Iron-catalyzed nitrogen removal as N2 from PAN-derived activated carbon

Polyacrylonitrile-derived activated carbon as a model of coal char has been heated in high-purity He at 10 °C/min up to 1000 °C with a flow-type fixed bed quartz reactor, and the catalysis of N2 formation by precipitated iron has been investigated by use of XPS, TEM and XRD methods. Fine iron particles with the average size of 15 nm increase remarkably the formation rate between 600 and 1000 °C, and N2 yield up to 1000 °C reaches about 65% at 1.9 mass% Fe. The XPS and XRD measurements after heat treatment exhibit that nitrogen functionality does not change significantly, but carbon crystallization occurs through the dissolution of iron nanoparticles into the carbon substrate. The in situ XRD analyses during heating reveal the formation of austenite that is solid solution of Fe and N (and/or C). Interestingly, the catalysis of N2 formation by iron and the formation of austenite occur at almost the same temperature range of 600–1000 °C. It is thus likely that nanoscale iron particles move in the carbon matrix and react with heterocyclic nitrogen in order to produce the solid solution, which is subsequently decomposed into N2.

Figure optionsDownload as PowerPoint slideHighlights
► Fine particles of FeOOH are precipitated onto PAN-derived activated carbon as a model of coal char.
► The resulting sample is heated in an inert gas at 10 °C/min up to 1000 °C with a fixed bed quartz reactor.
► Nanoscale iron particles can promote N2 formation from heterocyclic nitrogen at 600–1000 °C.
► The in situ XRD analyses during heating show the formation of solid solution of Fe and N (and/or C).
► The iron-catalyzed N2 formation may proceed through a mechanism involving the solid solution.