Oxidation of aldehydes to carboxylic acids over geopolymer supported CuO

This article focuses on the synthesis of copper (II) oxide impregnated mesoporous geopolymer (CuO/Geo) catalyst and its catalytic activity for the oxidation of aldehydes to the corresponding carboxylic acids. CuO/Geo was synthesised by a two-step method. Mesoporous geopolymer was prepared which was used as a support for CuO through incipient wetness method. The synthesized catalyst was characterized using FE-SEM, FT-IR, BET surface area, XRD and XPS. For the oxidation reaction, water was used as the solvent and oxygen as the sole oxidant. On the basis of the experimental observations, CuO/Geo was found to be a good catalyst with 67% conversion of benzaldehyde to benzoic acid, observed in 10 h at 80 °C. It was established from XPS analysis that the oxidation reaction took place via Cu²⁺/Cu⁺/Cu²⁺ transformations. Density functional theory calculations provided insights into the adsorption energetics and the reaction mechanism. The mechanism for benzaldehyde oxidation was developed and the rate determining step was identified. The product formation step was observed to be the rate determining step with the free energy barrier of 59.6 kcal/mol.