Effect of pore size of mesoporous molecular sieves (MCM-41) on Al stability and acidity

A matrix of mesoporous molecular sieves (MCM-41) with various Si/Al ratios and various pore sizes was synthesized. These were structurally characterized by X-ray diffraction, IR and Al-27 NMR. The relative acidity of these materials was estimated catalytically based on the isomerization selectivity of 2-methyl-2-pentene, The activity and selectivity of this reaction are affected by both the Si/Al ratio and the pore size at fixed composition. The stability of Al in the wall structure (as tetrahedral Al) is also affected by the pore size, the smallest pore size resulting in the most stable tetrahedral Al.