On the chemical condensation of the layers of zeolite precursor MCM-22(P)

Abstract

Chemical condensation of layers of silicates has been often proposed as an alternative to thermal condensation, finding limited success. The formation of the industrially relevant MCM-22 zeolite (MWW IZA code) from a mild hydrothermal precursor is the most important example of 2D-3D aluminosilicate condensation. Silanols of opposed layers have been condensed by acid-driven dehydration in concentrated nitric acid, as confirmed by powder XRD and 29Si NMR spectroscopy, implying interlayer template extraction and corresponding dealumination. Milder acid treatments favour template extraction and shrinkage of interlayer distance, but do not provide significant silanol condensation. Template extraction is further favoured by degradation of the organics in the presence of a Cu2+ homogeneous catalyst.