The Role of Lattice Oxygen in Selective Benzyl Alcohol Oxidation Using OMS-2 Catalyst: A Kinetic and Isotope-Labeling Study

The oxidation of benzyl alcohol by molecular O2 in the liquid phase using a heterogeneous octahedral molecular sieve (OMS) catalyst was studied. Typical batch reactor kinetic data were obtained and fitted to the classical Langmuir–Hinshelwood–Hougen–Watson (LHHW) model as well as to the Mars–van Krevelen (MvK) model of heterogeneously catalyzed reactions. A two-step Mars–van Krevelen model involving an exchange between the gas phase and lattice oxygen was found to give a better fit. This was further corroborated by an oxygen-isotope-labeling study. The changes in the 16O and 18O content of the product water confirm this observation. Kinetic isotope effects were also evaluated in mechanistic studies. The occurrence of this mechanism in the liquid phase explains the activity and high selectivity of the OMS-2 catalyst for this selective oxidation reaction.