Co–B nanoparticles supported on carbon film synthesized by pulsed laser deposition for hydrolysis of ammonia borane

Thin films of Carbon-supported Co–B nanoparticles were synthesized by using Pulsed Laser Deposition (PLD) and used as catalysts in the hydrolysis of Ammonia Borane (AB) to produce molecular hydrogen. Amorphous Co–B-based catalyst powders, produced by chemical reduction of cobalt salts, were used as target material for nanoparticles-assembled Co–B film catalysts preparation through PLD. Various Ar pressures (10–50 Pa) were used during deposition of carbon films to obtain extremely irregular and porous carbon support with high surface area prior to Co–B film deposition. Surface morphology of the catalyst films was studied using Scanning Electron Microscopy, while structural characterization was carried out using X-Ray diffraction. The hydrogen generation rate attained by carbon-supported Co–B catalyst film is significantly higher as compared to unsupported Co–B film and conventional Co–B powder. Almost complete conversion (95%) of AB was obtained at room temperature by using present film catalyst. Morphological analysis showed that the Co–B nanoparticles produced after the laser ablation process act as active catalytic centers for hydrolysis while the carbon support provides high initial surface area for the Co–B nanoparticles with better dispersion and tolerance against aggregation. The efficient nature of our carbon-supported Co–B film is well supported by the obtained very low activation energy (∼29 kJ (mol)⁻¹) and exceptionally high H₂ generation rate (13.5 L H₂ min⁻¹ (g of Co)⁻¹) by the hydrolysis of AB.     

Monodisperse nickel–palladium alloy nanoparticles supported on reduced graphene oxide as highly efficient catalysts for the hydrolytic dehydrogenation of ammonia borane

Addressed herein is the catalysis of reduced graphene oxide-supported monodisperse NiPd alloy nanoparticles (NPs) (rGO-NiPd) in the hydrolytic dehydrogenation of ammonia borane (AB). This is the first example of the use of NiPd alloy NPs as catalyst in the hydrolytic dehydrogenation of AB. Monodisperse NiPd alloy NPs (3.5 nm) were synthesized by co-reduction of nickel(II) acetate and palladium(II) acetylacetonate in oleylamine (OAm) and borane-tert-butylamine complex (BTB) at 100 °C. The current recipe allowed to control the composition of NiPd alloy NPs and to study the composition-controlled catalysis of rGO-NiPd in the hydrolytic dehydrogenation of AB. Among the all compositions tested, the Ni₃₀Pd₇₀ was the most active one with the turnover frequency of 28.7 min⁻¹. The rGO-Ni₃₀Pd₇₀ were also durable catalysts in the hydrolytic dehydrogenation of AB providing 3650 total turnovers in 35 h and reused at six times without deactivation. The detailed reaction kinetics of hydrolytic dehydrogenation of AB revealed that the reaction proceeds first order with respect to the NiPd concentration and zeroth order with respect to the AB concentration. The apparent activation energy of the catalytic dehydrogenation of AB was also calculated to be E_a^app = 45 ± 2 kJ*mol⁻¹.     

In situ facile synthesis of bimetallic CoNi catalyst supported on graphene for hydrolytic dehydrogenation of amine borane

Well dispersed magnetically recyclable bimetallic Co_xNi_1−x (x = 0, 0.1, 0.3, 0.5, 0.7, 0.9, 1) nanoparticles (NPs) supported on graphene have been synthesized via a facile in situ one-step procedure, using the mixture of sodium borohydride (NaBH₄) and methylamine borane (MeAB) as the reducing agent under ambient condition. These NPs were composition dependent for catalytic hydrolysis of amine boranes. Among all the CoNi/graphene catalysts tested, the Co_0.9Ni_0.1/graphene NPs exhibit the highest catalytic activity toward hydrolysis of AB with the turnover frequency (TOF) value of 16.4 (mol H₂ min⁻¹ (mol catalyst)⁻¹), being higher than that of most reported non-noble metal-based NPs, and even many noble metal-based NPs. Moreover, the activation energy (E_a) value is 13.49 kJ/mol, which is the second lowest value ever reported for catalytic hydrolytic dehydrogenation of ammonia borane, indicating the superior catalytic performance of the as-synthesized Co_0.9Ni_0.1/graphene catalysts. Additionally, Compared with other reducing agents, such as NaBH₄, AB, MeAB, and the mixture of NaBH₄ and AB, the as-synthesized Co_0.9Ni_0.1/graphene catalysts reduced by the mixture of NaBH₄ and MeAB exert the highest catalytic activity. The Co_0.9Ni_0.1 NPs supported on graphene exhibit higher catalytic activity than catalysts with other conventional supports, such as SiO₂, carbon black, and γ-Al₂O₃. Furthermore, the as-synthesized Co_0.9Ni_0.1/graphene NPs show good recyclability and magnetically reusability for the hydrolytic dehydrogenation of amine boranes, which make the practical reusing application of the catalysts more convenient.     

CuO–Ru0.3@Co3O4 nanocomposites act as a tandem catalyst for dehydrogenation of ammonia borane and hydrogenation of nitrobenezene

The development of catalysts with high activity for tandem reaction are all the ways pursued by chemists. Herein, CuO–Ru_0.3@Co₃O₄ has been synthesized and used as efficient tandem catalyst to promote the release of hydrogen from hydrolytic dehydrogenation of ammonia borane (AB) to catalyze the hydrogenation of nitrobenezenes (NBs). The catalyst exhibits the TOF of 29.87 min^?1 and provides the apparent activation energy of 45.2 kJ mol^?1 for the hydrolytic dehydrogenation of AB. Additionally, benefited from the magnetic separation capability, up to 99% of its initial catalytic activity is retained after four catalytic cycles.     

In situ synthesized Fe–Co/C nano-alloys as catalysts for the hydrolysis of ammonia borane

Composite catalysts Fe_0.3Co_0.7-doped carbon aerogel have been in situ synthesized by chemical reduction method and successfully employed in the hydrolysis of NH₃BH₃ (AB) at room temperature. The mass percent of the doped Fe_0.3Co_0.7 alloys can reach to the maximum value of 40 wt%. The prepared catalysts exhibit excellent catalytic activity, especially for the specimen of 40 wt% Fe_0.3Co_0.7/C, which shows high catalytic activity and long durability. Its maximum hydrogen generation rate is as high as 13,695.6 ml min⁻¹ g⁻¹ at 298 K and the activation energy is only 20.83 kJ mol⁻¹. Besides, this catalyst possesses preferable cycling stability at room temperature. The low cost, high catalytic activity and enhanced cycling stability can make it have a bright future in the application field of fuel chemistry.     

Fabrication of highly dispersed palladium/graphene oxide nanocomposites and their catalytic properties for efficient hydrogenation of p-nitrophenol and hydrogen generation

In this report, graphene oxide (GO) nanosheets decorated with ultrafine Pd nanoparticles (Pd NPs) have been successfully fabricated through a reaction between [Pd₂(μ-CO)₂Cl₄]²⁻ and water in the presence of GO nanosheets without any surfactant or other reductant. The as-synthesized small Pd NPs with average diameter of about 4.4 nm were well-dispersed on the surface of GO nanosheets. The Pd/GO nanocomposites show remarkable catalytic activity toward the hydrogenation of p-nitrophenol at room temperature. The kinetic apparent rate constant (k_app) could reach about 34.3 × 10⁻³ s⁻¹. Furthermore, the as-prepared Pd/GO nanocomposites could also be used as an efficient and stable catalyst for hydrogen production from hydrolytic dehydrogenation of ammonia borane (AB). The catalytic activity is much higher than the conventional Pd/C catalysts.     

Synergistic catalysis of MCM-41 immobilized Cu–Ni nanoparticles in hydrolytic dehydrogeneration of ammonia borane

Bimetallic Cu–Ni nanoparticles (NPs) were successfully immobilized in MCM-41 using a simple liquid impregnation-reduction method. All the resulting composites Cu–Ni/MCM-41 catalysts with various contents of Cu–Ni, and in particular Cu_0.2Ni_0.8/MCM-41 sample, outperform the activity of monometallic Cu and Ni counterparts and pure bimetallic Cu_0.2Ni_0.8 NPs in hydrolytic dehydrogeneration of ammonia borane (AB) at room temperature. The Cu_0.2Ni_0.8/MCM-41 catalyst exhibits excellent catalytic activity with a total turnover frequency (TOF) value of 10.7 mol H₂ mol catalyst⁻¹ min⁻¹ and a low activation energy value of 38 kJ mol⁻¹ at room temperature. In addition, Cu_0.2Co_0.8/MCM-41 also exhibits excellent activity with a TOF value as high as 15.0 mol H₂ mol catalyst⁻¹ min⁻¹. This obtained activity represents the highest catalytic active of Cu-based monometallic and bimetallic catalysts up to now toward the hydrolytic dehydrogeneration of ammonia borane (AB). The unprecedented excellent activity has been successfully achieved thanks to the strong bimetallic synergistic effects among the Cu–Ni (or Co) NPs of the composites.     

Hydrogen generation from the hydrolysis of ammonia borane using cobalt-nickel-phosphorus (Co-Ni-P) catalyst supported on Pd-activated TiO2 by electroless deposition

Catalytically active, low-cost, and reusable transition metal catalysts are desired to develop on-demand hydrogen generation system for practical onboard applications. By using electroless deposition method, we have prepared the Pd-activated TiO₂-supported Co-Ni-P ternary alloy catalyst (Co-Ni-P/Pd-TiO₂) that can effectively promote the hydrogen release from ammonia-borane aqueous solution. Co-Ni-P/Pd-TiO₂ catalysts are stable enough to be isolated as solid materials and characterized by XRD, SEM, and EDX. They are isolable, redispersible and reusable as an active catalyst in the hydrolysis of AB. The reported work also includes the full experimental details for the collection of a wealth of kinetic data to determine the activation energy (E_a = 54.9 kJ mol⁻¹) and effects of the amount of catalyst, amount of substrate, and temperature on the rate for the catalytic hydrolysis of AB. Maximum H₂ generation rate of ∼60 mL H₂ min⁻¹ (g catalyst)⁻¹ and ∼400 mL H₂ min⁻¹ (g catalyst)⁻¹ was measured by the hydrolysis of AB at 25 °C and 55 °C, respectively.     

Bamboo fungus-derived magnetic porous carbon encapsulated nickel stabilized Rh nanoparticles as efficient catalysts for hydrolytic dehydrogenation of ammonia borane

Biomass-derived porous carbons are generally used as supports for metal nanoparticle (NP) stabilizations, while the strong hydrophilicity of such materials makes the as-prepared catalysts hard to be isolated after reaction, significantly affecting their potential applications. Herein, magnetic N-functionalized carbon (CN) encapsulated Ni composite (Ni@CN) prepared via pyrolysis of bamboo fungus pre-absorbed with nickel nitrate is exploited as a matrix to synthesize Rh/Ni@CN hybrid, which can be used as a magnetically recoverable catalytic material for hydrolytic dehydrogenation of ammonia borane (AB) to generate hydrogen. The Rh/Ni@CN (Rh loading: 0.84 wt%) exhibits an optimal activity (turnover frequency: 351 min⁻¹) for hydrogen evolution from hydrolytic dehydrogenation of AB. Most importantly, this catalyst can be simply isolated by a magnet and reused at least five times with complete conversion of AB to hydrogen. The strong interaction between the two metals and the small size of Rh NPs are responsible for the improved catalytic activity for hydrolytic dehydrogenation of AB. This work provides an eco-friendly and efficient strategy to fabricate excellent catalysts in catalytic applications.     

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.     

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.     

Alloyed palladium-nickel hollow nanospheres with interatomic charge polarization for improved hydrolytic dehydrogenation of ammonia borane

Hydrolysis reaction of ammonia borane (AB) has been considered as a safe and efficient hydrogen generation method, in which designing cost-effective and high-performance catalysts plays vital role. In this work, we have developed well dispersed palladium-nickel hollow nanospheres (PdNi HNSs) with tunable shell thickness and compositions via a facile galvanic replacement approach. The as-prepared PdNi HNSs show composition-dependent catalysis in the hydrolytic dehydrogenation of AB. The Pd₈₄Ni₁₆/C exhibiting sphere-shaped hollow interiors with average 70 nm particle size and 10 nm thin wall, presents the highest catalytic activity with the turnover frequency of 76.0 (mol H₂ min^?1 (mol Pd)^?1) and the activation energy of 33.5 kJ mol^?1. The superior catalytic effect of PdNi HNSs in enhancing hydrolysis efficiency of AB can be ascribed to two major factors: (1) high active surface areas of the unique hollow structure; (2) enhanced H adsorption attributed to the coupling between Pd and Ni induces polarization charges on Pd catalytic sites, which is indicated by the first-principles calculation and X-ray photoelectron spectroscopy studies. Furthermore, the catalysts exert good long-term recycling stability and catalytic activity for the hydrolytic dehydrogenation of AB. This work represents a strategy may hopefully be extended to synthesize other Pd-based hollow nanostructure with reduced Pd usage and increased catalytic active sites, and also sheds light on the exploration of utilizing interatomic interactions to regulate species adsorption/activation for highly efficient catalytic performance.     

Rapid release of 1.5 equivalents of hydrogen from CO2-treated ammonia borane

This work addresses the accelerated dehydrogenation of ammonia borane (AB, NH₃BH₃) in two separate processes of CO₂ pre-treatment of AB and dehydrogenation of the treated AB. Decoupling these two processes can still keep the dehydrogenation activity of CO₂-treated AB and eliminate the purification step of H₂ from gas phase. When AB is exposed to 1.38 MPa of carbon dioxide (CO₂) at 70 °C, it shows the most favorable and controllable operating condition for the CO₂ pre-treatment. The pre-treatment enhances not only the rate but also the amount of hydrogen release at the dehydrogenation step; 1.5 mol H₂ per mol of AB rapidly desorbs at 85 °C in 1 h, corresponding to 10.1 wt.% of hydrogen with regard to pristine AB. Also, our observations show that the fast dehydrogenation resulted from the CO₂ pre-treatment is preserved for more than four days of storage. The degree of dehydrogenation is further confirmed by ATR-FTIR spectroscopic and elemental analyses of the solid product. The spectra display the N–H stretching mode involving π-bonded nitrogen (sp² N) at ca. 3434 cm⁻¹,while the atom ratio of H:B is found to be 2.84:1. Based on the hydrogen release measurements, spectroscopic observations and elemental analyses, we deduce that the predominant solid product of dehydrogenation of CO₂-treated AB at 85 °C is a polymer with an empirical formula of (NBH₃)_n. It corresponds to the solid product after 1.5 equivalent hydrogen release of AB.     

Effect of LDH composition on the catalytic activity of Ru/LDH for the hydrolytic dehydrogenation of ammonia borane

The hydrolytic dehydrogenation of ammonia borane (NH₃-BH₃, AB for short) in the presence of catalysts has been identified to be a safe and efficient way for hydrogen release. Understanding the dehydrogenation mechanism of AB is helpful and important to design efficient catalysts. So far, although the effects of various factors on dehydrogenation of AB have been studied, such as the noble metal particle size effect, crystal-phase effect and the support crystal plane effect, the effect of support composition on dehydrogenation of AB has rarely been reported yet. In this study, we choose composition-adjustable layered double hydroxide (MgAl-LDHs) as support for Ru nanoparticles, and use the as-prepared catalysts for comparing their catalytic activity towards the dehydrogenation of AB. The catalytic results demonstrate the catalytic activity of Ru/MgAl-LDHs is related to MgAl-LDHs composition, exhibiting a support-composition effect in the hydrolytic dehydrogenation of AB. Combining various characterizations, the different composition of MgAl-LDHs has an effect on the interaction between Ru nanoparticles and MgAl-LDHs, which directly affects the catalytic activity for the hydrolysis of AB. This study provides new important fundamental knowledge on the mechanism of AB hydrolysis over practical supported metal catalysts which can be used for a better catalyst design.     

Ruthenium supported on nitrogen-doped porous carbon for catalytic hydrogen generation from NH3BH3 hydrolysis

In this paper, ruthenium supported on nitrogen-doped porous carbon (Ru/NPC) catalyst is synthesized by a simple method of in situ reduction using ammonia borane (AB) as reducing agent. The composition and structure of Ru/NPC catalyst are systematically characterized. This catalyst can efficiently catalyze the hydrolysis of AB. The hydrogen production reaction is completed within about 90 s at a temperature of 298 K and the maximum rate of hydrogen production is 3276 ml·s⁻¹·g⁻¹ with a reduced activation energy of 24.95 kJ·mol⁻¹. The turnover frequency (TOF) for hydrogen production is about 813 mol_H2·mol_Ru⁻¹·min⁻¹. Moreover, this catalyst can be recycled with a well-maintained performance. After five cycles, the maximum rate of hydrogen generation is maintained at 2206 ml·s⁻¹·g⁻¹, corresponding to 67.3% of the initial catalytic activity. Our results suggest that Ru/NPC prepared by in situ reduction is a highly efficient catalyst for hydrolytic dehydrogenation of AB.     

Hydrogen generation from the dehydrogenation of ammonia–borane in the presence of ruthenium(III) acetylacetonate forming a homogeneous catalyst

Starting with ruthenium(III) acetylacetonate a homogeneous catalyst is formed which catalyzes the release of 1 equivalent of hydrogen gas from the dehydrogenation of ammonia–borane in toluene solution at low temperature in the range 50–65 °C. Mercury poisoning experiments showed that the catalytic dehydrogenation of ammonia–borane starting with ruthenium(III) acetylacetonate is a homogeneous catalysis. The final product obtained after the catalytic dehydrogenation of ammonia borane was thoroughly characterized by using ¹¹B Nuclear Magnetic Resonance and Infrared spectroscopies. The homogeneous catalyst formed from the reduction of ruthenium(III) acetylacetonate provides 950 turnovers (TTO) over 58 h and 27 (mol H₂)(mol Ru)⁻¹(h)⁻¹ value of initial turnover frequency (TOF) in hydrogen generation from the dehydrogenation of ammonia–borane at 60 °C before deactivation. Kinetics of this homogenous catalytic dehydrogenation of ammonia–borane was studied depending on the catalyst concentration, substrate concentration, and temperature. The hydrogen generation was found to be first order with respect to both the substrate concentration and catalyst concentration. The activation parameters of this reaction were also determined from the evaluation of the kinetic data: activation energy; E_a = 48 ± 2 kJ mol⁻¹, the enthalpy of activation; ΔH^# = 45 ± 2 kJ mol⁻¹ and the entropy of activation ΔS^# = −152 ± 5 J mol⁻¹ K⁻¹.     

Strategic synthesis of graphene supported trimetallic Ag-based core–shell nanoparticles toward hydrolytic dehydrogenation of amine boranes

We reported the synthesis and characterization of two trimetallic (Ag@CoFe, and Ag@NiFe) core–shell nanoparticles (NPs), and their catalytic activity toward hydrolytic dehydrogenation of ammonia borane (AB) and methylamine borane (MeAB). The as-synthesized trimetallic core–shell NPs were obtained via a facile one-step in situ procedure using methylamine borane as a reducing agent and graphene as the support under ambient condition. The as-synthesized NPs are well dispersed on graphene, and exhibit higher catalytic activity than the catalysts with other conventional supports, such as the SiO₂, carbon black, and γ-Al₂O₃. Additionally, compared with NaBH₄ and AB, the as-synthesized Ag@CoFe/graphene NPs reduced by MeAB exhibit the highest catalytic activity, with the turnover frequency (TOF) value of 82.9 (mol H₂ min⁻¹ (mol Ag)⁻¹), and the activation energy (E_a) value of 32.79 kJ/mol. Furthermore, the as-prepared NPs exert good durable and magnetically recyclability for the hydrolytic dehydrogenation of AB and MeAB. Moreover, this simple strategic synthesis method can be easily extended to the facile preparation of other graphene supported multi-metal core–shell NPs.     

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.     

Dehydrogenation of Ammonia Borane with transition metal-doped Co–B alloy catalysts

The catalytic performance of transition metal-doped Co–B ternary alloys were tested for H₂ generation by hydrolysis of Ammonia Borane (AB). Chemical reduction method was used to dope Co–B catalyst with various transition metals, namely Cu, Cr, Mo, and W, using their corresponding metal salts. All transition metals induce significant promoting effects on the Co–B catalyst by increasing the H₂ generation rate by about 3–6 times as compared to the undoped catalyst. The effect of metal dopant concentration on overall catalyst structure, surface morphology, and catalytic efficiency were examined by varying the metal/(Co + metal) molar ratio. Characterizations such as XPS, XRD, SEM, BET surface area measurement, and particle size analysis were carried out to understand the promoting role of each dopant metal during AB hydrolysis. Dopant transition-metals, in either oxidized or/and metallic state, act as an atomic barrier to avoid Co–B particle agglomeration thus preserving the effective surface area. In addition, the oxidized species such as Cr³⁺, Mo⁴⁺, and W⁴⁺, act as Lewis acid sites to enhance the absorption of OH⁻ group to further assist the hydrolysis reaction over alloy catalysts. The promoting nature of transition metal dopants in Co–B alloy powders is demonstrated by the evaluated low activation energy of the rate limiting step and high H₂ generation rate (2460 ml H₂ min⁻¹ (g of catalyst)⁻¹ for Co–Mo–B) in the hydrolysis of AB.     

Nanoporous Ni-based catalysts for hydrogen generation from hydrolysis of ammonia borane

We report nanoporous Ni, Ni–Fe, and Ni–Pt as catalysts for hydrogen generation from hydrolytic dehydrogenation of ammonia borane (NH₃BH₃, AB). The Ni and Ni–Fe nanoparticles with diameters of 20–25 nm were synthesized by a colloidal method in starch-containing aqueous solution. They exhibited considerable in situ catalytic performance but severely lost activity after separating from the reaction solution. Nanoporous Ni_1−xPt_x (x = 0.01, 0.08 and 0.19) with particle size below 5 nm was prepared from the isolated Ni nanoparticles through a replacement reaction. After centrifugation, drying, washing, and annealing, the obtained nanoporous Ni–Pt could attain remarkable activity, high hydrogen generation rate and efficiency, and low activation energy.