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.     

Alumina nanofiber-stabilized ruthenium nanoparticles: Highly efficient catalytic materials for hydrogen evolution from ammonia borane hydrolysis

Effective catalysts for hydrogen generation from ammonia borane (AB) hydrolysis should be developed for the versatile applications of hydrogen. In this study, ruthenium nanoparticles (NPs) supported on alumina nanofibers (Ru/Al₂O₃-NFs) were synthesized by reducing the Ru(Ш) ions impregnated on Al₂O₃-NFs during AB hydrolysis. Results showed that the Ru NPs with an average size of 2.9 nm were uniformly dispersed on the Al₂O₃-NFs support. The as-synthesized Ru/Al₂O₃-NFs exhibited a high turnover frequency of 327 mol H₂ (mol Ru min)^?1 and an activation energy of 36.1 kJ mol^?1 for AB hydrolysis at 25 °C. Kinetic studies showed that the AB hydrolysis catalyzed by Ru/Al₂O₃-NFs was a first-order reaction with regard to the Ru concentration and a zero-order reaction with respect to the AB concentration. The present work reveals that Ru/Al₂O₃-NFs show promise as a catalyst in developing a highly efficient hydrogen storage system for fuel cell applications.     

Pd nanoparticles supported on MIL-101 as high-performance catalysts for catalytic hydrolysis of ammonia borane

Well dispersed ultrafine Pd NPs have been immobilized in the framework of MIL-101, and tested for the catalytic hydrolysis of ammonia borane. The powder XRD, N₂ adsorption–desorption, TEM, and ICP-AES were employed to characterize the Pd@MIL-101 catalyst. The as-synthesized Pd@MIL-101 exhibit the highest catalytic activity toward hydrolysis of AB among the Pd-based nano-catalysts ever reported, with the TOF value of 45 mol H₂ min⁻¹ (mol Pd)⁻¹.     

One-pot co-reduction synthesis of orange-like Pd@Co@P nanoparticles supported on rGO for catalytic hydrolysis of ammonia borane

Transition metal phosphide based orange-like Pd@Co@P nanoparticles supported on reduced graphene oxide (Pd@Co@P/rGO) have been synthesized by a one-pot co-reduction at room temperature using methylamine borane (MeAB) as the reducing agent. The prepared Pd@Co@P/rGO nanoparticles were characterized by powder X-ray diffraction (XRD), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), selected area electron diffraction (SAED) and confocal Raman microscopy (Raman). Compared with Pd/rGO and Pd@Co/rGO, the Pd@Co@P/rGO catalyst has higher catalytic activity for the hydrolytic production of ammonia borane (AB) with the turnover frequency value (TOF) of 127.57 min⁻¹ and the activation energy of 39.05 kJ mol⁻¹. This excellent catalytic performance may be caused by the orange-like structure and good dispersion of Pd@Co@P/rGO nanoparticles, and the synergistic electron interactions between palladium, cobalt, and phosphorus.     

CoMoB nanoparticles supported on foam Ni as efficient catalysts for hydrogen generation from hydrolysis of ammonia borane solution

We report on CoMoB nanoparticles supported on foam Ni as catalysts for hydrogen generation from hydrolysis of ammonia borane (NH₃BH₃) solution. The CoMoB/foam Ni catalysts with different molar ratios of Co²⁺and MoO₄²⁻ were synthesized via the electroless-deposition technique at ambient temperature. In order to analyze the phase composition, chemical composition, microstructure, and electron bonding structure of the as-prepared samples, powder X–ray diffraction (XRD), inductively coupled plasma-mass spectroscopy (ICP-MS), scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) were used. The results showed that CoMoB nanoparticles were variously dispersed on the surface of the foam Ni and the catalytic activity correlated with the molar ratio of Co²⁺ and MoO₄²⁻. The highest hydrogen generation rate was 5331.0 mL min⁻¹ g_cat⁻¹ at 298 K, and the activation energy was calculated to be 45.5 kJ mol⁻¹ toward the hydrolysis of NH₃BH₃ solution. The better catalytic activity was largely attributed to the smaller particle size, higher surface roughness and the novel three-dimensional cone-like architectures of the obtained samples. The kinetic results show that the hydrolysis of NH₃BH₃ is a first-order reaction in catalyst concentration. In addition, the reusability experiment exhibited that the catalytic activity was reduced after 5 cycles and the reason of the decay was also investigated.     

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.     

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.     

Mitigation of polyborate precipitation on Pd/Fe2O3 sites during ammonia borane hydrolysis: An alternate insight into the role of oxygen vacancies

Understanding the stability of catalysts is essential for both fundamental science and industrial process design. Herein, we show that oxygen vacancies at the interfaces of Pd/Fe₂O₃ catalysts prevent the precipitation of polyborate byproducts on the catalyst's surface during ammonia borane (AB) hydrolysis, thereby enhancing the catalyst's stability. Fe₂O₃-supported Pd nanoparticles were synthesized by a solid-state approach wherein Fe₂O₃ support size was varied as 20 nm, 45 nm, and 70 nm while the Pd content was maintained at 5% by wt. With increasing cycles, the catalyst containing 20 nm Fe₂O₃ nanoparticle support is stable, while the catalysts with 45 and 70 nm Fe₂O₃ supports showed deterioration of catalytic activity. In lower support sizes, due to the fine dispersion of Pd, in-situ oxygen vacancies are created at Pd/Fe₂O₃ interface during AB hydrolysis. We propose that more water molecules congregate at the vacancy sites, which aids the solubility of polyborates, thereby extending the activity of the catalyst through multiple cycles.     

Effect of metal additives on the catalytic performance of Ni/Al2O3 catalyst in thermocatalytic decomposition of methane

Thermocatalytic decomposition of methane is proposed to be an economical and green method to produce CO_x-free hydrogen and carbon nanomaterial. In present work, 60 wt% Ni/Al₂O₃ catalysts with different additives (Cu, Mn, Pd, Co, Zn, Fe, Mg) were prepared by co-impregnation method to investigate promotional effects of these metal additives on the activity and stability of 60 wt% Ni/Al₂O₃ and find out a really effective promoter for decomposition of methane. The catalyst was characterized by N₂ adsorption/desorption, X-ray diffraction, scanning electron microscopy, inductively coupled plasma optical emission spectrometer and hydrogen temperature programmed reduction. While metal additives (5 wt%) were added into 60 wt% Ni/Al₂O₃, the activity stability of 60 wt% Ni/Al₂O₃ was improved and the CH₄ conversion of 60 wt% Ni/Al₂O₃ was also improved except Zn addition. Mn addition was found to improve the catalytic activity of 60 wt% Ni/Al₂O₃ significantly and the CH₄ conversion of 5 wt% Mn-60 wt% Ni/Al₂O₃ was ∼80%. Cu addition was found to remarkably improve the catalytic stability of 60 wt% Ni/Al₂O₃ and the CH₄ conversion of 5 wt% Cu-60 wt% Ni/Al₂O₃ decreased from 61% to 45% after 250 min of reaction time. Carbon nanomaterials formed in the thermocatalytic decomposition process were characterized by X-ray diffraction, scanning electron microscopy, thermal gravimetric analyzer and Raman spectroscopy. Carbon deposits consist of amorphous carbon and carbon nanofibers.     

Elucidation of cobalt disturbance on Ni/Al2O3 in dissociating hydrogen towards improved CO2 methanation and optimization by response surface methodology (RSM)

In this study, nickel (Ni) and cobalt nickel (Co/Ni) supported on alumina were successfully synthesized by a facile electrolysis procedure and were tested for CO₂ methanation. By applying the Ni/Al₂O₃ catalyst, CO₂ conversion reached up to of 10 μmol/g.s, which is 1.4 times higher than Co/Ni/Al₂O₃, followed by the parent Al₂O₃. The addition of Co into Ni/Al₂O₃ has formed spinel phase in Co/Ni/Al₂O₃, as well as caused a slight increase in the basicity, which directed to the higher formation of formate species as observed by in-situ CO₂ + H₂ FTIR study. Both catalyst followed the dissociative mechanism during the CO₂ methanation. However, bigger metal particles in Co/Ni/Al₂O₃ caused slower hydrogen dissociation compared to Ni/Al₂O₃, leading to lower yield of CH₄. The optimization study via the response surface methodology (RSM) showed that the yield of CH₄ was significantly affected by reaction temperature, followed by treatment time, the ratio of H₂:CO₂ and lastly the gas hour space velocity (GHSV).     

Ru nanoparticles loaded on tannin immobilized collagen fibers for catalytic hydrolysis of ammonia borane

A kind of Ru-based catalyst was prepared by using a natural polyphenolic polymer (bayberry tannin, BT) immobilized on collagen fiber (CF) as the stabilizer and carrier of Ru nanoparticles (NPs) and characterized to detect its main physicochemical properties. The CF-BT-Ru catalyst was found to be in an orderly fiber morphology with Ru NPs with about diameter of 2.6 nm highly distributed on the surface. The research on catalytic activity of CF-BT-Ru focused on the hydrolysis of ammonia borane (AB) to produce hydrogen. The influences of Ru loading, Ru dosage, AB concentration and temperature on the catalytic AB hydrolysis were investigated in detail, and the related thermodynamic parameters (activation energy (E_a), activation entropy (△S), activation enthalpy (△H) and Gibbs free energy (△G)) were calculated. The experimental results indicated that CF-BT-Ru exhibited high catalytic activity. Its turnover frequency (TOF) was as high as 322 ${\text{mol}}_{{\text{H}}_2}?{\text{mol}}_{\text{Ru}}^{?1}?{\text{min}}^{?1}$ and E_a was as low as 32.41 kJ mol^?1 for AB hydrolysis. Moreover, CF-BT-Ru exhibited satisfied reusability and stability. Its activity lost only one-fifth and no obvious agglomeration and leakage of Ru NPs were found after repeated use for 5 times.     

Silica embedded cobalt(0) nanoclusters: Efficient, stable and cost effective catalyst for hydrogen generation from the hydrolysis of ammonia borane

Cobalt(0) nanoclusters embedded in silica (Co@SiO₂) were prepared by a facile two-step procedure. In the first step, the hydrogenphosphate anion (HPO₄²⁻) stabilized cobalt(0) nanoclusters were in situ generated from the reduction of cobalt(II) chloride during the hydrolysis of sodium borohydride (NaBH₄) in the presence of stabilizer. Next, HPO₄²⁻ anion-stabilized cobalt(0) nanoclusters were embedded in silica formed by in situ hydrolysis and condensation of tetraethylorthosilicate added as ethanol solution. Co@SiO₂ can be separated from the solution by vacuum filtration and characterized by UV-Vis electronic absorption spectroscopy, TEM, SEM-EDX, ATR-IR and ICP-OES techniques. Co@SiO₂ are found to be highly active and stable catalysts in the hydrolysis of ammonia borane (AB) even at low cobalt concentration and room temperature. They provide an initial turnover frequency of 13.3 min⁻¹ and 24,400 total turnovers over 52 h in the hydrolysis of AB at 25.0 ± 0.5 °C. Moreover, Co@SiO₂ retain 72% and 74% of the initial activity after ten runs recyclability and five cycles reusability test in the hydrolysis of AB, respectively. The kinetics of hydrogen generation from the hydrolysis of AB catalyzed by Co@SiO₂ was studied depending on the catalyst concentration, substrate concentration, and temperature. The activation parameters of this catalytic reaction were also determined from the evaluation of the kinetic data.     

Preparation and detailed characterization of zirconia nanopowder supported rhodium (0) nanoparticles for hydrogen production from the methanolysis of methylamine-borane in room conditions

Uniformly dispersed Rh (0) nanoparticles supported on zirconia nanopowder were synthesized by a two-step and simple ex-situ method summarized by mixing rhodium (III) chloride hydrate with zirconia (nano-ZrO₂) aqueous solution in ambient conditions followed by reduction with NaBH₄. The ex-situ prepared nano-ZrO₂ supported Rh (0) nanoparticles (Rh/nano-ZrO₂) were characterized by various spectroscopic methods, including TEM, TEM-EDX, HR-TEM, P-XRD, XPS and ICP-OES. The catalytic activity of Rh (0) nanoparticles is 1050 h^?1 in terms of initial turnover frequency (TOF), which is the first study in the literature to produce hydrogen by catalytic methanolysis of methylamine-borane. In addition, the catalytic methanolysis of methylamine-borane by using Rh (0) nanoparticles was carried out in different catalyst/substrate concentrations and different temperatures to reveal rate equation and kinetic parameters. Consequently, Rh (0) nanoparticles are taken into account as an encouraging catalyst for the methanolysis of methylamine-borane and for providing a more fertile hydrogen storage gain in fuel cell operations.     

Pd nanoparticles anchoring to core-shell Fe3O4@SiO2-porous carbon catalysts for ammonia borane hydrolysis

A modified Stöber method is applied to synthesize the magnetic core-shell Fe₃O₄@SiO₂ particles, followed by compositing a series of porous glucose-derived carbon with ZnCl₂ as etchant. Then, ultrafine Pd nanoparticles (NPs) are successfully anchored to the resulting Fe₃O₄@SiO₂-PC composites with an in-situ reduction strategy. The particle sizes of Pd NPs are mainly centered in the range of 2.3–4.3 nm in the as-prepared Pd/Fe₃O₄@SiO₂-PC catalysts, owning a hierarchical porous structure with high specific surface area (S_BET = 626.0 m² g⁻¹) and large pore volume (V_p = 0.61 cm³ g⁻¹). Their catalytic behavior for the hydrogen generation from ammonia borane (AB) hydrolysis is investigated in details. The corresponding apparent activation energy is as low as 28.4 kJ mol⁻¹ and the reaction orders with AB and Pd concentrations are near zero and 1.10 under the present conditions, respectively. In addition, the magnetic catalysts, which could be easily separated out by a magnet, are still highly active even after nine runs, revealing their excellent reusability.     

Hydrogen generation by sodium borohydride hydrolysis on nanosized CoB catalysts supported on TiO2, Al2O3 and CeO2

A series of nanosized CoB catalysts supported on TiO₂, Al₂O₃, and CeO₂ were prepared. The catalysts were prepared by incipient-wetness impregnation. The sample was dried at 100 °C and then dispersed in water and reduced by an aqueous solution of sodium borohydrate at room temperature. An unsupported CoB cluster was used for comparison. The activities of the supported CoB catalysts were higher than that of unsupported one. The reaction rates of these supported CoB catalysts decreased in the order: CoB/TiO₂ > CoB/Al₂O₃ > CoB/CeO₂ > unsupported CoB. The reaction kinetics on various catalysts was also investigated.     

Salicylaldimine-Ni complex supported on Al2O3: Highly efficient catalyst for hydrogen production from hydrolysis of sodium borohydride

In this study, the Ni-based complex catalyst containing nickel of 1% supported on Al₂O₃ is used as for the hydrogen production from NaBH₄ hydrolysis. The maximum hydrogen production rate from hydrolysis of NaBH₄ with Ni-based complex catalyst supported on Al₂O₃ containing nickel of 1% is 62535 ml min^?1 g^?1 (complex catalyst containing 1 wt% Ni). The resulting complex catalyst is characterised by XRD, XPS, SEM, FT-IR, UV, and BET surface area analyses. The Arrhenius activation energy is found to be 27.29 kJ mol^?1 for the nickel-based complex catalyst supported on Al₂O₃. The reusability of the catalyst used in this study has also been investigated. The Ni-based complex catalyst supported on Al₂O₃ containing nickel of 1% is maintained the activity of 100% after the fifth use, compared to the first catalytic use. The n value for the reaction rate order of NaBH₄ is found to be about 0.33.     

Co3xCu3-3x(PO4)2 microspheres,a novel non-precious metal catalyst with superior catalytic activity in hydrolysis of ammonia borane for hydrogen production

Development of robust and cheap catalyst for fast hydrogen evolution from ammonia borane (AB) aqueous solution is an interesting and important topic in the field of hydrogen energy. Herein, a novel non-precious Co_3xCu_3-3x(PO₄)₂ catalyst possessing high reactivity in AB hydrolysis has been developed for the first time. By tuning the molar ratio of Co and Cu, a series of Co_3xCu_3-3x(PO₄)₂ with different x were synthesized and the catalytic behavior in AB hydrolysis was examined. At the optimal x of 0.8, an ultrahigh turnover frequency of 72.6 min⁻¹ was achieved. Additionally, the synergistic effect between Cu₃(PO₄)₂ and Co₃(PO₄)₂ was experimentally confirmed, and the reaction kinetics of AB hydrolysis catalyzed by Co_2.4Cu_0.6(PO₄)₂ were investigated. This work provides a simple route and some new insights for the fabrication of a cheap P-containing catalyst with robust catalytic performance.     

Ruthenium(0) nanoparticles supported on nanotitania as highly active and reusable catalyst in hydrogen generation from the hydrolysis of ammonia borane

Ruthenium(0) nanoparticles supported on the surface of titania nanospheres (Ru(0)/TiO₂) were in situ generated from the reduction of ruthenium(III) ions impregnated on nanotitania during the hydrolysis of ammonia borane. They were isolated from the reaction solution by centrifugation and characterized by a combination of advanced analytical techniques. The results reveal that highly dispersed ruthenium(0) nanoparticles of size in the range 1.5–3.3 nm were formed on the surface of titania nanospheres. Ru(0)/TiO₂ show high catalytic activity in hydrogen generation from the hydrolysis of ammonia borane with a turnover frequency value up to 241 min⁻¹ at 25.0 ± 0.1 °C. They provide unprecedented catalytic lifetime measured by total turnover number (TTO = 71,500) in hydrogen generation from the hydrolysis of ammonia borane at 25.0 ± 0.1 °C. The report also includes the results of kinetic study on the catalytic hydrolysis of ammonia borane depending on the temperature to determine the activation energy of the reaction (E_a = 70 ± 2 kJ/mol) and the catalyst concentration to establish the rate law of the reaction.     

Plasma-enhanced catalytic ammonia decomposition over ruthenium (Ru/Al2O3) and soda glass (SiO2) materials

Catalytic ammonia (NH₃) decomposition has been identified as a COx-free, sustainable hydrogen production method for fuel cell applications. In this study, the performance of plasma–catalyst-based NH₃ decomposition over ruthenium (Ru/Al₂O₃) and soda glass (SiO₂) catalytic materials at atmospheric pressure and ambient temperature was investigated. NH₃ decomposition reactions were conducted in a dielectric barrier discharge plasma plate-type reactor. NH₃ was fed into the plate catalytic microreactor at flow rates of 0.1–1 L/min and plasma voltages of 12–18 kV. Compared to plasma NH₃ decomposition without a catalyst, plasma–catalyst-based NH₃ decomposition showed a significant enhancement of the hydrogen production rate and energy efficiency. Furthermore, the hydrogen concentration results obtained over the Ru/Al₂O₃ catalyst were higher than those over the SiO₂ catalyst because Ru/Al₂O₃ possesses good electronic properties and exhibits high sensitivity to NH₃ decomposition. In addition, the resulting plasma heat enhanced the activation of the catalytic material, subsequently leading to an increase in the hydrogen production rate from NH₃. The maximum conversion rates were 85.65% and 84.39% for Ru/Al₂O₃ and SiO₂, respectively. Moreover, the energy efficiency of NH₃ decomposition over the Ru-based catalyst material was higher than that over the SiO₂ material. The presence of the catalyst active sites and plasma enhanced the mean electron energy, which could enhance the dissociation of NH₃. It can be concluded that the SiO₂ material can be utilised as a catalyst and that its combination with plasma accelerates the decomposition process of NH₃ and incurs a lower cost compared to Ru materials.