An investigation of the physical structure of MCM-41 novel mesoporous materials using a corrugated pore structure model

The preparation and pore structure characterization of MCM-41 materials wit h or without Al or Ti addition during synthesis are presented in this work. Such solids are intended for use as catalysts supports possessing advantag eous pore structure, total acidity and thermal stability characteristics. B ET surface areas up to 1483 m(2)/g were determined and compared with cumula tive surface areas obtained by methods like the conventional Roberts' and t he newly reported corrugated pore structure model-nitrogen (CPSM-nitrogen) [Ind. Eng. Chem. Res. I 39(2000) 3747; Ind. Eng. Chem. Res. II 39 (2000) 37 64]. CPSM predictions are in perfect agreement with estimates obtained by t he BET monolayer adsorption variant. Pore size distributions (PSDs) were de duced by using both the Roberts' and the CPSM methods. The superiority of t he latter method was confirmed, since apart from the prediction of intrinsi c PSDs, enabled the determination of tortuosity factors ranging ca. tau (CP SM) = 1-2.35, for the studied materials [Ind. Eng. Chem. Res. 40 (2000) 721 ]. These values are lower than those for traditional catalysts ca. tau = 3- 10 [Mass Transfer in Heterogeneous Catalysis, 1970, p. 37] and reflect the ordered pore structure of MCM-41 solids. Addition of Al (i.e. Si/Al = 5) ca used a PSD shift towards the micropore region (i.e. D-mean shift from 3.28 to 2.10 nm) in contrast to Ti addition (i.e. Si/Ti = 5) that caused a PSD s hift farther to the mesopore region (i.e. D-mean shift from 3.28 to 23.74 n m). Lower additions of Al or Ti (i.e. Si/Al = 20 and Si/Ti = 10) caused a p ore volume and surface area reduction but not a substantial shift of the in trinsic PSDs. (C) 2001 Elsevier Science B.V. All rights reserved.