Reactive oxygen species in selective heterogeneous catalytic oxidations

Heterogeneous catalysis is essential in industrial chemical processes, particularly selective oxidation reactions. Oxidative reactions are complex due to the occurrence of multiple reaction pathways, kinetic and thermodynamic effects, and the involvement of reactive oxygen species (ROS). ROS, including superoxide radical anions (O 2 · - ), hydrogen peroxide (H 2 O 2 ), hydroxyl radicals ( • OH), and singlet oxygen ( 1 O 2 ), can enhance selectivity or lead to overoxidation of reactants. Thus, ROS identification on a catalyst’s surface or under real-time conditions is crucial for determining mechanistic pathways and the key ROS species that contribute to high selectivity for oxidation processes. Tracking these reactive species can be challenging within heterogeneous systems. Most detection methods are hindered by the rapid decay of ROS, the complexity and cost of spin-trapping probes, lack of probe selectivity, and interference from other species in the reaction, which limits real-time ROS monitoring. There remains a need for reliable detection and scavenging methods, further combined with characterization techniques such as EPR, XPS, in situ DRIFTS, and oxygen isotope labeling. Prior review articles on ROS focus on applications in medicine, biological fields, and photocatalysis. This review examines the chemistry of molecular oxygen, generation mechanisms, and the detection of ROS in heterogeneous selective catalytic oxidations and our contribution to the field; we focus on literature published over the last five decades, highlight the specific challenges associated with studying these systems, and provide strategies for overcoming these limitations. Finally, we discuss in situ vs. ex situ ROS probing techniques and demonstrate their importance in dynamic catalytic systems.