An FT-IR and UV-VIS study on the structure and acidity of sol-gel derived silica foams

Novel acidic macrostructured mesoporous silica foams were synthesised by th e sol-gel method. The structure of the samples was investigated by IR and U V-VIS spectroscopy, and their acidity was measured by pyridine adsorption. Lewis and Broensted acidic centres were formed both in the silica-tungsto-p hosphoric acid and in the silica-alumina composite foams. The amount of aci d sites can be tuned by sample pre-treatment as well as changing the hetero poly acid loading or the Si/Al ratio of the foam, respectively. Because of the exceptionally high diffusion rates offered by the foam structure, the s ynthesised materials are expected to make an influence on the field of liqu id phase heterogeneous catalysis in the future. (C) 2001 Elsevier Science B .V. All rights reserved.