(632c) Kinetic Investigations of Carbonyl Reduction over Group VIII Metals: Acetone Hydrogenation

Oxygenate reduction is ubiquitous in the catalytic upgrading
of biomass, where most strategies employ supported group VIII metal catalysts
on account of their activity. We therefore seek to understand the kinetics of
oxygenate reduction, taking acetone hydrogenation over supported metal
catalysts as a model system. Acetone hydrogenation to isopropanol proceeds
through a Horuiti-Polanyi type mechanism over group
VIII metal catalysts, involving the sequential addition of hydrogen across the
carbonyl group. This leads to the formation of a kinetically relevant surface isopropoxide species, the binding energy of which is
thought to govern the overall rate of reaction. Through a combination of experimentally
measured macroscopic rates of reaction and microkinetic modelling, we
investigate the proposed Horuiti-Polanyi mechanism
and identify regions of kinetic interest. Quantum chemical calculations reveal
the existence of multiple rate determining steps over Pt surfaces, while
surface isopropoxide reduction dominates on more oxophilic surfaces like Ru. These predictions are
consistent with microkinetic modelling results based on measured experimental
rates, where changes in rate determining steps are rationalized based on the
stability of the isopropoxide surface intermediate.