| In recent years, hydrogen energy has become an ideal energy due to its zero carbon emission and high heat of combustion, when compared to traditional fossil fuels, and hence, has received more and more attention. Solid hydrogen storage materials like sodium borohydride and dimethylamine-borane have high hydrogen capacity, high stability, nontoxicity, and low prices when compared to ammonia-borane. Their hydrolysis by-product metaborate can be recycled; therefore, borohydride compounds have become a focus of future solid hydrogen storage materials.Polymer gels have been rapidly developing in the field of catalysts. Hydrogels with pendant groups(-SO3H、-OH、-COOH、-NH2) are hydrophilic polymers with crosslinked network. They have swellable, porous structures in water or organic solvent, and their chemical functionality and interaction with metals can be tailored. Hydrogels combine the properties of solid and fluid and their internal crosslinked structures are rich in water or organic solvent, which is suitable for dispersing metals, and thus become reaction sites in aqueous or non-aqueous conditions.Preparation of two types of magnetic polymer particles was developed in this study through nickel seeding without noble metal activation, followed by electroless plating of nickel onto hydrophobic and hydrophilic polymer nanospheres. Dynamic light scattering characterization of the Ni embedded hydrophilic copolymer nanogel particles in water shows their hydrodynamic diameters of approximately 411.9 nm which are larger than the diameters shown in the TEM image because the nanogel swells in water during the light scattering analysis. On the contrary, the hydrophobic cores of the poly(N-tert-butyl acrylamide)(PNt BAM) spheres bring about little absorptivity of water molecules in the interior. High resolution transmission electron microscopy and X-ray photoelectron spectroscopy demonstrated that the Ni was mainly in the form of Ni O. Hydrogel supported Pd/Ni alloys were also prepared and found that the Pd/Ni ratios can affect the sizes of nanoparticles. The metal nanoparticle sizes dispersed in the hydrogel is bigger than the hydrogel mesh sizes, which ensures that the metal nanoparticles can be firmly fixed in the hydrogel.The catalysts exhibited excellent activities for hydrogen generation from hydrolysis of dimethylamine-borane and sodium borohydride, in which they have high TOF and low activation energy and the hydrogel supported Pd/Ni catalyst has an activation energy of 34.95 k J/mol. These features are better than most of the monometallic noble catalysts. PNt BMA supported Ni particles can be reused at least 7 times and the hydrogel supported Pd/Ni catalyst can be recycled at least 21 times.Nowadays, aromatic amine compounds are very important organic intermediates, which are widely used in dye, pesticide, and pharmaceutical synthesis. Reduction of nitroarene with hydrazine hydrate has the advantages of high selectivity, lower price than sodium borohydride and the oxidation products of hydrazine hydrate are nitrogen and water which both are environmental friendly. The nanogel supported Ni catalyst exhibited good catalytic activity in hydrogen transfer reactions of aromatic nitro compounds with hydrazine hydrate as hydrogen donor. The effect of the hydrazine hydrate amount on the reaction was examined for the nitrobenzene reduction. The result showed that a molar ratio of 1:15 for the substrate to hydrazine hydrate was best suitable for reduction. The optimized conditions were used for reduction of a series of nitrobenzene compounds, giving rise to high yields of aromatic amines. Kinetic analysis showed that the Arrhenius activation energy was 133.7 k J/mol, the enthalpy was 130.9 k J/mol, and the entropy was 102.8 J/(mol?K). |
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