Hydrothermal synthesis of manganese oxide nanorods as a highly active support for gold nanoparticles in CO oxidation and their stability at low temperature

Nanostructured mesoporous alpha-MnO2 nanorods were synthesized via a simple hydrothermal process using MnSO4 center dot H2O and KMnO4 as precursors. A series of Au/MnO2 catalysts were prepared by a colloidal deposition (CD) method and were characterized by X-ray diffraction (XRD), nitrogen adsorption, scanning electron microscopy (SEM) and temperature programmed reduction of hydrogen (H-2-TPR) analysis. The influence of the preparation conditions of the supports on the catalytic performance of Au/MnO2 catalysts in CO oxidation has been investigated. The results show that the structure and properties of MnO2 products were strongly dependent on the hydrothermal time. One can distinguish the aspect ratio of MnO2 nanorods from SEM images. The obtained Au/MnO2 catalysts with 1 wt% Au exhibits excellent performance with a complete CO conversion at 20 degrees C (T-100% = 20 degrees C) and 50% CO conversion at -25 degrees C (T-50% = -25 degrees C). Furthermore, H-2-TPR studies reveal the superior activities have been attributed to the support unique reducibility and the interaction between Au and support. However, the U-shaped activity curves show a significant drop in CO conversion at low-temperature. With the help of temperature programmed desorption (CO2-TPD) and CO2 static adsorption studies, it confirms that the deactivation of catalytic activity was attributed to the adsorbed CO2 taking up the active sites, which can be desorbed by increasing the reaction temperature.