Local environment inside microporous materials and their consequences for catalysis and adsorption
Open Access
- Author:
- Thakkar, Jay
- Graduate Program:
- Chemical Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- November 09, 2020
- Committee Members:
- Xueyi Zhang, Dissertation Advisor/Co-Advisor
Xueyi Zhang, Committee Chair/Co-Chair
Robert Rioux, Committee Member
Michael John Janik, Committee Member
Amanda M. Johnsen, Outside Member
Phillip E Savage, Program Head/Chair - Keywords:
- catalysis
separation
ion exchange - Abstract:
- Microporous materials such as zeolites and metal-organic frameworks (MOFs) contain in-built active sites (e.g. Brønsted, Lewis and or ion-exchange) which are accessible to diffusing guest molecule species via pore channels of comparable sizes. These active sites depending on the structure, type, strength, and location determine the interactions (e.g. covalent, ionic and or van der Waals) experienced by the transporting molecules, in turn dictating process outcomes (product quality and quantity). As such this dissertation focuses on controlling and designing these unique and customizable local active sites present in zeolites and MOF materials for advancing energy related applications. Ion exchange and separation of critical rare earth elements is studied by exploiting the local active site environment generated by the presence of octahedral titanium in tetrahedral silicon setting in zeolitic titanosilicate, ETS-10. It is found that adsorption strength of these ions on ETS-10 are significantly different from each other (Y3+>Nd3+>Eu3+>Tb3+>Dy3+). This difference is exploited in separation of cations from aqueous Ni2+-Nd3+ solutions generated during recycling of NiMH batteries and a high solution separation selectivity is obtained. The high adsorption capacities of cations provided by ETS-10 is further utilized in performing gas phase ethylene dimerization reactions. Ni2+ exchanged ETS-10 is found to be selective for dimerization of ethylene and a high reaction activity, and catalyst stability is observed. Influence of active site local environment is also studied in Friedel-Crafts acylation reaction of isobutylbenzene. Traditional aluminosilicate zeolites with BrØnsted acid sites are utilized and zeolite Beta is found to provide the most suitable pore-topology where the reaction occurs inside the 3-dimensional pore channels. Apart from the experimental evaluations of the active site environment on the reaction outcomes, computation density functional theory studies are also performed on Ni-IRMOF-74 for adsorption of C4 isomers. It is observed that the C4 alkenes bind to the Lewis acidic Ni metal center through the double bond while the C4 alkanes bind via C-H bond. The interactions of alkenes are therefore naturally found to the stronger and C4 alkenes can thus be separated from alkanes using Ni-IRMOF-74.