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Density Functional Theory Comparison of Water Dissociation Steps on Cu, Au, Ni, Pd, and Pt

Abhijit A. Phatak^†^‡, W. Nicholas Delgass^†, Fabio H. Ribeiro^† and William F. Schneider*^‡^§

School of Chemical Engineering, Purdue University, 480 Stadium Mall Drive, West Lafayette, Indiana 47907, Department of Chemical and Biomolecular Engineering, and Department of Chemistry and Biochemistry, University of Notre Dame, 182 Fitzpatrick Hall, Notre Dame, Indiana 46556

J. Phys. Chem. C, 2009, 113 (17), pp 7269–7276

DOI: 10.1021/jp810216b

Publication Date (Web): April 8, 2009

* To whom correspondence should be addressed. E-mail: wschneider@nd.edu. Phone: (574) 631-8754., †

Purdue University.

, ‡

Department of Chemical and Biomolecular Engineering, University of Notre Dame.

, §

Department of Chemistry and Biochemistry, University of Notre Dame.

Abstract

We report a plane-wave, supercell density functional theory (DFT) investigation of the adsorption and dissociation of water on (111) surfaces of Cu, Au, Pt, Pd, and Ni, five metals of potential interest in the context of water gas shift (WGS) catalysis. Binding energies, preferred adsorption sites, and configurations for H₂O and its dissociation products (OH, H, and O) are determined on all five metals, as are the minimum energy paths (MEPs) and activation energies for H−OH and O−H dissociation. Results are compared with the diverse computational literature on H₂O dissociation over these metals. Both dissociation steps are found here to be highly endothermic on Au(111) and slightly endothermic on Pt(111) and Pd(111). The first H abstraction from adsorbed H₂O is exothermic on Cu(111) and Ni(111), but subsequent OH dissociation is endothermic on Cu(111) and slightly exothermic on Ni(111). Using a simple Langmuir equilibrium model, we show that under the high H₂ background pressures typical of low-temperature WGS, the surface coverage of OH is expected to be several orders of magnitude higher than that of O, consistent with a significant role of OH in surface CO oxidation.

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