Synthesis, characterization and catalytic activity of the pillared molecular sieve MCM-36

MCM-36 materials were prepared by swelling the layered MCM-22 precursors with large organic molecules and then pillaring the resulting material with polymeric silica. A mesopore region with 0.25–0.3 nm thickness between the microporous layers was identified. The BET surface area obtained for MCM-36 was 2.5 to 3 times higher than that of MCM-22. The sorption characteristics of linear alkanes are similar for MCM-22 and MCM-36 materials, indicating that sorption is dominated by the 10-membered ring microporous channel system and that the pore structure of the MCM-22 layers stays intact during the swelling and pillaring processes. Swelling and pillaring, however, decreased the concentration of Brønsted acid sites compared with the starting material. The largest fraction of strong Brønsted acid sites is located in this zeolite layer. Adsorption of 2,2,4-trimethylpentane indicates that only about 10% of the bridging hydroxyl groups are located in the mesoporous region. The superior catalytic performance of MCM-36 compared with MCM-22 for alkylation of isobutane with n-butene indicates that the open mesoporous structure can be successfully utilized to make acid sites of the layers accessible to large molecules.