Kentaro Teramura

Efficient utilisation of solar UV light ( λ > 300 nm) is essential for practical photocatalytic CO ₂ conversion. However, in conventional systems using water as an electron donor, slow water oxidation kinetics present a critical bottleneck that severely limits the CO production rate. Here, we demonstrate an efficient CO ₂ conversion system that overcomes this kinetic limitation by employing ammonia as an alternative electron donor over Mg-doped SrTiO ₃ loaded with Ag and Fe as dualcocatalysts (Ag–Fe/Mg–SrTiO ₃ ). Under UV irradiation ( λ > 300 nm), the optimised photocatalyst achieved a remarkable CO produc on rate exceeding 200 μmol h ⁻¹ . Mechanistic investigations revealed that the Fe cocatalyst played a crucial role in promoting ammonia oxidation, facilitating the rapid consumption of photogenerated holes, and significantly enhancing CO ₂ conversion activity. Furthermore, nitrite (NO ₂ ⁻ ) was successfully quantified as the primary oxidation product of ammonia, yielding a calculated e ⁻ / h ⁺ balance of approximately 1.2, validating the stoichiometric relationship of the reaction. This study offers a promising strategy for simultaneously achieving the upcycling of CO ₂ and effective utilisation of ammonia as both an energy source and an electron donor.

The selective electrochemical reduction of nitrate (NO3−) to ammonia (NH3) represents a promising route for sustainable NH3 production. However, achieving high NH3 selectivity remains challenging due to competing reactions. Additionally, many reported catalysts rely on noble metals and often require relatively elevated catalyst loadings to achieve high apparent activity, while most systems operate only at relatively low current densities. Herein, a fourteen-membered macrocyclic copper complex supported on Ketjenblack (Cu-14MR/KB) is reported as a cathode catalyst for the highly selective electrochemical reduction of NO3− to NH3. With a low Cu loading of 1.34 μmol cm−2, Cu-14MR/KB delivered a high Faraday efficiency for NH3 synthesis of up to 94.8% at a current density of −26.3 mA cm−2 and maintained high NH3 selectivity over a wide current density range from −26.3 to −150 mA cm−2. Notably, at −150 mA cm−2, Cu-14MR/KB achieved an NH3 yield rate of 604 μmol cm−2 h−1 with an NH3 Faraday efficiency of 86.4%. Furthermore, a more contracted Cu–N4 coordination environment was revealed in Cu-14MR than in CuPc, with a shorter Cu–N bond distance, suggesting relatively stronger Cu–N interactions. This work provides an efficient strategy for high-performance NO3− electroreduction using a low-loading and non-noblemetal catalyst.

The Mars–van Krevelen (MvK) mechanism, in which lattice oxygens and oxygen vacancies participate in the redox reactions of target molecules, has emerged as a novel catalytic strategy to replace conventional supported metal catalysis for the reverse water-gas shift (rWGS) reaction. Although loading Pd nanoparticles as a cocatalyst to promote the dissociation of H2 is crucial for the MvK-type rWGS, it also promotes the sequential hydrogenation of CO into CH4 because of the strong adsorption of CO on Pd. Here, we show that rWGS selectively proceeds over a Pd-Cu alloy loaded on SrTi0.8Mn0.2O3, which promotes rWGS through the MvK mechanism. We found that 5 wt% Pd-loaded SrTi0.8Mn0.2O3 (Pd/STMO) produced both CO and CH4 at 773 K with yields of 35.5% and 7.1%, respectively, whereas 5 wt% Pd-Cu-loaded SrTi0.8Mn0.2O3 (Pd-Cu(5.0)) selectively produced CO with a yield of 49.1%. High-angle annular dark-field scanning transmission electron microscopy, X-ray diffraction, and X-ray absorption spectroscopy confirmed the presence of a face-centered cubic alloy (PdCu3) and disordered alloy (Pd1−xCux) of Pd and Cu in Pd-Cu(5.0) with much larger particle sizes than the monometallic Pd particles in Pd/STMO. In situ Fourier-transform infrared spectra showed a strong absorption band of adsorbed CO species in Pd/STMO, while it became negligible in Pd-Cu(5.0). The formation of the alloy would offer isolated Pd species in the nanoparticles to suppress the adsorption of CO in a bridged configuration, which is amenable to the sequential hydrogenation to CH4, leading to selective rWGS over the alloy-loaded STMO. The present study demonstrates that employing an alloying strategy significantly enhances MvK-type rWGS.

Interfacial charge transfer (IFCT) has emerged as a novel strategy for selective photoactivation of adsorbed molecules through inner-sphere type electron transfer. Most IFCT systems require electron-rich functional groups such as hydroxyl or amino groups to form IFCT surface complexes, limiting their application to the oxidation of these functional groups. Herein, we demonstrate that nitrogen atoms in aromatic rings can be used to form a surface complex through acid–base interactions, which gives rise to IFCT with photocatalysts, and to promote the photooxidation of an aromatic methyl group of heteroaromatics. We found that 9-methylacridine (9-MA)-adsorbed on TiO2 exhibited an IFCT absorption band in the visible light region (400-500 nm), which can be attributed to the IFCT transition from 9-MA to TiO2. Under irradiation with a blue LED (λ = 465 nm), photooxidation of 9-MA into 9-acridinecarboxaldehyde (9-ACAl) proceeded in toluene, with a maximum yield of 44 %, which was 2.6 times higher than that under UV light irradiation (λ = 365 nm). The higher yield under visible-light irradiation can be attributed to the absence of photogenerated holes in the photocatalyst, which oxidize toluene to strongly adsorbed intermediates such as benzaldehyde and benzoic acid, causing deactivation of the photocatalyst. The present study opens up new IFCT systems utilizing the interaction of heteroatoms in aromatic rings with the surface of photocatalysts.

Ammonia is a promising zero-carbon energy carrier; however, its conventional production is energy-intensive and dependent on fossil fuels. The electrochemical reduction of nitric oxide offers a sustainable alternative for ammonia synthesis while simultaneously mitigating nitrogen oxide pollutants. In this study, a solid polymer electrolyte cell equipped with an anion-exchange membrane was employed to improve nitric oxide mass transport and suppress the competing hydrogen evolution reaction by establishing a localized alkaline environment. Using a copper catalyst supported on carbon, ammonia was successfully produced with a Faraday efficiency of 22%. The introduction of platinum as a secondary metal further enhanced the catalytic performance. Under continuous electrolysis at a current density of −50 mA cm ⁻² , the bimetallic copper–platinum catalyst achieved an ammonia formation rate of 2.2 mg h ⁻¹ cm ⁻² , a Faraday efficiency of 34%, and a nitric oxide-to-ammonia conversion of 23%. These results demonstrate an effective strategy for continuous ammonia electrosynthesis from dilute nitric oxide streams and suggest a promising approach for utilizing low-concentration nitrogen oxide sources.

The photocatalytic conversion of CO ₂ into valuable chemicals is a promising approach for artificial photosynthesis. The photocatalytic conversion of CO ₂ over Ag‐modified lanthanide titanates (Ln ₂ Ti ₂ O ₇ ) was investigated in this study under photoirradiation at wavelengths longer than 300 nm using 2‐propanol as a hole scavenger. Among the various Ln ₂ Ti ₂ O ₇ materials tested, La ₂ Ti ₂ O ₇ exhibited superior photocatalytic performance. The photocatalytic activity was strongly dependent on the crystallinity and surface area of the La ₂ Ti ₂ O ₇ host, with the optimal photocatalyst obtained by calcination at 1423 K for 2 h. Furthermore, the Ag cocatalyst loading method significantly affected the CO production rate, with chemical reduction facilitating the formation of highly dispersed, small metallic Ag nanoparticles (2–10 nm), which were essential for efficient CO ₂ reduction. In contrast, the photodeposition and impregnation methods resulted in the formation of larger, aggregated Ag particles (20–50 nm), leading to a lower photocatalytic activity. The optimised Ag/La ₂ Ti ₂ O ₇ photocatalyst achieved a CO formation rate of approximately 120 µmol h ⁻¹ with a high selectivity of 90%. The stoichiometric formation of acetone and isotopic labelling experiments using ¹³ CO ₂ confirmed that the reaction proceeded via the reduction of CO ₂ to CO, coupled with the oxidation of 2‐propanol.

Highly selective carbon monoxide production can be achieved during the electrolysis of carbon dioxide using a cathode catalyst composed of silver nanoparticles loaded onto a carbon support (Ag/C). Although generating abundant Ag species is desirable for efficient CO ₂ electrolysis, conventional methods tend to produce relatively large Ag particles at high loading levels. In this paper, an advanced Ag/C electrocatalyst is produced via ultrasonic reduction (Ag(USR)/C). Importantly, the activity of this electrocatalyst was demonstrated to be superior to those of Ag/C cathodes prepared via conventional methods. This activity was retained under various conditions. In particular, CO was formed during electrolysis when 10 vol.% CO ₂ was supplied to the Ag(USR)/C cathode, while only H ₂ was evolved on the Periodical Ag/C cathodes. Abundant Ag nanoparticles measuring a few nanometers in diameter were detected on the Ag(USR)/C electrocatalyst surface, whereas significantly larger Ag species were observed on the Periodical Ag/C catalysts. Additionally, electrochemical impedance spectroscopy suggested that electrons were injected into CO ₂ more efficiently when the Ag(USR)/C was employed. Accordingly, these small Ag nanoparticles exhibited superior activity in the efficient low‐concentration CO ₂ electrolysis and 100% CO ₂ electrolysis processes. These results confirm the high CO ₂ electrolysis activity of the Ag(USR)/C cathode.

The photocatalytic conversion of CO2 into valuable chemicals is a promising approach for artificial photosynthesis. The photocatalytic conversion of CO2 over Ag-modified lanthanide titanates (Ln2Ti2O7) was investigated in this study under photoirradiation with wavelengths longer than 300 nm using 2-propanol as a hole scavenger. Among the various Ln2Ti2O7 materials tested, La2Ti2O7 exhibited superior photocatalytic performance. The activity was strongly dependent on the crystallinity and surface area of the La2Ti2O7 host, with the optimal sample obtained by calcination at 1423 K for 2 h. Furthermore, the Ag cocatalyst loading method significantly affected the CO production rate. Chemical reduction facilitated the formation of highly dispersed, small metallic Ag nanoparticles (2–10 nm), which were essential for efficient CO2 reduction. In contrast, the photodeposition and impregnation methods resulted in the formation of larger, aggregated Ag particles (20–50 nm), leading to lower photocatalytic activity. The optimised Ag/La2Ti2O7 photocatalyst achieved a CO formation rate of approximately 120 µmol h−1 with high selectivity (>90%). The stoichiometric formation of acetone and isotopic labelling experiments using 13CO2 confirmed that the reaction proceeded via the reduction of CO2 to CO, coupled with the oxidation of 2-propanol.

Highly selective carbon monoxide production can be achieved during the electrolysis of carbon dioxide using a cathode catalyst composed of silver nanoparticles loaded onto a carbon support (Ag/C). Although generating abundant Ag species is desirable for efficient CO2 electrolysis, conventional methods tend to produce relatively large Ag particles at high loading levels. In this paper, an advanced Ag/C electrocatalyst is produced via ultrasonic reduction (Ag(USR)/C). Importantly, the activity of this electrocatalyst was demonstrated to be superior to those of Ag/C cathodes prepared via conventional methods. This activity was retained under various conditions. In particular, CO was formed during electrolysis when 10 vol.% CO2 was supplied to the Ag(USR)/C cathode, while only H2 was evolved on the other Ag/C cathodes. Abundant Ag nanoparticles measuring a few nanometres in diameter were detected on the Ag(USR)/C electrocatalyst surface, whereas significantly larger Ag species were observed on the other Ag/C catalysts. Additionally, electrochemical impedance spectroscopy suggested that electrons were injected into CO2 more efficiently when the Ag(USR)/C was employed. Accordingly, these small Ag nanoparticles exhibited superior activity in the efficient low-concentration CO2 electrolysis and 100% CO2 electrolysis processes. These results confirm the high CO2 electrolysis activity of the Ag(USR)/C cathode.