(548a) Engineering Catalyst Microenvironments for Metal-Catalyzed Hydrogenation of Biologically-Derived Platform Chemicals

Mirroring the evolution of traditional petroleum refineries, successful future biorefineries will rely on the production of value-added chemicals to supplement biofuels production.  One promising strategy for the production of biorenewable chemicals from biomass uses heterogeneous catalysis to upgrade biologically-derived platform molecules.  Such a scheme leverages the efficiency of heterogeneous catalysis and couples it with the ability of biocatalysis to generate molecules not easily accessible by other means.  The efficiency advantage is lost, however, if the heterogeneous catalysts used for upgrading are not stable in the presence of biogenic impurities or highly reactive feedstocks.  In this work, we use hydrogenation of the biologically-derived intermediate triacetic acid lactone (TAL) to demonstrate that these types of catalyst deactivation can be alleviated by appropriate catalyst design.  Specifically, we show that a traditional supported-Pd hydrogenation catalyst is inhibited by biogenic impurities such as amino acids, especially by methionine, which decreases the catalyst activity by 83% after 14 hours of low-concentration exposure (i.e., 0.01 mM).  This inhibition is mitigated by formation of a microenvironment surrounding the metal nanoparticles, achieved by overcoating the catalyst with poly(vinyl alcohol) (PVA), and the overcoated catalyst is stable in the presence of amino acids, including methionine.  Results from solid-state NMR studies are used to provide molecular-level insight into the interaction between methionine and the Pd surface for both the parent and PVA-overcoated catalysts.  Additionally, we show that deactivation of the Pd catalyst by deposition of carbonaceous residues in the presence of TAL is alleviated by formation of bimetallic PdAu nanoparticles.  Accordingly, the use of PVA to form microenvironments on a PdAu catalyst allows for an order-of-magnitude improvement in stability for the hydrogenation of biologically-produced TAL recovered from spent cell culture medium.