Oxygen-Activated Boron Nitride for Selective Photocatalytic Coupling of Methanol to Ethylene Glycol

The controllable photocatalytic C-C coupling of methanol to produce ethylene glycol (EG) is a highly desirable but challenging objective for replacing the current energy-intensive thermocatalytic process. Here, we develop a metal-free porous boron nitride catalyst that demonstrates exceptional selectivity in the photocatalytic production of EG from methanol under mild conditions. Comprehensive experiments and calculations are conducted to thoroughly investigate the reaction mechanism, revealing that the OB3 unit in the porous BN plays a critical role in the preferential activation of C-H bond in methanol to form ⋅CH2OH via a concerted proton-electron transfer mechanism. More prominent energy barriers are observed for the further dehydrogenation of the ⋅CH2OH intermediate on the OB3 unit, inhibiting the formation of some other by-products during the catalytic process. Additionally, a small downhill energy barrier for the coupling of ⋅CH2OH in the OB3 unit promotes the selective generation of EG. This study provides valuable insights into the underlying mechanisms and can serve as a guide for the design and optimization of photocatalysts for efficient and selective EG production under mild conditions.

Regulating the Spin State of Single Noble Metal Atoms by Hydroxyl for Selective Dehydrogenation of CH4 Direct Conversion to CH3OH

The key scientific challenge for methane (CH₄) direct conversion to methanol (CH₃OH) is considered to be the prevention of overoxidation of target products, which is restrained by the difficulty in the well-controlled process of selective dehydrogenation. Herein, we take single noble metal atom-anchored hexagonal boron nitride nanosheets with B vacancies (M_SA/B_1-xN) as the model materials and first propose that the dehydrogenation in the direct conversion of CH₄ to CH₃OH is highly dependent on the spin state of the noble metal. The results reveal that the noble metal with a higher spin magnetic moment is beneficial to the formation of the spin channels for electron transfer, which boosts the dissociation of C-H bonds. The promoted process of dehydrogenation will lead not only to the effective activation of CH₄ but also to the easy overoxidation of CH₃OH. More importantly, it is found that the spin state of noble metals can be regulated by the introduction of hydroxyl (OH), which realizes the selective dehydrogenation in the process of CH₄ direct conversion to CH₃OH. Among them, Ag_SA/B_1-xN exhibits the best performance owing to the dynamic regulation spin state of a single Ag atom by OH. On the one hand, the introduction of OH significantly reduces the energy barrier of C-H bond dissociation by the increase in the spin magnetic moment. On the other hand, the high spin magnetic moment of a single Ag atom during the process of subsequent dehydrogenation can be modulated to nearly zero. As a result, the spin channel for electron transfer between the adsorbed CH₃OH and reactive sites is broken, which hinders its overoxidation. This work opens a new path to designing catalysts for selective dehydrogenation by tuning the spin state of local electronic structures.