Nanocatalysis on Tailored Shape Supports: Au and Pd Nanoparticles Supported on MgO Nanocubes and ZnO Nanobelts.

Active Au and Pd nano-particles supported on MgO nano-cubes, ZnO nano-belts, and transition metal-contg. MgO nano-belts were synthesized by combining evapn. and deposition-pptn. techniques. The high activity and stability of Au/CeO2 and Pd/CeO2 nano-particle catalysts deposited on MgO cubes were remarkable and imply a variety of efficient catalysts can be designed and tested using this approach. The significant increase in concns. of corner and edge sites in MgO nano-cubes make them well-defined supports to study the detailed mechanism of catalytic activity enhancement.

Vapor-phase synthesis of metallic and intermetallic nanoparticles and nanowires: magnetic and catalytic properties.

In this paper, we present several examples of the vapor-phase synthesis of intermetallic and alloy nanoparticles and nanowires, and investigate their magnetic and catalytic properties. In the first example, we report the vapor-phase synthesis of intermetallic aluminide nanoparticles. Specifically, FeAl and NiAl nanoparticles were synthesized via laser vaporization controlled condensation (LVCC) from their bulk powders. The NiAl nanoparticles were found to be paramagnetic at room temp., with a blocking temp. of approx. 15 K. The FeAl nanoparticles displayed room-temp. ferromagnetism. In the second example, we report the vapor-phase synthesis of cobalt oxide nanoparticle catalysts for low-temp. CO oxidn. The incorporation of Au and Pd nanoparticles into the cobalt oxide support leads to significantly improved catalytic activity and stability of the binary catalyst systems. Finally, we report the synthesis of nanowires of Ge, Mg, Pd, and Pt using the vapor-liq.-solid (VLS) method where the vapor-phase growth of the wire is catalyzed using a proper metal catalyst present in the liq. phase.

Nature of magnetism in Co- and Mn-doped ZnO prepared by sol-gel technique

Magnetic properties of sol-gel-prepd. bulk samples of Co0.05Zn0.95O and Mn0.05Zn0.95O are reported before and after annealing in 5%H2/95%Ar at 573 K for 6 h. The as-prepd. samples are paramagnetic with the magnetic susceptibility c following the Curie-Weiss law: c = c0 + C/(T-q). The magnitudes of C are consistent with the magnetic moments expected for the Co2+ and Mn2+ states. After hydrogenation, the magnetism of Mn/ZnO is unchanged but Co/ZnO acquires room-temp. ferromagnetism (RTFM) with a magnetic moment of 0.35mB/Co site and hysteresis loop with coercivity Hc .simeq. 600 Oe, remanence Mr .simeq. 0.45 emu/g, and satn. magnetization Ms .simeq. 1.2 emu/g. Electron magnetic-resonance spectroscopy at 9.28 GHz gives signals corresponding to the Co2+ and Mn2+ states for the paramagnetic states and a broad FM signal for the hydrogenated Co/ZnO. This difference under hydrogenation between Co/ZnO and Mn/ZnO suggests that n-type doping leads to stabilizing of RTFM in Co/ZnO but not in Mn/ZnO, the latter perhaps requiring p-type doping.