Synthesis of High-Quality MCM-48 and MCM-41 by Means of the GEMINI Surfactant Method

Pure silica MCM-48 and MCM-41 materials were prepared using GEMINI surfactants, with the general formula [C n H 2 n +1 N + (CH 3 ) 2 −(CH 2 ) s −N + (CH 3 ) 2 C m H 2 m +1 ].2Br -, abbreviated as GEM n - s - m . The alkyl chain length ( n, m ) determines the pore size, whereas the length of the spacer ( s ) influences the crystallographic phase formed. A spacer length of 10−12 C yields the cubic MCM-48; smaller spacers favor the hexagonal MCM-41 phase. A hydrothermal treatment is introduced as an intermediate synthesis step, which strongly improves the quality and stability of the calcined materials. The hydrothermal treatment reduces the synthesis time of high-quality MCM-48 to only 2 days. Both GEM 18-12-18 and GEM 16-12-16 yield excellent MCM-48, with a surface area in the range 1200−1600 m 2 /g and pore volumes exceeding 1.2 mL/g. The maxima of the very narrow pore size distributions are found at r p = 13.1 and 12.2 Å, respectively. The GEM 16-10-16 and GEM 18-10-18 surfactants also yield MCM-48, but the quality of these materials is lower. The GEM 16-8-16 finally yields MCM-41.