It is well known that supercritical water is a favourable medium for biomass conversion followed by its hydrodeoxygenation (HDO). Moreover, the actual kinetics and mechanism of reaction occurring in the supercritical water are not yet completely understood, either by experimental or computational approaches. Within the framework of DFT, the major challenge is non-availability of models to simulate supercritical phase. In this study, the authors manually define the descriptors of a solvation model to describe an implicit supercritical phase. In order to examine the suitability of supercritical water for thermal and hydrotreatment of bio-oil model compounds, nine different reactions involving conversion of furfural, tetrahydrofuran, xylose, phenol, guaiacol, ferulic acid, acetic acid, 2-hydroxybenzaldehyde and hydroxyacetone have been considered. Further these reactions are also studied in gas and liquid phase to compare results of different phases, including supercritical water. It was found that while HDO of aromatic compounds like phenol and 2-hydroxybenzaldehyde was favourable in the supercritical phase, smaller molecules like acetic acid and hydroxyacetone did not show much advantage in the supercritical phase over gas and liquid phase. It was also found that the thermochemical parameter - Gibbs free energy change (ΔG) was equally influenced by the solvation effect and the effect of temperature-pressure under supercritical conditions. In several instances, the two effects were found to offset each other in the supercritical phase.

The hydrodeoxygenation of guaiacol is modelled over a (100) β-Mo2C surface using density functional theory and microkinetic simulations. The thermochemistry of the process shows that the demethoxylation of the guaiacol,...

The conversion of guaiacol to benzene, toluene and o‐cresol along with several important intermediates like phenol, catechol and others in aqueous phase has been theoretically studied under the framework of density functional theory (DFT). The bond dissociation energy (BDE) calculation has been performed on optimized structures of guaiacol, phenol and anisole; and accordingly several reaction pathways have been proposed. The thermochemical parameters like Gibb's free energy change and enthalpy change of the reactions have also been reported using M06‐2X functional. In BDE study of the three compounds, i. e., guaiacol, phenol and anisole, it is observed that the scission of H. at fifth carbon position of an aromatic ring is the highest energy demanding dissociation, whereas the cleavage of bond from the functional group attached to the aromatic ring has the least BDE. The formation of phenol from guaiacol is more likely to occur by simultaneous hydrogenation and demethoxylation of guaiacol amongst all proposed pathways in aqueous phase. Further, decomposition of phenol to benzene is likely to occur via direct dehydroxylation of phenol. The simultaneous hydrogenation and dehydroxylation of guaiacol in aqueous phase are most likely to produce anisole which can further be reduced to phenol by direct cleavage of methyl group followed by hydrogenation. Further, free energy change landscape shows the conversion of guaiacol to phenol to be kinetically most favourable conversion at low temperature and high pressure in the aqueous phase. Finally, the increase in temperature causes a decrease in Gibb's free energy change and enthalpy change of overall reactions, thereby increasing favourability of most of the reactions in aqueous phase. Furthermore, the comparison between gaseous and aqueous phase results have been made wherever applicable.

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