ACIDITY AND CATALYTIC PROPERTIES OF ALPO4-11, SAPO-11, MAPO-11, NIAPO-11, MNAPO-11 AND MNAPSO-11 MOLECULAR-SIEVES

The type 11 aluminophosphate molecular sieves containing different substituted elements (viz. Mg, Si, Mn, Ni) have been synthesized and characterized for their crystalline nature, N-2-sorption capacity and morphology. Also, the MnAPO-11 molecular sieves with different concentrations of framework-substituted Mn were prepared in order to investigate the changes in the acidity and catalytic properties with the concentration of framework substituted element. The acidity measurements over the alumino-phosphate of type 11 catalysts were carried out by the temperature programmed desorption (TPD) and the stepwise thermal desorption (STD) of pyridine using GC techniques. The results of TPD and the STD of pyridine suggests the existence of a broad site energy distribution over these materials. The site energy distribution and the number of strong acid sites are affected by the type of framework substituted element. The magnesium incorporated aluminophosphate of type 11 (MAPO-11) possesses a greater number of strong acid sites than the Mn/Ni/Si-incorporated aluminophosphates of type 11 (MnAPO-11, NiAPO-11, SAPO-11). Among the mono-framework substituted element aluminophosphate molecular sieves, MAPO-11 possesses a greater number of strong acid sites. In the bi-framework substituted element aluminophosphate molecular sieves (MnAPSO-11), the observed strong acid sites are higher in number than the mono-framework substituted element aluminophosphate (MnAPO-11). The catalytic activities of these materials in ethanol, n-hexane, cumene and o-xylene reactions were studied. MAPO-11 showed higher conversion in these reactions than AlPO4-11, MnAPO-11, NiAPO-11 and SAPO-11 catalysts. The overall higher conversion was observed over MnSAPO-11.