Serdar Akbayrak

Ruthenium(0) nanoparticles supported on multiwalled carbon nanotube as highly active catalyst for hydrogen generation from ammonia-borane.

Ruthenium(0) nanoparticles supported on multiwalled carbon nanotubes (Ru(0)@MWCNT) were in situ formed during the hydrolysis of ammonia-borane (AB) and could be isolated from the reaction solution by filtration and characterized by ICP-OES, XRD, TEM, SEM, EDX, and XPS techniques. The results reveal that ruthenium(0) nanoparticles of size in the range 1.4-3.0 nm are well-dispersed on multiwalled carbon nanotubes. They were found to be highly active catalyst in hydrogen generation from the hydrolysis of AB with a turnover frequency value of 329 min⁻¹. The reusability experiments show that Ru(0)@MWCNTs are isolable and redispersible in aqueous solution; when redispersed they are still active catalyst in the hydrolysis of AB exhibiting a release of 3.0 equivalents of H₂ per mole of NH₃BH₃ and preserving 41% of the initial catalytic activity even after the fourth run of hydrolysis. The lifetime of Ru(0)@MWCNTs was measured as 26400 turnovers over 29 h in the hydrolysis of AB at 25.0 ± 0.1 °C before deactivation. The work reported here also includes the kinetic studies depending on the temperature to determine the activation energy of the reaction (E(a) = 33 ± 2 kJ/mol) and the effect of catalyst concentration on the rate of the catalytic hydrolysis of AB, respectively.

Facile Synthesis of Three-Dimensional Pt-TiO2 Nano-networks: A Highly Active Catalyst for the Hydrolytic Dehydrogenation of Ammonia–Borane

Three-dimensional (3D) porous metal and metal oxide nanostructures have received considerable interest because organization of inorganic materials into 3D nanomaterials holds extraordinary properties such as low density, high porosity, and high surface area. Supramolecular self-assembled peptide nanostructures were exploited as an organic template for catalytic 3D Pt-TiO2 nano-network fabrication. A 3D peptide nanofiber aerogel was conformally coated with TiO2 by atomic layer deposition (ALD) with angstrom-level thickness precision. The 3D peptide-TiO2 nano-network was further decorated with highly monodisperse Pt nanoparticles by using ozone-assisted ALD. The 3D TiO2 nano-network decorated with Pt nanoparticles shows superior catalytic activity in hydrolysis of ammonia-borane, generating three equivalents of H2 .

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

Rhodium(0) nanoparticles supported on the surface of titanium dioxide (Rh(0)@TiO2) were in situ generated from the reduction of rhodium(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 show that (i) highly dispersed rhodium(0) nanoparticles with sizes in the range 1.3–3.8 nm were formed on the surface of titanium dioxide, (ii) Rh(0)@TiO2 shows high catalytic activity in hydrogen generation from the hydrolysis of ammonia borane with a turnover frequency value up to 260 min−1 at 25.0 ± 0.1 °C, (iii) the results of kinetic studies on the hydrogen generation from the hydrolysis of ammonia borane were also reported including the activation energy of 65.5 ± 2 kJ mol−1 for this reaction.

Metal Nanoparticles in Liquid Phase Catalysis

Tremendous efforts have been devoted on the development of efficient and safe hydrogen storage materials. Among them amine boranes, such as ammonia borane, dimethylamine borane, and hydrazine borane, have attracted much attention as promising chemical hydrogen storage materials. Recently, we have published many reports on the development of transition metal(0) nanoparticles dispersed in solution as highly active catalyst in hydrogen generation from amine boranes at room temperature. In this chapter, we put all the results given in those reports together to show (i) that transition metal(0) NPs dispersed in solution can catalyze the hydrogen generation from amine boranes at room temperature, (ii) how to improve the catalytic activity and durability of transition metal(0) NPs in solution by selecting a suitable stabilizer for a certain metal and varying the relative concentration of stabilizer in reaction solution.

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

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.

Dihydroxylation of olefins catalyzed by zeolite-confined osmium(0) nanoclusters: an efficient and reusable method for the preparation of 1,2-cis-diols

Addressed herein is a novel, eco-friendly, recoverable, reusable and bottleable catalytic system developed for the dihydroxylation of various olefins yielding 1,2-cis-diols. In our protocol, zeolite-confined osmium(0) nanoclusters (zeolite-Os0) are used as reusable catalyst and H2O2 served as a co-oxidant. Zeolite-Os0 are found to be highly efficient and selective catalysts for the dihydroxylation of a wide range olefins in an aqueous acetone mixture at room temperature. In all of the olefins surveyed, the catalytic dihydroxylation reaction proceeds smoothly and the corresponding 1,2-cis-diols are obtained in excellent chemical yield under the optimized conditions. The present heterogeneous catalyst system provides many advantages, such as being eco-friendly and industrially applicable over the traditional homogenous OsO4–NMO system for the dihydroxylation of olefins.

Immobilization of a molybdenum complex on the surface of magnetic nanoparticles for the catalytic epoxidation of olefins

Novel organic–inorganic hybrid heterogeneous nanocatalysts were obtained by covalent anchoring of a molybdenum(VI) complex of salicylidene 2-picoloyl hydrazine, MoO2(sal-phz)(CH3OH), (1) on the surface of magnetic nanoparticles functionalized by one of two routes: in the first method, the surface of magnetic nanoparticles is directly modified with 3-chloropropyltrimethoxysilane yielding 1A. In the second method, magnetic nanoparticles were silica-coated with tetraethoxysilane and then with 3-chloropropyltrimethoxysilane yielding the intermediate 2B. Then complex 1 was grafted on the surface of 1A or 2B through covalent interaction yielding 2A or 3B, respectively. The nanocatalysts 2A and 3B were characterized by FT-IR, XRD, SEM, TGA, EDX and vibrating sample magnetometry techniques. Nanocomposite 2A shows a much higher catalytic activity and stability in liquid phase epoxidation reactions, with t-BuOOH as the oxidant, compared to that of 3B. Additionally, the results of comparative study show that 2A is more active and reusable than the Mo complex immobilized SBA-15.

Synthesis, characterization, and catalytic activity of supported molybdenum Schiff base complex as a magnetically recoverable nanocatalyst in epoxidation reaction

Abstract A heterogeneous nanocatalyst was prepared via covalent anchoring of dioxomolybdenum(VI) Schiff base complex on core–shell structured Fe3O4@SiO2. The properties and the nature of the surface-fixed complex have been identified by a series of characterization techniques such as SEM, EDX, XRD, TGA, FT-IR, and VSM. The synthesized hybrid material was an efficient nanocatalyst for selective oxidation of olefins to corresponding epoxides with t-BuOOH in high yields and selectivity. The catalyst could be conveniently recovered by applying an external magnetic field and reused several times without significant loss of efficiency.

Nanoceria supported cobalt(0) nanoparticles: a magnetically separable and reusable catalyst in hydrogen generation from the hydrolysis of ammonia borane

Cobalt(0) nanoparticles supported on nanoceria (Co0/CeO2) were prepared from the reduction of cobalt(II) ions impregnated on the surface of ceria nanopowders. The magnetic Co0/CeO2 catalyst could be isolated from the reaction solution by using a magnet and characterized by using ICP-OES, XRD, TEM, EDX, BET and XPS techniques. The results reveal that cobalt nanoparticles with particle sizes in the range between 3.5 and 6.0 nm were successfully anchored on the surface of nanoceria. Co0/CeO2 is a magnetically separable and reusable catalyst in hydrogen generation from the hydrolysis of ammonia borane retaining its initial catalytic activity (TOF = 7.0 min−1) even after the fifth use. For comparison, other non-noble metal nanoparticles were also supported on nanoceria. Ni0/CeO2 and Cu0/CeO2 provide TOF values of 1.7 min−1 and 1.5 min−1, respectively, while Fe0/CeO2 is catalytically silent in the hydrolysis of ammonia borane at room temperature. The work reported here also includes the results of a kinetic study of the catalytic hydrolysis of ammonia borane depending on the temperature and catalyst concentration.

Nanozirconia supported ruthenium(0) nanoparticles: Highly active and reusable catalyst in hydrolytic dehydrogenation of ammonia borane

Nanozirconia supported ruthenium(0) nanoparticles (Ru0/ZrO2) were prepared by impregnation of ruthenium(III) cations on the surface of zirconia followed by their reduction with sodium borohydride at room temperature. Ru0/ZrO2 was isolated from the reaction solution by centrifugation and characterized by ICP-OES, XRD, TEM, SEM-EDS and XPS techniques. All the results reveal that ruthenium(0) nanoparticles were successfully supported on zirconia and the resulting Ru0/ZrO2 is a highly active and reusable catalyst for hydrogen generation from the hydrolysis of ammonia borane with a turnover frequency value of 173 min-1 at 25 °C. The reusability and catalytic lifetime tests reveal that Ru0/ZrO2 is still active in the subsequent runs of hydrolysis of ammonia borane preserving 67% of the initial catalytic activity even after the fifth run and Ru0/ZrO2 provides 72,500 turnovers (mol H2/mol Ru) before deactivation at 25 °C. Our report also includes the results of kinetic studies depending on the catalyst concentration and temperature to determine the activation energy (Ea = 58 ± 2 kJ/mol) for hydrolytic dehydrogenation of AB.