Are Spin-Forbidden Crossings a Bottleneck in Methanol Oxidation?

The rate of spin-surface crossing from the singlet to the triplet potential energy surface during methanol oxidation has been examined for classically spin-forbidden crossings. The Landau−Zener equation has been used to calculate the thermally-averaged spin transition probabilities for the nonadiabatic surface crossing reaction. Two active sites have been investigated: isolated vanadate species supported on silica (VOx/SiO2) and titania (VOx/TiO2). The results show that the rate of spin-surface crossing is much faster than the rate-limiting H-abstraction step on both active sites and is therefore not kinetically relevant.