Correlating the atomic-level compositions, structures, and reaction properties of Pt-zeolite catalysts
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Correlating the atomic-level compositions, structures, and reaction properties of Pt-zeolite catalysts


Heterogeneous catalysts are used for approximately 80% of the chemical catalysts used in the world, among which metal supported on zeolite catalysts are particularly versatile and widely used in chemical industries. The reaction properties of these catalysts depend strongly on the compositions and nanoscale architectures of the zeolite support, as well as the types and locations of metal species within the zeolite pores, which are influenced by the catalyst synthesis and treatment conditions. Understanding the atomic-scale structures of metal-zeolite systems is crucial to the development of strategies to control metal dispersion and thereby improve catalyst performance. However, these types of catalysts are complex and challenging to understand on the atomic scale, because of the presence of broad distributions of chemical environments. Here, solid-state nuclear magnetic resonance (ssNMR) methods are used to elucidate atomic-scale structures of various types of metal- zeolite materials. The results and analyses are complemented by analyses of other powerful techniques, such as electron paramagnetic resonance, extended X-ray absorption fine structures, X-ray diffraction, and high-resolution transmission electron microscopy. Detailed understandings of atomic structures of various metal-zeolite systems are obtained by advanced ssNMR methods, with a focus on industrially significant platinum supported on zeolites, e.g., bifunctional Pt on H+USY zeolite catalyst used for hydroisomerization and Pt on F-KL zeolite catalyst used for the aromatization of straight n-hexane. For example, two-dimensional (2D) solid-state NMR techniques are used to identify covalent bonding environments of 27Al and 29Si sites of the zeolite and to reveal interactions between dilute promoter species and zeolite support sites. High external magnetic field (up to 35.2 T) and fast magic angle spinning (up to 60 kHz MAS) methods are used to obtain well-resolved NMR spectra which enabled to elucidate distinct chemical environments present in various zeolite catalysts. Ultrawideline 195Pt NMR experiments are also implemented on high loading Pt supported on zeolite materials to identify types and distributions of 195Pt moieties. Moreover, recent advancements in NMR instrumentation enabled to conduct in-situ variable temperature and pressure (up to 200 bar & 240 oC) 13C and 1H MAS NMR measurements, which provide opportunities to identify types of reactants and products under reaction conditions. The methods, analyses, and results discussed in this thesis are expected to be of broad importance in understanding correlations between reaction properties and atomic-scale structures of industrially significant zeolite catalysts.

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