Hydrodeoxygenation of 4-Methylphenol over Unsupported MoP, MoS₂, and MoOx Catalysts

A study of the hydrodeoxygenation (HDO) of 4-methylphenol over unsupported, low-surface-area MoS 2, MoO 2, MoO 3, and MoP catalysts is reported. With the exception of MoO 3, the catalysts had the same physicochemical properties before and after the 5 h reaction at 623 K and 4.40 MPa H 2 . The used MoO 3 was partially reduced to a mixed oxide containing Mo 4 O 11, MoO 2, and Mo. Compared to the unused MoO 3, the used MoO 3 CO uptake increased by a factor of 100 following the reaction. The partially reduced Mo oxide catalyst had a high conversion for the HDO of 4-methylphenol because of Brønsted acid sites and the formation of anionic vacancies. The catalyst turnover frequency (TOF) based on CO uptake for the HDO of 4-methylphenol decreased in the order MoP > MoS 2 > MoO 2 > MoO 3, while the activation energy increased in the order of MoP < MoS 2 < MoO 2 < MoO 3 . The activity trends correspond to the increased electron density of the Mo among the catalysts. Two primary reactions, C−O hydrogenolysis to yield toluene and saturation of 4-methylphenol followed by rapid dehydration to produce 4-methylcyclohexene, were identified. The catalysts differed in their hydrogenation and isomerization capabilities. The MoP catalyst displayed the highest selectivity toward hydrogenated products, suggesting that the rate-limiting step over MoO 3, MoO 2, and MoS 2 was the saturation of 4-methylphenol to produce 4-methylcyclohexanol.