(521m) Molecular Design of Polymer-Modified Catalyst Supports for Improved Bio-Renewable Energy Processes: Theory, Synthesis and Experiments

A key challenge in the design of new catalyst formulations is elucidating those factors which control the activity, selectivity, and stability of catalytic materials; and leveraging these insights to synthesize materials with desirable properties. In this work, we report the design, synthesis, and characterization of a novel series of materials comprising supported metal and acid catalysts decorated with polymer brushes – i.e., polymer moieties of well-defined composition and dimensions grafted directly onto supports, proximal to active sites. Through non-bonding interactions with solvated reactant molecules, the polymer brushes create tailored local solvation environments so that select reactants are preferentially adsorbed from the bulk liquid phase into the local environment around the active sites. Conversely, undesired species (e.g., poisons) are excluded from the immediate vicinity of the active sites through non-favorable weak interactions with the polymer brushes. As a proof of concept, we demonstrate how polymer-modified solid acid catalysts enhance the selectivity of fructose dehydration to 5-hydroxymethylfurfural (HMF) by suppressing the hydration of HMF into an undesirable terminal product, levulinic acid. To this end, we use molecular dynamics (MD) simulations to estimate the solvation free energy change associated with transferring fructose and 5-hydroxymethyl furfural from the bulk solvent into the local solvation environment of the polymer brushes, modulating their length, composition and grafting density in the MD simulations, and quantifying the preferences of the solvated reactants for the polymer brushes versus the bulk liquid phase as a function of same. Those polymer-modified catalyst systems that, based upon our solvation free energy calculations, are anticipated to maximize selectivity to HMF were synthesized, and tested in bench-scale glass batch reactors. This work represents a new direction in heterogenous catalyst research: modification of solid catalysts with polymer moieties to tune weak interactions in the liquid phase, and therefore control reactivity and selectivity in liquid-phase reactions.