Metal exchanged ferrierites as catalysts for the selective reduction of NO x with methane

Abstract

Metal ion (Co 2+, Mn 2+ or Ni 2+) exchanged ferrierites are very active catalysts for the reduction of NO x 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°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 Co 2+ is a function of Co 2+ exchange level and increases with the Co 2+ loading until it reaches an optimum value, whereas the selectivity for methane decreases with increasing Co 2+ loading. The presence of water vapour suppresses the activity of Co-ferrierite; however, under wet conditions, its activity is still much higher than Co-ZSM-5 at T > 500°C.