Cobalt ferrite supported platinum nanoparticles: Superb catalytic activity and outstanding reusability in hydrogen generation from the hydrolysis of ammonia borane

Ultrafast joule-heating-assisted O, N dual-doping of unfunctionalized carbon enhances Ru nanoparticle-catalyzed hydrogen production

The development of a rapid and convenient strategy to regulate the surface microenvironment of inert carbon supports, along with the physicochemical properties of their supported metal nanoparticles, is essential for enhancing catalytic performance. In this study, we describe a straightforward and efficient solid-state microwave method that utilizes a household microwave oven to achieve the co-doping of oxygen and nitrogen in unfunctionalized carbon black (ONCB) using urea as a nitrogen source. The microwave solid-state treatment of commercial carbon black (CB) with urea not only introduces a significant number of heteroatomic functional groups but also substantially increases the pore size and pore volume of the matrix. These enhancements facilitate the uniform growth and dispersion of ultrafine Ru nanoparticles on the surface of ONCB. Consequently, the Ru/ONCB catalyst provides abundant catalytic active sites and mass transfer channels, thereby improving catalytic performance for hydrogen evolution from ammonia borane hydrolysis (ABH). The turnover frequency of Ru/ONCB for ABH reaches 4529 ± 238 min-1 (determined based on Ru dispersion), surpassing a range of analogues and many previously reported carbon-supported Ru catalysts. This study presents a simple and rapid strategy to regulate the surface microenvironment of unfunctionalized carbon support, thereby enhancing the catalytic performance of its supported metal nanoparticles for catalytic hydrogen generation.

Boron/nitrogen-trapping and regulative electronic states around Ru nanoparticles towards bifunctional hydrogen production

Developing a straightforward and general strategy to regulate the surface microenvironment of a carbon matrix enriched with N/B motifs for efficient atomic utilization and electronic state of metal sites in bifunctional hydrogen production via ammonia-borane hydrolysis (ABH) and water electrolysis is a persistent challenge. Herein, we present a simple, green, and universal approach to fabricate B/N co-doped porous carbons using ammonia-borane (AB) as a triple functional agent, eliminating the need for hazardous and explosive functional agents and complicated procedures. The pyrolysis of AB induces the regulation of the surface microenvironment of the carbon matrix, leading to the formation of abundant surface functional groups, defects, and pore structures. This regulation enhances the efficiency of atom utilization and the electronic state of the active component, resulting in improved bifunctional hydrogen evolution. Among the catalysts, B/N co-doped vulcan carbon (Ru/BNC) with 2.1 wt% Ru loading demonstrates the highest performance in catalytic hydrogen production from ABH, achieving an ultrahigh turnover frequency of 1854 min-1 (depending on the dispersion of Ru). Furthermore, this catalyst shows remarkable electrochemical activity for hydrogen evolution in alkaline water electrolysis with a low overpotential of 31 mV at 10 mA cm-2. The present study provides a simple, green, and universal method to regulate the surface microenvironment of various carbons with B/N modulators, thereby adjusting the atomic utilization and electronic state of active metals for enhanced bifunctional hydrogen evolution.

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.

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.

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.

Ultrafine Pt nanoparticles anchored on core-shell structured zeolite-carbon for efficient catalysis of hydrogen generation

Ammonia borane (AB) is a potential hydrogen storage material with high-efficiency hydrolytic dehydrogenation under a suitable catalyst. Noble metal catalysts have drawn a lot of attention. In this study, a carbon-coated zeolite was obtained by calcination at high temperatures using glucose as a carbon source. Pt nanoparticles were fixed on a core-shell composite support by a simple chemical reduction method. A series of catalysts were prepared with different synthesis parameters. The results show that PSC-2 has excellent catalytic performance for hydrolytic dehydrogenation of AB in alkaline solution at room temperature, and the turnover frequency (TOF) is 593 min-1. The excellent catalytic performance is attributed to the carbon layer on the zeolite surface which inhibits the aggregation or deformation of metals in the catalytic reaction. The metal-support interaction activates the water and accelerates the rate-limiting step of hydrolysis. The activation energy (E a = 44 kJ mol-1) was calculated based on the reaction temperature. In addition, the kinetics of AB hydrolysis was studied, and the effects of catalyst concentration, AB concentration and NaOH concentration on AB hydrolysis rate were further investigated. The high-efficiency catalyst prepared in this work provides a new strategy for the development of chemical hydrogen production in the field of catalysis.

A review of the catalytic conversion of glycerol to lactic acid in the presence of aqueous base

Lactic acid is a high-value-added chemical with large production, which is used in many industries including the production of pyruvic and acrylic acids. Lactic acid is largely obtained from the oxidation of glycerol, which is a prevalent by-product of biodiesel production. However, the oxidation of glycerol to lactic acid requires harsh reaction conditions such as high temperature and pressure as well as the use of a hefty strong base. In the presence of suitable catalysts, the production of lactic acid from glycerol can be achieved under mild conditions with 1 equivalent base per mole of glycerol. Herein, we review the reports of the catalytic conversion of glycerol to lactic acid in an aqueous alkaline medium considering the reaction conditions, catalytic activity for glycerol conversion and selectivity for lactic acid. We start first with the reports on the use of homogeneous catalysts that have high catalytic activity but miserable recovery. Next, we discuss the employment of colloidal metal(0) nanoparticles as catalysts in glycerol oxidation. The papers on the use of supported metal(0) nanoparticles are reviewed according to the type of support. We then review the polymetallic and metal/metal oxide nanocatalysts used for the conversion of glycerol to lactic acid in an alkaline medium. The catalysts tested for glycerol conversion to lactic acid without any additional bases are also discussed to emphasize the importance of a strong base for catalytic performance. The proposed mechanisms of glycerol oxidation to lactic acid in the presence or absence of catalysts as well as for the formation of side products are discussed. The available experimental kinetics data are shown to fit the mechanism with the formation of glyceraldehyde from glycerol alkoxide as the rate-determining step.

Maximizing hydrogen production by AB hydrolysis with Pt@cobalt oxide/N, O-rich carbon and alkaline ultrasonic irradiation

Non-precious metal oxide/carbon hybrid has been identified as a promising platform to stabilized precious metals for ammonia borane (AB) hydrolysis to produce hydrogen, whereas their facile and environmental-friendly synthesis remains...

Rhodium nanoparticles confined in titania nanotubes for efficient Hydrogen evolution from Ammonia Borane

Designing efficient catalysts for hydrogen evolution from hydrolysis of ammonia borane (AB) have attracted considerable attention. Rhodium (Rh) based catalysts with rational design present remarkable catalytic performance for the reaction. Herein, we report the confined Rh@TiO₂ catalysts synthesized by atomic layer deposition combining with the sacrificial template approach, in which the Rh nanoparticles are uniformly confined on the inner surface of the porous titania nanotubes. The optimized catalysts show high catalytic activity with a turnover frequency value of 334.1 mol_H2·mol_Rh^-1·min^-1 and better durability. Mechanistic investigation demonstrates that the cleavage of OH bands in water should be the rate determining step, and the appropriate concentration of NaOH can further enhance the hydrogen evolution activity. The catalysts can also achieve the hydrogenation of various organic substrates using AB as the hydrogen source. In addition, our present strategy is general and can be extended to the synthesis of other confined catalysts for various catalytic reactions.

Magnetically Isolable Pt0/Co3O4 Nanocatalysts: Outstanding Catalytic Activity and High Reusability in Hydrolytic Dehydrogenation of Ammonia Borane

The development of a new platinum nanocatalyst to maximize the catalytic efficiency of the precious noble metal catalyst in releasing hydrogen from ammonia borane (AB) is reported. Platinum(0) nanoparticles are impregnated on a reducible cobalt(II,III) oxide surface, forming magnetically isolable Pt⁰/Co₃O₄ nanocatalysts, which have (i) superb catalytic activity providing a record turnover frequency (TOF) of 4366 min^-1 for hydrogen evolution from the hydrolysis of AB at room temperature and (ii) excellent reusability, retaining the complete catalytic activity even after the 10th run of hydrolysis reaction. The outstanding activity and stability of the catalyst can be ascribed to the strong interaction between the platinum(0) nanoparticles and reducible cobalt oxide, which is supported by the results of XPS analysis. Pt⁰/Co₃O₄ exhibits the highest TOF among the reported platinum-nanocatalysts developed for hydrogen generation from the hydrolysis of AB.

A review on platinum(0) nanocatalysts for hydrogen generation from the hydrolysis of ammonia borane

This review reports a survey on the progress in developing highly efficient platinum nanocatalysts for the hydrolytic dehydrogenation of ammonia borane (AB). After a short prelude emphasizing the importance of increasing the atom efficiency of high cost, precious platinum nanoparticles (NPs) which are known to be one of the highest activity catalysts for hydrogen generation from the hydrolysis of AB, this article reviews all the available reports on the use of platinum-based catalysts for this hydrolysis reaction covering (i) early tested platinum catalysts, (ii) platinum(0) NPs supported on oxides, (iii) platinum(0) NPs supported on carbonaceous materials, (iv) supported platinum single-atom catalysts, (v) bimetallic- and (vi) multimetallic-platinum NP nanocatalysts, and (vii) magnetically separable platinum-based catalysts. All the reported results are tabulated along with the important parameters used in the platinum-catalyzed hydrolysis of AB. In the section "Concluding remarks and a look towards the future" a discussion is devoted to the approaches for making high cost, precious platinum catalysts as efficient as possible, ultimately lowering the cost, including the suggestions for the future research in this field.