Defect engineering on metal oxides (Zn, Mo and Fe) and their impact on the crude glycerol biofuel oxidation

Abstract

Defect engineering is an interesting area to improve the activity for alcohols oxidation because it promotes electronic changes through induced defects like oxygen vacancies (Ov) or doping with heteroatoms. Herein, Pd/Ov‒induced metal oxides bimetallic nanomaterials (Pd/Ov‒Fe2O3, Pd/Ov‒ZnO and Pd/Ov‒MoO3) were successfully synthesized and defect‒engineered boosting oxygen vacancies in the order ∼9–15%. The resulting materials had similar crystallite sizes (∼7.1 nm), metal‒support compositions (∼20 wt %), and bimetallic compositions (metal oxide ∼20 wt %). Electrochemical tests demonstrated that despite ZnO presented improved Ov, the electronic interaction between Pd and Ov‒Fe2O3 allowed to obtain higher current density (jmax). Pd/Ov‒Fe2O3 presented a jmax of 197.66 mA mg−1, being up to 2.2 times higher to that of Pd/C, while Pd/Ov‒MoO3 presented the most negative onset potential (−0.30 V). Electrochemical impedance spectroscopy, apparent activation energy tests and cyclic voltammetry tests involving synthetic solutions of glycerol, methanol and glyceraldehyde confirmed that the decrease of the onset potential is related to an enhanced electron transfer by Pd/Ov‒MoO3 resulting also in a decrease of the apparent activation energy (11.22 kJ mol−1). While the improved jmax of Pd/Ov‒Fe2O3 was related to its capability to oxidize crude glycerol and the mixtures because the efficient interaction between the defected metal oxide and palladium.