Understanding and Predicting Reactivity and Selectivity of Single Atom Catalyst

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Professors Talat S Rahman and Fudong Liu of the University of Central Florida (UCF) and Professor Sampyo Hong of Brewton Parker College are supported by an award from the Chemical Catalysis program in the Division of Chemistry to understand and predict the properties of single atom catalysts. Catalyst are used in academic and industrial chemical laboratories to speed up chemical reactions while selecting for specific products over others. Single atom catalysts are often made of nanoparticles - a billionth of a meter. Nanoparticles have unique properties which distinguish them from their bulk counterparts because of their reduced size and confinement. For example, bulk gold is an inert material, but in nanoparticle form it be very reactive with gases in the air (like carbon monoxide). The miniscule size of the nanoparticles also means reduced cost of the precious metal. The last decade has seen much research on nanocatalysts whose local environment can be controlled down to the single atom (usually on a supportive surface). The factors that control reactivity and product selectivity are of particular interest in nanocatalysts. In this project, Professors Rahman, Hong and Liu carry out joint computational and experimental studies of oxidizing (burning in a controlled way) methanol to form carbon dioxide and molecular hydrogen on singly-dispersed platinum, copper, and cobalt nanoparticle catalysts. The systematic coupling between theory and experiment helps set guidelines for the rational design of single atom catalysts with desired reactivity and selectivity properties. Professor Rahman leverages her position as the UCF site leader for the American Physical Society Bridge Program to mentor the graduate students from underrepresented minority groups that work on the project. Existing international collaborations help extend the outcomes globally. Undergraduate students at Brewton-Parker College are actively engaged in chemistry research, gaining useful experience for careers in academics or industry. This project is expected to result in strategies for predicting and controlling the reactivity of atomically dispersed nanocatalysts, as a function of their local atomic environment. Research components include: thermodynamics-assisted, density functional theory (DFT)-based calculations of electronic and geometric structure, vibrational dynamics and entropy, reaction pathways and energetics; and kinetic Monte Carlo simulations of reaction rates and turn over frequencies, as a function of ambient temperature and pressure; synthesis of the single atom catalysts. The research team will use scanning transmission electron microscopy (STEM) to confirm the single site status of targeted systems. Postdocs and graduate students will conduct an experimental determination of methanol partial oxidation reaction rates and turnover frequencies as well as studies of in situ diffuse reflectance infra-red Fourier transform spectroscopy (DRIFTS) to verify surface reactive intermediates and track reaction mechanisms. Theory and experiment working in tandem provide an understanding of reaction mechanisms and insights into factors such as charge transfer, strain, etc. that control site activity. More importantly, competing reaction pathways (and reaction intermediates) responsible for product selectivity are exposed, thereby providing a design control. A direct feedback between calculated and observed surface structure, reaction rates and turnover frequencies validates the theoretical approach and refines experimental parameters.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.