Synthesis and spectroscopic characterisation of aurichalcite (Zn,Cu 2+)5(CO3)2(OH)6; Implications for Cu-ZnO catalyst precursors

Abstract

The Cu-ZnO catalyst precursors with variable Cu:Zn ratio, between Zn-rich and Cu-rich compositions have been investigated by a combination of electronic and vibrational spectroscopy. Synthesized catalyst precursors exhibit two d-d transition bands of Cu2+ ions in a distorted octahedral symmetry, at 7,600 and 12,900 cm-1 (1,315 and 775 nm). The effect of structural cation substitution (Zn2+ and Cu2+) on band shifts is observed in the spectra of the synthetic catalyst precursors. The observation of two broad features at ∼ 7,600 and 12,900 cm-1 (1,315 and 775 nm) is a strong indication for Zn2+ substitution by Cu2+ ions. The result of multiple bands in the symmetric stretching and bending regions confirms the reduction of symmetry from D 3h to C 2v /C s for (CO3)2- ion in aurichalcite. The synthetic aurichalcite may be used as a standard for identification of spectral properties of naturally occurring anhydrous carbonate minerals. © 2007 The Author(s).