Migration of cations in layered oxides for creating a highly active interface toward CO preferential oxidation

Abstract

Rational design and integration of collaborative active species at an interface is a crucial issue for the development of advanced materials. In this work, we present a simple interlayer cation migration strategy utilizing the unique layered structure of CuCoO₂ to controllably construct an active interface. CuCoO₂–CeO₂ composites with a strongly coupled heterojunction interface were initially synthesized by an incipient wetness impregnation process and subsequent calcination, during which a large amount of Cuⁿ⁺ takes interlayer as a channel, migrating to the interface of the composite and even partially dope into the CeO₂ lattice due to charge imbalance. The composites were systematically characterized using TEM/HRTEM, ICP, XRD, XPS, Raman spectra, H₂-TPR, O₂-TPD, and in situ DRIFTS measurements. As the CeO₂ content in the composites increases, the Ce³⁺ content and surface areas of the samples increase gradually, and the Ce³⁺ content reached a maximum in 70%CeO₂–CuCoO₂. Meanwhile, the migration of interlayered Cuⁿ⁺ results in the generation of many oxygen vacancies and active CuO_x enriched at the interface, which promoted the activation of oxygen, adsorption of CO and redox ability of CeO₂–CuCoO₂ composites, thus optimizing the reaction path. Creating a strongly coupled heterojunction interface and inducing interfacial Cuⁿ⁺ site enrichment significantly improve the catalytic oxidation activity of CO preferential oxidation (CO-PROX) at low temperatures (i.e. CO conversion more than 95.0% at even 120 °C), much better than a physically mixed CeO₂ and CuCoO₂ sample (CO conversion about 90.0% at 220 °C). This work indicates that irreversible cation migration in layered oxide materials could be used for the fabrication of highly active catalysts.