Porous structured CuO-CeO₂ nanospheres for the direct oxidation of cellobiose and glucose to gluconic acid

Porous-structured CuO-CeO₂ nanospheres were synthesized using a hydrothermal method and were tested as catalysts for the direct oxidation of cellobiose to gluconic acid. Catalytic reaction along with catalyst characterization results and ¹⁸O-oxygen isotope labeled experiments revealed that the surface lattice oxygen of CuO in CuO-CeO₂ nanospheres was consumed during the oxidation of cellobiose. This provides a direct evidence of our previous work (Amaniampong et al., Angew. Chem. Int. Ed. 54 (2015) 8928–8933). Characterization results further suggested that the lattice oxygen in CeO₂ did not participate in the oxidation; nonetheless, the addition of CeO₂ to CuO enhanced the surface area of the catalyst composite which was crucial for the reaction. The spent catalyst upon re-oxidation regained its activity. In addition, isotope labeled deuterium oxide (D₂O) experiments suggested that hydrogen exchange between the solvent and the substrate (glucose) are not involved in the mechanistic formation of gluconic acid and confirmed the solvent had no direct influence in the formation of gluconic acid.