Thomas J. Schwartz

Dehydration of cellulose to levoglucosenone using polar aprotic solvents

Herein, we report an approach to produce levoglucosenone (LGO) from cellulose in yields up to 51% under mild reaction conditions (170–230 °C; 5–20 mM H2SO4) using polar, aprotic solvents such as tetrahydrofuran (THF). LGO can be used to make a wide variety of chemicals from biomass. The water content and solvent used in the reaction system control the product distribution. LGO is produced from the dehydration of levoglucosan (LGA). LGA is produced from cellulose depolymerization. Increasing the water content leads to the production of 5-hydroxymethyl furfural (HMF), obtaining a maximum HMF yield of 30%.

Engineering catalyst microenvironments for metal-catalyzed hydrogenation of biologically derived platform chemicals.

It is shown that microenvironments formed around catalytically active sites mitigate catalyst deactivation by biogenic impurities that are present during the production of biorenewable chemicals from biologically derived species. Palladium and ruthenium catalysts are inhibited by the presence of sulfur-containing amino acids; however, these supported metal catalysts are stabilized by overcoating with poly(vinyl alcohol) (PVA), which creates a microenvironment unfavorable for biogenic impurities. Moreover, deactivation of Pd catalysts by carbon deposition from the decomposition of highly reactive species is suppressed by the formation of bimetallic PdAu nanoparticles. Thus, a PVA-overcoated PdAu catalyst was an order of magnitude more stable than a simple Pd catalyst in the hydrogenation of triacetic acid lactone, which is the first step in the production of biobased sorbic acid. A PVA-overcoated Ru catalyst showed a similar improvement in stability during lactic acid hydrogenation to propylene glycol in the presence of methionine.

Coupling chemical and biological catalysis: a flexible paradigm for producing biobased chemicals.

Advances in metabolic engineering have allowed for the development of new biological catalysts capable of selectively de-functionalizing biomass to yield platform molecules that can be upgraded to biobased chemicals using high efficiency continuous processing allowed by heterogeneous chemical catalysis. Coupling these disciplines overcomes the difficulties of selectively activating COH bonds by heterogeneous chemical catalysis and producing petroleum analogues by biological catalysis. We show that carboxylic acids, pyrones, and alcohols are highly flexible platforms that can be used to produce biobased chemicals by this approach. More generally, we suggest that molecules with three distinct functionalities may represent a practical upper limit on the extent of functionality present in the platform molecules that serve as the bridge between biological and chemical catalysis.

Graphitic‐Carbon Layers on Oxides: Toward Stable Heterogeneous Catalysts for Biomass Conversion Reactions

Conversion of biomass-derived molecules involves catalytic reactions under harsh conditions in the liquid phase (e.g., temperatures of 250 °C and possibly under either acidic or basic conditions). Conventional oxide-supported catalysts undergo pore structure collapse and surface area reduction leading to deactivation under these conditions. Here we demonstrate an approach to deposit graphitic carbon to protect the oxide surface. The heterogeneous catalysts supported on the graphitic carbon/oxide composite exhibit excellent stability (even under acidic conditions) for biomass conversion reactions.

Characterizing Substrate–Surface Interactions on Alumina-Supported Metal Catalysts by Dynamic Nuclear Polarization-Enhanced Double-Resonance NMR Spectroscopy

The characterization of nanometer-scale interactions between carbon-containing substrates and alumina surfaces is of paramount importance to industrial and academic catalysis applications, but it is also very challenging. Here, we demonstrate that dynamic nuclear polarization surface-enhanced NMR spectroscopy (DNP SENS) allows the unambiguous description of the coordination geometries and conformations of the substrates at the alumina surface through high-resolution measurements of 13C-27Al distances. We apply this new technique to elucidate the molecular-level geometry of 13C-enriched methionine and natural abundance poly(vinyl alcohol) adsorbed on γ-Al2O3-supported Pd catalysts, and we support these results with element-specific X-ray absorption near-edge measurements. This work clearly demonstrates a surprising bimodal coordination of methionine at the Pd-Al2O3 interface.

Methionine bound to Pd/γ-Al2O3 catalysts studied by solid-state (13)C NMR.

The chemisorption and breakdown of methionine (Met) adsorbed on Pd/γ-Al2O3 catalysts were investigated by solid-state NMR. (13)C-enriched Met (ca. 0.4mg) impregnated onto γ-Al2O3 or Pd/γ-Al2O3 gives NMR spectra with characteristic features of binding to γ-Al2O3, to Pd nanoparticles, and oxidative or reductive breakdown of Met. The SCH3 groups of Met showed characteristic changes in chemical shift on γ-Al2O3 (13ppm) vs. Pd (19ppm), providing strong evidence for preferential binding to Pd, while the NC carbon generates a small resonance at 96ppm assigned to a distinct nonprotonated species bound to O or Pd. Additionally, NMR shows that the SCH3 groups of Met are mobile on γ-Al2O3 but immobilized by binding to Pd particles; on small Pd particles (ca. 4nm), the NCH groups undergo large-amplitude motions. In a reducing environment, Met breaks down by C-S bond cleavage followed by formation of C2-C4 organic acids. The SCH3 signal shifts to 22ppm, which is likely the signature of the principal species responsible for strong catalyst inhibition. These experiments demonstrate that solid-state magic-angle spinning NMR of (13)C-enriched Met can be a sensitive probe to investigate catalyst surfaces and characterize catalyst inhibition both before reaction and postmortem.

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.

Characterizing Substrate-Surface Interactions on Alumina-Supported Metal Catalysts by DNP-Enhanced Double-Resonance NMR Spectroscopy.

The characterization of nanometer-scale interactions between carbon-containing substrates and alumina surfaces is of paramount importance to industrial and academic catalysis applications, but it is also very challenging. Here, we demonstrate that dynamic nuclear polarization surface-enhanced NMR spectroscopy (DNP SENS) allows the unambiguous description of the coordination geometries and conformations of the substrates at the alumina surface through high-resolution measurements of 13C-27Al distances. We apply this new technique to elucidate the molecular-level geometry of 13C-enriched methionine and natural abundance poly(vinyl alcohol) adsorbed on γ-Al2O3-supported Pd catalysts, and we support these results with element-specific X-ray absorption near-edge measurements. This work clearly demonstrates a surprising bimodal coordination of methionine at the Pd-Al2O3 interface.

Characterizing substrate–surface interactions on alumina-supported metal catalysts by dynamic nuclear polarization-enhanced double-resonance NMR spectroscopy [Characterizing substrate-surface interactions on alumina supported metal catalysts by DNP-enhanced double-resonance NMR spectroscopy]

The characterization of nanometer-scale interactions between carbon-containing substrates and alumina surfaces is of paramount importance to industrial and academic catalysis applications, but it is also very challenging. Here, we demonstrate that dynamic nuclear polarization surface-enhanced NMR spectroscopy (DNP SENS) allows the unambiguous description of the coordination geometries and conformations of the substrates at the alumina surface through high-resolution measurements of 13C-27Al distances. We apply this new technique to elucidate the molecular-level geometry of 13C-enriched methionine and natural abundance poly(vinyl alcohol) adsorbed on γ-Al2O3-supported Pd catalysts, and we support these results with element-specific X-ray absorption near-edge measurements. This work clearly demonstrates a surprising bimodal coordination of methionine at the Pd-Al2O3 interface.

Correction to “Selective Hydrogenation of Unsaturated Carbon–Carbon Bonds in Aromatic-Containing Platform Molecules”

Carbon−Carbon Bonds in Aromatic-Containing Platform Molecules” Thomas J. Schwartz,†,‡ Spencer D. Lyman,‡ Ali Hussain Motagamwala,‡,§ Max A. Mellmer,‡,§ and James A. Dumesic*,‡,§ †Department of Chemical and Biological Engineering, University of Maine, Orono, Maine 04469, United States ‡Department of Chemical and Biological Engineering, University of Wisconsin−Madison, Madison, Wisconsin 53706, United States DOE Great Lakes Bioenergy Research Center, University of Wisconsin−Madison, Madison, Wisconsin 53726, United States