Controlling the synthesis and application of nanocrystalline spherical and ordered mesoporous alumina with high thermal stability

Abstract

High thermal stability nanocrystalline spherical mesoporous alumina (NSMA) and ordered mesoporous alumina (OMA) were synthesized in an acetic acid assisted sol–gel system by adjusting the mole ratio of n(acetic acid)/n(Al) and synthesis temperature to control the competition between the colloidal surface free energy (F) and the free energy of mesostructure self-assembly (ΔG). When F was dominant, with the mole ratio of n(acetic acid)/n(Al) set as 0.05–0.15 and the formation and aging temperature of the precursor solution set at 30 °C, the obtained alumina displayed a spherical morphology, and the nanocrystalline spherical mesoporous alumina dispersed well even when the calcination temperature increased up to 1100 °C; however, ordered mesoporous alumina was obtained with the increasing influence of ΔG when the mole ratio of n(acetic acid)/n(Al) was set as 0.10 and the lower formation and aging temperature set at 20 °C, and it retained a certain ordered structure with the specific surface area of 125 m² g⁻¹ even when the calcination temperature increased up to 1000 °C, which indicate the excellent thermal stability of its pore structure. Taking the as-synthesized aluminas as carriers, Pd-supported catalysts were obtained and their catalytic activity for CO and C₃H₆ oxidation was significantly improved compared to commercial alumina.