Computational insights into the deoxygenation reaction of biomass-derived phenolic compounds over Ni₂P (001) catalysts

This research sets the scene for understanding the interaction of phenolic molecules (i.e., phenol, o-cresol, m-cresol, and p-cresol) with Ni₂P catalyst surface and how their hydrodeoxygenation reaction progresses over the surface. The hydrodeoxygenation process is responsible for removing the oxygen content from the pyrolysis oil compounds, particularly through direct deoxygenation route. Ni₂P, which is one of the most common transition metal phosphides, serves as a candidate surface of this study. Two main investigations were carried out including the optimization of (1) adsorption configuration of the phenolic compounds and the (2) net charge distribution between the surface and the adsorbate. According to the adsorption energy studies, the horizontal configuration of the o-cresol molecule on the Ni₂P(001) hollow site presented the most optimized and stable configuration with the least negative adsorption energy (−0.26 eV), resulting in the most negative net charge density at −0.286 |e|, as determined by the Bader charge analysis. Upon adsorption on Ni₂P(001) surface, o-cresol undergoes significant charge redistribution, where the oxygen atom (-OH group) exhibits a net charge of −1.3443 |e|, indicating electron transfer to the surface. The catalytic pathway proceeded with deoxygenation followed by ring hydrogenation to produce toluene (C₇H₈), such that C–O bond dissociation has a reaction energy of −0.715 eV, while C–H bond formation step had a reaction energy of 0.011 eV.