Formation of N-2 during temperature programmed pyrolysis at 10degreesC/min of low rank coals up to 1350degreesC has been studied with a fixed bed quartz reactor. When Ca2+ ions are exchanged with the raw or demineralized coals by using a saturated aqueous solution of Ca(OH)(2), the Ca enhances the formation rate mainly at around 820 or 850-1100degreesC, respectively. The determination of mineral components removed by demineralization strongly suggests that the low temperature enhancement for the raw coals arises from synergistic effect between naturally present Fe ions and the added Ca. On the other hand, the rate increase observed for the demineralized coals in the higher temperature region originates from the intrinsic activity of the Ca catalyst, The X-ray diffraction (XRD) measurements after pyrolysis of the demineralized coals reveal that the average crystallite sizes of CaO derived from the exchanged Ca2+ are as small as 30-50 nm and the Ca promotes carbon crystallization upon pyrolysis. It is likely that fine particles of CaO catalyze N-2 formation at 850-1100degreesC through solid-phase reactions of heterocyclic nitrogen forms in char. (C) 2002 Elsevier Science Ltd. All rights reserved.