High-humidity tolerance of porous TiO2(B) microspheres in photothermal catalytic removal of NOx

Abstract

Semiconductor oxides are widely used to achieve photocatalytic removal of NOx (NO and NO2) species. These materials also exhibit enhanced oxidation ability in thermally assisted photocatalysis; however, many of them tend to be deactivated at high relative humidity (RH) levels. In the case of the benchmark P25 TiO2 photocatalyst, we observe a significant decrease in non-NO2 selectivity from 95.02% to 58.33% when RH increases from 20% to 80%. Interestingly, the porous TiO2(B) microspheres synthesized in this work exhibit 99% selectivity at 20% RH; the selectivity remains as high as 96.18% at 80% RH. The high humidity tolerance of the TiO2(B) sample can be ascribed to its strong water desorption capacity and easy O2 adsorption at elevated temperatures, which reflects the fact that the superoxide radical is the main active species for the deep oxidation of NOx. This work may inspire the design of efficient photothermal catalysts with application in NOx removal in hot and humid environments.