Processing of alumina low-density xerogels by ambient pressure drying

Alumina is utilized as a catalyst and catalyst support, applications that c an benefit from a high surface area and significant mesopore volume. Such c haracteristics can be achieved through ambient pressure drying (APD) using a methodology similar to that which has proven successful with silica. Alum ina 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 fa ctor reduces the capillary stresses that arise at the liquid-vapor interfac e, which iu 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 e thanol and water), did not provide significant porosity. Adding more water during sol-gel processing aided the preservation of mesopores during APD. ( C) 2001 Elsevier Science B.V. All rights reserved.