Uncertainty and misinterpretation over identification, quantification and transformation of reactive species generated in catalytic oxidation processes: A review

The identification of reactive radical species using quenching and electron paramagnetic resonance (EPR) tests has attracted extensive attention, but some mistakes or misinterpretations are often present in recent literature. This review aims to clarify the corresponding issues through surveying literature, including the uncertainty about the identity of radicals in the bulk solution or adsorbed on the catalyst surface in quenching tests, selection of proper scavengers, data explanation for incomplete inhibition, the inconsistent results between quenching and EPR tests (e.g., SO4 center dot- is predominant in quenching test while the signal of (OH)-O-center dot predominates in EPR test), and the incorrect identification of EPR signals (e.g., SO4 center dot- is identified by indiscernible or incorrect signals). In addition, this review outlines the transformation of radicals for better tracing the origin of radicals. It is anticipated that this review can help in avoiding mistakes while investigating catalytic oxidative mechanism with quenching and EPR tests.

Automated summary

This review clarifies common mistakes and misinterpretations present in the literature regarding the identification of reactive radical species using quenching and electron paramagnetic resonance (EPR) tests. It aims to help researchers avoid errors when investigating catalytic oxidative mechanisms with these tests.