Effects of Pd Nanoparticle Loading and Support Acidity on Liquid Phase Hydrodeoxygenation of Oxygenated Aromatics

The liquid phase hydrodeoxygenation (HDO) of guaiacol in aqueous medium was studied at 110 °C and relatively low hydrogen partial pressure (12.4 bar) over Pd/HY zeolite to explore the effects of Pd loading and catalyst acidity. Pd/HY catalysts with two different Pd loadings (0.075 and 2.5 wt %) were prepared using commercial HY zeolite supports with different SiO2/Al2O3 ratios (5.1, 12, and 30) via the strong electrostatic adsorption (SEA) method. On both catalysts, the primary products were aromatics (AR) (phenol and anisole) that progressively undergo ring hydrogenation at longer reaction times to yield nonaromatic (non-AR) products (cyclohexanone, cyclohexanol, and 1-methyl-1,2-cyclohexanediol). Increased acidity enhances the yields of the primary AR products. The near lack of AR products on Pd/KIT-6 catalysts indicates that both Pd and acidity are essential to form the AR intermediates. HDO experiments using model AR compounds reveal that substrates with adjacent oxygen (phenol and anisole) are more susceptible to ring hydrogenation compared to those wherein the oxygen atom is nonadjacent to the AR ring (i.e., benzyl alcohol). The HDO of benzyl alcohol over both Pd/Y30 and Pd/KIT catalysts yields predominantly toluene with turnover frequencies (TOFs) (36–885 s-1) increasing with Pd particle size in the range of 2–20 nm.