Atmospheric Hydrodeoxygenation of Guaiacol over Alumina-, Zirconia-, and Silica-Supported Nickel Phosphide Catalysts

This study investigated atmospheric hydrodeoxygenation (HDO) of guaiacol over Ni 2 P-supported catalysts. Alumina, zirconia, and silica served as the supports of Ni 2 P catalysts. The physicochemical properties of these catalysts were surveyed by N 2 physisorption, X-ray diffraction (XRD), CO chemisorption, H 2 temperature-programmed reduction (H 2 -TPR), H 2 temperature-programmed desorption (H 2 -TPD), and NH 3 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: Ni 2 P/ZrO 2 > Ni 2 P/Al 2 O 3 > Ni 2 P/SiO 2 . Product selectivity at zero guaiacol conversion indicates that Ni 2 P/SiO 2 promotes DMO and DDO routes, whereas Ni 2 P/ZrO 2 and Ni 2 P/Al 2 O 3 enhance DME. These differences were attributed to Ni 2 P morphologies on these supports: SiO 2 hosted small Ni 2 P particles, which were more active in H-transfer than large Ni 2 P clusters supported on ZrO 2 and Al 2 O 3 . Within the first hour of time on-stream testing, Ni 2 P/SiO 2 possessed relatively higher activity than Ni 2 P/ZrO 2 and Ni 2 P/Al 2 O 3 . Low coke accumulation and excess phosphorus, which may replenish the Ni 2 P phase to maintain its fully phosphided state, were likely responsible for the high activity of Ni 2 P/SiO 2 at the outset.