Catalytic consequences of inner- and outer-sphere interactions at the solid-liquid interface in zeolites

Bregante, Daniel Thomas

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https://hdl.handle.net/2142/117880 Copy

Description

Title

Catalytic consequences of inner- and outer-sphere interactions at the solid-liquid interface in zeolites

Author(s)

Bregante, Daniel Thomas

Issue Date

2020-04-21

Director of Research (if dissertation) or Advisor (if thesis)

Flaherty, David W.

Doctoral Committee Chair(s)

Flaherty, David W.

Committee Member(s)

• Murphy, Catherine J.
• Guironnet, Damien
• Peters, Baron G.

Department of Study

Chemical & Biomolecular Engr

Discipline

Chemical Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

Catalysis, Zeolites, Solid-Liquid Interfaces, Kinetics, Spectroscopy, Thermodynamics, Inner-Sphere, Outer-Sphere

Abstract

Catalytic transformations at solid-liquid interfaces are inherently complex, as they require considerations for adsorption, desorption, molecular rearrangement, charger transfer, and dispersive interactions, but also involve interactions mediated by the solvating molecules. The rational design of improved systems for a desired transformation, require that each of these types of processes and interactions be accounted for. Colloquially, interactions among surface intermediates bound directly to an active site are referred to as “inner-sphere” interactions, while those involving molecules within the second shell are known as “outer-sphere” interactions. This dissertation explores both inner- and outer-sphere interactions that influence the stability of catalytically relevant surface species within zeolite catalysts. We use a combination of experimental synthetic, kinetic, spectroscopic, and thermodynamic tools and analyses to develop quantitative structure-activity relationships to describe how orthogonal changes to the catalytic system result in large charges in activity and selectivity during alkene epoxidation. We developed a proposed series of elementary steps to describe alkene epoxidation with hydrogen peroxide over early transition metals substituted into zeolite frameworks. First, this model was used to show that apparent activation enthalpies linearly scale with functional measures of Lewis acid strength (i.e., inner-sphere interactions) and explain how changing the active site identity could result in 106- and 102-fold increases in rates and selectivities among groups 4 and 5 metals. Second, outer-sphere, dispersive interactions among pore walls and reactive species are shown to persist within liquid-phase catalysis, which show how titanium within the *BEA framework (Ti-BEA) catalyzes styrene epoxidation with rates 5-times greater than these same atoms supported on mesoporous silica. Third, the presence of hydrophilic surface functions in a Ti-BEA catalyst nucleate confined H2O clusters that differ significantly in physical and chemical properties from bulk H2O. These H2O structures reorganize to accommodate the formation of surface intermediates (e.g., transition states) that lead to large increases in excess entropy and lower the free energy of the aggregate complex and increase rates by a factor of 100. Finally, we discuss how lateral inner-sphere interactions among surface intermediates bound to a single active site can be mediated by the presence and size of a surrounding pore and can ultimately lead to differences in rates spanning an order of magnitude. Collectively, this dissertation lays the foundation to measure and interpret complex inner- and outer-sphere interactions within microporous materials and will aid in the rational design of improved materials.

Graduation Semester

2020-05

Type of Resource

Thesis

Copyright and License Information

Copyright 2020 Daniel Thomas Bregante

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