(2gf) Programmable Catalysts: Condensing Charges & Defect and Atom By Atom Engineering

Research Interests:

Programmable Catalysts: Condensing Charges & Defect and Atom by Atom Engineering

Advancement in heterogeneous catalysis is essential in solving global sustainability-related problems such as reducing emissions, repurposing plastic, valorizing biomass, and more. My primary research interest is to explore rational design of programmable catalytic materials that (1) can take advantage of catalyst-promoter interactions for tunable chemical properties and (2) that can utilize stimuli such as photons or electrical forces to modulate rate or selectivity. First, rational designs achieved by atomic engineering of non-metals and metals on an inert support material will enable a more holistic study of metal-support interactions/ structure-function relationships/ mechanism and a more consistent extraction of physical parameters (e.g., binding energy, activation energy, turnover frequency). Chemical properties such as ‘oxidative/ reductive’ potential for reactions such as hydrogenation, hydrodeoxygenation, etc. can be tuned by supporting metals on complex mixed oxides/nitrides (perovskites, solid solutions, super acids etc.) with different ‘reducibility’ made by varying compositions or introducing defects and vacancies.^1,2 Finally, introducing conductive thin films (graphene) on supported materials will enable charge density manipulation of active sites; this will reprogram them to affect activity and selectivity for thermal reactions.^3,4 Unlike typical electrochemical processes, which relies on ion transport through a liquid/gel electrolyte, my approach will utilize electrons condensed on a solid thermocatalytic capacitor (aka “a catalytic condenser”) that can carry out gas and/or liquid phase reactions at higher temperatures (T > 200 deg C).³ Since electrons have a higher charge mobility, the response to varying charges on the condenser devices will also be faster. As with every active site that are known to be dynamic in nature, operando and in-situ characterizations (such as XPS, Raman, or IR) while under reaction conditions will be utilized to study interactions of adsorbates and active sites, various metal-support interactions/phenomena, and more. Other avenues to pursue are the electro-mechano-stability of these dynamic electro-thermal-catalysts and to increase the surface area of these materials for scalability and real-world application.

Key word: Heterogeneous catalyst, electro-thermal-catalyst, atomic layer deposition, 2D films, atom-by-atom addition, charge modulation, catalyst stability, high surface area, kinetics.

1. Postdoctoral Research: Programmable Electro-catalyst with Graphene and Thin Films

(University of Minnesota – Twin Cities, 2021-Present; Advisor: Paul J. Dauenhauer)

Manipulation of electron density of catalytically active sites is known to enable regulation of surface chemistry for improved rate and selectivity to desired products. Combining the concepts from metal-oxide-semiconductor field-effect transistors and heterogeneous catalysts, we successfully fabricated a thermocatalytic capacitor (or catalytic condenser) platform that allows for voltage modulation to affect the catalytic rate and selectivity. This concept platform relies on a high-k dielectric layer and 2D monolayer graphene to accumulate or deplete charge from the active sites of the catalyst. Two case studies (metals and oxides) were investigated thoroughly. In the first study of 2-propanol dehydration, alumina (amorphous-Al₂O₃), the model catalyst for this reaction, was synthesized on the catalytic condenser by Atomic Layer Deposition (ALD). Unlike bulk alumina, which is an insulator (band gap of 9.9 eV), this thin film am-Al₂O₃ made by ALD with a shorter band gap ~4 eV, acted much like a ‘poor insulator’ or a defective semiconductor, allowing charge to pass through. Voltage modulation on rates of these devices were then demonstrated using a voltage-biased temperature programmed surface reaction (v-TPSR) on a customized vacuum-based reactor. Similarly, this effect was demonstrated on a metal Platinum-based condenser. Application of voltages shifted the binding energy of CO adsorbate on the Pt active sites by as much as 20 kJ/mol. Future studies from the group will take advantage of the rapid response and electronic control that can be achieved with these catalytic condenser devices.

2. Industry Process and R&D: Thin Film and Planarization (Intel Corporation, 2018-2021)

Area: Planarization of Metal Films by Selective Chemical Etching

Node: 7-nm and 5-nm process.

3. Ph.D. Research: Preparation of Active and Stable High-Surface Area Catalysts by ALD

(University of Pennsylvania, 2013-2017; Advisor: Raymond Gorte)

Deactivation of functional oxides through the loss of surface area is a major concern in heterogenous catalysis especially in the field of emissions control which involve high temperatures and extreme redox conditions. The conventional approach to maintain high surface area materials is to incorporate them onto a support which is less susceptible to sintering. However, these approaches tend to introduce large crystallites (~100 nm) and often do not improve the surface area of the functional material. To address this issue, we adopted and modified Atomic Layer Deposition (ALD) to engineer the surface of a high surface area support in a layer-by-layer manner with exceptional compositional control. However, since ALD was developed in the semiconductor industry to fabricate films as quickly as possible, there were some critical limitations that had to be considered and addressed prior to utilizing this process. My Ph.D. work centered on preparation of heterogeneous catalysts by a modified ALD process, which avoided these issues to prepare high-surface area active powder supports for metal nanoparticles such as the ‘intelligent’ (Pd on perovskite-film LaFeO₃) catalysts that exhibited excellent regeneration capability and resilience to coking and sintering. Pd metals supported on these oxides were used to study high temperature oxidation of methane emissions and industrial processes such as water-gas-shift and steam reforming.

Teaching Interests:

Teaching and mentoring have always been a major part of my career. Even after graduate school, while I was working, I continue to volunteer my weekends and nights to tutor math (ranging from elementary math, pre-algebra to even the SAT) for children in need. I was very fortunate to have good mentors and good teachers as role models. As naïve and cliché as it may sound, my goal in academia is to share what I know and to improve student’s understanding of topics to better help them solve problems in the future. In graduate school, I had the privilege to work with Prof. Warren Seider as his teaching assistant for Process Design and Control. The department also gave me this unique opportunity to create and provide a two-week introductory course on Mass and Energy balances for students who had never taken any engineering classes but decided to switch into the major late during their sophomore year. My mentor, Ray Gorte, also gave me several opportunities to lecture for his course on Heterogeneous Catalysis. While I was an undergraduate student at Hopkins, I was also active in teaching, having served as a teaching assistant for two courses, Chem. Eng. Data modeling and Mass & Energy balances, and as a tutor in Thermodynamics at the university’s learning center. Reflecting, as I write this, it seems that my passion for teaching has sunk its roots deep early on though it was never my intention at that time. If given the opportunity, as a faculty member, I will be excited to teach any Chemical Engineering courses, with slight inclination towards Thermodynamics and Process Control. If possible, I am also eager to develop new courses such as Nanotechnology and Heterogeneous Catalysis, or an introductory course on current trends in sustainable energy and major challenges. These courses serve two purposes. The introductory course would aim to inspire new students and to expose them to the challenges ahead, while the other course would serve to arm them with the knowledge to tackle these problems. In the laboratory, I was fortunate enough to be a mentor to many amazing undergraduate and graduate students. I pledge that the development of students in research will be an important focus throughout my career as a faculty member.

Selected Publications:

1. “Smart Pd Catalyst with Improved Thermal Stability Supported on LaFeO₃ prepared by ALD.” JACS, 2018. Onn TM, Monai M, Dai S, Graham GW, Pan X, Fornasiero P and Gorte RJ.
2. “Improved Thermal Stability and Methane-Oxidation Activity of Pd/Al₂O₃ by ALD of ZrO₂.”ACS Catalysis, 2015. Onn TM, S Zhang, Arroyo L, Chung YC, Graham GW, Pan X and Gorte RJ.
3. “Alumina Graphene Catalytic Condenser for Programmable Solid Acids.” JACS Au, 2022. Onn TM, et al. Neurock M, Abdelrahman O, Frisbie C D, Dauenhauer PJ.