2025 AIChE Annual Meeting

(254g) Dual Role of Reducible Transition Metal Oxide Promoters on Pt Catalysts for Phenolic Hydrodeoxygenation

Authors

Justin Marlowe - Presenter, Rutgers, The State University of New Jersey
Leah Abraham, University of California, Santa Barbara
Mahdi Abu-Omar, University of California, Santa Barbara
Phillip Christopher, University of California Santa Barbara
Catalytic hydrodeoxygenation (HDO) of lignin-derived phenolics is a promising route towards sustainable aromatic feedstocks. Inverse catalysts consisting of transition metal oxide domains on top of metal nanoparticle surfaces have exhibited remarkable (>96%) selectivity towards deoxygenated aromatics [1]. Our recent work [2] clarified that for WOx/Pt/SiO2 catalysts, selectivity enhancement to aromatics is partly ascribed to the dynamic decoration by WOx of Pt surface sites, thus suppressing undesired aromatic hydrogenation. However, the role of WOx species in deoxygenation has remained unclear.

Here, we address this uncertainty through an MOx/Pt/SiO2 catalyst series (M = W, Mo, Nb, Ti) utilizing MOxspecies with a broad range of chemical properties proposed to be relevant to HDO. By quantifying the extent of decoration by CO pulse chemisorption and relating this to reaction performance in the HDO of 4-propylphenol (PHE), we find that aromatic hydrogenation of the PHE substrate is correlated with the extent of MOx decoration on top of Pt, regardless of MOx identity. Consistent with our prior work, this indicates that suppression of aromatic hydrogenation is a steric effect, mediated through MOx domains blocking Pt sites which would otherwise perform hydrogenation. On the other hand, direct deoxygenation to 4-propylbenzene (BNZ) exhibits a complex dependence on both MOx identity and coverage.

By comparing characterization results (H2-TPR, NH3-TPD) to reaction performance, we find that neither oxygen vacancies nor acid sites explain observed deoxygenation activity. Instead, BNZ formation correlates well with the Lewis acidity of MOx cations at the MOx-Pt interface, analogous to trends known for COx hydrogenation. Thus, we propose that interaction between adsorbed intermediates and Lewis acidic MOx-Pt interfaces promotes C-O bond cleavage, clarifying the dual role of MOx in inverse catalysts for HDO.

References

[1] Wang, C. et al. ACS Catal. 2018, 8, 9, 7749-7759.

[2] Marlowe, J. et al. JACS. 2024, 146, 20, 13862-13874.