Hydrolytic Dehydrogenation Research Articles

Hydrolytic dehydrogenation of ammonia borane catalyzed by carbon supported Co core–Pt shell nanoparticles

Co core–Pt shell nanoparticles (denoted as Co1−x@Ptx where x=0.33, 0.43, 0.60, 0.68, 0.82) and carbon supported Co core–Pt shell nanoparticles (denoted as Co1−x@Ptx/C where x=0.60, 0.68, 0.82) (Co1−x@Ptx/C=43%), which are synthesized through a polyol reduction process with oleic acid as a surfactant, have been investigated as catalysts for hydrogen generation from hydrolysis of ammonia borane (NH3BH3) at 25±0.5°C. The as-prepared Co core–Pt shell nanoparticles are uniformly dispersed on carbon surface with diameters of about 3nm. It is found that the catalysts show favorable performance toward the hydrolysis of NH3BH3 and the catalytic activity is associated with the ratio of Pt to Co. Among the catalysts studied, Co0.32@Pt0.68/C (Co0.32@Pt0.68/C=43%) displays the highest catalytic performance, delivering a high hydrogen-release rate of 4874mLmin−1g−1 (per catalyst).

Co–SiO 2 nanosphere-catalyzed hydrolytic dehydrogenation of ammonia borane for chemical hydrogen storage

Cobalt clusters–silica nanospheres (15–30 nm) were synthesized using a Co(NH 3) 6Cl 3 template method in a polyoxyethylene-nonylphenyl ether/cyclohexane reversed micelle system followed by in situ reduction in aqueous NaBH 4/NH 3BH 3 solutions. The cobalt clusters are located either inside or on the outer surface of the silica nanospheres as shown by the transmission electron microscope (TEM)/energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS) measurements. The cobalt–silica nanospheres have a high catalytic activity for the hydrolysis of ammonia borane that generates a stoichiometric amount of hydrogen, and can be efficiently cycled and reused 10 times without any significant loss of the catalytic activity.

ChemInform Abstract: One‐Step Seeding Growth of Magnetically Recyclable Au@Co Core—Shell Nanoparticles: Highly Efficient Catalyst for Hydrolytic Dehydrogenation of Ammonia Borane.

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Bimetallic Au–Ni Nanoparticles Embedded in SiO2 Nanospheres: Synergetic Catalysis in Hydrolytic Dehydrogenation of Ammonia Borane

Gold-nickel nanoparticles (NPs) of 3-4 nm diameter embedded in silica nanospheres of around 15 nm have been prepared by using [Au(en)(2)Cl(3)] and [Ni(NH(3))(6)Cl(2)] as precursors in a NP-5/cyclohexane reversed-micelle system, and by in situ reduction in an aqueous solution of NaBH(4)/NH(3)BH(3). Compared with monometallic Au@SiO(2) and Ni@SiO(2), the as-synthesized Au-Ni@SiO(2) catalyst shows higher catalytic activity and better durability in the hydrolysis of ammonia borane, generating a nearly stoichiometric amount of hydrogen. During the generation of H(2), the synergy effect between gold and nickel is apparent: The nickel species stabilizes the gold NPs and the existence of gold helps to improve the catalytic activity and durability of the nickel NPs.

Monodisperse Nickel Nanoparticles and Their Catalysis in Hydrolytic Dehydrogenation of Ammonia Borane

Monodisperse nickel nanoparticles are prepared from the reduction of Ni(acac)(2) with borane tributylamine in the presence of oleylamine and oleic acid. Without any special treatment to remove the surfactants, the as-synthesized Ni nanoparticles supported on the Ketjen carbon support exhibit high catalytic activity in hydrogen generation from the hydrolysis of the ammonia-borane (H(3)NBH(3)) complex with a total turnover frequency value of 8.8 mol of H(2) x (mol of Ni)(-1) x min(-1). Such catalysis based on Ni nanoparticles represents a promising step toward the practical development of the H(3)NBH(3) complex as a feasible hydrogen storage medium for fuel cell applications.

The dehydrogenation of ammonia–borane catalysed by dicarbonylruthenacyclic(ii) complexes

The reactivity of ruthenacyclic compounds towards ammonia-borane's dehydrogenation was investigated by considering both hydrolytic and anhydrous conditions. The study shows that the highly soluble μ-chlorido dicarbonylruthenium(II) dimeric complex derived from 4-tert-butyl,2-(p-tolyl)pyridine promotes, with an activation energy E(a) of 22.8 kcal mol(-1), the complete hydrolytic dehydrogenation of NH(3)BH(3) within minutes at ca. 40 °C. The release of 3 eq. of H(2) entails the formation of boric acid derivatives and the partly reversible protonolysis of the catalyst, which produces free 2-arylpyridine ligand and a series of isomers of "Ru(CO)(2)(H)(Cl)". Under anhydrous conditions, hydrogen gas release was found to be slower and the dehydrogenation of NH(3)BH(3) results in the formation of conventional amino-borane derivatives with concomitant protonolysis of the catalyst and release of isomers of "Ru(CO)(2)(H)(Cl)". The mechanism of the protonolysis of the ruthenacycle was investigated with state-of-the-art DFT-D methods. It was found to proceed by the concerted direct attack of the catalyst by NH(3)BH(3) leading either to the formation of a coordinatively unsaturated "Ru(CO)(2)(H)(Cl)" species. The key role of "Ru(CO)(2)(H)(Cl)" species in the dehydrogenation of ammonia-borane was established by trapping and quenching experiments and inferred from a comparison of the catalytic activity of a series of dicarbonylruthenium(II) complexes.

Zeolite confined copper(0) nanoclusters as cost-effective and reusable catalyst in hydrogen generation from the hydrolysis of ammonia-borane

Herein we report the development of a cost-effective nanocluster catalyst for the hydrolytic dehydrogenation of ammonia-borane which is considered to be one among the new hydrogen storage materials. Zeolite confined copper(0) nanoclusters were prepared by the ion-exchange of Cu 2+ ions with the extra framework Na + ions in zeolite-Y followed by reduction of the Cu 2+ ions within the cavities of zeolite with sodium borohydride in aqueous solution and characterized by HR-TEM, XRD, XPS, SEM, EDX, ICP-OES, Raman spectroscopy and N 2 adsorption–desorption technique. Zeolite confined copper(0) nanoclusters are found to be active catalysts in the hydrolysis of ammonia-borane even at low temperatures (≤15 °C) and stable enough for being isolated as solid materials. They provide 1300 turnovers in hydrogen generation from the hydrolysis of ammonia–borane at room temperature. The average value of turnover frequency is 46.5 h −1 for the same reaction. More importantly, zeolite confined copper(0) nanoclusters were found to be isolable, bottleable and reusable catalysts in the hydrolytic dehydrogenation of ammonia-borane; even at fifth run the complete release of hydrogen from the hydrolysis of ammonia-borane at room temperature is achieved. The work reported here also includes the full experimental details for the collection of a wealth of kinetic data to determine the activation energy and the effect of catalyst concentration on the rate for the catalytic hydrolysis of ammonia–borane.

Water soluble laurate-stabilized rhodium(0) nanoclusters catalyst with unprecedented catalytic lifetime in the hydrolytic dehydrogenation of ammonia-borane

Herein we report, for the first time, the preparation and characterization of water soluble rhodium(0) nanoclusters stabilized by laurate (dodecanoate) anion and their catalytic activity in the hydrolysis of ammonia-borane. The water soluble laurate-stabilized rhodium(0) nanoclusters were prepared from the reduction of rhodium(III) chloride by dimethylamine-borane in solution containing sodium laurate at room temperature. The water soluble laurate-stabilized rhodium(0) nanoclusters in average size of 5.2 ± 2.7 nm could be isolated from the reaction solution and characterized by using UV–vis, TEM, XPS, XRD and FTIR spectroscopic methods. Catalytic activity of rhodium(0) nanoclusters was tested in the hydrolysis of ammonia-borane. They show exceptional catalytic activity and unprecedented catalytic lifetime in this reaction. They provide a TOF value of 200 mol H 2/mol Rh min and 80,000 turnovers in the hydrolysis of ammonia-borane in air at 25.0 ± 0.1 °C.

Room temperature hydrolytic dehydrogenation of ammonia borane catalyzed by Co nanoparticles

Amorphous and well dispersed Co nanoparticles (less than 10 nm) have been in situ synthesized in aqueous solution at room temperature. The as-synthesized Co nanoparticles possess high catalytic activity (1116 L mol −1 min −1) and excellent recycling property for the hydrogen generation from aqueous solution of ammonia borane under ambient atmosphere at room temperature. The present low-cost catalyst, high hydrogen generation rate and mild reaction conditions (at room temperature in aqueous solution) represent a promising step toward the development of ammonia borane as a viable on-board hydrogen-storage and supply material.

Preparation and catalysis of poly(N-vinyl-2-pyrrolidone) (PVP) stabilized nickel catalyst for hydrolytic dehydrogenation of ammonia borane

An amorphous nickel catalyst stabilized by poly(N-vinyl-2-pyrrolidone) (PVP) was synthesized by reduction in an aqueous NaBH4/NH3BH3 solution. Both the bare nickel catalyst and the PVP stabilized nickel catalyst contain grains with an amorphous structure after the reduction. The PVP stabilized nickel catalyst maintains high activity for hydrolysis of NH3BH3 to generate a stoichiometric amount of hydrogen with the cycle number up to 5, while the reaction rate in the presence of the bare nickel catalyst decreases with cycle number. After five cycles, the PVP stabilized nickel catalyst maintains the amorphous structure, while the agglomeration of nickel in the bare nickel catalyst is observed. The results indicate that PVP prevents agglomeration and crystallization of nickel nanoparticles, leading to higher durability than the bare nickel catalyst.

Hollow Ni–SiO 2 nanosphere-catalyzed hydrolytic dehydrogenation of ammonia borane for chemical hydrogen storage

Nickel clusters contained within silica nanospheres (20–30 nm) were synthesized by using a Ni(NH 3) 6Cl 2 crystal template method in a polyoxyethylene–nonylphenyl ether/cyclohexane reversed micelle system followed by an in situ reduction in aqueous NaBH 4/NH 3BH 3 solutions. Metallic nickel clusters exist inside the SiO 2 nanospheres prepared by the method while oxidized nickel clusters prepared by the conventional impregnation method were supported on the outer surface of silica as shown in the results of transmission electron microscope (TEM)/energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS) measurements. The nickel clusters inside of silica nanospheres show higher catalytic activity for hydrolysis of ammonia borane to generate stoichiometric amount of hydrogen than the supported nickel catalysts.

Identification of heat‐induced degradation products from purified betanin, phyllocactin and hylocerenin by high‐performance liquid chromatography/electrospray ionization mass spectrometry

Betanin, phyllocactin (malonylbetanin) and hylocerenin (3-hydroxy-3-methylglutarylbetanin) were isolated from purple pitaya (Hylocereus polyrhizus [Weber] Britton and Rose) juice, and their degradation products generated by heating at 85 degrees C were subsequently monitored by high-performance liquid chromatography/electrospray ionization tandem mass spectrometry. Thermal degradation of phyllocactin and hylocerenin in purified solution excluding the alleged protective effects by the juice matrix is reported for the first time. Betanin was predominantly degraded by hydrolytic cleavage, while decarboxylation and dehydrogenation were of minor relevance. In contrast, hylocerenin showed a strong tendency to decarboxylation and dehydrogenation, hydrolytic cleavage of the aldimine bond occurring secondarily. Phyllocactin degradation was most complex because of additional decarboxylation of the malonic acid moiety as well as generation and subsequent degradation of betanin due to phyllocactin demalonylation. Upon prolonged heating, all betacyanins under observation formed degradation products characterized by an additional double bond at C2-C3. Hydrolytic cleavage of the aldimine bond of phyllocactin and hylocerenin yielded previously unknown acylated cyclo-dopa derivatives traceable by positive ionization, while application of ESI(-) facilitated the detection of a glycosylated aminopropanal derivative and dopamine, which have never been described before as betanin degradation products.