Understanding and predicting reactivity and selectivity of single atom catalyst

Talat S Rahman and Fudong Liu of University of Central Florida and Sampyo Hong of Brewton Parker College are supported by an award from the Chemical Catalysis program in the Division of Chemistry (CHE #1955343, September 1, 2020- August 31, 2023) to understand and predict the reactivity and selectivity of single atom catalysts.

Nanoparticles have unique properties which distinguish them from their bulk counterparts owing to their reduced size and confinement. For example, bulk Au is an inert material, but in nanoparticle form it has higher activity towards (low temperature) CO oxidation than any other noble metal. The miniscule size of the nanoparticle also means reduced cost. The last decade has thus seen a flurry of activity in nanocatalysts whose local environment can be controlled down to the single atom (on a support), setting the stage for comprehensive examination of factors that control site reactivity and product selectivity. In this project, Professors Rahman, Hong and Liu will carry out joint computational and experimental studies of methanol partial oxidation leading to CO₂ and H₂ production on singly-dispersed Pt, Cu, and Co atomic sites on supports such as ZnO, CeO₂, γ-Al₂O₃, and graphene. Rates and turnover frequencies for this reaction of much industrial and fundamental interest will be determined and correlated to the electronic and geometric structure of the local atomic environment of the single atom catalyst. This systemic coupling between theory and experiment will help set guidelines for the rational design of single atom catalysts with desired reactivity and selectivity. The PI will leverage her position as the UCF site leader for American Physical Society Bridge Program to recruit more graduate students from underrepresented minority groups to work on the project. Existing international collaborations of the PIs will help extend the outcomes internationally. Benefits will extend to Brewton-Parker College through engagement of undergraduate students in chemistry research.

The immediate outcome will be paradigm-shifting strategies for predicting and controlling reactivity of atomically dispersed nanocatalysts, as a function of their local atomic environment. Research components include: 1) thermodynamics-assisted, density functional theory (DFT)-based calculations of electronic and geometric structure, vibrational dynamics and entropy, reaction pathways and energetics; 2) kinetic Monte Carlo simulations of reaction rates and turn over frequencies, as a function of ambient temperature and pressure; 3) synthesis of the single atom catalysts; 4) scanning transmission electron microscopy (STEM) to confirm the single site status of targeted systems; 5) experimental determination of methanol partial oxidation reaction rates and turnover frequencies; 6) in situ diffuse reflectance infra-red Fourier transform spectroscopy (DRIFTS) study to verify surface reactive intermediates and track reaction mechanisms. Theory and experiment working in tandem will provide an understanding of reaction mechanisms and insights into factors such as charge transfer, strain, etc. that control site activity. More importantly, it will expose competing reaction pathways (and reaction intermediates) responsible for product selectivity, thereby providing design control. A direct feedback between calculated and observed surface structure, reaction rates and turnover frequencies will validate the theoretical approach and refine experimental parameters.