422568 Decomposition Kinetics and Structure of Acetate on Au(110) Studied By Temperature Programmed Reaction Spectroscopy and Scanning Tunneling Microscopy

Thursday, November 12, 2015: 9:50 AM
355E (Salt Palace Convention Center)
Bonggeun Shong1,2, Fanny Hiebel1, Robert J. Madix3 and Cynthia M. Friend1,3, (1)Chemistry and Chemical Biology, Harvard University, Cambridge, MA, (2)Department of Chemistry, Chungnam National University, Daejeon, South Korea, (3)School of Engineering and Applied Sciences, Harvard University, Cambridge, MA

Nanostructured gold catalysts have demonstrated promising efficiency and selectivity for various chemical reactions. Adsorption structure and reaction mechanism of reactants and intermediates obtained from model studies on single crystal surfaces can provide insights into heterogeneous catalysis under working conditions. Au(110) exhibits a (1×2) missing row reconstruction with a high density of undercoordinated atoms, which makes it a useful model system for gold nanostructures. On the other hand, self-assembly of organic adsorbates is of interest for various applications. In catalysis, adsorbate-adsorbate interactions and their ordering, possibly accompanied by the reconstruction of the substrate, may affect their stability on the surface and the catalytic reactivity of the surface. Here, we present a study on the adsorption, ordering, and thermal decomposition of acetate (CH3COO) adsorbates on the Au(110) surface. Acetate is a key intermediate in a competing pathway to ethanol catalytic oxidation and a possible poison for Au/TiO2catalysts. 

Scanning tunneling microscopy (STM) shows that acetate self-assembles into highly ordered islands on Au(110) even at low coverages.1 The (1×2) reconstruction of the surface is lifted when covered by acetate. Decomposition kinetics of acetate adsorbates was studied through temperature-programmed reaction spectroscopy (TPRS). Decomposition of acetate occurs through C-C scission near 590 K to release mainly CO2 and CH3, similar to what was previously observed on Au(111).2,3 An isotherm/isostere analysis (complete analysis) of the coverage-dependent temperature programmed evolution of products from acetate on Au(110) was performed. While this reaction is unimolecular, the decomposition temperature observed in TPRS increases and the asymmetry of the peak shape grows with increasing coverage. Moreover, both the activation energy and apparent reaction order show dependence on the coverage of acetate. Such behavior indicates the presence of lateral attraction between the adsorbates, consistent with formation of islands as observed by STM. 

1. Hiebel et al., in preparation. 

2. Cremer et al., J. Phys. Chem. Lett., 2014, 5, 1126. 

3. Siler et al., ACS Catal., 2014, 4, 3281.

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