Cobalt ferrite modified with Hf(IV) as a catalyst for oxidation of ethyl acetate

Cobalt ferrite CoFe2O4 with spinel-like structure, modified with different contents of Hf(IV), was synthesized by a sol-gel method using propylene oxide as a gelating agent. The impact of the Hf(IV) content on the physicochemical characteristics of the catalysts and on the oxidation of ethyl acetate used as model molecule was studied. The phase homogeneity of the samples calcined at 550 degrees C was proved by X-ray diffraction and Mossbauer spectroscopy. No phase of HfO2 was detected by XRD. The tendency observed of a slight increase of the cell parameters of the samples modified with Hf(IV) in comparison with the pure CoFe2O4 is probably due to the larger ionic radius of Hf(IV) partially replacing Fe3+ in the spinel structure. The size of the crystallites as well as the lattice micro-strain were influenced by the modifying ion i.e. the increase of the Hf(IV) content caused an increase of the lattice micro-strain and a decrease of the average crystallite size in the range 46-37 nm. The conversion of ethyl acetate to CO2 is reflecting the values for the specific surface area, showing the sample with the highest Hf(IV) content as the best catalyst among the modified CFO tested samples.