Maria Flytzani Stephanopoulos

Distinguished Professor and the Robert and Marcy Haber Endowed Professor

Dept. of Chemical and Biological ENgineering
Tufts University
Medford, MA

 

 

Dr. Flytzani-Stephanopoulos is a Distinguished Professor and the Robert and Marcy Haber Endowed Professor in Energy Sustainability in the School of Engineering at Tufts University. She directs the Tufts Nano Catalysis and Energy Laboratory, which investigates new catalyst materials for the production of hydrogen and green chemicals. Pioneering work from her lab has demonstrated the use of single atom heterogeneous catalysts for several reactions of interest to fuels and chemicals processing. These catalysts with 100% atomic efficiency of precious metals and high selectivity to the desired product will enable more efficient and sustainable chemical process development. Dr. Flytzani-Stephanopoulos joined the Chemical Engineering faculty at Tufts in 1994. She holds ten patents and has written more than 170 technical papers. She has been an editor of the journal Applied Catalysis B: Environmental since 2002, and is an associate editor of Science Advances. She is the recipient of many awards and distinctions, including the Tufts Distinguished Scholar award, the Henry J. Albert award of the International Precious Metals Institute, the Giuseppe Parravano Memorial award of the Michigan Catalysis Society, the Graduate Teaching and Mentoring Award of the Tufts School of Engineering, and the Carol Tyler award of the IPMI. She holds Honorary Professorships at Tianjin University and the Beijing University of Chemical Technology, is a Fellow of the AAAS and the AIChE, and a member of the US National Academy of Engineering.

Lecture 1: The Changing Landscape of Heterogeneous Catalysts: Single Metal Atoms as Game-Changers
Tuesday, Oct. 23, 2018
Reception at 3:30 p.m., Cheney Room/1413 Engineering Hall
Lecture at 4:00 p.m., 1610 Engineering Hall

Lecture 2: Design of Single Atom Metal Catalysts on Various Supports
Wednesday, Oct. 24, 2018
Reception at 3:30 p.m., Cheney Room/1413 Engineering Hall
Lecture at 4:00 p.m., 1610 Engineering Hall

Lecture 1 abstract
 The Changing Landscape of Heterogeneous Catalysts: Single Metal Atoms as Game-Changers
Novel catalyst designs aiming at the development of energy-efficient, low-cost and sustainable processes are of great interest for applications to fuels and chemicals production, and to environmental pollution abatement. Identification of the active catalytic site and design of catalysts with 100% atom efficiency has been a long-standing goal in heterogeneous catalysis. A promising approach to reaching this goal through the controlled preparation of isolated single-atom heterogeneous catalysts has emerged in the recent literature. For catalytic metals, atomic dispersion affords better utilization, different (often better) selectivity than the extended metal, and new prospects for low-cost and green process development. Isolated supported metal atoms may be viewed as species bonded to a support, the latter serving as a ligand. An analogy between a homogeneous and a heterogeneous single-site catalytic center can thus be made. Single atom sites catalyze some, but not all reactions. It is crucial to understand the mechanisms behind catalysis by single atoms, as this will guide the new, improved catalyst designs. In this presentation, suitably stabilized catalytic sites as single metal atoms/cations on various supports will be showcased drawing examples from a variety of reactions, including the low-temperature water-gas shift reactions; methanol and ethanol dehydrogenation and steam reforming reactions; the direct methane conversion to oxygenates; and selective hydrogenation reactions on single-atom alloys. Reaction mechanisms involving single metal atoms/cations often transcend support structure and composition, thus allowing flexibility in the choice of the support. A unique “signature” of the metal (Au, Pt, Pd, Ni, etc.) at the atomic state is preserved, distinct however from the corresponding extended metal catalyst. Novel synthesis methods will be discussed as will be the stability of single-atom metal catalysts in various supports and reaction environments.

We describe three major trends in Process Systems Engineering that have emerged over the last decade and that can potentially help the industry to innovate and to remain competitive. First, we describe efforts for simultaneous product and process design, where the emphasis lies in tying the molecular structure of the products with the processing and macroscopic properties of the product. Second, we describe work that is aimed at modeling and optimizing processes for effectively exploiting fossil fuels like shale gas and alternative sources like biomass. We also address the issue of efficiently managing natural resources such as water. Third, we describe research efforts in enterprise-wide optimization that are aimed at designing and operating supply chains for the process industry in which planning, scheduling and control can be integrated more effectively. We conclude that Process Systems Engineering is broadening its scope in order to address problems that are of current and future interest.

Lecture 2 abstract
 Lecture 2: Design of Single Atom Metal Catalysts on Various Supports
Atomically dispersed supported metal catalysts offer new prospects for low-cost, highly efficient energy and chemicals production. In this presentation, the design of single-atom metal catalysts for the low-temperature water-gas shift, methanol and ethanol dehydrogenation reactions will be highlighted. Using oxide as well as metal hosts to stabilize the single atoms affords the use of such materials as probe catalysts to investigate mechanistically a variety of reactions. On the practical side, the considerable cost savings for precious metals, such as Pt, Pd, Rh, Ir used in atomic dispersions should not be overlooked, as these metals become scarcer and more expensive over time.

In our work, we investigate gold and platinum, atomically dispersed on various oxide supports, as catalysts for the low-temperature WGS reaction. Single-site [Au-Ox]- and [Pt-Ox]- species have emerged as the active sites for this reaction on any oxide support. Stabilization of the atomic species is easier on a reducible oxide support (CeOx, FeOx, TiOx), but can also be achieved on inert supports by the addition of alkali metals (cations). The reaction pathway is common (specific to the active metal atom) on any support and does not change with the alkali addition. The support thus serves as a carrier of the active single-atom centers. The distinguishing feature appears to be the type and number of anchoring points on each oxide surface. Metal clusters and nanoparticles, if present on the support, are spectator species and do not affect the activity of the isolated single-atom sites. Interestingly, we have reported identical findings for the steam reforming of methanol, and the dry methanol and ethanol dehydrogenation reactions to specific products; methyl formate and acetaldehyde, respectively. The latter reactions can also be catalyzed by a new class of single-site heterogeneous catalysts, namely Single-Atom Alloys that comprise catalytically active elements like Pt, Pd and Ni alloyed in a more inert host metal like Cu, Au or Ag at the single-atom limit. Single-atom alloys offer a unique approach towards rational catalyst design, one that combines surface science, catalysis and theory in a most efficient way. Model surfaces and nanoparticles that can host isolated atoms in the surface layers behave similarly in escaping the linear scaling relationships and allowing for the rational fine-tuning of activity and selectivity. Good stability is imparted by the strong metal-metal bonds between the host and the minority metal, and atomic dispersion can be maintained at high temperatures. Resistance to CO poisoning and to coking are additional advantages of these promising materials, as will be shown in the presentation drawing examples from alkyne hydrogenation and alkane dehydrogenation.