Oxygen Vacancies Induced by Transition Metal Doping in γ-MnO2 for Highly Efficient Ozone Decomposition.

Abstract

Transition metal (cerium and cobalt) doped γ-MnO2 (M-γ-MnO2, where M represents Ce, Co) catalysts were successfully synthesized and characterized. Cerium-doped γ-MnO2 materials showed ozone (O3) conversion of 96% for 40 ppm of O3 under relative humidity (RH) of 65% and space velocity of 840 L g-1 h-1 after 6 h at room temperature, which is far superior to the performance of the Co-γ-MnO2 (55%) and γ-MnO2 (38%) catalysts. Under space velocity of 840 L g-1 h-1, the conversion of ozone over the Ce-γ-MnO2 catalyst under RH = 65% and dry conditions within 96 h was 60% and 100%, respectively, indicating that it is a promising material for ozone decomposition. XRD and HRTEM data suggested that Ce-γ-MnO2 formed mixed crystals consisting of α-MnO2 and γ-MnO2 with specific surface area increased from 74 m2/g to 120 m2/g compared to undoped γ-MnO2, thus more surface defects were introduced. H2-TPR, O2-TPD, XPS, Raman, and EXAFS confirmed that Ce-γ-MnO2 exhibited more surface oxygen vacancies and surface defects, which play a key role during the decomposition of ozone. This study provides important insights for developing improved catalysts for gaseous ozone decomposition and promoting the performance of manganese oxide for practical ozone elimination.