# Review on Mechanisms and Kinetics for Supercritical Water Oxidation Processes
## 5 Conclusions and Future Perspectives
### Applications in Enhanced SCWO Processes  
Except for the optimal design of the reactor to make the SCWO system more efficient, enhanced treatments such as co-oxidation with auxiliary fuels, spilt oxidation, hydrothermal combustion and catalyzed oxidation not only make the removal of pollutants more efficient, but also achieve the directional transformation of pollutants. Some scholars have conducted various experimental studied on these enhanced treatments, but their mechanisms still need to be further clarified. Co-oxidation: the mechanism of producing active free radicals at different temperatures by different auxiliaries is not clear, and the strengthening effect of different additives is still controversial. It is very important to clarify the strengthening mechanism of different auxiliaries and their interaction with temperature in the selection of auxiliaries and temperature in the actual co-oxidation. Spilt oxidation: how reaction products produced in the first stage of spilt oxidation induce subsequent chemical reaction acceleration remains to be explained. Additionally, the location of oxygen and alcohol injection is also mostly determined by the experiment at present. Developing optimization methods combined with DCKMs and computational fluid dynamics to obtain such an optimal location is necessary for commercial device development. Hydrothermal combustion: although reactants can be rapidly degraded by high-temperature combustion, the migration of pollutants during combustion still cannot be explained due to the lack of mechanism models, especially the conversion of nitrogen to nitrate. Catalyzed oxidation: some scholars thought that catalysts produced activated oxygen, such as O\({}_{2}^{-}\), O and O\({}^{2-}\), to promote the removal of organics in the SCWO process [170; 171]. However, the DCKMs and detailed kinetic descriptions are still in shortage since the heterogeneous reactions between catalysts and reactants increase the model complexity. Based on the DCKMs of the model compounds, analyzing the mechanisms of each strengthening measure to achieve the directional transformation of pollutants will become a research hotspot in the future. Both the optimization of the reactor and the development of strengthening measures need to be based on a full understanding of the degradation of reactants, i.e., precise DCKMs are vital for the development of these enhanced treatments. However, most of the detailed chemical kinetic models are developed based on the gas-phase DCKMs since the reaction rates of small molecules reactions in SCWO process are fast due to the high pressure and can be described with a higher reaction constant (high-pressure limit). Hence, for organic compounds such as phenol, which have different reaction mechanisms in SCW and gas-phase, using gas-phase DCKMs to describe the SCWO process has large errors or is even no longer applicable. Relative to gas combustion, the oxidation reactions in SCW occur at a higher pressure and lower temperature, which need to add some intermediates that are stable in the collision and their reaction paths (e.g., C\({}_{6}\)H\({}_{5}\)OO in benzene oxidation mechanism). The dynamic parameters of the pressure-dependent reaction under high pressure (\(p>22.1\) MPa) also need to be investigated. With the development of computational chemistry, the specific experimental phenomena in the SCWO process can be well explained by the analysis of material structure characteristics and reactivity site predictions. Much more importantly, SCWO reaction barriers can be analyzed by computational chemistry, which provides the possibility to construct the chemical reaction path conforming to the SCWO environment (low temperature, high pressure, and high water concentration). Conceptualization, Z.J. and Y.L. ; resources, C.C. and C.Y. ; writing--original draft preparation, Z.J. ; writing--review and editing, Z.J., Y.L., C.Y., C.C., and J.L. ; supervision, S.W. All authors have read and agreed to the published version of the manuscript.