Effect of pretreatments in various atmospheres on the transient DeNO(x) activity of a Cu-MFI catalyst

Steady-state and transient activities of a 1.47 wt% Cu-MFI (Si/Al = 27) catalyst in the selective catalytic reduction of NOx with hydrocarbons (HC) were investigated in the 473-723 K temperature range with propene and propane as reducers, Under steady-state conditions (1000 ppm NO + 1700 ppm HC + 5% O-2) propene gives the highest NO conversion at 673 K while propane is a reducer which is much better at 573-623 K. Transient activities were also investigated by comparing the NO conversion in the presence of Oz after different pretreatments in WC or HC + NO. On the fresh, non-pretreated catalyst, a NO uptake fan be observed without any formation of N-2. Reacting the pretreated catalyst with NO + O-2 leads to transient formation of N-2 and CO2 with the following efficiency of the hydrocarbons: propene > propane, The pretreatment in HC + NO is significantly better than in HC alone and leads to formation of nitrogen-containing species which are further decomposed into N-2 and CO2, but only in the presence of O-2. These nitrogen-containing species cannot react with NO alone. (C) 1996 Academic Press, Inc.