Studying the atomic structure of an electron beam sensitive catalyst

Abstract

This work concerns catalysts and the optimisation of atomic structure to increase the catalytic efficiency and lifetime of said systems. Catalysts are used in many different applications, for example vehicles, chemical synthesis, biological reactions and food processing. The increasingly stringent regulations regarding vehicular emissions have brought about an intense research in automotive catalyst systems during the last decades. In this work we focus on the zeolite system Cu-SSZ-13, one of the leading candidates for state-of-the-art heavy-duty automotive catalyst systems, and developing a methodology for studying it with atomic resolution scanning transmission electron microscopy (STEM) imaging. Proper specimen preparation is one of the most important factors in order to achieve high-resolution. A substantial part of this work therefore concerns the study how to optimally prepare SSZ-13 samples for high-resolution imaging. Specifically, we try to find methods for imaging and specimen preparation that limit electron beam damage of Cu-SSZ-13. We present a protocol for specimen preparation of SSZ-13 that also includes information about different means of controlling the degree of sample hydration and its effect upon the sensitivity to electron beam damage. Beam damage effects and underlying mechanisms are discussed as well. We also present results from simulations of atomic resolution images of Cu-SSZ-13, which in turn can be used to support experimental results of future works.