(478g) Structure Sensitivity of Catalytic NO Oxidation: A First-Principles Study of Kinetic Properties At Two Pt Surfaces

Adsorbate coverage can have a large impact on the number and types of sites that are available for reactions at a surface.  Such coverage effects are critical, for instance, in understanding the catalytic oxidation of NO to NO₂ over Pt.¹  We are developing a unique computational approach incorporating the effects of surface structure, local adsorbate coverage, and external temperature and pressure to more reliably predict rates of catalytic surface reactions.  Here we demonstrate its effectiveness for predicting O₂ dissociation rates over the (111) and (321)² facets of Pt.

Coverage effects originating from interactions between nearby adsorbates on the surface are modeled by using DFT simulations to parameterize Ising-type cluster expansion (CE) models of O on each Pt surface.  These adsorbate-adsorbate interactions influence the availability and reactivity of “reaction sites”, and we are able to apply the CE with grand canonical Monte Carlo (GCMC) in novel ways to predict reaction rates.³  Conducting simulations under various external temperature and pressure conditions further allows us to relate rate predictions to these environmental conditions and deduce rate-derived properties such as apparent activation energies and rate orders.

We evaluate the capabilities of our reactivity model by comparing predicted rates and rate-derived kinetic properties with experimental results⁴ for catalytic NO oxidation.  Contrasting the kinetic properties of both Pt surfaces, we draw conclusions regarding the sensitivity of NO oxidation to the particular Pt surface structure.  These results represent major progress in reliably predicting macroscopic observables from atomic-scale simulations and increase the fundamental understanding of surface reactivity across varying surface facets.

References:

(1)  Getman, R. B.; Schneider, W. F.; Smeltz, A. D.; Delgass, W. N.; Ribeiro, F. H. Phys. Rev. Lett. 2009, 102, 076101

(2)  Bray, J. M.; Schneider, W. F. Langmuir 2011, 27, 8177.

(3)  Wu, C.; Schmidt, D. J.; Schneider, W. F. J. Catal. 2012, 286, 88.

(4)  Smeltz, A. D.; Delgass, W. N.; Ribeiro, F. H. Langmuir 2010, 26, 16578.