Bridging gaps in catalysis: from naphthalene decomposition to CO oxidation
Time: Wed 2024-10-30 10.00
Location: F3 (Flodis), Lindstedtsvägen 26 & 28, Stockholm
Video link: https://kth-se.zoom.us/j/64489297831
Language: English
Subject area: Chemical Engineering
Doctoral student: Lea Hohmann , Processteknologi
Opponent: Professor Christian Papp, Freie Universität Berlin, Tyskland
Supervisor: Universitetslektor Dan James Harding, Processteknologi; Professor Klas Engvall, Processteknologi; Universitetslektor Efthymios Kantarelis, Processteknologi, Materialvetenskap
QC 20241007
Abstract
Surface science techniques applied to simplified model systems have long been used to study catalytic mechanisms and aspects of surface reactions that aredifficult to isolate in real catalytic reactors. Experimental techniques are usually combined to obtain information on structure, surface kinetics, surfacedynamics, and reaction chemistry. Recently, a main focus in surface science has been to attempt to ”close the gap” to real catalysis: Pushing experimental techniques to higher pressure than typical ultra-high vacuum (UHV) conditions, working with structurally more complex catalysts and introducing some of the complexity of real reaction conditions.
In this thesis, experimental studies on two model systems are presented. In the first part, the reaction of naphthalene on Ni(111) and Fe(110) is examined as a model for catalytic tar decomposition used in biomass gasification. The effect of sulfur, a typical impurity in biomass, on the dehydrogenation ofnaphthalene on Ni(111) is elucidated with XPS and STM, and shown to lead to an inhibition of carbon bulk dissolution. The decomposition of naphthalene on Fe(110) was studied on the clean surface and in the presence of oxygen with XPS, TPD and SFG to enable a direct comparison to Ni(111). A very similar activity towards naphthalene decomposition is observed, as well as key differences in carbon-carbon bond cleavage, carbon formation and reactivityof ”dirty” surfaces.
In the second part, CO oxidation on Pd(110) is studied as a model system for palladium catalysts and a good example surface for the effect of surfacereconstruction and increase of pressure above UHV. The reaction was examined using the recently developed near-ambient pressure velocity map imaging (NAP-VMI) technique, which enables the simulatenous measurement of kinetic constants and dynamic information at pressures up to 10−3 mbar. Using the unique capabilities of VMI, two reaction channels with fast diffusion could be attributed to CO adsorption sites and an effective activation energy extracted.
The research presented here demonstrates the usefulness of these surfacescience methods in understanding catalytic mechanisms. It also illustrates some key limitations and opportunities for future developments in the field.