The influence of complexing agents on the cobalt-based catalysts properties and activities

Abstract

In this study, CoAl2O4 samples were synthesized using sol–gel method in the presence of citric acid (CoAlCA), malic acid (CoAlMA), oxalic acid (CoAlOA) and urea (CoAlU) as complexing agents. The presence of cubic spinel structure for both CoAl2O4 and Co3O4 phases was confirmed by XRD. FTIR analysis emphasized that the composition of Co3+ ions decreased in order: CoAlOA (50.3 %) > CoAlU (41.8 %) > CoAlMA (40.7 %) > CoAlCA (24.3 %), which denotes that the presence of oxalic acid as complexation agent favors cobalt oxidation from Co2+ to Co3+ and, consequently, the expansion of Co3O4 phase. In the presence of citric acid, as a complexing agent, tetrahedral Co2+ ions prevailed and CoAl2O4 is the dominant phase.The catalytic performances of CoAl2O4 spinel oxides have been evaluated in lactonization of 1,4-butanediol, coupled with acetophenone hydrogenation and in the Claisen-Schmidt condensation reaction of benzaldehyde with acetophenone and the results provided a good relationship between Co3+/Co2+ ratio, the reactants conversion and the products yield.