Multimodal Spectroscopy and Imaging of Chabazite Zeolite

Abstract

Zeolites are a type of crystalline aluminosilicate material that when produced synthetically find use in a variety of contexts, many of which are directly beneficial to society at large. One such application, which is of interest not only from the perspective of commercial profitability but perhaps more pertinently in today’s climate from an environmental point of view, is catalysis. Two important examples of commercialised catalytic reactions are selective catalytic reduction (SCR) and the methanol-to-olefins (MTO) reaction, which, respectively, involve the catalytic conversion of noxious NOx gases to nitrogen & water, and waste methanol to higher value petrochemicals. A central challenge in catalysis is the development of characterisation techniques capable of navigating the structurally and compositionally complex internal landscapes of zeolitic catalysts. While the bulk scale information gleaned through techniques like mass spectroscopy, XRD, and NMR provide an established benchmark against which zeolite behaviour is currently assessed, gaining spatially resolved insight into catalytic activity on a nanometric, single-catalyst length scale is highly desirable in current research efforts focused on optimising and improving existing catalytic systems. Laser-based characterisation, being non-destructive and capable of molecular excitation, is identified here as a viable but underexplored option for studying zeolites in a catalytic chemistry context. Time-resolved photoluminescence spectroscopy (TRPS) and confocal-lifetime microscopy are applied to zeolite systems, providing fresh insight into aspects of the zeolite’s synthesis process. TRPS is further combined with in situ setups to provide new information on zeolite behaviour during an active catalytic reaction as a function of time and temperature. Finally, combined IR spectroscopy and X-ray microscopy studies were conducted on Cu-containing forms of the high silica form (SSZ-13) of the zeolite chabazite (CHA)

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