Synthesis and spectroscopic characterisation of aurichalcite (Zn,Cu2+)5(CO3)2(OH)6; implications for Cu-ZnO catalyst precursors

The Cu-ZnO catalysts with variable Cu/Zn ratio, between Zn-rich and Cu-rich compositions have been investigated by a combination of electronic and vibrational spectra. Synthesized catalysts exhibit two d-d transition bands of Cu2+ ions in a distorted octahedral symmetry, at 7600 and 12900 cm-1 (1315 and 775 nm). The effect of structural cations substitution (Zn2+ and Cu2+) on band shifts observed in spectra of the synthetic samples. The observation of two broad features at ~7600 and 12900 cm-1 (1315 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 D3h to C2v/Cs 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