A Comprehensive Study on the Phase Structure, Surface Properties, and Active Oxygen Species of A₂B_2O7 Composite Oxides

Abstract

A₂B₂O₇ complex oxides have a great potential to be used in high-temperature catalytic processes. Herein, a series of A₂B₂O₇ (A = La, Nd, Sm, Gd, Er, Yb; B = Ti, Sn, Zr, Ce) compounds with all four kinds of typical sub-crystalline phases were synthesized to study their bulk and surface properties. FTIR spectroscopy was adopted as a novel method in this study to identify distinctively these phases. Whereas, it cannot be used to distinguish the subtle structure difference between disordered and ordered pyrochlores, nor that between the disordered defect fluorite and the rare earth. To discriminate these exquisite phase differences, XPS spectra must be supplementarily used. Specifically, it was discovered that the coordination numbers of the A- and B-site cations are the key factor affecting their binding energies. Furthermore, the electronegativity of the A- and B-site elements significantly influences the binding energy of surface lattice oxygen, reflecting their electrophilic and nucleophilic properties, which can thus be used to effectively identify the sub-crystalline phase. The oxygen vacancy concentration of different subcrystalline phases is the primary factor controlling the amount of surface chemisorbed oxygen species on A₂B₂O₇ compounds, with superoxide anions (O₂⁻) identified as the major species.

Keywords

A₂B₂O₇ composite oxides / Sub-crystalline phase structure / Active oxygen sites / Lattice disorder degree

Supplementary Materials

The following supporting information can be found at: https://www.sciepublish.com/article/pii/855,Table S1: ICP results of the samples; Table S2: Electronegativity of elements at A-site and B-site.

Acknowledgments

This research project is supported by the National Natural Science Foundation of China and the Natural Science Foundation of Jiangxi Province which is gratefully acknowledged.

Author Contributions

S.Z.: Investigation, Validation, Visualization, Writing—Original Draft, and Writing—Review & Editing; J.X.: Supervision, Project Administration, and Writing—Review & Editing; X.Y.: Investigation;Y.F.: Investigation; L.M.: Investigation; X.W.: Funding Acquisition, Project Administration and Writing—Review & Editing.

Ethics Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data will be made available on request.

Funding

This research was supported by the National Natural Science Foundation of China (22462011, 22376090), the Natural Science Foundation of Jiangxi Province (20252BAC240720, 20224BAB213017), the Key Laboratory of Jiangxi Province for Environment and Energy Catalysis (20242BCC32041).

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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