Applications of Metal-Organic Frameworks in Catalysis and Separations

Abstract

Metal-organic frameworks (MOFs) are a class of porous coordination polymers that has been the subject of intense investigation since there discovery almost 30 years ago. The combination of organic linker and metal node in a 3-dimensional framework leads to materials that are tunable, have high surface area and in most cases are highly porous. The applications of these materials spans from gas storage to catalysis. Chapter 2 describes the utilization of MOFs to catalyze the carbonation of propylene oxide to propylene carbonate. The design and construction of a packed-bed flow reactor was undertaken to allow systematic investigation. This systematic investigation of co-catalyst, catalyst synthesis, catalyst activation, node metal and node geometry resulted in high yielding conditions with low CO2 pressure (1-10 bar) and no added co-catalyst, conditions that previously, under batch conditions, lead to poor yields. These studies eventually resulted in the identification of a new catalyst, MIL-100(Sc), for this reaction. Chapter 3 investigates post-synthetic modification of MIL-101-SO3X through cation exchange. MIL-101-SO3X was treated with various potassium salts resulting in substitution at the sulfonate and establishing a relationship between conjugate acid pKa and MOF degradation. The exchange process demonstrated allow for rapid and complete conversion between protonated (–SO3H) and alkali metal exchanged (–SO3X) through brief (10 min) treatment with bicarbonate base followed by alkali chloride salt treatment for 1 h or by the utilization of high equivalents of alkali chloride salt relative to incorporated sulfonate. The exchange process was successful in generating previously unreported MIL-101-SO3X loaded with K, Rb, and Cs. Chapter 4 expands upon post-synthetic modification by investigating the conversion of aminated MOFs (IRMOF-3, UMCM-1- NH2, MIL-53(Al)-NH2, and UiO-66-NH2) into sulfonated MOFs by reaction with 1,3-propanesultone. This process can be performed both neat and in solvent leading to 26 and 61% loading of sulfonate. This mild procedure was used on a wide variety of aminated MOFs containing different node metals (Zn, Zr, Al) and organic linkers (2-aminoterephtalic acid and benzene tribenzoic acid) to generate sulfonates that would otherwise be difficult to access. Loading of Ir, Pd and Rh cationic catalyst was attempted resulting in improved loading in sulfonated MOFs. Further evaluation of cationic loading into post-synthetically modified MOFs is necessary to elucidate the primary contributed factors for exchange in these materials.