Effect of hydrogen on the synthesis of carbon nanofibers by CO disproportionation on ultrafine Fe₃O₄

Abstract

Carbon nanofibers (CNFs) are grown by catalytic CO disproportionation over ultrafine Fe 3 O 4 catalyst at a hydrogen concentration of 0-29.17%, and the time-depending rates of CNFs growth are continuously monitored and the morphologies of the as-synthesized CNFs are analyzed. Increasing H 2 concentration will lower CO dissociation energy and assist catalyst reconstruction so as to shorten the induction period and increase the growth rate of CNFs, but it will also increase the rate of catalyst deactivation because carbon hydrogasification is not possible and carbon diffusion in the catalyst particle is rate limiting. As a result of H 2 -induced catalyst reconstruction and carbon deposition, the morphology of the CNFs changes from twisty to helical and to straight and becomes less entangled when the H 2 concentration is increased. 