Synthesis of Pt decorated manganese oxide (MnO2/Mn5O8) nanorods and their catalytic activity for the reduction of 4-nitrophenol to 4-aminophenol

alpha-MnO2 nanorods (NRs) were synthesized by microwave irradiation and used as supports for platinum nano particles by wet impregnation with Pt(acac)2 as precursor. XRD analysis revealed that the samples without platinum (sample MP0) and with 1 % platinum (sample MP1) contained tetragonal alpha-MnO2. Samples with 3 % (sample MP3) and 5 % (sample MP5) of platinum contained monoclinic Mn5O8 in addition to alpha-MnO2 , with Mn5O8 dominating in sample MP5. Rietveld analysis showed that the lattice parameters of alpha-MnO2 increased slightly with Pt loading. SEM and STEM showed that higher Pt loadings resulted in shorter nanorods and different sizes and dispersions of PtNPs on their surface. XPS results showed a decrease in Pt(IV) and Pt(II) concentration with Pt loading, while Pt(0) increased. NEXAFS results showed the presence of Mn(II) in MP3 and MP5, which is consistent with XRD results detecting Mn5O8. The catalytic activity of the Pt/alpha-MnO2 nanorods was tested in the catalytic reduction of 4-nitrophenol to 4-aminophenol. MP1, with the lowest platinum content, exhibited the highest mass normalized rate constant kapp/mPt of 1.8 x 104 s-1 g-1. The study suggests that the presence of Pt(IV) is not a limiting factor for the catalytic reduction of 4-NP to 4-AP.