CO Oxidation on noble metal surfaces has been widely studied since the 1920’s and is of fundamental importance to the field of surface science and heterogeneous catalysis in addition to many important industrial applications. On Pt surfaces, the reaction is generally considered to proceed via Langmuir-Hinshelwood kinetics. Detailed kinetics studies suggest at low temperatures (<250°C), the surface is nearly covered with CO and the reaction rate is limited by the limited vacant Pt sites for O2 dissociation. Interestingly, CO oxidation on Pt nanoparticles under CO-poisoned conditions has been shown to be a structure insensitive reaction, where turnover frequencies do not change significantly with variations in nanoparticle size and as a result of surface structure. However, theoretical analyses of the proposed CO oxidation mechanism on Pt surfaces have predicted the reaction should exhibit structure sensitivity, where lower index facets of Pt are predicted to be more active.1
Recently it has been shown that CO dissociation2 and CO-induced Pt restructuring3 can play important roles in reaction kinetics on single crystals, but the impact of these processes under realistic conditions, and their potential role in explaining the anomalous structure insensitivity, has not been identified. In this work, we discuss the roles of CO dissociation and nanoparticle restructuring in the experimentally observed structure insensitivity for Pt nanoparticles ranging from 2-40 nm on oxide supports.4 Our results are justified by isotopic labeling experiments, nanoparticle geometry-dependent reaction kinetics in the absence of heat and mass transfer effects, in addition to in-operando DRIFTS measurements.
(1) Allian, A. D.; Takanabe, K.; Fujdala, K. L.; Hao, X.; Truex, T. J.; Cai, J.; Buda, C.; Neurock, M.; Iglesia, E. J. Am. Chem. Soc. 2011, 133, 4498–4517.
(2) McCrea, K. R.; Parker, J. S.; Somorjai, G. A. J. Phys. Chem. B 2002, 106, 10854–10863.
(3) Tao, F.; Dag, S.; Wang, L.-W.; Liu, Z.; Butcher, D. R.; Bluhm, H.; Salmeron, M.; Somorjai, G. A. Science. 2010, 327, 850–853.
(4) Kale, M. J.; Christopher, P. In Prep. 2015.