The thermodynamic mechanism of selective cocrystallization was investigated by combination of molecular dynamics (MD) simulations and phase diagram analysis, using system of urea and cresol isomers as model compounds. Hansen solubility parameters (HSPs) models were utilized to predict miscibility and cocrystal formation. Thermodynamic phase diagrams of cresol isomers and urea were measured with the help of process analysis technology. MD simulations were performed to investigate the intermolecular interactions between m‐ and/or p‐cresol and urea, by calculating the solvation free energies (SFEs) and analysing radial distribution functions (RDFs). The simulation and experimental results indicate that the solubility data of urea are apparently affected by the SFEs, which are linearly related with the concentration of urea. Moreover, it was also found that the type of O‐H···O=C hydrogen bond plays a critical role in the contribution of intermolecular interactions and is also a key factor for selective cocrystallization.

A fully interactive Cu/C/H/O reactive force field (ReaxFF) was developed for the Cu-metal surface catalysis system following three steps: (1) re-optimization of the Cu force field by an extended training set including additional Cu cluster properties, (2) combination of this re-optimized Cu force field and an existing C/H/O force field, and (3) fitting of interactions between Cu and C/H/O with extensive DFT data involving the various binding energies and elementary reaction steps. In addition, we developed an algorithm to search the transition state (TS) of elementary steps, which is the first TS searching program based on the ReaxFF theory framework, and a new algorithm is proposed to create reaction paths and coordinate scans with highdegrees of freedom. The comparison of results of DFT and ReaxFF indicate that the developed force field is capable of describing the properties related to reactive interactions between the Cu metal and C/H/O molecules. To test this developed Cu/C/H/O force field, a series of molecular dynamics simulations were performed. In Cu/C/H/O surface simulation, elementary C/H/O reactions involving H transfer and H 2 /CHO dissociations were observed supporting the complex C/H/O interactions on a Cu surface.In addition, two Cu/CHO example cases relevant to the chemical looping combustion process were also simulated: metal oxide (CuO) generation from reactions of metallic Cu with glucose and hydrocarbon fuel oxidation using a copper oxide as the oxidizer. Our simulation results indicate that the current Cu/C/H/O ReaxFF is able to capture the reaction details and distinguish the redox performances of different fuels.

Supercritical water gasification (SCWG) is considered as an excellent technique with great potential for lignin utilization, and the addition of a Ni catalyst is effective to achieve high gasification yields. To understand the size effect of Ni nanoparticles during the SCWG process, our simulations were performed by reactive molecular dynamics methods, and the detailed pathways of lignin decomposition and hydrogen production were obtained. The cleavage of the β-O-4′ linkages consists of three main pathways, and the size of Ni catalysts influences the cleavage pathways. During the ring-opening process, the Ni catalyst could accelerate the cleavage of C–O bonds and destroy the conjugated π bond of the aromatic ring. Moreover, the generation of H2 molecules occurs entirely on the Ni catalyst. The H radicals gradually approach each other via the transformation of adsorption sites, and the diffusion is the rate-limiting step for the H2 production, especially at the initial reaction stage. The results indicate that a smaller catalyst cluster possesses higher activity, and there are more active sites at the Ni surface to weaken C–C, C–O, C–H, and O–H bonds. Through the cyclic use, the stability of the 2.0 nm catalyst cluster is better than that of 3.0 and 4.0 nm clusters due to the lower surface oxidation degree.