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DOE OSTI2018

A Combined Experimental and Theoretical Study on the Activity and Selectivity of the Electrocatalytic Hydrogenation of Aldehydes

A detailed mechanistic study of the electrochemical hydrogenation of aldehydes is presented toward the goal of identifying how organic molecules in solution behave at the interface with charged surfaces and what is the best manner to convert them. Specifically, this study focuses on designing an electrocatalytic route for ambient temperature post-pyrolysis treatment of bio-oil. Aldehyde reductions are needed to convert biomass into fuels or chemicals. A combined experimental and computational approach is taken toward catalyst design to provide testable hypotheses regarding catalyst composition, activity, and selectivity. Electrochemical hydrogenation mechanisms for benzaldehyde and pentanal reduction are found to proceed by a coupled proton-electron transfer process. Initial results show that Au, Ag, Cu, and C catalysts exhibit the highest conversion to alcohol products. These catalysts are suitable because they show high cathodic onset potentials for H2 formation and low cathodic onset potentials for organic reduction. Conversion of aromatic aldehydes is found to be appreciably higher than aliphatic ones. Classical molecular dynamics simulations of solvent and substrate mixtures in an electrolytic cell were performed to assess how species concentrations vary at the solid/liquid interface and in the bulk as a function of applied voltage. Results show that an increase in voltage in the electrolytic cell decreases organic and increases water mole fractions at the solid/liquid interface. In this current study, charged cathodic surfaces result in carbonyl orientations at the surface that do not favor electron transfer. Repulsion of organic substrates to the bulk must be compensated by strong adhesion to the electrode surface. Implications on catalyst choice and process design are discussed.

Pyrolysis Oil upgrading, Atomistic Simulations, El↗

DOE OSTI2018

Impact of pH on Aqueous-Phase Phenol Hydrogenation Catalyzed by Carbon-Supported Pt and Rh

In aqueous phase, the rates of hydrogenation of aromatic substrates such as phenol on Pt/C and Rh/C are influenced by varying activity of hydronium ions. Decreasing the pH from 8 to 1 increases the rate of hydrogenation of phenol on Pt at 20 bar H 2 and 80 °C by 15-fold. This increase is attributed to weakening of the hydrogen binding energy (HBE) on the metal surface with decreasing pH. A weaker HBE at lower pH is also predicted by ab initio molecular dynamics simulations, providing atomistic insight into the impact of electrolyte ion distribution and interfacial solvent reorganization on HBE. The lower HBE results in a decrease in the activation energy for addition of adsorbed H from the metal to the adsorbed organic (with a Brønsted–Evans–Polanyi slope of ~1). In conclusion, the kinetic model derived accounts also for the lack of pH dependence at low hydrogen coverages (at 1 bar H 2 on Pt or up to 70 bar H 2 on Rh), when the weakening of the HBE decreases the hydrogen coverage.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2019

Chemoselective Hydrodeoxygenation of Carboxylic Acids to Hydrocarbons over Nitrogen-doped Carbon-Alumina Hybrid-Supported Iron Catalysts

Here, the establishment of catalyst systems for chemoselective hydrodeoxygenation (HDO) of carboxylic acids to hydrocarbons, such as the HDO of long-chain fatty acids to alkanes, is important for biomass-to-biofuel conversion. As the most abundant and probably the cheapest transition-metal on the earth, iron is a promising non-noble alternative to precious metals for large-scale conversion of biomass. However, it usually suffers from unsatisfactory activity. In this work, nitrogen-doped carbon-alumina hybrid-supported iron (Fe-N-C@Al 2 O 3 ) catalyst is established for chemoselective HDO of carboxylic acids to hydrocarbons. By using stearic acid HDO as the model reaction, n-octadecane and n-hepadecane are produced with yields of 91.9% and 6.0%, respectively. Triglycerides can also be converted into liquid alkanes with total molar yield of >92%. In addition, the iron catalyst can chemoselectively catalyze the HDO of carboxylic acid group in the presence of other functional groups such as an aromatic ring. This chemoselectivity is rarely seen before because the aromatic ring is usually easier to be hydrogenated than carrying out HDO of carboxylic acid group. The characterization results showed that both the formation of nitrogen-doped carbon-alumina hybrid and the iron-loading are important for the Lewis basicity of these catalysts, in order to adsorb the acid substrates. The addition of melamine as nitrogen precursor during pyrolysis eliminates undesired reactions between iron precursor and alumina support to form inactive hercynite phase, leading to the formation of Fe 3 C active phase for the hydrogenation of –COOH to –CH 2 OH and the hybrid of N-C and alumina for the HDO of -CH 2 OH to –CH 3 .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2019

Mechanistic Role of the Proton–Hydride Pair in Heteroarene Catalytic Hydrogenation

Kinetic and density functional theory studies probe the catalytic involvements of proton–hydride pairs in breaking the strong aromaticity of N-containing heteroarenes (pyridine and pyrrole) on sulfided Ru cluster surfaces. Under the sulfur chemical potentials relevant to hydrodenitrogenation catalysis, Ru clusters remain covered with a layer of sulfur-deficient RuSx on which a variety of reactive hydrogen species, which bind to Ru 4+ , S 2– , or Ru 4+ –S as Ru 4+ –(H δ– ), S 2– –(H δ+ ), and Ru 4+ –(SH 2 ), respectively, coexist. These reactive hydrogen species exhibit either proton or hydride character, depending on the electronegativity of their ligands (ruthenium and sulfur). For this reason, they participate in different hydrogen addition steps during the hydrogenation of heterocyclic-N compounds. Pyridine as the basic and pyrrole as the nonbasic heterocyclic model compounds undergo hydrogenation via distinctly different kinetically relevant steps because of their different proton affinities, which influence their interactions with the various reactive hydrogen species and in turn adsorption configurations. The hydrogenation of pyridine initiates from an initial, quasi-equilibrated proton attack onto the N atom, followed by a second hydridic hydrogen addition as the kinetically relevant step. In the contrasting case of pyrrole, the hydrogenation initiates via a kinetically relevant proton attack to its β-carbon that breaks its aromaticity before a hydride addition onto its α-carbon. Both reactions require a proton attack followed by a hydride attack, but their mechanistic differences lead to contrasting rate dependences with H 2 S pressure because the H 2 S pressure, together with H 2 pressure, gives the H 2 S:H 2 ratio that dictates the sulfur chemical potentials, the relative abundance of S anions and Ru cations coordinating to the hydrogen species, and in turn the surface concentrations of proton and hydride intermediates on Ru cluster surfaces. Finally, the catalytic involvements of proton–hydride pairs described here are general for hydrogenation reactions and, in particular, heteroarene hydrogenation in hydrotreatment processes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2017

Mechanism-Based Inhibition of the Mycobacterium tuberculosis Branched-Chain Aminotransferase by d - and l -Cycloserine

The branched-chain aminotransferase is a pyridoxal 5'-phosphate (PLP)-dependent enzyme responsible for the final step in the biosynthesis of all three branched-chain amino acids, l-leucine, l-isoleucine, and l-valine, in bacteria. We have investigated the mechanism of inactivation of the branched-chain aminotransferase from Mycobacterium tuberculosis (MtIlvE) by d- and l-cycloserine. d-Cycloserine is currently used only in the treatment of multidrug–drug-resistant tuberculosis. Our results show a time- and concentration-dependent inactivation of MtIlvE by both isomers, with l-cycloserine being a 40-fold better inhibitor of the enzyme. Minimum inhibitory concentration (MIC) studies revealed that l-cycloserine is a 10-fold better inhibitor of Mycobacterium tuberculosis growth than d-cycloserine. In addition, we have crystallized the MtIlvE-d-cycloserine inhibited enzyme, determining the structure to 1.7 Å. The structure of the covalent d-cycloserine-PMP adduct bound to MtIlvE reveals that the d-cycloserine ring is planar and aromatic, as previously observed for other enzyme systems. Mass spectrometry reveals that both the d-cycloserine- and l-cycloserine-PMP complexes have the same mass, and are likely to be the same aromatized, isoxazole product. However, the kinetics of formation of the MtIlvE d-cycloserine-PMP and MtIlvE l-cycloserine-PMP adducts are quite different. While the kinetics of the formation of the MtIlvE d-cycloserine-PMP complex can be fit to a single exponential, the formation of the MtIlvE l-cycloserine-PMP complex occurs in two steps. We propose a chemical mechanism for the inactivation of d- and l-cycloserine which suggests a stereochemically determined structural role for the differing kinetics of inactivation. Lastly, these results demonstrate that the mechanism of action of d-cycloserine’s activity against M. tuberculosis may be more complicated than previously thought and that d-cycloserine may compromise the in vivo activity of multiple PLP-dependent enzymes, including MtIlvE.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2024

Triplet Management at Ligand-Perovskite Interface to Enhanced Photovoltaics Performance

Aromatic organic molecules are widely used as passivators in perovskite solar cells (PSCs). Efforts have been devoted to improving the energy alignments, band edge states, and defect passivation functionalities. However, potential energy loss through triplet states in such conjugated molecules has not been investigated in the past. Here, we report the observation of charge transfer from FAPbI 3 to the triplet state of a pyrene (Pyr)-based cationic ligand. Such a potential loss channel can be suppressed via delicate triplet management in polycyclic aromatic compounds. Interestingly, a subtle structural modification from Pyr to the triphenylene (TP) core gave rise to shallower triplets that prohibit electron transfer from perovskites. This strategy has led to TP-passivated PSCs achieving an enhanced power conversion efficiency (PCE) of 24.69% from 23.10% in Pyr-passivated counterparts. Moreover, the devices retained above 80% initial PCE after 4000 h of light soaking, which likely benefited from the reduced triplet electron trapping at the ligand-perovskite interface.

14 SOLAR ENERGY↗

DOE OSTI2018

Self-Formed Hybrid Interphase Layer on Lithium Metal for High-Performance Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries are promising candidates for high-energy storage devices due to high theoretical capacities of both the sulfur cathode and lithium (Li) metal anode. Considerable efforts have been devoted to improving sulfur cathodes. However, issues associated with Li anodes, such as low Coulombic efficiency (CE) and growth of Li dendrites, remain unsolved due to unstable solid-electrolyte interphase (SEI) and lead to poor capacity retention and a short cycling life of Li–S batteries. In this paper, we demonstrate a facile and effective approach to fabricate a flexible and robust hybrid SEI layer through co-deposition of aromatic-based organosulfides and inorganic Li salts using poly(sulfur-random-1,3-diisopropenylbenzene) as an additive in an electrolyte. The aromatic-based organic components with planar backbone conformation and π–π interaction in the SEI layers can improve the toughness and flexibility to promote stable and high efficient Li deposition/dissolution. The as-formed durable SEI layer can inhibit dendritic Li growth, enhance Li deposition/dissolution CE (99.1% over 420 cycles), and in turn enable Li–S batteries with good cycling stability (1000 cycles) and slow capacity decay. Finally, this work demonstrates a route to address the issues associated with Li metal anodes and promote the development of high-energy rechargeable Li metal batteries.

25 ENERGY STORAGE↗

DOE OSTI2022

Role Evaluation of Active Groups in Lignin on UV-Shielding Performance

The contribution of the active groups in lignin to ultraviolet (UV)-shielding performance still remains unclear. In this study, we employed 16 lignin model compounds and theoretical calculations to ascertain the contribution of different functional groups to UV-shielding performance. These results showed that the order of UV-shielding performance on functional groups was -C=C–CHO > -C=C–COOH > -C=C–CH 2 OH > --C=C > quinone > -COOH > -OCH 3 ≈ -OH. Moreover, the synergism between the para-substituted electron-donating group -OH and the electron-withdrawing group allyl on the aromatic ring played a major role in UV-shielding performance of lignin models, whereas the additive effect of meta/ortho-substituted -OCH 3 played a secondary role. Furthermore, we found that the hydrophile–lipophile balance (HLB) value of lignin models also greatly affected the sunscreen protection factor (SPF) of lignin model-based sunscreens. A closer HLB value of lignin to 8.89 corresponded with a higher SPF of the lignin model-based sunscreen. The commercial photoprotective ingredient ethylhexyl methoxycinnamate (EHMC) and lignin models had a synergistic effect on UV-shielding performance caused by the π–π stacking interaction between the parallel-displaced stacked aromatic rings of lignin models and EHMC. Additionally, the UV irradiation test showed that these sunscreens prepared using lignin models and EHMC exhibited good photostability.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2025

Lignin-Derived Phenolic Compounds and Water Are Effective Cosolvents for Reductive Catalytic Fractionation

Reductive catalytic fractionation (RCF) is an effective lignin-first biorefining method to extract lignin as a stabilized oil from lignocellulosic biomass. To realize RCF at scale, process modeling has shown that minimizing the use of exogenous organic solvents is critical. To this end, here we investigate the ability of lignin-derived monomers to act as either solvents or cosolvents for RCF. We begin by examining the influence of lignin-derived aromatic compounds (4-propylguaiacol, 4-propylphenol, and propylbenzene) on RCF monomer yields and subsequently extend our analysis to mixtures of 4-propylguaiacol and either methanol or water. Here, we demonstrate that 4-propylguaiacol is an effective solvent for lignin extraction and depolymerization during RCF, especially when used in combination with water as a cosolvent. Cosolvent mixtures of 4-propylguaiacol and water enable up to 81% lignin extraction, monomer yields up to 25 wt %, and postreaction phase separation. However, unlike methanol, water as a cosolvent fails to inhibit aromatic ring hydrogenation when conducted over Ru/C as a catalyst, potentially leading to excess hydrogen consumption in a process utilizing this approach. Nonetheless, these results suggest a promising strategy for eliminating external organic solvents from RCF by utilizing mixtures of lignin-derived compounds and water as alternative extraction solvents.

09 BIOMASS FUELS↗

DOE OSTI2016

Furan production from glycoaldehyde over HZSM-5

Catalytic fast pyrolysis of biomass over zeolite catalysts results primarily in aromatic (e.g. benzene, toluene, xylene) and olefin products. However, furans are a higher value intermediate for their ability to be readily transformed into gasoline, diesel, and chemicals. Here we investigate possible mechanisms for the coupling of glycoaldehyde, a common product of cellulose pyrolysis, over HZSM-5 for the formation of furans. Experimental measurements of neat glycoaldehyde over a fixed bed of HZSM-5 confirm furans (e.g. furanone) are products of this reaction at temperatures below 300 degrees C with several aldol condensation products as co-products (e.g. benzoquinone). However, under typical catalytic fast pyrolysis conditions (>400 degrees C), further reactions occur that lead to the usual aromatic product slate. ONIOM calculations were utilized to identify the pathway for glycoaldehyde coupling toward furanone and hydroxyfuranone products with dehydration reactions serving as the rate determining steps with typical intrinsic reaction barriers of 40 kcal mol-1. The reaction mechanisms for glycoaldehyde will likely be similar to that of other small oxygenates such as acetaldehyde, lactaldehyde, and hydroxyacetone and this study provides a generalizable mechanism of oxygenate coupling and furan formation over zeolite catalysts.

09 BIOMASS FUELS↗

DOE OSTI2016

Bio-oil Stabilization by Hydrogenation over Reduced Metal Catalysts at Low Temperatures

Biomass fast pyrolysis integrated with bio-oil upgrading represents a very attractive approach for converting biomass to hydrocarbon transportation fuels. However, the thermal and chemical instability of bio-oils presents significant problems when they are being upgraded, and development of effective approaches for stabilizing bio-oils is critical to the success of the technology. Catalytic hydrogenation to remove reactive species in bio-oil has been considered as one of the most efficient ways to stabilize bio-oil. This paper provides a fundamental understanding of hydrogenation of actual bio-oils over a Ru/TiO2 catalyst under conditions relevant to practical bio-oil hydrotreating processes. Bio-oil feed stocks, bio-oils hydrogenated to different extents, and catalysts have been characterized to provide insights into the chemical and physical properties of these samples and to understand the correlation of the properties with the composition of the bio-oil and catalysts. The results indicated hydrogenation of various components of the bio-oil, including sugars, aldehydes, ketones, alkenes, aromatics, and carboxylic acids, over the Ru/TiO2 catalyst and 120 to 160oC. Hydrogenation of these species significantly changed the chemical and physical properties of the bio-oil and overall improved its thermal stability, especially by reducing the carbonyl content, which represented the content of the most reactive species (i.e., sugar, aldehydes, and ketones). The change of content of each component in response to increasing hydrogen additions suggests the following bio-oil hydrogenation reaction sequence: sugar conversion to sugar alcohols, followed by ketone and aldehyde conversion to alcohols, followed by alkene and aromatic hydrogenation, and then followed by carboxylic acid hydrogenation to alcohols. Hydrogenation of bio-oil samples with different sulfur contents or inorganic material contents suggested that sulfur poisoning of the reduced Ru metal catalysts was significant during hydrogenation; however, the inorganics at low concentrations had minimal impact at short times on stream, indicating that sulfur poisoning was the primary deactivation mode for the bio-oil hydrogenation catalyst. Reducing the sulfur content in bio-oil could significantly increase the lifetime of the hydrogenation catalyst used. The knowledge gained during this work will allow rational design of more effective catalysts and processes for stabilizing and upgrading bio-oils.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2017

Deactivation of Multilayered MFI Nanosheet Zeolite during Upgrading of Biomass Pyrolysis Vapors

Here, the catalytic fast pyrolysis (CFP) of biomass is a promising technology for producing renewable transportation fuels and chemicals. MFI-type catalysts have shown promise for CFP because they produce gasoline range hydrocarbons from oxygenated pyrolysis compounds; however, rapid catalyst deactivation due to coking is one of the major technical barriers inhibiting the commercialization of this technology. Coke deposited on the surface of the catalysts blocks access to active sites in the micropores leading to rapid catalyst deactivation. Our strategy is to minimize rapid catalyst deactivation by adding mesoporosity through forming MFI nanosheet materials. The synthesized MFI nanosheet catalysts were fully characterized and evaluated for cellulose pyrolysis vapor upgrading to produce olefins and aromatic hydrocarbons. The data obtained from pyrolysis-GCMS (py-GCMS), showed that fresh MFI nanosheets produced similar aromatic hydrocarbon and olefin yields compared to conventional HZSM-5. However, MFI nanosheets demonstrated a longer lifetime than HZSM-5 even though coke contents were also higher than for HZSM-5 because the mesopores enabled better accessibility to active acid sites. This conclusion was supported by results from post-reaction analysis of various spent catalysts collected at different points during the deactivation experiments.

09 BIOMASS FUELS↗

DOE OSTI2014

Understanding Boron through Size-Selected Clusters: Structure, Chemical Bonding, and Fluxionality

Conspectus Boron is an interesting element with unusual polymorphism. While three-dimensional (3D) structural motifs are prevalent in bulk boron, atomic boron clusters are found to have planar or quasi-planar structures, stabilized by localized two-center–two-electron (2c–2e) σ bonds on the periphery and delocalized multicenter–two-electron (nc–2e) bonds in both σ and π frameworks. Electron delocalization is a result of boron’s electron deficiency and leads to fluxional behavior, which has been observed in B13+ and B19–. A unique capability of the in-plane rotation of the inner atoms against the periphery of the cluster in a chosen direction by employing circularly polarized infrared radiation has been suggested. Such fluxional behaviors in boron clusters are interesting and have been proposed as molecular Wankel motors. The concepts of aromaticity and antiaromaticity have been extended beyond organic chemistry to planar boron clusters. The validity of these concepts in understanding the electronic structures of boron clusters is evident in the striking similarities of the π-systems of planar boron clusters to those of polycyclic aromatic hydrocarbons, such as benzene, naphthalene, coronene, anthracene, or phenanthrene. Chemical bonding models developed for boron clusters not only allowed the rationalization of the stability of boron clusters but also lead to the design of novel metal-centered boron wheels with a record-setting planar coordination number of 10. The unprecedented highly coordinated borometallic molecular wheels provide insights into the interactions between transition metals and boron and expand the frontier of boron chemistry. Another interesting feature discovered through cluster studies is boron transmutation. Even though it is well-known that B–, formed by adding one electron to boron, is isoelectronic to carbon, cluster studies have considerably expanded the possibilities of new structures and new materials using the B–/C analogy. It is believed that the electronic transmutation concept will be effective and valuable in aiding the design of new boride materials with predictable properties. The study of boron clusters with intermediate properties between those of individual atoms and bulk solids has given rise to a unique opportunity to broaden the frontier of boron chemistry. Understanding boron clusters has spurred experimentalists and theoreticians to find new boron-based nanomaterials, such as boron fullerenes, nanotubes, two-dimensional boron, and new compounds containing boron clusters as building blocks. Here, a brief and timely overview is presented addressing the recent progress made on boron clusters and the approaches used in the authors’ laboratories to determine the structure, stability, and chemical bonding of size-selected boron clusters by joint photoelectron spectroscopy and theoretical studies. Specifically, key findings on all-boron hydrocarbon analogues, metal-centered boron wheels, and electronic transmutation in boron clusters are summarized.

Environmental Molecular Sciences Laboratory↗

DOE OSTI2014

Synergistic Catalysis between Pd and Fe in Gas Phase Hydrodeoxygenation of m-Cresol

In this work, a series of Pd/Fe2O3 catalysts were synthesized, characterized, and evaluated for the hydrodeoxygenation (HDO) of m-cresol. It was found that the addition of Pd remarkably promotes the catalytic activity of Fe while the product distributions resemble that of monometallic Fe catalyst, showing high selectivity towards the production of toluene (C-O cleavage without saturation of aromatic ring and C-C cleavage). Reduced catalysts featured with Pd patches on the top of reduced Fe nanoparticle surface, and the interaction between Pd and Fe was further confirmed using X-ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM) and X-ray absorption near edge fine structure (XANES). A possible mechanism, including Pd assisted H2 dissociation and Pd facilitated stabilization of metallic Fe surface as well as Pd enhanced product desorption, is proposed to be responsible for the high activity and HDO selectivity in Pd-Fe catalysts. The synergic catalysis derived from Pd-Fe interaction found in this work was proved to be applicable to other precious metal promoted Fe catalysts, providing a promising strategy for future design of highly active and selective HDO catalysts.

09 BIOMASS FUELS↗

DOE OSTI2011

Tunneling Currents That Increase with Molecular Elongation

We present a model molecular system with an unintuitive transport–extension behavior in which the tunneling current increases with forced molecular elongation. The molecule consists of two complementary aromatic units (1,4-anthracenedione and 1,4-anthracenediol) hinged via two ether chains and attached to gold electrodes through thiol-terminated alkenes. The transport properties of the molecule as it is mechanically elongated in a single-molecule pulling setting are computationally investigated using a combination of equilibrium molecular dynamics simulations of the pulling with gDFTB computations of the transport properties in the Landauer limit. Contrary to the usual exponential decay of tunneling currents with increasing molecular length, the simulations indicate that upon elongation electronic transport along the molecule increases 10-fold. The structural origin of this inverted trend in the transport is elucidated via a local current analysis that reveals the dual role played by H-bonds in both stabilizing π-stacking for selected extensions and introducing additional electronic couplings between the complementary aromatic rings that also enhance tunneling currents across the molecule. The simulations illustrate an inverted electromechanical single-molecule switch that is based on a novel class of transport–extension behavior that can be achieved via mechanical manipulation and highlight the remarkable sensitivity of conductance measurements to the molecular conformation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2012

We report the observation of two transition-metal-centered nine-atom boron rings, Rh©B9 - and Ir©B9-. These two doped-boron clusters are produced in a laser-vaporization supersonic molecular beam and characterized by photoelectron spectroscopy and ab initio calculations. Large HOMO-LUMO gaps are observed in the anion photoelectron spectra, suggesting that neutral Rh©B9 and Ir©B9 are highly stable, closed shell species. Theoretical calculations show that Rh©B9 and Ir©B9 are of D9h symmetry. Chemical bonding analyses reveal that these complexes are doubly aromatic, each with six completely delocalized π and σ electrons, which describe the bonding between the central metal atom and the boron ring. This work establishes firmly the metal-doped B rings as a new class of novel aromatic molecular wheels.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2021

Controlling Amphiphilic Polymer Folding beyond the Primary Structure with Protein-Mimetic Di(Phenylalanine)

While methods for polymer synthesis have proliferated, their functionality pales in comparison to natural biopolymers–strategies are limited for building the intricate network of noncovalent interactions necessary to elicit complex, protein-like functions. Using a bioinspired di(phenylalanine) acrylamide (FF) monomer, we explored the impact of various noncovalent interactions in generating ordered assembled structures. Amphiphilic copolymers were synthesized that exhibit β-sheet-like local structure upon collapsing into single-chain assemblies in aqueous environments. Here, the systematic analysis of a series of amphiphilic copolymers illustrated that the global collapse is primarily driven by hydrophobic forces. Hydrogen-bonding and aromatic interactions stabilize local structure, as β-sheet-like interactions were identified via circular dichroism and thioflavin T fluorescence. Similar analysis of phenylalanine (F) and alanine-phenylalanine acrylamide (AF) copolymers found that distancing the aromatic residue from the polymer backbone is sufficient to induce β-sheet-like local structure akin to the FF copolymers; however, the interactions between AF subunits are less stable than those formed by FF. Further, hydrogen-bond donating hydrophilic monomers disrupt internal structure formed by FF within collapsed assemblies. Collectively, these results illuminate design principles for the facile incorporation of multiple facets of protein-mimetic, higher-order structure within folded synthetic polymers.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2021

Oxidative Catalytic Fractionation of Lignocellulosic Biomass under Non-alkaline Conditions

Biomass pretreatment methods are commonly used to isolate carbohydrates from biomass, but they often lead to modification, degradation, and/or low yields of lignin. Catalytic fractionation approaches provide a possible solution to these challenges by separating the polymeric sugar and lignin fractions in the presence of a catalyst that promotes cleavage of the lignin into aromatic monomers. In this work, we demonstrate an oxidative fractionation method conducted in the presence of a heterogeneous non-precious-metal Co-N-C catalyst and O 2 in acetone as the solvent. The process affords a 15 wt% yield of phenolic products bearing aldehydes (vanillin, syringaldehyde) and carboxylic acids (p-hydroxybenzoic acid, vanillic acid, syringic acid), complementing the alkylated phenols obtained from existing reductive catalytic fractionation methods. The oxygenated aromatics derived from this process have appealing features for use in polymer synthesis and/or biological funneling to value-added products, and the non-alkaline conditions associated with this process support preservation of the cellulose, which remains insoluble at reaction conditions and is recovered as a solid.

09 BIOMASS FUELS↗