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The catalytic hydrogenation of biomass-derived chemicals is essential in chemical industry due to the growing demand for sustainable and renewable energy sources. In this study, we present a comprehensive theoretical investigation regarding the hydrogenation of glycolaldehyde to ethylene glycol over a Ru/C catalyst by employing density functional theory and ab initio molecular dynamics simulations. With inclusion of explicit solvation, we have demonstrated that the glycolaldehyde hydrogenation is significantly improved due to the fast proton transfer through the hydrogen bond network. The enhanced activity could be attributed to the participation of the solvent water as the hydrogen source and the highly positively charged state of a Ru cluster in an aqueous phase, which are critical for the activation of aldehyde groups and proton-assisted hydrogenation. Overall, our findings provide valuable insights into glycolaldehyde hydrogenation over Ru/C catalysts in the aqueous phase, highlighting the importance of solvation effects in the biomass conversion. [ABSTRACT FROM AUTHOR]

Binary polymer systems show advantage in many applications. Herein, we study the conformational properties of a binary polymer system consisted of flexible and stiff polymers confined in slits using molecular dynamics simulation. The flexible and stiff polymers have the same chain length and concentration. Two surface enrichment structures, surface enrichment structure of stiff polymers and surface enrichment structure of flexible polymers, are observed dependent on the surface property and polymer concentration. In repulsive slits at high polymer concentration, surface enrichment structure of stiff polymers is observed as the unique structure. For attractive slits of the same attraction strength to both polymers, surface enrichment structure of stiff polymers even appears at low polymer concentration. Surface enrichment structure of flexible polymers can be observed when the surface attraction to the flexible polymers is much stronger than that to the stiff polymers. Our simulation results indicate that the structure of the binary polymer system can be controlled by varying the surface properties. [ABSTRACT FROM AUTHOR]

Recycle and reuse of waste asphalt materials in the pavement industry has brought tremendous contributions to the infrastructure sustainability and environmental preservation. The recent literature has suggested a great potential of plasticizers to be used for rejuvenating the oxidated paving asphalts. This study was aimed at assessing the rejuvenating effectiveness by rheological characterizations of two typical plasticizers, dibutyl phthalate (DBP) and tributyl citrate (TBC), selected based on the molecular structural differences. The underlying rejuvenating mechanisms were approached using molecular dynamics (MD) simulation, for probing the interactions between the plasticizers and oxidized asphaltenes and examining the outcomes in terms of deagglomeration. The results indicated that both plasticizers were highly effective in restoring the stiffness and elasticity properties as well as fatigue resistance of the aged asphalt. According to the simulations, the two plasticizers were able to deagglomerate the asphaltene associations. Owing to the high polarity and hydroxyl group, TBC appeared to be slightly more efficient in dissociating the asphaltenes, which explained its higher effectiveness in restoring the rheological properties as compared to DBP. Both the rheology and simulation results suggested that the plasticizers were rejuvenating instead of simply softening the aged asphalt. [ABSTRACT FROM AUTHOR]

• Rejuvenators were formulated by combining asphaltene dispersants with softeners. • All rejuvenation schemes effectively restored the rheology and moisture resistance. • Rejuvenated asphalts exhibited similar or better long-term performance than virgin. • Ionic liquid yielded the best dispersing efficiency and aromatic softener the least. • Polar groups and forming hydrogen bonding were speculated as primary contributors. The search and development of various asphalt rejuvenators have been following a trial-and-error methodology in essence; the imperative need of improved efficiency and versatility yearns for a general principle/framework of formulating rejuvenators. In this study, we propose one such formulation concept that rejuvenators can be designed by combining asphaltene dispersants (interacting with and dispersing asphaltenes) with softeners (diluting asphaltenes). This concept was preliminarily validated in an experimental program involving three rejuvenation schemes, namely using an aromatic softener alone (as the reference) and using it together with an ionic liquid or a phenolic compound (both acting as dispersants). Immediate and long-term rejuvenating effectiveness was evaluated based on viscoelastic properties, fatigue resistance, and moisture susceptibility. The results indicated that at respective optimum dosages, the three schemes all yielded satisfactory immediate performance of rejuvenation. After long-term aging, the rejuvenated asphalts demonstrated more desired viscoelastic characteristics in resisting high-temperature deformation and low-temperature cracking, and were more fatigue resistant, as compared to the virgin binder. Rejuvenation in all cases also recovered the moisture resistance nearly to the virgin level. Infrared spectrum analysis indicated that the performance restoration was accomplished by the agents blending physically with the aged binder, which decreased the concentrations of oxidation functional groups (carbonyl and sulfoxide). The incorporation of dispersants improved the aging resistance (in terms of high temperature viscoelasticity), and substantially reduced the need of aromatic softener while providing similar or better performance compared to using the softener alone, which would lead to pronounced environmental and economic benefits. The much higher dosage efficiency was ascribed to the capability of the dispersants in peptizing and dissociating the asphaltenes, as investigated by molecular dynamics simulations. The different dispersing behaviors of the additives were examined with reference to their chemical compositions and molecular structures. [ABSTRACT FROM AUTHOR]

Oxidative aging is an inevitable environmental factor that accelerates asphalt pavement deterioration. This study employed a molecular dynamics simulation to investigate the impact of aging on asphalt cement from the perspectives of thermodynamic properties, and diffusion and adhesion characteristics. Results indicate that aging increased bulk density from 1.008 to 1.081 g/cm3 and cohesive energy density by 15.6%, which was attributed to the promoted molecular polarity and intermolecular attractiveness. The enhanced molecular interactions also reduced molecular mobility, which led to an increase in the glass transition temperature by 30 K, suggesting that aging diminished the resistance of asphalt to thermal cracking. Simulations of the diffusion behaviors across different temperatures demonstrated that the Arrhenius relationship described well the temperature dependence of the diffusion coefficient, and that aging considerably slowed down the diffusion process as represented by Arrhenius prefactor D0, which dropped by 38.2%. The asphalt–aggregate adhesion was assessed using layered models with and without a water interlayer of different thicknesses. The adhesion was enhanced upon aging due to the significantly improved electrostatic interactions at the interface. Evaluation of the residual adhesion with the presence of interfacial water suggested that aging would raise the moisture susceptibility of asphalt pavement. The increase in molecular polarity was considered to be highly responsible for these aging consequences, and was thus further investigated via the electrostatic potential surface and dipole moment. [ABSTRACT FROM AUTHOR]

[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]

• Oxidative aging promoted and further stabilized asphaltene aggregation. • The driving force for aggregation was dispersion between the fused aromatic cores. • All additives reduced asphaltene aggregation and improved orientational randomness. • TBC exhibited the highest potential due to spatial distribution of four polar sites. Economic and environmental sustainability has been a significant stimulus to the use of recycled asphalt materials in the pavement industry. In this practice, rejuvenators are usually required to treat the oxidized asphalts with the aim to restore the physical properties and engineering performance. A critical function required for rejuvenators is that they can deagglomerate the asphaltene aggregates by effectively interacting with them. This study employed the techniques of molecular dynamics simulations and quantum chemical calculations, and investigated the impacts of oxidation on asphaltenes and the deagglomerating potential of three selected additives with different molecular structures and polarities, i.e., tributyl citrate (TBC), limonene, and myristamide. Analyses based on the aggregation number, orientational order parameter, and decomposition of the interaction energy indicated that oxidation strengthened the binding between the asphaltenes and thus promoted their aggregation behaviors. Among the three additives, TBC exhibited the highest rejuvenating effectiveness as it restrained the formation of large asphaltene aggregates and improved the orientational randomness of the aromatic cores. This capability was attributed to the highest number of polar sites in TBC and its three-dimensional spatial structure, which enhanced the compatibility and interactions with the aged asphaltenes. Based on the independent gradient model (IGM) method, the asphaltene aggregation is driven by the π-π interactions dominated by dispersion forces between the fused aromatic cores. The additives weakened the asphaltene interactions to different degrees, but the reversing effects were limited compared to the unaged state. [ABSTRACT FROM AUTHOR]

A theoretical study is conducted with three MX3$_{3}$ monolayer 2D materials (AlI3$_{3}$, AsI3$_{3}$, and IrBr3$_{3}$) on their electronic properties and how a halogen monovacancy affects their thermostability. Density functional theory (DFT) calculations are run to obtain the band structures and phonon dispersions for both pristine and defective structures. It is shown that AlI3$_{3}$ and AsI3$_{3}$ have indirect bandgaps of 2.40$2.40$ and 2.23$2.23$ eV, respectively. IrBr3$_{3}$ has a direct bandgap of 1.65$1.65$ eV. Phonon dispersions indicate that they are all thermodynamically stable in pristine state, but their defective counterparts are not. Ab‐initio molecular dynamics (AIMD) simulations are conducted for defective ones to further investigate their stability. It is found that AlI3 and AsI3 layers are decomposed while IrBr3 layer is bent. Further investigations are conducted by analyzing the bond energies and bond lengths of the three materials. It shows that AlI3$_{3}$ and AsI3$_{3}$ have lower bond energy and longer bond length, which makes them dissociated at the ambient temperature while higher bond energy and shorter bond length keep IrBr3$_{3}$ stabilized and enable its displacive phase transition in displacive limit. [ABSTRACT FROM AUTHOR]

• The aromatic additive was not capable of deagglomerating the asphaltenes due to low polarity and nearly planar structure. • The two polar additives disintegrated the asphaltene dimer by exfoliating off and separating the top monomer. • Hydrogen bonding and the distribution of polar groups were key to deagglomeration. • A single additive molecule yielded temporary dimer disintegration and could not prevent the eventual re-dimerization. Recycling agent plays an increasingly important role in promoting asphalt pavement sustainability, as it allows to bump up the incorporating dosage of recycled asphalt materials. The desired characteristics of a recycling agent includes not only the softening effect but also the capability of deagglomerating the oxidized asphaltenes by effectively interacting with them. The objective of this study was to provide novel insights into the deagglomerating potential of three additives selected based on the structural and compositional discrepancies, including an aromatic extract C 12 H 16 , a bio-additive myristamide C 14 H 29 NO, and a common plasticizer tributyl citrate (TBC) C 18 H 32 O 7. Steered molecular dynamics simulation was performed to obtain the intercalation in which each additive was intercalated between the stacking asphaltene sheets, with the objective to simulate the outcome of blending and mixing. These configurations were then subjected to long-time simulations during which the structural changes and the interactions were tracked. The results indicated that the aromatic extract yielded the least impact on the asphaltene dimer configuration during intercalation and had little deagglomerating effectiveness. Owing to the higher molecular flexibility and polarity, the other two additives produced more pronounced changes in the dimer structure during intercalation. They were able to disintegrate the dimer by exfoliating off and separating an asphaltene monomer, even though the effects were only temporary before re-dimerization occurred. Different types of interactions of the additives with the asphaltenes were visualized based on quantum chemical computations and discussed with respect to their contributions to the deagglomerating behaviors. [ABSTRACT FROM AUTHOR]

[Display omitted] • The plasticizers of DBP and TBC effectively restored the stiffness, relaxation capability, and crack resistance of the aged asphalt. • Both plasticizers lowered the glass transition temperature and broadened the transition region and linear viscoelastic relaxation spectrum. • TBC exhibited a stronger deagglomerating effect based on analytical characterizations and molecular dynamics simulations. • The higher rejuvenating effectiveness of TBC was due to its higher polarity and forming hydrogen bonds with asphalt molecules. Plasticizers are common additives used to enhance the flexibility and workability of polymer materials. Recent findings suggest a great potential for typical plasticizers being used as rejuvenators to recycle oxidized paving asphalts. This study investigated the rejuvenating effectiveness of two plasticizers via rheological evaluation and explored the underlying mechanism by analytical characterizations and molecular dynamics (MD) simulations. A conventional plasticizer dibutyl phthalate (DBP) and an environmentally friendly tributyl citrate (TBC) were selected given the discrepancies in their molecular structures. Both plasticizers were effective in restoring the rheological performance of the aged asphalt; TBC was relatively more efficient which was attributed to its higher molecular polarity and the formation of hydrogen bonds with the oxidized asphalt molecules. Analyses based on the gel permeation chromatography and differential scanning calorimetry suggested the capability of the plasticizers in dissociating the oxidized asphalt molecules and improving the molecular mobility. The improved molecular mobility was considered responsible for the reversing effect of the plasticizers, as compared to aging, in terms of widening the relaxation spectrum and broadening the glass transition region. The plasticizers' dissociating effect was confirmed and visualized in the simulations by inspecting their impacts on the spatial arrangement and distribution of the asphaltenes. [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]

• A comprehensive evaluation method was proposed for the interfacial characterization. • A clear boundary was noted between melamine formaldehyde (MF) and the asphalts. • MF achieved better blending with the neat asphalt than with the polymer modified. • Addition of MF enhanced the diffusion of all components in both asphalts. Various microencapsulation technologies involving different shell and core materials have been proposed in the literature for improving the asphalt mixture performance. The interfacial characteristics including adhesion between the microcapsule shell and asphalt largely determines the synergistic rheology of the blend. This study evaluated the impacts of melamine formaldehyde (MF) resin as the shell material on the interface and bulk properties of a neat and styrene–butadienestyrene (SBS) modified asphalt binders using the techniques of scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and molecular dynamics (MD) simulation. The clear interface without voids or cracks revealed in the SEM images suggested good adhesion between MF and both asphalts. Satisfactory interfacial binding was also suggested in the FT-IT results. The absorption peak strength of the neat asphalt was higher than that of SBS modified asphalt, and the binding of MF with neat asphalt was stronger than with the modified. The modified asphalt exhibited a slightly lower compatibility due to the high difference in the solubility parameter between SBS and MF, 9.783(J/cm−3)0.5. Introduction of MF promoted self-association of the asphaltenes and enhanced the diffusion of all the four fractions in both asphalt systems. Diffusion of the asphaltenes in the neat and modified asphalts saw the highest enhancement, which was increased to 5.3915 and 3.7893 (10-10m2s−1), respectively. Increase in diffusion coefficient was attributed to the high polarity and mobility of the MF molecules. [ABSTRACT FROM AUTHOR]