Different behaviors of birnessite-type MnO2 modified by Ce and Mo for removing carcinogenic airborne benzene

Abstract

Abstract In this study, Mo6+ and Ce3+, which are the typical high- and low-valence modifiers, were comparatively used as structural and catalytic promoters for birnessite-type MnO2 to remove gaseous benzene. Various characterizations were performed to elaborate how the surface properties of the nanomaterials led to the observed catalytic behaviors. The Mo species existed as highly dispersed MoO3 over the Mo MnO2 while Ce was incorporated into the MnO2 lattice. The activities of the lattice oxygen and oxygen vacancies over the Mo MnO2 were comparable to those of the pristine MnO2, thus resulting in similar catalytic performance. However, the replacement of lattice Mn by Ce inhibited the regular growth of the birnessite crystals and caused distortion of MnO2 lattice. Thanks to the high activity of the lattice oxygen, oxygen vacancies and surface adsorbed oxygen, benzene decomposition was significantly improved over the Ce MnO2. Ce MnO2(0.8) with a nominal Ce/Mn atomic ratio of 0.8 exhibited stable conversion of ∼90% for 395 ppm of benzene in dry gas under 120 L g−1 h−1 of space velocity and 350 °C. Moreover, under similar reaction conditions, the Ce MnO2(0.8) could also stand up water vapor and kept a moderate activity of 60% with 50% of relative humidity.