Decomposition of ammonia with iron and calcium catalysts supported on coal chars

Decomposition of NH3 to N2 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 °C 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 °C, all of Fe and Ca catalysts on the chars achieve complete decomposition of NH3. The co-feeding of H2 with 2000 ppm NH3 improves the performance of the 2% Fe catalyst at 750 °C, but contrarily the coexistence of syngas (CO/H2=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.