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M.L. Occelli, B. Drake, and S. A. C. Gould. 1993. Characterization of Pillared Montmorillonites with the Atomic Force Microscope (AFM). Journal of Catalysis 142: 337-348.

An atomic force microscope (AFM) has been used to investigate the surface features of samples of Ca-bentonite from Texas and Na-bentonite from Wyoming that were pillared with alumina clusters. Atomic-scale-resolution images of the clay surface consist of hexagonal arrays of bright spots. The nearest-neighbor distance in the two parent clays was found to be consistently greater after pillaring in numerous images, suggesting that the bulky Al13 clusters stretched the clays′ silicate layers. A number of images showed possible atomic resolution of oxygen atoms on the clay surface, suggesting that it can be possible to obtain resolution below the scale of the unit cell. Molecular-scale-resolution images of the cross-sectional area of extrudates formed using pillared Wyoming bentonite powder showed platelets about 9.0 apart, in agreement with X-ray diffraction (XRD) results. The presence of alumina debris or clusters on the silicate layer was not observed in any image examined, suggesting that the expended clay coking tendency during gas oil cracking can be attributed mainly to the strong Lewis-type acidity of the alumina pillars between the clay silicate layers.

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