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Selective acidic, oxidative and reductive reactions over ALPO-11 and Si or metal substituted ALPO-11

Elsevier Science & Technology
DOI: 10.1016/s0167-2991(06)81907-5


Publisher Summary Aluminophosphate molecular sieves are microporous crystalline inorganic solids. ALPO-11 and derivatives of ALPO-11 containing Si, V, Co, Mn have been synthesized using n-dipropyl amine as a template. The addition of these elements in ALPO-11 considerably influences the physical and catalytic properties of the materials synthesized, due to the generation of new catalytic centers. The samples were characterized by XRD, SEM, ESR, UV-Visible and sorption measurements. The acidic characteristics of the samples were evaluated in the hydrocarbon reactions, like toluene methylation, m-xylene isomerization, and isobutanol dehydration. The product pattern obtained in the methylation of toluene and isomerisation of m-xylene with Si or metal-substituted ALPO-11 is similar to that obtained for zeolites. For these two reactions, ALPO-11 did not show any catalytic activity. The studies distinguish two types of acid centers in ALPO-11 and SAPO-11. ALPO-11 being, very weakly acidic due to terminal hydroxyl group or weak Lewis acid sites, is not having catalytically active centers for alkylation and isomerisation, but is active for the isobutanol dehydration. Further studies indicate that metal-substituted ALPO-11 generates additional few stronger acid centers due to the substitution of M2+ in place of A13+ in the AEL structure. These acid centers are stronger than the acid centers of SAPO-11; however, acidity of these molecular sieves is much weaker as compared to that of a zeolite. Metal substituted ALPO's also exhibit activity in the hydrogenation of nitrobenzene and oxidation of benzyl alcohol, thus, demonstrating the reductive and oxidative properties, due to the introduction of new metallic sites.

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