Synthesis and characterization of mesoporous Ce-Mn-MCM-41 molecular sieves

Mesoporous Ce-Mn-MCM-41 molecular sieves with Si/(Ce+Mn) molar ratios of 43, 61, 79, and 97 were synthesized under hydrothermal conditions using CTMABr (cetyltrimethylammonium bromide) as surfactant and manganese acetate and cerium sulfate as sources of Mn and Ce, respectively . The Ce⁴⁺ and Mn ³⁺ ions were coordinated to the silica surface. They were then characterized using several techniques, e.g., XRD (X-ray Diffraction), FTIR (Fourier Transform Infra-Red Spectroscopy), N₂ physisorption, TG/DTA (Thermogravimetric/Differential Thermal Analysis), UV-vis/DRS (Diffuse Reflectance UV-vis Spectroscopy), and SEM (Scanning Electron Microscopy). XRD studies indicated that the materials had the standard MCM-41 structure. FTIR studies showed that cerium and manganese ions were incorporated into the hexagonal mesoporous materials. The thermal stabilities of the as-synthesized materials were studied using TG/DTA. A nitrogen adsorption isotherm was used to determine the specific surface area, pore diameter, and wall thickness of the calcined Ce-Mn-MCM-41. The morphology of Ce-Mn-MCM-41 was examined using SEM. The oxidation states of the incorporated cerium and manganese ions were determined using UV-vis/DRS; from these results we conclude that the Lewis acidity of the Ce-Mn-MCM-41 with Si(Ce+Mn) = 43 was higher than that of other Ce-Mn-MCM-41 samples.