Lignin, a component of non-edible biomass, is a promising candidate to provide drop-in substitutes for the production of aromatic monomers such as benzene, toluene, and xylenes (BTX), which are current derived from fossil resources. However, the realization of a lignin-to-BTX pathway requires catalytic hydrodeoxygenation (HDO) to remove oxygenated functionalities from lignin-derived monomers, which has proven challenging due to competing reactions such as aromatic hydrogenation leading to a lower value pool of products. The best reported heterogeneous catalysts for HDO of lignin derived aromatics consistent of an inverse, oxide-on-Pt structure, such as WO_x/Pt, which exhibit selectivities of >95% to deoxygenated aromatics, indicating successful suppression of hydrogenation side reactions. However, there remains a lack of fundamental information regarding the role of the oxide (WO_x) modifier on reactivity.

In this talk, I describe the systematic development of a tunable catalyst architecture that enables the deconvolution of HDO reactivity contributed by Pt and metal oxide sites, concluding in the elucidation of the role of oxide modifiers for inverse catalysts. Batch reactivity studies over mono- and multi-oxygenated phenolic substrates, representing potential lignin monomers, indicate that the inherent structure sensitivity of Pt nanoparticles, related to the exposed fraction of well-coordinated and under-coordinated Pt sites, is the dominant characteristic dictating reactivity in both oxide-modified and unmodified Pt catalysts in HDO. Utilizing a WO_x-modified Pt model catalyst with a combined approach of in situ characterization, reactivity, and theoretical analysis, a novel behavior of dynamic inverse oxide-on-Pt formation is identified. WO_x is observed to spontaneously and preferentially decorate well-coordinated Pt sites which are responsible for hydrogenation under reaction conditions, thus clarifying their role in suppressing aromatic hydrogenation during HDO. Expanding these results to other MO_x/Pt catalysts, where M represents reducible transition metal oxides WO_x, NbO_x, MoO_x, and TiO_x, we find that oxide-modified Pt catalysts exhibit similar overall activity towards deoxygenation of phenolics in HDO. Finally, it is determined that oxide-modified Pt catalysts facilitate deoxygenation through the same mechanism as unmodified Pt catalysts, facilitated to a small degree by the presence of oxide-metal interfaces which weaken the C-O bond. Thus, the activity of unmodified and oxide-modified Pt catalysts in HDO is clarified, and structure-activity relationships for both are developed.