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.     

Tungsten(VI) oxide supported rhodium nanoparticles: Highly active catalysts in hydrogen generation from ammonia borane

Herein, we report the use of tungsten(VI) oxide (WO₃) as support for Rh⁰ nanoparticles. The resulting Rh⁰/WO₃ nanoparticles are highly active and stable catalysts in H₂ generation from the hydrolysis of ammonia borane (AB). We present the results of our investigation on the particle size distribution, catalytic activity and stability of Rh⁰/WO₃ catalysts with 0.5%, 1.0%, 2.0% wt. Rh loadings in the hydrolysis reaction. The results reveal that Rh⁰/WO₃ (0.5% wt. Rh) is very promising catalyst providing a turnover frequency of 749 min^?1 in releasing 3.0 equivalent H₂ per mole of AB from the hydrolysis at 25.0 °C. The high catalytic activity of Rh⁰/WO₃ catalyst is attributed to the reducible nature of support. The report covers the results of kinetics study as well as comparative investigation of activity, recyclability, and reusability of colloidal(0) nanoparticles and Rh⁰/WO₃ (0.5 % wt. Rh) catalyst in the hydrolysis reaction.     

Nanosizing ammonia borane with nickel – An all-solid and all-in-one approach for H2 generation by hydrolysis

Ammonia borane NH₃BH₃ (AB) and nickel (Ni) have been considered together as an all-solid and all-in-one material for H₂ generation by hydrolysis at 20–50 °C. Our novel approach, denoted Ni/AB, consists of AB nanoparticles within a Ni matrix. Upon contact with water, Ni/AB readily hydrolyzes and liberates H₂ with a turnover frequency of 13.8 mol(H₂) mol_Ni^?1 min^?1 at 43.3 °C. The apparent activation energy, determined over the temperature range 23.5–50.4 °C, is low, with 19.5 ± 4.1 kJ mol^?1. These results imply that such a Ni matrix embedding AB acts as an effective catalyst. Beyond the catalytic performance, this is the first report of the successful utilization of an all-solid and all-in-one approach for the hydrolysis of AB, and the work brings unique perspectives for one-shot catalytic systems.     

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.     

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.     

La2O3-modified highly dispersed AuPd alloy nanoparticles and their superior catalysis on the dehydrogenation of formic acid

Formic acid (FA, HCOOH), a convenient and safe hydrogen storage material, has the great potential for fuel cell applications. However, hydrogen generation of FA is inefficient in the presence of heterogeneous catalysts at relatively low temperatures, which remains a big challenge. Herein, La₂O₃-modified highly dispersed AuPd alloy nanoparticles (AuPdLa₂O₃) with small particle size have been successfully anchored on carbon nanotubes (CNTs) by a facile co-reduction route. Moreover, the catalyst exhibits excellent catalytic activity and 100% hydrogen selectivity for hydrogen generation in the formic acid/sodium formate (FA/SF) system with the initial turnover frequency (TOF) value of 589 mol H₂ mol^?1 catalyst h^?1 at 50 °C and 280 mol H₂ mol^?1 catalyst h^?1 even at room temperature (25 °C). The present Au_0.3Pd_0.7-(La₂O₃)_0.6/CNTs with superior catalysis on FA dehydrogenation without any CO generation at room temperature can not only pave the way for practical application of hydrogen storage system, but also can be extended to other catalysis system.     

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.     

rGO supported PdNi-CeO2 nanocomposite as an efficient catalyst for hydrogen evolution from the hydrolysis of NH3BH3

The hydrogen economy is a proposed system that utilizes hydrogen to deliver energy. For the realization of this concept, how to safely, controllably and reversibly store and release hydrogen are critical problems which must be resolved. Metal alloys combined with suitable support materials are widely applied to various catalytic reactions. Here palladium nickel bimetallic nanoparticles doped with cerium oxide on a reduced graphene oxide (rGO) support were prepared by combining metal ion precursors and graphene oxide in a one-pot co-reduction approach. The as-received catalysts were characterized by XRD, TEM, SEM, XPS and ICP-OES, and the results revealed that PdNi-CeO₂ nanoparticles were uniform dispersal on rGO. The as-synthesized PdNi-CeO₂/rGO had been adopted as a heterogeneous catalyst for the hydrogen evolution from the hydrolysis of ammonia borane (NH₃BH₃, AB) at room temperature. Kinetically, the hydrogen-release rate was first-order with the increased concentration of catalysts. The optimized catalyst of Pd_0.8Ni_0.2-CeO₂/rGO with the CeO₂ content of 13.9 mol% exhibited an excellent activity with a turnover frequency value of 30.5 mol H₂ (mol catalyst)^?1 min^?1 at 298 K, and a low apparent activation energy (E_a) of 37.78 kJ mol^?1. The robust catalytic performance of the Pd_0.8Ni_0.2-CeO₂/rGO is attributed to the uniform controlled nanoparticle size, the synergic effect between the nanoparticles bimetallic properties, and the effective charge transfer interactions between the metal and support.     

PVP-stabilized platinum nanoparticles supported on modified silica spheres as efficient catalysts for hydrogen generation from hydrolysis of ammonia borane

Ammonia borane (AB) is considered to be a promising solid hydrogen carrier. In this work, poly(N-vinyl-2-pyrrolidone) (PVP)-protected platinum nanoparticles are supported on γ-methacryloxypropyltrimethoxysilane (γ-MPS) modified silica spheres (Pt-PVP/SiO₂(M)), which are firstly used as highly efficient catalysts for hydrolysis of AB. Platinum nanoparticles possess a tiny size of 2–3 nm and are uniformly dispersed over modified silica spheres. Pt-PVP/SiO₂(M) catalysts with a Pt loading amount of 1.30 wt% show the highest catalytic activity with a turnover frequency (TOF) value of 371 mol_H2 mol_Pt^?1 min^?1 (866 mol_H2 mol_Pt^?1 min^?1 corrected for the surface atoms) at 25 °C. The activation energy is calculated to be 46.2 kJ/mol. Furthermore, owing to the synergistic effect between the modifier of silica spheres and the capping agent of metal nanoparticles, Pt-PVP/SiO₂(M) catalysts have a higher loading amount (8.7 and 6.5 times) and TOF value (4.8 and 5.5 times) than the counterparts prepared without γ-MPS and PVP, respectively.     

Synthesis of polymer supported Ni (II)-Schiff Base complex and its usage as a catalyst in sodium borohydride hydrolysis

Influence of using as catalysis, Ni-Schiff Base complex which we previously synthesized [1] used to support with amberzyme oxirane resin (A.O.R.) polymer for increasing the catalytic activity in NaBH₄ hydrolysis reaction, to hydrogen generation was studied. The prepared catalyst was characterized by using SEM, XRD, BET, FT-IR analyze technique. Polymer supported Ni-Schiff Base complex catalyzed NaBH₄ hydrolysis reaction was investigated depending on concentration of NaBH₄, concentration of NaOH, temperature, percentage of Ni complex in total polymer supported Ni-Schiff Base complex and amount of catalyst factors. The maximum hydrogen production rate from hydrolysis of sodium borohydride with nickel-based complex catalyst compared to the pure nickel catalyst is increased from 772 mL H₂·g^?1 cat.·min^?1 to 2240 mL H₂ g^?1 cat.·min^?1 [1], and with supported amberzyme oxirane resin polymer this nickel based complex catalyst was increased to 13000 mL H₂·g^?1 cat.·min^?1 at 30 °C. The activation energy of complex catalyzed NaBH₄ hydrolysis reaction was found as 25.377 kJ/mol. This work also includes kinetic information for the hydrolysis of NaBH₄.     

Mo remarkably enhances catalytic activity of Cu@MoCo core-shell nanoparticles for hydrolytic dehydrogenation of ammonia borane

Ammonia borane (AB) has been identified as one of the most promising candidates for chemical hydrogen storage. However, the practical application of AB for hydrogen production is hindered by the need of efficient and inexpensive catalysts. For the first time, we report that the incorporation of Mo into Cu@Co core-shell structure can significantly improve the catalytic efficiency of hydrogen generation from the hydrolysis of AB. The Cu_0.81@Mo_0.09Co_0.10 core-shell catalyst displays high catalytic activity towards the hydrolysis dehydrogenation of AB with a turnover frequency (TOF) value of 49.6 molH₂ mol_cat^?1 min^?1, which is higher than most of Cu-based catalysts ever reported, and even comparable to those of noble-metal based catalysts. The excellent catalytic performance is attributed to the multi-elements co-deposition effect and electrons transfer effect of Cu, Mo and Co in the tri-metallic core-shell NPs.     

RuCo bimetallic alloy nanoparticles immobilized on multi-porous MIL-53(Al) as a highly efficient catalyst for the hydrolytic reaction of ammonia borane

Well-dispersed bimetallic RuCo alloy nanoparticles (NPs) were successfully immobilized on the multi-porous, water-tolerant metal organic frameworks MIL-53(Al) by a facile solvent impregnation method. Among the RuCo@MIL-53(Al) with different Ru/Co molar ratios, the Ru₁Co₁@MIL-53(Al) performed better and was superior to Ru@MIL-53(Al) and single RuCo NPs for the hydrolysis of ammonia borane (AB, NH₃BH₃), owing to the synergistic effect caused by the electronic and geometric interactions between Ru and Co atoms and bi-functional effect generated between the RuCo NPs and the MIL-53(Al) support. Compared with bimetallic Ru₁Ni₁ and Ru₁Cu₁ counterparts loadings, the Ru₁Co₁@MIL-53(Al) also showed better catalytic activity for the hydrolysis of AB. Moreover, the Ru₁Co₁@ MIL-53(Al) presented good durability and reusability in the catalytic reaction, and the activation energy (Ea) and turnover frequency values (TOF) were 34.32 kJ mol^?1 and 87.24 mol H₂ min^?1 (mol Ru)^?1, respectively.     

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.     

Investigation on salisylaldimine-Ni complex catalyst as an alternative to increasing the performance of catalytic hydrolysis of sodium borohydride

In this study, 5-amino-2, 4-dichlorophenol-3, 5-ditertbutylsalisylaldimine-Ni complex catalyst is synthesised and used as an alternative to previous studies to produce hydrogen from hydrolysis of sodium borohydride. The resulting complex catalyst is characterised by XRD, XPS, SEM, FT-IR and BET surface area analyses. Experimental works are carried out at 30 °C with 2% NaBH₄, 7% NaOH and 5 mg of catalyst. The maximum hydrogen production rate from hydrolysis of sodium borohydride with nickel-based complex catalyst compared to the pure nickel catalyst is increased from 772 ml min^?1g^?1 to 2240 ml min^?1g^?1 by an increase of 190%. At the same time, the hydrolysis reaction with pure nickel catalyst is completed in 145 min while the hydrolysis reaction with nickel-based complex catalyst is completed in 50 min. The activation energy of this hydrolysis reaction was calculated as 18.16 kJ mol^?1. This work also includes kinetic information for the hydrolysis of NaBH₄.The reusability of the nickel-based complex catalyst used in this study has also been studied. The nickel-based complex catalyst is maintained the activity of 72% after the sixth use, compared to the first catalytic use.     

Rapid preparation of Ru(0) nanoparticles stabilized with water-soluble biopolymer for hydrogen production from ammonia borane: Development of battery-like hydrolysis media

The biohybrid Na-Alg@Ru catalyst was prepared as a result of stabilizing Ru(0) nanoparticles with biopolymer chains of sodium alginate. The in-situ prepared Ru(0) nanoparticles had an average particle size of 1.023 ± 0.097 nm. The monodisperse Ru(0) nanoparticles prepared with a very practical, inexpensive and rapid method were used as a catalyst in hydrogen production by the hydrolysis reaction of ammonia borane (AB). The Na-Alg@Ru catalyst containing 3 mg Ru(0) metal catalyzed the hydrolysis of 50 mM AB with 100% yield, and the activation energy (E_a) of the reaction was estimated as 61.05 kJ mol⁻¹. In addition, the Na-Alg@Ru nanoparticles were prepared with acrylamide as p(AAm)/Na-Alg@Ru hydrogel films suitable for use in hydrogen production in fuel cells, which represents a battery-like environment, and used for hydrogen production from AB. Thus, it was shown that the catalysts prepared in a few nm size could easily be used in battery-like environments.     

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.     

Monodisperse PtCu alloy nanoparticles as highly efficient catalysts for the hydrolytic dehydrogenation of ammonia borane

Pt-M alloy nanoparticles (NPs) with well-defined size and compositions exhibit dramatically catalytic performance in chemical reactions. In this work, monodisperse PtCu NPs with controlled size and compositions were synthesized by the co-reduction method in the presence of oleylamine. These NPs have excellent catalytic activities in the hydrolytic dehydrogenation of ammonia borane (AB) and their activities were composition dependent. Among the different-composition PtCu NPs, the Cu₅₀Pt₅₀ NPs exhibit the highest catalytic activity with an initial turnover frequency of 102.5 mol_(hydrogen)·mol_(catalyst)^?1·min^?1 and an apparent activation energy of 36 kJ·mol^?1, which demonstrate the validity of partly replacing Pt by a first-row transition metal on constructing high performance heterogeneous nanocatalysts for the hydrolytic dehydrogenation of AB.     

Ceria supported manganese(0) nanoparticle catalysts for hydrogen generation from the hydrolysis of sodium borohydride

Herein we report for the first time the preparation and catalytic use of the ceria supported manganese(0) nanoparticles in hydrogen generation from the hydrolysis of sodium borohydride. They are in situ formed from the reduction of manganese(II) ions on the surface of ceria nanopowders during the catalytic hydrolysis of sodium borohydride in aqueous solution at room temperature. Manganese(0) nanoparticles are isolated from the reaction solution by centrifugation and characterized by a combination of analytical techniques. Nanoceria supported manganese(0) nanoparticles are highly active and long-lived catalysts providing a turnover frequency of 417 h^?1 and 45,000 turnovers in hydrogen generation from the hydrolysis of sodium borohydride at 25.0 ± 0.1 °C. They also have high durability as they retain 55% of their initial catalytic activity after the fifth cycle of hydrolysis providing a release of 4 equivalent H₂ gas per mol of sodium borohydride. The noticeable activity loss in successive runs of hydrolysis is attributed to the deactivation due to agglomeration. High activity and stability of ceria supported manganese(0) nanoparticles are ascribed to the unique nature of reducible cerium oxide. The formation of cerium(III) defects under catalytic conditions provides strong binding for the manganese(0) nanoparticles to oxide surface which makes the catalytic activity and stability favorable. Our report also includes the results of kinetic study of catalytic hydrolysis of sodium borohydride depending on the temperature, catalyst and substrate concentration.     

Efficient hydrogen evolution from ammonia borane hydrolysis with Rh decorated on phosphorus-doped carbon

Development of supported ligand-free ultrafine Rh nanocatalysts for efficient catalytic hydrogen evolution from ammonia borane (AB) is of importance but remains a tremendous challenge. Here, ultrafine and ligand-free Rh nanoparticles (NPs) (2.19 nm in diameter) were in-situ decorated on porous phosphorus-functionalized carbon (PPC) prepared by pyrolyzing hyper-cross-linked networks of triphenylphosphine and benzene. The resultant Rh/PPC showed excellent hydrogen production activity from AB hydrolysis (Turnover frequency: 806 min⁻¹). Kinetic investigations indicated that AB hydrolysis using Rh/PPC exhibited first-order and zero-order reactions with Rh and AB concentrations, respectively. Activation energy (E_a) toward hydrogen generation from AB with Rh/PPC is as low as 22.7 kJ/mol. The Rh/PPC catalyst was recyclable and reusable for at least four times. The oxygen- and phosphorus-functional groups are beneficial for the affinity of Rh complex on the PPC surface, resulting in ultrafine and ligand-free Rh NPs with high dispersity and ability to supply abundant surface accessibility to catalytically active sites for AB hydrolysis. This study proposes a feasible approach for the synthesis of ultrafine and ligand-free metal NPs supported on heteroatom-doped carbon by using hyper-cross-linked networks.     

Cu0.6Ni0.4Co2O4 nanowires,a novel noble-metal-free catalyst with ultrahigh catalytic activity towards the hydrolysis of ammonia borane for hydrogen production

In this work, we have prepared a series of Cu_xNi_1-xCo₂O₄ (x = 0, 0.2, 0.4, 0.5, 0.6, 0.8, and 1) nanowires with a diameter of approximately 30 nm, which were characterized by X-ray powder diffractometry, scanning and transmission electron microscopy, and X-ray photoelectron spectrometry. For the first time, the catalytic activity of these Cu_xNi_1-xCo₂O₄ nanowires in ammonia borane (AB) hydrolysis was investigated, and it was found that a significant synergistic effect exists between NiCo₂O₄ and CuCo₂O₄ in the hydrolytic reaction. Among these Cu_xNi_1-xCo₂O₄ samples, the Cu_0.6Ni_0.4Co₂O₄ nanowires showed the highest turnover frequency (TOF) of 119.5 mol_hydrogen min^?1 mol_cat^?1. This value is 1.66 times as high as that for CoP nanoparticles, which is the most active noble-metal-free catalyst towards AB hydrolysis ever reported in the literature. Because of the low cost and high catalytic performance, the Cu_0.6Ni_0.4Co₂O₄ nanowires can be a robust catalyst towards AB hydrolysis in practical applications.