Decomposition of NH3 to N-2 with Fe and Ca catalysts supported on brown coal chars has been studied with a cylindrical quartz reactor from a viewpoint of hot gas cleanup. The catalyst is prepared by pyrolyzing a brown coal with Fe or Ca ions added. In the decomposition of 2000 ppm NH3 diluted with He at 750 degreesC and at a space velocity of 45,000 l/h, 2-6 wt% Fe catalysts are more active than not only 6 wt% Ca catalyst but also 8 wt% Fe catalyst loaded on a commercial activated carbon. The transmission electron microscope observations show that fine iron particles with the sizes of 20-50 nm account for the higher catalytic performances. When reaction temperature is increased to 850 degreesC, all of Fe and Ca catalysts on the chars achieve complete decomposition of NH3. The co-feeding of H-2 with 2000 ppm NH3 improves the performance of the 2% Fe catalyst at 750 degreesC, but contrarily the coexistence of syngas (CO/H-2 = 2) deactivates it remarkably, whereas the addition of CO2 to syngas restores the catalytic activity of the Fe to the original state without syngas. The powder X-ray diffraction and temperature programmed desorption measurements strongly suggest that the Fe and Ca catalysts promote NH3 decomposition through cycle mechanisms involving the formation of N-containing intermediate species and the subsequent decomposition to N2. (C) 2003 Elsevier Ltd. All rights reserved.