Benzyl Alcohol Valorization via the In Situ Production of Reactive Oxygen Species

In this contribution, we outline the efficacy of Pd-based bimetallic catalysts toward the oxidative upgrading of benzyl alcohol via the in situ synthesis of H₂O₂ (and related reaction intermediates) from the elements. In particular, the formation of PdAu and PdFe nanoalloys is observed to be highly effective, offering high yields of benzaldehyde and near total selectivity to the desired product, with these catalysts outperforming alternative materials reported in the literature. Notably, the PdFe formulation also achieves high selective utilization of H₂, a key requirement if the in situ approach to chemical synthesis is to become economically viable. Correlative studies, focusing on the direct synthesis of H₂O₂ and further experiments utilizing preformed H₂O₂, coupled with Electron Paramagnetic Resonance (EPR) spectroscopy indicate that H₂O₂ itself is not primarily responsible for the observed catalysis, but rather, the performance of the PdAu and PdFe formulations can be related to the generation of reactive oxygen species (ROS). While the origin of these ROS is not fully understood, it is hypothesized that they are generated through a combination of (i) the desorption of reaction intermediates formed during H₂O₂ synthesis and (ii) through Fenton-mediated chemistry involving the synthesized H₂O₂, in the case of the PdFe-based materials. Importantly, our EPR studies also identify the noninnocent nature of the reaction solvent.