Imaging individual lanthanum atoms in zeolite Y by scanning transmission electron microscopy: Evidence of lanthanum pair sites

Abstract Images of La-exchanged NaY zeolite obtained with aberration-corrected scanning transmission electron microscopy (STEM) show that about 80% of the La cations were present as site-isolated species, with the remainder in pair sites. The observed distances between La cations in the pair sites ranged from 1.44 to 3.84 A, consistent with the presence of pairs of cations tilted at various angles with respect to the support surface. The actual distance between La cations in the pair sites is inferred to be approximately 3.84 A. The results suggest the presence of dimeric structures of La cations bridged with O anions, and the presence of such species has been inferred previously on the basis of X-ray photoelectron spectroscopy (W. Grunert, U. Sauerlandt, R. Schlogl, H.G. Karge, J. Phys. Chem., 97 (1993) 1413).