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This study investigates the detailed mechanism of CO2 conversion to CO using the manganese(I) diimine electrocatalyst [Mn(pyrox)(CO)3Br], synthesized by Christoph Steinlechner and coworkers. Employing density functional theory calculations, we thoroughly explore the electrocatalytic pathway of CO2 reduction alongside the competing hydrogen evolution reaction. Our analysis reveals the significant role of diimine nitrogen coordination in enhancing the electron density of the Mn center, thereby favoring both CO2 reduction and hydrogen evolution reaction thermodynamically. Furthermore, we observe that triethanolamine (TEOA) stabilizes transition states, aiding in CO2 fixation and reduction. The critical steps influencing the reaction rate involve breaking the MnC(O)–OH bond during CO2 reduction and cleaving the MnH–H–TEOA bond in the hydrogen evolution reaction. We explain the preference for CO2 conversion to CO over H2 evolution due to the higher energy barrier in forming the Mn-H2 species during H2 production. Our findings suggest the potential for tuning the electron density of the Mn center to enhance reactivity and selectivity in CO2 reduction. Additionally, we analyze potential competing reactions, focusing on electrocatalytic processes for CO2 reduction and evaluating “protonation-first” and “reduction-first” pathways through density functional theory calculations of redox potentials and Gibbs free energies. This analysis indicates the predominance of the “reduction-first” pathway in CO production, especially under high applied potential conditions. Moreover, our research highlights the selectivity of [Mn(pyrox)(CO)3Br] toward CO production over HCOO− and H2 formation, proposing avenues for future research to expand upon these findings by using larger basis sets and exploring additional functionalized ligands. [ABSTRACT FROM AUTHOR]

Alchemical free energy calculations via molecular dynamics have been applied to obtain thermodynamic properties related to solid–liquid equilibrium conditions, such as melting points. In recent years, the pseudo-supercritical path (PSCP) method has proved to be an important approach to melting point prediction due to its flexibility and applicability. In the present work, we propose improvements to the PSCP alchemical cycle to make it more compact and efficient through a concerted evaluation of different potential energies. The multistate Bennett acceptance ratio (MBAR) estimator was applied at all stages of the new cycle to provide greater accuracy and uniformity, which is essential concerning uncertainty calculations. In particular, for the multistate expansion stage from solid to liquid, we employed the MBAR estimator with a reduced energy function that allows affine transformations of coordinates. Free energy and mean derivative profiles were calculated at different cycle stages for argon, triazole, propenal, and the ionic liquid 1-ethyl-3-methyl-imidazolium hexafluorophosphate. Comparisons showed a better performance of the proposed method than the original PSCP cycle for systems with higher complexity, especially the ionic liquid. A detailed study of the expansion stage revealed that remapping the centers of mass of the molecules or ions is preferable to remapping the coordinates of each atom, yielding better overlap between adjacent states and improving the accuracy of the methodology. [ABSTRACT FROM AUTHOR]

Based on kinetic theory, the lattice Boltzmann method (LBM) is a versatile computational tool extensively applied to simulate diverse problems. It has particularly advanced in addressing general fluid flow, multiphase scenarios, and heat transfer. However, there is a notable gap in research concerning miscible fluids and an urgent need for thorough discussions on mass transfer via LBM in literature, emphasizing alternative modeling over traditional force and passive scalar models. Critical for applications, the understanding of mass transfer in miscible mixtures extends from scientific inquiry to engineering contexts. Hence, this review paper explores the dynamic interplay between mass transfer and fluid dynamics, focusing on the simulation of advection–diffusion problems for miscible non-reactive multicomponent mixtures through LBM. The paper categorizes two broad LBM strategies, the single-fluid and multifluid approaches, sheds light on their distinctive collision modeling techniques, and connects their mesoscale concepts to macroscopic properties and equations, such as viscosity, diffusion coefficient, and the Maxwell–Stefan and Fick equations. In the single-fluid strategy, we discuss the progress of the passive scalar models in mass transfer and the relevance of force models, such as the pseudopotential modeling, for simulation purposes. For multifluids, we detail the single collision technique and the alternative split collision scheme, in which, in this last one, we suggest classifying the models into explicit velocity-difference (Sirovich-based), equilibrium-adapted (Hamel-based), and quasi-equilibrium collision models. By providing a comprehensive overview, this text consolidates information regarding LBM mass transfer modeling, highlights directions for future research, and contributes to establishing a systematic approach for miscible mixtures. [ABSTRACT FROM AUTHOR]

Lignin is the main plant cell wall component responsible for recalcitrance in the process of lignocellulosic biomass conversion into biofuels. The recalcitrance and insolubility of lignin in different reaction media are due in part to the hydrogen bonds and π interactions that hold syringyl (S) and guaiacyl (G) units together and promote the formation of stable water-bridged dimeric complexes (WBDCs): S⋯G and S⋯S, in native lignin. The current understanding of how each type of interaction influences the stability of these complexes within lignin native cell walls is still limited. Here, we found by DFT calculations that hydrogen bonding is more dominant than π-stacking interaction between aromatic rings of WBDCs. Although there is a stronger interaction of hydrogen bonds between subunits and water and higher π-stacking interaction in the S⋯S complex compared to the S⋯G complex, the former complex is less thermodynamically stable than the latter due to the entropic contribution coming from the methoxy substituents in the S-unit. Our results demonstrate that the methoxylation degree of lignin units does not significantly influence the structural geometries of WBDCs; if anything, an enhanced dispersion interaction between ring aromatics results in quasi-sandwich geometries as found in "coiled" lignin structures in the xylem tissue of wood. In the same way as that with ionic liquids, polar solvents can dissolve S-lignin by favorable interactions with the aliphatic hydroxyl group in the α-position as the key site or the aromatic hydroxyl group as the secondary site. [ABSTRACT FROM AUTHOR]

New liquid–liquid equilibrium data of ternary systems of mono ethylene glycol + n‐pentane + methanol, mono‐ethylene glycol (MEG) + n‐pentane + ethanol, and mono ethylene glycol + n‐pentane + n‐butanol from 283.15 to 293 K are presented in this work. Binodal curves were obtained by the cloud point titration method. Tie‐line compositions were obtained through density and sound velocity measurements of phases in equilibrium. Results show that the solubility increases with temperature in all systems and decreases as the alcohol chain increases. The relative solubility data indicate that the alcohols are more soluble in MEG than in n‐C5. The obtained experimental data were successfully correlated using the CPA and the PC‐SAFT equation with appropriate binary interaction parameters. [ABSTRACT FROM AUTHOR]

The lattice Boltzmann method (LBM) has been increasingly adopted for modelling multiphase fluid simulations in engineering problems. Although relatively easy to implement, the ubiquitous Shan–Chen pseudopotential model suffers from limitations such as thermodynamic consistency and the formation of spurious currents. In the literature, the Zhang–Chen, Kupershtokh et al., the β‐scheme, and the Yang–He alternative models seek to mitigate these effects. Here, through analytical manipulations, we call attention to a unified model from which these multiphase interaction forces can be recovered. Isothermal phase‐transition simulations of single‐component in stationary and oscillating droplet conditions, as well as spinodal decomposition calculations, validate the model numerically and reinforce that the multiphase forces are essentially equivalent. Parameters are selected based on the vapour densities at low temperatures in the Maxwell coexistence curve, where there is a narrow range of optimal values. We find that expressing the model parameters as functions of the reduced temperature further enhances the thermodynamic consistency without losing stability or increasing spurious velocities. [ABSTRACT FROM AUTHOR]