Yasutaka Kuwahara

Integrating photothermal fundamentals, selective C ₁ pathways and reactor engineering for efficient solar-driven CO ₂ hydrogenation.

Achieving high‐density single‐atom catalysts (SACs) remains a fundamental challenge, particularly for precious metals such as Ru that readily aggregate under synthetic and catalytic conditions. Here, we report a rational precursor design strategy for fabricating high‐density Ru SACs via direct carbonization, yielding ordered carbonaceous frameworks (Ru‐OCFs) with high Ru loadings of up to 11.0 wt%. By expanding the scope of precursors for OCF synthesis beyond conventional macrocyclic coordination motifs to coordinatively flexible polypyridyl ligands, we show that Ru‐terpyridine crystals with thermally polymerizable ethynyl units serve as effective precursors for immobilizing single‐atomic Ru species within three‐dimensional porous carbon frameworks, without metal aggregation or post‐synthetic treatments. The resulting Ru‐OCFs retain the ordered structure and coordination environment of the precursor crystals while simultaneously developing microporosity with high specific surface areas of up to 670 m ² g ⁻¹ . As a proof of concept, the high‐density isolated Ru sites in Ru‐OCFs enable enhanced catalytic activity in liquid‐phase CO ₂ hydrogenation, achieving a high formic acid productivity of up to 19 mmol g _cat ⁻¹ h ⁻¹ , outperforming representative nanoparticle catalysts.

Achieving high‐density single‐atom catalysts (SACs) remains a fundamental challenge, particularly for precious metals such as Ru that readily aggregate under synthetic and catalytic conditions. Here, we report a rational precursor design strategy for fabricating high‐density Ru SACs via direct carbonization, yielding ordered carbonaceous frameworks (Ru‐OCFs) with high Ru loadings of up to 11.0 wt%. By expanding the scope of precursors for OCF synthesis beyond conventional macrocyclic coordination motifs to coordinatively flexible polypyridyl ligands, we show that Ru‐terpyridine crystals with thermally polymerizable ethynyl units serve as effective precursors for immobilizing single‐atomic Ru species within three‐dimensional porous carbon frameworks, without metal aggregation or post‐synthetic treatments. The resulting Ru‐OCFs retain the ordered structure and coordination environment of the precursor crystals while simultaneously developing microporosity with high specific surface areas of up to 670 m ² g ⁻¹ . As a proof of concept, the high‐density isolated Ru sites in Ru‐OCFs enable enhanced catalytic activity in liquid‐phase CO ₂ hydrogenation, achieving a high formic acid productivity of up to 19 mmol g _cat ⁻¹ h ⁻¹ , outperforming representative nanoparticle catalysts.

Carbon dioxide (CO2) hydrogenation to formic acid (FA) is a promising route for implementing sustainable hydrogen energy cycles. Although the reaction readily proceeds in alkaline aqueous media, with bases facilitating CO2 dissociation and activation, formate salts are formed as products, requiring additional post-treatment to yield pure FA. Under base-free conditions, an inherently high activation barrier is required; however, high temperatures reduce gas solubility and hence lower the activity, making FA synthesis at low temperatures under base-free conditions still challenging. Herein, we report efficient CO2 hydrogenation to FA in pure water by exploiting cooperative catalytic actions between PdAg nanoparticles (NPs) and poly(ethylenimine) (PEI) confined within hollow silica shells. The confined PEI functions as a heterogeneous base that activates water/CO2 molecules and promotes bicarbonate (HCO3–) formation and adsorption near the PdAg NPs, while the PdAg NPs hydrogenate the HCO3– to FA. As a result, the catalyst achieves a turnover number (TON) of 83 over 6 h at 4.0 MPa (CO2/H2 = 1:1) and 40 °C in the absence of any base additives, outperforming other Pd-based catalysts previously reported. Moreover, the hollow architecture suppresses leaching and aggregation of the core materials, imparting enhanced stability and reusability. This work demonstrates a novel strategy for boosting aqueous CO2 hydrogenation by utilizing metal–polymer cooperative catalysis and provides a practical synthetic protocol for robust heterogeneous catalysts for aqueous-phase CO2 conversion.

The photosynthesis of hydrogen peroxide (H ₂ O ₂ ) from O ₂ and H ₂ O using solar energy offers a sustainable alternative to conventional processes. However, the H ₂ O ₂ yield is lowered because the H ₂ O ₂ is decomposed by the photocatalysts that are typically used. In this study, porphyrin‐containing organosilica photocatalysts were developed for efficient H ₂ O ₂ production. The as‐synthesized photocatalysts successfully convert O ₂ and H ₂ O into H ₂ O ₂ upon irradiation with visible light. Organosilica with the optimal number of porphyrin sites exhibit H ₂ O ₂ production rate of 108 µmol·L ⁻¹ ·h ⁻¹ , which is 1.8‐times higher than that of the precursor porphyrin ligand. Decomposition of H ₂ O ₂ by the photocatalysts was negligible. Photoluminescence measurements revealed that the incorporation of an optimal number of porphyrin sites into the organosilica significantly enhanced the photocatalytic activity for H ₂ O ₂ production because of the suppression of aggregation‐induced quenching. The mechanistic study revealed that H ₂ O ₂ production over the porphyrin‐containing organosilica photocatalysts occurred predominantly via a direct two‐electron oxygen reduction reaction pathway involving singlet oxygen and photogenerated electrons. These findings open new avenues for efficient photocatalytic production of H ₂ O ₂ and have significant implications for the design of advanced silica‐based photocatalytic materials.

Photothermal CO ₂ hydrogenation to methanol is considered an ideal process for both mitigating CO ₂ emissions and producing high‐value chemicals by utilizing sustainable solar energy, in which catalysts combining both CO ₂ hydrogenation activity and photothermal conversion features are required. In this study, we demonstrate that oxygen‐deficient molybdenum suboxide catalyst coupled with Pt (Pt/H _x MoO _3‐y ) exhibits a high methanol production rate of 1.51 and 1.89 mmol g _cat ⁻¹ h ⁻¹ with CO ₂ conversion of 8.6% and 10.9% in the dark and under visible light irradiations, respectively, under relatively mild conditions (200°C, 2.0 MPa), outperforming other oxide analogs. The molybdenum suboxide catalyst provides abundant oxygen vacancies in the presence of H ₂ , which promote the activation of CO ₂ and modulate the band structure to show quasi‐metallic optical features, thereby expanding the light absorption range and imparting photothermal conversion properties. Based on reaction experiments and kinetic analysis, we demonstrate that the molybdenum suboxide catalyst kinetically promotes the CO ₂ hydrogenation by converting incident light into heat. This work provides a fundamental insight for the rational design of oxide‐based catalysts for photothermal CO ₂ conversion applications.

Hydrogen spillover has emerged as an effective approach to improving the hydrogen evolution reaction (HER) by enabling interfacial hydrogen transfer from metals to supports. As such, rational design strategies intended to reduce charge accumulation between these two components are crucial. High-entropy oxides (HEOs), which have adjustable chemical compositions, tunable oxygen vacancies and flexible electronic structures, are promising supports for spillover-based electrocatalysts. The present work investigated Rh/Pt@CrMnFeCoNiO, an amorphous HEO, as a high-performance hydrogen evolution electrocatalyst in acidic media. Various experiments and electrochemical characterizations confirmed that hydrogen spillover occurred on this material. Notably, both Rh on the HEO surface and atomically-dispersed Pt were found to promote charge transfer, accelerate hydrogen migration and facilitate hydrogen desorption. The overall hydrogen evolution pathway was found to comprise hydrogen adsorption on Rh sites with subsequent transfer to Pt sites followed by desorption from O sites. On the basis of this dual-site synergy, the Rh/Pt@CrMnFeCoNiO catalyst exhibited an ultralow overpotential of 4 mV at 10 mA cm⁻² and superior intrinsic activity compared with commercially available Pt/C. This work provides new insights into the rational design of spillover-based HER catalysts.

Mo doping in CeO ₂ enhances the photo-assisted RWGS reaction, owing to increased oxygen vacancies and a narrow band gap.