On the role of carbonaceous material in the reduction of Cu2+ to Cu+ in Cu-ZSM-5 catalysts Original Research Article

A multi-technique analytical approach has been used to show that carbonaceous material entrapped in the channels system of Cu- ZSM-5 catalysts may contribute to maintain the copper ions in the oxidation state +1. This suggests that the reduction of Cu2+ to Cu+ does not only occur via water elimination from CuOH+ species or via oxygen evolution from [Cu–O–Cu]2+ species, but also via oxidation of the carbonaceous materials to give CO and CO2. This mechanism occurs under high temperature (>300°C) treatments in vacuo or He of Cu-ZSM-5 catalysts containing carbonaceous species and strongly adsorbed water molecules in the first coordination shell of the Cu2+. Our results may support the hypothesis about the roles of O2 and hydrocarbons in the SCR of NOx; O2 maintains together with hydrocarbons the optimal valence state of copper (Cu+) necessary to have the maximum conversion of NOx and hydrocarbons into N2 and CO2.