Photo-assisted oxidation of gaseous benzene on tungsten-doped MnO2 at lower temperature

Abstract

Sunlight-driven processes have demonstrated immense potential for promoting conventional thermal catalysis, decreasing the energy consumed during these processes. In this study, the photo-assisted catalytic-combustion of benzene over tungsten (W)-doped MnO2 was evaluated under a Xenon-lamp irradiation. The introduction of W species into the MnO2 lattice promotes the photo-assisted reaction in several ways: (1) creating abundant oxygen vacancies (VO) on MnO2, which can serve as active sites for the chemisorption of O2 and (2) the doped W atoms form strong covalent interactions with the neighboring O atoms via W-O bridging bonds, thereby facilitating O2 polarization and electron transfer. Under irradiation, photo-generated holes facilitate the adsorption of molecular benzene on the O atoms close to VO sites; photo-excited electrons are trapped by the oxygen molecules, forming superoxide (O2−) radicals. These radicals can react with molecular benzene to generate reactive benzene species (e.g., acetic acid and n-butyric acid acetate), which are more likely to be oxidized by lattice oxygen at high temperatures. At 250 °C, the benzene conversion over 1.6% of W-doped MnO2 is 39.7%, which increases to 43.1%, 57.6%, and 68.2% with the assistance of the irradiation under infrared (>800 nm), visible and infrared (>420 nm), and full spectrum regions (141 mW/cm2). This work highlights the utilization of photo-excited electrons in a solar-driven chemical transformation, thereby providing a strategy for the utilization of solar energy in thermal catalysis.