ALUMINOSILICATE MESOPOROUS MOLECULAR-SIEVE MCM-48

Mesoporous aluminosilicate molecular sieves with the MCM-48 structure and atomic Si/Al ratios of 15-40 have been synthesized using aluminum chloride hexahydrate and aluminum sulfate as the sources of aluminum. The products were characterized by powder X-ray diffraction (XRD), the rmal analysis (TG/DTA), diffuse reflectance Fourier-transform infrared (DRIFT), Si-29 and Al-27 magic-angle-spinning (MAS) NMR, and nitrogen sorption. The quality of the product rapidly deteriorates as the alum inum content of the solid increases. The walls of the mesopores are es sentially amorphous, and the local atomic arrangement is similar to th at in amorphous aluminosilicates. The regular arrangement of uniform c hannels is the only element of order. Al-27 MAS NMR shows that when al uminum sulfate is used, both 4- and 6-coordinate aluminum is present i n the calcined products. On the other hand, when aluminum chloride hex ahydrate is used, aluminosilicate MCM-48 can be prepared with all alum inum in 4-coordination and the Si/Al ratio as low as 15. XRD shows tha t the substitution of the silicon by the larger aluminum atoms leads t o a contraction of the unit cell.