Akira Yoko

A continuous flow reaction process in which a metal salt solution is rapidly mixed with high-temperature water was employed to achieve rapid heating up to supercritical conditions. A quarter of a century has passed since the supercritical hydrothermal method was first proposed. This paper introduces recent advances in science and technology related to the supercritical process. Process design, kinetics, reaction atmosphere (redox) control, morphology control, organic modification of particles, n

We studied the formation of Ba_1−xSr_xZrO₃ (0 ≤ <italic>x</italic> ≤ 1) nanoparticles under highly super-saturated conditions, using supercritical water.

This study evaluated the reaction kinetics of hydrothermal synthesis for the nickel nitrate to nickel oxide reaction that occurs in a wide range of temperatures and pressures around the critical point of water. The effects of mass transfer on the reaction rate were evaluated using a two-flow mixing system from which the relation between the mass transfer rate and Re number and the kinetics under reaction control conditions was obtained. The hydroxyl ion concentration, which varies greatly around

Diffusion of A-site cations in A-site-deficient BaZrO3 and SrZrO3 perovskite oxides was investigated by first-principles nudged elastic band calculations. We found an energy barrier for surface diffusion that was significantly lower than that for bulk diffusion (3.41 eV vs 2.41 eV for Ba diffusion in Ba-deficient BaZrO3 and 3.07 eV vs 1.44 eV for Sr diffusion in Sr-deficient SrZrO3), which suggests unusually rapid cation diffusion at low temperatures in nanomaterials with a large proportion of s

CeO2 nanocasting in a mesoporous hard template provides a three-dimensionally (3D) interconnected skeleton framework consisting of CeO2 nanoparticles with particles smaller than 7 nm. Low-voltage high-resolution scanning electron microscopy with Ar-ion-beam cross-sectional polishing revealed numerous CeO2 (∼250 nm) clusters distributed in the SBA-15 mesochannels. Each CeO2 framework consists of CeO2 primary nanocrystals that are mutually and coherently connected. The mesochannel walls of the mes

Abstract In this study, organic surface‐modified Ce 1‐ x Zr x O 2 ‐δ nanoparticles were synthesized using supercritical hydrothermal method. X‐ray diffraction and energy‐dispersive X‐ray spectroscopy analysis results indicated Zr intake into the CeO 2 lattice and vice versa. Results obtained from thermogravimetric analysis proved surface modification of Ce 1‐ x Zr x O 2 ‐δ nanoparticles with carboxylic acids. Decreased particle size caused by surface modification along with induction of Zr into

Although the function and stability of catalysts are known to significantly depend on their dispersion state and support interactions, the mechanism of catalyst loading has not yet been elucidated. To address this gap in knowledge, this study elucidates the mechanism of Pt loading based on a detailed investigation of the interaction between Pt species and localized polarons (Ce³⁺) associated with oxygen vacancies on CeO₂(100) facets. Furthermore, an effective Pt loading met

Controlling particle size and structure is challenging in the synthesis of composite metal oxide nanoparticles. In this study, first-principles calculations based on density functional theory were used for perovskite-type composite oxides to elucidate the structure of nanoclusters, and it was revealed that their surface energy strongly depends on the constituent cations of the composite oxides. Particle size variation observed in supercritical hydrothermal synthesis can be explained by factors i

BaTiO3 formation was studied using a continuous flow reactor and water–ethanol mixed solvents exhibiting varying dielectric properties. The conditions under which BaTiO3 forms were explored by changing the solvent composition and the precursor concentration. Higher precursor concentrations were required for BaTiO3 formation in water-rich solvents than in ethanol-rich solvents. Moreover, smaller particles were obtained with increasing ethanol fraction, and they showed less growth, depending on th