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

A multi-technique analytical approach has been used to show that carbonaceo us material entrapped in the channels system of Cu- ZSM-5 catalysts may con tribute to maintain the copper ions in the oxidation state +1. This suggest s that the reduction of Cu2+ to Cu+ does not only occur via water eliminati on from CuOH+ species or via oxygen evolution from [Cu-O-Cu](2+) species, b ut also via oxidation of the carbonaceous materials to give CO and CO2. Thi s mechanism occurs under high temperature (>300 degrees C) treatments in va cuo or He of Cu-ZSM-5 catalysts containing carbonaceous species and strongl y adsorbed water molecules in the first coordination shell of the Cu2+. Our results may support the hypothesis about the roles of O-2 and hydrocarbons in the SCR of NOx; O-2 maintains together with hydrocarbons the optimal va lence state of copper (Cu+) necessary to have the maximum conversion of NOx and hydrocarbons into N-2 and CO2. (C) 1999 Elsevier Science B.V. All righ ts reserved.