METAL EXCHANGED FERRIERITES AS CATALYSTS FOR THE SELECTIVE REDUCTION OF NO(X) WITH METHANE

Metal ion (Co2+, Mn2+ or Ni2+) exchanged ferrierites are very active catalysts for the reduction of NOx with methane in the presence of excess oxygen. Co-ferrierite yields about twice the nitric oxide conversion compared to Co-ZSM-5 at T> 500 degrees C, previously the most active catalyst reported for this reaction, and Co-ferrierite is more selective in the use of methane. The temperature for maximum nitric oxide conversion is a function of zeolite type and the cation exchanged, and this temperature increases in the following order: Co-ZSM-5 < Co-ferrierite < Mn-ferrierite < Ni-ferrierite. The turnover frequency (TOF) normalized by Co2+ is a function of Co2+ exchange level and increases with the Co2+ loading until it reaches an optimum value, whereas the selectivity for methane decreases with increasing Co2+ loading. The presence of water vapor suppresses the activity of Co-ferrierite; however, under wet conditions, its activity is still much higher than Co-ZSM-5 at T> 500 degrees C.