Elucidation of Active Sites in Aldol Condensation of Acetone over Single-Facet Dominant Anatase TiO2 (101) and (001) Catalysts

H is a kinetically relevant step, which is consistent with kinetic and isotopic studies as well as DFT calculations. The 001 facet showed a lower apparent activation energy (or higher activity) than the 101 facet. This is likely caused by the weaker Lewis acid and Brønsted base strengths of the 001 facet which favors the reprotonation-desorption of the coupled intermediate, making the C-C coupling step more exothermic on the 001 facet and resulting in an earlier transition state with a lower activation barrier. It is also possible that the 001 facet has a smoother surface configuration and less steric hindrance during intermolecular C-C bond formation than the 101 facet.