Self-formation of hierarchical micro-meso-macroporous structures: Generation of the new concept "Hierarchical Catalysis"

The self-formation phenomenon of hierarchy with multiple-scaled porosity is reported. The structures of various chemical compositions, such as ZrO2, TiO2, Al2O3, Y2O3, Nb2O5, Ta2O5 ZrO2-SiO2, ZrO2-TiO2, ZrO2-Y2O3, aluminosilicates, aluminophosphates, silicoaluminophosphates, metallophosphates, are made of macrochannels (0.5-5 μm in diameter) with mesoporous or microporous walls. The hierarchically porous structures are prepared by just controlling the hydrolysis and polycondensation rates of the pre-selected inorganic sources. The textural, structural as well as morphological properties of each material are carefully studied by using a large series of techniques, such as XRD, NMR, TEM, SEM, N2 adsorption-desorption, Hg porosimetry, optical microscopy. On the basis of these multimodal porous structures, a new concept "Hierarchical Catalysis" has been proposed. This new concept can allow the realisation of a multiple steps reaction in one single catalyst in a cascade way without any separation processes. © 2007 Elsevier B.V. All rights reserved.