Synthesis and Characterization of Branched fcc/hcp Ruthenium Nanostructures and Their Catalytic Activity in Ammonia Borane Hydrolysis

Abstract

Several systems have shown the ability to stabilize uncommon crystal structures during the synthesis of metallic nanoparticles. By tailoring the nanoparticle crystal structure, the physical and chemical properties of the particles can also be controlled. Herein, we synthesized branched nanoparticles of mixed fcc/hcp ruthenium, which were formed using tungsten carbonyl [W(CO) 6 ] as both a reducing agent and a source of carbon monoxide. The branched particles were formed from multiple particulates off a central core. Highresolution transmission electron microscopy (HRTEM) clearly showed that the branched structures consisted of aligned hcp crystal domains, a mixture of fcc and hcp crystal domains with several defects and misalignments, and particles that contained multiple cores and branches. Branched particles were also formed with molybdenum carbonyl [Mo(CO) 6 ], and faceted particles of hcp and fcc were formed with rhenium carbonyl [Re 2 (CO) 10 ] as a carbon monoxide source. Without metal carbonyls, small particles of spherical hcp ruthenium were produced, and their size could be controlled by the selection of the precursor. The ruthenium nanoparticles were tested for ammonia borane hydrolysis; the branched nanoparticles were more reactive for catalytic hydrogen evolution than the faceted fcc/hcp nanoparticles or the spherical hcp nanoparticles. This work showcases the potential of crystal phase engineering of transition metal nanoparticles by different carbon monoxide precursors for tailoring their catalytic reactivity.P hysical and chemical properties, such as magnetism and catalytic activity, are intrinsically related to the crystal structure of nanomaterials. 1−3 Over the past two decades, a variety of noble metals have been produced in uncommon or previously unknown crystal structures, including Au, Ag, Pd, Rh, and Ru. 4 For example, face-centered cubic ( fcc) Ru nanoparticles were synthesized by Kitagawa et al., showing increased catalytic activity toward CO oxidation at larger particle sizes over nanoparticles made of the common crystal structure for Ru, i.e., hexagonal close packed (hcp). 5 Further work with fcc Ru and fcc Ru@Pt demonstrated enhanced catalytic properties over hcp Ru in the hydrogen evolution reaction, 6,7 hydrogen oxidation reaction, 8 and oxygen evolution reaction. 9 Nanoframes of fcc Ru were also reported to exhibit increased activity in the ammonium hydrolysis reaction compared to nanowires of hcp Ru. 6 These results indicate that fcc Ru is a promising system for increasing the activity of Ru catalysts. Shape-controlled fcc Ru nanoparticles have been synthesized as cages, frames, and cubes, using a core of a second metal as a template. 6,9,10 Branched or hierarchical nanoparticles have shown great promise in the stabilization of uncommon crystal structures because the reactions generally have multiple growth stages giving rise to complex morphologies. 11−14 Another common

Shape controlled iron oxide nanoparticles: inducing branching and controlling particle crystallinity

“…Etching typically occurs either during the growth or via a post-preparative step to remove material selectively from faceted surfaces and rearrange the particle into a multiply branched structure. 5,11 In aggregative growth mechanisms the final particles can be made up of aligned 6 or unaligned 12 crystal domains. The alignment of the crystal domains to form a single crystal occurs via aggregation in solution called oriented attachment where the facets of growing particles align in solution.…”

High-Grade Biofuel Synthesis from Paired Electrohydrogenation and Electrooxidation of Furfural Using Symmetric Ru/Reduced Graphene Oxide Electrodes

“… 16 The SAED pattern in Figure 1 e displays clear diffraction rings of (110), (101), and (112) corresponding to polycrystalline hcp Ru, indicating pure Ru NP formation under microwave irradiation. 28 The FE-SEM images in Figure 1 f,g show the morphology of the as-prepared Ru/RGO nanocomposite. The magnified FE-SEM image in Figure 1 g shows that the smaller diameter Ru NPs were successfully anchored onto the RGO framework.…”

Non‐Noble Metal‐Based Catalysts Applied to Hydrogen Evolution from Hydrolysis of Boron Hydrides

“…The hydrolysis of both NH 3 BH 3 and NaBH 4 solutions requires appropriate catalysts to improve their sluggish kinetics. The most well-known efficient catalysts are noble metal-based materials, [8][9][10][11][12][13][14][15][16] but their scarce reserves and accompanying expensive prices ineluctably impede their widespread commercial application. Therefore, it is urgent to develop efficient non-noble metal-based catalysts.…”