X-ray absorption edge and exafs study of the copper sites in zno methanol synthesis catalysts

Abstract

X-ray absorption edge and EXAFS data are presented for the binary form of the Cu-ZnO methanol synthesis catalysts. For the calcined catalyst, a significant amount of the Cu(II) is found to be doped into the tetrahedral sites of the ZnO lattice based on a quantitative analysis of X-ray absorption difference edges. Alternatively, the EXAFS spectra exhibit less evidence for this Cu(II)/ZnO site, which is attributed to disorder effects on the outer-shell Cu-Zn EXAFS. A quantitative analysis of the EXAFS for the reduced catalyst demonstrates that it contains metallic Cu, small Cu clusters, and a Cu oxide phase. Analysis of the X-ray absorption edges of the reduced catalyst shows that this oxide phase contains both Cu2O and tetrahedral Cu(I) sites. Thus, the dispersed phase in the methanol synthesis catalyst, which corresponds to ~50% of the Cu, consists of both a small Cu cluster component and Cu(I) doped into the ZnO lattice. © 1989, American Chemical Society. All rights reserved.