Effect of Hydrocarbon on DeNOx Performance of Selective Catalytic Reduction by a Combined Reductant over Cu-Containing Zeolite Catalysts

The effects of hydrocarbons (HCs) on a combined selective catalytic reduction (SCR) system by NH3 and mixed HCs for simulated exhaust over five different types of Cu2+-exchanged zeolite catalysts have been systematically examined according to the reaction temperature. CuSSZ-13 with three-dimensional (3D) small pores and CuFER with 2D medium- and small-pore channels showed good resistance to poisoning by heavy HCs such as dodecane (C12H26) and m-xylene (C8H10), while they were not tolerant to poisoning by short-chain HCs such as propylene (C3H6). The deNOx activities of CuZSM-5 and CuBEA containing 3D medium- and large-pore channels, respectively, were significantly decreased by the inclusion of C12H26 in the reaction feed stream. Another large-pore channel-based zeolite catalyst, CuMOR, showed a peculiar behavior of NOx reduction by the combined SCR: complete conversions of NO and NH3 without any side reactions in the medium-temperature region, probably due to small-pore side pockets alongside straight large-pore channels. The NH3/SCR performances of the catalysts tested varied depending on the structural features of the zeolite supports, while there were somewhat common features according to the reaction temperatures. Inhibition of surface NO oxidation by adsorbed HCs was the primary cause of the decrease in NH3/SCR performance at low temperature. In the medium-temperature region, NH3 reacted with HCs to form nitrile compounds through ammoxidation, resulting in a further decrease in deNOx activity due to a shortage of NH3 for NOx reduction. On the other hand, deNOx activity increased at high temperature due to NOx reduction by HCs present in the feed stream.