CHE 598 Seminar: Activity and Dynamics of Single Atom Pd- and Rh-Fe3O4(001) Catalysts
About the event
SPEAKER:
Dr. Zdenek Dohnalek, Laboratory Fellow and Deputy Director, Institute of Integrated Catalysis, Pacific Northwest National Laboratory
BIOGRAPHY:
Zdenek Dohnálek is a Laboratory Fellow at the Pacific Northwest National Laboratory, where he also serves as a Deputy Director of the Institute for Integrated Catalysis. He holds a Joint Appointment in the Gene and Linda Voiland School of Chemical Engineering and Bioengineering at Washington State University. His surface science studies focus on fundamental aspects of catalytic reactions for a zero-carbon footprint economy, such as biomass conversion and (CO2) hydrogenation. He employs atomically resolved imaging combined with ensemble-averaged spectroscopies to develop novel synthetic approaches yielding homotopic model catalysts containing supported single metal atoms, monodispersed oxide clusters, and thin films with tailored chemical properties. Such well-defined models are used to achieve detailed, site-specific, molecular-level understanding of the kinetics and dynamics of elemental reaction steps. In collaboration with theory, his experimental studies provide detailed structure-activity relationships that inform the design of future catalysts.
ABSTRACT:
Single-atom catalysis represents an exciting area of research due to the potential to uniquely transform the activity and selectivity of transition metal catalysts. However, our fundamental understanding of their activity and stability under reaction conditions is limited. To address this gap, scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy, and temperature programmed desorption (TPD) is employed together with density functional theory to investigate the effect of reactants on the structure and activity of model Pd–Fe3O4(001) and Rh–Fe3O4(001) single atom catalysts. H2 activation is probed via STM and DFT to show that H2 cleaves heterolytically and H is spilled over onto Fe3O4(001). Conversion of formate (from formic acid), which is one of the key intermediates in CO2 hydrogenation reactions, is used to follow the fate of dehydration and dehydrogenation reaction channels on Rh-Fe3O4(001). Trace amounts of Rh adatoms are found to cause a shift from the dehydration pathway to CO observed on bare Fe3O4(001) to dehydrogenation yielding CO2 on Rhad-Fe3O4(001). Highly unstable Rh adatoms readily convert to highly stable in-surface Rh that displaces iron in octahedral surface sites that are commonly present on high surface area Rh-Fe3O4 catalysts. Rhoct atoms are found to be destabilized by reaction intermediates and transiently form highly active Rhad’s that are present only during the reaction. Studies of hydroxylated surfaces reveal that surface hydroxyls are responsible for Rhoct destabilization. Understanding such dynamic processes is critical for the future design of catalysts with maximum activity and selectivity.