Toward the Synthesis of Extra-Large-Pore MCM-41 Analogues

A new approach is proposed for the synthesis of extra-large-pore (diameter > 7 nm) MCM-41 analogues, potentially useful as hosts for the synthesis of nanowires and as model porous solids for fundamental research. The approach is based on the recently demonstrated opportunity for elimination of the connecting pores in the walls of SBA-15 silica during high-temperature (about 1243 K) calcination, which afforded MCM-41 analogues, but the latter had a limited pore size (<7 nm) and small pore volume. Herein, we propose an approach to overcome these limitations by judiciously selecting SBA-15 silicas that exhibit a relatively small content of connecting pores (to reduce the shrinkage upon their elimination) and sufficiently large initial pore size. This approach allowed us to obtain materials with uniform pores of diameter up to 8.8 nm, which is much larger than that attainable for good-quality MCM-41, and with adsorption properties expected for MCM-41 analogues and appreciably different from those of SBA-15 prepared using standard procedure. It is expected that MCM-41 analogues with yet larger pore sizes can be obtained, when the proposed methodology will be applied for some of SBA-15 silicas reported to date.