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

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Nonoxidative dehydrogenation of methanol to methyl formate over a CuMgO-based catalyst was investigated. Although the active site is metallic copper (Cu 0 ), the best reaction conditions were obtained by tuning the ratio of Cu/Mg and doping the catalyst with 1 wt % of Pd to achieve a very specific activity for methyl formate synthesis. On the basis of the CO 2 temperature-programmed desorption study, the basic strength of the catalyst plays a role in the efficient conversion of methanol to methyl formate via dehydrogenation. These CuMgO-based catalysts show excellent thermal stability during the reaction and the regeneration processes. Approx. 80% methanol conversion with constant selectivity to methyl formate was achieved even after 4 rounds of usage for a total reaction time exceeding 200 h, indicative of their potential for practical applications.

Source of materialCa3TaGa3SÌ20i4 (CTGS) was prepared by solid-state reaction of a stoichiometric mixture of 99.99% CaCC>3, Ta2Ü5, SiCb and 98% Ga2Ù3 powders. The powders were ground, mixed for 12 h and pressed into tablets. The latter were heated at 1373 Κ for 6 h to decompose CaCC>3 completely and produced CTGS ceramics. The ceramic materials were put into an Ir crucible and melted by RF-heating using an atmosphere of pure nitrogen plus a small amount of oxygen in order to avoid the evaporation of gallium suboxide from the melt during growth. The crystal pulling and rotation rates were 1-3 mm/h and 15-30 rpm, respectively. When the length of the crystal was sufficient, the temperature was lowered to room temperature at a rate of 30-180 K/h. The colorless and transparent single crystals of CTGS (16-14 mm in diameter and 37 mm in length) suitable for X-ray structure analysis were obtained. DiscussionIn the structure of Ca3TaGa3SÌ20u, the Ca-O bond lengths in the Ca0 8 dodecahedra are 2.363 (3) (1)°) are larger than the remaining (103.9(2)°), which are slightly different from the ideal value for a tetrahedron. From the above discussion, it is clear that the CaOs, TaOô, GaÜ4 and S1O4 polyhedra of the CTGS structure are all distorted, which leads to a high efficiency of second harmonic generation (SHG) in CTGS crystals. The distortion of polyhedra in CTGS crystal is somewhat higher than that of the Ca3NbGa3Si20i4 crystals [2], the more polyhedrons distortion, the higher the SHG efficiency. The SHG efficiency was studied by the powder technique and emission of a strong green light (532 nm) was observed, with an intensity weaker than that generated by LiNbC>3 and La3GasSiOi4 crystals but stronger than that obtained from Ca 3 NbGa3SÍ20i 4 crystals.

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