UC Berkeley

Many industrial processes produce hot multicomponent mixtures that require extensive separations. The work presented in this dissertation describes the design, synthesis and characterization of metal–organic frameworks for industrially relevant separations conducted at temperatures above 200 °C. The modularity of metal–organic frameworks enables the rational design of metal sites for reversible binding of adsorbates at these temperatures informed by molecular principles. Chapter 1 introduces metal–organic frameworks as tunable adsorbents and motivates their development for gas separations conducted at elevated temperatures. High-temperature post-combustion carbon capture is introduced as an exemplar application and a brief survey of carbon dioxide-selective frameworks is presented to inform design principles for this application. Next, high-temperature separations of commodity chemicals including carbon monoxide (CO), ethylene (C2H4) and propylene (C3H6) are proposed and motivated, followed by a brief survey of frameworks employing metal-centered π-backbonding interactions to conduct separations of olefins and CO. Chapter 2 describes the synthesis and characterization of a porous metal–organic framework featuring terminal zinc hydride sites for high-temperature post-combustion carbon dioxide (CO2) capture. The framework reversibly captures CO2 at temperatures above 200 °C, conditions unprecedented for gas adsorption to a porous material. Gas adsorption and spectroscopic analysis reveal that CO2 reversibly inserts into the terminal zinc hydride sites, and that this mechanism is kinetically limited at ambient temperatures. Finally, extended cycling and breakthrough experiments confirm the robustness of the material and its potential to conduct deep capture under low CO2 concentrations and at high temperatures. Chapter 3 describes the synthesis and characterization of a metal–organic framework featuring open trigonal pyramidal copper(I) sites for high-temperature purification of π-acidic commodity chemicals. Gas adsorption, diffraction, spectroscopy, and density functional theory calculations reveal that the copper(I) sites activate adsorbates through metal–ligand π-backbonding interactions. Breakthrough experiments at elevated temperatures demonstrate that separation of these π-acids from one another and from other components is feasible, favoring CO over C2H4 and C2H4 over C3H6, and separation of CO is accomplished under humid conditions.