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The discovery of novel family of molecular sieves called M41S aroused a worldwide resurgence in the field of porous materials. According to IUPAC definition inorganic solids that contain pores with diameter in the size range of 20-500 A are considered mesoporous materials. Mesoporous silica and alumina based materials find applications in catalysis, adsorption, host- guest encapsulation etc. This article reviews the current state of art and outline the recent patents in mesoporous materials research in three general areas: Synthesis, various mechanisms involved for porous structure formation and applications of silica and alumina based mesoporous materials.

The changes in morphology due to the formation of polyethylene in the pores of three silica-supported, chromium oxide catalysts were followed by using mercury porosimetry and electron microscopy.Ethylene polymerization from 0.1 to 20 g of polymer/g of catalyst was carried out from the gas phase in a fluid bed reactor at 1-atm total pressure with a nitrogen diluent. A catalyst with 1.7 cm3/g pore volume fragmented due to the formation of polymer in the pores and thereby maintained an open structure. Catalysts containing 1.1 and 2.3 cm3/g pore volume did not fragment extensively, and the product polymer congested the pores and impeded the continued polymerization. Total pore volume and pore size are not the only controlling factors in the fracturing process. Mercury porosimetry showed that fracture of the 1.7 cm3/g catalyst started after a polymer yield of just 0.4 gPE/g^, maintaining monomer access to the active sites. The 0.1-1-^m catalyst fragments contained a pore microstructure much like that of the starting material, thus demonstrating how the pore structure of the original catalyst particles may influence the polymerization process after fragmentation is complete.

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