Surface structures of zeolites studied by atomic force microscopy

Surface structures of three zeolites, mordenite (MOR), heulandite (HEU), and Linde Type A (LTA), were investigated by using atomic force microscopy (AFM). The arrangement of 12-membered rings on the (0 0 1) surface of MOR was observed for the first time. Direct imaging of the morphological changes in the dissolving surface of HEU in an acidic or alkaline aqueous solution revealed that the aluminosilicate layers of HEU dissolved from terraces by a layer-by-layer process. This unique dissolution process is due to the characteristic pore structure of HEU. The AFM imaging of the (1 0 0) surface of LTA revealed that double four-rings (D4Rs) are stable units in the crystal growth of LTA and that each terrace has different structure depending on where the bulk structure terminates. This study demonstrates the potential use of AFM to provide information at the atomic level about the zeolite's surface structure vital to the further development of this important class of materials in the field of catalysis. (C) 2001 Elsevier Science B.V. All rights reserved.