Mechanism of selective catalytic reduction of NO over Ag/Al2O3 with the aid of non-thermal plasma

The mechanism of selective catalytic reduction (SCR) of NO by propene over Ag/Al(2)O(3) was investigated with the aid of non-thermal plasma (NTP) using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The HC-SCR reactions were proposed to be divided into two main processes, viz. nitration and reduction, which were aimed to generate isocyanate species (-NCO) and reduce NO(x), respectively. The nitration process of thermal HC-SCR was suggested to be effective only in presence of abundant electron-rich organic species. The efficiency of the reduction process was determined by the balance between the oxidation of isocyanate species and the reaction of isocyanate species with NO(3)(-). Thermal C(3)H(6)-SCR was found to be ineffective below 400 degrees C, mainly owing to the inability of propene oxidation to provide oxygenates for nitration. With the assistance of NTR the nitration process could be promoted by activating propene in an O-predominant or N-predominant environment to electron-rich organic oxygenates or C(x)H(y)O(z)N species (such as RCN and RNO(2), etc.), respectively. Nitrates reacts with electron-rich organic oxygenates effectively and generates isocyanate species. The C(x)H(y)O(z)N species can directly oxidized by oxygen or decomposed into isocyanate species over Ag/Al(2)O(3). The lack of nitrates or the inability of nitrates to provide enough NO(2)(+) in the reduction process probably leads to the low deNO(x) activities in NTP-assisted C(3)H(6)-SCR in presence Of SO(2) or at low temperatures below 250 degrees C. (C) 2008 Elsevier B.V. All rights reserved.