Selective hydrogenation on anatase TiO2-supported single atom catalysts
Restricted (Penn State Only)
- Author:
- Hu, Jeremy
- Graduate Program:
- Chemical Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- February 01, 2024
- Committee Members:
- Robert Rioux, Professor in Charge/Director of Graduate Studies
Robert Rioux, Major Field Member
Kristen Fichthorn, Minor Field Member
Lasse Jensen, Outside Unit & Field Member
Konstantinos Alexopoulos, Co-Chair & Dissertation Advisor
Michael Janik, Co-Chair & Dissertation Advisor - Keywords:
- heterogeneous catalysis
density functional theory
hydrogenation
single atom catalysts
metal oxides
titania - Abstract:
- One of the most important applications of catalysis is in hydrogenation, which is responsible for producing commodity chemicals that are crucial in a variety of industries ranging from pharmaceuticals to food and agriculture. The principal goal in catalytic hydrogenation is to find materials that are able to activate molecular hydrogen (H2) to a surface species that can “attack” unsaturated hydrocarbon moeities and selectively form C-H bonds. Single atom catalysts (SACs) supported on reducible metal oxides such as anatase TiO2 have demonstrated high activity and selectivity for a wide range of applications including selective hydrogenation. However, the understanding of the mechanisms of H2 activation, mechanisms of C-H bond formation, and how the choice of support contributes to the overall reaction on SACs is severely limited. Computational tools including density functional theory (DFT) and microkinetic modeling are used to evaluate anatase TiO2-supported SACs for hydrogen activation and selective hydrogenation reactions. A bifunctional catalyst model is proposed, where single metal atoms serve as active sites for H2 activation and provide a source of spillover H atoms to the bare TiO2 support, where the vast majority of C-H bond formation is then expected to occur. Under reduction conditions, oxygen vacancies (Ovac) readily form on the underlying TiO2 support, which has significant effects on H2 activation and C-H bond formation mechanisms. Study of the reactive hydrogen species on the support shows that hydrides (H-) bound in Ovac are highly stable and mediate selective C-H bond formation mechanisms with coadsorbed ligands. A dual-site microkinetic model is implemented to predict the performance of these catalysts under reaction conditions, such as the relative product selectivities. A wide variety of selective hydrogenation reactions are studied on these TiO2-supported SACs, including the chemoselective hydrogenation of aromatic carboxylic acids and semi-hydrogenation of C2 species.