Metal nanoparticles are widely used as heterogeneous catalysts, and their catalytic performance is governed by multiple factors, including reactive sites (facets, edges, and corners), particle size, interactions with supports, and the formation of new active sites such as perimeter sites, surface defects, and dopant-induced sites. Because these factors are intricately intertwined, a microscopic understanding of their roles is essential for rational catalyst design. Computational chemistry provides a powerful framework for systematically exploring reaction pathways and mechanisms under well-defined model conditions, where appropriate simplification is necessary to maintain feasible computational cost. In this article, we review our theoretical studies based mainly on density functional theory, focusing on how cluster size, reaction sites, external fields, dopants, and metal–support interactions influence catalytic reactivity. By integrating theoretical analysis with experimental findings, we demonstrate how this combined approach provides detailed insight into nanoscale elementary processes and practical guidelines for catalyst design.

We report a molecular-scale study of a one-dimensional coordination polymer formed on a Cu(111) surface. A tailored ligand, 2,7-dicyano-9,9-dimethylfluorene (DCF), was designed to reduce interactions with the surface while enabling directional coordination with Cu adatoms. Scanning tunneling microscopy reveals that the resulting DCF–Cu polymer exhibits pronounced flexibility dominated by the CN–Cu–CN coordination angle, which constitutes the primary internal degree of freedom governing the overall chain geometry. Temperature-dependent measurements show the onset of thermal motion above ～40 K for linear chain segments, whereas three-coordinated branches remain immobile up to 71 K, functioning as molecular-scale cross-links. These results directly connect polymer physics concepts with single-molecule motions on surfaces.

The surface chemistry of formic acid and the CO₂ hydrogenation process on the Pd/Cu(111) single atom alloy surface was investigated using synchrotron-radiation X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations. High-resolution XPS revealed that the decomposition process of formic acid on Pd/Cu(111) is almost identical to that on Cu(111). Density functional theory calculations showed that the indirect charge transfer from Pd to monodentate formate species through the Cu substrate, which causes the considerable chemical shift in Pd 3d_5/2. In addition, it was found that formate species are preferably adsorbed on the Cu site rather than the Pd site, implying the advantage of Pd/Cu(111) in methanol synthesis. Ambient pressure XPS (AP-XPS) demonstrated that hydrogen spillover drives CO₂ hydrogenation into formate and methoxy species even at room temperature. Semi-quantitative analysis of AP-XPS spectra proposed that carbonate acts as a reactive intermediate in methanol synthesis.

Electrochemical reactions are governed not only by electrode materials but also by the interfacial reaction field composed of electrolyte solutions. This article reviews our recent studies demonstrating that strong coupling enables the design of the physicochemical properties of water as a reaction field. Strong coupling provides a new framework for electrochemical reaction control by modifying dynamic hydration-mediated ion transport and electron transfer pathways.

Atmospheric-pressure plasma (APP) technology has attracted significant attention for its ability to generate reactive species from air using electrical energy. We have developed an air-based APP device that produces high-density dinitrogen pentoxide (N₂O₅) with exceptional selectivity. This achievement broadens the potential applications of plasma-generated, short-lived reactive nitrogen species in agriculture and related fields. As a representative application, plasma-generated N₂O₅ gas was shown to enhance plant immunity in Arabidopsis thaliana. Notably, cytosolic calcium signaling observed within seconds after N₂O₅ exposure indicates a rapid activation mechanism associated with subsequent gene expression changes. Furthermore, N₂O₅ treatment increased several valuable secondary metabolites in sweet basil leaves through the activation of plant defense responses. Based on these findings, we aim to develop sustainable farming systems that reduce dependence on chemical pesticides and fertilizers, contributing to a more sustainable future society.