Lignin Pyrolysis and in Situ Hydrodeoxygenation over MoO₃: Interaction between MoO₃ and Lignin

Lignin pyrolyses and in situ hydrodeoxygenation over MoO₃ with varying lignin/MoO₃ mass ratios (L/M) at different temperatures were studied in a free-falling reactor. The presence of MoO₃ not only facilitated the depolymerization of lignin to liquid and gas products but also catalyzed the in situ hydrodeoxygenation of the resulting liquid product to phenol, both of which were further intensified with the increases of temperature and the MoO₃ amount. Negative apparent solid yield and over 100% apparent gas yield were obtained in some cases because of the reaction of MoO₃ during lignin pyrolysis. To clarify this phenomenon, detailed TG/MS, XRD, and XPS investigations on spent MoO₃ were carried out. The results indicate that Mo⁶⁺ was partly reduced to Mo⁴⁺ and Mo⁵⁺ during the lignin pyrolysis, mainly caused by the reaction with carbon from lignin rather than hydrogen from carrier gas