Facile Synthesis of Co–B Amorphous Alloy in Uniform Spherical Nanoparticles with Enhanced Catalytic Properties

Abstract

Control of the size and morphology of metallic nanomaterials enables mastery of their properties to enhance their catalytic performances. In this work, uniform Co−B amorphous alloy nanoparticles were synthesized by a simple chemical reduction of [CoX 4 ] − with BH 4 − in the presence of Bu 4 P + . With the characterization of X-ray diffraction, selective area electronic diffraction, X-ray photoelectron spectroscopy, differential scanning calorimetry, and transmission electron microscopy, the resulting Co−B spherical nanoparticles were identified to be amorphous alloys in an average particle size around 55 nm. The synergistic effect of the halide anion and Bu 4 P + cation is essential for the formation of monodisperse and uniform spherical nanoparticles. During the Heck-type carbon−carbon coupling reactions and the hydrogenation of butyraldehyde to n-butanol, the as-synthesized Co−B catalyst was extremely active compared with the conventional Co−B obtained via the direct reduction of cobalt ions with BH 4 − in aqueous solution. In addition, the as-prepared Co−B amorphous alloy also exhibited recyclability during the hydrogenation of butyraldehyde due to better thermal stability, which was related to the higher surface B content and the uniform particle size. ■ INTRODUCTIONAmorphous alloys, a kind of metastable materials with longrange disordered but short-range ordered structure, have attracted growing attention from both academia and industry because of their superior corrosion resistance, high mechanical toughness, and excellent magnetic, electronic, and catalytic properties in comparison with their crystalline counterparts. 1−4 As heterogeneous catalysts, amorphous alloys have been widely studied because of their excellent catalytic performances. 1−7 To form and stabilize the amorphous structure, some metalloids (e.g., B or P) should be incorporated in amorphous alloys, thus significantly affecting their physical and chemical properties. 8,9 Chemical reduction of metallic ions with borohydride (BH 4 − ) in aqueous solution has been most often used to synthesize the kind of M−B amorphous alloy catalysts, 8,9 but vigorous and exothermic reactions between metallic ions and BH 4 − usually induce particle aggregation, thereby reducing catalytic activity. In addition, the nonuniform nanoparticles are also responsible for the ready crystallization of amorphous alloys. 10 Although size-control synthesis of M−B (M = Ni, Co) amorphous alloys could been achieved through microemulsions, 11,12 using large amounts of organic phase in these systems may cause several environmental problem in the preparation process. Recently, we successfully developed a facile method to prepare uniform M−B (M = Ni, Co) amorphous alloy nanoparticles using [M(NH 3 ) 6 ] 2+ as the metal source, 10,13 but the strong coordination of NH 3 to metallic ions and, thus, the very slow reduction process resulted in relatively large M−B particles (>100 nm) unfavorable for catalytic activity.The coordination of halide ligands to metallic ions is a welladdr...

Tailoring the shape of amorphous nanomaterials: recent developments and applications

“…Spherical structure is also favorable in terms of surface energy. Nanospheres are the most reported shape of amorphous materials in the last decade (see Table 1), and they can be composed of calcium carbonate (CaCO 3 ) [43][44][45][46][47], silicon (Si) [48][49][50][51][52], metals or their compounds [53][54][55][56][57][58][59][60][61]. CaCO 3 is abundant in the natural world, and a typical model system used to mimic the mineralization process of biominerals [43].…”

“…Apart from the common amorphous nanospheres composed of CaCO 3 and Si, and amorphous nanospheres of some other compounds, such as Se [53], TiO 2 [54][55][56][57], Co-B alloy [58], FePO 4 [60] and zinc citrate [61], have also been prepared, generally by facile solution routes. Recently, Kuai et al [59] reported an interesting aerosol-spray-as- …”

“…Because of their complex internal structure, the growth of amorphous nanomaterial is usually ruleless, resulting in irregular particles using solution approaches or thin films using deposition techniques as their conventional shape. Over the last decade, inorganic amorphous nanomaterials with a variety of novel shapes, with notable examples including spheres, wires, tubes, fibers, cubes, octahedra, polyhedra, flower-like spheres and arrays, which are summarized in spheres (hollow) CaCO 3 gas-diffusion solution method [43] spheres CaCO 3 solution method [44] spheres CaCO 3 solution method [45] spheres CaCO 3 solution method [46] spheres CaCO 3 solution method [47] spheres Si thermal decomposition [48] spheres Si solution method [49] spheres Si/Ti solution method [50] spheres Si:H thermal decomposition [51] spheres Si:H thermal decomposition [52] spheres Se solution method [53] spheres TiO 2 solution method [54][55][56] spheres (hollow) PbO-TiO 2 sol-gel method [57] spheres Co-B alloy solution method [58] spheres 2 solution method [80] nanoboxes Ni(OH) 2 solution method [81] nanocubes (hollow) Co(OH) 2 solution method [82] nanopolyhedra (hollow) CoS solution method [83] mesopores nanocubes ZnSnO 3 solution method and annealing [84] REVIEWS SCIENCE CHINA Materials Table 1, have been synthesized. In this review, we explain how these exquisite nanostructures can be obtained by a number of innovative methods.…”

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“…Taking into account the weaker coordination of halide ligands to metallic ions than that between NH 3 and metallic ions, 103 [CoX 4 ] 2À ions formed in the presence of KCl and Bu 4 PBr was used as cobalt sources for the preparation of Co-B amorphous alloy. 48 The simple reduction of [CoX 4 ] 2À ions with borohydride resulted in monodispersed and uniformly spherical NPs with an average particle size about 55 nm (Fig. 23).…”

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