ISSN:
1572-879X
Keywords:
time-resolved XAFS
;
energy-dispersive XAFS
;
Cu-ZSM-5
;
structure change
;
reduction process
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
Notes:
Abstract The time-resolved reduction process of copper cations in/on ZSM-5 during temperature-programmed reduction (300–700 K) was studied by energy-dispersive X-ray absorption fine structure (DXAFS) as well as transmission electron microscopy (TEM). Two Cu-ZSM-5 samples with different Cu loadings were prepared by an ion-exchange method. The Cu K-edge DXAFS spectra for isolated Cu2+ species in the channels of ZSM-5 and CuO particles on the outer surfaces 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. In contrast, CuO particles on the outer surfaces were reduced directly to Cu0 metallic particles around 450 K.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1023/A:1019020528353
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