Role of steps in the reactivity of the anatase TiO₂(101) surface

We studied the adsorption of water, methanol, and formic acid at terraces and steps on the stoichiometric anatase TiO₂(101) surface by means of density functional theory calculations. Our results show that the reactivity of the step edges is distinct from that of the (101) terraces and is instead similar to the reactivity of the extended (112) and (100) surfaces, which are exposed at their facets. More specifically, on the (101) terraces, all molecules are adsorbed in molecular (undissociated) form, and the adsorption energy is rather low (<1 eV). At step D-(112), adsorption energies are significantly larger than on (101) terraces, but molecular adsorption is still favored by water and methanol. At step B-(100), all of the molecules prefer to dissociate, even though the adsorption energy of water is lower than on the (101) terrace. The connection between reactivity and local structure is highlighted, and comparison with available experimental data is provided.