Determination of the Acidity of H(Mg)AlPO4-5 and H(Co)AlPO4-5 Molecular Sieves

Abstract

Abstract: The acidic sites of aluminophosphate molecular sieves, AlPO₄-5, containing various heteroatoms such as Mg²⁺ and Co²⁺ were investigated by using IRspectroscopy of adsorbed pyridine and temperature-programmed desorption(TPD) of NH_3. The band at 3680 cm^-1 is assigned to P—OH, and the band at 3820 cm^-1 can be attributed to the terminal Al—OH.The bands appearing in the region from 3660 to 3568 cm^-1 is possibly assigned to the bridging hy-droxyl groups M (OH) P (M=Mg,Co).The decreasing acidity sequence of acidic sites is: Co(OH)P>Mg(OH)P>P(OH)>Al(OH).The IRspectra of pyridine adsorbing these samples reveal that there are strong Band Lacidic sites in H(Mg)AlPO₄-5 and H(Co)AlPO₄-5, in contrast to AlPO₄-5.Additionally, the TPD-NH₃ experiments show the order of the acidic strength of these samples: H(Co)AlPO₄-5>H(Mg)AlPO₄-5>>AlPO₄-5.

Key words: AlPO₄-5, Acidity, Surface OH, Chemical adsorption, H(Mg,Co)AlPO₄-5 molecu-lar sieves

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XIAO Feng-shou, XU Ru-ren, XIN Qin. Determination of the Acidity of H(Mg)AlPO₄-5 and H(Co)AlPO₄-5 Molecular Sieves[J]. Chem. J. Chinese Universities, 1992, 13(5): 651.

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Determination of the Acidity of H(Mg)AlPO₄-5 and H(Co)AlPO₄-5 Molecular Sieves

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