The Role of Surface Hydroxyls in the Mobility of Carboxylates on Surfaces: Dynamics of Acetate on Anatase TiO 2 (101).

The dynamics of reactive intermediates are important in catalysis for understanding transient species, which can drive reactivity and the transport of species to reaction centers. In particular, the interplay between surface-bound carboxylic acids and carboxylates is important for numerous chemical transformations, including CO hydrogenation and ketonization. Here, we investigate the dynamics of acetic acid on anatase TiO(101) using scanning tunneling microscopy experiments and density functional theory calculations. We demonstrate the concomitant diffusion of bidentate acetate and a bridging hydroxyl and provide evidence for the transient formation of molecular monodentate acetic acid. The diffusion rate is strongly dependent on the position of hydroxyl and adjacent acetate(s). A facile three-step diffusion process is proposed consisting of acetate and hydroxyl recombination, acetic acid rotation, and acetic acid dissociation. This study clearly demonstrates that the dynamics of bidentate acetate could be important in forming monodentate species, which are proposed to drive selective ketonization.