In situ EXAFS analysis of the temperature-programmed reduction of Cu-ZSM-5.

High resolution in situ EXAFS during temperature-programmed reduction was performed on Cu-ZSM-5 to elucidate the state of copper under reaction conditions. Improvements in hardware and software allowed rapid acquisition of both XANES and EXAFS data during reduction, in particular, allowing observation of characteristic preedge features from various Cu oxidation states. EXAFS fitting and factor analysis of the normalized XANES edge were performed in an attempt to determine the number and type of Cu species present. The data suggests that initially only Cu(2+) is present in two different locations on the zeolite; both states reduce to Cu(1+) in both H(2) and CO, but under different conditions. Under H(2) conditions, migration of Cu(1+) to Cu(0) clusters is observed at 450 degrees C, while no metallic state is observed during CO reduction.