(4hg) Tailoring Active Centers on Surfaces and within Confined Spaces to Build Structure-Function Relationships through Kinetic and Spectroscopic Assessments

Rachel received her B.S. in Chemical Engineering from Rutgers University (summa cum laude) in May 2018 and earned her Ph.D. in Chemical and Biological Engineering from Princeton University in May 2024 working in Prof. Michele L. Sarazen’s group. Her Ph.D. dissertation is titled “Adsorption, reactivity, and deactivation mechanisms on metal-organic framework catalysts and sorbents”, which was recognized by the Jui Dasgupta Outstanding Dissertation Award. To date, her work has culminated in 6 first-author publications, 1 second-author publication, and over 50 presentations at regional, national, and international conferences. She also serves as the webmaster for the Catalysis Society of Metropolitan New York. Currently, she is a postdoctoral research fellow in Prof. Eranda Nikolla’s group at the University of Michigan where she is investigating mixed-metal oxides for atom efficient C₁ valorization to chemicals and fuels.

Research Interests

There is a long history and a rich diversity in the composition and properties of catalytic materials with active centers tailored to meet the demands of a given chemical transformation. Due to advances in chemical synthesis methods, analytical methods and spectroscopies, and computational architectures, modern catalyst structures have become more complex with the emergence of young material classes, like metal-organic frameworks (MOFs) or biomimetic metal complexes. Despite the influx of novel materials and the availability of material property modulation through synthetic means, insights into how intrinsic active center properties dictate catalyst performance metrics (reactivity, selectivity, stability) in these newer materials are scarce. This scarcity hinders future informed design efforts towards more efficient catalyst materials and therefore, my group will seek to understand how metal activity can be systematically controlled by designing the first coordination sphere for surfaces and the second coordination sphere (or higher) within confined spaces.

• Research topic 1: Nanoporous, flexible metal-organic frameworks for shape-selective oxygenate conversions

Selective oxidations are central to modern chemical processes and are sensitive to the chemical environment of active metal centers. While solvation in differing liquid media has been shown to impact product distributions based on the prevalence of non-covalent interactions, solvation within a solid with pores of molecular dimension can be more synthetically limited based on the availability of structure-directing agents. However, MOF architectures are modular through the design of their metal node and organic ligand identities and confer the ability to change metal or ligand species at synthesis inception or post-synthetically. Further, some MOF structures have demonstrated dynamic “breathing” behavior where the pore apertures expand/contract based on the identity of a pore-filling species. Here, we seek to delineate how metal/linker identities within a dynamic pore sensitive to the reaction media composition influence product selectivities and build a molecular-scale understanding of active site turnovers throughout the catalyst life cycle. The insights built from this project will inform the future design of catalysts for a broad portfolio of oxidation chemistries.

• Research topic 2: Transition-metal carbide structures for light hydrocarbon and oxygenate valorization

While MOF catalysts have shown notable reactivity and selectivity for a wide range of chemical transformations at mild reaction conditions, they are not thermochemically stable at higher temperatures and pressures. However, their tunability and unique structures and compositions still make them promising as catalyst precursor materials. By varying pyrolysis conditions, the rate of metal node migration to form metal clusters of different sizes can be controlled and depending on pyrolysis temperature, different metal, oxide, or carbide/nitride phases can be attained. Tuning the initial arrangement and composition of metals dispersed throughout the MOF framework has the potential to grant access to controlled synthesis of metal carbides with differing metals, phases, oxidation states, and particle size which are vital in governing reactivity and stability under reaction conditions.

• Research topic 3: Mixed-metal oxides for biomass upgrading

Mixed-metal oxides are ubiquitous in a wide range of catalytic industrial processes, especially those involving selective oxidative steps. Amongst mixed-metal oxides, perovskite and perovskite-like materials have well-defined crystal structures that make them amenable for mechanistic investigation. Compositional modularity allows diversity in physicochemical properties including acidity, basicity, oxophilicity, and redox nature that are important in controlling activity for many organic transformations. Through this project, we aim to investigate the impact of mixed-metal oxide composition on relevant physicochemical properties that determine catalyst activity descriptors for biomass conversions to useful fuels and chemicals.

Through almost 10 years of research experience working on supported metal nanoparticle and oxide catalysts for alkane dehydrogenation and methane steam reforming (Celik group), MOF oxidation catalysts and CO₂ adsorbents (Sarazen group), and mixed-metal oxide catalysts for oxidative methane coupling (Nikolla group), I have built a skill and knowledge toolbox based in rigorous microscopic, spectroscopic, and kinetic experimentalization across many reactor and catalyst designs that will enable me to guide my own independent career. Additionally, I intend to extend my dedication to mentorship and service over the years to encourage and support my own students in education, research, and in their career goals.

Teaching Interests

My teaching philosophy is centered on the idea that a teacher is more than a distributor of knowledge; instead, a teacher should serve as a guide and mentor in an inclusive, equitable, student-centric environment. Student identity is paramount in this framework and is a key consideration in how I approach each unique class and teaching setting. Students learn in diverse ways, which requires the teacher to provide stimulating and enriching environments that promote both educational and personal growth. I understand that students come from different socioeconomic and cultural backgrounds, so I frequently employ various teaching styles that depend on student feedback to address varying modalities of learning. For example, during my first interaction with my students, I ask their preferred learning styles (visual, hands-on, auditory, etc.) and consider their post-college aspirations so that I can adapt my teaching style to each student effectively. Through teaching, research, and mentorship, I am dedicated to supporting my students in their short-term (and long-term) goals with an aim to instill a sense of curiosity and efficacy in every student to encourage confidence to innovate and succeed in their future career paths.

My dedication to teaching has colored most of my educational career, extending from my high school years until the present. Most recently at Princeton, I served as a mentor in research for 8 students, spanning from high school seniors to senior undergraduates, with 5 as co-authors on 2 publications. In the classroom, I have been an Assistant in Instruction for CBE’s Core Laboratory class (CBE 346) in 2020, 2022, and 2023. Here, I was responsible for giving the main lecture on Simulink (a simulation package used to model multidimensional processes), as well as guiding students on various experiments (process (mixing, level, temperature) control, distillation, reaction kinetics), enforcing safety practices, and grading laboratory notebooks and prelab reports. Additionally, I aided the faculty instructional team in implementing changes to student manuals each year based on student feedback and in testing and proposing experimental alterations to enrich pedagogical value. During my independent career, I aim to integrate current industrial process or open research topic examples to enrich student understanding of core chemical engineering principles and reiterate their importance in modern contexts. Additionally, I would like to develop a course on green chemistry and engineering principles with a focus on the evolution of industrial heterogeneous catalysts and current sustainability efforts. Throughout my experiences inside and outside of the classroom, I have developed a wealth of tools and approaches that I intend to utilize and build upon to become a more effective teacher, committed to student success.

Select publications

1. Yang, R.A.; Hughes, S.N.; Cho, S.; and Sarazen, M.L. Implications of defect density for CO₂ capture on amine-functionalized MIL-101(Cr). ChemSusChem 2024, e202400249.
2. Yang, R.A. and Sarazen, M.L. Coupling deviations in local structure to long-range functionality in MOF materials. Catalysis 2023. 3, 100576.
3. Contributor to Addressing Rigor and Reproducibility in Thermal, Heterogeneous Catalysis. 2023. https://doi.org/10.5281/zenodo.8029159.
4. Yang, R.A.; Ganza, D.R.; Jiang, E.; Vandermel, J.A.; Sarazen, M.L. Solvent stabilization of branched aminopolymer/UiO-67(Zr) composite materials for CO₂ Mater. Adv. 2023. 4, 901.
5. Yang, R.A.; Moore, S.C.; Smith, M.R.; Trettin, J.L.; and Sarazen, M.L. Kinetic Impacts of Defect Sites in Metal-Organic Framework Catalysts under Varied Driving Forces. ACS Energy Lett. 2023.8,
6. Yang, R.A. and Sarazen, M.L. Mechanistic impacts of metal site and solvent identities for alkene oxidation over carboxylate Fe and Cr metal-organic frameworks. ACS Catal. 2022.12,
7. Yang, R.A. and Sarazen, M.L. Reaction pathways and deactivation mechanisms of isostructural Cr and Fe MIL-101 during liquid-phase styrene oxidation by hydrogen peroxide. Sci. Technol 2021.11, 5282.
8. Pennington, A.M.; Yang, R.A.; Munoz, D.T.; Traeger, S.M.; Celik, F.E. Photocatalytic Methane Steam Reforming over Defect-Rich Anatase TiO₂. J. Hydrogen Energy. 2018, 43, 15176.
9. Yang, R.A.; Darmon, J.M.; Chirik, P.J.; Sarazen, M.L. Catalytic implications of pore structure, nodal identity, and coordination environment on alkene oxidation by hydrogen peroxide over metal-organic frameworks. In preparation.
10. Hullfish, C.W.; Yang, R.A.; Sarazen, M.L. Insights into liquid-phase titration of Pd surfaces. In preparation.