Polyacrylonitrile-derived activated carbon as a model of coal char has been heated in high-purity He at 10 degrees C/min up to 1000 degrees C with a flow-type fixed bed quartz reactor, and the catalysis of N-2 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 degrees C, and N-2 yield up to 1000 degrees 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 N-2 formation by iron and the formation of austenite occur at almost the same temperature range of 600-1000 degrees 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 N-2. (C) 2011 Elsevier B.V. All rights reserved.