(3fv) Catalyzing Sustainable Chemistry with External Stimuli and Single-Atoms

Manish Shetty (PhD, Massachusetts Institute of Technology) – University of Minnesota

The imbalances in the carbon and nitrogen cycles concomitant with rampant industrialization have led to sustainability challenges that on a broader scale require new technological chemical solutions. A key strategy in mitigating and eliminating the imbalances is the utilization of a circular and distributed economy. The crucial steps in realizing the strategy are: (a) utilizing available abundant reactants such as N₂, CH₄, and biomass close to the source and/or the end-user, (b) converting harmful environmental pollutants such as nitrogenates and sulfides to environmentally benign molecules, and (c) upcycling and recycling of end-use products such as polymers with high reactivities and selectivities.

A number of challenges exist in realizing these goals including: (a) the properties of the feedstocks (e.g., biomass, CO₂ or CH₄) that are different than end-products (e.g., gasoline and olefins), (b) current catalysts and processes that are optimized for harsh conditions (e.g., pressure > 100 bar and temperature > 300^oC), and (c) low reactivities and selectivities under mild conditions (near ambient pressures and low temperatures) that are required for effective, safe and distributed deployment of catalytic technologies. To address these challenges, fundamentally different catalytic processes need to be developed that upgrade diverse feedstocks under mild conditions with high selectivity and reactivity. The central theme of my research is the development of next generation catalytic technology for chemical conversion that helps realize the goal of a circular and distributed economy.

The main roadblock in achieving high catalytic rates is the existence of a theoretical maximum rate constrained by the Sabatier principle. In addition, the existence of competing pathways along the reaction pathway lead to kinetically and thermodynamically favorable side products. To this end, both external stimuli (e.g., electric field, magnetic field and strain) and synthetic tools can be used to tune the electronic properties and tailor reactivity that include both rates and selectivity. External stimuli such as electric fields provide for an increase in reaction rates by up to two or three orders of magnitude [1] over the Sabatier maximum and modulate reaction pathways [2]. The synthesis of metal-oxide interfaces including single atom catalysts (SACs) provide for unique properties that tune the formation of desired products from small molecule chemical conversions such as CO₂ hydrogenation or CH₄ oxidation (thermal and electrochemical). This is achieved through the stabilization of desired intermediates and prevention of catalyst poisoning (e.g., CO on Pt [3]). Such interfaces also provide for sites that show facile C-N, C-O, and C-C cleavage required for removal of environmental pollutants including aromatic nitrogenates and oxygenates, and recycling of plastics [4].

Research in my group will aim to solve the practical challenges in catalyst design and engineering using external stimuli (electric field, magnetic field and strain) and metal-oxide interfaces on single-atom catalysts (SACs). The tools developed through the research will help in furthering the understanding of, and deliver insights and new technology for chemical transformations involving the valorization of carbon dioxide, methane and biomass, and removal of heteroatoms emanating from the conventional fossil fuel streams for pollution abatement.

Approach and Experience

My approach utilizes a combinatorial approach with a strong focus on characterization, kinetics and theory that rationalizes and increases the speed of tunable catalyst design and engineering. The insights developed can then be utilized towards meticulous catalyst design that delivers tunable functionality desirable for specific chemical transformation. In addition, such an approach will be used to identify and deploy novel and transformative next generation catalytic technologies.

My research has focused on the development of structure-activity relationships for inorganic metal and metal oxide catalysts and investigation of the effects of external stimuli such as electric field on reaction rate and selectivities. To this end, I have utilized synthetic methods, extensive in-situ and ex-situ characterization techniques (e.g., XPS, IR, PXRD), measurement of chemical kinetics and/or atomic-scale molecular modeling (e.g., density functional theory) to make, tune and investigate electronic and spatial properties relevant for tailored chemical conversions. Examples of my previous work, that utilize these approaches, are as follows:

Postdoctoral Projects

• “Electric-field Assisted Catalysis” under the supervision of Prof. Paul Dauenhauer, Department of Chemical Engineering and Materials Science, University of Minnesota.
  • Density functional theory computations to investigate the tuning of surface thermochemistry through electric fields [2].
• “Structural and Solvent Effects towards Rate Enhancement inside Zeolite Confinements” under the supervision of Prof. Johannes Lercher, Pacific Northwest National Laboratory (PNNL).
  • Elucidation of structural factors influencing enthalpic and entropic contributions towards the rate-enhancement inside zeolite confinements [7]

PhD Dissertation

• “Catalytic Upgrading of Biomass through the Hydrodeoxygenation (HDO) of Bio-oil Derived Model Compounds” under the supervision of Prof. Yuriy Román-Leshkov and Prof. William H. Green, Department of Chemical Engineering, Massachusetts Institute of Technology.
  • Synthesis of earth-abundant transition metal oxides, supported on inorganic oxides and encapsulated inside zeolite confinements for tailored conversion of biomass-derived oxygenates to fuel precursors [5, 6].
  • In-situ and ex-situ characterization to investigate metal-metal oxide interfaces on cobalt oxide catalysts that show facile and selective C-C, C-N and C-O bond cleavage [4]

Teaching Interests

My experience in teaching core undergraduate and graduate classes, and individual coaching has helped inform my ideas on teaching. My first experience in teaching was a teaching assistantship at the Indian Institute of Technology Bombay for Analysis of Transport Phenomena and Fluid Mechanics for a semester each in my final year. My later teaching experience was as a teaching assistant at the Massachusetts Institute of Technology (MIT) for graduate Thermodynamics.

Course Preferences: I am qualified to teach any course in chemical engineering, but my preference is for Introductory Chemical Engineering. Among the core classes, I would prefer to teach Chemical Thermodynamics and Reaction Kinetics. In addition, I am also qualified to teach chemical process design and/or engineering laboratory class.

Course Development: I am in the process of developing an advanced course on chemical kinetics and catalysis. This course will equip the graduate and undergraduate students with the fundamentals to perform research in their academic and computational labs. This course will include the analysis of complex reaction networks including the use of microkinetic modeling (MKM), transition-state theory (TST) approaches for quantitative understanding of the transition state of reactions, introduction on the spectroscopic and quantum chemical computational approaches to study active sites and electronic structure of the catalysts under reaction conditions.

This course will involve hands-on computational methods to model heterogeneous catalytic systems using Matlab to simulate the reaction system and integrate them to reactor process and design with the aid of available software packages such as Cantera. In addition, electronic structure software packages such as Gaussian and Vienna Ab Initio Simulation Package (VASP) will be used to computationally evaluate surface thermochemistry and energetics of typical reactions.

Selected Publications

1. M. A. Ardagh, M. Shetty, A. Kuznetsov, Q. Zhang, P. Christopher, D.G. Vlachos, O.A. Abdelrahman & P.J. Dauenhauer (2020). Catalytic Resonance Theory: Parallel Reaction Pathway Control. Chemical Science, 11, 3501-3510.
2. M. Shetty, M.A. Ardagh, Y. Pang, O.A. Abdelrahman & P. J. Dauenhauer (2020). Electric field assisted modulation of surface thermochemistry. ChemRxiv, doi.org/10.26434/chemrxiv.12127191.v1. Under revision in ACS Catalysis.
3. J. Gopeesingh, M.A. Ardagh, M. Shetty, S. Burke, P.J. Dauenhauer & O.A. Abdelrahman (2020). Resonance-Promoted Formic Acid Oxidation via Dynamic Electrocatalytic Modulation. ChemRxiv, doi.org/10.26434/chemrxiv.11972031.v1. Under revision in ACS Catalysis.
4. M. Shetty, D. Zanchet, W.H. Green & Y. Román-Leshkov (2019). Cooperative Co(0)/Co(II) sites stabilized by perovskite matrix enable selective C-O and C-C hydrogenolysis of oxygenated arenes. ChemSusChem, 12, 2171-2175.
5. M. Shetty, K. Murugappan, T. Prasomsri, W.H. Green, & Y. Román-Leshkov (2015). Reactivity and stability investigation of supported molybdenum oxide catalysts for the hydrodeoxygenation of m-cresol. Journal of Catalysis, 331, 86-97.
6. T. Iida, M. Shetty, K, Murugappan, Z. Wang, K. Ohara, T. Wakihara & Y. Román-Leshkov (2017). Encapsulation of molybdenum carbide nanoclusters inside zeolite micropores enables synergistic bifunctional catalysis for anisole hydrodeoxygenation. ACS Catalysis, 7, 8147–8151.
7. M. Shetty, H. Wang, F. Chen, N. Jaegers, D.M. Camaioni, O. Y. Gutierrez, J. A. Lercher (2020). Organization of alkanols in nanoscopic confinements directs the rate enhancement for the hydronium catalyzed dehydration. Under review in Angewandte Chemie.