Chemical, structural, and catalytic characteristics of Al-MCM-41 prepared by pH-controlled synthesis

Detailed investigations on the effect of pH adjustment at a value of 11 during Al-MCM-41 synthesis with regard to changes in structure, chemical composition, and catalytic activity are described. Long-range order (XRD), surface area (BET), and pore size distribution (BJH) improved remarkably when the pH of the synthesis gel was adjusted intermediately. The Si/Al ratio (AAS) and the yield of Al-MCM-41 nearly doubled in the case of a threefold pH adjustment. The catalytic activity for Friedel-Crafts acylation of 2-methoxynaphthalene was about three times higher for pH-adjusted samples. These effects became less pronounced with increasing number of adjustments. Comparable results were obtained when acetic, sulfuric, nitric, or citric acid was used for the pH adjustment. (C) 2000 Elsevier Science B.V. All rights reserved.