Surface structures of zeolites studied by atomic force microscopy

Surface structures of three zeolites, mordenite (MOR), heulandite (HEU), an d Linde Type A (LTA), were investigated by using atomic force microscopy (A FM). 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 i n the dissolving surface of HEU in an acidic or alkaline aqueous solution r evealed that the aluminosilicate layers of HEU dissolved from terraces by a layer-by-layer process. This unique dissolution process is due to the char acteristic 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 w here the bulk structure terminates. This study demonstrates the potential u se of AFM to provide information at the atomic level about the zeolite's su rface structure vital to the further development of this important class of materials in the field of catalysis. (C) 2001 Elsevier Science B.V. All ri ghts reserved.