Time-resolved energy-dispersive XAFS study on the reduction process of Cu-ZSM-5 catalysts

The time-resolved reduction process of copper cations in ZSM-5 during temperature-programmed reduction (300-700 K) was studied by energy dispersive X-ray absorption fine structure (DXAFS). The Cu K-edge DXAFS spectra for isolated Cu2+ species in the channels of ZSM-5 were recorded at an interval of 1 s during the reduction. The curve fitting analysis of the EXAFS data and the XANES analysis revealed that the isolated Cu2+ species in the channels were reduced stepwise. They were reduced to isolated Cu+ species at 400-450 K and the Cu+ species to Cu0 metallic clusters at 550-650 K. Small clusters like Cu4 were initially formed, followed by particle growth. A small part of them went out to the outer surfaces of ZSM-5 during the reduction.