Direct imaging of single metal atoms and clusters in the pores of dealuminated HY zeolite

Abstract

Zeolites are aluminosilicate materials that contain regular three-dimensional arrays of molecular-scale pores, and they can act as hosts for catalytically active metal clusters. The catalytic properties of such zeolites depend on the sizes and shapes of the clusters, and also on the location of the clusters within the pores. Transmission electron microscopy has been used to image single atoms and nanoclusters on surfaces, but the damage caused by the electron beam has made it difficult to image zeolites. Here, we show that aberration-corrected scanning transmission electron microscopy can be used to determine the locations of individual metal atoms and nanoclusters within the pores of a zeolite. We imaged the active sites of iridium catalysts anchored in dealuminated HY zeolite crystals, determined their locations and approximate distance from the crystal surface, and deduced a possible cluster formation mechanism.

Atomic Resolution Analysis of Silver Ion‐Exchanged Zeolite A

“…[7] In the case of scanning transmission electron microscopy (STEM) imaging, the scenario may be worse because the beam is concentrated on a very fine spot which can burn a hole above some threshold current density. [8] However, if a slightly different approach is made by using low-dose conditions, novel and excellent visual information can be achieved, especially in combination with aberration-corrected electron microscopes, [9] which can be used for dynamic imaging of single atoms [10] and clusters composed of a few atoms. [11] The motivation for the present work rests on the application of spherical aberration-corrected high-angle annular dark-field STEM (C s -corrected HAADF-STEM), where the contrast is related to Z 2 (atomic number) to study zeolite A (LTA structure type) which has an Si/Al ratio of 1:1 (the highest aluminum content possible and therefore the least stable zeolite under electron beam irradition).…”

Structure Determination of Zeolites by Electron Crystallography

“…During the very recent years STEM imaging has been successfully applied to studies of zeolites [73][74][75][76]. STEM-HAADF images are especially suitable for studies of, e.g., zeolites loaded with atoms or clusters of atoms.…”

Poisson noise removal from high-resolution STEM images based on periodic block matching

“…STEM images with such a small number of counts are generally deemed useless, so they are rarely acquired or published. However, the ability to extract information from extreme low-dose images would be a substantial advantage for a variety of problems, such as characterization of metallic catalyst particles [3] and polymers and molecular crystals [31].…”

“…Lowering the electron dose decreases the signal-to-noise ratio (SNR) of the acquired micrographs accordingly, degrading the quality or even completely prohibiting the extraction of desired information from the noisy micrographs. Examples of inorganic materials with high beam sensitivity, where scanning transmission electron microscopy (STEM) images of poor SNR have to be used, are both oxide [2] and metallic [3] catalysts. One important quantity that may be extracted from atomic-resolution electron micrographs is the positions of the atoms.…”