Preparation and pore structure stability at high temperature of silicon-doped ordered mesoporous alumina

Abstract

Silicon-doped ordered mesoporous aluminas with varying dopant concentration were designed and synthesized in an HCl-acidified sol–gel system with the solvent consisting of ethanol and 2-propanol. When calcined at 800 °C, all the samples yielded 2-D hexagonal P6mm structures. However, for different samples the original periodic structure was retained to a different level upon a high calcination temperature of 1000 °C. The surface area, pore volume, and mean pore size of the samples with the Si/Al molar ratios ranging from 6% to 11% calcined at 1000 °C were determined to be in the range of 235–250 m² g⁻¹, 0.60–0.65 cm³ g⁻¹ and 6.8–7.0 nm, respectively. Based on the structural and textural properties characterized by X-ray diffraction (XRD), differential thermal analysis (DTA), N₂ physisorption measurement, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS), it was speculated that the different degree of structure-retention is related to the shrinkage caused by the sintering and crystallization of the framework, which was determined by the silicon content in the framework. As compared with other samples, the sample with the Si/Al molar ratio of 11% showed better structure preservation during the thermal crystallization process, indicating the excellent thermal stability of its pore structure.