Active sites and reaction mechanisms over the catalysts for VOCs oxidation

Abstract

Volatile organic compounds (VOCs) have attracted widespread attention due to their great threat to the environment and human health. Catalytic oxidation was regarded as the most promising technology for reducing VOCs emissions because of high efficiency and low energy consumption, highlighting the demand for the exploitation of highly active catalysts. However, there still lacked a comprehensive review of active sites and reaction mechanisms for VOCs oxidation. In this work, the previously mentioned issues for varying catalysts were studied. It was summarized that highly dispersed metal sites facilitated the activation of C-H bonds and the opening of aromatic rings. Oxygen vacancies enhanced the activation and migration of oxygen species. Furthermore, the catalytic performances were primarily influenced by the textures and properties of the superficially active sites. Rationally controlling the density and coordination environment of active sites represented a viable approach for enhancing both the oxidation activity and stability of catalysts. The reaction mechanisms of VOCs typically involved multiple pathways, prevailingly influenced by the noumenal active sites and enthetic oxygens. Both of the abovementioned species were found to critically govern the VOCs oxidation reaction process, including lattice oxygen participation, adsorbed oxygen activation, and intermediate transformation, which determined the reaction efficiency and pathway, then provided a deeper understanding of the VOCs oxidation process from a microscopic aspect. This investigation was of great significance for elucidating the intrinsic relationship between active sites and reaction mechanisms and guiding the directional synthesis and design of catalysts.