Mechanism of the selective catalytic reduction of NO in oxygen excess by propane on H-Cu-ZSM-5 - Formation of isocyanide species via acrylonitrile intermediate

NO+ nitrosonium species have been evidenced by in situ FTIR spectroscopy, o n H-ZSM-5 and H-Cu-ZSM-5 zeolites under NO+O-2 flow (near reaction conditio ns) at 623 K. Propane introduction in the reaction stream leads to NO+ disa ppearing and to acrylonitrile detection among reaction products on H-ZSM-5. In the presence of copper, acrylonitrile adsorbed on Cu+ is rapidly decomp osed into ethylene and cyanide Cu+CN in these conditions. In a further step , cyanide isomerises into isocyanide Cu+NC. A reaction pathway involving H and Cu+ zeolitic sites is proposed for isocyanide species formation from r eactants. The transformation of isocyanide species into N-2 (already publis hed) is recalled in order to define a complete mechanism for NOx selective catalytic reduction. (C) 2001 Elsevier Science B.V. All rights reserved.