Direct synthesis without addition of acid of Al-SBA-15 with controllable porosity and high hydrothermal stability

Abstract

Using triblock copolymer Pluronic P123 as a structure-directing agent, water as solvent, tetraethyl orthosilicate (TEOS) and aluminium sulfate (Al2(SO4)3 18H2O) as silica and aluminium sources, respectively, a series of Al-SBA-15 with well-ordered mesostructure has been hydrothermally synthesized up to high aging temperature through a one-step approach in an environmentally friendly mineral acid-free medium. The influence of some synthesis parameters such as Si/Al molar ratio (5–100), P123/Si molar ratio (0.0025–0.014) and aging temperature (363–443 K) on the properties of the resultant materials were investigated by powder X-ray diffraction (XRD), nitrogen adsorption–desorption at 77 K, transmission electron microscopy (TEM), and solid state 27Al MAS NMR analyses. The textural properties of Al-SBA-15, such as specific surface area, pore volume and mesopore size, can be modified by simply adjusting those synthesis parameters. Solid state 27Al MAS NMR results show direct evidence that aluminium is introduced onto the wall structure and located mainly at tetrahedrally coordinated sites. The structural ordering increases with increasing aluminium sulfate amount in the gel from Si/Al of 100–5, with the aluminium species playing an important role in the formation of the ordered mesostructure. The increase of aging temperature causes widening of mesopores, which are still highly ordered upon aging at 443 K. The procedure allows the formation, up to high reaction temperature, of aluminium incorporated SBA-15 exhibiting high structural ordering and hydrothermal stability.