Evaluation of Silica-Supported Metal and Metal Phosphide Nanoparticle Catalysts for the Hydrodeoxygenation of Guaiacol Under Ex Situ Catalytic Fast Pyrolysis Conditions

A series of metal and metal phosphide catalysts were investigated for the hydrodeoxygenation of guaiacol under ex situ catalytic fast pyrolysis conditions (350 °C, 0.5 MPa, 12 H₂:1 guaiacol, weight hourly space velocity 5 h^-1). Ligand-capped Ni, Pt, Rh, Ni₂P, and Rh₂P nanoparticles (NPs) were prepared using solution-phase synthesis techniques and dispersed on a silica support. For the metal phosphide NP-catalysts, a synthetic route that relies on the decomposition of a single molecular precursor was employed. The reactivity of the NP-catalysts was compared to a series of reference materials including Ni/SiO₂ and Pt/SiO₂ prepared using incipient wetness (IW) impregnation and a commercial (com) Pt/SiO₂ catalyst. The NP-Ni/SiO₂ catalyst exhibited the largest reduction in the oxygen mol% of the organic phase and outperformed the IW-Ni/SiO₂ material. Although it was less active for guaiacol conversion than NP-Ni/SiO₂, NP-Rh₂P/SiO₂ demonstrated the largest production of completely deoxygenated products and the highest selectivity to anisole, benzene, and cyclohexane, suggesting that it is a promising catalyst for deoxygenation of aryl-OH bonds. The com-Pt/SiO₂ and IW-Pt/SiO₂ catalyst exhibited the highest normalized rate of guaiacol conversion per m² and per gram of active phase, respectively, but did not produce any completely deoxygenated products.