D-band surface states on wide band gap insulators. A conceptual model for surface states and catalysis on D-band perovskites

This paper proposes a conceptual model to describe some of the factors believed to be most important in catalyzing a reaction on a transition metal oxide. An hypothetical situation is constructed from a model reaction, the dimerization of ethylene to form cyclobutane, and a model perovskite, SrTiO3. A detailed discussion is given of the symmetry imposed energy barrier for the gas phase reaction. Using SrTiO3 as an example, it is shown that the perovskites possess highly localized, atomic-like d surface states of the required symmetry. Two semiquantitative examples are developed for the catalyzed dimerization of ethylene on the (100) surface of SrTiO3. A preliminary discussion is given of the role played by surface potentials in promoting the reaction.