(265d) Aqueous-Phase Hydrogenation of Acetic Acid On Monometallic Catalysts: A Combined Experimental and Theoretical Study

Hydrogenation of organic acids is an important step in the
conversion and upgrading of biomass-derived feedstock for the production of
valuable liquid fuels and chemical intermediates.  To develop a fundamental
understanding for this class of reaction, we are investigating the
aqueous-phase hydrogenation of acetic acid, one of the simplest carboxylic
acids, to ethanol, by a combined experimental and theoretical approach.  The
catalytic activity of monometallic Ni, Cu, Ru, Rh, Pd, Ir, and Pt catalysts
have been measured in a fixed bed reactor and found to be distinctly
different.  In agreement with previous studies of the hydrogenation of organic
acids,^1-4 Ru is by far the most active and selective catalyst, with
the rest of the metals being at least an order of magnitude less active.  For
additional mechanistic insight, periodic density functional theory calculations
have been performed to investigate the activation and subsequent hydrogenation
of acetic acid on the seven metals.  Our results suggest that the different
activity is dictated largely by the first C-O bond scission step of acetic acid
forming acetyl (CH₃CO)^5-7 across the metals.  A simple
reaction model allows the rate of acetic acid conversion to be estimated based
on readily calculated reactivity parameters.  Further investigation suggests
that the selectivity for ethanol on Ru is controlled by reaction conditions. 
Our study provides insight for the challenging task of developing new catalysts
for efficient biomass feedstock processing.

Work at UMass was supported with a grant from the ACS
Petroleum Research Fund.  The Center for Nanophase Materials Sciences is
sponsored at Oak Ridge National Laboratory by the Division of Scientific User
Facilities, U.S. Department of Energy.

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