Effect of solvent, in the sol-gel synthesis of CoAl₂O₄, on the structure and catalytic properties in 1,4-butanediol dehydrocyclization

This work presents the synthesis of CoAl₂O₄ spinel by the sol-gel method using different solvents, such as water, ethanol, methanol and butanol, and cobalt and aluminum precursors. The structure and optical properties were characterized by XRD, SEM, BET, FTIR spectroscopy and UV-vis spectroscopy analyses. Cubic spinel structure of both CoAl₂O₄ and Co₃O₄ phases was confirmed by XRD. The sample compositions (EDX) were as follows: CoAl₂O_3.5 (CoAl_W), CoAl_1.8O₄ (CoAl_E), CoAl_3.2O_6.7 (CoAl_M) and CoAl_2.4O₇ (CoAl_B); an excess of aluminum is observed on the catalysts synthesized in the presence of methanol and butanol as solvents, which leads to a decrease in activity for 1,4-butanediol lactonization reaction. The active sites in 1,4-butanediol dehydrocyclization are both Co³⁺ sites and oxygen vacancies, which are designated by the behaviour of alcohol in the presence of acetophenone or benzaldehyde as the hydrogen acceptor and from the variation of conversion with the ratio between Co³⁺ and Co²⁺ on the surface.