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.

Extremely efficient full solar spectrum light driven thermocatalytic activity for the oxidation of VOCs on OMS-2 nanorod catalyst

“…The relative OVD concentration is also determined by the average oxidation state (AOS) of Mn in the OMS-2 samples, which can be calculated by using the magnitude of Mn 3s multiplet splitting ( Fig. S3) according to the following formula [37,39]:…”

Different crystal-forms of one-dimensional MnO2 nanomaterials for the catalytic oxidation and adsorption of elemental mercury

“…7(c). The peaks observed at 642.7, 642.6 and 642.8 eV correspond to Mn 4+ for ␣-, ␤-and ␥-MnO 2 , respectively [29,30]. In addition, the molar ratio of Mn and O was calculated according to the XPS analysis, as shown in Table 2.…”

Photoelectrochemical performance of birnessite films and photoelectrocatalytic activity toward oxidation of phenol

“…With a bandgap energy of 1.8-2.1 eV (Sherman, 2005;Pinaud et al, 2011;Hsu et al, 2012), birnessite is also an important photoactive material that can adsorb part of solar spectrum up to ca., 600 nm (Hsu et al, 2012). Over the last decades, catalytic activity of birnessite has been observed in the oxidation of indigo carmine (Zaied et al, 2011), benzene (Ye et al, 2014;Hou et al, 2014), phenolic compounds (Nakayama et al, 2010;Chien et al, 2008;Hardie et al, 2007), etc. However, leaching of the reduced Mn species may impede the catalytic reaction and have a negative effect on the recycling of the manganese dioxide.…”