Growth of nitrogen-doped carbon nanotubes and fibers over a gold-on-alumina catalyst

Abstract

Nitrogen-doped carbon nanotubes (N-CNTs) were synthesized by chemical vapor decomposition of a N,C-precursor over a supported Au catalyst. Large quantities of carbon nanotubes with a compartmentalized structure containing ca. 5 at.% N were produced over a 1.5% Au/δ-Al 2O 3 catalyst with a mean diameter of Au particles equal to 2.8 nm under continuous flow conditions at 800 °С and 1 bar of the reaction gas mixture containing pyridine (Py) vapor (5 vol.%), Н 2 (10–20 vol.%) and Ar (balance). The majority of the N-CNTs obtained after 10 min have outer diameters (ODs) of 13–45 nm and closed tips without any encapsulated gold particles of the catalyst which indicates the “base-growth” mechanism of N-CNT formation. Carbon deposits synthesized for 30–135 min contain carbon fibers with OD values up to several micrometers, formed by self-assembling of N-CNTs, and individual N-CNTs. X-ray photoelectron spectra provide evidence for various chemical states of nitrogen (pyridinic, “quaternary” (graphitic) and pyrrolic nitrogen) in the N-CNTs, and these are discussed.