Mn-doped ordered mesoporous ceria-silica composites and their catalytic properties toward biofuel production

A series of Mn-doped ordered mesoporous ceria-silica composites was synthesized by using hexadecyltrimethylammonium bromide as a soft template under ammonia basic conditions. After template removal, Mn-doped mesoporous ceria-silica composites were thoroughly characterized by small-angle X-ray scattering, which revealed highly ordered 2D-hexagonal (p6m) framework. Other techniques such as wide-angle X-ray diffraction, N₂ adsorption, scanning and transmission electron microscopic analysis with energy-dispersive spectrometry mapping, inductive coupled plasma atomic emission spectrophotometry, ultraviolet-visible spectrometry, and ²⁹Si cross-polarization magic-angle spinning NMR were used to show the effect of Mn incorporation into the ceria-silica composites. The electronic states of the surface Mn and Ce species were also investigated by X-ray photoelectron spectroscopy. These Mn-doped mesoporous ceria-silica composites were successfully reduced under a flowing H₂/N₂ gas mixture at an elevated temperature without noticeable changes in their hexagonally ordered mesostructures. These materials were applied as heterogeneous and reusable catalysts for transesterification of different esters, such as methyl benzoate and ethyl cyanoacetate, in the presence of various alcohols, such as n-octanol and n-butanol, to produce biodiesels under solventless mild conditions.