Active oxygen species in heterogeneously catalyzed oxidation reactions

• The nature of active oxygen species determines selectivity in oxidation reactions. • No characterization technique can identify and quantify all active oxygen species. • Combination of characterization methods can provide a more complete picture. • Understanding active oxygen species will advance catalysts and process design. Active oxygen species generation in heterogeneously catalyzed hydrocarbon oxidation reactions have not been fully characterized. There is little consensus as to which the most active or selective species are. However, electron localization at a single oxygen atom—rather than shared over several—is necessary to activate very stable hydrocarbons like methane. This paper presents an overview of oxygen species formed on various catalytic surfaces and their role in hydrocarbon oxidation reactions. Since limitations of analytical methods are a significant bottleneck for understanding and engineering active oxygen species, approaches for characterizing and quantifying active oxygen are discussed. While several methods are effective for describing certain oxygen species, there is no method that comprehensively characterizes all active oxygen species. The most promising approach is oxygen isotope exchange coupled with infrared spectrometry and inline mass spectrometry.