Platinum/graphite nanofiber catalysts of various structure:: Characterization and catalytic properties

Platinum/graphite nanofiber (Pt/GNF) catalysts were prepared by impregnating three types of GNF (herringbone, H; ribbon, R; and platelet, P) with Pt salt dissolved in organic solvents. Electron microscopy showed small Pt particles (1.5-8 nm) in all catalysts. The ethanol-toluene solvent of the Pt salt corrupted the ordered nanofiber structure of Pt/GNF-P. Butanol solvent did not harm the nanofiber. Nevertheless, X-ray photoelectron spectroscopy (XPS) indicated that the structure of all three samples was essentially graphitic. Surface Pt enrichment was observed on Pt/GNF-H and depletion on the (corrupted) Pt/GNF-P. Catalytic properties were checked in the skeletal reactions of hexane in H-2 between 543 and 603 K. Both the activity and the formation of isomers were the most marked on Pt/GNF-H, where also the hydrogen migration to storage positions on the support was most pronounced. Repeated regeneration with oxygen did not alter the catalytic propensities. High isomerization selectivity is attributed to creating hydrogen-rich active sites on Pt by the back-migration of hydrogen retained by the nanofiber structure of the support. Product selectivities can be used as an indirect indicator for the hydrogen storage capacity of GNF samples.