Characterization by X-ray absorption, X-ray powder diffraction and magnetic susceptibility of Cu-Zn-Co-Al-containing hydroxycarbonates, oxycarbonates, oxides, and their products of reduction
- Universita La Sapienza, Rome (Italy)
Copper-based oxide systems are of interest for use as methanol synthesis catalysts. Copper-zinc-cobalt-aluminum-containing crystalline hydroxycarbonates having hydrotalcite structure have been prepared by coprecipitation. X-ray powder diffraction (XRPD), magnetic susceptibility, and extended X-ray absorption fine structure (EXAFS) indicate that Cu{sup 2+}, Zn{sup 2+}, and Co{sup 2+} are present in an octahedral environment. Calcination of the hydroxycarbonates at 723 K produces quasi-amorphous oxycarbonates where Cu{sup 2+} and Co{sup 2+} still retain octahedral coordination and cobalt is almost completely oxidized to Co{sup 3+}. The coordination of Zn{sup 2+}, at this stage, is intermediate between the octahedra one of the precursors and the tetrahedral one of ZnO and Zn-based spinels. Further calcination at 973 K produces a mixture of crystalline oxides such as CuO, ZnO, CuAl{sub 2}O{sub 4}, ZnAl{sub 2}O{sub 4}, and ZnCo{sub 2}O{sub 4}. EXAFS analysis of these samples indicates that copper is mainly in a fourfold coordination (Although two longer Cu-O distances are also detected), zinc is tetrahedral, and cobalt (as Co{sup 3+}) is essentially octahedral. EXAFS and XANES investigations performed after in situ reduction (10% H{sub 2}/N{sub 2}, at 523 and 623 K) on the oxycarbonates and oxides reveal that the total Cu{sup 2+} {yields} Cu{sup 0} reduction occurs only at 623 K in both series of samples, Co{sup 3+} is reduced to Co{sup 2+} only at 623 K in the oxycarbonates, and Zn{sup 2+} is never reduced.
- OSTI ID:
- 223734
- Journal Information:
- Journal of Solid State Chemistry, Journal Name: Journal of Solid State Chemistry Journal Issue: 2 Vol. 121; ISSN 0022-4596; ISSN JSSCBI
- Country of Publication:
- United States
- Language:
- English
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