Tungsten(VI) oxide supported rhodium(0) nanoparticles; highly efficient catalyst for H2 production from dimethylamine borane

It reports the preparation and characterization of tungsten(VI) oxide supported rhodium(0) nanoparticles (Rh⁰/WO₃ NPs) being used as catalysts in releasing H₂ from dimethylamine borane (DMAB). The reducible nature of WO₃ plays a significant role in the catalytic efficiency of rhodium(0) nanoparticles in the dehydrogenation of DMAB. The Rh⁰/WO₃ NPs were in-situ generated from the reduction of Rh²⁺ ions on the surface of WO₃ during the catalytic dehydrogenation of dimethylamine borane in toluene and isolated from the reaction solution after the dehydrogenation to be characterized by using SEM, TEM, XPS, ATR-IR and XRD. The results reveal the formation of Rh⁰ NPs with a mean particle size of 1.92 ± 0.34 nm dispersed on the surface of tungsten(VI) oxide. Rh⁰/WO₃ NPs are found to be very active catalyst releasing 1.0 equiv. H₂ per mole of dimethylamine borane under ambient conditions. Among the various WO₃ supported Rh⁰ NPs with different metal loadings, the sample with 0.1% wt. Rh provide the record catalytic activity (TOF = 2816 h^?1) which is one of the highest value ever reported for rhodium-based catalysts in H₂ generation from DMAB at 60.0 ± 0.5 °C. Rh⁰/WO₃ NPs were also reusable catalyst in dehydrogenation of DMAB retaining 55% of their initial catalytic activity in the 3rd run of the dehydrogenation reaction. Control experiments were performed at various catalyst concentrations and temperatures to investigate the kinetics of dehydrogenation and to calculate the activation parameters for the reaction.     

Carbon-supported small Rh nanoparticles prepared with sodium citrate: Toward high catalytic activity for hydrogen evolution from ammonia borane hydrolysis

Hydrogen generation from the hydrolysis of ammonia borane (AB) over heterogeneous catalysts is essential for practical applications. Herein, efficient hydrogen evolution from AB hydrolysis over the carbon-supported Rh nanoparticles synthesized with sodium citrate (Rh/C-SC) was achieved at 25 °C. The turnover frequency value of Rh/C-SC was 336 mol H₂ (mol_Rh min)^?1, whereas that of Rh/C catalyst only yielded a value of 134 mol H₂ (mol_Rh min)^?1. The improvement of the catalytic performance of Rh/C-SC catalyst could be attributed to the small Rh particles with highly active surface areas, which were prepared by using sodium citrate as the stabilizing agent. This result indicates that sodium citrate can be applied as a useful stabilizing agent for synthesizing active metal nanoparticles, thus highly promoting the practical application of AB system for fuel cells.     

Hydrogen evolution from hydrolysis of ammonia borane catalyzed by Rh/g-C3N4 under mild conditions

Developing effective catalysts for hydrogen evolution from hydrolysis of ammonia borane (AB) is of great significance considering the useful applications of hydrogen. Herein, graphitic carbon nitride (g-C₃N₄) prepared through the simply pyrolysis of urea was employed as a support for Rh nanoparticles (NPs) stabilization. The in-situ generated Rh NPs supported on g-C₃N₄ with an average size of 3.1 nm were investigated as catalysts for hydrogen generation from the hydrolysis of AB under mild conditions. The Rh/g-C₃N₄ catalyst exhibits a high turnover frequency of 969 mol H₂· (min·mol_Rh)^?1 and a low activation energy of 24.2 kJ/mol. The results of the kinetic studies show that the catalytic hydrolysis of AB over the Rh/g-C₃N₄ catalyst is a zero-order reaction with the AB concentration and a first-order reaction with the Rh concentration. This work demonstrates that g-C₃N₄ is a useful support to design and synthesis of effective Rh-based catalyst for hydrogen-based applications.     

Transition metal nanoparticle catalysts in releasing hydrogen from the methanolysis of ammonia borane

Ammonia borane (H₃N·BH₃, AB) is one of the promising hydrogen storage materials due to high hydrogen storage capacity (19.6% wt), high stability in solid state as well as in solution and nontoxicity. The methanolysis of AB is an alternative way of releasing H₂ due to many advantages over the hydrolysis such as having high stability against self releasing hydrogen gas. Here we review the reports on using various noble or non-noble metal(0) catalysts for H₂ release from the methanolysis of AB. Ni(0), Pd(0), and Ru(0) nanoparticles (NPs), stabilized as colloidal dispersion in methanol, are highly active and long lived catalysts in the methanolysis of AB. The catalytic activity, lifetime and reusability of transition metal(0) NPs show significant improvement when supported on the surface of solid materials. The supported cobalt, nickel, copper, palladium, and ruthenium based catalysts are quite active in H₂ release from the methanolysis of AB. Rh(0) NPs are highly active catalysts in releasing H₂ from the methanolysis of AB when confined within the void spaces of zeolite or supported on oxide nanopowders such as nanosilica, nanohydroxyapatite, nanoalumina or nanoceria. The oxide supported Rh(0) NPs can provide high activity with turnover frequency values as high as 218 min⁻¹ and long lifetime with total turnover values up to 26,000 in generation of H₂ from the methanolysis of AB at 25 °C. When deposited on carbon the bimetallic AgPd alloy nanoparticles have the highest activity in releasing H₂ through the methanolysis of AB.     

The doped Co on Rh/Ni@Ni–N–C that weakened the catalytic performance for ammonia borane hydrolysis

Alloy catalyst has been widely studied and used for hydrolytic dehydrogenation of ammonia borane (NH₃BH₃, AB) with excellent catalytic performance due to the synergistic effect of bimetal. Herein, a series of Rh_1-xCo_x/Ni@Ni–N–C catalysts were prepared by an impregnation reduction method. The optimized Rh_0.75Co_0.25/Ni@Ni–N–C catalyst exhibited good catalytic performance with turnover frequency of 223.08 mol_H2 mol_cat^?1 min^?1 at 303 K, but decreased the catalytic performance compared with Rh/Ni@Ni–N–C. According to the XPS and Raman analysis, the RhCo alloy nanoparticles could be loaded at the defect position of Ni@Ni–N–C, and the Co nanoparticles occupied the intercalation between Rh and the defective site of the carrier, which could weaken the catalytic activity of AB hydrolysis. Based on the above research, we proposed the catalytic mechanism of the activation of the RhCo–H species. This work provides a new strategy for designing alloy-supported nano-catalysts.     

Hydrogen generation by hydrolysis of ammonia borane with a nanoporous cobalt-tungsten-boron-phosphorus catalyst supported on Ni foam

In this study, quaternary cobalt-tungsten-boron-phosphorus porous particles supported on Ni foam (Co-W-B-P/Ni), which are prepared through ultrasonification-assisted electroless deposition route, have been investigated as the catalyst for hydrogen generation (HG) from hydrolysis of ammonia borane (NH₃BH₃, AB). Compared with Ni-supported binary Co-B and ternary Co-W-B catalysts, the as-synthesized Co-W-B-P/Ni shows a higher HG rate. To optimize the preparation parameters, the molar ratio of NaBH₄/NaH₂PO₂·H₂O (B/P) and the concentration of Na₂WO₄·2H₂O (W) have been investigated and the catalyst prepared with B/P value of 1.5 and W concentration of 5 g L⁻¹ shows the highest activity. The results of kinetic studies show that the catalytic hydrolysis of AB is first order with respect to the catalyst and AB concentrations. By using the quaternary catalyst with a concentration of 0.5 wt % AB, a HG rate of 4.0 L min⁻¹ g⁻¹ is achieved at 30 °C. Moreover, the apparent activation energy for the quaternary catalyst is determined to be 29.0 kJ mol⁻¹, which is comparable to that of noble metal-based catalysts. These results indicate that the Co-W-B-P/Ni is a promising low-cost catalyst for on-board hydrogen generation from hydrolysis of borohydride.     

Manganese oxide octahedral molecular sieves stabilized Rh nanoparticles for the hydrogen production from the ethylenediamine-bisborane hydrolysis

Ethylenediamine-bisborane (C₂H₁₄B₂N₂, BH₃NH₂CH₂CH₂NH₂BH₃, EDB), an important carbon derivative of ammonia-borane (AB), has come to the fore in recent years due to some disadvantages that limit the practical use of AB for the applications of hydrogen storage. EDB is a very promising chemical hydrogen storage material in the solid crystal form at room temperature, with a hydrogen content of 16.3% by weight, which decomposes rapidly at temperatures above 363 K. Despite all these superior features, studies on catalytic systems that catalyze the hydrogen production from the EDB are very few. In the present study, we report the synthesis, characterization, and application of manganese oxide octahedral molecular sieves (OMS-2) stabilized Rh nanoparticles (Rh@OMS-2) as highly efficient and reusable catalysts for the hydrogen production from the hydrolysis of EDB. The results of characterization using P-XRD, XPS, FT-IR, SEM, SEM-elemental mapping, TEM, HR-TEM, and ICP-OES disclose that Rh (0) nanoparticles were well spread on the surface of OMS-2 nanorods. Rh@OMS-2 showed a record catalytic activity in EDB hydrolysis with an initial turn-over frequency of 102.95 min^?1 (6177 h^?1) at 25 ± 0.1 °C, the highest value ever reported for the hydrolysis of EDB. In addition, the fact that the Rh@OMS-2 catalyst kept its initial activity at the end of the 7th cycle in the hydrolysis of EDB showed that the Rh@OMS-2 was reusable and stable heterogeneous catalyst in this catalytic transformation.     

Oxygen vacancy-engaged interfacial charge transfer modulation for upgrade Rh-catalyzed hydrogen and oxygen productions

Developing efficient modulation strategies to upgrade the catalytic activity and reusability of Rh-catalyzed hydrogen evolution from ammonia borane (AB) hydrolysis are definitely profitable but remains a grand challenge. Here, we develop a stepwise activation strategy to produce highly active and reusable Rh/CoFe₂O₄-SB-H₂ with abundant oxygen vacancies and strong electronic metal-support interaction through stepwise reduction of Rh/CoFe₂O₄ precursor using sodium borohydride and H₂ as the reducing agents. Under ultrasonic irradiation, Rh/CoFe₂O₄-SB-H₂ with an ultralow Rh loading of 0.20 wt% can be utilized as an excellent catalyst for hydrogen production from room-temperature AB hydrolysis with a high turnover frequency (TOF) of 1894 min⁻¹. The TOF value could be further promoted to 15,570 min⁻¹ in the alkaline ultrasonic environment. The catalyst has a superior reusability with 75% maintaining activity of initial one in the 10^th cycle. The strong electronic metal-support interaction, rich oxygen vacancies and ultrasound irradiation promote the oxidative cleavage of the O–H bonds in attracted H₂O and thus account for high performance toward hydrogen production from AB. This catalyst can also be utilized as an active catalyst for oxygen generation from H₂O₂ decomposition. The developed strategies can be applied to upgrade the performance of other reducible metal oxides supported metal catalysts toward catalytic applications.     

Methanolysis of ammonia borane catalyzed by magnetically isolable RHODIUM(0) nanoparticles

This article reports the preparation and employment of rhodium (0) nanoparticles (Rh⁰NPs) on the surface of magnetite nanospheres, denoted as Rh⁰@Fe₃O₄, as magnetically isolable nanocatalyst in the methanolysis of ammonia borane (MAB). The monodispersed Fe₃O₄ nanospheres are fabricated by a simple technique and used as nanosupport for Rh⁰NPs which are well stabilized and homogeneously distributed on the surface of nanospheres with a mean particle size of 2.8 ± 0.5 nm. The as-synthesized Rh⁰@Fe₃O₄ has a remarkable TOF value of 184 min⁻¹ in the MAB to produce H₂ gas in RT. Most of all, Rh⁰@Fe₃O₄ nanocatalyst can be reused, evolving 3.0 mol of H₂ gas for a mole of AB, keeping 100% of its initial activity even in the fourth reuse of MAB at 25 °C. Recovery of the Rh⁰@Fe₃O₄ nanocatalyst can be accomplished by simply approaching an external magnet, which eliminates many laborious catalyst removal steps in catalytic reactions. Reported are the outcomes of kinetic investigation, done by altering the concentration of substrate and catalyst together with temperature. Kinetic studies reveal that the catalytic MAB shows dependence on the concentration of reactants and temperature.     

Group 4 oxides supported Rhodium(0) catalysts in hydrolytic dehydrogenation of ammonia borane

Rh³⁺ ions are first impregnated on Group 4 metal oxides (TiO₂, ZrO₂, HfO₂) in aqueous solution and, then reduced with aqueous solution of NaBH₄ to form rhodium(0) nanoparticles (NPs) on the oxide surface. The analyses reveal that Rh(0) NPs are highly dispersed on the surface of TiO₂, ZrO₂, HfO₂. Rh⁰/MO₂ (M: Ti, Zr, Hf) NPs have high activity and reusability in releasing H₂ from the hydrolysis of ammonia borane with an initial turnover frequency of 643, 198, and 188 min⁻¹, respectively, at 25.0 ± 0.1 °C. The reusability of Rh⁰/ZrO₂ and Rh⁰/HfO₂ catalysts is higher than that of the Rh⁰/TiO₂ catalyst.     

Amino-group and space-confinement assisted synthesis of small and well-defined Rh nanoparticles as efficient catalysts toward ammonia borane hydrolysis

Hydrogen evolution from ammonia borane (AB) hydrolysis is of great importance considering the ever-increasing demand for green and sustainable energy. However, the development of a facile and efficient strategy to construct high-performance catalysts remains a grand challenge. Herein, we report an amino-group and space-confinement assisted strategy to fabricate Rh nanoparticles (NPs) using amino-functionalized metal-organic-frameworks (UiO-66-NH₂) as a NP matrix (Rh/UiO-66-NH₂). Owing to the coordination effect of amino-group and space-confinement of UiO-66-NH₂, small and well-distributed Rh NPs with a diameter of 3.38 nm are successfully achieved, which can be served as efficient catalysts for AB hydrolysis at room temperature. The maximum turnover frequency of 876.7 min^?1 is obtained by using the Rh/UiO-66-NH₂ with an optimal Rh loading of 4.38 wt% and AB concentration of 0.2 M at 25 °C, outperforming most of the previously developed Rh-based catalysts. The catalyst is also stable in repetitive cycles for five times. The high performance of this catalyst must be ascribed to the structural properties of UiO-66-NH₂, which enable the formation of small and well-dispersed Rh NPs with abundant accessible active sites. This study provides a simple and efficient method to significantly enhance the catalytic performance of Rh for AB hydrolysis.     

Solvent-free synthesis of Rh/meso-Al2O3 via mechanochemistry for hydrolytic dehydrogenation of ammonia borane

An effective strategy synthesis of Rh/meso-Al₂O₃ catalysts was demonstrated by mechanochemistry for hydrolytic dehydrogenation of ammonia borane (AB). These catalysts are characterized systematically by N₂ adsorption-desorption isotherms, X-ray diffraction (XRD), X-ray photoelectron spectrometry (XPS), scanning electron microscope (SEM), and transmission electron microscope (TEM). The results show that the turnover frequency (TOF) and activation energy (E_a) are 246.8 mol_H2·mol_Rh^?1·min^?1 and 47.9 kJ mol^?1 for hydrolytic dehydrogenation of at 298 K catalyzed by Rh/Al₂O₃-CTAB-400, obviously higher than those previously reported catalysts. Furthermore, catalyst Rh/Al₂O₃-CTAB-400 can be recycled by simple centrifugal separation and the catalytic activity is still well maintained after five cycles. In addition, a plausible mechanism for hydrolytic dehydrogenation of AB has also been proposed. This mechanochemical synthesis method exhibits great application prospects for the preparation of heterogeneous catalysts.     

High activity of Pd-WO3/C catalyst as anodic catalyst for direct formic acid fuel cell

Pd nanoparticles supported on the WO₃/C hybrid are prepared by a two-step procedure and the catalysts are studied for the electrooxidation of formic acid. For the purpose of comparison, phosphotungstic acid (PWA) and sodium tungstate are used as the precursor of WO₃. Both the Pd-WO₃/C catalysts have much higher catalytic activity for the electrooxidation of formic acid than the Pd/C catalyst. The Pd-WO₃/C catalyst prepared from PWA shows the best catalytic activity and stability for formic acid oxidation; it also shows the maximum power density of approximately 7.6 mW cm⁻² when tested with a small single passive fuel cell. The increase of electrocatalytic activity and stability is ascribed to the interaction between the Pd and WO₃, which promotes the oxidation of formic acid in the direct pathway. The precursors used for the preparation of the WO₃/C hybrid support have a great effect on the performance of the Pd-WO₃/C catalyst. The WO₃/C hybrid support prepared from PWA is beneficial to the dispersion of Pd nanoparticles, and the catalyst has potential application for direct formic acid fuel cell.     

Smart construction of oxidized-Ti3C2TX stabilized Rh nanoparticles for remarkable improving the catalytic performance for ammonia borane hydrolysis

Supported Rh nanoparticle (NP) catalysts have been widespread investigated for hydrogen production from ammonia borane (AB) hydrolysis. However, it is still challenging to develop an efficient strategy to improve the catalytic performances of supported Rh NP catalysts considering the high-cost and limited reserve of Rh. To overcome this limitation, we propose a facile but effective method to significantly improve the catalytic performance of Rh NPs by using oxidized-Ti₃C₂T_x (o-Ti₃C₂T_x) as a NP support. The systematic investigation results suggest that well distributed and ultrasmall Rh NPs with a diameter of 2.60 nm are successfully loaded on the o-Ti₃C₂T_x surface, which can be used as excellent catalysts for hydrogen release from AB hydrolysis. The corresponding turnover frequency (TOF) of 2021 min⁻¹ and activation energy of 18.7 kJ/mol are achieved, which are superior to that of Rh NPs supported on a fresh Ti₃C₂T_x support and most of previous reported Rh NP catalysts. Additionally, the reusability test shows that Rh/o-Ti₃C₂T_x can maintain 53% of the initial catalytic activity after the fifth run. This study opens a new avenue to adjust the catalytic activity of metal NP catalysts for use in field of catalytic applications.     

Structure-dependent activity and stability of Al2O3 supported Rh catalysts for the steam reforming of n-dodecane

Steam reforming of liquid hydrocarbon fuels is an appealing way for the production of hydrogen. In this work, the Rh/Al₂O₃ catalysts with nanorod (NR), nanofiber (NF) and sponge-shaped (SP) alumina supports were successfully designed for the steam reforming of n-dodecane as a surrogate compound for diesel/jet fuels. The catalysts before and after reaction were well characterized by using ICP, XRD, N₂ adsorption, TEM, HAADF-STEM, H₂-TPR, CO chemisorption, NH₃-TPD, CO₂-TPD, XPS, Al²⁷ NMR and TG. The results confirmed that the dispersion and surface structure of Rh species is quite dependent on the enclosed various morphologies. Rh/Al₂O₃-NR possesses highly dispersed, uniform and accessible Rh particles with the highest percentage of surface electron deficient Rh⁰ active species, which due to the unique properties of Al₂O₃ nanorod including high crystallinity, relatively large alumina particle size, thermal stability, and large pore volume and size. As a consequent, Rh/Al₂O₃-NR catalyst exhibited superior catalytic activity towards steam reforming reactions and hydrogen production rate over other two catalysts. Especially, Rh/Al₂O₃-NR catalyst showed the highest hydrogen production rate of 87,600 mmol g_fuel^?1 g_Rh^?1min^?1 among any Rh-based catalysts and other noble metal-based catalysts to date. After long-term reaction, a significant deactivation occurred on Rh/Al₂O₃–NF and Rh/Al₂O₃-SP catalysts, due to aggregation and sintering of Rh metal particles, coke deposition and poor hydrothermal stability of nanofibrous structure. In contrast, the Rh/Al₂O₃-NR catalyst shows excellent reforming stability with negligible coke formation. No significantly sintering and aggregation of the Rh particles is observed after long-term reaction. Such great catalyst stability can be explained by the role of hydrothermal stable nanorod alumina support, which not only provides a unique environment for the stabilization of uniform and small-size Rh particles but also affords strong surface basic sites.     

Facile construction of composition-tuned ruthenium-nickel nanoparticles on g-C3N4 for enhanced hydrolysis of ammonia borane without base additives

Developing high-efficiency and low-cost catalysts for hydrogen evolution from hydrolysis of ammonia borane (AB) is significant and critical for the exploitation and utilization of hydrogen energy. Herein, the in-situ fabrication of well-dispersed and small bimetallic RuNi alloy nanoparticles (NPs) with tuned compositions and concomitant hydrolysis of AB are successfully achieved by using graphitic carbon nitride (g-C₃N₄) as a NP support without additional stabilizing ligands. The optimized Ru₁Ni_7.5/g-C₃N₄ catalyst exhibits an excellent catalytic activity with a high turnover frequency of 901 min^?1 and an activation energy of 28.46 kJ mol^?1 without any base additives, overtaking the activities of many previously reported catalysts for AB hydrolysis. The kinetic studies indicate that the AB hydrolysis over Ru₁Ni_7.5/g-C₃N₄ is first-order and zero-order reactions with respect to the catalyst and AB concentrations, respectively. Ru₁Ni_7.5/g-C₃N₄ has a good recyclability with 46% of the initial catalytic activity retained even after five runs. The high performance of Ru₁Ni_7.5/g-C₃N₄ should be assigned to the small-sized alloy NPs with abundant accessible active sites and the synergistic effect between the composition-tuned Ru–Ni bimetals. This work highlights a potentially powerful and simple strategy for preparing highly active bimetallic alloy catalysts for AB hydrolysis to generate hydrogen.     

Improved methanol electro-oxidation reaction on PdRh-PVP/C electrodes

Here we report on the organometallic synthesis of polyvinylpyrrolidone (PVP)-stabilized palladium-rhodium nanostructures that display high electrochemical properties when used as carbon-supported electrodes (Pd_xRh_1-x-PVP/C) for methanol oxidation reaction (MOR). These nanostructures were synthesized by hydrogenation of the tris(dibenzylideneacetone)dipalladium(0) (Pd₂(dba)₃) and tris(allyl) rhodium (Rh(η³-C₃H₅)₃) complexes, in tetrahydrofuran (THF) under mild reaction conditions (room temperature and 3 bar H₂) and in the presence of PVP as stabilizer. The influence of methanol concentration (0.5, 1.0 and 2.0 M) as well as different scan rates (5–100 mV s^?1) was evaluated to determine changes in the stability and catalytic activity. The organometallic approach and the use of PVP for the preparation of PdRh electrode materials promoted the formation of highly dispersed nanostructures, that led to a remarkably enhanced methanol electro-oxidation in alkaline medium. This high catalytic behavior can reasonably arise from a synergistic effect between Pd and Rh metals as, under the applied conditions, Rh is expected to enhance the Pd ability to oxidize methanol to CO₂ (oxophilic character) as well as the catalyst stability. From all the evaluated electrode materials, Pd₈Rh₂-PVP/C electrode showed the highest mass activity at high methanol concentration (2.0 M) and low scan rate (10 mV s^?1). This catalyst showed a performance up to 26 times higher than that of Pd-PVP/C and interestingly an electroactivity superior to that of previously reported PdRh catalysts.     

Noble-metal-free Co@Co2P/N-doped carbon nanotube polyhedron as an efficient catalyst for hydrogen generation from ammonia borane

Developing an efficient catalyst for hydrogen (H₂) generation from hydrolysis of ammonia borane (AB) to significantly improve the activity for the hydrogen generation from AB is important for its practical application. Herein, we report a novel hybrid nanostructure composed of uniformly dispersed Co@Co₂P core-shell nanoparticles (NPs) embedded in N-doped carbon nanotube polyhedron (Co@Co₂P/N–CNP) through a carbonization-phosphidation strategy derived from ZIF-67. Benefiting from the electronic effect of P doping, high dispersibility and strong interfacial interaction between Co@Co₂P and N-CNTs, the Co@Co₂P/N–CNP catalyst exhibits excellent catalytic performance towards the hydrolysis of AB for hydrogen generation, affording a high TOF value of 18.4 mol H₂ mol metal^?1 min^?1 at the first cycle. This work provides a promising lead for the design of efficient heterogeneous catalysts towards convenient H₂ generation from hydrogen-rich substrates in the close future.     

Water soluble nickel(0) and cobalt(0) nanoclusters stabilized by poly(4-styrenesulfonic acid-co-maleic acid): Highly active, durable and cost effective catalysts in hydrogen generation from the hydrolysis of ammonia borane

This paper reports the in-situ generation and catalytic activity of nickel(0) and cobalt(0) nanoclusters stabilized by poly(4-styrene sulfonic acid-co-maleic acid), PSSA-co-MA, in the hydrolysis of ammonia borane (AB). PSSA-co-MA stabilized nickel(0) (PSMA-Ni) and cobalt(0) nanoclusters (PSMA-Co) having average particle size of 2.1 ± 0.6 and 5.3 ± 1.6 nm, respectively, were generated by in-situ reduction of nickel(II) chloride or cobalt(II) chloride in an aquoues solution of NaBH₄/H₃NBH₃ in the presence of PSSA-co-MA. The in-situ generated nanoclusters were isolated from the reaction solution and characterized by UV-Vis, TEM, XRD and FT-IR techniques. Compared with the previous catalyst systems, PSMA-Ni and PSMA-Co are found to be highly active catalysts for hydrogen generation from the hydrolysis of AB with the turnover frequency values of 10.1 min⁻¹ for Ni and 25.7 min⁻¹ for Co. They are also very stable during the hydrolysis of AB providing 22450 and 17650 turnovers, respectively. The results of mercury poisoning experiments reveal that PSMA-Ni and PSMA-Co are heterogeneous catalysts in the hydrolysis of AB. Herein, we also report the results of a detailed kinetic study on the hydrogen generation from the hydrolysis of AB catalyzed by PSMA-Ni and PSMA-Co depending on catalyst concentration, substrate concentration, and temperature along with the activation parameters of catalytic hydrolysis of AB calculated from the kinetic data.     

Oxygen vacancies and morphology engineered Co3O4 anchored Ru nanoparticles as efficient catalysts for ammonia borane hydrolysis

Developing efficient but facile strategies to modulate the catalytic activity of Ru deposited on metal oxides is of broad interest but remains challenging. Herein, we report the oxygen vacancies and morphological modulation of vacancy-rich Co₃O₄ stabilized Ru nanoparticles (NPs) (Ru/V_O-Co₃O₄) to boost the catalytic activity and durability for hydrogen production from the hydrolysis of ammonia borane (AB). The well-defined and small-sized Ru NPs and V_O-Co₃O₄ induced morphology transformation via in situ driving V_O-Co₃O₄ to 2D nanosheets with abundant oxygen vacancies or Co²⁺ species considerably promote the catalytic activity and durability toward hydrogen evolution from AB hydrolysis. Specifically, the Ru/V_O-Co₃O₄ pre-catalyst exhibits an excellent catalytic activity with a high turnover frequency of 2114 min^?1 at 298 K. Meanwhile, the catalyst also shows a high durability toward AB hydrolysis with six successive cycles. This work establishes a facile but efficient strategy to construct high-performance catalysts for AB hydrolysis.