Adsorption of tetraamineplatinum(II) hydroxide, a Pt catalyst precursor, from its aqueous solution onto a (0 1 0) surface of a natural zeolite heulandite was observed, in situ, by atomic force microscopy (AFM). The Pt complex exhibited certain adsorption habits on the surface, frequently forming a short chain along the zeolite a-axis, separated by three times the c unit cell length in the c direction. Possible adsorption sites on the surface were identified and discussed. The present work constitutes the first in situ atom-level observation of a liquid-phase preparation process of supported metal catalysts. (C) 2004 Elsevier B.V. All rights reserved.