Abstract
Large pore silico-magnesium aluminophosphate molecular sieve of type 36 with three-dimensional structure and monoclinic symmetry (unit cell composition: (Mg 0.948 Al 11.052 ) (Si 0.492 p 11.508 )O 48 : 1.13 NC 9 H 21 : 4.9 H 2 O) was synthesized. Pure MAPSO-36 was characterized by the XRD, SEM, XPS t.g./d.t.g./d.t.a. and i.r. techniques. In situ i.r. spectroscopic investigation of chemisorbed pyridine on MAPSO-36 revealed the presence of Bronsted and Lewis acid sites. The acid strength distribution on MAPSO-36 was investigated by temperature-programmed desorption (t.p.d.) and the stepwise thermal desorption (s.t.d.) of pyridine from 323 to 673 K. The t.p.d. of pyridine over MAPSO-36 indicated the presence of two types of acid sites and a stronger acidity than MAPO-36. MAPSO-36 showed high catalytic activity in the alcohol, linear, branched, and cycloalkanes and aromatic conversion reactions at 673 K. In ethanol, n -hexane, isooctane, and o -xylene conversion reactions, the catalytic activity and aromatics formation over MAPO-36 and the silicon-substituted MAPO-36 were compared. MAPSO-36 exhibited lower n -hexane conversion than HZSM-5; however, the aromatics yield was more. Enhancement in the acidity and catalytic activity of the silicon-substituted MAPO-36 indicates that the acidic and catalytic properties of MAPO-36 are strongly affected by the incorporation of silicon in the magnesium aluminophosphate framework.
Published Version
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