Mechanical Stability of Mesoporous Molecular Sieve MCM-48 Studied by Adsorption of Benzene, n-Heptane, and Cyclohexane

The synthesis of MCM-48 has been performed in a 5 L autoclave, and the progress of the synthesis has been monitored by X-ray powder diffraction and 29Si MAS NMR. The formation of MCM-48 progresses via an intermediate phase, whose conversion into the cubic phase is triggered by condensation of the silanol groups. The mechanical stability of silica mesoporous material MCM-48 has been investigated employing powder X-ray diffraction, nitrogen adsorption, and subcritical organic vapor (benzene, n-heptane, and cyclohexane) adsorption isotherms and breakthrough curves. The adsorption capacity is affected considerably by mechanical compression between 20 and 400 N mm-2, while the material is destroyed to a large extend at 480 and 600 N mm-2, which is reflected by a dramatic decrease in adsorption capacity and poor X-ray diffraction patterns. As a result of its three-dimensional structure, the mechanical stability of MCM-48 is larger compared to that of MCM-41 but still low compared to that of crystalline structures such as zeolites.