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1.
Proc Natl Acad Sci U S A ; 115(20): 5093-5098, 2018 05 15.
Artigo em Inglês | MEDLINE | ID: mdl-29712826

RESUMO

Amino acids are the building blocks for protein biosynthesis and find use in myriad industrial applications including in food for humans, in animal feed, and as precursors for bio-based plastics, among others. However, the development of efficient chemical methods to convert abundant and renewable feedstocks into amino acids has been largely unsuccessful to date. To that end, here we report a heterogeneous catalyst that directly transforms lignocellulosic biomass-derived α-hydroxyl acids into α-amino acids, including alanine, leucine, valine, aspartic acid, and phenylalanine in high yields. The reaction follows a dehydrogenation-reductive amination pathway, with dehydrogenation as the rate-determining step. Ruthenium nanoparticles supported on carbon nanotubes (Ru/CNT) exhibit exceptional efficiency compared with catalysts based on other metals, due to the unique, reversible enhancement effect of NH3 on Ru in dehydrogenation. Based on the catalytic system, a two-step chemical process was designed to convert glucose into alanine in 43% yield, comparable with the well-established microbial cultivation process, and therefore, the present strategy enables a route for the production of amino acids from renewable feedstocks. Moreover, a conceptual process design employing membrane distillation to facilitate product purification is proposed and validated. Overall, this study offers a rapid and potentially more efficient chemical method to produce amino acids from woody biomass components.


Assuntos
Aminoácidos/metabolismo , Biomassa , Nanopartículas/química , Nanotubos de Carbono/química , Aminoácidos/química , Catálise , Hidrogenação , Níquel/química , Rutênio/química
2.
Science ; 358(6368): 1307-1310, 2017 12 08.
Artigo em Inglês | MEDLINE | ID: mdl-29217572

RESUMO

Acrylonitrile (ACN) is a petroleum-derived compound used in resins, polymers, acrylics, and carbon fiber. We present a process for renewable ACN production using 3-hydroxypropionic acid (3-HP), which can be produced microbially from sugars. The process achieves ACN molar yields exceeding 90% from ethyl 3-hydroxypropanoate (ethyl 3-HP) via dehydration and nitrilation with ammonia over an inexpensive titanium dioxide solid acid catalyst. We further describe an integrated process modeled at scale that is based on this chemistry and achieves near-quantitative ACN yields (98 ± 2%) from ethyl acrylate. This endothermic approach eliminates runaway reaction hazards and achieves higher yields than the standard propylene ammoxidation process. Avoidance of hydrogen cyanide as a by-product also improves process safety and mitigates product handling requirements.

3.
Curr Opin Biotechnol ; 42: 40-53, 2016 12.
Artigo em Inglês | MEDLINE | ID: mdl-26974563

RESUMO

Lignin is a primary component of lignocellulosic biomass that is an underutilized feedstock in the growing biofuels industry. Despite the fact that lignin depolymerization has long been studied, the intrinsic heterogeneity of lignin typically leads to heterogeneous streams of aromatic compounds, which in turn present significant technical challenges when attempting to produce lignin-derived chemicals where purity is often a concern. In Nature, microorganisms often encounter this same problem during biomass turnover wherein powerful oxidative enzymes produce heterogeneous slates of aromatics compounds. Some microbes have evolved metabolic pathways to convert these aromatic species via 'upper pathways' into central intermediates, which can then be funneled through 'lower pathways' into central carbon metabolism in a process we dubbed 'biological funneling'. This funneling approach offers a direct, biological solution to overcome heterogeneity problems in lignin valorization for the modern biorefinery. Coupled to targeted separations and downstream chemical catalysis, this concept offers the ability to produce a wide range of molecules from lignin. This perspective describes research opportunities and challenges ahead for this new field of research, which holds significant promise towards a biorefinery concept wherein polysaccharides and lignin are treated as equally valuable feedstocks. In particular, we discuss tailoring the lignin substrate for microbial utilization, host selection for biological funneling, ligninolytic enzyme-microbe synergy, metabolic engineering, expanding substrate specificity for biological funneling, and process integration, each of which presents key challenges. Ultimately, for biological solutions to lignin valorization to be viable, multiple questions in each of these areas will need to be addressed, making biological lignin valorization a multidisciplinary, co-design problem.


Assuntos
Biomassa , Biotecnologia/métodos , Lignina/metabolismo , Bactérias/metabolismo , Engenharia Metabólica , Especificidade por Substrato
4.
Proc Natl Acad Sci U S A ; 111(33): 12013-8, 2014 Aug 19.
Artigo em Inglês | MEDLINE | ID: mdl-25092344

RESUMO

Lignin is an energy-dense, heterogeneous polymer comprised of phenylpropanoid monomers used by plants for structure, water transport, and defense, and it is the second most abundant biopolymer on Earth after cellulose. In production of fuels and chemicals from biomass, lignin is typically underused as a feedstock and burned for process heat because its inherent heterogeneity and recalcitrance make it difficult to selectively valorize. In nature, however, some organisms have evolved metabolic pathways that enable the utilization of lignin-derived aromatic molecules as carbon sources. Aromatic catabolism typically occurs via upper pathways that act as a "biological funnel" to convert heterogeneous substrates to central intermediates, such as protocatechuate or catechol. These intermediates undergo ring cleavage and are further converted via the ß-ketoadipate pathway to central carbon metabolism. Here, we use a natural aromatic-catabolizing organism, Pseudomonas putida KT2440, to demonstrate that these aromatic metabolic pathways can be used to convert both aromatic model compounds and heterogeneous, lignin-enriched streams derived from pilot-scale biomass pretreatment into medium chain-length polyhydroxyalkanoates (mcl-PHAs). mcl-PHAs were then isolated from the cells and demonstrated to be similar in physicochemical properties to conventional carbohydrate-derived mcl-PHAs, which have applications as bioplastics. In a further demonstration of their utility, mcl-PHAs were catalytically converted to both chemical precursors and fuel-range hydrocarbons. Overall, this work demonstrates that the use of aromatic catabolic pathways enables an approach to valorize lignin by overcoming its inherent heterogeneity to produce fuels, chemicals, and materials.


Assuntos
Lignina/química , Catálise
5.
J Am Chem Soc ; 136(11): 4137-40, 2014 Mar 19.
Artigo em Inglês | MEDLINE | ID: mdl-24601613

RESUMO

The bond energy of molecular fragments to metal surfaces is of great fundamental importance, especially for understanding catalytic reactivity. Thus, the energies of adsorbed intermediates are routinely calculated to understand and even predict the activity of catalytic materials. By correlating our recent calorimetry measurements of the adiabatic bond dissociation enthalpies of three oxygen-bound molecular fragments [-OH, -OCH3, and -O(O)CH] to the Pt(111) surface, it is found that these RO-Pt(111) bond enthalpies vary linearly with the RO-H bond enthalpies in the corresponding gas-phase molecules (water, methanol, and formic acid), with a slope of 1.00. This parallels the known trend for organometallic complexes, thus highlighting the local character of chemical bonding, even on extended metal surfaces. This allows prediction of bond enthalpies for many other molecular fragments to metal surfaces, and the energetics of important catalytic reactions.

6.
J Am Chem Soc ; 136(10): 3964-71, 2014 Mar 12.
Artigo em Inglês | MEDLINE | ID: mdl-24512006

RESUMO

Carboxylates adsorbed on solid surfaces are important in many technological applications, ranging from heterogeneous catalysis and surface organo-functionalization to medical implants. We report here the first experimentally determined enthalpy of formation of any surface bound carboxylate on any surface, formate on Pt(111). This was accomplished by studying the dissociative adsorption of formic acid on oxygen-presaturated (O-sat) Pt(111) to make adsorbed monodentate and bidentate formates using single-crystal adsorption calorimetry. The integral heat of molecular adsorption of formic acid on clean Pt(111) at 100 K is 62.5 kJ/mol at 0.25 monolayer (ML). On O-sat Pt(111), the integral heat of the dissociative adsorption of formic acid to make monodentate formate (HCOOmon,ad) plus the water-hydroxyl complex ((H2O-OH)ad) was found to be 76 kJ/mol at 3/8 ML and 100-150 K. Similarly, its integral heat of dissociative adsorption to make bidentate formate (HCOObi,ad) plus (H2O-OH)ad was 106 kJ/mol at 3/8 ML and 150 K. These heats give the standard enthalpies of formation of adsorbed monodentate and bidentate formate on Pt(111) to be -354 ± 5 and -384 ± 5 kJ/mol, respectively, and their net bond enthalpies to the Pt(111) surface to be 224 ± 13 and 254 ± 13 kJ/mol, respectively. Coverage-dependent enthalpies of formation were used to estimate the enthalpy of the elementary reaction HCOOHad → HCOObi,ad + Had to be -4 kJ/mol at zero coverage and +24 kJ/mol at 3/8 ML.

7.
J Am Chem Soc ; 135(13): 5208-11, 2013 Apr 03.
Artigo em Inglês | MEDLINE | ID: mdl-23461481

RESUMO

The enthalpy and sticking probability for the dissociative adsorption of methyl iodide were measured on Pt(111) at 320 K and at low coverages (up to 0.04 ML, where 1 ML is equal to one adsorbate molecule for every surface Pt atom) using single crystal adsorption calorimetry (SCAC). At this temperature and in this coverage range, methyl iodide produces adsorbed methyl (CH(3,ad)) plus an iodine adatom (I(ad)). Combining the heat of this reaction with reported energetics for Iad gives the standard heat of formation of adsorbed methyl, ΔH(f)(0)(CH3,ad), to be −53 kJ/mol and a Pt(111)­CH3 bond energy of 197 kJ/mol. (The error bar of ±20 kJ/mol for both values is limited by the reported heat of formation of I(ad).) This is the first direct measurement of these values for any alkyl fragment on any surface.

8.
J Am Chem Soc ; 134(50): 20388-95, 2012 Dec 19.
Artigo em Inglês | MEDLINE | ID: mdl-23181692

RESUMO

The heat of adsorption and sticking probability of methanol were measured on clean Pt(111) at 100, 150, and 210 K and on oxygen-precovered Pt(111) at 150 K by single-crystal adsorption calorimetry (SCAC). On clean Pt(111) at 100 K, the heat of methanol adsorption was found to be 60.5 ± 0.8 kJ/mol in the limit of low coverage, resulting in a standard enthalpy of formation (ΔH(f)°) of CH(3)OH(ad) of -263 ± 0.8 kJ/mol. The results at 150 and 210 K on clean Pt(111) were indistinguishable from the energetics measured at 100 K in the same coverage range. Calorimetry of methanol on oxygen-precovered Pt(111) at 150 K yielded the energetics of adsorbed methoxy, giving ΔH(f)°[CH(3)O(ad)] = -170 ± 10 kJ/mol and a CH(3)O-Pt(111) bond enthalpy of 187 ± 11 kJ/mol. By use of these enthalpies, the dissociation of adsorbed methanol on Pt(111) to form methoxy and a hydrogen adatom is found to be uphill by +57 kJ/mol. At coverages below 0.2 monolayer (ML), the sticking probability for methanol on both surfaces at or below 150 K was >0.95. At 210 K, ∼80% of the methanol beam pulse transiently adsorbs to clean Pt(111) with a surface residence time of 238 ms and heat of adsorption of 61.2 ± 2.0 kJ/mol, giving a prefactor for methanol desorption of 4 × 10(15±0.5) s(-1). These measured energetics for methoxy and methanol were compared to density functional theory (DFT) calculations from previous literature, showing DFT to routinely underestimate the bond energy of both adsorbed methanol and methoxy by 15-52 kJ/mol.

9.
Faraday Discuss ; 152: 227-39; discussion 293-306, 2011.
Artigo em Inglês | MEDLINE | ID: mdl-22455047

RESUMO

One important aid in understanding catalysis by gold nanoparticles would be to understand the strength with which they bond to different support materials and the strength with which they bond adsorbed intermediates, and how these strengths depend on nanoparticle size. We present here new measurements of adsorption energies by single crystal adsorption calorimetry, and new analyses of other recent measurements by this technique in our lab, which imply that: (1) small nanoparticles of metals like Au bind much more strongly to supports like titania and iron oxide which are generally observed to be effective in making Au nanoparticles active in catalysis than to supports like MgO which are considered less effective, (2) the thermodynamic stability of adsorbed intermediates for catalytic reactions can either increase strongly or decrease strongly with decreasing metal nanoparticle size below 8 nm, depending on the system, and (3) the reaction to insert O2 into the Au-H bond of adsorbed H on the Au(111) surface to make Au-OOH (O2,g + H(ad) --> OOH(ad)) is exothermic by -80 kJ mol(-1). This adsorbed hydroperoxy species is thought to be a key intermediate in selective oxidation reactions over Au nanoparticle catalysts, but its production by this reaction may also provide a route for O2 activation in less demanding reactions (like CO oxidation) as well. Its stability would be even higher on Au nanoparticles below 3 nm in diameter, but even there it is too unstable to be formed by combining adsorbed OH with an O adatom (OH(ad) + O(ad) --> OOH(ad)), which is estimated to be endothermic by 175 kJ mol(-1). The implications of the stability of metal nanoparticles versus particle size on different supports and of the stability and potential reactions of OOH(ad) in Au catalysis will be discussed.

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