Evolution of active sites on Pt-MoOx catalysts and their role in the formation of adipic acid from tetrahydrofuran 2,5-dicarboxylic acid

Pt-MoO x /TiO 2 catalysts are highly efficient for the hydrodeoxygenation (HDO) of tetrahydrofuran-2,5-dicarboxylic acid (THFDCA) to adipic acid (AA), while suppressing carboxyl reduction and decarboxylation/decarbonylation. However, the active site(s) governing HDO selectivity remains unclear. Here, surface characterizations, chemical probe analysis, spectroscopy, and kinetic studies were combined to investigate the formation, evolution, and reactivity of surface Pt, isolated MoO x , and Pt-MoO x interfacial sites during THFDCA conversion to AA. The Mo loading was systematically varied (Mo:Pt = 0:1 to 10:1 M ratio) to evaluate the progressive formation of active centers and control the extent of Pt decoration by MoO x . Pt/MoO 3 systems, where yields of up to 79% were obtained, served as references to evaluate the behavior of Pt-MoO x interfacial sites. Results from XRD, IR spectroscopy, O 2 -pulse chemisorption, HR-STEM, and EDS mapping demonstrated that Mo preferentially deposits on TiO 2 , forming highly dispersed MoO x species at sub-monolayer (Mo:Pt ≤ 2:1) and MoO 3 domains near monolayer (Mo:Pt ≥ 5:1) coverages. CO-FTIR, CO-pulse chemisorption, and H 2 -TPR showed that Mo progressively decorates neighboring Pt nanoparticles as its concentration increases, forming Pt-MoO x interfacial sites. Pt-MoO x /TiO 2 catalysts with Mo:Pt ≥ 5:1 exhibited local catalytic environments comparable to those of Pt/MoO 3 , consistent with their similar product distribution. Kinetic and catalytic analyses ultimately revealed a site-dependent reaction network in which THFDCA ring-opening occur on Pt-TiO 2 and Pt-MoO x ensembles, whereas HDO of 2-hydroxyadipic acid (2-HAA) to AA is only promoted at Pt-MoO x interfaces by BAS, likely through acid-catalyzed dehydration. The findings in this work provide mechanistic insights and design principles for selective biomass-upgrading catalysts.