Unlocking Enhanced Reversible Oxygen Storage Capacity via Noble Metal Exsolution in Titanium-Doped Lanthanum Strontium Ferrites for Catalytic Applications

Deblina Majumder^a, Alex Martinez Martin^a, Shailza Saini^a, Kalliopi Kousi^a, Evangelos I. Papaioannou^a

^aSchool of Engineering, Newcastle University, Newcastle upon Tyne, NE1 7RU, United Kingdom

^bSchool of Chemistry and Chemical Engineering, University of Surrey, Surrey, GU2 7XH, United Kingdom

^cSchool of Chemistry and Chemical Engineering, University of Surrey, Surrey, GU2 7XH, United Kingdom

^dSchool of Chemistry and Chemical Engineering, University of Surrey, Surrey, GU2 7XH, United Kingdom

^eSchool of Engineering, Newcastle University, Newcastle upon Tyne, NE1 7RU, United Kingdom

Proceedings of 24th International Conference on Solid State Ionics (SSI24)

Fundamentals: Experiment and simulation

London, United Kingdom, 2024 July 14th - 19th

Organizers: John Kilner and Stephen Skinner

Poster, Deblina Majumder, 593
Publication date: 10th April 2024

Lanthanum Strontium Ferrite (LSF), a perovskite material (formula: ABO₃, where A and B represent cations and O represents oxygen anions) has drawn significant attention in recent years due to its promising applications in oxygen storage materials and catalysis^1,2. This study investigates the synergistic effects of noble metal (Silver; Ag) exsolution and Titanium (Ti) doping on LSF to enhance its reversible oxygen storage capacity (ROSC)[AMM(1] and reactivity towards ethylene epoxidation. The incorporation of Ag into A and Ti into the B-site of LSF leads to the formation of a stable and innovative oxygen carrier material. This facilitates improved oxygen vacancy formation and corresponding lattice transportation at lower temperatures (around 400°C), promoting ethylene epoxidation catalysis.

The synthesis of Ag-exsolved and Ti-doped LSF (LASTFO) involves a multi-step process, including solid-state reaction and exsolution techniques. Powder X-ray diffraction (PXRD) analysis and Rietveld refinement reveal the perovskite structure of LSF with additional peaks corresponding to Ag species. Morphological analysis using Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) reveal the formation of nano-sized Ag particles dispersed on the surface of Ti-doped LSF grains.

The introduction of Ti into the B-site of LSF significantly enhances its ROSC, as evidenced by in-situ thermogravimetric analysis (TGA) under reducing conditions when LASTFO was treated under a reduced environment of Ar and oxidised using air in a cyclic manner. A systematic approach results in doubling the reversible oxygen carrying capacity of LASTFO compared to its non-Ti and non-Ag counterpart. The presence of Ti promotes the generation of oxygen vacancies at temperatures as low as 400°C, leading to improved oxygen storage capacity. Lattice transport in solid state ionic materials X-ray photoelectron spectroscopy (XPS) further elucidates the presence of metallic Ag as a result of exsolution and the role of Ti in facilitating oxygen vacancy formation.

We aim to deploy the exsolved metallic Ag towards ethylene epoxidation as they would act as active sites, promoting the selective formation of ethylene oxide. The unique surface anchoring properties of exsolved metal nanoparticles facilitate efficient oxygen transportation, ensuring prolonged reactivity during catalysis ^3,4. The study investigates the mechanism underlying the enhanced catalytic performance of LASTFO, which could be attributed to the synergistic effects of Ag exsolution and Ti doping. This study sheds light on the design of advanced perovskite-based materials for oxygen storage and catalytic applications, with potential implications in automotive exhaust treatment, energy and commodity chemical synthesis.

References:

[1] Neagu, D.; Tsekouras, G.; Miller, D. In situ growth of nanoparticles through control of non-stoichiometry. Nature Chem. 2013, 5, 916–923.

[2] Otto, Svenja-K.; Kousi, K.; Neagu, D.; Bekris, L.; Janek, J.; Metcalfe, S.I.2. ACS Appl. Energy Mater. 2019, 2, 7288–7298.

[3] Neagu, D.; Oh, TS.; Miller, D. Nano-socketed nickel particles with enhanced coking resistance grown in situ by redox exsolution. Nat Commun. 2015, 6, 8120.

[4] Papaioannou, E.I.; Neagu, D.; Ramli, W.K.W. Sulfur-Tolerant, Exsolved Fe–Ni Alloy Nanoparticles for CO Oxidation. Top Catal. 2019, 62, 1149–1156.

Acknowledgements:

We sincerely acknowledge the funding support provided by The Centre for Postdoctoral Development in Infrastructure, Cities and Energy (C-DICE) Ambassadorship grant, UKRI (UK Research and Innovation), and the Research England development fund. Additionally, we recognize the institutional support provided by the University of Surrey and Newcastle University. These funding sources have been essential in facilitating the execution of this current research project.

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