Atmospheric hydrodeoxygenation of guaiacol over alumina-, zirconia-, and silica-supported nickel phosphide catalysts

This study investigated atmospheric hydrodeoxygenation (HDO) of guaiacol over Ni₂P-supported catalysts. Alumina, zirconia, and silica served as the supports of Ni₂P catalysts. The physicochemical properties of these catalysts were surveyed by N₂ physisorption, X-ray diffraction (XRD), CO chemisorption, H₂ temperature-programmed reduction (H ₂-TPR), H₂ temperature-programmed desorption (H ₂-TPD), and NH₃ temperature-programmed desorption (NH ₃-TPD). The catalytic performance of these catalysts was tested in a continuous fixed-bed system. This paper proposes a plausible network of atmospheric guaiacol HDO, containing demethoxylation (DMO), demethylation (DME), direct deoxygenation (DDO), hydrogenation (HYD), transalkylation, and methylation. Pseudo-first-order kinetics analysis shows that the intrinsic activity declined in the following order: Ni₂P/ZrO₂ > Ni₂ P/Al₂O₃ > Ni₂ P/SiO ₂. Product selectivity at zero guaiacol conversion indicates that Ni₂P/SiO₂ promotes DMO and DDO routes, whereas Ni ₂P/ZrO₂ and Ni₂P/Al₂O₃ enhance DME. These differences were attributed to Ni₂P morphologies on these supports: SiO₂ hosted small Ni₂P particles, which were more active in H-transfer than large Ni₂P clusters supported on ZrO₂ and Al₂O₃. Within the first hour of time on-stream testing, Ni₂P/SiO₂ possessed relatively higher activity than Ni₂P/ZrO₂ and Ni₂P/Al ₂O₃. Low coke accumulation and excess phosphorus, which may replenish the Ni₂P phase to maintain its fully phosphided state, were likely responsible for the high activity of Ni₂P/SiO₂ at the outset.