A first principles analysis of the hydrogenation of C1C4 aldehydes and ketones over Ru(0001)

Journal Article · Thu Nov 01 04:00:00 EDT 2012 · Journal of Catalysis

DOI:https://doi.org/10.1016/j.jcat.2012.07.018· OSTI ID:1097965

Sinha, Nishant K. ^[1]; Neurock, Matthew ^[1]

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1. Univ. of Virginia, Charlottesville, VA (United States)

The structure and degree of substitution of C₁–C₄ oxygenate molecules can influence their chemisorption and reactivity on metal surfaces. Gradient-corrected periodic density functional theory calculations were carried out to analyze alkyl substituent effects on the hydrogenation of C₁–C₄ aldehydes and ketones to their corresponding alcohols. All of these aldehydes along with acetone were found to adsorb in a di-ση1η2(C,O) mode onto the Ru(0001) surface and result in rehybridization of the C=O bond. Steric hindrance from two alkyl substituents on the carbonyl backbone of methyl ethyl ketone (MEK), however, prevents it from binding di-ση1η2(C,O). It adsorbs instead atop a Ru atom in an g1(O) configuration through its oxygen atom. Hydrogenation of both aldehydes and ketones can occur through either a hydroxy or an alkoxy mechanism. The hydroxy route proceeds via the formation of the hydroxyalkyl intermediate R₁R₂C*OH by the addition of hydrogen to the oxygen of the carbonyl, whereas the alkoxy mechanism proceeds by the addition of hydrogen to the carbon end to form the alkoxy intermediate R₂CHO*). DFT calculations indicate that the activation barrier for the initial addition of hydrogen to the carbon to form the C–H bond in the alkoxy mechanism is independent of the substituent groups that are attached to the carbon center as these groups are oriented away from the surface in the transition state and thus have little influence on the activation energies. The activation barriers for the addition of hydrogen to the oxygen of the carbonyl to form the O–H bond in the hydroxy mechanism, however, was found to linearly correlate with the binding energy of the hydroxyalkyl intermediate that forms. This trend can be explained through the Brønsted–Evans–Polanyi relationship and the fact that both the hydroxyalkyl products and carbonyl reactants interact via their carbon centers and are correlated with one another. All of the carbonyls follow a similar trend in that the addition of hydrogen to the carbon of the carbonyl has a much lower barrier on Ru(0001) than the addition of hydrogen to the oxygen. The carbonyls thus readily react to form their alkoxy intermediates. Simple kinetic analyses and firstprinciple- based kinetic Monte Carlo simulations for formaldehyde over Ru(0001) show that the alkoxy is the most abundant surface intermediate and that the alkoxy route is more favorable than the hydroxy route.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Oak Ridge Leadership Computing Facility (OLCF); Pacific Northwest National Laboratory (PNNL), Richland, WA (United States), Environmental Molecular Sciences Laboratory (EMSL)
• Sponsoring Organization: DOE Office of Science; USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1097965
• Journal Information: Journal of Catalysis, Journal Name: Journal of Catalysis Journal Issue: C Vol. 295; ISSN 0021-9517
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
Environmental Molecular Sciences Laboratory