NICKEL-CATALYSTS SUPPORTED ON CARBON NANOFIBERS - STRUCTURE AND ACTIVITY IN METHANE DECOMPOSITION

Structures of Ni catalysts supported on filamentous carbon (CFC) produ ced by methane decomposition over coprecipitated Ni and Ni-Cu/alumina catalysts were studied by EXAFS and TEM. Thermal pre-treatment in N-2 at 350 degrees C of samples impregnated by nickel nitrate precursor wa s found to produce either NiO or nickel carbide, Ni3C, phase. This was explained by different reducing properties of the carbon nanofibers w hich depend on the surface structure. High stability of the Ni/C catal ysts in methane decomposition reaction at 550 degrees C was found with those prepared from only nickel chloride precursor, due to the format ion of large (30-70 nm) Ni particles further leading to new carbon fil aments growth. Data implies a common mechanism of the filamentous carb on deposition in all Ni-based catalysts, independent of the support (s ilica, alumina, carbon) being used. However, accumulation of filamento us carbon is strongly influenced by morphology and texture of the supp ort.