The Oscillatory Behaviour of Cu‐ZSM‐5 Catalysts for N2O Decomposition: Investigation of Cu Species by Complementary Techniques

Abstract

AbstractCopper‐exchanged ZSM‐5 (Cu‐ZSM‐5) is a promising catalyst thanks to the Cu redox pair. A particular feature of this material consists in the presence of spontaneous isothermal oscillations which take place during N2O decomposition reaction, depending on the operating conditions. In the present work, a set of five Cu‐ZSM‐5 catalysts was synthesised by three procedures and three different copper precursor concentrations: i) wet impregnation, ii) single ion exchange, and iii) double ion exchange. Catalytic tests revealed that the ion‐exchanged samples exhibit a low catalytic activity and no oscillatory behaviour, except for the twice‐exchanged sample which achieves an average N2O conversion of 26 % at 400 °C. Conversely, the impregnated samples reach higher levels of N2O conversion (66 % for Cu5ZSM5_WI and 72 % for Cu10ZSM5_WI) and demonstrate a similar oscillating pattern. Further investigations disclosed that the most active catalysts, characterised by the presence of oscillatory behaviour, have more abundant and easily reducible copper species (ICP, EDX and H2‐TPR) which interact better with the zeolitic support (FT‐IR). Catalytic tests under a long time on stream (TOS) suggest that either self‐organised patterns or deterministic chaos can be achieved during the reaction, depending on the operating conditions, such as temperature and contact time.