Ni-doped Carbon Nanofilaments (Ni-CNF): Preparation and Use as Reforming Catalyst

Abstract

The use of nanocarbons as heterogeneous catalyst support offers the possibility of achieving well-dispersed and thermally-stable catalysts. Because of their low internal diffusion resistance and relatively high specific surface, carbon nanotubes and carbon nanofilaments (CNF) are of special interest. This work reports on a CNF functionalization endeavour aimed at producing Ni-CNF as steam-reforming catalysts. Catalytic activity was studied parametrically on diesel and biodiesel steam reforming. Fresh and spent catalysts were investigated by scanning and transmission electron microscopy to visualize their morphology, by thermogravimetric analysis to evaluate metal (Ni) load, by X-ray diffraction to assess the presence of and changes in crystalline (and amorphous) phases, and by Brunauer Emmet and Teller analysis to appraise the catalyst surfaces. Reactants conversion and reformate composition (product yields) were reported over time-on-stream under various reaction conditions. Finally, CNF-supported Ni-catalysts were compared to equivalent multiwall carbon nanotube (MWCNT)-supported catalysts (Ni-MWCNT). The results demonstrated excellent initial reforming activity which declined relatively rapidly over time for Ni-CNF. The fast deactivation observed was due to CNF instability under reforming conditions which led to nanometrically-distributed Ni grain sintering and, consequently, loss of specific surface.