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[Display omitted] Achievement of superlubricity is an effective method to reduce friction and wear, which has a prominent influence on the operational efficiency and lifetime of a device. However, some burning issues still remain to be solved for the practical applications of superlubricity, such as the poor load-bearing capacity, especially in liquid superlubricity. Therefore, exploring an effective method to enhance the superlubricity performance is essential to accelerate the application of superlubricity. The friction properties between two different self-assembled monolayers (SAMs)—a perfluorocarbon SAM and a hydrocarbon SAM—and graphite in water were explored and compared by atomic force microscopy (AFM). Enhanced superlubricity performance due to the fluorination was observed. Specifically, we observed an approximately 85% reduction of the friction coefficient after fluorination, and superlubricity was achieved with extremely low friction coefficient of 0.0003. Moreover, 2.4-fold greater load-bearing capacity of the superlubricity was obtained after fluorination. The molecular origin of the superlubricity enhancement by fluorination was revealed by molecular dynamics (MD) simulations, indicating that the greater load-bearing capacity of the perfluorocarbon SAM was ascribed to the enhanced interaction between the water and SAM by fluorination to form a more robust layered water structure confined in the contact zone, which played a pivotal role in the superlubricity. [ABSTRACT FROM AUTHOR]

[Display omitted] • The furfural hydrogenation mechanisms are systematically investigated in vapor phase and aqueous phase. • A proton-shuttling mechanism in aqueous phase is proposed. • The presence of water enhances the stability and activity of reaction intermediates. • The dynamic charge separation between the catalyst and the intermediates results in low hydrogenation barriers. The catalytic hydrogenation of biomass-derived compounds in the aqueous phase is crucial to upgrading renewable biochemicals and biofuels. Herein, by combining density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations, we have explored the selective hydrogenation mechanism of furfural on the copper surface with a fully explicit solvation model. The presence of water solvent could significantly affect the reaction mechanism, in adjunct with the charge interactions between the reaction intermediates and the Cu surface. It demonstrates a proton-shuttling mechanism for furfural hydrogenation where the initial hydrogen source for reducing the carbonyl group is from the dissociation of the adjacent water. Furthermore, the water solvation effect results in the dynamic charge separation between the copper surface and the reaction intermediates, significantly reducing the energy barrier. These results deepen our mechanistic understanding of selective hydrogenation of furfural over Cu-catalysts, paving the way for upgrading renewable biomass derivatives in applications. [ABSTRACT FROM AUTHOR]

We reported that the dissolved tungsten bronze (H x WO 3) exhibits the best activity for selective C C bond cleavage. The active species with low coordinated and low valent W site calls for the selectivity to C 2 fragments via a homolytic cleavage of C C bond cleavage. [Display omitted] • The formation of a chelated metalacyclic complex with 5-membered ring is critical for C C cleavage of glucose on the W-based catalyst. • The low-valent W center experiences a redox cycle (+V → +VI → +V) during the C C cleavage that accounts for the high reactivity of W-based catalyst. • The surface decoration of reduced and low-coordinated W site could be efficient for selective cellulose conversion in aqueous phase. In chemistry, selective activation of C C bonds enables the direct production of valuable chemicals from widely available and inexpensive natural materials but remains a fundamental challenge due to their kinetic inertness. The selective cleavage of C C bond in glucose by tungsten oxide-based catalysts in aqueous phase pioneers a path for converting cellulose biomass into valuable ethylene glycol. However, debates regarding the active phase and how it selectively breaks the C 6 into C 2 fragments have persisted for over a decade. In this study, we present a comprehensive mechanistic investigation by modeling three potential active phases, i.e. the reduced WO 3-x surface, the dissolved tungstic acid, and tungsten bronze, in explicit solvent waters. By constrained molecular dynamics simulations, we have demonstrated that the low-coordinated W center can chelate with glucose, forming a metallacyclic complex with a 5-membered ring after the protonation of carbonyl group. The formation of 5-membered ring serves as the premise for the selectivity to C 2 fragments via homolytic cleavage of C C bond. Furthermore, the reduced W5+ center is suggested to be crucial in facilitating the cleavage process by stabilizing the dissociated C 4 intermediates via a redox process. In conclusion, we propose that the surface decoration of reduced and low-coordinated W sites can act as active heterogeneous catalysts for the selective conversion of cellulose in aqueous phase. These recent findings have the potential to provide valuable insights and strategies for C C bond activation in both biomass conversion and organic synthesis. [ABSTRACT FROM AUTHOR]