Time：March 18th, 2019, 3:00-5:00 pm
Venue：Conference Room on the First Floor, Energy Building A
Lecturer：Prof. Michael J. Janik, The Pennsylvania State University
Designing selective metal catalysts is challenged by identifying the active site in a heterogeneous distribution of local structures and compositions. Site isolated catalysts can help to define active site requirements for a given reaction by exposing a single active site composed of a controlled number of metal atoms in a specific arrangement. This talk will discuss our collaborative theory and experimental work (with the Rioux group at Penn State) to use intermetallic structures to design selective hydrogenation catalysts. Intermetallic compounds can isolate a small number of active atoms in an inert matrix of a second metal, with long range periodic atomic order and resistance to surface segregation. We have identified the Pd-Zn γ-brass phase as a starting point to study the catalytic effect of active site nuclearity, a key parameter in selective catalyst design. The prototypical Pd8Zn44 structure contains only isolated Pd atoms, but as the Pd concentration is increased by Zn substitution (Pd8+xZn44-x, x=1-3), a fixed number of Pd-Pd-Pd trimers are formed. Density functional theory calculations were used to establish the structure of these trimer sites on the surface, and predict that these sites will be active for acetylene hydrogenation but inactive to ethylene hydrogen. To prove this transition from monomer to trimer sites is catalytically impactful, H-D exchange and ethylene hydrogenation are used as probe reactions. The reaction kinetics of Pd8Zn44 for both reactions are distinct from the other Pd-Zn catalysts and this discrepancy is consistent with first principle calculations on model monomer and trimer Pd sites. The trimer containing Pd9Zn43 and Pd10Zn42 have ~1000 times higher activity compared to trimer-free Pd8Zn44, but the latter leads to net ethylene gain by only semi-hydrogenating acetylene, consistent with theoretical predictions. The Pd-Zn γ-brass phase also provides flexibility in modifying the composition of the active sites through incorporation of a third metal (Pt, Ni, Au or Ag). Rietveld refinement and DFT calculations suggest that Ni group elements form Pd-Pd-M clusters while Cu group elements can form Pd-M’-Pd clusters. Several Pd-M alloys involving these metals (notably Au, Cu and Ag) are known to be selective hydrogenation catalysts. We further share DFT predictions and microkinetic modeling towards designing active catalysts for alkene hydrogenation in the presence of aromatics.
Dr. Janik is a Professor of Chemical Engineering at Pennsylvania State University. His research interests are in the use of computational methods to understand and design materials for alternative energy conversion systems. Current activities address a wide-range of energy technologies including fuel cells and electrolysis, heterogeneous catalysis, and organic electronics. Research methods emphasize atomistic simulation using quantum chemical methods and kinetic modeling. Janik is affiliated with the Penn State Energy Institute, PSU-Dalian University of Technology Joint Center for Energy Research, the PSU Institutes of Energy and the Environment, and the Battery and Energy Storage Technology Center. He also holds the title of Visiting Professor at Dalian University of Technology. The Janik group currently includes 8 graduate students, 5 undergraduate students, and 2 post-doctoral research associates. Dr. Janik is also the Undergraduate Program Coordinator for the Chemical Engineering Department. Dr. Janik received his B. S. in Chemical Engineering from Yale University and his Ph.D. degree at the University of Virginia. He has co-authored approximately 150 papers, and co-edited the book “Computational Catalysis” (with Aravind Asthagiri), published by the Royal Society of Chemistry in 2013.
Contact: ZHANG Xiaochen, DNL0603