Modifying the Surface Properties of Heterogeneous Catalysts Using Polymer-Derived Microenvironments

This work uses transition state theory as applied to thermodynamically non-ideal systems to explore the origins of improvements in the stability and activity of supported metal catalysts containing polymer-derived microenvironments. The hydrogenation of triacetic acid lactone (TAL), which is the first step in the production of biorenewable sorbic acid, is used as a probe for the influence of a poly(vinyl alcohol)-derived (PVA-derived) microenvironment on the reduction of moderately polar compounds. The presence of the microenvironment causes a moderate decrease in the rate of TAL hydrogenation without causing a substantial change in the measured activation barrier or reaction orders. This decrease is explained in the context of a local solvation environment generated by the PVA. For comparison, the hydrogenation of lactic acid (LA) is used as a probe for the influence of a PVA-derived microenvironment on the adsorption of polar compounds. In this case, the reaction order in LA increases from zero-order to 0.3-order, indicating that the surface coverage by lactate is decreased by the presence of the microenvironment. The results presented indicate that polymer-derived microenvironments act as pseudo-solvents that alter the surface properties of supported metal catalysts, and we suggest that modifying catalysts with polymer-derived microenvironments is a generalizable methodology with applications in liquid-phase biomass conversion reactions.