Mo. Coppens et al., Synthesis of hierarchical porous silicas with a controlled pore size distribution at various length scales, CATAL TODAY, 69(1-4), 2001, pp. 331-335
Hierarchically structured porous materials are of great interest to catalys
is, where an accurately controlled pore texture at different length scales
can help to reduce or otherwise control transport limitations. A method is
presented to synthesize bimodal structured silicas, with an independently c
ontrolled small meso-and large meso-to macroporosity. Small primary MCM-41
particles assemble around micelles formed by a tri-block copolymer surfacta
nt that is added as a low-concentration ethanolic solution to the particles
, while these still form a flexible gel. Cross-linking of the particles in
an autoclave, followed by drying and calcination, leads to bimodal material
s with the controlled small mesopores of MCM-41, and a larger meso- to macr
opore size distribution that depends on the micelle shape and size. The lat
ter is a function of the conditions in the second step, such as the amount
and composition of the surfactant, the aging time, the temperature, the pH
and the type of solvent. Fine tuning of this procedure, application to othe
r primary structured particles, and combination with other structuring meth
ods, should enable to construct multi-structured hierarchical materials wit
h a desired texture at all scales. (C) 2001 Elsevier Science BN. All rights
reserved.