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

Abstract

Nanostructured mesoporous α-MnO₂ nanorods were synthesized via a simple hydrothermal process using MnSO₄·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 (H₂-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 °C (T_100% = 20 °C) and 50% CO conversion at −25 °C (T_50% = −25 °C). Furthermore, H₂-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.