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The Cu/ZnO system is a model for Cu/ZnO/Al2O3 catalysts, which are employed industrially for the synthesis of methanol. These catalysts are usually prepared from mixed basic carbonate precursors. A complex phase mixture, with constituents structurally related to the minerals rosasite andaurichalcite, is present at the industrially applied composition (Cu/Zn ≈ 70:30). Using minerals and phase-pure synthetic samples as references, a comprehensive characterisation of such a phase mixture, including the determination of the individual compositions of the different phases, has been attempted by complementary analytical laboratory techniques (XRD, TGA, IR). The results are critically discussed in light of the complexity of the system. A thermally very stable carbonate species ― well-known for mixed synthetic systems ― is also detected for the mineral reference samples. Significant amounts of amorphous phases are found to be present in the synthetic zincian malachite sample but not in synthetic aurichalcite or the catalyst precursor. A simplified explanation for the shift of the characteristic 20 reflection of the malachite structure as a function of Zn incorporation based on the varying average Jahn–Teller distortion of the MO6 octahedra is proposed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Raman spectroscopy at both 298 and 77K has been used to study a series of selected natural smithsonites from different origins. An intense sharp band at 1092 cm-1 is assigned to the CO32- symmetric stretching vibration. Impurities of hydrozincite are identified by a band around 1060 cm-1. An additional band at 1088 cm-1 is observed in the 298 K spectra but not in the 77K spectra is attributed to a CO32- hot band. Raman spectra of smithsonite show a single band in the 1405 to 1409 cm-1 range assigned to the ν3 (CO3)2- antisymmetric stretching mode. The observation of additional bands for the ν3g modes for some smithsonites is significant in that it shows distortion of the ZnO6 octahedron No ν2 bending modes are observed for smithsonite. A single band at 730 cm-1 is assigned to the ν4 in phase bending mode. Multiple bands be attributed to the structural distortion are observed for the carbonate ν4 in phase bending modes in the Raman spectrum of hydrozincite with bands at 733, 707 and 636 cm-1. An intense band at 304 cm-1 is attributed to the ZnO symmetric stretching vibration.

Minerals in the rosasite mineral group namely rosasite, glaucosphaerite, kolwezite, mcguinnessite, nullaginite and pokrovskite have been studied by Raman spectroscopy at 298 and 77 K and complimented with infrared spectroscopy. The spectral patterns for the minerals rosasite, glaucosphaerite, kolwezite and mcguinnessite are similar to that of malachite implying the structure is the same as malachite i.e. monoclinic. A comparison is made with the spectra of malachite. The symmetry of the carbonate anion in the rosasite mineral group is C2v or Cs and is composition dependent. Two (CO3)2- symmetric stretching modes are observed for the rosasite minerals at 1060 and 1090 cm-1. Two hydroxyl stretching modes are observed for the rosasite mineral group. The position of these bands is determined to be a function of the hydrogen bond lengths. Hydrogen bond distances for rosasite are calculated as 2.867, 2.799 and 2.780 A whereas for pokrovskite the distances are 3.280 and 2.999 A. The effect of lowering the temperature from ambient to 77 K results in a decrease of the hydrogen bond distances by 5%. Multiple Raman bands are observed in the 800 to 850 cm-1 and the 720 to 750 cm-1 regions and are attributed to ν2 and ν4 bending modes confirming the reduction of the carbonate anion in the rosasite structure.