Solvation Effects in the Hydrodeoxygenation of Propanoic Acid over a Model Pd(211) Catalyst [electronic resource]
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| Format: | Electronic eBook |
| Language: | English |
| Published: |
Washington, D.C. : Oak Ridge, Tenn. :
United States. Department of Energy. Office of Science ; Distributed by the Office of Scientific and Technical Information, U.S. Department of Energy,
2016.
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| Subjects: |
| 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 CH<sub>3</sub>CCOOH 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 CO<sub>2</sub> and C<sub>2</sub> 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 by ?-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) |
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| Item Description: | Published through Scitech Connect. 01/19/2016. "Journal ID: ISSN 1932-7447." Behtash, Sina ; Lu, Jianmin ; Mamun, Osman ; Williams, Christopher T. ; Monnier, John R. ; Heyden, Andreas Univ. of South Carolina, Columbia, SC (United States) |
| Physical Description: | Size: p. 2724-2736 : digital, PDF file. |