Al-containing MCM-41 type materials prepared by different synthesis methods: hydrothermal stability and catalytic properties

摘要

Al-containing MCM-41 type materials were prepared by three different synthesis methods(aluminum grafting on the calcined MCM-41, pH adjustment during the crystallization periodand crystallization in the presence of zeolite seeds). The samples were characterized bypowder XRD, nitrogen adsorption, 27Al MAS NMR and FTIR with pyridine as probemolecule. All the samples exhibit a high hydrothermal stability at high temperature just with aminor structural degradation. N2 adsorption data obtained for the sample prepared from a gelcontaining zeolite seeds suggest a higher structural resistance to the hydrothermal treatment incomparison with the samples prepared by other methods. A different type of pyridineadsorbed, probably interacting simultaneously with a Brönsted and a Lewis acid site, isobserved upon pyridine adsorption. This type of adsorption is stronger for the sampleprepared in the presence of zeolite seeds and is not observed on Al-grafted MCM-41.2The catalytic activity towards the isomerization of α-pinene depends mainly on the number ofBrönsted acid sites. The data obtained in this study strongly indicate that for this type ofmaterials, the Lewis acid sites do not influence the selectivity for the isomerization products.