Joint release by Tokyo Institute of Technology, Hokkaido University, and Japan Science andTechnology Agency

Nonthermal Plasma-Promoted CO2 Hydrogenation in Presence ofAlloy Catalysts
Nonthermal plasma (NTP) is used to activate CO 2 molecules for hydrogenation into
alternative fuels at low temperatures, also enabling the conversion of renewable electricity
to chemical energy. Researchers from Tokyo Tech combined experimental andcomputational methods to investigate the hydrogenation pathway of NTP-promoted CO2
on the surface of Pd2Ga/SiO2 catalysts. The mechanistic insights from their study can help
improve the efficiency of catalytic hydrogenation of CO 2 and allows the engineers to design
new concept catalysts.
Climate change accelerated by excess CO2 emissions has been a major concern over the past
few years. To deal with this problem, technologies that can not only reduce and remove
excess CO2 emissions but also transform them into value-added chemicals are being
developed. One such method is the hydrogenation of CO2 using renewable hydrogen toproduce alternative fuels.
Over the years different strategies have been developed to improve CO2 hydrogenation in thepresence of metallic catalysts. The most promising among them is nonthermal plasma (NTP).
It promotes hydrogenation of CO2 beyond the thermodynamic limit even at low temperatures
without deactivating metallic catalysts, which are vulnerable to higher temperatures. Despite
the rising popularity of this technique, the interactions between the NTP-activated species
and metallic catalysts are still not well understood.
Fortunately, a team of researchers from Tokyo Institute of Technology (Tokyo Tech), Japan,
led by Prof. Tomohiro Nozaki, devised a study to overcome this gap in understanding. In theirrecent breakthrough, published in the Journal of the American Chemical Society, theresearchers revealed the reaction dynamics for NTP-assisted CO2 hydrogenation on thesurface of Pd2Ga/SiO2 alloy catalysts that lead to the formation of formate. Prof Nozaki
explains “Reaction mechanisms like Eley-Rideal or E-R pathway have been proposed toexplain efficient CO2 conversion at lower temperatures and the activation energy for thisreaction decreases dramatically. Moreover, NTP produces a copious amount of vibrationallyactivated CO2 which is the key to enhancing CO2 conversion beyond the thermal equilibrium.”
The team investigated the reactions between NTP activated CO 2 and Pd2Ga/SiO2 alloy
catalysts in a fluidized-bed dielectric barrier discharge reactor (Figure 1 and Videos) andcompared them to conventional thermal catalysis. The results revealed that the CO 2
conversion into formate was more than two-fold in the case of NTP-assisted hydrogenation
when compared to thermal conversion. To further establish the mechanics of the mentioned
conversion, the scientists adopted in situ spectroscopic analysis and density functional theory(DFT) calculations.

The results revealed that the NTP activation gave rise to vibrationally excited CO 2 molecules
which directly react with hydrogen atoms adsorbed by the Pd sites on the catalyst via the ER pathway. One of the O atoms from the reacted species then got adsorbed at the neighboring
Ga site resulting in the formation of monodentate-formate or m-HCOO. The DFT calculations
also deduced a decomposition pathway for the same m-HCOO species.
This experimental-theoretical study showed that NTP can promote CO2 hydrogenation tolimits those conventional thermal methods can hardly reach. It also provided mechanistic
insights into NTP activated CO2 and catalyst interaction, which can be utilized to develop
better catalysts and improve the hydrogenation process. “With our research, we wanted toaccelerate the waste to wealth initiative. Capturing CO2 and using it as feedstock for synthesisof fuels and valuable chemicals will not only help us deal with climate problem but also slow
down fossil fuel depletion to some extent,” concludes Prof. Nozaki.

Reference
Authors:

Title of original
paper:
Journal:DOI:
Affiliations:

Dae-Yeong Kim,† Hyungwon Ham,‡ Xiaozhong Chen,† Shuai Liu,‡ Haoran Xu,‡ BangLu,‡ Shinya Fu-rukawa,*,‡ Hyun-Ha Kim,§ Satoru Takakusagi,‡ Koichi Sasaki,‖ andTomohiro Nozaki*,†
Cooperative catalysis of vibrationally-excited CO2 and alloy catalyst breaks thethermodynamic equilibrium limitation
Journal of the American Chemical Society
10.1021/jacs.2c03764†Department of Mechanical Engineering, Tokyo Institute of Technology, Japan‡Institute for catalysis, Hokkaido University, Japan§National Institute of Advanced Industrial Science and Technology, Japan‖Division of Applied Quantum Science and Engineering, Hokkaido University, Japan*Corresponding authors’ email: nozaki.t.ab@m.titech.ac.jp

Figure 1. Carbon dioxide recycling - innovative plasma-catalysis concept
Fluidized-bed dielectric barrier discharge reactor was used for CO 2 hydrogenation overPd2Ga/SiO2
Credit: Journal of the American ChemistryVideos: DBD generated in fluidized bed reactor
Side view, https://youtu.be/Bqvv3MK1mQM
Top view, https://youtu.be/HnTq8RoyAXw
Refer to the manuscript for detailed conditions.
Credit: Professor Tomohiro Nozaki of Tokyo Institute of Technology

Credit：Professor Tomohiro Nozaki of Tokyo Institute of TechnologyContacts
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About Tokyo Institute of Technology
Tokyo Tech stands at the forefront of research and higher education as the leading university
for science and technology in Japan. Tokyo Tech researchers excel in fields ranging frommaterials science to biology, computer science, and physics. Founded in 1881, Tokyo Techhosts over 10,000 undergraduate and graduate students per year, who develop into scientificleaders and some of the most sought-after engineers in the industry. Embodying the Japanesephilosophy of “monotsukuri,” meaning “technical ingenuity and innovation,” the Tokyo Techcommunity strives to contribute to society through high-impact research.
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About Hokkaido University
Founded in 1876 as Sapporo Agricultural College, Hokkaido University is one of the oldest,
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students all around the globe with the diverse degree programs offered and the all year roundscenic beauty. The campuses are located in the cities of Sapporo and Hakodate of Hokkaido
and 21 facilities are spread throughout Hokkaido and mainland Japan, contributing towards
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