(630a) Differences in Solvation Enthalpies and Entropies on Pt(111) Versus Pt/Al2O3 Particles and Their Influence on the Mechanism of Aqueous Phase Methanol Dehydrogenation

Production of H₂ via aqueous phase reforming (APR) is critical to the broader adoption of biorefining. In APR, oxygenates from biomass are converted to CO₂ and H₂ over supported metal catalysts under liquid water. A common catalyst is Pt/Al₂O₃. The literature shows that both the metal and the metal/support interface serve as active sites in the catalytic mechanism. In this presentation, we discuss the catalysis of methanol reforming at sites on the Pt(111) terraces of large nanoparticles away from the support interface and at sites at the Pt/Al₂O₃ perimeter. Liquid water is included using our previously developed multiscale sampling (MSS) method that combines density functional theory (DFT) with classical molecular dynamics (MD). Some of the main differences between the Pt/Al₂O₃ perimeter sites versus the Pt(111) terrace sites are that the perimeter sites are modestly confined and strongly hydrophilic. Because of these phenomena, solvation effects and roles of water are different on Pt(111) terrace versus Pt/Al₂O₃ perimeter sites. Whereas on Pt(111) terraces, the strength of interaction between the liquid water environment and the catalytic species defines the water structure, at Pt/Al₂O₃ perimeter sites, the hydrophilicity of the Al₂O₃ support combined with the hydrophobicity of the Pt particle leave the confined Pt/Al₂O₃ perimeter region largely unsolvated. This leads to differences in the enthalpies and entropies of solvation in these regions, which influence the dominant reaction pathways. This research provides fundamental insight into catalysis at metal/support/water interfaces and how these regions are significantly different than the single crystal models typically used to simulate catalytic performance.