Revisiting the mechanism of highly efficient CO oxidation by single iron atom catalysis on Pt(100)

Abstract

In a recent breakthrough experiment [Cao et al., Nature, 2019, 565, 631], a novel iron-hydroxide-based single-atom catalyst (SAC) deposited on platinum nanoparticles exhibited outstanding catalytic performance for CO oxidation over a broad range of temperatures. Herein, based on DFT calculations we revisit the mechanism of CO oxidation catalyzed by the Fe1(OH)3 SAC on Pt(100), as originally proposed in the same experimental work. We first found that the energy barrier (0.65 eV) for producing the second CO2 should be appreciably higher than that (0.21 eV) reported in the previous work, suggesting that the correct rate-controlling step corresponds to the production of the second CO2 instead of the first one. More importantly, by considering different possible pathways involving both the Langmuir–Hinshelwood and Eley–Rideal mechanisms, as well as the influence of pre-adsorption of gaseous reactants, we have found that there exists an energetically more favorable mechanism for CO oxidation over Fe1(OH)3/Pt(100). The rate-determining free energy barrier in the new mechanism is only 0.42 eV, about 40% smaller than that (0.68 eV) in the previous mechanism. According to microkinetic modeling, the new mechanism results in an overall reaction rate several orders of magnitude greater than that offered by the previous mechanism. The apparent activation energy derived from the new mechanism is 0.45 eV, much lower than that (0.67 eV) from the previous mechanism. Our findings may move us closer toward a full understanding of the experimental observations and provide valuable insights into the rational design of highly efficient SACs.