(6lc) Catalyst Design with Atomic Precision for Fuel Gas Processing and Pollution Purification Reactions

Research Interests:

Heterogeneous catalysis is a key enabler in identifying and navigating sustainable energy flow through our fragile ecosystem. For almost a century, the exploration of cost-effective supported metal catalysts is at the heart of both fundamental and industrial catalysis research. In order to allow such a large family of materials to match the elegant and promising chemistry of their corresponding homogeneous catalytic prototypes, perhaps the ultimate design goal of supported metal catalysts is to simultaneously maximize the dispersion of the supported metals and to display desired intrinsic chemistry per supported metal atom. Working towards this design goal presents both daunting tasks and new opportunities.

The emerging topical research area of single-atom catalysis is a subset of these efforts, and I have been very fortunate to participate in the journey of the birth, debate, expansion, and evolution of the single-atom catalysis research under the guidance of Prof. Maria Flytzani-Stephanopoulos at Tufts as a Ph.D candidate and at GM R&D as an independent researcher. Single-atom catalysis dramatically reduces the usage requirements of expensive and rare metals by stabilizing the supported metal atoms in a fully dispersed state as isolated bonded species that serve as active sites on various carrier (support) materials. These single-atom catalytic materials can also serve as appropriate platforms for many fundamental studies, where the detailed electronic structure, coordination condition, adsorption/desorption behavior, and broader scopes of geometry and ligand effects to the supported metal species can now be much more explicitly probed than in many previous heterogenous catalysis systems. My research work has focused on synthesizing, characterizing, and optimizing various supported single-atom catalysts for industrially important reactions, such as the water-gas shift reaction, self-coupling reactions of methanol, alkane and alcohol dehydrogenation, purification of airborne pollutants, and oxygen-reduction reaction in fuel cells. The main contributions are:

1. Unified the once elusive fact that similarly structured single-atom Pt₁- and Au₁-O(OH)_xspecies are the true catalytic centers for the low-temperature water-gas shift reaction on various support oxides, and thus broadened the material choices of making single-atom catalysts;
2. Invented an environmentally benign and facile synthesis route for single-atom-gold oxo-clusters in either supported or unsupported forms to selectively catalyze hydrogen upgrading and methanol self-coupling reactions, and thus bridged the gap between homogeneous and heterogeneous catalysis of the gold-oxo species;
3. Tackled the limitation of lacking neighboring metal atoms and their associated activity in the classic single-atom catalyst system by creating paired Pt-O-Pt ensembles while retaining 100 % metal dispersion. This new group of catalysts finds an alternative pathway for oxygen activation, which leads up to 1000 times higher activity than the Pt₁ single atoms for several emission control reactions.
4. Developed, patented, and licensed technologies of making sinter-resistant precious metal catalysts. The implementation of the commercialized technology grown from fundamental studies leads to about $0.2 billion savings of precious metal per year for General Motors.

The above research output extends across the clean energy generation sector as well as the energy-consumption processes that target zero emissions. The successful experience in these areas creates a foundation to construct my future research framework in designing various supported metal catalysts that aims to unlock new activity and selectivity for the utilization of several key chemical commodities, such as hydrogen, nitrogen, methanol, light olefins, oxygen and water. The new catalysts to be developed will inherit the design philosophy of atomic precision in my previous work. More importantly, I will utilize various single atoms, not necessarily as direct catalytic centers, but as building blocks to subsequently assemble catalytic centers comprising purposefully paired atoms. Understanding how the various support properties respond to these atomic-level changes of the catalytic centers in given reactions will be another important new research domain. Indeed, well-defined multi-atom catalytic species have been discovered on ideal crystal surfaces and under ultrahigh vacuum conditions. With the fast development of single-atom catalysis for practical catalytic reactions, now is the time to bridge these once isolated research areas and to bring the atomically precise multi-atom catalytic species into real-world engineering operations. The above research interests are also well aligned with the following technology focus areas of the nation:

1. Develop new catalytic systems to reduce hazardous molecules and greenhouse gas emissions that are hard to be regulated today;
2. Search for durable and affordable fuel cell catalysts to boost the competitiveness of the H₂-powered zero-emission vehicles;
3. Seek breakthrough catalytic technologies to stimulate the shale gas economy by making value-added products from saturated light alkanes;
4. Develop sustainable catalytic pathways of making renewable fuels by designing inorganic-organic hybrid catalysts that utilize environmentally benign energy input such as heat, photon, electricity, plasma and their combinations.

My independent grant application experience includes the International Precious Metal Institute Student Research Award in 2014 and the Internal Start-Up Research Award by General Motors in 2016. The interdisciplinary catalysis work has also stimulated my collaborations with synchrotron, microscopic and computational modeling experts from national laboratories and universities. I have greatly benefited from these inclusive and collaborative research interactions, and I will continue practicing such a spirit in my research collaborations with future colleagues and friends.

Teaching Interests:

Teaching has been an integral part of my career since 2010. I believe an important mission of education should provide the guidance to help our students become academically competent individuals as well as caring and inclusive human beings.

Besides working as a teaching assistant at Tufts, I have taught as an adjunct faculty in chemistry at South University in Michigan, and have mentored two visiting Ph.D students, three Master students, and three summer-intern students to carry out their research work in my laboratory at General Motors. I help the students, including those from underrepresented groups, cultivate their interest to learn, desire to work hard, and ambition to succeed, which in turn ignites my passion and commitment for higher education. As an extension from the in-class activities, my research work in catalysis serves as a versatile vessel for students to understand and practice their learning in several core courses of chemistry and chemical engineering, such as General Chemistry, Analytical Chemistry, Physical Chemistry, Materials Science, Reaction Engineering, and Transport Phenomena. With the university’s support in the future, I am very interested in sharing my education and research resources in the form of online academic videos and 3D virtual laboratory operation experience. This will also increase the engagement of the STEM field within the community it is serving, and sparkle the interest among the perspective students.

My education background in both chemistry and chemical engineering and work experience in both academia and industry have prepared me as a future educator who embraces diversity and equity. Conveying these values to our students is another critical mission of higher education. As the serving president of the Michigan Catalysis Society, where many college and graduate students gather at the monthly technical seminars, I have been taking initiatives to advocate emerging research domains and achievements from early-career professors, women scientists, and industrial researchers. These events, along with the associated social media channels, have become an important venue for new generations of students to find career role models in their field of research, as well as to celebrate and appreciate research findings from diverse fields.

Selected Publications:

Corresponding-Author Research Reports

1. “Surpassing the single-atom catalytic activity limit through paired Pt-O-Pt ensemble built from isolated Pt₁ atoms”, Nature Communications 2019, 10: 3808.
2. “Single-site Pt/La-Al₂O₃stabilized by barium as an active and stable catalyst in purifying CO and C₃H₆ emissions”, Applied Catalysis B: Environmental 2019, 244, 327.

First-Author Research Reports

3. “Single-atom-gold oxo-clusters prepared in alkaline solutions catalyze the heterogeneous methanol self-coupling reaction”, Nature Chemistry, In Press.
4. “A common single-site Pt(II)-O(OH)_x- species stabilized by sodium on active and inert supports catalyzes the water-gas shift reaction”, Journal of the American Chemical Society 2015, 137, 3470.
5. “Catalytically active Au-O(OH)_x- species stabilized by alkali ions on zeolites and mesoporous oxides”, Science 2014, 346, 1498.
6. “Atomically dispersed Au-(OH)_x species bound on titania catalyze the low-temperature water-gas shift reaction”, Journal of the American Chemical Society 2013, 135, 3768.
7. “Effects of CO₂ and steam on Ba/Ce-based NO_x storage reduction catalysts during lean aging”, Journal of Catalysis 2010, 271, 228.
8. “Pd-support interaction-defined selective redox activities in Pd−Ce₇Zr_0.3O₂−Al₂O₃ model three-way catalysts”, Journal of Physical Chemistry C 2009, 113, 12778.

Keynote Talks

9. Aftertreatment PGM Catalysts with Atomic Precision for Optimal Reaction Efficiency, 2018 CLEERS Workshop, 9/18/2018.
10. Atomically Dispersed Precious Metal Species on Various Oxide Supports for Catalytic Hydrogen Upgrading and Emission Control, Microscopy and Microanalysis 2016 Meeting, 07/27/2016.