Prof. Hiromi Yamashita has established a new catalytic design method, named as "nanoscale design", by precisely controlling the structure of heterogeneous catalysts and their surrounding reaction environments at the nanolevel. By applying advanced operando spectroscopy analysis and rigorous theoretical calculations, the activation mechanisms have been elucidated. This method has been applied to various environment-friendly catalytic reaction systems, leading to the development of catalysts with remarkably high activity compared to conventional catalysts. This demonstrates the potential to perceive catalytic design as a surface science. Here are the main achievements.

1. Design of Single-Site/Ultra-Fine Particle Photocatalysts in Nanospaces
The focus was made on the ability of nanoporous materials such as zeolites to fuse metal ions in an isolated state, leading to the development of "single-site photocatalysts" with structures and properties significantly different from conventional photocatalysts by introducing metal ions into pores and frameworks. Applications to CO₂ reduction and NO_X decomposition were attempted, clarifying the importance of surface coordination unsaturated sites (tetra-coordinated titanium oxide, bi-coordinate copper ions, etc.). Furthermore, high functionality was achieved by fixing photo-functional metal complexes as single-site photocatalysts in nanospaces, applied to hydrogen production from water. Additionally, mesoporous thin films incorporating single-site photocatalysts were developed and applied as superhydrophilic interfacial materials, while a method was developed to simultaneously deposit photocatalysts and hydrophobic polymers on substrates to create superhydrophobic interfacial materials with self-cleaning properties. On the other hand, the hybrid of ultra-fine semiconductor particles and nanoporous materials was conducted, modifying pore surfaces (with hydrocarbon, fluorine, apatite, graphene, etc.) and improving spatial characteristics (hydrophilicity/hydrophobicity, electrostatic field, spatial volume) to achieve reactant concentration and reaction efficiency. Unique higher-order nanostructures such as macro/mesoporous structures, core-shell structures, and yolk-shell (hollow space) structures were developed, leading to further activity improvements. Particularly, high-efficiency CO₂ reduction was enabled by integrating basic polymers capable of concentrating CO₂ with CO₂ reduction catalysts in hollow spaces.

2. Design of Plasmonic/MOF Photocatalysts Utilizing Nanostructures
Based on single-site photocatalysts, well-defined metal nanocatalysts were prepared and utilized for H₂O₂ synthesis and VOC combustion. Furthermore, by using rapid uniform heating via microwave heating and the regulated spaces of mesoporous materials, metal nanoparticles (Ag, PdAu, etc.) with precisely controlled shape, size, and color were prepared, leading to the development of plasmonic catalysts that can exhibit localized surface plasmon resonance under visible light irradiation and significantly enhance catalytic performance. Additionally, the design of metal-organic framework (MOF) photocatalysts aimed at H₂O₂ generation was conducted, creating reaction fields that inhibit the decomposition of generated H₂O₂ by hydrophobizing MOF surfaces. Furthermore, a two phases reaction system of water-organic solutions was developed, enabling the high-concentration production of H₂O₂.

3. Design of New Catalytic Materials Utilizing Hydrogen Spillover Phenomena
A catalyst preparation method has been developed utilizing the "hydrogen spillover phenomena," in which hydrogen molecules diffuse as atomic hydrogen on the surface of oxides through metals. Whether hydrogen diffuses on the surface of the support or is doped into the support depends on the basicity, surface functional groups, oxygen defects, and crystal phase of the oxide support. On Mo oxide, hydrogen activated by Pt spills over and is doped into the Mo oxide in large quantities, resulting in the preparation of reduced H_XMoO_3-y with numerous oxygen defects, demonstrating high activity for CO₂ reduction by functioning as a photothermal conversion catalyst under visible light irradiation. On the other hand, on oxides such as CeO₂, active hydrogen diffuses on the surface through hydrogen spillover, allowing the low-temperature rapid reduction and alloying of adjacent base metal ions. This phenomenon was utilized to develop a method for easily preparing high-entropy alloys and non-equilibrium alloy particles, designing catalysts that show high performance for CO₂ reduction, NO_X decomposition, and hydrogen production from hydrogen carrier molecules.

4. Design of New Visible-Light-Responsive Photocatalysts Using Ionic Engineering Methods
A photocatalyst preparation method has been developed utilizing ion implantation, which involves irradiating materials with ion beams focused and accelerated under an electric field. By implanting accelerated metal ions into TiO₂ photocatalysts, visible-light-responsive photocatalysts useful for NO_X decomposition and other applications were developed. Additionally, depositing low-energy ions onto substrates allowed the preparation of thin-film photocatalysts, leading to the development of light-functional interfaces demonstrating photoclean properties.

5. Design of Porous Metal Catalysts Using New Preparation Methods
Ultra-fine structures were prepared by thermal heat-treating amorphous alloys produced through liquid metal rapid quenching below their crystallization temperature. By selectively leaching only base metals through surface chemical treatments, high-activity porous　skeletal metal catalysts with exposed active metals on the surface were prepared. Additionally, by introducing channel structures using laser 3D printing and exposing active metals on the surface through surface chemical treatment, a metal self-catalytic reactor that functions both as a catalyst and a tube reactor was fabricated.

In summary, by utilizing advanced spectroscopic and microscopic techniques such as synchrotron operando XAFS and aberration-corrected STEM, Prof. Yamashita determined the nanolevel structure of catalysts and elucidated the reaction mechanisms through density functional theory (DFT) calculations. The precise structural control of special reaction fields, such as the nanopores of zeolites, mesoporous silica, MOFs, and thin film interfaces, was achieved. This led to the successful precise design of single-site photocatalysts (isolated metal ions, photo-functional metal complexes), ultra-fine particle semiconductor photocatalysts, plasmonic catalysts, high-entropy alloy particle catalysts, and porous metal catalysts with unique structures distinct from conventional ones. These nano-designed high-activity catalysts were extended to environment-friendly reactions such as hydrogen cycling reactions (hydrogen production from water and hydrogen carrier molecules, hydrogen peroxide synthesis), carbon dioxide reduction reactions (synthesis of CO, formic acid, methanol, methane), and air-water purification, revolutionizing catalyst development. Therefore, his achievements are recognized as worthy of the Chemical Society of Japan Award.