N-2 formation during pyrolysis of Mg-, Ca-, Sr- and Ba-loaded low rank coal at 1200 degreesC has been examined with a fixed bed quartz reactor in an inert atmosphere. At 10 degreesC/min, the Ca, Sr and Ba, except for Mg, increase considerably the formation rate between 850 and 1100 degreesC, and N-2 yield reaches greater than or equal to 60% at 1200 degreesC. The increase in the yield is almost equal to the decrease in yield of the corresponding char-N, which means that the Ca, Sr and Ba can enhance N-2 formation from char-N (and/or precursors) through solid phase reactions. In addition, all of the alkaline earth metals used promote secondary decomposition reactions of tar-N to NH3. When the effects of some factors on the catalytic activity of the Ca for N-2 formation are examined, pyrolysis temperature, heating rate and the sulfur in coal affect its performance. The in situ X-ray diffraction (XRD) measurements reveal that the Ca, Sr and Ba added are transformed to nanoscale particles of CaO, SrO and BaO with the mean crystalline sizes of 20-40 nm during heating at 900 degreesC where their activity for N-2 formation appears significantly. The oxides also enhance not only the proportion of crystallized carbon but yields of both H-2 and CO. These observations suggest strong interactions between fine particles of the oxides and char substrate. The mechanism of N-2 formation is discussed in terms of solid-solid reactions of CaO, SrO or BaO with heterocyclic nitrogen forms in char. (C) 2004 Elsevier B.V. All rights reserved.