Crystalline Mesoporous K_(2-x)Mn8O_(16) and ε-MnO2 by Mild Transformations of Amorphous Mesoporous Manganese Oxides and Their Enhanced Redox Properties

摘要

Synthesis of crystalline mesoporous K_(2-x)Mn8O_(16) (Meso-OMS-2), and e-MnO2 (Meso-ε-MnO2) is reported. The synthesis is based on the transformation of amorphous mesoporous manganese oxide (Meso-Mn-A) under mild conditions: aqueous acidic solutions (0.5 M H~+ and 0.5 M K~+), at low temperatures (70 °C), and short times (2 h). Meso-OMS-2 and Meso-ε-MnO2 maintain regular mesoporosity (4.8-5.6 nm) and high surface areas (as high as 277 m~2/g). The synthesized mesoporous manganese oxides demonstrated enhanced redox (H2-TPR) and catalytic performances (CO oxidation) compared to nonporous analogues. The order of reducibility and enhanced catalytic performance of the samples is Commercial-Mn2O3 < nonporous-OMS-2 < Meso-Mn2O3 < Meso-OMS-2 < Meso-e-MnO2 < Meso-Mn-A