Bio-oils Hydrodeoxygenation: Adsorption of Phenolic Molecules on Oxidic Catalyst Supports

The interaction of phenol, anisole, and guaiacol, representatives of oxygenate functions present in pyrolysis bio-oils, with oxides such as silica, alumina (pure or doped with K or F), and silica-alumina is investigated by infrared spectroscopy. While phenolic type compounds mainly interact via H-bonding with silica, chemisorption is their main mode of adsorption on alumina. Besides, guaiacol interacts very strongly by forming doubly anchored phenates instead of monoanchored ones with phenol and anisole. At temperatures typical of hydrodeoxygenation (HDO) operating conditions (similar to 673 K), the phenate type species cover 2/3 of the alumina surface. This study clearly indicates that substantial carbon deposition could take place on alumina-supported HDO catalysts. Hence, this suggests that silica-based supports should be considered as potential candidates to design HDO catalyst with better stability.