activity influenced by the nanocavities of hydrogen-bonded cages, metal-ligand coordination cages, and dynamic or reversible covalently bonded organic cages in different solvent media. Synthetic strategies for these three types of supramolecular systems are discussed briefly and follow similar and simplistic approaches manifested by simple starting materials and benign conditions. These examples demonstrate the progress of various functionalized molecular cages for specific chemical transformations in aqueous and nonaqueous media. Finally, we discuss the enduring challenges related to porous cage compounds that need to be overcome for further developments in this field of work.

Alkaline ultrasonic irradiation-mediated boosted H2 production over O/N-rich porous carbon anchored Ru nanoclusters

Developing efficient catalytic systems to boost hydrogen evolution from hydrolytic dehydrogenation of ammonia borane (AB) is of broad interest but remains a formidable challenge since the widespread usages of hydrogen have been considered as sustainable solutions to ensure future energy security. Herein, we developed an alkaline ultrasonic irradiation-mediated catalytic system with O/N-rich porous carbon supported Ru nanoclusters (NCs) (Ru/ONPC) to considerably boost the catalytic activity for hydrogen production from the hydrolytic dehydrogenation of AB. The uniformly distributed sub-2.0 nm Ru NCs on the ONPC were demonstrated to be efficient catalysts to boost hydrogen generation from the hydrolytic dehydrogenation of AB with the synergistic effect between ultrasonic irradiation and alkaline additive without any additional heating. An ultrahigh turnover frequency (TOF) of 4004 min^-1 was achieved in the developed catalytic system, which was significantly higher than that of ultrasound-mediated AB hydrolysis without alkali (TOF: 485 min^-1) and alkaline AB hydrolysis (TOF: 1747 min^-1) without ultrasound mixing. The alkaline ultrasonic irradiation was beneficial for the cleavage of the OH bonds in the attacked H₂O molecules catalyzed by the Ru/ONPC and thus considerably boost the catalytic hydrogen generation from AB. This study provides a tractable and ecofriendly pathway to promote the activity toward AB hydrolysis to release hydrogen.

Functional Group Regulated Ni/Ti3C2Tx (Tx = F, -OH) Holding Bimolecular Activation Tunnel for Enhanced Ammonia Borane Hydrolysis

Developing economical and efficient catalyst for hydrogen generation from ammonia borane (AB) hydrolysis is still a huge challenge. As an alternative strategy, the functional group regulation of metal nanoparticles (NPs)-based catalysts is believed to be capable of improving the catalytic activity. Herein, a series of Ni/Ti₃C₂T_x-Y (T_x = F, -OH; Y denotes etching time (d)) catalysts are synthesized and show remarkably enhanced catalytic activity on the hydrolysis of AB in contrast to the corresponding without regulating. The optimized Ni/Ti₃C₂T_x-4 with a turnover frequency (TOF) value of 161.0 min^-1 exhibits the highest catalytic activity among the non-noble monometallic-based catalyst. Experimental results and theory calculations demonstrate that the excellent catalytic activity benefits from the bimolecular activation channels formed by Ni NPs and Ti₃C₂T_x-Y. H₂O and AB molecules are activated simultaneously in the bimolecular activation tunnel. Bimolecular activation reduces the activation energy of AB hydrolysis, and hydrogen generation rate is promoted. This article provides a new approach to design effective catalysts and further supports the bimolecular activation model for the hydrolysis of AB.

The curious saga of dehydrogenation/hydrogenation for chemical hydrogen storage: a mechanistic perspective

Hydrogen storage is an indispensable component of hydrogen-based fuel economy. Chemical hydrogen storage relies on the development of lightweight compounds which can deliver high weight percentage of H₂ at moderate temperatures through dehydrogenation and can be recovered from the dehydrogenated mass by hydrogenation for reuse. In this feature article we primarily discuss the mechanistic underpinnings of the catalytic dehydrogenation of ammonia-borane, a potential candidate for hydrogen storage and the challenges associated with its regeneration from the dehydrogenated mass. Moreover, we highlight the mechanistic intricacies, viability, sustainability and unresolved issues of allied chemical hydrogen storage avenues such as the CH₃OH-CO₂ cycle.

Enhanced hydrogen generation by reverse spillover effects over bicomponent catalysts

The contribution of the reverse spillover effect to hydrogen generation reactions is still controversial. Herein, the promotion functions for reverse spillover in the ammonia borane hydrolysis reaction are proven by constructing a spatially separated NiO/Al2O3/Pt bicomponent catalyst via atomic layer deposition and performing in situ quick X-ray absorption near-edge structure (XANES) characterization. For the NiO/Al2O3/Pt catalyst, NiO and Pt nanoparticles are attached to the outer and inner surfaces of Al2O3 nanotubes, respectively. In situ XANES results reveal that for ammonia borane hydrolysis, the H species generated at NiO sites spill across the support to the Pt sites reversely. The reverse spillover effects account for enhanced H2 generation rates for NiO/Al2O3/Pt. For the CoOx/Al2O3/Pt and NiO/TiO2/Pt catalysts, reverse spillover effects are also confirmed. We believe that an in-depth understanding of the reverse effects will be helpful to clarify the catalytic mechanisms and provide a guide for designing highly efficient catalysts for hydrogen generation reactions.

Cobalt sandwich-stabilized rhodium nanocatalysts for ammonia borane and tetrahydroxydiboron hydrolysis

A bulky organocobalt sandwich-supported Rh nanoparticle is an efficient, stable and recyclable nanocatalyst for hydrolysis of both ammonia borane and tetrahydroxydiboron to H2.

Local charge transfer within a covalent organic framework and Pt nanoparticles promoting interfacial catalysis

A pyridine-functionalized covalent organic framework encapsulating Pt nanoparticles with local charge transfer was developed, which efficiently catalyzed H2 production from ammonia borane hydrolysis in water.

Advances and Prospects in Metal-Organic Frameworks as Key Nexus for Chemocatalytic Hydrogen Production

Hydrogen is a clean and sustainable energy carrier, which is considered a promising alternative for fossil fuels to solve the global energy crisis and respond to climate change. Social concerns on its safe storage promote continuous exploration of alternatives to traditional storage methods. In this case, chemical hydrogen storage materials initiate plentiful research with special attention to the design of heterogeneous catalysts that can enhance efficient and highly selective hydrogen production. Metal-organic frameworks (MOFs), a kind of unique crystalline porous materials featuring highly ordered porosities and tailorable structures, can provide various active sites (i.e., metal nodes, functional linkers, and defects) for heterogeneous catalysis. Furthermore, the easy construction of active sites in highly ordered MOFs, which can work as plate for the delicate active site engineering, make them ideal candidates for a variety of heterogeneous catalysts including chemocatalytic hydrogen production. This review concentrates on the application of MOFs as heterogeneous catalysts or catalyst supports in chemocatalytic hydrogen production. Recent progresses of MOFs as catalysts for chemocatalytic hydrogen production are comprehensively summarized. The research methods, mechanism analyses, and prospects of MOFs in this field are discussed. The challenges in future industrial applications of MOFs as catalysts for hydrogen production are proposed.

Efficient Near-Infrared-Activated Photocatalytic Hydrogen Evolution from Ammonia Borane with Core-Shell Upconversion-Semiconductor Hybrid Nanostructures

In this work, the photocatalytic hydrogen evolution from ammonia borane under near-infrared laser irradiation at ambient temperature was demonstrated by using the novel core-shell upconversion-semiconductor hybrid nanostructures (NaGdF4:Yb3+/Er3+@NaGdF4@Cu2O). The particles were successfully synthesized in a final concentration of 10 mg/mL. The particles were characterized via high resolution transmission electron microscopy (HRTEM), photoluminescence, energy dispersive X-ray analysis (EDAX), and powder X-ray diffraction. The near-infrared-driven photocatalytic activities of such hybrid nanoparticles are remarkably higher than that with bare upconversion nanoparticles (UCNPs) under the same irradiation. The upconverted photoluminescence of UCNPs efficiently reabsorbed by Cu2O promotes the charge separation in the semiconducting shell, and facilitates the formation of photoinduced electrons and hydroxyl radicals generated via the reaction between H2O and holes. Both serve as reactive species on the dissociation of the weak B-N bond in an aqueous medium, to produce hydrogen under near-infrared excitation, resulting in enhanced photocatalytic activities. The photocatalyst of NaGdF4:Yb3+/Er3+@NaGdF4@Cu2O (UCNPs@Cu2O) suffered no loss of efficacy after several cycles. This work sheds light on the rational design of near-infrared-activated photocatalysts, and can be used as a proof-of-concept for on-board hydrogen generation from ammonia borane under near-infrared illumination, with the aim of green energy suppliers.

Atomically ordered Rh2P catalysts anchored within hollow mesoporous carbon for efficient hydrogen production

Atomically ordered Rh₂P nanoclusters encapsulated within a high-surface-area hollow mesoporous carbon nanoreactor are catalytically active for hydrogen production via the electrocatalytic hydrogen evolution reaction and the room-temperature dehydrogenation of ammonia borane.

MOF-Directed Construction of Cu-Carbon and Cu@N-Doped Carbon as Superior Supports of Metal Nanoparticles toward Efficient Hydrogen Generation

The modulation of electronic behavior of metal-based catalysts is vital to optimize their catalytic performance. Herein, metal-organic frameworks (MOFs) are pyrolyzed to afford a series of different-structured Cu-carbon composites and Cu@N-doped carbon composites. Then a series of CO-resistant catalysts, namely, Co or Ni nanoparticles supported by the Cu-based composites, are synthesized for the hydrogen generation from aqueous NH3BH3. Their catalytic activities are boosted under light irradiation and regulated by the compositions and the fine structures of doped N species with pyridine, pyrrole, and graphitic configurations in the composite supports. Particularly, the optimized Co-based catalyst with the highest graphitic N content exhibits a high activity, achieving a total turnover frequency (TOF) value of 210 min-1, which is higher than all the reported unprecious catalysts. Further investigations verify that the light-driven synergistic electron effect of plasmonic Cu-based composites and Co nanoparticles accounts for the high-performance hydrogen generation.

The Hydrogen-Storage Challenge: Nanoparticles for Metal-Catalyzed Ammonia Borane Dehydrogenation

Dihydrogen is one of the sustainable energy vectors envisioned for the future. However, the rapidly reversible and secure storage of large quantities of hydrogen is still a technological and scientific challenge. In this context, this review proposes a recent state-of-the-art on H₂ production capacities from the dehydrogenation reaction of ammonia borane (and selected related amine-boranes) as a safer solid source of H₂ by hydrolysis (or solvolysis), catalyzed by nanoparticle-based systems. The review groups the results according to the transition metals constituting the catalyst with a mention to their current cost and availability. This includes the noble metals Rh, Pd, Pt, Ru, Ag, as well as cheaper Co, Ni, Cu, and Fe. For each element, the monometallic and polymetallic structures are presented and the performances are described in terms of turnover frequency and recyclability. The structure-property links are highlighted whenever possible. It appears from all these works that the mastery of the preparation of catalysts remains a crucial point both in terms of process, and control and understanding of the electronic structures of the elaborated nanomaterials. A particular effort of the scientific community remains to be made in this multidisciplinary field with major societal stakes.

Demonstration of Controlled Hydrogen Release Using Rh@GQDs during Hydrolysis of NH3BH3

Achieving the controlled release of H₂ through an effective approach still faces many challenges. Herein, high-quality graphene quantum dots (GQDs) are synthesized from a new precursor, 1,2,4-trihydroxy benzene, and a multifunctional platform of Rh@GQDs is further developed for the controlled H₂ evolution upon the hydrolysis of NH₃BH₃ (AB). More importantly, the designing concepts of multistep and stepless speed controls have been introduced in the domains of both H₂ evolution for the first time. Through a novel designing protocol, the rate of H₂ evolution can be freely regulated and constantly varied on demand by means of chelation between Zn²⁺ and ethylene diamine tetraacetic acid (EDTA). The density functional theory calculation indicates that Zn²⁺ has the priority to be adsorbed onto Rh(100) due to its larger adsorption energy (107.98 kcal·mol^-1) than that of AB (36.36 kcal·mol^-1). A controlling mechanism is presented such that Zn²⁺ will cover the active sites of the nanocatalyst to prevent the H₂ evolution, and EDTA can chelate Zn²⁺ to reactivate the nanocatalyst for the production of H₂, greatly facilitating use of this strategy in other catalytic reactions. Moreover, it is demonstrated that the protocol is equally valid for diverse hydrogen storage materials. Therefore, this work not only establishes whole new concepts for the controlled production of H₂ but also explains their mechanism, thus remarkably advancing the utilization of H₂ energy and significantly enlightening the controlled process of catalysis.

Facile preparation of Cu-Fe oxide nanoplates for ammonia borane decomposition and tandem nitroarene hydrogenation

A facile substrate involved strategy was used to prepare Cu-Fe LDO (layered double oxide) nanoplates. The material exhibited good-efficiency for decomposition of ammonia borane (AB) in alkaline methanol solution. Significantly, the material also demonstrated excellent catalytic performance in the reduction of various nitroarenes by coupling with AB hydrolysis in a one pot tandem reaction, and gave excellent yields of the corresponding amine products.

Synthesis and Dehydrogenation of Organic Salts of a Five-Membered B/N Anionic Chain, a Novel Ionic Liquid

We have synthesized the tetrabutylammonium ([Bu₄ N]⁺ ), tetraethylammonium ([Et₄ N]⁺ ), guanidinium ([C(NH₂ )₃ ]⁺ ), and methylguanidinium ([C(N₃ H₅ CH₃ )]⁺ ) salts of the [BH₃ (NH₂ BH₂ )₂ H]^- anion, a five-membered B/N anionic chain, in high yields by the metathesis reactions of Na[BH₃ (NH₂ BH₂ )₂ H] with the corresponding halides and characterized them by NMR (¹¹ B, ¹¹ B{¹ H}, ¹ H, ¹ H{¹¹ B}, ¹³ C), IR, elemental analysis, TGA-DSC, and TGA-MS. These complexes behave like ionic liquids (ILs), in which the melting point of the [Bu₄ N][BH₃ (NH₂ BH₂ )₂ H] is the lowest (-51 °C). The dehydrogenation of these ILs have been studied through the thermal decomposition and catalytic hydrolysis in aqueous solution using the noble or non-noble metals or their salts as catalysts, and the results indicate that these ILs of five-membered B/N anionic chain are promising hydrogen storage materials.