(647c) Predicting the Single-Site CO Oxidation Reactivity Trends on a Well-Defined Copper Oxide Film

               Single-site
catalysts have shown incredible promise for catalyzing kinetically challenging
reactions at surprisingly low temperatures.[1] However, debates in the
literature over the activity of these isolated atoms [1, 2] show the need for development of realistic computational
models for verification that these isolated species are responsible for the
catalytic activity. Recent collaborations between experiment and theory had
elucidated the atomistic behavior responsible for the oxidation of carbon
monoxide (CO) over a thin copper oxide film supported on bulk Cu(111) with
isolated Pt atoms present.[3] Further, CO
oxidation was shown to proceed at 345 K, i.e. at a considerably lower
temperature than the 425 K target required to meet future emission regulations.[4] This work delves further into this reaction
system to develop trends necessary for the design of real-world catalysts from
results on this model system.

            Instead
of using Pt atoms to catalyze CO oxidation, this work focuses on alternative
dopants, specifically Pd and Rh. Preliminary experimental results have shown
vastly different behaviors for these dopants at the suspected single-atom
limit, with Rh systems having nearly 100% CO conversion and Pd systems seeing
almost no conversion at all. These results provide respective upper and lower
bounds when compared to the Pt system studied previously, where about 33% of
the incoming CO was converted to CO₂ successfully (see Figure 1). We
present the modeling results that complement these experiments here, detailing
everything from likely locations of the catalytic atoms on the surface to
expected reaction barriers for CO oxidation. We further show and discuss the correspondence
between the experimental STM and TPD results. These results will be further
used to develop periodic trends related to the dopant type used for this
reaction to facilitate the design of future single-site catalysts.

Figure 1. Schematic illustration of the
underlying CO oxidation mechanism that was proposed to occur on supported
single-site Pt atoms, in which 33% of the CO gets oxidized to CO₂[3].            

References

[1] Y. Zhai, D. Pierre, R. Si, W.
Deng, P. Ferrin, A.U. Nilekar, G. Peng, J.A. Herron, D.C. Bell, H. Saltsburg,
M. Mavrikakis, M. Flytzani-Stephanopoulos, Alkali-Stabilized Pt-OH_x
Species Catalyze Low-Temperature Water-Gas Shift Reactions, Science, 329 (2010)
1633-1636.

[2] K. Ding, A. Gulec, A.M.
Johnson, N.M. Schweitzer, G.D. Stucky, L.D. Marks, P.C. Stair, Identification
of active sites in CO oxidation and water-gas shift over supported Pt
catalysts, Science, 350 (2015) 189-192.

[3] A.J. Therrien, A.J.R. Hensley,
M.D. Marcinkowski, R. Zhang, F.R. Lucci, B. Coughlin, A.C. Schilling, J.-S.
McEwen, E.C.H. Sykes, An atomic-scale view of single-site Pt catalysis for
low-temperature CO oxidation, Nature Catalysis, 1 (2018) 192-198.

[4]
Federal Registry, 81 (2016) 73478-74274.