2020.2.14About KUT / Academics / Research / Students Life

Research group led by Prof. Fujita develops new catalyst for converting greenhouse gases to hydrogen and chemical raw materials by light irradiation

A joint research group with members from Tokyo Institute of Technology, Kyushu University, Shizuoka University and KUT has succeeded in developing a photocatalyst*1 material that can cause a methane carbon dioxide reforming reaction (dry reforming) at lower temperatures than previously possible.

The members of the research group include Mr. Shusaku Shoji (3rd year doctoral student School of Materials and Chemical Technology, Department of Materials Science and Engineering, Tokyo Institute of Technology); Prof. Masahiro Miyauchi (Tokyo Institute of Technology); Dr. Hideki Abe (senior researcher, Tokyo Institute of Technology); Prof. Syo Matsumura (Kyushu University, Faculty of Engineering); Prof. Choji Fukuhara (Shizuoka University); and Prof. Takeshi Fujita (KUT School of Environmental Science and Engineering).

It is expected that the results of this research will lead to more efficient use of natural gas and shale gas*2 and will contribute to the reduction of greenhouse gases. In addition, since synthesis gas can be produced at much lower temperatures than with current technology, it will be possible to greatly simplify and improve the efficiency of processes such as gasoline production by using the new material in conventional industrial methods.

(a) Transmission electron microscope image of the newly developed photocatalyst; (b) high magnification image of particles of the same photocatalyst.

Dry reforming is an attractive reaction that can convert methane and carbon dioxide (both greenhouse gases) into useful chemical raw materials. However, with current technology, efficient performance of this reaction requires heating to 800°C or higher, and there are problems of deterioration of catalyst cohesion caused by heating and carbon emission reaction (soot as a by-product), so dry reforming has not been adopted by industry.

The photocatalyst developed by Prof. Fujita's group is a nanoscale composite of strontium titanate and rhodium metal: when irradiated with ultraviolet light, it enables conversion of methane and carbon dioxide at a rate exceeding 50%, even without heating. In order to achieve the same performance as conventional thermal catalysts, heating at 500°C or more is required. This attests to the high performance of the photocatalyst developed by the group.

Temperature dependence of catalytic activity (using a gas mixture of methane and carbon dioxide at a concentration of 1%)

Next, a detailed analysis was performed to elucidate the mechanism of the dry reforming reaction, and it was clarified that ions of lattice oxygen in strontium titanate act as a reaction medium. In the past, hydrogen ions have been used as the reaction medium in artificial photosynthesis reactions such as decomposition of water and carbon dioxide reduction (which are photocatalytic reactions) but the photocatalysis system developed in this study involves a new reaction using lattice oxygen ions as a medium. As a result, development for application in various gas phase reactions can be expected.

Reaction mechanism of dry reforming by photocatalyst

Prof. Fujita has participated in the project as a principal collaborator in catalyst search, contributing his specialization, nanostructure analysis from the field of electron microscopy. He said, "As a means of addressing the intensifying effect of global warming, we have developed a revolutionary photocatalyst that will stop the increase in carbon dioxide emissions.This achievement can be expected to be a great initiator. We will continue to address related issues one by one, aiming at achieving practical application."

The research results were published in the electronic version of the British science journal Nature Catalysis on January 27, 2020.

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【Information on the paper】
Journal: Nature Catalysis
Paper title: Photocatalytic uphill conversion of natural gas beyond the limitation of thermal reaction systems
Authors: Shusaku Shoji, Xiaobo Peng, Akira Yamaguchi, Ryo Watanabe, Choji Fukuhara, Yohei Cho, Tomokazu Yamamoto, Syo Matsumura, Min-Wen Yu, Satoshi Ishii, Takeshi Fujita*, Hideki Abe*, Masahiro Miyauchi*

*1 Photocatalyst
A generic term for substances that absorb light and exhibit catalytic action. Titanium oxide is a typical photocatalyst.

*2 Shale gas
A fossil fuel composed mainly of methane and ethane, found in nature stored in gaps between layers of slate (shale). Its existence has been known for a long time, but over the past decade, technological advances have enabled commercial mining, especially in North America.