The synthesis of AlMCM-41 molecular sieves with Si/Al ratios 14-32 is reported. Intermittent pH adjustments during synthesis may improve the long-range order of the mesopores. N-2 adsorption and Al-27 MAS NMR experiments reveal that all the AlMCM-41 samples contain a small amount of aluminum-rich extra-framework species both inside and outside the mesoporous channels after calcination. The proton exchanged AlMCM-41 catalysts are weak-medium acidic, and are catalytically active for isopropanol dehydration at moderate temperature and for cumene cracking at high temperature.