Effect of supercritical water on the stability and activity of alkaline carbonate catalysts in coal gasification

The stability and activity of alkaline carbonate catalysts in supercritical water coal gasification has been investigated using density functional theory method. Our calculations present that the adsorption of Na2CO3 on coal are more stable than that of K2CO3, but the stability of Na2CO3 is strongly reduced as the cluster gets larger. In supercritical water system, the dispersion and stability of Na2CO3 catalyst on coal support is strongly improved. During coal gasification process, Na2CO3 transforms with supercritical water into NaOH and NaHCO3, which is beneficial for hydrogen production. The transformation process has been studied via thermodynamics and kinetics ways. The selectively catalytic mechanism of NaOH and the intermediate form of sodium-based catalyst in water-gas shift reaction for higher hydrogen production has also been investigated. Furthermore, NaOH can transform back to Na2CO3 after catalyzing the water-gas shift reaction. Thus, the cooperative effects between supercritical water and Na2CO3 catalyst form a benignant circle which greatly enhances the reaction rate of coal gasification and promotes the production of hydrogen.

Development, applications and challenges of ReaxFF reactive force field in molecular simulations

As an advanced and new technology in molecular simulation fields, ReaxFF reactive force field has been developed and widely applied during the last two decades. ReaxFF bridges the gap between quantum chemistry （QC） and non-reactive empirical force field based molecular simulation methods, and aims to provide a transferable potential which can describe many chemical reactions with bond formation and breaking. This review presents an overview of the development and applications of ReaxFF reactive force field in the fields of reaction processes, biology and materials, including （1） the mechanism studies of organic reactions under extreme conditions （like high temperatures and pressures） related with high-energy materials, hydrocarbons and coals, （2） the structural properties ofnanomaterials such as graphene oxides, carbon nanotubes, silicon nanowires and metal nanoparticles, （3） interfacial interactions of solid-solid, solid-liquid and biological/inorganic surfaces, （4） the catalytic mechanisms of many types of metals and metal oxides, and （5） electrochemical mechanisms of fuel cells and lithium batteries. The limitations and challenges of ReaxFF reactive force field are also mentioned in this review, which will shed light on its future applications to a wider range of chemical environments.