Catalytic Decomposition of Residual Ozone over Cactus-like MnO 2 Nanosphere: Synergistic Mechanism and SO 2 /H 2 O Interference.

Ground-level ozone is an irritant and is harmful to human respiratory and nervous systems. Thus, four manganese oxides with different crystals were hydrothermally synthesized to decompose residual ozone (deO 3 ) in an ozone synergistic-oxidation system. Among them, a cactus-like MnO 2 -IV nanosphere exhibited the highest deO 3 activity, with excellent tolerance to water vapor and SO 2 /H 2 O, which could maintain >88% deO 3 efficiency in the high-humidity and sulfur-containing conditions. It benefits from the unique morphology, high specific surface area, superior redox properties, oxygen chemisorption capabilities, abundant surface-active hydroxyl species, and low valence Mn species. More importantly, the detailed interference mechanism of O 2 /O 3 /H 2 O/SO 2 molecules on MnO 2 -IV was revealed utilizing in situ diffused reflectance infrared Fourier transform spectroscopy and X-ray photoelectron spectroscopy. H 2 O generally caused recoverable deactivation, but that caused by SO 2 was irreversible. The synergistic effect of SO 2 /H 2 O promoted the formation of an unstable sulfate species, thereby deepening the deactivation but inhibiting the irreversible poisoning. Finally, nine specific steps to decompose ozone via surface-active hydroxyl/intermediates were established.