image: Researchers revealed how to create nano-scale imperfections to control specific reactions at the atomic level. view more
Credit: Nano Research
Crystal lattices are perfect arrangements of atoms and their bonds, repeating infinitely as exact replicas that will react to chemical invaders in precisely the same way — but not naturally. Many naturally occurring lattices, such as the ones found in minerals comprising metals and oxygen, have point defects, where there are fewer oxygen atoms than what would be expected in a perfect lattice. While called imperfections, these oxygen vacancies can induce desired properties, such as conductivity. Now, researchers may have determined how to create the nano-scale imperfections to control specific reactions at the atomic level.
Their results appeared first online on June 22 in Nano Research by Tsinghua University Press and Springer Nature. The same results will be published in the journal's print version in 2022 issue 1.
The team, based in China, used computational modeling to examine how adding a single atom to rutile titanium dioxide, a common natural mineral, could create oxygen vacancies or help migrate existing oxygen vacancies to more useful points in the material.
“In the last decade, single-atom catalysts have attracted world-wide research attention for performing with distinct reactivity and selectivity,” said paper author Wenming Sun, associate professor of chemistry, China Agricultural University. “These catalysts, which consist of single atoms dispersed onto metal oxide supports, achieve maximum atom efficiency, but they can deactivate during the synthesis process or in the process of the reaction.”
According to Sun, the catalysts are typically relatively rare precious metals, and they need to operate at high temperatures to achieve the desired effects. However, how the catalysts react and to what can be influenced by subtle temperature changes, as well as pressure, humidity and the local environment of single metal atoms — including the presence or absence of oxygen.
“Despite the advances in sample preparation and characterization, the fundamental understanding of how active sites work or deactivate is still very challenging,” Sun said. “Although great efforts have been devoted to revealing the correlation between synthesis methods, active sites and the performance of single-atom catalysts, critical questions remain about the exact local structures of active sites as well as their dynamical evolution under reaction conditions.”
The researchers set out to understand how a native oxygen vacancy may interact or react to the addition of a platinum atom, with specific focus on the following elements: how oxygen vacancy and its migration can affect the stability of isolated platinum atoms; how invasive platinum atoms can affect oxygen vacancy and its migration; and if invasive single platinum atoms and oxygen vacancies could form new interaction sites that could be useful for controlling reactions.
“To the best of our knowledge, the interplay of the two factors together with their synergistic effect is seldom investigated,” Sun said. “The evolution of the platinum atom’s local environment during oxygen vacancy migration should be seriously considered as an avenue to establish a more accurate understanding of the relationship between the material’s structure and function.”
In their analysis, Sun and the team examined the strength and nature of reactions cause by single atoms of platinum distributed at different sites on the titanium dioxide substrate. They found that under oxygen-rich conditions, a single platinum atom could replace a titanium atom with a coordination number of six, meaning that six other atoms could bond to it. The result is a platium-titanium bimetal center, which makes oxygen vacancy formation easier. This replacement also makes oxygen vacancy migration harder, leading a more stable local structure. The newly formed bimetal center also exhibits interesting characteristics when exposed to a water dissociation reaction, when water breaks into hydrogen and single ions of oxygen, according to the researchers, who plan to more closely investigate the changes. “These results can provide a quasi-dynamic perspective to understanding the structural active evolution of a single atom on a metal oxide surface,” Sun said.
Other contributors include first author Xiaoyang Wang, Department of Chemistry, China Agricultural University; Liang Zhang, Dassault Systemes (Shanghai) Information Technology Co., Ltd.; and Yuxiang Bu, Department of Chemistry, Shandong University.
The 2115 Talent Development Program of China Agricultural supported this work.
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Nano Research is a peer-reviewed, international and interdisciplinary research journal, sponsored by Tsinghua University and the Chinese Chemical Society. It offers readers an attractive mix of authoritative and comprehensive reviews and original cutting-edge research papers. After more than 10 years of development, it has become one of the most influential academic journals in the nano field. Rapid review to ensure quick publication is a key feature of Nano Research. In 2020 InCites Journal Citation Reports, Nano Research has an Impact Factor of 8.897 (8.696, 5 years), the total cites reached 23150, and the number of highly cited papers reached 129, ranked among the top 2.5% of over 9000 academic journals, ranking first in China's international academic journals.
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Journal
Nano Research
Article Title
Interplay between invasive single atom Pt and native oxygen vacancy in rutile TiO2(110) surface: A theoretical study