Peroxide is used by scientists to study metal oxide reactions.

In collaboration with the Center for Functional Nanomaterials (CFN), a U.S. organization, researchers at Binghamton University conducted research. S. Brookhaven National Laboratory’s Office of Science User Facility to learn more about how peroxides on the surface of copper oxide direct oxidation reactions by encouraging the oxidation of hydrogen while inhibiting the oxidation of carbon monoxide. They used two complementary spectroscopy techniques that had never been combined in this way to see these rapid changes. The Proceedings of the National Academy of Sciences (PNAS) have published the research’s findings.

According to materials scientist Anibal Boscoboinik at CFN, copper is one of the most researched and important surfaces in both corrosion science and catalysis. “Because there are so many mechanical components used in industry that are made of copper, it is crucial to comprehend this aspect of the corrosion processes.”.

“Copper is one of the most studied and important surfaces in catalysis and corrosion science.” Many mechanical parts used in industry are composed of copper, thus understanding this aspect of corrosion processes is critical.”

Anibal Boscoboinik, materials scientist at CFN.

Ashley Head, a materials scientist at CFN, stated, “I’ve always enjoyed looking at copper systems.” Some of their reactions and properties are really striking.

Researchers will have more control over the chemical reactions that oxide catalysts produce as a result of a better understanding of these catalysts, which could lead to clean energy solutions. Controlling the amount of oxygen and the number of electrons on copper is a crucial step for effective chemical reactions because copper, for instance, can catalytically form and convert methanol into valuable fuels.

As a stand-in, peroxide
Chemical substances called peroxides have two oxygen atoms connected by shared electrons. Peroxides are highly reactive due to the relatively weak bond that makes it possible for other chemicals to change their structure. By determining the composition of peroxide species formed with various gases, including O2, H2, and CO, scientists were able to change the redox steps of catalytic oxidation reactions on an oxidized copper surface (CuO) in this experiment.

Reduction and oxidation are combined in redox. The reducing agent loses an electron during this process, while the oxidizing agent gains one. Researchers found that a peroxide surface layer significantly improved CuO reducibility in favor of H2 oxidation when comparing these various peroxide species and how these steps were carried out. On the other hand, they discovered that it functioned as an inhibitor to stifle CuO reduction in opposition to CO (carbon monoxide) oxidation. They discovered that the peroxide’s opposing impact on the two oxidation reactions results from modification of the surface sites where the reaction occurs.

Scientists can use these gases to control these reactions more effectively by identifying these bonding sites and understanding how they encourage or inhibit oxidation. However, in order to fine-tune these reactions, researchers needed to have a clear understanding of what was taking place.

The location and binding energy of peroxide (OO) formation on copper oxide (CuO) Source: Proceedings of the National Academy of Sciences (PNAS).

The appropriate equipment for the task.
The team felt that because peroxides are so reactive and these changes occur so quickly, it was crucial to study this reaction in situ. It’s challenging to capture such a brief moment on the surface without the appropriate equipment or surroundings.

In-situ infrared (IR) spectroscopy has never before detected peroxide species on copper surfaces. By observing how the radiation is absorbed or reflected in reaction-related conditions, scientists can use infrared radiation to gain a better understanding of a material’s chemical properties. In this experiment, researchers were able to distinguish “species” of peroxide that would have otherwise been very challenging to identify on a metal oxide surface, due to very slight variations in the oxygen they were carrying.

“When I was researching the infrared spectra of these peroxide species on a surface and discovered there weren’t many publications, I became very excited. “It was thrilling that we could see these differences using a technique that isn’t frequently used for these kinds of species,” Head reflected.

The team also used a different spectroscopy method called ambient pressure X-ray photoelectron spectroscopy (XPS), as IR spectroscopy alone wasn’t sufficient to make sure. In XPS, electrons are forced out of the sample using X-rays with lower energy. Scientists can learn information about the chemical characteristics of the sample’s atoms from the energy of these electrons. This research was made possible in large part by the availability of both techniques through the CFN User Program.

The instruments we have and have modified here are one of the things in which we take great pride, according to Boscoboinik. “Since our instruments are interconnected, users can move a sample between these two techniques in a controlled environment and examine them in situ to obtain complementary information. In most other cases, a user would need to remove the sample in order to use it with another instrument, and that change in environment could affect its surface.

“A nice feature of CFN lies not only in its state-of-the-art facilities for science but also in the opportunities it provides to train young researchers,” said Guangwen Zhou, professor at the Thomas J. Watson College of Engineering and Applied Science and the Materials Science program at Binghamton University. “Each of the involved students has benefited from in-depth practical training with the microscopy and spectroscopy equipment available at CFN.”.

With the assistance of four Ph.D. Yaguang Zhu and Jianyu Wang, the first co-authors of this paper, as well as Shyam Patel and Chaoran Li, who were classmates in Zhou’s group, These students are all just beginning their careers; they all received their PhDs in 2022.

Future discoveries.
The findings of this study might be applicable to various other types of reactions and copper-alternative catalysts. These discoveries and the procedures and methods used to arrive at them may be used in subsequent studies. Metal oxides are frequently used as catalysts or as catalyst-related materials. It might be possible to block or improve surface reactions during other catalytic processes by adjusting peroxide formation on other oxides.

I work on other copper and copper oxide-related projects, such as converting carbon dioxide into methanol for use as a clean energy fuel, said Head. “An impact on other projects using copper and other metal oxides could be had by examining these peroxides on the same surface that I do.”.

More information: Yaguang Zhu et al, Tuning the surface reactivity of oxides by peroxide species, Proceedings of the National Academy of Sciences (2023). DOI: 10.1073/pnas.2215189120

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