Synthesis and characterization of copper-nickel ferrite catalysts for ethyl acetate oxidation

Materials with nominal composition Cu_0.5Ni_0.5Fe₂O₄ were prepared by sol-gel auto-combustion technique using corresponding metal nitrates and citric acid as complexating agent/fuel agent. Different ratios between citric acid and metal ions were used to control the combustion reaction. For comparison, Cu_0.5Ni_0.5Fe₂O₄ ferrite was also synthesised by co-precipitation. Mössbauer spectroscopy was used for analysis of synthesised samples both at room temperature and liquid nitrogen boiling temperature. Iron distribution in tetrahedral and octahedral positions of spinel lattice was determined. Different degrees of agglomeration of the ferrite phase were estimated by super-paramagnetic behaviour of samples. In addition, methods of X-Ray Diffraction, UV-Vis, FTIR, nitrogen physisorption, TPR with hydrogen were applied for structural characterization of the materials. Some quantities of secondary phases (Cu, Cu-Ni alloy and hematite) were found out in samples prepared by auto-combustion method. The catalytic activities of the samples in ethyl acetate oxidation reaction strongly depended on the variations in the structural and texture characteristics of the samples. The sample synthesized at the highest ratio of citric acid to metal ions is characterized by the smallest ferrite crystallite size, the higher surface area and the best catalytic activity.