Clean Technology 2008
U.M. Graham, R.A. Khatri, N.J. Coville, A. Dozier, B.H. Davis
University of Kentucky, US
Fischer Tropsch, nanochannels, iron catalyst, conversion, nanotubes
Carbon nanotubes (CNTs) represent a distinctive class of catalyst supports and provide promising scenarios for catalytic reactions including fuel synthesis. The mobility of supported catalytic nanoparticles (NPs) on CNTs typically results in agglomeration leading to a decrease in effectiveness of the catalytic behavior over time. Enhanced production of synfuels via Fischer Tropsch process relies on nano-sized transition metal catalysts, predominantly iron or cobalt. Here we present a CNT system which limits the surface mobility of ultra small iron catalyst particles on CNT surfaces during fuel synthesis as evidenced by long term stability and activity studies. This is accomplished through the embedding of the catalytic NPs in nano-sized channels or “docking stations” oriented normal to the CNT surface. Calcium is shown to play a significant role in the formation of the docking stations. Possible mechanisms for the formation of the docking-stations will be presented including the role of calcium nanoparticles as gasification catalyst. HRTEM and EELS mapping of calcium and iron nanoparticles allows the determination of spatial distribution of the 1-2 nm sized catalyst particles. The confinement or harboring of the 1-2 nm iron catalyst particles in the docking stations along the CNT walls is described for the first time.