Metal-Support Synergistic Catalysis in Pt/MoO3-x Nanorods toward Ammonia Borane Hydrolysis with Efficient Hydrogen Generation

Anchoring Platinum Nanoparticles onto Oxygen Vacancy-Modified Mixed Metal Oxides for Selective Oxidation Reaction of Aromatic Alcohols

Directed transformation of organic compounds under mild conditions, especially alcohol oxidation, presents great challenges in green chemistry. Herein, we report a platinum nanoparticle catalyst supported on zinc-gallium mixed metal oxides (denoted as Pt/ZnGa-MMOs), which displays superior catalytic activity for the selective oxidation reaction of benzyl alcohol to benzaldehyde (conversion: >99%; selectivity: >99%; reaction rate: 125 mmolbenzyl alcohol gPt-1 h-1). Both experimental studies [X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS), and X-ray absorption fine structure (XAFS)] and DFT calculations reveal the formation of an interfacial structure (Zn2+δ-Ov-Ga3-δ) on the ZnGa-MMOs support. Moreover, in situ Fourier transform infrared (FT-IR) spectroscopic analysis demonstrates that the Pt species acts as an intrinsic active center to promote the oxidation of the carbon-oxygen bond in the benzyl alcohol molecule, with the formation of the benzaldehyde. This work provides an effective strategy for the preparation of heterogeneous catalysts via constructing the support oxygen vacancy to anchor metal sites toward selective oxidation reactions.

Dual Catalytic Activity of Pd-Dispersed MOF for Ammonia-Free Hydrogen Generation from Ammonia Borane and Sodium Borohydride in Aqueous and Methanol Solvents

The development of effective catalysts for hydrogen (H2) generation from chemical hydrides is essential for advancing hydrogen-based energy technologies. Herein, we synthesized a Pd-dispersed CPO-27 catalyst exhibiting exceptional performance for hydrolysis of two boron-based chemical hydrides, i.e., ammonia borane (AB) and sodium borohydride (SB). The catalyst demonstrated activation energies of 22.7 and 18.12 kJ mol-1 for AB and SB hydrolysis respectively, confirming its proficient catalytic activity. To comprehensively understand the factors influencing the production of H2, we systematically investigated the effects of the two hydrides and catalyst concentrations on H2 evolution rates. Additionally, kinetic isotope effect studies were conducted to determine the rate-determining step of hydrolysis reactions. The Pd@MOF catalyst can efficiently capture released ammonia during AB hydrolysis, addressing a major limitation of this process. Notably, the Pd@MOF catalyst demonstrated its catalytic compatibility with methanol solvent too, exploring its applicability in various reaction environments. Overall, our study highlights the capability of the Pd@MOF catalyst toward H2 release from diverse complex hydrides in different solvent systems for H2 generation in clean energy applications.

V-doped activated Ru/Ti2.5V0.5C2 dual-active center accelerate hydrogen production from ammonia borane

Designing and constructing the active center of Ru-based catalysts is the key to efficient hydrolysis of ammonia borane (NH3BH3, AB) for hydrogen production. Herein, V-doped Ru/Ti2.5V0.5C2 dual-active center catalysts were synthesized, showing excellent catalytic ability for AB hydrolysis. The corresponding turnover frequency value was 1072 min-1 at 298 K, and the hydrolysis rate rB of AB was 235 × 103 mL·min-1·gRu-1. X-ray photoelectron spectroscopy results indicated that the interaction between V-doped Ti3C2 and catalytic metal Ru transfers electrons from Ti to Ru, resulting in electron-rich Ru species. According to density functional theory calculations, the activation energy and reaction dissociation energy of the reactants AB and H2O on V-doped catalysts were lower than those of Ru/Ti3C2, thus optimizing the catalytic kinetics of AB hydrolysis. The modification strategy of V-doped Ti3C2 provides a new pathway for the development of high-performance catalysts for AB hydrolysis.

Efficient Hydrogen Generation from Ammonia Borane Hydrolysis on a Tandem Ruthenium-Platinum-Titanium Catalyst

Hydrolysis of ammonia borane (NH3BH3, AB) involves multiple undefined steps and complex adsorption and activation, so single or dual sites are not enough to rapidly achieve the multi-step catalytic processes. Designing multi-site catalysts is necessary to enhance the catalytic performance of AB hydrolysis reactions but revealing the matching reaction mechanisms of AB hydrolysis is a great challenge. In this work, we propose to construct RuPt-Ti multi-site catalysts to clarify the multi-site tandem activation mechanism of AB hydrolysis. Experimental and theoretical studies reveal that the multi-site tandem mode can respectively promote the activation of NH3BH3 and H2O molecules on the Ru and Pt sites as well as facilitate the fast transfer of *H and the desorption of H2 on Ti sites at the same time. RuPt-Ti multi-site catalysts exhibit the highest turnover frequency (TOF) of 1293 min-1 for AB hydrolysis reaction, outperforming the single-site Ru, dual-site RuPt and Ru-Ti catalysts. This study proposes a multi-site tandem concept for accelerating the dehydrogenation of hydrogen storage material, aiming to contribute to the development of cleaner, low-carbon, and high-performance hydrogen production systems.

Regulation of Electronic Structures of the Urchin-Like NiCoP/CoP Nanocatalysts for Fast Hydrogen Evolution

The exploration of stable, efficient, and low-cost catalysts toward ammonia borane hydrolysis is of vital significance for the practical implementation of this hydrogen production technology. Integrating interface engineering and nano-architecture engineering is a favorable strategy to elevate catalytic performance, as it can modify the electronic structure and provide sufficient active sites simultaneously. In this work, urchin-like NiCoP/CoP heterostructures are prepared via a three-step hydrothermal-oxidation-phosphorization synthesis route. It is demonstrated that the original Ni/Co molar ratio and the amount of phosphorus are crucial for adjusting the morphology, enhancing the exposed surface area, facilitating charge transfer, and modulating the adsorption and activation of H2O molecules. Consequently, the optimal Ni1Co2P heterostructure displays remarkable catalytic properties in the hydrolysis of ammonia borane with a turnover frequency (TOF) value of 30.3 molH2 ⋅ min-1 ⋅ molmetal -1, a low apparent activation energy of 25.89 kJ ⋅ mol-1, and good stability. Furthermore, by combining infrared spectroscopy and isotope kinetics experiments, a possible mechanism for the hydrolysis of ammonia borane was proposed.

Visible light-assisted hydrogen generation from ammonia borane over Z-Scheme NiO-CuO heterostructures

The design and fabrication of cheap and high-efficiency catalysts for ammonia borane (AB) hydrolysis for hydrogen production is crucial for its commercial applications. Improvement of the catalytic performance of the catalysts with the assistance of sunlight, a costless resource, is extremely attractive. Herein, we have constructed Z-scheme heterostructured VO-NiO-CuO catalysts with strong interfacial electronic interactions and abundant oxygen vacancies to enhance hydrogen production from NH3BH3 solution under visible light illumination. The as-prepared VO-NiO-CuO catalysts exhibit excellent catalytic activity with a high turnover frequency (TOF) of 35.3 molH2 molcat.-1 min-1 toward AB hydrolysis under visible light. It is demonstrated that excellent catalytic performance is highly related to the effective separation and migration of charge on the catalyst surface. As a result, dual active sites were created, making it easier for various reactants to be adsorbed and activated on the catalyst surface. Furthermore, the density functional theory (DFT) calculations indicate that the adsorption and activation of H2O occurred mainly at the Ni site of VO-NiO-CuO. When the VO-NiO-CuO is irradiated with visible light, the photogenerated electrons assembled on the conduction band were transferred to the O atom through the Ni-O bond, which made the bond length of H2O molecules longer and OH bonds more prone to breaking, thus facilitating AB hydrolysis under illumination. The findings in this work pave the way to design novel and efficient heterostructured catalysts for fast hydrogen release from NH3BH3 under visible light irradiation.

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.

Recent Advances and Perspectives on Supported Catalysts for Heterogeneous Hydrogen Production from Ammonia Borane

Ammonia borane (AB), a liquid hydrogen storage material, has attracted increasing attention for hydrogen utilization because of its high hydrogen content. However, the slow kinetics of AB hydrolysis and the indefinite catalytic mechanism remain significant problems for its large-scale practical application. Thus, the development of efficient AB hydrolysis catalysts and the determination of their catalytic mechanisms are significant and urgent. A summary of the preparation process and structural characteristics of various supported catalysts is presented in this paper, including graphite, metal-organic frameworks (MOFs), metal oxides, carbon nitride (CN), molybdenum carbide (MoC), carbon nanotubes (CNTs), boron nitride (h-BN), zeolites, carbon dots (CDs), and metal carbide and nitride (MXene). In addition, the relationship between the electronic structure and catalytic performance is discussed to ascertain the actual active sites in the catalytic process. The mechanism of AB hydrolysis catalysis is systematically discussed, and possible catalytic paths are summarized to provide theoretical considerations for the designing of efficient AB hydrolysis catalysts. Furthermore, three methods for stimulating AB from dehydrogenation by-products and the design of possible hydrogen product-regeneration systems are summarized. Finally, the remaining challenges and future research directions for the effective development of AB catalysts are discussed.

Modulating the Acidic Properties of Mesoporous Mox-Ni0.8Cu0.2O Nanowires for Enhanced Catalytic Performance toward the Methanolysis of Ammonia Borane for Hydrogen Production

Rational construction of inexpensive, highly efficient, and stable catalysts for ammonia borane (AB) methanolysis is in high demand but still remains a great challenge. In this work, we have successfully fabricated uniform Mo_x-Ni_0.8Cu_0.2O nanowires using a simple hydrothermal method followed by a post-calcination treatment and flexibly modulated the acidity of their surface by changing the amount of Mo introduced into Ni_0.8Cu_0.2O. The Mo_0.1-Ni_0.8Cu_0.2O catalyst displayed strong catalytic activity toward AB methanolysis with an ultrahigh turnover frequency of 46.9 mol_H2 mol_cat.^-1 min^-1, which is even higher than some noble metal catalysts. In this work, an equation regarding the relationship between the quantity of moderated acid sites of catalysts and its corresponding activity toward AB methanolysis was first determined. A plausible mechanism for AB methanolysis catalyzed by Mo_x-Ni_0.8Cu_0.2O was proposed, and the benefits of the introduction of MoO₃ to Ni_0.8Cu_0.2O for enhancing the catalytic performance were also discussed. These findings can form a basis for the rational construction of inexpensive catalysts with robust performance toward AB methanolysis for hydrogen production.

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.