Controlable Chemistry Leading to Nanoscale Metal and Metal Boride Particles by way of Borohydride Reduction of Nickel and First Transition Metals

DELICIA ACOSTA; ELIO GONZO; HUGO DESTEFANIS

Cancun -Mexico

Congreso; International Material Research Congress, XVII- IMRC 2008; 2008

Sociedad Mexicana de Materiales A.C. y Association of Corrosion Engineers NACE International Section Mexico

It has been known for a long time that it is possible to precipitate black amorphous solids from solutions containing nickel by adding sodium or lithium borohydride [1]. The chemistry of the process is however not well understood. As a result, the literature is replete with various recipes for powder preparation given rise to products of varying nature and composition. These precipitates are considered to exhibit catalytic activity in all kinds of reduction reactions [2]. Although their composition remained unclear for 40 years, their annealing behavior was investigated and found to lead to crystalline Ni2B [3] or Ni3B and elemental nickel (Ni°) at temperatures near 773K.  In this report reaction steps leading to the formation of fine powders of nickel, and nickel borides are reported. Nickel boride (NiB) and nickel metal dopants boride (MNiB) amorphous catalysts were prepared following a previously reported technique [4]. Nickel borides doped with transition metal (Cr, Mn, Fe, Co, Cu, and Zn) MNiB, 4 % w/w respect to Ni were prepared by chemical reduction of nickel and metallic salts in methanol solution with borane-tetrahydrofurane (BH3-THF) complex obtained in aprotic solvent (THF anhydrous).  Different techniques were used to characterize these materials. The MNiB amorphous structure was verified by XRD. Thermal treatment in N2 shows Ni°, Ni2B and NiO phases.  Spongy-morphology was evident by SEM studies in all cases. XPS and TEM shows that doped and non-doped nickel boride were present as Ni° in metallic state as principal phase and nickel alloying with boron was observed in minor quantities. The oxidation stability, magnetic susceptibility and catalytic effect are correlated with parameters of each dopants metal. [1] Brown C, (1970) J. Org. Chem.35 (6), 1900. [2] Molvinger K, Lopez M, Court J, (1999) Tetrahedron Lett. 40, 8357, J. Catal. A: Chemical, 150, 1999, 267. [3] Glavee G, Klabunde K, Sorensen C, Hadjipanayis G, (1994),Langmuir 0, 4726. [4] Destefanis H, Acosta D, Gonzo E, (1992) Catalysis Today 15, 555:564.