Palladium(0) nanoparticles supported on polydopamine coated Fe3O4 as magnetically isolable, highly active and reusable catalysts for hydrolytic dehydrogenation of ammonia borane

Abstract

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 (Pd⁰/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 Pd⁰/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. Pd⁰/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 °C. Magnetically isolable Pd⁰/PDA–Fe₃O₄ catalysts preserve their initial catalytic activity even after the tenth use providing the release of 3 equivalent H₂ 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.