Unraveling defect chemistry in doped-ceria catalyst for oxidative coupling of lignin-based aniline and benzyl alcohol

Abstract

The defect chemistry of doped-ceria is vital but tangled for sustainable conversion of biomass resources. In this work, a group of Zr-doped CeO₂ solid solutions were prepared and the defect chemistry in CeZr_xO_y (0.02 ≤ x ≤ 5) catalyst was elucidated over the oxidative coupling of lignin-based aniline and benzyl alcohol. Varying the Zr molar fraction enabled to successfully adjust the defect sites of catalysts and further influence their catalytic performances. In addition, the optimal CeZr₁O_y catalyst exhibited a flexible temperature adaptability, wide substrate scope and superior reusability. Various characterizations, kinetic investigations, controlled experiments, DFT calculations and in situ DRIFT-IR technique were used to unravel the roles of Ce³⁺ and oxygen defects and the reaction mechanism. It was disclosed that Zr-doped defects can obviously increase surface Ce³⁺ cations, oxygen species (peroxide and superoxide anions) and oxygen vacancies. These coordinatively unsaturated sites were shown to play critical roles in absorbing and activating substrates hence can accelerate the formation rate of bio-based imines.