Deconstructing the Heterogeneity of Surface-Bound Catalysts: Rutile Surface Structure Affects Molecular Properties

Catalytic interfaces involving surface-bound molecular catalysts often exhibit a large structural heterogeneity from uncontrolled variation in surface morphology. Conventional spectroscopic techniques typically average over these different structural motifs within the sample, making it difficult to link the underlying surface morphology to the properties of the immobilized catalyst. Here we present the first direct comparison of the vibrational dynamics of a CO 2 reduction catalyst bound to two different single-crystalline TiO 2 surfaces, rutile (001) and (110), probed with transient surface-specific sum-frequency generation spectroscopy. We find that the change in surface structure between crystallographic faces alters both the vibrational frequency and relaxation time of the symmetric carbonyl stretching mode of the catalyst, with (001) displaying a lower frequency and longer relaxation time. This results from a change in the catalyst electronic structure and indicates that the molecular properties of the catalyst, likely including the catalytic properties, depend on the specific TiO 2 surface to which it is bound. The comparison of the molecular properties on these two single crystal surfaces is an essential step toward understanding how semiconductor surface structure influences catalyst behavior and identifying optimal surface structures for improved catalytic performance.