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Free keywords:
Zeolites model system;
Zeolites building units;
Ultra-thin aluminosilicates;
Surface science;
Topochemistry
Abstract:
Some of the basic building units found on many zeolites, as well as larger fragments found in specific cases, were imaged within the structure of an aluminosilicate ultra-thin film synthesized on a Ru(0001) substrate. These units have been suggested as possible precursors for the wide variety of zeolites reported to date. The reported structure consists of a planar sheet of double N-membered rings (polygonal prisms) sharing four-membered ring faces in the planes normal to the surface. The units are mostly double six-membered rings (d6r), with a significant population of pairs of double four- and eight-membered rings (d4r and d8r) and pairs of double five- and seven-membered rings (d5r and d7r), among other minority species. In particular, there is significant increase of the d4r and d8r units in this aluminum-containing film, when compared to pure-silica ones prepared in the same manner. These building blocks appear 25 (d6r), 17 (d4r) and 5 (d8r) times, in the set of 176 unique zeolite frameworks reported up to 2007. In addition, larger ensembles of rings observed in this system can be related to more complex ensembles in zeolites, such the α-cage in zeolite A. The structures were here identified by a combination of scanning tunneling microscopy, low energy electron diffraction, infrared reflection absorption spectroscopy and X-ray photoelectron spectroscopy experiments.
