Supported nano-metal catalysts are widely used in industrial processes. There is a trade-off between the activity and stability from mesoscale, which can be effectively tackled with the principle of compromise in competition (mechanisms A and B). To apply mesoscience methodology in this specific area, this work summarized research progress, where direct H₂O₂ synthesis was chosen as a typical case to identify and represent mechanism A (activity) and mechanism B (stability). It was found that mechanism A has been widely studied, while mechanism B still cannot reflect explosion. Subsequently, reaction heat and fusion enthalpy were proposed to represent mechanism B in this work, and the molecular thermodynamic model was identified as an effective tool for the study. A corresponding framework for mechanism B was constructed and the progress in developing the model for this particular purpose was provided. Finally, perspectives were discussed based on the linear non-equilibrium thermodynamics.

Abnormal melting point depression of metal nanoparticles often occurs in heterogeneous catalytic reactions, which leads to a reduction in the stability of reactive nanoclusters. To study this abnormal phenomenon, the original and surface-energy modified Gibbs–Thomson equations were analyzed in this work and further modified by considering the effect of the substrate. The results revealed that the original Gibbs–Thomson equation was not suitable for the particles with radii smaller than 10 nm. Moreover, the performance of the surface-energy modified Gibbs–Thomson equation was improved, and the deviation was reduced to (-350 ∼ 100) K, although further modification of the equation by considering the interfacial effect was necessary for the small particles (r < 5 nm). The new model with the interfacial effect improved the model performance with a deviation of approximately -50 to 20 K, where the interfacial effect can be predicted quantitatively from the thermodynamic properties of the metal and substrate. Additionally, the micro-wetting parameter αw can be used to qualitatively study the overall impact of the substrate on the melting point depression.

Cobalt-salen-based porous ionic polymers, which are composed of cobalt and halogen anions decorated on the framework, effectively catalyze the CO2 cycloaddition reaction of epoxides to cyclic carbonates under ambient conditions. The cooperative effect of bifunctional active sites of cobalt as the Lewis acidic site and the halogen anion as the nucleophile responds to the high catalytic performance. Moreover, density functional theory results indicate that the cobalt valence state and the corresponding coordination group influence the rate-determining step of the CO2 cycloaddition reaction and the nucleophilicity of halogen anions.

Wetting behavior of droplets made of choline chloride/urea (1:2), an archetypal deep eutectic solvent mixture, is studied using molecular dynamics simulations. The droplets are placed on a smooth model ionic substrate with positive and negative charges of the same magnitude q (0 e ≤ q ≤ 1.0 e), corresponding to a step-by-step change from a hydrophobic to hydrophilic surface. The molecular microstructure of the droplets and their spatial compositions are systematically studied in details on how they both change while gradually moving from hydrophobic to hydrophilic surface. It is observed that urea initially forms a monolayer on the surface with a planar orientation. This layer slowly shrinks while it becomes laterally more and more constrained. It becomes also molecularly more ordered when the surface becomes hydrophilic, at the same time as the contact angles become larger and larger. The anions (Cl-) are continuously pushed further away from the charged surface. While the contact angle increases and wetting decreases, and urea forms even a secondary stable layer where it changes its orientation and turns to have one of its amines facing up and carbonyl down. The average number of urea-urea H-bonds decreases linearly while the number of ion-pair contacts increases when the urea molecules are separating from the mixture. Our analysis gives a clear molecular understanding of the process and can be useful in many applications from membrane separation to catalysis.

Introducing materials with large interfaces to enhance process performance has become a feature of advanced chemical engineering, where the research focus has been changed from the traditional ideal isotropic fluid in the bulk phase to the highly non-ideal anisotropic confined fluid on the nano-micro interfaces, owing to the strong and asymmetric interactions between the complex fluids (supported metal nanoparticles, ionic liquids, proteins, etc.) and the sophisticated solid-surface (roughness, electrostatic effects, chemical heterogeneities, etc.). The traditional theories cannot be used to accurately describe the properties of the fluids at the complex solid-surfaces, due to the lack of considering molecular interactions between the fluid and solid-surface, and establishing new models is essential.

In this thesis, a generalized interfacial molecular thermodynamic model was proposed with the consideration of molecular interactions between the fluid and solid-surface. Firstly, the original and surface-energy modified Gibbs-Thomson equations were analyzed to calculate the melting points of mono noble metals and compared with the literature data, highlighting the importance of developing new models with the consideration of the interfacial effect. An empirical model was proposed to represent the interfacial effect for calculating the melting points of mono noble metals. Then, the mono noble metal nanoparticle supported at the flat solid-surface was chosen as the “model” system to develop a generalized model, and the developed model was extended to the supported alloy systems. The CO2 absorption capacity (or solubility) of the ionic liquids immobilized on the porous solid materials (substrates) was further investigated with the developed model. The main results were summarized as follows:

To develop models for representing the melting points of mono noble metal nanoparticles, the original and surface-energy modified Gibbs-Thomson equations were analyzed and then further modified empirically considering the effect of substrate. The results revealed that the original Gibbs–Thomson equation is invalid for the particles with radii smaller than 10 nm, and the performance of the surface-energy modified equation was improved but further modification by considering the interfacial effect is necessary for the particles smller than 5 nm in radius. The empirical model with the interfacial effect further improved the model performance, and the adjustable parameters can be predicted quantitatively from the thermodynamic properties of the metal and substrate. Additionally, the micro-wetting parameter αw can be used to qualitatively study the overall impact of the substrate on the melting point depression.

Combined with the analysis of the corresponding state theory, a generalized molecular thermodynamic model was developed. It was found that, the developed generalized model can provide accurate results of melting points with deviations within ± 15 K. The developed model was used to predict the melting point of Pt nanoparticles on the substrates of TiO2 and carbon (C), and the results showed that Pt on TiO2 was more stable than that on C, being consistent with the newly measured experimental results.

The generalized model was further parameterized based on the analysis of the interfacial tensions and molar volumes of Al-Si3N4, Pb-Si, Bi-C, and In-C, and the model showed the deviation was within ± 36 K. The model with fully generalized parameters was extended to the supported alloy nanoparticles to illustrate their stabilities, where the common catalysts, Pd-Au alloy nanoparticles supported on different substrates, developed for H2O2 reaction, were chosen as the examples. The model prediction displayed that the Pd-Au alloy nanoparticles supported on C/TiO2 (molar ratio: 0.01) with the mass proportion Pd5Au1 (i.e., mass ratio of 5:1) is more stable than the mono noble metals. Furthermore, the model prediction indicated that the supported alloy nanoparticles are more stable than the supported Pd.

The generalized model was also successfully extended to study the CO2 absorption capacity in the immobilized ionic liquids, where the Gibbs free energy of CO2 in the immobilized ionic liquids was modeled from both macro- and micro-analyses. The theoretical investigations revealed that the substrate has a crucial effect on the gas solubility in the ionic liquid immobilized on the substrates, and the performance of the model with the consideration of surface-energy and interfacial effects was further verified with the newly determined experimental data.

CO2 capture and separation (CCS) is a key step to mitigate greenhouse gas emissions and develop renewable energy. The trade-off between the rate and efficiency in the CO2 separation process cannot be solved with the traditional process intensification. Using nano-interface to realize process intensification has been widely used in the chemical process with multi-phase transfer, and CO2 separation is one of examples. This review summarizes the research work from the establishment of CO2 transfer model at nano-interface and the resistance regulation, the acquisition of the CO2 chemical potentials at equilibrium and at the nano-interface (the driving force regulation) and the molecular simulation analysis of the interface enhancement mechanism. Based on the theoretical studies, the resistance distribution for the CO2 separation process in a real absorption tower is further analyzed and a "three-stage strengthening scheme" is proposed to decrease the investment and operating costs. © All Right Reserved.

Metallosalen-based porous ionic polymers have the potential to combine the merits of homogeneous organometallics and heterogeneous porous ionic catalysts in carbon dioxide (CO2) cycloaddition conversion. Herein, a series of porous metallosalen hypercrosslinked ionic polymers (M-HIPs) were synthesized through a simple method. The M-HIPs with high metal and Br anion concentrations were evaluated by catalyzing CO2 cycloaddition with epoxides. Because of the cooperative effect between Br anions and metal active species in the porous channel, M-HIPs exhibited a high CO2 catalytic performance even under ambient conditions. Among the M-HIPs (M = Co, Al, Zn), Co-HIP showed the best catalytic performance for various epoxides and was stable after five runs. Density functional theory calculations support the fact that Co-HIP had the lowest energy barrier, which agreed with the experimental results.

Interfacial transfer at mesoscale is a common issue for all the multi-phase chemical processes, and the related study remains as a scientific challenge due to the complexities. Investigating the interfacial interactions at mesoscale to find out the regulation strategies is the key to realize process-intensification of mass-transfer and reaction for the advanced chemical industries. To accurately describe the behavior of fluids at the interface, a new molecular thermodynamic model that can describe the complex fluid-solid interface interaction. When the molecular thermodynamic modeling method is extended to the nano-micro interfacial transfer needs to be developed, calling for the coordination of advanced experiments at nano-micro scale and molecular with molocular thermodynamic modelling. Atomic force microscopy (AFM), which possess the sensitivity down to nanoscale, can directly obtain the interfacial interaction at nano-micro scale. The quantification of AFM-measured forces can be used to construct the coarse-grained molecular model and describe complex interfacial interaction. Then, the coarse-grained molecular model can reveal the molecular thermodynamic mechanism of nano- and micro- interface transfer, realizing quantitative prediction.

In this work, the CO₂ absorption working capacity and solubility in the ionic liquids immobilized into porous solid materials (substrates) was studied both experimentally and theoretically. The CO₂ absorption working capacity in the immobilized ionic liquids was measured experimentally. It was found that the CO₂ absorption working capacity and solubility increased up to 10 times compared to that in the bulk ionic liquids when the film thickness is nearly 2.5 nm in the [HMIm][NTf₂] immobilized into the P25. Meanwhile, a new model was proposed to describe the Gibbs free energy of CO₂ in the immobilized ionic liquids, and both macro- and micro-analyses of the CO₂ solubility in the confined ionic liquids were conducted. The theoretical investigations reveal that the substrate has a crucial effect on the gas solubility in the ionic liquid immobilized into the substrates, and the model performance was approved with the consideration of substrate effect.