(4au) Developing Intelligent High Surface Area Catalysts with Atomic Layer Deposition

Research Interests

It is well-established that metals­ and oxides play an important role in heterogenous catalysis by improving rates and selectivity. At the atomic level, these solid catalysts participate directly or indirectly through interactions of its surface sites with the reactants. With advances in characterization techniques, structural variations, metal-support interactions, and environmental stimuli were found to have some influences. Understanding these complexities, though has remained challenging, has provided some glimpse to better define the problem statements in designing practical catalysts. This is the motivation for many materials catalysts research in addition to our commitment to address the current serious environmental issues. However, conventional methods to prepare solid catalysts have several limitations, as will be discussed below. An interesting approach to better engineer materials is to adopt processes that can offer atom by atom construction with excellent composition control. It is important that we recognize that the life and activity of catalysts is in the details (of their structure).

Ph.D. Research: Preparation of Active and Stable High-Surface Area Catalysts by ALD
(University of Pennsylvania, 2013-2017; Advisor: Raymond Gorte)

Industry Experience: Thin Film and Planarization
(Intel Corporation, 2018-2021)

Deactivation of functional oxides through the loss of surface area is a major concern in heterogenous catalysis. 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 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 the high-surface area support in a layer-by-layer manner with exceptional compositional control. However, there were some critical limitations that had to be considered and addressed prior to utilizing this process.

ALD was developed in the semiconductor industry to fabricate films as quickly as possible. The design criteria of this process are very different from what is required for catalytic applications. Firstly, the emphasis on production output requires rapid cycling with high-velocity carrier gases that will create diffusion limitations in porous structures. Second, when carrier gases are used, most reagents pass through the reactor without being incorporated into the sample. This is prohibitively expensive for catalytic applications, but not so much in a high capital-intensive semiconductor industry. My Ph.D. work centered on modifying the ALD process, which avoided these issues to prepare high-surface area active supports for metal nanoparticles such as the ‘intelligent’ (perovskite-film) catalysts that exhibited excellent regeneration capability and resilience to coking and sintering.

Postdoctoral Fellow: Nanoparticles, Graphene, and ALD
(University of Minnesota - Twin Cities, 2021-Present; Advisor: Paul Dauenhauer)

Developing composite materials provides opportunities to study relationships between structure and properties that were previously deemed not possible. One avenue currently being explored is the combination of oxide films, graphene, and nanoparticles that exhibit unique electrocatalytic enhancements for several applications.

Future research:

Recent push for advances in sustainable energy technology has made it likely that electrical driven chemical transformation will play a significant role in the future. These electrochemical reactions occur at the interface of a solid and are therefore inherently heterogeneous. Developing fundamental understanding of reactions of interest will be necessary to enable rational design of useful composite materials. A lot of inspiration in surface design can also be drawn from studies of well-established thermal catalytic reactions. There are three areas that are of personal interest: the design of efficient and practical catalysts, developing electrochemical reactions beyond simple molecules, and the use of electrochemistry for treatment of water/waste.

Teaching Interests

Teaching and mentoring have always been a major part of my life. 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 along the way. 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 crash course on Mass and Energy balances for students who had never taken any engineering classes but decided to switch into the major later on. My mentor, Ray Gorte, also gave me several chances to lecture for his course on 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, Thin Films and Vapor Deposition, 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:

• “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.
• “Atomic Layer Deposition on Porous Substrates: Problems with Conventional Approaches and Systems.” Inorganics, 2018. Onn TM, Kungas R, Huang K, Fornasiero P and Gorte RJ.
• “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.