Steric Effect and Evolution of Surface Species in the Hydrodeoxygenation of Bio-Oil Model Compounds over Pt/HBEA

The formation and evolution of surface species during the hydrodeoxygenation of various bio-oil model compounds (anisole, m-cresol, and guaiacol) over Pt/HBEA and HBEA is investigated. Anisole and m-cresol form phenate and cresolate species on Lewis acid sites, while guaiacol can chemisorb more strongly forming bidentate surface species. The position of functional groups within these molecules has a strong influence on the degree of hydrodeoxygenation over Pt/HBEA, due to steric hindrance of the C-O scission step. Consequently, the highest yield of deoxygenated products is formed over anisole, followed by m-cresol and guaiacol. No deoxygenation products are produced from HBEA. On the basis of operando transmission FTIR spectroscopy experiments at 400 degrees C and 1 atm of hydrogen pressure, a timeline for the formation of polynuclear aromatics and graphitic coke from aromatics with different substituents is established for Pt/HBEA. The early formation of relatively small amounts of graphitic coke and polynuclear aromatics results in pronounced catalyst deactivation. In addition, the formation of strongly adsorbed monomeric species appears to restrict transport processes within the zeolite pores and contribute to deactivation.