(585c) Selective Hydrogenation of the Oxygenates : The Influence of the Nature of the Solvent

The liquid phase hydrogenation of oxygenate intermediates is an important step in the catalytic production of fine chemical and pharmaceutical intermediates(1) as well as in the conversion of platform chemicals derived from biorenewable resources into value-added chemicals and fuels(2). A significant number of experimental studies have been carried out to look at hydrogenation of ketones in a variety of solvents and it is well established that the reaction rate depends greatly on the solvent in which the reaction is carried out(3,4). The factors that control these differences, however, are not very well understood. A fundamental study of different elementary reactions at the interface of solid catalyst and the solvent can improve our understanding of the reaction mechanism as well as the synergic effects of the metal and the solvent on reaction kinetics and energetics. Towards this end we have carried out ab initio density functional theory calculations to investigate the hydrogenation of methyl ethyl ketone (MEK) on Ru(0001) catalyst surface in presence of three different solvents – water, methanol and isopropyl alcohol (IPA).

The structure of “liquid” water, methanol and IPA on Ru(0001) was obtained by carrying out ab initio simulated annealing studies. In presence of solvent, the binding of MEK to the Ru surface is weaker. The calculated activation barriers for the first hydrogenation step in the four media analyzed are listed below. We found that the activation barriers in presence of methanol and IPA are lower than that in vapor phase but is higher than that in water. This behavior can be attributed to greater hydrogen bonding capability of water over methanol and IPA which helps in stabilizing the reaction intermediate.

Medium Eact(eV)

Vapor 0.66

IPA 0.38

MeOH 0.33

H2O 0.21

References:

1. R.A. Sheldon and H. van Bekkum in “Fine Chemicals through Hetrogeneous Catalysis” Wiley-VCH, Weinheim, 2000.

2. N.S. Chang, S. Aldrett, M. T. Holtzapple, et al., Chemical Engineering Science 55, 5721 (2000).

3. S. Kishida, Y. Murakami, T. Imanaka, et al., Journal of Catalysis 12, 97 (1968).

4. S. Kishida and S. Teranishi, Journal of Catalysis 12, 90 (1968).