In Situ Time-Resolved Energy-Dispersive XAFS Study on the Reduction Processes of Cu–ZSM-5 Catalysts

Abstract

Abstract The reduction process of Cu–ZSM-5 was investigated by a time-resolved energy-dispersive XAFS (DXAFS) technique. The spectra were recorded every second and the entire spectra were analyzed to elucidate the dynamic change of the local structure around the Cu species. Two Cu–ZSM-5 samples with different Cu loadings were prepared by an ion-exchange method followed by calcination. In the low-loading sample (84% ion-exchanged), Cu2+ cations dispersed isolatedly in the channels of ZSM-5, while in the high-loading sample (104% ion-exchanged) CuO particles were formed. The isolated Cu2+ cations were reduced to isolated Cu2+ cations at 400–450 K and the Cu+ ions were reduced to Cu0 at 550–650 K. The curve fitting analysis of the DXAFS data revealed that Cu4–6 clusters were initially formed in the reduction process. The clusters went out to the outer surface and grew into big particles. On the contrary, the CuO particles on the outer surfaces were reduced directly to Cu0 metallic particles at ca. 450 K. The dynamic structure change around the Cu species in the zeolite during the reduction with H2 was monitored in situ by DXAFS technique for the first time.