title: Tremendous effect of the morphology of birnessite-type manganese oxide nanostructures on catalytic activity.
abstract: The octahedral layered birnessite-type manganese oxide (OL-1) with the morphologies of nanoflowers, nanowires, and nanosheets were prepared and characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric/differential scanning calorimetry (TG/DSC), Brunnauer-Emmett-Teller (BET), inductively coupled plasma (ICP), and X-ray photoelectron spectroscopy (XPS). The OL-1 nanoflowers possess the highest concentration of oxygen vacancies or Mn(3+), followed by the OL-1 nanowires and nanosheets. The result of catalytic tests shows that the OL-1 nanoflowers exhibit a tremendous enhancement in the catalytic activity for benzene oxidation as compared to the OL-1 nanowires and nanosheets. Compared to the OL-1 nanosheets, the OL-1 nanoflowers demonstrate an enormous decrease (ΔT(50) = 274 °C; ΔT(90) > 248 °C) in reaction temperatures T50 and T90 (corresponding to 50 and 90% benzene conversion, respectively) for benzene oxidation. The origin of the tremendous effect of morphology on the catalytic activity for the nanostructured OL-1 catalysts is experimentally and theoretically studied via CO temperature-programmed reduction (CO-TPR) and density functional theory (DFT) calculation. The tremendous catalytic enhancement of the OL-1 nanoflowers compared to the OL-1 nanowires and nanosheets is attributed to their highest surface area as well as their highest lattice oxygen reactivity due to their higher concentration of oxygen vacancies or Mn(3+), thus tremendously improving the catalytic activity for the benzene oxidation.
authors.affiliation: State Key Laboratory of Silicate Materials for Architectures, Wuhan University of Technology , 122 Luoshi Road, Wuhan 430070, China.
authors.forename: Jingtao
authors.initials: J
authors.lastname: Hou
authors.forename: Yuanzhi
authors.initials: Y
authors.lastname: Li
authors.forename: Mingyang
authors.initials: M
authors.lastname: Mao
authors.forename: Lu
authors.initials: L
authors.lastname: Ren
authors.forename: Xiujian
authors.initials: X
authors.lastname: Zhao
keywords: catalytic; manganese oxide; morphology effect; oxygen vacancy