Copper/Zinc Oxide Catalysts. Part XII. Solid Solution Formation in the CuO/ZnO System. X-Ray Powder Diffraction Study

Summary.

Coordination compounds Zn(mal)(H₂O)₂ (ZMH) (mal=maleate anion (C₂H₂(CO₂)₂^2-)), Cu_0.06Zn_0.94(mal)(H₂O)₂ (ZCMH), Cu(mal)(H₂O) (CMH), and physical mixtures of CMH and ZMH were used as precursors for calcination experiments in air at 500 and 1000°C lasting 18 hours. The obtained oxides were investigated by X-ray powder diffraction technique. Calcination at 500°C yielded pure zincite phase (ZnO), tenorite phase (CuO), or their mixtures. The calcination of the Zn-rich sample ZCMH at 1000°C lead to zincite phase displaying a slightly lower cell volume than the pure zincite phase obtained from Zn-only containing precursor (ZMH). These results suggest that the assumed solid solution Cu _x Zn _1−x O (x=0.01−0.02) exhibits a solubility limit lower than the copper content in the ZCMH precursor (6 mol-%). On the other hand, the calcination of the Cu-rich samples at 1000°C, in the presence of Zn(II), yielded tenorite phase exhibiting cell parameters significantly different from those reported for the pure tenorite phase, due to the formation of Zn_0.03Cu_0.97O solid solutions. All these results are corroborated by intensity analysis of the diffraction peaks.