AVS 63rd International Symposium & Exhibition
    Surface Science Tuesday Sessions
       Session SS-TuP

Paper SS-TuP4
Adsorption and Oxidation of n‑Butane on the Stoichiometric RuO2(110) Surface

Tuesday, November 8, 2016, 6:30 pm, Room Hall D

Session: Surface Science Poster Session
Presenter: Tao Li, University of Florida, Gainesville
Authors: T. Li, University of Florida, Gainesville
R. Rai, University of Florida, Gainesville
Z. Liang, University of Florida, Gainesville
M. Kim, Ohio State University
A. Asthagiri, Ohio State University
J.F. Weaver, University of Florida, Gainesville
Correspondent: Click to Email

The surface chemistry of late transition-metal (TM) oxides has drawn significant attention due to the observation and prediction of facile C-H bond cleavage of molecularly adsorbed n-alkanes at low temperatures. Previous studies have shown that PdO(101) readily promotes the dissociation of alkanes by a mechanism in which adsorbed σ-complexes serve as precursors to initial C-H bond cleavage. Density functional theory (DFT) calculations further predict that the formation and facile C-H bond activation of alkane σ-complexes should also occur on RuO2 and IrO2 surfaces, suggesting that the σ-complex mechanism is a common pathway for alkane activation on late TM oxides.

In this study, we investigated the adsorption and oxidation of n-butane on the stoichiometric RuO2(110) surface using temperature-programmed reaction spectroscopy (TPRS) and DFT calculations. At low coverage, molecularly adsorbed n-butane achieves a binding energy of ∼100 kJ/mol on RuO2(110), consistent with a strongly bound σ-complex that forms through dative bonding interactions between the n-butane molecule and coordinatively unsaturated (cus) Ru atoms. We find that a fraction of the n-butane reacts with the RuO2 surface during TPRS to produce CO, CO2, and H2O that desorb above ∼400 K and present evidence that adsorbed σ-complexes serve as precursors to the initial C−H bond cleavage and ultimately the oxidation of n-butane on RuO2(110). From measurements of the product yields as a function of surface temperature we estimate that the initial reaction probability of n-butane on RuO2(110) decreases from 9% to ∼4% with increasing surface temperature from 280 to 300 K and show that this temperature dependence is accurately described by a precursor-mediated mechanism. From kinetic analysis of the data we estimate a negative, apparent activation energy of −35.1 kJ/mol for n-butane dissociation on RuO2(110) and an apparent reaction prefactor of 6 × 10−8. The low value of the apparent reaction prefactor suggests that motions of the adsorbed n-butane precursor are highly restricted on the RuO2(110) surface. DFT calculations confirm that n-butane forms strongly bound σ- complexes on RuO2(110) and predict that C−H bond cleavage is strongly favored energetically. The n-butane binding energies and energy barrier for C−H bond cleavage predicted by DFT agree quantitatively with our experimental estimates. Our results support the idea that the σ-complex mechanism is a common pathway for alkane activation on late TM oxide surfaces that expose pairs of cus metal and oxygen atoms.