An investigation of the roles of surface aluminum and acid sites in the zeolite MCM-22

Ammonia adsorption studies reveal that the observed Lewis acidity in the zeolite MCM-22 is derived from at least two types of framework aluminum sites (Al(F)), that is, octahedral Al(F) and three-coordinate Al(F). Comparative ammonia or trimethylphosphine (TMP) adsorption experiments with MCM-22 confirm that octahedral Al species gives rise to the signal at delta(ISO) approximate to 0 in the (27)Al NMR spectrum; this is a superposition of two NMR signals from the different Al species on the water-re constructed zeolite surface. A sharp resonance assigned to framework Al reversibly transforms on ammonia adsorption to delta(ISO) (27)Al approximate to 55 from tetrahedral Al(F), while the broad peak is assigned to nonframework aluminium which results from hydrothermal treatment. This study also demonstrates the effectiveness of (27)Al magic angle spinning (MAS) and multiple quantum (MQ) MAS NMR spectroscopy as a technique for the study of zeolite reactions.

Oriented growth of MCM-22 zeolite films

MCM-22 zeolite films have been grown with layers vertical to the substrate under hydrothermal synthesis conditions, and characterized by X-ray diffraction and scanning electron microscopy.

PRINCIPAIS INDICADORES: AGRÍCOLAS, v. 3, n. 22, 2010.

2010

PRINCIPAIS INDICADORES: LEITE E DERIVADOS, v. 3, n. 22, 2010.

2010

PRINCIPAIS INDICADORES: MACROECONÔMICOS, v. 3, n. 22, 2010.

2010