Abstract In the process of photocatalytic synthesis of ammonia, the kinetics of carrier separation and transport, adsorption of nitrogen, and activation of the NN triple bond are key factors that directly affect the efficiency of converting nitrogen to ammonia. Here, we report a new strategy for anchoring MXene quantum dots (MXene QDs) onto the surface of ZnIn 2 S 4 by forming TiS bonds, which provide a channel for the rapid separation and transport of charge carriers and effectively extend the lifespan of photogenerated carriers. The unique charge distribution caused by the sulfurization of the MXene QDs further enhances the performance of the photocatalysts for the adsorption and activation of nitrogen. The photocatalytic ammonia synthesis efficiency of MXene QDs–ZnIn 2 S 4 can reach up to 360.5 μmol g −1 h −1 . Density functional theory calculations, various in situ techniques, and ultrafast spectroscopy are used to characterize the successful construction of TiS bonds and the dynamic nature of excited state charge carriers in MXene QDs–ZnIn 2 S 4 , as well as their impact on nitrogen adsorption activation and photocatalytic ammonia synthesis efficiency. This study provides a new example of how to improve nitrogen adsorption and activation in photocatalytic material systems and enhance charge carrier dynamics to achieve efficient photocatalytic nitrogen conversion. image 

Establishing carrier transport channels based on TiS bonds and enhancing the photocatalytic performance of MXene quantum dots–ZnIn2S4 for ammonia synthesis

Ammonia, a pivotal chemical feedstock and a potential hydrogen energy carrier, demands efficient synthesis as a key step in its utilization. The traditional Haber-Bosch process, known for its high energy consumption, has spurred researchers to seek ammonia synthesis under milder conditions. Advances in surface science and characterization technologies have deepened our understanding of the microscopic reaction mechanisms of ammonia synthesis. This article concentrates on gas-solid phase ammonia synthesis, initially exploring the latest breakthroughs and improvements in thermal catalytic synthesis. Building on this, it especially focuses on emerging external field-driven alternatives, such as photocatalysis, photothermal catalysis, and low-temperature plasma catalysis strategies. The paper concludes by discussing the future prospects and objectives of nitrogen fixation technologies. This comprehensive review is intended to provide profound insights for overcoming the inherent thermodynamic and kinetic constraints in traditional ammonia synthesis, thereby fostering a shift towards "green ammonia" production and significantly reducing the energy footprint.

Recent Advances in Ammonia Synthesis: From Haber-Bosch Process to External Field Driven Strategies.

Carbon-supported FeCoNiP/FeCoNi Mott-Schottky electrocatalyst for alkaline oxygen evolution reaction

The direct conversion of methane to hydrogen and high-value hydrocarbons under mild conditions is an ideal, carbon-neutral method for utilizing natural gas resources. Compared with traditional high-temperature thermal catalytic methods, using clean light energy to activate inert C-H bonds in methane can not only significantly reduce the reaction temperature and avoid catalyst deactivation, but also surpass the limitations of thermodynamic equilibrium and provide new reaction pathways. This paper provides a comprehensive review of developments in the field of photocatalytic non-oxidative conversion of methane (PNOCM), while also highlighting our contributions, particularly focusing on catalyst design, product selectivity, and the underlying photophysical and chemical mechanisms. The challenges and potential solutions are also evaluated. The goal of this feature article is to establish a foundational understanding and stimulate further research in this emerging area.

Photocatalytic non-oxidative conversion of methane.

The supported Ru co-catalyst induces upward band bending in the defective ZrO 2− x , forming an interfacial Schottky barrier that facilitates the separation of photogenerated charge carriers and provides energetic electrons for nitrogen activation. 

Defect ZrO2-x supported Ru nanoparticles as Mott-Schottky photocatalyst for efficient ammonia synthesis at ambient conditions

The ambient ammonia synthesis coupled with distributed green hydrogen production technology can provide promising solutions for low-carbon NH3 production and H2 storage. Herein, we reported Ru-loaded defective pyrochlore K2Ta2O6-x with remarkable visible-light absorption and a very low work function, enabling effective visible-light-driven ammonia synthesis from N2 and H2 at low pressure down to 0.2 atm. The photocatalytic rate was 2.8 times higher than that of the best previously reported photocatalyst and the photo-thermal rate at 425K was similar to that of Ru-loaded black TiO2 at 633K. Compared to perovskite-type KTaO3-x with the same composition, the pyrochlore exhibited a 3.7-fold increase in intrinsic activity due to a higher photoexcited charge separation efficiency and a higher conduction band position. The interfacial Schottky barrier and spontaneous electron transfer between K2Ta2O6-x and Ru further improve photoexcited charge separation and accumulate energetic electrons to facilitate N2 activation.

Defect pyrochlore-type Mott-Schottky photocatalysts for enhanced ammonia synthesis at low pressure.

Nonoxidative conversion of methane (NOCM) under mild conditions is a highly desirable technology for the low-carbon and atom-economical production of H2 and value-added chemicals. Here, we report the fabrication of CeO2 nanoisland patterns on the surface of Ce–Zr solid solutions. These ultrasmall CeO2 nanoislands with abundant step-edge structures provide unprecedented methane adsorption and activation, achieving the highest methane conversion rate of 1517 μmol g–1 h–1 for photocatalytic NOCM to date. Density functional theory calculations revealed that the low-coordinated Ce–O units at the stepped CeO2(111) surface possess more open planar configurations, which facilitate the cleavage of methane C–H bonds via a distinct metal–CH4 σ-complex mechanism that is energetically more favorable than the radical-like mechanism on the flat CeO2(111) surface. Moreover, the photocatalyst demonstrated a reversible and cooperative photoactivation process that enables the transition from the “resting state” to the “active state”, thereby enhancing the photoexcited charge separation efficiency and photocatalytic NOCM activities. 

Fabrication of Stepped CeO2 Nanoislands for Efficient Photocatalytic Methane Coupling

The technology of liquid organic hydrogen carriers presents great promise for large-scale hydrogen storage. Nevertheless, the activation of inert C(sp3)-H bonds in hydrocarbon carriers poses formidable challenges, resulting in a sluggish dehydrogenation process and necessitating high operating temperatures. Here, we break the shackles of C-H bond activation under visible light irradiation by fabricating subnanometer Pt clusters on defective Ce-Zr solid solutions. We achieved an unprecedented hydrogen production rate of 2601 mmol gcat.-1 h-1 (turnover frequency >50,000 molH2 molPt-1 h-1) from cyclohexane, surpassing the most advanced thermo- and photocatalysts. By optimizing the temperature-dominated hydrogen transfer process, achievable by harnessing hitherto wasted infrared light in sunlight, an astonishing 56% apparent quantum efficiency and a 5.2% solar-to-hydrogen efficiency are attained at 353 K. Our research stands as one of the most effective photocatalytic processes to date, holding profound practical significance in the utilization of solar energy and the exploitation of alkanes.

Liberating C-H Bond Activation: Achieving 56% Quantum Efficiency in Photocatalytic Cyclohexane Dehydrogenation.

Visible-Light-Driven Methanol-To-Ethanol Conversion via Carbene Pathway by Frustrated Lewis Pairs.

Boosting ammonia synthesis over MoO2 by Li intercalation

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