Targeted conversion of model phenolics in pyrolysis bio-oils to arenes via hydrodeoxygenation over MoOx/BaO@SBA-15 catalyst

Abstract

The bio-oils derived from fast pyrolysis of lignin contain large amount of phenolic components. Owing to the high oxygen content, these bio-oils could not be used as traffic liquid fuels. Hydrodeoxygenation (HDO) was an effective strategy to upgrade these phenolics into high value-added chemicals such as arenes. However, the challenge of upgrading phenolics into arenes lies in selective hydrogenolysis of the oxygen-containing groups (e.g. –OCH3 and –OH) while keeping the unsaturated aromatic rings intact. However, the competitive adsorption behavior of produced intermediates likely inhibits the further HDO of phenol to arenes. In this work, MoOx/SBA-15 with rich oxygen defects was synthesized, which is capable of inducing phenolics adsorbed in a “nonplanar” manner, weakening the intensity of CAr-OR (R = CH3 or H) bonds and preventing the excessive hydrogenation of aromatic rings. In addition, BaO coating was decorated on MoOx/SBA-15 to tune the surface acid-base properties so as to promote the adsorption of phenol and consume MeOH via alkylation reaction with phenol, enhancing guaiacol one-step HDO into benzene and toluene. Based on catalyst evaluation and characterization as well as density functional theory (DFT) calculations, the catalytic mechanism of phenolics HDO reaction over MoOx/BaO@SBA-15 was analyzed and discussed. Current work helps not only gain deep insights into the competitive interaction for mixed phenolics HDO reaction, but also shed light on the design and synthesis of high-efficient HDO catalysts for upgrading crude bio-oils into arenes.