Quantifying the activation energies of ROS-induced NOx conversion: Suppressed toxic intermediates generation and clarified reaction mechanism

Abstract

The generation and transformation of reactive oxygen species (ROS) is a key parameter in catalyzing photocatalytic gas-phase oxidation reactions for environmental remediation. Thus the determination, quantification and kinetic tracking of ROS are conclusively required to realize complete pollutant conversion and intermediates suppression. By quantifying the activation energies (Ea) and ascertaining the rate-determining step (RDS), a panoramic understanding is established in ROS-induced NOx oxidation reactions. To be specific, the BiOCl photocatalyst with tailored facets were designed and fabricated as model catalysts. It is proposed that the ROS generation and transformation pathways are along the path of OH → H2O2 → O2−, in which the H2O2 dissociation is the RDS for O2− generation. Moreover, it is concluded that NO2 is the primary intermediate in NO oxidation reaction, and the further transformation of NO2 requires the highest Ea among all the elementary reactions. Significantly decreased Ea and suppressed NO2 accumulation are realized on the {010} facet of BiOCl to achieve efficient NOx conversion. A new perspective is stated in this research to establish a comprehensive understanding between ROS generation mechanism and intermediates suppression for efficient NOx removal, which provides new insights into the application of photocatalysis technology for air pollution control area.