Processing of alumina low-density xerogels by ambient pressure drying

Abstract

Alumina is utilized as a catalyst and catalyst support, applications that can benefit from a high surface area and significant mesopore volume. Such characteristics can be achieved through ambient pressure drying (APD) using a methodology similar to that which has proven successful with silica. Alumina gels were synthesized using aluminum tri-sec-butoxide (AltsB) and ethyl acetoacetate (EtAc). Azeotropic distillation with toluene was then used to reduce the surface tension of the solvent and to create `poor wettability' (non-polar solvent, polar oxide network surface) in the gel. The latter factor reduces the capillary stresses that arise at the liquid–vapor interface, which in turn limits shrinkage during APD. The opposite poor wettability condition (non-polar surface in contact with a polar solvent), created by reacting the gel with silylating reagents in the mother liquor (primarily ethanol and water), did not provide significant porosity. Adding more water during sol–gel processing aided the preservation of mesopores during APD.