Effect of Phase Structure of MnO₂ Nanorod Catalyst on the Activity for CO Oxidation

Abstract

The R-, β-, γ-, and δ-MnO 2 nanorods were synthesized by the hydrothermal method. Their catalytic properties for CO oxidation were evaluated, and the effects of phase structures on the activities of the MnO 2 nanorods were investigated. The activities of the catalysts decreased in the order of R-≈ δ-> γ-> β-MnO 2 . The mechanism of CO oxidation over the MnO 2 nanorods was suggested as follows. The adsorbed CO was oxidized by the lattice oxygen, and the MnO 2 nanorods were partly reduced to Mn 2 O 3 and Mn 3 O 4 . Then, Mn 2 O 3 and Mn 3 O 4 were oxidized to MnO 2 by gaseous oxygen. CO chemisorption, the Mn-O bond strength of the MnO 2 , and the transformation of intermediate oxides Mn 2 O 3 and Mn 3 O 4 into MnO 2 can significantly influence the activity of the MnO 2 nanorods. The activity for CO oxidation was mainly predominated by the crystal phase and channel structure of the MnO 2 nanorods.

Gold on oxide-doped alumina supports as catalysts for CO oxidation

“…The TPR profile for samples doped with Mn showed two peaks (Table 2). According to what was seen in previous works (Hoflund et al 1995;Ferrandon et al 1999;Stobbe et al 1999;Arena et al 2001;PalDey et al 2005;Xu et al 2006;Ramesh et al 2008;Liang et al 2008;Wang et al 2008Wang et al , 2009Carabineiro et al 2010a), the reduction of MnO 2 to Mn 3 O 4 generates a peak at *350°C, whereas reduction of Mn 3 O 4 to MnO produces a peak at *450°C, sometimes with some overlapping between the two. This matches well with the results obtained for the Mn/alumina samples.…”

Remarkable promotion effect of trace sulfation on OMS-2 nanorod catalysts for the catalytic combustion of ethanol

“…No XPS peaks of other Mn species were observed. This suggests that manganese species were present predominantly as MnO 2 in all the samples (Liang et al, 2008). In addition, the results above indicated that the use of different precursors and the 0.5% SO 4 2− doping did not change the binding energy of Mn 2p.…”

Effect of MnO2 Crystalline Structure on the Catalytic Oxidation of Formaldehyde

“…The reduction peaks of δ-MnO 2 were similar to that of α-MnO 2 at 299 and 324°C, respectively. According to the literature, the lower temperature peak might be associated with the reduction of MnO 2 to Mn 3 O 4 , whereas the higher reduction peak should be attributed to the reduction of Mn 3 O 4 to MnO (Liang et al, 2008). The TPR profiles of β-MnO 2 and γ-MnO 2 were different from that of the α-and δ-MnO 2 .…”