Title: Solvation Effects in the Hydrodeoxygenation of Propanoic Acid over a Model Pd(211) Catalyst

Abstract

The effects of liquid water and 1,4-dioxane on the hydrodeoxygenation of propionic acid over Pd(211) model surfaces have been studied from first principles. Here, a microkinetic model with parameters obtained from density functional theory and implicit solvation models was developed to study the effects of these solvents on the reaction mechanism and kinetic parameters. In the presence of water, dehydrogenated derivatives of propionic acid and propionate are stabilized, and a new decarboxylation mechanism involving CH₃CCOOH surface species is facilitated, leading to a higher decarboxylation rate. However, stronger adsorption of CO in the presence of liquid water resulted in fewer free sites and an overall lower turnover frequency. By contrast, in the presence of 1,4-dioxane, the most dominant decarboxylation pathway does not involve a dehydrogenated propionate species, but propionate goes through decarboxylation to form CO₂ and C₂ fragments very similar to the mechanism in the gas phase. Again, in the presence of 1,4-dioxane, CO adsorbs more strongly, and fewer free sites are available for catalysis, leading to a slightly smaller turnover frequency. In all reaction environments, we observed that the decarbonylation mechanism is slightly preferred over the decarboxylation mechanism and that C–OH bond cleavage is the most rate-controlling step followed bymore » α-carbon dehydrogenation steps and (in liquid water) decarboxylation of dehydrogenated derivatives. Comparing solvent effects over Pd(211) with those over Pd(111), we observe that the free site coverage is reduced in the presence of solvents on all Pd surfaces, which reduces the activity of Pd(211). In addition, elementary steps that involve a carboxyl/carboxylate group changing its orientation from the surface to the liquid phase, such as the dehydrogenation of propionate, are significantly facilitated such that liquid water increased the activity of Pd(111).« less

Authors:

Behtash, Sina ^[1]; Lu, Jianmin ^[1]; Mamun, Osman ^[1]; Williams, Christopher T. ^[1]; Monnier, John R. ^[1]; Heyden, Andreas ^[1]

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+ Show Author Affiliations

1. University of South Carolina, Columbia, SC (United States)

Publication Date:

Tue Jan 19 00:00:00 EST 2016

Research Org.:

Univ. of South Carolina, Columbia, SC (United States)

Sponsoring Org.:

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

OSTI Identifier:

1656910

Grant/Contract Number:  

SC0007167

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Physical Chemistry. C

Additional Journal Information:

Journal Volume: 120; Journal Issue: 5; Journal ID: ISSN 1932-7447

Publisher:

American Chemical Society

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Redox reactions; Organic reactions; Chemical reactions; Solvents; Water