RESUMO
Low-temperature selective catalytic reduction (SCR) of NO is a new technique needing urgent development in flue gas cleaning. Elementary studies were done about selective catalytic reduction of NO from flue gas on magnetic iron oxides with ammonia at low and medium temperatures in a fluidized bed, such as Fe3O4 and gamma-Fe2O3. Magnetic field effects for NO removal on gamma-Fe2O3 were also researched with low assisted magnetic fileds. X-ray diffraction spectroscopy was used to identify and characterize the iron oxides catalysts. Results show that gamma-Fe2O3 is active in SCR at low temperatures, and Fe3O4 is apparently less active in SCR than gamma-Fe2O3, but Fe2O3 is also active in ammonia oxidation by O2 above 25 degrees C. Therefore, the optimal catalytic temperature zone in SCR on gamma-Fe2O3 includes 250 degrees C and adjacent temperature zone below it. Furthermore, a better NO conversion, which is 90%, is obtained at 250 degrees C on the gamma-Fe2O3 particle catalyst. In addition, chemisorption of NO on gamma-Fe2O3 is accelerated by assisted magnetic fields at 150-290 degrees C, thus the NO conversion is improved and higher NO removal efficiency of 95% is obtained at 250 degrees C. But the efficiency of NO removal decreases above 290 degrees C with the magnetic field. It is concluded that gamma-FeO3 catalyst is fit to be used in low-temperature SCR of NO with ammonia at 200-250 degrees C, which may suppress oxidation of ammonia and take advantage of positive effects by external magnetic fields.