Steam reforming of acetic acid as a biomass derived oxygenate: Bifunctional pathway for hydrogen formation over Pt/ZrO₂ catalysts

Mechanistic studies on steam reforming of acetic acid over Pt/ZrO₂ catalysts were performed as extension of our previous work [K. Takanabe, K. Aika, K. Seshan, L. Lefferts, J. Catal. 227 (2004) 101]. An overall picture of the bifunctional mechanism is established for steam reforming of acetic acid, where both Pt and ZrO₂ participate in the reaction. On Pt, bond breaking of acetic acid proceeds to form H₂, CO, CH₄, and CO₂ into gas phase, and to form the carbonaceous residue (most probably CH_x species), which can block Pt surface. Both pulse experiments as well as in situ IR data demonstrate that H₂O can be activated on ZrO₂ to create supplementary surface hydroxyl groups, which react to gasify the residue on Pt to give chiefly steam-reforming/water-gas shift products (H₂, CO₂), and thus the catalytic cycles continue. Importance of the Pt-ZrO₂ boundary sites is confirmed by the fact that the removal of the carbonaceous residue situated at the boundary sites results in catalyst regeneration.