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Palladium(0) nanoparticles supported on cobalt ferrite (Pd degrees/CoFe2O4) are found to be highly active catalyst, providing an unprecedented catalytic activity with a turnover frequency of 290 min(-1) in hydrogen generation from the hydrolysis of ammonia borane at room temperature. However, the initial catalytic activity of Pd degrees/CoFe2O4 catalyst is not preserved after the reuse of the catalyst in hydrolytic dehydrogenation of ammonia borane. The stability of the catalyst is improved by using the polydopamine (PDA) coated cobalt ferrite as support instead of bare cobalt ferrite. PDA coating of CoFe2O4 nanopowders was achieved by pH-induced self-polymerization of dopamine hydrochloride at room temperature and the thickness of PDA was optimized by changing the amount of dopamine hydrochloride. Palladium(0) nanoparticles supported on PDA coated cobalt ferrite (Pd degrees/PDA-CoFe2O4) were prepared by two step impregnation-reduction process and characterized by a combination of advanced analytical techniques. The results reveal that palladium nanoparticles with an average size of 1.4 +/- 0.3 nm are well dispersed on polydopamine layer with a thickness of 8.6 +/- 1.0 nm on the surface of cobalt ferrite nanopowders. Pd degrees/PDA-CoFe2O4 with a palladium loading of 1.08 wt% was found to be a highly active and reusable catalyst in hydrogen generation from the hydrolysis of ammonia borane with a turnover frequency of 175 min(-1) at 25.0 +/- 0.1 degrees C. Magnetically isolable Pd degrees/PDA-CoFe2O4 catalyst preserves its initial catalytic activity even after the tenth use providing the release of 3 equivalent H-2 per mole of ammonia borane. (C) 2017 Elsevier B.V. All rights reserved.

Magnetic ferrite nanopowders were coated with polydopamine which is inert against the hydrolysis of ammonia borane. Coating of ferrite powders was achieved by pH-induced self-polymerization of dopamine hydrochloride at room temperature. Palladium(0) nanoparticles supported on polydopamine coated ferrite (Pd-0/PDA-Fe3O4) were prepared by impregnation of palladium(II) ions on the surface of PDA-Fe3O4 followed by their reduction with sodium borohydride in aqueous solution at room temperature. Magnetically isolable Pd-0/PDA-Fe3O4 catalysts were characterized by a combination of advanced analytical techniques. The results reveal that palladium nanoparticles with an average size of 2.0 +/- 0.4 nm are well dispersed on polydopamine layer with a thickness of 3.0 +/- 0.5 nm on the surface of ferrite nanopowders. Pd-0/PDA-Fe3O4 with a palladium loading of 3.81% wt was found to be a highly active and reusable catalyst in hydrogen generation from the hydrolysis of ammonia borane with a turnover frequency value of 14.5 min(-1) at 25.0 +/- 0.1 degrees C. Magnetically isolable Pd-0/PDA-Fe3O4 catalysts preserve their initial catalytic activity even after the tenth use providing the release of 3 equivalent H-2 per mole of ammonia borane. The report also includes the results of kinetic studies on the hydrolytic dehydrogenation of ammonia borane performed at various temperatures and different catalyst concentrations.

Ruthenium(III) ion-exchanged zeolite Y, prepared by ion exchange of Ru+3 ions with the extra framework Na+ cations in zeolite Y with a Si/Al ratio of 2.5, is employed to catalyze the decomposition of nitrous oxide to nitrogen and oxygen. Catalytic activity of ruthenium(III) ion-exchanged zeolite Y is studied in the decomposition of nitrous oxide to nitrogen and oxygen depending on the ruthenium loading of zeolite and flow rate of nitrous oxide helium mixture in a continuous flow vertical reactor. The results collected reveal that ruthenium(III) ion-exchange zeolite with a ruthenium loading of 3.98 wt.% is highly active, long-lived, and reusable catalyst providing 100% conversion of nitrous oxide to sole nitrogen and oxygen at 350 degrees C without any side reaction. This catalyst can be bottled under ambient conditions and repeatedly used in successive runs of nitrous oxide decomposition for up to 5 months without significant loss in activity. Intrazeolite ruthenium(0) nanoclusters are slightly less active than the ruthenium(III) ion-exchanged zeolite Y in decomposition of nitrous oxide, which might be attributed to the migration of ruthenium(0) to the external surface before oxidation at high temperature. The other two metals of Group 8, iron(III) and osmium(III) ion-exchanged zeolite Y do not show activity as high as that of ruthenium(III) ion-exchanged zeolite Y in the same reaction. (C) 2014 Elsevier Inc. All rights reserved.

Chemically derived graphene (CDG) was prepared by hydrazine hydrate reduction of graphene oxide and used as support for palladium nanoparticles (Pd NPs) generated ex situ with controllable particle size and dispersion. The Pd NPs supported on CDG were well characterized by using a combination of advance analytical techniques and employed as catalyst in the dehydrogenation and hydrolysis of ammonia borane (AB) in organic solvents and aqueous solutions, respectively. Monodisperse Pd NPs of 4.5 nm were prepared from the reduction of palladium(II) acetylacetonate by tert-butylamine borane in the presence of oleylamine. They were readily impregnated on CDG which. has BET surface area of 500 m(2) g(-1). Pd NPs retain their particle size dispersion and stability when supported on chemically derived graphene. The resulting materials are highly active and stable catalyst for the dehydrogenation and hydrolysis of AB. In addition to their high activity and stability, these Pd NPs are also reusable catalyst in both dehydrogenation and hydrolysis of AB preserving 85% and 95% of initial activity after 5th and 10th runs, respectively. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Water soluble polymer stabilized iron(0) nanoclusters were prepared from the reduction of iron(III) chloride by sodium borohydride (SB) and ammonia borane (AB) mixture in the presence of polyethylene glycol (PEG) as stabilizer and ethylene glycol as solvent at 80 degrees C under nitrogen atmosphere. PEG stabilized iron(0) nanoclusters were isolated from the reaction solution by centrifugation and characterized by UV-Vis, TEM, HRTEM, XRD, ICP-OES and FT-IR methods. The particle size of PEG stabilized iron(0) nanoclusters ranges from 4.0 nm to 8.5 nm with a mean value of 6.3 nm. They are redispersible in water and yet highly active catalysts in hydrogen generation from the hydrolysis of SB and AB. They provide a turnover frequency of TOF = 6.2 and 6.4 min(-1) for the hydrolysis of SB and AB at 25.0 +/- 0.5 degrees C, respectively. The TOF values are the best ever reported for the iron catalysts and comparable to other non-noble metal catalyst systems in both hydrolysis reactions. Kinetics of hydrogen generation from the hydrolysis of AB in the presence of PEG stabilized iron(0) nanoclusters was also studied by varying the catalyst concentration, substrate concentration, and temperature. This is the first kinetic study on the hydrolysis of AB in the presence of an iron catalyst. Moreover, PEG stabilized iron(0) nanoclusters can be separated magnetically from the catalytic reaction solution using a magnet and show catalytic activity even after tenth run. (C) 2011 Elsevier B. V. All rights reserved.

Hydrogen phosphate (HPO4 (2-)) or poly(acrylic acid) (PAA) stabilized cobalt(0) nanoclusters were in situ generated from the reduction of cobalt(II) chloride during the catalytic hydrolysis of sodium borohydride (NaBH4) in the presence of stabilizers, HPO4 (2-) or PAA. Cobalt(0) nanoclusters stabilized by HPO4 (2-) or PAA were characterized by using UV-Visible spectroscopy, TEM, XPS and FT-IR techniques. They were employed as catalysts in the hydrolysis of NaBH4 to examine the effect of stabilizer type on their catalytic activity and stability. Detailed reaction kinetics of the hydrolysis of NaBH4 in the presence of both catalysts was studied depending on catalyst concentration, substrate concentration and temperature. PAA stabilized cobalt(0) nanoclusters provided higher total turnover number (TTON = 6,600) than that of HPO4 (2-) stabilized cobalt(0) nanoclusters (1,285 turnovers). However, the HPO4 (2-) stabilized cobalt(0) nanoclusters provided a lower activation energy (E (a) = 53 +/- A 2 kJ mol(-1)) than the PAA stabilized cobalt(0) nanoclusters (E (a) = 58 +/- A 2 kJ mol(-1)) for the hydrolysis of NaBH4. The use of two types of stabilizers in the preparation of the same metal(0) nanoclusters following the same methodology enables us to compare the electrostatic and steric stabilization in terms of the catalytic activity and stability of metal(0) nanoclusters.

Herein we report a new method for the synthesis and characterization of PVP-stabilized palladium(0) nanoclusters and their enhanced catalytic activity in Suzuki coupling and Heck reactions of aryl bromides with phenylboronic acid and styrene, respectively, under mild conditions. The PVP-stabilized palladium(0) nanoclusters with a particle size of 4.5 +/- 1.1 nm were prepared using a new method: refluxing a mixture of potassium tetrachloropalladate(II) and PVP in methanol at 80 degrees C for 1 h followed by reduction with sodium borohydride. Palladium(0) nanoclusters prepared in this way were stable in solution for weeks, could be isolated as solid materials and were characterized by TEM, XPS, UV-vis, and XRD techniques. The PVP-stabilized palladium(0) nanoclusters were active catalysts in Heck and Suzuki coupling reactions of arylbromides with styrene and phenylboronic acid affording stilbenes and biphenyls, respectively, in high yield. Recycling experiments showed that PVP-stabilized palladium(0) nanoclusters could be used five times with essentially no loss in activity in the Heck and Suzuki coupling reactions. Copyright (C) 2009 John Wiley & Sons, Ltd.