Preparation of macrostructured metal oxides by sedimentation-aggregation

A new and simple synthesis route allowing scaling up has been developed for metal oxides characterized by narrow pore size distribution in the macropo re range. The technique is based on sedimentation and aggregation of monodi spersed polystyrene beads in alcohol solutions of metal alkoxides. Accordin g to scanning electron microscopy, the calcined oxides (alumina, niobia. si lica and titania) exhibit spheric-like and interstitial-like pores consiste nt with tem plating produced by the beads that were coated individually wit h a layer of the metal precursors during sedimentation and randomly packed during aggregation. All the pores seem connected by macrowindows (50-80 nm diameter) likely formed at the bead contact points. The macropore structure collapses at 750 degreesC for niobia but is maintained up to 900 degreesC for alumina and silica and 1000 degreesC for titania. The pore collapse occ urs at the phase transition temperature between the gamma and alpha allotro pic forms of alumina. while for titania the formation of rutile does not le ad to collapse of the macroporous structure. (C) 2001 Elsevier Science B.V. All rights reserved.