Title: Ethanol Decomposition on Pd–Au Alloy Catalysts

Abstract

The mechanisms of ethanol (EtOH) decomposition via C–C or C–O bond cleavage on alloy surfaces are currently not well understood. Here, we model EtOH decomposition on close-packed Pd–Au catalytic surfaces using density functional theory (DFT) calculations and derived Brønsted–Evans–Polanyi (BEP) relationships. Three characteristic Pd–Au surfaces are considered, Pd₁Au₂(111), Pd₂Au₁(111), and a Pd monolayer (ML), Pd_ML(111), on a Au substrate. We show that, on close-packed Pd–Au surfaces, the C–C bond is easier to cleave than C–O, indicating that the formation of CH₄ and CO is favored as the products of EtOH decomposition. Interestingly, we find that, though the C–C and C–O activation barriers on Pd_ML(111) are generally lower than those on the other two surfaces, it is less active for EtOH decomposition due to a slow release of H₂ and possible carbon coking. Pd₂Au₁(111), on the other hand, has a higher theoretical reaction rate due to facile H₂ evolution from the surface and less carbon coking. A comparison of the surface d-band with the activation energy barriers shows that there is a trade-off between the barriers for C–C bond cleavage and H₂ association, with Pd₂Au₁(111) having the best performance. Temperature-programmed desorption experiments of EtOH on Pd/Au surfaces show significant C–C bondmore » cleavage and both CH₄ and CO production on surfaces with Pd–Au interface sites. Furthermore, neither Auger electron spectroscopy nor EtOH reflection–adsorption infrared spectroscopy provide evidence of C–O bond cleavage. Finally, the experimental reaction rate for methane production from C–C bond cleavage was higher on surfaces with more Au present due to minimal carbon contamination and the promotion of product desorption. This combined theoretical and experimental study shows that, though Au is catalytically inactive for EtOH decomposition, it can dramatically promote the surface activity for EtOH steam reforming due to the existence of active Pd–Au surface ensemble sites.« less

Authors:

Li, Hao ^[1]; Evans, Edward J. ^[1]; Mullins, C. Buddie  ^[1];

• Search DOE PAGES for author "Mullins, C. Buddie"
• Search DOE PAGES for ORCID "0000-0003-1030-4801"

Henkelman, Graeme  ^[1]

• Search DOE PAGES for author "Henkelman, Graeme"
• Search DOE PAGES for ORCID "0000-0002-0336-7153"

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+ Show Author Affiliations

1. Univ. of Texas, Austin, TX (United States)

Publication Date:

Thu Aug 30 00:00:00 EDT 2018

Research Org.:

Univ. of Texas, Austin, TX (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES); Welch Foundation

OSTI Identifier:

1617146

Grant/Contract Number:  

SC0010576; SC0018116; F-1841; F-1436

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Physical Chemistry. C

Additional Journal Information:

Journal Volume: 122; Journal Issue: 38; Journal ID: ISSN 1932-7447

Publisher:

American Chemical Society

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; palladium; gold; organic reactions; ethanol; bond cleavage